# Stepper Motor

Stepper motor or a Step motoris a brushless, synchronous motor which divides a full rotation into number of steps. A stepper motor can be visualized as the digital version of the electric motor.  Unlike a conventional motor, whose rotor moves continuously, the rotor of a stepper motor move in discrete steps as commanded. The motor’s position can be commanded to move and hold at any position.

The Stepper motors are manufactured with steps per revolution of 12,24,72,144,80 and 200 with stepping angles of 30, 15, 5, 2.5,2 and 1.8 degrees per step.
The Stepper motor can be controlled with or without feedback.

#### HOW DOES A STEPPER MOTOR WORK ? ITS PRINCIPLE OF OPERATION

The principle of operation of a Stepper motor is ELECTRO-MAGNETISM. Stepper motor is made of rotor and stator. Rotor is made up of permanent magnet and is the rotating part of a motor. Stator is made of electromagnet and is the stationary part of motor. Stator is in the form of windings.
When we supply current to stator’s windings, magnetic field is generated in stator. Now as the rotor is made of permanent magnet, it will try to move with revolving magnetic field of stator.
This is the basic principle of operation of stepper motor.

TYPES OF STEPPER MOTORS

On the basis of construction, a step motor can be divided as:-

1. Active rotor: Permanent magnet

2. Reactive rotor: Variable reluctance

3. Combination of active rotor and variable rotor: Hybrid Step motor

Now, we will further discuss on the stepper motor.

BASICS OF STEPPER MOTOR

Before moving further let us study some basic terms of Stepper motor

1. Step angle- angular displacement for one control signal.

2. Pull-in torque-maximum torque load at the shaft, at which at the motor can start without losing steps.

3. Pull-out torque-maximum torque that the motor can maintain at a certain speed, without losing steps.

4. Degree of rotation-how far the rotor will spin around its axis for each signal event.

5. Maximum no load start frequency- represents the maximum control impulse frequency at which the unloaded motor can start, stop or reverse without losing steps.

6. Limit start frequency- the maximum impulse frequency at which the motor can start without losing steps.

7. Maximum no load frequency- maximum impulse frequency the motor can follow without losing synchronization.

8. Maximum frequency-maximum frequency of impulses at which a motor keeps its timings for given set of torque and load.

PERMANENT MAGNET STEPPER MOTOR

The features of a permanent magnet stepper motor are:-

• Cylindrical permanent magnet rotor and poles set in radial direction.
• Stator usually has 2 windings primarily central tapped so as to allow unipolar driver circuit where the polarity of the magnetic field is changed by switching a voltage from one end to other of magnetic winding.
• When the stator windings are energized, magnetic fields that are generated interact with the permanent magnet’s flux, generating torque to move the rotor.
• Provide higher torque and shows holding torque even if magnetic field is not energized.
• The resolution can be increased by increasing the number of poles in the rotor or increasing the number of phases.
• The speed or torque is changed by the number of poles in stator.

VARIABLE RELUCTANCE STEPPER MOTOR

The features of a variable reluctance stepper motor are :

HYBRID STEPPER MOTOR

The basic features of a hybrid stepper motor are:-

• It is a combination of both permanent magnet and variable reluctance stepper motor.
• The rotor is magnetized as well as teethed. It is made of permanent magnet, place length-wise. This guide betters the magnetic flux to the preferred air gaps.
• The stator coils are wound on alternating poles with corresponding teeth. There are usually 2 winding phases distributed between pole pairs.
• It is the most common stepper motor.

STEPPING MODES

It refers to the pattern of sequence in which stator coils are energized.

For a step motor, there are 3 stepping modes-

1.Only 1 phase is energized at a time in a step motor, i.e., one phase on at a time.

2.2 phases are energized at a time, i.e.,  two phase on at a time.

3.In half drive, alternately one and two phases are on at a time.

Stepping Sequence

In order to get correct motion of the motor, a stepping sequence has to be followed. This stepping sequence gives the voltage that must be applied to the stator phase. Normally a 4 step sequence is followed.

When the sequence is followed from step 1 to 4, we get a clock wise rotation and when it is followed from step 4 to 1, we get a counter clockwise rotation.

 STEP NO a A b B 1 1 0 0 1 2 1 1 0 0 3 0 1 1 0 4 0 0 1 1

Category:

tags:

## Who's new

• ravirajpatil871...
• shubhambajoria
• yassir
• demiholyman890954
• scottgillum51169040