Large scale optical position sensitive detector

Abstract

This paper presents the development of a large scale optical position sensitive detector. The device is designed for the precise guidance of machines with respect to a reference laser plane in large working areas. The 1D detector has a measurement range of 1 [m] and, with the present implementation, a position measurement standard deviation of s <; ±0.6 [mm] in a 95% confidence interval. With this length it is orders of magnitude larger than all presently available position sensitive detectors. The instrument is based on a multi-camera image processing concept. An aluminum bar serves as the target for the laser. The target's surface is specially prepared to ensure optimal scattering of the laser light. Presently, four cameras with overlapping fields of view are deployed to observe the scattered light. Additional optical components reduce the susceptibility to extraneous light sources. Each camera is calibrated using Gram polynomials and the data from the four cameras is fused to give a consistent measurement over the complete measurement range. The linear nature of the computation's algebraic framework offers the advantage that the error propagation can be computed analytically. Weighted polynomial approximation determines the calibration coefficients and weighted polynomial interpolation is used to determine the measurement results. Complete testing of the instrument is presented, whereby cross validation ensures the correct determination of errors. A Kolmogorov-Smirnov test is performed to determine the statistical nature of the measurement errors.