ABSOLUTE, HIGH-RESOLUTION OPTICAL POSITION ENCODER

Modern computer-controlled manufacturing machinery requires the absolu te and highly accurate measurement of the linear position. Such an abs olute, optical linear position encoder is described here. It is based on the transilluminance of a glass scale with an inexpensive light-emi tting diode. The scale has two code tracks, one based on a pseudo-rand om binary sequence for the coarse determination of position and anothe r periodic code for accurate fine-position measurement. A single-lens telecentric optical system images the code tracks in a mechanically in sensitive way onto a custom photodetector This special detector IC is capable of determining the components of the (complex) Fourier transfo rm for the spatial frequency of the periodic code. The absolute optica l position encoder shows a resolution of 10 nm and an absolute accurac y of better than 100 nm over short distances, verified with a commerci al laser interferometer. (C) 1996 Optical Society of America