Position indicator for high speed printers

Claim 1

In a dot matrix printer for computer printout having an elongate platen and a print head carriage supported for relative movement therebetween longitudinally of the platen, a dot matrix print head on said carriage, said print head comprising a plurality of dot matrix print elements arranged transversely of the platen axis in a predetermined array, means for supporting said carriage for movement along said platen, means for activating said print elements at a predetermined location along said platen, means for driving said carriage with continuous motion along said platen, a position indicator, for ascertaining the position of said carriage longitudinally of said platen, comprising a rotary optical position encoder rotatably mounted on an axis fixed longitudinally of said platen, a carriage position responsive means connected to said encoder and to said carriage on opposite sides of said print head to transmit said relative movement to said encoder to rotate said encoder in synchronism with said relative movement, the connections between the print head and the responsive means being sufficiently close to said array of dot matrix print elements to accurately indicate the position of said dot matrix print head to within one or two mils of its true position despite play in the carriage support means, said position responsive means being flexible and non extensible under the forces necessary to drive said encoder and being separate from said carriage driving means, said flexible position responsive means being the sole means for driving said encoder, whereby said connections cause the encoder to accurately track the position of the dot matrix print array despite play in the carriage support, said encoder having a pattern of detectable indicia, and a detector responsive to said indicia to provide a signal indicative of the rate, amount and direction of movement rotation of said encoder, said encoder providing input to the means for activating said print elements in accordance with the indicated position.