Structural analysis method for optimized design of complex kinematic structures using static and dynamic models and application to a robotic walking simulator

Abstract

This paper describes an approach for structural analysis for design improvements of complex, e.g. hybrid, kinematic structures utilizing static and dynamic models. It is suitable to locate improvement potentials in existing mechanisms, facilitate goal-oriented design of new mechanisms or for a simulation-based controller synthesis e.g. a compliance-controller. To receive a model close to reality, mechanical influences, which are commonly neglected in conventional robot models, are analyzed regarding their relevance and if suitable integrated into the model. Investigated effects are the mechanical compliances of links and gears, compliances of the actuators resulting from the control circuits as well as non-linear frictional influences of the actuators. The kinematic and dynamic model is realized as an iterative solution instead of a closed analytic solution with extensive symbolic expressions. This leads to an analysis with clearly arranged aspects, further more the model is suitable for usage in a real-time control. The mechanical influences are analyzed analytically. The derived dynamic modeling is based on the Newton-Euler formulation. The approach is applied to the robotic walking simulator HapticWalker, a device for robot assisted gait rehabilitation. It consists of two identical hybrid parallel-serial manipulators. The forces calculated by the use of the developed model are in a good congruence with measured values. An obviously improved correspondence between measured and calculated values is achieved by the non-linear friction model of the actuators.