19-12-2012, 01:36 PM
STEPPER MOTOR
STEPPER MOTOR.ppt (Size: 525.5 KB / Downloads: 37)
INTRODUCTION TO STEPPER MOTOR
Electromechanical device which converts electrical pulses into discrete mechanical movements
Shaft of a stepper motor rotates in discrete step increments when electrical pulses are applied
Sequence of the applied pulses is directly related to the direction of motor shaft’s rotation.
Speed of rotation is directly related to the frequency of input pulses applied
STEPPER MOTOR THEORY OF OPERATION
PM type stepper motor permanent magnet is rotor and coils are put on stator.
The rotor will move precisely 90 degrees for each pulse of electricity that the motor receives
THEORY
When current flows holding torque is produced
Without power, rotor will detent or align to magnetic poles ,here 4 Such positions are present.
changing the current flow to the next stator winding, the magnetic field will be changed 90°& rotor will move 90° before its magnetic fields will again align with the change in the stator field.
The turn of the motor is controlled by the electric current which pours into different stator terminals
STEPPER MOTOR TYPES
There are three basic stepper motor types.
Variable-reluctance
Permanent-magnet
Hybrid
VARIABLE-RELUCTANCE TYPE
Consists of a soft iron multi-toothed rotor and a wound stator.
When the stator windings are energized with DC current &the poles become magnetized
Rotation occurs when the rotor teeth are attracted to the energized stator poles.
STEPPING MODES
Full Step Drive ----200 full steps per revolution and 1.8º full step angle
Half Step----- 400 full steps per revolution and 0.9º full step angle
Microstepping (Continiously varying motor currents )----more than 50000 full steps per revolution and (1/256) ºfull step angle
ADVANTAGES OF STEPPER MOTORS
The rotation angle of the motor is proportional to the input pulse
Excellent response to starting, stopping/reversing
The motors response to digital input pulses provides open-loop control
It is possible to achieve very low speed synchronous rotation
A wide range of rotational speeds can be realized
Very reliable since there are no contact brushes in the motor
Accuracy of 3 – 5% of a step and this error is non cumulative from one step to the next
CONCLUSION
All types and characteristics of a stepper motor are studied throughout this paper.
These are very popular in our day to day life due to a lot of advantages and also in digital control circuits, such as robotics because they are ideally suited for receiving digital pulses for step control