Data processing: generic control systems or specific application – Generic control system – apparatus or process – Specific compensation or stabilization feature
Reexamination Certificate
1998-02-27
2001-04-10
Sheikh, Ayaz (Department: 2155)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Specific compensation or stabilization feature
C700S029000, C700S045000, C700S083000, C360S077160, C360S078090
Reexamination Certificate
active
06216050
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to an actuator control system of a magnetic storage device, and specifically to an actuator control system that reduces the effects of aliasing inherent in the digital control.
2. Description of Related Art
The performance of an actuator control of a magnetic storage device, such as a hard disk drive (HDD), may be degraded by the aliasing caused by the mechanical resonances of a head suspension. In particular, the mechanical resonances resulting from the head gimbal assembly (HGA) and the actuator may reduce the robustness of a HDD, and furthermore raise the acoustic noise during a high-speed seek operation of a HDD.
One conventional approach to address the effects of such mechanical resonances is presented in the Japan Published Unexamined Patent Application No. 5-166312. According to this publication, a low pass filter (LPF) having a low pole is placed immediately after a digital-to-analog converter (DAC) to reduce the gain in the high frequency region where the resonance is located. Because the LPF also affects characteristics in the low frequency region, the effect of the LPF in the low frequency region is digitally compensated. This actuator control system is often referred to as a hybrid system because it incorporates a combination of analog and digital circuits.
Although the hybrid actuator control system described above has many desirable characteristics, it was designed based on the presumption that the HDD includes hardware with a processor having relatively high arithmetic processing power.
More specifically, this conventional approach was designed to operate with a state estimator to meet the high arithmetic processing power of the DSP. Unfortunately, such a high performance processor often increases the overall cost of a HDD. As a result, many currently available HDDs do not include such a processor; therefore, this conventional hybrid actuator control system approach may not be suitable for many HDDs available today. Accordingly, it is often desirable to simplify the algorithm to the extent that it can be processed by an ordinary microprocessor (MPU) (i.e., a processor without a state estimator) while taking advantage of the desirable characteristics of the hybrid control system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an actuator control system and a magnetic disk device that includes a the hybrid control system with a low pass filter (LPF).
It is also an object of the present invention to provide a hybrid actuator control system having a LPF that can be processed without a state estimator.
The present invention describes an actuator control system that responds to the position signal from an actuator. The actuator is driven by a control signal which is generated by a driver circuit. The actuator control system includes a LPF coupled between a digital-to-analog converter (DAC) for converting the digital control signal into an analog control signal and the driver circuit. Furthermore, the actuator control system includes a digital control device for compensating the phase delay caused by the LPF by digital control. The digital control device reconstructs the state model of a plant including the LPF to a state model using only directly observable state variables. This may be accomplished without requiring a state estimator. Furthermore, the digital control device collectively compensates for the phase delay due to the LPF as part of the plant when designing the feedback system.
The present invention also describes an actuator control system that responds to the position signal from an actuator. The actuator is driven by a control signal which is generated by a driver circuit. The actuator control system includes a LPF coupled between a DAC for converting the digital control signal into an analog control signal and the driver circuit. The actuator control system also includes a digital control device for compensating the phase delay caused by the LPF by digital control. The digital control device is designed to operate with a state equation of a system having a LPF converted into a controllable canonical form as shown by Equations (9) and (10). This conversion enables all state variables to be directly measured.
