Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Of record carrier
Reexamination Certificate
1998-09-03
2001-09-04
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Of record carrier
C369S053220, C369S044270
Reexamination Certificate
active
06285641
ABSTRACT:
The present invention relates to a device for writing to and/or reading from optical recording media having different structures.
A device of this type is disclosed, for example, in EP 0 294 490 or “IBM Technical Disclosure Bulletin, Vol. 29, No. 3, August 1986”. In these devices, the type of optical recording medium is determined using the reflectivity of the recording layer. In this case, the intensity of the reflected light is compared with two reference values, which permit a distinction (discrimination) between two types of recording media.
In the device disclosed in “IBM Technical Disclosure Bulletin, Vol. 29, No. 3, August 1986”, the reflectivity of the optical recording medium is used to determine the type thereof. The objective lens of the device is in this case moved from a reset position towards the recording medium. The signal emitted by a focus detector during this process is used to determine the type of optical recording medium. Only those regions of the signal characteristic which lie above a first reference value (LOW) are used here. If the magnitude of the signal lies above the first reference value but below a second, higher reference value (HIGH), then an AND gate emits a pulse which signals that a “write-once” recording medium has been inserted. If the magnitude of the signal lies both above the first reference value and above the second, higher reference value (HIGH), then a further AND gate emits a pulse which signals that a “read-only” recording medium has been inserted. This method functions whenever the recording media used can be identified unambiguously using the reference values. A relatively large number of different types of optical recording media makes it necessary to introduce, if appropriate, additional reference values, which are inevitably closer together, as a result of which the error probability rises. If a plurality of extreme values lying between the lowest and the highest reference value appear in the signal characteristic, then the result in this method may be that a plurality of contradictory statements relating to a single recording medium are output concerning its type, which may result in the device malfunctioning.
EP 0 294 490 discloses, for the purpose of determining the type of optical recording medium, evaluating the signal level of the RF signal, that is to say of the signal carrying the information read from the recording medium. In this case, provision is made for evaluating the signal level whenever the objective lens is in a position suitable for reading, that is to say its focus point lies on or almost on the reflecting layer of the recording medium. As long as the type of optical recording medium is still unknown, the device cannot be set optimally, that is to say the RF signal is subjected to a greater or lesser extent to interference, with the result that the signal level can actually be evaluated only during a very brief time interval. Depending on the level of the randomly read signal, it is possible in this case for large fluctuations to occur, with the result that it is necessary to take a large error bandwidth into account, that is to say in this case, too, the problem arises that with a wide variety of different types of optical recording media having different thicknesses and/or numbers of layers which is to be expected in the future, the signal levels used for the discrimination are so close together that unambiguous discrimination requires ever greater complexity or even becomes impossible. Moreover, unambiguous discrimination may be rendered virtually impossible by production-dictated slight fluctuations in the reflectivity of the optical recording medium.
It must therefore be regarded as disadvantageous with these known devices that the wide variety of different types of optical recording media having different thicknesses and/or numbers of layers which is to be expected in the future can no longer be identified reliably by means of a simple reference value analysis according to the prior art.
Devices suitable for reading from and/or writing to different types of optical recording media, in particular, should be capable of identifying the type of optical recording medium in order to be able correctly to select parameters for the reading and/or writing operation.
The object of the present invention, therefore, is to propose a device having a simple structure and an appropriate method by means of which different types of optical recording media can be identified reliably yet rapidly.
This object is advantageously achieved by means of the measures specified in the independent claims. Advantageous developments of the invention are evinced in the subclaims. In order to achieve the object, the invention provides an identification means which makes it possible to determine the type of optical recording medium by assessing the physical properties thereof. This has the advantage that the scanning or recording properties of the device, which differ for different types of optical recording media, are automatically set in a manner corresponding to the determined type of recording medium.
According to the invention, the identification means is capable of determining the layer thickness of the protective layer which covers the recording layer of the recording medium. This has the advantage that it is thereby possible to use recording media having different layer thicknesses as well in the device according to the invention. Future recording media of high storage density will have smaller layer thicknesses than conventional recording media, for example than CDs.
According to the invention, provision is made for carrying out, during the focusing operation of the device according to the invention, a plausibility check of the signals determined from the reflected light. A plausibility check of this type has the advantage of managing essentially without any additional hardware elements, since it is possible to utilize functions and components which are present in any case. This plausibility check may consist, for example, in implementing different scanning or recording properties, suitable for different types of recording media, of the device with corresponding focus settings. Since the respectively set values are coordinated with different types of optical recording media, that is to say with optical recording media having different physical properties, the signals emitted by the detection means lie in a meaningful range of values only when the setting of the device is matched to the type of recording medium inserted. The type of optical recording media involved can be derived from that setting for which these signals are the most plausible.
A further aspect of the present invention provides for evaluating a plurality of characteristic features in the time characteristic of the intensity of the light reflected from the optical recording medium, for the purpose of determining the physical properties and hence the type of the optical recording medium. This measure is based on the insight that the time characteristic of the intensity depends on the type of optical recording medium. In this case, the time characteristic also includes reflections at the air-substrate material transition layer or at the transition layers of different layers of the optical recording medium, with the result that a relatively large number of information items are available for the evaluation. The time characteristic of the intensity of the reflected light differs, for example, for optical recording media having different thicknesses. Optical recording media which can be prerecorded or are prerecorded on both sides have, for each side, only about half the thickness of a conventional optical recording medium, for example of an audio CD. A distinction can likewise easily be made between different optical properties, for example different refractive indices of the substrate material of the optical recording medium and different reflectivities of the optical recording layers used, particularly when two or more layers of recording layers are arranged one
Dang Lieu Kim
Schroeder Heinz-Jörg
Zucker Friedhelm
Deutsche Thomson-Brandt GmbH
Edun Muhammad
Kiel Paul P.
Tripoli Joseph S.
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