Abstract:
A lens driving device for use with a lens to photograph or image an object to be photographed or imaged may include a moving member holding the lens and made movable in the direction of an optical axis, and a supporting member for supporting the moving member through a spring member, wherein the lens is displaced and driven in the optical axis direction thereby to focus the image of the object. The supporting member may include a yoke having a cover portion having an entrance window for introducing the reflected light from the object into the lens, and a case portion for covering the outer circumference of the moving member. The cover portion and the case portion are formed integrally with each other.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a U.S. national stage of application No. PCT/JP2008/003315, filed on Nov. 13, 2008. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2007-295360, filed Nov. 14, 2007, the disclosure of which is also incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present application relates to a lens drive device in which a lens is driven to move in an optical axis direction for forming an image of an object to be photographed or imaged. 
       BACKGROUND 
       [0003]    As cell phones with cameras have become popular in recent years, chances photographing or imaging various objects to be photographed by using the cell phone have increased. For example, there is a case that an object such as a friend or landscape which is apart from a lens of a camera to some extent is photographed (normal photographing) and, alternatively, there is a case that an object such as a timetable for bus or petals of a flower at a position near the lens of the camera is photographed (close-up photographing). 
         [0004]    In the close-up photographing (macro-photographing), a lens position of a camera is required to locate at a slightly nearer position on an object side than a lens position at the time of normal photographing. Therefore, this type of photographing lens system is provided with a drive mechanism for driving a lens to move in the optical axis direction. The drive mechanism is driven by changing a state of a switch to move a lens in the optical axis direction (see, for example, Patent Reference 1). 
         [0005]    A lens drive device which is disclosed in Patent Reference 1 includes a movable lens body, a drive mechanism for moving the movable lens body in an optical axis direction, a fixed body (yoke) which movably supports the movable lens body in the optical axis direction, and a restriction means (flat spring) which restricts movement of the movable lens body. Further, the drive mechanism includes a magnet and a coil. In the structure as described above, while an electric current is supplied to the coil to generate an electromagnetic force, a restriction force against the electromagnetic force is generated by the restriction means and magnitudes of both the restriction force and the electromagnetic force are adjusted to stop the movable lens body at a desired position. 
         [0006]    [Patent Reference 1] Japanese Patent Laid-Open No. 2007-94364 
         [0007]    However, when the yoke and the flat spring are to be assembled, the yoke and the flat spring are required to be positioned in the optical axis direction and the radial direction. Specifically, for example, a jig which is structured so that a circular cylinder having substantially the same diameter as a lens-barrel (or lens) is stood on a pedestal is used for assembling. For example, a cover, a yoke, flat springs, a magnet and the like are required to fix in order by using the jig while positioning in the optical axis direction and the radial direction. In this manner, in the manufacturing steps for the lens drive device, positioning work is required many times due to influence of component accuracy and assembling accuracy of adhesion, fixing by welding and the like and thus working efficiency is not satisfactory. Especially, since the yoke which determines the outer shape dimension is conventionally formed by a bending work, its dimensional tolerance is difficult to make smaller and thus rattling is easily occurred in the radial direction. In order to prevent this problem, it is required that, at the time of assembling, fixing is performed while positioning in the radial direction is performed. 
         [0008]    In view of the problem described above, at least an embodiment of the present invention provides a lens drive device which is capable of reducing the number of times of a positioning work and is capable of improving working efficiency. 
       SUMMARY 
       [0009]    In order to solve the problem described above, at least an embodiment of the present invention provides as follows. 
         [0010]    (1) A lens drive device for use with a lens to photograph an object to be photographed, the lens drive device comprising: 
         [0011]    a movable body which holds the lens and which is movable in an optical axis direction; 
         [0012]    a support body which supports the movable body through a spring member;
       a magnet for moving the movable body in the optical axis direction; and   a coil which is attached to the movable body for moving the movable body in the optical axis direction;   wherein the support body comprises a yoke to which the magnet is fixed for moving the movable body in the optical axis direction;   wherein the yoke is formed by a drawing work so that the yoke comprises:
           a cover part which is formed with an incident window for taking reflected light from the object to be photographed into the lens and which is exposed as a front face of the lens drive device; and   
               
 
         [0018]    a case part which covers a periphery of the movable body and which is exposed as a side face of the lens drive device; 
         [0019]    wherein the cover part and the case part are formed in an integral manner, and 
         [0020]    wherein the lens is driven to move in the optical axis direction for forming an image of the object to be photographed. 
