Patent ID: 6963063

Claim:
A position encoder comprising: a scale comprising: a first graduation track comprising a first set of markings that are periodically arranged with a defined graduation period Δ, wherein Δ=(360°/rotation)/(N counts/rotation), wherein N is the number of counts per rotation to be detected by said position encoder; a second graduation track comprising a second set of markings that are periodically arranged with a defined graduation period Δ, wherein said second graduation track is shifted relative to said first graduation track by a distance Δ/4; and a third graduation track comprising a third set of markings that are periodically arranged with a defined graduation period Δ, wherein said first, second and third graduation tracks are positioned such that at any one time at least one, but never three, of said first, second and third graduation tracks will transmit light directed upon said scale; a scanning unit that is displaced relative to said scale, said scanning unit comprising: a first sensor that scans said first graduation track and generates a first scanning signal; a second sensor that scans said second graduation track and generates a second scanning signal; and a third sensor that scans said third graduation track and generates a third scanning signal; a circuit that generates quadrature signals based on said first and second scanning signals.