Limit Switches - optical / mechanical / proximity

[Gerald_D]

A synopsis of this thread will in future appear in this first post. This post will be edited from time to time - the date of this synopsis post is irrelevant. An experiment . . . . .

[GregA]

I was going through the factorymation website, and wanted to get an opinion from someone who had a working MM. They have a wide range of sensors, and by my reckoning it would cost ~$111+shipping to add a full set of optical limit switches. Would this be a worth while investment?

Specifically, I was looking at the diffuse reflective sensors. It would just be a matter of drilling mounting holes and a few strategic holes around the MM, and wiring the circuit. Two, three hours tops to install.

But then, what do I know... I seem to have a warped sense of how long something should take...

[J.R. Hatcher]

I remember reading that wiring these optical sensors gets pretty intense. Limit switches on the other hand are a piece of cake. Mach3 can handle all homing and all limit switches with just 2 wires ......... total.

[Doug_Ford]

Gerald has posted before that he doesn't use any limit or homing switches so I'm going to try that route for a while.

[J.R. Hatcher]

I don't know how to relocate without homing switches. If I were in the middle of a job, say line 68 and lost power for whatever reason how would I start again, short of homing? In Mach3 if you rehome and jog to coordinates for line 66 you just tell mach to "start from here" example line 67 and it continues from where it stopped.
Keep in mind I have never actually ran a cnc router so all of this is pure speculation on my part :D:D. Discussion is more than welcome, so just jump right in. And no I did not wake on the wrong side of the bed this morning.:)

[Doug_Ford]

J.R.,

I'm right there with you Bubba. Learning to operate this thing is a challenge. Have you watched the Coordinates video tutorial on the Mach site? That helped me alot. In a few minutes, I'm going out into the garage to try to finish getting my software configured. When I figure it out, I'll post something.

[Gerald D]

If you have a power failure during a cutting job, the chances are that you are going to scrap that sheet of wood rather than try to restart the process. A machine of this size and speed needs power to come to a controlled stop - if the power drops out suddenly the motion and cutting is "wild". (gantry also out of square). However, there are rare cases when one feels that a restart chould be attempted . . . .

In our case, without switches, we can run the carriages against the hard stops and tell the machine we are now located at the hard stops . . . . a definite reference position. Sounds too simple, doesn't it? :)
(In practice, we run close to the stop, switch off the drives, move the carriages by hand up against the stops, and then switch drives back on.)

[revved_up]

The carvewright machines (more like toys) have optical sensors and they have countless trouble with them. They get covered in sawdust, they have a problem reading in less than optimal lighting and many other problems just relating to the design of the machine.

But then again thats why I for one am here to learn and to (hopefully) build a tool and not a toy.

[GregA]

JR Hatcher,

The optical limit switches are an easy circuit. They have four wires. Two of the wires are power, and two of the wires are signal. Knowing that, all you need to do is power the power wires. Then you use a 5 volt power supply on the signal wires. Then depending if the switch is NO or NC there is either a current or not. The load on the optical switch is nominal, measured in mA. You could build your own fair-child circuit but... an off the shelf switch is $30. I know I can't build one for that. With the extra inputs on the PMDX-122 you could even get down to, XYZ limit events, rather than one global limit event, for homing purposes.

Although, you might need two sensors in the X axis for the deracking operation.

I was wondering about the sawdust. I wonder if the capacitive sensors can detect a hole in the metal?

[BernardR]

Greg, I used opto home/limit switches on my mill. As with most things there are trade offs; the biggest downside as far as I am concerned was the wiring and installation.

Mine I believe are typical, they are a 5 wire device, Receiver +5V, Receiver Gnd, Receiver TTL out, IR LED Return and IR LED +5/20mA, mine came on a 10" lead terminated in a 6 pin dual in line socket. In practice you run +5V, Gnd and the TTL signal wires to each device and connect a current limiting resistor from the +5V to the LED. I connected two switches for each axis in a small box, with slots milled for the actuating blades.

With 20/20 hindsight I would not go that way again, first you can't easily have a single series switch chain that is recommended by most experts, (it is possible but involves additional logic.) The wiring gets very messy, small boards with minature wiring, and special wiring to get to the BOB. On the positive side they are very quick acting and are very reliable.

[Gerald D]

. . . you just tell mach to "start from here" example line 67 and it continues from where it stopped. . .

One must realise that when you tell Mach to "go to here" it does so in a straight line, being the shortest route. That can catch you out if the starting point, before the "go to", is different to what was last in the program.

Let's say you are cutting out a bowl and you have a power failure. You move the table to the home position at the 0,0 corner and reset it. If you now say "go to the bottom of the bowl", it will try to move in straight through the side of the bowl - it won't go up and over the lip.

Recovering from a power failure takes a lot of concentration.

[smreish]

Gentlemen,
I am glad were having this discussion again.
I did a little light reading again last night - with baby on my chest :) - and was pondering the use of proximity switches again.
The MM runs very well with out them. Heck, my MultiCAM ran well without them when I turned them off. (sometimes necessary to get the table to cut full width) Had a problem getting to 49" when you resurfaced the table!

What I am going to do once the table is up and running is experiment with limits only when the new NCpod board arrives. As of now, I don't have the right amount of inputs available to do all the functions I have set aside for the table using a single pmdx-122 card. The NcPod has 6 additional inputs for specific homing use. Pretty necessary for my end use of adding an additional rotating index axis.
The proximity sensors work VERY well and work in all environments...wet, dusty, smelly, loud, sticky, etc. They are affordable and small. The only challenge will be using a secondary source/sink module to buffer the switch between the BOB and the switch...again, easy and affordable.

I will let you in on my findings when I get there next month.

Sean

[firebrick43]

We use a lot of optical sensors at work on all of the material movement conveyors and robot cells. Their reliability is much less that the simple limit switches on all of our machine tools. The reflectors get dirty/crack/knocked out of position. The Optical switches go bad quite frequently to. Some of the limit switches are so abused, swim in coolant, and beat upon still work, most of the time when they have to be replaced it is when they are physically destroyed. The only switches with worse reliability than optical switches is proximity switches.

When pieces of saw dust break the beam and cause an e stop, possibly scrapping a part, you will be cussing a storm

[Gerald D]

The only switches with worse reliability than optical switches is proximity switches.

That is very unusual :confused:

Mechanical limit switches have a problem down at the 5 volt levels if connected directly to the BOB. They become very sensitive to slightly imperfect contacts and show Open when they are actually Closed.

[revved_up]

I'm not sure if this is the right place for this or not but I have been watching a sellers store on ebay, http://stores.ebay.com/HUBBARD-CNC-INC he has limit switches for sale cheap but the things I really wanted to were the power supplies he has and he has (for lack of better terminology on my part) a pass thru db25 connector that is supposed to protect your computer and it breaks out the e stop and limit switches all in one. It has USB connectivity on one of the models. If I understand it right it goes between the pmdx and the computer so does it give the ability to ouput mach to the controller via usb and does it make it easier to set up e stops and limit/homing switches?

again this loosly fits this thread but feel free to move it and if anybody with more knowledge about this would look and give their input I would apprieciate it.

[firebrick43]

Gerald, we run everything at higher voltages, either 24 or 120 volts, 5 volt probably would be a problem

[smreish]

FYI....
from the Automation Direct Help pages.
They also offer 5v versions of the 12mm Prox sensor, but I don't know if the PMDX can source/Sink that amount of current. More homework to do with Mr. Richards :O

Sensors Frequently Asked Questions

« Return to the list of questions (http://support.automationdirect.com/faq/sensors.phtml)
Question Can proximity sensors be connected in series? Answer Yes. The number of proximity sensors connected in series is dependent on the available voltage to energize the PLC input or load. This voltage is calculated as the sum of voltage drops across each sensor subtracted from the available power supply voltage.

Let's use as an example three of the AutomationDirect APS24 series 3-wire NPN sensors, where the brown wire is positive, the black wire is the output, and the blue wire is the negative. The load will be a PLC input. By connecting the sensors in series, all of the sensors must be activated in order for the PLC to receive an input signal.

Start by connecting the brown wire (BN+) of each sensor in a daisy chain configuration to the positive terminal (+) of a 24 VDC power supply.

Next, connect one side of the load (PLC input module) to the first sensors's brown wire (BN+) and the other side to the black wire (BK).

Then connect that same sensor's blue wire (BU-) to the second sensor's black wire (BK).

Connect the second sensor's blue wire (BU-) to the third sensor's black wire (BK).

For the final termination, connect the third sensor's blue wire (BU-) to the negative (-) terminal on the 24 VDC power supply.


In the case of a 2-wire sensor using a sinking configuration, connect one side of the load (PLC input) to the positive terminal (+) of a 24 VDC power supply and the other side of the load to the positive (BN+) of the first sensor.

Then, connect the negative (BK or BU-) of the first sensor to the positive (BN+) of the adjacent sensor, continuing this patterns as many times as needed, staying within the voltage restrictions previously mentioned.

[Gerald D]

889

Do I understand this right? . . . .

890

[smreish]

gerald,
the automation direct nomenclature would suggest that you wiring is correct. But, for this scenario to work, all 3 switchs have to be high to output the signal. It acts more like an and+and+and circuit. My gut feeling is, for reliability that I use the 110v version of the sensors and isolate using a multipole relay to act like the series "contact" switches and have the pros energize the coil. I will draw it up later if I have a few minutes.
Sean

[Gerald D]

The way I envisaged the proxys to work, was for them all to permanently have metal in front of them (is that what you call "high"?). ie. they must all see a rail immediately in front of them. If any rail disappears, the chain is broken and the system switches. A rail could disappear by either:
- the sensor moving over the hole at the end of the rail (limit/home), or
- a car jumping off a rail when something goes horribly wrong.

[smreish]

Gerald,
I agree perfectly. That's why I like the Proximities. It will cause an interupt for things that happen other than overtravel. As we know, the overtravel of an axis will hit a hard stop and has no real implications.

So, if we use proxys, and want Mach 3 logic to work, we most certainly are going to have to reverse the "sense" of the proximity with a relay to allow for the BOB to correctly see both type of events and act as a Overtravel limit switch.

I will pull up my schematic and charts tonight to review the NPN PNP logic against true TTL sensors and see if I can come up with a signal flow that works well for the Proxy's. My true concern right now, is the voltage from the BOB. I don't have any success using a voltage as low as 5volts for limit switchss of any kind. 12V minimum. It would just happen that my Antek transformer was ordered with 5V, 12V and 56V outputs so I do have some room to make 12VDC or 110V AC work with the sensors.

...more later as I dig deeper into the school books.

Sean

[Gerald D]

Sean, I would like to avoid relays if possible. Not sure why you want to "reverse the sense" . . . . the BOB can be pulled up or down, Mach3 can be set active high or active low....?

As to the voltage for inputing to the BOB, couldn't it be dropped over a resistor?

....or transistor instead of relay?

[smreish]

hmm. Good points. I like the resistor idea to get the correct voltage at the bob. I'm convinced I have a working solution using proxys and 1 pmdx input. I'll order some proxys on Monday and get to work.

[Richards]

Sorry guys, but I spent the day getting a rush order out, so I'm late to this discussion.

Gerald, your schematic could work, but you'll lose about 1V for each NPN transistor. A normal TTL signal has to have at least 2.2V for a HIGH signal and not more than 0.7V for a LOW signal. Typically, it's best to not daisy-chain NPN transistors.

The way that I normally use proximity sensors is to have each sensor drive its own opto-coupler device. That way, it doesn't matter whether the proximity sensor works from 5V or 24V because all that it needs to do is to turn on an L.E.D (which takes about 10mA). Then, if I wanted to use multiple proximity sensors, I would connect the output from each opto-coupler to an AND gate or NAND gate (depending on whether I wanted a HIGH or a LOW signal). Although it would take a little bit of wiring, the cost is low when each opto-coupler costs less than $1 and each AND or NAND chip costs less than $0.50. Add a few resistors at $0.10 each and you have your circuit.

[smreish]

all members that are better at electronics than me, please step in here. After much reading tonight, this is my understanding of how to make standard 12-24vdc proximity switches work together.
The pull down value of the resistor needs to be determined on the test bench due to the fact that the voltage reduction value for each sensor is not known and not really published. Tech support said it dropped "some".....not much of a help.

I have added to Gerald's doodle for additional comments on the subject.


894

[Richards]

Sean,
The circuit that you posted has me confused. Right now, I can't see how it would work. Let's revisit Gerald's schematic and proximity switch diagram on post #17 and use the diagram as the starting point.

The BROWN wire simply feeds the DC+ voltage to the proximity switch.

The BLACK wire is connected to the NPN transistor's collector. AND, the BLACK wire is connected between the collector and the load. That means that when the NPN transistor is OFF, a voltage reading of the BLACK wire with be almost exactly the same as a voltage reading of the BROWN wire (if we measure the voltages in relation to Ground). When the NPN transistor is ON, the voltage reading will be almost exactly the same as a voltage reading of the BLUE wire, or Zero volts.

The BLUE wire is DC Ground.

So, looking at Gerald's schematic (which exactly matches the Automation Direct FAQ sheet), the top sensor, when off, will supply a + or high voltage to the PMDX-122 input. In fact, any time any ONE of the proximity sensors is OFF (transistor not conducting), the output signal to the PMDX-122 will be High. ALL three proximity sensors must be ON (all transistors conducting) before the signal going to the PMDX-122 will be Low. Even, then, the signal may not be Low enough to actually be seen as a Low signal by the PMDX-122 because of the possible voltage drop across the two bottom proximity switches. If they turn fully ON (saturated), then the circuit would probably work; however, if each proximity switch is not saturated and only pulls the voltage down to 0.25V or 0.35V, then the sum of all voltages might be higher than allowed (0.7V maximum for a Low signal).

