Table 1.3 Different scanning technologies.
| Scanning mode | Scan range | Scanning principle | Description | Commercial scanners |
|---|---|---|---|---|
| Non‐contact | Short range | Laser triangulation‐based 3D technology | Projects a laser light source onto the surface of the object and determine the amount of deformed light reflected from the surface | Sense 3D scanner |
| Structured light‐based 3D technology | Uses trigonometric triangulation of the structured light (white/blue). It measures the deformed light pattern from the surface of object based on digital light processing (DLP) technique | EinScan, EinScan Pro 2X | ||
| Long range | Pulse‐based laser | Based on laser beam’s time of flight. The projected laser light is collected by sensor and time of travel between emission and reception provides surface details | Lidar 3D scanner | |
| Phase shift laser | In addition to pulse‐based scanner, these systems modulate power of the laser thereby it allows comparison of the phase of the laser emitted and returned to the sensor | Lidar 3D scanner | ||
| Contact | Medium range | Coordinate measuring machine (CMM) | Involves measuring the degree of deformation of a probe by scanning several coordinate points on object’s surface | Altera SL bridge CMM |
| Arm‐based 3D scanners | Similar to CMM with additional provisions attachable 3D scanner unit for collecting large amount of points | Hexagon’s ROMER Absolute Arm scanner | ||
| Optically tracked 3D scanners | It uses a set of cameras to capture and track the location of scan in working space | Hexagon’s Leica Absolute Scanner and Creaform’s Metrascan 3D scanner |
1.8.2 Repairing and Post‐Processing
After the acquisition of the image, the captured 3D models are processed adequately to restore better precision and higher resolution during 3D printing. Scanned 3D models are subjected to digital processing to improve the quality of the acquired image. Any 3D solid files would be stored in STL form which is described in terms of small clustered triangular facets forming the 3D object (Szilvśi‐Nagy and Matyasi 2003; Wu and Cheung 2006). This format follows four basic principles such as common vertex, orientation rule, closed facets, and must have non‐negative coordinate values. Some of the common STL errors (Figure 1.8) and their causes are as follows: holes – caused by missing of facets during triangulation; gaps – occurs due to dislocation of vertices forming a boundary between the pairs; dislocation – a common error that occurs during computation when the same vertex is shared by two triangular facets; reverse oriented normal – a disordered pattern occurs when triangular facets fail to follow orientation rule; overlaps – inaccuracy during computation causes merging of facets one above the other; and redundancy – independent triangular facets stick out the regular topological structure (Liu et al. 2009). Common vertex is the sharing of two edges by the adjacent triangular facets. The orientation rule implies that the normal vector of the individual facets must follow the right‐hand rule and it should point towards the perimeter of the solid. The next principle is that all the triangular facets must be closed adequately without any gaps between the vertices. Finally, the model should possess a non‐negative coordinate value (Tan and Chen 2016).