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  #31  
Old Wed 07 March 2007, 21:36
Mike Richards
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Gerald, your approach with the E-stops is elegant. It would solve the problem as long as the sensor/switch/input latched itself like an E-stop does.

A properly designed limit switch should act that way. The ramp or cam or obstruction should continue to hold the N/C switch open until the condition has been corrected. My concern is that too many people don't realize that a switch that 'blips' OFF/ON/OFF or ON/OFF/ON momentarily, won't work without additional circuitry. That's the theory behind a latched relay or contactor. Anything that causes the coil to drop the contacts, will, by definition, keep the contacts from closing again until someone or something pushes a switch to re-latch the relay or contactor. It's relatively easy to design a micro-controller or logic circuit to act as a latch, but, I get the feeling that most CNC operators would rather not get involved with adding their own computer or logic circuitry to their controllers.

Running the power supply connections to the PMDX board through the contactor might be the best way to stop the steppers from stepping without damaging the circuitry. My philosophy about how a circuit should work often gets in the way of making the circuit practical.

My philosophy about emergency switches and limit switches is to cut the power from that particular circuit quickly and completely and to use fail-safe devices that prevent power from being restored until the operator manually turns the power back on. Probably overkill on my part. That philosophy dates back to my early years as a process control designer when I read horror stories about people being maimed or killed when someone defeated safety circuits. One particularly gruesome story told about a man who cut off an arm because someone had defeated one of the two switches that had to be pressed at-the-same-time for the cutter's blade to operate. Somehow, he had one hand and arm inside the machine pushing the material into position when he either pressed the other Operate button or somehow bumped the Operate button. Another man had both hands totally crushed in a 200-ton press when he personally rewired the machines two Operate buttons - that needed to be pressed at the same time - to a foot switch. He stepped on the foot switch when both hands were positioning some sheet metal. The owner of that shop was one of my best friends. Needless to say, he was overcome with grief when he realized that his employee had destroyed his own hands. He blamed himself for not personally checking the equipment for unauthorized modifications. His employee's reason for modifying the machine was very simple. He said, "I wanted to be a little bit more productive."

Every time I change a cutter in my Colombo spindle, the thought goes through my mind that the only thing that keeps that spindle from turning on is a 1.5 volt logic signal on a circuit surrounded by a very noisy 240V line and the latching contactor that is OFF and un-latched (thank goodness for that contactor). Some people don't realize that most TTL and computer circuits consider a voltage of 0 to 0.70 volts to be OFF and a voltage of 2.2 to 5 volts to be ON, so the difference between OFF and ON can be as little as 1.5 volts. That's really scary when you can watch on an oscilloscope voltage spikes on many of the TTL circuits that are many times that voltage.

Sometimes I think that designing safe, reliable, simple circuits that work in an industrial environment is impossible.
  #32  
Old Wed 07 March 2007, 23:27
Gerald_D
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Regarding mechanical latching of the cams/limits/e-stops, that is actually not essential. Once those NC switches have broken, they unlatch the main contactor (and Mach3). Re-making those switches will not close the contactor again, nor will Mach3 start without a reset at the keyboard.

The more I think about changing the cutters, the more I believe we have been amiss in not providing a disconnect switch right at the spindle/router. Whether our VFD is going to like it or not is a secondary issue.
  #33  
Old Thu 08 March 2007, 18:28
Mike Richards
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Gerald,
You and Mariss agree that cutting the power to the PMDX is the BEST way to stop a stepper. When I telephoned Gecko support a few minutes ago, Mariss answered the telephone, ran the math, and said that my idea of cutting the power between the power supply and the G202s would create an instantaneous current surge in excess of 400A per drive. In other words - disaster. On the other hand, cutting the power to the PMDX would cause no damage.

So, here's an updated schematic that shows the more proper way to stop the steppers when a Limit Switch is opened. This schematic will not allow the coil of the Contactor to be turned on unless ALL of the limit switches are closed OR the Limit Override Switch is turned on (which would also turn on the Warning Lamp as a visual indicator that the Limit Switches were no longer functional).



(NOTE: Gerald, if possible, please delete the posting of the other schematic or at least note that the schematic has been replaced with this schematic, so that there will be less confusion to those reading this thread.)
  #34  
Old Thu 08 March 2007, 23:48
Gerald_D
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Mike, your focus is "Limit Switches" while my focus is "E-Stops" - we are actually coming from two very different places. I personally don't regard limit switches as a personnel safety device (the mechanical stops prevent the gantry from landing on your toes) and my machines don't even have such switches.

The reason that I am mentioning this now, and possibly diverting this thread, is because Mach3 (together with PMDX) treat these switches differently to E-stops. These switches will stop motion "instantly", while Mach3 does not lose the calibration, and gives a facility to safely jog off the limit and carry on.

