Ship welding is a crucial part of ship building, requiring higher levels of robot coordination and working efficiency than ever before. To this end, this paper studies the coordinated ship-welding task, which involves multi-robot welding of multiple weld lines consisting of synchronous ones to be executed by a pair of robots and normal ones that can be executed by one robot. To evaluate working efficiency, the objectives of optimal lazy robot ratio and energy consumption were considered, which are tackled by the proposed dynamic Kuhn–Munkres-based model-free policy gradient (DKM-MFPG) reinforcement learning algorithm. In DKM-MFPG, a dynamic Kuhn–Munkres (DKM) dispatcher is designed based on weld line and co-welding robot position information obtained by the wireless sensors, such that robots always have dispatched weld lines in real-time and the lazy robot ratio is 0. Simultaneously, a model-free policy gradient (MFPG) based on reinforcement learning is designed to achieve the energy-optimal motion control for all robots. The optimal lazy robot ratio of the DKM dispatcher and the network convergence of MFPG are theoretically analyzed. Furthermore, the performance of DKM-MFPG is simulated with variant settings of welding scenarios and compared with baseline optimization methods. Compared to the four baselines, DKM-MFPG owns a slight performance advantage within 1% on energy consumption and reduces the average lazy robot ratio by 11.30%, 10.99%, 8.27%, and 10.39%.
The Hadamengou gold deposit is located in the western segment of the northern margin of the North China Craton (NCC). The mineralization age of the Hadamengou gold deposit is a matter of controversy. Based on the extensive collection the results of previous research, we infer that the Hadamengou gold deposit is exposed to prolonged geological evolution. It was formed as early as the Middle Hercynian orogen. The metallization mainly took place in the Early Indosinian epoch.
Abstract The Ordos Basin is the second largest sedimentary basin in China. The Yanchang Formation is the key oilbearing layer in the Ordos Basin. The stratigraphic time interval and the stratigraphic division of the Yanchang Formation has been highly debated with estimates ranging from Middle Triassic to Late Triassic. According to the latest studies on the stratigraphical division of Yanchang Formation, it was considered to be deposited as early as the Middle Triassic. Based on this new understanding, we reexamined the previous studies of the detrital zircons from the lower Yanchang Formation. The detrital zircons from the lower Yanchang Formation were divided into three groups based on their U-Pb ages: Paleozoic, Paleoproterozoic, and Neoarchean. The lack of Neoproterozoic U-Pb ages indicates no input from either the Qinling Orogen or the Qilian Orogen. The two older age groups (Paleoproterozoic, and Neoarchean) are likely derived from the North China Craton basement. The Paleozoic zircons were derived from the Inner Mongolia Paleo-uplift. The lower Yanchang Formation was mainly derived from the Inner Mongolia Paleo-uplift instead of being recycled from the previous sedimentary material from the central-eastern North China Craton as was previously hypothesized.
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