Fast Three-dimensional Measurement Research Articles

A fast three-dimensional measurement method based on color fringe projection and background intensity calibration

A fast three-dimensional measurement method based on color fringe projection and background intensity calibration

基于三通道二值条纹离焦投影的快速三维测量

基于三通道二值条纹离焦投影的快速三维测量

A novel and fast three-dimensional measurement technology for the objects surface with non-uniform reflection

Optical three-dimensional (3D) measurement of non-diffuse objects is challenging. At present, a common used method is to adjust the camera’s sensitivity several times to get fringe sequences with different brightness, and then extract the appropriate pixels for 3D shape reconstruction. However, the disadvantages of this method are obvious, including the large number of fringes needed, many useless redundant images, large amount of computation and time-consuming. In this paper, a novel method is proposed, which includes four major steps. Firstly, we set the intensity of the projected fringes to be maximum to ensure that the captured fringes have a good signal-to-noise ratio (SNR). Secondly, two sets of additional fringes are pre-captured to estimate the reasonable exposure time interval. Thirdly, appropriate exposure time is selected and the high-speed projection technology is used. Finally, appropriate pixels are extracted from the fringe sequences for 3D reconstruction, and then multiple phases are calculated and fused. Compared with the existing methods, the proposed method does not capture useless fringe patterns, and greatly improves the measurement efficiency while guaranteeing satisfactory 3D measurement results.

Laser line triangulation for fast 3D measurements on large gears

The causes of geometrical deviations from the production process and the prediction of application properties, such as noise behavior, wear, or material fatigue, are only possible by having detailed information about the gear geometry. The gold standard for the gear quality inspection is represented by dimensional measurements with a tactile sensor system. As a result for industrial applications, the slow serial measurement leads to the compromise of a random inspection of the gear geometry. For the purpose of a faster and more extensive surface acquisition, a laser line triangulation sensor is investigated providing 1280 points at a line width of 25 mm with up to 200 lines/s. The results at the tooth of a large cylindrical involute gear with a pitch circle diameter of 922 mm and a face width of 246 mm show the qualification for fast three-dimensional measurements of the convex and reflective surface. The detection of the complete profile line at once is possible. It is shown that the measurement deviation of laser line triangulation can be minimized by increasing the dynamic threshold. The measurement deviations amount to ± 8.2 μm and can be attributed to random and systematic errors. Compared to the standard gear inspection, an acceleration factor of 5700 was attained. An optical scanning of the complete tooth flank provides the prerequisite for an identification of surface defects in the form of breakouts and blemish.

Fast three-dimensional measurements for dynamic scenes with shiny surfaces

This paper presents a novel fringe projection technique for fast three-dimensional (3-D) shape measurements of moving highly reflective objects. By combining the standard three-step phase-shifting fringe patterns with a digital speckle image, dynamic 3-D reconstructions of shiny surfaces can be efficiently achieved with only four projected patterns. The phase measurement is performed by three-step phase-shifting algorithm as it uses the theoretical minimum number of fringe patterns for phase-shifting profilometry. To avoid the camera saturation, a dual-camera fringe projection system is built to measure shiny objects from two different directions. The erroneous phase obtained from a saturated pixel is corrected by the phase of its corresponding pixel in the other view which is free from the saturation problem. To achieve high measurement accuracy, the corresponding high light intensity areas in cameras are found by sub-pixel matches of the speckle pattern in either view. Benefited from the trifocal tensor constraint, the corresponding points in the two wrapped phase maps can be directly established, and thus, the difficulties in determining the correct fringe order for the discontinuous or isolated surfaces can be effectively bypassed. Experimental results indicate that the proposed method is able to successfully measure highly reflective surfaces for both stationary and dynamic scenes.

Quality-guided spatial phase unwrapping algorithm for fast three-dimensional measurement

A challenge problem associated with fringe pattern profilometry (FPP) systems is the unwrapping of phase maps resulted from complex object surface shapes. The simple path-following approaches are efficient in terms of computational burden and speed, but they suffer from the errors caused by large steps on the object surface and phase detection noise. Quality-guided flood-fill algorithms are robust and suitable for complex phase maps, but they are very expensive computationally and thus not suitable for fast measurement. In this paper we propose a new quality-guided spatial phase unwrapping algorithm. In the proposed method, the phase map is divided into two types of areas: high quality (HQ) areas corresponding to smooth phase variance and low quality (LQ) ones to rough phase changes. These two types of areas are unwrapped by means of two different approaches. That is, HQ areas are unwrapped by a simple algorithm and LQ ones are recovered by quality-guided flood-fill algorithm. Experiments show that the proposed approach is much faster than the quality-guided flood-fill algorithm in unwrapping complex phase maps, but the accuracy performance is very close to that of the latter.

