Error compensation for form errors of plate beamsplitter in near optical coaxial phase measuring deflectometry with reflection error model

The near optical coaxial phase measuring deflectometry (NCPMD) is one of the phase measuring deflectometry (PDM) techniques which is typically used for specular surface form measurement. The NCPMD utilizing a plate beamsplitter to folding the optical axis of display screen to make it close to the optical axis of the imaging system which makes the system more compact and has significantly reduced volume compared with the traditional PMD configuration. The NCPDM can achieve compact configuration, light weight, and reduce measurement error caused by structure shadows of the off-axis configuration of traditional PDM. However, the plate beamsplitter will lead measurement errors to the NCPMD system due to the beamsplitter will inevitably inherited certain form errors on the two surfaces during manufacturing process. In this paper, a reflection error model of the NCPMD system is proposed, and the measurement error caused by the reflection effect of the plate beamsplitter is determined by considering the influence of the unevenness of the upper and lower surfaces of the plate beamsplitter. Simulation studies show that the proposed reflection model can accurately determine the measurement errors caused by the form errors of the beamsplitter, which can be effectively used for subsequent error compensation.