Turning a Sow's Ear into a 3D Silk Purse (MCAD Modeling Column)31 Mar, 2007 By: IDSA ,Mike Hudspeth
Designers have many options for turning anything into a usable model.
We aren't all lucky enough to have started out with 3D solid modeling. Most of our products started on a drafting board or at least in 2D CAD. For the sake of discussion, I'll assume everyone has a 3D-modeling system now. What are we going to do about our legacy data? We have a huge amount of stuff that is at best 2D. What will we do when we have a component to incorporate into our design and we can't get a 3D model of it? Panic? Not yet. We have many choices for pulling data into our modeling software.
2D to 3D
Believe it or not, just because your data isn't a 3D solid model it's not useless. If it exists in digital form, its data can be used. CAD models are perfect examples. You can import 2D AutoCAD files into just about every 3D system. You even can use resulting geometry to generate models; both Solid Edge and SolidWorks are quite good at it. In Solid Edge, you tell the system which set of curves is the top view, which is the side and so forth until you have enough views to define the part. It will piece them together into a glass box, if you will, that describes the part (figure 1). When it's done, you pick which curves to extrude and such, and you can build a 3D model very quickly.
Figure 1. Solid Edge will use imported 2D curves to help you build a 3D model.
Even 2D scans of board drawings or bitmap photos of actual items are useful. You can import them into your modeling software and trace right over them, matching curvature and overall sizes (figure 2).
Figure 2. This model is merely a 3D surface with a bitmap applied to it. It s a great way to use bitmaps for visualization and concept work.
What happens when your pointy-haired boss drops a component on your desk and says that he wants you to design something to interface with it? A company I once worked for had been producing a part for more than 20 years, but the injection mold was wearing out, so I was asked to create a 3D model for new tooling. The first problem I faced was that the drawing didn't match the part in my hand. No one had bothered to update the drawing when changes were made to the part. We decided to get a 3D scan of our part.
3D scanners examine a physical part, measure points on its surface and then reproduce those points in 3D cyberspace. Some scanners are large and stationary, while others are small and handheld. The handheld scanners are a little more interesting to use than the stationary ones; as you move the scanner around the part being scanned, your hand shakes. (It's natural, you can't help it. Every time your heart beats, your whole body moves ever so slightly.) However, handhelds can go with you wherever you need to go. For example, a museum or university might use one to capture an ancient artifact. After the shape is captured, a bitmap of the object can be wrapped around the 3D shape. Voila! You have an accurate representation of the artifact that you can send to everybody and their brothers to study and enjoy.
Many sources provide 3D scanning. You can buy a scanner or hire a scanning service. Z Corp. sells its ZScanner 700 for $39,900 (figure 3). It's pretty easy to use. You affix 3D targets (little sticky dots) around your part then basically point and shoot. The ZScanner performs real-time data capture in one continuous scan then builds a surface entity on your computer screen as you go. It's neat to watch. It outputs a 3D STL file that you can import into just about any 3D solid modeling program.
Figure 3. Z Corp.'s ZScanner 700 is a real-time, handheld 3D scanner that helps users capture 3D data.
You also can go to a 3D scanning service. These places are very good at what they do. They can give you a variety of output formats. I have received STL files, which are faceted surface models; surface models; and even fully parametric SolidWorks files.
Before we get all excited about this scanning, remember that 3D scanning has its downsides. The scanner is capturing a point cloud it sees based on a grid that it projects onto your part. The scan is going to be accurate only in areas it can see. If you scan an object that has an undercut, chances are the scanner won't be able to see the undercut. And when it does see your part, the raw scan data can look pretty funky (figure 4). Surfaces created from this kind of data are going to be only interpolated representations. In other words, the scan only can be as accurate as the assumptions made. And when a company promises to deliver a fully parametric SolidWorks part, you must realize that there's no magic button that takes raw data and figures out what this is and what that should be. Somebody had to import the raw data or maybe surface data into SolidWorks and build from it. Most of the time, these scanning services will have access to an actual part (they had to scan something) that they can peruse and measure.
Figure 4. Raw data from a 3D scanner can be pretty scary. These features are merely cylinders on a slanted surface. Encouraging?
If you don't want to go the 3D scan route, you can have someone use a CMM (coordinate measuring machine). This device usually is stationary, so it'll be very accurate. You clamp your part into the machine, and it uses a probe to physically touch the part. Where it touches, it registers a data point. Of course, overall accuracy depends on how many points you capture.
For 3D modeling, you need as big a screen as you can get! I'll say that as loudly and as often as I can. True, you can zoom on a model to where a .005" component looks like the tall building that Superman jumps over in a single bound. But if you have a puny 15" monitor, you'll feel like you're looking through a microscope.
The kind of mouse you use can affect your design as well. If the mouse is uncomfortable or cumbersome, your work experience will suffer. Go with something with as many buttons as you can get—okay, three buttons are enough for most applications. And nowadays, you can reprogram what the buttons do. For example, say you do a lot of zooming. You can assign zoom to a control/right-mouse click. If you use the mouse every day, you'll memorize the layout and functions you assign quickly, so it can help you become more efficient.
Invest in the products of a company called 3Dconnexion, the maker of the popular Spaceball, SpaceMouse and Magellan products. 3Dconnexion recently revamped its whole line of 3D controllers (figure 5). The devices allow you to control your models with a level of intuitiveness you didn't even know could be reached. I wouldn't think of 3D modeling without one.
Figure 5. Warning! 3Dconnexion s Space product line is habit-forming. After you use these products, you ll never want to go back to what you did before.
If you have a big budget, you could look at a haptic input device such as SensAble Technologies' Phantom device (figure 6). The Phantom Omni, Desktop and Premium enable users to actually feel their models. That's right—feel. If you have ridges on a model and you can run the cursor over them, the Phantom device will give you resistance in all the right places. It feels like you're moving over a solid object.
Figure 6. Moving the pen and the arm will transmit the motion to the cursor. When the cursor contacts your virtual model, the arm transfers resistance back to the pen. It creates a very realistic sensation.
To Be 3D, or Not to Be
3D input is important to any engineer or designer. There are just too many times when you have to acquire 3D data to live without it. Whether you are reverse engineering a part or designing a mating component, 3D input can save you a lot of time and energy. It's important for you to know how to proceed and what technologies and methodologies to use. If you can find just one way to save yourself time and/or effort, you'll be better off than when you started.
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Mike Hudspeth, IDSA, is an industrial designer, artist and author based in St. Louis, Missouri.