Abstract:
Shafts are fixed to a base and extend in a direction parallel to a center axis of a through hole of the base. Two yoke arrangements are installed to the shafts. A lens holder frame holds a lens, which has an optical axis parallel to the central axis of the through hole of the base. The lens holder frame is axially placed in a space between the two yoke arrangements and is swingably supported by a plurality of wire springs, which are fixed to the base. Drive coils are fixed to the lens holder frame and generate a drive force to move the lens holder frame.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on and incorporates herein by reference Japanese Patent Application No. 2005-232277 filed on Aug. 10, 2005.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a lens drive apparatus, which drives a lens.  
         [0004]     2. Description of Related Art  
         [0005]     A vehicle drive assist system, which includes a onboard video camera to monitor a front side or a rear side of a vehicle, has been marketed. In this system, an image, which is captured by the onboard camera, is displayed on a monitor provided in a passenger compartment of the vehicle. In one previously known system, a stereo camera is used as the above video camera to measure a distance relative an obstacle. In another system, the distance measurement function of the above system is implemented as a scanning laser distance meter. In the scanning laser distance meter, a laser beam is scanned, i.e., swung and is transmitted through a transmission window toward an obstacle. The reflected light, which is reflected from the obstacle, is detected, and the distance to the obstacle is computed based on the detected light.  
         [0006]     Japanese Unexamined Patent Publication No. 10-96624 discloses one apparatus that scans the laser beam by swinging a mirror. Instead of swinging the mirror, a lens may be swung or move to scan, i.e., to swing the laser beam. In such a case, the mechanism recited in Japanese Patent No. 3317997 (corresponding to U.S. Pat. No. 5,303,089) or in Japanese Unexamined Patent Publication No. 10-123252 may be used to swing or move the transmitter lens. In the mechanism recited in Japanese Patent No. 3317997, a bobbin, which holds a lens, is supported by leaf springs, thereby enabling the simplified mechanism. In the mechanism recited in Japanese Unexamined Patent Publication No. 10-123252, multiple coil springs are used to support a lens. The coil springs extend in a direction of an optical axis. The lens is driven by an actuator. This mechanism enables wide range scanning at low costs and high reliability.  
         [0007]     The apparatus recited in Japanese Patent No. 3317997 is intended to be used in scanning of an optical disc, and the lens is moved in a single direction that is parallel to the optical axis of the lens. However, in the distance meter, which measured the distance by scanning the laser beam, the lens needs to be moved in the plane that is perpendicular to the optical axis. More specifically, the lens needs to be moved in a first direction, which is perpendicular to the optical axis, and in a second direction, which is perpendicular to the first direction. At this time, unlike Japanese Patent No. 3317997, the lens is placed in a plane, along which the leaf springs of the bobbin extend. In the apparatus recited in Japanese Patent No. 3317997, a yoke is made by bending a single metal plate, and another yoke is placed at an opening end of this yoke. When the lens is placed at the opening end of the yoke, there would not be a problem. However, when the lens is placed in the plane, along which the leaf springs of the bobbin extend, it is difficult to place the magnets, the coils and the yokes without causing interferences with the lens and the optical axis, so that these components need to be placed in remaining limited spaces. When the yokes are formed integrally, the assembling is not easy.  
         [0008]     Furthermore, the distance meter, which scans the laser beam, is often installed in the vehicle. In the case of the vehicle, durability of the distance meter needs to be higher than that of domestic appliances. However, the metal plate yokes alone cannot provide the sufficient rigidity, thereby resulting in the low durability of the distance meter.  
         [0009]     In the apparatus disclosed in Japanese Unexamined Patent Publication No. 10-123252, the assembling of the lens drive mechanism may not be troublesome. However, the support structure, which supports the lens by the coil springs, is not good enough in terms of the durability. Also, in the case where the apparatus is installed in the vehicle, the countermeasures against the vibration are not good enough.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a lens drive apparatus, which achieves an increased durability of the lens drive apparatus and relatively easy assembling of the lens drive apparatus.  
