Light weight, low torque, inexpensive drum type optical digital shaft angle encoder

Claim 1

An optical digital shaft angle encoder adapted for connection to a rotatable shaft, the angular position of which is to be digitally encoded by said encoder, comprising: a dish-like member comprising a peripherally flanged disk, said member secured to a shaft, the rotational angle of which is to be encoded; a code drum comprising a thin strip of material formed into a closed loop and having a pattern of optical properties in rows transverse to the length of said strip, said pattern providing digital representations of angular positions of said rows about said drum, said drum disposed in intimate contact with the peripheral flange of said dish-like member and extending axially outward therefrom; a shrink ring retainer disposed on the outside of said closed loop strip radially opposite to said peripheral flange and retaining said strip on said peripheral flange; optical detection means including a light source and a plurality of light responsive means, said source and said light responsive means disposed in proximity with said drum and aligned with one another and arranged so that light from said source will energize said light responsive means selectively in accordance with said code pattern; and digital utilization means responsive to said photo responsive means for receiving electrical signals digitally representing the position of said drum.