WO2004025627A2 - Apparatus and method for scanning an information track and record carrier - Google Patents

Apparatus and method for scanning an information track and record carrier Download PDF

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Publication number
WO2004025627A2
WO2004025627A2 PCT/IB2003/003761 IB0303761W WO2004025627A2 WO 2004025627 A2 WO2004025627 A2 WO 2004025627A2 IB 0303761 W IB0303761 W IB 0303761W WO 2004025627 A2 WO2004025627 A2 WO 2004025627A2
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WO
WIPO (PCT)
Prior art keywords
information
scanning
push
location
frack
Prior art date
Application number
PCT/IB2003/003761
Other languages
French (fr)
Other versions
WO2004025627A3 (en
Inventor
Hubert C. F. Martens
Benno Tieke
Johannes H. M. Spruit
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Priority to AU2003255980A priority Critical patent/AU2003255980A1/en
Publication of WO2004025627A2 publication Critical patent/WO2004025627A2/en
Publication of WO2004025627A3 publication Critical patent/WO2004025627A3/en

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/126—Circuits, methods or arrangements for laser control or stabilisation
    • G11B7/1263—Power control during transducing, e.g. by monitoring
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
    • G11B19/02—Control of operating function, e.g. switching from recording to reproducing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
    • G11B19/02—Control of operating function, e.g. switching from recording to reproducing
    • G11B19/12—Control of operating function, e.g. switching from recording to reproducing by sensing distinguishing features of or on records, e.g. diameter end mark
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
    • G11B19/02—Control of operating function, e.g. switching from recording to reproducing
    • G11B19/12—Control of operating function, e.g. switching from recording to reproducing by sensing distinguishing features of or on records, e.g. diameter end mark
    • G11B19/127—Control of operating function, e.g. switching from recording to reproducing by sensing distinguishing features of or on records, e.g. diameter end mark involving detection of the number of sides, e.g. single or double, or layers, e.g. for multiple recording or reproducing layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0045—Recording
    • G11B7/00456—Recording strategies, e.g. pulse sequences
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/007—Arrangement of the information on the record carrier, e.g. form of tracks, actual track shape, e.g. wobbled, or cross-section, e.g. v-shaped; Sequential information structures, e.g. sectoring or header formats within a track
    • G11B7/00736—Auxiliary data, e.g. lead-in, lead-out, Power Calibration Area [PCA], Burst Cutting Area [BCA], control information
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/2403—Layers; Shape, structure or physical properties thereof
    • G11B7/24035—Recording layers
    • G11B7/24038—Multiple laminated recording layers

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Recording Or Reproduction (AREA)

Abstract

In order to follow an information track (1) on an information carrier (2), a push-pull signal (PP) is generated. The polarity of the push-pull signal (PP) is different for different types of information carriers (2). Tracking means (8) should react differently to a push-pull signal (PP) with a positive polarity than to a push-pull signal (PP) with a negative polarity. The invention described is a method for scanning an information track (1) by determining the polarity of the push-pull signal (PP) first and putting the tracking means (8) in a first or second mode dependent on the polarity of the push-pull signal (PP). In the first mode the tracking means (8) react differently to the push-pull signal than in the second mode. The determination of the polarity of the push-pull signal (PP) can be done in several ways. The polarity can be stored on the information carrier (2), and the polarity determining means (9) read the polarity from the information carrier (2). Alternatively, the polarity determining means (9) can determine the polarity by directing the tracking means (8) to operate in the first and second mode subsequently, and check in which mode the scanning-location (6) was on-track.

Description

Apparatus and method for scanning an information track and record carrier
The invention relates to an apparatus for scanning an information track on an information carrier, comprising: scanning means for scanning a scanning-location on the information carrier; moving means for moving the scanning-location along the information track; - push-pull generating means for generating a push-pull signal which is indicative of a position of the scanning-location with respect to the information track, in a direction transverse to the information track; tracking means for positioning the scanning-location on the track in response to the push-pull signal, where the tracking means are able to move the scanning-location in a first direction transverse to the information track and in a second direction transverse to the information track in reaction to the push-pull signal, where the first direction is opposite to the second direction.
