The present invention relates to a method of setting the reproducing light quantity for playing an optical disc, and to an optical disc apparatus using that method; the invention holds the amount of degradation of information on the optical disc due to the reproducing light to within a predetermined range.
When an optical disc is played, there are mutually contradictory demands on the reproducing light quantity, as follows. From the perspective of reproduced signal quality, reproduction with the greatest quantity of light is advantageous because it can reduce noise. From the viewpoints of the ability of the optical disc to withstand quantities of reproducing light and the operating life of the semiconductor laser, reproduction with the smallest quantity of light is advantageous. Given these conflicting demands, the desired setting of the reproducing light quantity maintains a minimum reproduced signal quality without causing any degradation of the characteristics of the recorded marks on the optical disc, so that the optical disc can be used as long as possible.
In conventional optical disc apparatus, in still reproduction, in which the same track is reproduced repetitively, the track is affected by considerable thermal damage, which degrades the recorded marks that embody the information recorded on that part, and thus degrades the quality of the reproduced signal. To counter this problem, the reproducing light quantity has been controlled by detecting the reproduced signal amplitude and compensating for changes in the reproduced signal amplitude (see, for example, Patent Document 1).
Patent Document 1: Japanese Patent Application Publication No. 2001-34944 (pp. 1-6, FIG. 9)
With the conventional optical disc apparatus described above, because only changes in the reproduced signal amplitude are detected, even significantly degraded states of the recorded marks cannot be detected, so the recorded marks may degrade to an unreproducible state. As described in Patent Document 1 above, changes in the reproduced signal amplitude are detected by using user areas on the optical disc reproduced to display still images, so recorded marks that are necessary to the user may be degraded to an unreproducible state.
This invention provides an optical disc reproducing light quantity setting method for setting a quantity of light directed onto an optical disc for reproduction purposes, wherein:
an area of the optical disc in which information is recorded is test-reproduced by using a test-reproducing light quantity;
a reproduction time or a number of reproductions until a quality value of the test-reproduced signal reaches a prescribed value is determined; and
those values are used to determine a maximum reproducing light quantity assuring a prescribed reproduction time or number of reproductions and the determined maximum reproducing light quantity is set as a reproducing light quantity for regular reproduction.
With the present invention it is possible to prevent degradation, to an unreproducible state, of the recording marks that embody recorded information on the optical disc.
a and 12b are current-emission relationship diagrams similar to the diagram in
a and 13b are current-emission relationship diagrams similar to the diagram in
1 optical disc, 2 light source, 3 beam, 4 collimator lens, 5 prism, 6 objective lens, 7 focused spot, 8 focusing lens, 9 photodetector, 10 amplifier circuit, 11 signal processing unit, 12 control calculation unit, 13 light source control unit, 20 recordable optical disc, 21 user data area, 22 management area, 23 disc test area.
The first embodiment of the invention will now be described with reference to the drawings. In
The detected jitter value is sent to a control calculation unit 12, and then to a video processing unit 14, wherein audio, video, and other processing is performed.
The control calculation unit 12, which comprises, for example, a programmed computer, performs control and calculation processing for the entire optical disc apparatus.
The optical disc reproducing light quantity setting method in this embodiment sets the quantity of light directed onto the optical disc to reproduce it; an area on the optical disc in which information has been recorded is repeatedly test-reproduced by using a test-reproducing light quantity; the repeated reproduction time or the number (N) of repeated reproductions of the area required for the quality value of the test-reproduced signal to reach a prescribed value is determined; these values are used to determine a maximum reproducing light quantity that guarantees the prescribed reproduction time or number of reproductions; the determined maximum reproducing light quantity is set as the reproducing light quantity for regular reproduction. The reproduction time is proportional to the number of reproductions, so in the following description, the terms ‘reproduction time’ and ‘number of reproductions’ may be used with the same meaning.
The processing for setting the reproducing light quantity will be described with reference to
When a reproduction command for the optical disc is received from a video processing unit 14 (S10), the control calculation unit 12 issues a command to emit light with a first prescribed light quantity to a light source control unit 13 (S12). That is, a first test-reproducing light quantity is set and a command to emit light with that light quantity is issued.
The control calculation unit 12 also controls the photodetector 9, the signal processing unit 11, and so on so as to repeatedly reproduce a first prescribed area (test area) as described above with that light quantity (the first prescribed light quantity) and detect the jitter value (S14, S16, S18). That is, the control calculation unit 12 reproduces the first prescribed area a prescribed number of times (for example, M times) (S14), detects the jitter value (S16), and determines whether the detected jitter value has reached a prescribed value (has degraded'to a prescribed minimum reproduced signal quality level) (S18); if the prescribed value has not been reached, the control calculation unit 12 repeats the above reproducing step and subsequent steps (S14, S16, S18).
