Kirk Wallace wrote: > A while back I played with a KBIC speed controller which demonstrated > fairly good torque at high and low speeds. I was curious about how a PWM > amp would do, so I set up a Pico amp to a parport PWM signal at about > 25kHz and was surprised to find that low end torque was much less. I > thought the PWM frequency might have had something to do with the torque > issue, so I made a similar setup with a 50kHz PWM signal from a Pico PWM > controller and got similar results. Then I got to thinking, the Pico amp > is a PWM to voltage converter. The motor torque will be the torque for > the voltage that the motor happens to be driven with at the time. I > thought the KBIC had feed-back during the zero crossing period ,but I > didn't realize how important it is. So, in order for the PWM amp to have > good torque and speed control, feedback needs to be set up. Does this > seem correct? > Yes, you have it exactly. My PWM servo amps are truly PWM => voltage output, with no compensation for the motor resistance or back-EMF. You could, of course, use some kind of feedback. If you have a spindle encoder, you could make HAL read the encoder velocity and add a correction to the PWM output.
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