Step Angle in Stepper Motor

Basics of Stepper Motor

The stepper motor or stepping motor is an electromechanical energy conversion device which has a rotor movement in discrete steps. The number of pulses fed into the control circuit of the motor determines the angular rotation of the rotor.

Each input pulse initiates the drive circuit of the motor which produces one step of angular movement. The drive circuit has inbuilt logic which causes appropriate windings to be energised and de-energised by the solid state switches in the required sequential manner. In a stepper motor, the angular movement of the rotor is in steps, so this motor may be considered as a digital-to-analog converter. The stepper motor is also known as digital motor.

Depending upon the rotor arrangements, the stepper motors are of three-types −

• Variable reluctance (VR) stepper motor
• Permanent magnet (PM) stepper motor
• Hybrid stepper motor

Step Angle in Stepper Motor

The step angle of a stepper motor is defined as the angle by which the rotor of a stepper motor moves when one input pulse is applied to the stator of the motor. The step angle is expressed in degrees. The step angle decides the resolution of positioning of a stepper motor i.e. smaller the step angle, the higher is the resolution of positioning of the motor.

The resolution or step number of a stepper motor is defined as the number of steps it makes in one revolution of the rotor, i.e.,

$$\mathrm{Resolution =\frac{Number\:of \:steps}{Number\:of\:revolutions\:of\:the\:rotor}}$$

Hence, if higher the resolution, the greater is the accuracy of positioning of objects by the stepper motor.

Stepper motors can be designed for very small step angles. A standard stepper motor will have a step angle of 1.8° with 200 steps per revolution.

There are various designs of stepper motors available. The number of phases may vary from 2 to 6. To obtain the small step angle, the slotted pole pieces to increase the number of teeth together with multi-stack stator assemblies being used in the stepper motors.