Thanks Jeff. I was using a dial indicator and moving back and forth before and after setting "BACKLASH = 0.0005" and found no difference. I think I was homed but will verify next time I am at the machine and will also try your method to see what the hal pins believe. Is the "+" and "-" optional? -Tom
> On Oct 30, 2015, at 10:25 PM, Jeff Epler <[email protected]> wrote: > > For the following testing, I used the 2.7 branch at ref > v2.7.1-26-g21ae480 (26 commits past the most recent release, 2.7.1) > > I tested backlash compensation by modifying configs/sim/axis/axis.ini to > add backlash to the X axis: > > [AXIS_0] > ... > -BACKLASH = 0.000 > +BACKLASH = 0.100 > > I started with that configuration, homed all axes, and went into MDI > mode. > > I approached X0 first from the positive direction, and then used halcmd > to look at the relationship between the joint command and the motor > command: > [MDI in axis] > g0 x1 > g0 x0 > > [in a terminal window] > $ halcmd show pin axis.0.motor-pos-cmd axis.0.joint-pos-cmd > Component Pins: > Owner Type Dir Value Name > 23 float OUT 0 axis.0.joint-pos-cmd > 23 float OUT 0.93955 axis.0.motor-pos-cmd ==> Xpos > > And then I approached from the negative direction: > [MDI in axis] > g0 x-1 > g0 x0 > > [in a terminal window] > jepler@babs:~$ halcmd show pin axis.0.motor-pos-cmd axis.0.joint-pos-cmd > Component Pins: > Owner Type Dir Value Name > 23 float OUT 0 axis.0.joint-pos-cmd > 23 float OUT 1.03955 axis.0.motor-pos-cmd ==> Xpos > > In this case, I see that the motor positions differ by .1 inch depending > on the direction of approach. So the result of my testing is that > backlash compensation seems to operate as expected in at least one > situation. > > I got similar results when using incremental and continuous jogs -- the > difference between joint-pos-cmd and motor-pos-cmd was either 1.03955 or > 0.93955 depending on the direction of the last motion. > > (The specific values 1.03955 and 0.93955 depend on the details of how > the machine was homed and would differ from run to run at least on a > real machine) > > And now idle speculation as to why backlash compensation might be seen > not to operate at all for some users: I believe backlash compensation is > not activated until all axes are homed. So if you are using a > configuration that permits MDI & AUTO mode without homing, you might see > this happen (but this is just a memory of how linuxcnc used to work at > some time in the past and may not be accurate information for 2.7) > > Jeff > > ------------------------------------------------------------------------------ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