When the prescribed value, is reached in step S18, the control calculation unit 12 determines and stores the number of reproductions up to that time (the number of reproductions from the first reproduction in step S14, also referred to below as the ‘first number of reproductions’; if the same area is reproduced M times as described above every time step S14 is performed, the first number of reproductions equals a value obtained by multiplying the number of repetitions of steps S14, S16, and S18 by M) (S20).
The value of M need not be constant, but may be varied every time step S14 is repeated. For example, the value of M may be decreased as the jitter value increases and approaches the prescribed value.
Then, the control calculation unit 12 issues a command to the light source control unit 13 to change the reproducing light quantity (S22), and operates in the same way as above (S24, S26, S28). That is, the control calculation unit 12 issues a command to emit light with a second prescribed light quantity (differing from the above first prescribed light quantity) (S22). That is, a second test-reproducing light quantity is set and a command to emit light with that light quantity is issued.
The control calculation unit 12 also controls the photodetector 9, the signal processing unit 11, and so on so as to repeatedly reproduce a second prescribed area (test area) as described above with that light quantity (the second prescribed light quantity) and detect the jitter value (S24, S26, S28). That is, the control calculation unit 12 reproduces the second prescribed area a prescribed number of times (for example, M times) (S24), detects the jitter value (S26), and determines whether the detected jitter value has reached a prescribed value (has degraded to a prescribed minimum reproduced signal quality level) (S28); if the prescribed value has not been reached, the control calculation unit 12 repeats the above reproducing step and subsequent steps (S24, S26, S28).
When the prescribed value is reached in step S28, the control calculation unit 12 determines and stores the number of reproductions up to that time (the number of reproductions from the first reproduction in step S24, also referred to below as the ‘second number of reproductions’; if the same area is reproduced M times as described above every time step S24 is performed, the second number of reproductions equals a value obtained by multiplying the number of repetitions of steps S24, S26, and S28 by M) (S30).
The value of M need not be constant, but may be varied every time step S14 is repeated. For example, the value of M may be decreased as the jitter value increases and approaches the prescribed value.
The control calculation unit 12 then uses the first and second number of reproductions that it has obtained through the above operations and the corresponding first and second test-reproduction light quantities to determine a reproducing light quantity for use in reproduction (also referred to below as ‘regular reproduction’ to distinguish it from the test-reproduction performed in steps S14 and S24) for the intended use of the data (for example, watching or listening to the reproduced data) (S32). The method of determining the reproducing light quantity will be described later.
Then regular reproduction is performed with the determined reproducing light quantity (S34).
The relationship between reproduction time and the jitter value detected as an index of reproduced signal quality will be described with reference to
The relationship between the reproducing light quantity and reproduced signal quality will be described with reference to
Referring to
k=A*exp(−E/RT) (1)
Taking natural logarithms on both sides gives the expression in equation (2).
ln(k)=(−E/R)*(1/T)+ln(A) (2)
In the Arrhenius-plot diagram in
The vertical axis indicates the natural logarithm ln(1/N) of the reciprocal (1/N) of the reproduction time (number of reproductions) N taken for the jitter value to reach the tolerance setting, such as the reproduction time N taken for the jitter value to reach the tolerance setting Js, with each of the reproducing light quantities in
The intercept on the vertical axis in
By replacing k in equation (2) with (1/N), (1/T) with (1/L), (−E/R) with a constant Ka, and ln(A) with a constant Kb, the following equation (3) is obtained.
ln(1/N)=Ka*(1/L)+Kb (3)
In
In step S12 in
The above process has been described as being carried out on a graph, but it may be carried out by corresponding computational operations. For example, using the data Ne, Nd determined at the above two points, the following equation (4) obtained by substituting Ne and the corresponding Le for N and L in equation (3) and the following equation (5) obtained by substituting Nd and the corresponding Ld for N and L in equation (3) may be solved as simultaneous equations to obtain the constants Ka and Kb (by equations (6) and (7)), and the predetermined Ng may be substituted into equation (3), in which constants Ka and Kb have become known as shown by equations (6) and (7), to obtain the corresponding Lg.
ln(1/Ne)=Ka*(1/Le)+Kb (4)
ln(1/Nd)=Ka*(1/Ld)+Kb (5)
Ka={ln(1/Ne)−ln(1/Nd)}/{1/Le}−(1/Ld)} (6)
Kb={ln(1/Ne)·(1/Ld)−ln(1/Nd)·(1/Le)}/{(1/Ld)/{(1/Le)} (7)
When the processing shown in
In
As shown in
Similarly, if the result is ‘No’ in step S28, whether or not the number of reproductions has reached the prescribed value Nh is decided (S38); if this value has not been reached, the processing returns to step S24; if this value has been reached, a prescribed reproducing light quantity is set (S40), and regular reproduction is started (S34). This is because it has been determined that the optical disc has adequate endurance for the reproducing light quantity and accordingly the jitter value will not reach the prescribed value (the reproduction quality will not reach the prescribed value) even if the number of reproductions reaches the prescribed value Nh.
