Backlash compensated linear drive method for lead screw-driven printer

Abstract

A method of effecting time-linear travel of a lead screw-driven, carriage-mounted print head during the print cycle encompassed within a predetermined period of each motor-initiated advancement thereof. This is accomplished by incorporating a predetermined maximum possible amount of built-in backlash between the threaded coupling member and the lead screw, and by utilizing a predetermined time delay before printing commences so as to compensate for the backlash. The latter is employed to minimize friction and wear due selectively to any tolerance variations in the lead screw-drive nut threads, bow in the lead screw, or misalignment thereof relative to the carriage guide rods. As a result, wear of the moving parts that produce the friction is minimized. Printing of the first indicium associated with each motor-initiated advancement of the carriage is delayed until the stepping motor not only has been accelerated up to the desired rotational speed, but until the threaded member-lead screw backlash has been completely taken up, and any kinetic energy imparted carriage bounce forces resulting therefrom have been damped. As such, the carriage (and print head mounted thereon) will always be smoothly driven and at a substantially constant speed during each print cycle, so that successively printed indicia will be uniformly spaced along each print line. Before the printing of the last indicium is to take place, the motor is decelerated and stopped. Because of the inertia of the carriage and the threaded member-lead screw backlash, the carriage and the print head continue to move at the aforementioned constant speed during the printing of the last indicium.