Research On A New Bio-Prosthetic Hand And Its Dynamic Control

Although traditional commercial 1-DOF prosthetic hand is a typical biomechatronics system, it can only complete simple grasp which is far different from human hand and can't satisfy handicapped normal life. Nowadays, the general tendency of prosthetic hand is multi-DOF, light-weight, small-volume, high-reliability, easy control methods and satisfactory manipulative performance. Therefore, based on the key program of National Natural Science Foundation of China (NSFC)"Study on humanoid prosthetic hand system and its theory"(No. 50435040), HIT-DLR Prosthetic Hand II on international top is developed; kinematics, statics and dynamics of index finger are analyzed; dynamic based curve fitting and impedance based force control are researched.The biomechatronics HIT-DLR Prosthetic Hand II possesses similar externality of human hand, five fingers and 15 active joints. It's actuated by 3 step-motors and weight 500g. Based on under-actuated and coupling principle, the fingers are designed with high agility, reliability and modularization idea. The three finger transmission scheme is developed. Actuated by one motor, the scheme can make the mid finger, ring finger and little finger complete auto-adapted grasp for complex shaped objects. It can grasp coherently and stay original posture. The bio-thumb is designed. It can grasp along a cone surface actuated by a motor. The principle of under-actuate is realized in spatial linkages mechanism through using ball bearing. ADAMS simulations are performed for thumb position in order to guarantee its successful grasp for different objects. The calibrated torque sensor with stress-measuring which can interconvert is designed to measure base joint torque. Structure of prosthetic hand is designed with modularization and integration thinking, and the integration of structure, sensor, controlling and driving circuit system of the prosthetic hand is realized. The envelop designation is accomplished. It includes external perfection and mechanism modification. The grasp and loading experiments verify the designation ideas.Kinematics of linkages of index finger and spatial linkages of thumb are analyzed. The parameters design of coupling linkages are completed, decided and simulated in ADAMS. The statics model of index finger is constructed in order to determine the relationship between actuation torque and the support force from phalanges, which is verified through ADAMS simulation and experiments. Based on virtual spring approach, the dynamic analysis of under-actuated finger is achieved. The index finger is dynamically modeled in this way. Coherent results are obtained through MATLAB and ADAMS simulation. Experiments are performed to verify the dynamic analysis.As one of key issues of prosthetic hand, the performance of finger control plays an important role in the hand manipulation. A finger may be treated as a small robot, and the theories about robot kinematics and dynamics are also prepared for the finger control. Based on the platform of prosthetic hand control system, Experiments of curve fitting using computed torque have been performed. The experiments has eliminated the uncontrollable character in PID control, reduced fitting errors greatly, improved its dynamic performance and achieved good results. On the other hand, control with only signals of position sensors must brings out errors. To reduce control errors, a velocity observer based on dynamic model of the finger has been established and used in improving computed torque curve fitting algorithm. To complement the uncertain factors of dynamic model, the adaptive controller with velocity observer has been designed. Velocity errors have been reduced and ideal results of dynamic control have been achieved.When prosthetic hand works, the finger compliance is very important. As one of main ways realizing compliance, the impedance control is studied deeply and implemented widely. Position and force based impedance control have been researched through the base joint sensors. Therefore, the grasp force of finger's phalanges can be controlled through its base joint torque control. The velocity observer has been used in impedance control. Compensated with inverse dynamic equation, the force based impedance control can not only realize accurate force tracking, but achieve finger's dynamic control by the combination of curve fitting and force tracking.