Introduction to the types of motors and their differences

Motors play a key role in many motion control functions in numerous industries including packaging, food and beverage, manufacturing, medical and robotics. We can choose from several motor types based on function, size, torque, accuracy and speed requirements.

As we all know, the motor is an important part of the transmission and control system. With the development of modern science and technology, the focus of the motor in practical applications has begun to shift from the simple transmission in the past to the complex control; especially the speed and position of the motor. , Precise control of torque. However, the motor will have different designs and driving methods according to different applications. At first glance, it seems that the selection is very complicated. Therefore, for people to use the rotating motor, a basic classification has been carried out. Below we will introduce step by step the most representative, commonly used, and most basic motors in motors—control motors, power motors, and signal motors.

control motor

The control motor is mainly used in precise speed and position control, and is used as an "actuator" in the control system. It can be divided into servo motors, stepper motors, torque motors, switched reluctance motors, DC brushless motors, etc.

1. Servo motor

Servo motors are widely used in various control systems, which can convert the input voltage signal into the mechanical output on the motor shaft, and drag the controlled element to achieve the control purpose. Generally speaking, the servo motor requires that the speed of the motor is controlled by the applied voltage signal; the speed can change continuously with the change of the applied voltage signal; the torque can be controlled by the current output by the controller; the motor's response should be fast, The volume should be small and the control power should be small. Servo motors are mainly used in various motion control systems, especially servo systems.

Servo motors are divided into DC and AC. The earliest servo motors are general DC motors. When the control accuracy is not high, general DC motors are used as servo motors. At present, with the rapid development of permanent magnet synchronous motor technology, most of the servo motors refer to 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 displacement; more generally speaking: 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 angular displacement of the motor by controlling the number of pulses, so as to achieve the purpose of precise positioning; at the same time, we can also control the speed and acceleration of the motor rotation by controlling the pulse frequency, so as to achieve the purpose of speed regulation. At present, the more commonly used stepping motors include reactive stepping motors (VR), permanent magnet stepping motors (PM), hybrid stepping motors (HB) and single-phase stepping motors.

The main difference between stepper motors and ordinary motors lies in the form of pulse drive. It is this feature that enables stepper motors to be combined with modern digital control technology. However, the stepper motor is not as good as the traditional closed-loop control DC servo motor in terms of control accuracy, speed variation range, and low-speed performance; so it is mainly used in occasions where the accuracy requirements are not particularly high. Because the stepping motor has the characteristics of simple structure, high reliability and low cost, the stepping motor is widely used in various fields of production practice; especially in the field of CNC machine tool manufacturing, since the stepping motor does not require A/D conversion, it can It directly converts the digital pulse signal into angular displacement, so it has always been regarded as the most ideal CNC machine tool actuator.

In addition to applications in CNC machine tools, stepper motors can also be used in other machinery, such as motors in automatic feeders, as motors in general-purpose floppy disk drives, and in printers and plotters.

In addition, the stepper motor also has many defects; due to the no-load start frequency of the stepper motor, the stepper motor can run normally at low speed, but if it is higher than a certain speed, it cannot start, and it is accompanied by a sharp whistle; different The precision of the subdivision driver of the manufacturer may vary greatly. The larger the number of subdivisions, the more difficult it is to control the precision; and the stepper motor has large vibration and noise when it rotates at low speed.

3. Torque motor

The so-called torque motor is a flat multi-pole permanent magnet DC motor. The armature has more slots, commutation segments and series conductors to reduce torque ripple and speed ripple. There are two types of washing machine motors: DC torque motors and AC torque motors.​​

Among them, the self-inductance reactance of the DC torque motor is very small, so the responsiveness is very good; its output torque is proportional to the input current, and has nothing to do with the speed and position of the rotor; it can be directly connected to the load in a state of close to the locked rotor. No gear reduction is required, so a high torque-to-inertia ratio can be generated on the loaded shaft and system errors due to the use of reduction gears can be eliminated.

AC torque motors can be divided into two types: synchronous and asynchronous. Currently, squirrel-cage asynchronous torque motors are commonly used, which have the characteristics of low speed and large torque. In general, AC torque motors are often used in the textile industry, and their working principle and structure are the same as those of single-phase asynchronous motors, but due to the large resistance of squirrel-cage rotors, their mechanical properties are softer.

4. Switched Reluctance Motor

Switched reluctance motor is a new type of speed regulating motor with extremely simple and sturdy structure, low cost and excellent speed regulation performance. It is a strong competitor of traditional control motors and has strong market potential. However, there are also problems such as torque ripple, running noise and vibration, and it takes a certain time to optimize and improve to adapt to the actual market application.​​

5. Brushless DC Motor

The brushless DC motor (BLDCM) is developed on the basis of the brushed DC motor, but its driving current is an uncompromising AC; the brushless DC motor can be divided into a brushless speed motor and a brushless torque motor. . Generally, there are two types of drive currents for brushless motors, one is a trapezoidal wave (usually a "square wave"), and the other is a sine wave. Sometimes the former is called a DC brushless motor, and the latter is called an AC servo motor, which is exactly a type of AC servo motor.

In order to reduce the moment of inertia, the brushless DC motor usually adopts a "slender" structure. The brushless DC motor is much smaller in weight and volume than the brushed DC motor, and the corresponding moment of inertia can be reduced by about 40%-50%. Due to the processing of permanent magnet materials, the general capacity of brushless DC motors is below 100kW.

This motor has good linearity of mechanical characteristics and adjustment characteristics, wide speed regulation range, long life, easy maintenance, low noise, and no series of problems caused by brushes, so this motor has a great role in the control system. application potential.