| End-effector is an important manipulator for the robot to interact with environment. Because of simple structure, fewer degrees of freedom DOFs, poor adaptability and other shortcomings, earlier conventional end-effector is one of the most important factors which restricts the development and application of robots. Simulating the structure, function and size of human hand, robot multi-fingered dexterous hand with multiple joints and multiple DOFs is a new kind of end-effector which has better dexterity and adaptability as well as plays a positive role to promote application of robots. Therefore robot multi-fingered dexterous hand has both great research significance and application value.After 1990s, industrial robots with the general function have become saturated. Application of robots has been extending to agricultural, medical and service areas from industrial area, and its grasping targets are always crisp, tender or living objects. So, it requires the multi-fingered dexterous hand should have great flexibility. Based on the shortcomings of existing dexterous hands summarized in this paper, a new type of air-driven multi-fingered dexterous hand, named ZJUT Hand, is proposed. ZJUT Hand has good passive flexibility and can make up for the deficiency of existing dexterous hands in some ways. The main research work in this paper is as follows:(1) Side-sway joint driven by FPAs directly is proposed which can simulate swing movement of human hand. Based on statics and elasticity, force equilibrium equation of the FPA free end is established. And then the static model of the side-sway joint is obtained. According to the first law of thermodynamics, combined with the joint’s dynamic equation, the dynamic model of the side-sway joint is established. Experiments are carried out to test the static and dynamic characteristics of the joint and verify the mathematical model. There is certain error between experimental curve and theoretical curve, and the error cause is analyzed. Using a series dual loop control method, the output angle and output force of joint are controlled. The results show: when expected output angle is 15°, the loop dynamic response time is about 0.3s, and the steady-state relative deviation is less than 0.65%. When expected output force is 188Nmm, the loop dynamic response time is about 0.3s, and the steady-state relative deviation is less than 1.5%. The side-sway joint can meet the requirement for designing multi-fingered dexterous hand joint. (2) 4-DOF anthropomorphic finger with four joints is proposed. To achieve a high degree of modularity, five identical fingers and a palm constitutes the body structure of ZJUT Hand. The structural parameters of the fingers and the layout program of the hand are determined by the bionic optimization method. Simulation experiments are carried to verify the grasping ability of ZJUT Hand. The multi-sensory system for ZJUT Hand is developed.(3) Using D-H method, direct kinematics equation of ZJUT Hand finger is established. Analytical analysis show that there exits a redundant problem for solving inverse kinematics of the finger. An improved adaptive genetic algorithm IAGA is proposed. Simulation experimental results show that the IAGA can effectively solve inverse kinematics problem of the redundant finger. Experiments of finger position tracking are carried out, and the experimental results show: for different expected fingertip position, dynamic response time of position tracking is less than 0.5s, and the maximum position error is 1.12mm.(4) Based on differential kinematics theory, the static model of the finger is established. Semi-closed loop control experiments for static force tracking of the finger are carried out. It is concluded from experimental results that fingertip output force can be controlled easily. Characteristics of good passive flexibility of ZJUT Hand are summarized. Based on 5-component force/torque sensor intalled on the fingetip, a control strategy for dynamic adaptive fuzzy fingertip force tracking is proposed. Experiments of dynamic fingertip force tracking are completed. Experimental results show that the control strategy can realize fast and accurate dynamic fingertip force tracking under an unknown environment, and the force tracking error is within±0.15N.(5) The optimal grasping posture of ZJUT Hand’s palm is defined. A new method for grasping model identification based ANFIS is proposed. Simulation experimental results show that the method can easily establish the model of the target objects, and has very good recognition accuracy and convergence. Equivalent rules of target objects are presented and greatly improve the efficiency of identification. A general grasp planning program of multi-fingered dexterous hand is proposed. Finally, the grasp planning experiments for ZJUT Hand is completed. Experimental results show that ZJUT Hand is able to construct the models of two typical target objects, choose a reasonable number of fingers for grasping and position of contact points, perform stable grasping of the objects and complete the grasping force optimization.A new type of multi-fingered dexterous hand, ZJUT Hand, proposed in this paper is directly driven by flexible pneumatic actuator FPA developed by our research team. ZJUT Hand has characteristics of simple structure, easy control, and easy miniaturization and so on. It has better passive flexibility, and without lack of stiffness. It is suitable for application situation that requires relatively high flexibility and low response speed of the fingers, such as agricultural harvesting robot, finger rehabilitation robot and so on. |
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