Hardware Reference
In-Depth Information
60
VCM path
Micro−actuator path
Dual−stage Open−loop
40
20
0
−20
−40
10 2
10 3
10 4
200
0
−200
−400
−600
10 2
10 3
10 4
Frequency (Hz)
Figure 3.97: Open loop Bode plots.
20
0
−20
−40
−60
−80
−100
10 1
10 2
10 3
10 4
10 5
Frequency in Hz
Figure 3.98: Sensitivity function (S) and Complementary sensitivity function
(T ).
3. if the controller is capable of utilizing a microactuator with smaller range
of displacement without significant degradation of performance, the spec-
ifications for mechanical design can be relaxed and therefore the actuator
can be optimized better.
Figure 3.99 shows a 4 µin step response of the dual-stage control system.
The micro-actuator is not saturated so the linear controller and the nonlinear
controller behave in similar manner. Figure 3.100 shows the linear controller
response with a 10 µin step input. The position output is oscillatory, and the
settling time is as long as 1.5 ms. Increasing the reference signal amplitude
further makes the dual-stage control loop unstable. However, on the contrary,
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