WO1999017280A1

WO1999017280A1 - Optical disc reproducing apparatus and method for searching a track

Info

Publication number: WO1999017280A1
Application number: PCT/KR1998/000278
Authority: WO
Inventors: Hong-Moon Bae
Original assignee: Daewoo Electronics Co., Ltd.
Priority date: 1997-09-26
Filing date: 1998-09-11
Publication date: 1999-04-08

Abstract

An optical disc reproducing apparatus and a method for searching a track are disclosed. An optical pick-up moves toward a radius of the optical disc, irradiates an optical beam in the information recording area, and transforms the optical beam reflected from the optical disc into a high frequency signal to output. A data restoring part enables a track address and data to be restored by the high frequency signal provided by the optical pick-up. A tracking servo controls a tracking servo of the optical pick-up. In a memory, position information about at least one or more of a first and a second virtual target tracks is stored. An input part and a controlling part select a program recorded on the optical disc. Further, a controller controls the tracking servo to move the optical beam toward reducing the difference between a track address obtained from the memory and a target track address selected by the input part. In the event that it is impossible to provide the target track address from the data restoring part, the controller controls the tracking servo to reproduce information about the selected program by taking a closest track, which is searchable toward an outer track after passing the target track, to the original track, as a new virtual target track, with reference to position information about at least one or more of the first and the second virtual target tracks.

Description

OPTICAL DISC REPRODUCING APPARATUS AND METHOD FOR

SEARCHING A TRACK

Technical Field

The present invention relates to a system for reproducing programs recorded on an optical disc and a method for searching a track, and more particularly to, in the event that a readability of identifying information of a target track read out from a disc is poor due to a surface defect of the target track on the disc, an optical disc reproducing apparatus and a method for searching a track that seek an adjacent track where track identifying information read out from the disc is readable and that reproduce the data from the sought adjacent track. Background Art

Generally, in an optical disc such as a compact disc (CD), an laser disc (LD), a digital video disc (DVD) and the like, digital information is recorded first in the shape of a prominence and depression on the base plate of the optical disc, a reflection film is coated next, and then a transparent protection layer is formed. Therefore, after applying a beam to the optical disc, information recorded on the optical disc can be read out by detecting the difference of beam intensity caused by the phase difference of the beam reflected from the prominence and depression. Accordingly, if the surface of the optical disc is scrubbed or contaminated, the readability of the optical disc becomes poor.

Concerning this problem of errors generated by surface defects of the optical disc, the optical disc reproducing apparatus, to some extent, guarantees the recovering function of data by detecting and correcting the errors on signal processing. If the status of the surface defect, however, is beyond the capability of error correction of an applied apparatus or a method, the desired recovery of the damaged data will fail.

Meanwhile, in the optical disc reproducing apparatus, a method for searching a track can randomly access to the data recorded on the optical disc. Such a track search can be performed by reading out track addresses, calculating the difference between a target address and the readout address, and moving a beam toward reducing the difference between these addresses. Accordingly, if the address of the target track is not readable due to surface defects of the optical disc, the track search will not be completed perfectly, which results in the impossibility of reproducing information on the optical disc.

The United States Patent No. 4,845,697 entitled "METHOD OF TIME LIMITED SEARCHING FOR A TRACK ADDRESS ON AN OPTICALLY READ INFORMATION DISC" discloses a reproducing apparatus and a method of disc information . This patent relates to a method that finds out the position of information adjacent to a target track when the readability of the address code of the target track goes below a desired reference to perfect data reproduction. However, the control algorithm of the patent is complex since a zigzag scan over the area around the target track is needed to find the neighboring location of recorded information.

Disclosure of Invention

It is an object of the present invention to provide an optical disc reproducing apparatus and a method for searching a track that are capable of reproducing information on an optical disc successfully by taking the closest track, which is searchable toward the outer disc after passing the target track, to the original track, as a new target track in the event that the readout of the target track address is not possible.

