Question on Speed Control vs Torque Control

Thread Starter

Xavier Pacheco Paulino

Joined Oct 21, 2015
728
I'm controlling a Permanent Magnet DC motor with PWM for a treadmill. I'm using a reflective sensor with 6 pulses per rev to get a speed feedback. So I'm actually doing "speed control" directly, but not "torque control". So I have two specific questions:

1- Do I need direct torque control for this application by measuring the current? Or a combination of speed and torque control where a cascade PI is needed?

2- Do I strictly need to know the DC motor parameters (R, L, K, J, B) in order to do speed control?

It's okay I can vary the speed by changing the duty cycle. It works. But, beyond a simple analogy of pulse-width-modulation, I know it should be a whole lot more complicated than that.
 

MaxHeadRoom

Joined Jul 18, 2013
24,976
Most T.M. controllers such as the MC60 and MC2100 just use a simple motor current feedback monitoring drop across a series resistor. Any opto is usually used for display purposes.
I have been experimenting with simple speed control by constantly monitoring pulses and correcting this way.
Max.
 

Georacer

Joined Nov 25, 2009
5,182
I'd say that measuring current in a DC motor is kinda equivalent to the position derivative, so you could use this measurement if you want to do the "D" part of a PID controller.
But that's largely superfluous for your application.
 

Thread Starter

Xavier Pacheco Paulino

Joined Oct 21, 2015
728
What about the motor parameters (R, L, K, J, B)? Are they relevant in this application? I think they're not. In order to take those parameters into account I would also have to take into account the whole system characterisitc, i.e, belt, mechanical characteristic, etc , not only the motor, if I would like to know the system transfer function.
 
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