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CBeif.1
CBeif.1
Associate II
April 23, 2020
Question

I am trying to do laser engraving with a POWERSTEP01. But I get high frequency oscillations on my motor.

  • April 23, 2020
  • 14 replies
  • 6289 views

0693W000000WMx4QAG.jpg

I am in current control mode, and the stepper motor is using about 3 amps.

Is there anything I can do to reduce these oscillations.

Also note that the white line is about 0.010" thick.

I am using x16 microstepping, and I currently have 1600 microsteps per inch of resolution.

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14 replies

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chaaalyy
chaaalyy
Senior II
April 30, 2020

So it moves 4 steps (or 8 half steps...), until it reaches the same state again. If you divide this further to microstepping, let´s say from step 1 to 1 1/2: Just Q3 is switched from on to off state. Now say not just "off", say 50% (just to make it easy) and it moves from 1 to 1 1/4. Problem: we work in a digital world here and the only way to make this conversion is a pwm modulation...

CBeif.1
CBeif.1Author
Associate II
April 30, 2020

LoSpeedOpt is off, but from what I read, its for voltage mode only. (I'm in current mode)

I am using my own hardware, we developed a motherboard with 3 of these chips on the board.

chaaalyy
chaaalyy
Senior II
April 30, 2020

Ouch...

The controller mcu itself ? A stm32 mcu ? Then you have good chances to get some st examples up and running. But be aware: the coding style is ... let´s say "a little bit weird"... I used them in the beginning to play around more comfortably with the parameter settings. Therefore they aren´t too bad ;)

You can find it here:

https://www.st.com/content/st_com/en/products/embedded-software/mcu-mpu-embedded-software/stm32-embedded-software/stm32cube-expansion-packages/x-cube-spn3.html

If you use custom hardware: on the ihm03a1 board, for current sensing are 0.100 Ohm resistors used. So if you have different ones, recalculate the Tval´s for your motor ! (if i remember correctly, for 3A it should be TvalHold 140; TvalAcc and Dec 300 and TvalRun at 280 on the ihm03a1)... I used slightly lower (around 0.2A less) values for TvalRun than the standard 300, because the motor went a little bit hot, when running all the time at 3A ...

chaaalyy
chaaalyy
Senior II
April 30, 2020

Also a good explanation (more in-depth, even when it looks complicated at 1st sight...) :

https://www.researchgate.net/publication/3219650_Mixed-Mode_PWM_for_High-Performance_Stepping_Motors

The figures definitely help to understand the scope readings (but anyway they don´t explain the strange "slope"...)

CBeif.1
CBeif.1Author
Associate II
May 15, 2020

I attached an optical encoder to my stepper motor, and then captured my step pin, and the quadrature data using high speed logic analyzer,

I moved a distance of 6 inches in this plot.

I then plotted the difference in microsteps between my microstep position and encoder position (translated to microsteps).

Does this look normal? Is this normal stepper motor resonance? For x16 microstepping in current mode, I am off from -2 to 7 microsteps.

with a very high frequency oscillation. This definitely explains the oscillations I see in the laser engraving.

0693W000001cMtcQAE.png

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