         [0011]     To achieve the objective of the present invention, there is provided a lens drive apparatus, which includes a base, a plurality of shafts, two yoke arrangements, a lens holder frame and a plurality of drive coils. The base has a through hole, which penetrates through the base. The shafts are fixed to the base and extend in a direction generally parallel to a center axis of the through hole of the base. Each yoke arrangement holds a plurality of permanent magnets and surrounds the center axis of the through hole of the base. The yoke arrangements are supported by the shafts and are axially spaced from each other. The lens holder frame holds a lens, which has an optical axis generally parallel to the central axis of the through hole of the base. The lens holder frame is axially placed in a space between the two yoke arrangements and is swingably supported by a plurality of wire springs, which are fixed to the base. The drive coils are fixed to the lens holder frame and generate a drive force to move the lens holder frame. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:  
         [0013]      FIG. 1  is a front perspective view of a lens drive apparatus according to an embodiment of the present invention;  
         [0014]      FIG. 2  is a rear perspective view of the lens drive apparatus according to the embodiment;  
         [0015]      FIG. 3  is a front exploded perspective view of the lens drive apparatus according to the embodiment;  
         [0016]      FIG. 4  is a partial front perspective view of the lens drive apparatus according to the embodiment;  
         [0017]      FIG. 5  is a partial rear perspective view of the lens drive apparatus according to the embodiment;  
         [0018]      FIG. 6  is a cross sectional view of the lens drive apparatus taken along a Z-X plane, along which an optical axis of a transmitter lens of the lens drive apparatus passes;  
         [0019]      FIG. 7  is a plan cross sectional view of the lens drive apparatus taken along a Y-Z plane, along which the optical axis of the transmitter lens of the lens drive apparatus passes;  
         [0020]      FIG. 8  is a cross sectional view taken along line VIII-VIII in  FIG. 6 ;  
         [0021]      FIG. 9  is a schematic view showing a system that includes the lens drive apparatus according to the embodiment;  
         [0022]      FIG. 10A  is a schematic plan view indicating a modification of a yoke of the lens drive apparatus;  
         [0023]      FIG. 10B  is a schematic side view of the modification shown in  FIG. 10A ;  
         [0024]      FIG. 11  is a schematic plan view indicating another modification of the yoke of the lens drive apparatus;  
         [0025]      FIGS. 12A  to  12 B are schematic view indicating modifications of the cylindrical members of the lens drive apparatus; and  
         [0026]      FIG. 13  is a cross sectional view similar to  FIG. 8  indicating a modification of the lens drive apparatus. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     An embodiment of the present invention will be described with reference to the accompanying drawings.  
         [0028]     FIGS.  1  to  8  show a lens drive apparatus  10  according to the embodiment of the present invention.  FIGS. 1 and 2  are perspective views of the lens drive apparatus  10 .  FIG. 3  is a perspective view of the lens drive apparatus  10 .  FIGS. 4 and 5  are partial perspective views of the lens drive apparatus.  FIG. 6  is a cross sectional view along a Z-X plane of  FIG. 1 , along which an optical axis  14  of a transmitter lens  12  extends.  FIG. 7  is a cross sectional view along a Y-Z plane, along which the optical axis  14  of the transmitter lens  12  extends.  FIG. 8  is a cross sectional view along line VIII-VIII in  FIG. 6 .  
         [0029]     As shown in FIGS.  3  to  5 , in the lens drive apparatus  10 , the transmitter lens  12  is securely bonded to a holder (also referred to as a lens holder frame)  16 , which is made of resin, such as polyphenylene sulfide resin containing glass. An X-coil  18  is wound around the holder  16  in an X-Y direction. The X-coil  18  is made from, for example, a copper-clad aluminum wire. Furthermore, coil assemblies  20 A,  20 B are respectively bonded to opposed ends of the holder  16 , which are opposed to each other in the Y direction. Each coil assembly  20 A,  20 B is formed by insert molding a Y-coil  22 A,  22 B into a resin body. More specifically, each coil assembly  20 A,  20 B is molded from, resin, such as liquid crystal polymer resin containing glass, and the Y-coil  22 A,  22 B is made by winding, for example, a copper-clad aluminum wire.  
