Dynamic information storage or retrieval – Storage medium structure – Adjuncts or adapters
Patent
1997-11-17
2000-11-07
Miller, Brian E.
Dynamic information storage or retrieval
Storage medium structure
Adjuncts or adapters
G11B 724
Patent
active
061446327
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to optical data storage media such as compact discs and, in particular, to a semi-permanent enclosure for protecting the edges and faces of such data storage media during use. The invention also relates to a method of repairing minor surface defects and/or blemishes in optical data storage media.
Optical data storage media are becoming increasingly commonplace in everyday life. They are generally planar devices and have a substrate of clear plastics material or glass on which a surface formation of data "pits" is provided. The pitted surface is coated with a layer of diffused metal, such as aluminium, which serves to reflect incident light passing through the substrate from its opposing face. Data is generally read by a laser shone through the clear plastics material or glass, the incident light being distorted by the data pits and then reflected from the mirrored surfaces to be read by a pick-up.
For simplicity, in the text which follows, the term "disc" is used in a non-limiting sense to refer to optical data storage media of various types.
Damage to the read surface, that is to say the surface through which the laser reads the data pits, will result in distortion of the laser beam, causing errors in the reading of data. Similarly, damage to the reflective layer will result in a loss of reflectivity and loss of data, which will also lead to errors in reading of the data. A factor which is frequently overlooked is the possibility of damage to the reflective layer from the non-read side of the disc.
It is also desirable to avoid damage to the edge of the disc. If the edge becomes chipped, for example as a result of the disc being dropped, this may result in the reflective surface becoming exposed. In such circumstances, the reflective layer may tarnish and peel off. The purpose of the reflective layer is to reflect laser light back into the detector device of the playback apparatus. If the metallised layer is no longer reflective due to tarnish, or if portions thereof are missing altogether, the playback apparatus will receive no data from the damaged portion of the disc and will therefore skip. Once exposure of the reflective surface has occurred, it is difficult to stop progressive tarnishing and delamination. A disc damaged in this way rapidly becomes completely unplayable and must be replaced. Of course, in some cases, the stored data is unique and cannot be obtained from alternative sources.
From the foregoing, it is clear that any loss of laser light through dispersal is undesirable since this reduces laser intensity and may result in read errors. To combat this, manufacturers produce optical data storage media which have a degree of protection built in. The most vulnerable layers are the pitted surface, on which the readable data is stored, and the metallised layer. During manufacture, these are sandwiched between layers of glass or plastics material which form part of the completed disc assembly. The manufacturing process may also include the provision of a label which is also provided with a protective coating.
The present invention is defined as a "semi-permanent" enclosure in order to distinguish it from protective layers such as those described above which are provided as an inherent feature of the manufacturing process.
In addition to read errors resulting from surface damage to the disc as outlined above, laser distortion may arise from non-planarity or imbalance of the disc, for instance due to wobbling of the disc in a playback apparatus. Such distortion is equally likely to result in read errors.
Protective shields for optical discs are known, for example as described in U.S. Pat. No. 4,879,710. This patent discloses an optical disc protector comprising a transparent annular protective sheet provided with radially inner and outer rings of adhesive for securing the sheet to an optical disc. The adhesive rings are arranged so that they do not obscure the data portion of the disc. Such an arrangement suffers from the drawback that the film can be easily stripped
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Miller Brian E.
Optidisc International Limited
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