PRINT HAMMER MECHANISM HAVING DUAL ELECTRO-MAGNETIC COILS AND POLE PIECES

摘要

In a print hammer mechanism in which an elongated, resilient hammer element mounted at a fixed end thereof has an opposite free end thereof selectively released from a retract position for impact of a dot imprinting element carried by the free end of the element, an improved magnetic circuit is provided for use in release and retraction of the hammer element. The improved magnetic circuit includes a pair of elongated pole pieces of like configuration having back ends thereof mounted on opposite sides of a rare earth magnet and tips at the opposite front ends thereof disposed adjacent the free end of the hammer element to form a pair of gaps therewith. Improved magnetic properties are provided by the presence of two gaps, the close proximity of the tips so as to minimize the high reluctance magnetic path through the hammer element and the maintenance of a small air gap between one of the tips and the hammer element when the element is in the retract position in contact with the other tip to facilitate quick release of the hammer element. The magnetic characteristics are even further improved by the physical design of the magnetic circuit which minimizes fringing magnetic fluxes and which utilizes a pair of magnetic coils, each of which is mounted on a different one of the pole pieces adjacent the tip thereof. The use of two coils provides for substantially complete cancellation of the magnetic fields in both gaps upon energization to provide for quicker release of the hammer element from the retract position.