By Brett Duesing of Strategic Reach
NURBS have been used in high-end CAD systems for some years. For example, NURBS-based systems are behind the beautiful flowing curves in auto modeling. But now availability of low-cost NURBS-based systems is opening doors to use this modeling capability in a wide variety of new applications.
What are NURBS? The name refers to Non-Uniform Rational B-Splines, mathematical representations of 3-D geometry that can accurately describe any shape, from a simple 2-D line, circle, arc, or curve to the most complex 3-D organic free-form surface or solid. Because of their flexibility and accuracy, NURBS models can be used in any process from illustration and animation to manufacturing.
These 3D surface-generators are finding growing popularity among those who engineer objects that stray from strictly rectilinear bounds. The new aesthetics in high-concept product design and sculpted architectural forms have created increasing interest in curved surface construction. Industrial, automotive, and environmental designers are now tasked with design problems that non-NURBS CAD cannot solve. NURBS applications have thus become the all-purpose design modeler, crossing across disciplines and finding applications on projects of every scale, from the ornate scrolls of engagement ring settings, to arching hotel towers that dominate the skyline.
Moshe Safdie and Associates won a design
competition sponsored by the city of Singapore for
six-million-square-feet of casinos, hotels, and convention center
amenities. Rhino allowed the firm to produce innovative 3D forms in the
design as well as coordinate the workflow of development through
several designers, engineers, and outsourced consultants.
Many traditional software tools provide the means to model mechanical parts. Many times, however, projects are a little more complicated. This complication may be a more sophisticated shape or an area than needs higher accuracy. NURBS modelers can be used to solve those modeling problems that are difficult or perhaps even impossible in their current CAD tools.
Curves as NURBS
In rectilinear CAD systems, drawn curves are merely estimated; a view at a high resolution reveals the arcs as tiny stairsteps of right angles. In NURBS models, every point on the surface is calculated with pinpoint accuracy, regardless of resolution.
Although some 3D CAD applications may include a module to convert models to NURBS, this sideline function does not assist in solving curve-related design problems. Software wholly based on a NURBS engine, like those from Rhinoceros, CATIA, or Dassault, are able to parcel the surfaces into component parts, edit and enhance forms, and automatically perform analysis on curvilinear models – all of which require frequent NURBS re-calculation.
For instance in Ingeenium’s design of the SCARTT 4×4 (see sidebar), many of the motorized components of the car are simple machined parts. Rhinoceros can model and assemble these parts, as can any number of 3D CAD applications. There are parts of the car, however, which cannot simply be broken down into discrete dimensional lengths or individual radii, but are rather driven by demands of the design form – such as the bodywork around the unique headlamps. These are the shapes that are well suited for NURBS.
Input and output
Creation of shapes that are impossible in other CAD systems is the primary reason for turning to NURBS modeling. But use of the software is growing for other rationales as well. Because NURBS geometry can be easily exchanged in standard formats, and modelers can easily import other types of CAD, NURBS analyzers provide advantages in the way it relates to the processes of design and production.
Rhino, for example, easily imports geometry through IGIS and STEP files and places it in a NURBS environment. These universal CAD formats are in the export options in almost any other CAD application. This feature makes collaboration between different CAD uses easier.
Similarly, Rhinoceros exports its shapes in IGES and STEP formats, which comport with a variety of automated shop tools, such as computer numeric control (CNC) mills, laser cutters, or rapid prototype 3D printers. NURBS modelers are not just pretty pictures – highly accurate, they are
immediately ready to automatically guide the production process.
Here, a convex wall is intersected by a
concave doorway. The intersection of the two NURBS surfaces creates a
new curve, which must be defined as its own NURBS equation in order to
contruct the final panels. To extract important data out of a complex
model, a full-capability NURBS engine is needed. [Courtesy: AWIN, EMPAC
auditorium, Troy, NY]
Designers at BRIO Innovation modeled the
Callaway C16’s exterior (left) in Rhinoceros. Internal mechanical
systems were based mainly on the GM’s Corvette platform. 3D models of
the GM mechanics originated in Pro/Engineer, but could be seamlessly
incorporated into the full Rhino model (below) via IGES or STEP format exports.
Hollywood’s car customizer Eddie Paul
relies on Rhino to fabricate extension body parts for his shop’s
specialty promotion or movie stunt cars. The 3D models are quickly
configured for precise CNC-machining of curved body parts. The
automated cutting allows the shop to turn over rush jobs in just a few
NURBS in architecture
The easy import-and-export, the high accuracy of shapes, and flexible problem-solving capabilities have led designers of large-scale projects to use NURBS models as a vehicle for project management. Architects of the Marina Sands, an enormous casino-hotel complex in Singapore, used Rhinoceros to store a “master model” of the whole complex. The modeler allowed the architects to create the curvilinear towers and other sculpted motifs throughout the six-million-square-foot project.
As competition drives products toward more expressive designs and more ambitious engineering feats, engineers demand higher accuracy and more complicated shapes. More than ever, you need CAD to act as more than simply a drafting tool. NURBS modelers are growing in popularity because they can solve complex geometric problems. These robust modelers can not only describe any form, but also guide the saw that cuts it, as well as organize disparate parts of a sprawling project. Today, 3D modelers not only shape a product’s appearance, they also form the process of its manufacture.
NURBS helps invent the ultimate recreation 4X4 If the 4×4 SCARTT 500cc looks like something you’ve never seen before, Barcelona-based design firm Ingeenium will take full responsibility. The newly released recreation vehicle is the European answer to the host of familiar-looking All-Terrain Vehicles (ATVs) from North American and Asia. The Ingeenium design team gave the SCARTT a contemporary look that borrows more from the world of automobiles than of motorcycles.
The most difficult aspect of bringing the SCARTT into reality was a very fast design schedule. While the product development was a yearlong process, most of the crucial design tasks took place in six intensive weeks. Their initial plan was to construct a full-size physical model with automotive clay.
Due to the brief design timetable, the team saw serious limitations in using a physical model. An alternative approach offered promise: use a 3D computer tool called Rhinoceros. A powerful NURBS surfacer, Rhino performs the same sculptural constructions as the modelers used by big automakers, but costs only a small fraction of the price.
3D modeling proved to be the fastest way to prepare the design for prototyping. Accordingly, the group chose to work exclusively in Rhino. “Getting the basic design of the tubing chassis and the basic geometry of the motor and transmission components into 3D only took a couple of days,” recalls the team leader. “Using Rhino has been pretty convenient. We took two laptops with the software to the workshop where the motor parts were being assembled, and created the model from measurements taken on the spot.”
With the SCARTT’s components in virtual form, designers could make needed adjustments to interferences and clearances, or trim the model to fit in important exterior features, like the distinctive headlamps made by CSR. Perhaps most importantly, the 3D model quickly communicated the design to production as precise data.
The software exports to a multitude of 2D and 3D formats that speak directly to many automated fabrication processes such as CNC tooling and mold fabrication. The majority of body parts were created through resin transfer molding (RTM). It’s basically like fiberglass, but the process is more industrial than regular lamination. Many industrial processes now can read the 3D file directly, greatly speeding the delivery of prototypes and final products to market.Rhinoceros Inc.
Filed Under: 3D CAD, Software