Zheng Yang

Fast and accurate deflectometry with crossed fringes

Abstract Phase measuring deflectometry (PMD) acquires the two components of the local surface gradient via a sequence of two orthogonal sinusoidal fringe patterns that have to be displayed and captured separately. We will demonstrate that the sequential process (different fringe directions, phase shifting) can be completely avoided by using a cross fringe pattern. With an optimized Fourier evaluation, high quality data of smooth optical surfaces can be acquired within one single shot. The cross fringe pattern allows for one more improvement of PMD: we will demonstrate a novel phase-shift technique, where a one-dimensional N-phase shift allows for the acquisition of the two orthogonal phases, with only N exposures instead of 2N exposures. Therefore, PMD can be implemented by a one-dimensional translation of the fringe pattern, instead of the common two-dimensional translation, which is quite useful for certain applications.

Better 3D inspection with structured illumination: signal formation and precision

3D metrology faces increasing demands for higher precision and larger space-bandwidth-speed product (number of 3D points/s). In this paper we consider structured-illumination microscopy as a means for satisfying these demands, developing a theoretical model of the signal formation for both optically smooth and optically rough surfaces. The model allows us to investigate physical limits on precision and to establish rules that allow sensor parameter optimization for greatest precision or highest speed.

Single-shot phase-measuring deflectometry for cornea measurement

Abstract Phase-measuring deflectometry (PMD) has become a standard tool to measure the topography of specular surfaces. We implemented PMD for the measurement of the human cornea topography, exploiting an earlier idea of Lingelbach et al. Two problems occur: a large angular dynamical range and a single-shot measurement are required. We solve these problems by an optimized geometry with minimal occlusion and by single sideband demodulation with a pre-distorted fringe pattern with optimal fringe period. An in vivo measurement of an astigmatic cornea displays a deviation from the medical diagnosis of only 0.15 D, which is within the medical quantization step of 0.25 D.

A novel one-dimensional phase-shift technique by using crossed fringe for phase measuring deflectometry

In principle, PMD needs the two components of the local surface gradient. Therefore a sequence of two orthogonal sinusoidal fringe patterns have to be displayed and captured separately. It is easy and convenient by using a digital display, but it will be much difficult to build a PMD system with mechanic gratings. In this paper, we present a novel phase-shift technique by using the cross fringe pattern, in which a one-dimensional N-phase shift allows for the acquisition of the two orthogonal phases, with only N exposures instead of 2N exposures. Therefore, it make PMD possible be implemented by a one-dimensional translation of the fringe pattern, instead of the common two-dimensional translation, which will be quite useful for certain applications.

Flying Triangulation - Acquiring the 360 Topography of the Human Body on the Fly

We introduce a novel optical measurement principle: “Flying Triangulation”. It fills an important gap in 3D metrology because it enables an acquisition of the topography of moving objects. The immunity against relative motion between object and sensor also allows for medical applications. An easy acquisition of complex objects is possible – just by freely hand guiding the sensor around the object. No tracking is necessary. We will present a “Flying Triangulation” sensor for the intraoral measurement of teeth and a sensor realization for the full 360° 3D acquisition of a person’s head. Parts of the body can be captured with high precision by comfortably guiding the sensor, with real-time control of the result.