WO2006038143A1

WO2006038143A1 - Optical disk device having a tilt corrector, method for reading and/or writing an optical disk using an optical disk device having a tilt corrector

Info

Publication number: WO2006038143A1
Application number: PCT/IB2005/053151
Authority: WO
Inventors: Tony P. Van Endert
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2004-10-06
Filing date: 2005-09-23
Publication date: 2006-04-13
Anticipated expiration: 2007-04-06
Also published as: TW200634787A; CN101036187A; JP2008516365A; KR20070064655A; EP1800301A1

Abstract

An optical disk device (1) for reading and/or writing an optical disk (100) having a tilt corrector, characterized in that the optical disk device comprises a measurer for measuring tilt at an inner circumferential part and at an outer circumferential part of an optical disk and a selector for selecting, in dependence of the measured difference (STILT) between inner and outer circumference tilt value (TILTin-TILTout), a tilt correction curve (curve 1, 2, 3, 4, 5, 6) for determining the tilt correction as function of radius of the disk, at least some of the selectable curves being of curvilineair form.

Description

Optical disk device having a tilt corrector, method for reading and/or writing an optical disk using an optical disk device having a tilt corrector

The invention relates to an optical disk device for reading and/or writing an optical disk having a tilt corrector. A tilt corrector is a means for tilting an optical lens holder to correct for tilt errors.

The invention also relates to an optical reading and/or writing method using such an optical disk device.

Optical disk devices read and/or write information from or on optical disks. Such an optical disk may be for instance a DVD, a DVD+R or BD. Optical disk devices read and /or write from or on an optical storage disk using a laser and an optical system to guide the laser to positions on the optical disk. The optical system comprises a lens holder with a lens. During reading and/or writing the laser light should be on track and focused on the disk. Tracking and focusing means are used for this purpose. Such an optical disk device is e.g. disclosed in US 2003/021068. In or to the lens holder a means for tilting the lens holder is also provided. Tilting, i.e. rotating around an axis, allows an improved control over the movements of the lens holder and consequently an improved correspondence between the optical axis of the lens in the lens holder and the optical medium to be read or to be written. Radial tilt is one of the most important parameters with respect to a write or read performance of an optical disc. Therefore there is a need to provide a radial tilt position that is (near) optimal during the write and read process on an optical disc. One of today's used radial tilt calibration methods is based on jitter measurement during the write or read procedure because this gives the highest accuracy. During the write or read procedure tilt correction is performed , by determining the tilt error, calculating a tilt correction signal from the determined tilt error, and sending the tilt correction signal to the tracking means to properly align the lens holder so that the tilt error is corrected. A disadvantage of this method is that the write or read process has to be stopped repeatedly since tilt calibrations have to be done. After this process write or read procedure can be started again. The consequence of this known procedure is that throughput will be decreased. Japanese patent application 10- 222860' Optical disk reproducing method and optical disk device' describe an optical disk device in which the tilt of a disk is determined for inner and an outer circumference by two tilt sensors and for intermediate sectors of the disk intermediate tilt values are calculated and tilt correction is performed on the basis of the measured tilt at inner and outer circumference.

Although the device and method described in JP 10-222860 is described to remove the need for tilt correction during the write and/or read procedure, the inventors have realized that in many circumstance this is not the case.

It is an object of the invention to provide an improved optical disk device and improved an optical reading and/or writing method using an optical disk device.

To this end the optical disk device is characterized in that the optical disk device comprises a measurer for measuring tilt at an inner circumferential part and at an outer circumferential part of an optical disk and a selector for selecting, in dependence of the measured difference between inner and outer circumference tilt, a tilt correction curve for determining the tilt correction as function of radius of the disk, at least some of the selectable curves being of curvilineair form.

