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vedder.se forums • FOC encoder position control
Page 1 of 1

FOC encoder position control

Posted: 07 Jul 2016, 12:57
by pf26

Re: FOC encoder position control

Posted: 08 Jul 2016, 08:47
by rew
For velocity you're using the velocity of the actuator, instead of hte derivative of the position error, right?

For the standard: "look how well it's working!" step response test, there is no difference. But once you have a dynamic target, that doesn't hold up, Wouldn't it be better to take the difference of the target-velocyt and the actuator velocity?

Simone giertz had a "slave robot" as her latest video. I'm under time-pressure right now, so here is a link to one of her videos. Find her latest video yourself... https://www.youtube.com/watch?v=WcW70-6eQcY

In the case of dynamic targets, like with her slave robots, also taking the average of the target positions speed would help get the same response to a step as with a "step plus linear movement".

Re: FOC encoder position control

Posted: 08 Jul 2016, 17:17
by pf26
Yes, velocity is the velocity of the motor or the derivative of the encoder count (expressed in ERPM).
From the first document I mentionned, there seems to be a difference between PID and PIV even for static target step response (possibly they use a different loop for velocity control and then for position (probably slower) - I used the same loop for simplicity.

I think just taking the difference in velocity between actual and target could accumulate errors that could never be corrected.

As for the dynamic target, I changed the pos-pid-set command: Now I send a "next or future" target along with the position target. So that the control function automatically extrapolates linearly the position target, up to a fixed number of milliseconds.
Ideally, we should make this pos-pid-set with several parameters: position, speed, acceleration, and possibly max time of extrapolation. I think it will be required for robots/printers using trajectory planners.

Re: FOC encoder position control

Posted: 10 Oct 2018, 18:41
by raess
@pf26 can you post complete changes? For example: how is 'v_array_pointer' defined ... it's used without being defined before

Would be very interested to test this change!

Thanks
Robin