Qi Zeng

Bio: Qi Zeng is an academic researcher from Nanjing University of Aeronautics and Astronautics. The author has contributed to research in topics: Similarity (network science) & Ranging. The author has an hindex of 2, co-authored 5 publications receiving 21 citations.

A coaxial alignment method for large aircraft component assembly using distributed monocular vision

Abstract: The assembly of large component in out-field is an important part for the usage and maintenance of aircrafts, which is mostly manually accomplished at present, as the commonly used large-volume measurement systems are usually inapplicable. This paper aims to propose a novel coaxial alignment method for large aircraft component assembly using distributed monocular vision.,For each of the mating holes on the components, a monocular vision module is applied to measure the poses of holes, which together shape a distributed monocular vision system. A new unconstrained hole pose optimization model is developed considering the complicated wearing on hole edges, and it is solved by a iterative reweighted particle swarm optimization (IR-PSO) method. Based on the obtained poses of holes, a Plucker line coordinates-based method is proposed for the relative posture evaluation between the components, and the analytical solution of posture parameters is derived. The required movements for coaxial alignment are finally calculated using the kinematics model of parallel mechanism.,The IR-PSO method derived more accurate hole pose arguments than the state-of-the-art method under complicated wearing situation of holes, and is much more efficient due to the elimination of constraints. The accuracy of the Plucker line coordinates-based relative posture evaluation (PRPE) method is competitive with the singular value decomposition (SVD) method, but it does not rely on the corresponding of point set; thus, it is more appropriate for coaxial alignment.,An automatic coaxial alignment system (ACAS) has been developed for the assembly of a large pilotless aircraft, and a coaxial error of 0.04 mm is realized.,The IR-PSO method can be applied for pose optimization of other cylindrical object, and the analytical solution of Plucker line coordinates-based axes registration is derived for the first time.

High-Efficiency Posture Prealignment Method for Large Component Assembly via iGPS and Laser Ranging

Abstract: High-efficiency posture prealignment for large components is an important application in aircraft manufacturing. In this article, a new prealignment method for large components via indoor global positioning and laser ranging is proposed. Based on the smart automated guided vehicle (AGV) system, the component is transported from the previous processing station to the assembly station under the guidance of an indoor global positioning system (iGPS), and a predictive correction algorithm is proposed to solve the potential drift problem. The subsequent close-range prealignment is achieved with the proposed laser alignment method, and to improve the accuracy, the estimation of posture error is presented in detail, along with the layout optimization of laser displacement sensors (LDSs). The analysis indicates that the symmetric form with two LDSs on each edge is the most desirable layout. A prototype system is developed, and the verification experiment shows that the posture error is no more than 0.3 mm in translation and 0.02° in orientation. Besides the outstanding performance in precision and efficiency, it possesses great repeatability and applicability.

Configuration optimization of the feature-oriented reference system in large component assembly

Abstract: Multi-station measurement is a key technology for the high accuracy and efficiency of large component assembly. The unity of measurement coordinate systems (MCSs) and assembly coordinate system (ACS) is achieved by registration of enhanced reference system (ERS) points. As the transformation errors of assembly features are related to the configuration of ERS points, and to minimize them as possible, the feature-oriented reference system is of great importance, and a configuration optimization method is proposed in this paper. The detailed analyses with regard to structures, inspections, and tolerances of assembly features are conducted, and the complex constraints are established. By applying them and considering the direct connections between MCSs, the modified configuration model is built. The proposed optimization method is based on the improved binary particle swarm optimization (IBPSO), which involves a two-stage strategy and a novel mutation. The mutation is developed by using feasible centers to attract and correct infeasible particles, and simultaneously, to maintain the particle diversity. The performed experiments show that the method can effectively output optimal positions of ERS points, and the reference system is eventually hybrid on the premise of meeting accuracy requirements. The increase of ERS points is beneficial, but no further optimization happens when the amount reaches the upper limit. The limits are 12 and 18 when the measurement instruments are located at two and three different stations respectively.

