Abstract:
A lens driving apparatus includes: a lens holder including an auto-focusing first coil; a lens holder moving section; driving magnets disposed at four corners of the lens holder moving section; a camera-shake correction second coil; a plurality of suspension wires; an elastic member; and at least one damper compound, wherein the elastic member comprises first and second leaf springs mounted to first and second ends of the lens holder moving section, respectively, the second leaf spring is arranged apart from the fixed member compared to the first leaf spring, the fixed member is disposed at a position in the vicinity of the first leaf spring, the plurality of suspension wires extend along the first direction, are fixed to the fixed member and the second leaf spring, and the damper compound is disposed at a position in the vicinity of the second leaf spring.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of application Ser. No. 15/197,807, filed on Jun. 30, 2016, which is a continuation of application Ser. No. 14/138,321, filed on Dec. 23, 2013, now U.S. Pat. No. 9,405,088; which claims the benefit of priority from Japanese Patent Application No. 2012-282762, filed on Dec. 26, 2012, the disclosures of which are incorporated herein in their entirety by reference. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to a lens driving apparatus for use in a camera equipped with an auto-focusing function and a camera-shake correction function, a camera module, and a camera-equipped mobile terminal. 
       Description of Related Art 
       [0003]    Conventionally, as a camera installed in a mobile terminal such as a smartphone, a camera equipped with an auto-focusing function and a camera-shake correction function is known. Such a camera adopts a lens driving apparatus that automatically focuses on a subject to be captured by moving a lens barrel and can reduce an image defect by correcting a camera-shake (vibration) when capturing an image (for example, WO2011/021559). 
         [0004]    A lens driving apparatus disclosed in WO2011/021559 includes a lens holder moving section that supports a lens holder in which a lens barrel is fixed, wherein the lens holder is supported in such a manner as to be movable in the optical axis direction. In this lens driving apparatus, an auto-focusing first coil is disposed around the lens barrel (lens holder), and a permanent magnet is disposed to the lens holder moving section, whereby an auto-focusing lens driving section (hereinafter referred to as AF lens driving section) is configured. The AF lens driving section moves the lens holder in the optical axis direction by utilizing an electromagnetic force (Lorentz force) which acts on a first coil when a current is passed through the first coil, to thereby perform auto-focusing. 
         [0005]    In addition, in the lens driving apparatus disclosed in WO2011/021559, a second coil is disposed in a spaced relationship with an auto-focusing permanent magnet in the optical axis direction, whereby a camera-shake correction lens driving section is configured. The camera-shake correction lens driving section moves the lens holder moving section and the lens holder along a plane orthogonal to the optical axis direction by utilizing an electromagnetic force which is generated when a current is passed through the second coil, to thereby perform camera-shake correction. 
         [0006]    The portion at which the second coil is disposed is referred to as a fixed section since the portion does not move at the time of the camera-shake correction, whereas the lens holder and the lens holder moving section are referred to as a movable section since they rock at the time of the camera-shake correction. The movable section is supported to the fixed section by a supporting member such as a suspension wire for example so as to be able to rock. 
         [0007]    In the above-mentioned manner, the AF lens driving section and the camera-shake correction lens driving section share the permanent magnet, whereby the size and thickness of the lens driving apparatus can be reduced. 
         [0008]    Generally, a lens holder moving section has an external form which is square in plan view as viewed in the optical axis direction, and includes a substantially circular (which encompasses regular polygons) holder housing section which is formed at a center portion and configured to house a lens holder. A permanent magnet for auto-focusing and camera-shake correction is composed of a cuboid bar magnet, and disposed along the four sides defining the external shape of the lens holder moving section. That is, the permanent magnet is disposed in parallel with the outer periphery of the product. In addition, the second coil making up the camera-shake correction lens driving section has an ellipsoidal form with rounded corners matching the form of the permanent magnet. The second coil is also disposed in parallel with the outer periphery of the product. 
         [0009]    As used herein, the term “plan view” means a plan view in the optical axis direction. 
         [0010]    In recent years, because of a trend toward multi-functionality of mobile terminals and the advent of thin devices such as smartphones, there has been a growing demand for further reduction in size and thickness. However, it is difficult to achieve further size reduction with the configuration of the conventional lens driving apparatuses. 
         [0011]    More specifically, the conventional lens driving apparatus requires a sufficient space for disposing the permanent magnet in parallel with the outer periphery of the product around the holder housing section of the lens holder moving section. In addition, the external size of the fixed section at which the second coil is disposed is substantially the same as the lens holder moving section, which also hinders miniaturization. 