In the device and method described in JP 10-222860 the tilt value is determined by a rectilinear interpolation between the inner and outer circumference tilt. The inventors have realized that a disadvantage of this known device and method is that the resulting correction is often far from the actual tilt, and may even be of the wrong sign. In a disk and method in accordance with the invention a selector is used which has as an input the difference between the tilt at an inner and at an outer circumference. Dependent on this difference in tilt value a curve is chosen. At least some of the selectable curves are curvilinear, i.e. a non-linear dependence, as function of radius, of the tilt correction. Investigations have shown that radial tilt of an optical disc has several different shapes. Radial tilt value is also often a curvilinear function of the disc radius. Using a rectilinear function, as in the device and method of JP 10-222860 often corrects tilt errors only partially and may even increase errors, rather than decrease them. In preferred embodiments a single measurer is used for measuring the tilt at the inner and outer circumference. In JP 10-222860 two tilt sensors are used, located at the inner and outer circumference. Using a single measurer increases the accuracy of the tilt correction since any errors in the tilt determination due to difference between the sensors, such as differences in temperature, accuracy and/or bias error is avoided. Using e.g. a tilt calibration based on jitter allows a single measurer to be used.

In preferred embodiments the selector has at least one further input, selected from the tilt value at either the inner or outer circumference, rotation speed, type of operation, type of disk, humidity, temperature, average laser power, time of operation.

Even when the values for tilt on an inner and outer circumference are determined, the best choice for the curve describing the dependence of the tilt as a function of radius may be, at least to some degree, dependent on one or more further parameters. The selector may be in the form of an algorithm embedded in program code. In preferred embodiments the selector has at least one further input for temperature and/or humidity. These parameters have a considerable influence on the tilt curve. This embodiment is best combined with the embodiment in which the device comprises a single measurer for measuring tilt at an inner and an outer circumference.

In a further embodiments the disk device is characterized in that it has means to determine a tilt at a middle circumference of a disk for determining curve parameters.

In these embodiments a tilt is occasionally determined at a middle part of a disk. This determination is used for determining of curve parameters, i.e. the curvature of the curve determining the tilt between inner and outer circumference.

In these embodiments the shape of the curves are occasionally redetermined by measuring a tilt value at a middle circumference. This allows a more precise tilt correction. Basically this equates to a gauging procedure whereby occasionally a tilt value at a middle sector is measured to gauge the values for one or more curves.

Preferably the means to determine a tilt at a middle circumference is the single measurer for the tilt at an inner and outer circumference. Using the same device and technique for measuring all tilts avoids any problems due to difference in measuring techniques or devices.

Within the concept of the invention a 'selector' and similar terms are to be broadly understood and to comprise e.g. any piece of hard- ware (such as a selector), any circuit or sub-circuit designed for performing a selection function as described as well as any piece of soft-ware (computer program or sub program or set of computer programs including algorithms, or program code(s)) designed or programmed to perform a selection operation in accordance with the invention as well as any combination of pieces of hardware and software acting as such, alone or in combination, without being restricted to the below given exemplary embodiments. One program may combine several functions. A method in accordance with the invention is as a method for writing of or reading from an optical disk wherein an optical disk device is used for writing on or reading from an optical disk, wherein a tilt value is measured at an inner circumferential part and at an outer circumferential part of an optical disk and, in dependence of the measured difference between inner and outer circumference tilt value, a tilt correction curve for determining the tilt correction as function of radius of the disk is chosen, at least some of the selectable tilt correction curves curves being of curvilineair form, and said chosen tilt correction curve is used for correction of tilt during writing or reading of the optical disk.

The method in accordance with the invention may, in preferred embodiments by combined with any of method steps (such as the input of other parameters such as temperature etc) as described in respect of the device in accordance with the invention.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings:

Fig. 1 schematically shows in perspective an optical disk device according to the prior art.

Fig.2 illustrates tilt values as a function of radius Fig.3 illustrates in the form of a flow chart a tilt prediction algorithm

The figures are not drawn to scale. Generally, identical components are denoted by the same reference numerals in the figures.

Figure 1 shows schematically a device known from United States Patent

Application 2003/0210628.

A tilt compensation by detecting a jitter during a reproduction of the optical disc 100 is shown in this fig. 1.

