Like technology itself, the labels we use to describe technology-driven processes are fluid, a function of a particular time, place or stage of development. Even if we use a computer primarily for word processing, we don’t call it a word processor anymore. A term such as turnkey CAD, prevalent two decades ago, is now as dated as groovy or right on!

For the past decade or so, the process of recreating the design of an existing part has been called reverse engineering. But, reverse engineering suffers from two problems: it has a negative connotation related to piracy, and it does not properly describe new technologies for digitizing and processing any 3D shape for design, engineering and manufacturing.

Peter Marks, managing director of Design Insight, explains the short-comings of the term reverse engineering in his SME Blue Book, “Capturing a Competitive Edge Through Digital Shape Sampling and Processing (DSSP).”

“Reverse engineering has the connotation of capturing geometry solely to make a copy — legal in its intent or otherwise. However, the greatest benefit of scanning technology is to improve a product or its manufacturing process, not just make a copy. Reverse engineering steps backward, often with a poor fidelity copy, or at least lacking the design intent of the original. The potential of this technology is to move forward with product and process improvement, not repeat the past.”

The term that Marks uses — digital shape sampling and processing, or DSSP — accurately describes the process of capturing a part with a 3D scanner, reconstructing the measurement data (point clouds) into highly accurate polygon or NURBS surfaces, and using the resulting digital model for applications such as product design, tool and mold design and verification, customized manufacturing, recreating legacy parts, engineering analysis, and computer-aided inspection.

Closing the loop

Enlarge this picture DSSP inspection software qualifies cell phone housings.

Since its inception, reverse engineering has been synonymous with CAD/CAM. Although it complements CAD/CAM in important ways, DSSP is fundamentally different.

With its roots in drawing, CAD/CAM software is limited to prescriptive modeling methods. In other words, pre-defined geometry must be entered by an expert into modeling software. CAD/CAM starts in the virtual world with a goal to produce better products in the real world.

With its roots in imaging, DSSP offers descriptive modeling methods. The software extracts geometry and topology information from a physical part and describes it to a user. DSSP starts in the real world with a goal to produce high-quality digital models in the virtual world that can be used by CAD/CAM/CAE applications.

Combining DSSP and CAD/CAM creates a complete closed-loop solution — from real to virtual to real. In processes such as hybrid modeling, the distinctive capabilities of CAD and DSSP are combined to create a parametric model that offers great flexibility for generating multiple design variations that enable experimentation with form and function.

The power of two

Dual representations of data and physical phenomena have been behind many scientific breakthroughs. Take physics, for example. Maxwell, Hertz and others made great progress in understanding light as part of an electromagnetic spectrum. But it wasn’t until discrete particle models (photons) were set side-by-side with their continuous brethren that physics made a quantum leap. Today, models of light-as-a-wave and light-as-a-particle work side by side.

Engineers routinely examine mechanical and electrical events (signals, noise, vibration) in both the time and frequency domains. Problems that are extremely difficult to solve in one domain are often simple to solve in the other. The invention of the Fourier transform, which allows any time domain measurement to be examined in the frequency domain, has driven spectacular progress in many fields.

The two digital domains in the manufacturing world could be thought of as the shape domain (traditional CAD) and the point domain (DSSP). Traditional CAD is based on mathematics that define continuous curves and surfaces. It is great at modeling new products, particularly those with simpler boundaries. But, it’s cumbersome for capturing the complexity of the existing world.

The natural complement to continuous mathematics is discrete mathematics — handling geometry as sets of discrete points. This is what DSSP does. Discrete modeling bridges the gap between the point domain of measurement and the shape domain of design. When combined with the continuous mathematics of CAD/CAM, discrete modeling represents the next quantum leap in product design and manufacturing.

Alignment

DSSP aligns the physical and digital worlds, ensuring that the design model is an accurate representation of the as-built product. This alignment is often missing in CAD/CAM, where the ideal design represented by the CAD model almost always differs from the product that is actually manufactured. Accurate alignment between the digital representation and as-built product provides major benefits, including the following:

Faster development cycles due to fewer design iterations.

