Abstract:
A lens actuator includes a carrier having a tubular shape having a through-hole provided therein. The through-hole is arranged to mount a lens therein. The lens actuator further includes plural springs contacting upper and lower surfaces of the carrier, a coil fixed to the carrier, a first yoke, a second yoke, and a magnet contacting the first yoke and the second yoke. The coil is placed between the first yoke and the second yoke. This lens actuator moves the lens by a long distance, and has a small size.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a lens actuator mainly used in optical equipment, such as a camera or a mobile phone, for moving a lens. 
       BACKGROUND OF THE INVENTION 
       [0002]    Cameras and mobile phones have recently included lens actuators in order to provide for automatic focusing functions. Such lens actuator have been accordingly demanded to be small in size and be able to move lenses by long distances. 
         [0003]      FIG. 6  is a sectional view of a conventional lens actuator  501  disclosed in Japanese Patent Lain-Open Publication No. 2004-280031.  FIG. 7  is an exploded perspective view of the lens actuator  501 . Carrier  1  made of insulating resin has a cylindrical shape having a though-hole arranged to mount a lens into the through-hole. Carrier  1  is accommodated between case  3  and cover  2  placed over a top surface of case  3  so as to be movable in vertical directions. Cover  2  and case  3  are made of insulating resin, similarly carrier  1 . 
         [0004]    Upper spring  4  and lower spring  5  are made of thin metal plates. Upper spring  4  is placed between a bottom surface of cover  2  and a top surface of carrier  1  while being slightly compressed. Lower spring  5  is placed between a bottom surface of carrier  1  and an inner bottom surface of case  3  while being slightly compressed. Upper spring  4  and lower spring  5  hold carrier  1  at a predetermined position. 
         [0005]    Coil  6  is made a copper alloy wire wound annularly. Yoke  7  made of magnetic material, such as iron, has a substantially cylindrical shape and has a section of substantially U-shape. Coil  6  is fixed onto flange  1 A provided under an outer circumferential surface of carrier  1 . Yoke  7  covers coil  6 , and faces the outer circumferential surface of carrier  1 . 
         [0006]      FIG. 8  is a partially-enlarged view of lens actuator  501 . Plural magnets  8  having a substantially arcuate shape are attached onto an inside of outer wall  7 C of yoke  7 . Gap L 501  inside magnets  8 , inner wall  7 A of yoke  7 , top section  7 B of yoke  7 , and outer wall  7 C of yoke  7  provide a magnetic path along which a magnetic flux produced from magnets  8  passes. Coil  6  is placed in gap L 501  between the inner circumferential surface of magnets  8  and inner wall  7 A. 
         [0007]    Both ends of coil  6  made of conductive material, such as copper, are connected to plural electrodes  9  by soldering, respectively. Respective lower ends of electrodes  9  protrude outward from a bottom of case  3 . Spacer  10  made of insulating resin is placed on lower spring  5 , thus providing lens actuator  501 . 
         [0008]    Lens actuator  501  is mounted to a device, such as a camera or a mobile phone. Electrodes  9  are connected to an electronic circuit of the device. 
         [0009]    An operation of lens actuator  501  will be described below. When a user activates a push button of the device including lens actuator  501 , the electronic circuit of the device applies a voltage to electrodes  9  to cause a current to flow in coil  6 , accordingly producing a magnetic field, as shown in  FIG. 8 . Magnetic field M 501  directed from magnet  8  to inner wall  7 A of yoke  7  is produced around coil  6 , and applies a force in a vertical direction, such as upward direction of  501 A or downward direction  501 B, to coil  6 . This force causes coil  6  and carrier  1  having coil  6  mounted thereto to move in the upward direction  501 A or downward direction  501 B, thereby adjusting the focus of the lens mounted into carrier  1 . 
         [0010]    Upon the current flowing in coil  6  being released, respective elastic forces of upper spring  4  and lower spring  5  push carrier  1  to hold carrier  1  at the predetermined position. 
