An optical absolute position measurement method using a phase-encoded single track binary code.

We present a new absolute position measurement method using a single track binary code where an absolute position code is encoded by changing the phase of one binary state representation. It can be decoded efficiently using structural property of the binary code, and its sub-division is possible by detecting the relative positions of the binary state representation used for the absolute position encoding. Therefore, the absolute position encoding does not interfere with the sub-division process and so any pseudo-random sequence can be used as the absolute position code. Because the proposed method does not require additional sensing part for the sub-division, it can be realized with a simple configuration and efficient data processing. To verify and evaluate the proposed method, an absolute position measurement system was setup using a binary code scale, a microscopic imaging system, and a CCD camera. In the comparison results with a laser interferometer, the measurement system shows the resolution of less than 50 nm and the nonlinearity error of less than ±60 nm after compensation.