Servo driver is a kind of controller used to control servo motor. Its function is similar to that of frequency converter acting on ordinary AC motor. It is a part of servo system and mainly used for high-precision positioning system.
As an important part of modern motion control, servo driver is widely used in industrial robots, CNC machining centers and other automation equipment. There are generally three control modes: speed control mode, torque control mode and position control mode.

1. Speed mode.
The speed can be controlled by the input of analog quantity or the frequency of pulse. When there is an outer loop PID control of the upper control device, the speed mode can be located, but the position signal of the motor or the position signal of the direct load must be fed back to the upper for calculation. The position mode also supports direct loading of the outer ring to detect the 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 detection device at the direct final load end. The advantage of this is to reduce the error in the intermediate transmission process and improve the positioning accuracy of the entire system.

2. Torque control.
The torque control method is to set the output torque of motor shaft by inputting external analog quantity or allocating direct address. The set torque can be changed by changing the setting of analog quantity, or by changing the value of corresponding address through communication.
It is mainly used for winding and unwinding devices with strict requirements on materials, such as winding devices or fiber drawing equipment. The setting of torque shall be changed at any time according to the change of winding radius to ensure that the stress of materials will not change with the change of winding radius.
3. Position control.
In general, the position control mode determines the rotation speed by the frequency of external input pulses, and determines the rotation angle by the number of pulses. Some servo systems can directly assign values to speed and displacement through communication. Because position mode can strictly control speed and position, it is usually used for positioning equipment.