       SUMMARY OF THE INVENTION 
       [0012]    An object of the present invention is to provide a lens driving apparatus, a camera module, and a camera-equipped mobile terminal which can achieve miniaturization in comparison with conventional technology. 
         [0013]    A lens driving apparatus according to an embodiment of the present invention includes: a lens holder to which a lens barrel can be attached, the lens holder including an auto-focusing first coil; a lens holder moving section that is square as viewed in a plane orthogonal to a first direction along an optical axis, the lens holder moving section being configured to support the lens holder in such a manner that the lens holder is movable in the first direction; a driving magnet disposed at four corners of the lens holder moving section, the driving magnet being configured to move the lens holder in the first direction in cooperation with the first coil; a camera-shake correction second coil configured to move the lens holder in a second direction and a third direction in cooperation with the driving magnet, the second direction and the third direction corresponding to diagonal directions of the lens holder moving section; and a supporting section configured to support the lens holder moving section in such a manner that the lens holder moving section is movable in the second direction and the third direction. 
         [0014]    A camera module according to an embodiment of the present invention includes: the above-mentioned lens driving apparatus; a lens barrel held by the lens holder; and an imaging section configured to capture a subject image formed by the lens barrel. 
         [0015]    A camera-equipped mobile terminal according to an embodiment of the present invention includes the above-mentioned camera module. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]    The present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein: 
           [0017]      FIG. 1  is a perspective view illustrating an external appearance of a camera module according to an embodiment of the present invention; 
           [0018]      FIG. 2  is a perspective view illustrating an external appearance of a lens driving apparatus to be covered by a shield cover; 
           [0019]      FIG. 3  is an exploded perspective view illustrating a camera module; 
           [0020]      FIG. 4  is an exploded perspective view illustrating a movable section of the lens driving apparatus; 
           [0021]      FIG. 5  illustrates magnetizing directions of position detecting magnets; 
           [0022]      FIG. 6  illustrates the operating principle of auto-focusing in the lens driving apparatus; 
           [0023]      FIG. 7  illustrates the operating principle of camera-shake correction in the lens driving apparatus; 
           [0024]      FIGS. 8A and 8B  illustrate external shapes of the lens driving apparatus of the embodiment and a conventional lens driving apparatus, for comparison; and 
           [0025]      FIG. 9  illustrates a modification of a position detecting section. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Now, an embodiment of the present invention will be described with reference to the accompanying drawings. 
         [0027]      FIG. 1  is a perspective view illustrating an external appearance of camera module M according to an embodiment of the present invention.  FIG. 2  is a perspective view illustrating an external appearance of lens driving apparatus  1  to be covered by shield cover  2 .  FIG. 3  is an exploded perspective view illustrating camera module M.  FIG. 4  is an exploded perspective view illustrating movable section  10  of lens driving apparatus  1 . 
         [0028]    For the description, orthogonal coordinate system (X, Y, and Z) is used, as illustrated in  FIG. 1  to  FIG. 3 . In  FIG. 1  to  FIG. 3 , the X direction is the front-rear direction (depth direction), the Y direction is the horizontal direction (width direction), and the Z direction is the vertical direction (height direction). 
         [0029]    In  FIG. 1  to  FIG. 3 , the Z direction is the optical axis direction of a lens. In addition, the intermediate directions between the X and Y directions, or in other words, the diagonal directions in plan view in the Z direction of camera module M are u direction and v direction. The Z direction, u direction, and v direction correspond to a first direction, second direction, and third direction in the present invention, respectively. 
         [0030]    Camera module M illustrated in  FIG. 1  to  FIG. 3  is a camera module to be mounted to a smartphone, for example. Camera module M is equipped with auto-focusing function and camera-shake correction function, and is capable of automatically focusing on a subject to be captured and of capturing images without image blurring by correcting camera-shake (vibration) when capturing images. 
         [0031]    Camera module M includes a cylindrical lens barrel (not illustrated) that houses a lens, lens driving apparatus  1  that moves the lens barrel to perform auto-focusing and camera-shake correction, an imaging section (not illustrated) that captures an image of a subject, shield cover  2  that covers the entire camera module M, and the like. 
         [0032]    Shield cover  2  is a box that covers the outer peripheral surface of lens driving apparatus  1 . The upper surface  2   a  of shield cover  2  is square, and the lens barrel (not illustrated) faces the outside through circular opening  2   b  formed on upper surface  2   a . That is, camera module M is square in plan view, and lens driving apparatus  1  covered by shield cover  2  also is square in plan view. 
