HK1064494B - Device for writing to or reading from different optical recording medium - Google Patents

Description

Apparatus for writing or reading different optical recording media

The present application is a divisional application of the invention patent application with application number 97192914.9 and application date 1997 of 27.

Technical Field

The present invention relates to an apparatus for writing to and/or reading from optical recording media having different structures.

Background

Such a plant is disclosed, for example, in EP (European patent) 0294490 or "IBM technical publication, 8.1986, volume 29, third edition". In these apparatuses, the type of the 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 that make it possible to distinguish (discriminate) the two types of recording media.

In the apparatus disclosed in "IBM technical publication, 8.1986, volume 29, third", the type of optical recording medium is determined by the reflectivity thereof. In this case, the objective lens of the apparatus is moved from the home position toward the recording medium. In this process, the type of the optical recording medium is determined using a signal emitted from the focus detector. Only those regions of the signal characteristic which lie above the first reference value (low) are utilized here. If the signal amplitude is above the first reference value but below a second, higher reference value (high), the and gate signals a pulse that signals the insertion of a "write once" recording medium. If the signal amplitude is above both the first reference value and the second, higher reference value (high), then the further and gate sends a pulse signaling that a "read only" recording medium is inserted. This method is effective whenever the recording medium used can be definitely discriminated by using the reference value. The relatively large number of different types of optical recording media makes it necessary to introduce additional reference values which, if appropriate, are inevitably closer together, with a consequent increase in the probability of errors. If a number of extreme values between the lowest and the highest reference values occur in the signal characteristic, the result of this method may be to output a number of contradictory statements about the type of a recording medium, which may lead to malfunctions of the apparatus.

For determining the type of optical recording medium, EP 0294490 discloses measuring the signal level of a radio frequency signal, i.e. a signal carrying information read from the recording medium. In this case provision is made for measuring the signal level each time the objective lens is in a position suitable for reading, i.e. its focal point is at or almost at the reflective layer of the recording medium. As long as the type of optical recording medium remains unknown, the apparatus cannot be optimally adjusted, i.e. the radio frequency signal is disturbed to a greater or lesser extent, so that the signal level can actually be determined only for a very brief time interval. Depending on the signal level of the random readout, large fluctuations may occur in this case, so that a large error bandwidth must be taken into account, i.e. a problem also arises in this case, in the case of a wide variety of different types of optical recording media with different thicknesses and/or number of layers in the future, the signal levels used for authentication are so close that unambiguous authentication always requires greater complexity or even becomes impossible. Furthermore, due to slight fluctuations in the reflectivity of the optical recording medium as determined by production, unambiguous identification may become practically impossible.

It must therefore be considered disadvantageous for these known devices that a wide variety of different types of optical recording media with different thicknesses and/or number of layers in the future can no longer be reliably identified according to the prior art by means of simple reference value analysis.

Apparatuses suitable for reading from and/or writing to different types of optical recording media should in particular be able to discriminate the type of optical recording medium so that the parameters for the reading and/or writing operation can be correctly selected.

Disclosure of Invention

It is therefore an object of the present invention to propose an apparatus with a simple structure and a suitable method by means of which different types of optical recording media can be reliably and quickly identified.

To achieve the object of the present invention, there is provided an apparatus for writing or reading different optical recording media, the apparatus comprising: a focusing device for moving a focal point along an optical axis; a detecting device for detecting the intensity of the light reflected from the optical recording medium; a measuring device for determining the type of the optical recording medium by measuring the signal from the detecting device; and a controller for controlling the focusing means, the determining means performing a plausibility check, i.e. checking the signals emitted by the detecting means in order to determine whether they are within a range of reasonable values, i.e. whether they are reasonable, characterized in that: the controller specifying a parameter corresponding to a first type of device setting applicable to the recording medium; if the signal from the detection means is not reasonable, the determination means sends an output signal to the controller to change the parameter.

The present invention provides an authentication apparatus which makes it possible to determine the type of an optical recording medium by determining its physical properties. This has the advantage that the scanning or recording performance of the device is automatically adjusted in a manner corresponding to the determined type of recording medium, which differs for different types of optical recording media.

