Abstract:
The invention provides an optical disk device that has a laser unit including a first objective lens and a second objective lens. A numerical aperture of the first objective lens is different from a numerical aperture of the second objective lens. The optical disk device has a first focus driver that detects a first voltage value indicating the value of a driving voltage to drive the first objective lens when light beams are irradiated onto the surface of an optical disk via the first objective lens and a focus is achieved. The optical disk device has a second focus driver that detects a second voltage value indicating the value of a driving voltage to drive the second objective lens when light beams are irradiated onto the recording surface of said optical disk via the second objective lens and a focus is achieved. The optical disk device has a controller that discriminates the type of an optical disk, based on a difference between the first voltage value and the second voltage value.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical disk discrimination method for recording/reproducing information to/from multiple types of optical disks by using an optical pickup and an optical disc device using the method.  
         [0003]     2. Description of the related art  
         [0004]     In recent years, optical disks as disc-shaped recording media have been in general use as an external storage device of a personal computer. Such optical disks are available in a variety of types including a CD initially developed for the purpose of appreciation of music, a CD-R, a CD-RW, a DVD-ROM, a DVD-R, a DVD±RW, a DVD-RAM, and a Blu-ray Disc (hereinafter also referred to as a BD) developed for recording of data on personal computers. An optical disk device that supports these optical disks is designed so that multiple optical disks can be used on a single optical disk device. This means that an optical disk must have a feature to detect the type of an optical disk mounted on the optical disk.  
         [0005]     With these optical disks, the emission wavelength of laser beams used for recording/reproducing data differs between a CD system a DVD system and a BD system. The corresponding optical system differs according. It is thus important to discriminate the type of an optical disk mounted on an optical disk device.  
         [0006]     A related art optical disk device that supports both the CD system and the DVD system will be described referring to  FIG. 9 .  
         [0007]      FIG. 9  is a block diagram of the pickup controller of an optical disk device. In  FIG. 9 , a numeral  1  represents an optical disk,  2  a pickup module,  3  a spindle motor,  4  an optical pickup,  5  a carriage,  6  a feed part,  7  a feed motor,  8  an analog signal processor,  9  a servo processor,  10  a motor driving part,  11  a digital signal processor,  12  a laser driving part, and  13  a controller.  
         [0008]     Operation of a pickup controller thus configured in the related art will be described.  
         [0009]     In  FIG. 9 , the pickup module  2  is composed of the spindle motor  3  for rotating the optical disk  1 , the optical pickup  4  for reading an information signal from the optical disk  1 , and the feed part  6  for moving in the radial direction of the optical disk  1  the carriage  5  where the optical pickup  4  is mounted. The analog signal processor  8  generates a focus error signal and a tracking error signal based on signal output from an optical sensor (not shown) inside the optical pickup  4  in the carriage  5  provided inside the pickup module  2  and outputs the signals to the servo processor  9 .  
         [0010]     The focus error signal indicates a displacement of a light beam spot emitted from an objective lens (not shown) included in the optical pickup  4  from the recording surface of the optical disk  1  in the focal direction. The tracking error signal indicates a displacement of the optical spot from the information track of the optical disk  1  in the radial direction of the optical disk.  
         [0011]     The analog signal processor  8  generates a lens position signal indicating the relative positions of the objective lens and the carriage  5  by extracting the low range components of a tracking error signal.  
         [0012]     The servo processor  9  is composed of an ON/OFF circuit, an arithmetic circuit, a filter circuit and an amplifier circuit. The servo processor  9  performs focus/tracking control over the objective lens so that the light beam spot will trace the information track of the optical disk, and performs feed control so that the objective lens will maintain an almost neutral position by using the low range components of the tracking error signal. The feed part  6  is composed of a feed motor  7 , a gear (not shown), and a screw shaft (not shown). When the feed part  6  rotates the feed motor  7 , the carriage  5  moves as a feed motor pulse is periodically outputted from the feed motor  7 . The controller  13  controls the entirety of thus configured servo part.  
         [0013]      FIG. 10  is a block diagram of the focus control system of a related art optical disk device.  
         [0014]     In  FIG. 10 , a numeral  14  represents an objective lens,  15  a half mirror,  16  a division sensor,  17  a head amplifier,  18  a differential amplifier,  19  a division sensor,  20  a head amplifier,  21  a differential amplifier,  22  a selector switch,  23  a filter,  24  a selector switch, and  25  a driving circuit.  
         [0015]     Operation of a focus control system of an optical disk device thus configured will be described. To discriminate the type of an optical disk, generally laser beams having a longer wavelength for CDs are irradiated first and laser beams having a shorter wavelength for DVDs are irradiated next in consideration of the difference in the optical power level.  
