A vibrating touch-probe for micro cmm

A new type of vibrating touch-probe for measuring small part such as the die of a pick-up lens is proposed. The probe is excited by a piezoelectric actuator and the probe vibration is monitored by a capacitance sensor. When the probe does not touch an object, FFT analysis of the sinusoidal vibration of the probe shows a single line spectrum. As the probe touches the object, harmonic components appear in the spectrum. When the power of the second harmonic exceeds a threshold level, it is judged that the probe touches the object. By using this touching criterion, the measuring pressure can be less than a conventional touch probe. Experimental analysis shows the measuring performance of the probe including the sensitivity for an inclined plane. The result of the analysis indicates that the proposed touch probe is suitable for on-machine measurement of small parts.