Step 9. Tune The Servo System - Galil Motion Control CDS-3310 User Manual

Step C. Reverse positive direction (if desired)
Once you have closed the loop with the correct polarity, you can move on to the compensation phase
(servo system tuning) to adjust the PID filter parameters, KP, KD and KI. It is necessary to accurately
tune your servo system to ensure fidelity of position and minimize motion oscillation as described in
the next section.

Step 9. Tune the Servo System

Adjusting the tuning parameters is required when using servo motors. The system compensation
provides fast and accurate response and the following presentation suggests a simple and easy way for
compensation. More advanced design methods are available with software design tools from Galil,
such as the Windows Servo Design Kit (WSDK software )
The filter has three parameters: the damping, KD; the proportional gain, KP; and the integrator, KI.
The parameters should be selected in this order.
To start, set the gains to zero with the instructions
Increase KD gradually (maximum is 4095) and stop after the motor vibrates. A vibration is noticed by
audible sound or by interrogation. If you send the command
a few times, and get varying responses, especially with reversing polarity, it indicates system vibration.
When this happens, simply reduce KD.
Next you need to increase the value of KP gradually (maximum allowed is 1023). You can monitor the
improvement in the response with the Tell Error instruction
As the proportional gain is increased, the error decreases.
Again, the system may vibrate if the gain is too high. In this case, reduce KP. Typically, KP should
not be greater than KD/4.
Finally, to select KI, start with zero value and increase it gradually. The integrator eliminates the
position error, resulting in improved accuracy. Therefore, the response to the instruction
becomes zero. As KI is increased, its effect is amplified and it may lead to vibrations. If this occurs,
simply reduce KI.
After appropriate PID gains are found, burn them into the EEPROM with BN.
For a more detailed description of the operation of the PID filter and/or servo system theory, see
Chapter 10 - Theory of Operation.
Tuning must be done before configuring a distributed network (Chapter 11).
i
14 Chapter 2 Getting Started
The motor should now hold position.
Once the feedback polarity is correct (the motor does not run away), the positive direction of
motion may be backwards from the desired positive direction. If this is the case, the positive
direction can be changed with both the CE and MT commands while the motor is off. For
example MOX; CEX=2; MTX=-1; SHX.
KIX= 0 <return> Integrator gain
KPX=0 <return> Proportional gain
KDX=0 <return> Derivative gain
TEA <return> Tell error on A axis
KP 10 <return> Proportion gain
TEA <return> Tell error on A axis
TEA <return>
CDS-3310