Power transmission mechanism having cam-incorporated gear, and power transmission mechanism of imaging apparatus

1. A power transmission mechanism comprising:

at least one cam-incorporated gear which rotates in one direction by a driving force transmitted from a drive source via a planet gear when engaged with said planet gear, stops rotating when disengaged from said planet gear, and is provided with at least one surface cam including: a constant-radius cam portion formed so that a radial distance from a rotational axis of said cam-incorporated gear to said constant-radius cam portion is constant; a relief cam portion provided closer to said rotational axis than said constant-radius cam portion; and a non-constant-radius cam portion formed so that said constant-radius cam portion and said relief cam portion are connected via said non-constant-radius cam portion and so that a radial distance from said rotational axis to said non-constant-radius cam portion is non-constant;

a first swingable member and a second swingable member each of which includes at least one follower capable of slidably contacting said surface cam and is swingable between a first swing limit in which said follower comes in contact with said constant-radius cam portion and a second swing limit in which said follower is positioned in an immediate vicinity of said relief cam portion;

a first biaser and a second biaser which bias said first swingable member and said second swingable member to rotate said first swingable member and said second swingable member toward said second swing limits, respectively; and

a first swing movement limiter and a second swing movement limiter which hold said first swingable member and said second swingable member at said second swing limits via biasing forces of said first biaser and said second biaser, respectively,

wherein one of said first swingable member and said second swingable member, which is rotated toward said first swing limit from said second swing limit while being guided by said non-constant-radius cam portion, exerts a load torque on said cam-incorporated gear in a direction opposite to a rotational direction of said cam-incorporated gear, and the other of said first swingable member and said second swingable member, which is rotated toward said second swing limit from said first swing limit while being guided by said non-constant-radius cam portion, exerts a surplus torque on said cam-incorporated gear in a same rotational direction of said cam-incorporated gear,

wherein said cam-incorporated gear includes two rotational positions: a first neutral position in which said first swingable member is held at said second swing limit by said first swing movement limiter, said second swingable member is held at said first swing limit by said constant-radius cam portion, and said cam-incorporated gear receives no torque from either of said first swingable member and said second swingable member; and a second neutral position in which said second swingable member is held at said second swing limit by said second swing movement limiter, said first swingable member is held at said first swing limit by said constant-radius cam portion, and said cam-incorporated gear receives no torque from either of said first swingable member and said second swingable member,

wherein said surface cam is configured so that, when said cam-incorporated gear rotates from said first neutral position to said second neutral position, a commencement of rotation of said first swingable member from said second swing limit to said first swing limit that is caused by being guided by said non-constant-radius cam portion occurs before a commencement of rotation of said second swingable member from said first swing limit to said second swing limit that is caused by being guided by said non-constant-radius cam portion-, and a termination of said rotation of said first swingable member from said second swing limit to said first swing limit occurs after a termination of said rotation of said second swingable member from said first swing limit to said second swing limit,

wherein said surface cam is configured so that, when said cam-incorporated gear rotates from said second neutral position to said first neutral position, a commencement of rotation of said second swingable member from said second swing limit to said first swing limit that is caused by being guided by said non-constant-radius cam portion occurs before a commencement of rotation of said first swingable member from said first swing limit to said second swing limit that is caused by being guided by said non-constant-radius cam portion, and a termination of said rotation of said second swingable member from said second swing limit to said first swing limit occurs after a termination of said rotation of said first swingable member from said first swing limit to said second swing limit, and

wherein said non-constant-radius cam portion of said surface cam comprises a cam curve for making said load torque which acts on said cam-incorporated gear greater than said surplus torque which acts on said cam-incorporated gear when said cam-incorporated gear rotates from said first neutral position to said second neutral position and when said cam-incorporated gear rotates from said second neutral position to said first neutral position.