The invention also relates to a method for scanning an information track on an information carrier, comprising the steps of: (a) scanning a scanning-location on the information carrier, thereby generating a read signal;
(b) moving the scanning-location along the information track;
(c) generating a push-pull signal which is indicative of a position of the scanning- location with respect to the information track, in a direction transverse to the information track, and
(d) positioning the scanning-location on-track in response to the push-pull signal, the scanning-location being moved in a first direction transverse to the information track or in a second direction transverse to the information track in reaction to the push-pull signal, where the first direction is opposite to the second direction. The invention further relates to an information carrier which comprises an information track. Examples of an apparatus for scanning an information track on an information carrier are optical players and recorders such as CD and DND players. But also an apparatus that scans an information carrier in the form of a card with information tracks on it is an example of an apparatus for scanning an information track. In the case of CD and DND players the moving of the scanning-location along the information track is performed by rotating the information carrier. Such an apparatus is known from US 5,289,446. The apparatus from this US patent is able to position the scanning-location on the information track by using a so called 3-beam method. In the latter positioning the scanning-location on the information track will also be referred to as tracking, and the term "on-track" will be used for a position of the scanning-location substantially on the middle of the information track. In the 3-beam method the information track is scanned by projecting 3 laser spots on the information carrier. There is a central spot which is used to generate a read signal and two additional spots, also called satellites, which are used for tracking. The satellites are positioned before and after the central spot as seen in the tangential direction parallel to the information track. The satellites are also displaced in radial direction transversal to the information track. If the central spot is on-track then the satellite spots are off-track, one satellite spot on one side of the track and the other satellite spot on the other side of the track. When the spots are moved in radial direction then a sinusoidal signal is generated. Generally the sinusoidal signals from the satellite spots are 180 degrees out of phase with respect to each other. The push-pull signal used for keeping the scanning-location on-track can be generated by subtracting the two sinusoidal signals from the satellite spots. Generally the resulting push-pull signal, also called tracking error signal, is a sinusoidal signal with amplitude zero if the central spot is on-track, and becomes negative if the central spot is moved towards the center of the information carrier and becomes positive if the central spot is moved away from the center of the information carrier. Thus, if the tracking error is positive then the scanning-location should be moved towards the center of the information carrier to correct the tracking error, and if the tracking error is negative then the scanning- location should be moved away from the center of the information carrier to correct the tracking error. However, due to recent developments in the optical recording area information carriers are developed which will cause the effect that the tracking error signal will have a different polarity compared to the general tracking error signal as described before. Thus, this tracking error signal is a sinusoidal signal with amplitude zero if the central spot is on-track, and becomes positive if the central spot is moved towards the center of the information carrier and becomes negative if the central spot is moved away from the center of the information carrier. Thus, if the tracking error is negative then the scanning-location should be moved towards the center of the information carrier to correct the tracking error, and if the tracking error is positive then the scanning-location should be moved away from the center of the information carrier to correct the tracking error. The polarity of the latter push-pull signal will be referred to as negative polarity, subsequently the polarity of the generally used push- pull signal will be referred to as positive polarity. If the known apparatus would try to position the scanning-location on track by assuming the polarity of the push-pull signal positive then the scanning-location would be off-track if the apparatus would try to scan an information track of an information carrier with a negative polarity of the push-pull signal. Also, the other way around, if the known apparatus would try to position the scanning- location on track by assuming the polarity of the push-pull signal negative then the scanning- location would be off-track if the apparatus would try to scan an information track of an information carrier with a positive polarity of the push-pull signal. Besides the 3-beam method there are more methods to derive a push-pull signal. For instance, a push-pull signal can also be derived only from the central spot. The detector that transforms the reflection of the central spot into an electrical signal is split in two halves, a left halve and a right halve. If the central spot is not precisely on-track, then the part of the reflection of the central spot on the left halve will have a phase-difference with respect to the part of the reflection of the central spot on the right halve. This phase- difference causes an intensity difference between the signal on the right halve and the signal on the left halve. The push-pull signal is created by subtracting the current produced by the left halve form the current of the right halve. Also in this case the polarity of the push-pull signal can be positive or negative, creating the same problem as described before.
It is an object of the invention to provide an apparatus and method for scanning an information track on an information carrier which is able to correctly track an information track on information carriers with a positive polarity of the push-pull signal as well as correctly track an information track on information carriers with a negative polarity of the push-pull signal.
For this purpose, the apparatus as described in the opening paragraph is characterized in that the apparatus further comprises polarity determining means for determining a polarity of the push-pull signal and in that the tracking means are able to operate in a first mode and a second mode dependent on the polarity of the push-pull signal, where in the first mode a first range of values of the push-pull signal indicates that the scanning-location is positioned on a first side of the information track in a direction transverse to the information track and a second range of values of the push-pull signal indicates that the scanning-location is positioned on a second side of the information track in a direction transverse to the information track, and where in the second mode the first range of values indicates that the scanning-location is positioned on the second side of the information track and the second range indicates that the scanning-location is positioned on the first side of the information track (1), where the first and second side are opposite to each other with respect to the information track (1).
