Backlash compensation

[lumberjack_jeff]

How exactly is backlash compensation implemented in EMC?

I have significant backlash in my 4' x 8' gantry router... backlash which I'm trying to compensate for in software.

To verify the amount of backlash, I carved circles in plastic then measured the result. When I had enough backlash compensation baked in to create nearly perfect circles, I found that the compensation was about 40% of the actual backlash which could be measured with a dial indicator. Further, my parts (visualize two letters "S" mirrored and facing one another) were formed by 5 discrete changes in direction on one axis, which then have to accurately match a mating recess, dovetail-style. The inaccuracies in the male piece were inverse to the inaccuracies in the female one, thus my parts didn't fit together... or at least they didn't until I'd built in the backlash value which was actually measured with a dial indicator.

Bottom line, I can make the parts I need, or I can make accurate circles, but apparently not both.

[cyclestart]

Seeing as nobody else is responding.....

Originally Posted by lumberjack_jeff Bottom line, I can make the parts I need, or I can make accurate circles, but apparently not both.

Do you need to do both in the same program ? If not, 2 distinct configurations could be a work around.

It's the ugliest kludge imaginable. Otoh fixing backlash in software is it's own kludge. Hey we're hobby people (most of us), kludges is what we do

Hope someone comes along with a better solution.

[lumberjack_jeff]

Thanks Cyclestart, yes that is one option. It is unlikely that I'll have a need for jigsaw-puzzle joinery combined with hyper-accurate circles on the same project.

But I find the dual-configuration solution... unfulfilling.

[cyclestart]

Originally Posted by lumberjack_jeff But I find the dual-configuration solution... unfulfilling.

Unfulfilling is probably being generous

[chester88]

How much backlash are you talking about?
what kind of motors ? servo? steppers?
Are you using simple backlash or comp file for compensation?
backlash compensation is not very well documented.
http://www.linuxcnc.org/docs/devel/h...nfig.html#sub:[TRAJ]-section
http://wiki.linuxcnc.org/cgi-bin/emc...w_Compensation

[lumberjack_jeff]

Thanks Chester,
I have .015 on my Y axis (due to the gearbox on my stepper) and about .006 on my X (the geometry helps to mitigate some of the gearbox's backlash).

I'm using simple compensation because the lash is the same everywhere within its operating range.