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18 October 2002 Three-dimensional surface profile measurement by using liquid crystal grating with triangular intensity distribution patterns
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Proceedings Volume 4902, Optomechatronic Systems III; (2002)
Event: Optomechatronic Systems III, 2002, Stuttgart, Germany
This paper discusses a novel device for measuring 3D-surface profiles of objects using a grating pattern projection method. In particular, the configuration of a grating pattern generating and image processing system for calculating phase distribution from deformed grating images are described. In the grating pattern generating system, the grating is made from a liquid crystal (LC) with a stripe structure pattern which is driven by a pulse width modulation method. The intensity distribution made by the stripe LC grating is set to be triangular. The triangular distribution will be realized using low-bit gray levels. For instance, less than 11 gray levels will produce two patterns which is phase shifted by 1/4cycles; then, projection onto an object can be achieved twice. The deformed grating images posed by the object are detected by a CCD camera in the form of a two-phase image. The image processing system transforms the intensity distribution of the two-phase image into phase distribution which corresponds to the profile of the object. In this operation, linear regions are chosen where the intensities of the two-phase image change linearly by selecting the two-phase image alternately. The one cycle period is formed with four linear regions (quadrant), and the phase width in each quadrant is set to be π/2. Because the intensity distribution in the linear regions varies depending on the profile of the object, the phase distribution in each region is calculated using a simple linear operation using intensity variations or pixel number data.
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Hiroo Fujita, Akira Suguro, and Toru Yoshizawa "Three-dimensional surface profile measurement by using liquid crystal grating with triangular intensity distribution patterns", Proc. SPIE 4902, Optomechatronic Systems III, (18 October 2002);

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