For example, the first range of values of the push-pull signal are positive values and the second range are negative values of the push-pull signal. In this example, if the tracking means are in the first mode then the tracking means will react to a positive value of the push-pull signal by moving the scanning-location in the first direction thereby moving the scanning-location closer to the information track.
If an information carrier with an information track having a positive polarity of the push-pull signal should be scanned, then the polarity determining means establishes that the polarity of the push-pull signal is positive and the tracking means switches to the correct mode accordingly. If an information carrier with an information track having a negative polarity of the push-pull signal should be scanned, then the polarity determining means establishes that the polarity of the push-pull signal is negative and the tracking means operate at a different mode as is the case with a push-pull signal with a positive polarity. In this way both types of information carriers can be correctly scanned.
In an embodiment of the invention the different modes of the tracking means are realized by sign reversal means which are able to reverse a sign of the push-pull signal when put in a first state and which do not reverse the sign of the push-pull signal when put in a second state. In this embodiment the first range of values of the push-pull signal has an opposite sign with respect to the second range of values of the push-pull signal. This is a common implementation of the push-pull signal. In a further embodiment of the invention the polarity determining means are able to determine the polarity of the push-pull signal by reading push-pull data stored on the information carrier which indicates the polarity of the push-pull signal. This polarity can be stored in the information carrier in several ways. It can be stored in the information track. It can also be stored in a wobble of the information track. The wobble can be a varying width of the information track or an undulation of the information track in radial direction. By modulation of the wobble information can be stored in the wobble. The wobble can for instance be modulated in frequency or in phase. Also, the push-pull data can be stored in a chip which is implemented in the information carrier, the so called 'chip in disc'. This integrated circuit comprises means for transmitting additional information and means for receiving a signal for power supply of the integrated circuit. The receiving means comprise a photodiode. The receiving means can also be arranged to receive additional information. The additional information can be the push-pull data.
In a further embodiment of the invention the information carrier comprises at least two layers, each layer comprising at least one information track, and in that the push- pull data of at least one information track is stored on the information carrier. For instance, the push-pull signal of the first layer to be scanned can have a positive polarity so that the apparatus can scan the first layer normally. The second layer can have a negative or positive polarity. Then it is advantageous to have the information about the polarity of the second layer stored in the first layer. Also push-pull data of the first layer can be stored on the previous mentioned chip and push-pull data of the second layer can be stored on the first layer. Also other combination to store the push-pull data of the first and second layer are possible. For instance, the push-pull data of both layers can be stored in the wobble of the first layer. In an other embodiment of the invention the polarity determining means are able to determine the polarity of the push-pull signal by reading push-pull data which is stored in pre-pits which contain information and are located on the information carrier. The pre-pits can be preformed marks on an otherwise empty, to be written information carrier in which additional information can be stored, such as address information. In a further embodiment of the invention the polarity determining means are able to put the tracking means in a mode at which the tracking means position the scanning- location on-track by performing the steps of: directing the tracking means to the first mode; directing the tracking means to react to the push-pull signal, where the scanning-location is positioned on-track or off-track dependent on the polarity of the push- pull signal; directing the tracking means to the second mode; directing the tracking means to react to the push-pull signal, where the scanning-location is positioned on-track or off-track dependent on the polarity of the push- pull signal; determining at which mode of the tracking means the scanning-location is on- track, and directing the tracking means in the mode at which the scanning-location is on- track.
This embodiment does not require that information about the polarity of the push-pull signal is stored on the information carrier. When a disc is inserted the polarity determining means perform the previously mentioned steps. The mode of the tracking means at which the scanning-location is on-track is used as the mode in which the scanning is performed when reading or writing information from or to the information carrier.
Determining at which mode of the tracking means the scanning-location is on- track can be done in several ways. In one embodiment the scanning means are able to scan the scanning location by projecting a radiation beam on the scanning location, thereby detecting a reflected radiation beam, and the polarity determining means are able to determine at which mode of the tracking means the scanning-location is on-track based on a difference between an intensity level of the reflected radiation beam when the scanning- location is on-track and an intensity level of the reflected radiation beam when the scanning- location is off-track. In general the intensity level of the reflected radiation beam when the scanning-location is on-track is different from the intensity level of the reflected radiation beam when the scanning-location is off-track. This difference is used to determine when the scanning-location is on-track.
