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Technical Section Phone: 516-328-3970 www.technocnc.com 17 scanners determine the relative distance from the scanner to the surface. This is usually the Z coordinate. The machine positioning the scanner usually supplies the travel to collect the X and Y coordinates. Another subcategory of noncontact type of scanner is structured light types. These scanners work with a specific varying intensity of light and multiple images of the object from known positions. A mathematical algorithm is then used to create a surface with the measured amount of reflectivity. This basically recreates the 3D visible surface of the object. The speed and accuracy of the scanner varies greatly depending on the model and drive system of the CNC machine. In addition, the scanners share the same attributes from one manufacturer to another. Types of Laser Scanners There  are  a  number  of  different  types  of  laser displacement scanners, each offering advantages in certain applications. Interferometry is probably the most accurate but requires  the  greatest  precision  in  the  equipment and the surfaces to be measured. Triangulation looks at the angle of refl ection off the target surface and is generally very inexpensive but is limited by the inclination angle of the surface to be measured. Steeper angles produce very erratic results. Dynamic  focusing  uses  a  system  to  adjust  the focus of a camera to determine the distance. This method requires moving parts and is thus limited by its speed and cost of equipment. The  Conoscope  method,  used  by  the  Techno laser scanner, uses polarized light and holographic methods to determine the distance to the refl ecting surface. Because only a single beam is used, the angle of the surface does not affect the results and even measurements in “deep holes” can be taken. What to Scan and What to Scan with The different types of scanners are typically suited for different types of applications. The contact process is usually more  time  consuming  but  can  also  be  more  effi cient  for smooth engineered types of surfaces such as the fender of  a  car.  Because  of  the  contact,  specific  points  can  be digitized to get the features of the surface, such as an edge or cusp or hole. This allows for the features to be quickly and accurately recognized and digitized. Another advantage of contact scanner arms is that the surface generation is a more simple process. In most cases, the points being collected are directly used for creating splines or features in the software. There is generally little filtering that is required. The noncontact types of scanners are usually faster at collecting large numbers of data points but they typically are designed to gather points over a grid surface with a specific  spacing  along  the  X  and  Y  axes.  This  process collects what is called a “point cloud” with a greater number of XYZ coordinate pairs. This approach is better suited for collecting data off very detailed surfaces which might be found on hand-carved objects such as furniture or coins. The drawback to this approach is that the features such as the cusps, edges and sharp corners might not be captured completely in the grid being used to collect the data unless the grid is relatively fi ne and then a great number of points have to be collected. Collecting vast amounts of data often creates processing problems. Remember that the number of data points increases geometrically as the grid gets fi ner.