Thread: Limit and Home Switch Choice
Along with this thread and my own I can see there is never going to be a consensus of opinion with regard to limits and emergency stop circuits. All anyone can do is see what others have done and choose the bits that suit them best.
Here's how mine is going to be, I just changed a few things this weekend and will upload my 'as build' drawings later.
My emergency stop circuit consists of a big red button on the control panel and another in series on the machine, the limits are also in series with these buttons and a relay in the VFD indicating a fault condition is also in the circuit. Everywhere I have worked the limits, which I'm going to call 'ultimate limits' because that is what they are, always form part of the emergency stop circuit. These limits should never be activated, Mach3 has 'soft limits' for example that should operate first (don't know about Linux system).
I'm also using a PILZ emergency stop relay (@birchy it only cost £25 on ebay) so when the emergency stop circuit is activated the relay de-energizes removing power to the stepper drivers, sending Mach3 an E/stop signal, stopping the VFD by using a special emergency stop function and a Safe Torque Off (STO) feature.
The system can only be reset when all the relays and buttons are in the correct position and the VFD has been reset.
I also have a ‘stop’ button on the control panel that sends a STOP signal to the VFD and also stops Mach3 running. There is a ‘pause’ pushbutton that sends a ‘FeedHold’ signal to Mach3, it also stops the VFD.
To recover from a stop or pause condition a ‘reset’ button is pressed which also sends Mach3 an OEM signal to activate its RESET button and the VFD powers up again. Any time Mach3 is stopped it activates an Enable signal to stop the stepper drivers. Also in series with my pause button is a spindle over temperature switch and in series with my stop button is a relay that indicates if any of the AM882's have gone into alarm.
Last edited by EddyCurrent; 01-12-2013 at 09:06 PM.
Also When you release "Feedhold" Mach won't start the Spindle without an M3 command or OEM code to turn it back on and if you "Feedhold" chances are your in the middle of a job and just want to pause for something like clearing chips etc. . . That's the point of "Feedhold" it's not to be used for Emergency or any Safety feature.
Now has to the rest of the Limits and E-stop best way debate then it's Simply down to preference.
I prefer to have E-stop Buttons Kill power to everything. Limits I have separate and just have kill Signals to drives and Send Signals to Control to stop the code.
If drives have Fault signals like AM882 then they are wired in series with Limits and just Kill signals and inform control.
Feedhold is not for this purpose and shouldn't be used has such IMO. In Mach's case it also doesn't stop instantly either has it has to clear the Look-ahead buffer first so can't be relied upon to stop quickly.
Last edited by EddyCurrent; 02-12-2013 at 09:18 AM.
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