         [0033]    As illustrated in  FIG. 2  and  FIG. 3 , lens driving apparatus  1  includes fixed section  20  which is fixed so as to be unmovable when camera module M is mounted to a mobile terminal or the like, and movable section  10  that rocks in the X-Y plane with respect to fixed section  20 . Movable section  10  is disposed upwardly of fixed section  20  (in the Z1 direction) with a gap therebetween, and supported by a supporting member such as suspension wire  30  so as to be able to rock. 
         [0034]    As illustrated in  FIG. 3  and  FIG. 4 , movable section  10  includes lens holder  11 , magnet holder  12 , permanent magnet  13 , upper spring  14 , lower spring  15 , spacer  16 , position detecting magnet  17 , and the like. Magnet holder  12 , upper spring  14 , lower spring  15 , and spacer  16  make up a lens holder moving section that supports lens holder  11  so as to be movable in the Z direction. 
         [0035]    Lens holder  11  includes first coil  111 , upper coil holder  112 , and lower coil holder  113 . 
         [0036]    First coil  111  is an air-core coil through which a current flows at the time of auto-focusing, in which a wire is wound in a substantially octagonal cylindrical form. 
         [0037]    Upper coil holder  112  is an annular frame formed in an octagonal shape in plan view matching the external shape of first coil  111 . Upper coil holder  112  includes protrusions  112   a  protruding radially outwardly. On the upper surface of protrusion  112   a , boss  112   b  on which to attach upper spring  14  is formed. 
         [0038]    Lower coil holder  113  is an annular frame formed in an octagonal shape in plan view matching the external shape of first coil  111 . Lower coil holder  113  includes protrusions  113   a  protruding radially outwardly. On the bottom surface of protrusions  113   a , boss  113   b  on which to attach lower spring  15  is formed. 
         [0039]    Upper coil holder  112  and lower coil holder  113  tightly sandwich first coil  111 . In other words, lens holder  11  is a vertically-separable lens holder, and cylindrical barrel housing section  11   a  is formed by the inner peripheral surfaces of first coil  111 , upper coil holder  112 , and lower coil holder  113 . In lens holder  11 , the inner peripheral surface of first coil  111  is exposed. The lens barrel (not illustrated) is fixed to barrel housing section  11   a.    
         [0040]    In the above-mentioned manner, in lens driving apparatus  1 , lens holder  11  is made up of first coil ( 111 ) composed of an air-core coil, and a coil holding member (upper coil holder  112  and lower coil holder  113 ) that tightly sandwich first coil ( 111 ), and the inner peripheral surface of first coil ( 111 ) is exposed. 
         [0041]    In comparison with a coil in which a wire is wound around the outer peripheral surface of a coil holder, the coil internal diameter is reduced by the thickness of the coil holder, which is effective in miniaturizing lens driving apparatus  1 . 
         [0042]    The lens barrel (not illustrated) is fixed to barrel housing section  11   a  of lens holder  11  by bonding. Although there is a possibility that a foreign matter such as dust enters lens driving apparatus  1  in the case where the lens barrel (not illustrated) is threadedly engaged with lens holder  11 , such a defect can be prevented by the above-described fixing method. 
         [0043]    Magnet holder  12  has a square cylindrical form which is square in plan view. Magnet holder  12  is provided, at its four corners, with magnet housing sections  12   a  at which permanent magnets  13  are disposed. Magnet housing sections  12   a  are each formed in an isosceles trapezoidal form in plan view matching the external shape of permanent magnet  13 . 
         [0044]    Recesses  12   b  are formed at substantially the center of the four sides on the upper surface of magnet holder  12 . Protrusions  112   a  of upper coil holder  112  are disposed at respective recesses  12   b.    
         [0045]    In addition, two bosses  12   e , on which to attach upper spring  14 , are formed at each of the four corners on the upper surface of magnet holder  12 . In addition, protruding portions  12   g  are formed at the four corners on the upper surface of magnet holder  12  so as to surround suspension wires  30 . 
         [0046]    Recesses  12   c  are formed at substantially the center of the four sides on the bottom surface of magnet holder  12 . Protrusions  113   a  of lower coil holder  113  are disposed at respective recesses  12   c . The depth of recess  12   c  is so set that it is sufficiently greater than the height of protrusion  113   a  of lower coil holder  113 . The depth of recess  12   c  limits the migration length of lens holder  11  at the time of auto-focusing. 
         [0047]    In addition, on the bottom surface of magnet holder  12 , recess  12   d  adjacent to recess  12   c  is formed at the two sides facing each other in the X direction. Position detecting magnet  17  is disposed at recess  12   d . In addition, one boss  12   f  on which to attach lower spring  15  and spacer  16  is formed at each of the four corners on the bottom surface of magnet holder  12 . 