That reasoning is why most designers would make each proximity switch output feed a unique TTL gate. HOWEVER, if the proximity switches were running a relay (where the current being pushed into or pulled out of the coil was the only important thing), the circuit would probably work very well.

[Gerald D]

Although it would take a little bit of wiring, the cost is low when each opto-coupler costs less than $1 and each AND or NAND chip costs less than $0.50. Add a few resistors at $0.10 each and you have your circuit.

Thanks for taking time out of your busy schedule to look at this Mike. Have you got some some typical chip numbers for us?

I envisage that we would have to get a little printed circuit board made up and that we could post this little board out to the builders who want to go with proxies. In my minds eye I see 4 sets of 3 terminals for 4 proxies, a pair of terminals for 12VDC in and a pair of terminals for output to the PMDX. But I don't know what goes on the middle of the board yet . . . . :)

At one stage I thought the simplest was a relay per proxy - the proxy can drive a small relay directly.

[Richards]

Gerald,
For most people, using relays would be best. Many small relays only require the coil current to be 5 to 10mA, which should work with a proximity switch.

Building a circuit board to use 7400 AND chips (http://en.wikipedia.org/wiki/7400_series) and 4N25 (or similar) opto-couplers (http://ds.dial.pipex.com/isocom/4n25.htm) would not be hard, but I think your relay idea would be better.

[Gerald D]

For me, relays are easy to understand, troubleshoot & replace. But the key seems to be a neat little PC board with all the terminals clearly spelled out.

But, are we not reinventing the wheel here? Surely such boards are already floating around in some small CNC community? This forum has nearly 3000 members, mostly invisible_grab_plans_&_run types, but somebody must of heard of something somewhere? :)

[Doug_Ford]

If you smart guys can figure out what parts need to go into it and how they ought to be wired together, I'll be more than happy to buy the parts, assemble them, and use my machine as a test bed. Unfortunately, I have zero expertise to contribute to the design phase of the project. Sorry.

[Gerald D]

Thanks for the offer Doug.

Here is the spec on a typical $20 proxy from automation direct:
10 to 30V DC, can take 100mA load. . . .

899

Now to find a common relay, 12V coil, drawing under 100ma. Relay coils often rated in Watts - we want under 1.2 Watt (1200mW). I don't think the relay speed is important, but gold contacts would be nice for the low voltages of the parallel port.

[Gerald D]

. . . . and then thinking of the low contact voltages makes me doubt the use of relays all over again :(

[BernardR]

Sounds like you need a low signal PCB mount.
Have a look at some of these, alternatively reed relays would also suit your needs: http://www.mouser.com/catalog/633/1609.pdf.
Mouser is a good supplier in the states, but these type of relays are readily available through any reasonable electronics supply company worldwide.

[Gerald D]

Thanks Bernard! That V23079A1003B301 (http://catalog.tycoelectronics.com/TE/bin/TE.Connect?C=1&M=BYPN&PN=V23079A1003B301) looks good. The fact that it has the lowest price ($1.84) probably means it is the most popular. (Other options on futher pages all look okay - prices rather similar)

(It is available here in S.Africa from a RS Components at an equivalent price of $6 each)

[cobra427mnsi]

Gerald, are limit switches and proximity switches used for the same thing? (eg: homing and setting limit stops) I have been reading a lot lately about each type with variations within each type. It is all a bit confusing for the electronically challenged. I see from pics on JR's personal page that he has used a limit switch (I think that is a limit switch then again it might be a proximity switch). Now there is talk of low voltage relays etc.
Very confusing.

Paul

[Gerald D]

Sorry for the confusion Paul. Yes, they are used for the same thing. JR is using "limit" switches, they are not "proximity" switches

A limit switch contains a mechanical switch with contacts that physically open and close to make/break the circuit to the BOB. The BOB only draws a tiny current at a low voltage, so we must be sure that these contacts stay very clean. Gold-plated contacts prevent them from tarnishing.

A proximity switch has no moving parts. It has a transistor based output which is tricky to match correctly to the BOB. The talk of relays in this thread is to add a relay to each proxy, so that the proxy behaves like a classic "limit" switch.

Then, why not use a limit switch instead of a proxy right from the start? The proxy can look at the rail all the time, the limit switch can only see lumps at the ends. The limit switch might see a wood chip as the end of the rail, the proxy won't make that mistake. A limit switch won't know if a car has jumped off the rail, the proxy will shut everything down when a car jumps.

Proxies are standard on ShopBots and some other CNC machines I believe. We havn't got them neatly figured out for a MM yet. Limit switches are easy to figure out and they are also common on CNC machines, but they are known to be troublesome at low voltages/low currents if the wrong type is selected.

[cobra427mnsi]

Thanks for the reply, Gerald. You made it quite clear. I am a long way from any switches so I will wait to for you and the others to figure out the proximity switch option, that sounds like the better choice. This forum is a great resource when one doesn't quite understand how something works. I appreciate it when I can benefit from someone else's experience. I hope that I might be able to contribute something that would help others.

Thanks again
Paul

[Richards]

Here is a simple schematic that shows how NPN N/O type proximity sensors could be interfaced to a break-out-board. I used Balluff BES M12MI-NSC40B-SG4G sensors, which are NPN (sinking), Normally Open. Those sensors can use any DC voltage from 12V to 24V. I use 12V.

908

Basically, here's how the circuit works: 12VDC is applied to the circuit through a 1A fuse. D1 is an L.E.D. to show that voltage is present. R1 limits the current through the L.E.D. to about 10mA. C1 is a filter capacitor. U1 - U4 are the proximity sensors. U5 - U8 are opto-couplers. R3 - R6 are current limiting resistors to limit the current flowing through the opto-couplers' diode to about 10mA. R7 - R10 are pull-up resistors to hold an inactive signal to about 5V (High). U9 is a 7408 AND chip. As long as all of the proximity switches are OFF (not sensing a target), the output (pin 8) will be HIGH. If one or more of the proximity sensors is ON (sensing a target), the output will be LOW. C3 is a small decoupling capacitor that should be placed near pins 1 and 14 on U9. The 5VDC circuit has a fuse, L.E.D., resistor (330 ohm) and capacitor, that function similar to those components for the 12VDC circuit. The Ground lines are common and should be connected together.

From an e-mail by Mike:

I did a quick dirty board layout that I'm sending to you along with the
schematic. Feel free to give it to anyone who wants to have ExpressPCB
make three prototype boards. That service costs about $60 here in the
U.S.A. At any rate, anyone can play with the schematic and the layout
to make it do whatever is necessary. The software is free from
www.expresspcb.com (http://www.expresspcb.com/). (Of course it is only usable with ExpressPCB's
service.)

To make the parts fit the quick-turn board (3.8 X 2.5 inches), I had to
leave off the fuses. The screw-terminals that fit the board are Phoenix
Contact MKDS1,5/3.

One point of possible error is that I'm using NPN Normally Open
sensors. For this circuit to work, the circuit goes active whenever any
ONE of the sensors senses its target.

[Gerald D]

Looks more "professional" than a row of relays! What about some visible LED's to see which proxy has lost its target (the proxy's themselves have LED's but they are buried in the beast)?

Volunteers to make up a board & kits? :)

[Doug_Ford]

I don't mind attempting to build this system and using my machine as a test bed but I'm not sure anyone would want a kit I made if it included electronics.:D

[Doug_Ford]

One of my daughters is dating an electrical engineering major so I'll see if he can come up with a circuit board printout I can etch and drill. Mr. Richards, do you have a source from which you would recommend I order these parts?

[Doug_Ford]

Mr. Richards,

Is it possible that the part number on that proxy is BALLUFF ES-M12EL-NSC40B-S04G rather than SG4G? I couldn't find SG4G sensors.

[Richards]

Doug,
I just cross-checked the Balluff catalog (sensor catalog '05). The NPN sensor that I use is found on page 1.32 and has the part number BES M12MI-NSC40B-. The suffix, S04G is only found on the plastic parts bag. That suffix might be the quick-connector number that mates with this particular sensor. I bought two more sensors and some more cables from Fiero Fluid Power. The sensors cost $55 each and the cables are about $14 each, depending on the length. Today they only had 7.5m cables in stock.

I'm sending a schematic with board layout to Gerald. Everything was done using ExpressPCB, which is a company that provides quick turnaround circuit board manufacturing. They also give away their software to make designing simple circuit boards fairly easy. Their fastest prototype service costs about $60, which includes three 2-sided boards (without silk-screen or solder-mask). The only drawback is the board size for that service, 3.8 X 2.5 inches. This particular design just barely fit that layout. That same board with silk-screen and solder-mask costs about $11.50 each when thirty boards are ordered.

[Gerald D]

This PC board kept me awake last night.....it needs to be thought through a bit more:

- Location of board. To minimise wiring/cabling, this board should be riding the gantry or the y-car. Proxy's typically have 2 meter [6ft] leads - if all 4 proxy's have to reach the board without extensions then the location could be immediately after the y-chain.

- Housing. Since the board will not be in the control box, a housing needs to be selected and the board sized accordingly.

- Gantry autosquare. The 4th proxy for the slaved gantry motor needs to go independently to the BOB if autosquaring (http://www.mechmate.com/forums/showthread.php?t=605) is desired. Maybe a jumper option to have 4th proxy in series or independent?

- Z-zero. Many folk will be using a touch plate to zero the cutter height to the workpiece or the table. This can be in the same series circuit as the other switches, but the logic is reversed (contact is made instead of broken). Can terminals and chips be put on this board to connect the z-zero wires and reverse the logic?

- Junction central. Since we have already established this board is riding the car, in a housing, gathering all the proxy leads together (+z-zero) and has cabling to the PMDX, it might be useful that this board be expanded with more terminals to break out to all the pushbuttons (low-voltage) on the gantry. In effect, have this board extend the BOB all the way to the gantry . . . . .

Food for thought

[Doug_Ford]

Mike, Thanks for pointing me to the source and for designing this circuit and board layout.

Gerald, I don't know what I was thinking when I wrote my post last night. I can put together kits containing loose parts and ship to MM builders for my cost. With all of the help I've received during my build, this is my chance to pay something back.

I was thinking about the PC board too. It occurred to me that I might be able to use the MM to mill the cladding off if the components aren't crammed on there too closely. At least for the prototype anyway.

[Richards]

Gerald,
Normally, I build everything around a little 20-pin microcontroller so that features can be added with software - instead of a hardware redesign. The limitation of using a microcontroller is that most of them require a special programmer to write the program into the chip. The programmer that I use is fairly basic in operation, but it still costs about $1,000. It's had plenty of use on lot's of projects, but it isn't something that everybody would want to have on hand.

When this discussion first started, I thought about building a 'proper' auxiliary controller with 22mm bypass switches for each proximity sensor, 22mm indicator lamps to show the status of each sensor and as many other 'features' as the 20-pin microcontroller would allow, but just the 22mm parts and pieces for that device would cost well over $100.

However, if you can come up with a useful design that can be implemented with a microcontroller, I'll be happy to program chips for anyone who doesn't have access to a programmingr device.

[domino11]

Mike and Gerald,
I have access to a programming device as well if anyone needs devices programmed. Or even for board building, for the soldering challenged. :)

[Gerald D]

For those that havn't noticed it yet, more has been added to Mike's post with the schematic (post #37)

Mike, the programmed microcontroller approach is probably the most elegant. It would put those of us in Africa, India, etc. out of the loop for "upgrades" which are likely to be numerous in the beginning. But I have enough patience to hold back on getting the first few versions.

My approach to these things is from a hardware perspective, as you might have noticed above; It must fit in a box that rides the gantry. Leading into that box:
1 cable via the chains to the PMDX inside the control box
4 cables out to proxies
3 cables (one each) to the three pushbutton stations
1 pair of connection points for a touch plate (normally open)
1 pair of connection points for a touch probe (normally closed) *new requirement

[smreish]

A little something I found at Winford.com. An electronics supplier I use often for small break out relay boards and isolation contacts.


The board is available with three different relay coil voltages (5, 12, 24 VDC), allowing you to choose whichever is most convenient for your project. Please note that the relay coil voltage you select has no effect whatsoever on the voltages you can switch with the relay contacts.
For mounting on a panel, we suggest the rubber feet version (-FT), 1/4" nylon standoffs (http://www.winford.com/products/ssn.php) under the mounting holes, and #6 screws.
For more information, please see:
http://www.winford.com/img/pdf.gif RLP104 Datasheet (http://www.winford.com/download/rlp104_datasheet.pdf)
http://www.winford.com/img/pdf.gif RLP104 Schematic (http://www.winford.com/download/rlp104_schematic.pdf)Features


LED indicator for each relay
Relay contacts rated for 15A at 250VAC
Screw terminals for relay coils (accepts 16-26 AWG wire)
Screw terminals for contacts (accepts 12-24 AWG wire)
Approximate dimensions: 2.6" x 5.9"
Rubber feet or DIN rail mountDIN Rail Mount Version

These products are also available with DIN rail mounting clips for quick and convenient mounting where DIN rail is used. Product numbers ending with -DIN come with DIN clips already installed and ready to mount. The clips allow mounting on standard 35mm rail as well as 32mm rail. http://www.winford.com/products/pic/rlp104-12v-din.jpg (http://www.winford.com/products/pic/rlp104-12v-din_large.jpg)
(RLP104-12V-DIN pictured - rail not included)

[Gerald D]

Sean for that application I prefer to use this style (http://www.factorymation.com/s.nl/it.A/id.5416/.f?category=11127):

925

Only 6mm per relay, DIN rail mountable, any quantity and the relays are plug-in replaceable without fiddling with wires. I think there is version of this that is friendly to proxy's ("busbars" running through) but havn't been able to locate them. I seem to recall they were made by Phoenix?

