Research On Key Technology Of Multi Degrees Of Freedom Dexterous Hands For Space Robot

As the end effector of robot,humanoid dexterous hand with multi-sensing function is main aspects of bionic robot research.According to Space-Orbital Services requirements for space robot grasping fixed or floating targets in microgravity environment,refueling of satellites and disassembly of valuable parts for the abandoned aircraft,the dissertation emphasizes on designing a set of human-like dexterous manipulators with multiple sensing functions,large grip,high stability and precise motion,which is supported the 18^th Institute China Academy of Launch Vehicle Technology pre-research program“Research on Key Technology of Multi Degrees of Freedom Dexterous Hand for Space Robot”.Furthermore,this will combine with the space manipulator developed by ourselves,realizing Space Manipulator-Humanoid Dexterous Hand's ability to perform fine work in a cosmic microgravity environment.The research significance of this dissertation is that the research of dexterous hand and its intelligent grasping operation with multiple sensing functions can enhance the ability of space robot to finish fine positioning and steady grasping and other fine work under the extreme conditions of outer space microgravity environment,therefore improvingthe intelligence of space robot systems,which has a significant impact on space robots,precision operations in harsh environments,and advanced service robots.Human handis the most flexible and sophisticated end-effector evolved from the test of the natural environment.In order to make space robotcomplete complicated operation tasksout of the cabin instead of astronauts,the dexterous hand of the robot is required to have a similar scale,size and activity capability as human hand structure,that is determined by integration ofmechanical structure,precision transmission mechanism,sensing system and drive control system structure.In addition,humanoid dexterous hand must also have abilities to manipulate objects as well as human hand,such asenough position tracking accuracyof each finger when performing preciseand smart operation,enough force control accuracy when grasping fragile object,sufficient anti-interference ability and adaptability ofdexterous hand system when in face of changes in external environment and uncertainty oftarget object,therefore ensuring stability and flexibility of the whole system.These willput forward extremely high requirements on overall performance of humanoid dexterous hand system.A set ofmodular dexterous hand named CALT-18 is completely designed,with humanoid appearance and as many as 18 degrees of freedom.Based on concept of modular design and through integrated mechanical structure and compact transmission design,CALT-18 hand successfully realizes optimization of mechanical structure and modular andinterchangeability of each finger,and also enabling high integration of mechanical body structure,precisetransmission,sensing system,electrical control system and high-speed real-time EtherCAT communication system.Compared with most advanced hand of NASA Robonaut 2 with 13DOFs,CALT-18 hand system increases the overall degree of freedom and enhances the flexibility and operational ability,therefore improving its effective work space and smart operating space.Besides,compared with HIT/DLR-II hand,through way of tendon drive,CALT-18 hand on the one hand helps reduce overall size and weight of the whole hand,on the other hand helps spare sufficient space for using high-power motors without considering constraints of motor size.Thus the grip force is enhanced,making CALT-18 hand more conducive for engineering applications.In the field of multi-DOFmechanism and micro motion control,it is a very effective way using flexible tendons in limited space to realize long-distance transmission.However,fixing method of flexible tendon will affect transmission error and efficiency of mechanism.Therefore a kind of tendon clamping mechanism is invented for tendon drive transmission.Based on plastic deformation of high stiffness metal theory,flexible tendon could be strongly fixed to a metal block,providing sufficient clamping force and precisely control the dimensions of the metal block.Compared with general ways of knottingtendon,this method has significant value for precise installation of tendon in limited space.At the same time,it will ensuretendon strength andassembly accuracy,eliminateinstallation gap and realize precise transmission of tendon drive.Sensing system is the core part of dexterous hand to perceive the external environment and its own state.In this dissertation a miniature 2 DOFs fingertip force sensor and miniature knuckleangular displacement sensing system are developed.In view of demand of force perception of CALT-18 hand,force sensor elastomer and finger joint structure are designed integrally.The main work includes elastomer structure optimizedesign,strain gauge pasting,measuring bridge circuit design,signal conditioning and amplifier circuit design.Aftermeasuring experiment and algorithm calibration,ideal output characteristic curve is obtained,verifying the feasibility and effectiveness of the method of miniature two-dimensional force sensor for humanoid fingertips.More importantly,it solves the problem that force sensor is difficult to integrate in the narrow space of dexterous hand joints.Additionally,in view of demand of joint angle measurement,based on the law of electromagnetic induction,a novel contactless absolute angular position micro-sensor has been designed in the dissertation.It is mainly composed of three parts:a magnet having two portions shaped as circle segments with different center points,a hall effect sensor and a signal processing circuit.The linearity of the sensing system is improved by particularly designing spatial magnetic field distribution of asymmetric magnet,and Hall output signal is converted by the second-order low-pass filter circuit into linear analog voltage.Callibration experiment based on BP neural network has been performed on a prototype of the angular position sensor and the results demonstrate the proposed scheme is feasible.Kinematics and dynamics model of single finger are the basis of coordinated multi-finger control.Based on theory of space coordinate transformation,kinematic equation of single finger is solved and calculation method of finger Jacobi matrix is given.Based on the finite element theory,a simple and efficient modeling method of robot dynamics is presented in this dissertation.It has universal applicability for various complex robot systems,which can provide a theoretical basis for the high accuracy and real-time control of robot.Based on the kinematics and dynamics analysis,the electrical system structure and control strategy of CALT-18 hand are further studied.Several different impedance control algorithms are analyzed theoretically,laying theoretical foundation ofposition tracking in free space and force control in constrained environment of the CALT-18 dexterous robot hand.