When the reading of the optical disc 100 is started by optical disk device 1, a controller 106 monitors a jitter of reproduction data at constant time intervals. As the optical disc 100 is read, the jitter continuously varies. An optical pickup 101 reads record signals from the optical disc 100, and a reproduction signal detector 104 detects only a reproduction signal from the signals read by the optical pickup 101. A jitter detector 105 detects a jittering amount of the reproduction signal detected by a reproduction signal detector 104, and the detected jittering amount is input to the controller 106. The jittering amount detected at the constant time intervals from the optical disc 100 during the reproduction of the optical disc 100 is compared with a reference jittering amount stored in a storage unit. Where the detected jittering amount is larger than the reference jittering amount, a signal which minimizes the jittering amount is transmitted to a tilt driving IC 107, and the tilt driving IC 107 operates a tilt driver 103 tilting a guide 102.

A disadvantage of this known device and method is that the write or read process has to be stopped repeatedly since tilt calibrations have to be done. After this process write or read procedure can be started again. The consequence of this known procedure is that throughput will be decreased.

Japanese patent application 10-222860' Optical disk reproducing method and optical disk device' describe an optical disk device in which the tilt of a disk is determined for inner and an outer circumference by two tilt sensors and for intermediate sectors of the disk intermediate tilt values are calculated and tilt correction is performed on the basis of the measured tilt at inner and outer circumference.

Although the device and method described in JP 10-222860 is described to remove the need for continuous tilt correction during the write and/or read procedure, the inventors have realized that in many circumstance this is not the case.

Fig. 2 illustrates for various DVD+R disk measured tilt as function of radius of the disk. The drawn curved lines illustrate tilt as a function of radius for three DVD+R devices, where the dotted line gives a linear interpolation between an inner circumference tilt value and an outer circumference tilt value.

Fig.2 shows that a linear interpolation in large parts of the disk provides values for the tilt which are considerably off the mark. The non-compensated tilt error, i.e. the difference between the curved lines and the dotted lines, is often larger than the value of the curved line, and even in considerable parts of the disk for the curves DVD+R_2 and DVD+R_1 of the wrong sign, i.e. applying a tilt correction according to a linear interpolation makes the tilt problem worse, instead of reducing the problem. Thus using the known device and method it is often still needed to use a continuous radial tilt correction (as for instance described in US 2003/0210628) with the associated disadvantages.

In a device and method in accordance with the invention the difference between the tilt value an inside circumference and the radial tilt value at an outside circumference of the disk is measured and a choice of the curve shape depending on the result of the measured radial tilt difference ΔTILT=TILTin-TILTout. The device hereto comprises a selector, which schematically in the form of a flow chart of a tilt prediction algorithm is shown in figure 3.

Depending on the measured difference in tilt value a prediction curve 1 to 6 in this exemplary, non-restrictive example, is chosen. At least some of the curves are curvilinear, i.e. not rectilinear. For a rectilinear curve, i.e. a straight lie between beginning and end, there is no need to choose a curve, since the begin and end values TILTin and TILTout per definition determine the curve.

Apart from the difference in tilt ΔTILT, the selector may have more additional inputs having an influence on the selection of curves. These additional inputs may have an influence on the values of x or y, i.e. the cut-off values for deciding on the choice of curve, or on parameters of the curve, such as the curvature or introduction of higher order coefficients in one or more the curves 1 to 6 , or on both of such parameters.

In embodiments a single measurer or measuring procedure is used for measuring the tilt at the inner and outer circumference, TILTin and TILTout. In JP 10- 222860 two tilt sensors are used, located at the inner and outer circumference. Using a single measurer increases the accuracy of the tilt correction since any errors in the tilt determination due to difference between the sensors, such as differences in temperature, accuracy and bias errors is avoided, while the costs are reduced. Using e.g. a tilt calibration based on jitter allows a single measurer to be used. In embodiments an additional input is the tilt value at either the inner or outer circumference.

Of course if the selector has two inputs, where such inputs are the measured values at the inner and at the outer circumference, and a curve is chosen in dependence on the pair of values (TILTin;TILTout) this is within the scope of the claim, since the resulting curve is dependent on both values, and thus inherently dependent on the difference in combination with the tilt value at either the inner or outer circumference.

