Innovation Design And Analysis Of Metamorphic Mechanisms Based On Linear Dependence Of Screws

In today’s world,the environment is changing and the demands are rising.Reconfigurable mechanism represented by metamorphic mechanism has set off a new wave of technological innovation in global engineering.This dissertation focuses on the key problems of evolution mechanism,mechanism bifurcation and innovative comprehensive design faced by metamorphic mechanism and reconfigurable mechanism in the application of complex working conditions.Starting with the geometrical connotation of screw,an innovative design notion based on linear dependence of screws is firstly proposed,and then a series of novel metamorphic joints and its resultant metamorphic / reconfigurable mechanisms are designed.The main contents of this dissertation are summarized as follows:(1)Based on linear dependence of screws and the concept of metamorphosis,the variations of two screws among collinear,parallel,intersection or spatial noncoplanar evolve three new metamorphic joints,namely,a variable-length parallel joint,a variable-axis offset joint and a metamorphic spherical joint.Through the phase change of the above joints,the geometrical relations of collinear,parallel,intersection or spatial noncoplanar can be transformed respectively.(2)The view of linear dependence of screws is extended to Grassmann line geometry.Inspired by the evolution process of linear dependence of three line vectors,two variable-length ways forSarrus mechanism are obtained,that is,the reconfigurable joint and the anti-parallelogram unit,which induced two Sarrus-like metamorphic mechanisms.Further,when the anti-parallelogram unit is equivalent to a binary connecting link,two metamorphic mechanisms are proposed.Based on the assembly forms of the two limbs,Sarrus-extended mechanisms with plane symmetry and line symmetry are obtained.The analysis shows that the above metamorphic mechanisms maintain the original Sarrus mechanism branch and evolve more motion branches.(3)To explore the variation of four spatial line vectors and its evolved metamorphic mechanism,the origami unit equivalent to spherical 4R mechanism is selected as the carrier.Based on the proposed degenerate construction method of a spherical 4R mechanism,an integrated 8R mechanism is constructed.Then,combining the variation of four line vectors from spatial concurrent to spatial parallel or coplanar intersection,an 8R kinematotropic metamorphic mechanism is proposed.The configurations of the proposed mechanism under different constraints are analyzed based on screw theory.The results show that the 8R mechanism endows the kaleidocycle and deployable properties.Then,the mechanism evolution is explored.The evolved 6R and 4R linkages in terms of geometrical constraints show the 8R mechanism belongs to the intersection of kinematotropic mechanism and metamorphic mechanism.(4)As a follow-on to the proposed reconfigurable spherical(rS)joint,two novel single-loop metamorphic mechanisms are invented for the first time by inserting the rS joint,namely Schatz-derived mechanism and R(rS)R-R(rS)R mechanism.The motion characteristics are analyzed according to screw theory.The results give two reconfigutable manners: the phase change of the rS joints and the singular configuration of the mechanism.The Schatz-derived mechanism entails reconfiguration via the two manners.Remarkably,it realizes the switch between two assembly configurations without resorting to disassembly and reassembly,and maintains the characteristics of the original Schatz mechanism while the rS joint situates in phase R.The R(rS)R-R(rS)R metamorphic mechanism reconfigures the configuration based on phase change of the two rS joints.It changes the mobility and bridges gap between a spatial single-loop mechanism and a structure.(5)Meanwhile,resorting to the proposed rS joint to each limb,a novel 3-(rS)PS metamorphic parallel mechanism is presented.Based on screw theory and Grassmann line geometry,the mobility of moving platform is revealed with respect to the phase change of rS joints.Furthermore,the constraints provided by different assembly configutations of three limbs are analyzed in terms of Grassmann line geometry.The results show that the parallel mechanism has the metamorphic characteristics,the mobility varies from 6 to 3,and the motion types include 3R3 T,3R2T,3R1 T and2R1T.Under different assembly configurations of three limbs,it can generate more configurations.The mobility varies from 6 to 3,and the motion types include 3R3 T,3R2T,3R1 T,2R2T and 2R1 T.