The Research Of Analysis And Synthesis For Planar Four-bar And Five-bar Adjustable Mechanisms

In the automatic production, a machine is required to perform comparatively simple tasks respectively and quickly in case there is intelligence received to select one or the other task. Compared with multi-purpose robot manipulators with multiple actuators, single purpose, single input purely mechanical devices are more reliable, more accurate, much easier to manufacture and maintain, and more economical. Mechanisms with adjustable links can be used as such devices to perform highly respectively simple sets of tasks. These characteristics make adjustable mechanisms have very vast potential applications. Displacement analysis, guidance synthesis, path synthesis, dynamic analysis of planar four-bar and five-bar mechanisms arestudied in this thesis.Symbolic solutions to displacement analysis for some types of planar two-DOF five-bar linkages is proposed based on Groebner base method and computer symbolic manipulating technique in this thesis. A set of nonlinear polynomial equations is transformed into a set of equivalent triangularization equations by using the following operations: ordering of variables, forming all pairs of polynomials, finding S-polynomial, reduction etc. The analytical solutions in the closed form are obtained. Corresponding software is developed which can be used to find the symbolic solutions to displacement analysis for some types of planar two-DOF five-bar linkages. The influence of geometric parameters and input parameters on the output positions of the mechanism is investigated.A method is presented for rigid body guidance synthesis of a four-bar adjustable mechanism for two alternate tasks. There are many situations in the design ofmechanical devices in which it is necessary to guide a rigid body through a series of specified, finitely separated positions. The synthesis equations are established by using rigid body displacement matrix, and all solutions are obtained. The relationship between the number of the tasks, unknown variables and equations are analyzed. The rigid body guidance synthesis for two different tasks is performed by changing the length of input and output links.A mechanism for performing path synthesis is designed to guide one point on a moving rigid body such that it passes through a specified sequence of points on a path. The relationship between the number of the tasks, unknown variables and equations are discussed. A method for performing path synthesis of four-bar adjustable mechanisms for two alternate tasks is proposed based on BP neural network. A network is trained and all solutions are obtained. The method presented in this thesis can avoid tedious symbol derivation and reduce greatly computing work as compared with analytical approach. The errors between desired points and actual points are very small, and the path synthesis mechanism has higher accuracy.The analytical kinematics and dynamics models of planar five-bar mechanism are established. The influence of corresponding parameters on the driving torques is investigated. Then the dynamic model system of planar five-bar adjustable mechanism is divided into three subsystems. The inverse dynamic model is investigated based on BP neural network system that is trained and the solutions to inverse dynamic model problem can be obtained. The method presented in this thesis can avoid tedious symbol derivation and reduce greatly computing work as compared with analytical model approach.