Abstract:
An optical disk device is provided which can realize size and cost reduction and which includes: an optical pick-up; a drive source; a drive member for moving the optical pick-up by utilization of a drive force generated by the drive source; and a striking member for striking against the drive member, wherein abutment between the striking member and the drive member results in loss of synchronism of the drive source and a predetermined position of the drive member is determined. An optical component for use in the optical disk device is also provided.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical disk device using, for example, CD, DVD, MD, or Blu-ray Disc, and an optical component used in such a device.  
         [0003]     2. Related Background Art  
         [0004]     In recent years, in the field of an optical disk device, in order to attain a higher density, study of technology for decrease of wavelength of a light source and for increase of NA of an objective lens has been extensively conducted.  
         [0005]     Further, in some fields, a device using a 405 nm semiconductor laser and an objective lens of NA=0.85 has begun to be commercially manufactured.  
         [0006]     In a case where a short wavelength light source and an objective lens of a high NA are used, there remain the following basic problems. 
    (1) Being susceptible to tilt of disk     (2) Being susceptible to thickness error of transparent substrate     (3) Being susceptible to wavelength hop of light source    
 
         [0010]     Of the above problems, the problem (1) has been solved by using a transparent substrate of a small thickness. For example, a transparent substrate of about 100 μm thickness is used.  
         [0011]     The problems (2) and (3) are attempted to be solved by appropriately designing an optical system.  
         [0012]     For example, the problem (3) derived from a wavelength hop of a light source is attempted to be solved by additionally providing a chromatic aberration correcting lens which generates a chromatic aberration to cancel a chromatic aberration generated in an objective lens.  
         [0013]     With respect to the problem (2), various techniques have been considered which include, for example, (a) a technique in which a spherical aberration generated when an error generates in the thickness of a transparent substrate is cancelled by additionally providing a beam expander and changing a lens spacing to generate a spherical aberration, and (b) a technique in which a position of a collimator lens is changed in an optical axis direction to generate a spherical aberration, thereby canceling a spherical aberration derived from a thickness error of a transparent substrate.  
         [0014]     Such techniques are disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-236252.  
         [0015]     To briefly describe, in the case where a beam expander is used, as shown in  FIG. 11A , in a parallel light flux at an incidence side of an objective lens  45 , there is provided an expander  43  consisting of a lens  41  having negative power and a lens  42  having positive power, and the distance between the lens  41  and the lens  42  is changed depending on a thickness error of a transparent substrate to generate a spherical aberration.  
         [0016]     Further, in the case where the position of a collimator lens is changed, with a system as shown in  FIG. 11B , a collimator lens  44  is moved depending on a thickness error of a transparent substrate along an optical axis to generate a spherical aberration.  
         [0017]     Further, in order to realize such a movable optical system, it is necessary to accurately set a reference position of an optical component in connection with other components.  
         [0018]     Hence, in general, as means for detecting a reference position, an output signal of a position detecting means of a drive member such as a sensor is used.  
         [0019]     Such a technique is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-131113.  
         [0020]     A brief description will be made with reference to  FIG. 1  (shown in  FIG. 12  of the attached drawings) and  FIG. 5  (shown in  FIG. 13  of the attached drawings) of Japanese Patent Application Laid-Open No. 2003-131113 above.  
         [0021]     A spherical aberration correcting device  10  is consisting of a holder  11  that holds a convex lens  12  and a holder  13  that holds a concave lens  14 , and the holder  11  of the convex lens  12  is fixed to an unillustrated OP base of the device.  
         [0022]     The holder  13  of the concave lens  14  is fixed to a holder driving rack  15 , which has a light-shielding member  16  reciprocatable in a predetermined direction fixed thereto, and the other end portion of which is engaged with a lead screw  19  that is a rotation shaft of a stepping motor  17 .  
         [0023]     With the rotation of the stepping motor  17 , and by the engagement with the lead screw  19 , the holder driving rack  15  reciprocates in a direction shown by an arrow d, and in order to accurately perform the reciprocation in the direction d, a guide shaft  20  is provided.  
         [0024]     The light-shielding member  16  forms a light-shielding body  16   a  which can move in and out of a photosensor  30 , and a top end portion of which is located within a U-shaped package of the photosensor  30 .  
         [0025]     Further, both end portions of the lead screw  19  are rotatably borne by an angle  18 .  
         [0026]     The angle  18  is fixed to the unillustrated OP base.  
         [0027]     In one wall of the package  31  is mounted a light emitting member  33 , and in the other wall is mounted a light receiving member  34 .  
         [0028]     Further, the lower surface of the package  31  is integrally formed with pin portions  32  (each with a screw formed at a lower end thereof) to be inserted into long holes formed in the unillustrated OP base, and is constituted so as to be fixed to the OP base at a location where the reference position is adjusted.  
         [0029]     With the above described configuration, an output of the photosensor  30  is detected, and the reference position of the concave lens  14  is determined.  
         [0030]     In this configuration, an output in a state in which the light shielding body  16   a  completely shields the light receiving portion is defined as 0, and a position corresponding to L 2 ′, which is a half of an output L 2  when the light-shielding body  16   a  completely moves out of the light receiving portion, is defined as a reference position.  
         [0031]     Further, also in the conventional optical disk device, a position detecting means has been provided.  
