MechMate CNC Router Forum

Go Back   MechMate CNC Router Forum > Electrical & Electronic > 70. Control Systems
Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Reply
 
Thread Tools
  #1  
Old Sat 02 September 2006, 00:28
Mike John
Just call me:
 
E-Stops - Emergency Stops and then what?

wrong thread again?
In 'the other place' there is discussion on means of triggering the e-stop with a failure to the spindle or router.
Any thoughts on the matter, and the reverse? Stopping the router if the computer goes down.
edited to add Also stopping the router if just the control box goes down.

.............Mike
Reply With Quote
  #2  
Old Sat 02 September 2006, 01:50
Gerald_D
Just call me:
 
The way the MechMate is configured, the whole thing "E-stops" when:
- The spindle overheats
- The VFD controller has any form of fault (overheat, overload, power failure)ie. a common power failure causes an "e-stop"
- The computer control box stops sending valid signals.

However, there are different perceptions of what an "E-stop" really means in terms of "restartability"....

ShopBotters generally regard an E-stop as something of a "Pause" button and that one should be able to simply press a restart afterwards and everything carries on smoothly from where it left off.

On the MechMate, an E-Stop is pretty drastic - call it a crash-stop if you want. There is every chance that some steps are lost while the machine stops as quickly as possible, which in the interest of safety is the right thing to do. But, the MechMate's E-stop could also be downgraded to a "Pause" if that is what people want.
Reply With Quote
  #3  
Old Sat 02 September 2006, 03:09
Mike John
Just call me:
 
Imagine this
If a file had a command every 100 lines to go z max, then continue, it would be possible to return to that point after an emergency stop, and continue from there, effectively air cutting until you get to the point in the file that the E-stop happened.
I am not really advocating the z max thing, just suggesting that each file has a number of lines that you can recognise and return to.
I use jog moves for this, providing the file has such moves.
If you know where your x and y zero points are, you can also re-zero if necessary.

............Mike
Reply With Quote
  #4  
Old Sat 02 September 2006, 04:40
ralph hampton
Just call me:
 
Recovery would be easy if you had definite X,X,Z. On my current job, however (remachining turned legs), I've guessed the z-zero, and adjusted it after trying out.

R.
Reply With Quote
  #5  
Old Sat 02 September 2006, 04:55
Gerald_D
Just call me:
 
When you suddenly cut power to a fast-moving gantry (a real e-stop) the inertia will make the motors run on a bit. That "bit" is unknown to the computer - if you do a restart, the computer simply assumes the gantry is still at the point where the power was cut. (open-loop control)

Also, when power is interrupted and restored to a stepper, it moves to the nearest full-step position (every 0.4mm in our case).

Each job is different and they have different degrees of "salvage-ability" after a power failure in an open-loop control system. Our power failures are fortunately quite rare, and on the odd occasion when then did happen it was simple enough just to re-start the whole file from the beginning. First just a mil deep to see if it is tracking the same groove. I don't see how simple relays and things will make a re-start more accurate. Sure, more complex UPS's will reduce the effects of power failures, but strictly speaking, a UPS must also be cut off during a true Emergency Stop.
Reply With Quote
  #6  
Old Sat 02 September 2006, 06:01
ralph hampton
Just call me:
 
OK. so my question is, (from the other forum) if I put a ups on the control box, but let the shopbot software computer die with the power cut, will my latest xyz be secure?
After all, all I have done is cut the feed down the serial cable.
When this happens as a result of "serial communication failure" the XYZ seems to have held pretty (how???) accurately (even at 72mmps jog), but maybe the proceedure in the control box is different in each case.
I'm sure shopbot know the real answer to this one.

R.
Reply With Quote
  #7  
Old Sat 02 September 2006, 06:15
ralph hampton
Just call me:
 
Now, if the position is stored in the computer, then a ups on both control and computer, and a stop proceedure called by a relay when power dies to the router may be the best and safest solution.
Maybe the ups would have a signal outlet that could be used directly with an input in the control box (I think Brady was suggesting this on the other forum), but I have never played with a ups, and would need a bit of help on setting it up anyway.

R.
Reply With Quote
  #8  
Old Sat 02 September 2006, 07:05
ralph hampton
Just call me:
 
Gerald, OK, I read what you are saying about gantry inertia and full step restart. So how do the emergency stop (red button and keyboard Spacebar) get implemented in shopbot? the keyboard S is definitely recoverable, but the stop movement is ramped. I ask because with shopbot, there is the processor chip in the control box, and I didn't know how much of this type of function was implemented there.

r.
Reply With Quote
  #9  
Old Sat 02 September 2006, 07:38
Mike John
Just call me:
 
There is a way that you can recover.
Set the zero table co-ordinates to a known physical point.
Set the cutting file x,y,z zero's in relation to the table co-ordinates.
After a failure return to the table co-ordinates and re-zero.
Now re-zero the cutting file
Run the file from a line known to be before the failure.