To accomplish this object, the apparatus comprises an optical pick-up for moving toward a radius of the optical disc, irradiating an optical beam in the information recording area, and transforming a beam reflected from the optical disc into a high frequency signal to output; a data restoring part for restoring a track address and data from the high frequency signal provided by the optical pick-up; a tracking servo part for controlling a tracking servo of the optical pick-up; a memory for storing at least one or more position information about a first and a second virtual target tracks; an input part for selecting a program of the optical disc; and a control part for controlling the tracking servo part to move the optical beam toward reducing a difference between a track address informed by the data restoring part and a target track address selected by the input part and, in the event that the provision of the target track address is not available from the data restoring part, to reproduce selected program information by taking a closest track, which is searchable toward an outer track after passing the target track, to the original track, as a new virtual target track, with reference to at least one or more location information about the first and the second virtual target tracks.

Further, the first method of this invention comprises six steps: the first step is to move an optical beam toward the position of a target track to reduce the difference between a track address reproduced from an optical disc and a position value of a selected target track; the second step is to newly set a first adjacent track, as a first virtual target track, which passes the position of the selected target track at a first predetermined distance from the target track, in the event that the selected target track fails to be reproduced within the predetermined time; the third step is to repeat the second step until an address of this first virtual target track is searched; the fourth step is, once this first virtual target track is searched, to newly set a second adjacent track apart from the searched position toward an inner radius by a second predetermined distance which is shorter than the first predetermined distance, as a second virtual target track; the fifth step is to repeat the fourth step until a search for an address of this second virtual target track fails; and the sixth step is, in the event that a search for the address of the second virtual target track as set in the fourth step fails in the fifth step, to set the address of the just searched second virtual target track as a modified target track and to search this modified target track.

Furthermore, the second method of this invention comprises six steps: the first step is to move an optical beam toward a target track position to reduce the difference between a track address reproduced from an optical disc and a position value of a selected target track; the second step is, in the event that the reproduction of the selected target track fails despite a predetermined number of repetition, to newly set a first adjacent track passing this target track by a first predetermined distance as a first virtual target track; the third step is to repeat the second step until an address of the first virtual target track is searched; the fourth step is, once the virtual target track is searched, to newly set a second adjacent track apart from the searched position toward an inner radius by a second predetermined distance that is shorter than the first predetermined distance, as a second virtual target track; the fifth step is to repeat the fourth step until a search for an address of the second virtual target track fails; and the sixth step is, in the event of the failure of searching for the address of the second virtual track in the fifth step, to set the address of the just searched second virtual target track as a modified target track and to search the modified target track.

Brief Description of the Drawings

Further objects and advantages of this invention are best described with reference to the attached drawings, in which: FIG. 1 is a block diagram showing the first embodiment of an optical disc reproduction apparatus according to the present invention;

FIG. 2 is an illustration of a relationship between a target track and a virtual track on the optical disc during a track search of the optical disc reproduction apparatus according to the present invention; FIG. 3 is a flow chart explaining the first embodiment of a method for searching a track that uses the optical disc reproduction apparatus according to the present invention; and

FIG. 4 is a flow chart illustrating the second embodiment of the method for searching the track that uses the optical disc reproduction apparatus according to the present invention.

Best Mode for Carrying Out the Invention

With reference to the accompanying drawings, it is explained in detail how an optical disc reproducing apparatus and a method for searching a track of this invention are constituted and operate. Referring now to the drawings, and particularly to FIG. 1, there is a block diagram which shows an embodiment of the optical disc reproduction apparatus according to the invention. The optical disc reproduction apparatus includes a spindle motor 20 for rotating an optical disc 10, an optical pick-up 30, a data restoration part 40, a data precess part 50, a servo part 60, an input part 70, a memory 80, and a control part 90.

