If external forces try to move the rotor (Figure 5.40), the magnetic
flux will fight back. The more teeth misalignment exists, the larger
the generated torque.
Figure 5.39: Single Phase Energization
The torque diagram versus teeth misalignment is shown in (
Figure
5.42
). The maximum torque is obtained at one quarter of the tooth
spacing, which is equivalent to one full step.
Figure 5.40: External Force Applied
If the misalignment keeps increasing, at some point, the torque peaks
and then starts diminishing again such that, when the stator is exactly
between the rotor teeth, the torque becomes zero again (
Figure 5.41).
This is an unstable point and any misalignment or external force will
cause the motor to move one way or another. Jumping from one stable
point to another is called missing steps, one of the most critiqued
characteristics of stepper motors.
Figure 5.41: Unstable Point
Torque
Figure 5.42: Torque and Tooth Alignment
5-30 Section 5 – Motion Control Tutorial
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