         [0016]     When laser beams for CDs are irradiated, light reflected on the reflecting surface of the optical disk  1  in  FIG. 10  reaches the half mirror  15  via the objective lens  14 . For example, light for CDs passes through the half mirror  15  and impinges on the division sensor  16  and gain-adjusted by the head amplifier  17 . Differential arithmetic operation is made by the differential amplifier  18  on a signal from the head amplifier  17  to generate a focus error signal related to laser beams for CDs are used.  
         [0017]     The focus error signal thus generated that is related to laser beams for CDs are used as a signal to pass through the selector switch  22  and control a focus actuator via the filter  23 , selector switch  24 , and driving circuit  25 .  
         [0018]     The focus error signal is transmitted to the controller  13  for the controller  13  to control focus driving.  
         [0019]     Next, an exemplary method for discriminating the type of an optical disk mounted will be described.  
         [0020]      FIG. 11  is an explanatory drawing to discriminate the type of an optical disk.  
         [0021]     As shown in  FIG. 11 , the objective lens is brought closer to a recording surface from a distance to the optical disk. A focus error signal (FE signal) is detected and the detected s-curve characteristic and added value FS of the FE signal are obtained. The CD system or DVD system is determined as follows: when the normalized FE amplitude value shown in  FIG. 11  is greater than a threshold, a CD disk is assumed; when the value is smaller than a threshold, a DVD disk is assumed.  
         [0022]      FIG. 12  shows normalized FE amplitude values by optical disk type and optical disk device.  
         [0023]     As shown in  FIG. 12 , it is possible to set a threshold for a normalized FE amplitude value and use the threshold to discriminate between optical CD disks and optical DVD disks. When the detected normalized FE amplitude value is greater than the threshold, a CD disc is assumed. When the value is smaller, a DVD disk is assumed.  
         [0024]     A technique to discriminate the type of an optical disk is described on Patent Reference 1.  
         [0025]     Patent Reference 1: JP-A-2005-85351  
         [0026]     However, there are some cases where a CD disk and a DVD disk cannot discerned using a threshold specified based on a normalized FE amplitude value due to variations in the assembly of optical components of optical disk devices or variations in the manufacture of optical disks.  
         [0027]      FIG. 13  represents normalized FE amplitude values corresponding to several types of optical disks.  
         [0028]     Part A in  FIG. 13  corresponds to an optical disk device that determines a DVD disk as a CD disk because the s-curve amplitude value of the focus error of DVD is large. Part B in  FIG. 13  corresponds to an optical disk device that determines a CD disk as a DVD disk because the s-curve amplitude value of CD is small.  
         [0029]     In this way, each of the optical disk devices is accompanied by variations in the manufacture of optical components and amplitude of s-curve characteristic of a focus error signal. This results in failure to discriminate between CD disks and DVD disks.  
       SUMMARY  
       [0030]     An object of the invention is to provide an optical disk discrimination method capable of reliably discriminating the type of an optical disk even in the presence of variations in the s-curve characteristic of a focus error signal attributable to variations in the assembly of optical components and an optical disk device using the method.  
         [0031]     In order to solve such problems, the invention provides an optical disk device that has a laser unit including a first objective lens and a second objective lens. A numerical aperture of the first objective lens is different from a numerical aperture of the second objective lens. The optical disk device has a first focus driver that detects a first voltage value indicating the value of a driving voltage to drive the first objective lens when light beams are irradiated onto the surface of an optical disk via the first objective lens and a focus is achieved. The optical disk device has a second focus driver that detects a second voltage value indicating the value of a driving voltage to drive the second objective lens when light beams are irradiated onto the recording surface of said optical disk via the second objective lens and a focus is achieved. The optical disk device has a controller that discriminates the type of an optical disk, based on a difference between the first voltage value and the second voltage value.  
         [0032]     With this configuration, a laser unit with the greatest numerical aperture may be used to obtain the surface position of an optical disk. This accurately obtains the surface position because the target spot is focused on. The position of a recording surface is obtained by using a laser unit with the greatest substrate thickness of an optical disk. This avoids a contact of the laser unit with the substrate of the optical disk. As a result, the optical disk device can discriminate the type of an optical disk based on a difference in the voltage value obtained when the focuses are on the position of the surface and the recording surface of the optical disk.  
         [0033]     The optical disk device according to the invention is capable of reliably discriminate the type of an optical disk even in the presence of variations in the manufacture of optical disks. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]      FIG. 1  is a block diagram of an optical disk device according to an embodiment of the invention.  
