Print hammer mechanism having intermediate pivot fulcrum

Abstract

In a print hammer mechanism in which a thin, flat hammer spring is mounted at a fixed end thereof to a magnetic structure which includes a permanent magnet and a pole piece having a pole tip facing the opposite free end of the hammer spring on a side of the hammer spring opposite an impact printing tip, a pivot fulcrum is formed by an impact arrangement which faces an intermediate portion of the hammer spring between the fixed and free ends thereof. The permanent magnet normally pulls the hammer spring into a retract position in which the spring impacts and resides against the impact structure with the free end of the spring forming an air gap with the pole tip. Energization of a coil surrounding the pole piece releases the hammer spring from the retract position, enabling the spring to return toward a neutral position and then impact a printable medium such as a print paper-ink ribbon combination, following which the magnetic attraction of the permanent magnet returns the hammer spring to the retract position in which it strikes the impact structure and remains in the retract position pending the next energization of the coil. The location of the impact arrangement is such as to greatly minimize wear at its interface with the hammer spring while at the same time enhancing the release characteristics of the hammer spring. In a preferred embodiment the impact structure is formed by a secondary pole piece extending in parallel, spaced-apart relation along a portion of the length of the hammer spring from the fixed end thereof and terminating in a pole tip covered with a thin layer of Kapton.