In an other embodiment the determination at which mode of the tracking means the scanning-location is on-track is done by an apparatus of which the scanning means are able to provide a read signal which comprises a wobble signal, where the wobble signal is caused by a wobble of the information track, and of which the polarity determining means are able to determine at which mode of the tracking means the scanning-location is on-track based on a difference in amplitude of the wobble signal. The wobble can be a varying width of the information track, or a undulation of the information track. The effect of the wobble in the read signal is the greatest when the scanning location is on-track. The difference in amplitude of the wobble signal in the read signal can be used to establish if the scanning- location is on-track.
In an other embodiment the determination at which mode of the tracking means the scanning-location is on-track is done by an apparatus of which the scanning means are able to provide a read signal which comprises a wobble signal, where the wobble signal is caused by a wobble of the information track and where the wobble comprises information, and in which the polarity determining means are able to determine at which mode of the tracking means the scanning-location is on-track by checking at which mode the information contained in the wobble can be accurately read. The information can be stored in the wobble by modulation. For instance the frequency or the phase of the wobble can be varied in accordance with the information that needs to be stored in the wobble. The information can be address information of the information track. If the address information can be read accurately without errors than the conclusion is that the scanning-location is on-track. Of course due to circumstances there can be read errors, but then the conclusion is that the scanning-location is on-track when the read errors are the lowest.
If the information track already contains information, thus an already written information carrier, then in yet another embodiment of the invention the polarity determining means are able to determine at which mode of the tracking means the scanning-location is on-track by checking at which mode the information contained in the information track can be accurately read. Of course when the scanning-location is off-track then the information in the information track can not be accurately read. Accurately in this context means that the amount of read errors is such that the information in the information track can be restored.
These and other aspects of the invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which Fig. la shows an information carrier (top view), Fig. lb shows an information carrier (cross section), Fig. 2 shows an embodiment of an apparatus for scanning an information track,
Fig. 3 illustrates a detector,
Fig. 4a shows a push-pull signal with positive polarity in relation to the scanning-location position, Fig. 4b shows a push-pull signal with negative polarity in relation to the scanning-location position,
Fig. 5 shows an information track with a wobble, Fig. 6 shows a modulated wobble, Fig. 7 illustrates a flow chart of an embodiment of a method for scanning an information track,
Fig. 8 illustrates a flow chart of an example for determining the polarity of the push-pull signal, Fig. 9a shows a wobble spectrum measured off-track, and
Fig. 9b shows a wobble spectrum measured on-track.
Figure la shows an example of an information carrier 2 having an information track 1. The depicted information carrier 2 is disc shaped. However, other information carriers 2 can be used. For example information carriers 2 in the form of a card. Here the scanning-location 6 is moved along the information track 1 by linear translation. In the case of a disc shaped information carrier 2 the scanning-location 6 is moved along the information track 1 by rotating the information carrier 2. Figure lb shows a cross section of the disc shaped information carrier 2. The information frack 1 , being the position of the series of (to be) recorded marks representing information, is arranged in accordance with a spiral pattern of turns constituting substantially parallel tracks on an information layer. The information carrier 2 may be optically readable, called an optical disc. The information is represented on the information layer by recording optically detectable marks along the information frack 1, e.g. crystalline or amorphous marks in phase change material. The information frack 1 on the recordable type of information carrier 2 is indicated by a pre-embossed frack structure provided during manufacture of the blank information carrier 2. The frack structure is constituted, for example, by a pregroove which enables the information frack 1 to be followed. In Figure 2 an embodiment of the invention comprises rotating means 3a for rotating the information carrier 2. Scanning means 5 scan a scanning-location 6 on the information carrier 2. The scanning means 5 produce a read signal where from the information of the information track 1 can be derived. This is done by decoding electronics in the apparatus. The decoding electronics are known to the man skilled in the art and will therefore not be discussed further in this application. In a DVD recorder the scanning means 5 is an optical head which projects a laser beam on the information carrier 2. The scanning means output a signal which is fed to the push-pull generating means 7. The push-pull signal PP is fed to the tracking means 8. The mode of the tracking means 10 is controlled by the polarity determining means 9. The fracking means 8 comprise sign reversal means 8 a. If the sign reversal means 8a are put in the second state then the sign of the push-pull signal PP is reversed. If the sign reversal means 8 a are in the first state then the fracking means 8 are in the first mode, and if the sign reversal means 8a are in the second state then the fracking means 8 are in the second mode. The fracking means 8 reacts to the push-pull signal PP differently in the first mode compared to the second mode.