         [0030]     Furthermore, as shown in  FIG. 5 , the holder  16  includes holes  24 A- 24 D, in which one end of a corresponding one of wire springs (e.g., beryllium copper wire springs)  26 A- 26 D is fixed. In this case, the wire spring  26 A- 26 D is bonded in the hole  24 A- 24 D, and the end of the wire spring  26 A- 26 D, which is received through the hole  24 A- 24 D, is soldered to a circuit board (not shown). The ends of the X-coil  18  and the ends of the Y-coils  22 A,  22 B are also soldered to this circuit board, and the wiring on the circuit board electrically connects the X-coil  18  and the Y-coils  22 A,  22 B to the wire springs  26 A- 26 D.  
         [0031]     The other ends of the wire springs  26 A- 26 D are fixed to a spring support  28 . The spring support  28  is made of, resin, such as liquid crystal polymer resin containing glass. The other ends, i.e., the fixing portions, of the wire springs  26 A- 26 D will be described in detail with reference to  FIG. 6 . A portion B indicated in  FIG. 6  is indicated as a cross sectional view to show a structure of the fixing portion of the wire spring  26 B. Specifically, the spring support  28  includes hole segments  30 B,  32 B,  34 B, and the wire spring  26 B is received through the hole segments  30 B,  32 B,  34 B. As clearly shown in  FIG. 6 , the inner diameters of the hole segments  30 B,  32 B are substantially larger than the outer diameter of the wire spring  26 B. In contrast, the inner diameter of the hole segment  34 B is only slightly larger than the outer diameter of the wire spring  26 B, and thereby the portion of the wire spring  26 B received in the hole segment  34 B is securely bonded to the spring support  28 , more specifically to the inner peripheral wall of the hole segment  34 B of the spring support  28 . Furthermore, silicone gel is filled in a gap  36 B between an inner peripheral wall of the holes segment  32 B and an outer peripheral wall of the wire spring  26 B. The silicone gel filled in the gap  36 B damps the vibration of the wire spring  26 B. The hole segment  30 B serves as a relief hole for avoiding interference with the movement of the wire spring  26 B. The hole segment  32 B is not extended to the position of the hole segment  30 B in the positive Z direction (the left direction in  FIG. 6 ) to avoid excessive damping of the vibration of the wire spring  26 B by the silicone gel. The size of the spring support  28  is made relatively large in the Z direction to achieve the sufficient rigidity of the spring support  28 . In the above description, although only the wire spring  26 B is described, the other wire springs  26 A,  26 C,  26 D are fixed in the manner similar to that of the wire spring  26 B through the hole segments  30 A,  30 C,  30 D and the like of the spring support  28 .  
         [0032]     With the above structure, the holder  16  is supported by the spring support  28  though the wire springs  26 A- 26 D in such a manner that the holder  16  is movable in both of the X direction and the Y direction, i.e., in two dimensions. The spring support  28  further includes a through hole  38 , through which light (a laser beam) described below is conducted toward the transmitter lens  12 .  
         [0033]     In the above structure, the other ends (the right ends in  FIG. 6 )  26 A b - 26 D b  of the wire springs  26 A- 26 D are fixed to the spring support  28  in such a manner that the other ends  26 A b - 26 D b  of the wire springs  26 A- 26 D protrude from the spring support  28  and are soldered to a flexible circuit board (not shown). The flexible circuit board is in turn connected to an electric circuit (not shown). With the above structure, the X-coil  18  and the Y-coils  22 A,  22 B are electrically connected to the electric circuit (not shown) through the wire springs  26 A,  26 D.  
         [0034]     Furthermore, in the lens arrangement, which is assembled in the above described manner, the spring support  28  is fixed to a metal base frame  40  in such a manner that the through hole  38  of the spring support  28  is overlapped with a through hole  40   a  of the base frame  40  to allow transmission of the light therethrough. The base frame  40  alone or together with the spring support  28  serves as a base of the present invention.  
         [0035]     As shown in FIGS.  1  to  3 , stainless shafts  42 A- 42 D are fixed to the base frame  40 . Male threaded portions  42 A a - 42 D a ,  42 A b - 42 D b  are formed in opposed ends of the shafts  42 A- 42 D. Female threaded portions  44 A- 44 D are formed in corresponding portions of the base frame  40 , which receive the shafts  42 A- 42 D, respectively. The shafts  42 A- 42 D are fixed to the base frame  40  when the male threaded portions  42 A a - 42 D a  of the shafts  42 A- 42 D are threadably engaged with the female threaded portions  44 A- 44 D of the base frame  40 . At this time, in order to limit loosening of the thread engagement between each male threaded portion  42 A a - 42 D a  and the corresponding female threaded portion  44 A- 44 D, a nut  46 A- 46 D is threadably secured to the male threaded portion  42 A a - 42 D a  of each shaft  42 A- 42 D from the negative Z side (from the right side to left side in  FIG. 2 ).  
