Abstract:
A light-emitting element emits a light toward an optical disk. A plurality of light-receiving elements receives the light reflected from the optical disk. A light-shielding member is provided between the optical disk and at least one of the light-emitting element and the light-receiving elements so as to shield parts of the light at both sides in a radial direction of the optical disk. A tilt of the optical disk is detected according to an intensity distribution of the light on the light-receiving elements.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to a tilt detection device, an optical pickup and an optical disk device, and more particularly, to a tilt detection device applied to a storage device and so forth, which are computer peripherals using an optical disk as a storage medium, so as to detect a tilt of the optical disk, and an optical pickup and an optical disk device including the tilt detection device.  
           [0003]    2. Description of the Related Art  
           [0004]    Recently, optical disks have been used as recording media for recording a large amount of information. Such optical disks have been generally represented by read-only disks, such as a music CD (Compact Disc), and a CD-ROM on which various programs are recorded. Recently, however, CDs, such as a CD-R and a CD-E on which information can be written (recorded) have been widespread. The CD-R (CD-Recordable) is a writable (recordable) CD, and more specifically, is a CD on which information can be written once (thus, also referred to as CD-Write Once). The CD-E (CD-Erasable) is a CD on which information can be written more than once (also referred to as CD-RW: CD-Rewritable). Further, a DVD (Digital Versatile Disk) also has become prevalent. The DVD has a same diameter as the CD-ROM, and has a larger capacity than the CD-ROM. Information is recorded/reproduced to/from an optical disk, such as the CD-R, the CD-E or the DVD, by an optical disk device as shown in FIG. 1.  
           [0005]    [0005]FIG. 1 is a block diagram showing a main configuration of the optical disk device. As shown in FIG. 1, the configuration involves an optical disk  1 , a spindle motor  2 , an optical pickup  3 , a motor driver  4 , a read amplifier  5 , a servo part  6 , a CD decoder  7 , an ATIP decoder  8 , a laser controller  9 , a CD encoder  10 , a CD-ROM encoder  11 , a buffer RAM  12 , a buffer manager  13 , a CD-ROM decoder  14 , an ATAPI/SCSI interface  15 , a D/A converter  16 , a ROM  17 , a CPU  18 , and a RAM  19 .  
           [0006]    Besides, arrows shown in FIG. 1 indicate main directions in which data is transferred. In addition, although the CPU  18  controls each of the elements shown in FIG. 1, FIG. 1 shows the CPU  18  only with a thick-lined arrow to avoid complicated lines indicating connections with the above-mentioned elements.  
           [0007]    The optical disk  1  is rotationally driven by the spindle motor  2 . The spindle motor  2  is controlled by the motor driver  4  and the servo part  6  so that a linear velocity becomes constant. This linear velocity can be varied by degrees.  
           [0008]    The optical pickup  3  incorporates a semiconductor laser, optical systems, a focus actuator, a track actuator, a light-receiving element, and a position sensor, which are not shown in FIG. 1. A laser beam LB emitted from the semiconductor laser is projected on the optical disk  1  via the optical systems. Additionally, the optical pickup  3  can be moved in a sledge direction by a seek motor. The focus actuator, the track actuator and the seek motor are controlled by the motor driver  4  and the servo part  6  according to signals obtained from the light-receiving element and the position sensor so that a spot of the laser beam LB is located at a target position on the optical disk  1 .  
           [0009]    Upon reading data, a reproduction signal obtained by the optical pickup  3  is amplified and digitized by the read amplifier  5 , and thereafter is supplied to the CD decoder  7 . The digitized data is demodulated according to an EFM (Eight to Fourteen Modulation) in the CD decoder  7 . Specifically, recorded data is subjected, in units of eight bits, to the EFM so as to be converted from eight bits to fourteen bits, and three coupling bits are added thereto so as to make a total of 17 bits. In this course, the coupling bits are added so that numbers of “1” and “0” thitherto become equal on average. This process is referred to as “restraint of DC component” whereby a slice level variation of the DC-cut reproduction signal is suppressed.  
