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Author Topic: I seem to be gaining steps...  (Read 8209 times)

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Offline ethos

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Re: I seem to be gaining steps...
« Reply #10 on: March 14, 2010, 03:07:14 PM »

Offline Hood

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Re: I seem to be gaining steps...
« Reply #11 on: March 14, 2010, 03:13:47 PM »
Cant seem to open the view of the trace, can you attach it to your post?
Hood

Offline ethos

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Re: I seem to be gaining steps...
« Reply #12 on: March 14, 2010, 04:44:48 PM »
Traces attached...

Offline ethos

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Re: I seem to be gaining steps...
« Reply #13 on: March 14, 2010, 04:46:24 PM »
And traces for rapid movement...

Offline ethos

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Re: I seem to be gaining steps...
« Reply #14 on: March 14, 2010, 04:47:23 PM »
Closeup of artefacts in slow speed trace...

Offline Hood

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Re: I seem to be gaining steps...
« Reply #15 on: March 14, 2010, 06:43:18 PM »
Have you run the driver test to see what your pulse is like?
Hood

Offline ethos

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Re: I seem to be gaining steps...
« Reply #16 on: March 15, 2010, 04:05:59 PM »
Yes. It's a fast machine that runs with a stable clock up to 65kHz. There may appear to be some pulses missing in these traces, but this is because the width of the pulses is close to the sampling rate at this timebase, so the scope is not catching all of them. Sampling at higher rates shows a certain amount of jitter between pulses, but an average pulse rate that matches the desired feed rate.

What concerns me is the asymmetric profile of one channel of the stepper drive. I was expecting to see two phase shifted sinusoids, but the B channel appears to collapse each time it crosses the peak and at this point you can hear the stepper jump several steps. I am guessing that the motor lets go as the current falls sharply and gets pulled towards the next whole step.

Not sure if this might be due to a wiring issue in the stepper, or a driver fault?

I have checked my wiring against the manuals for the steppers and the drivers and all appears to be correct, but I have found at least one error in the driver docs so anything could be happening.

Terry

Offline Hood

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Re: I seem to be gaining steps...
« Reply #17 on: March 15, 2010, 04:51:08 PM »
If its the 9 amp drives from Arc Euro then I am guessing the error you found is the CW/CCW and Ste/Dir dip switch, it was the wrong way round in the docs on the drive I got. Then again they could have been changed as I got mine not long after they were out.

Dont really know enough about steppers to say but I would think what you expect to see would be correct but where the problem lies I dont know :(  Hopefully someone with more experience of steppers can help. If not the loan of the Gecko to test is still open.
Hood
Re: I seem to be gaining steps...
« Reply #18 on: March 18, 2010, 05:27:28 AM »

Listening to this very slow traverse, you hear a steady "clonk-clonk-clonk" until the point shown on the B+ trace where there is a steep asymmetric drop in current. At this point, you hear a sputter of steps, then back to the slow steady pace.

Hi I think I have a similar issue but I'm not sure wether my motor or my ballscrew the one that is making that tap tap tap noise after 20+ hours running.
do you have a recorded sound of that clonk clonk clonk?

Offline ethos

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Re: I seem to be gaining steps...
« Reply #19 on: March 18, 2010, 05:52:34 AM »
In this particular instance, the feedrate was set to 2mm/minute, so each 'clonk' is the sound of a single microstep. In my case, the problem is the fact that I get a nice regular pace of steps, then at a particular angle the motor spins forward several microsteps in quick succession.

Terry