Coupling dynamic stiffness identification of mechanical assembly with linear and planar connection by the indirect scheme of inverse substructuring analysis

Mechanical assembly is an important process in manufacturing electromechanical products and it directly affects the dynamic quality of a whole product. The traditional inspection and analysis of mechanical assembly quality mainly focuses on the “static quality”, such as the shape accuracy and dimensional coordination, while ignoring its “dynamic quality”, which is incomplete estimation on the assembly quality. Meanwhile, the assembly coupling dynamic stiffness is a key determinant of the dynamic quality of mechanical assembly. To overcome test operation difficulties in practical application which is caused by the direct scheme of inverse substructuring of the mechanical assembly coupling dynamic stiffness, it needs to discrete the non-ideal mechanical assembly connection interface including linear and planar connection interface so as to apply two kinds of indirect method of inverse substructuring analysis based on frequency response function (FRF) spectrum to recognize its coupling dynamic stiffness. The experimental models of mechanical assembly for the more practical linear and planar connections are designed, and the practicability of applying these two methods to recognize the dynamic stiffness after assembly coupled is verified

A Hazard Analysis Based Approach to Improve the Landing Safety of a Blended-wing-body Remotely Piloted Vehicle

AbstractThe BUAA-BWB remotely piloted vehicle (RPV) designed by our research team encountered an unexpected landing safety problem in flight experiments. It has obviously affected further research project for Blended-wing-body (BWB) aircraft configuration characteristics. Searching for a safety improvement is an urgent requirement in the development work of the RPV. Combining with vehicle characteristics, a new systemic method called System-Theoretic Process Analysis (STPA) has been imported to apply on the RPV flight experiment hazard analysis. An uncontrolled system behavior “path sagging phenomenon” is identified by implementing a 3 degree of freedom simulation based on wind tunnel experiment data and establishing landing safety system dynamics archetype, then a derived safety improvement requirement emerges. To obtain higher safety design effectiveness and considering safety design precedence, a new longitudinal control surface “belly-flap” is used to eliminate hazards in landing. Finally, Flight experiments show that the hazardous factor has been correctly identified and the landing safety has been efficiently improved

Investigation on dynamic characteristics of mechanical assembly

Mechanical assembly is important process affecting product dynamic quality. To completely inspect assembly quality, dynamic characteristic analysis is necessary. Based on substructuring dynamic analysis, this paper theoretically analyzes the changes of dynamic characteristics due to assembling process. Assembly coupling dynamic stiffness computed by inverse substructuring analysis is considered as a critical measure on the changes. The results obtained have been well validated by a lumped-parameter model for two-level of substructures

Eigenvalue analysis and estimation on dynamic quality of mechanical assembly

As an important manufacturing process, mechanical assembly affects directly product quality. Conventional quality inspections and estimations of mechanical assembly are primarily concentrated in “static quality”, such as size coordination, shaping and positioning tolerances, etc. However, mechanical assembly actually has its own dynamic quality, which contributes to that of whole product. Inspecting only static quality is thus incomplete for quality estimation of the assembly. On the basis of substructuring method, this paper at first applies eigenvalue analysis to investigate the effects of assembling process on the dynamic transfer-functions, expressed by spectral-based frequency response functions (FRFs), of substructural components involved in the process. Eigenvalue modules of FRF-matrix-ratios of FRF before assembling to that after assembling are analyzed to quantify the effects, which are consequently indicated by the mean module. Then, according to the explicit definition of “dynamic quality of mechanical assembly” introduced in this paper, dynamic quality matrix of mechanical assembly and its mean eigenvalue module are worked out and chosen to be the right quantitative measure and indicator for dynamic quality estimation of assembly system. Meanwhile, a lumped-parameter model and its experimental counterpart are employed to validate effectiveness of the analytical outcomes obtained and the quality estimation method established in the study

Comparison of hysteresis of high accuracy positioning system with piezoelectric actuators

