F8ld is a novel parametric approach for the construction of PPE, a face mask inspired from takeaway food packaging and kirigami techniques. The technique requires only foldable planar material with no gluing or binding of any kind. The design is customizable to the user’s face using an augmented reality application and automatic processing via a script in the Grasshopper environment. Using the proposed workflow, a personal mask can be constructed from paper printed on an ink-jet printer. This makes it one of the most affordable and fast techniques for artisanal PPE existent now.
The design is based on the polyhedral shape of an octagonal truncated pyramid. The apex of the pyramid is placed about 4 cm away from of the tip of the nose and its base points are resting on the face itself. The positioning of the control points of the truncated pyramid can be visualized in the figure below. The mask is in fact a hollowed-out model of the truncated pyramid where the large base is missing to allow for the protruding parts of the face to fit inside the polyhedral volume.
The folding of the mask from a planar cut pattern, can be regarded as a reverse sequence of the modelling steps undertaken as part of the design process. The finite states of the folding process that from the flat pattern to into the 3d model of the mask as well as some important intermediary steps are presented in the image below.
The fully unfolded model, presented in the image, is an eight-arm star-shaped planar pattern containing each face of the truncated pyramid exactly twice in two concentric rings. The pattern is also including several flaps and fold-in bellows. The flaps are used to keep the folded form in its shape and the bellows ensure surface continuity. The images a through f depict the assembly process and how the flat pattern becomes the truncated pyramid of the mask. The process reveals how folding doubles each face of the mask thus ensuring a continuous layer of material throughout the folded shape and thus air-tightness. Each important vertex can be followed from the flat pattern all the way to the final shape. Each vertex has a unique tag composed of a letter from a to h and a subscript number. The letters correspond to nodes in the octagonal polygon that is the base of the pattern. The numbers denote the relationship between the points connected to the same octagon vertex but part of different folded faces.
One important, albeit optional feature of the design is the possibility to include a filtering material between the double faces of the base of the truncated pyramid. Between the folding actions shown in image c and d above, a patch of filtering material can be inserted between the top layers of the truncated pyramid. The octagonal cut-out in the two faces is designed to facilitate the flow of air, through the filter. Presently one singular cut-out is designed but this can be replaced with an array of smaller holes that help to better secure the filtering material in place. Figure 3 shows a few variants of the filter cut-out patterns. Even though the design does not present a method to affix the mask to the user’s face, a simple, singular string looped through two holes on the side of the mask next to one of the vertices touching the face can resolve this problem. The overall rigidity of the folded object, especially along the axis of the face, will make two fixation points for the mask enough. In order make the representation clearer and simpler the affixing string is omitted from the figures.
Face customization for each user is achieved using and inexpensive ToF (time-of-flight) sensor present in most modern smartphones and used as a security feature in iOS phones for several years now. Using the arKIT api developed by apple and the Unity game development environment a custom app was created to scan the face of the user and fit the mask base geometry on it. From the app the geometry is automatically exported as and obj file. The file is imported and unfolded using a custom Grasshopper script and the Ivy extension. The image below shows a screen grab from the Unity application.
Scroll down for a series of videos showing the use of the proposed workflow.
