G76 doesn´t work right

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9 years 4 days ago #100929 by Skyline
G76 doesn´t work right was created by Skyline
Hey Guys,

I hope i´m at the right "adress" here for my topic.
Since weeks i can not solve my problem with G76 threading.

The problem is: Every cut, is a bit more behind or in front of the cut he did before. But all cuts are parallel. Here´s a pic:


So there has to be a problem to start every cut at the same point.
I tried a lot the last weeks and i´m 99% sure, it´s a (user-)software problem.

I use china components with a simple DB25-1205 breakout board.
My spindle encoder is a photocell at the gear which is directly at the spindle. He has a 0V/5V clear "digital" signal.
I use a 60° thread cuter.

Here´s a example of my code:

%
(GEWINDE TEST)
M3
G0X19Z5
G76 P3 Z-5 I-1 J0.05 R1 K0.8 Q0
G0X16Z180
M5
%

My HAL:
Code:
# Generated by stepconf 1.1 at Sat Sep 23 13:13:57 2017 # Änderungen an dieser Datei werden beim nächsten # Aufruf von stepconf überschrieben. loadrt trivkins loadrt [EMCMOT]EMCMOT base_period_nsec=[EMCMOT]BASE_PERIOD servo_period_nsec=[EMCMOT]SERVO_PERIOD num_joints=[TRAJ]AXES loadrt hal_parport cfg="0 out" loadrt stepgen step_type=0,0 loadrt encoder num_chan=1 loadrt abs count=1 loadrt scale count=1 loadrt lowpass count=1 loadrt pwmgen output_type=1 addf parport.0.read base-thread addf stepgen.make-pulses base-thread addf encoder.update-counters base-thread addf pwmgen.make-pulses base-thread addf parport.0.write base-thread addf stepgen.capture-position servo-thread addf encoder.capture-position servo-thread addf motion-command-handler servo-thread addf motion-controller servo-thread addf stepgen.update-freq servo-thread addf pwmgen.update servo-thread addf abs.0 servo-thread addf scale.0 servo-thread addf lowpass.0 servo-thread net spindle-cmd-rpm => pwmgen.0.value net spindle-on <= motion.spindle-on => pwmgen.0.enable net spindle-pwm <= pwmgen.0.pwm setp pwmgen.0.pwm-freq 1000.0 setp pwmgen.0.scale 624.0 setp pwmgen.0.offset 0.0128205128205 setp pwmgen.0.dither-pwm true net spindle-cmd-rpm <= motion.spindle-speed-out net spindle-cmd-rpm-abs <= motion.spindle-speed-out-abs net spindle-cmd-rps <= motion.spindle-speed-out-rps net spindle-cmd-rps-abs <= motion.spindle-speed-out-rps-abs net spindle-at-speed => motion.spindle-at-speed setp encoder.0.position-scale 62.000000 setp encoder.0.counter-mode 1 net spindle-position encoder.0.position => motion.spindle-revs net spindle-velocity-feedback-rps encoder.0.velocity => motion.spindle-speed-in net spindle-index-enable encoder.0.index-enable <=> motion.spindle-index-enable net spindle-phase-a encoder.0.phase-A net spindle-phase-b encoder.0.phase-B net spindle-phase-a encoder.0.phase-Z setp parport.0.pin-01-out-invert 1 net zstep => parport.0.pin-01-out setp parport.0.pin-02-out-invert 1 net xenable => parport.0.pin-02-out setp parport.0.pin-03-out-invert 1 net xdir => parport.0.pin-03-out net zdir => parport.0.pin-07-out setp parport.0.pin-08-out-invert 1 net xstep => parport.0.pin-08-out setp parport.0.pin-14-out-invert 1 net xenable => parport.0.pin-14-out net spindle-pwm => parport.0.pin-16-out net max-x <= parport.0.pin-10-in-not net min-z <= parport.0.pin-11-in-not net spindle-phase-a <= parport.0.pin-12-in net estop-ext <= parport.0.pin-15-in setp stepgen.0.position-scale [AXIS_0]SCALE setp stepgen.0.steplen 1 setp stepgen.0.stepspace 1 setp stepgen.0.dirhold 22650 setp stepgen.0.dirsetup 22650 setp stepgen.0.maxaccel [AXIS_0]STEPGEN_MAXACCEL net xpos-cmd axis.0.motor-pos-cmd => stepgen.0.position-cmd net xpos-fb stepgen.0.position-fb => axis.0.motor-pos-fb net xstep <= stepgen.0.step net xdir <= stepgen.0.dir net xenable axis.0.amp-enable-out => stepgen.0.enable net max-x => axis.0.pos-lim-sw-in setp stepgen.1.position-scale [AXIS_2]SCALE setp stepgen.1.steplen 1 setp stepgen.1.stepspace 1 setp stepgen.1.dirhold 22650 setp stepgen.1.dirsetup 22650 setp stepgen.1.maxaccel [AXIS_2]STEPGEN_MAXACCEL net zpos-cmd axis.2.motor-pos-cmd => stepgen.1.position-cmd net zpos-fb stepgen.1.position-fb => axis.2.motor-pos-fb net zstep <= stepgen.1.step net zdir <= stepgen.1.dir net zenable axis.2.amp-enable-out => stepgen.1.enable net min-z => axis.2.neg-lim-sw-in net estop-out <= iocontrol.0.user-enable-out net estop-ext => iocontrol.0.emc-enable-in loadusr -W hal_manualtoolchange net tool-change iocontrol.0.tool-change => hal_manualtoolchange.change net tool-changed iocontrol.0.tool-changed <= hal_manualtoolchange.changed net tool-number iocontrol.0.tool-prep-number => hal_manualtoolchange.number net tool-prepare-loopback iocontrol.0.tool-prepare => iocontrol.0.tool-prepared

