Basic of Stepper Motors

A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical movements. The shaft of this motor is rotates in discrete step increment when electrical pulses are applied in a proper sequence. Every discrete step of a stepper motor is measured in degree (it can be 1.8° or even smaller depends on the stepper motor type and stepping technique).

This kind of movement is different from DC motors. DC motors is rotates continuously when there is a voltage applied to it and stops when the voltage removed. When the voltage applied to DC motors reversed, the rotation is also reversed. For the stepper motor, we can change the direction of the shaft rotation by reverse the sequence of the applied pulses. The speed of stepper motor shaft rotation is directly related to the frequency input of the pulses. The length of rotation of the stepper motor is directly related to the number of pulses applied.

Even though the movements of stepper motor is measured is degree, this motor is also different from servo motors. Servo motors is actually a DC motor that has a feedback system that forms a close loop control system. Stepper motor is just open loop control system. There is no feedback system built inside this motor. Even though stepper motor is open loop control system, but this motor has ability to be accurately controlled in an open loop control system.

Inside the stepper motor there is a stator and a rotor. Stator is the stationary part of the motor. This includes the casing of the motor, as well as coils or electromagnet inside the casing. Rotor is the moving part of the motor. This includes the shaft, bearings, and permanent magnet. A stepper motor may have any numbers of coils. But these are connected in groups called "phases". All the coils in phase are energized together.

There are 2 type of stepper motor: unipolar and bipolar. Unipolar stepper motor, always energized the phases in same way. One lead of coil always be negative and the other lead always be positive. Bipolar stepper motor, use H-bridge circuitry to actually reverse the current flow through the phases. A bipolar stepper motor will have 4 wires (2 for each phase). A unipolar stepper motor will have 5 or 6 wires. The 5th and 6th of unipolar stepper motor is come from center tap of the phases. Sometimes these 2 wires are both internally connected, so the stepper motor has comes only with 5 wires. Some motors also come with flexible wiring that allows you to run the motor as either bipolar or unipolar (8 wire motors).

In this article, I will explain more about unipolar stepper motor. The illustration below is illustrate how the simple unipolar stepper motor works:

On the illustration above, the stepper motor is move 4 steps by energize the coils in a sequence. We can energize the coils of unipolar stepper motor by send electrical pulse to the 4 wires. The 4 wires of the stepper motor can be controlled by microcontroller GPIO pins with using driver circuitry. The other wires of the unipolar stepper motor is connected to the common positive source. If want to learn more about the stepper movement, you can view this video by pcbheaven.

Reference from:
- www.learn.adafruit.com