Punpongsanon, P. Wen, X. Kim, D. and Mueller S.
ColorFab: Recoloring 3D Printed Objects using Photochromic Inks.
In Proceedings of CHI ’18 , pp. 000-000.

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ColorFab: Recoloring 3D Printed Objects using Photochromic Inks.

Recent research has shown how to change the appearance of an object even after fabrication. These systems work based on photochromic inks. In this paper, we present ColorFab, a method for changing the color of a 3D-printed object even after fabrication. ColorFab works based on photochromic inks that can switch their appearance from transparent to colored when exposed to light of a certain wavelength. The color remains even when the object is re-moved from the light source. The process is fully reversible allowing users to recolor the object as many times as they want.

So far, these systems have been limited to single color changes, i.e., changes from transparent to colored. We demonstrate how to extend this approach to multi-color changes (e.g., red-to-yellow). For this we use a multi-color pattern with one color per voxel across the surface of the object. When recoloring the object, our system locally acti-vates only those voxels with the desired color and deac-tivates all other voxels off.

We describe ColorFab’s hardware/software system and the corresponding user interface that comes with a conversion tool for 3D printing as well as a painting interface that matches physical voxels with the desired appearance. We also contribute our own material formula for a 3D-printable photochromic ink.

Figure 1: By exposing UV light, photochromic inks transit from transparent to color. While, the process can reversable by exposing the photochromic inks with visible light (e.g., projector).

Figure 2: ColorFab is a method that allows users to recolor objects even after fabrication. To accomplish this, ColorFab uses (a) 3D printing of photochromic inks in a dense multicolor pattern. (b) When users apply a specific color texture using ColorFab’s user interface, only the voxels with the matching color are activated. (c) The same object recolored multiple times.

Figure 3: Converting a 3D model into the ColorFab voxel color representation and 3D printing it. User prepares the 3D model, and load into our ColorFab software, and (a) our software splitting the model into individual voxels. (c) Our software generating a set of files for 3D printing, user can then, 3D print the object. (d) The user starts by placing the object onto the rotating platform of the projector-camera setup. (e) Design the color of 3D printed object by ColorFab painting tool. (f) When the user hits the 'process' button, ColorFab computes which voxels need to be activated and then (g) selectively deactivating voxels. (f) Afterwards, users can take the object from the platform and use it with its new appearance.

Figure 4: With ColorFab's users can repeat the process to recolor the object as many times as they like.

Material for 3D Printing Photochromics
To enable the process described above, we developed our own photochromic ink suitable for 3D inkjet printing. While photochromic plastic filaments for extrusion based 3D printers exist (e.g., MakerBot Photochromic PLA), these types of printers are not suitable for printing full-color patterns in which each voxel has a different color.

For our ink development, we focused on 3D inkjet printing with polyjet 3D printers that mix the color binder directly into the jet-able base ink. A different formula will be required for powder- or paper-based inkjet 3D printers.

The materials detail and required equipment are available in our paper.

Figure 5: Ink mixing procedure. (a) Mixing base, (b) stirring base, (c) adding photo-initiator, (d) adding photochromic dye, (e) stirring photochromic ink, (f) filtering, and (g) degassing.