         [0021]    According to this embodiment, in a lens drive device including a movable body and a support body and, in which a lens is driven to move in the optical axis direction for forming an image of the object to be photographed, the lens drive device includes a magnet, a coil which is attached to the movable body, and a yoke to which the magnet is fixed for moving the movable body in the optical axis direction. In the lens drive device, the yoke is formed by a drawing work so that the yoke comprises a cover part which is formed with an incident window for taking a reflected light from an object to be photographed into the lens and which is exposed as a front face of the lens drive device, and a case part which covers a periphery of the movable body and which is exposed as a side face of the lens drive device, and the yoke structures the front face and the side face of the lens drive device as the support body. 
         [0022]    Therefore, for example, when the spring member and the movable body are to be accommodated into the yoke formed in a roughly box-like shape comprised of the cover part and the case part, positioning in the optical axis direction can be performed by the cover part. Further, positioning in the radial direction (direction perpendicular to the optical axis direction) can be performed by the case part. As a result, the conventional jig for positioning is not required. Since positioning work is simultaneously performed at the same time when accommodating work is performed as described above, the number of times of positioning work can be reduced and working efficiency can be improved. Further, the cover part and the case part are structured of one member which is formed by a drawing work. Therefore, in comparison with a conventional bending work, the dimensional tolerance can be restrained smaller and thus the cover part and the case part with a high degree of working accuracy can be easily formed. In addition, a part of magnetic path can be structured while magnetic flux from the magnet is prevented from leaking out the outside of the cover part and the case part and thus magnetic resistance can be reduced and a thrust force for the moveable body can be improved. 
         [0023]    (2) The lens drive device wherein a spacer for mounting the spring member, the spring member, and the magnet which is fixed to the case part are disposed in an inner side of the cover part so as to be superposed on each other in this order from a cover part side. 
         [0024]    According to this embodiment, a spacer for mounting the spring member, the spring member, the magnet which is fixed to the case part are disposed in an inner side of the above-mentioned cover part so as to be superposed on each other in this order from a cover part side. Therefore, the spacer and the spring member are capable of being positioned in the optical axis direction by the cover part and the magnet and, as a result, working efficiency can be improved. 
         [0025]    (3) The lens drive device wherein the spacer is abutted with an inner face of the case part to determine a position of the spacer in a direction perpendicular to the optical axis direction, and a position of the spring member in the direction perpendicular to the optical axis direction is determined with respect to the yoke through the spacer. 
         [0026]    According to this embodiment, the spacer is abutted with an inner face of the case part to determine a position of the spacer in a direction perpendicular to the optical axis direction. As a result, a jig for positioning is not required to be used as a conventional case. Since positioning work is simultaneously performed at the same time when accommodating work is performed, the number of times of positioning work can be reduced and, as a result, working efficiency can be improved. 
         [0027]    (4) The lens drive device wherein a face on a cover part side of the spacer is abutted with an inner face of the cover part to determine a position of the spacer in the optical axis direction, and a position of the magnet in the optical axis direction is determined with respect to the yoke through the spacer and the spring member. 
         [0028]    According to this embodiment, a face on a cover part side of the spacer is abutted with an inner face of the case part to determine a position of the spacer in a direction perpendicular to the optical axis direction, and a face on a cover part side of the spacer is abutted with an inner face of the cover part to determine a position of the spacer in the optical axis direction. As a result, a jig for positioning is not required to use as a conventional case. Since positioning work is simultaneously performed at the same time when accommodating work is performed, the number of times of positioning work can be reduced and, as a result, working efficiency can be improved. 
         [0029]    (5) The lens drive device wherein an external shape of the yoke is formed in a roughly rectangular shape having four corner portions, and the magnet is formed with two side faces which are respectively abutted with two inner side faces formed on the corner portion of the yoke, and the two side faces of the magnet are respectively abutted with two inner side faces of the yoke to determine a position of the magnet in a direction perpendicular to the optical axis direction on the corner portion of the yoke. 
