Contribution à l'étude des robots pleinement parallèles de type 6 R-RR-S

Abstract

A view on the contemporary robotics allowed us to notice the arrival of the first parallel robots on the market. A comparative study between serial and parallel robots can lead to the extension of their use for various purposes in the industrial environment, especially for heavy loads providing a good precision and a good dynamical behaviour. First, we have presented various classification criteria for parallel robots and then some sketches and prototypes of parallel robots which are classified with regard to the number of degrees of freedom are given. The prototype 6-RKS realised at LMecA has a special architecture and belongs to the manipulators family of type 6 R-RR-S.A discrete numerical method is used to find the Cartesian workspace for a constant orientation and the orientation workspace when the mobile plate centre is fixed. These algorithms can be used for any parallel manipulator. A map-making was realised and we could notice that the workspace, in position as well as in orientation, is bigger than the one of the linear driven manipulators of similar gage.We have proposed a pseudo-spherical representation of the workspace in orientation, in which the three parameters are in the same figure.We have developed the kinematical model and the inverse Jacobean matrices have been calculated. We have presented two approaches to deal with the singularities: the determination of the singular configurations which can be of two types corresponding to a given structure and the architectural singularity study.The statical model made it necessary the computation of the Jacobean matrix. We have determined the stiffness and compliance matrices for a given configuration as well as the maximal articulation torques and the maximal external loads.We have proposed a dynamical model for the fully parallel structures based on the Newton-Euler formalism. Its simplicity leads to a simple recursive calculation and finally to a linear system of 6 equations and 6 unknowns. This model has been applied to the 6-RKS manipulator and we have realised a dynamical simulation for several trajectories.