Enhanced stiffness modeling of serial and parallel manipulators for robotic-based processing of high performance materials

The thesis focuses on the enhancement of stiffness modeling of serial and parallel manipulators with passive joints under an essential loading. The developed technique takes into account different types of loadings: external force/torque applied to the end-point, internal preloading in the joints and auxiliary forces/torques applied to intermediate points. In contrast to previous works, the proposed technique includes computing an equilibrium configuration, which exactly corresponds to the loading. This allows to obtain the full-scale force-deflection relation for any given workspace point and to linearise it taking into account variation of the manipulator Jacobian because of the external force/torque. The proposed approach also enables designer to evaluate critical forces that may provoke non-linear behaviours of the manipulators, such as sudden failure due to elastic instability (buckling), which has not been previously studied in robotics. In the frame of this work, it is assumed that the manipulator elasticity is described by a multidimensional lumped-parameter model, which corresponds to a set of rigid bodies connected by 6-dof virtual springs. Each of these springs characterize flexibility of the corresponding link or actuated joint and takes into account both their compliance and joint particularities. To increase the model accuracy, the stiffness parameters of the spring are evaluated using FEA-based virtual experiments and dedicated identification technique developed in the thesis. This gives almost the same accuracy as FEA but essentially reduces the computational effort, eliminating repetitive re-meshing through the workspace.