Abstract:
An actuator includes an intervention member being interposed between an object lens and a bobbin for supporting the object lens and different from the bobbin in thermal conductivity, thereby preventing an occurrence of degradation of the lens characteristic of the object lens caused by unevenness of the temperature distribution in the object lens due to the heat generated by a coil.

Description:
[0001]    The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2002-274723 filed on Sep. 20, 2002, which is incorporated herein by reference in its entirety.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an optical pickup apparatus for playing back information recorded on an optical disk.  
           [0004]    2. Description of the Related Art  
           [0005]    A pickup apparatus for playing back information recorded on an optical disk such as a CD or a DVD is known. The pickup apparatus is an apparatus for applying a laser beam of a predetermined wavelength to an optical disk through an object lens and receiving the laser beam reflected on the optical disk at a light reception element, thereby reading information written onto the optical disk.  
           [0006]    The pickup apparatus performs focusing control of controlling the distance between the information record side of the optical disk and the object lens against warpage or runout of the optical disk and also performs tracking control of the object lens relative to the eccentricity of an information track of the optical disk. Accordingly, the laser beam is applied onto any desired track and the information recorded on the optical disk is read precisely.  
           [0007]    An actuator for performing the focusing control and the tracking control has a moving section, which is made up of the object lens, a bobbin for supporting the object lens, a plurality of coils placed on the bobbin, a linear elastic member for holding the bobbin movably, and the like. A proper amount of electric current is provided into each coil. The object lens is displaced together with the bobbin in the focus or tracking direction for a minute amount by the interaction between the electric current flowing through the coil and the magnetic field formed in the proximity of the coil, and the focus control or the tracking control is performed. Generally, the actuator is optimally designed considering enhancement of sensitivity, a decrease in dynamic tilt of the lens, and suppression of unnecessary resonance.  
           [0008]    However, when a current is provided to the coil, the coil generates heat and the heat is transferred through the bobbin to the object lens. The heat transferred to the object lens makes an uneven temperature distribution in the object lens, causing the refractive index of the object lens to be varied from one point to another. Accordingly, the lens characteristic of the whole object lens (particularly, astigmatism aberration) becomes deteriorated and it becomes difficult to precisely read information on the disk. The above problem becomes noticeable particularly when a lens made of a material having physical property value that largely changes by heat (e.g. plastic), is used.  
           [0009]    The effect of occurrence of the astigmatism aberration on a detection signal from the optical disk increases as the optical disk becomes a higher density and is turned at higher speed, degrading the detection signal remarkably. Therefore, unevenness of the temperature distribution cannot be ignored to intend to provide higher density and speed of optical disk expected in the future.  
         SUMMARY OF THE INVENTION  
         [0010]    The invention was made in view of such a conventional circumference and an object of the invention is to solve a problem of degradation of the lens characteristic of an object lens caused by unevenness of the temperature distribution in the object lens.  
           [0011]    In order to achieve the object, according to a first aspect of the invention, there is provided an optical pickup apparatus including: an object lens arranged to be opposed to an optical disk; a bobbin configured to support the object lens; and an intervention member being interposed between the object lens and the bobbin and is different from the bobbin in thermal conductivity. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0013]    [0013]FIG. 1 is a perspective view to show a pickup apparatus of a first embodiment according to the invention;  
         [0014]    [0014]FIG. 2 is an enlarged perspective view of an actuator of the pickup apparatus;  
         [0015]    [0015]FIG. 3 is an exploded perspective view of the actuator of the pickup apparatus;  
         [0016]    [0016]FIG. 4 is a perspective view of an actuator moving section of the first embodiment;  
         [0017]    [0017]FIG. 5 is a sectional view of the actuator moving section of the first embodiment;  
         [0018]    [0018]FIG. 6 is a perspective view of an actuator moving section of a second embodiment according to the invention;  
         [0019]    [0019]FIG. 7 is a sectional view of the actuator moving section of the second embodiment;  
         [0020]    [0020]FIG. 8 is a perspective view of an actuator moving section of a third embodiment according to the invention;  
         [0021]    [0021]FIG. 9 is a sectional view of the actuator moving section of the third embodiment;  
         [0022]    [0022]FIG. 10 is a sectional view of an actuator moving section of a fourth embodiment according to the invention; and  
         [0023]    [0023]FIG. 11 is a sectional view of an actuator moving section of a fifth embodiment according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Referring now to the accompanying drawings, there are shown preferred embodiments of the invention.  
