Motors; Stepper Motors; Figure 6.6-1 - Stepper Motor Operation; Figure 6.6-2 - Four-Phase Stepper Motor - Newport ESP6000 User Manual

6.6

Motors

There are many different types of electrical motors, each one being best
suitable for certain kind of applications. The ESP6000 controller card
supports two of the most popular types: stepper motors and DC motors.
Another way to characterize motors is by the type of motion they provide.
The most common ones are rotary but in some applications, linear motors
are preferred. Though the ESP6000 controller card can drive both stepper
and DC linear motors, the standard stage family supports only rotary
motors.

6.6.1 Stepper Motors

The main characteristic of a stepper motor is that each motion cycle has a
number of stable positions. This means that, if current is applied to one of
its windings (called phases), the rotor will try to find one of these stable
points and stay there. In order to make a motion, another phase must be
energized which, in turn, will find a new stable point, thus making a small
incremental move - a step. Figure 6.6-1 shows the basics of a stepper motor.
Figure 6.6-1 — Stepper Motor Operation
When the winding is energized, the magnetic flux will turn the rotor until
the rotor and stator teeth line up. This is true if the rotor core is made of
soft iron. Regardless of the current polarity, the stator will try to pull-in the
closest rotor tooth.
But, if the rotor is a permanent magnet, depending on the current polarity,
the stator will pull or push the rotor tooth. This is a major distinction
between two different stepper motor technologies: variable reluctance and
permanent magnet motors. The variable reluctance motors are usually
small, low-cost, large-step angle stepper motors. The permanent magnet
technology is used for larger, high-precision motors.
The stepper motor advances to a new stable position by means of several
stator phases that have the teeth slightly offset from each other. To illus-
trate this, Figure 6.6-2 shows a stepper motor with four phases and, to make
it easier to follow, it is drawn in a linear fashion (as a linear stepper motor).
A B C D A
Figure 6.6-2 — Four-Phase Stepper Motor
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