Abstract: The invention disclosed herein provides a method and apparatus for counteracting the effects of a localized drag on a sheet medium as it is being moved by a drive system, for example, in a printer or plotter to prevent misregistration of the sheet medium with the X-axis drive system as the sheet medium is moved past the print or plot head which creates a drag thereon. The sheet medium is stiffened in the region thereof which is contacted by the print or plot head by bending the sheet medium in a direction normal to the direction of movement of the sheet medium. The bend may be provided by a curved guide located between the print or plot head and the X-axis drive system. Friction is reduced between the sheet medium and the curved guide by mounting the curved guide, e.g., one or more rollers, to rotate freely under the action of the sheet medium moving thereover, or by pneumatically supporting the sheet medium above the curved guide as the sheet medium is moved thereover.

Abstract: A belt-drive tensioning system for a motor drive positioning system, especially for X-Y digital plotters. The tensioning system employs spring-loading involving motion along only one translational direction to accurately preset and maintain constant the desired belt tension. Preferred embodiments to provide a self-contained modular unit include a dual plate assembly in roller-bearing relationship, and the use of V-shaped mounting springs.