Patent ID: 7285965

Claim:
A paper-width detecting device disposed in a paper tray comprising: at least a paper guide movably disposed on the paper tray for accommodating different sizes of papers loaded in the paper tray; a conductive element attaching to the paper guide and moving simultaneously with the paper guide, wherein the conductive element has a plurality of first conductive portions; a circuit board having a plurality of parallel conductive wires, extending in a direction parallel to the moving direction of the conductive element and being formed by a plurality of separated second conductive portions on the surface of the circuit board, wherein an insulating region is formed between any two adjacent second conductive portions of each conductive wire and the first conductive portions correspondingly contact the second conductive portions and the insulating regions of each conductive wire as the paper guide moves; and a control-processing unit for providing an electric voltage between the conductive wires and the conductive element, such that the first conductive portions electrically contact the second conductive portions and the insulating regions of each conductive wire, wherein when the paper guide presses against the paper, the control-processing unit obtains a digital signal corresponding to the number of current passages formed between the first conductive portions and the corresponding conductive wire thereof so as to generate a paper-width value accordingly.