Stiffness Technical Research Of Parallel Pose-adjusting And Flexure Force Sensor Stewart-based Platform

The stiffness of Stewart platform parallel mechanism is the research’s starting pointin this paper, and it will provide technical support for meeting the parallel mechanism’sperformance requirements in the large-heavy parallel adjusting mechanism and the fullflexure parallel six-axis force sensor in the engineering practical applications. By theorganic integration of the three-dimensional modeling software, virtual simulationtechnology and data processing software, the overall structural stiffness modeling andoptimal design parameters of the system are respectively carried out and refined,furthermore, the performance index of the research object is determined. This paperstudies emphatically the technical problems of parallel mechanism encountered inengineering applications, and provides important theoretical basis for developing andresearching the novel parallel mechanism. meanwhile, it will also be for promotion onthe parallel mechanism in engineering application has important practical significance.The main research in this paper is as follows：Firstly, by introducing the second-order influence coefficient matrix of serial/parallel mechanism, the geometric meaning of Jacobian matrix transpose differential andexternal load’s product and the sub-element’s physical meaning of external load impactterm are given. The different transposed form of three-dimensional array is defined, theforward and reverse conservative stiffness model of the serial/parallel mechanism underdifferent space is set up, and the uniform conservative stiffness model of Stewart parallelmechanism considering the effect of the external load is also derived. The classificationand symmetrical problem of the second-order influence coefficient matrix is discussedand the significance of the external force impact on the mechanical stiffness.Secondly, the complete stiffness model of antenna subreflector adjusting mechanism(SAM) is constructed using the influence coefficient method of parallel mechanism andthe principle of virtual work. The axial line stiffness model of single branched chain isconstructed considering the effect of hooke hinge and spherical hinge on branch rod axialstiffness. The complete stiffness matrix of SAM is solved by introducing the varying parameter on condition that the fixed platform is movable, which solves fully thestiffness matrix calculation problem of SAM in any spatial position and orientation.Determine the stiffness performance evaluation index of SAM, and research the influencerules of structural parameters on its performance index.Again, the spatial6×6compliance matrix of the basic flexure hinges are built, suchas flexure rod, circular-arc flexure hinge, right-circular flexure hinge, flexure prismaticpair, and so on. The analytical calculation formula of variable rectangular cross sectiontorsional compliance is discussed and researched, and the each sub-element’s designcalculation formula of flexure spherical hinge compliance maxtrix is derived.Finally, based on the deformation superposition principle of flexure serial branchand the deformation compatibility condition of its parallel combination, the wholestiffness matrix of flexure parallel six-axis force sensor is built, and the force mappingrelationship between the six-axis external force of sensor and the axial force of branchrod is established. The optimal design method of sensor size is proposed based on theoptimal index of minimum singular value, and the influence rules of the sensor’s basicsize parameters on its performance index are analyzed.