Figure 6.6-12 - Torque And Tooth Alignment - Newport ESP6000 User Manual

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.
A diagram of torque phasing versus teeth misalignment is shown in Figure
6.6-12. The maximum torque is obtained at one quarter of the tooth spac-
ing, which is equivalent to one full step.
Torque
Figure 6.6-12 — Torque and Tooth Alignment
This torque diagram is accurate even when the motor is driven with half-,
mini-, or micro-steps. The maximum torque is still one full step away from
the stable (desired) position. When mini- and micro-stepping motors are
used in open-loop applications there is inherent error, but advanced
controllers like the ESP6000 can control the stepper motors with closed
loop operation to eliminate this problem.
Advantages
Stepper motors are primarily intended to be used for low-cost, micropro-
cessor controlled positioning applications. Due to some of their inherent
characteristics, they are preferred in many industrial and laboratory
applications. Some of their main advantages are:
• low cost full-step, open-loop implementation
• no servo tuning required
• good position lock-in
• no encoder necessary
• easy velocity control
• retains some holding torque even with power off
• no wearing or arcing commutators
• preferred for vacuum and explosive environments
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