Section 7 - Servo Tuning; Tuning Principles; Tuning Procedures - Newport ESP6000 User Manual

Section 7
Servo Tuning
7.1

Tuning Principles

7.2

Tuning Procedures

Section 7 — Servo Tuning
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The ESP6000 controller uses a PID servo loop with feed-forward. Servo
tuning sets the Kp, Ki, and Kd, and feed-forward parameters of the digital
PID algorithm, also called the PID filter.
Tuning PID parameters requires a reasonable amount of closed-loop
system understanding. First review the Control Loops paragraph in the
Motion Control Tutorial Section. If needed, consult additional servo
control theory books.
Start the tuning process using the default values supplied with the stage.
These values are usually very conservative, favoring safe, oscillation-free
operation. To achieve the best dynamic performance possible, the system
must be tuned for the specific application. Load, acceleration, stage
orientation, and performance requirements all affect how the servo loop
should be tuned.
Servo tuning is usually performed to achieve better motion performance
(such as reducing the following error statically and/or dynamically) or
because the system is malfunctioning (oscillating and/or shutting off due
to excessive following error.)
Acceleration plays a significant role in the magnitudes of the following
error and overshoot, especially at start and stop. Rapid velocity changes
represent very high acceleration, causing large following errors and
overshoot. Use the smallest acceleration the application can tolerate to
reduce overshoot and make tuning the PID filter easier.
In the following descriptions, it is assumed that a software utility is
being used to capture the response of the servo loop during a motion
step command, and to visualize the results.
NOTE
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