         [0048]    Permanent magnet  13  is a magnet having an isosceles trapezoidal columnar form. Permanent magnet  13  is disposed at magnet housing section  12   a  located at the four corners of magnet holder  12  with the long side of the isosceles trapezoid being positioned on the radially inner side. Specifically, four permanent magnets  13  are disposed to face first coil  111  in the u direction and the v direction. Magnet holder  12  and permanent magnet  13  define a space having an octagonal shape in plan view, in which lens holder  11  can move in the Z direction. 
         [0049]    Permanent magnet  13  is magnetized in such a manner that a magnetic field orthogonal to the radial direction is formed at first coil  111 . Here, permanent magnet  13  is magnetized in such a manner that the inner periphery side thereof is N pole, and the outer periphery side thereof is S pole. 
         [0050]    Upper spring  14  is a leaf spring made of beryllium copper, nickel copper, stainless-steel, or the like, for example and is composed of equally-shaped four members. Upper spring  14  includes magnet holder attaching section  14   a  to be fixed to the upper surface of magnet holder  12 , and lens holder attaching section  14   f  to be fixed to the upper surface of lens holder  11  (upper coil holder  112 ). Upper spring  14  elastically supports lens holder  11  with respect to magnet holder  12 . 
         [0051]    Magnet holder attaching section  14   a  has a form corresponding to a corner on the upper surface of magnet holder  12 . In magnet holder attaching section  14   a , engagement hole  14   d  which engages with boss  12   e  formed on the upper surface of magnet holder  12  is formed. In addition, in magnet holder attaching section  14   a , wire fixation hole  14   e  into which an end of suspension wire  30  is inserted is formed. 
         [0052]    Between lens holder attaching section  14   f  and magnet holder attaching section  14   a , arm section  14   b  extending along the external shape of lens holder  11  is formed. Engagement hole  14   c  which engages with boss  112   b  of upper coil holder  112  is formed in lens holder attaching section  14   f.    
         [0053]    Similarly to upper spring  14 , lower spring  15  is a leaf spring made of beryllium copper, nickel copper, stainless-steel, or the like, for example, and is composed of equally-shaped four members. Lower spring  15  includes magnet holder attaching section  15   a  to be fixed to the bottom surface of magnet holder  12 , and lens holder attaching section  15   e  to be fixed to the bottom surface of lens holder  11  (lower coil holder  113 ). Lower spring  15  elastically supports lens holder  11  with respect to magnet holder  12 . 
         [0054]    Magnet holder attaching section  15   a  has a form corresponding to a corner on the bottom surface of magnet holder  12 . In magnet holder attaching section  15   a , engagement hole  15   d  which engages with boss  12   f  formed on the bottom surface of magnet holder  12  is formed. 
         [0055]    Between lens holder attaching section  15   e  and magnet holder attaching section  15   a , arm section  15   b  extending along the external shape of lens holder  11  is formed. Engagement hole  15   c  which engages with boss  113   b  of lower coil holder  113  is formed in lens holder attaching section  15   e.    
         [0056]    At the time of fitting lens holder  11  to magnet holder  12 , boss  12   e  of magnet holder  12  is inserted into engagement hole  14   d  of magnet holder attaching section  14   a  of upper spring  14 , and fixed by thermal welding, for example. In addition, boss  112   b  of upper coil holder  112  is inserted into engagement hole  14   c  of lens holder attaching section  14   f , and fixed by thermal welding or bonding. 
         [0057]    Further, boss  12   f  of magnet holder  12  is inserted into engagement hole  15   d  of magnet holder attaching section  15   a  of lower spring  15 , and engagement hole  16   a  of spacer  16  disposed below lower spring  15 , and fixed by thermal welding, for example. 
         [0058]    In addition, boss  113   b  of lower coil holder  113  is inserted into engagement hole  15   c  of lens holder attaching section  15   e , and fixed by thermal welding or bonding. 
         [0059]    Thus, lens holder  11  is elastically supported by upper spring  14  and lower spring  15  in such a manner that lens holder  11  can be displaced in the Z direction in the state where lens holder  11  is positioned with respect to magnet holder  12 . 
         [0060]    In addition, when four protrusions  113   c  formed on the bottom surface of lower coil holder  113  contact the upper surface of spacer  16 , the entirety of lens holder  11  is lifted in the optical axis direction by the height of protrusion  113   c , whereby upper spring  14  and lower spring  15  are caused to generate a back tension. 