         [0025]    First Embodiment  
         [0026]    A pickup apparatus  1  of a first embodiment according to the invention will be discussed below with reference to the accompanying drawings.  
         [0027]    [0027]FIG. 1 is a perspective view to show the pickup apparatus  1  of the first embodiment according to the invention. The pickup apparatus  1  is placed in an optical disk unit of optical disk apparatus such as a CD player and a DVD player. The pickup apparatus  1  includes a pickup body  2  placed movably on guide shafts  3  and  3  and an actuator  6  placed fixedly on the pickup body  2 . The pickup apparatus  1  is opposed to the record side of an optical disk  5  placed on a disk placement section  4   a  that can be turned through a spindle  4 .  
         [0028]    [0028]FIG. 2 is an enlarged perspective view of the actuator  6 . FIG. 3 is an exploded perspective view of the actuator  6 . The actuator  6  has a yoke  10 , an actuator fixing section  20 , and an actuator moving section  30  that can be very little displaced relative to the yoke  10  and the actuator fixing section  20 . Attachment members  21  are fixed to sides of the actuator moving section  30 . Four longitudinal elastic members  15   a  to  15   d  are attached to attachment sections  21   a  of the attachment members  21 . The actuator moving section  30  is supported on the actuator fixing section  20  by the longitudinal elastic members  15   a  to  15   d.    
         [0029]    A pair of magnet members  11  is opposed to each other on the yoke  10  along the disk circumferential direction so as to sandwich the actuator moving section  30  between the magnet members  11 .  
         [0030]    [0030]FIG. 4 is a perspective view of the actuator moving section  30  of the embodiment. FIG. 5 is a sectional view of the actuator moving section  30 . The actuator moving section  30  includes an object lens  31 , a bobbin  32 , an intervention member  33 , a pair of tracking coils  34 , and a focus coil  35 .  
         [0031]    The bobbin  32  is a resin member having tracking coil retention sections  32   a  for winding the tracking coils therearound on opposed sides and containing a lens storing hole  32   b  shaped like a cylinder pierced up and down in the axial direction. The bobbin  32  is formed with an iris section  32   f  projected from the peripheral surface of the lens storing hole  32   b  to the radial inside. The iris section  32   f  matches the diameter of laser light incident on the object lens  31  with the effective diameter of the object lens  31 . The intervention member  33  is inserted into the top of the inner peripheral surface of the lens storing hole  32   b  and is placed on the inner peripheral surface of the lens storing hole  32   b  in an intimate contact manner.  
         [0032]    The intervention member  33  is a cylindrical-shaped member having the same shape as the inner peripheral surface of the lens storing hole  32   b . The intervention member  33  is formed at one end in the axial direction with a flange  33   a  bent to the outer diameter side. The flange  33   a  of the intervention member  33  is placed on a top face  32   c  of the bobbin  32  in an intimate contact manner. The intervention member  33  is formed at an opposite end in the axial direction with a flange  33   b  bent to the inner peripheral side. The intervention member  33  is formed of a material having higher thermal conductivity than the resin bobbin  32 . The object lens  31  is inserted into the inner peripheral side of the intervention member  33  and is fixed onto the inner peripheral surface and the flange  33   b  of the intervention member  33  in an intimate contact manner.  
         [0033]    The object lens  31  is a lens having a circular shape on the top view. It narrows down light of a predetermined wavelength emitted from a light source (not shown) positioned below the bobbin  32  and applies the light along the track formed on the information record side of the optical disk  5 . The object lens  31  allows the light reflected on the information record side of the optical disk  5  to pass through and sends the light to a light reception section having a light reception element (not shown). The object lens  31  is fixed onto the bobbin  32  through the intervention member  33  and is not in direct contact with the bobbin  32 .  
         [0034]    A pair of tracking coil retention sections  32   a  are projected from both sides of the bobbin  32  in the tracking direction. Each tracking coil retention section  32   a  is formed on a side with a tracking coil retention groove  32   d  and each tracking coil  34 ,  34  is wound along the tracking coil retention groove  32   d.    
         [0035]    The tracking coils  34  are coils for moving the actuator moving section  30  in the tracking direction. The disk circumferential components of the tracking coils  34  are opposed to the magnet members  11  placed in front and in rear. The magnetic field formed by each magnet member  11  is made almost vertical to the wiring direction of the coil.  
