Patent ID: 7173601

Claim:
A method for providing a position error indicator of an optical dithering element comprising: providing a photointerrupter comprising a light-emitting diode separated from a phototransistor by a slot with a constrained an aperture, wherein for a given size aperture, the current through the phototransistor is a function of the current through the light-emitting diode; disposing an optical dithering element arm at a setpoint within the aperture; positioning the optical dithering element to desired location and, in response, offsetting the optical dithering element arm from the setpoint within the aperture such that the amount of the aperture that is blocked relative to the amount blocked at the setpoint is indicative of the position of the optical dithering element; while offsetting the optical dithering element arm, controlling the current through the light-emitting diode such that a change in the amount of the aperture that is blocked results in a desired approximately proportional change in current through the phototransistor; based on any changes in the current through the phototransistor in response to positioning the optical dithering element, detecting a voltage indicative of the position of the optical dithering element; and comparing the detected voltage to a setpoint for a desired position of the optical dithering element and generating a signal indicative of the comparison.