Laser triangulation

R. Dorsch, G. Hausler, and J. Herrmaim, Laser Triangulation Fundamental Uncertainty in Distance Measurement, Applied Optics, Vol. 33, No. 7 (1994). 

Mechanical, optical, and electrical systems are mainly used to detect burrs. The stylus method, a mechanical system, can measure burr height, but optical methods can also be applied for this purpose. Among the most important optical systems are microscopes, autofocus methods, laser triangulation, and camera systems. For automatic burr detection in a production process, an electrical measuring method, for example, an inductive sensor system, can be applied. 

A wide range of techniques can be used to capture the surface roughness of a component using noncontact methods. Some of the more common instruments used to captore topographic data include confocal microscopy, laser triangulation, focus detection, and optical interferometry. A relatively recent branch of microscopy known as scanning probe microscopy (SPM) yields over 20 other instruments which are defined based on what probe-surface interaction they are monitoring. The SPM family is described in more detail elsewhere in this book and will be briefly mentioned in this article. 

The deflection is measured by using a laser triangulation and parallax method. The laser sensors are responsible for measuring the distance to the pavement surface, and the deflection is calculated from the difference between the slope of the beam and the slope of the pavement at the initial point and after the device moves to the next point. The device is provided with a data acquisition system used for data collection, storage and analysis (Elseifi et al. 2012). 

The deflection is measured by four laser triangulation sensors one is placed between the dual tyres and the other three are placed in front of the back axle. The laser between the dual tyres measures the pavement profile (maximum deflection) under axle load and the other three, spaced every 2.44 mm (8 ft), measure the unloaded pavement profile. The three lasers are mounted at approximately 1.1 m (3.6 ft) above the pavement surface into the truck body in a temperature-controlled enclosure (see Figure 16.53a). Two additional sensors are placed in front of the wheels to measure a secondary pavement deflection (Elseifi et al. 2012). 

Figure 2 shows results from an optical profilometer (ProScan 2000 made by Scantron Industrial Products, Taunton, UK) for an abraded steel surface. In this instrument, laser triangulation enables fine displacements of the sample in the X, Y and Z directions to be recorded. Figure 2(a) shows a plan representation of the area scanned. Fig. 2(b) a three-dimensional representation. Surface profiles along the two lines indicated in Fig. 2(a) are given in Figs. 2(c) and (d). 

Laser triangulation method is a technique which uses the law of sine to find the coordinates and distance of an unknown point by forming a triangle with it and two known reference points [2]. In Fig. 12.8, A and B are the two reference locations given by the camera and the sensor locations, and C is the location of the object point of interest. The distance from A to B can be measured as c, and the angles a and P can also be measured. Following the law of sine the distances a and b can be calculated. The coordinates of A and B are known, then the coordinate of C can also be calculated. The same principle is employed in various other scaiming methods. 

Laser triangulators Relative simplicity Performance generally independent of ambient light High data acquisition rate Safety constraint associated with the use of lasts source Limited range and measurement volume Missing data in correspondence with occlusions and shadows Cost... 

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