Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-06-12
2002-04-09
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053140
Reexamination Certificate
active
06370094
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical storage apparatus using an exchangeable medium such as CD, MO cartridge, or the like and, more particularly, to an optical storage apparatus for variably controlling a medium rotational speed for a constant linear velocity (CLV) and simultaneously correcting an eccentricity by using an eccentricity memory when a CD is reproduced.
Attention is paid to an optical disk as a storage medium as a center of multimedia which has rapidly been developing in recent years. For example, as for an MO cartridge of 3.5 inches, in addition to conventional MO cartridges of 128 MB and 230 MB, media of a high density recording such as MO cartridges of 540 MB and 640 MB and, further, a medium of a direct overwriting type are also being provided in recent years. As an optical disk drive, therefore, it is desirable that various media of 128 MB, 230 MB, 540 MB, and 640 MB, and further of the direct overwriting type which can be obtained at present can be used. In recent years, in personal computers which have rapidly been spread, a function for reproducing a compact disc (CD) which is known as a read only disk is indispensable. It is difficult to mount an optical disk drive of an MO cartridge as an exchangeable optical disk drive in addition to an optical disk drive for a CD from a viewpoint of a space and costs. In recent years, therefore, an optical disk drive which can use both of the MO cartridge and the CD has also been developed. According to the optical disk drive of the CD/MO compatible type, with respect to an optical system, a mechanism structure, and a controller circuit unit, a common use for both of a CD and an MO cartridge is realized as much as possible. Further, in recent years, a digital video disk (DVD) is also started to be spread and a common use for both of a DVD and an MO cartridge is also realized as much as possible in a manner similar to the CD.
SUMMARY OF THE INVENTION
In an optical disk drive using exchangeable media such as MO, CD, DVD, and the like, since a track eccentricity amount of a loaded medium is different every medium, the eccentricity amount of the medium is measured at a stage of an initializing process after the medium was loaded and an eccentricity offset current is supplied to a VCM synchronously with a medium rotation so as to set off the measured eccentricity amount. When tracks are regarded as straight lines, since the medium eccentricity draws a sine curve, what is called an eccentricity memory such as an RAM in which a sine value in which a rotational angle of a predetermined resolution is used as an address has preliminarily been stored is prepared, the eccentricity amount is obtained by reading out a corresponding cosine value from the eccentricity memory synchronously with an actual rotating position of the medium from an amplitude measured as eccentricity information and a phase for a rotational reference position, and an offset current is supplied so as to set off the eccentricity amount. In this case, in the MO cartridge, since the medium rotational speed is always constant owing to the constant angular velocity (CAV), it is sufficient to prepare one kind of eccentricity memory in which a sine value at each position in which the rotating position is used as an address has been stored.
In the media of a CD, a DVD, and the like, however, since a constant linear velocity (CLV) is used, the medium rotational speed has to be changed in order to keep a linear velocity constant in accordance with a position of an access track in the radial direction of the medium. When the rotational speeds are different in the radial direction of the medium as mentioned above, a time which is required for one rotation of the medium (rotational period) is also changed according to the rotational speed. A width of one address of the eccentricity memory has a value obtained by dividing the time required for one rotation by the number of addresses and the width of one address is changed depending on the rotational speed of the medium. Therefore, a plurality of kinds of eccentricity memories have to be prepared in accordance with the change in rotational speed of the medium and a capacity of the eccentricity memory is extremely large, resulting in a cause of disturbing a reduction in costs of the apparatus. Each time the medium rotational speed changes, different eccentricity memories have to be accessed, so that the number of accessing times of the memory also increases, resulting in an obstacle in realization of a high processing speed.
According to the invention, there is provided an optical storage apparatus which can efficiently correct an eccentricity by an access of an eccentricity memory of one kind even if a medium rotational speed is changed for a constant linear velocity (CLV).
According to an optical storage apparatus of the invention, a light beam from an optical unit is moved to a target track and is on-tracked by an access control unit provided for an MPU or the like by a driving control of a positioner using a VCM for moving a lens to irradiate the light beam onto a medium in the direction traversing medium tracks, and the optical storage apparatus further has a linear velocity control unit for variably controlling a rotational speed of the medium by a spindle motor in accordance with a radial position of the medium so as to set a linear velocity in the circumferential direction at the irradiating position of the light beam to a constant value. According to the invention, the optical storage apparatus is characterized by comprising: an eccentricity measuring unit for measuring an eccentricity amplitude (A) of one rotation of the medium and an eccentricity phase &phgr; for a start position of one rotation; an eccentricity memory in which an area from the start position of one rotation of the medium to an end position is divided into a plurality of regions every predetermined rotational angle and addresses are sequentially allocated and a sine value of each rotational angle increased by every predetermined rotational angle is stored in each address; a read control unit for generating an address (a) in the eccentricity memory corresponding to the rotating position of the medium where the light beam is irradiated at present by using the start position of one rotation of the medium as a reference and for reading out a corresponding sine value sinea from the eccentricity memory by a designation of the address (a); and an eccentricity correcting unit for obtaining an eccentricity amount (L) on the basis of the sine value read by the read control unit and the measurement values measured by the eccentricity measuring unit and for controlling the positioner so as to set off the eccentricity amount (L). Consequently, it is sufficient to use one kind of eccentricity memory. Even when the medium rotational speed differs depending on the reproducing position in the medium radial direction because of the constant linear velocity (CLV), the sine value in the eccentricity memory corresponding to the present rotating position of the medium when the light beam is irradiated at present can be read out by accessing the eccentricity memory of one kind. A memory capacity of the eccentricity memory can be remarkably reduced and costs of the apparatus can be reduced.
The read control unit has: a rotational period detecting unit for detecting a medium rotational period (medium rotational speed) according to the position in the radial direction of the medium where the light beam is irradiated at present; a 1-address rotating time detecting unit for detecting a 1-address rotating time showing a medium rotating time of one address by dividing the rotational period by the number of addresses in the eccentricity memory; a medium present position detecting unit for detecting a medium present position showing the rotating position of the medium where the light beam is irradiated at present by using the start position of one rotation of the medium as a reference; and a memory reading unit for comparing an address upper l
Ikeda Toru
Kishinami Masaya
Yabuki Eiji
Edun Muhammad
Greer Burns & Crain Ltd.
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