Aspects of probing on the micro scale

Abstract

This paper discusses the aspects that influence the interaction between a probe tip and a work piece during tactile probing in a coordinate measuring machine (CMM). The trend of component miniaturization results in a need for 3- dimensional characterization of micrometer sized features to nanometer accuracy. As the scale of the measurement decreases, the problems associated with the surface-probe interactions become increasingly apparent. The aspects of the interaction that are discussed include contact forces, surface forces, tip rotations, finite stiffness effects and probe repeatability. These aspects are investigated using the Gannen XP 3D tactile probing system developed by Xpress Precision Engineering using modeling and experimental verification of the effects. The Gannen XP suspension consists of three slender rods with integrated piezo resistive strain gauges. The deformation of the slender rods is measured using the strain gauges and is a measure for the deflection of the probe tip. It is shown that the standard deviation in repeatability is 2 nm in any direction and over the whole measurement range of the probe. The probe has an isotropic stiffness of 480 N/m and a moving mass below 25 mg. Finally, the TriNano CMM will be discussed. This novel coordinate measuring machine is designed for measuring three dimensional micro features with nanometer uncertainty. The TriNano has a kinematic and highly symmetrical design based on three parallel axes and obeys to the Abbe principle in its entire measurement volume.