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Types of Stepper Motor and Their Significances

A stepper motor is an electromechanical device that induces mechanical movements by converting electrical pulses. It is driven by digital pulses instead of continuously applied voltage, and it can step or rotate in fixed angular increments. Stepper motors are typically used in applications that require position control. They are assumed to follow digital instructions when used in a stepper motor/driver/controller system design. They are classified as open-loop systems due to their lack of feedback to keep control of the position. Stepper motors can be classified into three basic types:

1. Variable reluctance stepper motor – The wound stator and multiple soft iron rotors are the distinctive characteristics of this type of stepper motor. They work when the magnetic flux finds the lowest reluctance pathway using a magnetic circuit. In a typical application, VR stepper motors produce high step rates ranging from five to 15 degrees, and they do not have detent torque. Step angles are related to a number of teeth in the stator and rotor.

2. Permanent magnet stepper motor – PM stepper motors have permanent magnet rotors without teeth, but they are magnetized perpendicular to a rotation’s axis. The rotor rotates when the four phases are energized in a sequence, and this occurs due to the magnetic poles’ attraction. Permanent magnet stepper motors typically have 45 or 90 step angles, with relatively low step rates, but they provide high torque and better damping.

3. Hybrid stepper motor – This type of stepper motor bears the qualities of both permanent magnet and variable reluctance stepper motors. Its multi-toothed rotor resembles the VR motor. The shaft has an axially magnetized concentric magnet around it to enable higher detent, dynamic, and holding torque. Hybrid stepper motors enhance the performance in terms of torque, speed, and step resolution, so they are useful in applications that require high stepping speeds for operation. They come in step angles designed at 0.9 degrees, 1.8 degrees (commonly used), 3.6 degrees, and 4.5 degrees.

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