Ning Zhao

The robotic mobile fulfillment system (RMFS) utilizes robots to automate logistics handling. Although robots can replace workers, there are serious limitations and conflicts that make the system inefficient, resulting in a limited number of robots in the system. A conflict-free scheduling approach is studied, demonstrating better system efficiency, breaking the limit on the number of robots, and accommodating more robots in operation compared to the traditional strategy. A mathematical model aiming to minimize the total completion time is presented. An A $^\ast$ algorithm is modified for path planning, and an approach with two avoidance rules and six priority rules is proposed for conflict-free scheduling. Based on a case study involving four layout scales, the conflict-free scheduling is suitable for layouts with a higher number of robots, pillars, and a unidirectional path networks. More robots can be accommodated within the system, and even a threefold increase (45 to 150) will not result in a decrease in system efficiency, reducing the total completion time by 49.3%. In the largest layout system, the number of robots doubled (160 to 320) and the total completion time was reduced by 26.1%. This indicates the great potential for the conflict-free scheduling approach in future logistic applications, which could reduce resource consumption for scheduling and increase system efficiency. Note to Practitioners —This paper was motivated by the problem of multi-robot scheduling in robotic mobile fulfillment systems. It can be scalable to other layouts of multi-robot systems. The maximum permissible floor space for fire zoning in the fire regulations. Conflicts can easily occur if a large number of robots are operating in a limited space. Resulting in a limited number of robots in the system. This paper proposes a novel conflict-free scheduling to break the limit on the number of robots. The approach includes how to plan the path, which avoidance rules and priority rules to utilize. We mathematically model the path planning and conflict-free for multi-robot complete all task. We show the effectiveness of conflict-free scheduling in breaking the limit on the number of robots under different layouts. We define the ratio of the number of QR code squares to the number of robots, which is used to evaluate scheduling methods in various layout scenarios. The largest one has 3,880 QR codes, which is the maximum allowable floor space for single-story e-commerce warehouses. We doubled the number of robots and reduced the total completion time by 26.1%. In future research, we will consider more rules and several expansions of the layout.

So far nearly 110 billion pieces of express items have been handled by Chinese express delivery industry, with an average annual growth of 200%. Cross-belt sorting system serves as the most important express item sorting system and most of the sorting work has been automated fulfilled. However, operators are still needed and working pressure arisen with the growth of express items. Under the context of the industry 5.0, new technologies should be utilized to enhance both welfare of the workers and working efficiency of the cross-belt system. However, it’s hard to strike a good balance between express item handling efficiency and the happiness of operators. Digital twin technology bring new solution to this problem. Based on the ascertained human-machine features of the distribution center, the human-machine integration digital twin frame, consisting of physical space, virtual space, twin data center and supporting & application services, were proposed. The closed-loop interactions among biological human body, virtual human body, virtual equipment and physical equipment were achieved. The express item distribution center operation system was established based on the digital twin technologies. Besides, the physical-level data collection and storage, the human body fatigue efficiency conversion process on services levels and the virtual-level predication & decision-making were elaborated. Finally, methods to establish the cross-belt sorting system for the express item distribution center based on digital twin technologies were proposed. Feasibility of the aforesaid methods was verified by a simulation case study.

With the development of economic globalization, shipping exchanges between countries are rapidly increasing and the container throughput of shipping ports has increased quickly, and the operation of most seaport terminals in China has reached a bottleneck which puts forward new requirements for the efficiency of container shipping terminal operations. Therefore, locating for export containers intelligently is of great significance for the development of terminals. This paper focuses on receiving containers intelligently, and establishes the export container locating model based on the principle of actual shipping terminal operations. The Monte Carlo Tree Search algorithm for export container locating problem was proposed and constructed. After examples, the algorithm can effectively solve the problem that meet the constraints, which further proves the practicability of the algorithm and the correctness of the model. The research shows that the method of locating for export container based on Monte Carlo Tree Search algorithm can effectively solve the problem and maintain the green, energy-saving and sustainable development of the shipping terminal. The ideas and methods have certain academic value and reference significance for other NP-Hard problems.