         [0032]     Detailed description will be made below with reference to  FIG. 14 .  
         [0033]     An optical disk device  51  is composed of a chassis  52  as a structural base; a spindle motor  53  provided in the chassis  52 , for mounting and rotating a disk (not shown); an optical pick-up  54 ; an objective lens  55  provided in the optical pick-up  54 , for irradiating a light beam; a feed motor  56  (a stepping motor) provided in the chassis  52  and having a lead screw  58  for moving the optical pick-up  54  in a radial direction of the disk; and a guide shaft  57  for support the optical pick-up  54 .  
         [0034]     Thus, the disk rotated by the spindle motor  53  is irradiated with an optical beam from the objective lens  55  of the optical pick-up  54 .  
         [0035]     Further, the lead screw  58  integrally formed with a rotation shaft of the feed motor  56  and the optical pick-up  54  mesh with each other through an unillustrated rack, and by converting the rotational motion of the lead screw  58  to translational motion, the optical pick  54  moves in a radial direction of the disk with the guide shaft  57  being used as a guide.  
         [0036]     Thus, the optical disk device  51  records or reproduces an information on or from the disk.  
         [0037]     Further, at a portion of the chassis  52  on a disk outermost periphery side, there is provided a position detecting sensor  59  of contact-type, and the optical pick-up  54  moves to the disk outermost periphery side to abut against the position detecting sensor  59 , thereby performing the reference position detection.  
         [0038]     In this case, in addition to a required movable range (a movable range in which the objective lens  55  can access from an innermost periphery to an outermost periphery of the disk in the case of this prior art example), an overrun amount until when detected by the position detecting sensor  59  is required.  
         [0039]     Incidentally, although in the above-mentioned prior art example, the position detecting sensor  59  is provided at the outermost periphery portion, it may be provided at an innermost periphery portion.  
         [0040]     Further, in the above-mentioned optical disk device, the reference position detected by the position detecting sensor  59  is utilized as a home position in OFF state of a power supply of the optical disk device.  
         [0041]     For example, in a case of a disk medium so preformatted as to always access the innermost periphery of the disk at the time of activation, by locating the optical pick-up at a reference position at a disk innermost periphery side, the time required for transporting the optical pick-up after the power supply has been turned on is shortened.  
         [0042]     The operation of the optical pick-up  54  in OFF state of the power supply in this case will be described in detail with reference to  FIG. 15 .  
         [0043]     When an operator turns off the power supply switch, the optical pick-up  54  moves toward the position detecting sensor  59  (toward the outer periphery of the disk in this prior art example).  
         [0044]     After that, the optical pick  54  is detected by abutting against the position detecting sensor  59 , and by this detection signal, the optical pick-up  54  stops moving, and then the power supply of the device body is turned off.  
         [0045]     Further, examples of other applications than the above described include reference position detection for prevention of collision of an optical pick-up against a chassis body or spindle motor.  
         [0046]     As described in detail above, in a driving mechanism of the conventional optical component or product mounted with an optical component such as an optical disk device, any position detecting means is generally used.  
         [0047]     In recent years, for such optical component or product mounted with an optical component such as an optical disk device, size and cost reduction of the device have been required.  
         [0048]     However, when the above described position detecting sensor as position detecting means is used, there are posed the problems such as device size increase for providing disposition space thereof and cost increase due to increase of the number of parts.  
         [0049]     For example, when a position detecting sensor is used, and when an approximate center position of a movable range is set as a reference position as with the technique disclosed in Japanese Patent Application Laid-Open No. 2003-131113, a light-shielding member (light-shielding body  16   a ) of the position detecting sensor requires a length more than half the movable range because of its structure, thereby contributing to increase of the device size.  
         [0050]     Further, as also disclosed in Japanese Patent Application Laid-Open No. 2003-131113, in order to determine a reference position, it is firstly necessary to adjust an original position of a photosensor at a manufacturing factory, which contributes to cost increase.  
         [0051]     Incidentally, in the case of the structure in which position detection is performed by a position detecting sensor of contact-type at an end portion of a movable range, it is easy to obtain position precision of the sensor as compared to a non-contact-type sensor.  
         [0052]     This is because it is easy to determine the position in accordance with a part position, such as abutment through striking of a detected part against a detection means or the like and further because detection through contact makes it difficult to be affected by a temperature change.  
         [0053]     However, there will be an amount of overrun that the optical pick-up will make before the reference position is detected, at an end portion of the movable range, which contributes to increase of the device size.  
         [0054]     This overrun amount is necessary to surely secure the movable range in consideration of a tolerance and the like, and is determined by adding to a tolerance of parts to determine the movable range, a detection tolerance of the sensor, a stopping distance required from detection to actual stopping, and a margin.  
         [0055]     Further, in the case of the position detecting sensor of contact-type, there is mentioned the problem of shock (or impact) and vibration at the time of contact.  
         [0056]     Particularly, in an optical disk device of the recent years that performs high-density recording/reproducing, extremely high precision is required for optical components constituting the device.  
