Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-08-24
2004-11-02
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044340, C360S077040, C360S078090
Reexamination Certificate
active
06813227
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 2001-49866, filed Aug. 26, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to compensating for disturbances in an optical recording/reproducing apparatus using learning control, and more particularly, to an apparatus and method for compensating for disturbances, such as eccentricity in a disk drive system of the optical recording/reproducing apparatus by performing feed-forward control using an iterative learning method, storing a result of the feed-forward control, and applying the result of the feed-forward control to a compensator to compensate for disturbances.
2. Description of the Related Art
FIG. 1
shows an example of a tracking error signal generated due to eccentricity in an optical recording medium. Eccentricity occurring in the optical recording medium is due to a rotation shaft of a spindle inconsistently rotating a disk at a center of a track of the disk. In an optical recording medium drive system, the eccentricity of the optical recording medium has served as an important periodic disturbance factor, and its influence increases with an increase in speed multiple. Accurately following the track of the disk cannot be accomplished without compensating for the eccentricity. Accordingly, conventional systems have utilized various eccentricity compensation methods.
FIG. 2
is a block diagram of a pickup head (PUH) position control system in a typical optical recording/reproducing apparatus. The PUH position control system receives a position command directing a pickup head (not shown) to be positioned at a desired location. A signal representing an actual position of an actuator
220
of an optical recording medium drive for moving the pickup head is fed back in a negative direction and added to a position command signal in an adder
200
. An error signal e output from the adder
200
is applied to a controller
210
. The controller
210
performs a predetermined algorithm for compensating for the error signal e, and outputs a compensated signal to the actuator
220
. The actuator
220
moves the pickup head in response to the compensated signal received from the controller
210
. These operations are repeated, and thus the position of the pickup head is adjusted. However, this control system cannot deal with a disturbance, such as a large eccentricity.
FIG. 3
is a block diagram of an embodiment of a conventional PUH position control system in which a routine for performing disturbance compensation is added to the control system of FIG.
2
. In this system, a compensation routine
300
is performed on the assumption that a perfect sine wave Asin(&ohgr;t+&psgr;) is an eccentricity signal, having an eccentricity of A, a disk rotation frequency &ohgr;, and an eccentricity phase &psgr;. This compensation method is disclosed in U.S. Pat. No. 5,892,742, which is hereby incorporated by reference. In the operation of the system of
FIG. 3
, a feed-forward control input is calculated from an error waveform, as shown in
FIG. 1
, before control of tracking starts. That is, the size of the eccentricity is determined by a number of track errors generated during one rotation of a spindle over a track (i.e., during a cycle) shown in
FIG. 1
, and a phase of eccentricity is determined by a spindle index reference signal representing one rotation and a delay time at which the period of the track error is greatest. The thus-calculated feed-forward control input is added to the output of the controller
210
of
FIG. 3
to accomplish a track error compensation including compensation of eccentricity. This disturbance compensation method is very simply performed and so it can be easily applied. However, this disturbance compensation method is an open-loop control method, which does not consider the response characteristics of an existing servo (actuator) control system. There is a limit in the performance of the disturbance compensation method since periodic disturbances including eccentricity are not perfect sine waves.
FIG. 4
is a block diagram of another embodiment of a conventional PUH position control system in which a routine for performing disturbance compensation is added to the control system of FIG.
2
. The system of
FIG. 4
is disclosed in U.S. Pat. No. 5,550,685, which is hereby incorporated by reference, and is applied to hard disk drive systems. In this control system, first, a fixed feed-forward control input is obtained using a track error signal and stored in a table
400
prior to starting control. Then, upon control, errors generated due to disturbances are compensated using the stored control input. This control system also includes a separate adaptive feed-forward control unit
410
in preparation for changes in characteristics of repeatable run out (RRO) caused by external factors during operation of a drive system. A discrete Fourier transform (DFT) and an inverse discrete Fourier transform (IDFT) are sequentially performed to extract a specific frequency component from a position error signal PES, thereby obtaining a signal with a specific frequency component. The obtained specific frequency component signal is added to the error input of an existing servo control loop. In this way, error compensation control can be accomplished.
The system of
FIG. 4
is complicated since it accomplishes error compensation control in consideration of the entire closed-loop response characteristics, but can be considered a more effective disturbance compensation system than FIG.
3
. However, the system of
FIG. 4
considers only disturbances of a specific frequency component rather than disturbances with all frequency components actually present in a control region of the disk drive system, and it is difficult to cope with changes in a cycle such as variations in the speed multiple.
Therefore, in a periodic system such as the disk drive system, calculations of a control input in consideration with all frequency components within a control region is necessary for a high-performance disturbance compensation operation. Also, new disturbance compensation methods and apparatuses are required to effectively cope with changes in system cycle caused by a variation of the speed multiple and a variation of a control mode.
SUMMARY OF THE INVENTION
Various objects and advantages of the invention will be set forth in part in the description that follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To solve the above problem, an objective of the present invention is to provide an apparatus and method of compensating for disk disturbances having periodic disturbances with all frequency components within the control region of an optical recording medium drive servo system and considering variations in the rotation speed multiple of the optical recording medium in an optical recording/reproducing apparatus.
To achieve the above and other objectives, the present invention provides an optical recording medium drive servo system of an optical recording/reproducing apparatus having a head, the system including an actuator moving a position of the head for recording data on a recording medium or reproducing the recorded data from the recording medium; an error detector detecting a position error including a difference between a reference position on the recording medium and an actual position of the head; a compensator receiving the position error from the error detector and producing a value therefrom to drive the actuator; a first memory storing control inputs for compensating for the position error of the actuator due to a disturbance; a second memory converting the control inputs of the first memory according to a phase and storing converted control inputs; a timing controller generating addresses for the first memory and the second memory according to the phase; and an adder adding the con
Cho Seong-il
Jeon Jin-hoon
Jung Soo-yul
Seo Joong-eon
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
Tran Thang V.
Vuong Bach
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