           [0010]    The demodulated data is de-interleaved and is subjected to an error correction. Subsequently, this data is supplied to the CD-ROM decoder  14 , and is further subjected to an error correction for the purpose of enhancing a reliability of the data. The data subjected to the error correction twice as above is temporarily stored in the buffer RAM  12  by the buffer manager  13 . When the stored data is accumulated so as to form sector data, the sector data is transferred to a host computer (not shown in the figure) at one time via the ATAPI/SCSI interface  15 . In a case of music data, the data output from the CD decoder  7  is supplied to the D/A converter  16 , and is taken out as analog audio output signal.  
           [0011]    On the other hand, upon recording data, data transmitted from the host computer via the ATAPI/SCSI interface  15  is temporarily stored in the buffer RAM  12  by the buffer manager  13 . When the stored data is accumulated to a certain amount in the buffer RAM  12 , a recording operation is started. Prior to the start of the recording operation, the laser spot must be located at a start position of writing data. This position is obtained by a wobble signal engraved beforehand on the optical disk  1  by a wobbling track.  
           [0012]    The wobble signal includes absolute time information called ATIP. This information is extracted by the ATIP decoder  8 . A synchronizing signal generated by the ATIP decoder  8  is supplied to the CD encoder  10  so as to enable data to be written to an accurate position. The data stored in the buffer RAM  12  is subjected to processes of adding an error correction code and interleaving in the CD-ROM encoder  11  and the CD encoder  10 , and is recorded on the optical disk  1  via the laser controller  9  and the optical pickup  3 .  
           [0013]    Besides, EFM modulated data drives the semiconductor laser as a bit stream at a channel bit rate of 4.3218 Mbps (a normal speed). In this case, recording data constitutes an EFM frame in units of 588 channel bits. A channel clock means a clock at a frequency of the above-mentioned channel bits.  
           [0014]    [0014]FIG. 2 is a block diagram illustrating a main configuration of an information processing apparatus using the optical disk device shown in FIG. 1. As shown in FIG. 2, the configuration involves a CPU  20  of the information processing apparatus, an optical disk device  21 , an input device  22  such as a keyboard or a mouse, and a display device  23  by means of a CRT or a liquid crystal. The CPU  20  and the optical disk device  21  are connected to each other via the ATAPI/SCSI interface  15  shown in FIG. 1. According to an instruction from the input device  22 , the CPU  20  conducts a reading/writing of information from/to the optical disk  1  of the optical disk device  21 , and conducts a screen display on the display device  23  when necessary.  
           [0015]    By the way, Japanese Laid-Open Patent Application No. 6-139604 describes an example of a conventional tilt detection device which uses light-emitting diodes (LEDs) as light-emitting elements, and bipartite photodiodes (bipartite PDs) as light-receiving elements.  
           [0016]    According to such a tilt detection device, lights emitted from the LEDs are reflected on an optical disk, and are received by the bipartite PDs; a tilting of the optical disk shifts an intensity distribution of the lights on the bipartite PDs, thereby causing a difference between amounts of the lights received by the two PDs; according to the difference, the tilt of the optical disk can be detected.  
           [0017]    However, in reality, as shown in FIG. 3A, the light produced from the LED is expansive so as to be projected on a wide range on the optical disk. Since the optical disk has a micro track thereon, the light projected on the wide range undergoes a diffused reflection; accordingly, not only light undergoing a regular reflection on the optical disk, but also light reflected from the wide range, enters the PDs. When an optical pickup accesses the vicinity of an innermost periphery or an outermost periphery of the optical disk, the light expanding on the wide range does not meet on either side (still outer side from the outermost periphery, or still inner side from the innermost periphery) of the optical disk, as shown in FIG. 3B and FIG. 3C, and does not undergo a diffused reflection so as to return to the PDs.  
           [0018]    Therefore, in a case of a tilt detection device detecting a radial tilt of the optical disk, the amount of lights incident on the PD near an end portion of the optical disk reduces, thereby differentiating the amounts of lights incident on the two bipartite PDs so as to cause an offset therebetween, without an actual tilting of the optical disk; thus, an accurate tilt detection is inhibited. Besides, in a case of a tilt detection device detecting a tangential tilt of the optical disk, amounts of lights incident on the PDs vary, thereby possibly affecting a sensitivity of the tilt detection.  