         [0057]     Under such circumstances, avoidance of the disturbance such as shock, vibration and the like which may contribute to an error has been required.  
       SUMMARY OF THE INVENTION  
       [0058]     It is, therefore, an object of the present invention to provide an optical disk device and an optical component used in the device that can realize size and cost reduction of the device.  
         [0059]     To achieve the above object, according to one aspect of the present invention, there is provided an optical disk device comprising:  
         [0060]     an optical pick-up;  
         [0061]     a drive source;  
         [0062]     a drive member for moving the optical pick-up by utilization of a drive force generated by the drive source; and  
         [0063]     a striking member for striking against the drive member,  
         [0064]     wherein abutment between the striking member and the drive member results in loss of synchronism of the drive source and a predetermined position of the drive member is determined.  
         [0065]     According to another aspect of the present invention, there is provided an optical component for use in an optical disk device comprising:  
         [0066]     a drive source;  
         [0067]     a drive member for moving an optical component by utilization of a drive force of the drive source; and  
         [0068]     a striking member for striking against the drive member,  
         [0069]     wherein abutment of the striking member and the drive member results in loss of synchronism of the drive source and a predetermined position of the drive member is determined. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0070]      FIG. 1  is a block diagram showing an optical system of an optical pick-up device in accordance with the present invention;  
         [0071]      FIG. 2  is a graphical representation showing a relation between a thickness error of a transparent substrate and a distance between lens groups to correct the error in a case where a first lens group is moved;  
         [0072]      FIG. 3  is a graphical representation showing a relation between a thickness error of a transparent substrate and a distance between lens groups to correct the error in a case where a second lens group is moved;  
         [0073]      FIGS. 4A, 4B , and  4 C are schematic perspective views showing a spherical aberration correcting mechanism in accordance with the present invention;  
         [0074]      FIG. 5A  is a schematic perspective view showing a first support member and a second support member shown in  FIGS. 4A, 4B , and  4 C, and  FIG. 5B  is a cross-sectional view taken along line  5 B- 5 B of  FIG. 5A ;  
         [0075]      FIG. 6A  is a schematic perspective view showing structures of a stepping motor  25  and a nut member  21  shown in  FIGS. 4A, 4B , and  4 C, and  FIG. 6B  is a cross-sectional view taken along line  6 B- 6 B of  FIG. 6A ;  
         [0076]      FIG. 7  is a schematic diagram showing driving parameters of a first embodiment;  
         [0077]      FIGS. 8A and 8B  are schematic diagrams showing the effect of size reduction of a device in accordance with the first embodiment;  
         [0078]      FIGS. 9A, 9B , and  9 C are views of an optical disk device of a second embodiment;  
         [0079]      FIG. 10  is a flowchart showing the operation of an optical pick-up in OFF state of a power supply of the second embodiment;  
         [0080]      FIGS. 11A and 11B  are diagrams showing an outline of a first prior art example;  
         [0081]      FIG. 12  is a view showing an outline of the first prior art example;  
         [0082]      FIG. 13  is a graphical representation showing an outline of the first conventional example;  
         [0083]      FIG. 14  is a view showing an optical disk device of a second prior art example; and  
         [0084]      FIG. 15  is a flowchart showing the operation of an optical pick-up in OFF state of a power supply of the second prior art example. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0085]     Preferred embodiments of the present invention will be described below with reference to the drawings.  
       First Embodiment  
       [0086]     A first embodiment of the present invention will be shown below. The first embodiment shows a case where the present invention is applied to a spherical aberration correcting mechanism of an optical pick-up.  
         [0087]      FIG. 1  is a schematic diagram of an optical system of an optical pick-up device in accordance with the present embodiment.  
         [0088]     A beam emitted from a semiconductor laser  1  is split into a main beam and two subbeams by a diffraction grating  2 .  
         [0089]     The subbeams are used for generation of a servo signal for DPP (differential push-pull) detection.  
         [0090]     The beams from the diffraction grating are partially reflected by a PBS  3  and converged into a monitor PD  5  by a condenser lens  4 .  
         [0091]     An output of the monitor PD is used for controlling the emission power of the semiconductor laser  1 .  
         [0092]     The beams transmitted through the PBS  3  is made parallel light flux by a collimator lens  13  as a lens unit through a λ/4 plate  6 , and forms an image on an information recording surface by an objective lens  14  through a transparent substrate.  
         [0093]     Here, the optical disk  15  is formed of the transparent substrate and the information recording surface.  
         [0094]     The beams reflected by the optical disk  15  is converged by the objective lens  14 , and is reflected by the PBS  3  through the collimator lens  13  and the λ/4 plate  6 , and is then converged onto a RF servo PD  17  by a sensor lens  16 .  
         [0095]     By an output from the RF servo PD  17 , an information signal and a servo signal are obtained.  
         [0096]     Here, the wavelength of the semiconductor laser  1  is approximately 407 nm at the time of information reproduction, and the NA and focal length of the objective lens  14  are 0.85 and 1.1765 mm, respectively.  
         [0097]     Designed values of a projection system of the present embodiment are shown in Table 1.  
         [0098]     In Table 1, N (407) represents a refractive index at a wavelength of 407 nm, ΔN represents a change in refractive index when the wavelength is increased by 1 nm and corresponds to the dispersion in the vicinity of the wavelength of 407 nm.  
         [0099]     The aspherical shape is represented by Equation 1:  
       X   =           h   2     /   r       1   +       1   -       (     1   +   k     )     ⁢       h   2     /     r   2                 +     Bh   4     +     Ch   6     +     Dh   8     +     Eh   10     +     Fh   12     +     Gh   14           
 
