Stiffness Characteristics Research Of Large Deformation Compliant Bionic Foot

Bionics shape design of lower limb prosthesis has always been the subject for the study of humanoid robot and rehabilitative prosthesis, however, research and development of bionic foot has become one of interesting topics in the field of prosthetic engineering in recent years. In this paper, through measuring the structural shape of healthy human feet and analyzing their gait characteristics, the mathematic model of typical J/S-type which is the fully compliant energy-storing foot mechanism is built, and the pseudo-rigid-body model (PRBM) of it is established. The rigidity characteristics of the mechanism are also analyzed and discussed, and a new method for static analysis of large-deflection compliant mechanisms is put forth.Firstly, we discussed the structure of foot joint and motor function of various parts of foot (bones, muscles, ligaments) with the related knowledge of anatomy, sports biomechanics, prosthetic engineering, surveying and so on. And through studying the gait of lower limbs, we discuss the structural characteristics of foot joint of vibration reduction, impact resistance, energy- storing, the self-stabilization of normal walking and standing, etc. The relevant data of foot joint during walking are obtained, providing primary base for further research of compliant bionic foot.Secondly, based on the MATLAB platform, the mathematic model of typical J/S-type fully compliant energy-storing foot mechanisms is built, so we present a splitting and optimizing method of compliant mechanisms segments based on curvature and rigidity. Then, based on the pseudo-rigid-body model, the pseudo-rigid-body model of J/S-type bionic foot mechanism are established, the selection of the model parameters is further studied.On the basic of the pseudo-rigid-body model that is already established, using the influence coefficient method and virtual-work theory, the stiffness matrix is deduced. Rayleigh quotient is solved with singularity value of the matrix, else it presents stiffness adjudging index. This paper analyzes and studies the stiffness characteristic of J/S-type bionic foot mechanism.Finally, solid modeling and static deformation analyzing has been done for J/S-type mechanism by using Solid Works software, the calculation results are analyzed and compared with that of the pseudo-rigid-body model(PRBM), particularly on large- deflection analysis. The coincidence of the two results proved the veracity of its pseudo-rigid-body model (PRBM).