There is another facility in Mach3 to treat the same switches as "homing" switches for calibration - when in this mode, the operator does not have to do a "reset" when the switch is hit.

In short:
- while in normal cutting mode, the switches stop motion, the operator has to manually reset at the keyboard and jog away from the limit. The machine has not lost its calibration.
- while in homing/calibration mode, the switches act like our familiar z-zero plate, the machine does its little dance against the switch, backs off and waits. The machine is freshly calibrated.

The concept of limit/homing switches is well ingrained into the Mach3 software, literature, and videos. With respect, I think you are confusing the readers by coupling these as part of a power safety circuit.
  #35  
Old Fri 09 March 2007, 00:20
Mike Richards
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Gerald,
I agree that Mach 3 has provisions that make limit switches unnecessary. And, because my only experience with Mach 3 is on my test bench where I've never had a 'communications error' or a 'hiccup', maybe I'm just expecting unexplained errors to happen (like I've had with my Alpha). On more than one occasion, the Alpha has 'hiccuped', lost position, and then slammed into the stops before I could waddle over and hit the E-stop. Admittedly, these 'hiccups' are few and far between, but they have happened too often during the last (almost) three years. That is why I keep coming up with this particular type of circuit.

I also agree that when a limit switch is opened in the circuits that I've designed, that position will be lost and that the machine will have to go through a homing routine. For that, I prefer to use proximity switches that are totally separate from the limit switches. In my mind, the limit switch is the last resort to keep an axis from slamming into its stop, while a proximity switch could be placed at some convenient position to act as a homing switch. As long as the distance between the proximity switch and the true home position is know, offsets will take care of the rest.

Even though I prefer 'safety switches' for peace of mind, there's a Shopbot just across the street at the local High School where the students just plop down a piece of material, jog the axes to a corner of the material, give a Z2 command and start their cut. It's simple and effective and it doesn't require expensive and fragile circuits. The main difference between the High School shop and my shop is that at the High School, they don't allow the Shopbot to run unless a student is holding the E-stop in his hand to keep the unexpected from causing damage. In my shop, I nurse the machine the first few times a new design is run, but after those initial test runs, I do other work while the Shopbot does its work - and that's when the 'hiccups' happen.
  #36  
Old Fri 09 March 2007, 00:57
Gerald_D
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Don't get me wrong, I am not recommending that guys work without limit switches. The only thing that stops me from adding switches to my machines and to the drawings, is to find a commonly available, reliable, dust-proof system. (The drawings make provisons for 12mm proximity switches - but they can't be simply strung together in series) - this is a whole other thread by itself.

(The homing switch is a red herring here in this discussion because Mach allows the homing switch to be either the self-same switch as the limit switch, or the homing switch can be separate on its own input (movable or z-zero plate))
  #37  
Old Mon 12 March 2007, 23:51
Gerald_D
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When a USA-man-in-the-street buys a 220V appliance, takes it home, opens the box, finds that the power cord has 4 conductors (green, white, black, red) (maybe only 3, green/black/red?) without a plug at the end....what does he typically do? Is there a standard plug he can get from the hardware store? Are 220V plug outlets commonly fitted in the garage/basement/kitchen?

In case these sounds like stupid questions, over here all appliances for the man-in-the-street (except a stove) are 3 wire, plugs (from any store) are a DIY fit, and outlets are standard throughout a house or building. (Stoves are sold without a cord, and with a note: "to be installed by electrician....."

The main reason I ask about this is because I am dispatching a 220V motor to Atlanta tomorrow and I need to "plug it in" when I get there....
  #38  
Old Tue 13 March 2007, 08:32
Mike Richards
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The only 'standard' 220V-240V plugs that I've seen pre-installed are the receptacles for plugs that are found on electric clothes dryers and electric cooking ranges.

There are many other configurations that are available. Most Home Depot sized stores carry a variety of plugs and receptacles. Here's a link to a Hubbell reference chart. Many of the stores carry the Hubbell brand.
  #39  
Old Tue 13 March 2007, 11:39
Gerald_D
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The variety of pin configurations on that Hubbell chart had me gasping for air! And your Home Depot lets the DIY bloke loose among all these choices?....I am beginning to understand why fire-trucks feature in so many of your movies!

When ShopBot sells you a PRTAlpha for router duty, they imply that you have a DIY installation because they only insist on a licensed electrician for spindles. Does the average handyman really know how to handle those 4 wires?
  #40  
Old Tue 13 March 2007, 12:29
Mike Richards
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The chart makes everything look complicated, but it really isn't too bad. If we stay with two voltages 120V and 240V (although the chart says 125V and 250V), you'll note that the plugs/receptacles are sorted by their current rating and whether they are a standard plug/receptacle or a twistlock receptacle.