The choice of curves may by a quantized choice, i.e. in embodiments there is a limited number of distinct curves (more than one, for instance 6, as in the example) one of which is chosen dependent on the difference in tilt value ΔTILT and possible further inputs, or curves may be chosen by means of parameters which are dependent on the input(s). Also mixed forms may be used. So for instance, for small difference Δtilt a rectilinear curve is chosen, for a somewhat larger difference a standard second order curvilinear curve is chosen, of which the parameters are independent of the values ΔTILT, TILTin and/or TILTout, and for an even larger Δtilt, a higher curve form is chosen having higher order parameters which are dependent on the values ΔTILT, TILTin and/or TILTout and/or further inputs TILTin and TILTout can be measured in different manners:

For written/ROM discs: Tilt as function of jitter can be measured at the inside and outside of the disc during the start-up phase of the disc.

For empty recordable/rewritable discs: The radial tilt inside/outside measurements can be performed before writing data on the disc for example during an OPC (Optimum Power Control or Calibration) procedure. OPC procedures are known procedures in which a test writing is performed at begin and end test zones We start with OPC at the inside of the disc at recording speed. OPC will be done first and at least 3 tracks will be written with laser power from the first OPC. Than radial tilt calibration will be done on the middle track of that 3 written tracks. After tilt calibration power has to be calibrated again due to tilt change. This procedure will be repeated at the outside of the disc. This results in an good radial tilt value at the inside and at the outside of the disc.

Another sometimes-used method especially for empty disks is the square of the radial error signal (or push-pull signal). Such methods may also, within the scope of the invention, be used for acquiring tilt values at an inner and outer circumference of the disk, although, compared to a OPC procedure, these methods often provide tilt values with a relatively lower accuracy.

The present invention has been described in terms of specific embodiments, which are illustrative of the invention and not to be construed as limiting. The invention may be implemented in hardware, firmware or software, or in a combination of them. Other embodiments are within the scope of the following claims. For instance, the selector has at least one further input for temperature and/or humidity. These parameters have a considerable influence on the tilt curve. This embodiment is best combined with the embodiment in which the device comprises a single measurer for measuring tilt at an inner and an outer circumference.

In a further embodiments the disk device is characterized in that is arranged to perform a gauge procedure in which a tilt at a middle circumference of a disk is established for determining curve parameters.

Within the concept of the invention 'an inner' and 'an outer' circumference' is to be understood not necessarily to be so restrictively interpreted to only the innermost and only the outermost part of the disk. "Inner" denotes a part at or near the beginning of the disk, 'outer' at or near the end of the disk, they need not be the very first and very last of the tracks, although they might be.

The invention is embodied in each new characteristic and each combination of characteristics. Any reference signs do not limit the scope of the claims. The word "comprising" does not exclude the presence of other elements than those listed in a claim. Use of the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The figures and embodiments are shown by way of example and do not restrict the scope of the claims. For instance whereas in the figures the coils are wound on the holder, in embodiments the coil may be printed or otherwise provided on a foil which is attached.

Claims

CLAIMS:

1. An optical disk device for reading and/or writing an optical disk having a tilt corrector, characterized in that the optical disk device comprises a measurer for measuring tilt at an inner circumferential part and at an outer circumferential part of an optical disk and a selector for selecting, in dependence of the measured difference between inner and outer circumference tilt, a tilt correction curve for determining the tilt correction as function of radius of the disk, at least some of the selectable curves being of curvilineair form.

2. An optical disk device as claimed in claim 1, wherein the selector has at least one further input, selected from the tilt value at either the inner or outer circumference, rotation speed, type of operation, type of disk, humidity, temperature, average laser power, time of operation.

3. An optical disk device as claimed in claim 1, wherein the optical disk device comprises a single measurer for measuring the tilt at the inner and outer circumference.

4. An optical disk device as claimed in claim 1, wherein the disk device is characterized in that it has means to determine a tilt at a middle circumference of a disk for determining curve parameters.

5. Method for writing of or reading from an optical disk wherein an optical disk device is used for writing on or reading from an optical disk, wherein a tilt value is measured at an inner circumferential part and at an outer circumferential part of an optical disk and, in dependence of the measured difference between inner and outer circumference tilt value, a tilt correction curve for determining the tilt correction as function of radius of the disk is selected, at least some of the selectable tilt correction curves being of curvilineair form, and said selected tilt correction curve is used for correction of tilt during writing or reading of the optical disk.