Two-directional scanning method for reducing the shadow effects in laser triangulation

Abstract

A two-directional scanning method has been developed to reduce the shadow effects in laser triangulation probes. This method, which we call 2DS, uses an acousto-optic deflector (AOD) as a scanner to allow a diffracted beam to scan an object from two directions, and a position sensor to detect the shift of a spot projected from these two directions alternately by a time-sharing technique. The shadow effects are thereby reduced by this two-direction projection. First we determined the accuracy of the 2DS method by measuring the displacement of a plastic plate along the x- and y-axes and then comparing the results with those obtained using a linear gauge. Then we confirmed the capability of the method by using it to measure the cross sectional shape of a half-ball button, and then comparing the results with those obtained using a conventional one-directional scanning laser triangulation method. A relative uncertainty of 0.8% was obtained.

<title>Examining laser triangulation system performance using a software simulation</title>

“…The research by Zeng was based on a laser triangulation system that was unique in many ways [21]. A scanning laser beam was used instead ofa plane of light.…”

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On-Machine Optical Probe Based on Discrete Rotational Symmetric Triangulation

“…Edmond Wai Yan So et al successively proposed an online duallaser triangulation system and its improved version for fast building models in [27,28]. A similar method proposed by Lijiang Zeng et al used an acoustooptic deflector (AOD) as a scanner to allow a diffracted beam to scan an object from two directions and the shadow effects can also be mitigated [29]. A dual-laser system does to some degree mitigate the occlusion problem compared with single laser triangulation system, while it still does not completely solve it.…”

“…Images before and after noise reduction. (a) Center-of-gravity method (b) Peak subpixel method Extracting result of the two methods.Substituting it into(29), the relational expression of the object point depth can be obtained as Performance of the Optical Probe. In this section, performance of the optics in several aspects was investigated and values of several essential items such as repeatability accuracy, resolution, linearity, and sensitivity of the optics are provided.…”

Comparison of two-­dimensional phase retrieval methods from single interference fringe pattern

“…Three dimensional shape measurement can be carried out by using noncontact optical profilometry, including laser scanning methods [1], stereovision techniques [2], and structured-light-based methods [3][4]. Due to its whole-field nature, high speed, and high accuracy, structured-light-based methods have been widely used in optical 3-D profilometry [5].…”