Pattern Projection Method Research Articles

Dimensional Measurement by Projection of Locally Adapted Patterns

High‐strength structure components can be obtained by using an advantageously designed geometry. Examples are bar frame structures or organically shaped parts. Such components are challenging to manufacture due to their complex shape. This motivates the design of a new system for the 100% quality control of the geometric properties of such structures. Firstly, different measurement approaches and their usability for the measurement of high‐strength structure components are discussed. Then an optimized solution is suggested. A pattern projection method is introduced where the patterns adapt locally to the measured surface. This technique takes care of the special properties of high‐strength structure components within the production process. The paper presents a method how to obtain a measuring speed that can cope with a high production frequency without breaking the flow of the parts. Furthermore, measuring can take place in an industrial environment because it is relatively tolerant to movements of a component being measured. Therefore, the measuring procedure is divided into two steps. Within the adaptation‐step the luminescence and the resolution of the projected pattern is adapted to the object to be measured. The actual picture is taken and calculated in a second step in order to be robust to vibrations. The result of this measuring procedure is an optimized point cloud of several million points. The paper concludes with a description of the data processing procedures necessary in order to evaluate the correctness of the measured structure.

Measurement of free surface of liquid metal lithium jet for IFMIF target

Lithium (Li) flow experiment was conducted for a Li target of International Fusion Materials Irradiation Facility (IFMIF). In the experiment, Li plane jet of 10 mm in depth and 70 mm in width formed by a two contractions nozzle was tested in the velocity range of less than 15 m/s. In the present report, wave patterns (called as surface wakes) on the Li flow were measured by Pattern Projection Method. This is an image measurement of non-contact and three dimensions. The projected patterns, which were stripes in this study, were observed to be deformed according to the surface up-and-down. Three-dimensional surface shape could be obtained by analyzing the deformed patterns. By the method, surface wakes were successfully measured. The results were compared with a theoretical study and showed good agreement.

Effect of elastic compression stockings on oedema prevention in healthy controls evaluated by a three‐dimensional measurement system

The degree of oedema may differ at various sites on the leg. This study evaluated the degree of oedema at the calf, ankle and foot using a three-dimensional measurement system. By three-dimensional measurement system using the grid pattern projection method, the effects of four different types of elastic compression stockings on oedema prevention were compared in healthy subjects. Without stockings, a significant increase in the circumference and volume was seen at the ankle and foot in the evening compared with morning values. The average increase in circumference was greater at the foot than that at the ankle. A significant increase in circumference and volume in the evening after a day without stockings disappeared when elastic compression stockings were worn during the day. The coefficient of variation was greater for measurements at the foot than for those at the calf and ankle. Oedema develops easily in order of the foot, the ankle and the calf in healthy populations. Elastic stockings, even with a pressure as low as 8 mmHg, are effective on oedema prevention. In measurement at the foot, further developments are necessary to improve this system.

Discrimination of Metallic and Colored Surface States by Optical Pattern Projection Method

In the optical pattern projection method called by the authors for surface roughness measurement, the roughness is detected from the qualities of the output image, such as contrast, formed by an imaging system including a target surface. We will report the relation between the roughness and contrasts for metallic surfaces and the colored plastics in the range of Ra of about 0.1 �m and below, using a video camera. For the colored plastic surfaces, the authors explain that the sensitivity for gloss depends on the contrast of the formed image under additional illumination by other light sources.

