Superfast multifrequency phase-shifting technique with optimal pulse width modulation

Abstract

The technique of generating sinusoidal fringe patterns by defocusing squared binary structured ones has numerous merits for high-speed three-dimensional (3D) shape measurement. However, it is challenging for this method to realize a multifrequency phase-shifting (MFPS) algorithm because it is difficult to simultaneously generate high-quality sinusoidal fringe patterns with different periods. This paper proposes to realize an MFPS algorithm utilizing an optimal pulse width modulation (OPWM) technique that can selectively eliminate high-order harmonics of squared binary patterns. We successfully develop a 556 Hz system utilizing a three-frequency algorithm for simultaneously measuring multiple objects. Disciplines Computer-Aided Engineering and Design | Mechanical Engineering CommentsThis article is from Optics Express 19 (2011) Abstract:The technique of generating sinusoidal fringe patterns by defocusing squared binary structured ones has numerous merits for high-speed three-dimensional (3D) shape measurement. However, it is challenging for this method to realize a multifrequency phase-shifting (MFPS) algorithm because it is difficult to simultaneously generate high-quality sinusoidal fringe patterns with different periods. This paper proposes to realize an MFPS algorithm utilizing an optimal pulse width modulation (OPWM) technique that can selectively eliminate high-order harmonics of squared binary patterns. We successfully develop a 556 Hz system utilizing a three-frequency algorithm for simultaneously measuring multiple objects.

Absolute three-dimensional shape measurement using coded fringe patterns without phase unwrapping or projector calibration

“…It should be noted that since the fringe patterns are encoded and the projector is not calibrated, the phase quality is very poor. Figure 4(f) shows the unwrapped phase map after removing its gross slope, and the phase was unwrapped by using a multiple-frequency temporal phase unwrapping algorithm [64]. To further demonstrate the differences among these different approaches for smooth spherical surface measurement, we performed further analysis.…”

Comparison between LCOS projector and DLP projector in generating digital sinusoidal fringe patterns

“…From the 3D results, we find that LCOS projector can provide measurement with higher quality than DLP projector (the vertical stripes are less obvious). The temporal phase unwrapping algorithm that we used was introduced in, 23 and the phase-to-height conversion method was introduced in. 24 …”

Toward superfast three-dimensional optical metrology with digital micromirror device platforms

“…Albeit fast, this new system comes with its own challenges and setbacks: (a) the presence of high-frequency harmonics impacts the measurement accuracy; (b) the generated binary pattern has an optimal quality at a certain range, and the region for this range is relatively small thus the result may be a less accurate depth measurement; 29 (c) conventional calibration methods take into account that the projector is in focus yet this new capture method relies upon the projector being defocused; the result is needing a more complex calibration technique; 30 and (d) high-quality fringe patterns at different spatial frequencies are hard to generate simultaneously. 31 To overcome some of these challenges, the 3-D shape measurement field has borrowed pulse width modulation (PWM) techniques from the Power Electronics field with Fujita et al 32 and Yoshizawa and Fijita 33 implementing the PWM technique through hardware, Ayubi et al 34 realizing the sinusoidal pulse width modulation technique, Wang and Zhang 12 realizing the OPWM technique, and Zuo et al 35 further improving such a technique. These techniques each work to improve the phase quality, yet they too still face their own issues: especially if the stripes in the fringe images are either too narrow or too wide.…”