Mobility analysis of variable geometry trusses

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Virginia Tech


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.