آناليز قابليت اطمينان سيستم سروو الكتروهيدروليك بر اساس عدم قطعيت هاي ناشي از ساخت موجود در پارامترهاي شير سروو

چكيده انگليسي :

Reliability Analysis of an Electro Hydraulic Servo System Based on the Manufacturing Originated Uncertainties Existing in the Servovalve Parameters Mohsen Samadani m samadani@me iut ac ir 25th of September 2011 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Dr Saeed Behbahani behbahani@cc iut ac irAbstractThe most important part of every electro hydraulic servo system is its servo valve A servo valve consists of veryprecise and sensitive components A small change in the dimensions metallurgical characteristics and otherparameters of these components can produce instability and error in the performance of the system In the designphase the values of these parameters is considered as a crisp and certain numbers Nevertheless due tomanufacturing limitations the final value of these parameters always contains some tolerance and uncertainty These uncertainties in the system parameters creates a variance in the performance of the system from the idealcircumstances In practice it is possible that among the tens of thousands of produced valves some cannot satisfythe standard specifications and pass the quality control Therefore initial evaluation of the effect of fabricationmethods of the valve s components on the statistic performance of the system can help the manufacturer to improvethe reliability of its productions and decrease its expenses Reliability can be used with the other factors like costand accessibility as a useful criterion for comparing various methods and techniques of manufacturing In thisresearch a novel analytical method has been introduced in order to analyze the reliability of electro hydraulicsystems based on the manufacturing originated uncertainties existing in it In this method the number of failures ispredicted using Monte Carlo simulation technique For this aim the dynamic model of the system was developed inthe first stage Afterwards the uncertain parameters of the system were determined and based on the techniques anddegree of precision used for the production of each valve s component the achievable tolerances were estimated foreach parameter By using a random number generator each time a set of samples was selected from thesenumerical ranges and substituted for the parameters of the dynamic model of the system Simulations were thenperformed for each set of random values for thousands of times until a meaningful number of failures wereobserved in the performance of the system In the next stages by changing the manufacturing techniques andimproving the achievable tolerance of each parameter in each stage the simulations were performed again and thevarious cases were compared with each other Simulations showed that the most important parameters in thefrequency response of the system are length of air gaps in the torque motor and the diameter of flapper nozzles Bychanging the manufacturing process of the valve components which affect the value of these two parameters andimproving their normal distributions the number of system failures was decreased significantly On the other hand by changing the manufacturing processes of some parts like spool and sleeve and improving their dimensionalprecision no significant improvement was observed in the dynamic performance of the system The simulationsalso revealed that the length of spool lands and the width of sleeve slots play the main role in the internal leakage ofthe servo valve and by changing the machining technique and improving the dimensional tolerances of these twoitems the number of systems failures drop significantly It was also found that the clearance between spool andsleeve is not the dominant factor in the leakage of the valve Keywords Reliability Analysis Manufacturing Uncertainty Monte Carlo Simulation Method Electro Hydraulic Servo System Servovalve

صمداني، محسن

آناليز قابليت اطمينان سيستم سروو الكتروهيدروليك بر اساس عدم قطعيت هاي ناشي از ساخت موجود در پارامترهاي شير سروو

سيستم سرووالكتروهيدروليك , روش مونت كارلو