         [0061]    At this time, protrusions  112   a  of upper coil holder  112  are loosely fixed to recesses  12   b  formed on the upper surface of magnet holder  12 , and protrusions  113   a  of lower coil holder  113  are loosely fixed to recesses  12   c  formed on the bottom surface of magnet holder  12 . Further, lens holder attaching section  14   f  of upper spring  14  is distanced from the upper surface of magnet holder  12  by the height of protrusions  113   c  formed on the bottom surface of lower coil holder  113 . 
         [0062]    Specifically, by the distance between lens holder attaching section  14   f  of upper spring  14  and the upper surface of magnet holder  12 , a back tension is generated at upper spring  14 , and lens holder  11  (protrusions  112   a ) is pressed toward magnet holder  12 . In addition, lens holder attaching section  15   e  of lower spring  15  is distanced by the same amount as upper spring  14 , and accordingly a back tension is generated. With this configuration, in a non-energizing state, lens holder  11  does not move even when the posture of lens driving apparatus  1  is turned upside down. From this standard state, lens holder  11  moves upward (Z1 direction) at the time of auto-focusing (at the time of energization). 
         [0063]    Position detecting magnets  17 A and  17 B are disposed in recesses  12   d  formed on the bottom surface of magnet holder  12  (see  FIG. 5 ). Position detecting magnets  17 A and  17 B are cuboid bar magnets. Position detecting magnet  17 A is obliquely magnetized in the v direction, and position detecting magnet  17 B is obliquely magnetized in the v direction orthogonal to the u direction. The position of movable section  10  in the v direction can be detected by detecting the magnetic field formed by position detecting magnet  17 A, and the position of movable section  10  in the u direction can be detected by detecting the magnetic field formed by position detecting magnet  17 B. The magnetic fields formed by position detecting magnets  17 A and  17 B are detected by Hall devices  24 A and  24 B disposed to face position detecting magnets  17 A and  17 B in the Z direction. 
         [0064]    In addition, also in the case where position detecting magnet  17 A is obliquely magnetized in the u direction and position detecting magnet  17 B is obliquely magnetized in the v direction, Hall devices  24 A and  24 B can detect the position of movable section  10  in the u direction and the v direction. 
         [0065]    It is to be noted that, as position detecting magnets  17 A and  17 B, commonly used bar magnets magnetized in the longitudinal direction or the short direction may also be used. In this case, position detecting magnets  17 A and  17 B are obliquely disposed so that the magnetizing direction corresponds to the u direction or the v direction. 
         [0066]    Fixed section  20  includes coil board  21 , base member  22 , and the like. 
         [0067]    Similarly to magnet holder  12 , coil board  21  is square in plan view, and circular opening  21   a  is formed at the center of coil board  21 . In addition, at the four corners of coil board  21 , wire fixation hole  21   b  into which the other end (lower end) of suspension wire  30  is inserted is formed. 
         [0068]    At the four corners of coil board  21 , camera-shake correction second coil  23  is disposed to face permanent magnet  13 . Second coil  23  has a form of an isosceles trapezoid with rounded corners in plan view so as to correspond to the form of permanent magnet  13 . The form, arrangement, and the like of permanent magnet  13  and second coil  23  are so set that the radial edges of permanent magnet section  13  fall within the cross-sectional width of the coil, or more specifically, are so set that the magnetic field radiated from permanent magnet  13  in the Z direction traverses the opposing two sides of second coil  23  and returns to permanent magnet  13 . With this configuration, the driving force (electromagnetic force) for moving movable section  10  in the XY plane can be efficiently generated. 
         [0069]    Similarly to coil board  21 , base member  22  is square in plan view, and circular opening  22   a  is formed at the center of base member  22 . 
         [0070]    In addition, fixed section  20  includes a position detecting section that detects the position of movable section  10  in the XY plane, or more concretely, the position in the u direction and the v direction. In this example, as the position detecting section, Hall devices  24 A and  24 B are attached to base member  22 . Hall devices  24 A and  24 B are disposed at respective positions facing detecting magnets  17 A and  17 B. Hall devices  24 A and  24 B are magnetic sensors that detect a magnetic field by utilizing Hall effect. When the magnetic field formed by position detecting magnets  17 A and  17 B is detected by Hall devices  24 A and  24 B, the position of movable section  10  in the XY plane can be detected. 
         [0071]    In the above-mentioned manner, lens driving apparatus  1  includes the position detecting section that detects the position of the lens holder moving section (magnet holder  12 , upper spring  14 , lower spring  15 , and spacer  16 ) in the second direction (the u direction) and third direction (the v direction). 