         [0036]     After the fixation of the shafts  42 A- 42 D to the base frame  40 , stainless collars  48 A- 48 D are placed over the shafts  42 A- 42 D. The inner diameter of each collar  48 A- 48 D is only slightly larger than the outer diameter of the corresponding shaft  42 A- 42 D, so that the collar  48 A- 48 D is tightly fitted to the shaft  42 A- 42 D.  
         [0037]     Iron yokes  50 A,  50 B are installed to the positive Z side (the left side in  FIG. 2 ) of the collars  48 A- 48 D, and iron yokes  52 A,  52 B are installed to the positive Z side (the left side in  FIG. 2 ) of the iron yokes  50 A,  50 B. The yokes  50 A,  50 B,  52 A,  52 B form a yoke arrangement of the present invention. The yokes  50 A,  50 B,  52 A,  52 B have installation holes (more specifically, installation recesses)  54 A- 54 H, into which the shafts  42 A- 42 D are received. Each installation hole  54 A- 54 H opens at the lateral edge of the corresponding yoke  50 A,  50 B,  52 A,  52 B. With this structure, each shaft  42 A- 42 D needs not to be installed into the corresponding installation hole  54 A- 54 H in the Z-direction (the axial direction). Specifically, each shaft  42 A- 42 D may be installed into the corresponding installation hole  54 A- 54 H in the X-direction (the lateral direction). In this way, the assembling can be performed without causing interference with the holder  16 .  
         [0038]     Permanent magnets  56 A,  56 B are securely bonded to the yokes  50 A,  50 B, respectively, and permanent magnets  58 A,  58 B are securely bonded to the yokes  52 A,  52 B, respectively. The magnetic polarities of the magnets  56 A,  56 B,  58 A,  58 B will be described latter.  
         [0039]     Iron collars  60 A- 60 D are installed over the shafts  42 A- 42 D, respectively, on the positive Z side (the left side in  FIG. 2 ) of the yokes  52 A,  52 B. Similar to the collars  48 A- 48 D, the inner diameter of each collar  60 A- 60 D is only slightly larger than the outer diameter of the corresponding shaft  42 A- 42 D, so that the collar  60 A- 60 D is tightly fitted to the shaft  42 A- 42 D. Unlike the stainless collars  48 A- 48 D, the collar  60 A- 60 D are made of the iron since the collars  60 A- 60 D cooperate with the yokes  50 A,  50 B,  52 A,  52 B (and yokes  62 A,  62 B,  64 A,  64 B described below) and the magnets  56 A,  56 B (and permanent magnets  56 C,  56 D described below) as well as the magnets  58 A,  58 B (and permanent magnets  58 C,  58 D described below) to form a magnetic circuit.  
         [0040]     The yokes  62 A,  62 B, which are made of iron, are installed to the positive Z side (the left side in  FIG. 2 ) of the collars  6 OA- 60 D. Furthermore, the yokes  64 A,  64 B, which are made of iron, are installed to the positive Z side (the left side in  FIG. 2 ) of the yokes  62 A,  62 B. The yokes  62 A,  62 B,  64 A,  64 B form a yoke arrangement of the present invention, which is axially spaced from the yoke arrangement formed by the yokes  50 A,  50 B,  58 A,  58 B. Unlike the installation holes  54 A- 54 H of the yokes  50 A,  50 B,  52 A,  52 B, each of which opens at the lateral edge of the yoke  50 A,  50 B,  52 A,  52 B, installation holes  66 A- 66 H of the yokes  62 A,  62 B,  64 A,  64 B, which receive the shafts  42 A,  42 D, are formed as normal through holes, each of which does not open at the lateral edge of the yoke  62 A,  62 B,  64 A,  64 B. Specifically, the shafts  42 A- 42 D are installed through the installation holes  66 A- 66 H of the yokes  62 A,  62 B,  64 A,  64 B in the Z-direction (the axial direction).  
