Reversing the Physical Into Digital
Working from an existing part or product is sometimes easier than starting fresh. But when it comes to computer-aided design (CAD), the stumbling block has been in converting the physical object into a digital solids model. That’s no longer true with modern reverse engineering products. In fact, it’s now often faster to work from a 3D scan of an object than to redraw it.
Reverse engineering systems are part hardware—fixed or portable, contact (touch probe) or non-contact (3D laser), scanners and coordinate measuring machines (CMMs)—and part software. Nowadays, the software converts scanned point cloud data into CAD models quickly and, as many reverse engineering software vendors are just as quickly touting, one-click ease. This ease applies to importing the 3D data sets as well as the downstream processes of detailing, repairing, surfacing, and other steps toward full, accurate, watertight, history-complete, parametric CAD models. All of this leads to the goal of speeding up the creation of models in CAD and maintaining interoperability between scanned 3D data and CAD, computer-aided engineering (CAE), and computer-aided manufacturing (CAM) applications.
A little background first. At one time, reverse engineering software was basically a connect-the-dots application. The software created reasonably watertight meshes from scanned data. These meshes were then exported to CAD or CAE, or both, for surfacing, healing, tweaking, and modifying into new or reusable parts and products. Lost along the way were any of the benefits of parametric modeling, as well as the efficiencies of working within a single software program. Reverse engineering software now consists of point-cloud processors plus CAD plus sophisticated surfacing and healing capabilities plus finite element meshers plus visualization. At the very least.
Some scanning systems are sold as bundles of hardware and proprietary software, or hardware with some third-party software, or as standalone software that accepts inputs from a variety of CMMs. Prices range from $20,000 for the standalone (read: hardware-independent) high-end software to a tad under $1,000 to $3,000 for limited, but competent point-cloud data manipulation tools. Of course, standalone reverse engineering software packages differ. Downstream processes will determine software selection, for instance how the scanned datasets will be used, and whether the accuracy of the captured geometry is more important than the ability to modify the geometry, to name a few considerations.
Working within CAD
DezignWorks from Creative Dezign Concepts Inc. (dezignworks.net) is fully integrated in SolidWorks 2010, Autodesk Inventor 2011, and PTC Pro/Engineer Wildfire 3 and 4. Designers can capture shapes and complex surfaces, and perform other reverse engineering functions, directly inside these CAD packages when creating solids models. “Engineers shouldn’t have to move between two or three different applications to finish a product design,” says Jim Watson, CEO of Creative Dezign Concepts. In operation, DezignWorks automatically creates 2D and 3D features, incorporating its own cut and extrude command, and automatically turns the millions of captured scanned points into cross sectional lines, arcs, and splines. From these, designers can interactively create and edit sketch entities (lines, arcs, splines, and so on). DezignWorks can also create points at the center of a sphere, edge, or circle, and it can save any set of points as a text file for a solids modeler to create a curve through the points.
Where parametric models are key
Rapidform, Inc. (Sunnyvale, CA; rapidform.com) sells two products to convert physical objects to CAD models. (The company has a few others, including software for part inspection and 3D data collaboration.) Rapidform XOS (scan), a “second-generation” reverse modeling program, converts raw 3D scan data into high-quality polygon mesh models and NURBS surface models. This conversion takes three button clicks according to Rapidform. XOS can optimize point clouds and polygons, generate Class-A meshes, and perform direct color texture editing, color-aware polygon processing, and color parameter adjustments. XOS outputs can go directly to other CAE, CAM, and rapid prototyping programs.