         [0036]    When a current is provided to the tracking coil  34 ,  34 , a force for trying to move the actuator moving section  30  in the tracking direction acts by the interaction between the magnetic field formed by each magnet member  11  and the current in the tracking coil  34 ,  34 . The force changes with the direction of the current flowing through the tracking coil  34 ,  34 . Therefore, as the direction of the current flowing through the tracking coil  34 ,  34  is changed, the actuator moving section  30  swings in the tracking direction.  
         [0037]    On the sides of the bobbin  32 , the focus coil  35  is wound in the rotation direction around the optical axis of the object lens  31 . The focus coil  35  is a coil for moving the actuator moving section  30  in the focus direction. The disk radial component of the focus coil  35  is opposed to the magnet members  11  placed in front and in rear. The magnetic field formed by each magnet member  11  is made almost vertical to the wiring direction of the coil.  
         [0038]    When a current is provided to the focus coil  35 , a force for trying to move the actuator moving section  30  in the focus direction acts by the interaction between the magnetic field formed by each magnet member  11  and the current in the focus coil  35 . The force changes with the direction of the current flowing through the focus coil  35 . Therefore, as the direction of the current flowing through the focus coil  35  is changed, the actuator moving section  30  swings in the focus direction.  
         [0039]    The tracking coils  34  and the focus coil  35  generate heat as current flows. The heat is conducted asymmetrically to the intervention member  33  in response to the position of each coil placed on the bobbin  32 . The intervention member  33  is formed of a material having higher thermal conductivity than the resin bobbin  32  and thus rapidly conducts the asymmetrically conducted heat in the circumferential direction of the intervention member  33  and conducts the heat uniformly from the perimeter of the object lens  31  to the object lens  31 . Therefore, the temperature distribution in the object lens  31  becomes almost concentric and unevenness on the concentric circumference of the temperature distribution occurring in the object lens  31  is remarkably relieved. Thus, degradation of the lens characteristic of the object lens  31  is suppressed and the detection reliability of a detection signal is enhanced.  
         [0040]    The material of the intervention member  33  may be any material having higher thermal conductivity than the resin bobbin  32 ; preferably, having thermal conductivity twice or more as high as that of the resin bobbin  32 . The intervention member  33  is a component of the actuator moving section  30  and thus preferably is lightweight to such an extent that it does not degrade the sensitivity of the actuator.  
         [0041]    As described above, according to the pickup apparatus  1  of the embodiment, the object lens  31  is fixed onto the bobbin  32  through the intervention member  33  having higher thermal conductivity than the resin bobbin  32 . Therefore, the intervention member  33  acts so as to make an asymmetrical temperature distribution in the bobbin  32  uniform in the circumferential direction of the object lens  31 . Accordingly, the circumferential temperature distribution in the object lens  31  is made almost uniform, so that degradation of the lens characteristic of the object lens  31  is suppressed and the detection reliability of a detection signal is enhanced.  
         [0042]    Second Embodiment  
         [0043]    A pickup apparatus of a second embodiment according to the invention will be discussed below with reference to the accompanying drawings.  
         [0044]    [0044]FIG. 6 is a perspective view of an actuator moving section  40  of the embodiment, and FIG. 7 is a sectional view of the actuator moving section  40 . The actuator moving section  40  includes an object lens  41 , a bobbin  42 , an intervention member  43 , a pair of tracking coils  44 , and a focus coil  45 .  
         [0045]    The bobbin  42  is a resin member having tracking coil retention sections  42   a  for winding the tracking coils therearound on opposed sides and containing a through hole  42   b , as a lens storing hole, shaped like a cylinder pierced up and down in the axial direction. The bobbin  42  is formed with an iris section  42   f  projected from the peripheral surface of the through hole  42   b  to the radial inside. The iris section  42   f  matches the diameter of laser light incident on the object lens  41  with the effective diameter of the object lens  41 . The bobbin  42  is formed on a top face  42   c  with a step section  42   e  surrounding the through hole  42   b . The intervention member  43  is fixed onto the step section  42   e.    
         [0046]    The intervention member  43  is a plate-like member having a circular shape on the top view. It has almost the same shape as a side of the step section  42   e  and is fixed along the shape of the step section  42   e  in an intimate contract manner. A circular through hole  43   a  is made in the center of the intervention member  43 , and a step section  43   b  for placing the object lens  41  thereon is formed in the surroundings of the through hole  43   a . The intervention member  43  is formed of a material having higher thermal conductivity than the resin bobbin  42 .  
