GM’s Garage of Dreams Captured in 3-D A world-class garage of automotive dreams is tucked away in an unassuming brick building in a Michigan industrial park. Inside lies the legacy of General Motors in all its shining chrome glory. More than 100 years of automotive history and one of the most infl uential collections of automotive design is housed in the GM Heritage Center, an 81,000-square-foot facility located in Sterling Heights, MI. Inside the showroom is aisle after aisle of rare vintage vehicles from fi rst-off-the line production models to one-of-kind concepts. Virtually every one of the more than 200 vehicles is fully operational, and travel constantly to auto shows and other special events. GM’S HERITAGE AS BRAND EQUITY GM brands are as widely known as their automobiles, and their brand equity has generated a highly lucrative sideline business through the licensing of GM trademarks. Every product that mimics a GM body is a licensed product. GM’s licensing program is one of the world’s largest, generating more $3.4 billion in end retail sales from licensed products, according to Charlie Robertson, VO Equity Management Inc., who manages the GM trademark program. “In the past, we left the task of ensuring an accurate reproduction of the body in the hands of the licensee, and they had to sort of fi gure it out on their own. If what they came up with wasn’t right, we would ask them to make changes, of course, but we knew there had to be a better way.” The “better way” turned out to be precision 3-D scanning of important examples in the GM Heritage Collection. The trademark team turned to Steve Ellison, engineering manager at GM’s Manufacturing Engineering Technology group in Warren, MI. This group evaluates new 3-D scanning technologies for assembly and quality assurance, then determines how best to apply them to GM’s manufacturing operations around the world. The trademark team asked if there were any existing technologies producing highly accurate full-body vehicle scans— interior and exterior—to create usable models that could be supplied to trademark licensees. Fortunately, Ellison’s team had several ideas based on their usage of 3-D scanning technologies at various GM manufacturing facilities. These included the CogniTens Optigo white light scanning system and the Romer Infi nite 2. 0 portable arm coordinate measuring machine (CMM) with a ScanShark laser scanner. Both are products of the Hexagon Metrology (North Kingstown, RI) group of companies. Chris Purdy and K.C. Hahn, technical experts from the Manufacturing Engineering group, were sent to the Heritage Center to launch the new scanning project. “Providing an accurate computerized 3-D model as part of the trademark licensing process is an important value-add for the GM program, making it a more attractive opportunity for the licensee,” noted Charles Robertson. “Having 3-D models available of the licensed body style provides a double benefi t. First, it ensures that the reproduction is as accurate as possible for the protection of GM’s brand. Secondly, it makes the process of transferring the design to a licensed product so much easier on the part of the licensee. It also allows a far greater amount of detail than ever before. One of our fastest growing licensing avenues is video games. For them, having a 3-D model To work with makes their work that much easier, and the result that much more realistic.” CHROME TO CLOUD Purdy and Hahn began the project with the 1957 Cadillac Eldorado Brougham, an extraordinary example of the most exclusive and technically advanced production vehicle of its day. The team fi rst completed a fast scan of the major surfaces of the car’s body using the white light scanner, the Cognitens Optigo. This device projects a specifi c light pattern on a surface, then optically captures the contours of the surface beneath the pattern in a millisecond-long fl ash with three cameras mounted in the “head” of the device. The scanner sits on a rolling stand and is moved around the vehicle methodically— project-fl ash-capture-move, repeat. A highly accurate, though incomplete, model of the vehicle is captured in less than 1 hour. The resulting data fi le is a “point cloud,” a mathematical model of the 3-D position of all surface points gathered in relationship to one another. Point clouds can easily top hundreds of millions of individual data points when scanning something as large as a car. A series of retrorefl ectors—that look like white dots—are placed on the surface of the vehicle that allow the scanner to “see” the reference surface of the car. The white light scanner delivers a get-in-get-out-quick approach to the task, while the articulating arm delivers a more nuanced approach. The portable arm measuring machine functions in many ways like a human arm, it has a “shoulder,” “elbow” and “wrist.” The arm can rotate infi nitely in four of its joints, which is handy for getting into tight spaces. Mounted at the business end of the arm is a triangulation laser scanner, called the ScanShark V5. The scanner has a pistol grip handle that the operator holds to project a line of laser light on a surface. An integrated camera reads the refl ection of the light off the contour of the surface. This all happens with speed and precision. The scanner projects more than 7,600 points per laser line and 60 lines per second—translating into a data collection rate of more than 458,000 points per second, with point to point spacing of less than 0.0005 inch. However, because the arm/scanner combo is handheld, it allows the user to carefully and deliberately pass over the surface to be scanned. This is sometimes referred to as “painting” the part—as the points appear on-screen in the software, spraypaint like, as the scanner operates. Hahn explains the approach for the fi ll-in scanning. “Transferring the point cloud we gathered using the Optigo into Polyworks software (Innovmetric Software Inc., Quebec City, CA) allows us to add the additional laser scanned data to the point cloud in real time, while remaining in the same reference frame. This is important to make sure the new scans and the old data are aligned perfectly. So we are essentially adding the Romer data on top of the Optigo data to fi ll in the missing pieces. Normally in production, we use the Optigo on something like a single piece of sheet metal—a door or a hood—which works quickly and very well. But a complete vehicle is more complicated.” Purdy agrees, “This Cadillac has a lot of edge data, and other areas that are diffi cult to entirely capture with the Optigo, areas like the cut lines, side spears, the fi lleting in the hubcaps, and the inside of the wheel wells.” —Bill Fetter, Director of Marketing, Hexagon Metrology Inc.
Published by QualityMagazine. View All Articles.
This page can be found at http://digital.bnpmedia.com/article/Case+Studies/312580/30941/article.html.