Research Of Humanoid Under-actuated Mechanical Prosthetic Hand

A lot of researches have shown that,about half of the disabled patients are reluctant to use their prosthetic hands,the causes of this phenomenon based on the following problems which existing in these prosthetic hands : 1) the size, weight and appearance of the prosthetic hand have the large gap compared with the human hand; 2) the humanoid prosthetic hand driven by motors with rigid mechanical structure remote, it is easy to control, but less flexible; So this paper from the perspective of raising prosthetic hand’s flexibility and flexible operation, proposed to use the wire rope with coupling linkage, the torsional springs were added in each finger’s joint to increase the grasping softness, the movement coordination of each finger’s knuckle has been improved with using coupling linkage, this paper has designed a new type of multiple-degree of freedom under-actuated humanoid prosthetic hand.This paper analyzed the research status of the prosthetic hands, put forward the problems existing in the prosthetic hand and its development trend.With the analysis and comparison of the advantages and disadvantages of two kinds of typical driving mechanism which using in the prosthetic fingers, from the perspective of human natural hand’s bone structure and grasping way has carried on the comprehensive research,determined using a new type of under-actuated wire rope coupling linkage, to solve the the contradiction between complexity and flexibility, the mechanism of the prosthetic hand can reduce the weight, size, but raise the high reliability, the movement coordination, flexible operation at the same time.Then the design of the index finger and thumb, the thumb position, the installation of the palms and other four fingers are modified.Secondly, the kinematics of simplified linkages of index finger and thumb are analyzed.The positive kinematics solution and inverse solution of the prosthetic fingers were carried out;And selected the appropriate finger size and finger knuckles rotation angle, obtained the working space of index finger and thumb.The boost of working space and the grasping performance after adding the torsional spring to each finger’s joints have been analyzed, the optimal parameters of middle and far knuckle’s coupling linkage are obtained by simulation, the motion simulation of coupling linkage was carried out in the ADMAS software, obtained and analyzed the comparison of two different movements of each finger’s knuckles, the relationship between the displacement and time is concluded, the coupling motion of the prosthetic fingers is obtained with coupling linkage, the grasping coordination was promoted either.The statics and the grasping ability verification is analyzed to get the expression of finger’s contact force, obtained the Jacobi matrix of the prosthetic hand index finger and thumb, using MATLAB to calculate the finger mechanism of Jacobi matrix transpose matrix condition number of inverse distribution, the analysis results showing that the prosthetic finger can be within the scope of the larger rotation angle, it has a very good isotropic operating performance, the reasonable kinematic parameters of the prosthetic finger’s mechanism have been given; the grasping movement of prosthetic hand was simulated in the ADMAS, verified the space movement and grasping ability of the prosthetic hand complied with the design requirements.