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Author Topic: Anti-backlash acting crazy when jogging - Updated  (Read 2583 times)

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Offline PSG

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Anti-backlash acting crazy when jogging - Updated
« on: December 29, 2008, 10:51:16 AM »
Hello Guys!

Just finished building a new machine with a rack and pinion, with an A-axis slaved to the X-axis. Right now I am in the process of configuring Mach. The default screen set is different than the Mach 2 I was familiar with but so far everything seems to work with the exception of the anti-backlash.

When Anti-Backlash is enabled I can get the gantry to move properly in one direction. The motors sound good with no vibration/resonance, missing, etc. If I switch directions to move in the opposite the motors seem to run at half-power, grumble and growl, miss steps and then to add the icing on the cake after a bit of travel one the motors will reverse direction and cause the gantry to rack. I believe it is definitely related to the anti-backlash because of it gets disabled the motors will jog back and forth all day long without any issues. Making things a little crazier is that I can reactivate the anti-backlash after disabling and jogging all while in the same session and it seems to function properly.

Knowing that they do not always get along I have CV disabled. I have tried anti-backlash speeds of 20, 100, and 200 percent. What am I missing?

UPDATE:

To further add to my mystery I have found that if I try and jog more than 1 axis at a time (as in X and Y) the Y-axis will only move at half speed moving in the opposite direction and when it does do this the X motors (X and A) go out of sync and cause the gantry to rack. Again, doing nothing else but turning off the anti-backlash causes everything to operate smoothly. I have searched the forum and have not found any solution. Anybody have any ideas about why the anti-backlash makes the machine act crazy?
« Last Edit: December 29, 2008, 05:40:54 PM by PSG »

Offline jimpinder

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Re: Anti-backlash acting crazy when jogging - Updated
« Reply #1 on: December 30, 2008, 04:53:06 AM »
Have you got the A axis set as linear or angular - see General Config. The only difference that I know it that is then responds to mm or inches, whereas in angular it only responds to your basic setting. In angular, the movement say from 350 to 20 could be in either direction, the long way or the short way.

This may or may not affect backlash - since I assume you have the backlash set for each axis - since how will the machine know which way to apply backlash if it can move in either direction.
Not me driving the engine - I'm better looking.

Offline PSG

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Re: Anti-backlash acting crazy when jogging - Updated
« Reply #2 on: December 30, 2008, 09:31:04 AM »

I have all the axis set to "linear" on the config page.

What is driving me nuts is that I do not understand what would cause the motors to jog great in one direction and 1/2 speed in the opposite (only when anti-backlash is enabled) and why the machine would try and rack when jogging the X & Y at the same time (again only with anti-backlash enabled).

Offline Chaoticone

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Re: Anti-backlash acting crazy when jogging - Updated
« Reply #3 on: December 30, 2008, 09:41:54 AM »
PSG, I have sent you a personal message. Also, post your xml for us to see.

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!

Offline PSG

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Re: Anti-backlash acting crazy when jogging - Updated
« Reply #4 on: December 30, 2008, 10:42:28 AM »

It seems, but not 100% sure that with CV (and anti-backlash) turned on I am able to smoothly jog the X and Y (the backlash pause and hesitations do not bother me) but I still have not determined what caused the original problem with anti-backlash on where the X and A (slave) would reverse at half-power etc.

I will post the XML when I return in a few hours.