Abstract This paper presents the design and analysis of a
400-step hybrid stepper motor for spacecraft applications. The
design of the hybrid stepper motor for achieving a specific
performance requires the choice of appropriate tooth geometry.
In this paper, a detailed account of the results of two-dimensional
finite-element (FE) analysis conducted with different tooth
shapes such as square and trapezoidal, is presented. The use of
% more
corresponding increase in detent torque and distorted static
torque profile. For the requirements of maximum torque density,
less-detent torque, and better positional accuracy and smooth
static torque profile, different pitch slotting with equal tooth
width has to be provided. From the various FE models subjected
to analysis trapezoidal teeth configuration with unequal tooth
pitch on the stator and rotor is found to be the best configuration
and is selected for fabrication. The designed motor is fabricated
and the experimental results is compared with the FE results.
Index TermsHybrid stepper motor, Finite-element (FE)
analysis, torque, space application.
I. INTRODUCTION
The motor having the permanent magnet rotor and multiple
teeth both on the stator and rotor poles, with excitation in
stator poles is called the hybrid stepper motor. Stepper Motors
are divided in to two major groups, one without permanent
magnet and the other with permanent magnet. The term hybrid
is derived from the fact that the motor is operated under the
combined principles of permanent magnet and variable
reluctance motors. Hybrid stepper motors are widely used in
space applications, office and factory automation applications.
Hybrid stepper motors are highly preferred in space
applications as they can provide accurate positioning in open
loop system. The positional accuracy of the stepper motors
will be high only when its step angle is very small. Hence for
space applications hybrid stepper motor is the best choice as it
can offer small step angles in the ranges of 0.5
0
to 1.8
0
.The
other classes of stepper motors such as variable reluctance
Praveen R P
1
is a Ph.D Research Scholar in Cochin University of Science
and Technology,Kerala,India.
Ravichandran M H
2
and V T Sadasivan Achari
3
is with ISRO Inertial
Systems Unit, Trivandrum, Kerala, India.
Dr.Jagathy Raj V P
4
and Dr.G.Madhu
5
is with Cochin University of
Science and Technology,Kerala,India.
Dr.G R Bindu
6
is a Senior Lecturer in the Electrical Department of College
of Engineering,Trivandrum,Kerala,India.
stepper motor and permanent magnet stepper motor will be
suitable only for applications which require large step angles.
The design of a hybrid stepper unlike that of conventional ac
motors such as induction motor and synchronous motors using
equivalent magnetic circuit analysis is not easy because of the
complex air gap geometry, which results in complex air gap
permeance variation. Because of this, analysis using
Computational Electromagnetics, a complex task and this
results in the dependency of Finite Element Technique for
design and Analysis Purpose. Since Hybrid stepper motor has
a large number of teeth on the stator and rotor surface and a
very small air gap, the magnetic saturation in the teeth
becomes severe while increasing the flux density in the airgap.
In addition both radial and axial flux is produced because of
axially magnetized permanent magnet and geometric
characteristics [1]. This makes the analysis of hybrid stepper
motor more difficult using 2D FE modeling. Three
dimensional finite element analysis is one of the solution for
nonlinear analysis of axially unsymmetrical hybrid stepper
motor under this situation [2]. But in order to reduce the
computational time involved in the analysis a 2-D equivalent
of the 3-D model of the motor was developed and used.
II. FINITE ELEMENT ANALYSIS
Most electromagnetic problems involve either partial
differential equations or integral equations. While partial
differential equations are usually solved using the finite
difference method or finite element method, integral equations
are solved conveniently using moment method. In contrast to
other methods, the finite element method accounts for
nonhomogeneity of the solution region [3]. The systematic
generality of the method makes it a versatile tool for a wide
range of problems. Finite Element Analysis is used
extensively for the design and performance prediction of all
types and topologies of permanent magnet machines and for
calculating field distributions, torque and force. Commercial
Finite Element package has been used to carry out the
analysis.
III. DESIGN METHODOLOGY
The volume and mass of the motor should be minimal for
any optimal design and development of Hybrid Stepper Motor.
The volumetric efficiency as well as the torque to inertia ratio
Design and Finite Element Analysis of Hybrid Stepper
Motor for Spacecraft Applications
Praveen R.P.
1
, Ravichandran M.H.
2
, V. T. Sadasivan Achari
3
, Dr.Jagathy Raj V. P.
3
, Dr.G.Madhu
4
and Dr.G.R. Bindu
6
1051 978-1-4244-4252-2/09/$25.00 ©2009 IEEE