Abstract

An automatic lapping apparatus for lapping a piezoelectric material has upper and lower lapping plates, and a carrier disposed between the plates, for holding a piezoelectric material so that it is sandwiched between the plates. The carrier is rotatable to lap the piezoelectric material parallel to the lapping surfaces of the plates while supplying a lapping slurry therebetween. The apparatus also includes a sweep oscillator for applying a sweep signal corresponding to the count of a counter, through an AGC amplifier and a resistor to an electrode supported by one of the plates, a comparing circuit for determining whether the quartz crystal wafer is present underneath the electrode based on the level of the sweep signal applied to the electrode, a memory for storing output data from the comparing circuit at an address corresponding to the count, a dip detector for detecting a dip in the signal applied to the electrode and stopping operation of the counter, a frequency detector for reading the frequency from the sweep oscillator when the dip is detected and the presence of the piezoelectric material underneath the electrode is detected, a frequency determining circuit for determining whether the read frequency is a true resonant frequency of the quartz crystal wafer, a frequency comparator for determining that lapping is completed when the true resonant frequency falls within a predetermined target frequency, and an drive unit control circuit for stopping the carrier when the lapping is completed.