Step 9. Tune The Servo System - Galil Motion Control DMC-18 2 Series User Manual

corresponding axis is unavailable for an external connection. If an encoder is used for position
feedback, connect the encoder to the main encoder input corresponding to that axis. The commanded
position of the stepper can be interrogated with RP or DE. The encoder position can be interrogated
with TP.
The frequency of the step motor pulses can be smoothed with the filter parameter, KS. The KS
parameter has a range between 0.5 and 16, where 16 implies the largest amount of smoothing. See
Command Reference regarding KS.
The DMC-18x2 profiler commands the step motor amplifier. All DMC-18x2 motion commands apply
such as PR, PA, VP, CR and JG. The acceleration, deceleration, slew speed and smoothing are also
used. Since step motors run open-loop, the PID filter does not function and the position error is not
generated.
To connect step motors with the DMC-18x2 you must follow this procedure:
Step A. Install SM jumpers
Step B. Connect step and direction signals from controller to motor amplifier
Step C. Configure DMC-18x2 for motor type using MT command. You can configure the

Step 9. Tune the Servo System

Adjusting the tuning parameters is required when using servo motors (standard or sinusoidal
commutation). 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 Servo Design Kit (SDK 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 integrator to zero with the instruction
KI 0 (CR)
and set the proportional gain to a low value, such as
KP 1 (CR)
KD 100 (CR)
For more damping, you can increase KD (maximum is 4095). Increase gradually and stop after the
motor vibrates. A vibration is noticed by audible sound or by interrogation. If you send the command
TE X (CR)
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
KP 10 (CR)
DMC-18x2
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Each axis of the DMC-18x2 that will operate a stepper motor must have the
corresponding stepper motor jumper installed. For a discussion of SM jumpers, see
section Step 2. Install Jumpers on the DMC-18x2.
from the controller to respective signals on your step motor amplifier. (These signals are
labeled PWMX and SIGNX for the x-axis on the ICM-2900). Consult the documentation
for your step motor amplifier.
DMC-18x2 for active high or active low pulses. Use the command MT 2 for active low
step motor pulses and MT -2 for active high step motor pulses. See description of the MT
command in the Command Reference.
Integrator gain
Proportional gain
Derivative gain
Tell error
Proportion gain
Chapter 2 Getting Started • 21