Abstract: A curvilinear, semi-rigid paper guide for a bi-directional line printer mounted on a platen which provides a surface that bears against the moving print head as the print medium passes between the print head and the paper guide is disclosed. By adjusting the curvature of the paper guide, differences in the distances between adjacent drive sprockets of upper and lower print medium drive mechanisms may be compensated for thus ensuring the printing of straight, parallel and unskewed character lines. In addition, the present invention may be used in a line printer having a single print medium drive mechanism to compensate for nonlinearities in and non-parallelism between the surface of the platen and print head movement.

Abstract: There is disclosed a carriage control apparatus for a serial, impact computer printer. The carriage control apparatus comprises an encoder disk mounted for rotation on the carriage and having a coded pattern on its periphery, a photo sensor (and associated light source) for detecting the coded pattern and a drive means, preferably a serpentine toothed belt attached at each end to the printer's side frames that engages a sprocket wheel attached to the encoder disk to rotate the encoder disk in a fixed relationship to the carriage's position along the line of print of the printer.