Reverse engineering a swing bridge with Geomagic Design X
Ferry company turns to 3D scanning tech and simulation software for bridge maintenance work.
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Situated in a coastal dock system in North West England is a swing bridge that connects a dock with the mainland. The bridge was decommissioned and left in the open position following two incidents that had left it twisted.
A ferry company wished to get access across the bridge for car parking purposes, so they needed to have it in full working order again. However, this presented a Catch-22 situation.
To see if the bridge was functioning correctly, the company would need to close it. But if they closed the bridge and it wasn’t functioning correctly, it would jam in that position preventing entry to the dock.
While testing was impossible to carry out in the physical world, the company found a solution in the virtual one. They created a digital twin of the bridge using a long-range laser scanner and simulated the motion of the bridge if it were to be closed.
Scanning a swing bridge
This approach is the brainchild of 3D measurement specialist OR3D and its Service Manager Robert Wells. The UK-based company used a 3D scanner to capture all the detail of the bridge and Geomagic Design X to process the scan data and create a CAD model that would be used in the simulation software. The scanning was carried out with a team of two in a single day shift, resulting in 120 high-definition scans.
In Geomagic Design X, OR3D’s Application Engineer Sean Kean modelled the bridge, surrounding area, connecting parts – including the pintle and its central location – the roller track and any blocks the bridge sat on in the open position.
Accuracy of the essence
The modelling and the data processing took a few days due to the size and complexity of the model and the accuracy requirements.
“Once we modelled the bridge in Design X, we ran the simulations, and saw the bridge was going to collide in a certain position,” Kean explains. “That gave the company the confidence to try it for real.”
The simulation indicated the bridge would strike another surface by two or three millimetres. This prediction was proven correct in real-life testing. “We wouldn’t have been able to simulate this correctly without accuracy, both with the scan data and the CAD model. Realistically, Geomagic Design X is the only package able to do that,” Kean says.
A few features played a pivotal role in achieving this level of accuracy. For a start, there are the MeshSketch and the Deviation Analysis, two of Kean’s favourite tools. “Within the sketch we can immediately check the deviation between primitive sketch entities, be it a line, an arc or even a spline, and the data so we can see how accurately we’re drawing,” he explains.
The 3D deviation analysis enables Kean to see the deviation of the surface he created and the scan data using a colour map. This is vital for understanding how well he modelled the part. “Knowing how accurately we’re modelling allows us to go back to the customer and say with confidence what’s going to happen to the bridge. Without that constant feedback that you’re getting from Geomagic Design X it’s very difficult to model well,” he says.
More than traditional CAD
Another reason Kean reached for Geomagic Design X is that it includes all the important traditional modelling techniques of a CAD package in addition to the capabilities necessary for efficient scan editing.
Reverse engineering the bridge with a run-of-the-mill CAD solution wouldn’t result in the same level of quality, according to Kean. “Most CAD packages these days can handle some mesh format, but they cannot handle anywhere near the range of mesh formats that Design X can.”
Another area where Geomagic Design X beats CAD software is large data sets. “Terrestrial data, like the one we worked with in this project, is huge. Traditional CAD packages can’t handle that size of data. Initially, we’re probably talking about a few hundred million points and then we would decimate that down. But decimating is another thing you can’t do with traditional CAD packages,” Kean says.
Geomagic Design X gives him both options. It’s powerful enough to work with large data efficiently, but it also allows you to decimate the data to speed up the CAD modeling. “Traditional CAD software would have locked up at that point,” Kean says.
When OR3D delivered the model and the simulation, their client was blown away by the clarity and the accuracy of the data. The results are down to the scanning device, on the one hand, and the powerful capabilities of the software, on the other. “No other reverse engineering package is capable of anywhere near the modeling capability that Design X is,” Kean says.