5.6 Motors
There are many different types of electrical motors, each one being
best suitable for certain kind of applications. The ESP300 supports
two of the most popular types: stepper motors and DC motors.
Other technologies like interferometry or halography can be used but
they are significantly more expansive and need more space.
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.
5.6.1 Stepper Motors
The main characteristic of a stepper motor is that each motion cycle
has a number of stable position. 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 5.31) shows the basics of a stepper motor. When the winding
is energized, the magnetic flux will turn the rotor until the rotor and
stator teeth line up. This true of the rotor core is made out of soft iron.
Regardless of the current polarity, the stator will try to pull-in the
closest rotor tooth.
Figure 5.31: Stepper Motor Operation
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.
5-26 Section 5 – Motion Control Tutorial
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