         [0035]      FIG. 2  illustrates a focus error according to an embodiment of the invention.  
         [0036]      FIG. 3  illustrates a difference in focus driving values according to an embodiment of the invention.  
         [0037]      FIG. 4  illustrates the calculation of an adjustment value according to an embodiment of the invention.  
         [0038]      FIG. 5  shows an example of a normalized optical disk discrimination process that is based on the difference in focus driving according to an embodiment of the invention.  
         [0039]      FIG. 6  is a flowchart of disk discrimination processing according to an embodiment of the invention.  
         [0040]      FIG. 7  is a flowchart of substrate thickness discrimination processing according to an embodiment of the invention.  
         [0041]      FIG. 8  is a flowchart of an example of detailed discrimination of an optical disk according to an embodiment of the invention.  
         [0042]      FIG. 9  is a block diagram of the pickup controller of an optical disk device.  
         [0043]      FIG. 10  is a block diagram of the focus control system of a related art optical disk device.  
         [0044]      FIG. 11  is an explanatory drawing to discriminate the type of an optical disk.  
         [0045]      FIG. 12  shows normalized FE amplitude values by optical disk type and optical disk.  
         [0046]      FIG. 13  represents normalized FE amplitude values corresponding to several types of optical disks. 
     
    
     DETAILED DESCRIPTION  
       [0047]     Embodiments of the invention will be described referring to drawings.  
         [0048]      FIG. 1  is a block diagram of an optical disk device according to an embodiment of the invention.  
         [0049]     In  FIG. 1 , a numeral  101  represents a host computer as an external terminal device,  102  an optical disk device,  103  an interface,  301  an optical disk,  302  an optical pickup module,  303  an optical pickup,  304  a spindle motor,  305  a focus driving coil,  306  an objective lens,  307  a laser,  308  reflected light receiving means,  310  a carriage,  311  reflected light arithmetic means,  312  a digital servo controller,  313  a data processor,  314  focus driving coil control means,  315  disk discrimination means,  317  laser driving control means,  318  drive control means,  321  spindle motor driving means, and  322  adjustment value storage means.  
         [0050]     An optical disk device  102  thus configured according to an embodiment of the invention will be described.  
         [0051]     The host computer  101  and an optical disk device  102  transmits/receives information via the interface  103 . A request made to the optical disk  301  from the host computer  101  concerning the operation of the optical disk device  102  is transmitted to the optical disk device  102  via the interface  103 . This request is issued in a packet command of the interface from the host computer  101 . The optical disk device  102  receives this command on command receiving means  323  and operates un response to this command.  
         [0052]     The optical pickup module  302  is composed of a spindle motor  304  for rotating the optical disk  301  that performs at least recording or reproduction of information, the optical pickup  303  for performing at least recording or reproduction of information onto/from the optical disk  301  by using the light emission pattern of the laser  307 , and a feed part (not shown) for moving the carriage  310  where the optical pickup  303  is mounted in the radial direction of the optical disk  301 .  
         [0053]     The drive control means  318  controls the spindle motor driving means  321  to adjust the number of rotations of the spindle motor  304 .  
         [0054]     The optical pickup  303  includes the focus driving coil  305  for making control to bring the objective lens  306  of the optical pickup  303  closer to or away from the optical disk  301  by way of the focus driving coil control means  314 . The optical pickup  303  thus adjusts the objective lens  306  so as to focus on a predetermined position of the optical disk  301 .  
         [0055]     The reflected light receiving means  308  receives reflected light from the optical disk  301  and outputs a signal based on the received reflected light.  
         [0056]     From the outputted signal, a focus error signal (FE signal) or a tracking error signal (TE signal) are generated by the reflected light arithmetic means  311 , followed by processing of a focus error or a tracking error in the data processor  313  in the digital servo controller  312 .  
         [0057]     The data processor  313  also includes a feature to discriminate the type of the optical disk  301  based on a focus error signal.  
         [0058]     The adjustment value storage means  322  is storage means provided to adjust the variations in the optical system during manufacture of the optical disk device  102  and stores an adjustment value to normalize a focus driving value described later.  
         [0059]     The laser driving control means  317  selects a predetermined laser light source among a plurality of lasers such as a Blu-ray (BD) laser, a DVD laser and a CD laser before recording or reproducing information onto/from the optical disk  301  and performs driving control over the laser power of the laser  307 .  
         [0060]      FIG. 2  illustrates a focus error according to an embodiment of the invention.  FIG. 3  illustrates a difference in focus driving values according to an embodiment of the invention.  FIG. 4  illustrates the calculation of an adjustment value according to an embodiment of the invention.  