         [0030]    According to this embodiment, an external shape of the yoke is formed in a roughly rectangular shape having four corner portions, and the magnet is formed with two side faces which are respectively abutted with two inner side faces formed on the corner portion of the yoke, and the two side faces of the magnet are respectively abutted with two inner side faces of the yoke to determine a position of the magnet in a direction perpendicular to the optical axis direction on the corner portion of the yoke. Therefore, positioning work is simultaneously performed at the same time when accommodating work is performed, the number of times of positioning work can be reduced and, as a result, working efficiency can be improved. 
         [0031]    (6) The lens drive device wherein a face on a cover part side of the spacer is abutted with an inner face of the cover part to determine a position of the spacer in the optical axis direction, and the spacer is abutted with an inner face of the case part to determine a position of the spacer in a direction perpendicular to the optical axis direction, and a position of the magnet in the optical axis direction is determined with respect to the yoke through the spacer, and a position of the spring member in the direction perpendicular to the optical axis direction is determined with respect to the yoke through the spacer. 
         [0032]    According to this embodiment, a face on a cover part side of the spacer is abutted with an inner face of the cover part to determine a position of the spacer in the optical axis direction, and the spacer is abutted with an inner face of the case part to determine a position of the spacer in a direction perpendicular to the optical axis direction. As a result, a jig for positioning is not required to be used as a conventional case. Since positioning work is simultaneously performed when accommodating work is performed, the number of times of positioning work can be reduced and, as a result, working efficiency can be improved. 
         [0033]    (7) The lens drive device wherein a portion around the incident window of the cover part is protruded to an outer side in the optical axis direction to form a stepped part. 
         [0034]    According to this embodiment, the above-mentioned cover part is formed so that a portion around the incident window of the cover part is protruded to an outer side in the optical axis direction to form a stepped part. Therefore, a space made by the stepped part may be, for example, structured to provide a function as a spacer whose thickness is larger than a moving amount of the spring member. Therefore, in this case, the spacer is not required to use and, as a result, the lens drive device can be made thinner or its weight can be reduced. 
         [0035]    According to at least an embodiment of a lens drive device in accordance with the present invention, the number of times of positioning work can be reduced and, as a result, working efficiency can be improved. Further, the cover part and the case part are integrally formed with each other as a yoke by a drawing work whose working accuracy is higher than a conventional bending work and thus the working efficiency can be enhanced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which: 
           [0037]      FIG. 1  is a perspective outward appearance view showing a lens drive device in accordance with an embodiment of the present invention. 
           [0038]      FIG. 2  is an exploded perspective view showing a mechanical structure of a lens drive device in accordance with an embodiment of the present invention. 
           [0039]      FIGS. 3(   a ) and  3 ( b ) are perspective views showing a yoke in the lens drive device. 
           [0040]      FIG. 4  is a flow chart for explaining schematic assembling steps for the lens drive device. 
           [0041]      FIG. 5  is a perspective view showing a state where a spacer has been placed on the yoke shown in  FIGS. 3(   a ) and  3 ( b ). 
           [0042]      FIG. 6  is a perspective view showing a state where a spacer and a first flat spring have been placed on the yoke shown in  FIGS. 3(   a ) and  3 ( b ). 
           [0043]      FIG. 7  is a perspective view showing a state where, after a spacer and a first flat spring have been placed, a magnet is mounted on the yoke shown in  FIGS. 3(   a ) and  3 ( b ). 
           [0044]      FIGS. 8(   a ),  8 ( b ) and  8 ( c ) are views for explaining a yoke in a lens drive device in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0045]    Embodiments of the present invention will be described below with reference to the accompanying drawings. 
       [Mechanical Structure] 
       [0046]      FIG. 1  is a perspective outward appearance view showing a lens drive device  1  in accordance with an embodiment of the present invention.  FIG. 2  is an exploded perspective view showing a mechanical structure of a lens drive device  1  in accordance with an embodiment of the present invention. 
         [0047]    In  FIGS. 1 and 2 , the lens drive device  1  includes a yoke  11 , a spacer  12 , a sleeve  13 , a first plate spring  14 , a second plate spring  15 , a wire spring  16 , a magnet  17 , a coil  18  (a first coil  18   a  and a second coil  18   b ) and a holder  19 . A lens is driven to move in a direction of an optical axis “L” of the lens to form an image of an object to be photographed or imaged. 