         [0041]     The magnets  58 C,  58 D are securely bonded to the yokes  62 A,  62 B, respectively. Furthermore, the magnets  56 C,  56 D are securely bonded to the yokes  64 A,  64 B, respectively. The magnetic polarities of the magnets  58 C,  58 D,  56 C,  56 D will be described latter.  
         [0042]     The yokes  50 A,  50 B,  52 A,  52 B,  62 A,  62 B,  64 A,  64 B are fixed to the collars  48 A- 48 D,  60 A- 60 D by the bonding and the thread engagement of the nuts  68 A- 68 D to the male threaded portions  42 A b - 42 D b  of the shafts  42 A- 42 D on the positive Z-side (the left side in  FIG. 2 ) of the yokes  64 A,  64 B.  
         [0043]     Next, the operation of the lens drive apparatus  10  of the present embodiment will be described.  
         [0044]      FIG. 9  schematically shows a system, in which the lens drive apparatus  10  of the present embodiment is used.  
         [0045]     A laser beam is outputted from a laser beam source (a laser beam generator)  70  and is transmitted through a lens system  72 . Thereafter, the laser beam is tilted or swung in the left-right direction as indicated by an arrow D by moving the transmitter lens  12  of the lens drive apparatus  10  in the left-right direction. The beam  74  impinges onto an obstacle  76  and is reflected by the obstacle  76 . Then, the reflected beam  78 , which is reflected by the obstacle  76 , impinges onto a photodetector  82  through a receiver lens  80 , and a distance to the obstacle  76  is computed by an electric circuit based on the output of the photodetector  82 . The transmitter lens  12  is not only moved in the left-right direction but also in the up-down direction, so that the beam  74  can be also tilted or swung in the up-down direction.  
         [0046]     The mechanism for moving the transmitter lens  12  in the up-down direction and the left-right direction will be described in detail.  
         [0047]     As shown in  FIGS. 6 and 8 , a side  18 A of the X-coil  18  is held between the magnet  56 A and the magnet  56 C, and a side  18 B of the X-coil  18  is held between the magnet  56 B and the magnet  56 D. The magnetic polarities (the N-pole and the S-pole) of the magnets  56 A- 56 D are indicated in  FIG. 6 , and a magnetic field is developed in a direction of an arrow  84 ,  86  at each of the sides  18 A,  18 B. A magnetic flux, which flows from the magnet  56 C to the magnet  56 A, returns to the magnet  56 C through the following path: the yoke  50 A; the yokes  52 A,  52 B; the collars  60 A,  60 C; the yokes  62 A,  62 B; and the yoke  64 A. Furthermore, a magnetic flux, which flows from the magnet  56 B to the magnet  56 D, returns to the magnet  56 B through the following path: the yoke  64 B; the yoke  62 A,  62 B; the collars  60 B,  60 D, the yokes  52 A,  52 B; and the yoke  50 B.  
         [0048]     The direction of the electric current, which flows at the side  18 A of the X-coil  18 , is opposite from the direction of the electric current, which flows at the side  18 B of the X-coil  18 . Also, the direction  84  of the magnetic field is opposite from the direction  86  of the magnetic field. Thus, the direction of the thus generated force at the side  18 A coincides with the direction of the thus generated force at the side  18 B. Specifically, the direction of the force is the X-direction, which is perpendicular to the direction of the electric current and is also perpendicular to the direction of the magnetic field. In this way, by conducting the electric current in the X-coil  18 , the holder  16  and the transmitter lens  12 , which is installed to the holder  16 , can be moved in the X-direction.  
