Basic Motion Control – An Introduction to Stepper Motors

Stepper motors are brushless, synchronous electric motors that convert digital pulses into mechanical rotation. Due to their lower cost, high reliability, high torque at low speeds, and rugged construction, they are found in both industrial and commercial applications.

The Basic Idea

Every revolution of a stepper motor is divided into a discrete number of steps. The motor is sent a pulse for each step.

NEMA23 270oz/in 2.8A 1/4 Dual Shaft Stepper Motor (KL23H276-28-4B)

Typically a single rotation is 200 steps or 1.8 degrees of rotation per step.

Since a stepper motor can only take one step at a time, and each step is the same size, the motor's position can be controlled without feedback. Obviously, as the pulse frequency increases the discrete step movement will change into the continuous rotation – with the speed directly proportional to the pulse frequency.

Why Use a Stepper Motor?

1) Open-loop control makes the motor simpler and less costly to control.

2) The rotation angle of the motor is proportional to the input pulse.

3) Precise positioning and repeatability of movement.

4) Wide ranges are available since the speed is proportional to the frequency of the input pulses.

5) Quality stepper motors have an accuracy of 3 to 5% of a step and this error is non-cumulative step to step.

6) Excellent response to starting/stopping/reversing.

7) If the windings are energized the motor has full torque at standstill. When the load is directly coupled it is possible to achieve very low-speed synchronous rotation.

8) High MTBF – since there are no contact brushes in the motor.