A coarse adjusting motor (not shown) moves the optical pick-up 30 toward a radius of the optical disc 10. The optical pick-up 30 irradiates an optical beam onto the recording side of the optical disc 10, receives the beam reflected from the recording side, and generates a high frequency signal corresponding to an amount of the received beam. Accordingly, the optical pick-up 30 is focus-controlled to focus the optical beam onto a recording side and tracking-controlled to search and follow the tracks of the recording side.

The data restoration part 40 includes a high frequency amplifier 42, a wave former and decoder 44, and an error detection and correction part 46. The high frequency amplifier 42 amplifies the high frequency signal that is input to the data restoration part 40 and the amplified signal is restored into a digital signal through the wave former and decoder 44. In the error detection and correction part 46, an operation for detecting errors included in the decoded digital signal is implemented and, then, the detected errors are corrected and yielded as a track address and data. The data process part 50 processes the data provided by the data restoration part 40 in a predetermined data-processing way and results in reproducing audio signals or audio-video ones.

The servo part 60 includes a spindle servo 62, a focusing servo 64, and a tracking servo 66. To control a rotation velocity of the optical disc, the spindle servo 62 servo-controls the spindle motor 20. The focusing servo 64 servo-controls a focusing actuator which actuates up and down an object lens installed in the optical pick-up to control the focusing of the optical beam onto a recording side. The tracking servo 66 servo-controls a coarse adjusting motor that moves the optical pick-up 30 toward a radius of the optical pick-up and a tracking actuator that actuates the object lens left and right for the optical beam to be focused precisely onto a target track.

The input part 70, as a user interface, responds to the signals of a remote controller or of a key and generates a command signal that is the same as a selection signal of a recorded program on the optical disc. The memory 80 consists of a semiconductor such as a read only memory

(ROM), a random access memory (RAM) or a nonvolatile memory and stores location data (TXn, TXm) of a first and a second virtual target tracks.

The control part 90 includes a microcomputer or a microprocessor and its peripheral circuits. One aspect of the control part 90 is that it controls these elements to be provided by the data restoration part with a table of content (TOC) information reproduced from the TOC area of the optical disc 10 and that it obtains position information about the target track of the selected program with reference to the provided TOC information. Namely, the TOC contains this track address information that corresponds to the starting positions of various programs recorded on the optical disc 10. Accordingly, when searching a track, the control part 90 sets position information of the selected target track with reference to the reproduced TOC and moves the optical pick-up toward a radius through the tracking servo 66 in the servo part 60. Furthermore, the control part 90 compares position information of the predetermined target track with a track address in which the current optical beam obtained by the data restoration part 40 is located, and controls the optical pick-up to move toward reducing the difference. If the optical beam reaches the target track, this searching operation ends.

However, if a readability of the address of the target track on the recording side is damaged by scrubs or contaminations on the recording side of the optical disc 10 in which the target track to be searched is located, the searching operation of the track becomes incomplete due to the comparative difference in the control part 90. FIG. 2 depicts a relationship of the target and virtual tracks on an optical disc during the searching operation of the optical disc reproduction apparatus according to the present invention. In the recording side of the optical disc 10, if the position of a target track (TP) exists within a defect area 100 of the optical disc, it is impossible to search the target track and, consequently, the reproduction of the selected program fails.

To obviate this problem, the present invention provides skills as follows. Position information of one or more virtual tracks, for example a first and a second virtual tracks (TXn and TYm respectively), is stored in the memory 80 in advance, and the value of the original target track is replaced with the values of those virtual tracks acting as new target tracks in the event that it is difficult to search target tracks due to surface defects on the disc. Further, the positions of the searched virtual tracks are reset as altered target tracks with which the reproduction of the selected program begins.

Position information of the first virtual track (TXn) is set toward the outer- radius over the target track (TP) by a predetermined distance. This means that, to find a searchable adjacent track, position information of the first virtual track (TXn) is determined by escaping the defect area 100, with jumping every predetermined track.

Position information of the second virtual track (TYm) is set toward the inner-radius by a predetermined distance, for example by a distance of every track, to find a track that is searchable and close to the TP from the searched first virtual track (TXn).

