CALIBRATION OF STEWART PLATFORMS AND OTHER PARALLEL MANIPULATORS MINIMIZING INVERSE KINEMATIC RESIDUALS

This paper focuses on the accuracy enhancement of Stewart platforms th rough kinematic calibration. The calibration problem is formulated in terms of a measurement residual, which is the discrepancy between the measured leg length and the computed leg length. With this formulation , one is able to identify kinematic error parameters of the Stewart pl atform without the necessity of solving the forward kinematic problem; thus avoiding the numerical problems associated with any forward kine matic solution. By this formulation, a concise differential error mode l with a well-structured identification Jacobian, which relates the po se measurement residual to the errors in the parameters of the platfor m, is derived. Experimental studies confirmed the effectiveness of the method. It is also shown in this paper that the proposed approach can be applied to other types of parallel manipulators, assuming that the ir inverse kinematic solution is simpler than its forward kinematic so lution. Because this condition is satisfied by almost all parallel man ipulators, the method is very useful for kinematic calibration of such machines. (C) 1998 John Wiley & Sons, Inc.