Non-linear spring design for matrix type printing

Abstract

A non-linear spring design for use in a high speed solenoid assembly especially adapted for use in impact printers of the dot matrix type. The solenoid coil--when energized--drives the solenoid armature and a print wire connected thereto for impact against an inked ribbon and a paper document to form a dot upon the paper document. The armature is initially driven against an initially 'weak' spring biasing force of a large beam-radius spring member to facilitate rapid acceleration to impact velocity. The radial beam length of the spring member is continually shortened as the armature is displaced in the activated direction by contact at continuously varying support points on the armature head or flux ring, whereby the normally linear spring develops more force in a non-linear manner for the same displacement. Prior to the print wire striking the inked ribbon or paper document, the non-linear spring exerts a greater spring force upon the armature which spring force serves to limit impact velocity and to return the armature to the non-impact position at a more rapid rate when the solenoid coil is deenergized. The design reduces the complexity of an assembly enabling significantly increased printing speeds by reduction of the elapsed time between movement of the armature and print wire from the rest position to the impact position and the return time of the armature to the rest position.