Research On The Evolution Of Four-bar Mechanisms That Are Based On Screw Theory

The inventions and creativities of mechanism are satisfied to some kinds of human demands,so,the destination of mechanism research is according to changeable demands to design a new kind of mechanism to be satisfied with the demands.One of the most important way to sum up new methods for designing mechanism to sort out development tracks of mechanical evolutions.At present,The frequently-used ways of mechanical evolutions are still based on words、pictures to be described.However,many physical quantities such as force,speed that are digitalized by Screw Theory promote development of many fields about mechanics,such as the dynamics of mechanism,kinematics of mechanism.Even to the extent that numerical expression can promote some fields to be leap-forward development.The analysis method for degree of freedom to all mechanism which is base on Screw Theory is a good example to certify the importance of numerical expression.So,the breakthough points for the research of numerical expressions that are based on Screw Theory are the process of evolution about the most primary and fundamental planar crank-rocker mechanism to be the crank-slider mechanism and the process of evolution about the most primary and fundamental planar crank-rocker mechanism to be Bennett linkage.The study finds that all the motion pairs are evolved from the revolute pair and the innovative methods of mechanical design including the change of mechanical pairs,the change of relative position about components are described in numerical expression by Screw Theory.it not only promotes the recognition of mechanism evolutions to be precise,but also it provides a new way for the research of mechanism evolutions and innovation methods and make a good preparation to digitization of mechanical design,Meanwhile,it also can be convenient for the computer to analyse and show a process of the mechanism evolutions.Finally,the study gets an important conclusion by analyzing the DOF of four-bar mechanism with four prismatic pairs,crank-rocker mechanism,double crank mechanism from Screw Theory.If the rank of matrice that are consist of the same mechanism Plücker coordinate are regarded as an independent variable,the postures of mechanism are regarded as the dependent variable.When the independent variable is change,the dependent variable that corresponds to the posture of mechanism is the singularity position.