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Problem homing with index

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5 years 3 months ago #214263 by PCW
Replied by PCW on topic Problem homing with index
Yes basically that's right, except the stepgen must be run in velocity mode
and the PID output drives the stepgen velocity, not position

How encoders are arranged depends on the firmware used

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5 years 1 month ago - 5 years 1 month ago #219431 by ldmarsaglia
Replied by ldmarsaglia on topic Problem homing with index
I don't know if you're still stuck with homing only with the switches or if you solved it closing the loop with the encoders but here's a solution I did on one of our machines (a Mazak lathe) to overcome the problem of homing with index using open loop configuration.

As Peter says, it's not possible at the moment (version 2.8) for LinuxCNC to reset the counters to zero with an index pulse if you're using an open loop configuration with steppers or servos. This is because the index pulse resets the Mesa encoder counters by hardware if I understand it right. 

But, I could find a simple way of solving this with pretty good results. Basically I bypassed the home switch on the final homing stage (when the homing uses the latch velocity) by means of detecting the joint.N.home-state of the joints on the machine. So my homing sequence is working only with home switchs, but when the time comes to do the final home switch tripping, I just use the index pulse to fool LCNC and get a more accurate homing. This is not as good as hardware counter reset, but it's working flawleslly (tested with a dial indicator). The best way to be sure the repetability is good is to use a really slow latching speed.

I hope this serves to anyone facing this problem. This shows again how HAL is amazing when it comes to adapt LCNC to basically anything.

Thanks as always to everyone!
Last edit: 5 years 1 month ago by ldmarsaglia. Reason: Bad typing

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5 years 1 month ago #219861 by hoffb77
Replied by hoffb77 on topic Problem homing with index

 Basically I bypassed the home switch on the final homing stage (when the homing uses the latch velocity) by means of detecting the joint.N.home-state of the joints on the machine. So my homing sequence is working only with home switchs, but when the time comes to do the final home switch tripping, I just use the index pulse to fool LCNC and get a more accurate homing. This is not as good as hardware counter reset, but it's working flawleslly (tested with a dial indicator). The best way to be sure the repetability is good is to use a really slow latching speed.
 
I never considered doing that. Thank you.

I lost my ability to home to index on one of my machines when I installed Mach BRC's. Reason being, I couldnt get velocity mode to play nice so I run position mode and let the PID on the drives run velocity control. I wasnt sure why I lost index homing until I read what Peter said earlier in this thread.

I love this place!

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5 years 1 month ago #219863 by hoffb77
Replied by hoffb77 on topic Problem homing with index

 There is new firmware and support in LinuxCNC 2.9
for homing to index on pure step/dir systems if you want to try
it. This does require a direct input for the stepgen index though
it can be shared with an encoder index say on a 7I85/7I85S
Will this require stepgen to be in velocity mode? I am currently running a machine in position mode and would like to get index homing back. Unless there's a way to get the Machdrive BRC's to work with stepgen in velocity mode. The drive PID fights with the velocity signal coming from the controller. I'm happy with the performance in position mode using the drive PID but no index homing.........

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5 years 1 month ago #219937 by Stigoe
Replied by Stigoe on topic Problem homing with index

I don't know if you're still stuck with homing only with the switches or if you solved it closing the loop with the encoders but here's a solution I did on one of our machines (a Mazak lathe) to overcome the problem of homing with index using open loop configuration.

But, I could find a simple way of solving this with pretty good results. Basically I bypassed the home switch on the final homing stage (when the homing uses the latch velocity) by means of detecting the joint.N.home-state of the joints on the machine. So my homing sequence is working only with home switchs, but when the time comes to do the final home switch tripping, I just use the index pulse to fool LCNC and get a more accurate homing. This is not as good as hardware counter reset, but it's working flawleslly (tested with a dial indicator). The best way to be sure the repetability is good is to use a really slow latching speed.
Sorry for the late reply and lack of updates on progress. Life in general and work has interfered with my chance to work on this problem.

No, I haven't solved the problem yet. Are you using index pulses from the motor or from linear scales? I'm using linear scales and the distance between index pulses, at least on my X-axis, is 100mm. Do you have some examples from the .ini and .hal-files on how you did it?

I have tried to add the PID component, but when I try to home X-axis, I get "joint 0 following error -0.018577 is greater than limit 0.0.17250". It moves the correct direction. When I move X-axis away from operator (without PID enabled), encoder count is negative.

