Appendix A
S e r v o T u n i n g
In a Hurry?
We strongly recommend tuning the APEX615n before attempting to execute
any motion functions. If you must execute motion quickly (e.g., for testing purposes),
you should at least complete this appendix’s Controller Tuning Procedure and find a
proportional feedback gain that gives a stable response for your system. Then you can proceed
to execute your motion functions. Later on, you should read through this entire Servo Tuning
appendix and follow its procedures to ensure your system is properly tuned.
Servo System Terminology
This section gives you an overall understanding of the principles and the terminology used in
tuning the APEX615n Servo Controller/Drive.
Servo Tuning Terminology
The APEX615n uses a digital control algorithm to control and maintain the position and
velocity. The digital control algorithm consists of a set of numerical equations used to
periodically (once every servo sampling period) calculate the value of the control
signal output. The numerical terms of the equations consist of the current commanded and
actual position values (plus several values from the previous sampling period) and a set of
control parameters. Each control parameter, commonly called a gain, has a specific function
(see Servo Control Techniques later in this chapter). Tuning is the process of selecting and
adjusting these gains to achieve optimal servo performance.
When this control algorithm is used, the whole servo system is a closed-loop system (see
diagram below). It is called closed loop because the control algorithm accounts for both the
command (position, velocity, tension, etc.) and the feedback data (from the resolver,
encoder, or ANI input); therefore, it forms a closed loop of information flow.
When all gains are set to zero, the digital control algorithm is disabled. During system setup
or troubleshooting, it may be desirable to disable the algorithm and use the
SOFFS
command
to directly control the motor current; then you can test the drive/motor operation independently
from the controller.
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