Nipped rollers for centering images on sheet media

摘要

A sheet media position sensor device is disclosed which incorporates a pair of opposed nipped rollers positioned laterally across a sheet media transport path. One roller is electrically conductive while the opposed roller has an electrically conductive resilient coating. The coated roller is insulated at its mid point to divide the coating on the roller into two halves. A DC voltage is applied to the electrical conductive roller with current passing equally through each half of the adjacent coated roller. As sheet media is passed along the transport path and between the two nipped rollers, the sheet media acts as an insulator to reduce the actual contact area and therefore, the current flow between the conductive roller and the coated halves of the nipped roller. This reduced current flow is directly proportionate to the remaining contact area for each half of the roller which specifically identifies the lateral position of the sheet media. A plurality of current readings at predetermined time intervals produce multiple output signals which identifies the position of the sheet with respect to the center line of the transport path. These output signals can be used to realign and register a print image as it is applied to the sheet media.