According to the present invention, the discriminating apparatus can determine the (thickness of the) layer of the protective layer covering the recording layer of the recording medium. In the device according to the invention this has the advantage that recording media with different layer thicknesses can thus also be used. Future recording media with high storage densities will have smaller layer thicknesses than conventional recording media, such as CDs (compact discs).

According to the invention provision is made for a plausibility check of the signal determined from the reflected light to be made during the focusing operation of the device according to the invention. This type of plausibility check has the advantage of being handled virtually without any additional hardware parts, since it is possible to utilize functions and parts which are in any case available. Such a plausibility check may consist, for example, in realizing different scanning or recording performances of the device for different types of recording media with corresponding focus settings. Since the respectively set values are matched to different types of optical recording media, i.e. optical recording media having different physical properties, the signal emitted by the detection means lies within a meaningful range of values only if the setting of the device matches the type of inserted recording medium. The type of optical recording medium involved can be deduced from the one for which the signals are most reasonable for the setting.

Another aspect of the invention provides for determining a number of characteristic properties in the time characteristic of the intensity of light reflected from the optical recording medium in order to determine the physical characteristic and thus the type of optical recording medium. This measure is based on the insight that the temporal behavior of the light intensity depends on the type of optical recording medium. In this case, the temporal behavior also includes reflections at the air-substrate material transition layer or at the transition layers of the different layers of the optical recording medium, so that a relatively large number of information items can be used for the determination. For example, the temporal characteristics of the intensity of reflected light are different for optical recording media having different thicknesses. Optical recording media that can be pre-recorded or have been pre-recorded on both sides have only about half the thickness of conventional optical recording media, e.g. audio CDs, for each side. It is also easy to distinguish between different optical properties, such as different refractive indices of the substrate material of the optical recording medium and different reflectivities of the optical recording layers used, especially when two or more recording layers are arranged one on top of the other. In contrast to the prior art, in which recording media provided with two recording layers are determined using only the layer with the highest reflectivity, which can easily lead to incorrect allocation, such errors are practically excluded with the device according to the invention. In this case, the light reflected from the optical recording medium is detected by the detection device. In the simplest case, the detection means consist of a photodetector which emits an electrical signal proportional to the intensity of the light incident thereon. In an advantageous development, the detection device is assigned a processing stage in which the signal of the light detector is processed and/or conditioned.

According to the invention, the signal emitted during the movement of the focal spot along the optical axis is determined. Since the focal spot must in any case be moved towards the optical recording medium in order to find its correct position relative to the recording medium, this has the advantage of constituting a simple measure that does not require any additional circuitry and time.

According to the invention, the time interval between the extreme values of the emitted signal is determined. This has the advantage that the layer thickness or the spacing between the layers present can thus be determined in a simple manner. If the amplitude of the extreme value of the emitted signal is additionally determined, greater accuracy of the type of optical recording medium can be obtained. In this case, it is possible to determine only the order and magnitude of the extreme values, without taking into account the time interval otherwise. The amplitude of the extreme values, which may be the maximum and minimum, corresponds to the reflectivity of the corresponding recording layer. The comparison of the relative amplitudes or the absolute amplitudes of the extreme values makes it possible to reliably discriminate between the different types of optical recording media.

Furthermore, the invention shows the possibility of comparing the temporal characteristics of the intensity of the reflected signal with stored signal characteristics that are specific for different types of optical recording media. Each stored characteristic signal characteristic is assigned to the corresponding type of optical recording medium, and the type of recording medium can thus be determined using this comparison. In this case the comparison is effected either directly or by means of a suitable mathematical algorithm.

In an advantageous development of the invention, the focusing device has a multifocal lens, in particular a bifocal lens provided for a protective layer having a different thickness and covering the optical recording layer. This produces a considerable number of extrema in the temporal behavior of the reflected signal. This has the advantage of making it possible to more accurately discriminate this signal. The bifocal lens has two different focal lengths or can be adjusted to two different focal lengths to optically match two layers having different thicknesses. Optical matching to two or more different layers is achieved with corresponding multifocal lenses. It is within the scope of the invention to replace the lens with another suitable optical element, for example, an optical element such as a holographic optical element or a polarizer can produce multiple focal points.

