The presented book chapter provides an overview and detailed description about actual used laser scanner systems. It explains and compares the mainly used coordinate measurement methods, like Time-of-flight, Phasing and Triangulation and Imaging. A Technical Vision System, developed by the engineering institute at the Autonomous University Baja California (UABC) is presented. The mostly used mechanical principles to position a laser beam in a field of view are described and which mechanical actuators are applied. The reflected laser beam gets measured by light sensors or image sensors, which are explained and some principle measuring circuits are provided. The received measuring data gets post-processed by different algorithm or principles, which close the chapter.
TopIntroduction
Laser scanners are optical devices, which as the rule uses lasers to obtain certain information about surface topography, superficial coordinates or other characteristics, by physical sensing of light spot displacement across a surface relief. In opposition to stylus instruments, laser scanners’ measuring is contactless and thereby have higher scanning speeds.
One main task of laser scanners is receiving 3D spatial coordinates of the scanned surface, which is mainly realized by optical methods in a very large amount of applications. For example, (Wendt, Franke, & Härtig, 2012) describes a various concepts of large 3D structure measurement using four portable high-accurate tracking laser interferometers. Each of these interferometers tracks a single moving retroreflector and sends their data to a central control, which calculates the 3D point coordinate using the Pythagorean Theorem in space. An optical scanning tomography for time-resolved measurements of kinematic fields in the volume of structures is presented in (Morandi, Breman, Doumalin, Germaneau, & Dupre, 2014). This tomography uses a plane laser beam, which illuminates a transparent probe in layers and the scattered light of each layer is recorded then with a single camera. Measuring spatial coordinates using a non-diffracting beam is presented in (Ma, Zhao, & Fan, 2013). It is used a combined system with a laser beam and an optical system to measure the attitude angle of a probe. Another application of spatial coordinate measurement can be found in (Colombo, Colosimo, & Previtali, 2013), where laser welding is used within the automotive industry. The main objective is to online-monitor the welding conditions, in order to guarantee a constant product quality.
Laser scanning systems, as remote sensing technology are also known as light detection and ranging (Lidar) systems, are widely used in many areas, as well as in mobile robot navigation. (Kumar, McElhinney, Lewis, & McCarthy, 2013) uses an algorithm and terrestrial mobile Lidar data, to compute the left and right road edge of a route corridor. In (Hiremath, van der Heijden, van Evert, Stein, & ter Braak, 2014) a mobile robot is equipped with a Lidar-system, operating with time-of-flight principle, and which navigates in a field of maize. Lidar systems are also used in airborne laser scanners to receive geo-referenced points from terrain. In (Alexander, Erenskjold Moeslund, Klith Bøcher, Arge, & Svenning, 2013) an airborne laser scanner is used to estimate understory light conditions of vegetation plots in semi-open habitants and forest ecosystems.
Another area, where laser scanners are used to measure 3D spatial coordinates can be found in confocal microscopy. (Hong-Seok & Chintal, 2015) are presenting a high speed 3D dental intra oral scanner, which uses a confocal laser scanning microscope (CLSM) to achieve a high accurate 3D image of the oral cavity. A CLSM uses a focused laser beam to point-wise scan the surface of an examined object. Due to the focused laser beam, a CLSM can only measure images one depth level at a time.
Laser scanners can be categorized by design principles, measurement methods and used measuring signals. Design principles describe the characteristics by which a laser scanner is composed and define its construction. Three different main design principles can be determined for laser scanners:
Hand-held laser scanners are small and compact devices, which increasingly find applications, where flexibility and mobility play a central role for coordinate determination. In opposite to stationary laser scanners, they have a shorter scanning range. Hand-held laser scanners are often used as barcode readers or hand-held coordinate measurement device. Figure 1 shows an image of a barcode reader brand Motorola® and Figure 2 an image of a hand-held scanner brand Faro®.
Figure 1. Motorola LI4278 barcode reader