[ELECTRONICS] - Actuators and Sensors - Stepper motors - Microchip - Stepping Motors Fundamentals.pdf

AN907
Stepping Motors Fundamentals
Author: Reston Condit TYPES OF STEPPING MOTORS
Microchip Technology Inc. There are three basic types of stepping motors:
Dr. Douglas W. Jones permanent , variable reluctance and hybrid.
University of Iowa This application note covers all three types. Permanent
motors have a ized rotor, while variable
reluctance motors have toothed soft-iron rotors. Hybrid
INTRODUCTION stepping bine aspects of both permanent
Stepping motors fill a unique niche in the motor control and variable reluctance technology.
world. These motors monly used in measure- The stator, or stationary part of the stepping motor
ment and control applications. Sample applications holds multiple windings. The arrangement of these
include ink jet printers, CNC machines and volumetric windings is the primary factor that distinguishes
pumps. Several mon to all stepper motors different types of stepping motors from an electrical
make them ideally suited for these types of point of view. From the electrical and control system
applications. These features are as follows: perspective, variable reluctance motors are distant
1. Brushless – Stepper motors are brushless. The from the other types. Both permanent and
commutator and brushes of conventional hybrid motors may be wound using either unipolar
motors are some of the most failure-prone windings, bipolar windings or bifilar windings. Each of
components, and they create electrical arcs that these is described in the sections below.
are undesirable or dangerous in some
environments. Variable Reluctance Motors
2. Load Independent – Stepper motors will turn at Variable Reluctance Motors (also called variable
a set speed regardless of load as long as the switched reluctance motors) have three to five
load does not exceed the torque rating for the windings connected to mon terminal. Figure 1
motor. shows the cross section of a three winding, 30 degree
3. Open Loop Positioning – Stepper m