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8

Stepper motors

Chapter outline
8.1 Principles of stepper-motor operation ..................................................................................... 210
8.1.1 Multistack variable-reluctance motors............................................................................ 210
8.1.2 Single-stack variable-reluctance motors ......................................................................... 211
8.1.3 Hybrid stepper motors...................................................................................................... 213
8.1.4 Linear stepper motor........................................................................................................ 215
8.1.5 Comparison of motor types ............................................................................................. 215
8.2 Static-position accuracy.............................................................................................................. 216
8.3 Torque-speed characteristics ..................................................................................................... 217
8.4 Control of stepper motors ......................................................................................................... 220
8.4.1 Open-loop control............................................................................................................. 221
8.4.2 Translators and drive circuits ........................................................................................... 222
8.5 Summary...................................................................................................................................... 226
References........................................................................................................................................... 226

The motors discussed so far have been effectively analogue in nature, with the motor’s
speed being a function of the supply voltage; stepper motors, however, are essentially
digital. The rotary motion in stepper motors occurs in a stepwise manner from one
equilibrium position to the next, and hence a stepper motor’s speed will be a function of
the frequency at which the windings are energised. In industrial applications, stepper
motors are not widely used as the main robotic or machine-tool drive, but they are
widely used as an auxiliary drive (for example within product feed systems, or as a low
power end-effector’s actuator) or within a computer peripheral (for example within a
printer). While stepper motors have found widespread use is the drives within small
educational robots; this is largely due to their simplicity of control and the low system
cost, they can be found in a wide range of applications including drug delivery, solar cell
array pointing systems and XeY tables. There are a number of characteristics that make a
stepper motor the first choice for a low cost servo drive, including:
Stepper motors are able to operate with a basic accuracy of 1 step in an open-
loop system. This inherent accuracy removes the requirement for a positional or
speed transducer, and it therefore reduces the cost of the overall system.
Stepper motors can produce high output torques at low angular velocities,
including standstill with the hybrid stepper motor.

Electric Drives and Electromechanical Systems. https://doi.org/10.1016/B978-0-08-102884-1.00008-X 209
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