This paper describes a optimal scheduling method for stock production. We have constructed an optimizing method to decide variety of the half-finished products applying the simulated annealing method and an optimizing method to decide quantity and production timing of half-finished products applying inventory simulation method. The simulated annealing method is used for deciding what kind of half-finished products should be produced to prepare predicted final orders considering the productivity of half-finished products, the production waste of final products and generality of the half-finished products. The inventory simulation is applied to calculate the quantity and production timing of the half-finished products which satisfy a minimum inventory. It is revealed that higher productivity of half-finished products and lower inventory could be achieved by comparing with real production schedule.
An automatic generation of assembly or disassembly sequences is a significant problem for assemblies using robot manipulators. We need to judge feasibility of assembly/disassembly tasks based on geometric information of products. In previous research, only translational motion of subassembly has been considered. However, there are many cases in which a subassembly can be separated from another subassembly using rotational motion. In this paper, we propose a new algorithm with which we can search a posture of a subassembly to avoid collision with another subassembly. The algorithm is based on the Genetic Algorithm. The proposed method makes it possible to search a posture of a subassembly to realize assembly/disassembly tasks in a very short time.
This paper deals with an optimal production ordering problem for an acid rinsing process of a steelmaking plant. The problem is to determine the order of welding hot strip coils in an optimal way subject to complicated constraints. The strip coils are classified into several groups on the basis of their specifications, and the coils belonging to a same group must be arranged successively. Other constraints are precedence relationships between two adjoining coils. The genetic algorithm is applied for obtaining a suboptimal arrangement of strip coils. In our earlier paper we proposed a method for this problem. In this paper another method is proposed for individual description. A part of constraints is always satisfied in the new individual description. Numerical results are compared between the two methods.
In a new system of container terminal, its yard is divided into buffer area and stack area in order to separate ship loading/unloading and yard operations. Such a system then necessitates the shift operations between buffer areas and stack areas; import containers are moved from buffer area to stack area and export containers are moved from stack area to buffer area by two RMGs which travel on the same rails. As a result of analyzing the movements of two RMGs, which may interfere each other, we have reduced the scheduling problem of shift operations into two graph theoretical problems, paring problem and sequencing problem, where the paring problem is the maximum weight matching problem with degree constraints and the sequencing problem is a problem of seeking a shortest path that visits a given number of nodes, both of which have been studied in operations research. Furthermore, to deal with multilayer stacks of containers, the scheduling period is decomposed into overlapping subperiods, to which the above scheduling algorithm is applied. The resulting algorithm shows good performance in both quality of solutions and computational speed, and will be in operation in a real system of container terminal from April 1996.
Force-Directed Scheduling, which is one of effective scheduling methods in high-level synthesis of VLSI design automation, takes the long computational time, though it can optimize hardware cost. Therefore it can not be applied to large scale hardware descriptions. This paper describes an efficient approach for Force-Directed Scheduling. The proposed approach reduces the time for estimating hardware cost by neglecting hardly probable assignments instead of considering all possible assignments as was done in the previous approach. The proposed approach, consequently, can optimize hardware cost for large scale circuits with much less running time.
A new scheduling system has been developed for the steel-making process with complex material handling system and lead-time constraints. To devise its scheduling algorithm, our general approach to the multi-stage production scheduling was applied. The algorithm, which can satisfy various objectives and constraints by a combination of backward and forward scheduling, was installed in the new scheduling system using discrete-event simulation with crane assignment rules and pick up timing rules. This system, which can create a refined and reasonable schedule in short time, has contributed to improvement of efficiency in steel-making process.
Recently, some attempts have been made to decentralize vehicle movement control for AGV systems. However, some communication problem may deteriorate the efficiency of the vehicle movement under the protocol similar to the centralized control. Thus, we impose some restriction on the information received area of each vehicle. In this paper, we theoretically analyze the information received area which is necessary and sufficient for each vehicle to reach its destination in finite time. We also clarify necessary and sufficient conditions for the vehicle with the highest priority to continue onward movement.