ever changing backlash

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27 Jan 2011 12:32 #6848 by piasdom
i used backlash before and never had this problem. i set the backlash to .003" on all three axis,
ran the code and measured. ran the same code without changing anything. it was off by about .003".
ran the code again(no changes) and it was off another .003"(total .006" now). ran the code again(still no
changes) and saw it off by .009" now.
should the backlash code change every time it's ran ? i thought it would only set the backlash from zero
and not every time the codes ran. Thanks for any help !!

P.s. attached is my ini.

File Attachment:

File Name: Axis.ini
File Size:2 KB
Attachments:

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27 Jan 2011 13:24 #6849 by andypugh
Replied by andypugh on topic Re:ever changing backlash
I wonder if it is homing to the wrong side of the backlash?
What happens if you reverse the latch velocity? ie, if you now have rapid to switch, move off, slow move on, switch to rapid to switch, slow move off.

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27 Jan 2011 15:24 #6850 by piasdom
Replied by piasdom on topic Re:ever changing backlash
thanks, but i don't have any limit switches. it's one of the sherline mills. i have to set the limits
by knowing the limits. limits now are 10,10 and 8, but my machine doesn't go that far. if it
gets to the limit, i lose zero. again, Thanks for your reply !


andypugh wrote:

I wonder if it is homing to the wrong side of the backlash?
What happens if you reverse the latch velocity? ie, if you now have rapid to switch, move off, slow move on, switch to rapid to switch, slow move off.

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27 Jan 2011 23:08 #6851 by andypugh
Replied by andypugh on topic Re:ever changing backlash
How are you homing? I wonder if there is some sort of interaction between the processes.

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28 Jan 2011 00:36 #6852 by BigJohnT
Replied by BigJohnT on topic Re:ever changing backlash
Backlash will move the amount specified each time the direction changes. So when X for example goes from + direction to - direction a rapid move of the backlash amount occurs in the minus direction at the start of the move.

Is this a stepper machine? If so have you tried the stepper test to see if your losing steps?

John

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28 Jan 2011 18:28 - 28 Jan 2011 19:45 #6857 by piasdom
Replied by piasdom on topic Re:ever changing backlash
never had to do/use stepper test. in fact, never heard of it and if it's part of HAL,never used that either.
never had to BUILD a machine. thanks JohnT

p.s. it is a stepper motor. www.sherline.com


BigJohnT wrote:

Backlash will move the amount specified each time the direction changes. So when X for example goes from + direction to - direction a rapid move of the backlash amount occurs in the minus direction at the start of the move.

Is this a stepper machine? If so have you tried the stepper test to see if your losing steps?

John

Last edit: 28 Jan 2011 19:45 by piasdom.

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29 Jan 2011 00:07 #6859 by BigJohnT
Replied by BigJohnT on topic Re:ever changing backlash
The first test I would do is to comment out all backlash then run the stepper test for each axis to try and figure out if your loosing steps due to friction or something.

www.linuxcnc.org/docview/html/common_Ste...iagnostics.html#r1_3

John

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30 Jan 2011 01:04 #6867 by jmelson
Replied by jmelson on topic Re:ever changing backlash
piasdom wrote:

i used backlash before and never had this problem. i set the backlash to .003" on all three axis,
ran the code and measured. ran the same code without changing anything. it was off by about .003".
ran the code again(no changes) and it was off another .003"(total .006" now). ran the code again(still no
changes) and saw it off by .009" now.
should the backlash code change every time it's ran ? i thought it would only set the backlash from zero
and not every time the codes ran. Thanks for any help !!

P.s. attached is my ini.

File Attachment:

File Name: Axis.ini
File Size:2 KB

Most likely, the 10 inch/sec/sec acceleration you have set in your .ini file is too high, and the rapid jumps when the backlash correction attempts to jump to the opposite side of the backlash is exceeding the ability of your driver/motor to accelerate, causing lost steps. Try setting the MAX_ACCELERATION parameter in each axis section of the .ini file to a lower value and see if the problem improves.

Jon

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31 Jan 2011 11:09 #6893 by piasdom
Replied by piasdom on topic Re:ever changing backlash
manually with an edge finder.

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31 Jan 2011 12:23 #6895 by andypugh
Replied by andypugh on topic Re:ever changing backlash
piasdom wrote:

manually with an edge finder.


I wonder if backlash compensation is active during manual jogging? It is possible that it might not be,

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