The Kutzbach-Gru¨bler mobility criterion calculates the degrees-of-freedom of a general mechanism. However, the criterion can break down for mechanisms with special geometries, and in particular, the class of so-called overconstrained mechanisms. The problem is that the criterion treats all constraints as active, even redundant constraints, which do not affect the mechanism degrees-of-freedom. This paper examines the screw systems of a parallel mechanism to identify the redundant constraints. The screw system characteristics and relationships are then investigated for physical properties. Then a new approach to mobility analysis is proposed based on screw system decompositions. A new version of the mobility criterion is presented to eliminate the redundant constraints and correctly predict the platform degrees-of-freedom. Several examples of overconstrained mechanisms from the literature illustrate the results.
- Design Engineering Division and Computers and Information in Engineering Division
Screw System Analysis of Parallel Mechanisms and Applications to Constraint and Mobility Study
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Dai, JS, Huang, Z, & Lipkin, H. "Screw System Analysis of Parallel Mechanisms and Applications to Constraint and Mobility Study." Proceedings of the ASME 2004 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. Volume 2: 28th Biennial Mechanisms and Robotics Conference, Parts A and B. Salt Lake City, Utah, USA. September 28–October 2, 2004. pp. 1569-1582. ASME. https://doi.org/10.1115/DETC2004-57604
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