and Six Degree
and Line Contact Constraint
The pair of tetrahedra that move with intersecting edges is a parallel
mechanism with six line contact constraints; the six R-P-R-P-R joints.
It is also a six legged platform that moves, albeit with legs of zero length.
Such five degree of freedom joints or, conversely, ones that inhibit only
one degree of freedom, are conveniently studied with simple double triangular
mechanisms, of planar, spherical and spatial variety, which use them. Forward
kinematics, singularity and isotropy of all three types have been obtained.
However, much remains to be done concerning analysis of the spatial variety(RDTM).
Of particular interest are recent results which indicate that the forward
kinematics RDTM's are dual to the inverse kinematics of 6R wrist partitioned
serial chains, i.e., solvable is closed form. Though some controversy surrounds
this claim, confirmation (or otherwise, alas) is imminent.
V. Karakusevic, V.Krovi, P.J. Zsombor-Murray
Mon Jun 26 21:22:20 GMT 2000