A switch operable by an operator may also be provided for the purpose of identifying the physical characteristics and thus the type of optical recording medium. This has the advantage that this measure, which is particularly easy to implement, is cost-effective to implement. The switch may be, for example, a mechanical switch, a touch-sensitive switch, a contactless sensor or other similar element. A measure to increase the ease of operation is seen in providing a corresponding switch which can be activated by the optical recording medium or a cassette attached thereto.

The setting of the device according to the invention can be changed expediently for best matching with the type of recording medium by means of the method specified in the method claims.

The invention is described below with exemplary embodiments with reference to the drawings. Some of the advantageous improvements of the present invention can be found in the description.

Drawings

In the drawings:

figure 1 shows a schematic view of an apparatus according to the invention,

figure 2 shows a schematic illustration of the determination of the type of optical recording medium by means of a bifocal lens with a conventional CD,

FIG. 3 shows a schematic illustration of the determination of the type of an optical recording medium by means of a bifocal lens with pre-recording or prerecording on both sides, with a high storage density and with a recording layer, an

Fig. 4 shows a schematic illustration of the determination of the type of an optical recording medium by means of a bifocal lens, which is or can be prerecorded on both sides, has a high storage density and has two recording layers, using an optical recording medium.

Detailed Description

According to the schematic diagram shown in fig. 1, a reproducing and/or recording device for optical recording media AT having different storage densities uses a scanning device in a reproducing and/or recording device provided for the playback of audio CDs and for the playback of digital video discs. According to fig. 1, the scanning device consists of a laser diode LD, a grating G, a polarizing beam splitter PBS, a collimator lens CL, a quarter-wave plate WL, an objective lens OL, a concave lens KL, a cylindrical lens ZL and a detector PD. Although the digital video disc, hereinafter referred to as DVD, and the audio compact disc, hereinafter referred to as CD, have different storage densities, the scanning device shown in fig. 1 can be used for both types of recording media AT as well. Higher storage densities of DVDs are achieved with smaller pit sizes and reduced track pitches compared to CDs. In order to reproduce the information stored on the recording medium AT or to record corresponding information, the diameter of the scanning beam or the writing beam must be adapted accordingly to the size of the memory cells or pits used. In order to be able to read out the smaller pits of a DVD as well as the larger pits of a CD with the scanning device shown in fig. 1, the objective lens OL is designed as a bifocal lens. Different spot diameters can be realized on the information medium AT by means of a bifocal lens or a multifocal lens. This detector arrangement is advantageously used for both high and low storage density recording media AT.

For the purpose of the measurement, the output signal of the detection device PD is transmitted to a known measuring and regulating device (not shown here) and to a measuring unit AE, which receives additional information from components which are also not shown here. The output signal of the evaluation unit AE is transmitted to a controller SE which controls the focus drive FA as a function of signals from further components (not shown here), such as, for example, a regulating device. The focus driver is part of the focusing means FM for moving the objective lens OL along the optical axis OA in an exemplary embodiment. In a more general case, the focal point is moved along the optical axis. The recording medium AT is shown with two different layer thicknesses d1 and d 2. The layer thickness d2 shown to the right of the optical axis OA corresponds to the layer thickness of a conventional CD. The recording medium shown as an alternative to the left of the optical axis OA has two layers, the layer thickness being d 1. This is an example of a digital video disc DVD that can be pre-recorded or pre-recorded on both sides. The two focal points F1 and F2 and the objective OL designed in this case as a bifocal lens are more pronounced. The layer thicknesses d1, d2 are an indication of the type of optical recording medium, as explained here with the example of CD and DVD.

The shown apparatus for playback from and/or recording on an optical recording medium AT is capable of discriminating between different types of optical recording media like CD and DVD, for example, so that the controller SE can drive the focus driver FA with control signals adapted to the respective type of recording medium AT.

In the simplest exemplary embodiment, instead of the evaluation unit AE, a sensor or a mechanical switch SW, which can be actuated by the user of the device and is indicated by a dashed line in fig. 1, or a sensor S, which detects the type of the recording medium AT and is likewise indicated by a dashed line, is provided.

