A printing head for dot matrix printers, including novel electromagnet structures for driving individual printing wires. In each electromagnet, a pair of coils generally radial to the printing wire axis drive an armature coaxial with the printing wire and to which it is attached. The head is specifically designed for simple and reliable construction at low cost, operation at moderate speeds (60-100 cps) for extended periods with a long, powerful stroke, and includes high-reliability mounting elements for the print wire and armature, where problems have been experienced with prior art designs.

An improved printing cell and head for dot matrix impact printers, including an armature of exceptionally low mass mounted on a pair of straight, cylindrical spring elements, and driven by a pair of coils wired in parallel. By careful selection of the ramp angle of respective pole faces, and a resilient preset and energy-absorbing device, printing speeds of 2,500 Hz can be achieved with remarkably quiet operation.

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.

A print mechanism for a wire printer has a robust single-turn closed-loop transformer secondary winding as the moving part for driving a print wire into and out of a print position. Each secondary winding threads a transformer core on which is wound a multi-turn primary winding. A stack of such secondary windings, arranged with print wires in a closely spaced print row across the stack is supported in a static magnetic field produced by a magnetic assembly. Energization of a selected primary winding induces a large current flow in its associated secondary winding which reacts with the static magnetic field to drive the associated print wire into the print position. In one embodiment, the stack of secondary windings are all mounted on a single pivot and each secondary winding swings about the pivot as a whole upon energization of its associated primary winding. In another embodiment each secondary winding of the stack is formed so as to be elastically deformable whereby the portion of the secondary winding carrying the print wire is deflected into the print position under energization of its associated primary winding.