Kenichi Nakashima

Optimal control of a remanufacturing system

An optimal control problem of a remanufacturing system under stochastic demand is studied. The system is formulated by a Markov decision process, which is a class of stochastic sequential processes in which the reward and transition probability depend only on the current state of the system and the current action. The models have gained recognition in such diverse fields as engineering, economics, communications, etc. Each model consists of states, actions, rewards and transition probabilities. The paper considers two types of inventories: the actual product inventory in a factory and the virtual inventory used by a customer. The state of the remanufacturing system is defined by both inventory levels. One can obtain the optimal production policy that minimizes the expected average cost per period. The paper also considers some scenarios under various conditions and shows the example of controlling the remanufacturing system.

Analysis of a product recovery system

The continuous growth in consumer waste in recent years has seriously threatened the environment. Environmentally conscious manufacturing and product recovery has become an obligation to the environment and to society. Many countries are contemplating regulations that force manufacturers to take back used products from consumers so that the components and materials retrieved from the products may be reused and/or recycled. We focus on a product recovery system in a remanufacturing system. Product recovery aims to minimize the amount of waste sent to landfills by recovering materials and parts from old or outdated products by means of recycling and remanufacturing. It should be considered when designing and managing the manufacturing systems. We propose a new analytical approach to evaluating the product recovery system with stochastic variability. This model applies the traditional inventory theory to the production/inventory management with consideration for disposal and return. The system is formulated by a discrete time Markov chain. It is composed of the states denoted by the number of the inventory, the transition probabilities between states and the costs associated with the transitions. Using the Markov analysis, we can calculate the total expected average cost per period exactly. Numerical examples are given to show the property of the management system and optimize the product recovery system.

A NEW APPROACH TO ENVIRONMENTAL PERFORMANCE EVALUATION

This paper proposes a new approach to environmental-performance evaluation (EPE) with consideration for multiple types of environmental management systems (EMSs) for establishing a Plan-Do-Check-Act (PDCA) management cycle in the system. First, we summarize the background of the environmentally conscious society and manufacturing. Then, ISO14001 is explained as one of the useful approaches in realizing the environmental conscious management system. Finally, we suggest the new approach to EPE using data-envelop analysis (DEA). In this approach, we determine the input and output factors to obtain the performances of each EMS and compare the performances of the same type of companies using DEA. The result is used as information to maintain the continuous improvement in the system

Performance evaluation of a supplier management system with stochastic variability

We present a generalised stochastic Petri net (GSPN) model of a single-process, single-product, manufacturing facility with a supply management system for multiple vendors controlled by supplier kanbans. We consider a scenario with two vendors and obtain numerical results using the GSPN model. Its properties are investigated and the effect of the vendors activities on the system are discussed.

A design for a management information system with consideration for stochastic variability

A management information system (MIS) is one of the important systems to control materials and information harmoniously. The previous design approaches dealt with it qualitatively. Therefore, it was impossible to smooth the office works in the management system. In this paper, we design the MIS using a stochastic Petri net (SPN). First, we describe a typical MIS and explain the concept of SPN. Next, we construct the MIS as the SPN model and obtain the total expected sojourn time of documents in each section. Finally, we propose the design for the MIS with consideration for the smoothing of the office works.

Allocating kanbans for a production system in a general configuration with a new control strategy

We consider a production system in a general configuration with a new control strategy: the push policy for the part sending and the kanban mechanism for the work-in-process (WIP). The production system is composed of many stations (or workshops) such as an entry station, a set of workstations, a central station, and an exit station. This type of system is modeled as an open queueing network (OQN) in a general configuration with a Markov-type part sending policy and a machine no blocking (MNB) mechanism. The most important performance measures of the production system are the total throughput of the workstations and the total blocking flow of blocked parts sent from the workstations to the central station. This paper discusses an optimization problem with multiple objectives: allocate kanbans to the workstations so as to simultaneously maximize the total throughput and minimize the total blocking flow. Based on a semi-open decomposition approach, several useful properties of the system are characterized. These properties are used to develop a marginal algorithm for the optimization problem. Moreover, a dynamic simulation approach is devised as a tool for evaluating the quality of the solutions obtained by the algorithm. Numerical experiments are provided to demonstrate the efficiency of the algorithm through the simulation approach.

Cost Analysis of a Remanufacturing System

This paper deals with a cost management problem of a remanufacturing system with stochastic variability such as demand, remanufacturing rate and discard rate. We model the system with consideration for two types of inventories. One is the actual product inventory in a factory. The other is the virtual inventory that is used by customer. We define the state of the remanufacturing system by the both of the inventory levels. It is assumed that the cost function is composed of various cost factors such as holding, backlog and some kinds of manufacturing costs etc. The expected average cost per period is obtained by numerical computation. We also consider some scenarios under various conditions using design of experiments and discuss the effects of the cost factors on the remanufacturing system.

An optimal part sending policy for a production system in a general configuration with a new control strategy

We consider a production system in a general configuration with a new control strategy: the push mechanism for the part transport and the kanban technique for the work-in-process (WIP). The production system is composed of many stations such as an entrance station, a set of work stations, a central station, and an exit station, that are arranged in a general configuration. The push mechanism is followed for transporting a part from a station to a destination station. The kanban technique is adopted for controlling the WIP in a work station. The production system is modeled by a closed queuing network in a general configuration with a Markov part sending mechanism and a machine no blocking (MNB) technique. An optimal part sending policy that maximizes the expected system throughput is formulated into a long run average semi-Markov decision process. Three solution approaches are developed for obtaining optimal or suboptimal solutions. Numerical examples are given to evaluate the quality of the solutions obtained by the solution approaches.

Optimal control of a remanufacturing system with consideration for product life cycle

This paper deals with the cost management problem of a remanufacturing system with stochastic variability in the demand rate, the remanufacturing rate and the discard rate. We consider two types of inventories. One is the actual product inventory in the factory while the other is the virtual inventory that is still in use by the consumers. The state of the remanufacturing system is defined by considering the levels of both inventories. The cost function is composed of various costs such as the holding cost, backlogging cost and other manufacturing costs. We obtain the optimal production policy that minimizes the expected average cost per period. Numerical results provide insights on the effects of the various costs on the optimal policy.

Optimal inventory control with consideration for LCA

This paper proposes a new performance evaluation approach to an inventory management system based on an environmental conscious manufacturing system such as a remanufacturing system with consideration for Life Cycle Assessment (LCA). We here formulate an inventory system with single item based on newsboy problem. The system is evaluated by the total cost that includes the holding, the backlogged, the disposal and the CO2 penalty costs. In this approach, we consider two types of inventories: one is the actual product inventory in a factory whereas the other is the LCA inventory that denotes CO2 emission for all the life cycle of the product. This model also includes disposal and recycle rates. Using the suggested model, we can obtain the total inventory cost with consideration for the environment. Numerical examples are considered to illustrate the implementation of the methodology.