Patent Publication Number: US-9429815-B2

Title: Blade drive device and optical instrument

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of and claims priority to International Patent Application No. PCT/JP2013/072450 filed on Aug. 22, 2013, which claims priority to Japanese Patent Application No. 2012-210079 filed on Sep. 24, 2012 and Japanese Patent Application No. 2013-111175 filed on May 27, 2013, subject matter of these patent documents is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to blade drive devices and optical instruments. 
     (ii) Related Art 
     Japanese Unexamined Patent Application Publication No. 2009-175365 discloses a blade drive device in which an actuator drives a blade to open and close an opening in a board. The actuator is connected with a drive lever for driving the blade. The actuator and the drive lever are supported on the board. 
     The positional relationship between the actuator and the drive lever might increase the space on the board occupied by these members. This might increase the size of the board in the planar direction perpendicular to an optical axis direction, so that the size of the blade drive device itself might be increased. 
     SUMMARY 
     It is thus object of the present invention to provide a blade drive device having a reduced size in a planar direction perpendicular to an optical axis direction and an optical instrument having the same. 
     According to an aspect of the present invention, there is provided a blade drive device including: a board including an opening; first and second blades opening and closing the opening; and first and second actuators respectively driving the first and second blades, wherein the first and second actuators respectively include first and second stators, first and second rotors, and first and second coils, and respectively drive the first and second blades through first and second drive members, the first drive member is arranged to overlap the first stator and the first coil in an optical axis direction, and the second drive member is arranged to overlap the second stator and the second coil in the optical axis direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a blade drive device according to the present embodiment; 
         FIG. 2  is an exploded perspective view of the blade drive device according to the present embodiment; 
         FIG. 3  is an enlarged view of a rotor, a drive member, and an output member; 
         FIG. 4  is a sectional view around a leading blade, the drive member, the output member, and an actuator; 
         FIGS. 5A and 5B  are explanatory views of load applied to the drive member; 
         FIG. 6  is a perspective view of the drive member, the output member, and the rotor when viewed in an axial direction of an opening; 
         FIG. 7  is a sectional view of a blade drive device according to a variation; 
         FIG. 8  is a front view of the blade drive device; 
         FIG. 9  is an explanatory view of a unit; 
         FIGS. 10A and 10B  are front views of blade drive devices according to variations, and 
         FIG. 11  is a front view of a blade drive device according to a variation. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  are exploded perspective views of a blade drive device  1  according to the present embodiment. The blade drive device  1  is also referred to as a focal plane shutter. The blade drive device  1  is employed in an optical instrument such as a digital camera or a still camera. The blade drive device  1  includes boards  10 ,  10 A, and  10 B, a leading blade  20 A, a trailing blade  20 B, arms  31   a ,  32   a ,  31   b , and  32   b , and actuators  70   a  and  70   b . The boards  10 ,  10 A, and  10 B respectively include openings  11 ,  11 A, and  11 B. The leading blade  20 A and the trailing blade  20 B open and close these openings  11 ,  11 A, and  11 B. The actuators  70 A and  70 B drive the leading blade  20 A and the trailing blade  20 B, respectively. 
     The leading blade  20 A and the trailing blade  20 B each includes plural blades. Each of the leading blade  20 A and the trailing blade  20 B can shift between an overlapped state where the plural blades overlap one another and an expanded state where the plural blades are expanded. These plural blades in the overlapped state recede from the opening  11  to cause the opening  11  to be in a fully opened state. These plural blades in the expanded state close the opening  11  to cause the opening  11  to be in a fully closed state.  FIGS. 1 and 2  illustrate the blade drive device  1  in the fully opened state. 
     The leading blade  20 A is connected with the arms  31   a  and  32   a . The trailing blade  20 B is connected with the arms  31   b  and  32   b . As illustrated in  FIG. 2 , the arms  31   a ,  32   a ,  31   b , and  32   b  are rotatably supported by spindles  14   a ,  15   a ,  14   b , and  15   b  provided in the board  10 , respectively. 