If no mechanical switch is used, it is necessary to generate a signal by another method by means of which the physical properties of the optical recording medium AT to be read from and/or written to can be discriminated so that the controller SE can be adjusted accordingly.

This problem occurs when the intention is to read or write a conventional CD in a device for reading and/or writing digital video discs, DVDs. In order to solve the problem with a read-out unit having a relatively simple structure, regardless of the layer thickness differences d1, d2 of different types of optical recording media, a bifocal lens OL is employed. In this case, each of the two focal points F1, F2 generates an optical signal reflected from the recording medium. Only one of the two signals contains the stored information. Due to the different track widths in DVD and CD, it is also necessary to adapt the tracking adjustment circuit to the type of optical recording medium.

The optical recording medium to be read and/or written may be displaced from the focusing means FM by up to a few millimeters in height or distance, while the focus point F1 or F2 is allowed to leave the underside of the optical recording medium AT only a few micrometers relative to the recording layer AZS located AT the distance d1 or d2, respectively. For this purpose, in the exemplary embodiment an autofocus system is used which adjusts the distance between the objective lens OL and the recording layer AZS by means of the focus driver FA. The signal used to control the focus driver FA is derived from the signal emitted by the photo detector PD, i.e. the same as the readout information. For example, a so-called astigmatic method can be used for focusing.

After inserting the optical recording medium into the apparatus, the controller SE first brings the distance between the objective lens OL and the recording medium AT to a position where the focal point is AT or near the recording layer AZS of the optical recording medium, so that the automatic adjustment circuit, the adjustment range of which is limited, can be switched on. The operating range for focus adjustment is typically in the range of 10 to 100 microns, depending on the focusing method used.

In the initialization phase after the optical recording medium AT is inserted into the apparatus, the objective lens OL is usually moved AT a low speed in the direction of the recording medium AT. In a system with a conventional lens, i.e. one focus, a narrow pulse-like signal appears when the focus of the objective lens OL enters the recording medium AT, and another much larger pulse appears when the focus falls on the recording layer AZS. As long as the focal point is not near the surface or the recording layer AZS, virtually no reflected light impinges on the detector PD. A positive focus error signal FE results from, for example, the signal from the detector PD if the focal point is just below the reflecting surface, and is negative when the focal point is just above the reflecting surface. The value of the focus error signal FE is zero when the focus is in a position suitable for writing or reading. When the focus error signal FE is 0, the focus adjustment circuit is normally turned on.

As shown in the exemplary embodiment, if the bifocal lens OL is used, the number of pulses measured by the detector is doubled during initialization. Two pulses occur each time the focal points F1 and F2 pass through the air-recording medium interface and the recording layer AZS. This situation is illustrated in fig. 2 using a conventional CD.

The upper part of fig. 2 shows a detail of the recording medium AT, in this case the CD, which is rotated by 90 deg. compared to fig. 1. The recording layer AZS is located on the right and the recorded information is illustrated by elevations and depressions in the recording layer AZS. The lower part of fig. 2 shows the time axis t and the voltage RV output by the controller SE to the focus driver FA during the initialization phase already described above. The increased voltage RV moves the objective lens OL toward the recording medium AT. The signals emitted by the detector PD are also described as a focus error signal FE and a mirror signal M. In this case, the mirror signal M corresponds to the average intensity of light reflected from the optical recording medium. This may be, for example, the envelope of the information signal.

