1. Stepper MotorS – Variable reluctance
Stepper Motor
Contents:
 VR stepper motor - Definition
 Construction
 Principle of operation
 Modes of operation
 Switching circuit
 References
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor

2. Stepper MotorS – Variable
reluctance Stepper Motor
Definition
A stepper motor is a “pulse-driven” motor
that changes the angular position of the rotor in
“steps”
Types
 Variable Reluctance Stepper motor
 Permanent Magnet Stepper motor
 Hybrid Stepper motor
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor

3. conStruction - Stator
• The Stator is made up of silicon steel stampings with
inward projected even or odd number of poles or
teeth.
• Each and every stator poles carries a field coil an
exciting coil. In case of even number of poles the
exciting coils of opposite poles areconnected in
series.
• The two coils are connected such that their MMF gets
added .
• The combination of two coils is known as phase
winding.
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor

4. • The rotor is also made up of silicon steel stampings
with outward projected poles and it does not have any
electrical windings.
• The number of rotor poles should be different from
that of stators in order to have self-starting capability
and bi direction.
• The width of rotor teeth should be same as stator
teeth.
• Solid silicon steel rotors are extensively employed.
ConstruCtion - rotor
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor

5. PrinCiPle of oPeration
Toothed Rotor and Toothed Stator Reluctance of the magnetic
circuit formed by the rotor and
stator teeth varies with the
angular position of the rotor
Here, energize coils A and
A’ (Phase A)
Rotor “steps” to align rotor
teeth 1 and 4 with stator teeth
1 and 5
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor

6. Energize coils B and B’
(Phase B)
Rotor steps “forward”
Rotor teeth 3 and 6 align
with Stator teeth 1 and 5
Let Ns = # of teeth on the
stator
Nr = # of teeth on the
rotor
β = Step Angle in space
degrees
360s r
s r
N N
N N
β
−
= × °
×
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor

7. Mode 1 : One phase ON or full step operation
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor

8. Mode II: Two Phase on Mode
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor

9. Mode III: Half step Mode
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor

10. Switching Circuit for the
stepper motor
Close switches in order 1, 2, 3,
and 4 to turn the rotor “clockwise”
Close switches in reverse order -
4, 3, 2, and 1 to change rotation to
the opposite (counter-clockwise)
direction
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor

11. REFERENCES
S.No Books / Web Sources
1. K.Venkataratnam, ‘Special Electrical Machines’, Universities Press (India) Private Limited, 2008
2. T.J.E. Miller, ‘Brushless Permanent Magnet and Reluctance Motor Drives’, Clarendon Press,Oxford, 1989.
3. T. Kenjo, ‘Stepping Motors and Their Microprocessor Controls’, Clarendon Press London, 1984.
4.
R.Krishnan, ‘Switched Reluctance Motor Drives – Modeling, Simulation, Analysis, Design andApplication’, CRC
Press, New York, 2001.
5. P.P. Aearnley, ‘Stepping Motors – A Guide to Motor Theory and Practice’, Peter Perengrinus ,London, 1982.
6. T. Kenjo and S. Nagamori, ‘Permanent Magnet and Brushless DC Motors’, Clarendon Press, London, 1988.
7. K.Dhayalini, “Special Electrical Machines,” Anuradha Publications, 2017.
8. Google and Wikipedia
Kongunadu College of Engineering & Technology Stepper Motors – VR Stepper Motor