Compensation of Temperature Effects on an Automatic System for Diameter Measurement

This work describes the metrological characterization of an automatic measurement system for the identification of the diameter of rectified cylinders with multiple LVDT sensors. This system varies its temperature because of the fluctuation of the ambient temperature (from 15 to 35 degrees C) while the workpiece exhibits temperature gradients along its axis because of the grinding process used to obtain the final diameter; the effect of these temperature variations can reach up to 25 micrometers, that is very large considering a manufacturing tolerance of 12 micrometers. The first part of the work focused on the evaluation of the repeatability and reproducibility of measurements. The second part aimed to develop a compensation algorithm, for the interfering effects of temperature, based on multiple thermocouple measurements. The algorithm uses two Coefficients of Linear Thermal Expansion estimated by fit-to-purpose experiments, for the workbench and for the measurands respectively. This method allows to reduce measurement uncertainty to 1.1 micrometers.