         [0011]    In lens actuator  501 , as shown in  FIG. 8 , a magnet field is produced in a horizontal direction around coil  6  at the predetermined position, and a large magnetic field is produced at the center surrounded by magnets  8  facing coil  6 . The magnetic field produced by magnets  8  is directed toward top section  7 B in gap L 501  between coil  6  and top section  7 B of yoke  7 . Therefore, a magnetic field in gap L 501  is smaller than a magnetic field in gap L 502 . Accordingly, coil  6  which has moved in direction  501 A receives a small force from the magnetic field. In order to increase a moving distance of coil  6 , i.e., carrier  1 , it is necessary to increase the height of magnet  8 , accordingly increasing the size of lens actuator  501 . 
       SUMMARY OF THE INVENTION 
       [0012]    A lens actuator includes a carrier having a tubular shape having a through-hole. The through-hole is arranged to mount a lens therein. The lens actuator further includes plural springs contacting upper and lower surfaces of the carrier, a coil fixed to the carrier, a first yoke, a second yoke, and a magnet contacting the first yoke and the second yoke. The coil is placed between the first yoke and the second yoke. 
         [0013]    This lens actuator moves the lens by a long distance, and has a small size. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a sectional view of a lens actuator according to an exemplary embodiment of the present invention. 
           [0015]      FIG. 2  is an exploded perspective view of the lens actuator according to the embodiment. 
           [0016]      FIG. 3  is a partially-enlarged view of the lens actuator according to the embodiment. 
           [0017]      FIG. 4  is a partially-enlarged view of another lens actuator according to the embodiment. 
           [0018]      FIGS. 5A to 5D  are partially-enlarged views of still another lens actuators according to the embodiment. 
           [0019]      FIG. 6  is a sectional view of a conventional lens actuator. 
           [0020]      FIG. 7  is an exploded perspective view of the conventional lens actuator. 
           [0021]      FIG. 8  is a partially-enlarged view of the conventional lens actuator. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]      FIGS. 1 and 2  are a sectional view and an exploded perspective view of lens actuator  1001  according to an exemplary embodiment of the present invention, respectively. Carrier  11  has substantially cylindrical shape, a tubular shape, having a through-hole  11 B arranged to have a lens accommodated therein. Cover  12  covers a top surface of case  13 . Carrier  11  is accommodated between case  13  and cover  12  placed over the top surface of case  3 , and is movable in vertical directions. Carrier  11 , cover  12 , and case  13  are made of insulating resin, such as polycarbonate containing glass. Carrier  11  has flange  11 A protruding from an outer circumferential surface of carrier  11 . 
         [0023]    Coil  17  includes a copper-alloy wire coated with insulating resin and wound annularly. Inner yoke  18  made of magnetic material, such as iron, has a substantially cylindrical shape having through-hole  18 P therein. Plural outer yokes  19  made of magnetic material, such as iron, have a substantially arcuate shape. Coil  17  is fixed to flange  11 A of carrier  11 . Inner yoke  18  is surrounded by outer yokes  19 . Carrier  11  is accommodated in through-hole  18 P of inner yoke  18  such that carrier  11  is movable along center axis  1001 M of the cylindrical shape of inner yoke  18 . Outer circumferential surface  11 E of carrier  11  faces inner circumferential surface  18 A of inner yoke  18 . Outer circumferential surface  18 B of inner yoke  18  faces inner circumferential surfaces  19 A of outer yokes  19 . Outer yoke  19  has outer circumferential surface  19 B opposite to inner circumferential surface  19 A. Coil  17  is placed between inner yoke  18  and outer yokes  19  such that coil  17  is movable in a direction parallel to center axis  1001 M. 
         [0024]    Upper spring  14  and lower spring  15  are made of thin metal plate, such as, but not limited to, a steel plate and copper alloy plate. Carrier  11  has top end  11 C and bottom end  11 D in a direction of center axis  101 M. Upper spring  14  is placed between bottom surface  12 B of cover  12  and top surface  11 C of carrier  11  (flange  11 A) while being slightly compressed. Lower spring  15  is placed bottom surface  11 D of carrier  11  and top surface  16 A of lower cover  16  under case  13  while being slightly compressed. An elastic force produced by upper spring  14  and lower spring  15  which are slightly compressed urges carrier  11  from top surface  11 C and bottom surface  11 D, accordingly holding carrier  11  at a predetermined position along center axis  1001 M. 
