Multiturn absolute encoder using spatial filter

This paper describes a vernier-type multiturn absolute encoder which uses a spatial filter to interpolate between encoder slit positions. The absolute angle can be derived from the optical encoder which uses a LED, photodiodide array and a coded disc consisting of three tracks. The accuracy of angular measurement for a prototype encoder was as high as 1/1000,000, and the encoder can respond up to 3 000 rpm. The shaft revolutions are tallied by a magnetic bubble counter which uses a 'memory wheel' principle to count up to 32 487 turns. No electrical energy is used to store data or count revolutions.