Trends in Reverse Engineering30 Apr, 2008 By: Jeffrey Rowe
Affordability and greater ease of use result in more respect for the reverse-engineering market.
Over the years, reverse engineering (RE) has suffered from a lack of respect. While the "engineering" part of the term has always been regarded positively, the term as a whole has suffered because of the negative connotations associated with the word "reverse." In many people's minds, RE involves the illegal act of copying (in effect, stealing) an original design, whether the design is for software or a physical product. The old perception, however, is changing. As a result, RE's image is changing, too.
Simply put, RE is the process by which you digitally reconstruct a physical part. This is significant, because it's estimated that as many as 80% of new designs come from existing ones (usually from existing parts and assemblies). RE is part of a larger scheme increasingly known as digital shape sampling and processing (DSSP). DSSP involves several technologies that, put together, bridge the physical and digital worlds.
Unlike the time when RE was considered the process of illegally copying a product, legitimate RE applications now include the following:
- 1. creating data for refurbishing or manufacturing parts that have no associated CAD data
- 2. creating 3D data from a model or sculpture for game and movie animations
- 3. creating, scaling, or reproducing artwork
- 4. measuring, documenting, and recreating cultural objects or museum artifacts
- 5. generating data for creating dental or surgical prosthetics or for surgical planning
- 6. inspecting and conducting quality control by comparing a fabricated part to its CAD description.
Many potential users wrongly assume that RE technology is beyond their means. Today, such technology is available as an affordable desktop solution for small-and medium-sized businesses. Depending on the scanning technology used, you will find an entry-level price point of less than $15,000 that includes all the hardware and software needed for getting started in RE.
DSSP data for manufacturing purposes involves two distinct methods of describing and representing 3D forms. RE does this by handling geometry as sets of discrete points (whereas traditional CAD does it with shapes defined by continuous curves and surfaces). Combined, RE and CAD transform physical objects into digital objects (and ultimately back to physical objects). In other words, RE extracts geometric information from physical objects, and CAD reconstructs objects into a digital form that can be used for creating physical objects based on the scanned data.
RE is a process of examination. The part under consideration is not modified during the scanning/digitizing stage (that would make it re-engineering), although it can be modified in downstream applications, such as CAD.
The data-related portion of the RE process has two parts: scanning and data manipulation. Scanning, also called digitizing, is the process of gathering geometric point data from an object. Several different contact and noncontact technologies are used to collect this 3D data. Each technology has advantages and disadvantages, and their applications and specifications overlap.
What eventually results from each of the data-collection methods is a description of the physical object in 3D space called a point cloud. Point-cloud data typically defines points on the surface of a scanned object in terms of x, y, z coordinates. At each x, y, z coordinate in the data where there is a point, there is an associated surface coordinate of the original object.
There usually is too much data in the point cloud collected from a scanner/digitizer, and some of it will be unwanted noise. Without further processing, the data cannot be used by downstream applications, such as CAD/CAM software or in rapid prototyping. RE software is used to edit point-cloud data, establish the connections of the cloud points, and translate it into useful formats, including surface and solid models or STL files. It also combines several different scans of an object so that the data describing the object can be defined completely from all sides.
Several digitizing technologies are available today. They include contacting/feature-based (mechanical touch probe) and noncontacting (laser-based) instruments and hybrid systems.
Feature-based scanning systems. Feature-based scanning is a method by which features of an object are scanned by physical contact. A mechanical touch probe, also known as a contacting digitizer, is a physical-part contact device and method well suited for prismatic parts, such as an automotive transmission housing. The touch probe is a device that is connected to a computer and lets you know when and where in space contact is made with an object (figure 1).
Figure 1. A touch probe attached to a coordinate measurement system is used at the front end of reverse engineering a cam.
Disadvantages of contacting devices include the fact that they can distort soft objects. Additionally, they can be too slow for digitizing organically shaped parts because they usually require too much time and labor for scanning complex curved surfaces (although there are workarounds for this, such as scribbling a complex surface with the touch probe). On the other hand, such devices are not affected by the color, transparency, or reflectivity of a surface the way laser and other light-based systems can be. And while they can be relatively slow, contacting devices are often the fastest way to digitize simple surfaces for which just a relatively few data points are required.
Because feature-based scanning actually captures features on the fly, the resulting data is both native and feature based, so surface and solid-model features can be derived directly from the scan.
Point-cloud scanning systems. Point-cloud scanning is performed using a laser scanner that is a physical-part noncontact device. The method is well suited for organic, freeform, artistic parts, such as statues. It is also well suited to scanning soft objects with surfaces that might be distorted by a touch probe. Point-cloud scanning is not well suited, however, for prismatic or sharply faceted parts because too many points are captured.
The relative simplicity of the laser technique and its ability to quickly digitize a large object accurately with good resolution has made laser scanners increasingly popular for RE purposes. Laser-scanner products are available as complete systems or as self-contained measuring heads for mounting to standard touch-probe arms or customized mechanical fixtures (figure 2).
Figure 2. Laser scanning is well suited for capturing freeform shapes and soft objects with a high degree of accuracy.
One of the only significant disadvantages of point-cloud scanning is that there is more clean up required. This is because of the number of points captured for transforming the point cloud into something useful for modeling purposes. When point-cloud data is imported into a CAD product, the scanned shapes act as reference geometry for sketching, ultimately becoming solid models.
Hybrid systems. In an effort to maximize the advantages of touch-probe and laser-based systems, dual-capability systems are emerging that provide turnkey products with complementary capabilities. These instruments have both a contact probe and a laser head that can be used simultaneously. For example, broad areas can be quickly scanned using a laser device mounted on the articulating arm, and features on the object that might pose problems for the laser can be digitized by contact. In other words, all bases are (literally) covered.
Usually, collecting an object's data is the easiest part of any RE process. Normally, most scanning only requires a few seconds or a few minutes. On the other hand, manipulating that scanned data can be quite time consuming and labor intensive. However, scanned-data–manipulation techniques are rapidly improving and becoming much more time and cost effective.
Advancements in RE software and hardware will continue to drive the convergence of physical and digital design, allowing a true concept part to move through digital art to production-part methodology and workflow. Look for the integration and the capabilities of RE to continue to evolve and become more comprehensive, not to mention even more affordable and easier to use.
If you thought sophisticated RE capabilities were beyond your means or your budget, think again. It's more affordable and easier to implement than you think, and that might very well provide the compelling reason for finally switching from 2D to 3D as you start and end the entire process and workflow with 3D physical parts. RE is finally getting the respect it is due.