Robotic manipulation of deformable linear objects (DLOs) is important in many applications such as the assembly of deformable wire harnesses and cables in manufacturing. Despite some relevant work in modeling, few studies have studied the comprehensive dynamic modeling and precise automatic control of DLOs using robots due to their high degrees of freedom and high flexibility. To fill this gap, the precise single-arm and dual-arm robot manipulation control of DLOs is studied in this article. First, a more comprehensive dynamic model of DLOs is established based on a discrete elastic rod model, which takes into account the twisting deformation of DLOs. The collisions, contacts, and frictions between the DLOs and the plane, as well as the kinematic constraints of both ends of the DLOs, are also considered in the model. Second, practical dynamic control schemes of robots are proposed to realize the precise control of DLOs for both the single-arm control and dual-arm control. For validations, we built an experimental platform using an ABB Yumi robot to implement and validate the proposed approaches in addition to simulations. Finally, various DLO manipulation tasks are conducted and the results for both single-arm and dual-arm manipulations validate the proposed modeling and control approaches.

Loosening of threaded fasteners is a key failure mode, which is mainly caused by the slippage and friction behaviors on the thread and bearing surfaces, and will affect the integrity and reliability of products. Numerous scholars have conducted research on the loosening of threaded fasteners; however, comprehensive reviews on the loosening of threaded fasteners have been scarce. In this review article, we define loosening as a loss of preload and divide it into non-rotational and rotational loosening. The causes and mechanisms of non-rotational and rotational loosening are summarised. Some essential topics regarding loosening under transverse vibration have also attracted significant attention and have been investigated widely, including the loosening curve, critical condition of loosening, and influencing factors of loosening. The research carried out on these three topics is also summarised in this review. It is believed that our work will not only help new researchers quickly understand the state-of-the-art research on loosening, but also increase the knowledge of engineers on this critical subject. In the future, it is important to conduct more quantitative research on local slippage accumulation, and the relationship between local slippage accumulation and rotational loosening, which will have the potential to comprehensively unravel the loosening mechanism, and effectively guide the anti-loosening design of threaded fasteners.

Surface topography of sealing interface is a key factor affecting sealing performance. In industry, it has always been desirable to optimize the performance of static seals by optimizing the surface topography. The evolution of leak channels and the quantitative effects of surface topography on leak rates are expected to be clarified. This paper proposes a novel approach to calculate leak channels and leak rates between sealing surfaces for specific surface topographies, based on three-dimensional (3D) finite-element contact analysis. First, a macromechanical analysis of the entire sealing structure is conducted to calculate the interfacial pressure. Second, the surface topography data are measured and processed. Third, the interfacial pressure is used as the boundary condition applied on the microscale 3D finite-element contact model, which is built based on the specific surface topography. Fourth, the geometrical models of leak channels are extracted from the finite-element contact model, and the leak rates are calculated using the computational fluid dynamics (CFD) method. The proposed approach was applied to a hollow bolt-sealing structure. Finally, experimental results verified the accuracy and effectiveness of the proposed approach, which can provide valuable information for optimizing surface processing techniques, surface topography, and static seal performance.

The assembly process of aerospace products such as satellites and rockets has the characteristics of single- or small-batch production, a long development period, high reliability, and frequent disturbances. How to predict and avoid quality abnormalities, quickly locate their causes, and improve product assembly quality and efficiency are urgent engineering issues. As the core technology to realize the integration of virtual and physical space, digital twin (DT) technology can make full use of the low cost, high efficiency, and predictable advantages of digital space to provide a feasible solution to such problems. Hence, a quality management method for the assembly process of aerospace products based on DT is proposed. Given that traditional quality control methods for the assembly process of aerospace products are mostly post-inspection, the Grey-Markov model and T-K control chart are used with a small sample of assembly quality data to predict the value of quality data and the status of an assembly system. The Apriori algorithm is applied to mine the strong association rules related to quality data anomalies and uncontrolled assembly systems so as to solve the issue that the causes of abnormal quality are complicated and difficult to trace. The implementation of the proposed approach is described, taking the collected centroid data of an aerospace product’s cabin, one of the key quality data in the assembly process of aerospace products, as an example. A DT-based quality management system for the assembly process of aerospace products is developed, which can effectively improve the efficiency of quality management for the assembly process of aerospace products and reduce quality abnormalities.

Finite element analysis has been regarded as an effective research method for analyzing the loosening failure of bolted joints under vibration. However, there exist some factors, which influence the accuracy and reliability of loosening results, thus determining the explanations of the loosening mechanism. In this study, a 3D finite element model of a typical bolted joint was built to investigate the effects of several different factors on the loosening under transverse vibration loading. These influencing factors include preload generation, vibration parameter, and material model. Based on the simulation results, it was found that applying the method of pretension element to generate preload instead of the actual method of torque was reliable and efficient. For the vibration parameter, it showed that the decrease rate in preload was higher for a larger vibration amplitude. But once the bearing surface reached complete slip, the loosening rate would keep constant. This was because the thread surface at that time reached a sticking state. Vibration frequency was proved to have no effect on the loosening behavior. This result demonstrated that the quasi-static assumption for vibration frequency was reasonable. Additionally, it also indicated that plastic material models only affected the preload loss in the initial several vibration cycles and had no influence on the loosening rate of preload after several vibration cycles. Finally, experiments were conducted to confirm qualitatively the results obtained based on finite element analysis.