KINEMATIC CALIBRATION USING THE PRODUCT OF EXPONENTIALS FORMULA

We present a method for kinematic calibration of open chain mechanisms based on the product of exponentials (POE) formula. The POE formula r epresents the forward kinematics of an open chain as a product of matr ix exponentials, and is based on a modern geometric interpretation of classical screw theory. Unlike the kinematic representations based on the Denavit-Hartenberg (D-H) parameters, the kinematic parameters in t he POE formula vary smoothly with changes in the joint axes, ad hoc me thods designed to address the inherent singularities in the D-H parame ters are therefore unnecessary. Another important advantage is that si mple closed-form expressions can be obtained for the derivatives of th e forward kinematic equations with respect to the kinematic parameters . After introducing the POE formula, we derive a least-squares kinemat ic calibration algorithm for general open chain mechanisms. Simulation results with a 6-axis open chain are presented.