On 04/10/2013 07:18 AM, Javier Ros wrote: > Is apparently a stepper motor that is controlled as a brushless. > Essentially a stepper is a brushless. This needs a encoder, probably one > with a index pulse correctly positioned, > so that the electronics can compute the switching accurately. > > This means, even if the control of the drive looks like a STEP DIR control, > internally there are position and current loops, theoretically such a drive > could offer, velocity and > current control (I've not checked for the above reference). > > The only limitations seem to be related to control at hih rpms, performance > degrades in comparison with brushless. I would say that this is related to > the higher pole count of the steeper, If you were to design one of these from the ground up, since position would be verified from a 10,000 step encoder, and the stepper would be run as a type of servo motor, the stepper driver would function much differently. It would generate commutation from the encoder, then it would drive a current into one coil to draw the motor towards the commanded position. PID would decide how hard to hit the motor by the difference between commanded position and current encoder position. Since this works like a servo and not a stepper with feedback, the stepper motor could be designed with less steps per rev. less steps per revolution would require less soil current reversals, and would allow the motor to step faster. If a 1mH coil standard stepper could be driven to 3000 RPM, one with 100 steps per rev instead of 200 could be driven at 6000 RPM. One with 50 steps per rev could be driven at 12000 RPM. The control circuit would have to do some tricky math to keep cogging to a minimum, but it's likely possible to make a very fast but still accurate stepper system this way.
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