RE: [CAD_CAM_EDM_DRO] Re: Backlash

If you have set up a servo correctly, and it is a full PID servo, there will
be no follow error, or at least down to one encoder pulse.

If you integral is wrong, and improperly adjusted, you will have a following
error.





Dr. Mark Vaughan Ph'D. B.Eng. M0VAU

Managing Director

Vaughan Industries Ltd, reg in UK no 2561068

Water Care Technology Ltd, reg in UK no 4129351

Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH, UK.
Phone/Fax 44 1872 561288

RSGB DRM111(Cornwall)

_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Polaraligned
Sent: 24 March 2007 20:05
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Backlash



So you have .0004" backlash in your radial bearings. Only way
to eliminate that is to either adjust for proper preload or replace
with matched set of angular contact bearings. There are angular
contact bearing sets made specifically for ballscrew applications.
(Read $$$.)
That leaves you with about .0035" backlash somewhere in the rest
of your assembly. I am currently dealing with these problems right
now on my BP. What kind of motors are you driving the Axis with?
Your motor can be contributing to you're error. Servos can have a
a following error. I am not a stepper person but I believe they can
have an error also. Your ballscrews can be stretching a bit. Your
yoke can be flexing a bit. Your bearing mount can be flexing a bit.
Your ballnut can have a bit of backlash under load. Your belt can be
stretching a bit. All these little
things can add up fast. My backlash was .005" in the center of travel
and to my suprise was .011" at the ends of travel. I suspect that
this was because the ends of travel tightened up a bit and caused
a lot of stretching. I am in the process now of having the table
rescraped.
Try loosening up your gibs and measuring your backlash
then. You might be able to see if something is flexing.
How about removing your knee chip guard and trying to get the
DTI on the ballnut itself.

Good luck,
Scott





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