Mechanism Research Of Pin-Bar Systems

With continuous innovation and development of structural form, the traditional structural theory is always unable to meet the need of engineering application. The appearance of new structural forms, such as space deployable structures, pantadome systems and cabledome structures and so on, set demands on the development of mechanism theory. Due to the feature of these structures that there are always mechanism motion in their forming process with their initial forms of mechanism, the traditional structural theory has limitations when applied in the analysis and simulation on these problems and mechanism theory is needed for accurate analysis and simulation. Based on the current mechanism theory, this thesis takes a study on the issues of mechanism motion path and its bifurcation of pin-bar systems, which enriches the theory of mechanism motion and related analysis method.Considering the fact that there are only tiny elastic deformation in the process of pin-bar mechanism motion from geometric unstable state to the geometric stable state, the thesis first studies the method for simulating the kinematic path of rigid pin-bar systems without considering elastic deformation. Based on the equilibrium matrix theory, the mechanism displacement is divided into two parts, one of which is the combined mechanism displacement model and the other is the displacement of member length modification. The proper combination coefficient of the mechanism displacement model is determined by the gradient of potential energy of external forces. With the help of the work above, the kinematic path for rigid pin-bar systems under external forces can be simulated.The thesis takes further research on the kinematic path analysis which elastic deformation is considered. The generalized inverse of equilibrium matrix is used to solve the elastic deformation in the process of mechanism motion, and then the mechanism deformation coupled with the elastic deformation is analyzed to simulate the kinematic path and members' internal force. Based on the study above, some programs are compiled and used to simulate the lift-up process of pandadome and tensile construction process of cabledome and some other problems. The results show that the proposed method is effective.Bifurcation of kinematic path is also investigated. Considering the relationship between bifurcation and singularity theory, the singularity theory and compatible equation are used to analyze the bifurcation of kinematic path of both 1-DOF and 2-DOF mechanisms. A method for judging the bifurcation point is proposed by tracing the rank of Jacobian matrix. These work makes the problem of bifurcation of kinematic path effectively analyzed.