FIG. 3 illustrates a flow chart to explain the first embodiment of a method for searching a track with an optical disc reproduction apparatus of the present invention. If this reproduction apparatus is set onto a tray, the optical disc 10 is loaded by a loading mechanism (302). The loaded optical disc 10 is rotated by the spindle motor 20 and, from a lead-in-area of the optical disc 10, TOC information is read out to be provided to the control part 90 (304). If a user selects a program that the user intends to reproduce through the input part 70, position information of the target track (TP) corresponding to a starting position of the selected program is set by referring to the TOC (306, 308) in the control part 90. After this, the search operation of the selected target track is implemented in the control part (310). Further, the control part 90 compares track addresses read out during the optical beam's movement toward the outer-radius with position information of the target track which was set previously to check the completion of the search operation. The control part 90 continuously checks whether the predetermined search time (tl) has elapsed (314). In step 312, once the search preparation is completed successfully, the reproduction operation can be implemented by reading the program data from the searched target track (TP) (342).

If, the completion of the search of the target track (TP) fails within the predetermined search time (tl) in step 314, the control part 90 concludes that the search of the target track (TP) is not possible, and takes position information (TX1) of the first virtual target track from the memory 80 to assign the target track (TP) with the TX1 (316). The search for the TX1 is executed (318), and its completion is checked (320). If the completion of the search is not successfully checked, it is checked whether or not the predetermined search time (t2) has elapsed (322). If not, the lapse of the search time (t2), the step 318 should be carried out. In step 322, if the search of the TX1 is not completed within the search time

(t2), the TX1 is changed to the TX2 (324) and step 316 is initiated. If the track search is performed by resetting the TX2 in step 316 and the search of TX2 is completed in step 320, then it can be regarded as that the currently searching track is out of the defect area 100. However, if the TX2 is not searched, the same searching operation as above that position information of the first virtual track is changed to next one should be repeated until the track search is completed successfully.

If the search of the TX2 is achieved in step 320, then a new search for the unsearchable position is implemented with moving the optical beam reversely, namely, toward the inner-radius. This means that, in the TX2 position, the control part 90 changes the TX2 with the TY1 (326) by taking position information of the second virtual target track (TY2) from the memory 80. The newly reset TY1 is searched (328) and the completion of the search is checked (330). If the completion of the search is checked in step 330, it is checked whether a preset search time (t3) has elapsed (334) or not. If not, the step 328 is implemented.

If the TY2 is searched by the search time (t3) in step 330, the TY1 is changed to TY2 (332) and step 326 is executed. In step 326, a track search operation is performed by resetting the TY2. If the TY2 is completed in step 330, then the TY2 is altered with the TY3 in step 332 and the search operation is repeatedly implemented. If the search of the TY3 fails to be completed within the search time (t3) in step 334, then it can be understood that the optical beam has moved into the defect area 100. Unlike the above case, if the TY3 is sought, the same searching operation as above that changes position information of the second virtual track with next one should be repeated until the track search fails.

If the TY3 is not sought within the search time (t3) in step 334, the previously found TY2 is taken as an amended target track (ATP) (336) and then the ATP becomes a target for the search. In step 338, it is checked whether the ATP is searched or not (340), and, in the event of the completion of the search for the ATP, the program data selected from the ATP is reproduced (342).

As shown in the above embodiments of the present invention, if it is not possible to search the target track, a search operation passing a searchable adjacent track toward the outer-radius from a current beam position is primarily performed by a coarse search. Then, the next step of the search operation to seek an unsearchable location is performed in a reverse direction, that is, toward an inner-radius from the position determined by the coarse search, and, just before the discovery of an unsearchable position, the position of a searchable track is taken as an amended target position.

