Patent ID: 7368705

Claim:
A position encoder, comprising: a scale including a periodic first track and two or more periodic second tracks operative to generate corresponding periodic first and second energy patterns, the second tracks having distinct but generally similar periods; detector circuitry operative in response to the periodic energy patterns to generate corresponding sets of analog signals, the analog signals within each set representing amplitudes of the corresponding energy pattern at predetermined spatial locations; and processing circuitry operative in response to the sets of analog signals: (i) to generate linked position estimates, each linked position estimate representing a sampled phase of a corresponding one of the second energy patterns linked to a sampled phase of the first energy pattern; and (ii) to generate one or more beat track estimates by an algebraic combination of the linked position estimates such that each beat track estimate represents a corresponding beat track having a beat period greater than the period of the second tracks from whose linked position estimates the beat track estimates are generated, wherein the period of a predetermined one of the second tracks has a non-integer ratio with the period of the first track, and wherein the processing circuitry is further operative: (iii) to generate a virtual track by applying a frequency-dividing function to the linked position estimates for another of the second tracks, such that the period of the virtual track has an integer ratio with the period of the predetermined second track; and (iv) to link the predetermined second track with the virtual track.