Compensation of thermal errors in vision based measurement systems using a system identification approach

This article presents a method to compensate thermal influences on optical 3D measurement devices which are widely used as high-accurate localisation devices. Thermal expansion caused by ambient temperature changes or by self-heating of the measurement device itself leads to a changing device geometry which in turn can lead to significant positioning errors since an accurate knowledge of the device geometry is essential for triangulation based 3D reconstruction. The changing imaging geometry of the device results in changing camera parameters which can be determined during a calibration step. The dependency between temperature change and the change of the camera parameters can be modeled using system identification methods. The device temperature is considered as the input signal to a linear time invariant (LTI) system and the vector of camera parameters describing the imaging geometry as the corresponding output. Once the model is determined for a specific camera it can be used online to adjust the values of the camera parameters.