[smreish]

Gerald,
Funny you looked that one up! I use them regularly from FactoryMation. Exceptionally small form factor and they have both NC and NO contacts. Plus, 3 voltages to choose from 12vdc, 24v ac/dc, 110v ac/dc.

The PC board in the previous post was for discussion/reference only for those interested in making a board of their own. Not for me...I like machine automation gear - easier to replace.

Bus bars are available for these relays.

If you look at the accessories page (http://www.factorymation.com/s.nl/it.A/id.5416/.f?category=11127) associated with this relay, you will see they sell them in 20 & 30 connection lengths...cut to fit. Three colors available.

[Richards]

Gerald,

What you've described should be fairly simple to construct, but, we'll need some more information.

PMDX:
How many signals to the PMDX and what polarity (active High or active Low)? (I'm assuming three signals; one from the proximity switches and two from the touch plate - one active high and one active low.)

Proximity switches:
NPN or PNP?
Normally Open or Normally Closed? (I use NPN, Normally Open)

Pushbutton Stations:
Are all three pushbutton stations linked serially?
What do you want this auxiliary box to do when a pushbutton on one of the pushbutton stations is pressed?

Touch Plate:
Normally open contact: Is this contact Active Low (input always sees +5V until the cutter touches the plate)?
Normally closed contact: Is this contact Active High (input is at ground potential until the cutter touches the plate)?

Voltages:
+5V
+12V
Common Ground
(Voltages supplied from the control box via the PMDX cable?)

L.E.D.s:
+5V present
+12V present
One L.E.D. for each proximity switch?
One L.E.D. for touch plate N/O
One L.E.D. for touch plate N/C

Bypass Switches:
Do you want switches to bypass each proximity switch?

[Gerald D]

Mike, I am not ignoring you, just giving all of this careful thought. . . . . . .

Would love some other folk to chip in with wish lists as well.

In my mind's eye I see it as a way of bringing the PMDX-122 (at least a large part of it) all the way to the gantry. The part of the PMDX that stays in the control box "drives" (geckos and relays for dust collectors, etc) - the part out on the gantry "receives" (limits, homes, p/buttons, touch plate, probe)

Out on the gantry we have lots of wires to be terminated and held securely.....I see mostly a lot of stupid terminals and relatively little board space with smart chips on it .......

Anybody else?

[Doug_Ford]

As long as we get proximity switches, I'll be a happy camper. I'd love to add the laser pointer but I don't know that we necessarily need it to be connected to the PMDX. Might be nice to turn on and off with a pendant so I guess a connection to the PMDX would help in that regard.

[revved_up]

I posted a while back but cant remember which thread about a company on ebay that was selling boards that worked in conjunction with the bob to enable connections for limit switches and e stop functions but nobody ever weighed in with their opinions on it.

[sailfl]

Craig

Here it is:

I'm not sure if this is the right place for this or not but I have been watching a sellers store on ebay, http://stores.ebay.com/HUBBARD-CNC-INC he has limit switches for sale cheap but the things I really wanted to were the power supplies he has and he has (for lack of better terminology on my part) a pass thru db25 connector that is supposed to protect your computer and it breaks out the e stop and limit switches all in one. It has USB connectivity on one of the models. If I understand it right it goes between the pmdx and the computer so does it give the ability to ouput mach to the controller via usb and does it make it easier to set up e stops and limit/homing switches?

again this loosly fits this thread but feel free to move it and if anybody with more knowledge about this would look and give their input I would apprieciate it.

You just needed to do a search on your name.

[revved_up]

yes thankyou, thats the post, he however has other boards besides that one that I was refering to that handle limits and estops maybe something to look into but as I am the least informed I just wanted to point a direction.

[Greolt]

Touch Plate:
Normally open contact: Is this contact Active Low (input always sees +5V until the cutter touches the plate)?
Normally closed contact: Is this contact Active High (input is at ground potential until the cutter touches the plate)?


You'll have to forgive me if I'm barking up the wrong tree. :)

With the simple touch plate that I advocate, the second option is not so desirable.

It implies to me that the tool is at 5v. This may come into conflict with normal machine grounding.

Greg


EDIT: I see on more careful reading that this was not what Gerald originally suggested

"1 pair of connection points for a touch plate (normally open)"
"1 pair of connection points for a touch probe (normally closed)"

Probe not Plate. :)

[smreish]

Here is my proposed proximity homing/limit switch layout w/ relays.
Prox switches rated at 10-30VDC...I am supplying 12Vdc from output on Antek transformer. I ordered 5v, 12v and 56v outputs on my transformer.

Based on the wiring logic supplied by factorymation pdf...I believe I have this correct. Any takers to verify my schematic?

Sean

987

[Gerald D]

Your schematic shows +12 and -12V, therefore 24V relay coils. Was that your intention?

[smreish]

12v coils.
I wasn't infering a differential voltage of 24 volts...only 12volts. I should correct the schematic to reflect otherwise.
The system, ideally, would be using the 12v I have native in the box and not introduce another voltage.

Thanks for looking at this.

SEan

[Gerald D]

My only other "schematic" comment is that you indicated one proxy each on each axis. My choice would be definitely 2 proxies on x-axis, 1 on y-axis and a "maybe" for the z-axis. The z-axis hassles are when it dives too deep and a fixed proxy can never detect that. (Some folk have sliding limit switches on the z).

[Richards]

Sean,
Those proximity switches must be Normally Closed for your circuit to work, otherwise you'll only get a 'contact' signal when all three sensors fault at the same time.

[Gerald D]

Mike the metal targets will be present in front of the proxys in the "normal" condition. In the presence of that metal, the NO switches will close.

The targets are "abnormal" in this case - we are not trying to sense bolt heads or lumps of metal at the ends of travel. We look at the rail all the time, but there are holes at the end of the rails. When the proxy sees the hole, it changes state and opens the relay. Also when the car jumps off the rail.

[Richards]

Gerald,
Sorry. I should have remembered that the sensors are actually going 'active' when they sense the 'hole', which, as you pointed out, makes Sean's circuit work perfectly.

[smreish]

Gerald,
Thanks for verifying the "logic". I assumed we wanted to see the rail at all times incase of a "jump the track". Thus NO logic on the Prox.

Glad I ordered the correct thing....no canceling that order now :)

[ekdenton]

Are these proximity switches or sensors necessary? Is there an advantage to have them or are they just a nicety? I see three of them in some of the posts, why not six?

What is their purpose?

Can I do without these proximity or limit switches to start out with and add them later?

[Doug_Ford]

Hey Ed,

Gerald wrote earlier that he still doesn't have switches on his machines. I don't have them on mine at the moment but I think I'd like to have them. I guess I'm just clumsier than Sean D. So I guess the answer to your question is that they're a nicety.

You actually only need four switches or sensors. One on both ends of the gantry, one on the car and one on the Z axis.

You can definitely start out without them and than add them later.

[Greg J]

Ed,

Agree with Doug. You certainly don't need them to get going or to have a productive machine.

I'm adding the prox. sensors, shuttle Pro, and Z-zero plate to make the mundane, every project essential starting point/process more efficient. I don't want to spend my time zeroing or finding my hard/soft limits for each new project.

You can add all or none of these items at any point. That is the beauty of building your own machine. Like any good receipt, you start with a good base (Gerald's design) and "add to taste".

[smreish]

Ed, (and others)
It took me less than 6 hours to mount,run all the cable, terminate and configure Mach 3 to work with the proximities. Gerald did all the hard work - he gave us a place to mount the sensors and a way for them to activate at the end of each axis. The only axis not accounted for was the z, which I made the mount, tapped the holes and painted in the above mentioned time frame. Cost was about 150.00 with all the cable and shipping. DEFINITELY a time saver when setting up the machine. Plus, the work offsets are nice to come back to after a "morning" home. I just click "ref all", click offset....and were cutting. ....almost shop labor proof...."almost" :)

[smreish]

I have fielded a number of Emails and PM's recently to explain my installation of the proximity sensors on the MM per Gerald's design intent. A quick summary below based on my choices and design input from Mr. Richards, Doug, Gerald and others.

MechMate Proximity Limits

Schematic for installation: (this is correct, NO contacts wired in series to the PMDX input)
prox_layout.pdf (http://www.mechmate.com/forums/attachment.php?attachmentid=987&d=1203305487)

Details: FactoryMation
qty description
3 SI12-C2 NPN NO H (http://www.factorymation.com/s.nl/c.415232/it.A/id.5200/.f?category=14129) m12QD proximity sensors, 10-30vdc
1 *cant find the part number* prox sensor like above with 30mm body length
4 PIR6W-1P-12VDC (http://www.factorymation.com/s.nl/c.415232/it.A/id.5416/.f?category=11127) slim relay
3 MOD.14/4 LC5 (http://www.factorymation.com/s.nl?c=415232&it=A&id=5270&category=) 5m qd cable. (right angle connector) - x and z axis. I extended each cable with 4 core cable to meet my needs.
1 MOD.14/4 LC5 (http://www.factorymation.com/s.nl?c=415232&it=A&id=5270&category=) 5m qd cable. (straight connector - ycar only)

Please note that the prox switch is NO logic
The relays are wired NO logic.

[sailfl]

Sean,

You forgot that you actually need 4 sensors. 2 for x and 1 for each y and z.

The diagram need one additional sensor added. I only know this because Sean and I talked about it.

[smreish]

Nils,
Correct, I didn't update the schematic like the parts list I just posted.
All still applies. Just add 1 more sensor in series for the x axis for a total of 4. Good catch.
Thanks,
Sean

[Gerald D]

In my mind's eye we still have a "box" riding on the gantry, with a logic board inside, as discussed in this thread a month ago. The blue thing in the sketch below. Realise that there are 35 wires and 4 screens to be taken care of inside there . . . .

1050

[Richards]

Gerald,

What you've posted is a classic multiplexer/demultiplexer, which is just another name for 'switch box'. The next thing that we'll need is a chart that lists each device and its destination, such as:
Push Button Station 1, Red PB (N/O) -> Pin 11
Push Button Station 2, Red PB (N/C) -> Pin 11

From that, a circuit can be drawn and a circuit board can be built.

[smreish]

I just get drawn into the forum whenever Mike post's something.
It's like watching Einstein discuss the theory of relativity. :)

[Greg J]

Mike the metal targets will be present in front of the proxys in the "normal" condition. In the presence of that metal, the NO switches will close.

The targets are "abnormal" in this case - we are not trying to sense bolt heads or lumps of metal at the ends of travel. We look at the rail all the time, but there are holes at the end of the rails. When the proxy sees the hole, it changes state and opens the relay. Also when the car jumps off the rail.

Ed,

Gerald's post answers the NO question.

[Doug_Ford]

The next thing that we'll need is a chart that lists each device and its destination, such as:
Push Button Station 1, Red PB (N/O) -> Pin 11

I'll try my hand at this but I may need help with the Z zero plate and the black button on Gerald's 4 button station.

[Greg J]

Sean, or anyone

Ed asked myself a question that I can't answer. I thought I understood the wiring and logic, but I don't.

On the relays, what pin numbers are you using for the latching side? In your earlier photo, it looks like pins 12 and 14. That makes no sense because its an open circuit :confused:

Pins 11 and 12 makes sense, but that would be NC and you said it's NO. Also, on three NO relays in series, how can the BOB recognize anything when only one out of three switch's closes.

A1 and A2 are jumper-ed and that makes sense.

[smreish]

Greg,
Pins 11 and 14 of the relay are wired in series to the input #15 on my PMDX.
It's open when not energized, closed when energized. Whenever the machine is powered "on", it's energized and closed.
When homing or seeking limits, the proximity switch "sees" the hole in the rail, opens the relay, opens the switch and activates the pmdx. Then, because the Mach routine for homing is smart. Mach will seek the switch, activate, them reverse the axis until it is cleared then move to the next axis. Mach's sequence is designed around using multiple switches (regardless of type) to utilize only 1 input on the BOB, thus freeing up inputs for other things. Like a pause and resume button on the gantry, or z-zero function button.

Page 8 of the pmdx manual show's "loosely" multiple switches configured to a single input for this reason.

Ed and I have exchange multiple emails over the past number of days discussing the NO / NC reasoning.

I like the switches powered in parallel, but input wired to the BOB in series via a NO contact. I have many reasons for this, but mostly a NO contact would show a failure to the BOB if one of the sensors is not powered on or a wire is broken because the switch MUST activate and pull in the relay to work. A NC switch in this case may not show a fault until you try to home or hit the limit, then you would find the machine crash into the hard stop....or you get to listen to the z-axis grind teeth for lunch.

Let me know if I have explained this logic well enough...I feel like the NO / NC switch choice battle isn't over on the forum yet.

For me, my MM works like a champ set up like this and I have even de-railed the machine on purpose to test me theory....its works well.

*Gerald and Mike can chime in here and help me any time now :)*
Sean

[Greg J]

Sean,
Everything was making perfect sense until this part.


I like the switches powered in parallel, but input wired to the BOB in series via a NO contact. I have many reasons for this, but mostly a NO contact would show a failure to the BOB if one of the sensors is not powered on or a wire is broken because the switch MUST activate and pull in the relay to work. A NC switch in this case may not show a fault until you try to home or hit the limit, then you would find the machine crash into the hard stop....or you get to listen to the z-axis grind teeth for lunch.


What NO contact ? Am I missing something in your schmatic?

[sailfl]

Sean

I wish you guys would have these talks on the threads because I am sure that others like me would like to be able to understand this stuff. I want to understand how these things work. I am learning many things and I hope once I get my machine built and running that I will be able to share some of my software experience.

[Doug_Ford]

Greg J,

I was waiting on Sean to answer this one but it looks like he's signed off so let me see if I can answer it.

The prox has a normally open switch inside it. When the circuit is energized, it closes as long as the metal rail is in front of the sensor. That's the way I understand it anyway.