         [0025]      FIG. 3  is a partially-enlarged view of lens actuator  1001 . Plural magnets  20  made of neodymium-base permanent magnet have substantially arcuate shapes having inner circumferential surfaces  20 A and outer circumferential surfaces  20 B. Inner circumferential surfaces  20 A of the magnets are attached onto outer circumferential surface  18 B of inner yoke  18  while contacting end  18 C of inner yoke  18 . Outer circumferential surfaces  20 B of the magnets are attached onto inner circumferential surfaces  19 A of outer yokes  19  while contacting ends  19 C of outer yokes  19  facing end  18 C of inner yoke  18 . Coil  17  and magnets  20  are placed between inner yoke  18  and outer yokes  19 . Coil  17  is located in gap L 1  surrounded by magnets  20 , outer circumferential surface  18 B of inner yoke  18 , and inner circumferential surfaces  19 A of outer yokes  19 . Magnetic field M 1  produced by magnets  20  passes through inner yoke  18 , gap L 1 , and outer yokes  19 . Thus, inner yoke  18  and outer yokes  19  provide a magnetic path along which magnetic field M 1  crossing coil  17  passes. No portion of magnets  20  are positioned between coil  17  and inner yoke  18 . No portion of magnets  20  are positioned between coil  17  and outer yokes  19 . Coil  17  and magnets  20  are arranged in parallel to center axis  1001 M. 
         [0026]    Both ends of the wire of coil  17  are connected to electrodes  21  by soldering, respectively. Electrodes  21  are made of conductive material, such as, but not limited to, copper alloy. Respective lower ends of electrodes  21  protrude outward from a bottom of case  13 , thus providing lens actuator  1001 . 
         [0027]    Lens actuator  1001  is mounted to a device, such as a camera and a mobile phone. Electrodes  21  are connected to an electronic circuit of the device. 
         [0028]    An operation of lens actuator  1001  will be described below. When a user activates a push button of the device including lens actuator  1001 , the electronic circuit of the device applies a voltage to electrodes  21 , thereby causing a current to flow in coil  17 . Coil  17  which magnetic field M 1  crosses, as shown in  FIG. 3 , receives a force in upward direction  1001 A and downward direction  1001 B which are parallel to center axis  100 M and perpendicular to magnetic field M 1 . This force causes coil  17  and carrier  11  having coil  17  mounted thereto to move in directions  1001 A and  1001 B from the predetermined position so as to adjust the focus of the lens fixed to carrier  11 , thus performing automatic focusing. 
         [0029]    Upon the current flowing in coil  17  being released, respective elastic forces produced by upper spring  14  and lower spring  15  move carrier  11  back to the predetermined position. 
         [0030]    As shown in  FIG. 3 , magnetic field M 1  is produced around coil  17 . Magnetic field M 1  is uniformly strong along the entire height of coil  17  and in gap L 1  and gap L 2  between coil  17  and magnets  20 , accordingly causing coil  17  to move reliably in directions  1001 A and  1001 B with a large force. 
         [0031]    Coil  17  and magnets  20  are arranged vertically between inner yoke  18  and outer yokes  19 . This arrangement reduces the distance between inner yoke  18  and outer yokes  19 , accordingly allowing lens actuator  1001  to have a small diameter. 
         [0032]      FIG. 4  is a partially-enlarged view of another lens actuator  1002  according to the embodiment. In  FIG. 4 , the same components as those of lens actuator  1001  shown in  FIGS. 1 to 3  are denoted by the same reference numerals, and their description will be omitted. Lens actuator  1002  includes inner yoke  118  and outer yokes  119  instead of inner yoke  18  and outer yokes  19  of lens actuator  1001  shown in  FIG. 3 . No portion of magnets  20  are positioned between coil  17  and inner yoke  118 . No portion of magnets  20  are positioned between coil  17  and outer yokes  119 . In lens actuator  1001  shown in  FIG. 3 , height  18 R of inner yoke  18  in the direction of center axis  1001 M of inner yoke  18  is smaller than height  19 R of outer yokes  19  in the direction. This structure produces magnetic field M 2  in a slanting direction from end  18 D of inner yoke  18  opposite to end  18 C toward end  19 C of outer yokes  19 . In lens actuator  1002 , height  118 R of inner yoke  118  in the direction of center axis  1001 M is equal to height  119 R of outer yokes  119  in the direction. This structure does not produce magnetic field M 2  in the slanting direction shown in  FIG. 3 . Therefore, a large magnetic field is produced between inner yoke  118  and outer yokes  119 , accordingly causing coil  17  and carrier  11  to move with a large force. 
