Media thickness compensation for print head

Abstract

In high-speed serial-type wire printer with platen for backing impression-receiving media and carriage for traversing print head having printing wires reciprocable at right angles to platen to effect impressions against media along a print line on platen; a print head mounted on the carriage for independent movement perpendicular to print line, biasing means urging print head away from platen, and a plurality of individually selected rotatable stop members on a shaft in a series extending for length of platen, the shaft being carried by adjustable bearings to insure its being axially parallel to platen, with each stop member comprising polyhedron presenting plurality of peripheral faces each differently spaced from shaft, and a roller on print head for engagement with stop member faces by the biasing means, the print head thereby being maintained a predetermined distance from the media during traversing of carriage regardless of the thickness of the media so as to accommodate media of different thicknesses. A pair of secondary rollers on carriage equidistantly spaced transversely on opposite sides of roller on print head are resiliently maintained in engagement with a rail on machine frame by the biasing means to stabilize and prevent canting of carriage and print head. Each stop member detented by spring pawl engaging in peripheral transverse slots separating faces of stop member, with a bail movable by any spring pawl not engaging a slot to open a control switch to prevent machine operation unless all stop members are in an operative position presenting one of their faces for engagement by the print head roller.