Inverse Substructuring Analysis And Experimental Study On Quantitative Measures For Dynamic Quality Of Mechanical Assembly

An electromechanical product consists of a number of parts and or components assembled into a whole via a certain connections or couplings to realize predetermined functions.The assembling process affects the dynamic transferring behaviors of the substructures and their connectors or coupling interfaces involved in the assembly.A running product is easily subjected to external dynamic excitation resulting in dynamic quality problems,such as vibration,noise and manipulation instability,etc.Dynamic quality of the assembly has directly influence on the dynamic quality of the whole product.Existing quality control of mechanical assembly focuses primarily on inspecting and evaluating the static quality measures,such as tolerance and size-coordination.While in the assembly dynamic quality,there is lack of effective method for the inspection and evaluation,due to insufficient related research work.In view of the advantageous properties of inverse substructuring dynamic analysis,which is a newly-developed method in mechanical structural dynamics and simply called inverse substructuring approach,this study disentangles completely and introduces systematically the critical theories at first.Then,investigations in depth on the essential problem to find quantitative measure(s)of the assembly dynamic quality are carried out,concentrating on the two keys,assembly-coupling dynamic stiffness and assembly dynamic quality matrix.And theoretical analysis and experimental studies are provided to explore the effectiveness of applying the inverse substructuring approach.Firstly,in order to verify the effectiveness of applying the inverse approach to identify the stiffness as a quantitative measure of the dynamic quality,five indirect inverse substructuring approaches,called ‘indirect scheme',are studied in detail.Specifically,(1)The lumped-parameter analytical models with two-level substructures are established for the assembly-unit systems with three-and four-point couplings respectively.Taking the first indirect scheme as a case study,the assembly-coupling dynamic stiffness of the systems are simulated and computed by both direct inverse substructuring analysis,called ‘direct scheme',and the indirect schemes.The simulated stiffness are also analyzed in comparison of the given ones.Thus the theoretical completeness of applying the five indirect schemes to identify the stiffness are validated for point-coupling assembly-unit systems,together with their applicable conditions.(2)The experimental models of typical mechanical assembly-unit systems with ‘two-point,line-and surface-' couplings are designed and constructed.The FRF-data involved in both direct and indirect schemes identify the stiffness are obtained by use of vibro-excitation tests before assembling at component level and after assembling at system level.(3)The five indirect schemes are applied to identify the stiffness of the point-coupling experimental model.The results are analyzed and compared to both the result identified by direct scheme and the measured stiffness.These works are carried out to verify the effectiveness of the indirect schemes in application of identify the point-coupling stiffness.(4)The first and second indirect schemes are applied to identify the line-and surface-coupling stiffness of the experimental models,respectively.They obtain consistent results and thus verify the effectiveness of the two schemes in application of identifying the line-and surface-coupling stiffness.In order to improve the system of quantitative measures for inspecting dynamic quality of mechanical assembly by inverse substructuring approach,this study uses eigenvalue analysis to explore the effect of assembling process on dynamic transfer characteristics of the coupling structures involved.As a result,the mean eigenvalue module of assembly dynamic quality matrix is proposed to be another quantitative measure on dynamic quality of mechanical assembly,for which the formula computing the mean module is provided.Both analytical and experimental model systems with two-point coupling assembly-unit are applied to explore the feasibility of applying this quantitative measure.The outcomes of both theoretical analysis and experimental studies of this thesis provide further the fundamentals for applying inverse substructuring approach to dynamic quality inspection of mechanical assembly.They have creative academic value to the improvement on the technical method of inspecting the dynamic quality,and are instructive to its engineering application.