You have any idea where´s my problem?

I hope you understand everything I write. If you need more information, please write what you need.
I´m glade about every help :)

Best regards
Matthias
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9 years 4 days ago - 9 years 4 days ago #100931 by PCW
Replied by PCW on topic G76 doesn´t work right
You can only use encoder A for index if you have 1 pulse per turn
(you seem to have 62)

This means every threading pass you could start randomly at any of the 62 shaft
positions.

I do think its arguable that the encoder component should have the option of generating a simulated
index signal by dividing the count. This would not work quite as well as a real index signal
( The index position would be forgotten when LinuxCNC was shut down )
but would allow threading with a single detector having multiple counts per turn
Last edit: 9 years 4 days ago by PCW.

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9 years 4 days ago #100932 by Skyline
Replied by Skyline on topic G76 doesn´t work right
Oh, okay. How do i have to change it?

net spindle-phase-a encoder.0.phase-Z ?

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9 years 4 days ago #100933 by PCW
Replied by PCW on topic G76 doesn´t work right
You would need to add a 1 pulse per rev detector and wire it to phase-Z

You could retain the 62 PPR A signal if you have enough parallel port inputs available
if not you would wire the 1 PPR signal to A and Z as you have now

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9 years 4 days ago #100935 by Skyline
Replied by Skyline on topic G76 doesn´t work right
Okay, so I need a 1PPR at Z, so it would work. If 62 PPR would stay at A, what would it do?
Is there any option to use my 62 PPR without 1 PPR and it still stays 62 PPR? Because 1 PPR is pretty inaccurate?
I´ve got the feeling, i don´t understand something basicaly how it works.

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9 years 4 days ago - 9 years 4 days ago #100936 by PCW
Replied by PCW on topic G76 doesn´t work right
There are at least three main options here:

1. One wire 1PPR threading: simple but poor tracking if the spindle speed varies
2. Two wire ( A and Z ) multiple PPR threading: better tracking if spindle speed varies
3. Three wire ( A,B,Z ) multiple PPR threading, good tracking and reversable ( for tapping etc )

Note for the 1 PPR option, you must use the encoders "position-interpolated" rather than "position"
pin so that the Z axis moves smoothly rather than stepping every spindle count
Last edit: 9 years 4 days ago by PCW.
The following user(s) said Thank You: andypugh

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