GrabCAD is a collection of lots and lots of pixels - and GrabCADrs too. But on your screen, its bit-mapped pixel by pixel. Voxels are essentially the three-dimensional version - a point in space that together forms a shape. Although CAD users are familiar with surfaces, solids, NURBS and meshes, voxels are coming into the picture in design and manufacture, with unexpected consequences.
Out of Cornell University, Dr. Hod Lipson and Jonathan Hillier at the Creative Machines Lab have been exploring the possibilities and ramifications of 'bitcrunching' CAD and manufacturing. In essence, much of design and manufacturing is outwardly 'analogue' - pieces are either carved away via a lathe, cast with molten liquid or extruded through a nozzle. Of course, CAM and CAD couldn't be possible without digital technology - but in some ways, nothing is made in bits are they?
This is how they describe the future.
Imagine a desktop fabricator capable of making perfectly repeatable, arbitrary, multi material 3D objects with microscale precision. The objects would be composed of millions or even billions of small physical building blocks (voxels). Some building blocks could be hard, some could be soft. Some could be red, others green or blue. Some could be conductive and others could perform computation or store energy. Some could even be sensors and others actuators, and so on and so forth. With a relatively small repertoire of building block types and a rapid assembler, one could assemble a relatively large variety of machines at high resolution.
For a better visual demonstration, watch this video.
Of course, attaching these pieces would be the difficult part. In a lot of ways, these voxels are no different from your ordinary lego blocks - they have common joints to attach themselves together. The variety of shapes is infinite - the essential method of joining them is the same. However, the 'voxelation' (think pixelation) of an object, that is to say, the fidelity of the shape is difficult to attain in manufacturing and in design.
In order to have nice smooth surfaces, the voxels have to be very very small. Having a fabricator like the one shown above, depositing tiny micro-sized voxels is beyond the reach of most high-end stepper motors to drop the voxels precisely, let alone the necessary deposition technique. Secondly, Bit-mapping 3 dimensional objects in voxels is incredibly intensive, forcing a computer to handle large data-sets.
Lipson and Hillier argue that creating the right type of voxels so that they organize themselves was the key, using a set of different types that interlocked in a particular manner to create a whole galaxy of designs with "an object more precise than the fabricator that created it."
By geometric design, the voxels will self-align upon assembly so a fabricator need only place the voxel within a certain distance of its final position. Thus, the precision of the final part depends only on the tolerances of the voxels. This is analogous to a child with 1 mm hand placement precision assembling LEGOe structures with 5mm precision.
The other problem of creating digital files that are easy to handle in CAD without losing fidelity is, and has always been, a matter of compression. Over the past few years Cornell has been pushing the development and adoption of the Additive Manufacturing Format, or AMF. Described by Lipson in an article in Engineering.com as a hybrid of modelling techniques, it allows for graded or lattice structures to be created, an ability that Voxel-based manufacturing can do. A compressed AMF file records essential 'bits' and the complete 'map', saving a great deal of space.
Together, the possibilities for Engineering and Design are endless. Graded changes in density over a volume. Placing different voxels of different materials at crucial points to strengthen or weaken a design, making it squishy or solid depending on design intent and engineering requirements. Self-constructing designs. However amazing the possibilities, Voxel-based fabrication is still in it's infancy. There is no pressing shortage of difficult challenges to be resolved, and a niche is bound to present itself shortly as a home.
For further reading, take a look everything on Cornell's Creative Machine Lab website about their Rapid Assembler. There is also a great read on AMF here as well as a fabulous website called VoxelFab by Joris Peel which goes over the possibilities. Like giant, voxelated Killer Whales (found in downtown Vancouver, Canada, by Douglas Coupland)
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