Mechanism for controlling position of optical element

Abstract

An optical element position control mechanism includes an optical element holding member which holds an optical element of a photographing system and is guided in an optical axis direction; a drive mechanism for moving the optical element holding member in the optical axis direction; and a biasing device including an arm which is swingable about a swing axis, the swing axis being substantially orthogonal to the optical axis, and the arm extending substantially orthogonal to the swing axis and having a free end portion which engages with the optical element holding member to bias the optical element holding member in the optical axis direction.

What is claimed is: 
     
       1. An optical element position control mechanism comprising:
 an optical element holding member which holds an optical element of a plurality of optical elements of a photographing system and is guided in an optical axis direction; 
 a drive mechanism for moving said optical element holding member in said optical axis direction; 
 a biasing device including an arm which is swingable about a swing axis, said swing axis being substantially orthogonal to said optical axis, and said arm extending substantially orthogonal to said swing axis and having a free end portion which engages with said optical element holding member to bias said optical element holding member in said optical axis direction; and 
 a rotational ring that rotates to move at least one of said optical element elements, wherein said rotational ring is provided separately from said optical element, and wherein said drive mechanism and biasing device are positioned radially outside said rotational ring. 
 
     
     
       2. The optical element position control mechanism according to  claim 1 , wherein said biasing device comprises a torsion spring including:
 a coiled portion supported by a support member provided separately from said optical element holding member, a central axis of said coiled portion being substantially coincident with said swing axis; 
 a first arm portion which constitutes said arm and extends radially outwards from said coiled portion to be engaged with said optical element holding member at the free end portion thereof; and 
 a second arm portion which extends radially outward from said coiled portion to be engaged with said support member, 
 wherein said torsion spring varies an amount of resilient deformation thereof in a direction of rotation of said torsion spring about said central axis of said coiled portion in accordance with movement of said optical element holding member. 
 
     
     
       3. The optical element position control mechanism according to  claim 2 , wherein an amount of angular displacement of said first arm portion in a rotation direction thereof from a free state of said first arm portion at which said first arm portion is disengaged from said optical element holding member until when said first arm portion comes into a force-applied state at which said first arm portion is engaged with said optical element holding member is greater than an amount of angular displacement of said first arm portion in said rotation direction thereof between a forward movement limit and a rearward movement limit of said optical element holding member in said force-applied state. 
     
     
       4. The optical element position control mechanism according to  claim 1 , wherein said arm of said biasing device comprises a lever pivoted at one end thereof on a support member, which is provided separately from said optical element holding member, the other end of said lever being engaged with said optical element holding member, and
 wherein said biasing device comprises a lever biasing member for biasing said lever in one of forward and reverse rotational directions about said swing axis. 
 
     
     
       5. The optical element position control mechanism according to  claim 4 , wherein said lever biasing member comprises a torsion spring including:
 a coiled portion supported by said support member, a central axis of said coiled portion being substantially coincident with said swing axis; 
 a first arm portion which extends radially outwards from said coiled portion to be engaged with said lever; and 
 a second arm portion which extends radially outwards from said coiled portion to be engaged with a spring-hooked portion of said support member, 
 wherein said torsion spring varies an amount of resilient deformation thereof in a direction of rotation of said torsion spring about said central axis of said coiled portion in accordance with a swing movement of said lever. 
 
     
     
       6. The optical element position control mechanism according to  claim 4 , wherein said lever biasing member comprises an extension spring, one end and the other end of which are engaged with said lever and said support member, respectively, a length of said extension spring varying in accordance with a swing movement of said lever. 
     
     
       7. The optical element position control mechanism according to  claim 6 , wherein a distance from said swing axis to an engaging portion of said lever which engages with said extension spring is smaller than a distance from said swing axis to an engaging portion of said lever which engages with said optical element holding member. 
     
     
       8. The optical element position control mechanism according to  claim 1 , wherein said swing axis and said free end portion of said arm of said biasing device are positioned outside said rotational ring in one and the other of two spaces provided on both sides of a plane, respectively, which is substantially parallel to said swing axis and lies on said optical axis. 
     
     
       9. The optical element position control mechanism according to  claim 1 , wherein said drive mechanism comprises:
 a screw shaft which rotates on an axis thereof parallel to said optical axis; and 
 a nut which is screw-engaged with said screw shaft and moves forward and rearward in said optical axis direction by forward and reverse rotations of said screw shaft, 
 wherein a position of said optical element holding member in said optical axis direction is determined by contact of said optical element holding member with said nut, and 
 wherein said biasing device biases said optical element holding member in a direction to bring said optical element holding member into contact with said nut. 
 
     
     
       10. The optical element position control mechanism according to  claim 1 , wherein said drive mechanism comprises:
 a guide member including at least one guide surface inclined with respect to said optical axis direction; and 
 a follower which projects from said optical element holding member to slide on said guide surface, 
 wherein said follower is pressed against said guide surface of said guide member by a biasing force of said biasing device. 
 
     
     
       11. The optical element position control mechanism according to  claim 10 , wherein said guide member comprises a cam shaft extending in said optical axis direction,
 wherein a lead groove serving as a cam groove, in which said follower is slidably engaged, is formed on a peripheral surface of said cam shaft, and 
 wherein said guide surface is positioned inside said lead groove. 
 
     
     
       12. The optical element position control mechanism according to  claim 1 , further comprising:
 a stationary cylindrical portion positioned inside said biasing device and surrounding said photographing optical system; and 
 a protective wall member provided as a separate element from said stationary cylindrical portion, and fixed to said stationary cylindrical portion to create an accommodation space between an outer peripheral surface of said stationary cylindrical portion and said protective wall member, said biasing device being accommodated in said accommodation space. 
 
     
     
       13. The optical element position control mechanism according to  claim 12 , wherein said protective wall member is integral with an image pickup device holder which holds an image pickup device so that said image pickup device lies at an image forming position. 
     
     
       14. The optical element position control mechanism according to  claim 12 , wherein one of said stationary cylindrical member and said protective wall member comprises a swing movement support projection which supports a swing center portion of said biasing device to allow a swing movement of said arm about said swing axis. 
     
     
       15. The optical element position control mechanism according to  claim 12 , wherein said protective wall member comprises a side wall portion substantially parallel to a swing plane in which said arm of said biasing device swings about said swing axis. 
     
     
       16. The optical element position control mechanism according to  claim 12 , wherein said stationary cylindrical member comprises a rotational-ring guide mechanism, provided on an inner peripheral surface of said stationary cylindrical member almost over an entire circumferential range of said stationary cylindrical member, for rotationally guiding said rotational ring, positioned inside said stationary cylindrical member, to control a position of said rotational ring in said optical axis direction. 
     
     
       17. The optical element position control mechanism according to  claim 1 , wherein said optical element holding member is guided linearly without rotating about said optical axis. 
     
     
       18. The optical element position control mechanism according to  claim 1 , wherein said drive mechanism comprises a motor and a reduction gear train.