         [0061]     Referring to  FIG. 2 , a numeral  301  represents an optical disk,  210  an objective lens for BDs,  220  an objective lens for CDs and DVDs (generally represented by  301  in  FIG. 1 ),  230  a BD laser light source, and  240  a double-wavelength laser light source for CDs and DVDs. Light sources of three wavelengths are thus provided.  
         [0062]     Included are the objective lens  210  for gathering light beams for a BD laser light source and the he objective lens  220  for CDs and DVDs. The numerical aperture of the objective lens  210  is greater than 0.8 and the numerical aperture of the objective lens  220  for CDs and DVDs is selected within a range of 0.5 to 0.7.  
         [0063]     A method will be described for discriminating the type of the optical disk  301  by way of substrate thickness discrimination, in particular between a CD and a DVD, based on  FIGS. 2, 3  and  4 .  
         [0064]     In the process of substrate thickness discrimination, a laser  230  for BDs, a laser for DVDs and a laser  240  for CDs are turned on in this order with a spindle motor  304  turned OFF. Each time a laser is turned on, the corresponding objective lens is oriented in the focus direction to perform focus-related measurement. A difference in the substrate thickness is detected based on then obtained FE signal amplitude, FE signal symmetry, number of s-shaped waveforms of an FE signal, and focus driving value (focus-achieved voltage value) to discriminate between a BD, a DVD and a CD.  
         [0065]     While the spindle motor is kept OFF in this embodiment, the spindle motor  304  may be turned ON when it is desired to save the operation time. Or, the spindle motor  304  may be turned OFF only when the BD laser is driven to perform focus measurement. In this way, it is possible to prevent the objective lens  210  for BDs from coming into contact with the optical disk  301 .  
         [0066]     When a voltage is supplied to the focus driving coil  305  to bring the objective lenses  210 ,  220  closer to the optical disk  301  from a distance to the same, a focus error value (FE value) is measured. In the measurement result, the FE values are represented in an s-curve as shown in  FIG. 2 ( b ). The zero-crossing points of the s-curve, FBD, FDVD and FCD are called the focus driving value of respective lasers.  
         [0067]     Calculation of a difference in the focus driving error will be described based on  FIG. 3 . A drive value FBD for the surface of the optical disk  301  is obtained in calculating an FE value by driving the BD laser. The CD laser is driven to obtain the focus driving value FBD of s-curve detection for the recording surface of the disk, and then a difference in the focus driving value is calculated.  
         [0068]     Difference in focus driving value=FCD−FBD  
         [0069]     Next, an adjustment value mentioned later is obtained from the adjustment value storage means  22  and the adjustment value is used to normalize the difference in the focus driving value.  
         [0070]     Normalized difference in focus driving value=Difference in focus driving value/adjustment value×1000  
         [0071]     As described later, the BD substrate thickness is determined first in the determination of substrate thickness with the BD laser. A focus driving value for the surface of the disk  301  can be obtained in this BD determination.  
         [0072]     A method for obtaining an adjustment value will be described in accordance with  FIG. 4 .  
         [0073]     An adjustment value is a value set for each optical disk device  102 . The value is set in consideration of the influence of variations in the s-curve amplitude value of FE value due to variations in the optical axis of an optical system and may be used to discriminate the real optical disk  301 .  
         [0074]     As shown in  FIG. 4 , before the optical disk device  102  is used, the laser  230  for BDs is used to obtain the focus driving value FBD for the surface of the optical disk  301  and the focus driving value FDVD for the recording surface by the DVD laser  240 . The difference between these values is stored as an adjustment value into the adjustment value storage means  322 .  
         [0075]     An adjustment value stored into the adjustment value storage means  322  is called when the optical disk  301  is mounted on the optical disk device  102  and is used to discriminate the type of the optical disk  301 . The adjustment value need not be calculated again once it is previously stored when the optical disk device  102  is manufactured.  
         [0076]      FIG. 5  shows an example of an optical disk discrimination process that is based on the difference in focus driving according to an embodiment of the invention.  
         [0077]      FIG. 5 ( a ) shows a difference in focus driving for each optical disk device.  FIG. 5 ( b ) shows a normalized difference in focus driving for each optical disk device.  
         [0078]     By setting a threshold line to about  2100  based on the difference in focus driving shown in  FIG. 5 ( a ), it is possible to classify the types of an optical disk into a DVD and a CD. When the normalized difference in focus driving shown in  FIG. 5 ( b ) is used for discrimination t is possible to classify the types of an optical disk into a DVD and a CD by setting the threshold line to about  720 .  
