Research on the Static Characteristics and Motion Analysis of Large Flexible Dexterous Finger

The end-effector is the main part of the robot to complete its operation function. Initially, the robot was assembled with single degree of freedom holder and used to operate some simple action, such as grasping, handling, etc.. But due to the fact that the holder was simple configuration, slow motion and single function, so it was poor generality and could only complete some specific tasks. Based on this situation, people began to study the end-effector with multiple functions and dexterous operation, and began to study the humanoid dexterous hand with multi-joint and multi-finger from studying the human hand. But with the further development of robot technology, the traditional rigid end-effector gradually showed up the shortcomings of complex structure, hard to control and low degree of flexibility etc., and then people put forward the concept of flexible pneumatic actuator.Flexible pneumatic actuator is not only a robot driver but also a robot actuator, it has the advantages of simple structure, convenient manufacture, high conversion efficiency and high degree of flexibility etc., but also has the disadvantages of insufficient rigidity and low response speed. It is suitable for the situation which requiring higher flexibility and security, such as agricultural harvest, finger recovery etc. This paper studies a new type of flexible pneumatic actuator, named large flexible dexterous finger, it is recently proposed by Zhejiang University of Technology. The main work and achievements in this paper is as follows:(l)The simple position and orientation geometric model of the finger was established with the foundation of geometric analysis, and also the plane kinematic model and spatial kinematic model of the finger was analyzed by the modified D-H coordinates, the inverse kinematic model of the finger was established by coordinate transformation. The Jacobian matrix introduced, then the finger static balance equation was established through the equilibrium relationship of force and moment. The velocity expression of any point on the finger was obtained by deriving fingertip’s position and orientation coordinate, then the finger kinetic energy equation was obtained by integrating the finger velocity.(2)The ANSYS software and its basic analysis process was introduced, then the bend characteristics of the large flexible dexterous finger was simulated. The large flexible dexterous finger was regarded as a cantilever beam, and the conclusion that it is minimal of the finger’s bending deflection in the case of its own-weight was obtained by theoretical analysis and simulation, and explained that it can ignore the own-weight’s effect when analyze the finger characteristics in the future. The relationship between internal pressure and bending angle of the finger was obtained by simulation and experiment, and the contrast curve was drawn, found that the simulation result was agree with the experimental result. Emphasized that some factors which may cause errors in experiment. The the relationship between fingertip’s position and orientation and bending angle of the finger was obtained by simulation and experiment, fingertip’s coordinate of simulation and experiment was drawn. Through the comparison to verify correctness of the simulation result and the experimental result. Illustrated that the large flexible dexterous finger’s compliance is good when grasp objects of different shapes by simulating several finger’s grasping gesture. At the end, the structure stability of the large flexible dexterous finger was analyzed, found that finger instability critical internal pressure load is0.53Mpa.(3)The peculiar grasping forms of human-hand was introduced, several grasping posture of human-hand was described detailedly. The standard of dexterity when the dexterous hand grasps objects was expounded, Various grasping mode and mode properties of the dexterous hand was introduced, and pointed out that the dexterous hand can realize stable grasp in condition of satisfying force closure and form closure. The structure scheme of the large flexible three-fingered hand was put forward, the structure and the working principle of the large flexible three-fingered hand was introduced. A method that using the BP neural network to classify the grasping mode of the large flexible three-fingered hand was proposed, and the BP neural network grasping pattern classifier was established, and verified it is feasible of the classifier by the test samples. At the end, the grasping mode of the large flexible three-fingered hand was analyzed, and the mathematical model of the three-fingered hand was established.