In Figure 3 an example of a detector 11 is shown. The detector 11 picks up a reflected radiation beam which is reflected by the information carrier 2. The detector 11 is split into two halves 12 and 13. If the scanning-location is on-frack then the intensity of the reflected radiation beam that falls on the left halve 12 of the detector 11 is substantially equal to the intensity of the reflected radiation beam that falls on the right halve 13 of the detector 11. The detector 11 generates two cunents i\ and ir as a result of the spot 14. If the scanning location is not on-frack then the intensity of the spot 14 is not equally distributed over the left halve 12 and the right halve 13. Therefore, the two currents are not equal to each other. The push-pull signal can be generated, for example, by subtracting ij from ir. Figure 4a shows an example of a push-pull signal PP in relation to the position of the scanning-location 6 with respect to the information frack 1, the push-pull signal PP having a positive polarity. If the scanning-location is exactly on-track then the push-pull signal PP has a value around zero. If the scanning-location is positioned on a first side of the information frack then the push-pull signal PP is positive, and if the scanning-location is positioned at a second side of the information frack, opposite to the first side, then the push- pull signal PP is negative. In Figure 4b the polarity of the push-pull signal PP is negative. Now, if the scanning-location is positioned on the first side of the information track then the push-pull signal PP is positive, and if the scanning-location is positioned at the second side of the information frack then the push-pull signal PP is negative. In order to keep the scanning- location 6 on-track for both types of push-pull signals, the tracking means 8 should react differently to the push-pull signal PP shown in Figure 4a and to the push-pull signal PP shown in Figure 4b. In the embodiment of the invention shown in Figure 2 this is done by first determining the polarity of the push-pull signal PP by the polarity determining means 9 and then switching the sign reversal means 8a to a state such that the fracking means 8 reacts correctly to the push-pull signal PP.
In Figure 7 a flow chart is shown of an embodiment of a method for scanning an information track 1 on an information carrier 2 according to the invention. The flow chart starts in step S and ends in step E. In step a the information carrier 2 is rotated around the point of rotation 4. In the next step b a scanning-location 6 on the information carrier 2 is scanned. In step c the push-pull signal PP is generated. The polarity of the push-pull signal PP is determined in step e. If the polarity of the push-pull signal PP is positive then the positioning of the scanning-location 6 in response to the push-pull signal PP is performed in the first mode, indicated in Figure 7 by step dl . If the polarity of the push-pull signal PP is negative then the positioning of the scanning-location 6 in response to the push-pull signal PP is performed in the second mode, indicated in Figure 7 by step d2.
The polarity of the push-pull signal PP can be determined in several ways. One way is to have the polarity of the push-pull signal PP stored on the information carrier 2. The polarity determining means 9 then merely has to read the polarity stored on the information carrier 2 and put the fracking means 8 in the correct mode accordingly. In
Figure 5 an example is show of a wobbled information frack 1. The wobble in this example is formed by an undulation of the information frack 1 in a direction transverse to the information track 1. The read signal produced by the scanning means 5 will contain a wobble signal in it which is caused by the wobble. By modulating the wobble in frequency or in phase, one can store information in the wobble. In Figure 6 an example is shown of a wobble which is frequency modulated in order to store information. In this example a low frequency represents a logical 1 and a high frequency represents a logical 0. Each time one period of the wobble signal stands for one bit information, i the example a bit stream of 5 bits are shown representing 11001. In this way also the polarity of the push-pull signal PP can be stored in the wobble.
