Quality Applications

NVision's ModelMaker Benefits Suitable for measuring soft or delicate materials such as foam, rubber or clay Interfaces with most major software packages for reverse engineering and inspection Optional tripod provides complete portability in the field www.nvision3d.com

Laser Scanner Provides More Accuracy in Inspecting Highly Contoured First Articles
NVision's ModelMaker

Realizing that many of its clients sought reverse engineering and inspection services, management at Virtual Surfaces Inc. needed a more advanced measurement method of not only capturing enough data points to represent a contoured surface but also of comparing two surfaces against each other. In addition, the high-volume data capture had to be accomplished quickly and accurately. After evaluating the products on the market, Virtual Surfaces chose NVision's ModelMaker. The major components of the portable system are a 3-D laser sensor, a mechanical digitizer on which the sensor is attached, a PC and software that extracts, displays and manipulates data.

 The combination of a laser scanner and surface modeling software provides a fast and thorough inspection method for first articles with contoured surfaces. "This technology provides a fast, accurate answer to the question 'Is this part good or bad?'" says Arthur Andersen, president of Virtual Surfaces Inc. Previous inspection methods for these parts--done via manual measuring and coordinate measuring machines--captured only critical dimensions.

 It's difficult to inspect a contoured part with manual measurements because there's no way to document the shape of curved surfaces. A technician can get only critical dimensions, such as the location of hole centers, the diameters of holes and wall thicknesses. Moreover, this approach is time-consuming and only as accurate as the person taking the measurements. It's also difficult to inspect contoured parts with CMMs because they must touch the part. Although these machines can acquire data points more quickly than a person, for a typical part, they will capture only several thousand data points over several days. This relatively small number of points can't completely define a curved surface. ModelMaker, on the other hand, quickly captures millions of data points.

 The other limit of CMM inspections is accuracy. "One of our clients did a study of the accuracy of CMMs and found that some points could be as much as 0.005 in. off," recalls Andersen. "Even though only a dozen or so points would normally be erroneous, that would have a significant effect on the accuracy of the resulting digital model."

 When clients need to determine how a part is matching up against the model, they send the IGES surface file along with the physical part. To capture the shape of the part, the technician simply holds the laser sensor so that a line of laser light appears on it. The ModelMaker's sensor is a single viewpoint laser stripe sensor. Laser stripe sensors, which are significantly faster than simple laser point sensors, work by projecting a line of laser light onto the object while a small CCD camera views the line as it appears on the surface. The mechanical digitizer, a FaroArm from FARO Technologies, moves freely about the part, allowing the technician to easily position the sensor and rapidly capture data with a high degree of resolution. As the technician moves the sensor over the surface of the part, a dedicated interface card translates the video image of the line into 3-D coordinates. This data is then combined with the Cartesian and angular coordinates generated at each position of the mechanical arm. The result is a dense cloud of 3-D data describing the surface of the part.

 The data is then exported from ModelMaker into Surfacer, a surface-modeling program from the Imageware division of SDRC. Virtual Surfaces uses the software to compare the point cloud to a CAD model. This process, called registration, superimposes the point cloud from the scanned data onto the CAD surface model. The resulting color-coded plot shows exactly how much the collected data points deviate from the CAD model.

 Generally it takes only one or two days to perform the inspection, generating millions of data points. A similar inspection using a CMM typically takes several days to a week, and, even then, only captures a limited number of data points. Obtaining several hundred-thousand data points on a complex part with a CMM could take three to four weeks.

 "Our most important use of this technology, at this point, is helping small manufacturing companies improve the quality of their products," explains Andersen. "By using a ModelMaker laser scanner to provide a quick, accurate and affordable evaluation of existing parts, we bring the benefits of digital technology to companies that might not be able to afford them otherwise."