I think you have a good handle on E-stopping. Now you need to address how you get out of E-stop. Once you hit a limit switch, all the power is shut down. How do you get the machine off the limit switch without power? Does your machine have hand cranks? I assume that you have separate home switches to home the machine (some of us use the limit switches to do that).
Personally, I don't like the idea of the limit switches in series. I would like the computer to know which limit was hit. So, if the X+ limit is hit, the computer could allow motion in the X- direction to get off the X+ limit switch. One might argue that *soft* limits are supposed to handle that case. Or, you could have each of the limit switches have it's own relay. (Or be a muli pole switch.) Then the limit switches could be in series AND the computer could tell which limit had been hit. A separate limit override could then short across the series chain of limit switches to close the chain while the computer jogged off of the limit. That limit override might even be a manual press switch that had to be held while the jog took place. I guess there are really two e-stop cases. Case 1 is the bug in the g-code case where there is a need to hit the big red button. That might be fairly frequent. Case 2 is the hardware/software case where the machine "went crazy" and ran through the soft limits. That should NEVER happen. Case 1 should be easy to recover from. Case 2 does not have to be easy to recover from. Sorry I've rambled. If you have the answer to getting out of e-stop, you're all set. Ken [EMAIL PROTECTED] Mark Kenny Products Company, LLC 55 Main Street Voice: (203)426-7166 Newtown, CT 06470 Fax: (203)426-9138 http://www.MarkKenny.com -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Anders Wallin Sent: Friday, December 15, 2006 4:55 PM To: Enhanced Machine Controller (EMC) Subject: [Emc-users] E-stop circuit ? Hi all, could I have some comments on the following E-stop circuit idea. The core idea emerging from thinking about this is to wire dangerous things in series(wire OR) and use the end result of this in parallel(wire AND). That way the E-stop chain is cut if device1 OR device2 OR device 3... fails, and the resulting signal stops EMC AND cuts power to VFD AND cuts power to servo drives AND ... Here is what I have come up with: start at the HAL pin E-stop-out. It will be high whenever EMC thinks it's OK to go out of E-stop. E-stop-out drives the coil of a NO(normally open) relay. This relay connects +12 V to the beginning of the E-stop chain only if E-stop-out is high. On the +12V wire, a number of NC(normally closed) switches follow: Red E-stop buttons (2), Limit switches(6), NC relays on the servo amps(3). At the end of the chain we are going to have either +12V if everything is OK, or 0V if we are in E-stop. Use the +12V to power the coils of three NO relays (coils in parallel): 1. one relay connects +5V to E-stop-in telling EMC everything is OK 2. one relay grounds the Poweron/ input of a Pico Systems power switch - that will give power to the servo drives. 3. one relay connects 230 VAC power to a VFD which powers the spindle motor If the E-stop chain breaks for any reason all of the relays will go to their NO state making E-stop-in go low, cutting power to servo drives, and cutting power to the VFD. If this sounds confusing there's a picture at http://www.anderswallin.net/temp/e-stop.png which might help... (the E-stop chain is the blue line, the VFD relay would obviously be two-pole, a transistor driving relay1 is needed) Some questions I have: -wiring three relays in parallel at the end of the chain will result in three times the current needed to pull one coil of the relays. Is this going to be a problem ? (other than that the +12V supply must cope) -is it a good idea to just cut the AC power to the VFD in an E-stop situation ? are there any other better ways to safely stop the spindle ? -should I also hardwire the servo drive amp-enable signals so that they go low on E-stop? -If I connect the common terminal of the limit switches to the 'upstream' end of the E-stop chain, can I wire the unused NO output of the limit switch to another HAL pin ? This way an E-stop due to a limit switch could be diagnosed by EMC as coming from a specific limit (+/-) and axis (XYZ). thanks for any comments, Anders ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
