Research on a Handheld 3D Laser Scanning System for Measuring Large-Sized Objects.

Xiaomin Wang,Liqin Zhou,Zexiao Xie,Kun Wang

doi:10.3390/s18103567

Abstract

A handheld 3D laser scanning system is proposed for measuring large-sized objects on site. This system is mainly composed of two CCD cameras and a line laser projector, in which the two CCD cameras constitute a binocular stereo vision system to locate the scanner’s position in the fixed workpiece coordinate system online, meanwhile the left CCD camera and the laser line projector constitute a structured light system to get the laser lines modulated by the workpiece features. The marked points and laser line are both obtained in the coordinate system of the left camera in each moment. To get the workpiece outline, the handheld scanner’s position is evaluated online by matching up the marked points got by the binocular stereo vision system and those in the workpiece coordinate system measured by a TRITOP system beforehand; then the laser line with workpiece’s features got at this moment is transformed into the fixed workpiece coordinate system. Finally, the 3D information composed by the laser lines can be reconstructed in the workpiece coordinate system. A ball arm with two standard balls, which is placed on a glass plate with many marked points randomly stuck on, is measured to test the system accuracy. The distance errors between the two balls are within ±0.05 mm, the radius errors of the two balls are all within ±0.04 mm, the distance errors from the scatter points to the fitted sphere are distributed evenly, within ±0.25 mm, without accumulated errors. Measurement results of two typical workpieces show that the system can measure large-sized objects completely with acceptable accuracy and have the advantage of avoiding some deficiencies, such as sheltering and limited measuring range.

Highlights

3D contour measurement has been widely applied in many fields, such as heritage conservation, aerospace, automobile manufacturing and so forth
The 3D contour measurement based on optics [1,2,3,4,5,6] has been known as one of the most significant technologies with many advantages such as high accuracy, high efficiency, non-contact, which includes light coding, moire topography, structured light technique and space-time stereo vision and so forth
To achieve an appropriate measuring range, the distance L from the intersection point of two optical axes N to the line between the optical points of the two cameras is designed as L = 300 mm and the angle of the two optical axes is designed as 38.6◦ considering two factors: (1) at least 5 same marked points can be synchronously captured to a large extent by the two cameras for the binocular stereo matching up; (2) the depth of field should be kept within a suitable range

Summary

Introduction

3D contour measurement has been widely applied in many fields, such as heritage conservation, aerospace, automobile manufacturing and so forth. The coordinate measuring machine (CMM) and the articulated arm measurement system (AAMS) are the frequent-used 3D measurement devices. AAMS is portable and flexible, which could measure an object on site but its largest measurement scale is generally within several meters. The 3D contour measurement based on optics [1,2,3,4,5,6] has been known as one of the most significant technologies with many advantages such as high accuracy, high efficiency, non-contact, which includes light coding, moire topography, structured light technique and space-time stereo vision and so forth. Phase measurement profilometry (PMP) [9] can measure the contour of a moving object in real-time but it fails to find the optimum

Results

Discussion

Conclusion