Physically based rendering method to derive realistic simulation of chromatic confocal measurements

Abstract

One important cause for limited traceability in optical metrology is the presence of systematic measurement errors caused by the interaction of the sensor and the measured object. These effects are complex and influenced by many factors, hence, they may differ significantly even among similar measurement systems. This also implies, that it is usually necessary to model the whole measurement chain including the relevant characteristics of the measured surface.We are currently developing a model of a chromatic confocal point sensor dedicated to simulate object-dependent systematic measurement errors and estimating task-specific measurement uncertainties. The simulations already cover all relevant fundamental aspects of the system, some important details are currently being developed. We recently introduced realistic reflection characteristics based on methods originating in physically based rendering. We show how to phenomenologically describe the light-object-interaction using bidirectional reflectance distribution functions and how the principle of Monte Carlo Ray Tracing can be adopted for this use case.We can already show the general influence of surface curvature and slope and can qualitatively predict systematic effects. However, simulations using the current model still show clear deviations from measurement results. While some effects are caused by non-ideal characteristics of the real system, others are likely caused by the approximations within our model. Therefore, further investigations and model developments are pursued.