Design And Research Of Bistable Foot Structure Based On Tensegrity Structure

As the only part in contact with the ground,the foot structure plays an important role in the gait fluency and anti-tip support ability of the whole humanoid robot.However,it can be found through literature research that the current research on foot structure design usually focuses on the adaptive and support ability of ankle joint,but ignores the important role of metatarsophalangeal joint(MPJ)as the end joint of foot in the process of body movement,which means that there is still a gap in the design of MPJ in foot structure.In order to achieve the unification of passive compliance during walking and rigid locking during running of MPJ,this paper develops a new foot structure with state switching capability based on bistable tensegrity structure,using the characteristics of mixed rigidity and flexibility of tensegrity structure to meet the demand of passive compliance while providing better rigid support capability.On this basis,the singular position characteristic of the four-bar mechanism is used to provide active locking for the MPJ that switches to the running state,fully reproducing the functional performance of the MPJ of the human foot in the walking and running states,and providing solutions for the integration of the motion modes of the foot structure.The contents of the research in this paper include:Firstly,from the functional performance of human MPJ in different states,a tensegrity structure model with bistability switching capability is established,and its excellent self-stabilization and self-recovery capabilities are combined to meet the functional requirements of the foot structure’s MPJ.The self-stabilization capability of the model is verified based on the force density method,the kinematic analysis is combined with the two types of Lagrangian equations,and the stiffness matching method is proposed to verify the theoretical correctness of the bistability switching of the structure.Secondly,the tensegrity structure model is equivalently mapped to a mechanical structure,and in order to improve the joint locking ability of the foot structure under running condition,a four-bar mechanism is added at the MPJ to realize the singular position locking function by optimizing the shape of the bar.The simulation environment is built based on Solidworks 3D software and ADAMS simulation software to analyze the motion characteristics of MPJ during flexion and the working space when the rear palm is raised,and to discuss the promotion effect of joint stiffness variation on the self-recovery ability of tensegrity structure.Thirdly,we introduce the process and material matching method of the required parts for the prototype,and complete the assembly and state switching function of the foot structure.The three-dimensional capturing experimental platform is built to verify the gait fluency,the state locking performance of the MPJ is tested based on the tensile test platform,and the performance of the foot structure in terms of biomechanics is verified by using the lower limb experimental platform and mechanical acquisition module.Finally,to enhance the objectivity of the experiment,three foot structures were tested based on the same experimental platform to compare the differences in functional performance and their own properties,and to illustrate the advantageous characteristics of the foot structure.