In hal, it is necessary to connect several index-related pins together
to make everything work right:
axis.#.index-enable
motenc.0.enc-##-index-enable
pid.#.index-enable
It's also very important to have your hal threads in the right order
read hardware
motion
pid
write hardware
When this is done, motion sees both the step change in axis position and
the falling index-enable. It changes its commanded position to match.
When these new values for command and feedback are seen by pid, the P, I
and D terms function properly since they are all calculated in terms of
the difference of command and feedback. By contrast, FF0, FF1 and FF2 are
calculated in terms of command only, and would have a 1-cycle glitch
when command takes its big step. But when pid sees the falling edge of
index-enable, it holds the computed FF* values for that one cycle,
fixing the glitch.
If you don't have all these things right, then you will get a 1-cycle
(1ms typ) glitch in the PID output, which can often be heard as a BANG
when an axis is first homed after power-on.
I am not sure whether these things are correct or not in the motenc
sample files, so you will want to delve into the hal and make sure. I
rather suspect that at least the connection to pid.#.index-enable is
missing in the hal file, because this is a comparatively new featuer
(only 4 years old, probably:)
I double checked, and I'm right that pid index-enable isn't hooked up in
the motenc sample configuration. Here are the (untested by me!) changes
you'd need to make to motenc_motion.hal with the old lines show with "-"
and the modified lines shown with "+":
diff --git a/configs/motenc/motenc_motion.hal b/configs/motenc/motenc_motion.hal
index 8e5be93..19eeeab 100644
--- a/configs/motenc/motenc_motion.hal
+++ b/configs/motenc/motenc_motion.hal
@@ -70,6 +70,6 @@ setp pid.1.maxoutput [AXIS_1]MAX_OUTPUT
setp pid.2.maxoutput [AXIS_2]MAX_OUTPUT
# Connect index pulses to motion controller.
-net Xindex motenc.0.enc-00-index-enable <=> axis.0.index-enable
-net Yindex motenc.0.enc-01-index-enable <=> axis.1.index-enable
-net Zindex motenc.0.enc-02-index-enable <=> axis.2.index-enable
+net Xindex motenc.0.enc-00-index-enable <=> axis.0.index-enable
pid.0.index-enable
+net Yindex motenc.0.enc-01-index-enable <=> axis.1.index-enable
pid.1.index-enable
+net Zindex motenc.0.enc-02-index-enable <=> axis.2.index-enable
pid.2.index-enable
Jeff
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