Evaluation on the probing error of a micro-coordinate measuring machine

Abstract

Micro-coordinate measuring machines (micro-CMMs) with small probes (φ300 μm or smaller), low probing force and high accuracy working stage have been developed in recent years for three-dimensional (3D) measurement of micro structures. In general, the performance of the micro-CMM depends on the accuracy of its working stage and the probing system. The accuracy of the working stage of a micro CMM can be assessed by laser interferometry to the order of a few tens of nanometers. However, the accuracy of its probing system is difficult to assess due to the small probe size and low probing force. The probing error of a micro-CMM (model F25 by Carl Zeiss) was investigated at our laboratory. The probes used in the system are based on silicon membrane and piezo-resistive elements. The stylus size of the probes ranges from φ120 μm to φ300 μm. The effect of various sources, including the stylus size, on the probing error of the system was evaluated by means of certified precision spheres with reference to ISO 10360-2:2001. Based on the results obtained, possible ways to reduce the probing error are discussed. This is illustrated by the uncertainty analysis of the diameter measurements of a ring gauge using the system.