Cam mechanism for the film-advancing system in a cinematographic device

Claim 2

A drive mechanism for intermittently advancing film having perforations through a motion picture projector, said mechanism comprising: a reciprocatable pulldown claw mounted on the projector for reciprocative movement relative thereto and adapted to engage the film through the perforations to intermittently advance the film; first and second pivotable arms mounted on the projector for synchronous pivotal movement relative thereto, said first arm being pivotally connected to said pulldown claw to impart reciprocative movement to said claw in response to pivotal movement of said first arm; spring means connecting said second arm to said pulldown claw for biasing said first and second arms toward each other; and a rotatable cam member mounted on the projector for rotation about an axis between said first and second arms, said cam member having first and second cam surfaces in contact with said first and second arms, respectively, at diametrically opposite points on a line perpendicular to and intersecting said axis.

Claim 3

A mechanism for driving a film-advancing means in a cinematographic device to intermittently advance film through the device, said mechanism comprising: rotatable cam means having an axis of rotation and defining a pair of cam surfaces; means for rotating said cam means; first and second displaceable follower members coupled to the film-advancing means for imparting reciprocative movement to the film-advancing means, said first and second follower members contacting said cam surfaces, respectively, at first and second locations spaced on a line intersecting said axis; whereby rotation of said cam means effects equal and opposite synchronous displacement of said first and second follower members relative to said axis substantially along said line, and said mechanism thereby operates under substantially constant torque conditions, said first follower member being directly connected to the film-advancing means; and a spring connecting said second follower member to the film-advancing means so that said spring urges said first and second follower members into contact with said cam surfaces; whereby a variation in torque load on said cam means caused by displacement of said first follower member is compensated for by equal and opposite displacement of said second follower member.

Claim 4

A mechanism for driving a film-advancing means in a cinematographic device to intermittently advance film through the device, said mechanism comprising: rotatable cam means having an axis of rotation and defining a pair of cam surfaces; means for rotating said cam means; first and second displaceable follower members coupled to the film-advancing means for imparting reciprocative movement to the film-advancing means, said first and second follower members contacting said cam surfaces, respectively, at first and second locations spaced on a line intersecting said axis; whereby rotation of said cam means effects equal and opposite synchronous displacement of said first and second follower members relative to said axis substantially along said line, and said mechanism thereby operates under substantially constant torque conditions, said first follower member being directly connected to the film-advancing means; and a spring connecting said second follower member to the film-advancing means so that said spring urges said first and second follower members into contact with said cam surfaces; whereby a variation in torque load on said cam means caused by displacement of said first follower member is compensated for by equal and opposite displacement of said second follower member.