Andrew Wilson, Editor, [email protected]
Time to market is critical, especially in the mobile-phone market where new products are constantly being developed. Suppliers to manufacturers in this market must produce a variety of parts, modules, or complete systems in large quantities at short notice. To ensure that the quality of these parts meets the expectations of the manufacturer, initial (or “first” parts) are produced, and the parts, material, molds, and injection conditions must be verified and accepted by both parties in a process known as first article inspection. This process defines the quality of the parts that will be produced in volume and is a critical process for both the supplier and manufacturer.
“Traditionally, the way to check the quality of preproduction parts is to measure their dimensions using coordinate-measuring machines (CMMs),” says Rick White, director of business development at Capture 3D (Costa Mesa, CA, USA; www.capture3d.com). “After positioning the part, a large number of individual measuring points are defined and measured and a dimensional report created. If the tested part is accepted, mass production can start. If modifications are required, the process is repeated.”
“Due to the reduced time to measure the data and the increased measurement information that is captured by such systems, mobile-phone companies are now beginning to automate this measurement process using 3-D-based scanning systems,” says White. “Using these systems, high-density point-cloud data can be captured, manipulated with off-the-shelf CAD packages, and compared to original CAD data. These reports are visual and easy to read and make decisions from.”
At the recent Turbo Expo show (Montreal, QC, Canada) in May, Capture 3D demonstrated the ATOS II, a 3-D measurement system originally developed by GOM Optical Measuring Techniques (Braunschweig, Germany; www.gom.com). In the ATOS II system a two-dimensional pattern of light stripes is projected onto the object by moving a slide grating across a light source (see figure). The pattern is then imaged with two 1.3-Mpixel Camera Link cameras from VDS Vosskühler (Osnabrück, Germany; www.vdsvossk.de) that are placed at an angle relative to the projector. Because the shape of the light stripes will deviate due to the object’s height above the surface, this deviation is used to determine the object’s 3-D shape.
“In principle, one camera and one light source could be used to perform this 3-D measurement,” says White. “However, using two cameras allows weighted average values of 3-D measurements to be computed, thus providing a more accurate 3-D measurement. Second, any part-occlusion effects are eliminated. Finally, because the two cameras observe the projected pattern from different perspectives, a better interpretation of the deformation of the projected pattern on a discontinuous surface can be obtained.”
After digitizing the image data with a PCI-X based Camera Link frame grabber from DALSA (Waterloo, ON, Canada), the ATOS system automatically creates 3-D point-cloud data. “Because the ATOS system is PC-based,” says White, “a number of off-the-shelf 3-D packages can create a 3-D model using these point-cloud data.” These include Catia from IBM (Armonk, NY, USA; www.ibm.com), ProEngineer from Parametric Technology (Needham, MA, USA; www.ptc.com), and NX from UGS PLM Software (Plano, TX, USA; www.ugs.com), a company recently acquired by Siemens.
From this color map, any deviation of the scanned part with the original CAD model can be visualized. Cross sections can be cut, inspection points defined, and critical dimensions measured. Digitizing the inside and outside of a mobile-phone shell can be accomplished in less than 30 minutes and the final inspection results produced in less than an hour after scanning is started.
Using the ATOS system, keywords such as batch, part model, measuring area, and date can be defined in the measurement project for customized and automated reporting. Screen snapshots can also be captured and measured data with tolerance information and defined features tabulated in pdf or html format. Measured data can also be exported in Microsoft Excel or in PC-DMIS CMM software from Wilcox Associates (North Kingstown, RI, USA; www.pcdmis-ems.com) for process control, further analysis, or archiving purposes.
The system also has been used in the turbine-manufacturing industry, since turbine-blade inspection poses challenges such as analyzing the twist of a newly manufactured blade compared to its CAD model. This is difficult to accomplish using CMM systems, which depend on operators to accurately capture the points that will show whether or not the blade is twisted within the allowable tolerance. Often, there is not enough point data to make an accurate comparison.
Many Capture 3D customers use features in Geomagic Qualify (Research Triangle Park, NC, USA; www.geomagic.com) to automate twist analysis. The software allows them to align a cross section of the scanned model to reference data and automatically generate statistics on the twist of the blade. Using this software, constraints can be placed on maximum rotation and twist tolerance.
