Research On Mechanical Design Of Underactuated Prosthetic Hand And It’s Adaptive Grasping Characteristics

The humanoid prosthetic hand is an important instrument for the disabled people to realize the reconstruction of hand function.Compared with general purpose manipulators,the prosthetic hand has higher requirements for anthropomorphic design in terms of appearance,weight and perception function.At present,underactuated design is the major choice to achieve light-weight design for humanoid prosthetic hands.However,the underactuated finger has an incomplete restraint mechanical system structure.The uncontrollable distribution of the contact force between fingers and objects on different phalanx surfaces often leads to the failure grasping of the prosthetic hand.Therefore,how to design the underactuated finger mechanism with anthropomorphic motion,optimal mechanical adaptability and mechanism stability is one of the difficult problems in the research of underactuated hand.How to realize the electromechanical integrated design of the prosthetic hand with force/position/current/temperature sensing functions based on the underactuated mechanism is the bottleneck problem limiting the wide application of the prosthetic hand.At present,the grasp-state plane method is the most commonly used method for the optimal design of underactuated fingers and the analysis of their adaptive grip characteristics.However,coupled-adaptive underactuated finger has both adaptive and coupled motion characteristics.The traditional grasp-state plane method is difficult to analyze the adaptive grasping characteristics of such fingers,which limits the wide application of coupling adaptive fingers in the field of prosthetic hands.In order to establish an adaptive gripping characteristic analysis method applicable to couplingadaptive underactuated fingers and realize the design of highly integrated electromechanical prosthetic hands,this paper focuses on coupling-adaptive finger mechanism design,adaptive grasping characteristic analysis of the coupling-adaptive finger and mechatronic integration design of underactuated hand.This paper designs an underactuated finger mechanism with coupling-adaptive characteristics.This mechanism is composed of a driving four-bar mechanism,an adaptive five-bar mechanism and a coupled four-bar mechanism.This mechanism uses the linear motion pair and the compressed spring to realize the switch between the coupling motion and the adaptive motion of the finger,so that the underactuated finger can perform the anthropomorphic coupling motion in free space and the adaptive grasping motion after touching the object.On this basis,this paper designs the linkage parameters of the coupling-adaptive mechanism with the joint motion angle and dimension of the anthropomorphic finger as the constraint conditions and the joint coupling motion ratio linearization as the optimization objective.It lays a foundation for the kinematic analysis,statics modeling and integrated design of the coupling-adaptive finger.This paper establishes the coupling-adaptive finger kinematics and mechanics model.Based on the transmission characteristics of coupling-adaptive nine-link mechanism,this paper solves the analytical expressions of kinematic relations between the joint angles and between the joint angles and the driving angles of the underactuated finger by geometric method.On this basis,this paper designs the analytical solution method of finger inverse kinematics based on joint coupling proportional coefficient compensation,and establishs the forward and inverse kinematics models and static mechanics models of underactuated fingers.It provides a mathematical basis for the analysis of adaptive grip characteristics of coupling-adaptive underactuated fingers.This paper analysis the adaptive grasping characteristics of coupling-adaptive fingers.Based on the distribution state of the contact force between fingers and objects on the finger surface,this paper proposes a mathematical description method of the underactuated finger grip mode.Based on this method,this paper studies the adaptive grip characteristics and evolution rules of underactuated fingers,and establishs a quantitative analysis method for the stability of underactuated finger mechanisms,which provides a theoretical basis for the analysis of adaptive grip characteristics of coupled adaptive fingers.This paper develops a humanoid prosthetic hand with force/position/current sensing function based on coupling-adaptive finger,to solve the problem of mechatronics integration design of underactuated prosthetic hand.On this basis,this paper builds the underactuated prosthetic hand mechanism performance analysis experiment platform and the prosthetic hand grip experiment platform,and carries out the underactuated finger mechanical adaptability and mechanism stability analysis experiment,the prosthetic hand grip experiment and the disabled application experiment,to verify the underactuated finger mechanical adaptability and mechanism stability and other adaptive grip characteristics,verify the variety of gripping modes and practical value of coupling-adaptive humanoid artificial hand.The results of this study provide theoretical basis and technical support for promoting the independent innovation and wide clinical application of coupling-adaptive multi-sensing prosthetic hand.