         [0048]    In  FIGS. 1 and 2 , a lens barrel into which the lens is assembled is not shown. The lens drive device  1  makes the sleeve  13  formed in a cylindrical shape move along the optical axis “L” direction in both directions, i.e., an “A”-direction (front side) approaching to an object to be photographed (imaging object) and a “B”-direction (rear side) approaching to an opposite side to the object to be photographed (image side) (see  FIG. 1 ). Further, the sleeve  13  which holds the lens barrel (not shown) into which one or plural lenses are assembled is structured so as to be movable in the direction of the optical axis “L” together with a wire spring  16  and the like, which correspond to an example of the “movable body”. Further, the yoke  11 , the spacer  12 , the holder  19  and the like correspond to an example of the “support body” which supports the sleeve  13  and the like so as to be movable in the direction of the optical axis “L” through the first plate spring  14  and the second plate spring  15 . Further, the sleeve  13  and the like are driven in the direction of the optical axis “L” by the coil  18  and the magnet  17 . 
         [0049]    The yoke  11  is exposed as a front face and side faces of the lens drive device  1  and the yoke  11  is provided with a cover part  11   a  which is formed with a circular incident window  111  in its center for taking a reflected light from an object to be photographed or imaged into the lens (see  FIG. 2 ). Further, the yoke  11  is provided with a case part  11   b  which covers an outer periphery of the sleeve  13  (see  FIG. 2 ). The cover part  11   a  and the case part  11   b  are formed in an integral manner. When the yoke  11  structured as described above is used, positioning of the spacer  12  and the first flat spring  14  can be performed easily. Details of the positioning will be described below in the paragraphs of [Positioning with Yoke]. 
         [0050]    The spacer  12  is attached to the yoke  11  and its center is formed with a circular incident window  121  for taking a reflected light from an object to be photographed into the lens. The holder  19  holds an imaging element (not shown) on an image side. 
         [0051]    The coil  18  is structured of the first coil  181  and the second coil  182 , which are disposed in two layers in the direction of the optical axis “L”, and each is formed in a circular ring shape. The first coil  181  and the second coil  182  are wound around an outer peripheral face of the sleeve  13  so as to have a predetermined space between them. Further, eight magnets  17  are disposed so as to be superposed on each other in two layers in the optical axis direction. The magnets  17  on the front side of the respective magnets  17  are faced to the first coil  181  on an outer peripheral side and the magnets  17  on the rear side are faced to the second coil  182  on an outer peripheral side and, as shown in  FIG. 2  and the like, the eight magnets  17  are fixed to four corner portions on an inner peripheral face of the yoke  11  whose outer shape is formed in a roughly rectangular shape. 
         [0052]    In this embodiment, each of the magnets  17  is magnetized so that the inside face and the outside face are magnetized to be different from each other. For example, four magnets  17  disposed on the front side are magnetized so that their inside faces are magnetized to be an “N”-pole and their outside faces are magnetized to be an “S”-pole, and four magnets  17  disposed on the rear side are magnetized so that their inside faces are magnetized to be an “S”-pole and their outside faces are magnetized to be an “N”-pole. 
         [0053]    The first plate spring  14  and the second plate spring  15  are formed of a metal thin plate and their thicknesses in the direction of the optical axis “L” is set to be the same as each other. Further, as shown in  FIG. 2 , the first plate spring  14  is attached to a front end face in the optical axis direction of the sleeve  13 , and the second plate spring  15  is attached to a rear end face in the optical axis direction of the sleeve  13 . In this embodiment, as shown in  FIG. 2 , although notational symbols are not shown, each of the first plate spring  14  and the second plate spring  15  includes a circular arc-shaped sleeve side mounting part, a spacer side mounting part which is attached to the spacer  12 , and an arm part which is formed between the sleeve side mounting part and the spacer side mounting part for restricting movement (urging) in the optical axis direction of the sleeve  13 . The respective mounting parts are fixed to the spacer  12  or the holder  19  by using welding, adhesion or both of them. 
         [0054]    Further, the second plate spring  15  is structured of two spring pieces which are electrically separated from each other and serve as means for supplying an electric current to the coil  18  from an external power supply. A winding start of the coil  18  is electrically connected to one of the two spring pieces and its winding end is electrically connected to the other of the two spring pieces. 