An other way to determine the polarity of the push-pull signal PP is to put the fracking means 8 in the first and the second mode subsequently, and determine at which mode the scanning-location 6 was on-track. In Figure 8 an implementation of step e of the flow chart shown in Figure 7 is shown. In step f the positioning of the scanning-location 6 is performed by operating in the first mode. The scanning-location 6 can be on-track or off- track dependent on the polarity of the push-pull signal PP. In step g the positioning of the scanning-location 6 is performed by operating in the second mode. If the scanning-location 6 was on-frack in step f then the scanning-location 6 is off-track in step g and the other way around. In step h it is determined in which step, thus in which mode, the scanning-location was on track. Dependent on this determination the next step is dl or d2 as shown in Figure 7. Determining if the scanning-location 6 was on-track can be done in several ways. If scanning is done by measuring a reflected radiation beam, then the difference in intensity of the reflected radiation beam between reflection on-track and off-track can be used to determine in which mode the scanning-location 6 was on-track. If the information frack 1 comprises a wobble as shown in Figure 5 then the difference in amplitude of the wobble signal present in the read signal can be used to determine in which mode the scanning-location 6 was on-frack. In Figure 9a and 9b a wobble spectrum is shown measured when the scanning-location 6 is off-track and on-frack respectively. The information carrier 2 is a DND recordable disc. On the horizontal axis the frequency of the wobble signal in kHz is shown and on the horizontal axis the amplitude of the wobble signal in dB's is shown. The amplitude of the wobble signal shown in Figure 9b where the scanning-location 6 is on-frack is 3 dB's higher than the amplitude of the wobble signal shown in Figure 9a. The determination of the mode at which the scanning-location 6 is on-frack consequently is easy. The wobble shown in Figure 5 is an example of a wobble which is an undulation of the information frack 1 in the radial direction. For this embodiment also other forms of wobbles will function, for example a wobble of the information frack 1 by varying the width of the information frack 1. If the information frack 1 comprises a wobble as shown in Figure 5, i.e. an undulating information frack 1, then determining if the scanning- location 6 was on-frack can be done on the basis of a difference between a variation of an intensity level of the reflected radiation beam when the scanning-location 6 is on-frack and a variation of an intensity level of the reflected radiation beam when the scanning-location 6 is off-track. The variation of the intensity level of the reflected radiation beam when the scanning-location 6 is off-track is larger than the variation of the intensity level when the scanning-location 6 is on-frack. As can be seen in Figure 5, due to the undulation of the information frack 1, the distance between the information tracks 1 is varied. If the scanning- location 6 is off-track than the intensity level of the reflected radiation beam varies due to the varying distance between the information tracks 1. If the scanning-location 6 is on-frack then the variation is of the intensity level is less. Alternatively, the conclusion at which mode the scanning-location 6 is on- track can be done by ascertaining at which mode the information contained in the wobble can be accurately read. If the scanning-location is off-track then the wobble amplitude is less and also the wobbles of two tracks adjacent to the scanning-location 6 influence the wobble signal retrieved from the read signal. This makes the information contained in the wobble impossible to read, or at least more errors are made when trying to read this information when the scanning-location 6 is off-track.
Although the invention has been explained mainly by examples of the DND system, similar embodiments are suitable for other optical playing and recording systems. Also for the information carrier 2 an optical disc has been described, but other media, such as a magnetic disc, may be used. It is noted, that in this document the word 'comprising' does not exclude the presence of other elements or steps than those listed and the words 'a' or 'an' preceding an element does not exclude the presence of a plurality of such elements, that any reference signs do not limit the scope of the claims, that the invention may be implemented by means of both hardware and software, and that several 'means' may be represented by the same item of hardware. Further, the scope of the invention is not limited to the embodiments, and the invention lies in each and every novel feature or combination of features described above.

Claims

CLAIMS:
1. Apparatus for scanning an information frack on an information carrier, comprising: scanning means for scanning a scanning-location on the information carrier; moving means for moving the scanning-location along the information track; - push-pull generating means for generating a push-pull signal which is indicative of a position of the scanning-location with respect to the information frack, in a direction fransverse to the information track; tracking means for positioning the scanning-location on the frack in response to the push-pull signal, where the fracking means are able to move the scanning-location in a first direction fransverse to the information frack and in a second direction fransverse to the information track in reaction to the push-pull signal, where the first direction is opposite to the second direction, characterized in that the apparatus further comprises polarity determining means for determining a polarity of the push-pull signal and in that the fracking means are able to operate in a first mode and a second mode dependent on the polarity of the push-pull signal, where in the first mode a first range of values of the push-pull signal indicates that the scanning-location is positioned on a first side of the information frack in a direction fransverse to the information track and a second range of values of the push-pull signal indicates that the scanning-location is positioned on a second side of the information track in a direction transverse to the information track, and where in the second mode the first range of values indicates that the scanning-location is positioned on the second side of the information frack and the second range indicates that the scanning-location is positioned on the first side of the information frack, where the first and second side are opposite to each other with respect to the information frack.
2. Apparatus as claimed in claim 1, characterized in that the moving means comprise rotating means for rotating the information carrier about a point of rotation.
3. Apparatus as claimed in one of the claims 1 and 2, characterized in that the first range of values of the push-pull signal has an opposite sign with respect to the second range of values of the push-pull signal and in that the tracking means comprise sign reversal means having a first state where the sign of the push-pull signal is reversed and a second state where the sign of the push-pull signal is not reversed, and where the sign reversal means switch between the first and the second state dependent on the polarity of the push-pull signal.
