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Author Topic: Accuracy Problem  (Read 7050 times)

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Offline RICH

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Re: Accuracy Problem
« Reply #10 on: May 11, 2009, 07:46:09 AM »
Just a few comments Kevin,
1. A paper disc with a single fine reference line attached to the motor shaft can provide for comparing
actual steps to commanded steps. Poor mans mechanical encoder for checking if steps are lost ( your trying to isolate the commanded steps to physical movements delivered ).

2. No backlash implemented in your xml. The closer you try to get to perfect the harder it is to find the
what is causing the out of tolerance. AT .05mm ( .002" ) your in the area that a number of things can be
adding up to the tolerance call it the "system influence" . Lead screw tolerance, backlash, your measurements, etc.

Just thinking out of the box FWIW,


Re: Accuracy Problem
« Reply #11 on: May 13, 2009, 12:12:38 AM »
Thanks for the help and encouragement.  I'm making some progress,  but not there yet.  While thinking about the pulse frequency it reminded me that I'd been limited on microstepping the drives by my frequency.  So I increased it to 35,000 and increased the microstepping on the drives from 8 to 16, which now means 1600 pulses per mm movement.  Step and direction have been moved back to 5 (as the Z axis would not drive correctly with lower settings at 1600 pulses per mm).  Although this hasn't cured the issue yet (butI've still got room to play with the step/direction values over 5) it has decreased the problem.  I think I'm still losing the same number of steps, but because each one now moves the machine by half the amount due to the higher microstepping the problem is reduced.  On a simple 2d program I think that this would be virtually un-noticable now.  It's just complex programs with lots of code that are an issue.