         [0055]    A case part  11   b  of the yoke  11  is set to be larger than a dimension in the optical axis direction of a region where the first coil  181  and the second coil  182  are disposed and larger than a dimension in the optical axis direction of the magnet  17 . Therefore, leakage flux is capable of being reduced which is generated from a magnetic path structured between the front side magnets  17  and the first coil  181  and from a magnetic path structured between the rear side magnets  17  and the second coil  182 . As a result, linearity between a moving amount of the sleeve  13  and an electric current supplied to the first coil  181  and the second coil  182  can be improved. 
         [0056]    The lens drive device  1  is provided with a circular ring shaped wire spring  16 . The wire spring  16  applies an urging force in the direction of the optical axis “L” to the sleeve  13  due to a magnetic attractive force acting between the magnets  17  and the wire spring  16 . Therefore, the movable body (sleeve  13  and the like) is prevented from being displaced by its own weight at a not-energized time of the coil and, as a result, the movable body (sleeve  13  and the like) is capable of maintaining a desired posture. In addition, impact resistance is improved. 
         [0057]    In the lens drive device  1  in accordance with an embodiment of the present invention, a characteristic structure is the shape of the yoke  11  and the spacer  12  and the first flat spring  14  are positioned by the yoke  11 . The yoke  11  and positioning of the yoke  11  will be described below with reference to  FIGS. 3(   a ) through  7 . 
         [0000]    [Positioning with Yoke] 
         [0058]      FIGS. 3(   a ) and  3 ( b ) are perspective views showing the yoke  11  in the lens drive device  1 . Especially,  FIG. 3(   a ) is a perspective view showing the yoke  11  which is viewed from the front side and  FIG. 3(   b ) is a perspective view showing the yoke  11  which is viewed from the rear side. 
         [0059]    As shown in  FIGS. 3(   a ) and  3 ( b ) and  FIG. 4 , the yoke  11  in this embodiment is structured of the cover part  11   a  having an incident window  111  and the case part  11   b  which corresponds to a side face and covers an outer periphery of the sleeve  13  (or magnet  17 ). The cover part  11   a  and the case part  11   b  are made of a ferromagnetic plate (magnetic body) or the like such as a steel plate, and they are formed by a drawing work. Therefore, easiness of working can be enhanced. In addition, a drawing work is capable of enhancing working accuracy in comparison with a conventional bending work. For example, a bending work is performed with accuracy in a dimensional tolerance of the order of 1/10. However, in a drawing work in this embodiment, working is performed in a dimensional tolerance of the order of 1/100. Further, since the cover part  11   a  is made of a magnetic body, the cover part  11   a  is capable of structuring a part of the magnetic path and thus a magnetic resistance can be made smaller and a thrust force for the sleeve  13  can be enhanced. However, the present invention is not limited to this embodiment and other materials and working methods may be adopted. 
         [0060]    Steps for assembling the lens drive device  1  with the use of the above-mentioned yoke  11  will be described below.  FIG. 4  is a flow chart for explaining schematic assembling steps for the lens drive device  1 .  FIG. 5  is a perspective view showing a state where the spacer  12  has been placed on the yoke  11  shown in  FIGS. 3(   a ) and  3 ( b ) (step S 2  in  FIG. 4) .  FIG. 6  is a perspective view showing a state where the spacer  12  and the first flat spring  14  have been placed on the yoke  11  shown in  FIGS. 3(   a ) and  3 ( b ) (step S 3  in  FIG. 4) .  FIG. 7  is a perspective view showing a state where, after the spacer  12  and the first flat spring  14  have been placed, the magnet  17  is mounted on the yoke  11  shown in  FIGS. 3(   a ) and  3 ( b ) (step S 4  in  FIG. 4) . The assembling steps shown in  FIG. 4  may be performed mechanically or may be performed by hand. 
