Inverse projected-fringe technique for measurement of dimensions and surface profile of axisymmetric objects

Abstract

An inverse projected-fringe technique based on simulating the system of a projector-part-camera is proposed for an on-machine inspection of axisymmetric parts. The parts considered for this study are relatively large, have high specular surfaces and have sharp slopes. A computer simulation-based method and the CAD model of the part was used to produce the inverse fringes as well as to find an appropriate trace passing through the symmetrical axis of the part that offers the best signal to noise ratio (SNR). This technique measures the deviation from a master-part and provides an accuracy of better than 10 microns for the part with a radial dimension of about 10 cm. It is shown that the proposed technique improves the SNR and the repeatability of the system compared to the standard fringe projection technique, in particular for the areas with a steep slope.

Adaptive Binocular Fringe Dynamic Projection Method for High Dynamic Range Measurement

“…From Figure 7, the reflectivity of the white area of checkerboard is obviously higher than that of the black area, while black areas have high ambient light intensity. As shown in Figure 7, if Zhang’s method [26] is used, surface reflectivity can be divided into three intervals: (0, 1], (1, 2], and (2, 2.7]. The corresponding projected light intensities are I1P=240−701=140,I2P=240−702=70,I3P=240−702.7=56.…”

“…Compared with other HDR methods [23,24,25,26,27], ABFDP method extends high dynamic range measurement from monocular fringe projection to binocular fringe projection. The intensity modification mask is calculated without pre-known geometry information.…”

“…Addressing that it is difficult to improve the dynamic range by hardware for the most camera sensors [6], many experts have carried out a series of approaches to solve the HDR measurement problem. The methods can be divided into several categories: multi-exposure method [12,13,14], light intensity adjustment method [15,16], color invariance method [17,18,19], polarization method [20,21,22], adaptive fringe pattern method [23,24,25,26,27], and others [28,29]. Considering that the dark regions and bright regions of the fringe image require different exposure times, multi-exposure method becomes a way for HDR problem [12,13,14].…”

“…Obviously, polarization methods require additional hardware and are time-consuming. The adaptive fringe pattern method is another solution, which computes the optimal illuminations according to the correspondence of camera–projector [23,24,25,26,27]. For the problem of strong internal reflection, Xu and Aliaga developed an adaptive corresponding algorithm [23], which may take hours to inspect an unknown scene.…”

“…Lin presented a fast 3D shape measurement technique to improve the signal-to-noise ratio during the measurement [25]. Farahi [26] put forward an inverse projected-fringe technique for on-machine inspection, based on the correspondence of projector-part-camera. Zhang [27] studied a method to calculate several groups of fringe patterns with optimal light intensities generated based on the intensity response function of camera.…”