Speaker: Andres Kecskemethy (Universität Duisburg, Germany)
The computer simulation of the human musculoskeletal system is playing an increasingly important role in medical diagnosis as well as in the planning of corrections, physiotherapeutic programs and prosthetic implants. The basic goal of computer simulation is to reproduce mechanical motion within the musculoskeletal system in a biofidelic manner based on individual patient parameters. This makes it possible for physicians to compare functional properties of patients prior and after medical treatment, or even, as a long-term objective, to predict therapeutic effects before grasping the scalpel. In this seminar, the foundations of simulation of mechanical systems based on multibody dynamics and their application to the dynamics of the human leg are presented. Multibody dynamics is a well-known field of research of mechanical engineering that has been developed in the last twenty years and has been applied to a great variety of systems, such as road and rail vehicles, robots, tool machines, etc. In the technical setting, it has become the primary environment of development for innovative systems, as virtual reality methods have proved to reduce costs and design-cycle time significantly. Our approach for multibody dynamics consists of employing object-oriented methods that allow the user to build dynamic models as executable programs, which are then open for extensions and linking to other existing software packages, such as computer graphics, control theory, signal analysis, etc. This is in contrast to existing methods, which use the monolithic, all-inclusive program structure. The basic idea of the object-oriented approach is to mimic real-world mechanical parts by corresponding software objects that transmit motion and forces as in the real system. In this way, a model can be built as an assembly of individual "kinetostatic transmission elements" that can be triggered intuitively at the generic level, i.e., whose transmission properties can be accessed without regard to their internal structure. We show how with these basic functions it is possible to solve all problems of dynamics. The ideas are then applied to the mechanical model of the human lower extremity, displaying a model of hip, upper and lower leg, and foot, consisting of 15 degrees of freedom and 43 individual muscles. Parameters for bones and muscles are taken for a generic case from literature. Simulations involve geometry (muscle extensions during walking), inverse dynamics (joint torques computed from motion capturing systems and force plate output describing contact force at the feet), as well as preliminary results for the dynamics (trajectories of the lower extremity based on muscle activation profiles). The developed software has been extended by a 3D user interface that allows the user to perform simulations online and hence to assess the physical parameters directly at the computer monitor. The software is being applied at the Children's Hospital of the University of Graz for treatment of children with spastic diplegia. Comparison of simulations and measurements at the gait lab show a good agreement of the computed inverse dynamics and experimental data. Further illustrative examples for the concepts developed in this talk are taken from mechanism analysis, rail vehicles, and biomechanics of neck and forearm.