Index finger system force capabilities under simulated pathological conditions

When dealing with the design of robotic fingers driven by tendons, one can be inspired by the human index finger tendon distribution. The structure of the designed robot finger has to minimize the number of tendons required without sacrificing either the actuated degree of freedom or the maximal output force produced at the fingertip. In this paper, a biomechanical study of the index finger under normal and abnormal conditions is developed. Under abnormal conditions, when some pathology affects the musculo-tendon units, the number of intact muscular actuators will be reduced. A three-dimensional biomechanical model for a static force analysis is developed through anatomical and kinematic studies. An optimization approach is then used to determine muscle force distributions corresponding to maximal fingertip strength when performing isometric force tasks. Further common cases of injured flexors and extensors are analyzed. The simulation method of such abnormalities is described and the results are reported. This investigation allows us to analyze the importance of the tendons distribution in order to enhance the robotic hands design process. In fact, the obtained force distributions are linked to the further required motor torques of the artificial robotic finger driven by tendons. Hence, the developed approach can be with great help whenever the motor sizing process is investigated.