What is a servomotor? How to control the servo motor?

Servo control is a human activity that controls the generated motion and the movement of objects to meet certain purposes. The so-called servo control refers to the effective control of the position, speed, acceleration and other changes of the object movement. This kind of control has been popularized in various fields. Servo control system refers to the feedback control system used to accurately follow or reproduce a process.

1. Command part: output device of action command signal

2. Drive part: a device that receives the output of the command part and drives the actuator (such as motor) to act

3. Feedback part: device for detecting the execution structure or load status

4. Actuator: receives the output signal of the driving part to generate the rotating torque, position and other states

Control mode:

Generally, servo has three control modes: speed control mode, torque control mode and position control mode.

1. Speed control

Speed loop block diagram

(1) Speed control means that the motor operates according to the given speed command

(2) The application of speed control is quite wide, including: continuous speed regulation system requiring fast seat response; Positioning system with upper closed loop; A system that requires multiple column speeds for fast switching.

(3) Generally, the servo speed is given as an analog quantity, that is, the amplitude of the analog quantity determines the given speed, and the positive and negative determination of the motor response depends on the speed command gain (Pn300).

matters needing attention

(1) The speed loop gain Pn102 is usually set higher to make the whole system respond faster, and the motor rigidity will also be enhanced. However, large gain may cause system vibration. In general, this parameter should be set higher when the load inertia is large.

(2) The speed loop integration time Pn103 is used to eliminate the static error. The larger the value is set, the slower the response is, and the longer the time to reach the command is. Generally, the greater the load inertia, the greater the integration time should be set.

(3) When the upper computer is closed loop, soft start deceleration time parameters Pn306 and Pn307 should not be set as far as possible.

(4) If there is no upper computer for closed loop and the motor is expected to stop completely through analog quantity, zero clamping or proportional control must be adopted.

(5) When the upper computer is used as the position closed loop, the analog quantity cannot be automatically zeroed.

2. Torque control

(1) Non speed control, control output torque is a typical torque control.

(2) Often used for tension control and other occasions

(3) The input is analog quantity, and the relationship between analog quantity and torque depends on the torque command gain.

(4) For example, if you set Pn400 as 100, it means that if you enter 10 ν The output torque of the motor can reach * * * * of its rated torque when the analog quantity of.

matters needing attention

(1) Torque control shall first limit the motor speed. The motor speed can be limited by analog quantity or by setting parameters.

(2) The smaller the torque command gain Pn400 is set, the greater the torque corresponding to the same analog quantity.

3. Position control

Position control is widely used in various positioning occasions and can directly replace various stepping drive systems. Generally, the servo motor controls the position by receiving pulses. The number of pulses determines the position, and the frequency of pulses determines the speed of the motor. The position equivalent of a pulse depends on the mechanical structure and electronic gear.

matters needing attention

(1) The displacement of each point is composed of two parameters. The actual programmed displacement is composed of the algebraic sum of the two parameters. Note the unit of the two parameters.

(2) Pay attention to the speed of searching the reference point. If the speed is too high, set the soft start acceleration and deceleration to reduce the impact on the machine.

(3) In point control, 1CN can be realized without any input or output.

(4) At present, only the sequence can be changed.

(5) The user can communicate with the servo via Modbus protocol through the touch screen, and then modify the position, speed, etc. through the touch screen.

Comparison of three control modes:

(1) If there is no requirement for the speed and position of the motor, as long as a constant torque is output, of course, the torque mode is used.

(2) If there is a certain accuracy requirement for the position and speed, but the real-time torque is not very concerned, the torque mode is not convenient, but the speed or position mode is better. 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 requirements, the position control mode has no high requirements for the upper controller.

(3) As far as the response speed of the servo driver is concerned, the torque mode calculation amount * is small, and the driver's response to the control signal * is fast; The position mode has a large amount of calculation, and the driver responds slowly to the control signal.

(4) When the dynamic performance in motion is required to be high, the servo motor needs to be adjusted in real time. If the operation speed of the controller itself is very slow (such as PLC, or low-end motion controller), position control is used. If the operation speed of the controller is relatively fast, the position ring can be moved from the driver to the controller in the speed mode to reduce the workload of the driver and improve the efficiency (such as most middle and high-end motion controllers); If there is a better upper controller, it can also be controlled by torque to remove the speed loop from the driver, which is generally only possible for high-end dedicated controllers to do so, and at this time, there is no need to use a servo motor.