2. The power transmission mechanism according to claim 1 , wherein said surface cam of said cam-incorporated gear comprises a first surface cam and a second surface cam with which said follower of said first swingable member and said follower of said second swingable member can come in sliding contact, respectively, said second surface cam being different in shape from said first surface cam.

3. The power transmission mechanism according to claim 2 , wherein said cam-incorporated gear is installed in an imaging apparatus, said imaging apparatus comprising:

a mirror that is movable between a viewing position, in which said mirror reflects incident light from an imaging optical system toward a viewfinder optical system, and a retracted position, in which said mirror is retracted so that light that is passed through said imaging optical system is incident on an image pickup medium without being reflected by said mirror; and

a shutter which prevents said light that is passed through said imaging optical system from being incident on said image pickup medium when shut, and allows said light that is passed through said imaging optical system to be incident on said image pickup medium when opened,

wherein said first swingable member comprises a mirror drive lever which moves said mirror from said viewing position to said retracted position and from said retracted position to said viewing position by rotating from the second swing limit thereof to the first swing limit thereof and from the first swing limit thereof to the second swing limit thereof, respectively, and

wherein said second swingable member comprises a shutter charge lever which carries out a shutter charge operation of said shutter by rotating from said second swing limit to said first swing limit, wherein said shutter is allowed to travel when said shutter charge lever is at said second swing limit.

4. The power transmission mechanism according to claim 1 , wherein said cam-incorporated gear comprises a shared surface cam with which each of said followers of said first swingable portion and said second swingable portion can come into sliding contact.

5. The power transmission mechanism according to claim 4 , wherein said cam-incorporated gear is installed in an imaging apparatus provided with a shutter which prevents light that is passed through an imaging optical system from being incident on an image pickup medium when shut, and allows said light that is passed through said imaging optical system to be incident on said image pickup medium when opened,

wherein said first swingable member comprises a shutter charge lever which carries out a shutter charge operation of said shutter by rotating from said second swing limit to said first swing limit, wherein said shutter is allowed to travel when said shutter charge lever is at said second swing limit, and

wherein said second swingable member comprises a balancer lever, said follower of said balancer lever being formed on said balancer lever to be capable of coming into slidable contact with said shared surface cam at a different position from said follower of said shutter charge lever.

6. The power transmission mechanism according to claim 1 , wherein said power transmission mechanism is installed in an imaging apparatus, said imaging apparatus comprising:

a mirror that is movable between a viewing position, in which said mirror reflects incident light from an imaging optical system toward a viewfinder optical system, and a retracted position, in which said mirror is retracted so that light that is passed through said imaging optical system is incident on an image pickup medium without being reflected by said mirror;

a shutter which prevents said light that is passed through said imaging optical system from being incident on said image pickup medium when shut, and allows said light that is passed through said imaging optical system to be incident on said image pickup medium when opened;

a mirror drive lever which is swingable between a mirror-down position to hold said mirror in said viewing position and a mirror-up position to hold said mirror in said retracted position; and

a shutter charge lever which is swingable between a charge release position to allow said shutter to travel and a charge position to carry out a shutter charge operation of said shutter after completion of traveling thereof,

wherein said cam-incorporated gear comprises:

a first cam-incorporated gear which includes a mirror control cam that controls a swing movement of said mirror drive lever and a first shutter control cam that controls a swing movement of said shutter charge lever; and

a second cam-incorporated gear which includes a second shutter control cam for controlling said swing movement of said shutter charge lever,

wherein said planet gear is selectively engaged with said first cam-incorporated gear and said second cam-incorporated gear,

wherein said mirror drive lever and said shutter charge lever serve as said first swingable member and said second swingable member, respectively, in association with said first cam-incorporated gear,

wherein said shutter charge lever serves as said first swingable member in association with said second cam-incorporated gear, and

wherein said power transmission mechanism further comprises a balancer lever adopted to serve as said second swingable member which includes a follower capable of coming in slide contact with said second shutter control cam.

