Research On Mobility Of Complex Multi-loop Mechanism And Its Multi-mode Design

Facing increasing international competition,the development of high-end machinery and equipment with excellent performance and independent intellectual property rights is the fundamental guarantee for the realization of the transition from "Made in China" to "Created in China".The design level of the mechanism determines the performance of the equipment.The mechanism has the advantages of easy processing and installation,large carrying capacity,good transmission performance,low cost,and high reliability,which is the most commonly used and the most basic structural part of mechanical equipment,and it is also a key part of theory of mechanism research in domestic and foreign academic.As the functional requirements of mechanical equipment in the fields of high-end manufacturing,construction machinery,rehabilitation and medical,weaponry,aerospace become more and more diverse,and the applications are becoming more and more extensive,the mechanism design has changed from a simple mechanism to a more complex mechanism with multiple degrees of freedom,multiple loops,re-configurable,variable stiffness,rigid and flexible coupling.Therefore,the complex mechanism is a promising research direction,which has great practical guiding significance for the research and development of high-end mechanical equipment in our country.This dissertation takes the branch,full rotation,and singularity of the complex mechanism the mechanism as the starting point to discuss the mobility of the complex mechanism in detail,and then,the topology design of complex multi-mode mechanism is studied.The main content of this dissertation are as follows:1)Based on the tools of loop equation,polynomial discriminant,joint rotation space,the input-output relationship equation of planar/spherical mechanism is established,and the corresponding branch diagram is drawn.The branch of complex planar mechanism and spherical one-degree-of-freedom six-bar and two-degree-of-freedom seven-bar mechanism are recognized.A method of judging whether the motions of each loop in the mechanism are coupled by using the branch points in the branch graph is proposed,and the application characteristics of decoupling and coupling mechanisms are compared and analyzed.2)Based on the existence condition of crank in planar four-bar mechanism and the N-bar rotation theorem for judging the existence of crank in planar closed-loop single chain,and a method for analyzing the determination of crank in multi-loop mechanism by combining branch graph with N-bar rotation theorem is put forward,which is verified in planar Stephenson six-bar mechanism,and two sufficient conditions for the existence of crank in multi-loop linkage mechanisms are summarized.3)The geometric drawing method of equivalent subgraph is proposed to identify the singularity of complex multi-loop mechanism,and the concept of degradation equivalent subgraph and the basic atlas of mechanism are established.The singularity identification problem of planar seven-bar and eight-bar are solved by two splitting methods.Aiming at the disadvantage of complicated disassembly and subgraph recognition for complex multi-loop mechanism using degradation equivalent subgraph,a method of virtual equivalent subgraph with instantaneous center of mechanism speed as the basic element is proposed,and the singular positions of the famous butterfly eight-bar and the two-degree-of-freedom seven-bar with three topological structures are recognized.Facing the problem of uncertain instantaneous center recognition of linkage mechanism,the method of instantaneous center virtual loop is proposed to solve the problem of instantaneous center recognition of complex multi-loop mechanism,and the application range of instantaneous center virtual equivalent subgraph is further expanded.4)Based on the mathematical graph theory and the transmission angle of the mechanism,the intelligent identification method that used the difference of the instantaneous factor and loop factor in independent loops of the topological graph to determine the singular position of the mechanism are proposed,and the singular positions of the single-degree-of-freedom 12-bar mechanisms and the two-degree-of-freedom nine-bar,11-bar mechanisms are determined for the first time.5)According to the mechanism characteristics that the planar linkage mechanism will break through the shackles of its dead point position and form new motion modes,three types of replaceable multi-mode mechanism motion modules,namely,scale change type,torque increase type and multiple combination type,are proposed,and a variety of new topological configurations with multiple motion modes are obtained by combining the singularity recognition graph theory of linkage mechanism.Combining multi-mode module with the embryonic graph synthesis method of mechanism,the topological graph of multi-mode linkage mechanism is automatically synthesized,and the corresponding adjacency matrix is obtained.Combined with the branch identification diagram of linkage mechanism,the relationship between multi-mode linkage module and scale is discussed,and the scale optimization criterion of linkage mechanism is put forward.