Micro-motor subdivision control technology

Micromotor is a widely used actuator used in various automation control systems. Its precision is required to reach the nanometer level, and it has very high requirements for the stability of the system. The traditional motor control technology cannot meet the design requirements at all, and the motor subdivision technology solves the potential problems to a certain extent.

1. Understanding Micromotors

A micromotor is an actuator that converts electrical pulses into angular displacement. When the micro-driver receives the pulse signal, it drives the micro-motor to rotate a fixed step angle according to the set direction, and its rotation runs in a fixed angle step. So we can easily control the rotation angle of the motor by controlling the number of pulses, and at the same time we can control the speed and acceleration of the motor rotation by controlling the pulse frequency.

There are three main types of commonly used micromotors: variable reluctance, permanent magnet and hybrid. The variable reluctance type consists of a basic rotor and stator. There are teeth or slots on the rotor. It always goes to the position of less reluctance in the stator magnetic field. It can produce moderate torque with a step angle of 0.9°-15°. The rotor of a permanent magnet micromotor is made of cylindrical permanent magnets with teeth or slots on it. The torque is relatively small, there is a holding torque, and the step angle is 7.5°~90°. Widely used in computer peripheral equipment and instrumentation industries. Hybrid micromotors combine the advantages of permanent magnet micromotors and variable reluctance motors. Hybrid stepper motors have high torque and hold when power is off. The step angle is about 0.9°~15°.

The reasons for segmentation

Many people say that the subdivision of micro-motors is to improve positioning accuracy. In fact, this is not the more important factor. Subdivision can actually greatly improve the running performance of the motor. Take the two-phase hybrid micromotor as an example. If the rated current of the motor is 5A, using the conventional drive mode, the winding phase current changes from 0 every time the motor runs. To 5A or from 5A to 0, the sudden change of this current will inevitably cause the vibration of the motor. If the subdivision technology is used, if it is 50 subdivisions, the change of the winding energy and current in each step of the motor operation is only 0.1A, which can greatly improve the vibration of the motor. At the same time, after the subdivision, the output torque of the motor is actually increased, especially the three-phase action motor, the torque ratio is increased by about 30-40% without subdivision, which improves the resolution of the motor and reduces the step distance. Angle, increase the uniformity of the step distance, so the subdivision of the micro motor can be said to have many benefits.

Third, the realization method of subdivision control technology

Take a two-phase reactance micromotor as an example. If the motor has N beats and f pulses are input per second, the speed of the rotor is . When f is constant, changing N will change the speed. After the motor is subdivided, N increases to increase the number of running beats, thereby reducing the step angle and reducing the motor speed to maintain the normal running speed of the motor, and the corresponding number of pulses needs to be increased.

If each time the input pulse is switched, only a part of the rated current of the corresponding winding is changed, then each step of the rotor rotation is only a part of the original step angle. The rated current is divided into how many stages to switch, and how many steps does the rotor take to complete an original step angle. Through the step control of the phase current of the micromotor, the motor can run at a smaller unit step angle. Thereby reducing step size and low frequency oscillations. In short, the idea of subdivision drive is to change the original simple rotor current on-off process, gradually change the current size and direction of each phase winding, so that the spatial composite magnetic field inside the motor gradually changes, so that the original one step angle energization method It becomes a step wave that follows the current, and it becomes a multi-step. Due to the high frequency of the commonly used chopper, the current fluctuation of each stage can be ignored, which can be roughly regarded as a DC output.