Random access line printer

TL;DR: An impact printer of the dot matrix type capable of printing in either the forward or reverse direction is described in this article, where means for determining the position of the print head at any given instant are provided.

Abstract: An impact printer of the dot matrix type capable of printing in either the forward or reverse direction. Means are provided for determining the position of the print head at any given instant. Upon completion of a line of print the print head is abruptly halted. The next line of characters is examined to determine the end points of its character field. Comparisons are made to determine whether the print head lies within or beyond the end points. In cases where the print head lies beyond the end points of the character field, the printing occurs by moving the head in a direction toward the closest end point and then printing. If the print head occupies the location between the end points the position of the head is loaded into a pair of counters which are simultaneously counted up and down respectively. The outputs of the counters are continuously compared against the values representing the end point locations whereupon the first favorable comparison determines the shortest distance of print head travel for starting printing. High speed electronic circuitry is provided for storing data representing the next line to be printed in both forward and reverse formats whereupon the decision as to the direction in which data is printed automatically controls the appropriate storage medium. Novel video detection means is provided both for determining the direction of head movement at any instant and for controlling the printing positions. The use of delayed strobes derived directly from the video control allows printing to start immediately from the rest position, and provides accurate registration of delayed strobes relative to strobe pulses regardless of the velocity of the carriage. The printer has the ability of printing expanded characters and includes electronic circuitry to prevent data in the expanded character format from being lost in cases where the inputted data representing the expanded character format exceeds the print line capacity of the printer whereby any overflow will automatically be printed on the second succeeding line of print.