Stepper motors are simple, reliable, and do not require an encoder or other electronic components to detect position in the inside. Furthermore, the fact that stepper motors also have high precision is what makes this motor appealing.
Controlling the angle of rotation is very easy because it is proportional to the number of digital pulses input to the motor. Other benefits include the ability to rotate at low speed, to remain securely locked in position when halted, and to use open-loop position control.
The disadvantages are a tendency to generate vibration and noise and being prone to loss of synchronization when the load changes unexpectedly.
The following are some of the products in which stepper motors are used.
Air conditioning louvers
Types of stepper motors
Stepper motors can be grouped into the following three categories depending on the structure of the motor shaft’s rotor.
Permanent magnet (PM) motor
The rotor contains a permanent magnet. This structure is that it cannot provide flexibility over the angle of rotation (step angle).
Variable reluctance (VR) motor
The rotor contains cores structured like the teeth of a gear. This allows for more flexibility in setting the step angle.
Hybrid (HB) motor
The rotor contains both a permanent magnet and cores structured like the teeth of a gear. This type of motor combines the advantages of PM and VR motors.
Stepper motors can also be grouped into the following two categories based on how electric current flows through the coil.
Current in a unipolar motor always flows through each coil winding in the same direction. This keeps the associated control circuit simple and works well for high-speed drive. The disadvantage is that it produces less torque than a bipolar motor.
Current in a bipolar motor can flow through the coil windings in both directions. The benefits are a simple internal design that makes good use of the motor windings and minimizes temperature rise.
How stepper motors are controlled
The rotation of a stepper motor is controlled precisely by applying electric signals. The signals are pulses generated by turning electricity on and off, and the angle of rotation is determined by the number of pulses input to the driver. Likewise, the speed of the motor is proportional to the pulse rate.
The angle, speed, and direction of rotation can be controlled using any of the following three pulse input patterns.
Single pulse mode
In this mode, pulses are input to drive rotation and the direction signal is held high or low to specify the direction of rotation.
Double pulse mode
In this mode, separate clockwise (CW) and counter-clockwise (CCW) pulse inputs determine the direction of rotation. That is, CW pulses turn the motor clockwise and CCW pulses turn it counter-clockwise.
Phase A/phase B pulse mode
In this mode, separate phase A and phase B pulses are input with a phase offset of about 90° and the generated direction of rotation is determined by whether this phase difference is leading or lagging. That is, the motor turns clockwise if phase A is leading and counter-clockwise if phase B is leading.