How to Debug and Control Servo Motor by Analog Signal?

Motion controller usually adapts two types of command mode to control servo motor:

Digital pulse

This mode is similar to the control mode of stepper motor. The motion controller sends"pulse/direction" type pulse command signal to servo driver, when servo driver operates in position control mode, position closed loop is completed by servo driver. This mode of servo motor has the advantages that system debugging is simple and is difficult to cause interference, but has the disadvantage that the response of servo system is slightly slow.

Analog signal

In this mode, motion control system sends -10V analog voltage command to servo driver and receives position feedback signals from position detection elements, such as motor encoder or linear grating, etc., when servo driver operates in speed control mode, position closed loop is completed by motion controller. Europe and America servo products mostly adapt such operation mode, which has the advantage that response of servo is rapid, but the disadvantage is that they are sensitive to site interference and debugging is complex.

The following introduces the general debugging steps how the motion controller controls the servo motor by analogue signal:

1. Parameter initialization

Before connecting the wires, first initialize the parameter. On controller: Choose the control mode, reset the PID parameter, the enable signal is set off when controller is energized as default, store this condition and ensure that when controller is energized next time, this condition is as default. On servo driver: Set the control mode, set to enable controlling from outside, gear ratio output by encoder signal, set the proportional relation between control signal and motor speed. Generally, it is suggested that maximum design speed in servo operating should correspond to 9V control voltage.

2. Wire connection

Shut down the controller and connect the signal wire between controller and servo. The following wires must be connected: Analogue output wire of controller, universal signal wire, encoder signal wire output by servo. After the wire connection is rechecked and there is correct, energize the controller of motor. Now, motor should have no motion and can rotate easily by external force. If not, check the setting of enable signal and the wire connection. Use external force to rotate motor to check if the controller can detect the motor position change. If not, check wire connection and setting of encoder signal.

3. Direction testing

For one closed loop control system, if the direction of feedback signal is incorrect, the consequences must be disastrous. Turn on the enable signal of servo by controller. Now, servo motor should rotate at a lower speed, which is called "Zero Drift". Generally, there is command parameter of zero drift inhibition on controller. Use this command or parameter to check if the speed and direction of motor can be controlled by this command. If not, check the parameter setting for analogue connection and control mode. Ensure that motor rotates clockwise and encoder count increases if positive value is provided while motor rotates counterclockwise and encoder count decreases if negative value is provided. If motor has load and stroke is limit, this mode is not recommended. Do not provide too high voltage when testing and it is suggested that the voltage is below 1V. If the direction does not match, correct the parameter on controller or motor.

4. Zero drift inhabitation

During closed loop control, the existence of zero drift inhabitation will have certain influence on control effect and it is better to restrain it. Use the parameter of zero drift inhabitation on controller or servo to adjust the motor carefully, so as to make the speed close zero. Since zero float itself has some randomness, it is not necessary to require the motor speed must be zero.

5. Closed loop control building

Turn on the servo enable signal again by controller and input a smaller ratio gain on controller. For the input extent, this can only by feeling. Just to be sure, you can input the minimum allowable value of controller. Turn on the universal signal of controller and servo. Now, motor should enable to act roughly according to motion command.

6. Closed loop parameter adjustment

Adjust the control parameter finely to ensure that motor moves according to the command from controller. This work is necessary to do.