A Step Towards Testing of Foot Prostheses Using Real-Time Substructuring (RTS)

Despite extensive research in prostheses development, amputees still have to cope with severe limits. Tasks, such as climbing stairs and running or walking on soft ground are demanding and represent obstacles in everyday life. Design verification of new devices helps to accelerate the development. However, current test procedures do not include the dynamic interaction between a prosthesis and the human. Real-time Substructuring (RTS) enables investigation of the dynamic behavior of a system, here human and prosthesis, by splitting it into numerically simulated components and one physical component. As this test imitates real dynamic conditions, foot prostheses can be improved during the development stage. In this preliminary study, a one-dimensional mass-spring-mass system is investigated. The upper mass, representing the human being, is simulated numerically on the computer. It is coupled virtually to a prosthesis, represented here as a spring-mass system, which is mounted on a Stewart Platform. Both systems exchange displacement and force information. The upper mass tries to follow a periodic desired trajectory, which is influenced by the coupling. This paper describes the experimental setup and the effect of delay compensation. In addition, it is shown how the accuracy and stability of the RTS simulation depends on the problem description, i.e. how much the system is governed by the mechanical properties of the numerical part. Although we are specifically considering the application of RTS to prosthetics, the current research tackles generic problems that will also help to enhance other applications involving contact, e.g. the docking of satellites.