7i95T spindle control via Modbus RS485 and SPINX1A

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21 Oct 2024 10:40 #312731 by vmihalca
I was able to start the spindle, direction works fine, but I have a problem with the speed.
My lathe max speed is 3000 rpm, when I set this speed, the pwm value is 0.999 so almost 1, which I think is correct.
When I set 700rpm, I get 0.23 on the pwm.value, which is also correct, however, the voltage measured between SP- and SPV is 5.8V so it spins way faster than it should.
How can I scale the value of the potentiometer so that between SP- and SPV I get the correct voltage.
Between SP- and SP+ I have 10.75V so this would mean 3000 rpm, so for 1500rpm, between SP- and SPV, I should have 5.37volts or smth like this.

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21 Oct 2024 14:29 #312753 by PCW
Normally, you would set the PWM scale to the spindle RPM
at SPV+ (so if the spindle RPM is 3000 at 10V, you would set
the PWM scale to 3225 (3000*10.75/10)

Then the PWM value is set directly in RPM.

If you have issues with non-linearity, check
that SPV+ is constant at different spindle settings.
Other possible causes of non-linearity are PID settings
or incorrect PWM frequency

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21 Oct 2024 15:52 #312765 by vmihalca
pwm frequency is set to 5000
I've set the scale to 3225, it doesn't seem to make any difference.
I was not using PID for spindle speed, I was using lincurve.
However, I think that as long as PWM value is correct, the problem is somehwere else. I think the PWM value should go between 0 and 1, at max speed its 0.999, at 1500 rpm is almost 0.5, which seems correct to me.

I don't know what else to check :/

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21 Oct 2024 16:09 #312769 by PCW
Is this with a SPINX1A?

The SPINX1A should have better than 1% linearity

Does the 10,75V vary?
 

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21 Oct 2024 16:23 #312772 by vmihalca
Yes its SPINX1A, the 10.75 voltage comes from the VFD, I have a delta VFD,and I have wired this way:
+10v -> spinx SP+
ACM -> spinx SP-
AVI -> spinx SPV

Between SP+ and SP-, I measure 10.75

If I reduce the RPM at 100 rpm, the pwmgen value is correct, but the voltage between SPV and SP- is still 5.45

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21 Oct 2024 16:47 #312773 by PCW
That sounds like either the SPINX1A is damaged or perhaps the wiring is incorrect.

I would verify SPINX1 operation by running SPV+ and SPV- from 5V and GND from the
7I95 to verify its operation independent of the VFD

Also SPINX1A PWM frequency should be 20 KHz (though this should just affect ripple)

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22 Oct 2024 11:48 #312843 by vmihalca
The problem was that I had pwmgen.00.offset-mode set to 1
Once I set this to zero, now the voltage is correct.
I've set the pwm_frequency to 5000 initially, then after your last comment, I increased it to 20000, but didn't noticed any difference.
Not sure what this does exactly and why would it matter if its higher.

Thanks for your help so far!

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22 Oct 2024 14:55 #312865 by PCW
The SPINX1A has a 2 pole ~ 100 Hz RC filter to average the PWM signal.

Too low a PWM frequency will let noticeable ripple through the filter.
Too high a PWM frequency will result in poor linearity, (as the switcing
time of the OPTO becomes a significant part of the cycle time)

For the SPINX1A, 20 KHz is about the optimum compromise between ripple and linearity.
The following user(s) said Thank You: vmihalca

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