         [0047]    The object lens  41  is inserted into the top of the step section  43   b  of the intervention member  43 . The object lens  41  is a lens having a circular shape on the top view and is placed so that a convex part of the lens is positioned in the through hole  43   a  of the intervention member  43 . The object lens  41  narrows down light of a predetermined wavelength emitted from a light source (not shown) positioned below the bobbin  42  and applies the light along the track formed on the information record side of an optical disk  5 . The object lens  41  allows the light reflected on the information record side of the optical disk  5  to pass through and sends the light to a light reception section having a light reception element (not shown). The object lens  41  is fixed onto the bobbin  42  through the intervention member  43  and is not in direct contact with the bobbin  42 .  
         [0048]    A pair of tracking coil retention sections  42   a  is projected from both sides of the bobbin  42  in the tracking direction. Each tracking coil retention section  42   a  is formed on a side with a tracking coil retention groove  42   d  and each tracking coil  44 ,  44  is wound along the tracking coil retention groove  42   d . The configuration of placement and the function of the tracking coils  44  are the same as those of the tracking coils  34  of the first embodiment.  
         [0049]    On the sides of the bobbin  42 , the focus coil  45  is wound in the rotation direction around the optical axis of the object lens  41 . The focus coil  45  is a coil for moving the actuator moving section  40  in the focus direction. The configuration of placement and the function of the focus coil  45  is the same as those of the focus coil  35  of the first embodiment.  
         [0050]    The tracking coils  44  and the focus coil  45  generate heat as current flows. The heat is conducted asymmetrically to the intervention member  43  in response to the position of each coil placed on the bobbin  42 . The intervention member  43  is formed of a material having higher thermal conductivity than the resin bobbin  42  and thus rapidly conducts the asymmetrically conducted heat in the circumferential direction of the intervention member  43  and conducts the heat uniformly from the perimeter of the object lens  41  to the object lens  41 . Therefore, the temperature distribution in the object lens  41  becomes almost concentric and unevenness on the concentric circumference of the temperature distribution occurring in the object lens  41  is remarkably relieved. Thus, degradation of the lens characteristic of the object lens  41  is suppressed and the detection reliability of a detection signal is enhanced.  
         [0051]    As described above, according to the embodiment, the object lens  41  is fixed onto the bobbin  42  through the intervention member  43  having higher thermal conductivity than the resin bobbin  42 . Therefore, the intervention member  43  acts so as to make an asymmetrical temperature distribution in the bobbin  42  uniform in the circumferential direction of the object lens  41 . Accordingly, the circumferential temperature distribution in the object lens  41  is made almost uniform, so that degradation of the lens characteristic of the object lens  41  is suppressed and the detection reliability of a detection signal is enhanced.  
         [0052]    Third Embodiment  
         [0053]    A pickup apparatus of a third embodiment according to the invention will be discussed below with reference to the accompanying drawings.  
         [0054]    [0054]FIG. 8 is a perspective view of an actuator moving section  50  of the embodiment, and FIG. 9 is a sectional view of the actuator moving section  50 . The actuator moving section  50  includes an object lens  51 , a bobbin  52 , an intervention member  53 , a pair of tracking coils  54 , and a focus coil  55 .  
         [0055]    The actuator moving section  50  of the embodiment differs from the actuator moving section  40  of the second embodiment only in that the intervention member  53  is improvement in the intervention member  43 ; other components  51 ,  52 ,  54 , and  55  are identical with the components  41 ,  42 ,  44 , and  45  of the second embodiment.  
         [0056]    The intervention member  53  of the third embodiment is a plate-like member having a circular shape on the top view. It has almost the same shape as a side of a step section  52   e  of the bobbin  52  and is fixed along the shape of the step section  52   e  in an intimate contract manner. A circular through hole  53   a  is made in the center of the intervention member  53 , and a step section  53   b  for placing the object lens  51  thereon is formed in the surroundings of the through hole  53   a . The intervention member  53  is formed of a material having higher thermal conductivity than the resin bobbin  52 .  
