Aya Ishigaki

Iterated Local Search Algorithm for Flexible Job Shop Scheduling

The flexible job shop scheduling problem (FJSSP) is an extension of the classical job shop scheduling problem (JSSP). The classical JSSP determines the job sequence for each machine. In contrast, FJSSP decides not only the job sequence but also the machine assignment for jobs; thus, it is a combinatorial optimization problem of a larger scale. To efficiently solve an FJSSP, which is non-deterministic polynomial-time hard, we require a heuristic method. In previous studies, the FJSSP has been solved by neighborhood algorithms, which employ various metaheuristic methods. Some approaches constrain the neighborhood operation from jobs on a critical path and simultaneously change the machine assignment and job sequence. However, a method that can independently change machine assignment and job sequence may improve the efficiency of FJSSP because the solution of JSSP already exists. In this study, we investigate the effect of continuing to change job sequence and machine assignment, and job sequence and machine assignment change are iterated using a local search method. In numerical experiments, the effects of the frequency of job sequence change and machine assignment change on the performance of the solution are investigated. Finally, we find the best machine assignment and job sequence change method for FJSSP.

Effect of Material Prices for Global Supply Chain Network with Trans-Pacific Partnership

Manufacturing firms are getting more global and forming global supply chain networks to pursue lower production costs and emerging markets including Asia. The global supply chain network consists of domestic as well as international suppliers, factories and markets. Then, the supply chain network applies customs duties when parts and products are transported across overseas borders. Additionally, several treaties of customs duty such as Free Trade Agreement (FTA) and Trans-Pacific Partnership (TPP) are unavoidable for designing the global supply chain network.On the other hand, current fluctuations of oil and energies price cannot be ignored for the global supply chain network. This study analyzes influences by fluctuating the material prices on the global supply chain network with the customs duty and TPP. Firstly, the global supply chain network with customs duty and TPP is modeled. Next, the model is formulated with integer programming. Finally, sensitivity analysis is conducted in order to investigate the effect on the global supply chain network by fluctuations of material prices.

Linear Physical Programming Oriented Approach of Reverse Supply Chain Network Design for Costs and Recycling Rate

In the recent years, economic grows and population increasing bring consumptions for numerous amount of assembly products and materials resources all over the world. As the result of it, the material starvation has been getting a serious problem globally. In order to circulate materials from End-of-Life (EOL) assembly products, manufactures have to design reverse supply chain networks for the EOL products. The reverse supply chain includes transportation of the EOL products from collection centers to recovery facilities and/or a disposal facility. Then, the costs are required for recycling, transportation and facilities. Additionally, the EOL product statuses differ by users situation, and average recycling rate and cost of each product and part depend on the statues. To design the reverse supply chain network, decision maker (DM) decides transportation roots, the number of products flowed on each root and production volumes at each facility in order to minimize the total cost while maximizing the average recycling rate on the whole network. However, the relationship between the recycling rate and the costs become trade-off. Therefore, the DM has to solve them simultaneously. On the other hand, Linear Physical Programming (LPP) is known as a method to solve multi-objective problems (Messac et al., 1996). It allows the DM to express his ideals as desirable ranges for each criterion. One of the most significant advantages using LPP is that the DM does not need to specify the weights for each criterion. This study designs a bi-objective reverse supply chain network to collect and recycle the EOL assembly products for the costs and the recycling rate using LPP. First, based on previous study (Ijuin et al., 2017), the reverse supply chain network is modeled to transport the EOL products from the collection centers to the recovery facilities depending on the EOL product status which includes the recycling cost and rate. Next, the reverse supply chain network is formulated with the LPP in order to minimize the total cost while maintaining the recycling rate of the whole network. Finally, a case study is conducted, the results by the LPP and the integer programming (Ijuin et al., 2017) are compared.

Study on Multi-item Process Production System Considering Setup Time

In recent years, production plants are shifting to multi-item small-volume production with the diversification of market needs. However, frequent item switching in a single facility increases the setup time, resulting in a decrease in the production rate, or the operating ratio of facilities. In this study, we consider process production scheduling for a factory with long setup time that produces garbage bags of multiple varieties. In the experiment, several items switching patterns were set based on actual examples, and the influence of differences in setup method in continuous production of difficult to process products on production time and setup time was investigated. As a result of the comparison of the conventional production schedule, by changing the setup method, it was possible to improve the production time and setup time without increasing the loss.

An Application to Stochastic Vehicle-Routing Problem in a Waste Collection

In this research, we consider a dynamic collection plan with stochastic demands. Each customer has a known position and a random demand. Each vehicle has the same capacity. This problem differs from the well-known stochastic vehicle-routing problem with that re-pickup occurs if the capacity constraint of a vehicle is exceeded. This problem arises in several situations such as waste collection and less-than-truckload motors. Many stochastic vehicle-routing problems deal with issues related to customer delivery. In this case, a stock-out occurs owing to the variation of demand. Several studies deal with a stock-out risk as a constraint. The studies are added to the objective function as a penalty. However, in this research, it is necessary to add the excess distance to the objective function by re-pickup. The aim of this research is to model the dynamic collection plan by considering the variation of demand and develop a search algorithm. In this research, the vehicle-routing problem that assigns n customers to K vehicles can be formulated as a combinatorial optimization problem. The proposed search algorithm is applied to an actual trash collection problem.

Optimal Storage Assignment for an Automated Warehouse System with Mixed Loading

In this study, an automated warehouse system with mixed loading is considered. The majority of previous studies considered assumptions that were similar to those for a single-shuttle system with single loading. Due to the increased number of items in recent years, storage assignment strategies with single loading are not feasible because of the shortage of storage racks. This study adopts a storage policy with mixed loading for an automated warehouse system, which enables the use of one warehouse. Additional movement and transshipment operations, which involve mixed loading, are considered in this paper.

Performance Evaluation of Electric Vehicle and Fuel Cell Vehicle Using the Biomass Gasification System Considering the Change of the Traffic Flow

In this research, we propose the low emission fuel supply system for electric vehicle and/or fuel cell one. In our system, we consider the traffic situation on the express way in domestic area. There are plenty of waste biomass resources which are generated by trimming trees and/or grass at the both sides of road on the express way. Here, we assume the biomass gasification system of Blue Tower (BT) using trimming trees and/or grass. Through BT system, electricity due to gas engine or fuel cell and/or H2 due to the purification system can be produced. Moreover, the traffic flow would be depending upon seasonal condition. Based on the uncertainties, we consider the production plan for the fuels.