[Doug_Ford]

The next thing that we'll need is a chart that lists each device and its destination, such as:
Push Button Station 1, Red PB (N/O) -> Pin 11

Will someone please check my work before Mr. Richards starts designing a circuit.

Push button station 1 (On Car)
Red PB (NC) -> J6 Estop
Red PB (NC) -> Contactor
Green PB (NO) -> Pin 15
Yellow PB (NO) -> Pin 13
Black PB (Gerald, I can't remember what you had in mind here. I think it was for the Z zero.)

Push button station 2 (On Gantry Front)
Red PB (NC) -> J6 Estop
Red PB (NC) -> Contactor
Green PB (NO) -> Pin 15
Yellow PB (NO) -> Pin 13

Push button station 3 (On Gantry Back)
Red PB (NC) -> J6 Estop
Red PB (NC) -> Contactor
Green PB (NO) -> Pin 15
Yellow PB (NO) -> Pin 13

Z Prox (NO) -> Pin 12
Car Prox (NO) -> Pin 12
X Front Prox (NO) -> Pin 12
X Back Prox (NO) -> Pin 12

Z Zero Plate (NO) -> Pin 11
Probe (NC) -> Pin 11

[Greg J]

Thanks Doug,

I think that does help.

The Prox. is NO, but since it see's the rail, it activates (sorry if terminology is incorrect). Since it's "activated" (closed) the solenoid in the relay is energized, closing the latch in the relay.

Now, under normal conditions, all three relays are closed, because the Prox. sensors are seeing the rail and are closed. When the Prox. see's the hole at the end of the rail, it opens, de-energizing the solenoid in the relay, opening the latch. The BOB see the new condition and knows it's at zero (if ref all) or in a fault (if gantry de-rails, or whatever).

Aaaah, light bulb is starting to glow.

Does that help Nils?

[revved_up]

Sean, where does the +-12vdc come from?

[Gerald D]

There was a good question in here last night, which the poster shyly decided to delete again:

"I am trying to wrap my head around the layout and wiring of either proximity sensors or the switches. I take it that the main purpose of these is to allow mach to be programed to set the router in a home position in all three axis's.

Okay if that is the goal, I do not understand wiring three or four sensors in series NO would work. Reason being, how does mach know which sensor tripped when they are all in series? "

Your car is parked in your garage and the garage door is closed. You get in the car, start the engine and you are now going to drive. Your name is Mach3, you are blindfolded. You (Mach3) puts the car in reverse and drives. Mach3 hears a bang, (the garage door is hit). Mach3 puts the car in Drive, goes forward and hears another bang (the front wall is hit). Mach3 being a normally bright person has figured out that the bang after reverse is the door and the bang after Drive is the front wall. Mach3 only needs one bang sensor.

On the router table, you can wire everything in series, to make one big sensor, because Mach3 is smart enough to know what it was doing before it hits this sensor, and therefore figures out which part of the sensor it hit.

And then, to give some perspective, this bit:
"I take it that the main purpose of these is to allow Mach to be programed to set the router in a home position in all three axis's."

The reason we manage to mostly get by without any switches is because we "home" the machine to the corner of the material lying on the table. After changing a cutter, manually jog the cutter over the corner of the material and set x and y to zero from the keyboard. Then jog the cutter till it just touches the surface and set z to zero. Then start the cut.

A home switch on the z-axis can never tell you the distance between the cutter and the material. Home switches on the x & y can only tell you the distance to the material if the material is located to the same spot everytime.

But there are times (not many) when we wish we did have proximity switches . . .
- When there has been a glitch (power failure?) in the middle of a sheet of material and we need to find the reference points again.
- When the cutter hits a clamp and the car jumps off the rail.

[sailfl]

To go along with the list Doug made for the Circuit, please add an output.

Laser Control (NC) -> Pin 14

Thank you

[Gerald D]

Nils, we are not getting into lasers. . . . yet.

(Besides, from the little I have read, lasers often need an analog ramp up/down for engraving, to avoid burning through when motors are accelerating/decelarating.)

[sailfl]

Gerald,

You misunderstood..... I am not getting into lasers for cutting. This the crosshair laser.

Discussed here: http://www.mechmate.com/forums/showthread.php?t=596

Hope that clears that up. I have my hands full just trying to understand the router build. I could have made it clearer and said crosshair laser.

We need an output for the crosshair laser. NC -> Pin 14

[Doug_Ford]

Gerald,

I think Nils was talking about a laser pointer like Greg (Down Under) has set up on his machine.

[Greg J]

Doug mentioned it awhile back on another thread, but I think it's worth repeating.

Mach has a great tutorial video on coordinate systems that explains this homing / zeroing / etc.

http://www.artsoftcontrols.com/Videos/Mach3%20Video%20Selections/Mach3%20Video%20Selections.html

[Gerald D]

The crosshair laser is only fed with a battery.

[sailfl]

Gerald,

I respect your knowledge and your design. But Greg Greolt has a cheap less than $5.00 crosshair laser that he uses on his machine that he turns on and off with a button on a Mach3 page. I don't believe it is powered by a battery though I am sure there are battery versions out there.

I am getting the feeling that you don't like this idea so you will not hear any more about from me.

[Gerald D]

My impression was that you need to stand close to the laser to line it up with a mark on the job - that's when you just switch it on. Some of these lasers have the battery and switch built in (keyring type, board pointer, whatever, (shooters pistol type?)). Using mach to turn it on seems like an overkill.

[ekdenton]

Sorry guys I posted and deleted the question above that Gerald reposted. Reason for deleting is that I wanted to think about it some more before asking that. Since I posted that Sean has answered it for me.

I was seeing the layout with the three relays NO and the sensors NO. What I failed to think about yesterday was when the sensors are powered up and see the rail the go NC and the relays go NC, which closes the open circut from common to pin #11. The when any sensor trips it opens the closed circut giving a signal to the BOB.

I get it now. I knew Sean had his working and it was something simple that I just wasn't seeing or grasping yet. Thanks for the replies and explaining better.

I see exactly what you are saying also Gerald, It would be hard to have the same thickness and size material placed in the exact same place every time, and if your memory is like mine it would be easy to ruin alot of material or break a bit or worse by not manually setting it for each project.

I think I will use the sensors but for more for safety than anything else.

[Doug_Ford]

I agree Gerald. I worry that we may be making the MM electronics too complicated. That may discourage new builders from taking the leap and later on when my machine breaks and this info is no longer in my head, it will be harder to diagnose. At most, I would use simple push on/push off switch mounted on the car to turn on\off the laser pointer and some wires to supply power. Better yet, run it off the battery.

[Gerald D]

http://www.uie.com/articles/simplicity/

I hate batteries as much as the next guy, but we can't design an input to a laser pointer if we havn't got a clue what it needs. I am fairly confident that a 12V DC supply to the gantry could be converted for use by the laser pointer and that a simple local switch could control it.

[revved_up]

bump

Sean, where does the +-12vdc come from?

I guess what I'm asking is did you add another output to your power supply or did you draw power from somewhere else?

[Gerald D]

He gets it from his Antek supply

[revved_up]

how many times can you tap from the same 12v output? I still have to order my power supply so maybe I should ask for two 12v outputs instead of one.

[krymis]

I don't know if this has been cover but here is an idea for switches that works great. I use them on my minimills the ih mill, my minilathes and my
12x36 lathe. not one problem amongst them. It is an easy setup with common parts.

http://www.industrialhobbies.com/howto/product_instructions/v3_build_instructions/installing_optical_limits_pt1.htm

http://www.industrialhobbies.com/howto/product_instructions/v3_build_instructions/installing_optical_limits_pt2.htm

http://www.industrialhobbies.com/howto/product_instructions/v3_build_instructions/installing_optical_limits_pt3.htm

the working part http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=QVA11134-ND
and last is a post about the setup at cnczone http://www.cnczone.com/forums/showthread.php?t=48607&highlight=optical+limit

[smreish]

hey guys
been working a little late and saw the comments. The 12v comes from my antek transformer. I ordered it with 12v 5v and 56v taps all voltages are redistributed thru dinnectors power blocks for use. Mainly to preserve wiring standards from gecko. The 12v is used for the pmdx and now the prox's. 5v for the ncpod later.

Ed, I am so glad the wiring use finally "clicked" in your head. Don't hesitate to email me with any other questions. I am glad to help those that are trying to build the machine.

The relays and simple wiring was really easy. On mm #2 I will relocate a wiring block and power distribution to the gantry. It will greatly simplify my big blue box.

[Gerald D]

Chris, your switches could be technically okay, but they are not readily available off-the-shelf around the world, so I can't include them in the design. Do you have dust seals where the rod enters the housing? Also, we would loose the jump-the-rail-protection that the proximity switch gives us.

[Richards]

Looking back at post #70 where Gerald posted a drawing that showed various input devices connected to a box as well as an output connection going to the control box, we still need to define the STATE of each input and we need to define which output line each input uses.

By STATE, I mean the Active State of the device. For instance, the State of an Normally Open proximity switch when used with the MechMate would be Normally Closed or Active, since the usual condition of the proximity switch is to sense metal except when a limit has been reached (the hole in the metal). So, if I knew that there were going to be four proximity switches on the machine and that all of the proximity switches would normally be turned on and that all of the proximity switches were NPN signal type, I could easily design a circuit that monitored the proximity switches (or relays to which the proximity switches were connected) and then generate the proper signal for one of the signal lines going to the control box (pin 11, 12, 13, or 15, or even the E-stop signal line - if desired).

The same goes for the push-buttons. Are they Normally Closed or are they Normally Open? (Normally Closed is safer because a broken or faulty push-button would be detected as the machine powers up). When they are active, do they give a 12V signal or do they give a GND signal (0V)? A circuit designer would say that a switch giving out a 12V signal when it is active is SOURCING and that a switch that is at 0V when active is SINKING.

If I were building the most simple and the most robust interface, I would use a series design for the proximity switches, just like Sean's in post #67. I would use Normally Closed push-button switches connected in series for each of the different push-button circuits. The zero plate would be a Normally Open configuration, because that would be the most straight-forward. By wiring the proximity sensors in series (through relays), if any sensor 'detected' a hole, the input state for the sensors would go from 0V to 12V, signaling that a limit had been reached. In the same manner, if any one of the Red push-button switches was pushed, the circuit would be 'broken' and the input signal for the Red circuit would go from 0V to 12V, signaling that at least one of the Red switches was active. The Zero plate would be just the opposite. When contact was made between the plate and the cutter, the input signal would go from 12V to 0V, signaling that contact had been made.

Of course, using more complex circuitry, any input (switch or sensor) could be either High or Low, On or OFF and gates inside the box could be jumpered so that the correct signal was sent to the control box, but that would require much more circuitry and it would also give the builder many more possibilities to mess up by jumpering something backwards.

So, who wants to define the STATE of each device?

[Doug_Ford]

So, who wants to define the STATE of each device?

I'll take a stab at that too. Unfortunately, I'm going to be tied up with work for at least a couple of weeks so I probably won't have a rapid response.

[ekdenton]

how many times can you tap from the same 12v output? I still have to order my power supply so maybe I should ask for two 12v outputs instead of one.



Craig, I will take a crack at answering your question.
You can run as many things as you want off the VR as long as the max current draw from the items that you are running off the VR stay under the current rating of the VR. Say if it is a 1amp VR, add up the current draw from everything you will connect to it and it needs to be under the 1 amp. If I remember correct from the PMDX literature I read, the PMDX draws a maximum of 300mA (if this is wrong someone who knows will correct me) I don't know what the proximity sensors draw, they also have some small LED's. Check the total amps they draw and add the 300mA that the PMDX draws, then check the amp rating on the VR.

EXAMPLE:
PMDX 300mA (check to make sure)
Proximity Sensors ??? maybe 120mA (just a guess check to make sure) X4=480mA
Laser pointer ??? guessing 100mA (check to make sure)

880mA would be 120mA under.:):)

If you were to add an array of superbright LED's (like I want to do) under the gantry to light the work area, then you may need an alternate source of power. The superbright LED's draw 100mA, so 20 of those under the gantry would draw 2 amps, but would brighten the work area very nice.:D:D

[revved_up]

Thanks ED, Thats what I like about this forum, Lots of help!! yours was actually the 3rd answer I received thanks for looking out.

[ekdenton]

I have the proximity sensors now and they draw 200mA each and I checked the PMDX and it draws 200mA max. So if the redimade antek supply has a 1amp voltage regulator on it, you will be at 1 amp if you use 4 proximity sensors. So if you add anything else you will probably need an alternate source of power.

I also added a question in the power supply about this subject (moved back here):

"Gerald, this brings up a question to you, for those who are using the pre-made voltage supply from Antek, with the Voltage regulator to run the PMDX. If they also run 4 of the proximity sensors also, that will be using up 1amp of avalilable current for the motors. Will adding the sensors in addition to the PMDX be any reason for alarm?

I am using the 2amp 12v supply from factorymation, but thought it would be a good question to talk about."

[Gerald D]

What is making your proxies draw 200 mA? Did you measure it?

Here is a typical spec sheet:
http://factorymation.info/sensors/Inductive.pdf

They draw less than 15 milliamp by themselves (if they were connected directly to the PMDX for eaxample), so the 4 proxies by themselves are extremely light on current consumption.

However, they can drive up to 200mA each, and will do that if you have a fairly "big" relay on each one, that is mostly in the energised condition.

So, to keep the current consumption down, either:
- drive logic chips instead of relays
- if using relays, use low-current relays
- if using relays, consider using them mostly non-energised.

Alternatively, size for a bigger power supply.

[Gerald D]

If you are using this relay:
http://catalog.tycoelectronics.com/TE/bin/TE.Connect?C=1&M=BYPN&PN=V23079A1003B301

which has a 1029 ohm coil resistance, it will draw only 11.6 milliamp at 12V. Therefore, 4 proxies and 4 of those relays together will be close to 0.1 amp, which is no cause for concern.

