Devices and methods herein generally relate to sheet feeding systems, and more particularly to sheet feeding systems that feed sheets to a printing engine.
Special purpose machines, such as printing devices, that feed individual sheets, such as cut sheets of print media (paper, transparencies, plastic sheets, card stock, etc.) commonly utilize closely spaced opposing rollers (one or more of which may be powered) that form a nip to move the individual cut sheets along a media path. One or more specialized circuits (such as a speed control circuit or other form of special-purpose controller) control the speed at which the nips feed sheets along the media path. Some nips are spaced a distance from each other that is less than the length of the sheets of media being fed along the media path. In such situations, if the sheet feeding speeds of the adjacent closely-spaced nips are not properly controlled, undesirable consequences can occur, such as sheet stretching, sheet buckling, etc., which can result in printing errors, print jams, damage to the nips, etc.
In one example, the speeds of the registration and transfer nips within a printing device should be correctly matched, or image defects can occur. Matching the sheet feeding speeds of the nips and the mechanical design can alleviate such problems; although, this may result in a system that is very hard to control precisely. If the sheet feeding speeds are not well matched, such devices cannot guarantee that they will always meet image quality targets. More specifically, such systems are very sensitive to hardware variation, and if tolerances such as roll diameters and media path lengths are not properly controlled, errors can occur.