A Measurement Method for Robot Peg-in-Hole Prealignment Based on Combined Two-Level Visual Sensors

Abstract: Vision measurement plays a significant role in robot automatic assembly. In this study, a new measurement method for robot peg-in-hole prealignment via a combined two-level vision system is proposed. The assembly system and a global coordinate system calibration procedure based on a dynamic coordinate system are developed to construct an accurate transformation between the coordinate systems. The subsequent hole pose is obtained with the proposed image processing method and the hole edge matching method, followed by the 3-D hole reconstruction and spatial circle fitting algorithm. A low-cost pose determination is proposed based on hole edge point selection. The experiment and analysis indicate that the hybrid measurement system has high precision in the local hole pose and global robot pose measurement accuracy. The peg-in-hole assembly results verify the measurement and calibration accuracy sideways. Our hybrid measurement system enhances the vision measurement range, local accuracy, and robot automation.

High-Efficiency Posture Prealignment Method for Large Component Assembly via iGPS and Laser Ranging

Abstract: High-efficiency posture prealignment for large components is an important application in aircraft manufacturing. In this article, a new prealignment method for large components via indoor global positioning and laser ranging is proposed. Based on the smart automated guided vehicle (AGV) system, the component is transported from the previous processing station to the assembly station under the guidance of an indoor global positioning system (iGPS), and a predictive correction algorithm is proposed to solve the potential drift problem. The subsequent close-range prealignment is achieved with the proposed laser alignment method, and to improve the accuracy, the estimation of posture error is presented in detail, along with the layout optimization of laser displacement sensors (LDSs). The analysis indicates that the symmetric form with two LDSs on each edge is the most desirable layout. A prototype system is developed, and the verification experiment shows that the posture error is no more than 0.3 mm in translation and 0.02° in orientation. Besides the outstanding performance in precision and efficiency, it possesses great repeatability and applicability.

A Coaxial Alignment Method for Large Flange Parts Assembly Using Multiple Local Images

Abstract: The large flange parts in aero-engines are usually manually assembled. Collision damage caused by assembly alignment error often occurs in the assembly process, which affects the assembly accuracy and product reliability. The machine vision-based alignment methods usually achieve the high-precision measurement of the parts by obtaining the high-resolution images of the whole parts with a combination of laser distance sensors. Hence, existing methods are high costly and inefficient. In this paper, a new alignment method based on the principle of coaxial alignment for large flange parts is proposed. The proposed method first obtains multiple high-precision image pairs from the local field of views at the fitting surfaces of flanges. The clearance and bolt holes in each image pair are then extracted via edge recognition and Hough Transformation. Two optimization models are built to calculate the translation adjustment and rotation adjustment. The optimization model 1 is built with the translation adjustments of the flange as the variables and the consistency of the clearances as the objective function. The algorithm to solve the model based on the gradient-descent method is proposed. The positions of the bolt holes in the images are subsequently adjusted based on the translation adjustment, and the rotation adjustment is calculated by solving the built optimization model 2. The experiments show that the proposed method can be applied to the assembly process of large flange parts, and the visual servo control model based on this method also has good stability.

A Noncontact Control Strategy for Circular Peg-in-Hole Assembly Guided by the 6-DOF Robot Based on Hybrid Vision

Abstract: Facing some special operating environments or conditions, existing control methods for the peg-in-hole assembly guided by robots always have their own disadvantages, for example, low efficiency or poor adaptability. For the above problem, in this article, a new circular peg-in-hole assembly control strategy is proposed for the 6-Degree of Freedom (DOF) robot based on hybrid visual measurements, avoiding peg-in-hole contacts during the robotic operation. In the strategy, the pose of the monocular camera mounted at the end-effector is adaptively adjusted to improve the image quality through an algorithm based on the rough pose measurement of the target hole by the binocular camera; the accurate 3-D pose of the hole is determined by an algorithm based on processing of high-quality images and the compensation of the orientation error. Combined with the robotic collision-free path planning, the automatic peg-in-hole assembly can be implemented in real setting. The assembly precision of the robotic system based on the proposed method is validated and discussed based on experimental results. Then, the minimal peg-in-hole interval relative to the alignment error is modeled through the spatial relation analysis to analyze the applicable condition of the robotic system with the control strategy. Also, the reliability of the proposed strategy is verified through experimental tests under some applicable conditions. Finally, suggestions and plans of future works are discussed for further extension of the application area of the proposed strategy, such as fields of precision and ultraprecision manufacturing. This contribution has the major significance on the automatic peg-in-hole assembly under 3-D operating environment.