[ekdenton]

No I didn't measure, just going off what the data sheet that came with them said that they draw.

They do have four small LED's though.

[Gerald D]

I think you might have misread the data sheet ;) At that sort of current they would be getting quite warm . . . .

They have the ability to drive that much current, but you shouldn't be using them near the limit for this application.

[Gerald D]

See post #32 in this thread for info on a relay choice

[ekdenton]

Maybe you are right. Seems like alot considering the size of the LED's. A small LED draws 20mA and these look like about 3mm.

Here is what was on the wiring diagram....exactly the way they wrote it.

10-30VDC I=200mA

Usually it will give a max current draw but that was all that it said.

[ekdenton]

Those relays look good, thanks Gerald.

Looking at those relays though brings me back to the original point or question though, for those who are using the voltage regulator and also the sensors. Not trying to be a pest about this or anything just trying to make sure that those using the voltage regulator off the transformer are aware of the current draw when adding additional circutry like the sensors and relays.

I didn't even think about the draw from the relays and they will be drawing anytime the sensor sees rail to keep the contacts closed. The ones at mouser draw 140mA each.

[Gerald D]

Doodling a little PC board for relays for the proxies:

1080

The top relay is for the occasion when the second X-gantry proxy is used in the current Mach squaring method.

[Gerald D]

ED, check that Mouser spec again - it is 140 milliWatt.

Of course your point is valid - the power supply must be sized to feed all the consumers.

A 300VA supply can feed about 2000 of those relays if it has nothing else to do. :)

[ekdenton]

oops your right Gerald it is mW rather than mA.

Nice drawing I will save that. What cad program are you using for drawings like that?

[Gerald D]

AutoCad2000 LT

[Doug_Ford]

Looking back at post #70 where Gerald posted a drawing that showed various input devices connected to a box as well as an output connection going to the control box, we still need to define the STATE of each input and we need to define which output line each input uses.

So, who wants to define the STATE of each device?

Well, I've read and reread Mr. Richards' post several times and I've pondered the control systems for a while. I hate to admit it but I think this is over my head. As most of you are aware, I'm certainly no electronics whiz. I know I volunteered to try to figure this out but the crap I'm likely to come up with will most likely be worthless and only set us back. Sorry Gerald, Mike, and the rest of you guys. :(

[ekdenton]

Gerald, this is what I was thinking of doing on the gantry, as in post #70.
Does this look like it could work to you? Proximity sensors and relays are NO, so that when hot they are all in a closed state. All sheilding tied to box with star washers and terminal rings, also grounded one side only in control box.

I think two of the seven conductor will need to be dedicated to the voltage supply to the box (a +12v and a -12v). Which will leave 5 avaliable. I am only using two of the "three pushbutton type" stations so I think I will be okay with just the 7 conductor cable only.

This brings a 12vdc supply onboard the Mechmate gantry for anything else like laser pointers or lighting, ect. under the gantry.

Sorry my drawing res is kinda bad I can't figure out how to save as a photo from my CAD without pasting to clipboard first and it kills the res.

[Gerald D]

When you do a screen capture from CAD, go for GIF format rather than JPG.

Will look at details later . . .

[smreish]

Schematic for installation:
prox_layout.pdf (http://www.mechmate.com/forums/attachment.php?attachmentid=987&d=1203305487)

I received a message from Ed, but have also fielded a few queries from others on how the Proximity relays really work and how to wire them to the PMDX using only 1 input.

1 - refer to the pdf schematic link above. You can also see pictures of the installation in post 247 of my this thread.

Steps (and JR will keep me honest - I am nowhere near my machine right now to check things)

1 - wire according to schematic.
2 - set your mach 3 settings in the Ports and Pins box to input 15.(or your setting. For example. Map x - home to 15, map y - home to 15, map z - home to 15.
3 - I'll check my configs in the morning to see if I have it active hi or active low....I can't remember right now.


Mapping all the homes to the same pin number will allow mach 3 to cycle through the homing sequence and set the z, then y, then x.

In the Mach screen you push the long vertical bar (near the DRO readouts) to "refall" and it will run this sequence.

That is all. It works well and all the time.

[ekdenton]

thanks sean, I have mine working now.

There were some issues though. I am using pin 12. Doesn't matter you can use any of the unused pins on J5 as long as you enter that pin in the ports and pins. Remember also (i didn't at first) to assign A to home to the same pin #. After grinding gears for a second I remembered my slave motor.

I had to reverse the homing direction by changing to home neg for X,Y and A in the homing window of mach 3. Z doesn't have to change.

Active low boxes stay unchecked so they be active high.

Only issue I have left is the travel to home speed is slow all the time not just the last inch.

[ekdenton]

got the travel speed set now for 80% that is better

[Alan_c]

Only issue I have left is the travel to home speed is slow all the time not just the last inch.

Ed

Good progress.

That travel will always be slow as when the machine is homing, it does not know where the the last inch is, it only knows to look for a limit switch somewhere in that direction. Its best to jog close to the limits and then "refall".

If I remember correctly, the big iron machines like Multicam will not allow you to jog until it is referenced, but Mach3 allows it.

[smreish]

Alan,
Your very correct. If you lost the home on my big multicam, you could not jog the machine except at "seek" speed. Which is the same slow speed it looks for the home switch. A real bummer if you lost home in the parked gantry 10 feet away from home. It took 10 minutes to rehome the machine!

Ed....great to hear you got it all worked out.

SEan

[cobra427mnsi]

Ed

Good progress.

That travel will always be slow as when the machine is homing, it does not know where the the last inch is, it only knows to look for a limit switch somewhere in that direction. Its best to jog close to the limits and then "refall".

If I remember correctly, the big iron machines like Multicam will not allow you to jog until it is referenced, but Mach3 allows it.

Here's a thought. Could a proximity switch be used to change the jog (feed) speed. If so, theoretically speaking, one could use two proximity switches set a few inches apart. When the first one is detected it will slow down the jog rate so you would not over run the second one when homing.

[Richards]

I'm only using Mach 3 on the test bench, not on my machine, so I'm not fully aware of the day to day sequence of events that you use when starting up your machines; however, on my machine, I manually jog the X and the Y axes to a point about 2 inches from the proximity sensors, and then run my homing routine. The manual jog, even from opposite ends of the machine, takes only a few seconds. I move the Z-axis to a point about 1/2-inch above the contact plate before running the Z-Zero routine.

[smreish]

Mike,
I do the same thing. It only takes a few seconds to get close, then run the routine. Works like a champ - every day.

Sean

[J.R. Hatcher]

I just checked, it takes 16 sec. to home 101" (full table length) on my machine.

[dmoore]

I really liked where everyone was going with a "professional" control box mounted on the y-Car. "Richards" - would it be possible to get a design based on the last few posts?

[sailfl]

Yes, but you need to included expansion, please.

[Richards]

It looks like we're making this much too difficult. Look at the 7408 chip and the 7430 chip to see how many inputs can be combined to make one official input. Typically, all the limit switches can be connected to the same input. In the same manner, all of the proximity switches can be connected to one input. All that is normally needed is one "glue" chip like the 7408 or the 7430 to handle everything.

Two weeks ago, I had to deliver a very simple CNC type device to the Maker Faire in San Mateo, California. It used three N/O switches and one proximity switch in its circuit. The whole circuit cost less than $10, including a proto board, 4N25 opto-isolators and wiring.

Sometimes, it seems like we try to find the most difficult way to solve a simple problem. All of the suggestions on this thread would work, but most are overly complex.

[Greg J]

Keep It Simple Stupid (KISS).

I have not seen any better than Mr. Richards.

[ekdenton]

Gerald's circut drawing works good , that is how I did mine. I have power now at the gantry I used a jack like in the photo below and wired as in my drawing earlier in this thread. I had it all correct first try just didn't know enough about Mach 3 to know to hit the ref all home tab:o


If you use the microswitches you could maybe build the circut for less than $10, if you don't include the cost of the enclosure box. I think the concern was on the microswiches was durability and longivity in the dusty enviornment? The advantage of capacitive proximity sensors that some are using from factorymation is that they are sealed from dust and moisture and although nothing is foolproof, probably will be more durable than the microswitches. At least that is what I gathered from reading this thread from the beginning and some of the personal pages.

1415

[Richards]

I may have mislead when I gave the $10 figure. The $10 is for the glue chip and the proto board. It does not include the limit switches/proximity sensors. The proximity sensors that I use cost about $75 each (with cable). The 22mm push-button switches that I normally use cost about $15 each.

[Robert M]

Hi Sean,
After reading a few post on this proximity limits, I’m still very curious to see how you type of installation fits on the Y car.
I’ve seen your pics from your thread #247 and David’s new ones, but David uses Diell BIG 18mm in a different holder approach.
If not to much asking, could you post a few detail pics out of your Y car proxy installation ?
Thanks, Robert ;)

[Greg J]

Robert,

Couldn't find your personal thread ...

Here are a couple of pictures of my Y car Prox. What are you wondering about?

That darn high gloss paint. :)
1438

1439

[dmoore]

Hi Sean,
After reading a few post on this proximity limits, I’m still very curious to see how you type of installation fits on the Y car.
I’ve seen your pics from your thread #247 and David’s new ones, but David uses Diell BIG 18mm in a different holder approach.
If not to much asking, could you post a few detail pics out of your Y car proxy installation ?
Thanks, Robert ;)

Robert - the spec'ed proxy is 12mm for M1 18 022, so the 6mm isn't too much larger. I purchased the 18mm units due to cost - $10. If you maintain the same center line (1" from the back edge of the angle), using a different sensor shouldn't be an issue. I think the bigger issue is the total length of the sensor, it's distance needed to sense the rail and the height of the cable (right angle or straight).

I'd recommend waiting to build the stops until you have your gantry and y-car done and working. I'd then weld the end-stops onto the rail after you have mounted the stopper lips (M118022). Just in case....

[dmoore]

Here are a couple of pictures of my Y car Prox. What are you wondering about?

Greg -

Can you tell me what that bracket bolted to the y-car next to the proxy sensor is for?

Thanks,
david

[smreish]

Pics of the proximity mounts that I promised last night.

1565
y axis

1566
x axis


1567
z - axis

[Kobus_Joubert]

A question about the proxy sensor holes. On the drawings Gerald indicates 20mm. My biggest drill is 18mm and I don't own a reamer. Can I leave it at 18mm ?

[smreish]

18mm "should" work for most cable connector ends. I happen to use a modular *make to suit your needs* style of QD connector for proximities. It's body needs a 19mm hole to clear. If you have the standard off the shelf factory made connector, the hole may work for you. If you want an easy larger hole, you can pick up a Greenlee (TM) or similar variable stepped drill bit that will makes holes from 1/4" up to 7/8" - (7mm to 24 mm ) The bit is around the 40 dollar range, but Harbor Freight has them for around 20 dollars US.

...and yes, the y chain bracket is placed just off centerline on the y car. You can see it just above the sensor in the photo. The mamba parts were not release yet when I built my MM. Thus, I had to improvise my E chain bracket and support from scratch and guidance from Gerald across the pond on clearances and location suggestions.

Have a great day.
Sean

[J.R. Hatcher]

I think Kobus is talking about the 20mm proxy target holes in drawing 10 10 246

[sailfl]

Kobus,

How big around are your proximity sensors? If they are smaller than 18mm you should be fine.

[smreish]

JR,
Thanks...typing before coffee dangerous! 18mm fine for target hole as long as your centermark and drilling is accurate. The 12mm sensors I used work fine on 13mm holes in other applications.

[Kobus_Joubert]

I have not bought the proxy sensors yet. So when it comes to that I must just make sure that they are smaller than the sensor target hole (18mm)

[dmoore]

I wonder what actual size the holes have to be to break? It would seem that sensor type, distance from hole, metal used, etc all have a part to play. Does anyone in the automation world have some input on this?

I did find this:

http://web1.automationdirect.com/static/manuals/proxatcmcf/ak910series.pdf

[javeria]

Sorry if I am interrupting, but look at this one,seems to be a nice package for the limits and affordable too.http://cnc4pc.com/images/C16R1_A.jpg
http://cnc4pc.com/images/C16R1_D.jpg

http://www.cnc4pc.com/Store/osc/product_info.php?products_id=183

what say? is it comparable enough to the proximity switches?

[Richards]

The opto devices will work, BUT, as always there may be a problem.

As you can see, the device is built in a "U" shape. On one side of the "U" is the infared LED, on the other side of the "U" is the detector. In the face of the "U", is usually found a hole (1/8", 3mm). That hole is small enough that dust and debris can easily clog it. Normally, whenever the light beam is interrupted, whether by clogging or by sensing the target, the machine would stop.

With the amount of heavy dust that a CNC router makes, it would be very difficult to use that kind of detector.

[dmoore]

I'm sure you could make these work, though be aware of:

These are optical based sensors and thus can be triggered by dust or chips
Requires redesign of the X and Y stops. Also, due to their size, they would have to be very percise
The current design with proxys allows for tripping if the X or Y come off the rails anywhere between to ends (they do this by looking for the rail and then tripping when they don't see it). To do this with these sensors, it would require a vertical rail along the entire length of X and Y.
If the gantry or car jumped off the rails, it would likely break the sensors
The cords (6' each) are too short and would have to be lengthened
There will be a much higher possiblity of accidental tripping due to the low voltage of the sensors and lack of shielding cables
The kit includes 6 sensors, the MechMate only requires 3 (or four if you want a sensor on both sides of X)
It is possible to use industrial proxy sensors with relays for about the same price. I purchased mine from automation-overstock.com, the proxys were $10 each ($40 total) and the quick disconnect 15ft cables were $5.50 each ($22 total). Add to that about $10 in relays.