Rapidform XOR (redesign) goes quite a bit further. XOR is a “third-generation” reverse modeling program that converts data from any 3D scanner into a fully parametric solids model. These are in no way static, “dumb” CAD files; XOR creates “intelligent” models by capturing the original design intent from the scanned object(s), that is, by automatically detecting features on the scanned object (such as revolves, extrusions, sweeps, and fillets). The resulting fully editable models with modeling history can then be exported to any CAD program. (In addition to creating parametric models with native, complete history trees, XOR3 can also save models in CATIA V4’s native .model file format.) According to Rapidform, “Traditional first- and second-generation reverse engineering approaches require a perfected mesh, which can sometimes take hours to refine. With XOR, you skip directly to making the CAD model. XOR uses 3D scan data as a template on which to build a CAD model, rather than converting the scan data into a NURBS surface model. You don’t need to spend much time cleaning or editing the point cloud or polygon mesh itself.”
But even before export to CAD, XOR has tools for editing the 3D scanned data. When modifying a geometry, the program’s built-in analyzer shows deviations from the original 3D scan in real time. This helps keep finished models faithful to their original parts. It also saves time because the designer stays within XOR when checking the accuracy of a model. XOR also has wizards to identify and align 3D scan data to an ideal design coordinate system, and to automatically extract design features from 3D scan data.
Making reverse engineering easier
In addition to one- and three-click simplicity, the reverse engineering software vendors are taking stabs at entire portions of their software’s user interface. For instance, XOR3 has a more intuitive batch process interface. A designer need only drag-and-drop commands in the order they’re to operate in a window, and then point XOR3 at a folder of scan data. XOR3 will then automatically process each scan and generate optimized mesh models.
Geomagic Studio, the reverse engineering product from Geomagic (geomagic.com), also integrates with leading 3D mechanical CAD packages. (Geomagic’s other flagship product, Geomagic Qualify, is for 3D inspection.) Studio has one-button commands to convert point clouds to polygon models and NURBS surfaces. A single click can also detect and automatically correct errors in the polygon mesh. Another click converts 3D data to a parametric model in one of several CAD formats (neutral and proprietary). The conversion automatically trims, joins, cuts, or subtracts surfaces and solids. This capability helps create better, fully parametric, native-format CAD models faster that can be put to immediate use.
The latest version of Studio, version 12, which can run on Microsoft Windows 7, has a number of usability enhancements, such as new right-click context menus and the ribbon-style user interface (plus additional customizing options). Studio 12 also has improved profile editing, freeform parameterization, and fitting of lofted surfaces in parametric surfacing. A new option in Studio, akin to creating fillets in CAD, blends primary surfaces that have a constant radius. Studio can automatically enter the radius value or a designer can do that manually. Downstream, CAD software will recognize these as parametric fillets. Studio 12 also has a new command for designers to automatically reduce the number of surface patches in a patch layout, while maintaining the accuracy of the model. This is one of many tweaks making Studio run faster—up to 40% faster, according to company officials.
Beyond “just” reverse engineering
The latest version of Pointools Edit from UK-based Pointools (pointools.com) is another standalone reverse engineering program revised to run on 64-bit operating systems. (Incidentally, this is important because 64-bitness lets designers and engineers work with huge 3D datasets from scanning devices.) In addition, Pointools Edit has point-cloud layer-based editing to segment, clean, and recolor 3D data sets. Color errors can be corrected using a “3D brush” tool. Layers can be locked for precise masking control. Other tools help clean the “noise” and obstructions that can also get captured with laser scanned data.
For downstream work, Pointools Edit includes commands for visualizing, measuring, animating, and exchanging point cloud data. Visualization tools make the mass of point cloud data intelligible, by including point lighting, plane and edge shading, and various types of stereoscopic viewing. The data from measuring distances and extracting point locations can be exported to a comma or tab-delimited file for spreadsheets, databases, and other applications. An animation wizard and graph editor lets users create and fine-tune AVI and MOV movies. Import/export support for Autodesk 3D Studio MAX and Maya and NewTek, Inc. Lightwave lets users merge externally rendered footage with point cloud data to create fly-through animations. Last, on the collaboration front, multiple users can simultaneously access the point cloud database in Pointool, which is crucial for product design teams working in networked environments.