         [0072]    To be more specific, lens driving apparatus  1  includes: a first position detecting magnet (position detecting magnet  17 B) disposed along a side of the lens holder moving section ( 12 ,  14 ,  15 ,  16 ) and magnetized in the second direction (the u direction); and a second position detecting magnet (position detecting magnet  17 A) disposed along a side of lens holder moving section ( 12 ,  14 ,  15 ,  16 ) different from the side along which first position detecting magnet is disposed and magnetized in the third direction (the v direction). The position detecting section is made up of first Hall device ( 24 B) disposed to face first position detecting magnet ( 17 B) in the first direction (the Z direction), and second Hall device ( 24 A) disposed to face second position detecting magnet ( 17 A) in the first direction (the Z direction). 
         [0073]    Since components (such as coil, for example) having an influence on the magnetic field formed by position detecting magnets  17 A and  17 B are not disposed between position detecting magnets  17 A and  17 B and Hall devices  24 A and  24 B, the accuracy in the detection of magnetic field by Hall devices  24 A and  24 B is improved. 
         [0074]    Movable section  10  and fixed section  20  are coupled by a supporting member such as suspension wire  30 . To be more specific, four suspension wires  30  extend along the Z direction, and support the entirety of movable section  10  in such a manner that movable section  10  can rock in the XY plane. An end (upper end) of each of four suspension wires  30  is inserted into protruding portion  12   g  of magnet holder  12 , and fixed to wire fixation hole  14   e  of upper spring  14  by soldering. The other end (lower end) of each of four suspension wires  30  is inserted into wire fixation hole  21   b  of coil board  21 , and fixed by soldering. 
         [0075]    It is to be noted that two of four suspension wires  30  are used also for supplying electricity to first coil  111 . In addition, the number of suspension wires  30  is not limited to four, and it suffices that a plurality of suspension wires  30  are provided. 
         [0076]    A damper (not illustrated) is disposed between magnet holder  12  and upper spring  14  so as to surround suspension wire  30 . Specifically, magnet holder  12  includes protruding portions  12   g  protruding radially outwardly at the four corners of magnet holder  12 . Protruding portions  12   g  are each provided at a position near wire fixation hole  14   e  in such a manner as to surround suspension wire  30  with a gap therebetween. The damper (not illustrated) is disposed between protruding portion  12   g  and upper spring  14  in such a manner as to surround suspension wire  30 . The damper (not illustrated) can be readily applied by using a dispenser for example. For example, ultraviolet curable silicone gel (trade name: TB3168E, viscosity: 90 Pa·s) available from ThreeBond Co., Ltd. may be employed as the damper (not illustrated). It is to be noted that the damper (not illustrated) is not limited to the ultraviolet curable resin, and any materials may be used as long as a damper effect is obtained. 
         [0077]    Since unnecessary resonance is suppressed by disposing the damper (not illustrated) between magnet holder  12  and upper spring  14  in such a manner as to surround suspension wire  30 , the operation of lens driving apparatus  1  is remarkably stabilized. In addition, since the damper (not illustrated) reduces the impact which is caused when the apparatus is dropped, the impact resistance of lens driving apparatus  1  is improved. 
         [0078]    In addition, Hall devices  24 A and  24 B and a sensor board (not illustrated, FPC: Flexible printed circuits) on which a control section is mounted are disposed between coil board  21  and base member  22 , as the imaging section. Further, an imaging device (not illustrated) is disposed below base member  22 . The imaging device (not illustrated) is composed of a charge-coupled device (CCD) image sensor, a complementary metal oxide semiconductor (CMOS) image sensor, or the like, for example. The imaging device (not illustrated) captures a subject image formed by means of the lens barrel (not illustrated), converts this image into an electrical signal, and outputs this signal to the control section (not illustrated). 
         [0079]    The control section (not illustrated) performs auto-focusing by controlling the current to be passed through first coil  111 . In addition, the control section (not illustrated) performs camera-shake correction by controlling the current to be passed through second coil  24  on the basis of the position detection signal detected by two Hall devices  24 A and  24 B so as to offset the rock detected by two direction gyros (not illustrated). 
         [0080]      FIG. 6  illustrates the operating principle of auto-focusing in lens driving apparatus  1 . 
         [0081]    When auto-focusing is performed in lens driving apparatus  1 , permanent magnet  13  and first coil  111  cooperate with each other to move lens holder  11  in the Z direction. That is, the AF lens driving section includes permanent magnet  13  and first coil  111 . To be more specific, in order to perform auto-focusing, the AF lens driving section moves lens holder  11  in the Z direction by utilizing an electromagnetic force (Lorentz force) which acts on first coil  111  when a current is passed through first coil  111 . 
