Stepping Motors Fundamentals
Author: Reston Condit Microchip Technology Inc. Dr. Douglas W. Jones University of Iowa
TYPES OF STEPPING MOTORS
There are three basic types of stepping motors: permanent magnet, variable reluctance and hybrid. This application note covers all three types. Permanent magnet motors have a magnetized rotor, while variable reluctance motors have toothed soft-iron rotors. Hybrid stepping motors combine aspects of both permanent magnet and variable reluctance technology. The stator, or stationary part of the stepping motor holds multiple windings. The arrangement of these windings is the primary factor that distinguishes different types of stepping motors from an electrical point of view. From the electrical and control system perspective, variable reluctance motors are distant from the other types. Both permanent magnet and hybrid motors may be wound using either unipolar windings, bipolar windings or bifilar windings. Each of these is described in the sections below.
Stepping motors fill a unique niche in the motor control world. These motors are commonly used in measurement and control applications. Sample applications include ink jet printers, CNC machines and volumetric pumps. Several features common to all stepper motors make them ideally suited for these types of applications. These features are as follows: 1. Brushless – Stepper motors are brushless. The commutator and brushes of conventional motors are some of the most failure-prone components, and they create electrical arcs that are undesirable or dangerous in some environments. Load Independent – Stepper motors will turn at a set speed regardless of load as long as the load does not exceed the torque rating for the motor. Open Loop Positioning – Stepper motors move in quantified increments or steps. As long as the motor runs within its torque specification, the position of the shaft is known at all times without the need for a feedback mechanism.