The kinematic models of revolute and prismatic pairs in presence of flexible bodies are discussed. Both discrete and continuous representations of body deformations are considered. In particular, it is shown, by geometrical considerations and anumerical example, that, for chains with prismatic pairs, a discrete approach can lead to geometrically wrong results. RRR and RPR single loop modules with flexible links are introduced and a continuous representation of flexibility for the "guide" bodyis adopted to obtain a model of the RPR closed chain. The closure equation that determine the pair variable of the prismatic pair is given. An example of solution of the RPR chain is compared with a graphical model created with a variational CAD systemand with the results obtained by a discrete approach.
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