4. Apparatus as claimed in one of the claims 1 to 3, characterized in that the polarity determining means are able to determine the polarity of the push-pull signal by reading push-pull data stored on the information carrier which indicates the polarity of the push-pull signal.
5. Apparatus as claimed in claim 4, characterized in that information carrier comprises a chip, and in that the push-pull data is stored on the chip.
6. Apparatus as claimed in one of the claims 4 and 5, characterized in that the information carrier comprises at least two layers, each layer comprising at least one information track, and in that the push-pull data of at least one information frack is stored on the information carrier.
7. Apparatus as claimed in claim 6, characterized in that the push-pull data of the information tracks of both layers are stored on the information carrier.
8. Apparatus as claimed in claim 4, characterized in that the polarity determining means are able to determine the polarity of the push-pull signal by reading push-pull data which is stored in a wobble of the information frack by modulation of the wobble.
9. Apparatus as claimed in claim 4, characterized in thaf the polarity determining means are able to determine the polarity of the push-pull signal by reading push-pull data which is stored in pre-pits which contain information and are located on the information carrier.
10. Apparatus as claimed in one of the claims 1 to 3, characterized in that the polarity determining means are able to put the tracking means in a mode at which the fracking means position the scanning-location on-frack by performing the steps of: directing the fracking means to the first mode; directing the fracking means to react to the push-pull signal, where the scanning-location is positioned on-frack or off-track dependent on the polarity of the push- pull signal; directing the fracking means to the second mode; directing the tracking means to react to the push-pull signal, where the scanning-location is positioned on-frack or off-track dependent on the polarity of the push- pull signal; - determining at which mode of the fracking means the scanning-location is on- frack, and directing the fracking means in the mode at which the scanning-location is on- frack.
11. Apparatus as claimed in claim 10, characterized in that the scanning means are able to scan the scanning location by projecting a radiation beam on the scanning location, thereby detecting a reflected radiation beam, and in that the polarity determining means are able to determine at which mode of the fracking means the scanning-location is on-frack based on a difference between an intensity level of the reflected radiation beam when the scanning-location is on-frack and an intensity level of the reflected radiation beam when the scanning-location is off-track.
12. Apparatus as claimed in claim 10, characterized in that the scanning means are able to scan the scanning location by projecting a radiation beam on the scanning location, thereby detecting a reflected radiation beam, where the reflected radiation beam comprises a wobble signal, where the wobble signal is caused by an undulation of the information frack, and in that the polarity determining means are able to determine at which mode of the fracking means the scanning-location is on-frack based on a difference between a variation of an intensity level of the reflected radiation beam when the scanning-location is on-frack and a variation of an intensity level of the reflected radiation beam when the scanning-location is off-track.
13. Apparatus as claimed in claim 10, characterized in that the scanning means are able to provide a read signal which comprises a wobble signal, where the wobble signal is caused by a wobble of the information frack, and in that the polarity determining means are able to determine at which mode of the fracking means the scanning-location is on-frack based on a difference in amplitude of the wobble signal.
14. Apparatus as claimed in claim 10, characterized in that the scanning means are able to provide a read signal which comprises a wobble signal, where the wobble signal is caused by a wobble of the information frack and where the wobble comprises information, and in that the polarity determining means are able to determine at which mode of the fracking means the scanning-location is on-track by checking at which mode the information contained in the wobble can be accurately read.
15. Apparatus as claimed in claim 10, characterized in that the polarity determining means are able to determine at which mode of the fracking means the scanning- location is on-frack by checking at which mode the information contained in the information frack can be accurately read.
16. Method for scanning an information frack on an information carrier, comprising the steps of:
(a) scanning a scanning-location on the information carrier, thereby generating a read signal;
(b) moving the scanning-location along the information frack;
(c) generating a push-pull signal which is indicative of a position of the scanning- location with respect to the information frack, in a direction fransverse to the information frack, and (d) positioning the scanning-location on-frack in response to the push-pull signal, the scanning-location being moved in a first direction fransverse to the information frack or in a second direction fransverse to the information frack in reaction to the push-pull signal, where the first direction is opposite to the second direction, characterized in that the method further comprises the step of (e) determining a polarity of the push-pull signal, and where step (d) operates in a first or a second mode dependent on the polarity of the push-pull signal, where in the first mode a first range of values of the push- pull signal indicates that the scanning-location is positioned on a first side of the information frack in a direction transverse to the information frack and a second range of values of the push-pull signal indicates that the scanning-location is positioned on a second side of the information frack in a direction fransverse to the information track, and where in the second mode the first range of values indicates that the scanning-location is positioned on the second side of the information track and the second range indicates that the scanning-location is positioned on the first side of the information frack, where the first and second side are opposite to each other with respect to the information frack.
