Experiment and design of a high-resolution optical encoder

Abstract

An optical mechanism proposed in this paper is composed of a movable part and a fixed part for the increment high-resolution optical displacement encoders. A parallel light source is set on the moving part and a double-concave lens, a specially designed optical grating and a phototransistor array receiver are set on the fixed part. The parallel light emitted from the movable part passes through the double-concave lens and the specially designed optical grating; it is then projected onto the phototransistor array receiver to indicate the displacement of the movable part. The relationship equation of the lens is developed to design an optical mechanism, which can enlarge the displacement so that it becomes observable. Based on the simulation results, three different radii in the curvature of the double-concave lens were proposed. The simulation results indicated that the optical mechanism with 50 times magnification could make the 10 nm movement intervals of a light source be about 500 nm movement intervals in the detecting surface. Furthermore, considering the limitation of the precision of existing tools, an experimental system with a 200 nm resolution was established to verify the possibility of the proposed structure. The experimental result indicates the possibility of using the proposed theorem to achieve the desired results.