Industrial Applicability

Turning now to FIG. 4, a flow chart explains the second embodiment according to a method for searching a track, which employs an optical disc reproduction apparatus of the present invention. Comparing the first embodiment with the second one, as every step is identical, it is numbered as same as that of FIG. 3, except for step 315 that the searchability of the target track corresponding to the starting point of the selected program is not decided by the elapse of time but by the number of trials for the search, and that it treats the situation where the target track cannot be searched by more than a predetermined number of trials as an unsearchable state. Although preferred embodiments of the invention have been described in detail with reference to the accompanying drawings, it should be understood that the present invention is not limited to those preferred embodiments and that various changes and modifications can be effected by one skilled in the art within the spirit and scope of the invention as hereinafter claimed.

Claims

What is claimed is:

1. An apparatus for reproducing information recorded on an optical disc, said apparatus comprising: an optical pick-up means for moving in a radial direction of said optical disc, irradiating an optical beam in the information recording area and transforming a beam reflected from said optical disc into a high frequency signal to output; a data restoring means for restoring a track address and data from said high frequency signal supplied by said optical pick-up means; a tracking servo means for controlling a tracking servo of said optical pick-up means; a data storing means for storing at least one or more position information of a first and a second virtual target tracks; an input means for selecting a program of said optical disc; and a control means for controlling said tracking servo means to move said optical beam toward reducing a difference between said track address acquired from said data restoring means and a target track address selected by said input means and, in the event that the supply of said target track address from said data restoring means is not available, to reproduce said selected program information by taking a closest track, which is searchable toward an outer disc after passing said target track, to the original track, as a new virtual target track, with reference to position information about at least one or more said first and said second virtual target tracks.

2. The apparatus as claimed in claim 1, wherein each of said first virtual target tracks are arranged by a first distance and said second virtual target tracks are arranged within said first distance by a second distance which is shorter than said first distance.

3. A method for searching a track search in an optical disc reproducing apparatus, said method comprising the steps of: i) moving an optical beam toward a target track position to reduce a difference between a track address reproduced from an optical disc and a position value of a selected target track; ii) newly setting a first adjacent track passing a position of said selected target track by a first predetermined distance, as a first virtual target track, in the event that said reproduction of said selected target track fails within a predetermined time; iii) repeating said step ii) until an address of said first virtual target track set in said step ii) is searched; iv) newly setting a second adjacent track apart from the searched position toward an inner radius by a second predetermined distance which is shorter than said first predetermined distance, as a second virtual target track, in the event that said address of said virtual target track is searched; v) repeating said step iv) until a search for an address of said second virtual target track set in said step iv) fails; and vi) setting said address of said searched second virtual target track as a modified target track and searching said modified target track, in the event that said search for said address of said second virtual target track set in said step iv) fails in said step v).

4. The method as claimed in claim 3, wherein each of said first virtual target tracks are arranged by a first distance and said second virtual target tracks are arranged within said first distance by a second distance which is shorter than said first distance.

5. A method for searching a track in an optical disc reproducing apparatus, said method comprising the steps of: i) moving an optical beam toward a target track position to reduce a difference between a track address reproduced from said optical disc and a position value of a selected target track; ii) newly setting a first adjacent track passing a position of said selected target track by a first predetermined distance, as a first virtual target track, in the event that said reproduction of said selected target track fails in predetermined times of trials; iii) repeating said step ii) until an address of said first virtual target track set in said step ii) is searched; iv) newly setting a second adjacent track apart from the searched position toward an inner radius by a second predetermined distance which is shorter than said first predetermined distance, as a second virtual target track, in the event that said address of said virtual target track is searched; v) repeating said step iv) until a search for an address of said second virtual target track set in said step iv) fails; and vi) setting said address of said searched second virtual target track as a modified target track and searching said modified target track, in the event that said search for said address of said second virtual target track set in said step iv) fails in said step v).

6. The method as claimed in claim 5, wherein each of said first virtual target tracks are arranged by a first distance and said second virtual target tracks are arranged within said first distance by a second distance which is shorter than said first distance.