Xmega 256a3u, stepper driver using a rotary encoder

sq2eer · Joined: 16 Aug 2011 Posts: 7 Location: Pelplin

Hello, I would like to ask for help in writing a program that controls a stepper motor using a rotary encoder.
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Compiler version :2.0.8.3
Compiler build :2.0.8.3.005
IDE version :2.0.8.3.003
Serial number Mad

x-xxxx-xxxxx
Windows OS :Windows 7 Ultimate
Company :
Owner :Jacek
Windows dir :C:\Windows
App data dir :C:\Users\Jacek\AppData\Roaming\MCS Electronics
System dir :C:\Windows\system32

the microcontroller is xmega 256a3u, encoder configuration

MWS · Joined: 22 Aug 2009 Posts: 2262

The video explains it quite well, however the stepper functionality is encapsulated within a lib called 'AccelStepper', this functionality you have to implement yourself.
For this purpose I suggest to use a timer interrupt, to compare actual with set position and put out step/en/dir.

Code for stepper control is short and can be placed directly into the interrupt service routine.
Motor speed can be controlled by TOP of timer (in combination with config timer CLEAR_TIMER), alternatively a soft timer, as you've tried to implement, is thinkable.
Controlling the interrupt speed itself will be likely faster, will eat up less power and run smoother than creating an 1/00s timer value and updating steppers in the main loop.
One more (power hungry) way is a fast timer interrupt, wherein a soft timer works, speed is controlled via this soft timer and stepper is updated also from therein, this would be the approach if more steppers need to be taken care of. Speed of the timer decides then over max speed of the motors.

The whole thing will become a bit more complicated if you want to have acceleration ramps, however for this simple experiment with one motor you can likely omit ramps and control directly via timer ISR.

EDC · Joined: 26 Mar 2014 Posts: 971

Cause me and Jacek we are from Poland then we know each other from polish forums.

Jacek`s goal was to use Xmegas bulit in hardware quadrature encoders decoding with using event system.
This gives result in the 16bit timer/counter 0-65535.

Jacek want to control motor with the encoder into the left, stop and right manually for test Very Happy

This is not very complicated when first turn it right because value grow from zero->65535. Difference always can be measured by substract prev value from actual. But when first turn is into the left or we overflow timer turning encoder backward then from 0 we got 65535. This was some challenge Very Happy

So yesterday, after quick scratch my head I came with this simple solution (for test only, without any interrupts).

sq2eer · Joined: 16 Aug 2011 Posts: 7 Location: Pelplin

Hello everyone, this is a test control of the Z axis from the lathe in manual mode. The video shows how nicely the motor reacts to turning the encoder https://www.youtube.com/watch?v=uV2L4_Cck_I then I had not yet set the timer division by four (four edges of channels a and b) so the motor did four times as many revolutions as the encoder at the end of the movie, I exaggerated with shooting and a driver error popped up now, when I give thanks, the reading from the encoder for four is very good and all thanks to Bartek EDC, I greet everyone Jacek.

MWS · Joined: 22 Aug 2009 Posts: 2262

hgrueneis · Joined: 04 Apr 2009 Posts: 902 Location: A-4786 Brunnenthal

Just my input on ramps for steppers. I usually use a percentage calculation of the Distance to be accomplished with max. acceleration and start out frequency as limits. This works quite well and does not need a "FUZZY License". Could also be implemented with rotary sensor.
Best regards
Hubert

sq2eer · Joined: 16 Aug 2011 Posts: 7 Location: Pelplin

Hello

MWS - we have such a coordinate system in lathes
as EDC wrote earlier this is a test program and needs some fine-tuning.

hgrueneis - can you explain it with some example.

Regards Jacek.

MWS · Joined: 22 Aug 2009 Posts: 2262