Abstract:
A focal-plane shutter includes: first, second, and third boards each including an opening and arranged in an optical axis direction passing through the openings; a first blade arranged between the first and second boards and capable of opening and closing the openings; a second blade arranged between the second and third boards and capable of opening and closing the openings; first and second arms arranged between the second and third boards, connected to the second blade, made of synthetic resins, and capable of rotating about respective different fulcrums; and a drive member connected to the first arm and driving the first arm.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of and claims priority to International Patent Application No. PCT/JP2013/078868 filed on Oct. 24, 2013, which claims priority to Japanese Patent Application No. 2012-241981 filed on Nov. 1, 2012, subject matter of these patent documents is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    (i) Technical Field 
         [0003]    The present invention relates to focal-plane shutters and optical devices. 
         [0004]    (ii) Related Art 
         [0005]    Japanese Unexamined Patent Application Publication No. 09-179167 discloses a focal-plane shutter driving a blade by two arms. 
         [0006]    To improve the shutter speed, it is contemplated that two arms are made of synthetic resins for reduced weight. In this case, the rigidity of the arms are reduced, so that the arms might flap in the optical axis direction when the blade stops after moving from a state of closing an opening to a state of opening the opening. This might damage the arms. 
       SUMMARY 
       [0007]    According to an aspect of the present invention, there is provided a focal-plane shutter including: first, second, and third boards each including an opening and arranged in an optical axis direction passing through the openings; a first blade arranged between the first and second boards and capable of opening and closing the openings; a second blade arranged between the second and third boards and capable of opening and closing the openings; first and second arms arranged between the second and third boards, connected to the second blade, made of synthetic resins, and capable of rotating about respective different fulcrums; a drive member connected to the first arm and driving the first arm; and a support member provided within a working region of the first arm when viewed in the optical axis direction or in a position close to the first arm and distant from the second arm in an opened state where the second blade opens the openings, the support member being provided in the first board side and supporting the second board. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a front view of inner structure of a focal-plane shutter according to the present embodiment; 
           [0009]      FIG. 2  is an external perspective view of the focal-plane shutter; and 
           [0010]      FIG. 3  is a sectional view around a support member. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  is a front view of inner structure of a focal-plane shutter  1  according to the present embodiment.  FIG. 2  is an external perspective view of the focal-plane shutter  1 . The focal-plane shutter  1  is employed in an optical instrument such as a digital camera or a still camera. The focal-plane shutter  1  includes a board  10 , a leading blade  20 A, a trailing blade  20 B, arms  31   a ,  32   a ,  31   b , and  32   b , drive members  40   a  and  40   b , output members  50   a  and  50   b , and rotors  72   a  and  72   b . Additionally, the rotors  72   a  and  72   b , and the output members  50   a  and  50   b  are omitted in  FIG. 1 . The board  10  includes an opening  11 . The leading blade  20 A and the trailing blade  20 B open and close the opening  11 . The rotor  72   a  is included in an actuator for driving the leading blade  20 A. The rotor  72   b  is included in an actuator for driving the trailing blade  20 B. Each actuator includes a stator around which a coil is wound, and is omitted in  FIGS. 1 and 2 . 
         [0012]    The leading blade  20 A includes plural blades  21   a  to  23   a . The trailing blade  20 B also 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 recede from the opening  11  in the overlapped state to bring the opening  11  into a fully opened state. These plural blades close the opening  11  in the expanded state to bring the opening  11  into a fully closed state.  FIGS. 1 and 2  illustrate the state where the expanded leading blade  20 A closes the opening  11  and the trailing blade  20 B recedes from the opening  11 . 
         [0013]    The leading blade  20 A is connected to the arms  31   a  and  32   a . The trailing blade  20 B is connected to the arms  31   b  and  32   b . As illustrated in  FIG. 1 , 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. 
         [0014]    The drive members  40   a  and  40   b  drive the arms  31   a  and  31   b , respectively. The drive members  40   a  and  40   b  are provided with drive pins  43   a  and  43   b  connected to the arms  31   a  and  31   b , respectively. The board  10  is formed with escape slots  13   a  and  13   b  for permitting the movement of the drive pins  43   a  and  43   b , respectively. The drive members  40   a  and  40   b  will be described later in detail. The rotors  72   a  and  72   b  are respectively connected to the output members  50   a  and  50   b . The rotation of the rotors  72   a  and  72   b  rotates the output members  50   a  and  50   b , so the drive members  40   a  and  40   b  rotates, which drives the leading blade  20 A and the trailing blade  20 B, respectively. The positions of rotational axes of the output members  50   a  and  50   b  and the drive members  40   a  and  40   b  are different from one another. 
