System and method for detecting low paper in a printer using continously variable measurements

摘要

A system determines the level of paper (44) available in paper supply for printing. The system comprises a signal emitter (50) and a variably activated receiver (54). The receiver (54) alters an electrical parameter such as a resistance in accordance with the portion of the emitted signal received at the receiver (54). This alterable electrical parameter is in an electrical circuit that generates a signal proportional to the received portion of the emitted signal. An array of variably activated receivers may be arranged opposite a signal emitter to receive the signal portion not blocked by a paper supply. Alternatively, the array of variably activated receivers may be located adjacent to the signal emitter to receive the portion of the emitted signal reflected from the paper supply. The receiver uses the received or reflected signal to generate a signal having a magnitude proportional to the received or reflected signal. The signal from each of the receivers may be summed to generate a signal with a magnitude range that corresponds to the full and empty conditions of the paper supply at its extremes. Thus, the system of the present invention is able to provide a continuously variable signal indicative of the available paper in the supply over its entire range.