Research On Trajectory Synthesis Method Of Spatial Four-bar Linkage Based On Numerical Atlas Method

With the changing needs of the times,the design of construction machinery is becoming more and more demanding and the design and efficiency of mechanical products is becoming a key focus of engineering research.The linkage mechanism has a very important role in engineering applications.The four-bar mechanism is one of the most widely used types of linkage mechanism,and the scale synthesis of non-whole cycles is more common in practical engineering.In this paper,we investigate the trajectory synthesis of spatial four-bar mechanisms(RCCC mechanism and RSCR mechanism)based on the numerical mapping method.Firstly,this paper establishes the mathematical model of trajectory under the standard installation position through the inherent characteristics of spatial RCCC and RSCR mechanisms.The trajectory mathematical models of the spatial RCCC and RSCR mechanisms are pre-processed and analyzed by projecting the trajectory curves onto the plane O-yz after rotating the corresponding input member corners around the x-axis.The projection allows the characteristics of the trajectory to be discovered,generalized and its trajectory characteristic parameters to be extracted.Secondly,combined with the findings of the pre-processing,the method of trajectory synthesis for general mounting positions is proposed.In order to eliminate the influence of the mounting angle of the mechanism,a database of mounting angles of the mechanism is established and the mounting angle parameters of the mechanism are derived by sampling the target trajectory and rotating the angle in the database and then comparing it with the error of the characteristic sampling points.On this basis,the mechanism without mounting angle parameters is analyzed and the relationship between the sampling points of the mechanism and the rotation and centrifugal angles of the mechanism is deduced.The wavelet transform is used to extract the wavelet characteristic parameters of the mechanism and to build a dynamic adaptive mapping library of the linkage trajectory curves of the spatial RCCC mechanism.By comparing the curve parameters of the target mechanism with the parameter pixels in the library,the optimal target mechanism is found.Theoretical formulas for the actual rod length dimensions and mounting positions of the mechanism are given,and the trajectory synthesis of the spatial RCCC mechanism is realized.Finally,the trajectory synthesis of the spatial RSCR mechanism is investigated accordingly on the idea of realising the trajectory synthesis of the spatial linkage mechanism based on the RCCC mechanism.Combined with the discovery of feature parameters by preprocessing,a database of mechanism mounting angles is established to determine the spatial mounting angle parameters of the target mechanism.The target trajectories of the mechanism at general mounting positions are normalised and the parameters of the normalised mechanism linkage trajectories are analysed in combination with wavelet theory parameter methods.Using the numerical mapping method,a dynamic adaptive mapping database for the spatial RSCR mechanism is established,and by extracting the basic dimensional groups of the target trajectory,a method for calculating the actual dimensions and mounting positions of the target mechanism is deduced.The trajectory synthesis problem of the noninteger-period spatial RSCR mechanism is thus completed.The correctness and validity of the method are verified by combining the calculation examples.