Newport MM4006, User Manual

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MM4006
8-Axis Motion Controller/Driver
Section 7
Servo Tuning
7.1 Servo Tuning Principles
The MM4006 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. Yo u s h o u l d f i r s t r e v i e w t h e C o n t r o l L o o p s
paragraph in the Motion Control Tutorial Section and, if needed, consult
additional servo control theory books.
Always start the tuning process using the default values supplied with the
MM4006 for each motion device type, or for the generic Default type. These
values are usually v e r y conservative, favoring safe, oscillation -free
operation for a tighter, more responsive system that minimizes following
error. To achieve the best dynamic performance possible, the system must
be tuned for your specific application. Load, acceleration, stage orientation
and performance requirements all affect how the servo loop should be
tuned for best results.
7.1.1 H a r d w a r e Requirements
Tuning is best accomplished when the system response can be measured.
This can be done with external monitoring devices but this can introduce
errors.
The MM4006 controller avoids this problem by offering a Trace capability.
When Trace mode is activated, the controller can record real and desired
positions simultaneously. These are the basic pieces of information that
the controller uses to calculate the PID filter. The sample interval can be as
fast as the servo update cycle (0.0005 sec) and the total number of samples
can be up to 4000 points.
With these powerful capabilities, there is no need for additional hardware
to perform servo tuning.
7.1.2 S o f t w a r e Requirements
The MM4006 controller offers two types of trace capabilities. One is a sin-
gle axis Trace mode supported b y the SP, XS, TM, XN and TT commands
and the other is a Global Trace mode in which
all axes are sampled. This is
controlled by the SQ, XQ, GQ, NQ and TQ commands. The two modes are
completely independent.
Performance data for tuning can be acquired in two ways: you could write
custom software using the commands mentioned o r use the NMCServo
NEWPORT software that has all the necessary functions, including plotting
performance and saving the results.
For a detailed description of the NMCServo software and its operation
please review NMC Softwares User's Manual.
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EDH0181En1020 — 03/03