What is laser scanning?
Confused by the difference between laser scanning and structured light 3D scanning? Our quick guide explains the similarities and differences between the two methods of data capture.
Non-contact 3D scanning is a fast, accurate and non-destructive method of capturing digitally the shape of physical objects for use in design, visualisation and inspection. This can be achieved by using either structured light 3D scanning or laser scanning.
Each technology has its advantages, but we have chosen to use the internationally-respected German measurement company GOM’s structured blue light 3D scanning as the most accurate. (iReviews, 2014)
GOM ATOS Triple Scan 3D Scanning System
The information below is based on common industrial 3D scanners for application on objects in the range of 50mm-5metres.
Laser stands for Light Amplification by the Stimulated Emission of Radiation. 3D laser scanning uses laser light to scan parts. Commonly, laser scanners come in two variants: handheld, where the stripe sweeps over the part like a paint gun, or are tripod mounted where the laser line sweeps across an area or measures a single point. The scanners can also be attached to an arm or traditional CMM gantry, however this sometimes limits scanning to a finite size along with introducing another level of uncertainty to the measurement.
Laser scanner mounted on tripod
Structured light 3D scanning
The GOM optical 3D scanner uses two high resolution digital cameras in order to capture the data. A light emitting diode (LED) and digital projector projects a fringe pattern across the surface of the object using a narrow wavelength of blue light. Applying the principles of triangulation, the sensor measures to a high level of accuracy the divergence and convergence of the fringe pattern. This creates a high density point cloud of surface measurements.
Both laser scanners and structured light 3D scanners produce dense point clouds or polygon mesh which can be inspected directly to a computer aided design (CAD) model, geometry or manufacturing drawings or reverse engineered using specialist software.
What are the differences in the technologies?
Laser scanners sample the data once as the line passes the illuminated object. Structured light 3D scanners sample the data many times, with fringe patterns of blue light of varying width and phase that capture the shape of the object. The accuracy of a structured light 3D scanner is described as inherently higher than that of a laser scanner, due to the repeatability of the readings (LMI3D, 2011), offering a higher resolution as well as higher accuracy (compared to Faro ScanArm V3). Both systems are largely unaffected by the ambient light conditions, making either type of system suitable in industrial applications.
Due to the higher level of accuracy afforded by structured light 3D scanning, it is particularly suitable for: measuring fine detailed items; capturing defined edges of parts such as turbine blades and pressed steel items; scanning tool surfaces; measuring high accuracy components.
Very reflective materials generally do not scan well with either system, which can be avoided by applying a fine coat of white powder spray of titanium dioxide to dull the surface of the object. For even the most sensitive artefact this is a useful solution and allows the scanner to capture the precise measurements of the shape, whether organic or geometric. Both laser scanning and structured light 3D scanning systems can capture data in this way.
Although some scanners claim to scan polished surfaces without any surface preparation, Physical Digital® would question the accuracy of the data and the processing and sampling to the raw data before being presented to the user. This may be suitable for low accuracy reverse engineering but not for quality inspection.
The newest generation of structured light scanners have the ability to apply reflection detection technology in order to offset and remove areas that would otherwise produce poor data.
Structured light 3D scanning is suitable for a wide range of objects, from parts of under 10mm to entire aircraft
Lasers focus light intensity and energy into a very small area and there is therefore an inherent safety issue. The greatest concern is eye-safety. Blue light technology does not pose any safety concerns as it does not have the intensity given by laser scanning, this makes the technology easy to implement in a wide range of enviroments without the need for special training or safety measures.
Both laser scanners and structured light 3D scanners are similar in portability. Physical Digital has chosen to invest in entirely mobile 3D scanning equipment, the GOM ATOS III and Compact Scanning systems, which have been used across the UK, Europe and the world. These systems can also be integrated for use in automated cells for faster, repeat inspection. Physical Digital offers the UK’s leading GOM ScanBox 5120 automated 3D scanning system on a service basis for clients.
Physical Digital's automated 3D scanning cell, the ScanBox
The potential scanning area of the GOM system can be extended without impacting on the accuracy of the scan data through the added benefit of using a photogrammetry system***. Photogrammetry is a separate metrology system designed to capture reference points using multiple digital images, using a verified DSLR camera. The GOM system can use these reference points to extend the potential scanning area, which means it is possible to capture entire aircraft or boats. Laser scanners do not have access to the photogrammetry system and often have to move the arm and ‘re-datum’ to extend the measurement area, this is highly reliant on the geometry of the part and a highly trained user.
*** ≈ 0.02mm/m
The ATOS Professional and GOM Inspect Professional software provide a complete 3D scanning and inspection solution for the structured light 3D scanners we use at Physical Digital. Unlike any scanner that uses 3rd party software, all measuring data is held in the software so vital information can be recalled at any time, such as calibration information, measurement temperature, part numbers and lighting or movement changes, along with maintaining a fully parametric link from measurement data to final report. This offers a huge advantage over every other system on the market and provides the unbroken chain of custody required for high liability manufacturing.
Read more about the structured light technology offered by Physical Digital, or visit the GOM website at www.GOM.com.
To discuss how your project can benefit from the 3D scanning offered by our expert team, call 01483 750200.
iReviews, 2014. 2015 Best 3D Scanners Over $50000. [Online]
Available at http://3d-scanners.ireviews.com/2015-best-3d-scanners-over-50000-review [Accessed 3rd February 2016].
LMI3D, 2011. 3D scanners laser versus white light. [Online] This blog post was previously posted on Mon, Dec 19, 2011 on 3D3 Solutions blog. LMI Technologies acquired 3D3 Solutions on May 1, 2013.
Available at: http://go.lmi3d.com/3d-scanners-laser-versus-white-light [Accessed 17th February 2016]