So, a 240V/20A receptacle can receive either a 15A plug or a 20A plug (which is how I've wired my planner, my dust collector and my air compressor).

A few minutes at the hardware store looking at the various plugs and receptacles takes most of the mystery out of everything.
  #41  
Old Tue 13 March 2007, 13:50
Gerald_D
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Okay, I have ordered a Hubbell HBL5666C plug for the 230V 11.5Amp Single Phase motor going to Atlanta. Let's hope the organisers can provide a suitable receptacle - I'll check with them tomorrow. Price of that plug out here: $25 - high because of rarity....
  #42  
Old Wed 14 March 2007, 17:11
David Rosenbleeth
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Gerald: Just ask the guys where you are planning to plug it in what amp receptacle, how many leads, and whether their receptacle is twist lock or not and then you can be sure to have the right one. Odds are a Home Depot is close to them (They are everywhere around Atlanta) and you could even make sure you have the right one by checking it out once you are there. The right amp plug will, of course, be determined by the circuit, not the motor. Most light industrial outlets here are 20 amp unless there is a dedicated reason to go higher. Of course the key word is "most".

By the way: I'm about a 10 Hour drive from Atlanta-Comne on down while you're here.
  #43  
Old Wed 14 March 2007, 23:54
Gerald_D
Just call me:
 
10 hour drive - sure!

The plug I ordered here is the only "American" 230V plug that I could find stocked in South Africa. But at least I have a reference point to tell the exhibition organisers what I am bringing. They must have catered for stuff from Europe before, so I am not too worried about it.
  #44  
Old Wed 25 April 2007, 17:53
Hugo Carradini
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Hello Gerald and forum friends.
I moved to a new shop and that was a lot of work that keep me very busy for the last couple month.
Now I am ready to keep working on my project.
I got all my electronics except the cables (I will use normal cables for my "kitchen project" and the G203 "vampire drives that I hope arrive this week.
I all ready got the PK296A1ASG7.2 motors, Piltron transformer 300 VA 2x25 VAC 6amp, PMDX-135 Module, PMDX-122 card, ENSTO Rotary Load Break Disconnect Switch, 3 Pole, 600V, 40, and TECO IEC Contactor - 16A, 120VAC / 60Hz Coil, 3 Pole 600V, 1 N.O. Aux and the micelaneas in the list.
The question I have right now is how to install the contactor. I think many people is going to use the TECO IEC Contactor because is in the list you suggested and would be nice to know how to install it to the basic package. As soon I get my office strait out I will post the assemble process of the electronics so it can be cheeked out.
Thanks for your help.
Hugo Carradini
PD. My Web site is working now www.vitrales.com.ve
  #45  
Old Thu 26 April 2007, 05:19
Gerald_D
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Welcome back! From the spec sheet:


What is the supply voltage in your country? Single phase? Split phase? Three phase?

Normally 1, 3, 5 is used for incoming mains. 2,4,6 go out. Terminals A1 and A2 are lower down (normally under 13 and 14).
  #46  
Old Thu 26 April 2007, 10:13
Hugo Carradini
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Hello Gereald.
We work with 110 and 220 volts
110 uses a hot line and a neutral line and the 220 uses 2 hot lines and a neutral line.
I am planing in base of 110 volts system .
  #47  
Old Thu 26 April 2007, 10:32
Gerald_D
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So Hugo, you can follow the drawing right at the top of this thread. Here are your contactor connections:

  #48  
Old Thu 26 April 2007, 14:10
Mike Richards
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Gerald,
After looking at your schematic, I think that pushing the N/O pushbutton is going to be an exercise in futility. If Contactor connector 3 is the connection for the incoming Neutral (as stated above), shouldn't the N/C pushbutton be connected between Contactor connector 3 and the Coil connection A1? That way, when the N/O pushbutton is closed, the coil will receive power from L1 and the coil will also have a complete circuit through the N/C switch to neutal. Also, when the N/O pushbutton is closed, switch terminals 13 and 14 will close and the Contactor will be self-latching. The Contactor will remain turned on until the N/C pushbutton is opened or until the disconnect/breaker feeding power to L1 is opened.
  #49  
Old Thu 26 April 2007, 14:36
Gerald_D
Just call me:
 
Mike, after re-visiting the circuit, yes, you are right, pushing the NO will not do anything because the Neutral is broken.

But, I'll have to think harder about your suggested solution, because the neutral won't be isolated anymore - it will continue deeper into the circuit via the coil. I have a funny feeling that we are using a double-pole NO pushbutton to start the circuit? (Right now I am packing for 5 days away, 4 days back and then 10 days away again - need to chew on this one carefully....)

