Research On Key Technology Of Full Circumference Roundness Inspection Of Aero-Engine Case

The casing is an important part of an aero engine,its roundness design and installation accuracy directly affect the performance of the engine.The traditional visual-based deformation detection method of the casing can only detect the partial blade tip clearance or the roundness of the casing end face due to the light occlusion,but cannot achieve the full-circumferential roundness detection of the inner wall of the casing.The traditional limit method is an indirect measurement of the deformation of the receiver,the measurement accuracy is limited,and at the same time,it is also impossible to detect the roundness of the receiver in the full circumferential direction.To this end,this paper proposes a method for global and full-circumferential roundness detection of the inner wall of the casing based on the capacitance gap measurement principle,focusing on gap measurement model construction,measurement influencing factor analysis and compensation,measurement system miniaturization and other key technologies to carry out research.The main work as follows:1.To solve the problem that the traditional measurement method cannot realize the roundness detection of the receiver,a method based on the capacitance gap measurement principle for the global and full circumferential roundness detection of the inner wall of the receiver is proposed.The sheet-type capacitance sensor is installed at the tip of the blade.The inner wall of the casing is the electrode plate to be measured.Based on the variable pole pitch capacitance gap measurement principle,the tip gap value of the global blade is measured.The space coordinates of each measurement point are determined by the gap value and the inner and outer containment circle centers are calculated to realize the aero-engine engine.Finally achieve the accurate detection of the global and circumferential roundness of the inner wall of the engine casing.2.Aiming at the problem that the curvature of the inner wall of the casing to be tested affects the accuracy of the tip gap measurement,based on the mathematical relationship between the capacitance of the parallel plate capacitor and the pole distance,an improved gap measurement model with the curved electrode plate as the electrode plate to be tested is established,and the core is analyzed.The law of the influence of pole radius and pole plate curvature on the gap measurement error,a gap measurement compensation model for curved pole plates is proposed.After simulation verification,the use of the compensation model can reduce the relative error of the gap measurement of non-planar pole plates by more than that.3.In view of the small installation space of the sensor,unstable signal transmission and easy packet loss,etc.,the measurement sensor module has been miniaturized and signal transmission anti-interference design.The use of digital capacitance measurement method effectively reduces the volume of the sensor;the sensor housing is made by combining metal and plastic materials,and the Modbus protocol and Zig Bee wireless networking are combined during the data transmission process to reduce the impact of external electromagnetic fields on the measurement circuit.Avoid signal interference and packet loss caused by metal structures and improve data transmission quality.4.The prototype of the measurement system was built,the measurement sensor module calibration experiment was carried out,the factors affecting the measurement accuracy were analyzed,and the uncertainty calculation of the roundness error evaluation was carried out.Experimental results show that the absolute error of the gap sensor does not exceed 10 μm in the measurement range of the tip gap of 600-2000 μm,and the accuracy is better than 0.5%.It can be used for the global and full circumferential roundness detection of the inner wall of the casing.