Ryosuke Tomohiro

Proposal of variable sequential sampling plan having desired operating characteristics indexed by quality loss

The proportion of non-conforming items has been traditionally utilised as an evaluation criterion for quality of items. However, the proportion of non-conforming items is not necessarily useful as a proper evaluation criterion for controlling high-quality manufacturing in recent years. Accordingly, in order to achieve further quality improvement and innovation, more careful quality evaluation has been required newly. Then, a concept of quality loss in the Taguchi methods has been devised as a severe criterion of quality evaluation. Hereby, a variable single sampling plan having desired operating characteristics (OCs) indexed by quality loss has been proposed in the area of statistical quality control. By the way, the most economical sampling inspection in the average sample number (ASN) is the sequential sampling plan based on the Wald’s sequential probability ratio test. Then, from the viewpoint of cost reduction, we discuss a variable sequential sampling plan having desired OC indexed by quality loss with the aim of expansion of the utility of variable sampling plan for quality loss. As the result, the design procedure of the sequential sampling plan for satisfying some required design conditions indexed by quality loss is provided. In addition, the effectiveness of the proposed sequential sampling plan is verified through some numerical examples.

Reconsideration of negotiation procedure for buyback contract in supply chain

There are some studies about a negotiation procedure between a supplier and a retailer in a supply chain model with a buyback contract. The negotiation procedure in the above studies consists of three successive steps. Through the three successive steps, several candidates for the bargaining solution have been screened step by step, and eventually, the bargaining solution has been uniquely decided. However, the preceding studies of the negotiation procedure have not given a full explanation of the mathematical signification to each role that first and second steps perform on the bargaining solution obtained at third step. Therefore, the purpose of this study is to clarify each role of first and second steps in the negotiation procedure of the preceding studies. Specifically, based on the property of Hessian matrix, we have reconsidered the roles of first and second steps to the global optimality of the bargaining solution obtained at third step.