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The technology and application of 3D scanning

How three-dimensional scanning works and its value to product manufacturers.

Interest in three-dimensional (3D) scanning technologies has grown over recent years. This is due in part to advances in technology that have allowed scanners to become smaller, more portable and more powerful, as well as the increasing range of different applications envisaged across multiple industries.

A variety of 3D scanners is available, which utilise either laser technology or structured light to create a 3D file of a target object. Certain scanners are better suited to particular applications. For example, some scanners are ideal for digitising small objects at a short range, while others are better suited for digitising large objects at a mid-to-long range. Scanners vary in resolution and accuracy, and may use their own proprietary software and file types or may involve formats that are more freely interchangeable with industry-standard computer aided design (CAD) programs.

Most 3D scanners are laser-based and use a process called ‘trigonometric’ triangulation. This involves two or more lasers being shone at a point on an object, after which the angles of the reflected beams are recorded by one or more sensors (figure 1). When repeated across millions of points, the distances between the scanner and these points on the object and the directions of the beams as they bounce back build up into a 3D map of the surface of a scanned object. Once the 3D scan is complete, it can be assessed and measurements such as distance, volume, area and angle can be taken from it.

There are several advantages to the use of 3D scanners over other measurement tools. Because they use lasers rather than visible light, 3D scanners easily handle objects with shiny or dark surfaces that might otherwise be difficult to illuminate and digitise. Digitising an object in three dimensions no longer requires the use of a large machine fixed to a single laboratory or workshop location – many 3D scanners are hand-held or otherwise portable. 3D laser scanners are less sensitive to fluctuations or extremes in light levels than other optical measurement tools. Scanning equipment is usually quick and simple to use, and has a low running cost.

Figure 1: A number of laser beams can be used to collect 3D scan data

Applications for 3D scanning

3D scanning is becoming a widely-used tool in the footwear industry and has many applications in the manufacturing process. Scanners are utilised at the conceptualising stage of the footwear design process, where designers can use a scan of an existing item of footwear as the starting point for creating illustrations or renders of new designs. Likewise, having obtained a good quality scan of a sample of footwear and imported it into CAD software, its shape and dimensions can be adjusted to visualise it in a number of different sizes. The use of 3D scanning in this way helps to shorten the design process, as new features can be designed to perfectly fit existing footwear designs without the need for multiple design iterations.

Designers can also use 3D scanning to catalogue ‘legacy’ footwear designs, thus turning them into editable 3D models that can then be updated or remodelled. This blending of craft with science – of analogue processes with digital technology – gives designers and manufacturers a degree of previously unattainable creative freedom.

Tooling (which had been hand-made or hand-finished), can be scanned to preserve its exact dimensions and to capture the subtle details of previous manual modifications. This ensures that future tooling can be made to the same standard and, subsequently, that components made using this tooling are consistent. Likewise, scanning a component made using this tooling will allow its shape and dimensions to be compared to the 3D model of the tool, aiding quality control and inspection. It also permits engineers to monitor any deterioration of the tool or mould over time, and to predict any tool failure.

The effectiveness of the footwear setting process can also be assessed by comparing a 3D scan of the finished footwear to a scan of the last on which the footwear was made, to highlight any shrinkage or sagging of the material after setting.

3D scanning at SATRA

‚Äč Figure 2: The basic elements of SATRA's hand-held 3D scanner

SATRA has an advanced hand-held 3D scanner as part of a suite of 3D imaging and modelling tools (see figure 2). This equipment is capable of scanning to an accuracy of 0.03 mm, and provides highly detailed 3D scans of even complex objects in a matter of minutes.

After a brief calibration procedure, small reflective circular stickers are placed on the object to be scanned, which serve as reference points for the multiple measurements that the scanner will take during the scanning procedure. There is no need to clamp either the scanner or the target object in place, as the stickers enable the software to track the object’s position and location in relation to the scanner, even when the object is moved or rotated. A wide range of target object sizes can be scanned – from small footwear components up to large instrument panels or pieces of equipment.

Figure 3: A 'point cloud' (or 'mesh'), which defines the geometry of a 3D shape

One of the most useful applications for the scanner is its ability to export a scanned object as a ‘polysurface’ (consisting of two or more surfaces joined together), rather than a ‘point cloud’ (a set of data points in an X, Y and Z coordinate system). Three- dimensional scans are usually in the form of a point cloud or mesh – a series of billions of points or locations that when viewed as a whole resemble a mesh, and which define the geometry of a 3D shape. However, this mesh (figure 3) can be quite difficult to manipulate in CAD software.

A designer wanting to turn this mesh into an editable 3D surface might have to spend hours rebuilding it and adjusting details before it can be manipulated. By contrast, the software associated with SATRA’s 3D scanner can do this automatically, to create a surface over a mesh. This surface can then be exported into other programs, where it can be edited and used as the starting point for further modelling.

Such a capability greatly accelerates the process of reverse engineering or prototyping, and files created in this way can be quickly sent to a 3D printer for rapid printing.

Quality control and inspection are important aspects of the testing work carried out at SATRA, and the 3D scanner is being used for several applications relating to quality and conformity.

Once an object has been scanned, software associated with the scanner allows for detailed measurements to be taken from the scan. For instance, the distance or angle between points, the circumference or volume of a particular section or surface area can all be calculated with great accuracy. This means that the surface of a scanned object can be finely scrutinised for such details as radius and curvature, as well as any isolated dips and peaks on the surface. This is especially useful when inspecting equipment used for impact testing, such as test anvils and sample holders.

Equipment like this must obviously conform to very specific dimensional requirements and specifications, and needs to be checked regularly to ensure that even after repeated impacts it has not been dented or deformed in such a way that it no longer meets the requirements.

Using the 3D scanner, an older scan of the equipment can be compared to a scan taken on the day of inspection. These can be aligned or overlaid using software, to produce a colour map to highlight any dimensional differences between the two objects.

A similar process can also be carried out to compare the scan of a piece of equipment currently in use to the CAD model on which the equipment is based. If no such CAD model exists, one can be modelled, using the dimensions given in the appropriate standard.

SATRA’s scanner has been used to scan the ‘anthropomorphic’ (people-shaped) dummies used in fall-arrest testing, to establish whether they have sustained damage or deformities and to check that they still meet the specifications. An overlay of the two scans quickly highlights the exact location of any damage, allowing repairs to be made and extending the service life of the dummy.

In the field of research, where an enormous variety of products are tested, the scanner has been helpful in assessing how accurate an item’s production process is, by comparing a number of products from the same batch. Multiple scans can be analysed to look for such irregularities as warping of the material or degradation, which can be made more obvious by taking surface area measurements.

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