Research On Layout Optimization Of Workshop Facilities

The facility layout plays an important role in manufacturing industry. As a part of facility planning, the facility layout considers how to place the machines and storehouse and how to organize the material handling and operators in a pre-defined workshop. The major objective is to optimize the design goals, such as reduction of the material handling costs and improvement of the machine efficiency. A well-designed facility layout can speed up material handling, minimize the residence time during the production process, and significantly improve production efficiency. Theoritically, the facility layout problem under discussion is one type of combinatorial optimization problems, which belongs to NP-hard problem. Compared with cutting and packing problems, its problem description, mathematical modeling and solving process are much more complicated and also more difficult. As the facility layout problem is still unresolved in the engineering world, research on this problem has important practical significance.The work is supported by the National Natural Science Fundation of China (No. 60674078,50575031). Focusing on the layout in production workshop facilities, we look for effective methods to solve the layout problem. Facility layout can be classified into block layout and detailed layout. The former ignorzes the size and shape of facilities, and its solution is the relative position of the facilities in the workshop. In contrast, the latter takes into account the size and the shape of facilities, and its solution is the coordinate and the orientation of the facilities in the workshop. Compared with the block layout, solution of the detailed layout is more complicated, since it considers more objectives and constraints. The contents of the dissertation are as follows:(1) We propose a relative position-coded differential evolution (DE) with different encoding process from other algorighms for the loop layout problem, since encoding is the key of evolutionary algorithms. The proposed algorithm notices that the solution result of the loop layout problem is the relative position of the facilities, so it has following favourable characteristics:i it avoids mapping from float-point vectors to integer sequence; ii the coding space of the new algorithm corresponds to the solution space of loop layout; iii it resolves the illegal chromosomes in the solving process.(2) We propose a connectivity graph generation approach for obstacle-avoiding Manhattan shortest path calculation in detailed layout problem. Material handling cost, the reduction of which is the main aim of the detailed layout problem solution, is determined by the distance among facilities. Thus, the shortest path among facilities directly affects the quality of the layout optimization solution for detailed layout problem. By makeing full use of the characteristics of Manhattan distance which are different from those of Euclidean distance. the proposed approach can shorten the time of facility distance calculation in detailed layout.(3) We establish a mathematical model which is more adaptable to the actual environment and developed a satisfaction-based differential evolution to solve the detailed layout. In modeling, the mathematical model takes acount not only the shape of facilities, but also the pickup/dropoff point, the connectivity, the shortest path and orderliness of the facilities. In solving, because of multi-constraints, multi-objectives and NP-hard nature of the detailed layout problem, it is very difficult to find the global optimal solution. Therefore, we developed a method to find the satisfactory solution instead of the global optimal solution. The proposed method combines the satisfactory optimization theory and computational intelligence algorithm, and uses the overall satisfaction function as a differential evolution algorithm objective function to solve the detailed layout problem.(4) We give some key technologies while developing the facility layout optimization and simulation of the system prototype, including:â‘ we derive a local scale-based 3D model retrieval method from the 3D model retrieval method from the CAD model library;â‘¡simplification method of irregular solid model based on Pro/E secondary development for geometry data extraction;â‘¢interference calculation module for calculating interference between facilities in detailed layout;â‘£layout simulation based on Pro/E secondary development, to show the layout results in Pro/E three-dimensional simulation environment to facilitate comprehensive evaluation.In this dissertation, we present the mathematical models and corresponding solving methods for loop layout and detailed layout problems. Besides, we give some key technologies in developing facilities layout optimization and simulation of the system prototype. This method is expected to be applied to other fields where other types of facilities planning are involved, such as airports, hospitals, offices and so forth.