         [0082]    As illustrated in  FIG. 6 , at first coil  111 , a radially inward magnetic field is formed by permanent magnets  13 . Accordingly, when a counterclockwise AF current is passed through first coil  111 , upward electromagnetic force F AF  (Lorentz force) is generated in first coil  111  according to Fleming&#39;s left hand rule. As a result, lens holder  11  (lens barrel) moves in the Z1 direction. 
         [0083]    Since the magnitude of an electromagnetic force generated in first coil  111  changes when the value of the AF current changes, automatic focusing is achieved by controlling the value of AF current to adjust the migration amount of lens holder  11  (lens barrel). 
         [0084]    It is to be noted that when lens holder  11  keeps on moving in the Z1 direction at the time of auto-focusing, protrusions  113   a  finally come into contact with recesses  12   c  of magnet holder  12 , and thus further movement thereof is limited. 
         [0085]    In other words, in lens driving apparatus  1 , lens holder ( 11 ) includes a protrusion (protrusions  113   a  of lower coil holder  113 ) protruding radially outwardly, and the lens holder moving section (magnet holder  12 ) includes an engaging section (recesses  12   c ) which is to be engaged with the protrusion ( 113   a ) and restricts the movement of lens holder ( 11 ). 
         [0086]    With this configuration, recesses  12   c  of magnet holder  12  function as a physical stopper at the time of auto-focusing, whereby damage and the like can be prevented when movable section  10  excessively moves due to malfunction. 
         [0087]      FIG. 7  illustrates the operating principle of camera-shake correction in lens driving apparatus  1 . 
         [0088]    When camera-shake correction is performed in lens driving apparatus  1 , permanent magnet  13  and second coil  23  cooperate with each other to move lens holder  11  in the XY plane. That is, the camera-shake correction lens driving section includes permanent magnet  13  and second coil  23 . To be more specific, in order to perform auto-focusing, the camera-shake correction lens driving section moves lens holder  11  in the XY plane by utilizing an electromagnetic force (Lorentz force) which acts on second coil  23  when a current is passed through second coil  23 . 
         [0089]    As illustrated in  FIG. 7 , at second coil  23 A disposed in the u1 direction, a magnetic field that traverses second coil  23 A in the Z direction is formed by permanent magnet  13 A. Accordingly, when a clockwise IS current is passed through second coil  23 A, a u2-directional electromagnetic force is generated in second coil  23 A according to Fleming&#39;s left hand rule. Since second coil  23 A is fixed, as a reaction thereto, u1-directional Force F IS  acts on permanent magnet  13 A. 
         [0090]    In addition, at second coil  23 B disposed in the u2 direction, a magnetic field that traverses second coil  23 B in the Z direction is formed by permanent magnet  13 B. Accordingly, when a counterclockwise IS current is passed through second coil  23 B, a u2-directional electromagnetic force is generated in second coil  23 B according to Fleming&#39;s left hand rule. Since second coil  23 B is fixed, as a reaction thereto, u1-directional Force F IS  acts on permanent magnet  13 B. 
         [0091]    As a result, lens holder  11  (lens barrel) moves in the u1 direction as movable section  10 . 
         [0092]    Conversely, when a counterclockwise IS current is passed through second coil  23 A, and at the same time a clockwise IS current is passed through second coil  23 B, lens holder  11  (lens barrel) moves in the u2 direction as movable section  10 . 
         [0093]    Likewise, when an IS current is passed through second coils  23 C and  23 D disposed in the v1 direction and v2 direction, lens holder  11  can be moved in the v1 direction or v2 direction. 
         [0094]    In the above-mentioned manner, lens driving apparatus  1  includes: lens holder ( 11 ) that has auto-focusing first coil ( 111 ) disposed around the lens barrel (not illustrated) and holds the lens barrel; the lens holder moving section (magnet holder  12 , upper spring  14 , lower spring  15 , and spacer  16 ) that is square as viewed in a plane orthogonal to the first direction (the Z direction) along the optical axis and supports lens holder ( 11 ) in such a manner that lens holder ( 11 ) is movable in the first direction (the Z direction); a driving magnet (permanent magnet  13 ) that is disposed at the four corners of lens holder moving section ( 12 ,  14 ,  15 ,  16 ) and moves lens holder ( 11 ) in the first direction (the Z direction) in cooperation with first coil ( 111 ); camera-shake correction second coil ( 23 ) that moves lens holder ( 11 ) in the diagonal direction of lens holder moving section ( 12 ,  14 ,  15 ,  16 ), that is, in the second direction (the u direction) and third direction (the v direction), in cooperation with driving magnet ( 13 ); and the supporting section (fixed section  20 , suspension wire  30 ) that supports the lens holder moving section ( 12 ,  14 ,  15 ,  16 ) in such a manner that the lens holder moving section is movable in the second direction (the u direction) and third direction (the v direction). 
