patbob Wrote:
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> If I understand you right, the answer is yes, but
> why bother? You're halving the applied voltage to
> the windings that way and thereby limiting the
> possible torque. The microstepping controller
> chips (such as the AllegroMicro's 3967) already do
> an H-bridge with regulated directional current
> through the windings.. which is sort of the same
> thing without the voltage limit.
There are 2 reasons:
At first the dedicated stepper motor drivers are more expensive & are special ics which are not as commonly available.
The second reason is to try to do microstepping in software for better repeatability and accuracy. The way these stepper motor ics do microstepping induces some error in-between steps meaning that for example 3/16 steps aren't 0.1875 but rather something like 0.175 - 0.2 steps depending on the direction and how far the next full step is.
A lot of higher-end microcontrollers already include several high resolution d/a converters and would offer the possibility to compensate for these errors. (This could be relatively easy calibrated on the machine using calipers to measure the distance from a reference point)
On the voltage: Since this would have to be designed from the ground up anyway this could be taken into consideration from the start meaning that we would simply use a higher power supply voltage in the first place.
The idea is to think of the steppers more like 2 (or 4) phase synchronous motors rather than the traditional way. From what i've read 3 phase synchronous motor controllers use mosfets driven by a combination of frequency and amplitude modulation to archive continuous traction control.
If you think about it stepper motors are the same thing as 3 phase permanent magnet motors only that high power electrical engineering is considered something different. But it is not, there are steppers which have more beef than some small scale ac motors...