[SOLVED] Rotary axis homin on index not working

Aciera
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3 years 5 months ago #271811 by Aciera

Rotary axis homin on index not working was created by Aciera

I'm trying to get a rotary joint to home using an encoder index.
I would expect the motor to rotate (according to the 'HOME_LATCH_VEL' set in the ini and upon finding the index pulse stop and reset the absolute position to zero.
What I see is the motor starts turning finds the index and then returns to, what seems to me, the old absolute zero position.
This is on Version 2.9 from a recent bookworm install.

Any ideas?

Attachment not found

Warning: Spoiler!

#******************************************************************************************************
# --- PID SETUP ---
setp     pid.a.Pgain                                  [JOINT_3]P
setp     pid.a.Igain                                  [JOINT_3]I
setp     pid.a.Dgain                                  [JOINT_3]D
setp     pid.a.bias                                   [JOINT_3]BIAS
setp     pid.a.FF0                                    [JOINT_3]FF0
setp     pid.a.FF1                                    [JOINT_3]FF1
setp     pid.a.FF2                                    [JOINT_3]FF2
setp     pid.a.deadband                               [JOINT_3]DEADBAND
setp     pid.a.maxoutput                              [JOINT_3]MAX_OUTPUT
setp     pid.a.error-previous-target                  TRUE
setp     pid.a.maxerror                               .01

# --- STEPGEN SETUP ---
setp     hm2_7i76e.0.stepgen.04.dirsetup              [JOINT_3]DIRSETUP
setp     hm2_7i76e.0.stepgen.04.dirhold               [JOINT_3]DIRHOLD
setp     hm2_7i76e.0.stepgen.04.steplen               [JOINT_3]STEPLEN
setp     hm2_7i76e.0.stepgen.04.stepspace             [JOINT_3]STEPSPACE
setp     hm2_7i76e.0.stepgen.04.position-scale        [JOINT_3]STEP_SCALE
setp     hm2_7i76e.0.stepgen.04.step_type             0
setp     hm2_7i76e.0.stepgen.04.control-type          1
setp     hm2_7i76e.0.stepgen.04.maxaccel              [JOINT_3]STEPGEN_MAXACCEL
setp     hm2_7i76e.0.stepgen.04.maxvel                [JOINT_3]STEPGEN_MAXVEL

# --- ENCODER SETUP ---
setp     hm2_7i76e.0.encoder.03.counter-mode         0
setp     hm2_7i76e.0.encoder.03.filter               1
setp     hm2_7i76e.0.encoder.03.index-invert         0
setp     hm2_7i76e.0.encoder.03.index-mask           0
setp     hm2_7i76e.0.encoder.03.index-mask-invert    0
setp     hm2_7i76e.0.encoder.03.scale                [JOINT_3]ENCODER_SCALE

#--- OPEN LOOP STEPPER SIGNALS ---
net a-index-enable <=> joint.3.index-enable                <=> pid.a.index-enable   <=> hm2_7i76e.0.encoder.03.index-enable
net a-enable        <= joint.3.amp-enable-out               => pid.a.enable       => hm2_7i76e.0.stepgen.04.enable
net a-pos-cmd       <= joint.3.motor-pos-cmd                => pid.a.command
net a-vel-cmd       <= joint.3.vel-cmd                      => pid.a.command-deriv
net a-output        <= pid.a.output                                               => hm2_7i76e.0.stepgen.04.velocity-cmd
net a-pos-fb        <= hm2_7i76e.0.stepgen.04.position-fb   => pid.a.feedback     => joint.3.motor-pos-fb

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Aciera
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3 years 5 months ago #271817 by Aciera

Replied by Aciera on topic Rotary axis homin on index not working

Here is a HalScope shot with the encoder positions.
Rotary:

Attachment not found

And my (linear) Y axis also using an index:

Attachment not found

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Aciera
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3 years 5 months ago #271818 by Aciera

Replied by Aciera on topic Rotary axis homin on index not working

So it seems to me that with the rotary homing the joint position is not set to zero.

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chris@cnc
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3 years 5 months ago #271820 by chris@cnc

Replied by chris@cnc on topic Rotary axis homin on index not working

I seems your encoder feedback is missing?
net a-pos-fb <= hm2_7i76e.0.encoder.03.position

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Aciera
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3 years 5 months ago #271826 by Aciera

Replied by Aciera on topic Rotary axis homin on index not working

Ah, yes the linear axis is indeed closed loop and the rotary is not since that runs on a servo controller. So does that mean that I have to fully close the loop for that rotary in linuxcnc to be able to use index homing?
I was hoping to avoid that since that would mean two positional pids in the system.

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PCW
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3 years 5 months ago #271830 by PCW

Replied by PCW on topic Rotary axis homin on index not working

It is possible to home open loop stepgen systems to index using
the right firmware (firmware with step/dir index support)

This firmware exports a stepgen index enable pin and has stepgen
hardware that emulates encoder behaviour on index. The stepgen index
input is normally shared with encoder index inputs of the same channel
so you might have to re-arrange stepgens for this to work.

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chris@cnc
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3 years 5 months ago #271832 by chris@cnc

Replied by chris@cnc on topic Rotary axis homin on index not working

I set the linuxcnc PID to 1 and tune the servo controller. It works...

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Aciera
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3 years 5 months ago #271835 by Aciera

Replied by Aciera on topic Rotary axis homin on index not working

Thank you both.

The stepgen index
input is normally shared with encoder index inputs of the same channel
so you might have to re-arrange stepgens for this to work.

On my 7i76e i use three stepgens using closed loop with index homing (stepper/glasscales), one stepgen with home switch and the one in question with a step/dir servo controller with index homing from the controller index feedback. Would that work?

I set the linuxcnc PID to 1 and tune the servo controller. It works...

Hm, if I do that I always get an 'offset' in the DRO after homing. The absolute value in the DRO is not 0 but say 1.5. This value decreases with the homing latch velocity but i'm already crawling.

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PCW
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3 years 5 months ago #271839 by PCW

Replied by PCW on topic Rotary axis homin on index not working

As chris@cnc suggested, using encoder feedback for the rotary axis
is probably the simplest solution.

Then all axis would be settup similarly

If you wanted to use stepgen index you would need to arrange
the stepgen channel using index to match the encoder channel
(they are mis-matched now)

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Aciera
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3 years 5 months ago #271844 by Aciera

Replied by Aciera on topic Rotary axis homin on index not working

So the only thing I would have to switch around is to use stepgen.03 with encoder.03 instead of using stepgen.04 with encoder.03? That seems easy enough.
So far I have not found a solution for the homing offset issue I'm having with the encoder feedback.

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