[smreish]

I should have take a picture of my machine today.
The "snow plow" effect was working well. I had inches of buildup on the end of the machine and proximities worked the whole time.

Optical scares me in this application.

Sean

[dmoore]

Sometimes, it seems like we try to find the most difficult way to solve a simple problem. All of the suggestions on this thread would work, but most are overly complex.

I believe you are correct. In the end I used four relays I pulled from junk yard cars. Total cost: $2.

[ekdenton]

Found some interesting reading about the capacitive proximity switches. I kind of understand now why the dust doesn't affect them.



http://www.kirbyrisk.com/allen-bradley/racatcd/c112/proximit/2922.pdf

[javeria]

Thanks all for your inputs. anywayz this thread does point to wiring of the proximity switches to the mechmate control box dosnt it........wait let me look back.

[bbreaker]

how, thank's a lot for this reading, i understand a lot of thing's now i start with this.

a question to Gerald, how did you fix the proximity target in 20mm hole after adjustement.

thank's

[ekdenton]

hi mickey, I haven't seen any posts lately by gerald he must still be on vacation.
If you epoxy them it would be a permenant set, would it be better to use a spot of silicone? That stuff holds well but yet can be removed later if needed, and it shouldn't take much at all to hold those into place.

I am not sure if you would ever need to remove them if they are in the correct spot but for some reason it seems IMHO not to epoxy or JB weld them into place.

[bbreaker]

ok ED thank's, i go with epoxy it's very strong and if i make litle spot i can remove it if i whant to make change.

[smreish]

The adjustment for the proximity limit can be either with the ecentric disk that is in the drawing package, or, like I have done, have a G-code offset programmed into mach 3. This lets you home the machine to what-ever the proximity limit is, then the machine offsets each time back to the G-code values.
It's a great thing to know you can rehome a machine to the "HARD" limits and find your soft position again. I have found that even if I E-stop the machine and reset everything, I was able to get back to where I stopped. NOW, I don't recommend this method...I was just curious to see If I could do it!

[Gerald D]

how did you fix the proximity target in 20mm hole after adjustement.

Havn't done it myself yet, but I thought that masking tape over the top would work???

[javeria]

Whats difference between a npn and a pnp NC proximity switch.

[Gerald D]

PNP (http://www.sesensors.com/content/EN/support-service/term-definition.asp?word=120)
NPN (http://www.sesensors.com/content/EN/support-service/term-definition.asp?word=106)

[javeria]

Thanks G' got it!

[javeria]

My proxi setup

Works wonderfully well !

[shaperx]

Sean, In your post May 14th you set Map home to pin #15 are you putting Y++ ,Y-- ,x++, x--,z++ and z-- all to pin #15?

[smreish]

Yes,
Everyone is mapped to the same input.
Mach knows how to cycle the inputs based on the active axis when homing.
Sean

[ekdenton]

Sean, In your post May 14th you set Map home to pin #15 are you putting Y++ ,Y-- ,x++, x--,z++ and z-- all to pin #15?

Mark,
Sean is right but it doesn't have to be pin #15 in peticular, I think I used pin #12. I wasn't sure if you may have been asking if a different pin besides #15 would work. Anyway any of the unused pins except for GND on J5 will work as as long as you map home to the same pin that your proximities are hard wired to. Don't forget to also map home your slave motor too if your using one on your x axis. I figured that one out after some gear grinding.

[Robert M]

Hi Sean & Greg,

I was reading back into this thread and it slap me right in my face !!:eek:
For some reason I can’t remember why or it got lost ( I doubt that one !) I never got back to thanks you guys for the extra effort & time for your reply to my call !! (#136)
Sorry, no offences guys :o:o
Amicalement, Robert ;)

[javeria]

HI Folks,

while setting up my other CNC machine where I have used the proxi's i came across people tellin me that u need a good machine zero setting so that when power fails - the software uses the machine zero to accurately position itself relatively to the job.

so the Q here by me is - are the proxi's good enough to be used for Zeroing the machine in case of power failures - I am still learning folks - hope this Q is not a dumb one.

RGDS
IRfan

[Gerald D]

That is a question that most people should think to ask, but they don't. ;)

Apparently, the prox switch is very "repeatable" and switches at exactly the same distance every time, provided that you always approach the "target" at the same speed. This is what I hear from the regular users - havn't tried it myself yet.

[paco]

I use proximity switches to calibrate/zero my machine ion X and Y.

No matter which type of zeroing system you use (and how much you pay for), you should test it with a dial indicator to see how accurate you can recover a cut after an event such as a power failure or machine crash.

My system get me back to work within 0.005" +/- 0.002 which is very acceptable for my requirements... and it was very affordable (proximity switches).

[javeria]

I believe that once limits and home are set in Mach, mach slows down the machine when approaching them, so we might assume that the limits approach the targets with a similar velocity every time.

aint that right!

[javeria]

Thanks G and paco, its relieved me of tension on the proximity switch front.!

:)

[javeria]

HI G' and All,

This is particularly a Q on Mach and the proximites, so kindly move this thread if this is not in the right place.

I put on the proximites like we did here on my other cnc - all 3 of em now report to Pin11 on the parallel port. I have the auto limit over ride activated.

Now if I move the X towards limits and then then the limits are activated and then reset - and the axis remains in the same position - and now Y is in movement then we have a situation where the other limits dont work.

My Q is -
1. will this be a problem?
2. Am I doing some thing wrong by activating the Limit Auto Overide.
3. Since I have not yet homed the machine, will it be a problem in homing the machine axes? as once Y has homed then the limits get activated and then X needs to be homed and still the limits are activated - i mean all the proxies report to the same pin right?

4. Do ya think I still need a lesson in Mach for proximities settings?

thats it folks

RGDS
IRfan

[J.R. Hatcher]

If I understand your situation right, the limit override is there so you can move the active axis off the limit switch then continue.

[javeria]

what about homing the axis initially, I will try it today though.

[ekdenton]

JR is right from what I understand in Mach 3 the overide button is to move away from a tripped limit switch or sensor.

there should be some info on the initial set up earlier in this thread if I remember correct, but you will have to go into Mach 3 and set your home coordinates, also assingn the pin # on your BOB that you have your sensors wired to and then go to homing in mach 3 and assign the axis's to home. I think I had to watch the the Mach 3 tutorial a few times on homing before I figured out what to do. Don't forget to assign the slave motor also so you don't grind your pinion gears when you try to home. If you have it set up correct you can hit the ref all home button in mach 3 (long vertical button by the axis coordinate buttons) and it should start traveling twards home. Mine all went the right direction the first time but I think it is possible that sometimes they will move the wrong direction and you will have to correct this. (I forgot already how to reverse direction but I know Gerald has a post somewhere on that if it happens, it is pretty simple to do).

[javeria]

yup even me after seeing the videos - the homing in Mach - is like it sees the limit switch and then comes back a step, but what I did not understand is the setting of soft limits - anyways learning and learning as usual

and yes it was number 4

"4. Do ya think I still need a lesson in Mach for proximities settings?"

:)

[William McGuire]

For those of you using proximity switches, I have a question...

Are the distances of the switches very specific? As I see it, there is a 3/4 inch hole in the rail, but isn't there a rack directly below that hole? If so, does a 2mm range or a 4mm range switch just sense metal less than 2mm or 4mm direcly below it and cannot sense anything farther... such as the rack at 6mm? Or have I missed something?

[Gerald D]

That's right, a 4mm range proxy is oblivious to metal 6mm away.

The range is stated for iron(steel) getting within the range. For alu, the range is much less.

[Richards]

During the last few days, I've been playing with proximity sensors again. Much to my chagrin, most of what I've been experimenting with has already been discussed here in the forum. What's worse, is that I wrote some of the posts. (Oh well, when you loose your memory, everything is new and interesting - over and over and over again.)

Anyway, I've designed a small micro-controller card that accepts up to five NPN type sensors (either Normally Open or Normally Closed - as long as all sensors on the machine are of the same type). Since the micro-controller uses a computer program, the controller could be made to do almost anything necessary involving NPN proximity sensors.

The prototype card and program senses each proximity sensor and outputs a common active signal when any of the sensors goes active. It also outputs a separate output signal for each sensor.

So far, I've tested it with 12mm sensors with a 4mm range and 18mm sensors with a 5mm range, both types are shielded 3-wire sensors. I've also tested some two-wire unshielded sensors that seem to work as well as the shielded sensors. The standard unshielded 12mm sensors have a 4mm range. (To get that range with a shielded sensor, you have to buy the more costly 2X style.) All of the sensors that I currently have are Normally Open, but Fiero Fluid Power promised me four 18mm Normally Closed sensors next week.

Since it's well below freezing in the shop, I'll have time to run a few tests - if anyone has questions about proximity sensors that haven't already been answered.

[sailfl]

Mike,

I have a lot of those (senior) moments also. It is a frustrating but what can you do. Wait until the mind finds what it was looking for.

[smreish]

Nils,
Maybe now would be a good time to mention if your using Aluminum rail with the Vee rails you should use longer distance (extended distance) sensing proximity switches.
If you have steel rails, you may use any sensing distance units you want!

Happy new year.
...back to changing diapers and drinking an adult beverage. (it's amazing how well a diaper works as a coaster):D

Cheers

[Gerald D]

Here is an un-shielded proximity sensor on the left and a shielded sensor on the right:

3165

The "shielding" in this case refers to whether the sensing tip is surrounded by a metal shield or not. The metal shield is for the reduction of mechanical damage - it is not for the reduction of electrical interference.

For the MechMate, we are perfectly happy with unshielded sensors, which gives double the sense range of a shielded sensor. A 12mm unshielded sensor should have about 4mm range for steel (iron) and about 1mm range if sensing aluminium.

[sailfl]

Sean makes a good point. I had to go to 8mm sensors to be able to get my proximity switches to work. I could not get the 4mm to work on the X and Y.

[Gerald D]

How close did you try and mount the 4mm sensors to the alu? Theoretically you should have been able to mount at less than 1mm without the sensor actually touching the rail anywhere along its length of travel.

[sailfl]

I had problems with them being too close. Having painted the aluminum might had an effect on them being able to sense. They were so close that in some places they would rub. I kept having to adjust them so I just decided it was easier to get the 8mm sensors. They seem to be working great.

[Richards]

The standard distance for iron/steel for most flush/shielded 18mm sensors is 5mm instead of the standard 2mm for 12mm shielded sensors. Unshielded/non-flush sensors have 2X the sensing distance. 18mm is 50% larger, so they would require a much larger target hole. (I use them to sense the hex-head of a 1/4-inch bolt instead of a hole, so they work fine for my application.)

By the way, Gerald's method of always sensing the rail until a target hole is detected is a much more secure method, especially when the gantry lifts off the rails, which does happen to me occasionally when I get careless. An 18mm sensor would probably require at least a 1-inch (25mm hole).

The Balluff catalog, shows various models of the GlobalProx (inexpensive) non-flush/unshield sensors in 12mm size with sensing distances of 4mm, 6mm and 8mm. That same catalog shows various models of the GlobalProx non-flush/unshielded sensors in 18mm size with sensing distances of 8mm, 12mm and 16mm.

From AutomationDirect.com, they have the 4mm AM1-AN-2H 3-wire sensor for $18.50 (NPN, Unshielded - 4mm distance, quick-disconnect), the AM1-AO-2H sensor, 2-wire for $18.50 (NPN or PNP, Unshielded - 4mm distance, quick-disconnect). The 8mm distance models are AM1-AN-4H (3-wire) and AM1-AO-4H (2-wire) for $25.00 each. Quick disconnect cables are available in lengths of 2-meters to 7-meters for $9.25 to $14.50 each.

The 18mm sensors are the same price with sensing distances of 8mm and 12mm. Substitute AK1 for AM1 for the 18mm models.

I ordered some 2-wire sensors by mistake and found that they are probably the ideal sensor for this application, especially when you want to have complete flexibility in wiring your machine. They can be wired either NPN or PNP. They only handle 50% of the load current of the 3-wire models, but I limit the load to 10mA anyway, which is only 10% of their rated capacity. Other than that, I can't seem to find any practical difference to keep me from using the 2-wire sensors.

I have used the standard sensors (with wiring permanently attached) and the quick disconnect models. I prefer the quick disconnect. With cable lengths of 5m or 7m, I could permanently wire the cables to the machine, with one end going to the sensor and the other end going to a wiring/junction box. From the junction box, I could wire a multi-conductor cable going to the opto-isolator board in the control box. By doing that, repairing or replacing a sensor would only require unbolting the sensor from the machine and unscrewing the cable from the sensor.

The six-pin optoisolator chips that I like to use (4N25, 4N27, TIL-111) work well with 10mA current from the sensors, so I use a 1,000 ohm 1/2-watt resistor with 12VDC and a 2,200 ohm resistor with 24VDC. Resistance isn't critical. +/- 25% seems to work fine. The 1/2-watt size would be best, especially using Gerald's method of always sensing the rail. With a 24VDC power supply, a 2.2K resistor would always pull about 1/4 watt when sensing the rail. A 1/2 watt resistor would not get overly hot and a 1-watt resistor would be even better. With a 12V power supply, a 1,000 ohm resistor would pull about 1/8 W, so a 1/2 W resistor would be ideal. Usually, the 1/2 watt resistors cost about one-cent each, if you buy them in 100 quantity packages. Radio Shack sells them in packages of 5 for $1.00.

You'll probably find that a few 330 ohm, 1,000 ohm, 2,200 ohm and 4,700 ohm resistors will handle the majority of jobs when interfacing external electrical components to computer controlled devices. The 330 ohm size is ideal for controlling current to L.E.D.s when you use a 5VDC power supply. The 2.2K and 4.7K resistors are used as pull-up devices to ensure that the computer senses 5VDC when a device is disconnected or Off. As already mentioned, the 1K size can be used to limit current to about 10mA through devices when you use a 12VDC power supply and the 2.2K size works well when you use 24VDC.

