In the mechanical design, we often use stepper motor, for example, with a stepper motor to drive the synchronous belt shaft, to achieve linear motion;
For example, using a stepper motor to drive the ball screw shaft can also convert the rotational motion into linear motion. Because no feedback system is required, the greatest advantage of stepper motors is that they can achieve good accuracy at low cost. In fact, in addition to the movement platform in the machine, the existence of stepper motor can also be found in life. Such as printers, scanners, cameras, ATMs, 3D printers and so on.
So, what is the principle of the stepper motor?
In a word, one or more sets of coils in the stator are energized in turn. The current in the coils generates a magnetic field. The rotor, in order to find a new equilibrium position, automatically adjusts its position to the magnetic field, thus achieving movement.
1. Type of stepper motor:
Like other types of motors, stepper motors are also composed of a stator and a rotor.
In the stepper motor, the stator is mainly responsible for generating the magnetic field, and the rotor is responsible for following the magnetic field.
The main characteristics of the stator include phase number, magnetic log, and coil configuration.
The number of phases is the number of independent coils, and the logarithm indicates how many pairs of magnetic fields are generated per phase.
2-phase stepper motors are the most commonly used, while 3-phase, 5-phase motors are not commonly used.
Because the construction of the stepper motor will affect the step distance, speed, torque, and control mode.
So, next I will talk about the construction of several kinds of asynchronous motors.
They differ mainly in how the rotors are made.
(1) permanent magnet rotor
The first, permanent magnet rotor, is the simplest and cheapest.
The rotor in the middle is made of a permanent magnet.
When the stator coil is energized to generate a magnetic field, the rotor magnet automatically aligns with the magnetic field and follows the rotation.
The coil is energized, and the middle rotor automatically alters the magnetic field generated by the coil. Because the rotor is made of a magnet, the magnetic flux of the magnet is large, and the torque is large, so it ensures a better output torque and braking torque.
The brake torque means that the motor will stop spinning whether the coil is energized or not. This is because the interaction between the permanent magnet and the stator will produce a certain torque, which must be overcome by the external force before the motor can move.
In the catalog of the motor manufacturer, some are also written as cogging torque, or residual torque.
(2) variable reluctance stepping motor
This kind of motor, the rotor is made of soft magnetic material, the rotor has many teeth, different tooth shape distribution, can produce different resolution, the coil is energized to attract the rotor, causing rotation.
The advantages of this structure are that it can achieve high speed and high resolution, and there is no braking torque, but the torque is smaller than the permanent magnet type, which is not suitable for small motors.
Since there are no permanent magnets, this motor can be used in environments with strong magnetic fields.
(3) Mixed type
Hybrid, as the name suggests, is a mixture of permanent magnet and variable reluctance.
Motion principle of hybrid stepper motor
The rotor has two crowns that are magnetized in the axial direction, one for the North Pole and one for the South Pole.
With this configuration, the hybrid stepper motor has the advantages of both permanent magnet and variable reluctance, especially with high resolution, high speed and high torque.
Hybrid stepper motor usually has 200 steps per turn, that is, the step distance is 360/200=1.8°, this type of motor is limited by manufacturing, the minimum can only be φ19mm at present.
Of course, good features require more complex structures and controls, so they are more expensive.
