GS-C200 datasheet(29/31 Pages) STMICROELECTRONICS

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Figure 20. Typical Single Step Response.

ELECTRONIC DAMPING

Any stepper motor system when driven at very low

stepping rates, has an oscillatory step response as

shown in fig. 20.

This oscillatory behaviour is due to fact that the

motor reaches the stall position after each excita-

tion change through an acceleration and a succes-

sive deceleration. This causes the motor shaft to

rotate with jumps instead of uniform motion.

Another consequence of this oscillatory single step

response is that the long system settling time can

cause mechanical stresses to the driven load.

A second tedious effect is the enhancement of the

rotor oscillation when the driving step rate ap-

proaches the natural resonance frequency of the

motor. If the step rate is lower than this frequency,

the motor is behind the equilibrium position and the

velocity is near to zero when the next excitation

change occurs.

When the step rate is increased to a value close to

the natural resonance frequency, an increase of the

oscillations also occurs, and as soon as the oscilla-

tion amplitude exceeds the step amplitude, the

corrispondence between the rotor position and the

excitation sequence is lost and any subsequent

rotor movement is erratic as shown in fig. 21.

A simple method to reduce the oscillations problem

is to use the half step driving, but this also limits the

maximum speed of the system.

When this limitation is not acceptable, other two

basic techniques may be adopted to damp the

system oscillations:

A mechanical damper

An electronic damping circuit.

Figure 21. Slow Speed Step Response.

GS-C200 / GS-C200S

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