A flexible and cost-effective compensation method for leveling using large-scale coordinate measuring machines and its application in aircraft digital assembly

Abstract

In the assembly process of large-size aerospace products, the leveling and horizontal alignment of large components are essential prior to the installation of an inertial navigation system (INS) and the final quality inspection. In general, the inherent coordinate systems of large-scale coordinate measuring devices are not coincident with the geodetic horizontal system, and a dualaxis compensation system is commonly required for the measurement of difference in heights. These compensation systems are expensive and dedicated designs for different devices at present. Considering that a large-size assembly site usually needs more than one measuring device, a compensation approach which is versatile for different devices would be a more convenient and economic choice for manufacturers. In this paper, a flexible and cost-effective compensation method is proposed. Firstly, an auxiliary measuring device called a versatile compensation fixture (VCF) is designed, which mainly comprises reference points for coordinate transformation and a dual-axis inclinometer, and a kind of network tighten points (NTPs) are introduced and temporarily deployed in the large measuring space to further reduce transformation error. Secondly, the measuring principle of height difference is studied, based on coordinate transformation theory and trigonometry while considering the effects of earth curvature, and the coordinate transformation parameters are derived by least squares adjustment. Thirdly, the analytical solution of leveling uncertainty is analyzed, based on which the key parameters of the VCF and the proper deployment of NTPs are determined according to the leveling accuracy requirement. Furthermore, the proposed method is practically applied to the assembly of a large helicopter by developing an automatic leveling and alignment system. By measuring four NTPs, the leveling uncertainty (2σ) is reduced by 29.4% to about 0.12 mm, compared with that without NTPs.

Feature extraction from point clouds for rigid aircraft part inspection using an improved Harris algorithm

“…if n p,the , n p,est < τ otherwise (11) where np,the and np,est are the theoretical and estimated normals at P, respectively. As illustrated in [35], we use the parameter τ = 10° and input the same octahedral model with 40%, 50%, and 60% noise.…”

“…These technologies have gradually replaced the coordinate measuring machine (CMM) for measurement of complex structures that involve free-form surfaces. Extracting critical part features from a point cloud with high precision and efficiency has always been an active research area, and is especially important in the new paradigm of measurement-assisted assembly, as it can improve the final manufacturing accuracy of the aircraft product [7][8][9][10][11].…”

An accurate calibration method of a combined measurement system for large-sized components

“…Over the last decade, there have been rapid developments in 3D measurement systems and supporting methods [4,5], addressing the primary requirements of accuracy and efficiency. According to the measurement principle, the main 3D measurement devices [6][7][8][9][10][11][12][13] include a coordinate measuring machine (CMM) [6,7], laser tracker [8,9], laser radar [10], theodolite [11], indoor global position system (i-GPS) [12], photogrammetry [5], total station [13], and 3D scanners based on structured light [14,15]. However, both large-sized structures and small key features reduce the measurement accuracy and efficiency when utilizing a single measurement instrument.…”

A coordination modelling approach for assembly of multi-constrained objects based on measured skin model

“…In the cell, the robot locates the rib into the spars with the aid of the Leica laser tracker system (Rooks, 2001). Comac has developed an automatic docking platform for the docking of wing and fuselage of large passenger aircraft (Zhu et al , 2015; Deng et al , 2018a, 2018b). In these applications, the sensors and on-line measuring equipment are used to get the measurement data of the control features.…”

“…The physical portion refers to the assembly objects, automatic tooling, sensors, measuring equipment and all other physical devices. There have been a lot of relative works about digital assembly system for aircraft components (Deng et al , 2018a, 2018b; Jiang et al , 2016). The virtual portion is regarded as the digital copy of the physical system.…”