Estun servo motor – three modes of servo control

The speed control and torque control of the servo motor are controlled by analog quantity, and the position control is controlled by generating pulses. The specific control method to use should be selected according to the customer's requirements and what kind of motion function is satisfied.

Generally, there are three control modes for servo: speed control mode, torque control mode, position control mode, speed control and torque control are all controlled by analog quantity. Position control is controlled by generating pulses. The specific control mode should be selected according to the customer's requirements and what kind of motion function is satisfied. If you don't have any requirements for the speed or position of the motor, just output a constant torque, of course, in torque mode. If you have certain accuracy requirements for position and speed, and you 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 effect will be better with speed control.

If the requirements are not very high, or there is basically no real-time requirements, there is no high requirement for the upper controller with position control. In terms of the response speed of the servo drive, the torque mode has the least amount of calculation, and the driver responds the fastest to the control signal. The position mode is the most computationally intensive, and the driver is the slowest to respond to the control signal. When there are relatively high requirements for dynamic performance in motion, it is necessary to adjust the motor in real time. If the controller itself is very slow (such as a PLC, or a low-end motion controller), it can be controlled by position. If the computing speed of the controller is relatively fast, you can use the speed mode to move the position loop from the driver to the controller to reduce the workload of the driver and improve efficiency (such as most mid-to-high-end motion controllers); If there is a better upper controller, it can also be controlled by torque and the speed ring can also be removed from the drive, which is generally only possible with high-end dedicated controllers, and there is no need to use a servo motor at all.

If you don't have any requirements for the speed or position of the motor, just output a constant torque, of course, in torque mode.

If you have certain accuracy requirements for position and speed, but are not very concerned about real-time torque, it is better to use speed or position mode. If the upper controller has a better closed-loop control function, the effect will be better with speed control. If the requirements are not very high, or there is basically no real-time requirements, there are no high requirements for the upper controller with position control.

In terms of the response speed of the servo drive, the torque mode has the least amount of calculation, and the driver responds the fastest to the control signal. The position mode is the most computationally intensive, and the driver is the slowest to respond to the control signal.

When there are relatively high requirements for dynamic performance in motion, it is necessary to adjust the motor in real time. If the controller itself is very slow (e.g. a PLC, or a low-end motion controller), it is controlled by position. If the computing speed of the controller is relatively fast, the position ring can be moved from the driver to the controller in the speed mode, so as to reduce the workload of the driver and improve efficiency; If there is a better upper controller, it can also be controlled by torque and the speed ring can also be removed from the drive, which is usually only possible with high-end dedicated controllers.

Generally speaking, there is a more intuitive way to compare the quality of drive control, which is called response bandwidth. When the torque control or speed control, through the pulse generator to give it a square wave signal, so that the motor continues to rotate, reverse, constantly adjust the frequency, the oscilloscope is displayed is a sweep signal, when the apex of the envelope reaches the highest value of 70.7%, it means that it has been out of step, at this time the frequency of the level, can explain the quality of the control, the general current loop can do more than 1000HZ, and the speed loop can only do tens of hertz.

Torque control: The torque control mode is to set the output torque of the motor shaft through the input of external analog quantity or the assignment of the direct address, which is specifically manifested as 10V corresponding to 5Nm, when the external analog quantity is set to 5V, the output of the motor shaft is 2.5Nm: if the motor shaft load is lower than 2.5Nm, the motor rotates, 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 (usually generated under the condition of gravity load). The set torque can be changed by changing the setting of the analog quantity in real time, and the value of the corresponding address can also be changed by means of communication.

The application is mainly in the winding and unwinding device that has strict requirements for the force of the material, such as the wire rao device or the optical fiber pulling equipment, the setting of torque 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.

Position control: The position control mode is generally to determine the size of the rotation speed through the frequency of the external input pulse, and to determine the rotation angle through the number of pulses, and some servos can directly assign the speed and displacement through communication. Since the position mode can have a very tight control of speed and position, it is generally used in positioning devices.

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

Speed mode: The speed can be controlled by the analog input or the frequency of the pulse, and the speed mode can also be positioned when the outer loop PID control with the upper control device is controlled, but the position signal of the motor or the position signal of the direct load must be fed back to the upper position for calculation. The position mode also supports the direct load outer ring to detect the position signal, 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, which has the advantage that the error in the intermediate transmission process can be reduced, and the positioning accuracy of the whole system is increased.

Talking about the three rings, the servo motor is generally controlled by three rings, and the so-called three rings are three closed-loop negative feedback PID adjustment systems. The innermost PID ring is the current loop, which is completely carried out inside the servo drive, and the output current of each phase of the driver to the motor is detected by the Hall device, and the PID is adjusted by the setting of the negative feedback current, so as to achieve the output current as close as possible to the set current, and the current loop is to control the torque of the motor, so the operation of the driver in the torque mode is the smallest, and the dynamic response is the fastest.

The second ring is the speed loop, through the signal of the motor encoder detected to carry out negative feedback PID adjustment, its loop PID output is directly the setting of the current loop, so the speed loop control includes the speed loop and the current loop, in other words, any mode must use the current loop, the current loop is the root of the control, in the speed and position control at the same time the system is actually carrying out the current (torque) control to achieve the corresponding control of speed and position.

The third ring is the position ring, which is the outermost ring, which can be built between the driver and the motor encoder, or 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 the calculation of all three rings in the position control mode, and the system calculation amount is the largest and the dynamic response speed is the slowest.

Estun servo motor – three modes of servo control

Estun servo motor – three modes of servo control

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