         [0033]      FIG. 5A  is a partially-enlarged view of still another lens actuator  1003  according to the embodiment. In  FIG. 5A , the same components as those of lens actuator  1001  shown in  FIGS. 1 to 3  are denoted by the same reference numerals, and their description will be omitted. Lens actuator  1003  includes inner yoke  218  and outer yokes  219  instead of inner yoke  118  and outer yokes  119  of lens actuator  1001  shown in  FIG. 3 . No portion of magnets  20  are positioned between coil  17  and inner yoke  218 . No portion of magnets  20  are positioned between coil  17  and outer yokes  219 . Inner yoke  218  has inner circumferential surface  218 A and outer circumferential surface  218 B opposite to inner circumferential surface  218 A. Each of outer yokes  219  has inner circumferential surface  219 A and outer circumferential surface  219 B opposite to inner circumferential surface  219 A. Inner circumferential surfaces  20 A of magnets  20  are attached onto outer circumferential surface  218 B of inner yoke  218  while contacting ends  218 C of inner yoke  218 . Outer circumferential surfaces  20 B of the magnets are attached onto inner circumferential surfaces  219 A of outer yokes  219  while contacting ends  219 C of outer yokes  219  facing end  218 C of inner yoke  218 . Height  218 R of inner yoke  218  in the direction parallel to center axis  1001 M is equal to height  219 R of outer yokes  219  in this direction. A portion of inner circumferential surface  218 A contacting end  218 D of inner yoke  218  opposite to end  218 C of inner yoke  218  is chamfered, thus having slant portion  218 H. A portion of outer circumferential surface  219 B contacting end  209 D of outer yoke  219  opposite to end  219 C of outer yoke  219  is chamfered, thus having slant portion  219 H. Slant portions  218 H and  219 H reduce leakage of the magnetic flux between ends  218 D and  219 D. 
         [0034]      FIG. 5B  is a partially-enlarged view of still another lens actuator  1004  according to the embodiment. In  FIG. 5B , the same components as those of lens actuator shown in  FIGS. 1 to 3  are denoted by the same reference numerals, and their description will be omitted. Lens actuator  1004  includes inner yoke  318  and outer yokes  319  instead of inner yoke  18  and outer yokes  19  of lens actuator  1001  shown in  FIG. 3 . No portion of magnets  20  are positioned between coil  17  and inner yoke  318 . No portion of magnets  20  are positioned between coil  17  and outer yokes  319 . Inner yoke  318  has inner circumferential surface  318 A and outer circumferential surface  318 B opposite to inner circumferential surface  318 A. Outer yokes  319  have inner circumferential surfaces  319 A and outer circumferential surfaces  319 B opposite to inner circumferential surfaces  319 A. Inner circumferential surfaces  20 A of magnets  20  are attached onto outer circumferential surface  318 B of inner yoke  318  while contacting end  318 C of inner yoke  318 . Outer circumferential surfaces  20 B of magnets  20  are attached onto inner circumferential surfaces  319 A of outer yokes  319  while contacting ends  319 C of outer yokes  319  facing end  318  of inner yoke  318 . Height  318 R of inner yoke  318  in the direction parallel to center axis  1001 M is equal to height  319 R of outer yokes  319  in this direction. Outer yoke  319  has end  319 D opposite to end  319 C of outer yoke  319 . Inner yoke  318  has end  318 D opposite to end  318 C of inner yoke  318 . Outer yoke  319  has bend portion  319 H protruding from end  319 D of outer yoke  319  toward end  318 D of inner yoke  318  opposite to end  318 C of inner yoke  318 . Bend portion  319 H partially covers an opening between end  318 D of inner yoke  318  and end  319 D of outer yokes  319 . The structure reduces the difference between respective intensities of a magnetic field in gap L 32  close to end  318 D and end  319 D and a magnetic field in gap L 33  close to magnets  20  within gap L 31  between inner yoke  318  and outer yoke  319 , thus producing a substantially uniform magnetic field in gap L 31 . 
