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Title: | 3-D PROFILING SYSTEM FOR INSPECTION OF FREE STANDING OBJECTS | Authors: | LAM CHIAN PRONG | Issue Date: | 1992 | Citation: | LAM CHIAN PRONG (1992). 3-D PROFILING SYSTEM FOR INSPECTION OF FREE STANDING OBJECTS. ScholarBank@NUS Repository. | Abstract: | Non-contact optical methods in which structured light is projected on the surf ace to be profiled are useful in the measurement of profiles of 3-D surfaces in many industrial applications. Some optical techniques. such as illumination by black and white projection grids, or scanning the surface with a light stripe, are not suitable owing to speed and resolution limitations. Illumination by a periodic sine wave intensity distribution has been shown to satisfy both speed and resolution requirements. Two improved versions of this technique. both of which overcome previous limitations and also achieve higher depth resolution. are described here. The first version, the incremental profiling technique, involves calculating the change in height between two adjacent points on the surf ace from the change in phase angles associated with the rays that image the two points. This is possible by making use of collimated illumination. As a result. there is no dependence on a reference plane for height calculations. With an incremental approach. high accuracy is achieved since errors are kept to a minimum. The second version of the profiling system also uses sine wave illumination for surface profiling. Obtaining the absolute height profile involves a calibration step in which a volume look-up table (LUT) of heights is constructed. By comparing phase maps of objects with the LUT, heights are obtained. With this approach. there is no need for reference planes to be present and high speed profiling can he achieved due to its simplicity. However, since transmission gratings used for generating sine wave patterns are not perfect. both profiling systems require compensation techniques to correct for grating irregularities as well as errors in phase angle measurement. Test results obtained from profiling objects such as adhesive tapes and moulds used in plastic ophthalmic lens making show that the depth resolution achieved by both systems is better than 30 microns. | URI: | https://scholarbank.nus.edu.sg/handle/10635/169993 |
Appears in Collections: | Master's Theses (Restricted) |
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