Abstract:

The control chart based on the geometric distribution(g-type chart )has been shown to be competitive with p or np chart for monitoring the proportion,especially for applications in high quality manufacturing environments.However when the cases with LCL=0 occur, plotting values beneath the LCL is impossible given the non-negative nature of units such type of lower control limit has no ability to detect rate increase. In fact,situation with a LCL is not uncommon. In this paper we propose the g-type chart with asymmetric control limits.It is found that with the nonzero LCL,the power to detect rate increase has much improved and the power to detect rate decrease is nearly fixed, while the in-control average run length(ARL)is the almost the same as the conventional(symmetric) control chart. In practice,the quantitative results of the paper can be used to determined the control limits.

Key words: asymmetric control limits, ARL, OC curve, symmetric control limits, asymmetric control limits, ARL, OC curve