         [0061]    In  FIG. 4 , first, the yoke  11  whose rear side is directed to the upper side is placed on a work bench (step S 1 ). Specifically, as shown in  FIG. 3(   b ), the yoke  11  is placed in a reverse state so that the cover part  11   a , i.e., the upper face in the optical axis direction (front side face) is a bottom face. Next, the spacer  12  is placed on the inside of the yoke  11  (step S 2 ). Specifically, the spacer  12  is placed as shown in  FIG. 5 . In this case, an adhesive may not be used. Further, at the time of placing, positioning in the radial direction with respect to the optical axis “L” is simultaneously performed by the case part  11   b  of the yoke  11 . In addition, at the time of placing, positioning in the optical axis direction is simultaneously performed by the cover part  11   a  of the yoke  11 . In this embodiment, two directions, i.e., “X” direction and “Y” direction in  FIG. 2  which are perpendicular to the optical axis direction are defined as two directions as described in the drawing. A length in the “X” direction between side end faces from an “a” face to an “a′” face, and a length in the “X” direction between side end faces from a “b” face to a “b′” face, which are located at four corners of the spacer  12 , are set to be equal to a length in the “X” direction from an “A” face to an “A′” face of the inner face of the case part  11   b  of the yoke  11  shown in  FIG. 3(   b ). Similarly, a length in the “Y” direction between side end faces from a “c” face to a “c′” face, and a length in the “Y” direction between side end faces from a “d” face to a “d” face, which are located at four corners of the spacer  12 , are set to be equal to a length in the “Y” direction from a “C” face to a “C′” face and a length in the “Y” direction from a “D” face to a “D′” face of the inner face of the case part  11   b  of the yoke  11  shown in  FIG. 3(   b ). Therefore, when the spacer  12  is placed on the inside of the yoke  11 , the spacer  12  is positioned with respect to the yoke  11 . In other words, the position in the radial direction of the spacer  12  is determined with respect to the optical axis “L”. Further, an upper face  12 Z face which is a face on the cover part  11   a  side of the spacer  12  is abutted with an under face of the cover part  11   a  of the yoke  11  without a space and thus, when placed on the under face of the cover part  11   a , the position in the optical axis direction of the spacer  12  is determined. In this embodiment, the position of the spacer  12  is determined by using the side end faces which are disposed at four corners of the spacer  12  and the inner face of the case part  11   b  of the yoke  11 . However, the above-mentioned two members may be positioned by using other faces, for example, by using center portions. 
         [0062]    Next, the first flat spring  14  is mounted on the spacer  12  (step S 3 ). Specifically, as shown in  FIG. 6 , the spacer side mounting part of the first flat spring  14  is attached by utilizing a pin  12 P which is provided at a predetermined position of the spacer  12  through an adhesive. In other words, in the step S 3 , the position in the radial direction of the spacer  12  is determined by the yoke  11  and then the flat spring  14  is fixed to the spacer  12  with the pin  12 P provided at a predetermined position of the spacer  12  as a reference. Further, the pin  12 P is provided at four corner positions of the spacer  12  respectively and thus positioning in the radial direction of the flat spring  14  is simultaneously performed with respect to the optical axis “L” at the same time when the flat spring  14  is mounted. In this embodiment, the yoke  11  and the flat spring  14  are positioned each other through the pins  12 P provided on the spacer  14 . However, the flat spring  14  may be positioned with respect to the yoke  11  similarly to the positioning of the spacer  12  with respect to the yoke  11 . 
         [0063]    Next, the magnet  17  is mounted on the first flat spring  14  (step S 4 ). Specifically, the magnet  17  is mounted as shown in  FIG. 7 . In this case, positioning in the radial direction of the magnet  17  is simultaneously performed by the case part  11   b  of the yoke  11  at the time when the magnet  17  is mounted. In other words, the side face  17 X of the magnet  17  is abutted with the inner side face, i.e., “N” face of the case part  11   b  of the yoke  11  and the side face  17 Y is abutted with the inner side face, i.e., “D” face of the yoke  11 . Since a corner part  17 S is formed between the side faces  17 X and  17 Y of the magnet  17 , even when four corners on the inner side of the yoke  11  is provided with an “R” part to the extent that the “R” part does not contact with the corner part  17 S, instead of being formed with a perpendicular portion, two faces, i.e., the side faces  17 X and  17 Y of the magnet  17  are abutted with the inner face of the yoke and thus positioning in the radial direction is performed surely. In this description, only one of the magnets has been described, in other words, the magnet facing the coil  181  on an object to be photographed side (front side) of the magnets, which are disposed on the upper and lower sides at four corners, has been described. Other magnets which are located at other positions are similarly abutted with the inner face of the yoke  11 . 
         [0064]    As described above, in the series of the steps, i.e., the step S 1  through the step S 4 , positioning in the optical axis direction and the radial direction are performed by the cover part  11   a  and the case part  11   b  of the yoke  11  and thus manufacturing steps with a high degree of working efficiency are obtained. 
