Parallel manipulators are being thought of as a solution to many problems involving control
and manipulation. They offer significant advantages over serial manipulators in terms of increased
strength and rigidity. Variable geometry trusses (VGTs) are a special class of parallel
trusses.
Literature on VGTs has covered many interesting problems, yet there has been no conscious
effort to formulate a definition for a VGT. The major emphasis of this thesis is developing a
set of precise kinematic rules for defining and analyzing VGTs.
Traditional mobility criteria, when applied to parallel geometries, predict results which are
often confusing and sometimes inaccurate. Based on the set of rules developed, mobility
equations are derived for planar and spatial VGTs. The equations are tested on a sufficiently
large number of VGT configurations to convince the author about the validity of the set of rules
and the equations derived. Using the mobility equations, different candidate geometries can
be analyzed and compared. In addition, the equations can be used in the type and number
synthesis of VGTs.
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