The transistors/LEDs inside the sensors normally drop about 1.5V, but normally you can disregard that voltage drop, especially if you use optoisolators. The difference in sensing time is a fraction of a millisecond. Since you will normally use a fixed speed in your zeroing routine, the delay in optoisolator turn-on time will be a constant, so you won't need to even consider it.

All of the sensors that I've tried can handle a load of at least 100mA, so you could directly drive the coil of a small DC relay. However, relays cause electrical noise when they open/close, so I don't use them unless I'm switching high current AC loads. Normally, I build an interface circuit to drive DC devices or Solid State Relays to drive lower current AC devices. Electrical noise is hard to trouble-shoot, so I avoid using devices that create electrical noise.

All of the sensors that I've tried are rated to work with voltages ranging from 10VDC to 30VDC. I have tried using them at 5V, just to verify that they would NOT work at 5V. Sure enough, they don't work at 5V. (Shopbot supplied a 12V proximity sensor with their pre-PRS models that would work at 5V, but the sensing distance was critical. The luxury of having at least a 1/8-inch (3mm) gap between the sensor and the target, instead of the 0.5mm (1/50-inch) is so much better.)

[kanankeban]

I just finished reading all the thread post by post. But it seems that theirs no concenced solution am I right:confused:? Seems their are a lot of ways of doing the proximity switches...
Could someone point me out to the easiest way (schematic) for someone with poor knowledge in electronics.

[Gerald D]

Yes, this thread has rambled on far too long - a simple issue has been made to look rather complicated. any volunteers for a re-write?

[xkadet]

Fantastic thread everyone-- but I can certainly see how a non-electronic might be somewhat confused still at this point. A lot to read, as well and that's why a summary by one of you gurus would be most welcome and appreciated by the unwashed heathen among us --without electronics skills to speak of. I add just a few suggestions which you can blatently ignore if you want. Any one wanting more detail can read and read and read....

One main point that deserves a separate line of it's own, again:
Prox sensors aren't replacements for mechanical switches!!
They're completely different and functionality is much greater. You will waste your time trying to make them act like 2/axis mech swiches. One-per-axis is all you need, minimally for a reasonable prox switch setup on a 3 axis machine.

Come on guys, let's put a cap on this one. It's too good to leave hanging! And thanks again to all of you for putting forward all the effort and info. We who have benefited salute you.

What I'd like to see, personally:
1. A simple schematic using relays (one part number that works with 24v coil and right current draw will suffice) to a typical BOB with hole sensing proxs (again, one p/n that works will suffice 12-24V N0/NPN). Use as few abbreviations as possible for the unschooled of us. If a resistor is needed somewhere, indicate how to determine what R value to use.
If anything/wiring has to be shielded, please indicate so. Any wire lenght/ga limits on the sensor p/n you list above?? Is telephone cable ok?
Please don't use pin numbers on the BOBs, there's lots to choose from out there and a clearer picture is helpful here.
Wire colors on the sensors is good; brn, blu, blk.


Important note: Advice to the unshooled reading this, pull up the spec sheet on anything you're using, sensor, relay, and read the spec sheet. There's a ton of helpful info right there in condensed form.


If you want to get into And/Nand gate switching and that sort of thing... read it in the thread, it's in here. Just give something to the non electronically inclined that's simple enough to implement with out a lot of room for error. Yeah, I'm asking for a prox switch implementation for idiots.

Using the mech switches is discussed in the thread and is easy. Most BOBs show how to implement mech switches so this shouldn't be a problem. Just, as recommended, use switches with gold contacts so you'll have good contact. Hopefully hysteresis won't confuse the issue for you. This was never addressed in the thread that I found.

Use good advice and stay away from opto sensors. Nuff said. Want to know why? read.

Everyone interested and still confused should read the post above by Richard (AKA Mike) and the one below by Gerald D.

(Please don't ask another question without reading these posts:)


GERALD Posted in March 2008 the following GREAT Explanation:::

There was a good question in here last night, which the poster shyly decided to delete again:

"I am trying to wrap my head around the layout and wiring of either proximity sensors or the switches. I take it that the main purpose of these is to allow mach to be programed to set the router in a home position in all three axis's.

Okay if that is the goal, I do not understand wiring three or four sensors in series NO would work. Reason being, how does mach know which sensor tripped when they are all in series? "

Your car is parked in your garage and the garage door is closed. You get in the car, start the engine and you are now going to drive. Your name is Mach3, you are blindfolded. You (Mach3) puts the car in reverse and drives. Mach3 hears a bang, (the garage door is hit). Mach3 puts the car in Drive, goes forward and hears another bang (the front wall is hit). Mach3 being a normally bright person has figured out that the bang after reverse is the door and the bang after Drive is the front wall. Mach3 only needs one bang sensor.

On the router table, you can wire everything in series, to make one big sensor, because Mach3 is smart enough to know what it was doing before it hits this sensor, and therefore figures out which part of the sensor it hit.

And then, to give some perspective, this bit:
"I take it that the main purpose of these is to allow Mach to be programed to set the router in a home position in all three axis's."

The reason we manage to mostly get by without any switches is because we "home" the machine to the corner of the material lying on the table. After changing a cutter, manually jog the cutter over the corner of the material and set x and y to zero from the keyboard. Then jog the cutter till it just touches the surface and set z to zero. Then start the cut.

A home switch on the z-axis can never tell you the distance between the cutter and the material. Home switches on the x & y can only tell you the distance to the material if the material is located to the same spot everytime.

But there are times (not many) when we wish we did have proximity switches . . .
- When there has been a glitch (power failure?) in the middle of a sheet of material and we need to find the reference points again.
- When the cutter hits a clamp and the car jumps off the rail.

[Gerald D]

Keith, your second para: . . . .

One main point that deserves a separate line of it's own, again:
Prox sensors aren't replacements for mechanical switches!!
They're completely different and functionality is much greater. You will waste your time trying to make them act like 2/axis mech swiches. One-per-axis is all you need, minimally for a reasonable prox switch setup on a 3 axis machine.

. . . . has me confused.

I am of the opinion that prox switches can be replacements for mechanical switches. We need one or the other, not both.

[Richards]

I think that we're getting goals mixed up. The way I see it, there are three different 'goals':

1. Emergency Stop

2. Mechanical limit

3. Homing

An Emergency Stop (E-Stop) switch needs to kill both the power to the control box and the step pulses that are controlled by the Break-Out-Board. Two functions means two poles. A mechanical 2-pole switch is called for, i.e. one pole would open the coil on a self-latching contactor and the other pole would break the pulse-stream going from the Break-Out-Board to the stepper drivers. Because we would want the circuit to be as safe as possible, Normally Closed switches should be used, that way, we'll know immediately if a switch fails. Normally Closed mechanical switches can be connected in series, so, as many E-Stop switches can be mounted on the machine as safety requires.

A mechanical limit switch is used to protect the machine from a run-away axis. It usually only cuts the pulse stream from the Break-Out_Board. One function means that it is a one-pole switch. Again, to be safe, Normally Closed switches should be used. As long as Normally Closed switches are used, all of the switches can be connected in series. We really don't care which axis is in trouble, or even which end of the axis is in trouble. All we want to do is to stop ALL motion before something mechanical slams into something else.

Homing switches are used to detect when an axis is at a specific spot (relative to the "home" position of an axis). Repeatability is essential. Mechanical switches are NOT necessarily repeatable. Mechanical switches "bounce" (open and close a number of times each time they actuate); therefore, the time delay before a switch is activated is indeterminate. Proximity sensors work very well as homing switches. Because of the repeatability requirement, each sensor should be on its own circuit (series connections should NOT be used). Also, because of the repeatability requirement, mechanical relays should not be part of the circuit. Mechanical relays act like mechanical switches in that their contacts bounce just like the contacts of a mechanical switch. This is an excellent place to use an inexpensive micro-controller. In the 50 milliseconds that it takes for a mechanical switch to settle, even a relatively slow microcontroller can run 50,000 instructions. Homing routines are normally software controlled. Determining 'which' homing switch/sensor is active is a function of the software (program). In other words, the software might command the 'Y' axis to move in the (+) direction, then when a homing switch/sensor goes active, the program knows that the 'Y' axis has reached its (+) home switch/sensor position.

In the real world, both mechanical and solid state switches are used for homing an axis. If you use good quality switches and slow speeds, mechanical switches can do an excellent job. Personally, I prefer solid state proximity sensors simply because I've spent way too much time over the years writing de-bounce routines in software to compensate for mechanical bounce. In every case, a solid state proximity switch was more repeatable than a mechanical switch.

On my machine, I have one E-Stop switch that kills power to all coils on all contactors in the control box. I use the E-Stop switch when something bad is going to happen to me or to the machine. I know that when I press the E-Stop switch that the machine will lose its position and I also know that the part that I'm cutting might be ruined before the machine stops. The E-Stop switch is there for safety. I also have two proximity sensors that act as homing sensors as well as limit switches. When used as homing sensors, the software routine knows exactly how far from 0,0 the targets are when a sensor is detected. The limit switch function stops the machine via built-in software if either the X-axis or the Y-axis goes too far. The limit switch function acts much like the E-Stop function in that position is lost and the part may be ruined AND the power to the contactor coils stays ON.

One other point needs to be made: There has to be some type of switch/sensor over-ride or bypass. On my machine, software allows me to slowly jog an axis away from a proximity sensor. Without that software routine, I would need a mechanical on/off switch to bypass the limit switch/sensor.

[Gerald D]

Mike, Mach3 has a software routine for overiding a limit switch.

[xkadet]

you don't replace limit switches post design/install with a prox switch. Design for prox or mechanical, but they aren't strictly interchangeable, different method of application and operation.

Sorry to start up more confusion here.

[Richards]

Gerald,
I'm going to learn more about Mach 3. I promise :). It has so many possibilities that will reward those who spend a little time studying.

Keith,
The problem with all electronics is that using simple, off-the-shelf parts is not always the best way to solve a problem - like limit switches. Relays have been used for decades in controllers of all types, but today's process control computers just don't like the electrical noise that a relay contact can produce, particularly when the goal is to accurately and consistently set the "home" position. Some users are starting to have issues with electrical noise. If they're like me, that's when it's time to read and re-read every post that talks about grounding. But, eliminating a cause of electrical noise is just as important as funneling that noise away.

My basic advice to anyone building a Mechmate would be to include a proper E-Stop switch but adding limit and/or home switches/sensors can be delayed. Granted, using a proximity sensor to find home is quick and painless, but it doesn't take hardly any time at all to manually pull the gantry against its stops and then jog to the 0,0 position. I ran my machine for about a year without attaching the proximity sensors. I hit the stops a few times, but no damage was done (except to my ego). The sensors make my life a little easier, but, if they stopped working, I wouldn't shut the machine down while I waited for replacement parts.

[sailfl]

Mike

After reading about some of the issues that ShopBot users experience with the controller software and that they can't do some simple things that Mach3 allows, I am grateful that Mach3 is what I have to use.

[xkadet]

Ok, I get it. Now we're left with just use steppers and forget the limit sensing unless you're willing to do the head-work to figure the further refinement of limit sensing. Seems like most of all that you need to do proxs is in this thread already, but no debounce discussion of length that I've seen. However, there's a great debounce "treatise" here for those still not so fatigued to continue this thread... :D
:http://www.ganssle.com/debouncing.pdf
you need a 7414 shmitt triggered hex inverter, couple resistors, a diode, a cap. The small circuit is spelled out along with values for the parts. Thanks to Jack for putting this together.

[Gerald D]

Keith, a couple of guys here use proximity switches driving quality relays to limit and home their machines with trouble-free success.........what value are you trying to add to that?

[Richards]

Keith,
Thanks for the information. Figure 1 on page 11 is a classic circuit that I've often used. It uses a simple 7400 NAND chip (which is the chip upon which most TTL logic is based). The 7400 requires a N/O and a N/C contact on the switch or the relay, but it is a simple circuit.

However, my feeling is that if I have to add a circuit, I'll just use a proximity sensor with an opto-isolator to handle the two different voltages. By doing that, no debouncing is required. Twelve to twenty-four volts is supplied to the proximity sensor and five volts is fed to the computer via the opto-isolator.

[javeria]

Twelve to twenty-four volts is supplied to the proximity sensor and five volts is fed to the computer via the opto-isolator.

That's how it is set up on both of my machines and works flawlessly.

[xkadet]

Thanks for the positive input and all the suggestions. Completely altered my sensing strategy based on the inputs and reading this thread. I'm really just casting about trying to figure out what's a reliable approach that won't make things miserable down the road or take forever to implement.

I think most everything anyone would need to implement a good limit sensing strategy is here, now. I've attached a fairly lousy pict of my router as of a week ago. Now all I've got to do is put in the work table and wire the electrical, and then the fun starts. Going from 6 sensors to 3 will be a treat.

regards,

[isladelobos]

HI all.

Reading about This Pdf (http://www.mechmate.com/forums/attachment.php?attachmentid=987&d=1203305487), I think not is possible only one Relay (http://www.factorymation.com/s.nl/it.A/id.5416/.f?category=11127)?

[martin77pl]

I am reading this thread as well. I received my proxies yesterday. Them interface relays shown in post 50 by Gerald are made in Poland. Do I need four of them as there are four proxies?

[Gerald D]

Yes, you need a relay for each proximity switch - 4 relays in total

[gixi]

I found some time ago this item on eBay and I'm wondering if is good for our project. On eBay the item number is :330322787424. And the seller is carolbrent. He also sell limit switches. All at good price. But again: this is good for MM project ?
He sell a kit : CNC stepper motor Limit BOARD COMBO WITH 6 SWITCHES kit.
It looks OK from my point of view, and most important is easy to get conected al switches.

