Free flight hammer for impact printer

Claim 1

Impact printing apparatus comprising: a medium for receiving print; a character element juxtaposed to said medium and adapted to contact with said print receiving medium; and hammer means including an impact area movable between a rest position and an impact position thereby causing contact between said character element and said print receiving medium, the improvement residing in said hammer means comprising: a stationary magnetic structure comprising a high permeability material and electrically energizable windings, said stationary magnetic structure having an opening therein with said material on opposite sides thereof so as to form an axially extending unobstructed magnetic air gap; a movable magnetic structure rigidly coupled to said impact area, said movable magnetic structure comprising a high permeability material adapted to move substantially axially through said opening from a first position partially closing said magnetic air gap to a second position in a direction toward said character element substantially closing said magnetic air gap upon energization of said windings, the distance between said first and said second positions being less than the distance between said rest and said impact positions, the length of said movable magnetic structure being greater than the length of said axial air gap and greater than the distance between said rest and said impact positions, said movable magnetic structure being free for axial movement through said gap such that said movable magnetic structure substantially closes said air gap before and until said impact area causes a character element to contact said medium and said movable magnetic structure is in substantially free flight at a substantially constant velocity when said contact occurs; and a detent spring contacting said movable magnetic structure for maintaining said impact area away from said character element except when said windings are energized, said spring providing insufficient resistance to substantially affect the free flight of said movable magnetic structure.