SECTION 6: T200 FUNCTIONAL OVERVIEW T200 User's Manual
PAGE 6-41
(B) also shows θ
err
when J
est
is tuned correctly, θ
err
steps with a slight ripple superimposed. θ
err
is a measure of
the model uncertainty, and of any disturbance torque which may be present. Normally there will be some viscous
friction present, so that θ
err
will step appropriately when the shaft velocity makes a step change.
• As a final check of proper tuning, display observer velocity on TP1, and compare it with the actual velocity
response which was shown on TP2 in Figure (A). These should be identical.
• Switch on the observer by using the OO command, (reference Section 8), and then Y to the subsequent prompt to
enable use of the observer velocity estimate. Figure (D) shows the velocity loop response when the observer is
switched into the loop. Note the lack of overshoot, because of a better measurement of velocity. The servo noise
generated is also reduced.
• In order to achieve higher gains, the compensator filter frequency may now be set higher, using the SW command,
(refer to Section 8). Typically this frequency may be set to 600 Hz, depending on motor servo noise. The P and I
gains may now be tuned up again, in the normal fashion described in 6.7.2.8Velocity Loop Tuning. Figure (E)
compares the response of an observer based system with a normal velocity loop system. Now the response settles in
just 2.2 mS, whereas without the observer the step settled in about 12 mS. The observer response also shows a
smaller overshoot.
CAUTION:-If
err
oscillates excessively when the velocity makes a step change, as
shown in Figure (C), then do not use the observer, since the load may not be modeled
adequately by the observer.
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