         [0015]    The output members  50   a  and  50   b  and the drive members  40   a  and  40   b  are respectively formed with gear portions  55   a ,  55   b ,  45   a , and  45   b . The gear portions  55   a  and  45   a  mesh with each other, and the gear portions  55   b  and  45   b  mesh with each other, so that the rotation of the output members  50   a  and  50   b  respectively rotate the drive members  40   a  and  40   b . The arms  31   a  and  31   b  are partially attached with reinforcement members  31 A and  31 B. The arms  31   a  and  31   b  and the reinforcement members  31 A and  31 B are made of synthetic resin, and each thereof has a thin plate shape. 
         [0016]    As illustrated  FIG. 2 , the board  10  is formed with a positioning portion  19   a  near one end of the escape slot  13   a . Likewise, a positioning portion  19   b  is formed near one end of the escape slot  13   a . The other ends of the escape slots  13   a  and  13   b  are provided with Ga and Gb for absorbing the impact of the drive members  40   a  and  40   b , respectively. In addition, the board  10  is assembled with a holder holding the above actuators not illustrated. 
         [0017]    As illustrated in  FIG. 1 , the board  10  is secured with a support member GS. The support member GS is separate from the board  10 . Further, the board  10  is provided with plural support projections is to  4   s . The support member GS and the support projections is to  4   s  will be described later. Furthermore, in  FIG. 1 , working regions R 1  and R 2  of the arms  31   b  and  32   b  are depicted by dotted lines. 
         [0018]      FIG. 3  is a sectional view around the support member GS. Additionally,  FIG. 3  is the sectional view taken along line passing through the support member GS, the drive pin  43   b , and the spindle  14   b  in  FIG. 1 . As illustrated in  FIG. 3 , the focal-plane shutter  1  includes boards  10 A and  10 B besides the board  10 . The boards  10  to  10 B are arranged in this order in the optical axis direction. That is, the board  10 A is provided between the boards  10  and  10 B. Like the opening  11  provided in the board  10 , an opening is provided in each of the boards  10 A and  10 B. The leading blade  20 A and the arms  31   a  and  32   a  are arranged between the boards  10  and  10 A. The trailing blade  20 B and the arms  31   b  and  32   b  are arranged between the boards  10 A and  10 B. The board  10 A prevents the interference of the leading blade  20 A with the trailing blade  20 B and the interference of the arm  31   a  with the arm  31   b . The board  10  is an example of a first board. The board  10 A is an example of a second board. The board  10 B is an example of a third board. The leading blade  20 A is an example of a first blade. The trailing blade  20 B is an example of a second blade. 
         [0019]    A holder  80  assembled on the board  10  holds the actuators not illustrated. The actuator includes the rotor  72   a , the stator, and the coil. The holder  80  is assembled on the board  10 . A spindle  84   b  of the holder  80  is fitted into a support hole  42   b  of the drive member  40   b  for rotation. Therefore, the drive member  40   b  is rotatably supported. The drive pin  43   b  extends in a predetermined direction and is connected to the arm  31   b  arranged between the boards  10 A and  10 B. As mentioned above, the arm  31   b  is connected to the trailing blade  20 B. The arm  31   b  is an example of a first arm. The arm  32   b  not connected to the drive pin  43   b  but to the trailing blade  20 B is an example of a second arm. Additionally, the board  10 A is provided with an escape slot for receiving the drive pin  43   b . The board  10 B is provided with an escape slot  13   b B. 
         [0020]    The support member GS is secured to a surface, of the board  10 , facing the board  10 A, and supports the board  10 A from the board  10  side. The support member GS is made of a rubber. In particular, the support member GS is a foamed rubber forming bubbles, but not limited to this. For example, the support member GS may be made of a synthetic resin having no elasticity or may be a rubber, a leaf spring, a coil spring, or the like having elasticity. The support member GS may be integrally formed in the board  10 . In an inner peripheral edge of the board  10 , a receiving portion  18  protrudes inwardly from the inner peripheral edge. The receiving portion  18  supports the board  10 A from the board  10 B side. In other words, the receiving portion  18  receives the board  10 A serving as the second board between the receiving portion  18  and the support member GS from the board  10 B side serving as the third board. Herein, the support member GS is secured near the receiving portion  18 , and an end portion of the board  10 A is sandwiched between the support member GS and the receiving portion  18 . Further, the support projections is to  4   s  formed in the board  10  also support the board  10 A from the board  10  side. 
