Sheet detector for electrophotographic copier

In apparatus in which sheets of relatively inextensible material are advanced along a path, a detector for sensing the position of one of said sheets along said path including in combination first and second pairs of opposing feed rollers arranged at spaced locations along said path, each of said pairs of rollers forming a nip for positively gripping one of said sheets, means for driving said first and second pairs of feed rollers at such different speeds as to advance one of said sheets along said path while producing a tension in said sheet between said first and second pairs of rollers, and means for sensing said tension to produce an indication of the simultaneous presence of said sheet in the nips of said first and second pairs of feed rollers, said sensing means providing a first output in response to any tension below a predetermined level and providing a second output in response to any tension above said predetermined level.

In apparatus in which sheets of relatively inextensible material are advanced along a path, a detector for sensing the position of one of said sheets along said path including in combination first and second pairs of opposing feed rollers arranged at spaced locations along said path, each of said pairs of rollers forming a nip for positively gripping one of said sheets, means for driving said first and second pairs of feed rollers at such different speeds as to advance one of said sheets along said path while producing a tension in said sheet between said first and second pairs of rollers, and means for sensing the torque transmitted to one of said feed rollers by said driving means to produce an indication of the simultaneous presence of said sheet in the nips of said first and second pairs of feed rollers.

In apparatus in which sheets of relatively inextensible material are advanced along a path, a detector for sensing the position of one of said sheets along said path including in combination first and second pairs of opposing feed rollers arranged at spaced locations along said path, each of said pairs of rollers forming a nip for positively gripping one of said sheets, means for driving said first and second pairs of feed rollers at such different speeds as to advance one of said sheets along said path while producing a tension in said sheet between said first and second pairs of rollers, and means for sensing said tension to produce an indication of the simultaneous presence of said sheet in the nips of said first and second pairs of feed rollers, said driving means including a first gear, means for rotating said first gear, a second gear coupled to one of said feed rollers, and an intermediate gear engaging said first and second gears, said sensing means including means for supporting said intermediate gear for rotation on an axis, means mounting said supporting means for translational movement of said axis in response to tension in said sheet, and means for sensing translational movement of said axis.

In apparatus in which sheets of relatively inextensible material are advanced along a path, a detector for sensing the position of one of said sheets along said path including in combination first and second pairs of opposing feed rollers arranged at spaced locations along said path, each of said pairs of rollers forming a nip for positively gripping one of said sheets, means for driving said first and second pairs of feed rollers at such different speeds as to advance one of said sheets along said path while producing a tension in said sheet between said first and second pairs of rollers, and means for sensing said tension to produce an indication of the simultaneous presence of said sheet in the nips of said first and second pairs of feed rollers, said driving means including a first gear, means for rotating said first gear, a second gear coupled to one of said feed rollers, and an intermediate gear engaging said first and second gears, said sensing means including an arm supporting said intermediate gear for rotation on a first axis, means mounting said arm for pivotal movement about a second axis spaced from said first axis in response to tension in said sheet, and means for sensing pivotal movement of said arm.

In apparatus in which sheets of relatively inextensible material are advanced along a path, a detector for sensing the position of one of said sheets along said path including in combination first and second pairs of opposing feed rollers arranged at spaced locations along said path, each of said pairs of rollers forming a nip for positively gripping one of said sheets, means for driving said first and second pairs of feed rollers at such different speeds as to advance one of said sheets along said path while producing a tension in said sheet between said first and second pairs of rollers, and means for sensing said tension to produce an indication of the simultaneous presence of said sheet in the nips of said first and second pairs of feed rollers, said driving means including a first gear, means for rotating said first gear, a second gear coupled to one of said feed rollers, and an intermediate gear engaging said first and second gears, said sensing means including means for supporting said intermediate gear for planetary motion about one of said first and second gears and means for sensing the torque exerted by said intermediate gear about said one of said first and second gears.

In apparatus in which sheets of relatively inextensible material are advanced along a path, a detector for sensing the position of one of said sheets along said path including in combination first and second pairs of opposing feed rollers arranged at spaced locations along said path, each of said pairs of rollers forming a nip for positively gripping one of said sheets, means for driving said first and second pairs of feed rollers at such a constant speed ratio as to advance one of said sheets along said path while producing a tension in said sheet between said first and second pairs of rollers, and means for sensing said tension to produce an indication of the simultaneous presence of said sheet in the nips of said first and second pairs of feed rollers.