Hardware Reference
In-Depth Information
1
s
2
+ 1244s +1.7 × 10
9
µm/V ,
(3.180)
P
M
(s)=
20
×
5.45
×
10
7
s
2
+ 2450s +1.7 × 10
9
s
2
+ 4524s +2.08
×
10
9
s
2
+ 6032s +3.64 × 10
9
µm/V .
(3.181)
C
V
(z)=
1.6(z
−
0.9875)
2
(z −0.2846)(z −0.99)
z
2
−
1.416z +0.9415
z
2
−1.297z +0.92
z
2
+0.1525z +0.95
z
2
+0.4155z +0.0144
V/V ,
(3.182)
z
2
+1.32z +0.7856
z
2
+0.6232z −0.277
z
2
+0.148z +0.9
z
2
+0.439z +0.84
C
M
(z)=
1.227(z
−
0.081)
z −0.9158
V/V .
(3.183)
The models of the plant is obtained from experimental frequency response mea-
sured using a laser Doppler Vibrometer (LDV) whose measurement scale is set
at 2 µm/V. The gain of the microactuator driver is 20. The controller is im-
plemented using a digital signal processor (DSP) in the commercially available
DSP board dSPACE 1103 with sampling frequency of 25 kHz. The VCM
controller C
V
(z) includes two notch filters to cancel the resonances of the VCM
actuator at around 3.0 kHz and 6.5 kHz. For the resonance-compensated VCM
model, a lead-lag compensator is used to achieve desired gain margin and phase
margin. As the microactuator's phase loss is less than that of the VCM, a lag
compensator in series with two notch filters to cancel microactuator resonances
at 6.5 kHz and 9.6 kHz is chosen as its controller C
M
(z)toachievethetar-
get open-loop bandwidth. The sensitivity and the complementary sensitivity
functionsachievedwiththisdesignareshowninFigure3.98.
Step Responses Considering Saturation
To show that the proposed method is effective in dealing with the problem
of saturation in the secondary stage actuator, we limit the amplitude of the
microactuator input to ±0.15 V which restricts the microactuator output to ±
0.12 µm, or ±4.8 µ at steady state. In reality, the microactuator is capable of
producing much larger displacement. The rationale for studying this extremely
small displacement range of microactuator includes,
1. this emulates the saturation of microactuator without reaching the hard
limit, and makes a challenging test ground for the controller,
2. for very high performances, the microactutor is to be placed closer to
the R/W head resulting in smaller mechanical amplification factor and
hence limited range of displacement range, and