         [0100]     wherein X is a distance in the optical axis direction; h is a height in a direction perpendicular to the optical axis; and k is a conical coefficient, and is shown in Table 2.  
                                                                 TABLE 1                                   Remarks   r   d   N(407)   ΔN                                    1   LD   ∞   0.78               2       ∞   0.25   1.52947   −0.00008       3       ∞   1.19       4   Diffraction   ∞   1   1.52947   −0.00008       5   grating   ∞   1.6       6   PBS   ∞   2.6   1.72840   −0.00042       7   λ/4 plate   ∞   1.15   1.56020   −0.00020       8       ∞   1.46       9   Collimator   ∞   1.29   1.58345   −0.00014       10       −2.28   0.71   1.80480   −0.00053       11       ∞   0.8       12       13.49   0.74   1.80480   −0.00053       13       4.967   1.26   1.58345   −0.00014       14       −4.411   6.5       15   Objective   0.89427   1.57   1.70930   −0.00021       (Aspherical   lens       lens 1)       16       −3.38795   0.27       (Aspherical       lens 2)       17   Transparent   ∞   0.08   1.62068   −0.00038       18   substrate   ∞   0                  
 
         [0101]    
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
               
               
                 Aspherical 
                 Aspherical 
                 Aspherical 
               
               
                 coefficient 
                 lens 1 
                 lens 2 
               
               
                   
