Rotary displacement measuring apparatus

A rotary displacement transducer comprising

• an axle whose rotary displacement is to be determined, said axle being mounted to rotate about its long axis,
• emitter means mounted on the axle to define a plurality of concentric tracks circumscribing the axle to rotate as the axle rotates, each of said tracks being segmented to define a plurality of spaced-apart, conductive sections for producing electric fields when energized, wherein the sections of said tracks are formed to define a Gray code whose value changes incrementally relative to rotation of the tracks by a certain amount past a fixed radial locus,
• means for energizing said conductive sections,
• detector means disposed adjacent to the tracks of the emitter means and including a plurality of sensors, each positioned adjacent a respective track to detect the electric fields of said respective track as the axle and tracks are rotated, and produce signals representing such detection, wherein said sensors are positioned in an array coincident with said radial locus to produce signals representing the Gray code values of the tracks at the radial locus, and wherein said detector means further includes a second plurality of sensors disposed in an arc adjacent a selected track and positioned relative to sections of a selected track to produce signals representing Vernier measurements of the rotary displacement of the selected track as it rotates by said certain amount relative to the second plurality of the sensors, and
• means for processing the sensor signals to produce an output signal indicating the rotary displacement of the tracks and thus of the axle.