Apparatus for predicting tool life

A work load monitor which comprises:

• (a) a memory section for storing a predetermined number of work load values of a tool as digital data,
• (b) an averaging processing section for calculating a mean value of the work load values,
• (c) a band width setting section for setting an allowable width of fluctuation of each of the work load values from the mean value calculated in the averaging processing section,
• (d) an abnormal signal detecting section for comparing a difference between the mean value calculated in the averaging processing section and each of the work load values with the allowable width set by the band width setting section, and then outputting abnormal signals when the difference is in excess of the allowable width,
• (e) a counter section for counting a number of the abnormal signals output,
• (f) a normalizing section for calculating a normalized ratio of the number of the abnormal signals output to the predetermined number of work load values, and externally outputting the normalized ratio, and
• (g) a comparing section for outputting an alarm so as to report a significant change of the work load values, when the normalized ratio is larger than a predetermined value.