Thermal influences as an uncertainty contributor of the coordinate measuring machine (CMM)

Abstract

Estimates of the measurement uncertainty are crucial, without which precision measurements are useless from a practical point of view. Dimensional compliance with geometric product specifications (GPS) plays a key role in decision-making in manufacturing engineering. Without rigorous uncertainty assessment, manufacturers risk making incorrect decisions. Coordinate measuring machine (CMM) measurements are suitable when complex measurement tasks of a workpiece must be made, such as measurements of positional tolerances or repetitive measurements. Here, we attempted to solve problems related to the thermal influences in the assessment of uncertainty in Coordinate Metrology. Task-specific experiments based on the identification of residual errors using a hole plate standard calibrated by Physikalisch-Technische Bundesanstalt (PTB) were performed to compare the measurement uncertainty results in the different temperature ranges. The thermal issues of CMMs include measurements of the temperature of the environment and CMM errors, estimation of the uncertainties of the thermal errors of the CMM, and reduction of the uncertainties related to thermal errors of CMMs. Computation of the thermal errors must account for environmental influences and internal heat sources of the CMM. Assessment of the uncertainty of thermal errors covers almost all factors related to the uncertainty of the CMM. The state-of-the-art technique for determining the uncertainty of the measurements is discussed.