For the exemplary embodiment, assume that the bifocal lens is designed in such a way that the intensity measurable at focal point F2 is about half the intensity measurable at focal point F1, and that focal point F1 is provided for reading digital video disk DVDs. The part of the bifocal lens OL which yields the focal point F2 is corrected spherically to a layer thickness of the recording medium AT of d 2-1.2 mm, and the part of the bifocal lens OL which yields the focal point F1 is corrected spherically to a layer thickness of d 1-0.6 mm, which correspond to the layer thicknesses of CD and DVD, respectively. As shown in fig. 2, four pulses, hereinafter also referred to as peaks, occur for the CD while the objective lens OL is moved toward the recording medium. In this case, the peak value of the mirror signal M is maximum when the focus error signal FE crosses through zero from the positive toward the negative range. The first peak occurs when the focal point F2 of the CD passes over the surface of the recording medium. The intensity of the light reflected here is low because the reflectivity of the surface is low, typically about 4%, and the focal point has large aberrations. The mirror signal M is therefore small. The second peak occurs when the focus F1 of the DVD passes through the substrate surface. In this case, the intensity of the reflected light, and thus also the peak in the mirror signal, is low. Precisely, on the one hand, due to the low reflectivity of the surface and, on the other hand, due to the spherical aberration of the focal point F2 being even larger than that of the focal point F1, due to the larger numerical aperture. The third peak occurs when the focus F2 of the CD reaches the recording layer AZS. The intensity of the light reflected here is high, because the reflectivity of the recording layer AZS is high, typically at least 70% for a conventional CD, and on the other hand only small aberrations occur. And thus the corresponding peak is also high. The fourth peak occurs when the focus F1 of the DVD falls on the recording layer. Although the intensity of the light focused on the focal point F1 is about twice as high as the intensity of the light focused on the focal point F2, according to the assumption of the present exemplary embodiment, the intensity of the light reflected here is about as high as that on the focal point F2 due to large aberrations.

Fig. 3 illustrates a schematic cross-sectional view of a digital video disc DVD with a half layer thickness d1 and the corresponding signal characteristics. In this case, four peaks also appear in the mirror signal M. The first peak occurs when the focal point F2 of the CD passes over the surface of the recording medium. It is small due to low reflectivity and large aberrations. The same applies to the second peak occurring when focal point F1 passes through the substrate surface. When the focal point F2 falls on the recording layer, a third peak is generated. The intensity of this peak is greater than the intensity of the first two peaks, but is still smaller due to the large aberrations of that part of the bifocal lens OL that is corrected to layer thickness d2 and produces focus F2. A fourth peak occurs when the focal point F1 falls on the recording layer. Since the portion of the bifocal lens OL that produces this focal point is corrected to the layer thickness d1 and twice the intensity occurs at focal point F1 as compared to focal point F2, the fourth peak is about twice the third peak.

Fig. 4 shows the signal characteristics and a cross-sectional view of a digital video disc having two recording layers AZS located one above the other. The first two peaks in the mirror signal M correspond to those described with respect to fig. 2 and 3. A third peak occurs when the focal point F2 of the CD falls on one or two recording layers. This peak in the mirror signal is here larger than the original peak, but is still smaller due to the large aberrations. If these aberrations are sufficiently small, that is to say if the entire optical system, in particular the bifocal lens OL, is correspondingly well corrected, it is possible to distinguish between the two peaks. In general, however, these peaks will be superimposed on each other in such a way that only a broadened peak is possible, as shown in fig. 4. When the focus F1 of the DVD falls on the first recording layer AZS1, a fourth peak is generated in the mirror signal M. For the focal point F1 in combination with the substrate thickness d1, the intensity of the light reflected here, and thus also the height of this peak, is about the same as the third peak, since the bifocal lens OL has the smallest aberrations and appears twice as strong at the focal point F1 compared with the focal point F2, but the reflectivity of the first recording layer AZS1 is only around 30%. When the focal point F1 falls on the second recording layer AZS2, an additional, fifth peak in the mirror signal occurs. The intensity of this peak is about the same order of magnitude as the previous intensity. Although the fourth and fifth peaks are superimposed on each other, they can be distinguished separately in the mirror signal. The difference is even more pronounced in the focus error signal FE.

According to the present invention, provision is made for measuring the intensity of each peak in the mirror signal M while the objective lens OL is moved up to the recording medium AT. In this case the intensity at the instant of the positive-negative crossing of the focus error signal FE is taken. The type of the optical recording medium is determined based on the temporal characteristics and/or height distribution of the peaks. The decision process takes into account various properties of the optical recording medium, such as the reflectivity of the respective reflective surfaces, reduced intensity modulation due to spherical aberration, temporal characteristics, etc.

