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3D Scanning

What Are 3D Scanners?

There are many different devices that can be called 3D scanners. Any device that measures the physical world using lasers lights or x-rays and generates dense 'point clouds' or polygon meshes can be considered a 3D scanner. They go by many names, including 3D digitizers, laser scanners, white light or structured light scanners, industrial CT(Computed Tomography), LIDAR(Laser Imaging Detection and Ranging) and DSSP(Digital Shape Sampling & Processing). The common uniting factor of all these devices is that they capture the geometry of physical objects with hundreds of thousands or millions of measurements.

 

3D Scanning is a non-contact, non-destructive process of digitally capturing the shape of physical objects with equipment that uses a laser or light to measure the distance between the scanner and the object. In other words, 3D laser scanning is a way to capture a physical object’s exact size and shape into the computer world as a digital 3-dimensional representation.

 

3D laser scanners measure fine details and capture free-form shapes to quickly generate highly accurate point clouds. 3D laser scanning is ideally suited to the measurement and inspection of contoured surfaces and complex geometries which require massive amounts of data for their accurate description and where doing this is impractical with the use of traditional measurement methods or a touch probe.

3D scanning can capture data of very small objects all the way up to full size aircraft and buildings. It can be used for reverse engineering, computer-aided inspection, or simply documenting the shape for future use.

 

Structured Light (White or Blue Light) 3D Scanners

Structured light 3D scanner projects a series of patterns onto the object. By examining the edges of each line in the pattern, they calculate the distance from the scanner to the object’s surface and by using trigonometric triangulation. The distance between the laser source and the sensor is known very precisely, as well as the angle between the laser and the sensor. As the laser light reflects off the scanned object, the system can discern what angle it is returning to the sensor at, and therefore the distance from the laser source to the object’s surface. Thus, with the digital information it can construct a 3D scan of the object.

 

Conceptually, 3D scanning is not unlike 2D flatbed scanning. The difference is that a third level of data, depth is recorded. Where scanning your object once will record a frame including depth, multiple scans from differing angles will build a full 3D model of your subject.

 

 

Process

 

An object that is to be scanned is placed on the bed of the digitizer. The structured light will be projected above the surface of the object. At the same time, 2 sensor cameras continuously record the changing distance and shape of the projected line in three dimensions (XYZ) as it sweeps along the object.

 

The shape of the object appears as millions of points called a “point cloud” on the computer monitor as the scanner 'moves around' capturing the entire surface shape of the object. The process is very fast, gathering up to 750,000 points per second and very precise (to ±.0005").

 

After the huge point cloud data files are created, they are registered and merged into one three-dimensional representation of the object and post-processed with various software packages like Geomagic or Rapidform. They are then translated to a suitable file type (.STL, IGES, STEP)  for a specific applications like 3D printing or CAD software.

 

3D scanning is the fastest, most accurate, and automated way to acquire 3D digital data for reverse engineering. Again, using specialized software, the point cloud data is used to create a 3D CAD model of the part’s geometry. The CAD model enables the precise reproduction of the scanned object, or the object can be modified in the CAD model to correct imperfections.

 

If the data is to be used for inspection, the scanned object can be compared to the designer’s CAD nominal data. The result of this comparison process is delivered in the form of a “color map deviation report,” in PDF format, which pictorially describes the differences between the scan data and the CAD data.

 

3D Scanning Procedure

 

There is often the wrong assumption that 3D scanning is a fully automated “magical” process.Place the part in front of the 3D scanner, press a button, and out comes a digital 3D model. The reality of building a complete digital model of an object from all angles is a process of scanning multiple sides of an object, aligning the scans, and merging them to create a polygon mesh. From here the data can be used to do either 3D modeling or measurement applications.

 

3D Scanning Basic Work Flow

  • Part Mounting and Part Preparation

  • Reference Points

  • 3D Scanning

  • Processing Scanned Data

 

1a. Part Mounting

This the most import stage of the scanning process. The amount of work you prepare upfront will determine the quality of scan and the amount of time you are going to spend for the scan. Any bad decisions here will become ten times worse as you progress.

 

Plan and position of the object to be scan so that the scanner can capture as much information of it as possible. Use fixtures to help you position and secure your object to be scanned. It could be a sophisticated commercially made fixture system or a quick ‘handmade’ object that is good enough for your needs.

 

1b. Part Preparation

What are the restrictions for 3D scanning?

 

If a scan object does not provide sufficient contrast (e.g. dark or transparent) such that the cameras cannot well record the projected fringe pattern, you need to spray the surface of the scan object with suitable means like, for example, titanium dioxide powder.

Below are some examples of surfaces which need to be prepared before scanning.

 

  • Highly reflective surfaces e.g. mirrors, glossy painted surfaces

  • Transparent, translucent or emissive surfaces

  • Highly occluded surfaces with no line of sight e.g. hair

  • Deep concave or Undercuts segments

 

To overcome problems that have the characteristic in a andb, we can use a Dye Penetrant Inspection (DPI) spray to prepare the scan object surface. After scanning, the dye can be wash off easily with water.

 

  • Object to be scan is transparent

  • Scan object being prepared by spraying it with DPI

  • DPI is transparent when wet.

  • DPI turn into opaque matt white when dry

  • Object being scanned

  • Wash away DPI with water when scanning completes.

 

 

2. Reference Points

Reference Points are self-adhesive or magnetic marks (measuring markers) which are applied to the scan object. They have a define geometry and a high contrast (white circle on a black background). In addition, the reference points serve as connection points for the individual measurements and take care that these individual measurements can be transformed into a common coordinate system.

 

With reference points placed on the object to be scanned or in tits vicinity, the individual measurements are transformed into one common coordinate system. This means that the individual measurements are transformed into a common 3D view with a perfect fit. The ATOS 1 scanner software will automatically identifies the 3D coordinate of these reference points.

 

Advantages of Reference Point Markers

  • During scanning, less overlapping areas are required.

  • During scanning, the user does not need to concentrate on capturing reference points.

  • No limitation of size and complexity.

  • Virtual assembly of individual measurement series with ATOS 1 software.

 

Examples of Position of Reference Points

The reference points are well distributed on the object body shown here. They are just applied to relatively plane parts, so that the points can automatically and without any problems be filled in the 3D view.

 

The model of the car shown here is placed on a standard rotation table and may only be moved by the rotating table. The reference points on the car model are reference points are so called common reference points and are used for the transformation of the top-view project with the bottom-view project in order to get a common overall 3D view.

 

3. 3D Scanning

If you have already done the preparations and planning as above, his is the “easy” part.Point the scanner and press the button. You will need to scan from multiple directions to get complete coverage. Between 20 to 50 scans for most objects. Ensure critical areas are captured.

 

4. Processing Scanned data

Scanned data will be process and digitize by the ATOS 1 software. It will automatically align separate scans. When the data capturing is completed, the software will automatically convert it into a single mesh of non-overlapping triangles. It also have Mesh editing capabilities. Export it to Geomagic for further processing and conversion to other types of data depending on what you need the scanned data for.