Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2002-08-07
2004-07-06
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044270, C369S044340, C369S047100
Reexamination Certificate
active
06760285
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a disk device for carrying out at least one of recording and reproducing of information by irradiating a disk-shaped recording medium or a disk with a light beam, and a method of adjusting a servo mechanism of creating a focusing error signal indicative of a deviation of the focal point of a light beam applied onto a disk from a recording face of the disk and a tracking error signal indicative of a deviation of the focal point of the light beam applied onto the disk from a track on the disk on the basis of the common light reflected from the disk and further executing a focusing servo of controlling the focal point of the light beam applied on the disk to follow a recording face of the disk and a tracking servo of controlling the focal point of the light beam applied on the disk to follow the track on the disk.
The disk device is provided with a servo mechanism of creating a focusing error signal indicative of a deviation of the focal point of a light beam applied onto a disk from a recording face of the disk and a tracking error signal indicative of a deviation of the focal point of the light beam applied onto the disk from a track on the disk on the basis of the common light reflected from the disk and further executing a focusing servo of controlling the focal point of the light beam applied on the disk to follow a recording face of the disk and a tracking servo of controlling the focal point of the light beam applied on the disk to follow the track on the disk.
In a disk device for carrying out recording or reproducing of information for a DVD which is a kind of an optical disk, a single-beam phase difference system is generally adopted in order to create a tracking error signal. As shown in
FIG. 3
, the single beam phase difference system is to take a sum of output signals A and C and a sum of output signals B and C from four segments on diagonal lines into which a photo-diode
101
divided to receive light reflected from the disk to acquire a tracking error TE which is a signal indicative of a phase difference between these two sum signals A+C and B+D. In this case, generally, a level difference between the two sum signals A+C and B+D is used as a focusing error FE. Namely, the focusing error and tracking error are created on the basis of the common light reflected from the disk.
Meanwhile, whenever the disk is replaced by another disk, the disk device performs focusing balance adjustment and tracking balance adjustment. The focusing balance adjustment is to adjust the servo mechanism so that the reproduction quality is optimum while the focusing servo is active.
Incidentally, information is reproduced from the disk when the full-added signal (sum signal of A+B+C+D of output signals A, B, C and D from the four segments of the photo-diode
101
in
FIG. 3
) is processed as a signal read from the disk). The reproduction quality is improved as the amplitude of the full-added signal increases. Therefore, in order to perform the focusing balance adjustment, for example, the servo mechanism may be adjusted so that the amplitude of the full-added signal is maximum while the focusing servo is active.
The tracking balance adjustment is to adjust the servo mechanism so that the amplitude difference (hereinafter referred to as “tracking balance deviation”) between an upper side and lower side relative to zero (reference level) of a waveform occurring in the tracking error signal when the focal point of the light beam applied on the disk crosses a track of the disk is cancelled.
Incidentally, since the disk has eccentricity, in a state where the disk rotates and the tracking servo is not active, the focal point of the light beam applied to the disk crosses the track of the disk. Therefore, in order to perform the tracking balance adjustment, the servo mechanism may be adjusted so that the DC component of the tracking error signal is zero (reference level) in a state where the disk rotates and the tracking servo is not active.
In order to perform the focusing balance adjustment accurately, since this adjustment is performed on the basis of the amplitude of the full-added signal, it must be performed in a state where the tracking servo operates normally (the focal point of the light beam applied to the disk follows the track on the disk).
On the other hand, if the tracking balance deviation is too large, the tracking servo does not operate normally (even when the tracking servo is made active, the focal point of the light beam applied onto the disk does not follow the track on the disk). In other words, unless the tracking balance is somewhat small, the tracking servo does not operate normally and hence the focusing balance adjustment cannot be performed.
In view of the fact as described above, in a conventional method of adjusting the servo mechanism, in order to assure accurate focusing balance adjustment, the focusing balance adjustment was performed after the tracking balance adjustment had been performed. Further, in a series of operations for adjusting the servo mechanism, the tracking balance was not performed after the focusing balance adjustment had been performed.
Incidentally, the Unexamined Japanese Patent Application No. Hei7-153210 discloses that the tracking balance adjustment is performed after the focusing balance adjustment is performed. However, this is not relative to a servo mechanism in which the focusing error signal and tracking error signal are created on the basis of the common beam of light reflected from the disk as in a single beam phase difference system, but the servo mechanism of a three-beam system (in which the focusing error signal and tracking error signal are created on the basis of different beams of light reflected from the disk).
However, in a servo mechanism in which the focusing error signal and tracking error signal are created on the basis of the common beam of light reflected from the disk as in a single beam phase difference system, implementation of the focusing balance adjustment influences the tracking error signal.
Therefore, in the conventional method of adjusting the servo mechanism, even after the tracking balance adjustment is performed, the subsequent focusing balance adjustment generates the tracking balance deviation. As a result, the tracking balance deviation cannot be cancelled. In the state where the tracking balance deviation has not been cancelled, the focal point of the light beam applied on the disk cannot follow the track of the disk so that the recording quality of information and the reproducing quality for the disk will be attenuated.
SUMMARY OF THE INVENTION
Thus, this invention intends to provide a method of adjusting a servo mechanism in which the focusing error and tracking error are created on the basis of the common light reflected from a disk and which tracking balance deviation can be surely shifted.
In order to attain the above object, this invention provides a disk device for carrying out at least one of recording and reproducing of information by irradiating a disk-shaped recording medium or a disk with a light beam, comprising:
a photo-diode divided into four segments for receiving light reflected by the disk;
a focusing error signal creating circuit for creating a focusing error signal which is a level difference between a first sum signal indicative of a sum of output signals from two segments on one diagonal line of the photo-diode and a second sum signal indicative of a sum of output signals from two segments on the other diagonal line thereof;
a tracking error signal creating circuit for creating a tracking error signal indicative of a phase difference between the first sum signal and the second sum signal;
a focusing drive signal creating circuit for creating a focusing drive signal to set the value of the focusing error signal at the reference level;
a tracking drive signal creating circuit for a tracking drive signal to set the value of the tracking error signal at the reference level;
a focusing actuator fo
Hirashima Minoru
Kuwayama Yasunori
Edun Muhammad
Funai Electric Co. Ltd.
Morgan & Lewis & Bockius, LLP
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