     Drive members  40   a  and  40   b  drive the arms  31   a  and  31   b , respectively. Thus, the arms  31   a  and  31   b  correspond to driven members that are driven by the drive members  40   a  and  40   b  and that drive the leading blade  20 A and the trailing blade  20 B, respectively. The drive members  40   a  and  40   b  are provided with drive pins  43   a  and  13   b  connected with the arms  31   a  and  31   b , respectively. The boards  10 ,  10 A, and  10 B are respectively formed with escape slots  13   a ,  13   a A, and  13   a B for permit-ting the movement of the drive pin  43   a . Likewise, they are respectively formed with escape slots  13   b ,  13   b A, and  13   b B for permitting the movement of the drive pin  43   b . The drive members  40   a  and  40   b  will be described later in detail. 
     The board  10  is assembled with holders  80  and  90  holding the actuators  70   a  and  70   b . The holder  80  is formed. with support walls  81   a  and  81   b  that respectively support the actuators  70   a  and  70   b . The holder  80  is secured on the hoard  10 . The holders  80  and  90  are secured to each other. The holder  90  is provided with plural engaging claws  98 . The holder  80  is provided with plural engaging portions  88  which are respectively engaged with the engaging claws  98 . The holders  30  and  90  are secured to each other by engaging the engaging claws  98  with the engaging portions  88 . The holders  80  and  90  are made of a synthetic resin. 
     The actuator  70   a  includes: a rotor  72   a  rotatably supported by the holder  80 ; a stator  74   a  excited to generate magnetic force between the stator and the rotor  72   a;  and a leading blade coil  76   a  for exciting the stator  74   a . The rotor  72   a  is fitted with an output member  50   a  as will be described later in detail. The output member  50   a  is connected with the drive member  40   a . Therefore, the rotation of the rotor  72   a  drives the output member  50   a  and the drive member  40   a  to drive the arm.  31   a  and the leading blade  20 A. The actuator  70   b  has the same arrangement, The rotation of a rotor  72   b  of the actuator  70   b  drives the drive member  40   b  to drive the trailing blade  20 B. 
     The support walls  81   a  and  81   b  of the holder  80  are respectively formed with escape holes  85   a  and  85   b . The escape hole  85   a  receives a connection portion where the drive member  40   a  and the output member  50   a  are connected with each other. Likewise, the escape hole  85   b  receives a connection portion where the drive member  40   b  and an output member  50   b  are connected with each other. The holder  80  is formed with spindle portions  87   a  and  87   b  for supporting the rotors  72   a  and  72   b  for rotation, respectively. A printed circuit. board  100  is secured on an upper portion of the holder  90 . The printed circuit board  100  supplies the coils  76   a  and  76   b  with power. 
       FIG. 3  is an enlarged view of the rotor  72   a , the drive member  40   a , and the output member  50   a . Additionally,  FIG. 3  illustrates a state where the rotor  72   a , the drive member  40   a , and the output member  50   a  are assembled into the blade drive device  1 . The drive member  40   a  includes: an arm portion  41   a  having a plate shape; a support hole  42   a  formed at one end of the arm portion  41   a  and serving as a fulcrum of rotation; and the drive pin  43   a  formed at the other end of the arm portion  41   a  and extending in a predetermined direction. Also, a gear portion  45   a  is formed on the upper portion of the arm portion  41   a . The rotor  72   a  includes a cylindrical portion  72   a   3 , and a permanent magnet  72   a   1  having a ring shape and fitted with the cylindrical portion  72   a   3 . The permanent magnet  72   a   1  is energized to have different polarities in the circumferential direction. The permanent magnet  72   a   1  is fitted with the upper side of the cylindrical portion  72   a   3  and is not rotated relative thereto. The output member  50   a  is fitted with the lower side of the cylindrical portion  72   a   3  and is not rotated relative thereto. Thus, the output member  50   a  rotates together with the rotor  72   a . The permanent magnet  72   a   1  and the cylindrical portion  72   a   3  are integrally formed with each other. 
