Print hammer mechanism

Abstract

A hammer mechanism which undergoes reciprocating motion across platen-supported paper webs in a dot matrix printer effects printing by momentarily energizing coils associated with selected resilient hammer elements mounted on a common magnetic structure to neutralize a magnetic field from the common magnetic structure and release the hammer elements from a retracted position. Each end of the common magnetic structure extends to define dummy hammer positions adjacent the first hammer element on each end, providing uniform magnetic field strength to the end hammer elements and to all hammer elements in between. The hammer elements are fabricated and mounted as individual elements of resilient magnetic material with mounting of the elements being accomplished in pairs using a common plate for each pair and screws which have a portion of reduced diameter directly behind the head thereof to provide easy access to the shaft of the screw in the event of breakage during installation. The hammer mechanism is surrounded by a housing having a front face adjacent the hammer elements which is of magnetic material to increase the flux density for hammer elements of given size and which has an opening therein equipped with a filter to permit the exit of cooling air introduced under pressure into the housing while preventing contaminants from getting inside the housing.