.........Mike
Reply With Quote
  #10  
Old Sat 02 September 2006, 09:30
Gerald_D
Just call me:
 
Mike, those steps are completely logical, and will always work, but it just takes too long for the folk who are wanting relays, UPS's etc.

Ralph, I don't know how ShopBot implement the E-Stop these days. With our older machine it seems as if the red button & space bar only send a gentle request to the control PC to stop the motion by ramping down. In the Alpha's there are contactors (relays) that get opened, presumably instantly. In the MechMate, pulses get cut instantly (together with contactors opening) without ramp down.

The space bar on Mach3 (Mechmate, Ascension) is a ramp down stop called "Feedhold". The non-ramped stop is Alt-S, but this hasn't made sense to me because using 2 buttons is slower than the ramp.
Reply With Quote
  #11  
Old Sat 02 September 2006, 10:02
ralph hampton
Just call me:
 
Mike and Gerald:
I tend to do most of my work off XY table coordinates anyway. It is just that re-zeroing those with shaped cutters is tricky at best, so I would have to change cutter especially to re-zero. As for Z - see my first post in this topic, though I am developing a routine for cutter change maintaining Z for such situations.
As for PRT estop, I will play with it and measure next time my machine is fully free.

R.
Reply With Quote
  #12  
Old Sat 02 September 2006, 10:55
Mike John
Just call me:
 
Ralph, you could zero x and y from the shaft of the bit, with an adapted z plate.

Fiddly but possible

.............Mike
Reply With Quote
  #13  
Old Sat 02 September 2006, 11:56
ralph hampton
Just call me:
 
LOL
Reply With Quote
  #14  
Old Sat 02 September 2006, 13:56
Gerald_D
Just call me:
 
Remember that "home" position switches are a typical way of finding x,y table positions after a power failure. Mach3 has excellent methods of working with home switches, including independent switches for the two ends of the gantry to get it square. Mach can drive the x-motors independently until the gantry is square.
Reply With Quote
  #15  
Old Sat 02 September 2006, 19:20
Patrick Toomey
Just call me:
 
I took a 12 volt dc "wall wart" power supply and hooked it up to a small relay. The other end of the relay is hooked up to my e-stop line on the bot controller. I have a UPS powering my control computer and the ShopBot controller. This way if the power fails, the relay closes and trips the e-stop. I ended up getting a 240vac to 12vdc supply and hooking it up to the power line that feeds the spindle after the breaker. This means that now if the shop power goes out or if the spindle breaker pops it will trigger the e-stop. We have power failures every few days during the summer so this has saved my butt too many times to count. I also use it as a quick stop if lightning starts getting to close for comfort. If we hear a close strike we just pull the power cord for the UPS out of the wall and the bot stops and the controller and pc are now disconnected from wall power for safety. I had a 600VA UPS on there which worked to keep the machine up for about 10 minutes. I have since switched to a 2000VA extended runtime unit which can power it for over an hour just in case the power is out for awhile.

I would imagine you could use this type of thing to trigger a freehold in Mach so that you have a chance to resume like the ShopBot allows after their "sort of" e-stop.
Reply With Quote
  #16  
Old Sun 03 September 2006, 06:38
ralph hampton
Just call me:
 
Patrick, that sounds kind of sensible. You are saying that an Estop is reliable on position recovery, more so than an interuption to the serial feed, which kind of makes sense. Belkin do some 1.2kva ups's, which should cover 2 computers plus control box for a ten minute run-down, and I'll pop down to maplin and talk about relays.
I already have a makeshift estop limit switch to my Z axis top limit, so it can work in with that.

Thanks,

R.
Reply With Quote
  #17  
Old Sun 03 September 2006, 06:48
ralph hampton
Just call me:
 
Gerald,
I don't actually have any home switches at present - I must try some out. I can see their relevance now.
I guess an isolated metal contact connected through estop (as my last post ref Ztop) should do the trick - I guess that accuracy is not as vital as repeatability.

r.
Reply With Quote
  #18  
Old Sun 03 September 2006, 09:55
Gerald_D
Just call me:
 
Ralph, I don't have any "home" switches either, yet.

With the Mach3 guys, a home switch is very standard because Mach3 always remembers coordinates relative to "machine zero", even if you set another 0,0 somewhere else on the table. I think the later ShopBot versions can do the same, but I havn't seen a discussion on it.