     The output member  50   a  includes: a cylindrical portion  52   a  having a substantially cylindrical shape and fitted with the cylindrical portion  72   a   3 ; a projection portion  54   a  projecting from the cylindrical portion  52   a  in the radially outward direction; and a gear portion  55   a  formed at one end of the projection portion  54   a . The gear portion  55   a  of the output member  50   a  meshes with the gear portion  45   a  of the drive member  40   a . Thus, the force of the output member  50   a  is transmitted to the drive member  40   a . Therefore, the gear portion  45   a  of the drive member  40   a  corresponds to a first connection portion connected with the output member  50   a.    
       FIG. 4  is a sectional view around the leading blade  20 A, the drive member  40   a , the output member  50   a,  and the actuator  70   a . Additionally,  FIG. 4  is the sectional view of the blade drive device  1  viewed in the direction perpendicular to the axial direction of the opening  11 . The board  10 A is omitted in  FIG. 4 . The support hole  42   a  of the drive member  40   a  is rotatably fitted onto a spindle  84   a  of the holder  80 . Accordingly, the drive member  40   a  is rotatably supported. Thus, the support hole  42   a  corresponds to a support portion that rotatably supports the drive member  40   a . The drive pin  43   a  extends in a predetermined direction and is connected with the arm  31   a  arranged between the boards  10  and  10 B. Thus, the drive pin  43   a  of the drive member  40   a  corresponds to a second connection portion connected with the arm  31   a . As mentioned above, the arm  31   a  is connected with the leading blade  20 A. The connection between the output member  50   a  and the drive member  40   a  is ensured through the escape hole  85   a . Specifically, the gear portions  45   a  and  55   a  are positioned in the escape hole  85   a.    
     Also, as illustrated in  FIGS. 3 and 4 , the gear portion  45   a  of the drive member  40   a  is positioned between the support hole  42   a  and the drive pin  43   a . Therefore, the load applied to the spindle  84   a  fitted into the support hole  42   a  can be reduced, thereby making the diameter of the spindle  84   a  smaller than conventional one. A following description will be given of the load exerted on the drive member  40   a.    
       FIGS. 5A and 5B  are explanatory views of the load exerted on the drive member  40   a .  FIG. 5A  is the explanatory view of the load exerted on the drive member  40   a  in the present embodiment, and  FIG. 5B  is the explanatory view of the load exerted on a drive member having a structure different from the present embodiment. In the present embodiment, the arm portion  41   a  of the drive member  40   a  is formed with the drive pin  43   a  fitted into the arm  31   a , and the support hole  42   a  fitted with the spindle  84   a . Thus, the arm portion  41   a  of the drive member  40   a  can be considered as a both-end-supported beam B that is supported at points A 2  and A 3 , as illustrated in  FIG. 5A . The point A 3  corresponds to the support hole  42   a . The point A 2  corresponds to the second connection portion where the arm  31   a  is connected with the drive member  40   a . Herein, it can be considered that the gear portion  45   a  formed on the arm portion  41   a  to which the force is transmitted from the output member  50   a  is a load P exerted on the beam B. The length of the beam B is represented by  21 . A point A 1  where the load P is exerted is considered as the center of the beam B. The point A 1  corresponds to the first connection portion where the drive member  40   a  and the output member  50   a  are connected with each other. In this case, the magnitude of the shear stress in the point A 3  is P/2. The magnitude of the bending moment in the point A 3  is zero. 
     In contrast, in  FIG. 5B , the point A 1  where the load is exerted is positioned outside the point A 3 , and the point A 3  is positioned between the points A 1  and A 2 . That is,  FIG. 5B  illustrates a conventional structure where the support hole  42   a  of the present embodiment is positioned between the gear portion  45   a  and the drive pin  43   a  of the drive member  40   a . As mentioned above, the point A 3  means the fulcrum where the drive member  40   a  is rotatably supported. Therefore, a part of the beam B between the points A 1  and A 3  can be considered as a cantilever beam that is supported at the point A 3 . The magnitude of the shear stress exerted on the point A 3  is P. The magnitude of the bending moment exerted on the point A 1  is PL. Thus, the shear stress and the bending moment exerted on the point A 3  of the beam B illustrated in  FIG. 5A  are smaller than those of the beam B illustrated in  FIG. 5B , respectively. 
