Impact of thermal gradients on the geometry correction of a bridge coordinate measuring machine

If the problems related to the parts and measurement strategy of Coordinate Measuring Machines (CMMs) are not taken into consideration, temperature variations become the main source of measurement uncertainties. Indeed, they may cause variations in geometry as well as reference point drift. The effect of drift is sometimes minimized by CMM users and is not well quantified in general. The aim of this paper is to present a physical method to determine the evolution of CMM geometry and drift which is based directly on CMM temperature variations and construction parameters, i.e. the position of the axes measurement scales and reference points of each axis. The method is applied to a Zeiss CMM Contura G2. The consequences of these CMM evolutions are simulated in the measurement of a sphere generated by a Renishaw Machine Checking Gauge. The proposed method falls within the framework of an uncertainty assessment methodology performed by multi-level Monte Carlo simulation, where the first level corresponds to the characterization of the CMM evolution.