         [0021]    Next, the position of the support member GS will be described. As illustrated in  FIG. 1 , the support member GS is provided at a position close to the arm  31   b  and distant from the arm  32   b  in the state where the trailing blade  20 B opens the opening  11 . That is, it is provided near the arm  31   b.    
         [0022]    For example, the rotor  72   b  causes the output member  50   b  and the drive member  40   b  to rotate from the state where the trailing blade  20 B closes the opening  11 . Thus, the drive pin  43   b  of the drive member  40   b  moves within the escape slot  13   b  and abuts the positioning portion  19   b . At this time, the impact is applied to the drive member  40   b , so the arm  31   b  might flap in the optical axis direction. When the arm  31   b  flaps in the optical axis direction, the load is applied to the arm  31   b , so the arm  31   b  might be damaged. In particular, since the arm  31   b  engages with the drive pin  43   b , the area of the arm  31   b  is formed to be greater than that of the arm  32   b . In addition, the reinforcement member  31   b  is also attached to the arm  31   b . Thus, the arm  31   b  is formed to be heavier than the arm  32   b . For this reason, the arm  31   b  tends to flap. Further, in the opened state where the opening  11  is opened, the blades of the trailing blade  20 B are brought into the overlapped state. Therefore, the trailing blade  20 B further tends to flap in the optical axis direction, and the arm  31   b  tends to flap. 
         [0023]    In the present embodiment, the support member GS is provided near the arm  31   b  in the opened state of the trailing blade  20 B. The support member GS presses the board  10 A, whereby the board  10 A suppresses the arm  31   b  from flapping. This can prevent the damage to the arm  31   b . Further, since the support member GS has elasticity, it is possible to absorb the impact generated from the arm  31   b . Furthermore, as illustrated in  FIG. 1 , the support member GS overlaps the arm  31   b  when viewed in the optical axis direction. Accordingly, the flapping of the arm  31   b  can be effectively suppressed thereby absorbing the impact. 
         [0024]    Further, like the support member GS, the receiving portion  18  is formed at a position close to the arm  31   b  and distant from the arm  32   b  in the opened state where the trailing blade  20 B opens the opening  11 . That is, it is formed near the arm  31   b . Since it is formed near the arm  31   b  when viewed in the optical axis direction in the opened state of the trailing blade  20 B, the board  10 A can be stably held between the receiving portion  18  and the support member GS. It is thus possible to suppress the flapping of the arm  31   b.    
         [0025]    Also, since the flapping of the arm  31   b  is suppressed, it is also possible to suppress the flapping of the arm  32   b . Therefore, the arm  32   b  is prevented from being damaged. 
         [0026]    In addition, the support member GS may be provided within the working region R 1  when viewed in the optical axis direction. Moreover, the support member GS may be provided at a position closer to the arm  32   b  than to the arm  31   b  in the opened state. 
         [0027]    As illustrated in  FIG. 1 , the support projections  3   s  and  4   s  integrally formed in the board  10  and supporting the board  10 A are provided within the working region R 1  of the arm  31   b  when viewed in the optical axis direction. It is thus possible to press the flapping of the arm  31   b  in the optical axis direction in cooperation with the support member GS. Further, the support projection may be provided not only within the working region R 1  but also within the working region R 2 . It is also possible to suppress the flapping of the arm  32   b  in the optical axis direction. 
         [0028]    Furthermore, the support projections is and  2   s  are formed at positions to overlap the trailing blade  20 B in the optical axis direction in the opened state. This suppresses the trailing blade  20 B from flapping through the board  10 A. 
         [0029]    In this way, the arm  31   b  is suppressed from flapping, thereby suppressing the trailing blade  20 B from flapping. Accordingly, the operation noise of the focal-plane shutter can be reduced. 
         [0030]    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. 
         [0031]    In the present embodiment, the leading blade  20 A and the trailing blade  20 B are driven by use of the actuators. However, the present invention is not limited to this. For example, the operation of an electromagnet and a spring may drive the blade through the drive member. Further, in the present embodiment, in order to suppress the flapping of the arm  31   b  driving the trailing blade  20 B, the support member GS is provided in the board  10  at the arm  31   b  side. However, in order to suppress the flapping of the arm  31   a  driving the leading blade  20 A, such a support member may be provided in the board  10 B at the arm  31   a  side.