Design And Control Of Deployable Truss-type Grasping Robotic Hand

As abandoned space objects in orbit around the earth gets more and more in recent years,it has brought many obstacles to human space exploration,and therefore the countries in the world begin to increasingly focus on the space debris recycling problem.At present,the existing technologies for recycling space debris mainly include the space manipulator capture technology,the space flying net and flying claw technologies,and the space truss-type grasping mechanism technology,etc.Compared with other recycling technologies,the truss-type grasping mechanism technology has the advantages of good manoeuvrability,high rigidity,simple driving and wide application range.Based on the background of recycling space debris,this dissertation focuses on the design of deployable truss-type robotic hand,dynamic modelling methods,motion control methods,and grasp planning,etc.To solve the general space debris grasping problem and the transport problem in space application,the design and analysis of deployable truss-type grasping robotic hand based on scissor mechanism and double parallelogram mechanism are studied.First,a class of deployable truss-type grasping robotic hand is proposed,this robotic hand can be folded into a compact configuration for transport and deployed in a large configuration to grasp large objects;and its deployment motion and grasping motion are kinematically decoupled.To improve reliability and stability of the robotic hand,a deployable robotic hand with a locking joint is proposed by designing a locking mechanism.Then,the kinematics and deployment performance,workspace,manipulability measure,compactness and stiffness of the deployable truss-type robotic hand are analysed in detail.The results show that the robotic hand has the characteristics of good dexterity and high rigidity.Based on the analysis of the characteristics of the series parallel mechanism and the deployable mechanism,the efficient dynamic modelling method of the deployable trusstype grasping mechanism is studied based on the recursive Newton Euler method.First,the geometric relationships of all the links in the deployable grasping mechanism are directly used to obtain the kinetic energy,potential energy and generalized force of the system,and the dynamic model is then established based on Lagrangian mechanics.This methodinvolves many geometric relationships and high computational complexity.Second,to improve the calculation efficiency of the dynamic model,the geometric characteristics and constraint relationship of the deployable grasping mechanism are ingeniously used to transform the modelling problem of the spatial closed-loop mechanism into that of the plane mechanism,so as to reduce the complexity of the dynamic modelling;the mutual force relationship caused by the deployment motion and grasping motion is used to establish the dynamics of the deployable grasping mechanism by using the recursive Newton Euler method;and the dynamic coupling analysis of the mechanism is completed.Through the characteristics analysis of the dynamic model of the deployable grasping mechanism,the adaptive robust control methods for the deployment motion and the deployment grasping coordination motion of the deployable grasping mechanism are studied.First,to solve the over-constraint problem of the deployable grasping mechanism,an adaptive robust controller is designed by using the extended state observer(ESO)and the nominal part of the dynamic model.Then,considering the dynamic coupling characteristics of the deployable grasping mechanism,a PD controller based on the dynamic feed-forward is designed for the deployment grasping coordination motion of the deployable grasping mechanism by using the recursive dynamic model.Finally,to reduce the dependence on accurate dynamics and enhance the ability to deal with unknown disturbances,a new adaptive extended state observer(AESO)is designed to improve the convergence performance of the ESO.To further improve the system robustness,by using the discontinuous projection based parameter adaptation law and traditional adaptive robust control method,a modified adaptive robust controller based on AESO is designed for the deployment grasping coordination motion of the deployable grasping mechanism.To improve the stability of the enveloping grasp of the deployable grasping robotic hand,by analysing the force closure of the multi-point-contact grasp,the optimal enveloping grasp planning method of the deployable truss-type robotic hand is studied.First,compared to the fingertip grasp mode,the advantages of the enveloping grasp mode of the deployable robotic hand are analysed.Then,the relationship between grasping force and force closure is established,and a quantitative judgement method of the force closure of the enveloping grasp is formed by using the contact geometric constraint relationship between the grasping robotic hand and the object to be grasped.Through simulationverification,the effects of the friction coefficient and the deployment length on the force closure evaluation index of the enveloping grasp are summarized.Finally,taking the force closure evaluation index as the optimization objective function,and taking the finger length of the deployable robotic hand as the optimization variable,an optimal enveloping grasp planning method of the deployable robotic hand is established by considering the constraint relationship of the grasping operation.To verify the mechanical performance of the deployable truss-type robotic hand,the control performance of various control methods and the enveloping grasp performance,the prototypes and its experimental control systems of the deployable truss-type robotic hand are built.Based on the built experimental prototype systems,different control experiments are completed,including the experimental verification of the deployment motion control method of the deployable grasping mechanism,experimental verification of two coordination motion control methods of the deployable grasping mechanism.Finally,the force closure of the enveloping grasp and the reconfiguration of the deployable truss-type robotic hand are verified on different experimental platforms of the deployable truss-type robotic hand.To sum up,the design and control of deployable truss-type grasping robotic hand are studied in depth,which can provide an important technical support for the completion of space missions such as space debris recycling and on-orbit servicing,and has important theoretical and engineering significance.