           [0019]    Further, without an accurate tilt detection, information cannot be recorded/reproduced accurately.  
         SUMMARY OF THE INVENTION  
         [0020]    It is a general object of the present invention to provide an improved and useful tilt detection device, an optical pickup and an optical disk device in which the above-mentioned problems are eliminated.  
           [0021]    A more specific object of the present invention is to provide an a tilt detection device, an optical pickup and an optical disk device which can accurately detect a tilt of an optical disk even at an innermost portion or an outermost portion of the optical disk.  
           [0022]    In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a tilt detection device including a light-emitting element emitting a light, a plurality of light-receiving elements receiving the light reflected from an optical disk, and a light-shielding member provided between the optical disk and at least one of the light-emitting element and the light-receiving elements so as to shield parts of the light emitted from the light-emitting element and/or the light reflected from the optical disk, the parts being located at both sides in a radial direction of the optical disk, wherein a tilt of the optical disk is detected according to an intensity distribution of the light on the light-receiving elements.  
           [0023]    According to the present invention, the light emitted from the light-emitting element does not spread over a wide range on the optical disk in the radial direction; besides, light spread over a wide range on the optical disk in the radial direction undergoing a diffused reflection does not enter the light-receiving elements. Therefore, the tilt of the optical disk can be detected accurately even at an innermost portion or an outermost portion of the optical disk.  
           [0024]    Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 is a block diagram showing a main configuration of an optical disk device;  
         [0026]    [0026]FIG. 2 is a block diagram illustrating a main configuration of an information processing apparatus using the optical disk device shown in FIG. 1;  
         [0027]    [0027]FIG. 3A to FIG. 3C are explanatory views illustrating paths of laser light emitted from a conventional tilt detection device and paths of reflected light thereof;  
         [0028]    [0028]FIG. 4 is a block diagram illustrating a main configuration of an optical pickup;  
         [0029]    [0029]FIG. 5A is a perspective view of an optical pickup including a tilt detection device according to a first embodiment of the present invention;  
         [0030]    [0030]FIG. 5B is a front view of the optical pickup shown in FIG. 5A as viewed in a radial direction of an optical disk;  
         [0031]    [0031]FIG. 6A and FIG. 6B are diagrams illustrating an example of a radial tilt correcting part adopting a mechanism inclining the optical pickup;  
         [0032]    [0032]FIG. 7 is a perspective view of the tilt detection device according to the first embodiment of the present invention;  
         [0033]    [0033]FIG. 8 is a plan view of the tilt detection device as viewed in a direction indicated by an arrow A shown in FIG. 7;  
         [0034]    [0034]FIG. 9 is an internal structure view of the tilt detection device as viewed in a direction indicated by an arrow B shown in FIG. 7;  
         [0035]    [0035]FIG. 10 is a perspective view of a tilt detection device according to a second embodiment of the present invention;  
         [0036]    [0036]FIG. 11 is a plan view of the tilt detection device as viewed in a direction indicated by an arrow A shown in FIG. 10; and  
         [0037]    [0037]FIG. 12 is an internal structure view of the tilt detection device as viewed in a direction indicated by an arrow B shown in FIG. 10. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    A description will now be given, with reference to the drawings, of embodiments according to the present invention. Elements in the following figures that are identical or equivalent to the elements shown in FIG. 1 are referenced by the same reference marks, and will not be described in detail.  
         [0039]    [0039]FIG. 4 is a block diagram illustrating a main configuration of an optical pickup. As shown in FIG. 4, the optical pickup includes a semiconductor laser  30 , a coupling lens  31 , a beam splitter  32 , a rise mirror  33 , a quarter-wave plate  34 , an objective lens  35 , a condenser lens  36 , a light-receiving element  37 , a tracking coil  38 , and a focusing coil  39 .  