         [0079]     In other word, a result greater than a preset threshold assumes a DVD and one smaller than a preset threshold assumed a CD irrespective of whether a difference in focus driving or a normalized difference in focus driving is used in discrimination of a disk.  
         [0080]     As shown in  FIG. 5 ( a ) and  FIG. 5 ( b ), discrimination using a normalized difference in focus driving is an easier approach to discriminate between a CD and a DVD.  
         [0081]      FIG. 6  is a flowchart of disk discrimination processing according to an embodiment of the invention. When discrimination processing of the optical disk  301  starts (S 110 ), substrate thickness discrimination processing is executed (S 120 ) and it is determined whether the disk is discriminated through substrate thickness discrimination processing (S 130 ). In case the disk is not discriminated, the disk is determined unsupported (S 150 ) and the processing is terminated.  
         [0082]     When the disk is discriminated through substrate thickness discrimination processing (S 130 ), detailed disk discrimination processing is executed (S 140 ) and the optical disk discrimination processing is terminated (S 160 ).  
         [0083]      FIG. 7  is a flowchart of substrate thickness discrimination processing according to an embodiment of the invention.  
         [0084]     In  FIG. 7 , when the substrate thickness discrimination processing starts (S 310 ), the BD laser is turned on to perform BD system substrate thickness discrimination processing (S 320 ). The BD laser is used to detect the focus error value (FE value) and the number of s-curves (S 330 ) of the optical disk  301 . A normalized FE amplitude value is obtained (S 340 ) and it is determined whether the normalized FE amplitude value obtained is greater than a threshold (S 350 ). In case the obtained value is greater than the threshold, the disk is determined as a BD disk (S 360 ). In case the obtained value is equal to or smaller than the threshold, the BD laser is turned off (S 370 ) and the CD laser is turned on (S 380 ). The CD laser is used to detect the FE value and the number of s-curves (S 390 ). A difference between the focus driving value of BD (drive value for the surface of an optical disk) and the focus driving value of the CD laser is obtained (S 400 ). An adjustment value specific to the optical disk device  1  is read from a storage device (S 410 ). A normalized difference in focus driving is calculated from the obtained difference in focus driving and the read adjustment value (S 420 ). It is determined whether the normalized difference in focus driving is smaller than the threshold (S 430 ). In case the normalized difference in focus driving is smaller than the threshold, the disk is determined as a CD (S 440 ). Otherwise, the CD laser is turned off (S 450 ) and the DVD laser is turned on (S 460 ). The DVD laser is used to detect the FE value and the number of s-curves (S 470 ) and it is determined whether there are no s-curves of a CD or a DVD (S 480 ). In case there are no s-curves or in case no s-curves are found, the disk is determined unsupported (S 500 ) and the processing is terminated. In case an s-curve is found, the desk is determined as a DVD (S 490 ) and the substrate thickness discrimination processing is terminated (S 510 ).  
         [0085]      FIG. 8  is a flowchart of an example of detailed discrimination of an optical disk according to an embodiment of the invention.  FIG. 8 ( a ) shows discrimination of an optical BD disk. When the detailed BD disk discrimination starts (S 710 ), it is determined whether the wobbling cycle is smaller than a threshold (S 720 ). In case the wobbling cycle is smaller than the threshold, the disk is determined as a BD-R/RE (S 730 ). Otherwise, the disk is determined as a BD-ROM (S 725 ).  
         [0086]      FIG. 8 ( b ) shows discrimination of an optical CD disk. When the detailed CD disk discrimination starts (S 740 ), it is determined whether the wobbling cycle is smaller than a threshold (S 750 ). In case the wobbling cycle is smaller than the threshold, the disk is determined as a CD-R/RW (S 770 ). Otherwise, the disk is determined as a CD-ROM (S 760 ).  
         [0087]      FIG. 8 ( c ) shows discrimination of an optical DVD disk. When the detailed DVD disk discrimination starts (S 780 ), the disk is discriminated based on a tracking error (TE value) (S 790 ). In case the discrimination result is TE 1  based on the level of the TE level (S 800 ), the disk is determined as a DVD-ROM (S 840 ). In case the discrimination result is TE 2  (S 810 ), the disk is determined as a DVD±R (S 850 ). In case the discrimination result is TE 3  (S 820 ), the disk is determined as a DVD-RAM (S 860 ). In case the discrimination result is TE 4 , the disk is determined as a DVD±RW (S 870 ).  
         [0088]     This application is based upon and claims the benefit of priority of Japanese Patent Application No 2006-121476 filed on Jun. 26, 04, the contents of which are incorporated herein by reference in its entirety.