The servo drive is simply a controller used to control the servo motor. Its function is similar to that of the inverter acting on a common AC motor. It is part of the servo system and is mainly used in high-precision positioning systems. Generally, the servo motor is controlled by three modes: position, speed and torque to realize high-precision transmission system positioning. At present, it is a high-end product of transmission technology. The following article will introduce you to the working principle of the servo drive.

The servo driver adopts digital signal processor (DSP) as the control core, which can realize more complicated control algorithms, realize digitalization, networking and intelligence; power devices generally adopt drive circuit designed with intelligent power module (IPM) as the core. The IPM integrates the drive circuit and has fault detection and protection circuits such as overvoltage, overcurrent, overheat and undervoltage. A soft start circuit is also added to the main circuit to reduce the impact of the startup process on the driver.

Servo drive working principle diagram

      Servo drive working principle diagram

First, the power driving unit rectifies the input three-phase electric or commercial power through a three-phase full-bridge rectifying circuit to obtain a corresponding direct current. After rectification of three-phase electricity or mains, the three-phase sinusoidal PWM voltage inverter is used to drive the AC servo motor. The whole process of the power drive unit can be simply the process of AC-DC-AC. The main topology circuit of the rectifier unit (AC-DC) is a three-phase full-bridge uncontrolled rectifier circuit. Servo drives generally have three control modes: position control mode, torque control mode, and speed control mode. The position control position control mode generally determines the rotation speed by the frequency of the externally input pulse, and determines the angle of rotation by the number of pulses. Some servos can directly assign speed and displacement by communication, due to the position mode. It has very strict control over speed and position, so it is generally applied to positioning devices.

The torque control torque control mode is to set the external output torque of the motor shaft through the external analog input or the direct address assignment. The set torque can be changed by changing the analog setting in real time. It can also be realized by changing the value of the corresponding address by means of communication. The application is mainly in the winding and unwinding devices that have strict requirements on the material, such as the winding device or the fiber-optic device. The torque setting is changed according to the change of the radius of the winding to ensure the stress of the material. It will change as the winding radius changes.

The speed mode can control the rotation speed through the analog input or the frequency of the pulse. The speed mode can also be positioned when the outer ring PID of the upper control device is controlled, but the position signal of the motor or the position signal of the direct load must be used. Give feedback to the upper level for calculation. The position mode also supports the direct load outer loop detection position signal. At this time, the encoder at the motor shaft end only detects the motor speed, and the position signal is provided by the direct final load end detection device. This has the advantage of reducing the intermediate transmission process. The error increases the positioning accuracy of the entire system.

■ If there is no requirement for the speed and position of the motor, as long as a constant torque is output, of course, the torque mode is used.
■ If there is a certain accuracy requirement for position and speed, and the real-time torque is not very concerned, it is not convenient to use the torque mode. It is better to use the speed or position mode.
■ If the host controller has a better closed-loop control function, the speed control effect will be better. If the requirements are not very high, or there is basically no real-time requirement, the position control mode is adopted. Servo feed system requirements

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