7. The power transmission mechanism according to claim 6 , wherein said first cam-incorporated gear, said second cam-incorporated gear, said mirror drive lever, said shutter charge lever and said balancer lever are supported by a side of a mirror box which supports said mirror in a manner to allow said mirror to swing, and

wherein at least one of said first swing movement limiter and said second swing movement limiter comprises a protrusion formed on a side surface of said mirror box.

8. The power transmission mechanism according to claim 1 , wherein said non-constant-radius cam portion comprises two non-constant-radius cam portions which are formed so that one end of said constant-radius cam portion and one end of said relief cam portion are connected via one of said two non-constant-radius cam portions and so that the other end of said constant-radius cam portion and the other end of said relief cam portion are connected via the other of said two non-constant-radius cam portions.

9. The power transmission mechanism according to claim 1 , wherein said driving force is transmitted from said drive source to said cam-incorporated gear via a reduction gear train and said planet gear.

10. The power transmission mechanism according to claim 1 , wherein said power transmission mechanism is incorporated in an SLR camera.

11. A power transmission mechanism provided in an imaging apparatus, said imaging apparatus including a mirror that is movable between a viewing position, in which said mirror reflects incident light from an imaging optical system toward a viewfinder optical system, and a retracted position, in which said mirror is retracted so that light that is passed through said imaging optical system is incident on an image pickup medium without being reflected by said mirror; and a shutter which prevents said light that is passed through said imaging optical system from being incident on said image pickup medium when shut, and allows said light that is passed through said imaging optical system to be incident on said image pickup medium when opened, wherein said power transmission mechanism comprises:

a cam-incorporated gear which rotates in one direction by a driving force transmitted from a drive source via a planet gear when engaged with said planet gear, stops rotating when disengaged from said planet gear, and is provided with a first surface cam and a second surface cam each of which includes: a constant-radius cam portion formed so that a radial distance from a rotational axis of said cam-incorporated gear to said constant-radius cam portion is constant; a relief cam portion provided closer to said rotational axis than said constant-radius cam portion; and a non-constant-radius cam portion formed so that said constant-radius cam portion and said relief cam portion are connected via said non-constant-radius cam portion and so that a radial distance from said rotational axis to said non-constant-radius cam portion is non-constant;

a mirror drive lever which includes a first follower capable of coming in sliding contact with said first surface cam of said cam-incorporated gear, wherein said mirror drive lever is swingable between a first swing limit in which said first follower comes in contact with said constant-radius cam portion and a second swing limit in which said first follower is positioned in an immediate vicinity of said relief cam portion, and moves said mirror from said viewing position to said retracted position and from said retracted position to said viewing position by rotating from the second swing limit thereof to the first swing limit thereof and from the first swing limit thereof to the second swing limit thereof, respectively;

a shutter charge lever which includes a second follower capable of coming in sliding contact with said second surface cam of said cam-incorporated gear, wherein said shutter charge lever is swingable between a first swing limit in which said second follower comes in contact with said constant-radius cam portion and a second swing limit in which said second follower is positioned in an immediate vicinity of said relief cam portion, and wherein said shutter charge lever carries out a shutter charge operation of said shutter by rotating from the second swing limit thereof to the first swing limit thereof, wherein said shutter is allowed to travel when said shutter charge lever is at the second swing limit thereof;

a mirror drive lever biaser which biases said mirror drive lever in a direction to rotate said mirror drive lever toward said second swing limit;

a shutter charge lever biaser which biases said shutter charge lever in a direction to rotate said shutter charge lever toward said second swing limit;

a first swing movement limiter which holds said mirror drive lever at said second swing limit via a biasing force of said mirror drive lever biaser; and

a second swing movement limiter which holds said shutter charge lever at said second swing limit via biasing force of said shutter charge lever biaser,

