Intro to Stepper Motors
A stepper motor is a permanent magnet or variable reluctance dc motor that has the following performance characteristics:
1. Rotation in both directions
2. Precision angular incremental changes
3. Repetition of accurate motion or velocity profiles
4. A holding torque at zero speed
5. Capability for digital control.
A stepper motor can move in accurate angular increments knows as steps in response to the application of digital pulses to an electric drive circuit from a digital controller. The number and rate of the pulses control the position and speed of the motor shaft. Generally, stepper motors are manufactured with steps per revolution of 12, 24, 72, 144, 180, and 200, resulting in shaft increments of 30, 15, 5, 2.5, 2, and 1.8 degrees per step.
Stepper motors are either bipolar, requiring two power sources or a switchable polarity power source, or unipolar, requiring only one power source. They are powered by dc current sources and require digital circuitry to produce the coil energizing sequences for rotation of the motor.
There are several stepping modes that you can use to drive the stepper motor.
1. Single Stepping – the simplest mode turns one coil ON at a time. 48 pulses are needed to complete one revolution. Each pulse moves rotor by 7.5 degrees. The following sequence has to be repeated 12 times for motor to complete one revolution.
2. High Torque Stepping – high power / precision mode turns ON two coils on at a time. 48 pulses are needed to complete one revolution. Each pulse moves rotor by 7.5 degrees. The following sequence has to be repeated 12 times for motor to complete one revolution.
3. Half Stepping – stepping is doubled and motor needs 96 pulses to complete one revolution. Each pulse moves rotor by approximately 3.75 degrees. Notice the mix of single stepping mode (lighter green) and high torque mode (darker green).