Classification and application of motors

Update:16 Aug 2019
Summary:

As we all know, the motor is an important part of the t […]

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 to the complicated control; especially the speed and position of the motor. , precise control of torque. However, the motor has different design and driving methods depending on the application. At first glance, it seems that the selection is very complicated, so in order to make a basic classification according to the use of the rotating electric machine. Below we will gradually introduce the most representative, most commonly used and most basic motors in the motor - control motors and 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. Can be divided into servo motor, stepper motor, torque motor, switched reluctance motor, DC brushless motor and so on.
Servo motor
Servo motors are widely used in various control systems to convert the input voltage signal into mechanical output on the motor shaft and drag the controlled components to achieve control purposes. Generally, the servo motor requires the speed of the motor to be controlled by the applied voltage signal; the speed can continuously change with the change of the applied voltage signal; the torque can be controlled by the current output by the controller; the motor is reflected quickly, The volume should be small and the control power should be small. Servo motors are mainly used in various motion control systems, especially the servo system.

The servo motor has DC and AC. The earliest servo motor is a general DC motor. When the control accuracy is not high, the general DC motor is used as the servo motor. With the rapid development of permanent magnet synchronous motor technology, most 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, 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 to achieve precise positioning. At the same time, the speed and acceleration of the motor can be controlled by controlling the pulse frequency 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 difference between a stepper motor and a normal motor is mainly in the form of its pulse drive. It is this feature that the stepper motor can be combined with modern digital control technology. However, the stepping motor is not as good as the traditional closed-loop controlled DC servo motor in terms of control accuracy, speed variation range and low-speed performance; therefore, it is mainly used in applications where the accuracy requirements are not particularly high. Stepper motors are widely used in various fields of production practice because of their simple structure, high reliability and low cost. Especially in the field of CNC machine tools, because stepper motors do not require A/D conversion, The digital pulse signal is directly converted into an angular displacement, so it has been considered as the most ideal CNC machine tool actuator.
In addition to its application on CNC machines, stepper motors can also be used on other machines, such as motors in automatic feeders, as general-purpose floppy disk drives, as well as in printers and plotters.
In addition, stepper motors also have many defects; stepper motors can run normally at low speeds due to the no-load start-up frequency of stepper motors, but they cannot start at higher speeds than with a certain speed, accompanied by sharp howling sounds; The subdivision driver accuracy of the manufacturer may vary greatly. The larger the subdivision number, the more difficult it is to control the accuracy; and the stepper motor has greater vibration and noise when rotating 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, commutator counts and series conductors to reduce torque ripple and speed pulsation. The torque motor has two kinds of DC torque motor and AC torque motor.

Among them, the DC torque motor has a small self-inductance reactance, so the 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 a low speed when it is close to the locked state. Without gear reduction, a high torque-to-inertia ratio can be produced on the shaft of the load and the system error due to the use of the reduction gear can be eliminated.
AC torque motors can be divided into synchronous and asynchronous. Currently, squirrel-cage asynchronous torque motors are used, which have the characteristics of low speed and large torque. Generally, an AC torque motor is often used in the textile industry, and its working principle and structure are the same as those of a single-phase asynchronous motor. However, since the squirrel-cage rotor has a large electrical resistance, its mechanical characteristics are soft.
4. Switched reluctance motor
Switched reluctance motor is a new type of speed-regulating motor. Its structure is extremely simple and sturdy, its cost is low, and its speed regulation performance is excellent. 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, which require some time to optimize and adapt to the actual market application.

5. Brushless DC motor
Brushless DC motor (BLDCM) is developed on the basis of brushed DC motor, but its driving current is uncompromising AC; brushless DC motor can be divided into brushless rate motor and brushless torque motor. . Generally, there are two kinds of driving currents of a brushless motor, one is a trapezoidal wave (generally "square wave"), and the other is a sine wave. Sometimes the former is called DC brushless motor, the latter is called AC servo motor, and it is also a kind of AC servo motor.

In order to reduce the moment of inertia, brushless DC motors usually adopt a "slender" structure. Brushless DC motors are much smaller in weight and volume than brushed DC motors, and the corresponding moment of inertia can be reduced by 40% to 50%. Due to the processing of permanent magnet materials, the general capacity of brushless DC motors is below 100 kW.
The motor has good linearity of mechanical characteristics and adjustment characteristics, wide speed range, long life, easy maintenance and low noise, and there is no series of problems caused by brushes. Therefore, this kind of motor has great control system. Application potential.

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