This document provides an overview of stepper motors, including: - Their working principle is that they rotate through discrete angular steps in response to input current pulses. They come in different types like permanent magnet, variable reluctance, and hybrid. - Applications include computer peripherals, textile machines, robotics, printers, drives, machine tools, and process controls where incremental motion is required. - Advantages are low cost, high reliability, and high torque at low speeds. Disadvantages include resonance effects at low speeds and decreasing torque with increasing speed.

1. ELECTRICAL MACHINE II
EEE303
Stepper Motors
Presentation

2. OUT LINE
• Introduction
• Working principle
• Types of stepper motors
• Applications
• Conclusion

3. Introduction
A stepper motor (or step motor) is a brushless DC electric motor that
divides a full rotation into a number of equal steps.
The name stepper is used because this motor rotates through a fixed
angular step in response to each input current pulse received by its
controller.
Their popularity is due to the fact that they can be controlled directly
by computers, microprocessors and programmable controllers(PLC).

4. Introduction
To achieve full rated torque, the coils in a stepper motor must reach their
full rated current during each step.
N.B torque ~ current
as the motor speeds up, less and less time is spent at full current.
 As speeds further increase, the current will not reach the rated value,
and eventually the motor will cease to produce torque.

5. Pictures of some stepper motors

6. Working principle
The unique feature of a stepper motor is that its output shaft
rotates in a series of discrete angular intervals or steps,
Such motors develop torques ranging from 1 µN-m (in a tiny wrist
watch motor of 3 mm diameter) up to 40 N-m in a motor of 15 cm
diameter suitable for machine tool applications.
Their power output ranges from about 1 W to a maximum of 2500
W. the only moving part in a stepping motor is its rotor which has
no windings, commutation or brushes.
This feature makes the motor quite robust and reliable

7. Stepper motor specifications
Steppers should be sized according to published torque curve, which is
specified by the manufacturer at particular drive voltages or using their
own drive circuitry.
Step motors adapted to harsh environments are often referred to as
IP65 rated

8. Stepper motor system
A stepper motor system consists of three basic elements,
Indexers - The indexer (or controller) is a microprocessor capable of
generating step pulses and direction signals for the driver.
Drivers - The driver (or amplifier) converts the indexer command signals
into the power necessary to energize the motor windings.
.
Stepper motors - The stepper motor is an electromagnetic device that
converts digital pulses into mechanical shaft rotation.

9. Merits and demerits of stepper motors
• Advantage
 low cost,
 high reliability,
 high torque at low speeds
and
 a simple, rugged
construction that operates in
almost any environment.
• Disadvantage
 resonance effect often
exhibited at low speeds
decreasing torque with
increasing speed.

10. Current waveforms
• A stepper motor is a poly_phase AC synchronous motor
and it is ideally driven by sinusoidal current.
• A full step waveform is a gross approximation of a
sinusoid, and is the reason why the motor exhibits so
much vibration..

11. Continue…
Step Angle
 The angle through which the motor shaft rotates for each command pulse is called
the step angle β.
 The most common step sizes are 1.80 , 2.50 , 7.50 and 150 .
 The value of step angle can be expressed either in terms of the rotor and stator
poles (teeth) Nr and Ns respectively or in terms of the number of stator phases
(m) and the number of rotor teeth.
 The number of mechanical degrees corresponding to a given number of
electrical degrees is

12. continue…
 Stepping motors are designed to operate for long periods with
the rotor held in a fixed position and with rated current flowing
in the stator windings.
If f is the stepping frequency (or pulse rate) in pulses per second
(pps) and β is the step angle, then motor shaft speed is given by
n = β × f/ 360 rps = pulse frequency resolution

13. Simple Stepper motor and its associated control unit
Two-pole three-phase stator with a permanent-magnet rotor. If a dc voltage is applied to
phase a of the stator and no voltage is applied to phases b and c, then a torque will be
induced in the rotor which causes it to line up with
the stator magnetic field B.

14. (a) sketch of the output voltage from the control unit as a series of control pulses are input.
(b) A 2-nd table showing the output voltage from the control unit as a function of pulse number.
In general, if a stator has N phases, it takes 2N pulses per electrical revolution
in that motor. Therefore, the relationship between the speed of the motor in
revolutions per minute and the number of pulses per minute becomes

15. Types of Stepper Motors
 stepper motors can be divided into the following 3 basic categories :
1. Permanent Magnet Stepper Motor
2. Variable Reluctance Stepper Motor
3. Hybrid Stepper Motor
Permanent magnet motors use a permanent magnet (PM) in the
rotor and operate on the attraction or repulsion between the rotor
PM and the stator electromagnets.
Variable reluctance (VR) motors have a plain iron rotor and operate
based on the principle that minimum reluctance occurs with
minimum gap, hence the rotor points are attracted toward the stator
magnet poles.
Hybrid stepper motors are named because they use a combination of
PM and VR techniques to achieve maximum power in a smallpackage
size.

16. Applications
. Such motors are used for operation control in
 computer peripherals
 textile industry
 IC fabrications and robotics etc.
• Applications requiring incremental motion are
typewriters,
line printers,
tape drives, floppy disk drives,
numerically-controlled machine tools, process control systems
and X-Y plotters.

17. Conclusion
• Any Questions just Google it!!!
thanks for your attention!!!