Do You Know How Servo Drive Work?

Servo motors are an important part of modern motion control and are often used in automation equipment such as industrial robots and CNC machining centers. In particular, servo motors that control AC permanent magnet synchronous motors have developed into research hotspots at home and abroad. Current, speed and three-position closed-loop control algorithms based on vector control are widely used in the design of AC servo motors. Whether it is meaningful to control the speed in the algorithm plays a key role in the entire servo control system, especially the speed control performance.

The working process of servo drive

Servo motors all use digital signal processor (DSP) as the control core, which can achieve more complex control algorithms, digitization, networking, and intelligence; power devices usually take the drive circuit equipped with intelligent power modules (IPM) as the core, and IPM integration It has a control circuit, and has detection and protection circuits for overvoltage, overcurrent, overheating and undervoltage faults. A soft start circuit is also added to the main loop to reduce the influence of the starting process on the drive.

First, the control unit rectifies the input three-phase power supply or the mains power supply through the three-phase full-bridge rectifier circuit to obtain the corresponding direct current. After the AC servo motor is rectified by the three-phase power supply or the mains, it is driven by a three-phase sine wave PWM voltage inverter. The entire process of the power drive unit can be simply regarded as an AC-DC-AC process. The main topology circuit of the rectifier unit (AC-DC) is a completely uncontrolled three-phase bridge rectifier circuit. High quality Servo motors generally have three control methods: position control, torque control and speed control.

Position control The position control mode generally determines the rotation speed by the frequency of externally input pulses, and determines the rotation angle by the number of pulses. There are also some servos that can directly assign speed and displacement through communication. Due to the position mode It can have very strict control on speed and position, so it is generally used in positioning devices.

Torque control The torque control method is to set the external output torque of the motor shaft through the input of the external analog quantity or the direct address assignment, and the set torque can be changed by instantly changing the setting of the analog quantity . The torque setting should be changed at any time according to the change of the winding radius to ensure that the force of the material will not change with the change of the winding radius.

Speed mode can control the speed through analog input or pulse frequency. When the upper controller has outer loop PID control, the speed mode can also be used for positioning, but the motor position signal or direct load position signal should be used, and input and return to the upper position for calculation. The position mode also supports the direct load of the position signal detected by the outer loop. At this time, the encoder at the end of the motor shaft only detects the motor speed, and the position signal is output by the direct detection device at the end of the load. It can reduce the intermediate transfer process. The error increases the positioning accuracy of the entire system.

If there is no requirement for the speed and position of the motor, just output a constant torque, of course, use the torque mode.

If you have a certain accuracy requirement for position and speed, but are not very concerned about real-time torque, it is not convenient to use torque mode, and it is better to use speed or position mode.

If the upper 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 method is adopted.

The above is the working process of the servo drive. If you want to know more information about professional servo drives, please contact Ouke. Ouke is a professional supplier which provides Fanuc servo motor, Siemens servo drive, Mitsubishi servo motor, Fanuc servo drive, Fanuc servo motor encoder, Fanuc circuit boards, etc.