The Workspace of Three-Degree-of-Freedom, Four-Jointed Spherical Wrist Mechanisms
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In this paper, orientational workspace of three-degree-of- freedom, four-jointed spherical wrist mechanisms have been investigated. We have derived the workspace boundary equations via both geometric consideration and Jacobian analysis. It is shown that for the first type wrist mechanisms with links 2 and 3 coupled, the workspace boundary consists of circles centered at fixed axis of rotation; while for the second type mechanisms with links 1 and 2 coupled, the boundary consists of two branches of curves. The workspace is divided by inner and outer boundaries into regions of accessibility zero, two and four. The criteria for full workspace design as well as for maximum four-root region have been established.