Thursday, November 8, 2018

3D Scanning Technology 

2.1. An Overview of 3D Scanning Technology 3D scanning technologies are potential tools for increasing productivity, while at the same time securing quality in product development. Generally, 3D scanning can be of big help in resolving the issues concerning ways of creating 3D CAD data for objects that do not have pre-existing computer models. Creating good digital representations is often of crucial importance when using today’s manufacturing methods. Today 3D scanners are available to digitize objects from microscopic to large constructions in size. Data points are captured with speeds ranging from a few points per second to more than a million points per second. There are handheld manual devices available as well as large size automatic scanning equipment [1].

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There are mainly two methods for obtaining coordinates of an object’s geometrical shape. The first one is mechanical method which uses mechanical arms where the object is fixed on a table; the coordinates of the points picked by the inspector by means of touch-probes are transferred to the computer. With this system, measurement of formed and large surfaces may take hours or even days depending on the details of the object and accuracy of the measurement required. Accuracy levels up to 1 μm can be achieved by using this method. This level of sensitivity depends on the experience of the inspector and type of the equipment used. The second one is non-contacting scanning methods which can be classified in to three main categories optical, acoustic and magnetic. 

Optical scanning systems based on techniques such as laser scanning, fringe projection, photogrammetry etc. are being applied successfully for the 3D measurement and virtual reconstruction of object surfaces in many areas. Fringe projection scanning systems generally work with white structured light where the light pattern is projected on the object’s surface while one or two cameras record the reflected light while laser scanning systems can obtain data by sending laser light onto the object and processing the data obtained from the returning light [7–9]. The advantages of these scanners are that they are more portable compared to contact systems and their sensitivity levels are partially independent of the inspector. 

Optical scanning systems, e.g. laser or fringe projection can obtain a large amount of point data in a short period of time and the accuracy of laser systems vary typically from 1 μm up to 20 μm, whereas fringe projection systems have the capability of 10 μm up to 60 μm. Since the accuracy of the non contact systems are continually improving, they are now widely adopted for many applications in the industry [10]. 

Optical technology is generally preferred method because it gives a greater flexibility in the digitization of surfaces and provides higher resolution and accuracy when compared to mechanical technology [11,12]. Because of speed of measurement and greater flexibility, there is an increasing demand for optical scanning systems [13–15]. The advantage of contacting devices is that they do not depend on the color and reflective characteristics of the surfaces to be scanned which might be the case with optical scanners. 

2.2. The 3D scanner used in this study The Opto-TOP HE Breuckmann 3D optical scanning system used in this study utilizes 3D white light fringe projection technology to provide a fast and extensive capture of complex surfaces. This allows the simultaneous measurement of a large portion of the object in a single view. Over a million points can be captured in each image. Each of these scanned images takes around one second (Figure 2).

The equipment is portable and does not require the use of a mechanical positioning device. The scanner is designed to allow a quick change of lenses. The projector which is connected to the camera by means of a carbon fiber bar, projects the fringe patterns in rapid sequences providing a flexible system capable of measuring very small or very large objects. A carbon fiber base structure ensures optimum mechanical and thermal stability of the sensor. Calibration may be performed by the user within minutes, ensuring a high degree of accuracy. Featuring 1.4 mega pixels (optionally 6.6 mega pixels) and a digital zoom, the digital camera provides maximum resolution