Festo Контроллер двигателя SEC-ST - Manual (Page 11)

Contents and general instructions
IX
Festo SEC−ST−48−6−P01−EN en 0606c
General information on stepping motor systems
Description
Stepping motors are a special type of synchronous motor
triggered through electrical pulses from a required control
unit. Here, a pulse always corresponds to the same rotational
angle. This permits positioning without acknowledgement.
Due to their "digital" rotation, stepping motors are used as
switch mechanisms and in positioning technology. It should
be noted that the control system does not receive any kind of
acknowledgement that the motor has, in fact, performed its
step.
Accuracy and resolution
The step angle depends on the structural form; for the two−
phase Festo stepping motors type MTR−ST, the angle is 1.8°
(+/−5%) in full step. A single step takes place when the two
coils receive full alternating current. Here, the stepping motor
performs a step of 1.8° each time the current to the coils alĆ
ternates.
But it is also possible to supply the two coils simultaneously
with different current shares. The result is a 1/2, 1/4, 1/5,
1/8, 1/10 or 1/32 of a step, depending on the current share.
This allows considerable refinement in the maximum resoluĆ
tion of positions to which a stepping motor can run.
The smallest incremental path (resolution) on a positioning
axis is determined by the motor’s step angle (number of
steps per revolution) and the feed constant of the positioning
axis (determined by the diameter of the input pinion or the
slope of the spindle).