     Thus, in the present embodiment, the large load is not applied to the spindle  84   a  that rotatably fits into the support hole  42   a  of the drive member  40   a . Accordingly, it is possible to make the diameter of the spindle  84   a  smaller than that of the conventional structure where the support hole  42   a  is arranged between the gear portion  45   a  and the drive pin  43   a . This reduces the size of the blade drive device  1  in the planar direction. 
     Also, as illustrated in  FIG. 4 , the gear portion  45   a  of the drive member  40   a  and the gear portion  55   a  of the output member  50   a  are positioned in the escape hole  85   a  of the holder  80 . This reduces the thickness of the blade drive device  1 . 
     Also, the size of the escape hole  85   a  is set so as to permit the connection between the gear portions  45   a  and  55   a . Thus, the escape hole  85   a  is comparatively large. This reduces the weight of the holder  80 . 
     Also, the gear portions  45   a  and  55   a  are connected with each other in the escape hole  85   a , thereby arranging the drive member  40   a  and the output member  50   a  close to each other. This reduces the whole size of the drive member  40   a  and the output member  50   a . Further, this reduces the total weight of the drive member  40   a  and the output member  50   a . Thus, the blade drive device  1  is reduced in weight. 
       FIG. 6  is a perspective view of the drive member  40   a , the output member  50   a , and the rotor  72   a  when viewed in the axial direction of the opening  11 . In other words,  FIG. 6  is the perspective view of the drive member  40   a , the output member  50   a , and the rotor  72   a  when viewed in the axial direction of the rotor  72   a . As illustrated in  FIG. 6 , the drive pin  43   a  overlaps the rotor  72   a . Specifically, a part of a trajectory of the drive pin  43   a  overlaps the rotor  72   a . The rotor  72   a  and the drive member  40   a  are arranged in such a manner, thereby reducing the size of the blade drive device  1  in the planar direction. Additionally, as illustrated in  FIG. 6 , the gear portion  45   a  is arranged on a straight line that connects between the center of the support hole  42   a  and the center of the drive pin  43   a.    
       FIG. 7  is a sectional view of a blade drive device  1 ′ according to a variation.  FIG. 7  corresponds to  FIG. 4 . A drive member  40   a ′ includes a support spindle  42   a ′. The support spindle  12   a ′ is rotatably fitted within each hole formed in a holder  80 ′ and the board  10 . Thus, the support spindle  42   a ′ corresponds to a support portion that rotatably supports the drive member  40   a . In such a manner, the drive member  40   a ′ may be rotated by the support spindle  42   a ′. In such a configuration, the load exerted on the support spindle  42   a ′ is small. It is thus possible to make the size of the diameter of the support spindle  42   a ′ small, thereby reducing the size or the blade drive device  1 ′. 
     In the embodiment according to the present invention, the blade drive device  1  has been descried as the focal plane shutter. The focal plane shutter according to the present invention is not a type for using springs as drive sources of the leading blade  20 A and the trailing blade  20 B, but a type for using the electromagnetic actuators  70   a  and  70   b . In a general focal plane shutter, the space, in which a blade drive mechanism for driving the leading blade and the trailing blade can be configured, is limited to a region near one of the short sides of the opening  11  on the board  10  in the present embodiment, that is, a region defined by the holders  80  and  90  on the board  10 . 
     In a case of the focal plane shutter equipped with the leading blade and the trailing blade driven by the electromagnetic actuators  70   a  and  70   b , in order to ensure high speed in these days, the space might be needed for a coil. Thus, the blade drive mechanism might be increased in size. In the focal plane shutter according to the present embodiment, the gear portion  45   a  of the drive member  40   a  is positioned between the support hole  42   a  and the drive pin  43   a , and the large load is not applied to the spindle  84   a . This can make the diameter of the spindle  84   a  small. Also, the trajectory of the drive pin  43   a  partially overlaps the rotor  72   a , thereby reducing the size of the blade drive mechanism in the planar direction. Further, the gear portion  45   a  of the driving member  40   a  and the gear portion  55   a  of the output member  50   a  are arranged in the escape hole  85   a , whereby the thickness of the blade drive mechanism can be reduced in thickness direction, that is, in the direction of the spindle  84   a . Thus, in the focal plane shutter of the blade drive device  1  according to the present invention, the thickness thereof is reduced in the optical axis direction parallel to the spindle  84   a , and the size is reduced in the direction perpendicular to the optical axis direction. 
