Ballistic print hammer assembly

Claim 1

In a print hammer assembly having an elongated hammer with a head portion near one of its ends and being mounted on a rigid pivot, the other end of the hammer being coupled to the armature of an electromagnetic actuator, the actuation of the actuator imparting axial motion to the armature and rotational motion to the hammer about the pivot from a rest position to a printing position in which a printing medium and a type character situated on a type carrier are impacted into engagement, the improvement comprising: said electromagnetic actuator including said armature and a stator having a generally cylindrical cavity which has a bottom and a mouth, said armature being elongated and partially disposed within said cavity so that a portion thereof extends outside the cavity mouth, an elongated slot extending through said portion, said slot having first and second ends, and a central armature cavity having a bottom and a mouth which opens into the first end of the armature slot; the other end of the hammer extending through said slot and being adapted for motion within the slot between its first and second ends; impression control spring means located within said armature cavity and arranged to continually urge said hammer toward the second end of the slot; and means for actuating the stator to produce said axial and rotational motions of the armature and hammer, said armature bottoming against the stator cavity bottom prior to the hammer head portion reaching the printing position such that the hammer continues to rotate due to its rotational inertia toward the printing position in a free-flight condition, the duration of which is a function of the thickness of the print medium, the impression control spring means continually acting upon the other end of the hammer to decelerate the hammer during the free-flight condition so that the rotational hammer velocity is relatively higher for a thick print medium than for a thin print medium.