Research On Key Techniques Of Pneumatic Ejection Test Rig

Impact test is generally used to examine the safety, reliability and validity of civilian or military devices in the condition that they are impacted by external forces or subjected to sustained forces. Conventional approaches adopted by an impact test in engineering includes mechanical, hydraulic and pneumatic modes. Due to the simple mechanical structure and fast and efficient response,the pneumatic impact device becomes a more promising test device than mechanical and hydraulic shock test apparatus. Based on the study of a pneumatic catapult test device, this paper presents a high-performance shock test equipment. The main contents are as follows:Firstly, the scheme of the test bench is proposed and many focuses are put on the mechanism motion scheme, the pneumatic circuit programs and electronic control system program. On that basis, the paper proposes a composite mechanical structure with functions of pre-stored energy, accompanied firing catapults and water-type damping brake. Besides,detailed mechanical designs are carried on the ejection device, the braking the top tight unit of the test bench.Secondly, the dynamic characteristics of the bench is studied. By analyzing the catapult process, motion equations of moving parts in the firing and the complete pressure emission process are established. The changing curves of speed and stroke of the moving parts as well as the pressure in the air chamber are obtained via simulation with the help of MATLAB program.At the same time,a corresponding relation table between the launching speed of the test piece and the initial pressure of the gas chamber is established. Then the process of firing along the tube and the cylinder is analyzed via dynamics simulation by finite element analysis software.Simulation results show that along with the tube action is reliable.Then, the braking process of moving parts are modeled and simulated. As the performance of the braking device is analyzed, the mathematical model that a brake cone inserts brake tank is established. Consequently, a changing curve involving the speed of moving parts, stroke and liquid pressure is obtained through MATLAB simulation analysis. Results verify the stability of the braking device.Finally, according to the functional requirements for measurement and control system, the hardware architecture and software architecture of the test system is confirmed and the whole measurement and control system is designed. Then, the hardware is determined based on the Siemens 300PLC, and major hardware is connected. At the same time, the software system of the test bench is analyzed and designed based on the hardware structure, including the design of lower computer software systems based on Siemens WinCC 300PLC and the configuration on the software PC interface.