Abstract: Through regular testing for the same position in a vertical machining center by ball bar,the data sequence of Y axis backlash value of machining center was obtained.The past and now known or unknown the information of Y axis backlash value is regarded as a grey system.The mathematical model of gray system was established.Time series data of monotonically increasing was generated by accumulating.The albino form of differential equations of grey system GM (1,1) was established.Then the calculation accuracy was improved by correcting of residual model.The corrected model GM (1,1) is used to predict the variation of Y axis backlash values.For the maintenance at late stage of machining center,eliminating backlash provide a basis.

Key words: machining center, ball screw, backlash, ball bar, detection, grey prediction