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Stepping Motor Fundamentals
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By
Reston Condit, Microchip Technology and Douglas W. Jones, University of Iowa
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Industrial Control Designline
(06/01/2009 2:53 PM EDT)
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INTRODUCTION
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:
-
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.
- Holding Torque:
Stepper motors are able to
hold the shaft stationary.
- Excellent
response to start-up, stopping and
reverse.
The following sections discuss the most common types
of stepper motors, what circuitry is needed to drive
these motors, and how to control stepping motors with
a microcontroller.
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 following sections.
Click here to read the rest of the technical
paper.
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