               
             
             
               
                 k 
                 −4.71569E−01 
                 −8.03122E+02 
               
               
                 B 
                  1.85624E−02 
                  6.93685E−01 
               
               
                 C 
                 −3.32437E−03 
                 −7.23881E−01 
               
               
                 D 
                  2.00843E−02 
                 −1.08028E+01 
               
               
                 E 
                 −2.46799E−02 
                  5.02375E+01 
               
               
                 F 
                  3.71610E−02 
                 −6.88792E+01 
               
               
                 G 
                 −2.00730E−02 
                  0 
               
               
                   
               
             
          
         
       
     
         [0102]     As can be seen from Table 1, the collimator lens  13  is composed of the spherical lenses only, and is an optical element which can easily be produced and is inexpensive.  
         [0103]     Here, a case where a thickness error is generated in the transparent substrate of the optical disk  15  will be described.  
         [0104]     In a case where a thickness error is generated in the transparent substrate, a spherical aberration is generated as well known. Especially when a short-wavelength light source and a high-NA objective lens are used, the influence of the spherical aberration is great.  
         [0105]     Therefore, in the optical system of the present embodiment, by changing a distance between a first lens group  11  constituted by a lens  7  and a lens  8  of the collimator lens  13 , which is a lens unit, and a second lens group  12  constituted by a lens  9  and a lens  10 , the generated spherical aberration is corrected.  
         [0106]     In each of  FIGS. 2 and 3  is shown a relation between the thickness error of the transparent substrate and the distance between the lens groups to correct the error.  
         [0107]      FIG. 2  shows a case where the first lens group  11  is moved with the second lens group  12  being fixed.  
         [0108]     The moving amount per 1 μm of the transparent substrate thickness error is approximately 28 μm.  
         [0109]     Further,  FIG. 3  shows a case where the second lens group  12  is moved. In this case, the moving amount per 1 μm of the transparent substrate thickness error is approximately 20 μm.  
         [0110]      FIGS. 4A, 4B , and  4 C are schematic views of a spherical aberration correcting mechanism in accordance with the present invention.  
         [0111]     Specifically,  FIG. 4A  is a schematic perspective view,  FIG. 4B  shows a state in which a drive member and a driven member to be described later are in contact with each other, and  FIG. 4C  shows a state in which the drive member and the driven member are not in contact.  
         [0112]      FIG. 5A  is a perspective view showing a first support member  18  and a second support member  19  to be described later, and in  FIG. 5B  is a cross-sectional view taken along line  5 B to  5 B of  FIG. 5A .  
         [0113]     Further,  FIG. 6A  is a schematic perspective view showing the structure of a stepping motor  25  and a nut member  21  to be described later, and  FIG. 6B  is a cross-sectional view taken along line  6 B to  6 B of  FIG. 6A .  
         [0114]     Reference numeral  18  denotes a first support member to support the first lens group  11 , and reference numeral  19  denotes a second support member to support the second lens group  12 , and each lens group is fixed to each support member.  
         [0115]     Incidentally, in the present embodiment, the first lens group  11  is a fixed lens group while the second lens group  12  is a movable lens group, and the first support member  18  for supporting the fixed lens group is adhered and fixed to an optical base  24  (only a portion necessary to describe the present embodiment is illustrated in the figures).  
         [0116]     In the present embodiment, each support member has a substantially cylindrical shape which is coaxial with the corresponding lens group, and the second support member  19  is slidably inserted into the first support member  18 .  
         [0117]     Further, a protruding portion  20  is integrally provided at a part of the second support member  19 , and a nut member  21  is abutted against an end face  20   a  of the protruding portion  20 .  
         [0118]     On the other hand, a coil spring  22  is abutted against an end face  20   b  opposing to the end face  20   a , and the coil spring  22  is provided while being urged between the end face  20   b  and a coil receiving portion  24   a  of the optical base.  
         [0119]     Further, reference numeral  25  denotes a stepping motor which is a drive source, and a lead screw  26  is integrally formed with a rotation shaft of the stepping motor  25 .  
         [0120]     Reference numeral  27  denotes an angle member fixed to the stepping motor  25 , and a bearing part  28  of the lead screw  26  is provided.  
