Process monitoring chart is proposed to monitor the parts whether irregular deterioration occurred, supposing that the deterioration characteristic can be continuously monitored with development of sensor technology.In order to evaluate the amount ofdeterioration per unittime, a mixed effect model is estimated with consideration to operating conditions and parts peculiar effect and so on. A method to set up the control limit to the monitored amount of deterioration is proposed using the model.Transition of deterioration is nonstationary and a process accumulating incremental deteriorations. Monitoring the increment of deterioration, we are able to set up narrow control limits at each time independently of the past transition of deterioration. The proposed method was applied to machine tool wear data, and the method was verified.

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