Lagging movement in one axis

[johnd]

I have converted a cincinatti bed mill using Rutex drives (2020) and Mach 3. Recently I have developed backlash in the X axis, approximately .03". I went through and tried to determine if it was mechanical and where. I used a dial indicator off of the table and rocked the ball screw back and forth and could not find any slop in the screw and nut. I pulled the motor off and checked the pulleys to see that they were tight to the shaft. No problem . The gear belt was in excellent shape. I retightened the belt tension. No improvement. I removed the cover on the encoder (US Digital EB5d (not sure)) and put a target /pointer out of a piece of tape. I rocked the ball screw back and forth with a vise grip on the end of the shaft. I see no encoder change on the screen. The motor was fighting to reposition itself.
To eliminate the problem with regard to positioning I went into the config. section of mach 3 and enabled the backlash on the x axis with a value of .0315". This works fine in running a program but trying to locate or center and moving the axis .0001" does not work. I spent around 20 minutes trying to indicate a center with a coax indicator- futile. ANY Suggestion woul;d be appreciated. I had previously blown the rutex card on this axis. This was due to a heat problem. I now have three seperate muffin fans serving the mother board. Tom E. if you are out there I would appreciate a response.

[Al_The_Man]

Originally Posted by johnd I rocked the ball screw back and forth with a vise grip on the end of the shaft. I see no encoder change on the screen. The motor was fighting to reposition itself.

Unless using a Galil card, Mach does not close the loop back to the controller, just to the drive.
The drive closes the loop.
So you won't see any difference on the screen.
Al.

[Torchhead]

Originally Posted by johnd no encoder change on the screen. The motor was fighting to reposition itself. To eliminate the problem with regard to positioning I went into the config. section of mach 3 and enabled the backlash on the x axis with a value of .0315". This works fine in running a program but trying to locate or center and moving the axis .0001" does not work. I spent around 20 minutes trying to indicate a center with a coax indicator- futile. ANY Suggestion woul;d be appreciated. I had previously blown the rutex card on this axis. This was due to a heat problem. I now have three seperate muffin fans serving the mother board. Tom E. if you are out there I would appreciate a response.

Rutex drives from the factory are typically tuned "loose" (or not at all). I had a customer that blew a drive and bought another and it was "spongey" meaning it would let you turn the shaft quite a ways before it corrected. Since there are no adjustments on the drives for tuning it has to be done in software. Unless you have the Rutex motherboard (this machine did not) it proved impossible to get communication or tune the drives. I read somewhere that the tuning application did not work with Windows version above 98 but maybe they have fixed that. We were never able to tune the drive from the PC so the customer was forced to send the drive to the company that built the controller and have them tune it in their test fixture.

If you don't have backlash in the mechanics then the only thing left is the drive tuning. As stated the loop (error detection and correction) is done at the drive. The Rutex drives allow for a lot more error in their options than a Gecko (which is 128 counts) so you can tune the Rutex a lot looser.

TOM CAUDLE
www.CandCNC.com