Nov 10, 2015 | By Alec

Cool 3D printed robots and other tools filled with electrics can be found all over the web, but the amount of work that goes into them goes far beyond simple 3D printing and can often scare people away. While a number of research projects have been trying to find ways to make that process simpler by, for instance, stopping 3D printing and inserting electronics, an even cleverer solution has come out of Germany. A team of researchers from the Technische Universität Darmstadt has developed a platform called Capricate, which essentially turns surfaces on 3D printed objects into sensors with the help of carbon-filled ABS filament.

This intriguing platform is detailed in a promising research paper called ‘Capricate: A Fabrication Pipeline to Design and 3D Print Capacitive Touch Sensors for Interactive Objects’, and has been developed by experts Martin Schmitz, Mohammadreza Khalilbeigi, Matthias Balwierz, Roman Lissermann, Max Muhlhauser, Jurgen Steimle.

As they explain in their paper, 3D prints are often passive in their nature due to the complexity of embedding electronics. ‘The design of touch electrodes is still a tedious task and often requires expert knowledge in CAD. This is partially due to the fact that custom-shaped areas on a 3D surface need to be selected, extruded, and fused manually with the original model,’ they argue. While most people resort to assembling separate parts alongside electronics, this process does put limitations on the shape of the object in question. That, they say, isn’t a problem with Capricate. ‘[This is] a fabrication pipeline to design and print capacitive touch sensors embedded in 3D printed objects. It is based on a multi-material 3D printing approach and uses affordable off-the-shelve materials and 3D printers. Our design tool allows users to easily create custom shaped touch sensors on 3D surfaces of objects,’ they write in their paper.

Now this system truly seem to be the real deal, as design itself is largely unaltered and can take place in standard 3D modeling environments used for passive objects. The touch-sensitive areas are subsequently added through Capricate, and can be 3D printed on a desktop 3D printer capable of 3D printing multiple material. The result can finally be hooked onto a wide range of controllers such as Arduino or capacitive multi-touch surfaces such as tablets. Sounds too simple, but it’s true.

So how does it work? In Capricate, users can simply select parts of the model using a simple interaction technique: ‘After selecting whether a touch button or grid should be created, she indicates the rough location and the approximate size of the sensor on the 3D surface. The user is supported by a 3D visualization that closely follows the 3D surface as the mouse cursor hovers over a part of the object,’ they explain. This can be used to create sensors that can be hooked to controllers through standard ‘banana connector’ sockets’ or through on-screen capacitive forwarding to a smartphone or tablet. Two techniques for creating sensors on custom-shaped areas of doubly curved surfaces are even included: ‘The first technique consists of curved surface touch electrodes, which closely follow the curvature. To significantly speed up the fabrication process, the second technique utilizes flat subsurface touch electrodes and an automatic sensor calibration to account for the variance in overlying non-conductive material,’ the researchers write.

Now you might think that this would be impossible to 3D print, but the German team insists that it is easily done on most desktop 3D printers, with the help of custom G-code injected into existing slicing routines. ‘We used an Ultimaker Original 3D printer with Dual Extrusion Kit (ca. $1500) and a commercially available conductive ABS material (cABS) with 5-8% carbon by Torwell Technologies (ca. $50 per kg), which has an average resistivity of 8Ω * mm. We identified an optimal extrusion temperature of 230◦C (nozzle diameter 0.8 mm) with the cooling fan turned off,’ they say.

Switching between materials (the cABS for sensors, the PLA for regular surfaces) can be a bit complex, but they’ve prevented clogging and residuals as well. ‘To prevent clogging cool down the previously used extruder to the non-flowing state (to 150◦C for conductive and 100◦C for non-conductive material). Then, extrude the next material on a garbage stack located at the printing origin,’ they advise. Residuals, meanwhile, can be dealt with by retracting the material by 1 mm. ‘While the print head moves more than 1 cm without extruding, lift the z axis by 1 mm and lower it before continuing extrusion,’ they add.

Of course, there are some limitations to this technique. Geometries consisting of very small structures with high curvatures will present some difficulties, while more than touch sensing isn’t yet possible, the added value of Capricate is undeniable. And to back up their claims, the German researchers have 3D printed a wide range of individualized wearables such as rings and wristbands, a glasses frame that recognizes touch, and even a mountain range that projects data on the mountains touched.

Capricate, in short, offers a wide range of making options to users of any experience level. While the German team from Darmstadt will be busy with a number of studies revolving Capricate over the forseeable future, a commercial version would be very welcome in any makerspace.



Posted in 3D Printing Technology



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