Mesa 7i96s PID Spindle Setup
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11 Mar 2025 15:36 - 11 Mar 2025 15:52 #323685
by scda
Mesa 7i96s PID Spindle Setup was created by scda
Hi all,
I am working on a weiler cnc lathe retrofit. So far it works well, the only thing left ist the PID tuning of the spindle speed.
The spindle also works without PID but the offset to the actual speed varies quite a bit (not linear), I was hoping to correct this with a PID loop.
VFD: Huanyang with analog voltage input (0-10V).
Currently I am trying to figure out how to implenent the PID setup for this.
How can I scale the PID output to 0-10V (or 0-4600 rpm) ? Currently my PID output can be negative and so the pwmgen.value of the Mesa7i96s spindle is negative which does not work for my setup. I feed the PID ouput to the scaled pwmgen input.
I think the system has to adjust the current value sent to the pwmgen.value just below and above the current setpoint in order to adjust for velocity offset. I was thinking of using the sum function (which kind of works but also does not really correct the non-linearity) but I think there must be an easier way...
Cheers,
David
I am working on a weiler cnc lathe retrofit. So far it works well, the only thing left ist the PID tuning of the spindle speed.
The spindle also works without PID but the offset to the actual speed varies quite a bit (not linear), I was hoping to correct this with a PID loop.
VFD: Huanyang with analog voltage input (0-10V).
Currently I am trying to figure out how to implenent the PID setup for this.
How can I scale the PID output to 0-10V (or 0-4600 rpm) ? Currently my PID output can be negative and so the pwmgen.value of the Mesa7i96s spindle is negative which does not work for my setup. I feed the PID ouput to the scaled pwmgen input.
I think the system has to adjust the current value sent to the pwmgen.value just below and above the current setpoint in order to adjust for velocity offset. I was thinking of using the sum function (which kind of works but also does not really correct the non-linearity) but I think there must be an easier way...
Cheers,
David
Last edit: 11 Mar 2025 15:52 by scda.
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11 Mar 2025 16:18 #323686
by PCW
Replied by PCW on topic Mesa 7i96s PID Spindle Setup
Normally this is just done with normal PID,
with FF0 set to 1 and PWM scale set to RPM at 10V
PID would mainly be for Keeping constant RPM vs load.
If you have major non-linearities, these can be corrected with
the lincurve component.
with FF0 set to 1 and PWM scale set to RPM at 10V
PID would mainly be for Keeping constant RPM vs load.
If you have major non-linearities, these can be corrected with
the lincurve component.
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11 Mar 2025 16:42 - 11 Mar 2025 16:54 #323689
by scda
Replied by scda on topic Mesa 7i96s PID Spindle Setup
Thanks. Yeah I think the main problem was that I have set the P value too high (above 2 is too much --> runaway). So the system seems to be working now.
- I set a non-zero value to the DEADBAND setting (10)
- I am using a low pass filter on the encoder feedback signal before feeding it to the PID loop
- I use a low P value to stop the system "from running away"
#======================================================================================
# Spindle0
#======================================================================================
setp pid.s.Pgain [SPINDLE_0]P
setp pid.s.Igain [SPINDLE_0]I
setp pid.s.Dgain [SPINDLE_0]D
setp pid.s.bias [SPINDLE_0]BIAS
setp pid.s.FF0 [SPINDLE_0]FF0
setp pid.s.FF1 [SPINDLE_0]FF1
setp pid.s.FF2 [SPINDLE_0]FF2
setp pid.s.deadband [SPINDLE_0]DEADBAND
setp pid.s.maxoutput [SPINDLE_0]MAX_OUTPUT
setp pid.s.error-previous-target true
setp hm2_7i96s.0.pwmgen.00.enable 1
setp hm2_7i96s.0.pwmgen.00.scale [SPINDLE_0]MAX_RPM
setp lowpass.0.gain [SPINDLE_0]LOWPASS_GAIN
setp hm2_7i96s.0.encoder.04.counter-mode 0
setp hm2_7i96s.0.encoder.04.filter 1
setp hm2_7i96s.0.encoder.04.index-invert 0
setp hm2_7i96s.0.encoder.04.index-mask 0
setp hm2_7i96s.0.encoder.04.index-mask-invert 0
setp hm2_7i96s.0.encoder.04.scale [SPINDLE_0]ENCODER_SCALE
net spindle-index-enable => pid.s.index-enable
net spindle-enable => pid.s.enable
net spindle-vel-cmd-rpm => pid.s.command
net spindle-vel-fb-rpm => pid.s.feedback
net spindle-output <= pid.s.output => hm2_7i96s.0.pwmgen.00.value
net spindle-vel-cmd-rps <= spindle.0.speed-out-rps
net spindle-vel-cmd-rps-abs <= spindle.0.speed-out-rps-abs
net spindle-vel-cmd-rpm <= spindle.0.speed-out
net spindle-vel-cmd-rpm-abs <= spindle.0.speed-out-abs
net spindle-enable <= spindle.0.on # => hm2_7i96s.0.pwmgen.00.enable
net spindle-cw <= spindle.0.forward => hm2_7i96s.0.outm.00.out-04
net spindle-ccw <= spindle.0.reverse => hm2_7i96s.0.outm.00.out-05
net spindle-revs => spindle.0.revs
net spindle-at-speed => spindle.0.at-speed
net spindle-vel-fb-rps => spindle.0.speed-in <= hm2_7i96s.0.encoder.04.velocity
net spindle-vel-fb-rpm_raw => hm2_7i96s.0.encoder.04.velocity-rpm => lowpass.0.in
net spindle-vel-fb-rpm <= lowpass.0.out
net spindle-index-enable <=> spindle.0.index-enable
Last edit: 11 Mar 2025 16:54 by scda.
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11 Mar 2025 17:16 #323692
by PCW
Replied by PCW on topic Mesa 7i96s PID Spindle Setup
You should never get a runaway, but you will get oscillations with a too high PID value
To avoid a runaway around 0 speed where a negative PID output may occur might require
some hal magic, say using the PID output sign to run the VFD direction signal or forcing the
PWM value to 0 when the PID output is negative.
To avoid a runaway around 0 speed where a negative PID output may occur might require
some hal magic, say using the PID output sign to run the VFD direction signal or forcing the
PWM value to 0 when the PID output is negative.
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