When the reproduction time or number of reproductions taken for the reproduced signal quality value to reach the prescribed value is actually determined, the degradation characteristic of the recorded marks depends significantly on the material in which the recorded marks are formed, and accordingly, the prescribed reproducing light quantity may be set when the optical disc apparatus is manufactured, from overall considerations of the need to reduce the time required for starting reproduction and the need to improve the setting precision of the reproducing light quantity as much as possible.
In order to reduce the time taken for deciding the reproducing light quantity, the rotational rate (rotational velocity) of the optical disc may be increased (raised) above the rotational rate in regular reproducing. In that case, it is possible to maintain the setting precision of the reproducing light quantity while reducing the evaluation time by setting the test-reproducing light quantity to a value multiplied by an appropriate factor (and increasing the reproducing light quantity, if the rotational rate is increased).
The reproducing light quantity may be set by holding the gas constant R fixed and selecting an appropriate representative value for the activation energy E, thereby making the slope of line Ka in
In order to avoid the lengthening of the time until reproduction starts, caused by the operations shown in
In the above method, the jitter value is used as an index of reproduced signal quality, but an error rate may be used instead.
In the above example, the area to be reproduced with the test-reproducing light quantity was not specified, but it may be specified randomly for each reproduction in order to prevent a particular area from deteriorating rapidly through being overly reproduced.
The first embodiment of the invention produces the effect that the recorded marks that embody recorded information on an optical disc are not degraded to the extent that they cannot be reproduced. In addition, if characteristic degradation of an optical disc occurs even with the reproducing light quantity that guarantees the minimum reproduced signal quality, it is possible to notify the user and give the user a chance to make a decision, such as whether to continue or halt reproduction, thereby enabling an optimal selection to be made according to the intended purpose or application.
A second embodiment will now be described. The schematic drawing showing the structure of the optical disc apparatus in the second embodiment is the same as
In
In the second embodiment as well, it may be so arranged that when the processing in
As described in relation to the first embodiment with reference to
When the reproduction time or number of reproductions taken for the reproduced signal quality value to reach the prescribed value is actually determined, the degradation characteristic of the recorded marks depends significantly on the material in which the recorded marks are formed, and accordingly, the preset reproducing light quantity may be set when the optical disc apparatus is manufactured, from overall considerations of the need to reduce the time required for starting reproduction and the need to improve the setting precision of the reproducing light quantity as much as possible.
In order to reduce the time for deciding the reproducing light quantity, the rotational rate (rotational velocity) of the optical disc may be increased (raised) above the rotational rate in regular reproducing. In that case, it is possible to maintain the setting precision of the reproducing light quantity while reducing the evaluation time by setting the test-reproducing light quantity to a value multiplied by an appropriate factor (and increasing the reproducing light quantity, if the rotational rate is increased).
In order to avoid the lengthening of the time until reproduction starts, caused by the operations shown in
In the above method, the jitter value is used as an index of reproduced signal quality, but an error rate may be used instead.
The second embodiment enables the test of reproduced signal quality to be performed by using a test area located outside the user data area, with the effect that the risk of degrading important content in the user data area can be further reduced. Another effect is that the recorded marks that embody recorded information on the optical disc are not degraded to the extent that they cannot be reproduced. In addition, if characteristic degradation of an optical disc occurs even with the reproducing light quantity that guarantees the minimum reproduced signal quality, it is possible to notify the user and give the user a chance to make a decision, such as whether to continue or halt reproduction, thereby enabling an optimal selection to be made according to the intended purpose or application.
The third embodiment of the invention will now be described. The schematic drawing showing the structure of the optical disc apparatus in the third embodiment is the same as
In
In the third embodiment, when the light emission quantity is adjusted, the light source control unit 13 can freely set the central value C or the amplitude M of the applied high frequency amount shown in
As shown in
An optical disc's sensitivity to reproducing light and the amount of degradation caused by reproducing light depend greatly on the recording film material used by the manufacturer: some optical discs react sensitively to variation in the central value C; some optical discs react sensitively to variation in the amplitude value M.
A management area indicating information about the manufacturer and recording film material is provided on the inner circumference side of the optical disc, so when the management area is reproduced, the manufacturer and recording film material can be identified.
Accordingly, if the central value C or amplitude value M is adjusted selectively, the reproducing light quantity can be adjusted efficiently responsive to the degradation due to reproducing light.
Number | Date | Country | Kind |
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2007-130032 | May 2007 | JP | national |
2007-238807 | Sep 2007 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2008/056312 | 3/31/2008 | WO | 00 | 10/15/2009 |