A stepper motor is an open-loop controlled motor that converts electrical pulse signals into angular or linear displacement; it is also known as a pulse motor. Under non-overload conditions, the motor's speed and stopping position depend only on the frequency and number of pulse signals, and are unaffected by load changes. When a stepper driver receives a pulse signal, it can drive the stepper motor to rotate a fixed angle in a set direction, called the "step angle".
Stepper motors are controlled by pulse signals; each pulse input causes the stepper motor to move one step. The step angle of a stepper motor's rotation is proportionally controlled based on the motor's structure. If the microstepping control of the control circuit remains unchanged, the step angle is theoretically a fixed angle. In actual operation, there will be slight differences in the step angle, mainly due to inherent errors in the motor's structure, and these errors do not accumulate.
A typical two-phase stepper motor rotates its rotor through the repulsion and attraction of magnetic fields from different poles. As shown in the diagram above, phase A generates a north pole magnetic field that attracts the rotor's south pole, while phase B generates a south pole magnetic field that attracts the rotor's north pole, thus driving the stator to rotate. Changing the direction of the current in the stator coils of phases A and B will produce another step of rotation. Continuously changing the direction of the current in the stator coils of phases A and B will produce continuous rotation of the motor.
The working principle of a stepper motor is actually the same as that of an electromagnet. It is an open-loop control stepper motor component that converts electrical pulse signals into angular or linear displacement. By controlling the sequence, frequency, and number of electrical pulses applied to the motor coil, the direction, speed, and rotation angle of the stepper motor can be controlled. With the help of a linear motion actuator or gearbox, more complex and precise linear motion control requirements can be achieved.
Stepper motors rotate by the number of pulses; the required number of revolutions corresponds to the number of pulses. Therefore, stepper motors can achieve precise positioning. Furthermore, the speed and acceleration of the motor can be controlled by adjusting the pulse frequency, i.e., controlling the interval between pulses, thus achieving speed regulation. Each input electrical pulse causes the motor to rotate one angular distance and move one step forward. Its output angular displacement is directly proportional to the number of input pulses, and its rotational speed is directly proportional to the pulse frequency. Changing the energizing sequence of the windings controls the motor's forward and reverse rotation. For example, energizing phases A, B, and C in the forward rotation sequence will cause the motor to rotate in the reverse sequence, while energizing phases C, B, and A in the reverse sequence will cause it to rotate in the reverse. Therefore, the rotation of a stepper motor can be controlled by adjusting the number and frequency of pulses and the energizing sequence of each phase winding.
unipolar stepper motor
This type of stepper motor is called unipolar because the current flows in only one direction in each winding. It is also called a two-wire stepper motor because it contains only two coils. The two coils have opposite polarities, are wound on the same iron core, and have the same center tap. Unipolar stepper motors are also called four-phase stepper motors because they have four drive windings. Unipolar stepper motors have five or six leads.
If a stepper motor has 5 leads, one of them is a common wire (connected to V+), and the other 4 are connected to the 4 phases of the motor. If a stepper motor has 6 leads, it is a multi-stage unipolar stepper motor with two windings, each with a center tap lead. But how do you identify these leads? Please read on.
1. Identify the connector of a 5-wire unipolar stepper motor.
bipolar stepper motor
Bipolar stepper motors are so named because each winding can be energized in both directions. Therefore, each winding can be both the neutral (N) and source (S) poles. They are also called single-winding stepper motors because each pole has only a single winding, and two-phase stepper motors because they have two separate coils.
Bipolar stepper motors have four leads, two for each winding. Compared to unipolar stepper motors of the same size and weight, bipolar stepper motors have greater driving capability because the electric field strength in their magnetic poles (not a single coil with a center tap) is twice that of a unipolar stepper motor. Each winding of a bipolar stepper motor requires a reversible power supply, typically provided by an H-bridge drive circuit. Because bipolar stepper motors have greater output torque than unipolar stepper motors, they are always used in designs with limited space. This is also why the drive for the stepping mechanism of the floppy disk drive head always uses a bipolar stepper motor.