         [0049]     Furthermore, as shown in  FIGS. 7 and 8 , the Y-coil  22 A is held between the magnet  58 A and the magnet  58 C, and the Y-coil  22 B is held between the magnet  58 B and the magnet  58 D. The magnetic polarities of the magnets  58 A- 58 D are indicated in  FIG. 7 . More specifically, the surface of each of the magnets  58 A- 58 D are magnetized such that two opposite poles (the N-pole and the S-pole) are located on the surface of the magnet  58 A- 58 D, which is axially opposed to the corresponding coil  22 A,  22 B. A direction of the magnetic field at a side  88 A of the Y-coil  22 A is indicated by an arrow  92 . Furthermore, a direction of the magnetic field at a side  90 A of the Y-coil  22 A is opposite from the direction of the magnetic field at the side  88 A and is indicated by an arrow  94 . The direction of the electric current, which flows at the side  88 A of the Y-coil  22 A, is opposite from the direction of the electric current, which flows at the side  90 A of the Y-coil  22 A. Also, the direction  92  of the magnetic field is opposite from the direction  94  of the magnetic field. Thus, the direction of the thus generated force at the side  88 A coincides with the direction of the thus generated force at the side  90 A. Specifically, the direction of the force is the Y-direction, which is perpendicular to the direction of the electric current and is also perpendicular to the direction of the magnetic field.  
         [0050]     Similarly, the magnetic field at a side  88 B of the Y-coil  22 B has a direction indicated by an arrow  96 , and the magnetic field at a side  90 B of the Y-coil  22 B has a direction indicated by an arrow  98 . The direction of the electric current, which flows at the side  88 B of the Y-coil  22 B, is opposite from the direction of the electric current, which flows at the side  90 B of the Y-coil  22 B. Also, the direction  96  of the magnetic field is opposite from the direction  98  of the magnetic field. Thus, the direction of the thus generated force at the side  88 B coincides with the direction of the thus generated force at the side  90 B. Specifically, the direction of the force is the Y-direction, which is perpendicular to the direction of the electric current and is also perpendicular to the direction of the magnetic field.  
         [0051]     At the other sides (the vertical sides in  FIG. 7 ) of the Y-coil  22 A,  22 B, which are other than the sides  88 A,  88 B,  90 A,  90 B, although the force is generated in the X-direction, the direction of the force generated due to the magnetic field in the direction of the arrow  92 ,  96  is opposite from the direction of the force generated due to the magnetic field in the direction of the arrow  94 ,  98 . Thus, these forces are cancelled with each other and thereby will not be actually exerted in the X-direction.  
         [0052]     The direction of the force generated by the Y-coil  22 A in the Y-direction and the direction of the force generated by the Y-coil  22 B in the Y-direction coincide with each other. Therefore, by conducting the electric current through the Y-coils  22 A,  22 B, the holder  16  and the transmitter lens  12  can be moved in the Y-direction.  
         [0053]     As described above, according to the present embodiment, the yokes  50 A,  50 B,  52 A,  52 B,  62 A,  62 B,  64 A,  64 B are connected by the cylindrical shafts  42 A- 42 D and the cylindrical collars  60 A- 60 D to increase the rigidity. Thereby, the durability of the lens drive apparatus  10  is improved. Furthermore, the yokes  50 A,  50 B,  52 A,  52 B,  62 A,  62 B,  64 A,  64 B, the shafts  42 A- 42 D and the collars  60 A- 60 D do not interfere with the movable part (the holder  16  and the transmitter lens  12 ) at the time of the assembling of the lens drive apparatus  10 , so that the assembling of the lens drive apparatus  10  is eased.  
         [0054]     Furthermore, the vibration of the wire springs  26 A- 26 D is effectively damped by filling the silicone gel at the spring support  28 . Because of such measures taken against the external disturbance (the vibration), the lens drive apparatus  10  of the present embodiment can be effectively used in the system(s) installed in the vehicle or the like.  
         [0055]     The embodiment of the present invention has been described. However, the present invention is not limited this particular embodiment, and the embodiment can be modified in various ways without departing from the scope of the present invention.  
         [0056]     The magnets and the coils may be modified in various ways. For example, the X-coil  18  and the magnets  56 A- 56 D may be modified in a manner similar to that of the Y-coils. Furthermore, each of the Y-coils  22 A,  22 B is held between the magnet  58 A,  58 B and the magnet  58 C,  58 D. Alternatively, one of the magnet  58 A,  58 B and the magnet  58 C,  58 D may be eliminated to leave only the single magnet  58 A,  58 B or  58 C,  58 D near the Y-coil  22 A,  22 B. Even in this modification, the presence of the two opposite poles, i.e., the N-pole and the S-pole on the surface of the single magnet  58 A,  58 B or  58 C,  58 D allows generation of the magnetic field, which flows from the N-pole of the surface to the S-pole of the surface, and this magnetic field can create the force similar to that of the above one. In this way, the number of the magnets can be advantageously reduced.  