     Next, the arrangements of the actuators  70   a  and  70   b  in the blade drive device  1  will be described.  FIG. 8  is a front view of the blade drive device  1 . Additionally, parts are omitted in  FIG. 8 . As illustrated in  FIG. 8 , the rotors  72   a  and  72   b  are arranged to sandwich the coils  76   a  and  76   b . In other words, the rotors  72   a  and  72   b  are respectively located at both ends of the holder  80  in the movable direction. of the leading blade  20 A and the trailing blade  20 B. In such a way, although the actuators  70   a  and  70   b  are adjacent to each other, the rotors  72   a  and  72   b  are spaced apart from each other. This prevents the rotors  72   a  and  72   b  from magnetically influencing each other and from influencing the driving properties of the rotors  72   a  and  72   b . It is therefore possible to ensure the desired driving properties of the leading blade  20 A and the trailing blade  20 B. Herein, the leading blade  20 A and the trailing blade  20 B are an example of first and second blades. The actuators  70   a  and  70   b  are an example of first and second actuators. The rotors  72   a  and  72   b  are an example of first and second rotors. The coils  76   a  and  76   b  are an example of first and second coils. 
     For example, the exposure operation is performed as follows. In the state where the leading blade  20 A closes the opening  11  and the trailing blade  20 B recedes from the opening  11  and the rotors  72   a  and  72   b  stop, the rotor  72   a  starts rotating and the leading blade  20 A moves away from the opening  11  to open the opening  11 . After that, the rotor  72   b  starts rotating and the trailing blade  20 B closes the opening  11 . In this manner, the timing when the rotor  72   a  starts rotating is different from the timing when the rotor  72   b  starts rotating in the exposure operation. Therefore, for example, there is a state where one of the rotors  72   a  and  72   b  is rotating and the other stops. Thus, in a case where the two rotors  72   a  and  72   b  are adjacent to each other, the rotation of one of the rotors  72   a  and  72   b  might change the magnetic field to influence the other of the rotors  72   a  and  72   b . Specifically, the change in the magnetic field of the rotor  72   a  that firstly starts rotating might cause variations in the timing when the rotor  72   b  starts rotating. This might cause variations in the period from the time when the leading blade  20 A starts opening the opening  11  to the time when the trailing blade  20 B fully closes the opening  11 , that is, in the exposure period. However, in the present embodiment as mentioned above, the rotors  72   a  and  72   b  are not adjacent to each other, whereby the driving properties of the rotors  72   a  and  72   b  are prevented from being influenced. 
     Additionally, the actuators  70   a  and  70   b  are arranged such the longitudinal directions thereof are the same as the movable direction of the leading blade  20 A and the trailing blade  20 B. Further, the actuators  70   a  and  70   b  are arranged in the longitudinal direction. Furthermore, the rotors  72   a  and  72   b  are respectively arranged at both ends of the whole region of the actuators  70   a  and  70   b  in its longitudinal direction. It is therefore possible to further ensure the interval between the rotors  72   a  and  72   b . This prevents the rotors  72   a  and  72   b  from magnetically influencing each other and from influencing the driving properties of the rotors  72   a  and  72   b.    
     Also,  FIG. 8  illustrates the rotational ranges of the drive members  40   a  and  40   b . Herein, when the blade drive device  1  is viewed in the direction of the optical axis passing through the opening  11 , at least part of the drive member  40   a  and at least part of the output member  50   a  overlap the stator  74   a  or the coil  76   a . Likewise, at least part of the drive member  40   b  and at least part of the output member  50   b  overlap the stator  74   b  or the coil  76   b . Therefore, the coils  76   a  and  76   b  each having a large size can be employed. Likewise, the stators  74   a  and  74   b  each having a large size can be employed. Accordingly, the torque and the speed of the rotors  72   a  and  72   b  can be improved. Thus, the movement speed of the leading blade  20 A and the trailing blade  20 B can be improved, so the shutter speed can be improved. Additionally, at least part of the drive member  40   a  or at least part of the output member  50   a  may protrudes from at least part of the stator  74   a  and the coil  76   a . Likewise, at least part of the drive member  40   b  or at least part of the output member  50   b  may protrudes from at least part of the stator  74   b  and the coil  76   b . Herein, the output members  50   a  and  50   b  are an example of first and second output members. The drive members  40   a  and  40   b  are an example of first and second drive members. The stators  74   a  and  74   b  are an example of first and second stators. 
