Dynamic information storage or retrieval – Storage medium structure – Adjuncts or adapters
Reexamination Certificate
2000-03-01
2001-05-29
Miller, Brian E. (Department: 2754)
Dynamic information storage or retrieval
Storage medium structure
Adjuncts or adapters
Reexamination Certificate
active
06240061
ABSTRACT:
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 metallized 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 metallized 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 at the edge of the disc due to the need for the contact adhesive bands to be very narrow so as not to overlie the data surface. Subsequent peeling of the film allows dust and other particles to become trapped under the film and to interfere with integrity of the laser signal. In severe cases, the film may be lifted sufficiently to cause interference with the mechanics of the playback apparatus.
In another protective arrangement known from U.S. Pat. No. 4,736,966, an optical data storage device such as a data card is provided with a plurality of peelable transparent protective layers. When a layer becomes too severely scratched for efficient reading of data, it is removed by peeling. This approach has a number of disadvantages. Firstly, the data is obscured at the outset by the number of layers interposed between the read surface and the pick-up. This problem is exacerbated if the optical disc is intended for recording as well as playback, since the signal to be recorded will be attenuated by the interposed protective layers. Further attenuation occurs on reading, so the playback signal may be very weak and severely distorted. Another disadvantage is that the removal of successive layers by peeling leaves a residue of adhesive which needs to be cleaned away prior to playback. The very act of cleaning may damage the next layer of protective film.
In European Patent Application No. 0 375 298 A2, a protective shield for an optical disc is described which is designed to be stripped from the disc immediately prior to the recording of data thereon by laser irradiation. The shield thus serves to protect the disc in the post-manufacture phase, during storage, transport and purchase by an end user. Such shields are formulated with anti-static properties to minimize attraction of air-borne dust particles. This ensures that the data is recorded on a “clean” disc. However, no provision is made for protecting the disc after recording.
European Patent Application No. 0 300 733 A1 describes a heat-shrinkable shield for optical discs. One of the drawbacks of this arrangement is that special equipment is required to ensure even application of heat to the shield to effect shrinkage thereof around the disc to be protected. Temperature control is also important to prevent damage to the substrate. This arrangement is therefore unsuitable for use by non-experts.
In British Patent Application No. 2 217 507 A, annular protective shields are disclosed for attachment to compact discs through the intermediary of a transparent or translucent gum. A special apparatus is also disclosed for applying the shields to compact discs. The shields are shown attached to the non-read surfaces of discs, since the applicant believes that the non-read surface is particularly vulnerable to damage by virtue of having only a relatively thin protective layer of u.v.-curable lacquer. While there are undoubtedly some grounds for this belief, the document does not address the problem of protecting the read surface of optical discs from accidental damage.
It is therefore an object of the present invention to provide means for protection against accidental damage to the opposed faces and edge surface of an optical disc. It is a further object of the present invention to provide means for protection against accidental damage to an optical disc which is capable of being fitted by a non-expert and without the need for special equipment. It is also an object of the present invention to provide means for protection against accidental damage to an optical disc which means is capable of being kept in place during use of the disc in standard playback apparatus, including apparatus; having a multiple disc magazine, and which fits into a standard disc “jewel” case for normal storage. It is yet another object of the present invention to provide means whereby the dynamic qualities of an optical disc are enhanced during use by elimination or suppression of wobbling or other imbalances. It is a still further object of the present invention
McDermott & Will & Emery
Miller Brian E.
Optidisc International Limited
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