Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Patent
1989-10-13
1992-07-07
Envall, Jr., Roy N.
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
369 4434, 369 4435, 369 54, 235454, 235476, G11B 709
Patent
active
051289172
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to an optical memory card, and more particularly, to a tracking device for an optical memory card.
2. Background Art
Optical recording media on which digital data is recorded by forming optically changed patterns such as bright and dark pits have recently been attracting considerable attention. Since data can be recorded on such optical recording media at a high density, optical recording media offer the ability to provide large capacity memories. Proposals have therefore been made not only for disk type optical memories but also for card type memories.
In an optical memory card of the above described type, optically or magneto-optically changed states are formed in a discrete fashion on the surface of the card in correspondence to the data to be recorded, such changed states being read by irradiating an optical beam such as laser beam thereon.
In practice, fine irregularities or a bright and dark pattern may be formed on the surface of the recording medium, i.e., on the surface of the card, and the recorded data is read by utilizing the difference in the reflectivity, the index of refraction or the transmittance of the optical beam irradiated on the fine irregularities or the bright and dark pattern. Alternatively, the thermomagnetically recorded data is read from the recording medium by utilizing variations in polarization caused owing to the magnetooptic effect of the optical beam irradiated on the recording medium.
As shown in FIG. 6, data is generally written on a card 81 on data tracks 82 formed adjacent to and along tracking lines 80 provided in the longitudinal direction of the card 81. Data thus recorded is generally read from or written on any arbitrary data track 82 first by moving a reading or writing optical system in the transverse direction of the tracks and selecting a target data track and then by moving the card 81 in the direction of the tracks and running a reading or writing beam relative to the card 81 along that data track 82 while making the optical system follow the tracking line corresponding to the target data track.
When the optical system follows tracking lines, an optical image 8 of the associated tracking line is received by light-receiving elements 7a and 7b, and an amplifier 9 outputs a signal representing the difference occurring in the outputs of these elements as a tracking error signal, as shown in FIG. 4. The tracking error signal is a signal proportional to any deviation occurring during the tracking. Deviation occurring during the tracking is corrected by moving a mobile objective lens of the optical system in the transverse direction of the track in correspondence to this tracking error signal. The mobile objective lens is held on a lens retaining portion provided in the optical system by spring members such as hair springs in such a manner as to be movable in the vertical and horizontal directions. Electromagnetic force is utilized to move the mobile objective lens. Vertical movement of the objective lens is utilized for focusing control, whereas horizontal movement thereof is utilized for the tracking control.
However, in the above-described optical memory card, there is a possibility that a normal tracking error signal cannot be obtained due to dust or scratches existing on the optical memory card and thus that a tracking servo circuit cannot be operated normally. This makes normal tracking control and, hence, normal writing of data on and reading of data from the optical memory card impossible.
Accordingly, one countermeasure that has been considered is to store a tracking error signal that is obtained immediately before detection of dust or a scratch and to substitute this stored signal for a tracking error signal when the dust or scratch is detected. However, in a card-type optical memory, the existence of a certain degree of skew of the tracking lines relative to an optical system is unavoidable in terms of the accuracy with which the tracking lines are in practice made parallel to the sides of the
REFERENCES:
patent: 4787076 (1988-11-01), Deguchi et al.
patent: 4821251 (1989-04-01), Hosoya
patent: 4879707 (1989-11-01), Getreuer et al.
Envall Jr. Roy N.
Kabushiki Kaisha CSK
Young W. R.
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