         [0057]    The intervention member  53  is formed on the top face with a plurality of grooves  53   c  concentrically along the circumferential direction. These grooves  53   c  increase the surface area of the intervention member  53  and function as a radiating fin of a heat sink for dissipating the heat conducted to the intervention member  53  to the outside. The intervention member  53  fixes the object lens  51  so that the object lens  51  and the bobbin  52  do not come in direct contact with each other.  
         [0058]    The tracking coils  54  and the focus coil  55  generate heat as current flows. The heat is conducted asymmetrically to the intervention member  53  in response to the position of each coil placed on the bobbin  52 . The intervention member  53  is formed of a material having higher thermal conductivity than the resin bobbin  52  and thus rapidly conducts the asymmetrically conducted heat in the circumferential direction of the intervention member  53 . Thus, the circumferential temperature of the intervention member  53  becomes almost uniform and the heat is conducted uniformly from the perimeter of the object lens  51  to the object lens  51 . Therefore, the temperature distribution in the object lens  51  becomes almost concentric and unevenness on the concentric circumference of the temperature distribution occurring in the object lens  51  is remarkably relieved. Thus, degradation of the lens characteristic of the object lens  51  is suppressed and the detection reliability of a detection signal is enhanced.  
         [0059]    Further, as the surface area coming in contact with the outside air increases in the presence of the grooves  53   c  formed on the top face of the intervention member  53 , the heat conducted to the intervention member  53  is dissipated to the outside for aggressively decreasing the amount of heat flowing into the object lens  51 . Therefore, a temperature rise in the object lens  51  is suppressed, so that degradation of the lens characteristic of the object lens  51  is suppressed. Accordingly, the reliability of a signal detected through the object lens  51  is enhanced.  
         [0060]    As described above, according to the embodiment, the object lens  51  is fixed onto the bobbin  52  through the intervention member  53  having higher thermal conductivity than the resin bobbin  52 . Therefore, the intervention member  53  acts so as to make an asymmetrical temperature distribution in the bobbin  52  uniform in the circumferential direction of the object lens  51 . The grooves  53   c  formed on the intervention member  53  dissipate the heat conducted to the intervention member  53  to the outside for aggressively decreasing the amount of heat flowing into the object lens  51 . Accordingly, the circumferential temperature distribution in the object lens  51  is made almost uniform and the amount of heat flowing into the object lens  51  is decreased, so that degradation of the lens characteristic of the object lens  51  is suppressed and the detection reliability of a detection signal is enhanced.  
         [0061]    Fourth Embodiment  
         [0062]    A pickup apparatus of a fourth embodiment according to the invention will be discussed below with reference to the accompanying drawing.  
         [0063]    [0063]FIG. 10 is a perspective view of an actuator moving section  60  of the fourth embodiment. The actuator moving section  60  includes an object lens  61 , a bobbin  62 , an intervention member  63 , a pair of tracking coils  64 , and a focus coil  65 .  
         [0064]    The actuator moving section  60  of the embodiment has the intervention member  63  functioning as an iris section in place of the iris section  32   f  formed in the bobbin  32  of the actuator moving section  30  of the first embodiment. Other components are identical with those of the first embodiment.  
         [0065]    The intervention member  63  is a cylindrical-shaped member having the same shape as the inner peripheral surface of a lens storing hole  62   b . The intervention member  63  is formed at one end in the axial direction with a flange  63   a  bent to the outer diameter side. The flange  63   a  of the intervention member  63  is placed on a top face  62   c  of the bobbin  62  in an intimate contact manner. The intervention member  63  is formed at an opposite end in the axial direction with a flange  63   b  bent to the radial inside and projected. The tip of the flange  63   b  projects to the proximity of the surface of the object lens  61  for limiting the diameter of laser light incident on the object lens  61 . This means that the flange  63   b  functions as an iris for matching the diameter of laser light incident on the object lens  61  with the effective diameter of the object lens  61 .  
         [0066]    The intervention member  63  is formed of a material having higher thermal conductivity than the resin bobbin  62 . The object lens  61  is inserted into the inner peripheral side of the intervention member  63  and is fixed onto the inner peripheral surface and the flange  63   b  of the intervention member  63  in an intimate contact manner. In the embodiment, for the flange  63   b  to limit the diameter of laser light, the flange  63   b  is formed of an optically nontransparent material.  