In an idealized method of studying the exemplary embodiment, the velocity of objective lens OL can be determined from the time difference between the first two peaks and the known distance between focal points F1 and F2. From the velocity information and the time elapsed between the occurrence of the second and third peaks, the layer thickness d1 or d2 can be derived, since this time is directly proportional to the thickness d1 or d2 divided by the difference between the two foci (F2-F1). In this way, the layer thickness d1 or d2 and thus the type of optical recording medium CD or DVD, respectively, can be determined.

If the intensity distribution of the third and fourth or third to fifth peaks is used, the conventional CD is involved if the intensity difference between the third and fourth peaks is small. If the fourth peak is much larger than the third peak, a DVD with one recording layer AZS is involved. If the fourth peak is split into the fourth and fifth peak, a DVD with two recording layers AZS1 and AZS2 is involved. In this case, the third peak may also have been split. The multiple splitting of the third or fourth peak indicates a digital video disc having a number of recording layers AZS1 to AZSn, where n corresponds to the number of recording layers and the number of splitting.

Another possible way of determining the type of optical recording medium is to store in the memory SP signal characteristics, for example the temporal characteristics of the mirror signal M or the focus error signal FE, for each possible recording medium type. The stored signal characteristics are then compared with the currently measured signal characteristics in the comparing means VE and on the basis of this comparison the type of optical recording medium actually inserted is determined. In this case, it is possible to use various mathematical methods to correlate the time scales of the measured and stored curves and to determine the maximum possible correspondence between the curves. For example, the maximum value may be determined using fourier transform and/or convolution integration methods.

The respective devices advantageously operate in the manner described below. In order to adapt the settings of the apparatus for writing and/or reading an optical recording medium AT to the type of optical recording medium AT, the following procedure is implemented: moving the focal points F1, F2 along the optical axis OA in accordance with settings applicable to the first type of apparatus for the recording medium, detecting the light reflected from the optical recording medium AT during this operation and generating a signal corresponding to the intensity of the reflected light, checking to see if this signal lies within a reasonable range of values, and if appropriate repeating the preceding steps with another type of setting applicable to the recording medium; then the settings of the type for which the signal lies in or closest to a reasonable range of values are selected for the optical recording medium AT and the settings of the device are adapted accordingly.

Another method of adapting the settings of an apparatus for writing and/or reading an optical recording medium AT to the type of optical recording medium AT comprises the steps of: the focal points F1, F2 are moved along the optical axis OA and the light reflected from the optical recording medium AT during this operation is detected, the type of the optical recording medium AT is determined using the characteristic features characteristic in the temporal characteristics of the reflected light, and the parameters of the apparatus are set to values suitable for the determined type of the optical recording medium AT. In this case, the difference between the extreme values of the time characteristic of the reflected light is determined in order to determine the type of the optical recording medium AT. Furthermore, in order to determine the type of the recording medium AT, it is provided to compare the relative and/or absolute values of the extreme values of the time characteristic of the reflected light with each other or to compare the time characteristic of the reflected light with a stored reference time characteristic.

Provision is further made for the time characteristic of the reflected light to be determined by means of a mirror signal (M) or a focus error signal (FE) and/or a focusing means FM with different focal points F1, F2.

Claims (3)

1. Apparatus for writing or reading different optical recording media (AT), comprising:

a focusing device (FM) that moves the focal point (F1, F2) along the optical axis;

a detection device (PD) for detecting the intensity of the light reflected from the optical recording medium (AT);

a measuring device (AE) for determining the type of the optical recording medium by measuring the signal from the detecting device; and

-a controller (SE) for controlling the Focusing Means (FM), -a measuring means (AE) for performing a plausibility check, i.e. checking the signals emitted by the detecting means (PD) in order to determine whether they are within a range of reasonable values, i.e. whether they are reasonable, characterized in that:

the controller (SE) specifies parameters corresponding to a first type of device settings applicable to the recording medium;

if the signal emitted by the detection device (PD) is not rational, the evaluation device (AE) emits an output signal to the controller (SE) in order to change the parameter.

2. The apparatus of claim 1, wherein: the measuring device (AE) measures a signal emitted by the detection device (PD) while moving the focal points (F1, F2) along the optical axis.

3. The apparatus of one of the preceding claims, wherein: the focusing device (FM) has a multifocal lens (OL).