STEPPER MOTOR

By,

Rohini Haridas

Assistant Professor,

Dept of Electrical Engineering,

SSGM College of Engineering,Shegaon

Introduction

�A stepper motor is a form of ac motor. The input given to

this motor is in the form of electric pulses.

�Stepper motor is known by its important property to convert

a train of input pulses i.e. square wave pulse into a precisely

defined increment in the shaft position.

�Each pulse moves the shaft through a fixed angle.

�The angle through which the motor turns or shaft moves for

each pulse is known as the step angle, expressed in degrees

�As such angle is dependent on the number of input

pulses,the motor is suitable for controlling position by

controlling the number of input pulses

Step Angle

�The magnitude of step angle for stepper motor is given by

Where,

α = Step angleα = Step angle

ms = number of stator phases

Nr= Number of rotor poles or teeth

Steps per revolution is given by i.e. resolution

α

0360=

Numerical

1. Calculate the stepping angle for a three phase ,24 pole

permanent magnet stepper motor

Given:

ms = 3

Nr = 24Nr = 24

Solution :

= 360/(3*24)

=step/50

Numerical

2. Calculate the stepping angle for a three phase ,16-teeth

variable reluctance stepper motor

Given:

ms = 3

Nr = 16Nr = 16

Solution :

= 360/(3*16)

=step/5.7 0

Difference between Conventional

Motor and Stepper motor

� Input to SM is in the form of electric pulses whereas input

to CM is from constant voltage source

�A CM has a free running shaft whereas shaft of SM moves

through angular steps

Types of stepper motors

�Permanent Magnet Stepper Motor

�Variable Reluctance Stepper Motor

Rotor

Stator

Coils

Outside Casing

StatorCoils

2

1

S

N

1

2

Stator

Rotor

Internal components of a Stepper Motor

Permanent Magnet Stepper Motor

Permanent Magnet Stepper Motor

Rotor will always orient so that the nearest rotor south pole is aligned with the energized stator poles

Rotor will always orient so that the nearest rotor south pole is aligned with the energized stator poles

1

N

SStators

Cross Section of a Stepper Motor

2 2

S

1N

Rotor

Four Steps per revolution i.e. 90 deg. steps.

Eight steps per. revolution i.e. 45 deg. steps.

Variable Reluctance Stepper Motor

�The principle of operation of a variable reluctance

stepper motor is based on the property of flux lines to

occupy low reluctance path.

� The stator and rotor therefore get aligned such that

the magnetic reluctance is minimum

Variable Reluctance Stepper Motor

Practical Stepper motor operation

The top electromagnet (1) is turned on, attracting the nearest teeth of a gear-shaped iron rotor. With the teeth aligned to electromagnet 1, they will be slightly offset from electromagnet 2

The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the nearest teeth slightly to the right. This results in a rotation of 3.6°in this example.

The bottom electromagnet (3) is energized; another 3.6°rotation occurs.

The left electromagnet (4) is enabled, rotating again by 3.6°. When the top electromagnet (1) is again enabled, the teeth in the sprocket will have rotated by one tooth position; since there are 25 teeth, it will take 100 steps to make a full rotation in this example.

APPLICATIONS

Film Advance

Labeling Machines

Rotating Tube Cutter

Advantages:-

Low cost for control achieved

Simplicity of construction

Low maintenance

Advantages

Will work in any environment

+

Control sequence to turn a stepper motor

Step 1 0 0 1 1

Step 2 1 0 1 0

Step 3 1 1 0 0

Step 4 0 1 0 1

CW CCW