Hello Guest it is December 09, 2019, 02:35:37 AM

Author Topic: backlash and slaved axis  (Read 1382 times)

0 Members and 1 Guest are viewing this topic.

backlash and slaved axis
« on: March 31, 2015, 12:34:07 PM »
Hello,

as per title, have a question regarding setting up backlash on slaved axis.

If I have "Y" and "A" set up as slaved axis on a machine, how would you setup backlash, does the "Y" and the "A" axis get different numbers?

What about if one stepper motor drives one direction and the other drives the other direction, how would backlash be dealt with in this appliaction?
(think of a rack and pinion driven machine with two steppers each driving on a rack, but in opposite directions to get the carriage to move obviously in one direction).

Thanks for your time, any advice welcome
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Offline RICH

*
  • *
  •  7,376 7,376
    • View Profile
Re: backlash and slaved axis
« Reply #1 on: March 31, 2015, 05:23:57 PM »
robert,
I am not aware of any answers to the questions you asked. IE; Never applied backlash to a slaved axis and don't remember ever seeing a post about it how it behaves when applied to two axes.

Suggest you try setting the backlash for each axis AND observe how it works.
If Y & A are different try it with different settings for each, or both the same, experiment....
Do this with low settings for the shuttle wheel setting and backlash speed.

RICH
Re: backlash and slaved axis
« Reply #2 on: March 31, 2015, 07:54:26 PM »
Thanks Rich for the response.

I have tried it already (would not have asked without having a go), but I got some real odd behaviour.

Set Y = 0.2mm backlash, A = 0mm -> no difference
Set Y = 0mm backlash, A = 0.2mm -> no difference
Set Y = 0.2mm backlash, A = 0.2mm -> backlash got way worse (like 0.4mm or worse (basically the A axis did not move (sorry only one dial indicator and I was focusing in on the A).
thought I'd give it a go .... set Y = 0.2mm, and A = - (yes minus) 0.2mm and it seemed to advance ~0.2mm.... on the A axis...

Hence a little stumped after an evening of playing with a dial indicator.

Thanks

Rob
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Offline RICH

*
  • *
  •  7,376 7,376
    • View Profile
Re: backlash and slaved axis
« Reply #3 on: April 01, 2015, 06:46:41 AM »
Are you using a SS?
Have not used mine in a long time, but at that time, BC didn't work with the SS.
Haven't kept up with what is going on with the SS.
If yes then that may be the problem.

If no then..........

Did you try with low settings as suggested?

Put a piece of tape extending out like a flag on the coupling so you can watch what is happening or not happening.
Increase the backlash ( even if not correct ) to a larger amount so there is time to watch the axes and no need for an indicator.

If you have never used BC before you may want try BC on an axis which is not slaved and then you will know
how the settings affect the backlash and what to look for.

I am just curiuos if or how well BC works for a slaved axis since never tried it here. Note that BC is done when there is a change in direction.

Don't have any other suggestions.

RICH
« Last Edit: April 01, 2015, 06:53:50 AM by RICH »
Re: backlash and slaved axis
« Reply #4 on: April 01, 2015, 06:17:22 PM »
Err, yes using a USB SS, in hindsight that probably is the problem.

I was wondering is there anyway that you could prefix some code into to the way that mach looks at trajectory moves so that it ignores the first 20 steps say when changing direction (which is equivalent to my backlash), the catch would be when making minor moves or combined axis moves ....

probably not is the answer

Thanks again for your time
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”