How does 3D scanning work?

What is 3D scanning? What are the advantages of using DLP compared to a scanning laser for your inspection applications?

Beside projection lenses and light engines used in many different industries like 3D printing, In-Vision designs and manufactures projectors for optical metrology systems
Beside projection lenses and light engines used in many different industries like 3D printing, In-Vision designs and manufactures projectors for optical metrology systems

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Optical metrology, or the measurement of items with light, has a long history with many advances. One of the most promising of these is 3D scanning, which offers a more efficient design and prototyping experience, as well as limits the occurrence of design flaws. How can 3D scanning benefit you? Before you can determine its potential in your line of work, you’ll want to know more about the two types of measurement lights commonly used in this tech. You’ll see it being harnessed in every part of society - from architecture to medical devices – and it’s certain to inspire your use of 3D scanning, too.

What optical metrology offers

By definition, optical metrology may be an expansion of the traditional metrology fields defined above. However, in today's industrial and scientific communities, optical metrology is most commonly seen through the use of 3D scanning for inspection and measurement.

3D inspection

3D part inspection uses optical tools to display a virtual 3D replica image for further visual assessment or critique. This is helpful during the pre-production phase of product development and manufacturing. It can alert designers to flaws they might not otherwise see when looking at the original part at 100% scale. The software also plays a role here, as R&D teams may choose to put the 3D image through several test assessments, looking for what may happen in routine use environments. Through these tests, point-of-failure is often identified early enough to make a difference in the overall design. 

3D measurement

Since metrology is the science of measurement, it stands to reason that 3D technology is having the most influence on how item traits are quantified. 3D measurement grants access to the intricate and often inaccessible dimensions of a variety of items.

3D scanning technologies

There are two main 3D scanning methods used for 3D inspection and measurement, the most common are:

Laser triangulation -  This method relies on 3D laser mapping equipment, and the technology involves running a laser beam along the item's surface for measurements and inspection. It requires data to be acquired line by line. An entire scan must be done so that each dot of data can be understood in relation to one another (also known as "triangulation.")

Structured light  technology – Also known as “fringe” projecting, this much-faster method of 3D scanning and data collection uses Digital Light Projection (DLP) systems to create a model with just a sampling of camera captures. Compared to triangulation, it can provide better distance accuracy and works with discontinuous objects that haven’t been accurately measured with more traditional methods. 

Of these, it's apparent that DLP solutions have an advantage, and while the tech is in the early stages of its lifecycle, the options to early adopters are many. Here’s more about how the two compare:

Laser Triangulation: Pros and Cons

This type of 3D scanning tech is very precise and can yield measurement results within tens of micrometers. For those doing very detailed work, this has a significant advantage. This technology can also be packaged into very affordable machines, compared to some of the more complicated machines used for projecting other light types. Laser triangulation scanners can be used anywhere, and some handheld scanners have been developed for capturing measurements on the go.

Unfortunately, the scanning must be done at a very close range, and another significant disadvantage is that not all surfaces reflect the laser light accurately. A very shiny surface, for example, isn’t as scannable. Transparent surfaces also create a challenge.   

Structured light technology: Pros and Cons

The other light source used in 3D scanning is the structured light technology, used in DLP systems across all industries. It measures the triangulation of light, as well, but is projected by LCD or LED machines and then captured by cameras. For this reason, it must only be used at close range, like the laser tech. It can be mounted on tripods or used with handheld camera systems, however, making it an ideal choice for mobile scanning needs. 

What benefits can you see from this projected light option? For one, it’s incredibly fast. Compared to other options, it can capture an imagine in mere seconds – even on a large or complicated surface. Accuracy is also an advantage, as structured light can pick up the tiniest detail and display with incredible resolution. The only time structured light may not be as advantageous is in a well-lit scenario. Using this 3D scanning tech outside may not work, as the light from the DLP system would be drowned out by the intense light of the sun. This tech works best in low-light settings or where light can be controlled to create the ideal environment. 

Which tech is best? Surface type, scan environment and time to scan may be your biggest considerations. What you scan may be most important factor when choosing a 3D scanning tool. 

Current and future uses of DLP technology

Industrial Manufacturing is the go-to application we think of when discussing DLP tech advances. The future of the automated factory includes high speed 3D metrology systems based on DLP projectors for fast part inspection and quality control. The automotive industry is an early adopter of this technology and is already using DLP projectors mounted on robotic arms to speed along the assemblies.

Health applications also abound, and one promising area is dermatology, where DLP is successfully used for mapping the terrain of human skin surfaces. From measuring the depth of wrinkles and fine lines, to accurately capturing the roughness of skin, this is one example of how 3D tech is influencing the skin creams and treatments used today. Large-scale applications will be able to produce images of greater segments of the body, much like how CT scans are already being used. With the addition of DLP tech to body scanning, medical professionals will have another tool for planning complicated surgery techniques, as well as documenting procedures post-op. 

Automation is changing everything

Finally, while the benefits of DLP-based measuring are significant, there is another factor to consider: automation. By not having to manually scan or be present for the entire scanning process, there is significant time and resource savings with the potential for more accurate results. These high-quality automated scanners are potentially more user-friendly, as well. Automation opens up the field to more industries with interest in 3D inspection and measurement and brings products to market faster than ever before. 

To achieve quality results from any automated DLP scanning system, there must be no compromise in the components that make up the system. For a 3D part inspection or measurement using DLP to work effectively, an autonomous micro projector (or “light engine”) should be included. These light engines come in a variety of specifications, with the option to have one built custom for your needs. The In-Vision Mercury light engine, for example, boasts a resolution of 1440x1080 and is compatible with a variety of screw-on lenses for varying throw ratios, working distances, and feature sizes. If the available lenses don’t meet your project specs, however, custom mods are an option, as well.