Research On Energy Spectrum Optimization Of Vibration Excitations Produced By Repetitive Shock Machine

The technology of Reliability Enhancement Testing (RET) has received more and more attention in the field of reliability engineering recently, but the applications and popularizations of RET are subject to some new testing equipments. Repetitive Shock (RS) machine is one of the main vibration testing equipments for RET in these days. Comparing with Electrodynamic Shaker, RS machine can produce super-gaussian and broadband random vibration excitations, which is one of its main merits. However, the energy spectrum characteristic of vibration excitations has some demerits, which limits the applications of RS machine. Therefore, research on energy spectrum optimization of vibration excitations produced by RS machine has become an urgent problem in the field of reliability engineering.Aiming at the main demerit that middle and low frequency energy of vibration excitations produced by RS machine is lower, firstly, the influence factors of vibration excitations are analyzed and the optimization targets are presented according to the practical applications of RS machine. Secondly, the problem of energy spectrum optimization of vibration excitations is described and analyzed in detail based on linear system theory. Finally, the key factors of the problem are summarized, namely the mechanism of pneumatic vibrator producing original excitation signals, the dynamic optimization design for pneumatic vibrator, the response mechanism of platen vibration signals, the dynamic optimization design for platen. The main contents and conclusions of the dissertation are as follows:1. Aiming at the problem of pneumatic vibrator producing original excitation signals, the working principle of pneumatic vibrator is analyzed and the mechanical model is constructed. According to impact dynamics theory, impact signals produced by pneumatic vibrator are studied and their analytical formulas are deduced detailedly. Combining theoretical analysis and engineering experiment with numerical simulation, the generating method of original excitation signals produced by pneumatic vibrator is proposed. The mechanism of pneumatic vibrator producing original excitation signals is disclosed, which will lay the theoretical foundation for the dynamic optimization design for pneumatic vibrator.2. After analyzing the mechanism of pneumatic vibrator producing original excitation signals, middle and low frequency performance of two common kinds of pneumatic vibrators are evaluated. The relations between middle and low frequency energy of original excitation signals and impact signals produced by pneumatic vibrator are discussed. The variation regularities of middle and low frequency energy of original excitation signals with the parameters of pneumatic vibrator are disclosed by means of numerical calculation and analytical calculation, respectively. Hereby, the guidance principles of the dynamic optimization design for pneumatic vibrator are put forward.3. Aiming at the response problem of platen vibration signals and the shortcomings of the traditional method, the mechanical model of platen is constructed. Based on transfer function and superposition method, a new method to calculate the dynamic responses of platen is presented. The response mechanism of platen vibration signals is disclosed, which will provide the theoretical guidance for the dynamic optimization design for platen. Researches on simulation and experiment show that the new method has higher accuracy and efficiency than the traditional method.4. After analyzing the response mechanism of platen vibration signals, the dynamic model of RS machine is constructed according to linear system theory. The influence of natural frequencies and damping of platen on middle and low frequency transfer characteristic of the dynamic model is analyzed deeply. The dynamic optimization design method for sandwich platen is proposed and a new sandwich platen is designed. By means of finite element simulation, the dynamic optimization design problems for platen and external geometry constraint are discussed further. Hereby, the guidance principles of dynamic optimization design for platen and external geometry constraint are put forward.5. Relying on the self developed vibration equipment and the introduced vibration equipment, the presented guidance principles are testified by means of comparing with energy spectrum characteristic and super-gaussian characteristic of vibration excitations produced by the equipments consisting of different pneumatic vibrators and platens, respectively. Finally, the typical module-level electronic products are selected to carry out vibration enhancement comparison experiments. The experimental results show that the self developed vibration equipment whose pneumatic vibrator and platen have been optimally designed has superior efficiency.In summary, after disclosing the mechanism of pneumatic vibrator producing original excitation signals and the response mechanism of platen vibration signals, this dissertation investigates the energy spectrum optimization problems of vibration excitations produced by RS machine, which consist of the dynamic optimization design for pneumatic vibrator and platen. The methods and conclusions of this dissertation are very important for improving and developing RS machine.