         [0095]    According to lens driving apparatus  1 , since the driving magnet (permanent magnet  13 ) and second coil ( 23 ) are disposed at the four corners of the apparatus which is square in plan view to effectively utilize the dead space in the conventional lens driving apparatuses, the space for disposing driving magnet ( 13 ) and second coil ( 23 ) can be reduced, and miniaturization can be achieved in comparison with conventional apparatuses. 
         [0096]    It is obvious that the external shape of camera module M according to the embodiment (see  FIG. 8A ) is smaller than that of the conventional camera module (see  FIG. 8B ) when substantially the same external shape of first coil  111  and substantially the same thickness of the permanent magnet are employed as illustrated in  FIG. 8 . 
         [0097]    The present inventor estimates that the conventional lens driving apparatus having a size of 11.5 mm×11.5 mm can be miniaturized to the size of 8.5 mm×8.5 mm, by more than 45% in planar dimension. 
         [0098]    While the invention made by the present inventor has been specifically described based on the preferred embodiments, it is not intended to limit the present invention to the above-mentioned preferred embodiments but the present invention may be further modified within the scope and spirit of the invention defined by the appended claims. 
         [0099]    For example, as position detecting magnets  17 A and  17 B, commonly used bar magnets which are magnetized in the longitudinal direction or the short direction may also be used. In this case, position detecting magnets  17 A and  17 B are obliquely disposed so that the magnetizing direction corresponds to the u direction or the v direction. 
         [0100]    In addition, while position detecting magnets  17 A and  17 B are disposed at two sides of magnet holder  12  facing each other in the embodiment, position detecting magnets  17 A and  17 B may also be disposed at adjacent two sides. Also in this case, it suffices that one of position detecting magnets  17  is magnetized in the u direction and the other of position detecting magnets  17  is magnetized in the v direction. 
         [0101]    In addition, it is also possible to dispose position detecting magnets  17 A and  17 B on fixed section  20  side, and Hall devices  24 A and  24 B on the movable section  10  side. 
         [0102]    In addition, it is also possible that, as illustrated in  FIG. 9 , Hall device  24 A, which detects the position of movable section  10  in the u direction, is disposed to face one of permanent magnets  13 A and  13 B (in  FIG. 9 , permanent magnet  13 A) in the Z direction with a gap therebetween, and Hall device  24 B, which detects the position of movable section  10  in the v direction, is disposed to face one of permanent magnets  13 C and  13 D (in  FIG. 9 , permanent magnet  13 C) in the Z direction with a gap therebetween. Here, permanent magnets  13 A and  13 B are disposed to face each other in the u direction, and permanent magnets  13 C and  13 D are disposed to face each other in the v direction. 
         [0103]    In this case, since permanent magnets  13 A and  13 C are used for the position detection, it is not necessary to dispose position detecting magnets  17 A and  17 B unlike the embodiment. However, since second coils  23 A and  23 C are disposed between permanent magnets  13 A and  13 C and Hall devices  24 A and  24 B, a magnetic field which is generated when a current is passed through second coils  23 A and  23 C is undesirably detected by Hall devices  24 A and  24 B. In other words, under the influence of a magnetic field which is generated when a current is passed through second coils  23 A and  23 C, the detection accuracy of Hall devices  24 A and  24 B may be decreased. 
         [0104]    In view of the above, when permanent magnets  13 A and  13 C are used for the position detection, it is preferable to employ separation-type coils, as second coils  23 A and  23 C, which are each separated at the center thereof in the longitudinal direction, as illustrated in  FIG. 9 . By disposing Hall devices  24 A and  24 B just below the portions where second coils  23 A and  23 C are separated, it is possible to prevent the problem that the detection accuracy of Hall devices  24 A and  24 B is decreased by a magnetic field which is generated when a current is passed through second coils  23 A and  23 C. 
         [0105]    Further, as the position detecting section that detects the position of movable section  10  in the XY plane, an optical sensor composed of a combination of a photointerrupter and a reflection plate may be employed. 
         [0106]    While camera module M and lens driving apparatus  1  to be mounted in a smartphone are described in the embodiment, the camera module and the lens driving apparatus according to the embodiment of the present invention are applicable to laptop computers, tablet personal computers, mobile terminals such as mobile game machines, Web cameras, and camera apparatuses such as in-vehicle cameras. 
         [0107]    The embodiment disclosed herein is merely an exemplification and should not be considered as limitative. The scope of the present invention is specified by the following claims, not by the above-mentioned description. It should be understood that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors in so far as they are within the scope of the appended claims or the equivalents thereof.