wherein one of said mirror drive lever and said shutter charge lever, which is rotated toward the first swing limit thereof from the second swing limit thereof while being guided by said non-constant-radius cam portion, exerts a load torque on said cam-incorporated gear in a direction opposite to a rotational direction of said cam-incorporated gear, and the other of said mirror drive lever and said shutter charge lever, which is rotated toward the second swing limit thereof from the first swing limit thereof while being guided by said non-constant-radius cam portion, exerts a surplus torque on said cam-incorporated gear in a same rotational direction of said cam-incorporated gear,

wherein said cam-incorporated gear includes two rotational positions: a first neutral position in which said mirror drive lever is held at the second swing limit thereof by said first swing movement limiter, said shutter charge lever is held at the first swing limit thereof by said constant-radius cam portion of said second surface cam, and said cam-incorporated gear receives no torque from either of said mirror drive lever and said shutter charge lever; and a second neutral position in which said shutter charge lever is held at the second swing limit thereof by said second swing movement limiter, said mirror drive lever is held at the first swing limit thereof by said constant-radius cam portion of said first surface cam, and said cam-incorporated gear receives no torque from either of said mirror drive lever and said shutter charge lever,

wherein said surface cam is configured so that, when said cam-incorporated gear rotates from said first neutral position to said second neutral position, a commencement of rotation of said mirror drive lever from the second swing limit thereof to the first swing limit thereof that is caused by being guided by said non-constant-radius cam portion of said first surface cam occurs before a commencement of rotation of said shutter charge lever from the first swing limit thereof to the second swing limit thereof that is caused by being guided by said non-constant-radius cam portion of said second surface cam, and a termination of said rotation of said mirror drive lever from the second swing limit thereof to the first swing limit thereof occurs after a termination of said rotation of said shutter charge lever from the first swing limit thereof to the second swing limit thereof,

wherein said surface cam is configured so that, when said cam-incorporated gear rotates from said second neutral position to said first neutral position, a commencement of rotation of said shutter charge lever from the second swing limit thereof to the first swing limit thereof that is caused by being guided by said non-constant-radius cam portion of said second surface cam occurs before a commencement of rotation of said mirror drive lever from the first swing limit thereof to the second swing limit thereof that is caused by being guided by said non-constant-radius cam portion of said first surface cam, and a termination of said rotation of said shutter charge lever from the second swing limit thereof to the first swing limit thereof occurs after a termination of said rotation of said mirror drive lever from the first swing limit thereof to the second swing limit thereof, and

wherein said non-constant-radius cam portion of each of said first surface cam and said second surface cam of said cam-incorporated gear comprises a cam curve for making said load torque which acts on said cam-incorporated gear greater than said surplus torque which acts on said cam-incorporated gear when said cam-incorporated gear rotates from said first neutral position to said second neutral position and when said cam-incorporated gear rotates from said second neutral position to said first neutral position.

12. A power transmission mechanism provided in an imaging apparatus, said imaging apparatus including a shutter which prevents light from being incident on an image pickup medium when shut, and allows said light to be incident on said image pickup medium when opened, wherein said power transmission mechanism comprises:

a cam-incorporated gear which rotates in one direction by a driving force transmitted from a drive source via a planet gear when engaged with said planet gear, stops rotating when disengaged from said planet gear, and is provided with a surface cam including: a constant-radius cam portion formed so that a radial distance from a rotational axis of said cam-incorporated gear to said constant-radius cam portion is constant; a relief cam portion provided closer to said rotational axis than said constant-radius cam portion; and a non-constant-radius cam portion formed so that said constant-radius cam portion and said relief cam portion are connected via said non-constant-radius cam portion and so that a radial distance from said rotational axis to said non-constant-radius cam portion is non-constant;