From .ini (X-axis)
Code:
FERROR = 0.050 MIN_FERROR = 0.010 # MIN_LIMIT = -6.000 # MAX_LIMIT = 0.000001 MIN_LIMIT = -0.000001 MAX_LIMIT = 6.000 HOME_OFFSET = 0.500 #HOME_OFFSET = 0.025 HOME_SEARCH_VEL = -0.750 HOME_LATCH_VEL = 0.100 HOME_IGNORE_LIMITS = YES HOME_SEQUENCE = 0 HOME_USE_INDEX = YES HOME_FINAL_VEL = 0.200 #ENCODER FEEDBACK ENCODER_SCALE = 5080 P = 90 I = 0 D = 0 FF0 = 0 FF1 = 1 FF2 = 0.0005 BIAS = 0 DEADBAND = 0.0001 MAX_OUTPUT = 0

From .hal
Code:
net xindex-enable axis.0.index-enable <=> hm2_5i25.0.encoder.02.index-enable setp hm2_[HOSTMOT2](BOARD).0.stepgen.00.step_type 0 setp hm2_[HOSTMOT2](BOARD).0.stepgen.00.control-type 1 setp pid.x.Pgain [AXIS_0]P setp pid.x.Igain [AXIS_0]I setp pid.x.Dgain [AXIS_0]D setp pid.x.bias [AXIS_0]BIAS setp pid.x.FF0 [AXIS_0]FF0 setp pid.x.FF1 [AXIS_0]FF1 setp pid.x.FF2 [AXIS_0]FF2 setp pid.x.deadband [AXIS_0]DEADBAND setp pid.x.maxoutput [AXIS_0]MAX_OUTPUT setp pid.x.error-previous-target true setp pid.x.maxerror [AXIS_0]MAXERROR # ---Encoder feedback signals/setup--- setp hm2_5i25.0.encoder.02.counter-mode 0 setp hm2_5i25.0.encoder.02.filter 1 setp hm2_5i25.0.encoder.02.index-invert 0 setp hm2_5i25.0.encoder.02.index-mask 0 setp hm2_5i25.0.encoder.02.index-mask-invert 0 setp hm2_5i25.0.encoder.02.scale [AXIS_0]ENCODER_SCALE # ---closedloop stepper signals--- net x-pos-cmd <= axis.0.motor-pos-cmd net x-vel-cmd <= axis.0.joint-vel-cmd net x-output => hm2_5i25.0.stepgen.00.velocity-cmd #net x-pos-fb <= hm2_5i25.0.encoder.02.position #net x-pos-fb => axis.0.motor-pos-fb net x-enable <= axis.0.amp-enable-out net x-enable => hm2_5i25.0.stepgen.00.enable #net x-index-enable <=> pid.x.index-enable net x-enable => pid.x.enable #net x-pos-cmd => pid.x.command net x-pos-fb => pid.x.feedback net x-output <= pid.x.output #net xpos-cmd axis.0.motor-pos-cmd => hm2_[HOSTMOT2](BOARD).0.stepgen.00.position-cmd net x-pos-cmd axis.0.motor-pos-cmd => pid.x.command #net x-output => hm2_5i25.0.stepgen.00.position-cmd net x-pos-fb hm2_5i25.0.encoder.02.position => axis.0.motor-pos-fb #net xpos-fb hm2_[HOSTMOT2](BOARD).0.stepgen.00.position-fb => axis.0.motor-pos-fb

Feeling a bit lost right now... :-)

Stig

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5 years 1 month ago #219940 by PCW
Replied by PCW on topic Problem homing with index

 There is new firmware and support in LinuxCNC 2.9
for homing to index on pure step/dir systems if you want to try
it. This does require a direct input for the stepgen index though
it can be shared with an encoder index say on a 7I85/7I85S
Will this require stepgen to be in velocity mode? I am currently running a machine in position mode and would like to get index homing back. Unless there's a way to get the Machdrive BRC's to work with stepgen in velocity mode. The drive PID fights with the velocity signal coming from the controller. I'm happy with the performance in position mode using the drive PID but no index homing.........
 

Yes, the stepgen must be set for velocity mode, but this has nothing to do
with the drives mode (99.99% of step/dir operated drives use position mode)
(that is, the stepgen output is always a position signal)

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