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
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