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What Are the Control Methods of Servo Motors?

What Are the Control Methods of Servo Motors?

If you have no requirements for the speed and position of the motor, as long as you output a constant torque, you only need to use the torque mode.

If there is a certain accuracy requirement for position and speed, but the real-time torque is not very concerned, use speed or position mode.

1. Position control of AC servo motor:

In the position control mode, the rotation speed is generally determined by the frequency of the external input pulse, and the rotation angle is determined by the number of pulses. Some servos can also directly assign speed and displacement through communication. Since the position mode can strictly control the speed and position, it is generally used in positioning devices.

Applications such as CNC machine tools, printing machinery and so on.

2. Torque control of AC servo motor:

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 assignment of the direct address. For example, if 10V corresponds to 5Nm, when the external analog quantity is set to 5V, the motor shaft output 2.5Nm: If the motor shaft load is lower than 2.5Nm, the motor rotates forward, the motor does not rotate when the external load is equal to 2.5Nm, and the motor reverses when it is greater than 2.5Nm. The set torque can be changed by immediately changing the setting of the analog quantity, or can be realized by changing the value of the corresponding address through communication.

It is mainly used in winding and unwinding devices that have strict requirements on the force of the material, such as winding devices or fiber-pulling equipment. The torque setting should be changed at any time according to the change of the winding radius to ensure the force of the material. It will not change with the change of winding radius.

3. Speed mode of AC servo motor:

The rotation speed can be controlled by analog input or pulse frequency, and the speed mode can also be used for positioning when there is an outer loop PID control of the upper control device. However, the position signal of the motor or the position signal of the direct load needs to be fed back to the host for calculation.

The position mode also supports direct load outer ring 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 detection device at the end load end. The advantage of this is that it can reduce errors in the intermediate transmission process and increase the positioning accuracy of the entire system.

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