Possibility for Control and Optical Filter Wheel Positioning Based on a Hall Sensor

This paper presents a controlling and positioning approach for an optical filter disk. In the known applications where Hall-effect sensors and magnets (radially positioned) are applied, the purpose of the latter is to help developing a binary code used mainly for filter identification. The number of sensors is equal to the maximum number of magnets that participate in forming the filter identity code. Therefore, three sensors and the corresponding number of magnets radially positioned for each position are required for the identification of seven filters. The precise position of the filter disk is reached by counting up the steps of a stepper motor. The presented approach applies only one Hall-effect sensor. The fore working front of one magnet, positioned along the disk periphery, is used to precisely mark each filter position. At a certain distance after the main magnet, a second one is positioned in order to form an identity code. The paper contains an algorithm for optical filter disk control and positioning, along with the mathematical formalism on which it is based.