Research On Static Stiffness And Structure Optimization Of6-PTRT Parallel Robot

As a precision positioning device, high stiffness is a prerequisite of high precision,stable structure and high speed for6-PTRT parallel robot. Static stiffness is a measure ofthe movable platform in the base coordinate system brought about by tiny elasticdeformation of all the parts between the base and the movable platform. In order toimprove the positioning performance of the mechanism, in this paper, a stiffness modelbased on kinematic theory was established, and the static stiffness of6-PTRT parallelrobot was studied with the softwares of ANSYS, MATLAB, which provides atheoretical guidance for structural design, precise control and performance evaluation ofthe positioning device.Firstly, the kinematics model of6-PTRT parallel robot was established, and thefirst-order movement influence coefficient was got through the kinematic analysis.What’s more, the workspace was drew with the three dimensional searching method inMATLAB. The static stiffness model based on the first-order movement influencecoefficient was established according to the method of partial differential, which notonly did not ignore the truth that the branches would have different stiffness undertension or compression, but also considered the stiffness of active and passive joints,and the impact of external forces. The static stiffness matrix of moving platform and itsstiffness distribution rules in certain position were given by numerical calculation. Thekey links that affect stiffness was obtained by comparing the stiffness value of variousfactors. Rayleigh quotient, a scalar was cited to evaluate the static stiffness.Secondly, start simulation analysis in ANSYS, simplified the Hooke hinge intoflexible joints or coupling ball joints, and established three different finite elementmodels. The static analysis in FE models gave static stiffness and the weak parts. Theexperimental test results on the robot verified the correction of the FEA results andtheoretical stiffness model. What’s more several factors that cause the difference wasgave.Finally, the relationship curves between static stiffnesses and structural parameterswere got through the parameters analysis with theoretical stiffness model, and whichgave a direction to improving static stiffness. And then, an optimization model undermixed load was established, and by the optimization of the structural parameter, thestiffness along the load was strengthened and the drift of the end actuator was reduced,which provides a basis for the further design.