Printing piston assembly

In a printing apparatus of the type having a printing station, a force resisiting means for resisting a printing force, a force exerting means positioned in printing alignment with said printing station for exerting a printing force toward said force resisting means, and an image carrier and a font element with at least one raised character, each being disposed between said force resisting means and said force exerting means and each being positionable in printing alignment with said printing station wherein said force exerting means comprises:

• a generally wedge shaped element with a curved force exerting surface of a constant radius of curvature extending through an arc of less than approximately ninety degrees;
• support and guide means for supporting and guiding said force exerting surface in rolling movement with respect to said printing station between first and second positions such that a normal printing force is exerted against successive portions of said raised character to transfer an image of said raised character to said image carrier, said support and guide means including a first support and guide means comprising a support and guide surface for supporting and guiding a first point on said wedge shaped element in translational movement between first and second positions corresponding respectively to said first and second positions of said force exerting surface, said first support and guide means further including a track means positioned on each side of said wedge shaped element and a roller means rotatably mounted to said wedge shaped portion on each side thereof at the center of the radius of curvature of said curved force exerting surface for rolling engagement with said track means, said track means having a generally flat portion of a length such that a portion of said roller means extends past an end of and below the surface of said flat portion when said first point is in its first and second positions;
• said support and guide means further including a second support and guide means for supporting and guiding a second point on said wedge shaped element in translational movement between first and second positions corresponding respectively to said first and second positions of said force exerting surface;
• and
• means for moving said force exerting surface in rolling movement between first and second positions.