Displacement Analysis of a Spatial 7R Mechanism—A Generalized Lobster’s Arm

[+] Author and Article Information
J. Duffy, S. Derby

Department of Mechanical Engineering, Rensselaer Polytechnic Institute, Troy, N. Y. 12181

J. Mech. Des 101(2), 224-231 (Apr 01, 1979) (8 pages) doi:10.1115/1.3454042 History: Received May 28, 1978; Online October 21, 2010


An input-output equation of degree 24 is derived for a spatial 7R mechanism with consecutive pair axes intersecting. This mechanism is essentially the mathematical model for the kinematic analysis of a lobster’s arm which is an open 6R chain with mutually perpendicular consecutive pair axes, the geometry of which was first described by Willis [4] in 1841. The analysis of this special 7R mechanism constitutes a major step towards the solution of the general 7R mechanism with seven axes arbitrarily oriented in space.

Copyright © 1979 by ASME
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