02-05-2011, 10:24 AM
Presented by-
ABHAY KUMAR BHARTI
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Stepper Motor
Stepper Motors
more accurately controlled than a normal motor allowing fractional turns or n revolutions to be easily done
low speed, and lower torque than a comparable D.C. motor
It is a Electromechanical device
It is Brushless
step motor rotates in discrete step angles
Stepper Motor Diagram
Working
It works on the principle of electromagnetism
It is a soft iron or magnetic rotor shaft surrounded by the electromagnetic stators
the rotor and stator have poles which may be teethed or not depending upon the type of stepper.
In case of a permanent magnet type stepper:- the stators are energized the rotor moves to align itself along with the stator
In case of a variable reluctance stepper:-
rotor moves to have a minimum gap with the stator
Stepper Motor Types
Variable Reluctance
Unipolar/Bipolar Permanent Magnet
Hybrid Step Motor
Variable Reluctance Motors
This is usually a four wire motor – the common wire goes to the +ve supply and the windings are stepped through
Our example is a 30o motor
The rotor has 4 poles and the stator has 6 poles
Example
Variable Reluctance MotorsDiagram
Unipolar Motors
This is usually a 5 or 6 wire motor – with a centre tap on each of the two windings – the two taps are typically wired to the +ve
Our example is a 30o motor
The rotor has 6 poles and the stator has 4 poles
Example
Unipolar Motors
Torque vs. Speed
Motor Control Circuits
Fundamentally a circuit as below is required
Motor Control Circuits
We must deal with the inductive kick when the switches are turned off. We can shunt this using diodes.
Hybrid Stepper Moter
It is a combination of both permanent magnet and the variable reluctance.
It has magnetic teethed rotor which better guides magnetic flux to preferred location in the air gap.
The magnetic rotor has two cups:-
a.) North pole
b.) South pole
rotor cups are designed so that that the north and south poles arrange in alternative manner.
Hybrid Moter (ckt. Diagram)
Working
The Hybrid motor rotates on same principle of energizing the stator coils in a sequence
Stepper Motor Step Angles
Advantage
The rotation angle of the motor is proportional to the input pulse.
The motor has full torque at standstill (if the windings are energized).
Excellent response to starting/stopping/
reversing.
Very reliable since there are no contact brushes in the motor.
motors response to digital input pulses provides open-loop control, making the motor simpler and less costly to control.
Disadvantage
Resonances can occur if not properly controlled.
Not easy to operate at extremely high speeds
Application
It used in floppy disk drives, flatbed scanners, computer printers, plotters, slot machines, and many more devices
In the field of lasers and optics they are frequently used in precision positioning equipment such as linear actuators, linear stages, rotation stages and mirror mounts