There are three control methods for servo motors: position control, speed control, and torque control. What is used here is position control.

Before position control, it is necessary to set the parameters of the servo motor. For example, after calculation, it is found that 1000 pulses are required for the servo motor to rotate once and move forward by 10cm. Then, connect the PLC and servo drive. The working position that needs to be reached by the servo motor is 25cm, so 2500 pulses are sent to the servo driver through the PLC. After the PLC sends out the pulses, it continues to send 1000 pulses, and the motor reaches 35cm. This positioning is relative motion positioning. Servo has two positioning methods: relative motion and absolute motion.

Extended Information

1. Initialize parameters

Initialize parameters before wiring. 

On the control card: select the appropriate control mode; Reset the PID parameters to zero; When the control card is powered on, the default enable signal is turned off; Save this state to ensure that the control card is in this state when powered on again.

On the servo motor: set the control mode; Enable external control through settings; Gear ratio of encoder signal output; Set the proportional relationship between control signal and motor speed. Generally speaking, it is recommended to set the maximum design speed in servo operation to correspond to a control voltage of 9V. For example, Shanyang sets the speed corresponding to 1V voltage, with a factory value of 500. If you only want the motor to work below 1000 rpm, then set this parameter to 111.

2. Wiring

Power off the control card and connect the signal line between the control card and the servo. The following lines must be connected: analog output line of the control card, enable signal line, and encoder signal line of the servo output. After rechecking the wiring for any errors, power on the motor and control card (as well as the PC). At this point, the motor should not move and can be easily rotated with external force. If not, check the setting and wiring of the enable signal. Rotate the motor with external force and check if the control card can correctly detect the change in motor position. Otherwise, check the wiring and settings of the encoder signal

3. Test direction

For a closed-loop control system, if the direction of the feedback signal is incorrect, the consequences will definitely be catastrophic. Activate the servo signal through the control card. At this point, the servo should rotate at a lower speed, which is the legendary 'zero drift'. Generally, there are instructions or parameters on the control card to suppress zero drift.

Use this command or parameter to see if the speed and direction of the motor can be controlled through this command (parameter). If it cannot be controlled, check the parameter settings of the analog wiring and control mode. Confirm that a positive number is given, the motor rotates forward, and the encoder count increases; Given a negative number, the motor rotates in reverse and the encoder count decreases. If the motor has a load and limited travel, do not use this method. Do not apply excessive voltage during testing, it is recommended to be below 1V. If the directions are not consistent, you can modify the parameters on the control card or motor to make them consistent.

4. Suppress zero drift

In the closed-loop control process, the presence of zero drift will have a certain impact on the control effect, and it is best to suppress it. Use control cards or servo to suppress zero drift parameters, carefully adjust them to make the motor speed approach zero. Due to the inherent randomness of zero drift, there is no need to require the motor speed to be absolutely zero.

5. Establish closed-loop control

Release the servo enable signal again through the control card, and input a smaller proportional gain on the control card. As for how much is considered small, it can only be felt. If you are really worried, enter the minimum value allowed by the control card. Turn on the enable signals for the control card and servo. At this point, the motor should be able to roughly make movements according to the motion instructions.

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