Adaptive spatiotemporal structured light method for fast three-dimensional measurement

We present a high-speed 3-D spatiotemporal shape measurement technique by means of structured light. Current methods use a constant number of images that do not take into account the available temporal continuity of the measured object. That is, they focus on acquiring and processing as quickly as possible a fixed number of images to solve for the correspondence problem and later obtain the 3-D shape by triangulation. The number of images used imposes the use of some spatial support. The major contribution of our research is a new spatiotemporal scheme that, depending on the object's movement, adaptively uses the maximum number of projected images consistent with the local temporal continuity, therefore solving the correspondence problem with the minimum possible spatial support for each position. This is achieved by the use of a hybrid color pattern composed of an analog sinusoidal periodic code in the red channel and a digital binary spatial code in the blue channel that is cyclically displaced. No subpixel calculation is used and it is possible to implement error correction strategies that make the method fast and reliable, enabling dynamic online 3-D measurement of objects in movement.

Initial observations of fine plasma structures at the flank magnetopause with the complex plasma analyzer SCA-1 onboard the Interball Tail Probe

Abstract. The fast plasma analyzer EU-1 of the SCA-1 complex plasma spectrometer is installed onboard the Interball Tail Probe (Interball-1). It provides fast three-dimensional measurements of the ion distribution function on the low-spin-rate Prognoz satellite (about 2min). The EU-1 ion spectrometer with virtual aperture consists of two detectors with 16 E/Q narrow-angle analyzers and electrostatic scanners. This configuration allows one to measure the ion distribution function in three dimensions (over 15 energy steps in 50 eV/Q–5.0 keV/Q energy range in 64 directions) in 7.5 s, which makes it independent of the slow rotation speed of the satellite. A description of the instrument and its capabilities is given. We present here the preliminary results of measurements of ions for two cases of the dawn low- and mid-latitude magnetopause crossings. The properties of observed ion structures and their tentative explanation are presented. The 12 September 1995 pass at low latitude at about 90° solar-zenith angle on the dawn side of the magnetosphere is considered in more detail. Dispersive ions are seen at the edge of the magnetopause and at the edges of subsequently observed plasma structures. Changes in ion velocity distribution in plasma structures observed after the first magnetopause crossing suggest that what resembles multiple magnetopause crossings may be plasma blobs penetrating the magnetosphere. Observed variations of plasma parameters near magnetopause structures suggest nonstationary reconnection as the most probable mechanism for observed structures.

Initial observations of fine plasma structures at the flank magnetopause with the complex plasma analyzer SCA-1 onboard the Interball Tail Probe

The fast plasma analyzer EU-1 of the SCA-1 complex plasma spectrometer is installed onboard the Interball Tail Probe (Interball-1). It provides fast three-dimensional measurements of the ion distribution function on the low-spin-rate Prognoz satellite (about 2min). The EU-1 ion spectrometer with virtual aperture consists of two detectors with 16 E/Q narrow-angle analyzers and electrostatic scanners. This configuration allows one to measure the ion distribution function in three dimensions (over 15 energy steps in 50 eV/Q–5.0 keV/Q energy range in 64 directions) in 7.5 s, which makes it independent of the slow rotation speed of the satellite. A description of the instrument and its capabilities is given. We present here the preliminary results of measurements of ions for two cases of the dawn low- and mid-latitude magnetopause crossings. The properties of observed ion structures and their tentative explanation are presented. The 12 September 1995 pass at low latitude at about 90° solar-zenith angle on the dawn side of the magnetosphere is considered in more detail. Dispersive ions are seen at the edge of the magnetopause and at the edges of subsequently observed plasma structures. Changes in ion velocity distribution in plasma structures observed after the first magnetopause crossing suggest that what resembles multiple magnetopause crossings may be plasma blobs penetrating the magnetosphere. Observed variations of plasma parameters near magnetopause structures suggest nonstationary reconnection as the most probable mechanism for observed structures.