2. Figure 2 shows a simplified model to simulate a recording head flying over a rough disk surface in computer hard disk drives. The head has mass m and is supported by a suspension with stiffness k₁. Moreover, the moving disk surface will generate an air bearing lifting the head slightly above the disk surface (e.g., in the order of 20 nm). The air bearing is simplied as a linear spring with stiffness k2 and damping coefficient c. Let x(t) be the roughness of the disk surface and serve as the input excitation to the head/suspension system. Moreover, y(t) is the relative displacement of the head to the disk. In real hard disk drive applications, we want to keep y(t) almost constant, so that the head can follow the disk surface to perform read/write operations. (a) Show that the equation of motion is mi+cy + (k1 + k2) y = −mä – k₁x (2) 1 (b) Derive the frequency response function. Plot the magnitude and phase of the frequency response function. In plotting the frequency response function, let's define k1 k1 + k2 W₁ = W2= m m (3) Describe the motion of the head in the following three frequency ranges: 0 < w< W1, W1

Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
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2. Figure 2 shows a simplified model to simulate a recording head flying over a rough disk surface
in computer hard disk drives. The head has mass m and is supported by a suspension with
stiffness k₁. Moreover, the moving disk surface will generate an air bearing lifting the head
slightly above the disk surface (e.g., in the order of 20 nm). The air bearing is simplied as
a linear spring with stiffness k2 and damping coefficient c. Let x(t) be the roughness of the
disk surface and serve as the input excitation to the head/suspension system. Moreover, y(t)
is the relative displacement of the head to the disk. In real hard disk drive applications, we
want to keep y(t) almost constant, so that the head can follow the disk surface to perform
read/write operations.
(a) Show that the equation of motion is
mi+cy + (k1 + k2) y = −mä – k₁x
(2)
1
(b) Derive the frequency response function. Plot the magnitude and phase of the frequency
response function. In plotting the frequency response function, let's define
k1
k1 + k2
W₁ =
W2=
m
m
(3)
Describe the motion of the head in the following three frequency ranges: 0 < w< W1,
W1 <ww2, and w₂ <w.
(c) If we want to design the disk drive so that the head can follow the disk surface for a
wide frequency range, how should we choose k₁, k2, and m?
10
0
Acceleration
Charge
q(t)
10
Voltage
-20
a(t) Hbag(s)
Hamp(s)
v(t)
-30
Figure 3: Block diagram of an airbag
sensor
-50
-60
01 02
5 10 20
F-0.5 Hz
Figure 4: Magnitude of Gamp (w)
F-33 kHz
Transcribed Image Text:2. Figure 2 shows a simplified model to simulate a recording head flying over a rough disk surface in computer hard disk drives. The head has mass m and is supported by a suspension with stiffness k₁. Moreover, the moving disk surface will generate an air bearing lifting the head slightly above the disk surface (e.g., in the order of 20 nm). The air bearing is simplied as a linear spring with stiffness k2 and damping coefficient c. Let x(t) be the roughness of the disk surface and serve as the input excitation to the head/suspension system. Moreover, y(t) is the relative displacement of the head to the disk. In real hard disk drive applications, we want to keep y(t) almost constant, so that the head can follow the disk surface to perform read/write operations. (a) Show that the equation of motion is mi+cy + (k1 + k2) y = −mä – k₁x (2) 1 (b) Derive the frequency response function. Plot the magnitude and phase of the frequency response function. In plotting the frequency response function, let's define k1 k1 + k2 W₁ = W2= m m (3) Describe the motion of the head in the following three frequency ranges: 0 < w< W1, W1 <ww2, and w₂ <w. (c) If we want to design the disk drive so that the head can follow the disk surface for a wide frequency range, how should we choose k₁, k2, and m? 10 0 Acceleration Charge q(t) 10 Voltage -20 a(t) Hbag(s) Hamp(s) v(t) -30 Figure 3: Block diagram of an airbag sensor -50 -60 01 02 5 10 20 F-0.5 Hz Figure 4: Magnitude of Gamp (w) F-33 kHz
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