Control motors are mainly used for precise speed and position control and as “actuators” in control systems. They can be categorized into servo motors, stepper motors, torque motors, switched reluctance motors, brushless DC motors, and so on.
1. Servomotors
Servo motors are widely used in various control systems to convert input voltage signals into mechanical outputs on the motor shaft and drag the controlled components to achieve control purposes. Generally speaking, servo motors require that the rotational speed of the motor should be controlled by the added voltage signal; the rotational speed can be changed continuously with the change of the added voltage signal; the torque can be controlled by the current output from the controller; the reflection of the motor should be fast, the volume should be small, and the control power should be small. Servo motors are mainly used in a variety of motion control systems, especially follower systems.Servo motor has DC and AC, the earliest servo motor is a general DC motor, in the case of control precision is not high, before the use of general DC motor as a servo motor. Currently with the rapid development of permanent magnet synchronous motor technology, the vast majority of servo motors are AC permanent magnet synchronous servo motors or DC brushless motors.
2. Stepper motor
The so-called stepper motor is an actuator that converts electrical pulses into angular displacements; to put it more plainly: when the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in the set direction. We can control the number of pulses to control the angular displacement of the motor, so as to achieve the purpose of precise positioning; at the same time, you can also control the frequency of pulses to control the speed of motor rotation and acceleration, so as to achieve the purpose of speed regulation. At present, the more commonly used stepper motors include reactive stepper motors (VR), permanent magnet stepper motors (PM), hybrid stepper motors (HB) and single-phase stepper motors.
The difference between a stepper motor and an ordinary motor lies mainly in the form of its pulse drive, and it is this feature that allows stepper motors to be combined with modern digital control technology. However, the stepper motor is inferior to the traditional closed-loop control DC servo motor in terms of control accuracy, speed change range, and low-speed performance; therefore, it is mainly used in occasions where the accuracy requirements are not particularly high. Because of its simple structure, high reliability and low cost, stepper motor is widely used in various fields of production practice; especially in the field of CNC machine tool manufacturing, because the stepper motor does not need A/D conversion, and can directly convert digital pulse signals into angular displacements, so it has always been regarded as the ideal CNC machine tool actuating element.
In addition to their use in CNC machine tools, stepper motors can also be used in other machinery, such as as motors in automatic feeders, as motors in general-purpose floppy disk drives, and also in printers and plotters.
In addition, stepper motors also have many defects; due to the existence of no-load start frequency of stepper motors, so the stepper motor can run normally at low speeds, but if higher than a certain speed can not be started, and accompanied by a sharp whistling sound; different manufacturers of subdivided drive precision may vary greatly, the larger the subdivided fraction of the accuracy is more difficult to control; and, stepper motors rotate at low speeds when the larger the vibration and noise.
3. Torque motors
The so-called torque motor is a flat multi-pole permanent magnet DC motor. Its armature has a higher number of slots, commutator plates and series conductors to reduce torque pulsations and speed pulsations. There are two types of torque motors: DC torque motors and AC torque motors.
Among them, the DC torque motor has a very small self-induced reactance, so its responsiveness is very good; its output torque is proportional to the input current, independent of the speed and position of the rotor; it can be directly connected to the load at low speeds in a nearly blocked state without gear reduction, so it can produce a very high torque-to-inertia ratio in the load’s shaft and can eliminate the systematic errors due to the use of reduction gears.
AC torque motors can be divided into synchronous and asynchronous types, and the commonly used type is the squirrel cage asynchronous torque motor, which is characterized by low speed and large torque. Generally, AC torque motors are often used in the textile industry. Their working principle and structure are the same as those of single-phase asynchronous motors, but their mechanical characteristics are softer due to the higher resistance of the squirrel-cage rotor.
4. Switched reluctance motors
The switched reluctance motor is a new type of speed motor with extremely simple and robust structure, low cost and excellent speed control performance, which is a strong competitor of traditional control motors and has strong market potential. However, there are problems such as torque pulsation, operation noise and vibration, which need some time to be optimized and improved to adapt to the actual market application.
5. Brushless DC motors
Brushless DC motors (BLDCM) are based on brush DC motors, but their drive current is unadulterated AC; brushless DC motors can be further divided into brushless rate motors and brushless torque motors. Generally, brushless motors have two types of drive currents, one trapezoidal (usually “square”) and the other sinusoidal. The former is sometimes called a brushless DC motor, and the latter is called an AC servomotor, which is also a type of AC servomotor.
Brushless DC motors are usually of “slender” construction in order to minimize the moment of inertia. Brushless DC motors are much smaller in weight and volume than brushed DC motors, and the corresponding moment of inertia can be reduced by about 40%-50%. Due to the processing problems of permanent magnet materials, brushless DC motors generally have a capacity of less than 100kW.
This kind of motor’s mechanical characteristics and regulation characteristics of good linearity, wide speed range, long life, easy maintenance and low noise, there is no brush caused by a series of problems, so this kind of motor in the control system has great potential for application.
Post time: Jul-03-2024