a shutter charge lever which includes a first follower capable of coming in sliding contact with said surface cam of said cam-incorporated gear, is swingable between a first swing limit in which said first follower comes in contact with said constant-radius cam portion and a second swing limit where said first follower is positioned in an immediate vicinity of said relief cam portion, and wherein said shutter charge lever carries out a shutter charge operation of said shutter by rotating from the second swing limit thereof to the first swing limit thereof, wherein said shutter is allowed to travel when said shutter charge lever is at the second swing limit thereof;

a balancer lever which includes a second follower capable of coming in sliding contact with said surface cam of said cam-incorporated gear at a different position from said first follower of said shutter charge lever, and is swingable between a first swing limit where said second follower comes in contact with said constant-radius cam portion and a second swing limit where said second follower is positioned in an immediate vicinity of said relief cam portion,

a shutter charge lever biaser which biases said shutter charge lever in a direction to rotate said shutter charge lever toward the second swing limit thereof;

a balancer lever biaser which biases said balancer lever in a direction to rotate said balancer lever toward the second swing limit thereof;

a first swing movement limiter which holds said shutter charge lever at the second swing limit thereof via a biasing force of said shutter charge lever biaser; and

a second swing movement limiter which holds said balancer lever at the second swing limit thereof via a biasing force of said balancer lever biaser,

wherein one of said shutter charge lever and said balancer lever, which is rotated toward the first swing limit thereof from the second swing limit thereof while being guided by said non-constant-radius cam portion, exerts a load torque on said cam-incorporated gear in a direction opposite to a rotational direction of said cam-incorporated gear, and the other of said shutter charge lever and said balancer lever, which is rotated toward the second swing limit thereof from the first swing limit thereof while being guided by said non-constant-radius cam portion, exerts a surplus torque on said cam-incorporated gear in a same rotational direction of said cam-incorporated gear,

wherein said cam-incorporated gear includes two rotational positions: a first neutral position in which said shutter charge lever is held at the second swing limit thereof by said first swing movement limiter, said balancer lever is held at the first swing limit thereof by said constant-radius cam portion of said surface cam, and said cam-incorporated gear receives no torque from either of said shutter charge lever and said balancer lever; and a second neutral position in which said balancer lever is held at the second swing limit thereof by said second swing movement limiter, said shutter charge lever is held at the first swing limit thereof by said constant-radius cam portion of said surface cam, and said cam-incorporated gear receives no torque from either of said shutter charge lever and said balancer lever,

wherein said surface cam is configured so that, when said cam-incorporated gear rotates from said first neutral position to said second neutral position, a commencement of rotation of said shutter charge lever from the second swing limit thereof to the first swing limit thereof that is caused by being guided by said non-constant-radius cam portion of said surface cam occurs before a commencement of rotation of said balancer lever from the first swing limit thereof to the second swing limit thereof that is caused by being guided by said non-constant-radius cam portion of said surface cam, and a termination of said rotation of said shutter charge lever from the second swing limit thereof to the first swing limit thereof occurs after a termination of said rotation of said balancer lever from the first swing limit thereof to the second swing limit thereof,

wherein said surface cam is configured so that, when said cam-incorporated gear rotates from said second neutral position to said first neutral position, a commencement of rotation of said balancer lever from the second swing limit thereof to the first swing limit thereof that is caused by being guided by said non-constant-radius cam portion of said surface cam occurs before a commencement of rotation of said shutter charge lever from the first swing limit thereof to the second swing limit thereof that is caused by being guided by said non-constant-radius cam portion of said surface cam, and a termination of said rotation of said balancer lever from the second swing limit thereof to the first swing limit thereof occurs after a termination of said rotation of said shutter charge lever from the first swing limit thereof to the second swing limit thereof, and

wherein said non-constant-radius cam portion of said surface cam of said cam-incorporated gear comprises a cam curve for making said load torque which acts on said cam-incorporated gear greater than said surplus torque which acts on said cam-incorporated gear when said cam-incorporated gear rotates from said first neutral position to said second neutral position and when said cam-incorporated gear rotates from said second neutral position to said first neutral position.