         [0065]    On the other hand, the coil  18  is wound around the sleeve  13  (step S 5 ), a sleeve side mounting part of the second flat spring  15  is attached to the rear side end face of the sleeve  13  (step S 6 ) and the holder  19  is attached to the sleeve  13  so as to sandwich the second flat spring  15  (step S 7 ). As a result, a sleeve assembly is completed (step S 8 ). The sleeve assembly is inserted from the rear side of the yoke  11  (step S 9 ). 
         [0066]    Finally, a wire spring  16  is put into the yoke  11  from the incident window  111  (front side) of the cover part  11   a  (step S 10 ). Therefore, in the lens drive device  1  in accordance with this embodiment, a diameter of the incident window  111  (and the incident window  121  of the spacer  12 ) is set to be larger than a diameter of the wire spring  16 . Accordingly, the wire spring  16  can be put in a final stage of the assembling steps (see  FIG. 4 ) and, as a result, a degree of freedom for assembling work can be enhanced. Further, since the wire spring  16  can be easily put in through the incident window  111  of the cover part  11   a , even when a sudden design modification is required (for example, due to demand by a customer), the demand can be rapidly coped with. In this embodiment, a diameter of the incident window  111  is set to be larger so that the wire spring  16  can be put in through the incident window  111 . However, the spacer  12  whose thickness is thicker than a moving amount of the first flat spring  14 , in other words, the spacer  12  whose thickness is thicker than a moving amount in the optical axis direction of the movable body (sleeve  13 ) is disposed between the cover part  11   a  and the flat spring and thus, even when the movable body is moved to a maximum amount, the movable body can be prevented from projecting from the cover part  11   a . Further, when the wire spring  16  is not required, a diameter of the incident window  111  may be made smaller. In this case, even when the movable body (sleeve  13 ) is moved to a maximum amount, the movable body is prevented from abutting with the cover part  11   a  by means of that the spacer  12  whose thickness is thicker than a moving amount of the first flat spring  14  is placed. 
         [0067]    As described above, when the lens drive device  1  in accordance with this embodiment is to be assembled, the spacer  12  whose thickness is thicker than the moving amount of the first flat spring, the first flat spring  14 , and the magnet  17  which is to be fixed to the case part  11   b  are disposed on an inner side of the cover part  11   a  of the yoke  11  so as to be sequentially superposed on each other in this order from the cover part  11   a . Therefore, the spacer  12  and the first flat spring  14  are positioned by the case part  11   b  and thus working efficiency can be enhanced. In other words, in this embodiment, since the yoke  11  which is structured so that the cover part  11   a  and the case part  11   b  are integrally formed of each other is formed by drawing working, the yoke  11  is formed with a high degree of working accuracy. Therefore, when the spacer  12 , the first flat spring  14  and the magnet  17  are disposed in this order along the inner peripheral face of the case part  11   b , positional accuracy in the radial direction is secured. Similarly, when the above-mentioned structural elements are superposed on each other with the cover part  11   a  as a reference face, positioning in the optical axis direction is easily performed. 
       [Basic Operation] 
       [0068]    In the lens drive device  1  in accordance with this embodiment, the movable body is normally located on an imaging element side (image side at a non-energized time of the first coil  181  and the second coil  182 ). In this case, the wire spring  16  restricts displacement of the movable body by a magnetic attraction force acting between the magnet  17  and the wire spring  16 . However, a distance between the wire spring  16  and the magnet  17  is maintained to some extent and thus the magnetic attraction force between the wire spring  16  and the magnet  17  does not become too strong. According to this structure, the center axis of the movable body is prevented from being displaced and, as a result, deterioration of tilt characteristics can be prevented. 
         [0069]    In this state, when a current is supplied to the first coil  181  and the second coil  182 , upward (front side) electro-magnetic forces are respectively applied to the first coil  181  and the second coil  182 . Therefore, the first coil  181 , the second coil  182  and the sleeve  13  begin to move to an object to be photographed side (front side). 
