Aug 15, 2016 | By Benedict

Autodesk has explained how users can achieve sub-pixel resolution for DLP 3D printing using the company’s open-source Ember 3D printer. The technique uses grayscale anti-aliasing to effectively smooth out a print along its edges.

On the whole, 3D printer resolution tends to be thought of as a black-and-white issue. Z-axis resolution is easy to assess, and although XY resolution can be more difficult to measure, a 3D printer’s resolution is more-or-less limited by the precision of its light source (SLA, DLP) or size of its extruder nozzle (FDM). In spite of this, 3D software specialist Autodesk has pointed out a (literal) gray area which can be exploited to obtain “sub-pixel” resolution on its Ember DLP 3D printer—and on any other DLP 3D printer, for that matter.

DLP (digital light processing) 3D printers create 3D printed objects by curing thin layers of a light-sensitive polymer liquid with a projector. Generally, users can only create 3D printed objects as detailed as the projector itself will allow. However, with Autodesk’s handy tip, users can employ an anti-aliasing (smoothing of jagged edges) technique which effectively ups the resolution of a DLP 3D printer by partially curing individual pixels to different degrees.

When creating a 3D printed object with a DLP 3D printer like the Autodesk Ember, the printable area is divided into “voxels,” 3D units out of which a shape can be built. If a pixel (the XY plane of the voxel) is marked as “white,” the projector will cure the resin occupying the space of that particular pixel, building up a cured, 3D voxel; if it is “black,” the projector will avoid curing that area of resin. In an experiment, Autodesk staff asked themselves what would happen if they printed a “gray” pixel—would it print half a voxel? And if so, where would that half-voxel end up?

Richard Greene, a prominent member of Autodesk’s Ember development team, created an experiment where he printed a solid row of voxels followed by a row of pixels ranging in brightness from dark to light. “[Greene] found that pixels darker than a certain shade don’t print at all,” explained Autodesk’s Steve Kranz. “Then, at a certain point, hemispherical bumps form attached to the previously printed layer. A brighter pixel produces a taller bump, and as the pixel gets brighter the voxel grows wider and slightly taller. This means the size of the voxel can be controlled by varying the the luminosity of a single pixel.”

By using gray values on an image, Greene was able to “place” a 3D cube virtually anywhere on the printing area—even in between pixels—giving him a much greater degree of precision. The trick also allowed for the creation of precise vertical slopes: Greene made a 3D model of a vertical pillar, standing at a 90 degree angle to a base, which consisted of solid white voxels. By adding a one-pixel-wide gradient of 32 gray values down the side of the pillar, the Autodesk expert was able to create a precise slope on which each layer was roughly one-and-a-half microns thinner than the layer below. This resulted in a draft angle of 3.6 degrees, all within a single 50-micron-wide pixel.

The implications for this clever technique are potentially significant, and they should be attainable using any kind of DLP 3D printer. Additionally, Autodesk is currently looking at ways to of adding noise and textures to image slices, potentially giving prints a more “injection-molded look” and making it harder to see the tell-tale layer lines of the 3D printer. “These grayscale tricks don’t magically allow you to print sub-pixel features, but they do allow you to reduce the layer lines and some other artifacts you see on 3D prints,” Kranz concluded.



Posted in 3D Printing Technology



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YoMomma wrote at 8/19/2016 2:43:16 AM:

How is this anything new? WTF! Next they'll say Autodesk invented grayscale.

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