A technique for the calibration of instrumented spatial linkages used for biomechanical kinematic measurements

Abstract

Instrumented spatial linkages (ISL's) are finding wide applications in biomechanics for measuring all six degrees of freedom of relative location and attitude between two anatomical bodies moving through limited ranges of motion. The objective of this paper is to present a calibration scheme which will re-evaluate initial estimates of various kinematic and electrical parameters describing such linkages in order to minimize the error in linkage measurements over a specified field of motion. This technique may be separated into two parts — a mechanical calibration of the overall linkage and an iterative numerical synthesis of linkage parameter estimates based upon data from the mechanical calibration. Because certain linkage parameters may not be determined with a high degree of confidence (due to component compliance, assembly, or gauging errors), numerical re-evaluation of these parameters will provide a better analytical description of the linkage and produce superior accuracy in ISL measurement calculations. Use of an accurate mechanical calibration apparatus and a non-linear regressive Marquardt optimization formulation has demonstrated the effectiveness of this technique in reevaluating such parameters and subsequently improving and estimating the accuracy of ISL measurements.