| 摘要 |
The invention provides a NC unit provided with an ultrasonically oscillating tool, capable of indenting pits at equal pitches and detecting an amount of wastage of a stylus. In the NC unit, a PLL circuit outputs an ultrasonic signal S at a frequency equivalent to the resonant frequency of the ultrasonically oscillating tool and the frequency of the output signal S undergoes changes following up any change in the resonant frequency due to wear and tear of the stylus. Accordingly, the frequency of the output signal S has a value corresponding to the amount of wastage of the stylus. A frequency detection circuit 40 detects the frequency of the output signal S, and delivers data indicating the frequency to a CPU. When applying a process for indenting pits at equal pitches, the CPU changes over a synchronizing/changeover circuit so as to deliver the output signal S from the PLL circuit to an interpolative operation circuit. This will cause traveling velocities of respective motors to be synchronized with an oscillation speed of the stylus of the ultrasonically oscillating tool thus enabling indentation of the pits at equal pitches.
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