     Additionally, as illustrated in  FIGS. 4, 7, and 8 , when the blade drive devices  1  and  1 ′ are viewed in the direction of the optical path passing through the opening  11 , the rotational ranges of the drive members  40   a  and  40   a ′ are set not to overlap a region R beneath the spindle portion  87   a . Likewise, the rotational range of the drive member  40   b  is set not to overlap a region beneath the spindle portion  87   b . This can ensure the thicknesses of portions of the holder  80  supporting roots of the spindle portions  87   a  and  87   b  that respectively support the rotors  72   a  and  72   b  for rotation. This makes it possible to ensure the rigidity of the root portions of the spindle portions  87   a  and  87   b , thereby supporting the rotors  72   a  and  72   b  in a stable manner. 
     Further, the ratio of the gear portion  45   a  to the gear portion  55   a  is set such that the rotational speed of the drive member  40   a  is greater than that of the output member  50   a . That is, the pitch diameter of the gear portion  45   a  is larger than that of the gear portion  55   a . Likewise, the ratio of the gear portion  45   b  to the gear portion  55   b  is set such that the rotational speed of the drive member  40   b  is greater than that of the output member  50   b . Therefore, the drive members  40   a  and  40   b  can be respectively rotated much faster than the rotors  72   a  and  72   b , thereby improving the movement speed of the leading blade  20 A and the trailing blade  20 B. This also improves the shutter speed. 
     Further, as mentioned above, the drive force of the actuator  70   a  is transmitted to the leading blade  20 A through the gear portions  45   a  and  55   a . There is backlash between the gear portions  45   a  and  55   a  in order to facilitate the rotation thereof. That is, a certain clearance between the gear portions  45   a  and  55   a  is ensured. The drive member  40   a  rotates and the drive pin  43   a  abuts the end portion of the escape slot  13   a  and the like, so the leading blade  20 A stops. When the leading blade  20 A stops, the impact is applied to the drive member  40   a . This impact can be absorbed by the backlash provided between the gear portions  45   a  and  55   a . It is therefore possible to reduce the load on the drive member  40   a  and the output member  50   a . It is also possible to prevent the bound of the drive member  40   a  when the drive member  40   a  abuts the end portion of the escape slot  13   a  or the like. This prevents the leading blade  20 A receding from the opening  11  from moving toward the opening  11  again due to the bound of the drive member  40   a . The drive member  40   b , the output member  50   b , and the trailing blade  20 B have the same arrangement. Herein, the gear portions  55   a  and  55   b  are respective examples of first and second output teeth portions. The gear portions  45   a  and  45   b  are respective examples of first and second following teeth portions. 
     Additionally, the output members  50   a  and  50   b  are integrally formed with the rotors  72   a  and  72   b , respectively. For example, laser welding is used, but other welding or insert molding may be used. Further, the rotor  72   a  and the output member  50   a  may be integrally made of a resin mixed with magnetic powder. 
       FIG. 9  is an explanatory view of a unit U. The unit U includes the holders  80  and  90 , and the actuators  70   a  and  70   b . In such a way, the two actuators  70   a  and  70   b  are attached to the holders  80  and  90  to be assembled into the single unit U, handled, and managed. In this manner, the unit U integrated with the holders  80  and  90  is attached to the board  10  or the like, so the blade drive device  1  is accomplished. Thus, the unit U can be tested for operation before being attached to the board  10  or the like. For example, in a case where the actuator  70   a  or the like is found defective in the operation test after the blade drive device  1  is accomplished, the defective actuator  70   a  or the like has to be replaced. Alternately, the blade drive device  1  equipped with normal parts has to be abolished. However, in the present embodiment, the actuators  70   a  and  70   b  are handled as the unit U, so the operation test of the unit U can be performed before being attached to the board  10 . It is therefore possible to prevent the influence on the driving properties of the rotors  72   a  and  72   b , and it is possible to avoid replacing defective parts and to avoid wasting normal parts. This suppresses an increase in manufacturing cost. 
