Hardware Reference
In-Depth Information
20
0
−20
−40
−60
10 1
10 2
10 3
10 4
10 5
200
100
0
−100
−200
10 1
10 2
10 3
10 4
10 5
Hz
Figure 3.76: Frequency response of the closed-loop system.
r:y, g:y_v,b:y_m
0.6
0.4
0.2
0
−0.2
−0.4
−0.6
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
time in sec
Figure 3.77: DSA output in response to reference input r =0.5 sin(200πt)+
sin(8000πt). Solid line: y p , dash-dot line: y v , dotted line: y m .
Simulation results for a 1 µm step response are shown in Figure 3.79 and
Figure 3.80. It is observed that the micro-actuator moves very quickly to the
setpoint first, and then slowly moves back to zero while VCM moves to the set-
point. This servo-mechanism significantly improves the dynamic performance
of the system. It is also observed that neither the output of the micro-actuator
nor that of the VCM exceeds its limit.
We can see from the above results that state feedback control design in
conjunction with the state observer design works well for the dual-stage servo
system in time domain. The design allows low frequency disturbance tracked
by VCM and high frequency disturbance tracked by micro-actuator. However,
 
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