Hammer assembly for a serial typing device

Claim 1

A hammer assembly for a serial typing device comprising a platen, a characters-bearing element having a plurality of characters carried by a corresponding plurality of flexible laminae and means for selectively positioning said laminae in front of said platen in a printing position; said hammer assembly comprising a typing hammer, an electromagnet for actuating said typing hammer in a direction substantially perpendicular to said platen to flex the selected lamina and to strike the corresponding character against said platen, said electromagnet comprising a fixed core, a movable armature directly fixed to said hammer and an energizable coil surrounding said fixed core, means for varying the impact energy of said hammer only by varying the duration of energization of said coil, said means comprising a pole surface of said fixed core inclined with respect to the direction of movement of said hammer, and pole surfaces of said movable armature parallel to the inclined pole surface of said fixed core and a control circuit which energizes said coil with a current of a substantially constant amplitude and a length of time substantially directly proportional to the impact energy to be applied to said hammer, guide means in said fixed core for guiding said hammer, a cavity provided in said hammer, a felt impregnated with lubricating oil contained in said cavity and a hole provided in said hammer and communicative with said guide means for lubricating said guide means.