         [0040]    The light beam LB (a linearly-polarized light) emitted from the semiconductor laser  30  as a diffuse light is collimated by the coupling lens  31 , and enters the beam splitter  32 . The beam splitter  32  transmits or reflects the light through/on a laminated plane thereof according to a difference in directions of polarization of the light. Since the light beam LB incident on the beam splitter  32  is a collimated light, and oscillates in parallel with an incidence plane of the beam splitter  32 , the light beam LB is transmitted through the beam splitter  32 . The transmitted light beam LB changes direction on the rise mirror  33 , and thereafter enters the quarter-wave plate  34 . At the quarter-wave plate  34 , the linearly-polarized light is converted into a circularly-polarized light. Thereafter, the light beam LB enters the objective lens  35 . The light beam LB incident on the objective lens  35  is concentrated on a recording surface of the optical disk  1 . The light reflected from the recording surface reenters the objective lens  35  and the quarter-wave plate  34 . In this course, the circularly-polarized light is reconverted into the linearly-polarized light, which is different from the light originally entering the quarter-wave plate  34  by 90 degrees in phase so as to oscillate perpendicularly. This light is reflected by the beam splitter  32  in a direction perpendicular to the incidence direction. Subsequently, the light is concentrated by the condenser lens  36 , and thereafter is received by the light-receiving element  37 . Then, an amount of the light received by the light-receiving element  37  is converted into an electric signal, thereby reproducing information recorded on the optical disk  1 . Besides, the light-receiving element  37  is divided, and according to an amount of the light received by each of the divided light-receiving elements, a tracking error signal and a focusing error signal are generated. Then, according to these signals, electric current is applied to the tracking coil  38  and the focusing coil  39  so as to perform a tracking servo and a focusing servo.  
         [0041]    [0041]FIG. 5A and FIG. 5B are diagrams illustrating a structure of the optical pickup including a tilt detection device according to a first embodiment of the present invention. Specifically, FIG. 5A is a perspective view of the optical pickup, and FIG. 5B is a front view of the optical pickup shown in FIG. 5A as viewed in a radial direction of the optical disk. As shown in FIG. 5A and FIG. 5B, the optical pickup  3  comprises a tilt detection device  40  and a housing  41  that is an exterior packaging of the optical pickup  3 . The optical pickup  3  includes the elements shown in FIG. 4 mounted on the housing  41 . The optical pickup  3  is supported by two parallel shafts (not shown in the figure) so as to be movable in the radial direction of the optical disk  1 . An axle bearing  41   a  is provided on one side part of the housing  41 , and a U-shaped portion  41   b  is provided on the other side part of the housing  41 . One of the two parallel shafts is inserted into the axle bearing  41   a,  and the other shaft is engaged with the U-shaped portion  41   b.  The objective lens  35  is provided outwardly on an upper surface of the housing  41 , i.e., on a surface facing the optical disk  1 .  
         [0042]    Besides, since the optical disk  1  has-a high density, the laser spot on the optical disk  1  is concentrated narrowly; therefor, a numerical aperture of the objective lens  35  is increased. With this structure, an increase in inclination of an optical axis of the objective lens  35  to the recording surface of the optical disk  1  results in a large aberration, exerting adverse influence on a recording quality and a reproducing quality of an information signal. To prevent this influence, the tilt detection device  40  detecting a tilt of the optical disk  1  is mounted on the surface of the housing  41  facing the optical disk  1 .  
         [0043]    According to the tilt detected by this tilt detection device  40 , the tilt is corrected by a tilt correcting part so that excellent recording/reproduction can be performed to the optical disk  1 . For example, a mechanism inclining the optical pickup  3 , a mechanism inclining the objective lens  35 , an optical part to correct aberration caused by the tilt within the optical pickup  3 , and so forth may be used as the tilt correcting part.  