         [0121]     As shown in  FIGS. 6A and 6B , the lead screw  26  is engaged with the nut member  21 , and by the abutment of an end face  27   a  of the angle member  27  against an abutting portion  21   a  of the nut member  21 , the nut member  21  is slidable without being rotated in the direction of the rotation axis of the lead screw  26 .  
         [0122]     Incidentally, in the present invention, the stepping motor  25  is regarded as a drive source, the nut member  21  as a drive member, and the second support member  19  as a driven member.  
         [0123]     Next, the operation will be described in detail.  
         [0124]     In a case where the drive member and the driven member are in contact with each other as shown in FIG.  4 B, the second support member  19 , which is the driven member, is held by the nut member  21 , which is the drive member, and by the urging force of the coil spring  22 , thereby adjusting the lens spacing.  
         [0125]     Further, by moving the nut member  21  in a direction shown by an arrow D, the second support member  19  is similarly moved in the direction of the arrow D by the urging force of the coil spring  22 .  
         [0126]     Thereby, firstly, an end face  19   a  of the second support member  19  abuts against a stopper portion  24   b  of the optical base.  
         [0127]     After that, by moving the nut member  21  further in the direction of the arrow D, the drive member and the driven member are brought into a non-contact state.  
         [0128]     Further, as shown in  FIG. 4C , by moving the nut member  21  further in the direction of the arrow D, the nut member  21  abuts against the stopper portion  24   b  of the optical base  24 , and this abutting position is defined as a reference position in accordance with the present invention.  
         [0129]      FIG. 7  shows driving parameters of the drive member.  
         [0130]     In the figure, 0 denotes a reference position; E 1  and E 2  denote end points of a movable range (E 1  being more apart from the point O); T denotes the distance between E 1  and E 2  in which the drive member and the driven member are in contact state; and R denotes the distance between O to E 2  in which the drive member and the driven member are in non-contact state.  
         [0131]     Thus, a distance S of the movement from the most distant point E 1  of the movable range to the reference position can be represented by S=T+R.  
         [0132]     Here, when the nut member  21  is located at the most distant point E 1  of the movable range, an input is given in such a manner as to move the nut member  21  by the distance represented by S+arbitrary movable amount α=S 1 .  
         [0133]     In this manner, when pulses of a number which can perform movement by the distance S 1 =S+α, is inputted into the stepping motor, the nut member  21 , independently of its location between the reference position O and the end point E 1  of the movable range, abuts against the stopper portion  24   b , and the stepping motor  25  loses synchronism, so that the nut member  21  inevitably stops moving at the reference position O.  
         [0134]     After that, by applying input pulses of a number corresponding to the distance to the target point, the nut member  21  is moved to the target position, so that the position adjustment of the second support member  19  as the driven member (i.e., adjustment of lens spacing) is performed.  
         [0135]     Incidentally, the adjustment method of the lens position is the same as described for the prior art example. Specifically, after the reference position has been determined, the nut member is moved to, for example, the center position of the movable range, and an arithmetic operation for spherical aberration correction is performed by an unillustrated control device, and the stepping motor  25  is driven again, and then, the nut member is stopped moving at a position where the spherical aberration is corrected.  
         [0136]     At this time, the distance to the center position of the movable range taken as the target value may be determined from, for example, the designed value and the like, and the parameters of the adjustment result after the adjustment has been made once based on the designed value may be also used.  
         [0137]     Of course, when abutted against the reference position, since the drive member and the driven member are in non-contact state, avoidance of shock and vibration to the optical parts such as lens or the like due to the loss of synchronism is also realized.  
         [0138]     Further, the effect of size reduction by the present invention will be described below with reference to  FIGS. 8A and 8B .  
         [0139]      FIGS. 8A and 8B  are views each showing a part of an optical system to explain the effect of the size reduction, and  FIG. 8A  shows a prior art example while  FIG. 8B  shows the present embodiment.  
         [0140]     For clarity, the same numerals are employed in the figures as are employed in  FIG. 1  for equivalent parts, and reference numeral  29  denotes a deflection mirror to irradiate a disk surface perpendicularly with a beam.  
         [0141]     In  FIGS. 8A and 8B , the driven member is the second lens group  12 .  
