KEYWORDS: Mirrors, Sensors, Motion measurement, Beam splitters, Laser sources, Reflectivity, 3D metrology, Laser systems engineering, Protactinium, Control systems
A measurement system that can measure the six-degree-of-freedom motions of arbitrary objects is proposed. The measurement system utilizes a special mirror looking like a triangular pyramid and having three reflective lateral surfaces, which is to be mounted on the objects of interest. Once a laser beam illuminates the top of the mirror, the mirror reflects and splits the beam into three beams. These reflected beams are detected by three position-sensitive detectors (PSD), respectively. Based on the signal outputs of the PSDs, the three-dimensional position and orientation of the mirror can be computed, which, in turn, determines the three dimensional position and orientation of the object. This paper proposes two options in applying the measurement principle, one of which has its laser beam source fixed in space, and the other controls the translational motion of the laser beam source to track the mirror. In this paper, the principle of the measurement is proved to be valid through theoretical analysis and experiments. And the advantages and disadvantages of both options are discussed.
Optical inspection techniques have been widely adopted in industrial areas since they provide fast and accurate information on product quality, process status, and machine conditions. The technologies include sensing using vision, laser scattering and imaging, x-ray imaging, and other optical sensing, and data processing for classification and recognition problems. Frequently, data processing tasks are very difficult, which is mainly due to the large volume, the complexity, and the noise of the raw data acquired. Artificial neural networks have been proven to be an effective means to cope with the problems difficult to solve or inefficient to solve by convectional methodologies. This paper presents the applications of neural networks in optical inspection tasks. Among the variety of industrial areas, this paper focuses on the inspection tasks involved in printed circuit board manufacturing processes and semiconductor manufacturing processes, which are the most competing industries in the world today. In this paper, the inspection problems are addressed and the optical techniques together with neural networks to solve such problems are reviewed. The application cases to which neural networks are applied are also presented with their effects.
In this research, we propose a 3D volume reconstruction method using x-ray images and present a series of calibration methods to implement it in an x-ray imaging system. In our previous work, we have proposed an advanced 3D reconstruction algorithm based on algebraic reconstruction technique(ART), called a uniform and simultaneous ART(USART). In practice, however, there are two main issues to implement it in a realized x-ray imaging system. The first one is huge computation time and memory required in achieving 3D volume, which is a common limitation in ART methods. The second issue is the problem on system calibration for determining the geometry of the x-ray imaging conditions which are necessary information in ART method. This work addresses solving out these problems : We propose a fast computing model of USART, where spherical voxel elements are employed in computation to reduce computation time and memory. And a calibration method is proposed here to identify the x-ray imaging geometry based on a cone beam projection model. For this purpose, a reference grid pattern is locally displaced to predetermined positions, and then their relative coordinates are determined by analyzing the image variations according to the displacements of the grid pattern. The validity of the proposed 3D reconstruction method is investigated from a series of experiments.
A new measurement method to measure vibrational motions of objects is presented. The original principle is similar to the previous work that utilized a 3-facet mirror to obtain three dimensional positions and orientations of rigid bodies. While the previous work was presented for only stationary objects, in this paper, we newly investigate the feasibility of this method for dynamic applications. The 3-facet mirror that looks like a triangular pyramid having an equilateral cross-sectional shape. The mirror has three lateral reflective surfaces inclined 45 degrees to its bottom surface, and is mounted on the object whose motion is to be measured. As optical components, a He-Ne laser source and three position-sensitive detectors (PSD) are used. The laser beam is emitted from the He-Ne laser source located at the upright position and vertically incident to the top of the 3-facet mirror. The laser beam is reflected from the 3-facet mirror and splits into three sub-beams, each of which is reflected from the three facets and finally arrives at three PSDs, respectively. Since each PSD is a 2-dimensional sensor, we can acquire the information on the three dimensional position and orientation of the 3-facet mirror. From this principle, we can get the motion of any object simply by mounting the 3-facet mirror on the object. In this paper, the measurement principle and a series of experiments are presented. The experiments include measurements of vibrational motions of a piezoelectric actuator that moves the 3-facet mirror in a single axis. The experimental results are compared with those of a laser doppler vibrometer. Through the experiments, the proposed sensor is proven to be an effective means for measuring dynamic motions of objects.
12 In this paper, a new measuring system is proposed which can measure 6-DOF motion of rigid bodies. Its measurement principle is based on detection of laser beam reflected from a specially fabricated mirror whose shape is a triangular pyramid having an equilateral cross-sectional shape. The 3- facet mirror is mounted on the object whose 6-DOF displacement is to be measured. The measurement is operated by a laser-based optical system composed of a 3-facet mirror, a laser source, three position-sensitive detectors (PSD). In the sensor system, three PSDs are located at three corner points of a triangular formation, which is an equilateral triangular formation lying parallel to the reference plane. From this arrangement, 6-DOF displacement of any object can be simply determined. In this paper, we model the relationship between the 6-DOF displacement of the object and the outputs of three PSDs. A series of experiments is performed to demonstrate the effectiveness of the proposed method. The experimental results show that the proposed sensing system can be an effective means of obtaining 3D position and orientation of arbitrary objects.
In this paper, a new measuring system is proposed which can measure the 3D position and orientation of rigid bodies. Its measurement principle is based on detection of laser beam reflected from a specially fabricated mirror that looks like a triangular pyramid having an equilateral cross-sectional shape. The mirror has three lateral reflective surfaces inclined 45 degree(s) to its bottom surface. We call this mirror 3-facet mirror. The 3-facet mirror is mounted on the object whose position and orientation are to be measured. The measurement is operated by a laser-based optical system composed of a 3-facet mirror, a He-Ne laser source, three position-sensitive detectors.
A sensor system for inspecting the layer surface quality in stereolithography process is proposed in this paper. Since stereolithography process builds 3D shape by forming layers repeatedly, it is very important to process each layer of stereolithography process products in some favored conditions: Every layer should be cured uniformly and hardly enough so that the adjacent two layers can stick together to each other. However, in many applications, two kind of defects are frequently found, i.e. void and delamination. Void is cavity inside the built part and delamination is detachment of the bond between two adjacent layers. To inspect such defects, we propose a sensor system which consists of a laser source, a galvanometer scanner, a photo- detector, a few lenses, and a beam splitter. In this sensor system, the laser beam and the field of view of the detector are co-axially positioned and scanned over the product surface by the galvanometer. The reflected light is then detected by the photo-detector. And from the photo-detector signal, the surface condition and quality of the layer being inspected can be estimated. Since stereolithography products are very transparent, the system needs very fine tuning of the system parameters that include the power of laser beam and the sensitivity of the detector, and etc. The experimental results are obtained for products of a variety of shapes and several cases are presented and discussed in detail.
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