Patent ID: 7259858
Filing Date: 2007-08-21
Classification: B41J,B65H

Abstract:
1. A detector for monitoring movement of imaging media along a transport path, the detector comprising: a light source positioned to transmit light across the transport path at a selected location; a sensor positioned to receive light from the light source after the light crosses the transport path and configured to provide an output signal having a frequency based on an irradiance of the received light, wherein imaging media positioned at the at least one location affects the irradiance of the received light based on an optical density of the imaging media; and a controller configured to measure the frequency of the output signal, to compare the measured frequency to a threshold frequency, and to provide a control signal indicative of the presence of imaging media at the selected location based on the comparison; wherein the controller determines the threshold frequency based on a no-media frequency, wherein the no media frequency comprises a measured frequency of the output signal when imaging media is known not to be present at the selected location along the transport path; and wherein the controller periodically adjusts the threshold frequency by periodically measuring the no-media frequency and determining an adjusted threshold frequency based on the measured no-media frequency.