MARCH 19, 1999 - SME CONFERENCE - RAPID PROTOTYPING AND MANUFACTURING '99
By Lisa Federici

How 3D Scanning Technology Impacts Product Development

In order to meet the challenges of today's rapidly changing business landscape, companies are taking a close look at their methods, adopting new techniques, and looking for ways to make production more efficient and cost effective. Among the recent technological advances, there is a growing interest in the availability of fast, affordable optical range laser scanning. Manufacturing companies in particular are looking to the scanning industry as a potential tool for increasing productivity and resolving issues concerning the need to create a 3D digital file for an object where none had existed before.

Scanning a 3D image and sending the scan to prototyping or CAD software programs saves not only hours of painstaking work, but thousands of dollars as well. Reproducing an object by physically drawing it into the computer is difficult, and the result often does not match the original. Although reverse engineering is a method companies have used for some time, a truly cost-and-labor-effective method to go about it has not existed until now. Laser scanning also opens the door for many firms that initially prefer to sculpt objects in traditional mediums to retain the tactile and visual advantages that CAD systems lack.

More than three-quarters of the Fortune 100 companies depend on visual computing to help them design their products. Embracing this new technology allows firms both large and small to meet the computing challenges that are pivotal to their competitive strength. Laser scanning can provide a measurable difference for improved quality and accelerated time-to-market, while reducing costs for new products.

Laser scanning is accomplished by using a laser device that collects range data. The most common method for acquiring range data is active optical triangulation. Range data is produced by placing a depth value on a regular sampling lattice from the surface of the object. Then, by connecting triangular elements with the nearest neighbors, a range image is created.

Generally, a 1D or 2D sensor is swept linearly across the object or circularly around it. As this is not usually enough information to reconstruct the entire object being scanned, multiple passes must be made from different orientations. Specially written algorithms are required to merge multiple range images into a single description of the surface. Although this technology has been in use for over twenty years, the recent development of stable imaging sensors such as CCD's and lateral effect photodiodes has increased its speed and accuracy dramatically.

There are several different types of scanners that accomplish this: their primary differences are in the structure of the illuminant (typically point, stripe, multi-point or multi-stripe), dimensionality of the sensor (linear array of CCD grid), and the scanning method (move the object or move the scanner hardware).

One of the most obvious benefits to 3 dimensional scanning is the tremendous increase in speed with which a prototype can be reproduced. Traditional methods call for the object to be measured and redrawn in a CAD program. This is extremely time consuming, and organic shapes are almost impossible to model using this method. Objects such as an ergonomically designed handle or new toy design can easily be sculpted and then scanned to insure the intended result. Laser scanning is at its best when dealing with shapes of this sort.

Often, the time to market can make or break a new product. It is much easier to predict the future when the future is a few weeks away rather than a few months away. In some cases, the resulting time savings can allow a manufacturing project to start later. This means that companies have time to work with clients longer in the conceptual process. Details can be fully explored, and customer requirements clearly understood before committing to the production stage. The entire scanning and post-editing process can happen in as little as 4 to 5 hours. This kind of time saving also means that companies have the ability to respond rapidly to changes in the market place. And because laser scanning technology is relatively quick, it is generally much cheaper than other types of scanning.

A couple of scanning hardware manufacturers have now developed scanners that accurately digitize the human body. Companies that need to produce ergonomically designed products such as safety helmets, orthopedic braces or prosthetic devices can use this technology as a fast and safe method for collecting surface information of the human body.

Yet another advantage for the manufacturing community is that, in many instances, G-code can be created for CNC milling right from scan data, or from an STL file without taking the extra step of producing a NURBS surface model. This means that a prototype can be made and approved, scanned, and a mold made of any proportion quickly and easily, all of this happening in a matter of days. Scan data can be translated to nearly any file format: DXF, OBJ, 3Dstudio Max, Iges, ASCII, STL, .HRC, Inventor and others.

Product verification is another example of the benefits of scanning. After a product has been produced, it can be scanned and the resulting data compared to the CAD drawing. Deviations from the specs can then be accurately determined. Another routine use for scanning is periodic inspection of multiple parts to analyze how closely the product adheres to the original. This allows for greatly improved quality control, and helps to detect flaws in the manufacturing process.

Another benefit that is not so obvious, but can have a far-reaching effect on a company, is that once the object is in the computer, complex ideas can be conveyed accurately and easily. In today's world, manufacturing processes are carried out by multiple parties, often from different locations around the globe. The client and the design process can be in one place, while the manufacturing occurs in another. The synergistic effect of having several people collaborating on the development of an idea substantially broadens the scope of the design and manufacturing process. Once a prototype has been scanned, the engineering, analysis, quality control and various other functions that used to take place consecutively, can take place concurrently before committing to manufacturing. All parties involved with the project can work from the same digital file. The result is a shortened development cycle, improved product performance and greater flexibility-positive ramifications at every level.

When looking at this technology for use in the manufacturing industry, it is important to know how the surface information is gathered, and what its advantages and limitations are. There are many variables that effect the laser, and subsequently effect the quality of the information. Reflectivity of the surface, color of the object, undercuts, narrow opening, and sharp edges can all pose challenges. Other things to consider are placement of the object in relation to the scanner, and operator experience. These challenges are greatly reduced with the right equipment and an experienced operator.

Operator experience is a critical factor with optical laser scanning. The operator must follow certain guidelines and be able to predict how the laser will react. The individual scans must be viewed carefully before merging, so that any unacceptable data will be thrown away. And the operator must have a clear understanding of how lasers work. Competing lighting in the room, the distance the object is from the scanner and the color of the object can all effect the laser. The technician needs to be able to clearly distinguish acceptable form unacceptable data, and needs to be able to accurately analyze the point cloud-the native product of scanners.

In the case of reverse engineering, it is important to establish what it is you want to do with the data, and just as important, what is, or is not, important to you in terms accuracy. Accuracy is the million dollar question in the manufacturing community. What the accuracy of the scan will be is asked of the scanning industry as frequently as what file outputs are possible. It is important to understand the range of accuracy for the particular scanning hardware being used, and then to take into consideration the factors already mentioned above. Both file translations and certain types of files have a margin of error. In applications such as STL, where the product will have finishing work done after being produced, this may not be an issue. And in most cases of CNC milling, the drill bit is larger than the deviation anyway.

Many companies want to use optical laser scanning for inspection purposes. In these instances, a software package especially designed for interpreting point cloud is needed. It is then imperative to gather the cleanest, most accurate data possible. Sometimes the manufacturer does not want the data altered in any way, so it is critical to choose scanning hardware or service bureau that can produce proven results.

If the desired result is to get a PRT file format for use in CAD programs, then a surface must be created over the point cloud. There are many programs and methods that make this possible. The point cloud data can be sliced in order to generate B-splines, and a surface lofted from there, or a surface may be generated right over the point cloud.

Other considerations with this type of scanning are the cost and the time it takes to complete a project. This method is relatively fast compared to other types of scanning. Because three to four parts can be scanned and processed in a day, the cost tend to be lower. Because the object is never touched physically, it is not harmed in any fashion, and as there are no radiation rays, this is the preferred method for collecting surface data of the human body.

How can a company determine whether or not optical laser scanning is right for their project? First, determine what you want the data for. Second, look objectively at the object and decide whether it lends itself to scanning. And thirdly, consider the cost and timeline desired. The laser scanning industry has come a long way in recent years. There are many options currently available that can be scheduled into a planned project with relatively predictable and cost effective results. These recent improvements have opened the door to even the average user, who may never before considered using automated 3D model creation from real objects in product production.