In the aero engine, as one of the most important supporting components, casing has to suffer various loads such as gravity, axial force of gas, inertial force and inertial moment etc transmitted from the turbine rotor and other structural parts, which may lead to the radial geometrical deformation of the casing, especially at the region of the fixture fringe. Also, oversized deformation of the fixture fringe might produce huge hidden dangers to the flight. Therefore, aiming at the measuring assignment of the radial geometrical deformation of the fixture fringe, a non-contact measuring system is set up in the paper, as well as the mathematical model presented in detail. Composed of auxiliary fixing devices, force loading devices and laser displacement sensors etc, the measuring system could be utilized to detect the deformation at every mount on the outer wall of the inspected casing, and then calculate the deformation parameters of the fixture fringe by the mathematical model. As the experiment results shown, through collecting the outputs of the sensors and substituting them into the mathematical model established, the contour features and eccentricity displacement of the fixture fringe after deformation could be derived, which is of certain practicality in the improvement of the whole performance of the aero engine.
As the development of the measuring technology, laser displacement sensors become the most commonly used ones in the field of dimensional metrology as a result of their versatility and mature technology. However, as the differences of environment conditions and the variation of measured surfaces, the measuring errors of the laser displacement sensor may be large when used in actual application, in which the nominal accuracy of the laser sensor cannot be reached. Therefore, a precsion optimization method for the laser displacement sensor is proposed in the paper based on analysis of the principle of optical trigonometry, which can be used to reduces the measuring errors. The method is a kind of spatial filtering algorithm based on the self-adjusting domain. On the basis of the idea of spatial filtering, the method could determine the measuring errors and the optimization region according to the different measured surfaces automatically. As the experiment results show, the optimization method could be used to describe the measured object precisely and decrease the measuring error to up to 50%, which may deal with the low accuracy of the optical scanning and measuring task. With the accuracy optimization method proposed in the paper, the sensor can reach the measuring accuracy of micrometer level. Therefore, the measurement of high efficiency and high precision can be achieved.
In the field of aeronautics, the geometry and dimensional accuracy of the blade edges has a large influence on the aerodynamic performance of aero engine. Therefore, a non-contact optical scanning system is established to realize the measurement of leading and trailing edges of blades in a rapid, precise and efficient manner in the paper. Based on the mechanical framework of a traditional CMM, the system is equipped with a specified sensing device as the scanning probe, which is made up by two new-style laser scanning sensors installed at a certain angle to each other by a holder. In the measuring procedure, the geometric dimensions of the measured blade edges on every contour plane are determined by the contour information on five transversals at the leading or trailing edges, which can be used to determine the machining allowance of the blades. In order to verify the effectiveness and practicality of the system set up, a precision forging blade after grinded is adopted as the measured object and its leading and trailing edges are measured by the system respectively. In the experiment, the thickness of blade edges on three contour planes is measured by the optical scanning system several times. As the experiment results show, the repeatability accuracy of the system can meet its design requirements and the inspecting demands of the blade edges. As a result, the optical scanning system could serve as a component of the intelligent manufacturing system of blades to improve the machining quality of the blade edges.
In the field of aeronautics, the tip clearance of rotor exerts a crucial influence on the performance of the aero engine. As defined as the radial distance between the top of the blade and the inner wall of the casing, the tip clearance of too large or small size will adversely affect the normal running of the engine. In order to realize accurate measurement of the tip clearance in a simple way, a non-contact measuring method by the chromatic confocal displacement sensor is proposed in the paper. The sensor possesses the advantages such as small volume, good signal-to-noise ratio, high accuracy and response frequency etc., which make it be widely used in engineering and industry. For testing the performance and potential application of the sensor, a simulation testing platform is established. In the platform, a simulation blisk is installed on the air bearing spindle and a chromatic confocal displacement sensor is fixed on the platform to measure the displacement variation of the blade tip, which can be used to characterize the variation of the tip clearance. In the simulation experiments, both of single and continuous measurement of the tip clearance of the 36 blades on the blisk is executed. As the results of experiments show, the chromatic confocal displacement sensor can meet the requirements of measuring task, in which both of high measuring efficiency and accuracy could be achieved. Therefore, the measuring method proposed in the paper can be utilized in the actual assembling sites of the aero engine.
In order to improve the quality and efficiency of forging process, it needs to execute on-line dimensional measurement of the forgings. In the paper, a laboratory color vision measuring system is set up and the combination of digital and physical filtering is adopted to improve the image quality based on the radiation characteristics of high-temperature forgings. The digital filtering technology is a kind of image processing methods, in which the R component of the forging image is removed. While, the physical filtering technology is achieved by optical filters installed in front of the CCD, in which strong self-emitted radiation from the hot parts can be filtered out. In order to evaluate the image quality, the image contrast is applied, which is generally defined as the difference value between average gray scale of object region and that of background region. In the experiments, image contrast derived with filters at different sample points set from 800°C to 1200°C is compared to determine the optimal scheme of filters to be selected. Results of experiments indicate that the application effect of filters is dissimilar when the forging is in different temperature ranges. Through comparison, the optimal selection scheme of filters is determined to derive high quality image of forgings at different temperatures, which lays a solid foundation for the subsequent image processing.
For solving the difficult problem that there is no effective way to measure abnormal holes located at blade erection loop of aero-engine case, an image measurement system based on high precision air-bearing turntable is established in this paper. The issue that monocular vision can’t measure curved surface has overcome by using high precision turntable to make sure high positioning accuracy of the surface abnormal holes and high-resolution microscope lens which is used to image local tiny features. Besides, an algorithm of determining the boundary points of a trailing edge on the contour of abnormal hole is proposed to achieve a rapid fitting and accuracy. After experiments and analysis, results show that the system can be used to measure local tiny features on curved surfaces validly and efficiently.
As to the inspection of small and medium workpieces with complex surfaces such as blades, a non-contact optical measuring system is built up in the paper. With the system, the measurement task of such parts can be accomplished in a rapid, precise and efficient manner. Based on the laser displacement sensor, probe head and the mechanical framework of CMM etc, the system combines the advantages of optical sensor and CMM together to cope with the measurement of sculptured surfaces. In the system, the unit direction vector of measuring beam can be obtained through calibration method, which is based on solving of a series of overdetermined nonlinear equations. After that, the one-dimensional length of the laser beam can be transformed to the three-dimensional coordinates of the points on the surface. At the same time, the coordinates of measuring points can be converted to the same world coordinate system to complete the construction of point clouds through coordinate system transformation. Finally, a standard gauging block is measured by the system at 10 different orientations. Compared with the real value, the errors of the 10 measuring results are all smaller than 0.05mm, which manifests the practicability and validity of the system.