In the paper, high accuracy positioning systems with flexible elements are investigated. In the analyzed systems, piezoelectric actuators are used for the transmission of motion and the hystereric phenomenon in them is investigated. Effect of the hysteretic phenomena to the precision of the high accuracy positioning systems is of special importance. For the investigations, a special experimental setup was designed and produced as well as the method of the experimental procedure was proposed. The experimental setup includes a computer, a piezocontroller, an inductive displacement sensor and a dynamic data collector. The dynamic data collector is used for the collection of data and for the transfer of data to the software for further processing. Numerical modelling of the hysteretic was performed by using the Matlab/Simulink software. In the process of investigations, it was determined that the maximum dispersion error of the hysteretic model is less than 5 % when compared with the experimental results. Thus, it is concluded that the proposed method of hysteretic phenomenon modelling is suitable for modelling of high accuracy positioning systems with flexible elements, which are controlled by piezoelectric actuators

An Improved Lumped Parameter Model for a Piezoelectric Energy Harvester in Transverse Vibration

An improved lumped parameter model (ILPM) is proposed which predicts the output characteristics of a piezoelectric vibration energy harvester (PVEH). A correction factor is derived for improving the precisions of lumped parameter models for transverse vibration, by considering the dynamic mode shape and the strain distribution of the PVEH. For a tip mass, variations of the correction factor with PVEH length are presented with curve fitting from numerical solutions. The improved governing motion equations and exact analytical solution of the PVEH excited by persistent base motions are developed. Steady-state electrical and mechanical response expressions are derived for arbitrary frequency excitations. Effects of the structural parameters on the electromechanical outputs of the PVEH and important characteristics of the PVEH, such as short-circuit and open-circuit behaviors, are analyzed numerically in detail. Accuracy of the output performances of the ILPM is identified from the available lumped parameter models and the coupled distributed parameter model. Good agreement is found between the analytical results of the ILPM and the coupled distributed parameter model. The results demonstrate the feasibility of the ILPM as a simple and effective means for enhancing the predictions of the PVEH

Determining coupling dynamic stiffness of structural connection by tested FRFs

Identifying coupling dynamic stiffness of structural connection is often needed in substructural dynamic analysis. To overcome the faultiness of conventional approaches existed, five indirect schemes of inverse substructuring analysis by using tested frequency response functions (FRFs) are provided. And the first indirect scheme is verified by three mass-rubber models constructed as two-level substructures with mono-coupling, bi-coupling and tri-coupling connection. Compared to existing direct scheme of inverse substructuring analysis, it shows better performance with acceptable precision of determining the stiffness

Effect of Scrophularia ningpoensis extract on diabetes in rats

Purpose: To investigate the effect of Scrophularia ningpoensis extract (SNE) on streptozotocin-induced diabetic rats.Methods: SNE was obtained by steeping the dried Scrophularia ningpoensis in water at 60 oC three times, each for 1 h, before first drying in an oven at 100 oC and then freeze-drying the last extract thus obtained. Diabetic rats were prepared by a single intraperitoneal injection of a freshly prepared solution of streptozotocin (50 mg/kg). The rats were randomly divided into 6 groups of ten rats each: negative control group, control group, reference group (glibenclamide1 mg/kgbody weight) as well as SNE groups, (50, 100 and 200 mg/kg). Blood glucose and plasma insulin levels were evaluated in order to determine antihyperglycemic effect. Oxidative stress was evaluated in liver and kidney by antioxidant markers, viz, lipid peroxidation (LPO), superoxide dismutase (SOD), reduced glutathione (GSH), glutathione peroxidase (GPx) and catalase (CAT); blood serum levels of creatinine and urea were determined in both diabetic control and treated rats.Results: Compared with diabetic rats, oral administration of SNE at a concentration of 200 mg/kg daily for 30 days showed a significant decrease in fasting blood glucose to 120.21 ± 3.37 mg/dL (p < 0.05) and increased insulin level to 13.31 ± 0.67 uU/mL (p < 0.05). Furthermore, it significantly reduced biochemical parameters (serum creatinine, 0.86 ± 0.24 mg/dL, p < 0.05) and serum urea (41.86 ± 1.59 mg/dL, p < 0.05).Conclusion: The results suggest that SNE may effectively normalize impaired antioxidant status in streptozotocin-induced diabetes in a dose-dependent manner. SNE has a protective effect against lipid peroxidation by scavenging free radicals and is thus capable of reducing the risk of diabetic complications.Keywords: Scrophularia ningpoensis, Diabetic, Antihyperglycemic, Antioxidant Oxidative stress, Fasting blood glucos