PS. I have purchased vBulletin software and will be converting this board so that the start of threads don't go so deep into the archives.
  #50  
Old Thu 26 April 2007, 14:37
Gerald_D
Just call me:
 
As the first post shows (the faulty diagram):
  #51  
Old Thu 26 April 2007, 15:46
Mike Richards
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Gerald,
You're right. A 2-pole, 1-throw N/O Pushbutton could be used to activate the relay. Once the Contactor's coil was activated, the coil would be held in the active state by switch contacts 13 and 14.

Good luck on your trip(s).
  #52  
Old Thu 26 April 2007, 18:08
Hugo Carradini
Just call me:
 
Thanks Gerald.
I will be posting photos soon.
  #53  
Old Thu 26 April 2007, 23:06
Gerald_D
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Thanks Mike. Off to Oudtshoorn in an hour's time for a little break before the Atlanta visit.
  #54  
Old Tue 01 May 2007, 13:05
Gerald_D
Just call me:
 
The long drive cleared the head. The Neutral going "permanently" to the coil of the contactor is no problem - there is a big multipole "disconnect" just to the left of the contactor. Follow Mike's "shouldn't the N/C pushbutton be connected between Contactor connector 3 and the Coil connection A1? That way, when the N/O pushbutton is closed, the coil will receive power from L1 and the coil will also have a complete circuit through the N/C switch to neutal. Also, when the N/O pushbutton is closed, switch terminals 13 and 14 will close and the Contactor will be self-latching. The Contactor will remain turned on until the N/C pushbutton is opened or until the disconnect/breaker feeding power to L1 is opened." until I can fix that drawing. Sorry for the slip.
  #55  
Old Wed 02 May 2007, 05:29
Gerald_D
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Mike, is this better?:

  #56  
Old Wed 02 May 2007, 06:53
Mike Richards
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Gerald,
That looks good.

When the Disconnect is closed, Neutral is connected to the coil and L1 is available to the coil through the N/O switch. When the N/O switch is closed momentarily, the coil is energized and the contactor's auxiliary switch is closed, making the contactor self-latching. At that point L1, N, and L2 are passed through the contactor. When either the Disconnect or any of the N/C switches are opened, even momentarily, the coil loses power and the contactor opens all of it's switches.
  #57  
Old Wed 02 May 2007, 08:04
Gerald_D
Just call me:
 
Thanks Mike. I still have to draw a "single phase" 230V version for "non-America" and that means the L2-L2-L2 rail at the bottom gets deleted. This is where somebody at some point upstream swops L1 and N around, and I was worried about the L1 getting deep into the circuit (via the coil) by mistake. We don't want a maintenance guy to find 230 V inside the circuit when it is OFF, but that is exactly what the Disconnect is there for.
  #58  
Old Thu 14 June 2007, 18:01
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
Quote:
Originally Posted by Gerald_D View Post
Thanks Mike. I still have to draw a "single phase" 230V version for "non-America" and that means the L2-L2-L2 rail at the bottom gets deleted. This is where somebody at some point upstream swops L1 and N around, and I was worried about the L1 getting deep into the circuit (via the coil) by mistake. We don't want a maintenance guy to find 230 V inside the circuit when it is OFF, but that is exactly what the Disconnect is there for.
Where does the BOB E-stop come into the picture from the one push button operator?

Greg
  #59  
Old Thu 14 June 2007, 21:39
Mike Nash
Just call me: Mike Nash
 
Bessemer, Alabama
United States of America
Hi Gerald,

I do industrial controls for a living in the US. I just saw this thread and one thing that jumps off the page at me is the location of the Off/Estops vs the On Pushbutton. The ideal hookup would have L1 - Estops - Off - (On & Seal In Contact in parallel) - Coil - Neutral. The problem with the schematic below is that you can bypass/defeat the Estops simply by holding the On pushbutton in. Or if either the On or Seal In contact welded or if the operator switch broke you could not easily turn it off.

As far as I can see, you also have no need of the L2 line in the US anyway. The only benefit would be requiring it if the 110V router needed more than 20A since that is typically the max rating for a 110V outlet and wiring. The 220V lines can be run in 10 Gauge which is good for 30A per NEC.

Hey, I really admire what you are doing here!

Mike Nash


Quote:
Originally Posted by Gerald_D View Post

  #60  
Old Fri 15 June 2007, 00:45
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Mike N, where have you been hiding while we needed you? Welcome!

You are dead right; the E-stops in the latest circuit can be defeated. Not good. Back to the drawing board....

The reasons I added the L2 are:
- Separates the noisy router from the control circuit (in 110V cases)
- Provides expansion/upgrade possibilities for folk wanting to add dust collectors or VFD's for spindles (also makes a progression to 3-phase easier - the right components are already in the box)
- 220 is a respectable voltage that I am more familiar with.
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