Analysis of working principle of variable reluctance motor
Stepper motor, also known as pulse motor, is an actuator in digital control system. Its function is to transform pulse electric signal into corresponding angular displacement or linear displacement reactive stepping motor. It is widely used in practice, its structure and The working principle is also easy to master. It operates differently in different power-on modes, and we can change its operating characteristics accordingly.
The rotor is composed of a silicon steel sheet or an electric iron such as an electric iron rod. The outer surface of the rotor is a multi-tooth structure. (The rotor has a magnetoresistance change when it rotates. It is called a variable reluctance motor, VR for short, also called reactive stepping. Motor). When the stator coil is energized, the stator poles are magnetized, attracting the rotor teeth and generating torque, moving it one step. Compared with the magnetic attraction torque and the repulsive torque generated by the permanent magnet motor, the VR type generates only the suction torque.
The structure and working principle of the VR type variable reluctance reaction type stepping motor are shown in the figure below. In the figure above, 12 poles are evenly distributed on the stator, and each of the poles is separated by 30°, and the four coils which are 90° apart (three slots are separated) form a phase winding. The number of teeth of the rotor is 8. When the phase winding is energized, the stator pole attracts the rotor teeth, so that the air gap reluctance reaches a minimum position.
Next, the working principle of the VR type variable reluctance reaction type stepping motor will be described from step 1 to step 3.
The first step is a simplified diagram of the first phase coil. The hatching indicates the first phase stator excitation, the rotor is attracted by the first phase stator pole, and the rotor teeth are turned below the stator pole.
The second step: the first phase winding current is turned off, the second phase winding is energized, the rotor rotates one step (15°) counterclockwise, and rotates to stop under the second phase stator magnetic pole.
The step angle of the VR variable-resistance stepping motor cannot be directly calculated by the θs=180°/PNr formula in the previous article, but is twice the calculated value of the equation θs=180°/PNr. That is, the resolution is compared with the permanent magnet type. Although the number of teeth of the rotor is the same, the VR type is only 1/2.
The third step: the third phase winding is also energized, and the rotor is also rotated counterclockwise by 15°, and stops at the relative position of the third phase magnetic pole of the stator. At the next moment, the first phase winding is energized, and the rotor position of step 3 is rotated counterclockwise by 15° to the first phase stator pole, and the state of step 1 is restored. The excitation phase is continuously switched, and the 1 phase, 2 phase, 3 phase, and 1 phase are rotated counterclockwise. This is the working principle of the VR type stepping motor.
If it rotates clockwise, the commutation sequence is 1 phase, 3 phase, and 2 phases. At this time, the step angle is 1/3 of the pitch of the rotor tooth, that is, the pitch of the tooth is divided by the number of phases to obtain the step angle, and the output torque is different from that of the permanent magnet motor, which is proportional to the square of the exciting current.
Because the VR type variable reluctance reaction type stepping motor does not use permanent magnets, its stator and rotor magnetic field strength is proportional to the excitation current. To increase the magnetic field strength, a large excitation current is required. Therefore, there is usually a higher temperature rise.
