Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Reexamination Certificate
2002-01-25
2004-08-10
Le, N. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
C073S579000, C073S660000, C369S247100
Reexamination Certificate
active
06774615
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a resonance-frequency measuring method used for an information recording and/or reproducing device, an information recording and/or reproducing device, and an electric filter, and, more particularly, to a resonance-frequency measuring method for measuring a resonance frequency of a mechanism unit of an information recording and/or reproducing device driven by the mechanism unit to record and/or reproduce information, an information recording and/or reproducing device, and an electric filter.
An information recording and/or reproducing device, such as a hard disk drive, is required to record and/or reproduce information at a high speed with a high recording density. These requirements raise a problem of head vibration due to a resonance of a mechanism unit. In order to repress a resonance component of the mechanism unit, such an information recording and/or reproducing device incorporates a notch filter for removing a resonance component from a head-driving signal. Since mechanism units of different devices have different resonance frequencies, a cutoff frequency of the notch filter needs to be set individually by measuring a resonance frequency for each different device. Therefore, an efficient method for measuring a resonance frequency has been desired.
2. Description of the Related Art
First, a description will be given, with reference to the drawings, of a hard disk drive.
FIG. 1A
is a cross-sectional view of a structure of a hard disk drive.
FIG. 1B
is a plan view of the structure of the hard disk drive.
FIG. 2
is a block diagram of the hard disk drive.
A hard disk drive
1
mainly comprises a disk enclosure
11
and a circuit assembly
12
. The disk enclosure
11
contains a magnetic disk
21
, a spindle motor
22
, a magnetic head
23
, a head arm
24
, a voice coil motor
25
(a mechanism unit), and a head IC (Integrated Circuit)
26
. The magnetic disk
21
is fixed to a rotating shaft of the spindle motor
22
, and revolves in accordance with the rotation of the spindle motor
22
.
The magnetic head
23
is arranged opposite the magnetic disk
21
, and acts magnetically on the magnetic disk
21
so as to record and/or reproduce information. The magnetic head
23
is fixed on an end of the head arm
24
. The head arm
24
is coupled with the voice coil motor
25
at the other end so as to be revolved by the voice coil motor
25
. Along with the revolution of the head arm
24
, the magnetic head
23
moves in a radial direction of the magnetic disk
21
.
The magnetic head
23
is connected to the head IC
26
. The head IC
26
amplifies a signal that is to be recorded on the magnetic disk
21
by the magnetic head
23
, and supplies the amplified signal to the magnetic head
23
. The head IC
26
also amplifies a reproduction signal that is reproduced from the magnetic disk
21
by the magnetic head
23
, and supplies the amplified reproduction signal to the circuit assembly
12
.
As shown in
FIG. 2
, the circuit assembly
12
includes a read channel (RDC)
31
, an MPU (Micro Processing Unit)
32
, a ROM (Read Only Memory)
33
, a servo controller (SVC)
34
(an actuator; a driving unit), a hard disk controller (HDC)
35
, a RAM (Random Access Memory)
36
, and an IDE (Integrated Device Electronics) connector
37
.
The read channel
31
is connected with the head IC
26
. The read channel
31
supplies a record signal to the head IC
26
, and also demodulates a reproduction signal amplified by the head IC
26
into reproduction data. The reproduction data demodulated by the read channel
31
is supplied to the HDC
35
. The HDC
35
temporarily stores the reproduction data in the RAM
36
, and thereafter, supplies the reproduction data to a host computer (not shown in the figure) via the IDE connector
37
.
Record data is supplied from the host computer to the IDE connector
37
. The HDC
35
temporarily stores the record data in the RAM
36
. Upon recording, the HDC
35
reads the record data from the RAM
36
, and supplies the record data to the read channel
31
. The read channel
31
modulates the record data so as to generate a record signal. The record signal generated by the read channel
31
is supplied to the head IC
26
. The head IC
26
amplifies the record signal, and supplies the amplified record signal to the magnetic head
23
. The magnetic head
23
magnetizes the magnetic disk
21
by producing a magnetic field corresponding to the record signal so as to record the record signal on the magnetic disk
21
.
In the above-mentioned course, the MPU
32
is supplied with the reproduction data demodulated by the read channel
31
. The MPU
32
reads a location signal (a present location signal) indicating an address on the magnetic disk
21
from the reproduction data, and performs a tracking servo control. The MPU
32
generates a control signal, i.e., a tracking error signal, corresponding to a difference between the read location signal and a location signal (an aimed location signal) representing a location where aimed information is recorded, and performs a notch-filter process to the generated control signal. Thereafter, the MPU
32
supplies the control signal to the servo controller
34
. The notch-filter process removes a device's natural resonance frequency component from the control signal.
The servo controller
34
controls the voice coil motor
25
according to the control signal supplied from the MPU
32
so as to regulate a reading position of the magnetic head
23
reading a signal from the magnetic disk
21
.
Thus, the magnetic head
23
can scan the aimed location on the magnetic disk
21
so as to obtain the aimed information.
In this course, the voice coil motor
25
exhibits a device-specific resonance frequency. Therefore, a firmware executed by the MPU
32
includes a resonance-frequency measuring process for measuring the device-specific resonance frequency so as to match a cutoff frequency in the notch-filter process to the device-specific resonance frequency.
FIG. 3
is a functional block diagram of a conventional example of a tracking servo control system.
It is noted that a subtracter
41
, a controller
42
, a notch filter
43
, an adder
44
, a sine-wave disturbance generator
45
, an FFT calculator
46
, and an adjuster
47
are realized by the firmware as processes of the MPU
32
.
The subtracter
41
is supplied with the aimed location signal and the present location signal, and calculates the difference between the aimed location signal and the present location signal so as to output difference information. The difference information is supplied to the controller
42
. Based on the difference information supplied from the subtracter
41
, the controller
42
generates the control signal for controlling the voice coil motor
25
.
The control signal generated by the controller
42
is supplied to the notch filter
43
. The notch filter
43
deducts a preset cutoff frequency component from the control signal. The control signal without the unnecessary component is supplied from the notch filter
43
to the adder
44
. The adder
44
adds a sine-wave disturbance signal supplied from the sine-wave disturbance generator
45
to the control signal supplied from the notch filter
43
. The control signal including the sine-wave disturbance signal is supplied to the servo controller
34
.
Based on the control signal supplied from the adder
44
, the servo controller
34
generates a driving signal for driving the voice coil motor
25
. The driving signal generated by the servo controller
34
is supplied to the voice coil motor
25
. The voice coil motor
25
is driven by the driving signal supplied from the servo controller
34
so as to alter a position of the magnetic head
23
.
The magnetic head
23
reads a signal from the magnetic disk
21
at the altered position. This reproduction signal reproduced by the magnetic head
23
is supplied to the head IC
26
. The head IC
26
amplifies the reproduction signal supplied from
Hara Takeyori
Hashimoto Shuichi
Kagami Yoshiyuki
Kosugi Tatsuhiko
Kubohara Ryuki
Fujitsu Limited
Greer Burns & Crain Ltd.
Lair Donald M
Le N.
LandOfFree
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