         [0070]    In this case, elastic forces which restrict movement of the sleeve  13  are respectively occurred between the first flat spring  14  and the front end of the sleeve  13  and between the second flat spring  15  and the rear end of the sleeve  13 . Therefore, when the electro-magnetic force for moving the sleeve  13  to the front side and the elastic forces which restrict the movement of the sleeve  13  are balanced with each other, the sleeve  13  is stopped. Further, when a current in a reverse direction is supplied to the first coil  181  and the second coil  182 , downward (rear side) electro-magnetic forces are respectively applied to the first coil  181  and the second coil  182 . 
         [0071]    In this case, the sleeve  13  (movable body) can be stopped at a desired position by means of that a current amount supplied to the first coil  181  and the second coil  182  and elastic forces acting on the sleeve  13  of the first flat spring  14  and the second flat spring  15  are adjusted. In this embodiment, since the sleeve  13  is stopped by utilizing the balance of the electro-magnetic force with the elastic force, different from a case that two members are abutted with each other such that the sleeve  13  is engaged with an engaging part or the like, occurrence of collision noise can be prevented. 
       Principal Effects of Embodiment 
       [0072]    According to the lens drive device  1  in accordance with this embodiment, the yoke  11  is formed in a roughly box-like shape (see  FIGS. 3(   a ) and  3 ( b )), which is structured so that the cover part  11   a  and the case part  11   b  are formed in an integral manner and, when the spacer  12 , the first flat spring  14 , the magnet  17  and the like are to be accommodated in the yoke  11 , positioning in the optical axis direction is performed by the cover part  11   a  and positioning in the radial direction is performed by the case part  11   b . Therefore, even when a conventional positioning jig is not used, respective structural elements such as the spacer  12 , the first flat spring  14  and the like can be positioned and, as a result, the number of times of positioning work is reduced and working efficiency can be improved. 
         [0073]    Further, the yoke  11  is comprised of one member which is formed by a drawing work and thus a dimensional tolerance is restrained smaller in comparison with a conventional bending work and a structural member with a high degree of working accuracy can be easily formed. 
         [0074]    Further, since the spacer  12  and the first flat spring  14  are sandwiched by the cover part  11   a  and the magnet  17  (see  FIG. 7 ), the spacer  12  and the first flat spring  14  are capable of being positioned in the optical axis direction and thus working efficiency can be enhanced. 
       Modified Embodiment 
       [0075]      FIGS. 8(   a ),  8 ( b ) and  8 ( c ) are views for explaining a yoke  11  in the lens drive device  1  in accordance with another embodiment of the present invention.  FIG. 8(   a ) and  FIG. 8(   b ) are views showing the above-mentioned embodiment. Further,  FIG. 8(   a ) and  FIG. 8(   b ) are side views when viewed in the direction of the arrow “X” in  FIG. 2 . 
         [0076]    As shown in  FIG. 8(   c ), a cover part  11   a  of the yoke  11  is formed so that a portion around an incident window  111  is protruded to an outer side in the optical axis “L” direction and a stepped part is formed with an upper face  11   a ′ and a lower face  11   a ″. When a space is secured by the upper face  11   a ′ and the lower face  11   a ″ as described above, the space is capable of functioning as the spacer  12  shown in  FIG. 8(   b ). In addition, the stepped part structured by the upper face  11   a ′ and the lower face  11   a ″ is, similarly to the above-mentioned embodiment, formed by a drawing work and thus working is easy and working accuracy can be enhanced. 
         [0077]    Therefore, when the cover part  11   a  of the yoke  11  is structured of the upper face  11   a ′ and the lower face  11   a ″ as shown in  FIG. 8(   c ), the spacer  12  may be eliminated and thus the lens drive device  1  can be made thinner or its weight can be reduced. 
         [0078]    When the spacer  12  is used as the embodiment described above, the spacer  12  may be formed in any shape. For example, the spacer  12  may be formed in one-plate shape or in a separate shape which is disposed at four corners. In the latter case, the weight of the lens drive device  1  can be reduced in comparison with a case where the one-plate shaped spacer  12  is used. 
         [0079]    Further, the lens drive device  1  may be mounted on various electronic apparatuses in addition to a cell phone with a camera. For example, the lens drive device  1  may be mounted on a PHS, a PDA, a bar code reader, a thin digital camera, a monitor camera, a camera for confirming the rear side of a vehicle, a door having an optical authentication function and the like. 
         [0080]    At least an embodiment of a lens drive device in accordance with the present invention is effective to enhance working efficiency for positioning. 
         [0081]    While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. 
         [0082]    The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.