Design And Modeling Of Motion-Decoupled Mechanism For Cable-driven Joints

Compared with traditional rigid manipulator,the cable-driven manipulator has the advantages of simple structure,low power consumption,low inertia,high ratio of load to self-weight,good flexibility and so on.It is especially suitable for medical instruments,home service and other fields,which require high amount of safety.However,due to the alignment of the ropes,there is a problem of motion-coupling between the manipulator joints,leading to the degradation of driving accuracy.Moreover,the tension flexibility of the driving cable,the hysteresis and the dead zone of the cable driving,makes it difficult to control the joint precisely.Therefore,it is of great significance to study the decoupling and transmission characteristics of the cable-driven motion.The main contents are as follows:Firstly,based on the multi-joint serial manipulator,the kinematic coupling of the cable-driven joints is analyzed,and a kind of novel cable alignment scheme is proposed to realize the decoupling-motion of the multi joints.Based on this cable alignment,the modular joints are designed.After that,the configuration analysis of the cable-driven series manipulator is carried out.According to the task type of space transportation,to maximize the flexibility of the robotic arm,the parameter optimization of the link is carried out.Then,a motion decoupling verification experiment system is designed and constructed.In order to pre-tension the driving cable,a pre-tensioning device is designed to fine-adjust the pre-tensioning force.Then,the experiment is designed to analyze the minimum preload of the cable and the maximum load of the system.And the experimental results show that the proposed method can realize the motion decoupling between the joints.Finally,the friction model of the cable-driven transmission is studied in this paper.Firstly,the friction model of cable-pulley transmission system is developed,and the general friction model is obtained by experimental methods.Then,based on the ‘static friction + Coulomb' friction model,the friction force model between cable and contact surfaces is established and verified.In order to realize the controllable cable-driving,the amount of the dead zone is analyzed.Studies with the transmission characteristics have significance reference to the precise force coordinated control of the cable-driven system.