Patent ID: 7709784

Claim:
An optical encoder with code wheel misalignment detection, the optical encoder comprising: a light detector configured to receive a light beam propagated through apertures of a code wheel, the light detector comprising: at least two photodetectors positioned side by side to each other, the two photodetectors configured to receive a first portion of said light beam and generate in response thereto, first and second encoder output signals of the optical encoder; an upper code wheel misalignment photodetector located above the two photodetectors, the upper code wheel misalignment photodetector configured to receive a second portion of said light beam and generate in response thereto, a third output signal for code wheel misalignment detection; and a lower code wheel misalignment photodetector located below the two photodetectors, the lower code wheel misalignment photodetector having a photocurrent generating area that is substantially equal to a photocurrent generating area of the upper code wheel misalignment photodetector, the lower code wheel misalignment photodetector configured to receive a third portion of said light beam and generate in response thereto, a fourth output signal for code wheel misalignment detection, wherein the fourth output signal is substantially equal to the third output signal when the code wheel is in alignment and substantially equal amounts of light are incident upon the upper and lower code wheel misalignment photodetectors; and a code wheel misalignment circuit for operating upon the third and fourth output signals provided to the code wheel misalignment circuit, the code wheel misalignment circuit configured to detect a difference between the amplitudes of the third and fourth output signals due to a code wheel misalignment that results in at least a partial blockage of light incident upon at least one of the upper or the lower code wheel misalignment photodetectors, and generate therefrom, an error signal indicative of the code wheel misalignment, when the detected difference exceeds a predetermined threshold.