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RESEARCH PAPERS

Forward Position Analysis of Nearly General Stewart Platforms

[+] Author and Article Information
Chang-de Zhang, Shin-Min Song

Department of Mechanical Engineering, University of Illinois at Chicago, Chicago, IL 60680

J. Mech. Des 116(1), 54-60 (Mar 01, 1994) (7 pages) doi:10.1115/1.2919376 History: Received June 01, 1992; Online June 02, 2008

Abstract

This paper presents the closed-form solution of the forward position analysis of the nearly general Stewart platform, which consists of a base and a moving planar platform connected by six extensible limbs through spherical joints in the two planar platforms. It becomes a general Stewart platform if the centers are not constrained to those two planes. In this study, the coordinate transformation matrix is used to represent the position of the moving platform. Based on the six dependency equations of the rotation matrix and the six constraint equations related to the six link lengths, a set of six 4th degree equations in three unknowns are derived. Further derivations produce 21 dependent constraint equations. By simultaneous elimination of two unknowns a 20th order polynomial equation in one unknown is obtained. Due to dual solutions of other unknowns, this indicates a maximum of 40 possible solutions. The roots of this polynomial are then solved numerically and the realistic solutions are constructed using computer graphics.

Copyright © 1994 by The American Society of Mechanical Engineers
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