         [0142]     In the figures, reference character c denotes a movable range necessary for the driven member, and reference character h denotes an overrun amount required for the detection by a position detecting means (not shown) such as a sensor of the prior art example as described above, and it is assumed that also in the embodiment shown in  FIG. 8B , movement of the same distance as above is performed until the loss of synchronism.  
         [0143]     However, it is possible to perform size reduction at least by an amount corresponding to the stopping distance required from detection by the detection means to stopping.  
         [0144]     Further, reference character m denotes a motion range of the driven member calculated by c+h, reference character β 1  denotes the length of an optical path formed by optical elements fixed to the optical base between the semiconductor laser  1  and the first lens group  11 , reference numeral β 2  denotes the length of an optical path formed by the deflection mirror  29  fixed to the optical base between the second lens group  12  and the objective lens  14 , and reference character L denotes the entire optical path length calculated by m+B 1 +B 2 .  
         [0145]     Here, the reason why the attention is paid to the entire optical path length is that in a unit mounted with an optical element such as an optical pick-up, the optical path length of the optical element group becomes a parameter to determine the size of the device.  
         [0146]     Thus, in the prior art example, at least a length L determined by adding the motion range m of the driven member to B 1 +B 2  is required.  
         [0147]     In contrast to this, in the present embodiment, since it is possible to perform the movement with the drive member being in non-contact with the driven member, the overrun mount can be disposed, for example, within the range of β 2  (c corresponding to T in  FIG. 7  and h corresponding to R in  FIG. 7 ).  
         [0148]     Hence, the motion range m′ of the driven member (the second lens group  12 ) remains to be the required movable range c, and the entire optical path length L′ of the present embodiment can be reduced by the overrun amount h than the prior art example, so that the size reduction of the device can be realized.  
         [0149]     Of course, when compared to the prior art example, since a sensor becomes unnecessary, size and cost reduction of the device just by the space required for the provision of a sensor can be realized.  
         [0150]     Incidentally, in the embodiment shown in  FIGS. 4A  to  4 C, the overrun amount h is disposed at a position which is offset in the radial direction of the disk with respect to the optical axis, thereby obtaining the effect of the present invention.  
       Second Embodiment  
       [0151]     A second embodiment of the present invention will be described below. The second embodiment shows a case where the present invention is applied to an optical pick-up moving mechanism of an optical disk device.  
         [0152]      FIGS. 9A, 9B , and  9 C are schematic views each showing an optical disk device, and  FIG. 9A  shows the present embodiment,  FIG. 9B  shows a conventional example in which a position detecting sensor  59  to be described later is provided on a disk inner periphery side, and  FIG. 9C  shows a conventional example in which a position detecting sensor  59  is provided on a disk outer periphery side.  
         [0153]     The basic structure of the present optical disk device is the same as the prior art example shown in  FIG. 14 , and like numerals denote like parts.  
         [0154]     In  FIGS. 9A, 9B , and  9 C, a two-dot chain line shows a disk-shaped recording medium in which an information is recorded/reproduced.  
         [0155]     Further, reference numeral  60  denotes a nut member which is a drive member, reference numeral  61  denotes a stopper portion of an optical pick-up  54  integrally formed with a chassis  52 , reference numeral  62  denotes a coil spring to press the optical pick-up  54  to the nut member  60 , and reference numeral  63  denotes a nut abutting portion integrally formed with the chassis  52 .  
         [0156]     Further, the nut member  60  is formed with a rotation stopper by an unillustrated method, and is constituted to be movable in the radial direction of the disk by the rotation of a feed motor  56  which is a drive source.  
         [0157]     Moreover, the optical pick-up  54  corresponds to the driven member in accordance with the present invention, and is constituted to be slidable relative to each of a guide shaft  57  and a lead screw  58 .  
         [0158]     In the present embodiment, the coil spring  62  is provided so as to contain the lead screw  58  therein such that one end thereof urges a side surface of the optical pick-up  54  and the other end abuts against an end face of the unillustrated chassis  52 .  
         [0159]     Reference character c in the figures denotes a distance by which the objective lens  55  is moved by a feed motor  56  in order to access from the innermost periphery to the outermost periphery of the disk, and reference character h denotes an overrun amount.  
         [0160]     Incidentally, in the present embodiment, the overrun amount is taken as h similarly to the above described prior art example, and in  FIG. 9A , it is shown as a moving distance of a surface abutting against the optical pick  54  of the nut member  60 .  
