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Author Topic: MPG with Feed Hold SAFETY ISSUE  (Read 1371 times)

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Offline CRS

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MPG with Feed Hold SAFETY ISSUE
« on: June 13, 2017, 04:16:02 PM »
Hi guys, me again,

I wonder if anyone has experienced this. On one machine we have added an external MPG wheel to the front console, it works very well using Chaoticone’s script for his CNC4PC Pendant.  Slightly modified, but all good.  A five position rotary selector switch for OFF, and the four axes X, Y, Z, and A.

When running G Code, the MPG and Jogging are not available of course, but when Feed Hold is pressed, if the MPG is not in the OFF position, which can happen, and it is accidentally bumped, then it mimics the Cycle Start command and the G Code starts running again.  I must say, that makes you sit up and take notice!

Well, just make sure the switch for the MPG is in the OFF position….  Yes of course, but if things can go wrong, then they might.  It gets better.  When Feed Hold is press again or Cycle Stop is pressed in an attempt to halt the unwanted action, the screen freezes and the machine just keeps on running.  I assume Mach or the PC is still running the G Code in the background.  It then requires E-Stop to halt the action.  Not very convenient.

That part may just be on our set up for whatever reason, but I assume the MPG acting as a proxy Cycle Start is normal.  My thought is to set things up like on my current mill and I have seen elsewhere, where the selector switch unless in the OFF position actually prevents the Cycle Start from acting.  Not sure if that is what is happening internally, but that is the effect.

Is this a good solution?

Have a normally closed contact from the OFF position in the selector switch activate an input, say input 63, then modify the Cycle Start function to include that input in the things it looks for before it can be actioned?

I have the input happening and have attempted to add that input to the “if/then” statement in the Cycle Start script, but I really have no idea what I am doing.  I don’t want to just keep trying stuff as this is more than just a desire, it’s now quite a potential safety issue if I don’t get it right, or get it half right.

Any suggestions welcome and anyone with an external MPG wired in, be aware.  If using a pendant with a Dead Man switch, then that takes care of it, but we don’t want a Dead Man switch, as I believe one of your hands is rendered unusable while holding in the switch.

Craig.
Re: MPG with Feed Hold SAFETY ISSUE
« Reply #1 on: June 14, 2017, 04:41:31 PM »
Craig,

I run mach4 all the time and I am surprised to hear about this issue.  I am curious if there could be cross talk going on that is sending a mcCntlCycleStart() command.  Could you open -> Diagnostics -> Logging and start the file running and then turn on Logging, then press FeedHold and then bump the MPG.  After you have a log of this issue please save it and upload it to this post so we can see what is happening.

Thanks,
Andrew
MachMotion
Andrew
MachMotion

Offline CRS

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Re: MPG with Feed Hold SAFETY ISSUE
« Reply #2 on: June 15, 2017, 04:20:38 AM »
Hi Andrew,

Thanks so much for taking the time to make contact.   And I do apologise for taking a while to answer you, I only just noticed the email from Mach support in my Inbox.

The log file is done and should be uploaded along with this.  That is another thing I have learned.  I wondered what that logging thing was for.

Together with another chap, we are doing two conversions, and it happens the same with both machines.  That could of course be that I have made an error and that error has been passed on to the other machine.

Just in case this MPG/Feed Hold thing is an issue that is inherent, I have, through some trial and error, managed a work around.  For anyone interested, this is what I did.

Using the normally closed contacts from the OFF position on the axis Selector switch, I wired it to an input on the Ethernet Smooth Stepper via my CNCRoom MB2 breakout board and set it to Active High.  Mapped that input to the “Motion Inhibit” input for Mach via the ESS config and that was that.  When the MPG is in the OFF position, you can run G Code, but when the MPG has an axis selected, the input goes high, then any motion related to G Code is stopped.

It is not ideal and I found it somewhat surprising that it doesn’t actually inhibit all motion including the MPG. But for now it works.  If code is running and you turn the MPG axis selector switch, it will halt the G Code and act in a similar way to a Feed Hold command.  Like I said, not ideal, but not a big safety issue either.  Select OFF and off it goes again.

Thanks again Andrew, look forward to hearing back from you.

Craig Smith

Offline smurph

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Re: MPG with Feed Hold SAFETY ISSUE
« Reply #3 on: June 15, 2017, 07:42:14 PM »
We experimented with jogging in feed hold but took it out but failed to take it out for MPG movements.  It will be corrected in the next build released. 

Steve

Offline CRS

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Re: MPG with Feed Hold SAFETY ISSUE
« Reply #4 on: June 15, 2017, 08:03:14 PM »
Ah ha Steve, so you're the culprit!

But seriously now.   What you say makes sense,.... and that is why I can't jog in Feed Hold, but I can MPG (verb).

Steve, can you see any issue with what we have done with the Motion Inhibit input?  You know how things seem logical and obvious, until it all goes wrong.

Thanks for letting us know that Steve.  Good man.

Craig.

Offline smurph

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Re: MPG with Feed Hold SAFETY ISSUE
« Reply #5 on: June 15, 2017, 10:51:13 PM »
I would use the ISIG_MPG_INHIBIT instead.  As a workaround until the next release.  You can use the PMC to hold it high when no axis is selected on the MPG.  You could also use that signal along with the machine state and hold it high when the machine is in any of the feed hold states. 

Steve

Offline CRS

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Re: MPG with Feed Hold SAFETY ISSUE
« Reply #6 on: June 15, 2017, 11:10:00 PM »
Thanks Steve,

Reading what you said kind of makes sense to me, unfortunately I am just not at that level where I can do any of that stuff yet.  I will have to go looking and find out what a PMC is, haven't come across that one.

I will read your reply another 5 or 6 hundred times and I am sure the penny will drop.  Ignorance is not bliss when it comes to this stuff hey.  I do long for the day when I won't screw up my face when I read things like this.  It is prematurely aging me.

Regards,

Craig.

Offline smurph

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Re: MPG with Feed Hold SAFETY ISSUE
« Reply #7 on: June 16, 2017, 02:12:11 AM »
PMC == programmable machine controller.  It is a ladder logic software PLC.  Search of PMC in this forum for how to use it. 

Steve

Offline CRS

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Re: MPG with Feed Hold SAFETY ISSUE
« Reply #8 on: June 17, 2017, 10:52:39 PM »
Hi Steve,

Thanks for explaining about PMC.  Actually looking back at other posts you have helped me on, you did in fact explain it to me already.  Sorry about that.

Over the last days I looked at it and read the help, but still too much for me to comprehend.  I also pondered and did copy and paste stuff into the script using the mpg inhibit, but not there yet.  Being that I am not at a stage Lua wise to be able to heed your advice and use the ISIG_MPG_INHIBIT, (I did try), do you have an approximate ETA on the next Mach4 Build that will hopefully not include the MPG crazy behaviour thing?

I know it's a copout, but if it's not too far away, for now I will just go with using the Motion Inhibit.  My family needs me back....

Thank you Steve

Craig.