[
x
(
i
)
v
(
i
)
x
(
i
-
2
)
u
(
i
-
1
)
u
(
i
-
2
)
u
(
i
-
3
)
w
(
i
)
]
=
[
1
-
a
3
1
+
2
a
3
a
3
p
2
p
3
p
4
0
-
a
3
1
+
2
a
3
a
3
p
2
p
3
p
4
0
1
-
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
1
0
0
1
0
0
0
0
0
1
]
×
&AutoLeftMatch;
[
x
(
i
-
1
)
v
(
i
-
1
)
x
(
i
-
3
)
u
(
i
-
2
)
u
(
i
-
3
)
u
(
i
-
4
)
w
(
i
-
1
)
]
+
[
p
1
p
1
0
1
0
0
0
]
u
(
i
-
1
)
Equation
(
9
)
y
(
i
)
=
[
1
0
0
0
0
0
0
]
[
x
(
i
)
v
(
i
)
x
(
i
-
2
)
u
(
i
-
1
)
u
(
i
-
2
)
u
(
i
-
3
)
w
(
i
)
]
Equation
(
10
)
where
x(I): control output
x(I-1), x(I-2), x(I-3): previous values of x(I)
u(I): control input
u(I-1), u(I-2), u(I-3): previous values of u(I)
v(I): state variable of quasi speed term
w(I): integral term of output
y(I): output of ADC.
One aspect of the present invention includes a digital control device that is adapted to control a system having a LPF based on the state feedback shown by Equation (11).
u
(
i
)
=
[
f
1
f
2
f
3
f
4
f
5
f
6
f
7
]
[
x
(
i
)
v
(
i
)
x
(
i
-
2
)
u
(
i
-
1
)
u
(
i
-
2
)
u
(
i
-
3
)
w
(
i
)
]
Equation
(
11
)
where f
1
, f
2
, f
3
, f
4
, f
5
, f
6
, f
7
: parameters, and
x(I): control output
x(I-2): previous value of x(I)
u(I): control input
u(I-1), u(I-2), u(I-3): previous values of u(I)
v(I): state variable of quasi speed term
w(I): integral term of output.
Another aspect of the present invention includes a digital control device designed with the state equation of a system having a LPF by being converted into a controllable canonical form of a speed system shown by Equations (12) and (13).
[
v
(
i
)
v
(
i
-
1
)
u
(
i
-
1
)
u
(
i
-
2
)
u
(
i
-
3
)
w
v
(
i
)
]
=
[
1
+
a
3
-
a
3
p
2
p
3
p
4
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
1
0
0
0
0
1
]
×
&AutoLeftMatch;
[
v
(
i
-
1
)
v
(
i
-
2
)
u
(
i
-
2
)
u
(
i
-
3
)
u
(
i
-
4
)
w
v
(
i
-
1
)
]
+
[
p
1
0
1
0
0
0
]
u
(
i
-
1
)
Equation
(
12
)
y
v
(
i
)
=
[
1
0
0
0
0
0
]
[
v
(
i
)
v
(
i
-
1
)
u
(
i
-
1
)
u
(
i
-
2
)
u
(
i
-
3
)
w
v
(
i
)
]
Equation
(
13
)
where
v(I): control speed
u(I): control input
u(I-1), u(I-2), u(I-3): previous values of u(I)
y
v
(I): quasi speed
w
v
(I): integral of y
v
(I)
An additional aspect of the present invention includes a digital control device that provides a transfer function matrix G from the state equation of a system including the low pass filter by a calculation based on Equation (4).
G
=
C
(
zI
-
A
)
-
1
B
=
p
1
z
-
1
+
p
2
z
-
2
+
p
3
z
-
3
+
p
4
z
-
4
1
-
(
2
+
a
3
)
z
-
1
+
(
1
+
2
a
3
)
z
-
2
-
a
3
z
-
3
Equation
(
4
)
where p
1
, p
2
, p
3
, and p
4
respectively are:
p
1
=b
11
p
2
=a
1
b
31
+b
12
+b
21
−a
3
b
11
−b
11
p
3
=ab
11
−b
12
−ap
3
b
12
−a
3
b
21
+b
22
−a
1
b
31
+a
2
b
31
+a
1
b
32
p
4
=a
3
b
12
−a
3
b
32
+a
2
b
32
where
G: transfer function matrix
I: unit matrix
A, B: constants.
The transfer function of Equation (4) is reconstructed to a discrete state equation based on the input u, output y, and delay values of them to
Ono Hiroyuki
Ueda Tetsuo
International Business Machines - Corporation
Jean Frantz B.
Lee Monica D.
Raissinia Abdy
Sheikh Ayaz
LandOfFree
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