The Economic Design of Continuous Inspection Procedures: A Review Paper

This paper studies the major developments of the economic design of inspection procedures for continuous production. Such procedures are mainly proposed for the aim of trouble shooting, and can be classified under two headings: itemwise inspection and grouped inspection. In the first class, more papers have been written on the surveillance of the proportion of defectives than on the surveillance of a quality characteristic, and it is seen that a majority of the papers has been influenced by Girshick and Rubin's (1952) work. Some of the more important procedures are presented. In the second class, the papers reviewed deal exclusively with the surveillance of a variable quality characteristic, using control charts. It is seen that, among these papers, Duncan's contributions (1956, 1971) are more important and practical. Comments are made on the advantages and limitations of each procedure. In the last section there is a discussion on some practical points for consideration in the selection of an inspection procedure. Finally, the paper points out some desirable research areas for future study. In this paper we review some major developments of sampling inspection procedures for continuous production processes, from an economic point of view. Products are being made continuously in a conveyor belt and an inspection station is located somewhere in the line, possibly at a point after a production stage that has a good chance of causing a variation in the quality. Is it often not desirable to group the product artificially into batches in order to apply the batch-by-batch inspection plans because batching under such circumstances may interfere with the production efficiency, require extra storage space, lead to rejecting articles not yet produced, and the like. It is more practical to inspect items (itemwise sampling) or to inspect groups of several items (grouped sampling) at a certain rate and to diagnose the condition of the production in progress. The form of a continuous sampling inspection procedure is more complex than the batch-by-batch inspection scheme, and each such procedure has a restricted area of application.