RS’ free of charge IDf-to-Collada converter allows EDA tools to connect with the popular Google SketchUp 3D Modelling package.
Ever had a design that did not quite fit the mould? You have laid out the PCB and made sure that your design meets all the design rule criteria. Everything is going fine until someone points out that the stiff ening bar needed to strengthen the outer casing fouls a connector.
These are the moments when the worlds of mechanical computer aided design (MCAD) and electronic (ECAD) collide. For years, they have proceeded along parallel lines and only interact at the very late stages of the design when everything is finalised and problems are discovered.
Designs that utilise standard package dimensions of a standard packaging format, there is less to go wrong. You can rely on the standard measurements for mounting holes to be confident that the PCB will go in the space provided – just as long as you have not used some very tall components. But this “safe” approach can only get you so far.
Heat is a concern for many designs. A hot-running processor will need a large heatsink that might block the cooling flow of air for other critical components. It is hard to see how airfl ow might be constricted from the pure 2D view of a PCB layout package. A much clearer picture emerges only when you move into the 3D world to see how the PCB, components, connectors and packaging fit together. The ability to do this earlier in the design is crucial to keeping project lead times to an absolute minimum. A better link between ECAD and MCAD is not just about avoiding mistakes.
Many of today’s products demand a sleeker, more attractive look than a standard eurocard chassis. More electronics systems are having to fit in alongside moving mechanical components – and are constrained by the size and shape of these subsystems. If you can obtain as early as possible an interactive visual representation of the design, it is much easier to see how it works aesthetically and mechanically, and you can identify sizing or user-interface placement issues that aren’t readily apparent in schematic mode.
Despite the attraction of linking the two domains together, the gap between ECAD and MCAD has taken a surprisingly long time to close. This is true even in big projects, such as those encountered in aircraft and automobile design. Problems with mismatched specifications that resulted in expensive rework for engineers on both sides of the gap led to a push to create standards that could link ECAD and MCAD tools together.
The main standards that were created came from the PDES consortium of which a number of the large aerospace and automotive companies were members. PDES came up with the STEP series of standards that included support for electrical and mechanical CAD data. However, support for these standards remains patchy. A few of the ECAD vendors decided to base their efforts on STEP but focused on building links to specific third-party tools such as Pro/Engineer or SolidWorks.
One of the more successful proprietary links was the Intermediate Data Format (IDF). Developed in the early 1990s, the format has evolved to include support for more 3D data and even thermal characterisation data to allow designs to be more easily passed to heatflow simulation software. IDF is now supported by a number of ECAD and MCAD vendors as a way of exchanging design data between their respective tools.
However, the MCAD tools that support IDF exchange represent a significant financial investment for engineering teams, especially if the bulk of the package design work is going to be outsourced to another specialist company. There is no real need to invest in an expensive MCAD infrastructure if another team or company has the tools needed to take a mechanical concept and turn it into mouldings, assemblies and CNC milling programs.
Free tools such as Google SketchUp have appeared that are ideal for creating realistic product design concepts and mock-ups. More importantly, SketchUp has been designed to allow collaborative design. Users can search for models that already exist in a 3D ‘warehouse’ of shapes and designs and build them into a design. So, if you see a packaging design that would fit your product and want to incorporate that into your electronic system design, it is simply a matter of downloading it. SketchUp even supports the interactive manipulation of moving parts, making it easier to see how an electromechanical system, possibly with fl exible circuits will look and feel in different orientations, making it much easier to check whether a cable will interfere with other parts as it moves around.
The difficult part, until now, has been marrying the physical design of one of these SketchUp objects with the PCBs and connectors that need to fit inside it. Natively, SketchUp does not support the IDF file format. Instead, data exchange is based around the Collaborative Design Activity (COLLADA) interchange file format. Maintained by the Khronos Group, the XML-based COLLADA format has become the key interchange format for people working in interactive 3D – its support for movable, interactive objects makes it a good choice for SketchUp. Unfortunately, it is not a format understood by ECAD tools.
To close the loop, RS Components has created a file converter that can take IDF files and rework them into the COLLADA format. By combining an ECAD tool which generates IDF files for use with MCAD software, with Google SketchUp, designers have available to them an end-to-end solution for visualising complete electronic systems in 3D.
Once a converted PCB layout has been imported into SketchUp, the designer can refine the look of the model. Connectors and other assemblies are represented in detail in the huge library of 3D component models that RS have assembled and made available for download. For example, pushbuttons and sensors can be moved into place showing how they will integrated with the PCB layout and the external packaging.
This capability gives electronic designers more power to make educated design decisions immediately rather than waiting for expensive prototypes, external modelling or spending valuable time convening design reviews. At the same time, electronic engineers can gain more insight into the MCAD domain and use that knowledge to create more manufacturable designs.
In that way, the full benefits of removing the metaphorical brick wall that always seemed to exist between the two disciplines of electronic and mechanical design will be realised.
Article from eTech issue #7
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