Research On Underactuated Prosthetic Hand Based On Postural Synergy

Human hand is an important interface of human and nature. People utilize their hand to manipulate tools and explore space. While the contact environment is changing, the hand also can feel the current status and adjust the changing. These all reflect the hand is a very complex and important part of the human body. Therefore, the lack of hands will greatly reduce the quality of people life. As a substitute for human hand, the prosthetic hand can help the disabled restore confidence and improve the quality of life. An ideal prosthetic hand should be able to finish various kinds of daily work by the control of muscle electrical or brain electrical signal. Under the relatively strict restrictions on the size and weight of the prosthetic hand, completely recreating the grasping ability of human hand is a very difficult task with the current mechanical and electrical technology. One of the main difficulties is the number of degree of freedom is too many, and the grasping posture is complicated, each joint of the current prosthetic hand could not be driven by an “one-on-one” form under the strict restrictions on the size and weight. Therefore, in order to simplify the mechanical and electrical system of the prosthetic hand, part of the prosthetic hand adopted global coupling way, which can reduce the each finger’s degree of freedom to one. In addition, some other prosthetic hands adopted the underactuated way to achieve an envelope grasp though the coordinate of passive and active degree of freedom. In this paper, based on subject in the national "973" plan, a postural synergy underactuated prosthetic hand with few drivers, various grasping posture, easy to control, low prices and highly-anthropomorphic movement is developed.The main content of the article including the structure analysis of human hand, the postural synergy planning of the prosthetic hand, the design of the synergy mechanism between the fingers, the design of underactuated finger, and the simulation and experiment of the postural synergy underactuated prosthetic hand. At first, based on the structure analysis of human hands, with our foregoing analysis results of the human hand grasping posture, the joints of prosthetic hand is divided into different modules in a new way and then the postural synergy matrix is obtained. According to hand postural synergy manner and the specific postural synergy matrix, the mechanical implementation of postural synergy matrix is determined, which can be integrated in the palm. In order to improve the grasp envelope of the prosthetic hand, the anthropomorphic underactuated fingers are designed. The diversity of grasp postures and movement anthropomorphism of the prosthetic hand is evaluated by ADAMS simulation, MATLAB simulation and finger move anthropomorphic assessment. To test the actual grasping performance of the prosthetic hand, a control system of the underactuated synergy prosthetic hand is developed. Then, the analysis and experiment of the joint move, the transmission error test and analysis, the static grasping reappear experiment and the experiment of grasping object are finished. The experiment results show that the joint movement characteristic of human hand is accurately reconstructed. Moreover, the developed prosthetic hand can grasp different objects with a variety of postures.