High-quality 3D shape measurement with binarized dual phase-shifting method

<p>ABSTRACT</p> <p>3-D technology is commonplace in today's world. They are used in many dierent aspects</p> <p>of life. Researchers have been keen on 3-D shape measurement and 3-D reconstruction</p> <p>techniques in past decades as a result of inspirations from dierent applications ranging from</p> <p>manufacturing, medicine to entertainment. The techniques can be broadly divided into contact</p> <p>and non-contact techniques. The contact techniques like coordinate measuring machine</p> <p>(CMM) dates way back to 1950s. It has been used extensively in the industries since then.</p> <p>It becomes predominant in industrial inspections owing to its high accuracy in the order of</p> <p>m. As we know that quality control is an important part of modern industries hence the</p> <p>technology is enjoying great popularity. However, the main disadvantage of this method is</p> <p>its slow speeds due to its requirement of point-by-point touch. Also, since this is a contact</p> <p>process, it might deform a soft object while performing measurements.</p> <p>Such limitations led the researchers to explore non-contact measurement technologies</p> <p>(optical metrology techniques). There are a variety of optical techniques developed till now.</p> <p>Some of the well-known technologies include laser scanners, stereo vision, and structured</p> <p>light systems. The main limitation of laser scanners is its limited speed due to its point-by-point</p> <p>or line-by-line scanning process. The stereo vision uses two cameras which take pictures</p> <p>of the object at two dierent angles. Then epipolar geometry is used to determine the 3-D</p> <p>coordinates of points in real-world. Such technology imitates human vision, but it had a</p> <p>few limitations too like the diculty of correspondence detection for uniform or periodic</p> <p>textures. Hence structured light systems were introduced which addresses the aforementioned</p> <p>limitations. There are various techniques developed including 2-D pseudo-random codication, binary codication, N-ary codication and digital fringe projection (DFP). The</p> <p>limitation of 2-D pseudo-random codication technique is its inability to achieve high spatial</p> <p>resolution since any uniquely generated and projected feature requires a span of several</p> <p>projector pixels. The binary codication techniques reduce the requirement of 2-D features</p> <p>to 1-D ones. However, since there are only two intensities, it is dicult to differentiate</p> <p>between the individual pixels within each black or white stripe. The other disadvantage is</p> <p>that n patterns are required to encode 2n pixels, meaning that the measurement speeds will</p> <p>be severely affected if a scene is to be coded with high-resolution. Dierently, DFP uses</p> <p>continuous sinusoidal patterns. The usage of continuous patterns addresses the main disadvantage</p> <p>of binary codication (i.e. the inability of this technique to differentiate between</p> <p>pixels was resolved by using sinusoid patterns). Thus, the spatial resolution is increased up</p> <p>to camera-pixel-level. On the other hand, since the DFP technique used 8-bit sinusoid patterns,</p> <p>the speed of measurement is limited to the maximum refreshing rate of 8-bit images</p> <p>for many video projectors (e.g. 120 Hz). This made it inapplicable for measurements of</p> <p>highly dynamic scenes. In order to overcome this speed limitation, the binary defocussing</p> <p>technique was proposed which uses 1-bit patterns to produce sinusoidal prole by projector</p> <p>defocusing. Although this technique has signicantly boosted the measurement speed up to</p> <p>kHz-level, if the patterns are not properly defocused (nearly focused or overly defocused),</p> <p>increased phase noise or harmonic errors will deteriorate the reconstructed surface quality.</p> <p>In this thesis research, two techniques are proposed to overcome the limitations of both</p> <p>DFP and binary defocusing technique: binarized dual phase shifting (BDPS) technique and</p> <p>Hilbert binarized dual phase shifting technique (HBDPS). Both techniques were able to achieve</p> <p>high-quality 3-D shape measurements even when the projector is not sufficiently defocused.</p> <p>The harmonic error was reduced by 47% by the BDPS method, and 74% by the HBDPS</p> <p>method. Moreover, both methods use binary patterns which preserve the speed advantage of the binary technology, hence it is potentially applicable to simultaneous high-speed and</p> <p>high-accuracy 3D shape measurements.</p>

Name thesis:degree_name

Master of Science

Level thesis:degree_level

thesis

Discipline thesis:degree_discipline

Mechanical Engineering

Department dc:contributor.department

Department of Mechanical Engineering

Year dc:date.issued

2018

Author dc:creator

• Basu, Saptarshi

Advisor dc:contributor.advisor

• Beiwen Li

Language dc:language.iso

en

Identifier

archive/lib.dr.iastate.edu/etd/16706/

OAI identifier oai:identifier

oai:dr.lib.iastate.edu:20.500.12876/30889