Research On Fault Analysis And Test Sample Optimization Methods For Civil Aircraft Servo Actuator Systems

As an important system of civil aircraft flight control system, servo actuator system drives airplane steering surface to control the flight attitude mainly executing commands from pilot or controller, which is closely related to aircraft performance and flight safety. Research shows that fault rate of the fly-by-wire system is great high. Therefore, the analysis of in-depth fault mechanism and the research of improving test method of reliability and security are so important subject in the process of the fly-by-wire flight control system of civil aircraft development.In order to detect the potential fault, the fault injection test is usually carried out at the final assembly stage of aircraft. Actually, this test is a process of sampling inspection, which selects a part of the fault pattern of the system and optimizes distribution of the sample that is needed. We can get the conclusion of the test of high reliability by injecting a reasonable-structure and comprehensive set of fault samples. Based on servo system of civil aircraft as the research object, this paper focuses on three aspects-the fault analysis in the design of testability test method, the optimization method of fault sample selection and the evaluation method of fault sample set.First of all, the structure of the servo-actuator system of the civil aircraft is briefly introduced. Also take Boeing 777 as example. By qualitative analysis and quantitative analysis of the fuzzy fault tree, a systemic analysis of the relevant factors which caused the output instability of electro-hydraulic actuator is carried out.Then, to solve the question that test result is imprecise in sampling allocation based on failure rate, allocation plan of samples based on failure attribute and analytic hierarchy process(AHP) in testability demonstration test is presented. On the basis of comprehensive consideration of failure attribute elements such as failure rate, fault pervasion intensity and harm extent of failure, the failure attribute model and the calculation model of failure attribute value are established, and the sample selection is based on analytic hierarchy process(AHP). Sample randomness and the low representative level of the sample method based on mathematical/statistical models are avoided.In the end, to evaluate the testability verification experiment fault sample after sample selection, a quantitative evaluation method of the fault sample based on the three-level index system which contains sample size assessment, the structure of the sample evaluation and fault injection assessment is put forward. Select structural coverage function and functional coverage function for validation, then the quantitative evaluation of sample set is calculated.