Development of Piezo-element Sensor for Touch Trigger Probe

A touch trigger probe sensor for coordinate measuring machines (CMM) detects a contact between a spherical stylus tip and an object to be measured. The conventional probes are not suitable for high speed measurement and high accuracy measurement of sub-micrometer order. A piezo-element novel sensor construction and a detecting circuit are proposed. To detect the impulsive contact force, four piezo-elements are mounted on a base of the stylus. The impulsive force brings a longitudinal wave and a bending wave which transmit separately in the stylus. The time difference between two waves arriving to the piezo-elements enlarges the detected position error. The two waves are detected electrically by the piezo-elements and separated by the detecting circuit, and the former signal is delayed so that two waves are seemed to arrive simultaneously at the piezo-elements. By the above signal processing, the error are improved to at most 50nm dispersion, at all of the force directions in a half sphere of the spherical stylus tip for a probing speed of 3-60mm/s.