         [0044]    [0044]FIG. 6A and FIG. 6B are diagrams illustrating an example of a radial tilt correcting part  42  adopting the mechanism inclining the optical pickup  3 . The optical pickup  3  and a driving mechanism for moving the optical pickup  3  are placed on a same base. This base is provided on the optical disk device rotatably so as to move at least up and down with respect to the radial direction of the optical disk  1 . Further, the optical disk device comprises a driving mechanism for rotating the base. The driving mechanism is controlled to rotate the base precisely according to the tilt detected by the tilt detection device  40  so as to incline the optical axis of the objective lens  35  so that an angle of the optical axis of the objective lens  35  to the surface of the optical disk  1  maintains 90 degrees. Specifically, as shown in FIG. 6A, when the optical disk  1  is bent upwards, the base is rotated upwards; as shown in FIG. 6B, when the optical disk  1  is bent downwards, the base is rotated downwards; thereby, an angle of the laser beam LB is corrected so that the laser beam LB is always projected perpendicularly to the surface of the optical disk  1 . Besides, the mechanism shown in FIG. 6A and FIG. 6B is driven especially upon performing a recording/reproduction with respect to a DVD.  
         [0045]    [0045]FIG. 7 is a perspective view of the tilt detection device  40 . FIG. 8 is a plan view of the tilt detection device  40  as viewed in a direction indicated by an arrow A shown in FIG. 7. FIG. 9 is an internal structure view of the tilt detection device  40  as viewed in a direction indicated by an arrow B shown in FIG. 7.  
         [0046]    As shown in FIG. 7, an opening  40   e  is formed in an upper surface of an exterior packaging (a light-shielding cover  40   d  mentioned hereinafter) of the tilt detection device  40 . The laser beam LB comes in and out via this opening  40   e . As shown in FIG. 8, the tilt detection device  40  includes an LED  40   a  as a light-emitting element, and a bipartite PD  40   b . The LED  40   a  and the bipartite PD  40   b  are arranged in parallel on a substrate. A division line of the bipartite PD  40   b  is perpendicular to the radial direction so that two PDs (light-receiving elements) composing the bipartite PD  40   b  are arranged in the radial direction. Accordingly, by comparing amounts of light received by the two PDs, a radial tilt of the optical disk  1  can be detected. Additionally, the LED  40   a  and the bipartite PD  40   b  are sealed by a translucent resin  40   c . The light-shielding cover  40   d  forming the exterior packaging of the tilt detection device  40  is mounted outside the translucent resin  40   c . Besides, as shown in FIG. 9, the opening  40   e  is formed in the light-shielding cover  40   d  at a part opposing the LED  40   a  and the bipartite PD  40   b . This opening  40   e  is rectangular, with two opposing sides being parallel with the radial direction and the other two opposing sides being parallel with a tangential direction of the optical disk  1 . The division line of the bipartite PD  40   b  is located at the center of the two sides parallel with the tangential direction.  
         [0047]    The light-shielding cover  40   d  is formed of a material, such as a black resin or a metal sheet, which does not transmit light emitted from the LED  40   a . In addition, the light-shielding cover  40   d  does not necessarily need to be provided as a light-shielding member; instead, a light-shielding paint, such as a black paint, may be applied on a surface of the resin  40   c  sealing the-LED  40   a  and the bipartite PD  40   b.    
         [0048]    The light emitted from the LED  40   a  is a diffuse light. As shown in FIG. 9, part of the light emitted from the LED  40   a  which does not pass through the opening  40   e  is shielded by the light-shielding cover  40   d . The light emitted from the LED  40   a  does not spread over a wide range on the optical disk  1  in the radial direction. Besides, only part of the light reflected from the optical disk  1  which passes through the opening  40   e  enters the bipartite PD  40   b , and light undergoing a diffused reflection on a wide range of the optical disk  1  is shielded by the light-shielding cover  40   d.    
         [0049]    According to the above-described structure, even when the optical pickup  3  is moved in the radial direction of the optical disk l so that the tilt detection device  40  is located in the vicinity of an outer end or an inner portion without a track and a reflective surface, of the optical disk  1 , the amounts of light incident on the bipartite PD  40   b  are not differentiated so as to cause an offset therebetween; thus, the radial tilt can be detected accurately. Besides, the accurate detection of the tilt improves the precision of the tilt correction, thereby enabling information to be recorded/reproduced accurately to/from the optical disk.  
         [0050]    Besides, in the above-described first embodiment, the opening  40   e  has the form of a rectangle. However, the form of the opening  40   e  is not limited to the rectangle, and may be other form that restricts the opening in the radial direction; for example, lines at the edges of the opening on both sides of the LED  40   a  in the radial direction do not need to be parallel with the tangential direction, but may be curves, such as circular arcs. At this point, for the purpose of causing the reflected light to stably enter the two PDs composing the bipartite PD  40   b , the two lines at the edges of the opening are preferred to be symmetrical about the division line of the bipartite PD  40   b.    
