Both speed control and torque control are controlled by analog quantities. Position control is controlled by pulse. The specific control method should be selected according to the customer's requirements and what kind of sports function is satisfied.
If you do not require the speed and position of the motor, just output a constant torque, of course, using the torque mode.
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, and the speed or position mode is better.
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, there is no high requirement for the upper controller by the position control method.
In terms of the response speed of the servo drive, the torque mode calculation amount is the smallest, the driver has the fastest response to the control signal; the position mode calculation amount is the largest, and the driver has the slowest response to the control signal.
When there is a high requirement for dynamic performance in motion, the motor needs to be adjusted in real time. Then if the controller itself is slow (such as PLC, or low-end motion controller), it is controlled by position. If the controller is running faster, you can use the speed mode to move the position loop from the drive to the controller, reducing the workload of the drive and improving efficiency (such as most mid-to-high-end motion controllers); if there is better upper control It can also be controlled by torque, and the speed loop is also removed from the drive. This is generally only a high-end dedicated controller to do this, and at this time, no servo motor is needed at all.
Generally speaking, the driver control is good, each manufacturer said that he did the best, but now there is a relatively straightforward comparison method called response bandwidth. When torque control or speed control, give him a square wave signal through the pulse generator, so that the motor continuously rotates and reverses continuously, and the frequency is constantly increased. The oscilloscope displays a sweep signal when the envelope is When the apex reaches 70.7% of the highest value, it means that it has lost the step. At this time, the frequency of the frequency can show the product of the cow. The general current loop can be made above 1000Hz, and the speed loop can only be used for dozens. hertz.
For a more professional statement:
1. Torque control: The 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 specific performance is, for example, 10V corresponds to 5Nm, when the external analog quantity is set. When the motor is set to 5V, the motor shaft output is 2.5Nm: if the motor shaft load is lower than 2.5Nm, the motor will rotate forward. When the external load is equal to 2.5Nm, the motor will not rotate. When the motor is larger than 2.5Nm, the motor will reverse (usually generated under gravity load). ). The set torque can be changed by changing the analog setting in real time, or by changing the value of the corresponding address by communication.
The application is mainly used in the winding and unwinding devices which have strict requirements on the material stress, such as the wire drawing device or the fiber drawing device. The torque setting is changed according to the change of the radius of the winding to ensure the stress of the material is not It will change as the winding radius changes.
2. Position control: The position control mode generally determines the rotation speed by the frequency of the externally input pulse. The number of pulses is used to determine the angle of rotation. Some servos can directly assign speed and displacement through communication. Since the position mode has strict control over speed and position, it is generally applied to positioning devices.
Applications such as CNC machine tools, printing machinery, etc.
3. Speed ​​mode: The rotation speed can be controlled by the analog input or the frequency of the pulse. The speed mode can also be positioned when the outer ring PID control of the upper control device is used, but the position signal or direct load of the motor must be used. The position signal is given to the upper feedback 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 detecting device. This has the advantage of reducing the intermediate transmission process. The error increases the positioning accuracy of the entire system.
4, talk about the 3 ring, the servo is generally three ring control, the so-called three ring is three closed-loop negative feedback PID adjustment system. The innermost PID loop is the current loop. The loop is completely inside the servo driver. The Hall device detects the output current of each phase of the driver to the motor, and the negative feedback gives the current setting PID adjustment, so that the output current is as close as possible. Equal to the set current, the current loop is to control the motor torque, so in the torque mode the driver's operation is the smallest, the dynamic response is the fastest.
The second ring is the speed loop. The negative feedback PID is adjusted by the detected signal of the motor encoder. The PID output in the ring is directly set by the current loop, so the speed loop control includes the speed loop and the current loop. In other words, the current loop must be used in any mode. The current loop is the fundamental of control. At the same time of speed and position control, the system actually performs current (torque) control to achieve corresponding control of speed and position.
The third ring is the position loop, which is the outermost ring. It can be built between the drive and the motor encoder. It can also be built between the external controller and the motor encoder or the final load, depending on the actual situation. Since the internal output of the position control loop is the setting of the speed loop, the system performs all three loop operations in the position control mode. At this time, the system has the largest amount of calculation and the slowest dynamic response speed.
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