         [0067]    When each coil is energized, the tracking coils  64  and the focus coil  65  generate heat as current flows. The heat is conducted asymmetrically to the intervention member  63  in response to the position of each coil placed on the bobbin  62 . The intervention member  63  is formed of a material having higher thermal conductivity than the resin bobbin  62  and thus rapidly conducts the asymmetrically conducted heat in the circumferential direction of the intervention member  63 . Thus, the circumferential temperature of the intervention member  63  becomes almost uniform and the heat is conducted uniformly from the perimeter of the object lens  61  to the object lens  61 . Therefore, the temperature distribution in the object lens  61  becomes almost concentric and unevenness on the concentric circumference of the temperature distribution occurring in the object lens  61  is remarkably relieved. Thus, degradation of the lens characteristic of the object lens  61  is suppressed and the detection reliability of a detection signal is enhanced.  
         [0068]    As described above, according to the embodiment, the object lens  61  is fixed onto the bobbin  62  through the intervention member  63  having higher thermal conductivity than the resin bobbin  62 . Therefore, the intervention member  63  acts so as to make an asymmetrical temperature distribution in the bobbin  62  uniform in the circumferential direction of the object lens  61 . Accordingly, the circumferential temperature distribution in the object lens  61  is made almost uniform, degradation of the lens characteristic of the object lens  61  is suppressed, and the detection reliability of a detection signal is enhanced. Since the intervention member  63  also has the iris function, in a case where object lenses different in effective diameter are used, the shape of the intervention member  63  is changed matching each object lens without changing the shape of the bobbin, whereby it is made possible to handle different object lenses.  
         [0069]    Fifth Embodiment  
         [0070]    A pickup apparatus of a fifth embodiment according to the invention will be discussed below with reference to the accompanying drawing.  
         [0071]    [0071]FIG. 11 is a perspective view of an actuator moving section  70  of the embodiment. The actuator moving section  70  includes an object lens  71 , a bobbin  72 , an intervention member  73 , a pair of tracking coils  74 , and a focus coil  75 .  
         [0072]    The intervention member  73  of the embodiment is an annular member shaped almost like a rectangle on the sectional view and is placed on an iris section  72   c  in contact with an inner peripheral surface  72   b  of the bobbin  72  and an upper surface  72   e  of the iris section  72   c  projected from the inner peripheral surface  72   b . The intervention member  73  is formed of a material having higher thermal conductivity than the resin bobbin  72 . The object lens  71  is fixed in contact with the inner peripheral surface  72   b  of the bobbin  72  and the intervention member  73 .  
         [0073]    Heat conducted as the tracking coils  74  and the focus coil  75  generate heat is conducted asymmetrically in response to the position of each coil placed on the bobbin  72 ; some is conducted to the intervention member  73  and some is conducted directly to the object lens  71 . The intervention member  73  is formed of a material having higher thermal conductivity than the resin bobbin  72  and thus rapidly conducts the asymmetrically conducted heat in the circumferential direction of the intervention member  73  and conducts the heat uniformly from the perimeter of the object lens  71  to the object lens  71 . In the embodiment, some heat is conducted directly to the object lens  71  and therefore the temperature distribution in the object lens  71  becomes asymmetric as compared with the case in the first to fourth embodiments; however, unevenness on the concentric circumference of the temperature distribution occurring in the object lens  71  is remarkably relieved as compared with the case where the intervention member  73  is not used. Thus, degradation of the lens characteristic of the object lens  71  is suppressed and the detection reliability of a detection signal is enhanced. Since the intervention member  73  is simplified in shape as compared with the intervention member  33 ,  43 ,  53 ,  63 , the parts costs can be suppressed to low costs.  
         [0074]    As described above, according to the first to fifth embodiments according to the invention, the object lens is fixed to the bobbin symmetrically with respect to the optical axis through the intervention member formed of a material having higher thermal conductivity than the bobbin. Particularly, according to the first to fourth embodiments, the object lens and the bobbin are not in direct contact with each other. Therefore, it is made possible to make the circumferential temperature distribution in the object lens  51  almost uniform and it is made possible to suppress degradation of the lens characteristic caused by unevenness of the circumferential temperature distribution.  
         [0075]    In the embodiments according to the invention, the specific shapes of the intervention members have been described, but the invention is not limited to them; an intervention member for making it possible to uniformize the circumferential temperature distribution based on the heat from the bobbin and uniformly coming in contact with the object lens in the circumferential direction may be used. For example, in a case where the object lens has a special shape, an arbitrary intervention member adapted to the shape of the object lens may be used.  
         [0076]    Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.