17. Method as claimed in claim 16, characterized in that the step (b) of moving the scanning-location is performed by rotating the information carrier.
18. Method as claimed in one of the claims 16 and 17, characterized in that the first range of values of the push-pull signal has an opposite sign with respect to the second range of values of the push-pull signal and in that in the second mode of step d the sign of the push-pull signal is reversed.
19. Method as claimed in one of the claims 16 to 18, characterized in that the polarity of the push-pull signal is determined by reading push-pull data stored on the information carrier which indicates the polarity of the push-pull signal.
20. Method as claimed in claim 19, characterized in that the information carrier comprises a chip, and in that the push-pull data is stored on the chip.
21. Method as claimed in one of the claims 19 and 20, characterized in that the information carrier comprises at least two layers, each layer comprising at least one information frack, and in that the polarity of the push-pull signal of at least one information track is determined by reading push-pull data stored on the information carrier.
22. Apparatus as claimed in claim 21, characterized in that the polarity of the push-pull signals of the information fracks of both layers are determined by reading push-pull data stored on the information carrier.
23. Method as claimed in claim 19, characterized in that the polarity of the push- pull signal is determined by reading push-pull data which is stored in a wobble of the information track by modulation of the wobble.
24. Method as claimed in claim 19, characterized in that the polarity of the push- pull signal is determined by reading push-pull data which is stored in pre-pits which contain information and are located on the information carrier.
25. Method as claimed in one of the claims 16 to 18, characterized in that the polarity of the push pull signal is determined by performing the steps of:
(f) positioning the scanning-location on-frack or off-track dependent on the polarity of the push-pull signal by operating in the first mode;
(g) positioning the scanning-location on-frack or off-track dependent on the polarity of the push-pull signal by operating in the second mode, and
(h) determining at which of the steps f and step g the scanning-location is on- track.
26. Method as claimed in claim 25, characterized in that the scanning of the scanning-location is performed by projecting a radiation beam on the scanning-location and detecting a reflected radiation beam, and in that step h is performed on the basis of intensity levels of the reflected radiation beam at step f and step g.
27. Method as claimed in claim 25, characterized in that the scanning of the scanning-location is performed by projecting a radiation beam on the scanning-location and detecting a reflected radiation beam, where the reflected radiation beam comprises a wobble signal, where the wobble signal is caused by an undulation of the information frack, and in that step h is performed on the basis of a difference between a variation of an intensity level of the reflected radiation beam when the scanning-location is on-frack and a variation of an intensity level of the reflected radiation beam when the scanning-location is off-track.
28. Method as claimed in claim 25, characterized in that the read signal comprises a wobble signal, where the wobble signal is caused by a wobble of the information frack, and in that step h is performed on the basis of amplitude levels of the wobble signal at step f and step g.
29. Method as claimed in claim 25, characterized in that the read signal comprises a wobble signal, where the wobble signal is caused by a wobble of the information frack and where the wobble comprises information, and in that step h is performed by determining at which of the steps f and g the information contained in the wobble can be accurately read.
30. Method as claimed in claim 25, characterized in that step h is performed by determimng at which of the steps f and g the information contained in the information frack can be accurately read.
31. Information carrier which comprises an information frack, characterized in comprising push-pull data which indicates a polarity of a push-pull signal to be used for scanning the information track.
32. Information carrier as claimed in claim 31 , characterized in that the information carrier comprises a chip, and in that the push-pull data is stored on the chip.
33. Information carrier as claimed in one of the claims 31 and 32, characterized in that the information carrier comprises at least two layers, each layer comprising at least one information track, and in that the push-pull data of at least one information track is stored on the information carrier.
34. Information carrier as claimed in claim 33, characterized in that the push-pull data of the information tracks of both layers are stored on the information carrier.
35. Information carrier as claimed in claim 31, characterized in that the information frack comprises a wobble and in that the push-pull data is stored in the wobble by modulation of the wobble.
36. Information carrier as claimed in claim 31, characterized in that the information carrier comprises pre-pits which contain additional information and the push-pull data is stored in the pre-pits.
PCT/IB2003/003761 2002-09-11 2003-08-21 Apparatus and method for scanning an information track and record carrier WO2004025627A2 (en)

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WO2004025627A3 (en) 2004-06-03
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AU2003255980A8 (en) 2004-04-30
AU2003255980A1 (en) 2004-04-30

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