Design Of Global Constant Balance Parallel Mechanism And Its Balance Performance Analysis

In recent years,the research on gravity balance of robot has always been one of the priority fields of research in robotic mechanism.When the parallel mechanism is working,the driving joint will produce the corresponding driving force to overcome the gravity of the moving platform and the load.And when the mechanism bears heavy load,the driving force to drive the load to achieve the desired trajectory will be great,which not only affects the working life of the mechanism,but also reduces its working efficiency and motion accuracy.The above problems can be effectively solved by gravity balance,besides,the parallel mechanism will have higher bearing capacity and better dynamic performance.Based on the research of translational parallel mechanism with constant Jacobian matrix,a type of global constant balance parallel mechanism which is consisted by inter-outer layer parallel mechanism is proposed,and the balance performance of the mechanism is simulated and verified.The main research is as follows:Firstly,based on the 6-UPS,4-UPS-UPU,4-UPU and 3-PUU space parallel mechanism,and the 3-PRRR parallel mechanism is used as the balancing mechanism,the global constant balance parallel mechanism with internal and external double layer structure are designed.According to the formula of G-K,the degree of freedom of the global constant balance parallel mechanisms is verified.Then,the related performance of the 3-PRRR balancing mechanism is analyzed.Secondly,based on the influence coefficient method,the first and second order influence coefficient matrix is established,then the velocity and acceleration mapping between the moving platform,the links and the active joints are solved.Furthermore,the dynamic models of inner and outer mechanisms are established under inertial system,and then the overall dynamic model of the global constant balance parallel mechanism is established based on the relationship between action and reaction.Thirdly,the ?(balance coefficient),F(average driving force),balance force and additional force of the mechanism is defined.Based on the dynamics model of the global constant balance parallel mechanism,the balance performance of 6UPS/(3PRRR)+S and3PUU/3PRRR parallel mechanisms are analyzed,respectively.The balancing performance of this mechanism is analyzed by using the value of F under the condition of the same balance coefficient,and the advantages of global constant balance parallel mechanism have been proved by compared with existing balance mechanism and counterweight law.Finally,the mechanical characteristics of parallel mechanism with constant Jacobian matrix are analyzed.The criterion that the translational parallel mechanisms can achieve constant Jacobian matrix is given.Then,when the Jacobian matrix is solved by the influence coefficient method,the difference between parallel mechanism with constant Jacobian matrix and general mechanism is analyzed.A simple method for solving the forward position solution by Jacobian matrix is proposed.Furthermore,based on the3-PPRR parallel mechanism,the effect of constant Jacobian matrix on dynamics,motion/force transmissibility and dexterity are analyzed.