         [0051]    Further, the two sides parallel with the radial direction are not necessary in the opening  40   e , and the shielding of light may be realized by separately fixing light-shielding covers divided in the radial direction by bonding and so forth.  
         [0052]    [0052]FIG. 10 is a perspective view of a tilt detection device  50  according to a second embodiment of the present invention. FIG. 11 is a plan view of the tilt detection device  50  as viewed in a direction indicated by an arrow A shown in FIG. 10. FIG. 12 is an internal structure view of the tilt detection device  50  as viewed in a direction indicated by an arrow B shown in FIG. 10.  
         [0053]    As shown in FIG. 10, an opening  50   e  is formed in an upper surface of an exterior packaging (a light-shielding cover  50   d  mentioned hereinafter) of the tilt detection device  50 . The laser beam LB comes in and out via this opening  50   e . As shown in FIG. 11, the tilt detection device  50  includes an LED  50   a  as a light-emitting element, and a bipartite PD  50   b . The LED  50   a  and the bipartite PD  50   b  are arranged in parallel on a substrate. A division line of the bipartite PD  50   b  is perpendicular to the tangential direction so that two PDs (light-receiving elements) composing the bipartite PD  50   b  are arranged in the tangential direction. Accordingly, by comparing amounts of light received by the two PDs, a tangential tilt of the optical disk  1  can be detected. Additionally, the LED  50   a  and the bipartite PD  50   b  are sealed by a translucent resin  50   c . The light-shielding cover  50   d  forming the exterior packaging of the tilt detection device  50  is mounted outside the translucent resin  50   c . Besides, as shown in FIG. 12, the opening  50   e  is formed in the light-shielding cover  50   d  at a part opposing the LED  50   a  and the bipartite PD  50   b . This opening  50   e  is rectangular, with two opposing sides being parallel with the radial direction and the other two opposing sides being parallel with the tangential direction. The division line of the bipartite PD  50   b  is located at the center of the two sides parallel with the radial direction.  
         [0054]    The light-shielding cover  50   d  is formed of the same material as the light-shielding cover  40   d  shown in FIG. 9. Besides, as in the first embodiment, a light-shielding paint, such as a black paint, may be applied on a surface of the resin  50   c.    
         [0055]    Light emitted from the LED  50   a  is a diffuse light. As shown in FIG. 12, part of the light emitted from the LED  50   a  which does not pass through the opening  50   e  is shielded by the light-shielding cover  50   d . The light emitted from the LED  50   a  does not spread over a wide range on the optical disk  1  in the radial direction. Besides, only part of the light reflected from the optical disk  1  which passes through the opening  50   e  enters the bipartite PD  50   b , and light undergoing a diffused reflection on a wide range of the optical disk  1  is shielded by the light-shielding cover  50   d.    
         [0056]    According to the above-described structure, even when the optical pickup  3  is moved in the radial direction of the optical disk  1  so that the tilt detection device  40  is located in the vicinity of an outer end or an inner portion without a track and a reflective surface, of the optical disk  1 , a sum of the amounts of light incident on the bipartite PD  40   b  does not vary. Therefore, the sensitivity of the tilt detection does not fluctuate; thus, the tilt can be detected accurately.  
         [0057]    Besides, also in the above-described second embodiment, the opening  50   e  has the form of a rectangle. However, the form of the opening  50   e  is not limited to the rectangle, and may be other form that restricts the opening in the radial direction; for example, the lines at the edges of the opening may be curves, such as circular arcs. At this point, for the purpose of causing the reflected light to stably enter the two PDs composing the bipartite PD  50   b , the form of the opening is preferred to be symmetrical about the division line of the bipartite PD  50   b.    
         [0058]    The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.  
         [0059]    The present application is based on Japanese priority application No. 2002-115818 filed on Apr. 18, 2002, the entire contents of which are hereby incorporated by reference.