         [0035]      FIG. 5C  is a partially-enlarged view of still another lens actuator  1005  according to the embodiment. In  FIG. 5C , the same components as those of lens actuator  1001  shown in  FIGS. 1 to 3  are denoted by the same reference numerals, and their description will be omitted. Lens actuator  1005  includes inner yoke  418  and outer yokes  419  instead of inner yoke  18  and outer yokes  19  of lens actuator  1001  shown in  FIG. 3 . No portion of magnets  20  are positioned between coil  17  and inner yoke  418 . No portion of magnets  20  are positioned between coil  17  and outer yokes  419 . Inner yoke  418  has inner circumferential surface  418 A and outer circumferential surface  418 B opposite to inner circumferential surface  418 A. Outer yoke  419  has inner circumferential surface  419 A and outer circumferential surface  419 B opposite to inner circumferential surface  419 A. Inner circumferential surfaces  20 A of magnets  20  are attached onto outer circumferential surface  418 B of inner yoke  418  while contacting end  418 C of inner toke  418 . Outer circumferential surfaces  20 B of magnets  20  are attached onto inner circumferential surfaces  419 A of outer yokes  419  while contacting ends  419 C of outer yokes  419  facing end  418 C of inner yoke  418 . Height  418 R of inner yoke  418  in the direction parallel to center axis  1001 M is equal to height  419 R of outer yokes  419  in this direction. Inner yoke  418  has end  418 D opposite to end  418 C of inner yoke  418 . Outer yoke  419  has end  419 D opposite to end  419 C of outer yoke  419 . Inner yoke  418  has bend portion  418 H protruding from end  418 D of inner yoke  418  toward ends  419 D of outer yokes  419 . Bend portion  418 H partially covers an opening between end  418 D of inner yoke  418  and end  419 D of outer yokes  419 . The structure reduces the difference between respective intensities of a magnetic field in gap L 42  close to end  418 D and end  419 D and magnetic field in gap L 43  close to magnets  20  within gap L 41  between inner yoke  418  and outer yoke  419 , thus producing a substantially uniform magnetic field in gap L 41 . 
         [0036]      FIG. 5D  is a partially-enlarged view of still another lens actuator  1006  according to the embodiment. In  FIG. 5D , the same components as those of lens actuator  1001  shown in  FIGS. 1 to 3  are denoted by the same reference numerals, and their description will be omitted. Lens actuator  1006  includes inner yoke  518  and outer yokes  519  instead of inner yoke  18  and outer yokes  19  of lens actuator  1001  shown in  FIG. 3 . No portion of magnets  20  are positioned between coil  17  and inner yoke  518 . No portion of magnets  20  are positioned between coil  17  and outer yokes  519 . Inner yoke  518  has inner circumferential surface  518 A and outer circumferential surface  518 B opposite to inner circumferential surface  518 A. Outer yoke  519  has inner circumferential surface  519 A and outer circumferential surface  519 B opposite to inner circumferential surface  519 A. Inner circumferential surfaces  20 A of magnets  20  are attached onto outer circumferential surface  518 B of inner yoke  518  while contacting end  518 C of inner yoke  518 . Outer circumferential surfaces  20 B of magnets  20  are attached onto inner circumferential surfaces  519 A of outer yokes  519  while contacting ends  519 C of outer yokes facing end  518 C of inner yoke  518 . Height  518 R of inner yoke  518  in the direction parallel to center axis  1001 M is equal to height  519 R of outer yokes  519  in this direction. Inner yoke  518  and outer yokes  519  have width  518 W and  519 W, respectively, in radial direction  1006  perpendicular to center axis  1001 M. Widths  518 W and  519 W are determined so that the total volume of outer yokes  519  becomes equal to the volume of inner yoke  518 . According to their diameters, in general, width  518 W is determined to be larger than width  519 W. The structure produces a uniform magnetic field. 
         [0037]    The present invention as been described with reference to the foregoing embodiments. It is noted that the present invention may be embodied in other forms without departing from the spirit of the invention. The present 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.