PERMANENT MAGNET, STORED ENERGY, PRINT HEAD

摘要

PERMANENT MAGNET, STORED ENERGY, PRINT HEAD A print head for a dot matrix serial printer, including a high energy permanent magnet (13) surrounded by a plurality of coil/post combinations (15, 17) each aligned with a print hammer (23), is disclosed. The high energy permanent magnet (13) is centrally mounted on a ferromagnetic base plate (11) having a plurality of outwardly extending arms (41). A coil/post combination (15,17) is mounted on each arm (41). The coil/post combinations (15, 17) are surrounded by an apertured spacer ring (19) formed on a nonmagnetic material. The hammers (23) are formed by the inwardly extending arms of a print hammer disc (21) mounted on the spacer ring (19) such that a hammer (23) is aligned with each coil/post combination (15, 17). The tips of the hammers overly a stepped pole (25) mounted on the outer end of the high energy permanent magnet (13). When the coils (15) are deenergized, the magnetic flux produced by the permanent magnet (13) stresses the hammers (23) by pulling them against the tips of their related posts (17). While pulled toward the stepped pole, the hammer tips remain spaced therefrom. The hammers and the stepped pole (25) are sized, configured and positioned such that the tips of the hammers lie in the step region (109) of the stepped pole (25). As a result, magnetic flux flowing between the stepped pole (25) and the hammer tips is split between two main paths, one lying generally orthogonal to the plane of the hammers and the other lying generally coplanar with the plane of the hammers. Energization of any coil (15) by a pulse of appropriate polarity and magnitude cancels the magnetic force pulling the related hammer (23) against the related post (17), releasing the hammer (23). The stored energy created by stressing the hammer (23) causes the hammer (23) to press an associated dot printing wire (27) against a ribbon resulting in the printing of a dot on a print receiving medium. Termination of the coil energization pulse results in the hammer (23) being reattracted to its related post (17). Splitting the magnetic flux at the stepped pole (25) reduces the magnetic force at the stepped pole, allowing the hammers (23) to be more readily released.