         [0057]     Each of the yokes  50 A,  50 B,  52 A,  52 B is formed as the straight yoke piece that extends along a single straight line. Alternatively, as shown in  FIG. 10A , two L-shaped yokes (L-shaped yoke pieces)  100  may be used in combination. In such a case, portions of the yokes  100 , which receive the shafts  42 A- 42 C, may be formed as oblique recesses  102 A- 102 C, each of which is recessed in an oblique direction between the X-direction and the Y-direction. In this way, the yokes  100  may be installed to the shafts  42 A- 42 C by moving the yokes  100  in the X-Y plane.  
         [0058]     Furthermore, as shown in  FIG. 10B , two portions of the yoke  100 , each of which is mounted with the corresponding magnet  56 A,  58 A, may be formed as a protrusion  104 , which protrudes from the rest of the yoke  100 , to adjust the position of the magnet  56 A,  58 A in the Z-direction.  
         [0059]     In this way, the number of the yokes can be advantageously reduced.  
         [0060]     This is also applicable to the yokes  62 A,  62 B,  64 A,  64 B. However, in the case of the yokes  62 A,  62 B,  64 A,  64 B, it is not required to slide the yokes  62 A,  62 B,  64 A,  64 B in the X-Y plane to install the same to the shafts  42 A- 42 D. More specifically, these yokes  62 A,  62 B,  64 A,  64 B may be configured to be installed to the shafts  42 A- 42 D in the Z-direction (the axial direction). For example, the yokes  62 A,  62 B,  64 A,  64 B may be configured as a square frame yoke  106 , as shown in  FIG. 11 . In this way, the number of the yokes can be advantageously reduced, and the assembling of the lens drive apparatus  10  can be eased.  
         [0061]     Furthermore, in the above embodiment, the shafts  42 A- 42 D and the collars  48 A- 48 D,  60 A- 60 D are formed separately. Alternatively, as shown in  FIG. 12A , a cylindrical member  108 , which includes a male threaded portion  110  and a female threaded portion  112 , may be used as the shaft. In this case, the cylindrical members  108 , each of which has the length that corresponds to the corresponding collar  48 A- 48 D and the corresponding collar  60 A- 60 D, may be provided. Then, the male threaded portion  110  of the cylindrical member  108 , which corresponds to the collar  48 A- 48 D, is threadably engaged with the base frame  40 , and the female threaded portion  112  of this cylindrical member  108  is threadably engaged with the male threaded portion  110  of the other cylindrical member  108 , which corresponds to the collar  60 A- 60 D. The female threaded portion  112  of the cylindrical member  108 , which corresponds to the collar  60 A- 60 D, may be threadably engaged with a bolt in place of the nut  68 A- 68 D.  
         [0062]     Furthermore, as shown in  FIG. 12B , a positioning portion  114  may be provided in addition to the threaded portion to advantageously increase the positioning accuracy.  
         [0063]     Through use of the cylindrical members  108  described above, the assembling work can be accelerated. Furthermore, the shape of the cylindrical members  108  may be modified in various ways.  
         [0064]     Also, it should be noted that the cylindrical member  108 , which corresponds to the collar  48 A- 48 D, does not need be aligned with the cylindrical member  108 , which corresponds to the collar  60 A- 60 D, along the straight line.  
         [0065]     The vibration of the wire springs  26 A- 26 D is damped by the silicone gel filled at the spring support  28 . Alternatively, a suitable damping mechanism may be provided between the holder  16  and the adjacent yokes or the adjacent collars to damp the vibration. For instance, as shown in  FIG. 13 , damper springs  61 A- 61 D may be provided between the holder  16  and the collars  60 A- 60 D.  
         [0066]     Also, in some cases, a position sensor is required to obtain the position information of the transmitter lens  12 . In such a case, the position sensor may be fixed to the corresponding yoke or shaft through a sensor fixing member. For instance, such a sensor  91  may be provided to the yoke  50 B in  FIG. 13 .  
         [0067]     Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.