[Gerald D]

That board (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=330322787424&ru=http%3A%2F%2Fshop.ebay.com%3A80%2F%3F_from%3DR4 0%26_trksid%3Dp3907.m38.l1313%26_nkw%3D33032278742 4%26_sacat%3DSee-All-Categories%26_fvi%3D1&_rdc=1) is for mechanical limit switches, not for proximity switches. Mechanical limit switches have mounting and wood dust problems.

[cncb]

I apologize if this has been answered, I read this thread in its entirety! Is the reasoning for 4 proxy switches so that there is a second proxy switch on the gantry for reasons of autosquaring? Thanks.

[smreish]

Brian,
4 proxies total.
2 on the gantry
1 on the y car
1 on the z

2 on the gantry (can be used for autosquaring) but more importantly for bilateral detection of a derail.

[cncb]

Makes total sense. Thanks Sean.

[paul60]

I was thinking of using reed switches as limit switches just found a post that says, not a good idea.
will go with micros switches what type micro switches are best and where can i locate them .
will be importing them from the usa.
thanks
woodguy

[cncb]

Microswitches, the roller kind? I have those on my machine now and have used them in the past and I do not like them. They are for the most part cheap and outdated technology and as I have read here there has been great success with the inductive proximity sensors listed in this very thread. You will pay more up front but they are better for our application.

[Claudiu]

Please advise me on this one:

1.st : I understood that E-Stops have to be set up with two contactors each, first one interupting general electricity and the other one giving a contact to the BOB (PMDX 122) activating the charge pump. Please just confirm if I can leave it like this.

2.nd : If Proximity sensors are all setup in series thru relais giving signal to one input Pin 15. According to Sean´s Layout.
How is then the homing functioning? Should not each sensor and relay have it´s own input signal?
Or giving the two sensors on the gantry each one input, and one common input for the Y Car and the Z? So I could use 3 inputs for proxies and one remains left for the Probe?

I saw that the new PMDX 125 has alot more inputs to choose from, but as I use 122 it seems that lining up in series all proxies u never know which one gave the signal and homing is not functional!?

Thanks for advise.
Claus

[KenC]

Hi Claus,
I'm also looking for a solution to your Q1.;)

Q2. In a ideal world + common logic, every switch should have their own input port but each D-25 pin parallel port can only have 8 bi-directional (in/out), 5 in, 4 out. Then you don't have any more port for your touchoff probe or other input of your choice. You can have more if you daisy wheel a second BOB & use a second Parallel port, then you can do whatever your heart desire. Its a compromise.
As long as you "tell" Mech3 & EMC2 you are sharing ports, & follow a predetermined protocol, the software are clever enough to tell which switch activated the input port. Its the electronics + software thingy, they defy common sense & they do work. But now the bigger question is how many switch, which type & what position to choose that is bothering me...
Again, you may worry the software will screw up, but hey, what else won't?
I hope this is helpful & not misleading;)

[bradm]

Claus (and Ken):

Many (most?) contactors have one or more "auxiliary contacts" - and are often expandable with more. So you can potentially use an auxilliary contact on the contactor that interrupts the main power to inform the BOB of the status of the contactor.

On your second question, the software only moves one motor at a time during the critical parts of the homing process, so it knows which limit is being hit. Note that in the early phases of the homing process, it can move all of the motors at once, until the first limit is hit. Then it has to back off to figure out which limit triggered.

[Gerald D]

I think we are getting confused with word choices:

A "contactor" is similar to a relay. It contains pairs of "contacts" for opening and closing circuits.

The E-stop pushbutton switch also has one or two pairs of "contacts".

Claus, in your Q1, I believe that you meant two "pairs of contacts" instead of two "contactors"?

[Claudiu]

Gerald, you are right. Sorry for my english. I meant two pairs of contacts. On the E-Stop switch I use can be mount 3 pairs in a first row.
One pair of contacts will interrupt general electricity in the control box and the other pair of contacts give signal (contact) to BOB. Right?

For the sec. question to give you some background about my
Constellation: PMDX 122, Mach 3, 4 pcs ProxSensor NPN (http://www.ifm.com/ifmus/web/dsfs!IF5251.html)and 4pcs. Relay like the one in the pic.
7707

The reason I am badly confused about homing is because I`v never seen it work in reality, I don`t know the sequences and how it is done by the software. I`m totally lost.

Ken said I have 5 inputs and 4 outputs, should I use them like this?
Variant A
1. Input Gantry far
2. Input Gantry near
3. Input Y and Z chained
4. Input Probe
5. Input ?

Variant B (Brad, does it mean homing is done by software Mach3 and recognizes by itself?)
1 Input this classic scheme (http://www.mechmate.com/forums/attachment.php?attachmentid=987&d=1203305487)
2 Input Probe.

Which of the Variants is mostly used make homing procedure available?

Shame on me....:o:o:o:o
Thanks

[Gerald D]

On the E-Stop switch . . . . . One pair of contacts will interrupt general electricity in the control box and the other pair of contacts give signal (contact) to BOB. Right?

Right.

[bradm]

Claus, look here: http://www.mechmate.com/forums/showthread.php?t=605 for some discussion of how homing works when the switches are wired as per the scheme (schematic) you noted above.

[Johannescnc]

Hey Sean. can you tell me why they are wired in sires and not to separate inputs? :confused: I can't see how this would work for homing...

[smreish]

John,
Let's see if I can explain.
Mach is funny, that it actually has a built-in homing macro for finding home. It is designed to step through it's seek-n-find sequence going x, then x1, then y, then y 2, then z. Depending on the number of motors you have and such, it will configure the routine to home accordingly. If you have and x1 and x2 motor, then the auto squaring feature will be active. If you choose to use this feature, be prepared to make the eccentric holes in the rail adjustable to fine tune the "perfect square" of the machine.

.... back to explaining.

Since Mach already does this homing routine, you can wire the contacts in series to one input on the BOB. The downfall to this "series relay logic" is for some reason any of the axis' that is active is triggered by a limit/prox switch not on that axis, the machine will be improperly homed and usually ends up derailing the machine.

The only time this happened is when I physically triggered a prox sensor on an "alternate" axis during the routine to see what would happen. Good thing my estops work!

The mach3/artsoft manual explains the routine in detail.

Does this answer your request? Sorry for the delay - I have been out on vacation for a while.

refer to my post WAY back in time for the wiring part (http://www.mechmate.com/forums/showthread.php?p=9510&postcount=247)of this reply.

Sean

Further autosquaring discussion moved here (http://www.mechmate.com/forums/showthread.php?p=34771&postcount=26)

[Johannescnc]

Thanks for your reply Sean. hope the the vacation time was good...
The delay did give me time to reflect. I have a machine running Mach in Jacksonville with micro switches. So I am familiar with the workings of Mach 3.
I guess the question comes from the PDF diagram showing all switches open. So if my thoughts are correct then during normal state (proxies not over a hole) would keep all circuits closed. And when the homing routine is active each axis will in turn move over the home hole and back off re-closing each relay in turn.
I am sure this has been covered before, and don't want to add any confusion but rather contribute clarity.

[smreish]

John
Clarity understood. Yes, the proximities are always in a "hold the switch" closed when active and any incident that causes release will fault the machine. Similar in logic to an estop switch circuit where every switch in the circuit is required to work and be active for the entire system to work. Helpful when you attempt to derail the machine.

Hope this helps.

Sean

[sprayhead]

I had a crazy idea and would like to throw it out there.

Imagine if we could electrically isolate each V-Wheel from the gantry.
Imagine if we put a wire on the wheel (on it's holding screw) and also a wire on the rail that the wheel rolls on.

Wheel on rail = closed circuit
wheel off rail = open circuit

Would it be ok to wire this circuit to a break out board?

I know that probably most guys don't think that's needed at all, as the MM is safe, gantry won't come off the rail, but still, would it be an electrically feasible alternative for a protective system against derailments? of course, considering that we could somehow isolate the wheels from the gantry itself.


regards,
francis :confused:

[sailfl]

Francis,

The question becomes is the work involved necessary for the number of times that the machine derails. I have never had my machine derail. The proximity switches will stop the power if you derail. But the other question I have is, what will you be able to do even if you have a system in place? You system will only sense that you have derailed. It isn't going to stop the derailing. I think you have to be going pretty fast to derail.

[Gerald D]

Francis, such a system will cause huge frustration........one speck of dust between the rail and roller and the system stops cutting.....

[smreish]

Nils,
My derails usually happen when a shop rag was left on the end of the machine and rollers ran over it! Thus causing just enough of a distance gap between rail and sensor to fault the machine. The main reason for adding cow pushers to the gantry for the x rails.

Francis, Good idea in theory...most likely will drive you bonkers in clinical practice.

Good day.
Sean

[sprayhead]

Thanks all for the responses

Indeed using the actual wheel as the contact point will probably drive the operator off his chops.

Perhaps using a brass brush as a rail scrapers and using that as the contact. I think I've seen cheap small brass brushes for sale on autoshops, it might be an idea.

But, the proximity sensors are great aren't they. Another question, how far from the steel do they start reporting an open circuit?

francis

[smreish]

Francis.
The sensing distance varies on the quality and type of unit. Mine sense 0-3mm. Thus, I set them to "just be active" closer to the 3mm distance away. 3.5-3.75 mm activates the derail fault.

[sprayhead]

Sean,

That's great news! thank you. 3mm is such a small gap, these things are very sensitive.

I'm starting to like very much these proximity sensors :D

Just one more question...
(an affirmation first)... When the sensor rolls over the hole it opens the continuity of the circuit and mach3 reads that active low signal and stops the gantry, abruptly.

(question) To carry on with the cutting, do you just Jog out of the hole?
But if the sensor goes past the hole, with the inertia of the gantry when stopping, mach doesn't just carry on right? I take that it faults for good.

thanks,
francis

[sailfl]

Francis,

If you have the limit switches set up correctly with Mach, the software will warn you that you are going to have a limit problem when you start your cut. So you should not be running past the hole with the limit switch active and hitting the stops.

[Johannescnc]

Thanks all for the responses

Indeed using the actual wheel as the contact point will probably drive the operator off his chops.


But, the proximity sensors are great aren't they. Another question, how far from the steel do they start reporting an open circuit?

francis

A old adage comes to mind "why fix what isn't broke?" or something like that..:o

and It seems that you can adjust the distance of the sensors ... from my understanding (no hands on experience) is that they are sensitive enough to trip in case of an obstacle on the track... :eek: or some other unforeseen reason.
And BTW, thanks Sean for your answer to my question which I have had since first reading the Mach 3 manual... :rolleyes:

[sprayhead]

Guys, I did see that someone wrote about reed switches, and that they weren't the best option for the MM.

What was the reason again? :confused:

I suppose that for homing and limiting purposes they would be good, wouldn't they? I have seen them in Normally Closed electrical configuration from General Electric company.

It's just that they seem a lot easier and simpler than proximity switches, for wiring.

I have read the whole thread a few times and I am still not sure what's up with the proximity switches... what signal comes out of them and why and how to connect each proxy to a relay.

Francis

[KenC]

Francis, I'm in the learning process too, I treat the proximity switch as a switch & they need a DC voltage to work. The proximity switch don't "send" signal but the BOB input port "detect" a ON (1) or OFF (0) condition of the circuit.

Hope this helps.

[Tokamak]

This is the way I keep track of how the proximity sensor works. The diagram that comes with the sensor is confusing. Hope this helps. This is the NPN NO Style.

Interlocks of this type should always be wired FAIL SAFE. This means that if a cable is disconnected the machine will sense an error. Normally Open (N.O.) contacts usually give this fail safe condition.

[KenC]

Thanks for sharing, its really helpful.

[PEU]

this ebay seller (http://stores.ebay.com/auspiciouse)sells proximity switches and solid state relays, anyone purchased from him already?

[KenC]

I am also looking into his prox switch too, specs look ok...

[Johannescnc]

skeptical... seem too cheap to me... or all the others over priced? :confused:
but... for the price, it may be worth the risk. but IMO, will it be worth it when they fail?
VALUE?

[KenC]

Definitely affordable, one can afford to have more spares & still better off. I had given ups asking why the Chinese can supply at such price... & accept the reliability set back...
My concern is the range, is 4mm sufficient?

[Gerald D]

4mm is a perfect range. Does that site tell you the diameter and the voltage range? (I couldn't see it at first look)

[Johannescnc]

well my point Ken, was, do we want to spend our time using our machine or working on it...

[KenC]

Gerald, Voltage range 6~36V, 12mm Dia.
They also have some with 2mm range, same V & Dia.

John, from my experience, electronics part will either fail in the first 5min or last the perceived life span lets (just say say 2 years...). Off the shelve price of reputable proxi sensors goes at around US$80~100, at least US$250 saving.... about a days salary of a CEO in a mid size company here.... Changing a sensor won't take more the 2 hours... Under such scenario, I won't mind work on the machine....

[domino11]

He also has a 15mm detection range with a 30MM dia, a 5mm Detection range with 18mm Dia and a 8mm Detection Range with18mm dia. What sesor would be more suited to users who are using the aluminum angle?

[smreish]

Heath,
As Nils and I found out, the Aluminum angle being a non-ferrous material requires a "little" longer sensing distance to work really well. If memory is right, we had the 3-5 mm sense and didn't work as well as the 7-15mm sense.

[domino11]

So the 8mm or 15mm would be a better choice for the aluminum rails. The 8mm seems a little better at 18mm dia versus the 15mm at 30mm dia to work with.

[KenC]

At the price that they are offering, we can experiment with it. ;)
Just place an order for 5 pcs of the 4mm dist dia.12mm sensor, 1 for spare...

[swatkins]

Please let us know how long it take to recieve them Ken :) Did you order any relays?