カメラ用焦点合せセンサを用いた顕微鏡用自動焦点合せ検出系の開発

An automatic focus detection system for microscopes using the stripe pattern projection method has been developed in this study. Although there are various methods that can be used in the automatic focus detection units of microscopes, the stripe pattern projection method is widely used because automatic focusing can be achieved even on a mirror or rough surface. In the conventional equipment with automatic focusing, the stripe pattern projection unit is set in the illumination unit, and the optical unit for focal position detection is set elsewhere. Therefore, the designer had to develop the automatic focus detection system, when the new equipment was developed. Size and cost reduction for the system are attempted by setting both the stripe pattern projection unit and the optical unit for focal position detection in the commercially available universal illumination unit. An automatic focus detection sensor used for a commercially available camera is adopted and a cylindrical lens is set in front of the sensor. The illuminance of the real image plane is increased and the detection time of the sensor is reduced by one-fifth. As a result of using the objective lens of 0.65 numerical aperture and 40× magnification, the automatic focusing accuracies of ±0.5μm and ±1.0μm have been achieved for samples with a mirror and rough surface, respectively.

A tracking fringe method for measuring the shape and position of a swimming fish

A novel tracking fringe projection method is developed to simultaneously measure variations in both the position and the shape of a moving object. The method combines a commonly used fringe pattern projection method and a laser tracking technique into one optical system. In this new system, two tracking fringes are used to track the object, while one fringe is used for reference fringe. The order of conventional fringes can be determined by measuring the angle of reference fringe. The method enables us to simultaneously measure the position and shape of a moving object, such as a swimming fish.

3-D shape measurement by self-referenced pattern projection method

A shape measurement system using time sequential space encoding with multi-gray scale patterns has been developed [1–3]. However, some objects that have colored surfaces and unevenness of reflectivity could not be measured using these methods. Therefore the reference projection images are added to the system. By the reference projection method, the colored objects could be measured by comparing observed space encoding images with the reference images. However the number of projections increased. In this paper, the self-referenced pattern projection method is proposed. This method reduces the number of projections and it is able to measure objects under an illuminated environment and to measure colored objects. Using this system, the measuring space is encoded into n! sub-spaces with n projections. If there is a commercial projector to encode space with high pixel-resolution and brightness in the near future. it would greatly benefit this method to be able to divide the measuring space into the most sub-spaces when it has the least pattern projections.

Simultaneous measurement of the position and shape of a swimming fish by combining a fringe pattern projection method with a laser scanning technique

A novel scanning fringe projection method is developed to simultaneously measure the variations in both position and shape of a swimming fish. This method combines the commonly used fringe pattern projection method and a laser scanning technique into one optical system. In this new system, one or more reference fringes are generated by an acousto-optic deflector, and laser triangulation is used to determine the order of the reference fringe. These reference fringes are then combined with the conventional fringe pattern, and the fringe order is determined from the reference fringes. The method enables us to simultaneously measure the position and shape of a moving object. We successfully apply the method to a swimming fish.

映像情報センシングのための処理技術 マルチスペクトル光投影レンジファインダによる形状計測

The range finder proposed in this paper is based on color pattern projection method so that it can measure small objects. The color pattern consists of stripes, whose color is continuously changed in such a way that hue changes linearly. The advantages of the system are that it requires only commonly available optical system, it uses a low-cost commercial CCD camera and a LCD projector, and it can measure the whole field of view simultaneously.

A three-level checkerboard pattern (TCP) projection method for curved surface measurement

This paper describes a new pattern projection method by which the 3D range and shape of a curved surface can be measured simply, rapidly and precisely. A three-level checkerboard pattern (TCP) is projected onto a curved surface, and the projection pattern on the surface is observed by a well-defined camera. The spatial feature codes of the TCP are used to match an observed pattern image to the slide mask pattern. This method provides high spatial resolution and makes it possible to take highly accurate measurements of stable and moving object surfaces. A new approach for rapid and precise calibration of the slide projector is also presented. In our experiments using real objects about 0.8 m from the camera, the surface measurement error was 0.5–1 mm in S.D. and 2 mm maximum, which corresponds to a relative accuracy of about 0.2%. This result coincides well with the theoretical prediction from image digitizing errors. The semi-automatic procedure for surface measurement together with camera and projector calibrations can be completed within 40 s, which includes CPU time of about 5 s in VAX11/780 (1 MIPS)