Design Of Underactuated Prosthetic Hand With Coupled Adaptive Motion Characteristics

Humanoid prosthetic hand can help upper limb amputees recover part of the hand function,which is an important tool to help amputees return to normal life.At present,the main humanoid prosthetic hand mainly includes coupling driving prosthetic hand and underactuated prosthetic hand.Because of the simple structure of coupling drive,the commercial prosthetic hand often adopts the coupling drive scheme,but the commercial prosthetic hand usually has only two phalanxes,so the motion is relatively rigid and can not adapt to the shape of the object well;Underactuated prosthetic hand can well adapt to the shape of the object,but the mechanism is often more complex,and the appearance is far from the hand.At the same time,the use of underactuated mechanism is easy to cause the instability of the grasp.In this paper,the existing problems of humanoid prosthetic hand are studied.By analyzing the motion characteristics of human hand,an underactuated prosthetic hand with coupled-adaptive motion function is developed.The prosthetic hand has the characteristics of good anthropomorphism,high stability,strong adaptability and compact structure.Firstly,this paper analyzes the motion characteristics of human hand and designs the overall degree of freedom configuration scheme of prosthetic hand.Each finger is regarded as a basic unit,and the dimension of the degree of freedom of the finger is reduced by principal component analysis.Then,taking the metacarpophalangeal joints of each finger as the research object,this paper analyzes the correlation between the metacarpophalangeal joints of each finger,and uses the correlation coefficient to cluster the metacarpophalangeal joints.After that,the overall degree of freedom configuration scheme of the prosthetic hand is determined according to the analysis results of the human hand motion characteristics.Then the overall degree of freedom configuration scheme of the prosthetic hand is implemented.Using the combination of planar cross coupled four-bar linkage and adaptive five bar linkage,a finger structure with coupled-adaptive motion function is designed.Using the combination of worm gear mechanism and tendon rope mechanism,the coupled thumb is designed.Through the analysis and improvement of the existing differential mechanism,a three finger differential mechanism between the middle finger,ring finger and little finger is designed.Then,the function of the coupled underactuated finger is verified by Adams.Then the force model of the finger is established,and the adaptability of the finger and the grasping stability of different contact states are analyzed.The influence of link parameters and joint coupling on finger stability and the distribution of contact force are discussed.After that,the model and analysis of the inter finger differential mechanism are carried out.Finally,an underactuated prosthetic hand prototype is used for experimental research.The coupled motion function and adaptive motion function of the finger were tested,and then the stability of the finger was verified by experiments,and then the finger compliance and fingertip output force were tested.Then the motion function of the differential mechanism between fingers is tested.Finally,the grasping performance and the diversity of grasping modes are verified by grasping a variety o f different objects.