(For the G-coders, google "G55 offset)
Reply With Quote
  #19  
Old Sun 03 September 2006, 10:54
Mike Richards
Just call me:
 
I've seen both home switches and limit switches on CNC routers. The home switch was usually a highly repeatable sensor switch (optical or magnetic) while the limit switch was usually a robust mechanical switch. Different inputs on the controller board would be used so that a home switch would not trigger an emergency stop. The home switch would be used to accurately sense the home position of an axis with fixture offsets calculated from the home position. The limit switch would be used to interrupt power to the axis (or to the entire machine) when further movement on that axis would damage the machine.
Reply With Quote
  #20  
Old Sun 03 September 2006, 11:11
ralph hampton
Just call me:
 
I guess the problem with a contact type limit switch is if dust gets in the way it wouldnt work, or work to a different position. I guess I could buy the shopbot ones, but by the time they've flown accross the pond, it gets a bit pricy. What sort of sensor switch am I looking for?

Thanks,

R.
Reply With Quote
  #21  
Old Sun 03 September 2006, 12:58
Mike Richards
Just call me:
 
You might want to look at proximity sensors. Go to this web site and then search for proximity sensors.

http://web4.automationdirect.com/

The 12mm inductive proximity sensors would be my first choice. They work on the same principle that the Shopbot sensors use. The sensor activates when it is in close proximity to a metal object (bolt head).
Reply With Quote
  #22  
Old Sat 17 February 2007, 18:05
Hugo Carradini
Just call me:
 
Gerald ¿What type of E-stop device you use? There are different types in http://www.automation4less.com/store...ts.asp?cat=824.
Reply With Quote
  #23  
Old Sat 17 February 2007, 20:03
Mike Richards
Just call me:
 
Hugo,
I hope you don't mind if I butt in. Because every CNC controller can be built to handle exactly the devices that you need on your machine (router or spindle, mechanical switches or proximity sensors, lights, bells, vacuums, etc), you'll probably have to become your own electrical engineer. The E-stop devices that you looked at might just be the actuator (push button) without the contact block (where you connect the wires). The different types listed allow you to use different voltages for the built-in light on the more expensive models.

Believe me when I say that designing your own controller can be exciting and frustrating. Everyone of us who has ever designed any electronic device has asked exactly the same questions that you're asking. It's all new to everyone of us at some point in our life. Unfortunately, because there are some many things to learn before the controller easy to understand, it can be frustrating. But, if you study it carefully, and build some test circuits so that you can see how it works, it will become easy as time goes on.
Reply With Quote
  #24  
Old Sat 17 February 2007, 23:33
Hugo Carradini
Just call me:
 
Yes I know what you mean. Thats what I been doing so far and I guess is the only way you can "almost" control your stuff at the end.
The only problem we got in this part of the world is that most of the electronics has to be imported and that takes time when you are trying different systems.
Anyway thanks for your comments
Reply With Quote
  #25  
Old Sun 18 February 2007, 00:23
Gerald_D
Just call me:
 
Hugo, those illustrations are only of the "operators" (the switch "head") and not the whole switch. I would pick 2AML4 (twist release) or 2AMPP4 (pull release). What other E-stops do you already have in your workshop (on other equipment) - do they have twist or pull releases? If they don't have a release system, use 2AM4.
Reply With Quote
  #26  
Old Sun 18 February 2007, 00:29
Gerald_D
Just call me:
 
Our MechMate has 2 "contact blocks" under each E-Stop head/operator. Both contacts are normally closed (NC) - pushing the E-stop opens both contacts.....and holds them open until the head/operator is released.

One contact block opens the main contactor and therefore carries 110/220V mains power.

The other contact block opens the circuit of the PMDX control card making the signal to Mach3.

Because of the two voltage levels, the contact blocks are mounted as far apart as possible (if your style of E-stop allows it) and they are fed by separate screened cables.
Reply With Quote
  #27  
Old Sun 18 February 2007, 21:10
Hugo Carradini
Just call me:
 
OK. That really help me understand the basic off what I need to look at.
Thanks
Reply With Quote
  #28  
Old Fri 04 May 2007, 11:29
Hugo Carradini
Just call me:
 
Gerald and friends ¿How do you install the pause button? I have checked all around and haven't find no information. I know I can stop and keep going through Mach3 using the key board but would like to know how to do it in a button installed in the gantry.
Thanks in advance
Reply With Quote
  #29  
Old Fri 04 May 2007, 15:00
Gerald_D
Just call me:
 
Hugo, here is a new thread for you! (This was done after a big dinner - I might regret it in the morning)
Reply With Quote
  #30  
Old Sat 05 May 2007, 21:08
Hugo Carradini
Just call me:
 
That?s great.
Thanks
Hugo Carradini
Reply With Quote
Reply

Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 05:14.


Powered by vBulletin® Version 3.8.3
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.