Conduit connectors are widely used in the manufacturing of aviation equipment such as aircraft engines and aircraft assemblies. The surface roughness of conduit connector is a key quality characteristic to ensure the sealing connection of pipeline systems. Small deviations in the surface quality of conduits can lead to significant quality issues in aircraft, so high-precision measurement of micro roughness of conduit connector surfaces is of great significance for controlling aircraft quality and optimizing support manufacturing processes. Compared with contact measurement methods, optical measurement methods take an irreplaceable position in micro-nano scale roughness measurement which have many advantages such as non-destructive, high-precision and high-speed. An optical measurement method for surface roughness of aircraft conduit connector based on a triangular structured illumination system is proposed in this article, which combines high-precision fringe phase analysis algorithm and accurate height mapping algorithm to realize morphological restoration and the calculation of the roughness of the tested area. Relational experiment is carried out to verify the feasibility of the proposed method.
Micro-nano 3d measurement method based on fringe projection technology is widely used in many detection scenarios due to large non-contact, field of view, high accuracy and high adaptability. However, there is a problem that the nonlinear motion of the scanning actuator introduces random scanning error in the actual measurement system, which leads to the reduction of absolute accuracy and measurement repeatability. In this paper, a random scanning error suppression method is proposed to solve this problem. The principle of mutual calibration of the second order slope of the theoretical modulation curve and the second order slope of the actual modulation curve of the grating fringe is used to achieve the accurate value of the scan step. The feasibility and progressiveness of this method are proved by theoretical derivation, simulation and experimental verification, which demonstrate that the measurement repeatability is better than 1nm in simulation, the absolute precision is better than 3nm and the measurement repeatability is better than 2nm in experiment.
The structured light measurement method uses the principle that the fringe modulation information is sensitive to the object height information to realize the mapping from the fringe modulation information to the height information, which can be utilized to restore the three-dimensional shape of the object, smooth and rough surfaces. This method has a simple measurement system and belongs to coaxial measurement, which is considered a highly promising measurement method and has good application prospects in the field of aircraft surface shape measurement, surface defects detecting, etc. In most SIM, two essential parameters need to be accurately obtained to restore the 3D shape of the object which are the focus position of each pixel and the scan step. For years, researchers have constantly improved the structure of SIM system to obtain more accurate focus position to realize optimized measurement results. Meanwhile, the preset value of the scan step is directly substituted into calculation. However, the actual value of the scan step is very likely inconsistent with the preset value due to various factors in practical such as nonlinear motion of scan actuator, which will introduce great error into the measurement result. However, in the current structured light measurement methods, there is no solution to the problem of errors caused by the scanning system, which limits the further improvement of measurement accuracy and repeatability. In this paper, a random scanning error suppression method is proposed to solve this problem. The principle of mutual calibration of the second order slope of the theoretical modulation curve and the second order slope of the actual modulation curve of the grating fringe is used to achieve the accurate value of the scan step. Theoretical analysis and simulation are carried out to verify the feasibility of the proposed method.
With the characteristics of high stealth and supersonic, the new generation fighter aircraft has become the backbone of national defense. The geometric shape of the aircraft surface directly determines its key indicators. As a result, the accurate three-dimensional detection of the aircraft surface has become a key part of the aircraft manufacturing industry. In this paper, a 3D detection method of aircraft surface based on auto-focus technique is proposed, which can achieve the measurement effect of "what can be seen is what can be detected". The measurement system is mainly composed of an optical system with a small depth of view and a longitudinal scanning mechanism with a high moving precision, which can realize fast, comprehensive and reliable three-dimensional shape detection. In the process of longitudinal scanning, the needed images are captured by the camera which is carried by the scanning mechanism. Further, combined with the auto-focus technique, the three-dimensional point cloud of the entire imaging plane can be obtained. This method is a non-contact optical measurement method, which has a simple measurement system in structure and does not need to actively project any form of structured light. In summary, the proposed method has the characteristics of non-damage, high efficiency and low cost. At the same time, the proposed method has good robustness for the surfaces to be measured with different materials, shapes and sizes on the aircraft surface, which is especially suitable for the acquisition of three-dimensional point clouds in the surface area with complex texture and large roughness.
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