Two reasons for microstepping; suppress resonance and increase resolution.
1) Suppress Resonance:
A step motor is a first-order, mechanically resonant system just like a mass-spring. It is ready, willing and eager to resonate given any provocation just like a weight attached to a coiled spring suspended from a ceiling. Left alone, the weight will be still; pull down on it, then let go and it will oscillate up and down for a long time.
The amount of energy invested in oscillation is the old Mass times Velocity squared thing. At 10 microsteps the "tweak" applied to the mass is 1/10th as large as for a full step so the energy will be only 1/00th compared to a full step. The motor turns with almost no perceptable vibration.
2) Increase resolution:
Most step motors have a "+/- 5% non-accumulative tolerance" specification. This means any given step will be 1.8 degrees, give or take +/- 0.09 degrees.
Put another way, any given step will fall within a 0.18 degree error range. 360 degrees (1 revolution) divided by 0.18 degrees gives 2,000 radial locations, meaning as a transducer, the motor's native accuracy is 1 part out of 2,000.
There are however only 200 full steps per revolution and this means accuracy is 10 times better than resolution; you are not getting your money's worth because this accuracy gets under-utilized.
At 10 microsteps, resolution equals the motor's accuracy. Any microstep resolution more than 10 gets you "empty resolution" just like having a digital caliper that displays 1 millionth of an inch but is accurate to only .001". The extra digits look pretty but mean nothing.
Mariss  |