Application of Symbolic Computation in Robot Pose Error Modeling

This paper presents an application of symbolic computation in geometrical error modelling and simulation of an industrial robotic manipulator. A program named SCRPE (Symbolic Computation of Robot Pose Errors) has been developed to automatically generate error model equations for the end-eflector of N degree-of-freedom robots. The SCRPE utilizes symbolic manipulation capability of MACSYMA (a Lisp-base artificial intelligence language). The prime reasons of this work are to provide a base for comparison, performance assessment and accuracy judgment of numerous error calibration and compensation models available in the literature; and to represent output results in a concise form eliminating completely the manual derivation process. When such computer generated outputs are fed to a simulation program, saving in computational time for error estimation is realized. As an example, the mathematical error model considered here is based on small perturbation in link parameters defined in accordance with a classical Denavit-Hartenberg notation. The time required to compute first and second order terms of the model are compared for numerous robots. The worst case scenario takes 290 seconds for a PUMA 600 series robot, which is insignificant compared to the time required for accurate manual derivation. The SCRPE program is user-friendly, interactively menu-driven and has been developed on VAX 750 Digital computer under the VMS operating system. Interested readers can obtain the program copy by contacting the first author.