         [0161]     The driving parameters of the drive member of the present embodiment are the same as the first embodiment, and the description thereof will be therefore omitted.  
         [0162]     That is, the reference position O in  FIG. 7  described in the first embodiment corresponds to a state in which the nut member  60  abuts against the nut abutting portion  63 , and the distance R in non-contact state corresponds to h in the figures, and the distance T in contact state corresponds to c in the figures.  
         [0163]     Next, the moving operation of the optical pick-up  54  to the reference position in OFF state of the power supply will be described with reference to  FIG. 10 .  
         [0164]     In a case where the power supply switch is turned off by an operator, the feed motor  56 , which is a stepping motor, is rotated in such a direction as to allow the optical pick-up  54  to approach the reference position by applying pulses of a number corresponding to the distance S′ shown in  FIG. 7 .  
         [0165]     Thereby, by the nut member  60  and the coil spring  62 , the optical pick-up  54  is moved and abuts against the stopper portion  61 , and the nut member  60  then abuts against the nut abutting portion  63  to lose synchronism.  
         [0166]     After movement by the pulses of the number corresponding to the distance S′, the feed motor  56  stops rotating, and after that, the power supply of the device body is turned off.  
         [0167]     Next, the effect of size reduction in accordance with the present invention will be described.  
         [0168]     As is seen from  FIGS. 9B and 9C , in the conventional examples, the optical pick  54  is required to move by the distance m 1  (=c 1 +h) or m 2  (=c 2 +h) obtained by adding the overrun amount h to the access movement distance c from the innermost periphery to the outermost periphery of the optical pick-up  54 .  
         [0169]     Here, as shown in  FIG. 9B , in a case where the position detecting sensor  59  is provided at the inner periphery side, there is required a device structure in which the optical pick-up  54  is further movable to the disk inner periphery side by the overrun amount h.  
         [0170]     However, with such a structure, since the optical pick-up  54  and the spindle motor  53  interfere with each other, there arises a problem that the recording region on the disk inner peripheral side is reduced by the overrun amount h.  
         [0171]     That is, as shown in  FIG. 9B , although the moving amount m 1  of the optical pick-up  54  can be constituted so as to be the same as the moving amount m′ of the present embodiment shown in  FIG. 9A , in that case, there arises a problem that the access movement distance c 1  of the optical pick-up  54  (the range in which disk recording can be performed) will become c 1 &lt;c.  
         [0172]     Further, as shown in  FIG. 9C , in a case where the position detecting sensor  59  is provided on the disk outer periphery side, there can be adopted such a device structure that the access movement distance c 2  of the optical pick  54  becomes c 2 =c.  
         [0173]     However, the moving amount m 2  of the optical pick-up  54  becomes a distance including the overrun amount h.  
         [0174]     In contrast to this, in the present embodiment shown in  FIG. 9A , the moving amount m′ of the optical pick-up  54  consists of only the access movement distance c from the disk innermost periphery to the outermost periphery, so that the size reduction of the chassis  52  which contains the optical pick-up  54  is realized.  
         [0175]     Of course, as with the first embodiment, when compared to the prior art example, since a sensor becomes unnecessary, size and cost reduction of the device just by the space required for the provision of a sensor can be realized.  
         [0176]     Further, as with the first embodiment, when abutted against the reference position, since the drive member and the driven member are in non-contact state, avoidance of shock and vibration to the optical pick-up  54  due to the loss of synchronism is also realized.  
         [0177]     Incidentally, in the present embodiment, the overrun amount h is provided at a position within a region U which is approximately opposite to the region occupied by the optical pick-up  54  with respect to the spindle motor  53 .  
         [0178]     The reason is that such position is spatial room in an ordinary disk device, and therefore that it is easy to provide the arrangement of the present invention there.  
         [0179]     Further, the present invention is not limited to the above described embodiments and can also be applied to, for example, the expander mechanism shown in the prior art example.  
         [0180]     Further, although in the first embodiment, the state R of non-contact of the drive member and the driven member is formed on the side of the optical path length β 2  constituted by the deflection mirror  29 , it may be formed on the β 1  side.  
         [0181]     Further, although in the second embodiment, the overrun amount h is disposed on the disk inner periphery side, it is naturally possible to dispose it on the outer periphery side.  
         [0182]     This application claims priority from Japanese Patent Application No. 2004-348550 filed on Dec. 1, 2004, which is hereby incorporated by reference herein.