More accurate computer-aided engineering analysis.

Better fit and finish of final products.

Less manufacturing waste.

Assessment of wear and tear through the life of the product.

The ability to customize products in mass quantities.

Faster and more accurate quality inspections.

How it works

DSSP requires two essential components: scanner hardware to capture point data, and software to process point data into useful digital results.

Technology advances made by manufacturers of optical scanners during the last decade were the first steps in making DSSP possible. Previously, engineers were limited to manually capturing one point at a time. Optical scanners have made it possible to collect millions of points in the time it used to take to record a few points. DSSP enables capturing the entire bounding surface geometry of a physical object — including product features, colors and even textures.

Mechanical data collection methods such as those used by coordinate measurement machines (CMMs) are still important to some inspection applications, but increasingly all forms of inspection are moving from contact mechanical to non-contact optical technology.

Gathering millions of points of data has little or no value, of course, unless the data can be processed easily into digital models with the quality needed for downstream applications. That’s where software plays a critical role.

The combination of greater price/performance for desktop computers and innovation in geometry processing algorithms has moved DSSP forward at a breathtaking pace. Point-cloud data that would choke a high-end computing system five years ago is now easily digested by modern PCs. Gaps and noise in scanning data that used to take days to resolve are now corrected automatically in the best DSSP software. Conversion to polygons and NURBS surfaces, once requiring days of tedious work, can now be handled in minutes using a natural, intuitive workflow. Interaction between parametric CAD software and programs such as Geomagic Studio and Qualify is fast and intuitive.

Accurate repeatability of DSSP software is making it possible, especially in applications such as digital quality inspection, to move analysis and reporting tasks from experts in offsite offices to staff on shop floors. Experts can now spend more time on product development and manufacturing design processes. Automated reporting using 3D graphics in standard formats enables inspection results to be easily understood and shared throughout the enterprise.

DSSP in action

DSSP has made major inroads in early adopter markets such as automotive. One major automaker uses DSSP to reduce NURBS surfacing time for complex assemblies such as engine and transmission housings by as much as 80 percent. The resulting models, generated from as-built parts rather than original CAD models that might no longer closely represent the manufactured parts, are used for faster, more accurate FEA and CFD analysis.

Many of the same issues dealt with by automotive and other DSSP adopters in industries such as aerospace and consumer products — the need to quickly generate new designs based on existing products, digital inventory of parts, ability to conduct CFD analysis on as-manufactured parts and assemblies, and automated inspection and quality control — are major issues for appliance manufacturers. Manufacturers of parts and assemblies that are integral to appliances have already reaped major benefits of DSSP.

Cascade Computing of Sweden uses DSSP to perform fast inspections of cell phones for a subcontractor working with Ericsson, Nokia and Siemens. Geomagic Qualify computer-aided inspection software enables Cascade to compare models based on a specified level of tolerance of 0.003 mm. Within five minutes, the software displays deviation results using color-coded representations that are easy to decipher. Geomagic Qualify also automatically generates a green and red “go/no-go” display.

Now and ahead

Over the past five years, DSSP has made a steady migration from research labs to central design, engineering, inspection and manufacturing operations of companies throughout the world.

In appliance design, DSSP will play a central role in recreating legacy parts and developing digital inventories, providing as-manufactured models of physical parts for accurate engineering (especially fluid and air-flow) analysis, rapid design of new products based on existing designs, quality inspection, continuous analysis and improvement throughout the product lifecycle, and other disciplines that will evolve over time.

With DSSP, appliance makers now have the ability to digitize physical objects in their true forms, including the wear and tear that they receive in everyday use. DSSP frees designers, engineers and manufacturers from two decades of limitations proliferated by the blank-screen design of CAD systems, providing the ability to go beyond mainly mechanical shapes to model an endless variety of organic shapes.

Not only are the possibilities of DSSP nearly endless, but timeless as well — the point data captured today and converted to 3D shape data will still be usable 50 years down the road.

For more information, email: inquiry@geomagic.com