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Author Topic: Gecko line count faults setup help  (Read 1359 times)

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Gecko line count faults setup help
« on: September 08, 2017, 11:51:19 AM »
I have been able to get my axis moving however they will only move enough to get the line count to go to the fault mode at the drive.  I am sure I have something in setup goofed up but wanted to run some things past you guys to see if I am missing the forest for the trees.  I have a PMD-126/107 going to Gecko G320X drives controlled by Mach III.  I have CUI encoders set to 500ppr and my lead screw requires 5 turns to make 1".  I set up in Mach to have 2500 pulses per unit.  The drives move accordingly so I am confident that I have the pin #s setup correctly for the servo output from Mach.  Do I need to run a "charge pump" to make things happy?
Re: Gecko line count faults setup help
« Reply #1 on: September 08, 2017, 02:57:53 PM »
Hi,
dont know what the fault it but I don't think it is a charge pump fault. Does you breakout board require a charge pump? This was the original idea
behind the charge pump, if Mach was active and working it would produce a charge pump signal, in absence of the signal the board would shutdown.
Not many people use it anymore.

In the manual there is a procedure for testing the encoder, did you follow it? The only other thing that occurs to me is that you have the motor going backwards,
the step/dir signal say go 2000 pulses clockwise but the motor takes off in the wrong direction. Easy to swap the two motor wires an try it.

Craig
My wife left with my best friend...
     and I miss him!
Re: Gecko line count faults setup help
« Reply #2 on: September 08, 2017, 03:05:38 PM »
The encoder passes the paper test.  I did some PID adjusting and am able to get the axis to move like they should just at a super slow rate.  I know this has to do with motor tuning...trying to figure that out now.
Re: Gecko line count faults setup help
« Reply #3 on: September 08, 2017, 05:16:33 PM »
Hi,
OK, you couldn't get any useful movement irrespective of speed if the motor were backwards.

Next question, and please excuse me if I'm asking another dumb question or treating you as such, but do you have
the current limit pot turned up enuf for the motor to develop useful torque? I see in the manual the direction
of rotation for increasing current limit has changed between models. It occurs to me that if the current is restricted
then the motor cannot accelerate and could only follow at very slow speeds.

Craig
My wife left with my best friend...
     and I miss him!

Offline rcaffin

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Re: Gecko line count faults setup help
« Reply #4 on: September 11, 2017, 05:30:43 AM »
I find the charge pump really valuable for safety. I would strongly recommend using it.
Actually, I strongly recommend all sorts of safety features.

Cheers
Roger
Re: Gecko line count faults setup help
« Reply #5 on: September 11, 2017, 08:11:20 AM »
I have the current limit set all the way counter clockwise.  I have been trying to get the encoder ppr set so the movements are accurate and I think I have that set however somewhere in making those adjustments I can no longer make the table move.  I am fairly certain the problem is in the PID tuning just not sure what I need to adjust to make it all come together.  I do not have an oscilloscope to do my tuning so I found some "by ear" tuning instructions that are okay at best.  Is there a good way to find out how much juice my servos actually require on an older machine (1983)?  I have some legible labels and I have tried to get info about them before but got stuck trying. 
Re: Gecko line count faults setup help
« Reply #6 on: September 11, 2017, 02:26:10 PM »
Hi,
you haven't yet established that you have current for the motor. Unless you have a clamp meter or an ammeter you are going on what you believe
to be a good setting. May I suggest trying the current limit pot at the midway point, if your motor responds then it may be that your belief concerning
the direction of rotation to get full current is wrong.

When I did control engineering at university, a long time ago now of course, the starting point was no Integral, plenty of Proportional with just enuf
Derivative to keep it stable. Towards the end of the tuning process add some Integral to eliminate following error.

Craig
My wife left with my best friend...
     and I miss him!
Re: Gecko line count faults setup help
« Reply #7 on: September 11, 2017, 02:46:47 PM »
I know that I don't have the correct diagnostic equipment to do this the correct way however I was able to tune the PID and now have 2 working axis that seem to respond well.  These are older servos and this is my first experience so I am trying to listen when tuning.  One axis is working very well with no ambient noise and it sound like other examples I have seen in videos.  The Y axis seems to have a little "feedback" kind of like a tick noise here and there that I can't seem to get rid of regardless of where the PID is.  They do both respond to Mach III and are correlated correctly regarding distance and DRO.
Re: Gecko line count faults setup help
« Reply #8 on: September 11, 2017, 02:55:51 PM »
Hi,
you are making progress, there's a reason most control engineers are bald, they pull their hair out trying to set PIDs!

That you have one working well and another presumably identical servo not suggests that it may in fact be an electrical or
mechanical fault within the offending servo. Can you, without further PID adjustment, swap the output of the good drive to the
dodgy servo? Might go some way to confirming/diagnosing the status of the servo and mechanicals.

Craig
My wife left with my best friend...
     and I miss him!

Offline rcaffin

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Re: Gecko line count faults setup help
« Reply #9 on: September 11, 2017, 05:03:50 PM »
The occasional 'tick' sounds like noise coming in somewhere to me.
PID tuning - smile ... But I agree with joeaverage as to method.

Cheers
Roger