Line–planes deflectometry

Abstract

The key issue in phase measurement deflectometry is the solution of incident light which is used to determine the surface normal. To restore the 3D mirror surface information, line–planes deflectometry is proposed to determine the surface normal from the reflected light and the incident light planes containing incident light. To this end, a point light source is used to replace the continuous surface light source of traditional deflectometry. Accordingly, the incident light is calculated by the intersection of incident light planes which are determined by two or more projected lights of a point light source. Finally, the precise mirror surface is restored through the radial basis function interpolation from the gradient which is transformed from the normal information. To verify the proposed method, a line–planes deflectometry system is developed with two projectors and one camera. The system can be applied for two measurement modes concerning different measurement requirements: the ‘line–plane model’ and the ‘line–planes model’. The ‘line–plane model’ can be inferred with a measurement error of less than 0.25 mm to measure objects with low accuracy and non-connectivity. In contrast, the ‘line–planes model’ can be used to measure objects with high accuracy and good area connectivity, and the measurement error is about 1 µm.