Abstract
In shape measurement systems using a grating projection method, the phase analysis of a projected grating provides accurate results. The most popular phase analysis method is the phase shifting method, which requires several images for one shape analysis. Therefore, the object must not move during the measurement. The authors previously proposed a new accurate and high-speed shape measurement method, i.e., the one-pitch phase analysis (OPPA) method, which can determine the phase at every point of a single image of an object with a grating projected onto it. In the OPPA optical system, regardless of the distance of the object from the camera, the one-pitch length (number of pixels) on the imaging surface of the camera sensor is always constant. Therefore, brightness data for one pitch at any point of the image can be easily analyzed to determine phase distribution, or shape. This technology will apply to the measurement of objects in motion, including automobiles, robot arms, products on a conveyor belt, and vibrating objects. This paper describes the principle of the OPPA method and example applications for real-time human motion capture and modal analysis of free vibration of a flat cantilever plate after hammering. The results show the usefulness of the OPPA method.
Highlights
There is a strong demand for high-speed three-dimensional shape measurement; examples include inspection of products on a conveyor belt of a production line, shape measurement performed by moving objects such as automobiles and robot arms, vibration measurement of vibrating objects and soundproofing analysis, and more
In the case of the one-pitch phase analysis (OPPA) method, since the red point data are obtained with only one image, the time resolution is good
The images of the grating lines were recorded with a high-speed camera, and the time-varying images were analyzed according to the OPPA method to obtain the height distribution of the object
Summary
There is a strong demand for high-speed three-dimensional shape measurement; examples include inspection of products on a conveyor belt of a production line, shape measurement performed by moving objects such as automobiles and robot arms, vibration measurement of vibrating objects and soundproofing analysis, and more. Regarding high-speed shape measurement, the author previously proposed the integrated phase-shifting method for obtaining the phase of the projected grating in real-time [1]. The number of pixels to perform Fourier transformation is small, and fast calculation enables real-time processing By combining this method with a high-speed camera and performing batch processing, analysis of high-speed phenomena becomes possible. Utilizing the characteristics of the OPPA method, which allows phase analysis of a grating with a single image, it measures the vibration mode of a flat cantilever plate in combination with a high-speed camera [16]. As a typical application example of the OPPA method, which is the most important feature, that measures all fields of view at high-speed, as a typical example of motion capture capable of real-time all-pixel three-dimensional coordinate measurement and post-processing, vibration distribution measurement using a high-speed camera. The resonance frequencies of 1st to 4th modes are compared with the frequencies obtained by the laser displacement meter, finite element method, and theoretical numerical method
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