Research of intelligent segment-fitting algorithm for increasing the measurement accuracy of quadrant detector in straightness measuring system

Abstract

In this paper, we propose an intelligent segment-fitting algorithm to increase the measurement accuracy of quadrant detector (QD) in straightness measuring system. Add-subtract algorithm and polynomial fitting are usually adopted to acquire the estimate of the spot projected on QD. The accuracy of QD is limited by the nonlinear relationship between the spot position and its estimate. In order to obtain higher accuracy, the polynomial fitting order must be higher with more calculation amounts, so the new algorithm is designed to optimize the nonlinearity. Through the specific method mentioned in the new algorithm, the whole measurement range of QD can be divided into several segments intelligently. And the data in each segment and between adjacent segments can be simply expressed by the third order polynomial fitting and linear interpolation. The experiment results verified that the algorithm could increase the measurement accuracy with good real-time performance. Within the measurement range of ±250 μm, the residual RMSE of the QD using the proposed algorithm, compared with that using the third order polynomial fitting, was reduced more than 80%, and the calculation amount was reduced to about 1/4 of that using the seventh order polynomial fitting.