Re: EMC-programming request

There is always cumulative elasticity in machine axes. DeVlieg used
(sorry,my info is from the 1960's and before) an unwind cycle in which the
ball screw of a heavy axis is brought to position, or before it. then
unwound to reverse sensor (resolver) movement, then unwound again, stopping
finally on the desired point. The idea was to take all torsion out of the
screw when making rapid positioning that did not involve milling.

Every machine has such elasticities, sometimes measured in fractions of an
inch, some involving at least a few millionths. If there were no room in
even precision bearing races, the balls couldn't roll. In this extreme
case we're talking millionths. This means when a heavy axis is plugged, or
otherwise stops rapidly, even if there is no torsion or other elasticity in
the drive mechanism, the balls or rollers will roll out of the center of
thir races.

It might be most practical to include backlash compensation that is speed
sensitive, and has the option of no, one or two compensations. The
algorythm cou;ld allow the user to set it up for a particular machine by
entering constants, with zero, meaning no compensation, as default inputs
and as default inputs on low speed motion

At 10:33 AM 7/19/99 -0400, you wrote:

>From: Fred Proctor <proctor@...>
>
>>I'd like to gather as much information on backlash compensation as I
>can. The algorithm works like this:
>
>/* begin */
>if (moving positive) then
> comp_value = backlash / 2
>else if (moving negative) then
> comp_value = -backlash / 2
>else
> /* leave comp_value as is */
>endif
>
>comp_output = command_output + comp_value
>/* end */
>
>One variation of this sets the comp_value to 0 in the last else clause,
>which moves the motor into the middle of the backlash range when motion
>stops. This resulted in an extra motion in the reverse direction when a
>move stopped, which I didn't like, but if there's a good reason for this
>someone let me know.
>
>--Fred
>
>--------------------------- ONElist Sponsor ----------------------------
>
>ONElist: your connection to people who share your interests.
>
>------------------------------------------------------------------------
>Welcome to CAD_CAM_EDM_DRO@...,an unmodulated list for the

discussion of shop built systems in the above catagories.

>To Unsubscribe, read archives, change to or from digest.
>Go to: http://www.onelist.com/isregistered.cgi
>Log on, and you will go to Member Center, and you can make changes there.
>bill,
>List Manager
>