Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2002-11-05
2004-12-21
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06833974
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a head positioning device having an actuator of two-stage structure, and a disk drive using the same.
BACKGROUND OF THE INVENTION
With the evolution of multimedia in recent years, there are strong demands in the market for such disk drives having high recording density with a capability of positioning a head promptly into a target position on a recording medium of discoidal shape, to read and/or write a large volume of image data, sound data, text data and the like at high speed. There are also proposed a variety of techniques for positioning a head at high speed with high accuracy. As the techniques of achieving the high-speed and high-accuracy positioning, some of them draw attention as they employ a method of controlling two drive mechanisms, a main drive mechanism and a subsidiary drive mechanism, in such a manner as to function cooperatively to position the head.
The main drive mechanism is used primarily for a large motion of the head such as a seek operation and jumping across a plurality of tracks, and it rotates a head support mechanism by using a voice coil motor (hereinafter referred to as “VCM”) or the like around a shaft mounted to a chassis to move the head and head slider. The subsidiary drive mechanism is used mainly for a high-speed minute positioning of the head such that it follows a track, jumps over a single track and the like, and it is controlled over a wide band, but within a small movable range, by a piezo-electric component such as a piezo element, disposed to a tip end of the main drive mechanism to position the head and the head slider with a quick response. A drive mechanism provided with the main drive mechanism and the subsidiary drive mechanism is generally called two-stage actuator or piggyback actuator. The main drive mechanism and the subsidiary drive mechanism are called coarse actuator and fine actuator respectively. The control method using a two-stage actuator for positioning of the head as described above is proposed as one of the high-speed and high-accuracy positioning techniques (Japanese Patent Laid-open Publication, No. H10-255418, for example).
A piezo element used as the fine actuator, in particular, has functions of both a piezoelectric effect and a reverse-piezoelectric effect. That is, the piezo element has a capability of positioning control by using a minute displacement due to a strain produced as the reverse-piezoelectric effect by a control voltage, while it also capable of detecting a minute distance of displacement using a voltage generated with the piezoelectric effect by the displacement. Another technique of controlling an actuator called self-sensing actuator is thus proposed, using both of the above functions (refer to Transactions of the Japan Society of Mechanical Engineers, Vol. 64, No. 624, pages 2931-2937, published August 1998, under the title of “Tracking control of a cantilever beam using self-sensing actuator based on virtual bridge circuit”). In addition, a control technique of the two-stage actuator is also proposed as the technique that applies the above actuator control technique to a disk drive, in which a piezo element defining the fine actuator is mounted to a head support mechanism driven by a coarse actuator, thereby making it capable of controlling high-speed and high-accuracy positioning by using both functions of the piezoelectric effect and the reverse-piezoelectric effect of the piezo element (Japanese Patent Laid-open Publication, No. S60-35383, for example).
Furthermore, there is also proposed another technique of controlling the two-stage actuator, in which a fine actuator using a piezo element is made to function as a sensor for detecting vibrations and/or impacts applied to a disk drive for the purpose of correcting a displacement of a head position due to the vibrations and/or the impacts (e. g., Japanese Patent Laid-open Publication, No. H04-330679).
FIG. 5
depicts a structural diagram of a head positioning device provided with a two-stage actuator and is capable of making correction of any displacement of a head position due to vibrations and the like by using its fine actuator to function as a vibration sensor. Referring now to
FIG. 5
, the head positioning device will be described hereafter as an example of the prior art.
In
FIG. 5
, magnetic head
12
(hereinafter referred to as “head”), which reads and write data to and from magnetic disk
11
(hereinafter referred to as “disk”), i.e. a kind of recording media of a discoidal shape, is mounted integrally to a tip of head slider
13
. The head slider
13
is mounted to a tip end of fine actuator
52
, and the fine actuator
52
is connected to one end of head support mechanism
14
. The head support mechanism
14
is driven by coarse actuator
51
to rotate about rotary shaft
140
mounted to a main body of the disk drive, and to position the head
12
in cooperation with function of the fine actuator
52
. Furthermore, the coarse actuator
51
moves the head support mechanism
14
including the head
12
to a target position “R” in response to coarse motion drive signal “d1” from control unit
96
. The fine actuator
52
is controlled by fine motion drive signal “d2” of the control unit
96
in a manner that the head
12
mounted to the tip end of the head support mechanism
14
is displaced, or shifts, slightly by distance “Y2” from center position “Y1” located along a line extending from the head support mechanism
14
. The head
12
reads present position signal “y” indicating position “Y”, where the head
12
is located presently, from a servo data recorded beforehand on the disk
11
. At the same time, the displacement distance “Y2” of the fine actuator
52
from the center position “Y1” to the head position “Y” can be detected using a piezo element or the like. In this instance, the piezo element detects the actual distance “Y2” of a minute displacement of the fine actuator
52
to produce relative displacement signal “y2”. The control unit
96
receives the present position signal “y”, the relative displacement signal “y2” and target position signal “r” directed to it for a movement toward the target position “R”, performs respective computations, and produces coarse motion drive signal “d1” and fine motion drive signal “d2”. The head
12
is positioned into the target position “R” according to these drive signals obtained as a result the computations. The structure discussed above thus accomplishes positioning control to the target track.
In this example of the prior art, the control unit
96
additionally receives gate signal “g” for vibration detection. The control unit
96
detects external vibrations in response to a command given by the gate signal “g” for vibration detection, and corrects any deviation in position of the head due to the vibrations and the like.
FIG. 6
depicts an operational timing chart illustrating an operation for correcting an influence of external vibrations in the example of the prior art. As shown in
FIG. 6
, this head positioning device of the prior art uses coarse actuator
51
to carry out rough positioning from time
0
to time T
1
. It further carries out the positioning from time T
1
to time T
2
in a manner to locate the head
12
into a target track by displacing the fine actuator
52
to such an extent as shown by the displacement distance “Y2”. It then holds the fine actuator
52
to maintain the displacement distance constant for duration between time T
2
and time T
3
, or a gate period, and detects vibration data from the fine actuator
52
in response to the gate signal “g” for vibration detection. In other words, the control unit
96
keeps the displacement distance “Y2” of the fine actuator
52
unchanged when the head
12
reaches the target position “R”. During this period, the fine actuator
52
itself functions as a sensor, and the control unit
96
uses relative displacement signal “y2” as the vibration data. In addition, the control unit
96
feeds back the vibration data into control signals of the fine actuator
Koso Hiroshi
Kuwajima Hideki
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
Slavitt Mitchell
Sniezek Andrew L.
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