Static Modeling And Variable Stiffness Method Of Cable-driven Flexible Manipulators

With the advance of science and technology,robotics technology is developing rapidly.Nowadays,the application of robots is no longer limited to specific tasks in simple and structured environments,and is gradually developing into sophisticated tasks in complex and unstructured environments.Such as post-disaster search and rescue,disease inspection and treatment,pipeline inspection and maintenance,space environment exploration,on-orbit services,and military reconnaissance,etc.Traditional rigid manipulators are difficult to meet the above requirements.The cable-driven flexible manipulator uses lightweight cables to drive a series of tandem joints.Through the relative rotation of each joint,the bending of the operating arm is realized.The cable-driven flexible manipulator has the advantages of many degrees of freedom,strong dexterity,and strong adaptability to complex and unstructured environments.And it has important applications in the fields of medical health,industrial automation,and aerospace.However,compared with traditional rigid manipulators,the cable-driven flexible manipulator has lower stiffness and poor accuracy,which has become a major bottleneck restricting the development of this type of manipulator.This paper takes the cable-driven flexible manipulator as the research object,and conducts research on the stiffness problem of such manipulator.Different from traditional rigid manipulators,the cable-driven flexible manipulator has the characteristics of a series manipulator and a cable-driven parallel robot,and reflects multiple mapping relationships in kinematics.First of all,the kinematic model of the typical cable-driven flexible manipulator is established,and the triple mapping relationship of the manipulator's the driving cable space(cable lengths),the joint space(joint angles)and the task space(end poses)is explained.Secondly,the statics model of the cable-driven flexible manipulator is established,and the relationship between the cable driving force,the gravity of the manipulator,the external load and the arm shape is described.At the same time,based on the statics model,six kinds of tension distribution algorithms for driving cables are proposed,and the static balance workspace of the manipulator under each algorithm is analyzed.Based on the kinematic and static model,the stiffness model of the cable-driven flexible manipulator is established.Different from traditional methods,the stiffness model proposed in this paper takes into account the influence of the Jacobian matrix change(ie,the Hessian matrix),and avoids the error caused by the pseudo-inverse calculation of the Jacobian matrix,which is more accurate than traditional methods.In addition,this paper proposes two stiffness modeling methods,namely analytical and numerical methods.Simultaneously,the characteristics of the two methods are compared and analyzed,and the applicable occasions of each method are given.Based on the stiffness model established in this paper,the main influencing factors of the stiffness of the cable-driven flexible manipulator are analyzed,and a method of variable stiffness for this type manipulator is proposed,that is,taking stiffness as the goal,kinematic and static equations as constraints,and by changing the arm shape in real time,the stiffness control in the process of following a specific trajectory can be realized.Finally,a cable-driven flexible manipulator experimental platform is set up to carry out the motion accuracy experiment and variable stiffness control experiment to further verify the effectiveness of the kinematics,statics,stiffness model and variable stiffness method proposed in this paper.This paper aims to establish the stiffness model of the cable-driven flexible manipulator,and explore its variable stiffness method.In order to realize the active stiffness control of the manipulator under different task requirements,achieve the ultimate goal of being strong if you want high stiffness and being soft if you want low stiffness,and provide a theoretical basis for solving the stiffness and accuracy problems of such cable-driven flexible manipulators.