Digital technology takes shape

4 September, 2008

Imagine your client wants you to develop a special-purpose vehicle based on a standard passenger vehicle. Chances are, however, that you won’t have access to the original design information. This means you’d have to generate the data yourself or revert to traditional manual design methods.

In the past, when automotive design and engineering specialist MIRA was faced with this situation – a common occurrence – it had to outsource the creation of the necessary data and live with the added cost and lack of control over the quality, or turn the job down. Now, digital shape sampling and processing (DSSP) technology means everything can be done in house.

The services MIRA offers range from one-off projects, such as performance testing an existing vehicle component or assembly, to turn-key projects that start from a blank sheet and involve the design, development, engineering and prototyping of a complete vehicle. It might also include the design of the production line and facilities required for manufacturing the final vehicle.

DSSP encompasses the convergence of multiple technology advances. It describes the ability to use scanning hardware and processing software to digitally capture physical objects and automatically create accurate 3D digital models with associated structural properties for downstream design, engineering, inspection and custom manufacturing. It requires scanner hardware to capture point data, and software to process the point data into useful digital results.

MIRA has used touch probe coordinate measuring machines (CMMs) to collect discrete point measurements for some years, but these aren’t suitable for the digital capture of complex geometric shapes or products made from deformable materials such as plastics. So, the company moved to DSSP in 2006, with the technology taking the form of a FARO Laser ScanArm optical scanner and Geomagic Studio 3D modelling software.

Its two main uses are benchmarking projects which often involve testing vehicle components and assemblies for compliance with pedestrian and passenger safety regulations. Design-led activities might involve developing a special-purpose vehicle from a production vehicle or producing Class A surfaces from styling models.

On the benefits, Dave Wykes, senior engineer, Vehicle and Systems Engineering Group at MIRA, said: “When there is no original design information available for us to work with, we are able to rapidly create our own accurate 3D digital model of the component or vehicle that will form the basis of our new design. This gives us the information we need to take on into the design and/or analysis process and enables us to have confidence in the feasibility of our downstream design and engineering activities.”

Creating the model
Much of the new design work, engineering analysis and benchmark testing needs a 3D digital model, so the starting point is to perform a digital scan. The FARO Laser ScanArm 3D digitiser fully integrates a contact/non-contact measurement device and laser scanner and can capture 19,000 points/sec. The data is saved as a point cloud which represents the set of

three-dimensional points that describes the outline of the object. The point cloud is then brought into Geomagic Studio software. This software extracts geometry and topology from measurement data and creates high-quality 3D digital surface models that can be used within other CAD, CAE and CAM applications for downstream functions such as detailed design, engineering analysis, simulation and machining.

Depending on the point cloud size, the first step in the process of creating a 3D digital model may be to reduce the data to a more manageable amount, without affecting its accuracy, using random, uniform and curvature-based point sampling. It may also be necessary to eliminate ‘noise’ generated during scanning. Then, a polygon model has to be created from the point cloud data, often achieved automatically using the Wrap feature. Tools then allow the polygon model to be refined, resulting in an accurate digital polygon model of the original object.

If the model is for a design-led project, Geomagic Studio can convert the polygon model into a high quality NURBS (non-uniform rational b-spline) surface model which can be exported into CATIA V5 CAD software for detailed design engineering work where it can be modified for incorporation into the digital ‘master’ model of a new or revised product. If the model is required for benchmarking or engineering analysis, the polygon model is saved as an STL file in Geomagic Studio for export to a CAE application.

Accuracy
In design-led projects, Geomagic Studio and CATIA CAD software in tandem enables the engineers to take a project seamlessly from initial surface model creation through design modification, engineering analysis, documentation and into prototype production.

One example is in the motorsport industry. World Rally Car and European Touring Car Championship cars are based on standard passenger vehicles but have roll cages which

are often of a bespoke design and have to meet international standards. Testing is usually though a physical crash test which can be expensive and time-consuming.

Now, however, the engineers at MIRA can create accurate 3D models and export these to CATIA for design development or to CAD software for engineering analysis. This means MIRA is the only organisation in the UK that is able to certify bespoke roll cage designs to international standards without the need for crash testing.

The company also uses a similar approach to new vehicle design such as hybrid, emergency or mobility vehicles, that are based on existing vehicles but where no CAD data is available.

Apart from giving MIRA the ability to design and engineer automotive parts as well as complete vehicles in less time and with greater accuracy, DSSP, CAD and CAE enable it to avoid the tendency to ‘over-engineer’ a product. With a digital model everything can be digitally simulated and tested, saving both time and cost.