Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-12-15
2002-12-31
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044290, C369S044350
Reexamination Certificate
active
06501711
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pickup drive apparatus and a pickup drive method, which perform either recording operation or reproducing operation with respect to a recording medium such as a CD and a DVD.
2. Description of the Related Art
Conventionally, in a recording/reproducing apparatus for recording/reproducing information on a recording medium (will be referred to as an “optical disk” hereinafter) such as a CD (Compact Disk) and a DVD (Digital Video Disk, or Digital Versatile Disk) with employment of a pickup, a tracking servo control is carried out by using a radial contrast signal by way of a pickup drive apparatus having an arrangement shown in
FIG. 15
in order to properly control a position of the pickup along the radial direction.
In
FIG. 15
, very small spot light “SP” is irradiated from a pickup onto grooves “G” and lands “L”, which are alternately positioned along a radial direction “&thgr;rd” of an optical disk, and thus, return light such as reflection light produced by this spot irradiation is detected by a photodetector
1
.
In the photodetector
1
,
4
light receiving units a
1
, a
2
, b
1
, b
2
for receiving the above-described return light are provided, detection signals outputted from the respective light receiving units a
1
, a
2
, b
1
, b
2
are added to each other by an adder
2
, so that an RF signal “S
RF
” is produced. This RF signal S
RF
is processed by either a low-pass filter or an envelope detecting circuit
3
to thereby produce a radial control signal “S
RD
”. Furthermore, the radial control signal S
RD
is compared with a predetermined threshold value “V
REF
” by a comparator
4
, so that a binary ON/OFF track signal “S
TR
” is produced. Then, a tracking servo control is carried out based on the ON/OFF track signal S
TR
so as to properly control the position of the pickup in the radial direction.
FIG. 16
illustrates a principle idea of this tracking servo control. In this drawing, when the optical spot SP is moved in the same radial direction as while the optical pickup is moved along the radial direction “&thgr;rd”, intensity of the above-described return light is changed in response to an irradiation position of the optical spot SP, and the amplitude of the radial contrast signal “S
RD
” is changed in connection to this intensity change. When this amplitude change is compared with a predetermined threshold value V
REF
, such an ON/OFF track signal “S
TR
” is produced, the level of which is inverted at a boundary portion between a groove “G” and a land “L”. In this ON/OFF track signal S
TR
, a position of a groove G is indicated by a logic level “H”, whereas a position of a land L is indicated by a logic level “L”.
Then, the irradiation position of the optical spot SP with respect to the groove G corresponding to the recording track is properly controlled by performing the servo control as follows: That is, within a time period Tsink during which the ON/OFF track signal S
TR
becomes the logic level “H”, such a servo control (will be referred to as “track capturing”) is carried out in order that the optical pickup is positioned at the center of the groove G. Within a time period Tout during which the ON/OFF track signal S
TR
becomes the logic level “L”, such a servo control (will be referred to as “track escaping”) is performed in order that the optical pickup is shunted from the land L.
On the other hand, very recently, write-once type CD-Rs and DVD-Rs into which information can be written only once, as well as CD-RWs and DVD-RWs into which information is rewritable have been developed. However, when the tracking servo control is carried out by employing the above-described conventional pickup drive apparatus with respect to these optical disks, in the case that the above-described optical spot SP is irradiated on such an unrecorded region of the optical disk on which information is not yet recorded, both the radial contrast signal S
RD
and the ON/OFF track signal S
TR
, which represent the positions of the groove G and the land L, shown in
FIG. 16
, cannot be obtained. Accordingly, there is such a case that the irradiation position of the optical spot SP with respect to the groove G cannot be properly controlled.
In other words, since the optical reflectivities and the diffraction characteristics with respect to the optical spot are different from each other as to the groove G on which the information is recorded (namely, recorded pit is present), and the land L, it is possible to detect the position of the groove G and the position of the land L as a difference in the respective contrast based upon both the radial contrast signal S
RD
and the ON/OFF track signal S
TR
, which are obtained from the return light. As a result, the above-described proper servo control can be done. However, as to such a groove G on which no information is recorded (namely, recorded pit is not present) and the land L, when a groove interval is made narrow in order to increase the recording density, there is substantially no difference in the respective contrast. As a consequence, it is not possible to detect the position of the groove G and the position of the land L based upon the radial contrast signal S
RD
and the ON/OFF track signal S
TR
. There are some cases that the above-described proper servo control cannot be carried out.
As a result, there are some cases that while the optical spot is correctly located with respect to the unrecorded groove G (positioning), the information can be hardly recorded thereon. Also, as known from a so-called “random access operation”, when the pickup is moved along the radial direction with respect to the optical disk, the following difficult case may occur. That is, in this random access operation, the servo control can be quickly converged in such a manner that the pickup is moved to a desirable address area, and then the optical spot is positioned to a groove G at this address area.
SUMMARY OF THE INVENTION
The present invention has been made to solve the problems of the above-described conventional apparatus, and therefore, has an object to provide a pickup drive apparatus and a pickup drive method, capable of realizing a highly precise tracking servo control, and also a recording/reproducing apparatus equipped with such a pickup drive apparatus.
To achieve the above-described object, according to an aspect of the present invention, there is provided a pickup drive apparatus for driving/controlling a pickup used to irradiate an optical spot on a recording medium having a pre-pit between tracks, comprising: light detecting means for detecting return light produced by irradiating the optical spot; first signal producing means for producing a tracking error signal based upon the detection output of the light detecting means; second signal producing means for producing a control signal corresponding to the component of the pre-pit based upon the detection output of the light detecting means; control means for performing a tracking control in response to the tracking error signal; and supply means controlled so as to supply the tracking error signal to the control means in response to the control signal.
With employment of the above-described arrangement, the detection output containing the information of the track can be obtained by detecting the return light returned from the recording medium by the light detecting means. The first signal producing means produces the tracking error signal based upon the detection output, and this tracking error signal indicates the irradiation position of the optical spot. The second signal producing means produces a control signal corresponding to the component of the pre-pit based upon this detection output. Then, the supply means supplies the tracking error signal to the control means in response to the control signal so as to servo-control the pickup. As a result, the servo control is carried out in such a manner that the optical spot is positioned.
In particular, since the control signal is not produced based upon
Kikuchi Ikuya
Sato Mitsuru
Tateishi Kiyoshi
Pioneer Corporation
Tran Thang V.
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