A high resolution optical shaft encoder

This paper describes the development of an optical shaft encoder which is direct reading and has a resolution of 16 bits. The principles of design of the encoder, which employs a novel multi-element l.e.d. array as light source, are given. The smallest feature size on the encoder disc pattern is 20 μm × 4 μm. The angular position of the encoder shaft is obtained in serial form by pulsing the array elements in turn to produce a pulse train in a single detector placed behind the encoder disc. The fabrication and assembly of the mechanical components of the encoder are described, together with details of the electronic control package. Finally an indication is given of possible further develop-ments of the instrument.