       FIG. 10A  is an explanatory view of a blade drive device  1 ″ according to a variation. Additionally, similar components will be denoted by the similar reference numerals, and a detailed description of such components will be omitted. Further, parts are omitted in  FIG. 10A . As illustrated in  FIG. 10A , actuators  70   a ″ and  70   b ″ are arranged away from each other to sandwich the opening  11 . Also in this case, the rotational ranges of drive members  40   a ″ and  40   b ′ are set not to overlap spindle portions  87   a ″ and  87   b ″. Thus, rotors  72   a ″ and  72   b ″ can be supported in a stable manner. 
       FIG. 10B  is an explanatory view of a blade drive device  1 ′″ according to a variation. Additionally, similar components will be denoted by the similar reference numerals, and a detailed description of such components will be omitted. Further, parts are omitted in  FIG. 10B . The blade drive device  1 ′″ is provided with a single actuator  70   b ′″, but not the leading blade  20 A or the actuator  70   a . The blade drive device  1 ′″ is mounted on a camera in which an electronic leading blade can artificially move. As sequentially resetting charges stored in an image pickup element for every pixel line in a predetermined direction, the electronic leading blade artificially moves. Also in this case, the rotational range of a drive member  40   b ′″ is set not to overlap a spindle portion  87   b ′″, thereby supporting a rotor  72   b ′″ in a stable manner. 
       FIG. 11  is an explanatory view of a blade drive device  1   c  according to a variation. Additionally, similar components will be denoted by the similar reference numerals, and a detailed description of such components will be omitted. Further, parts are omitted in  FIG. 11 . Adjacent actuators  70   ac  and  70   bc  are arranged to face the same side. In other words, only a coil  76   bc  is arranged to be sandwiched between rotors  72   ac  and  72   bc , the rotor  72   bc  is arranged at the end of the whole region of the actuators  70   ac  and  70   bc , and the coil  76   ac  is arranged at the other end thereof. Also in this case, the rotational ranges of drive members  40   ac  and  40   bc  are set not to overlap spindle portions  87   ac  and  87   bc . Thus, rotors  72   ac  and  72   bc  can be supported in a stable manner. 
     Further, even in the above case where the rotors  72   ac  and  72   bc  only sandwich the coil  76   bc , the rotors  72   ac  and  72   bc  are prevented from magnetically influencing each other and are prevented from influencing the driving properties of the rotors  72   ac  and  72   bc . Even in a case where the rotors  72   ac  and  72   bc  only sandwich the coil  76   ac , the same effect is achieved. That is, the rotors  72   ac  and  72   bc  that are an example of first and second rotors have only to sandwich at least one of the coils  76   ac  and  76   bc  that are an example of first and second coils. 
     While the exemplary embodiments of the present invention have been illustrated in detail, the present invention is not limited to the above-mentioned embodiments, and other embodiments, variations and modifications may be made without departing from the scope of the present invention. 
     Finally, several aspects of the present invention are summarized as follows. 
     According to an aspect of the present invention, there is provided a blade drive device including: a board including an opening; first and second blades opening and closing the opening; and first and second actuators respectively driving the first and second blades, wherein the first and second actuators respectively include first and second stators, first and second rotors, and first and second coils, and respectively drive the first and second blades through first and second drive members, the first drive member is arranged to overlap the first stator and the first coil in an optical axis direction, and the second drive member is arranged to overlap the second stator and the second coil in the optical axis direction. 
     Since the first drive member is arranged to overlap the first stator and the first coil in an optical axis direction and the second drive member is arranged to overlap the second stator and the second coil in the optical axis direction, the blade drive device has a reduced size in a planar direction perpendicular to the optical axis direction. 
     According to another aspect of the present invention, there is provided an optical instrument having the above blade drive device.