SCF '20: Proceedings of the 5th Annual ACM Symposium on Computational Fabrication

Full Citation in the ACM Digital Library

SESSION: Session 1

Morph & Slerp: Shape description for 3D printing of concrete

Synthesis of shapes that are guaranteed to be physically produced by Robotic 3D printing of concrete, needs research attention. This is necessitated by the rapid development of the hardware, commercial availability of and interest in concrete printing. Further the need is amplified by the lack of easy-to-implement-and-use shape-design tools. Together, they provide the context of the proposed work.

A necessary feature for geometries to be ‘printable’ is that each consecutive layer onto which material is deposited should change gradually such that it has sufficient overlap with the preceding layer (spatial coherence of print paths). The computational handling of these aspects have been introduced by Bhooshan et al. (2018) including the use of a time evolving scalar-field to represent the shape to be designed – the so-called Function Representation (FRep). This paper significantly extends the previous work by (a) fully parametrising the shape description for 3D printing of concrete by decomposing the shape as a combination of shape interpolation (Morph) and affine interpolation (Slerp), and (b) replacing the linear, cross-fading interpolation scheme resulting in physically problematic artefacts with a scheme that produces smooth, spatially coherent outcomes.

An easy-to-implement software application has been prototyped. It couples the shape description with a guiding heuristic to design topologically complex, physically plausible shapes with relative ease. The coupling significantly reduces the effort and expertise needed to produce shapes that are printable whilst also providing intuitive, visual feedback to designers. This is particularly useful in the current context where computer simulation of the stability of the layers during printing is actively being developed, experimental in nature and still computationally expensive. The presented approach does not, however, automatically guarantee printable outputs. The shape description and outputs may, nonetheless, be readily used as good candidates for further optimisation to guarantee print readiness.

Design and Fabrication of Elastic Geodesic Grid Structures

Elastic geodesic grids (EGG) are lightweight structures that can be easily deployed to approximate designer provided free-form surfaces. In the initial configuration the grids are perfectly flat, during deployment, though, curvature is induced to the structure, as grid elements bend and twist. Their layout is found geometrically, it is based on networks of geodesic curves on free-form design-surfaces. Generating a layout with this approach encodes an elasto-kinematic mechanism to the grid that creates the curved shape during deployment. In the final state the grid can be fixed to supports and serve for all kinds of purposes like free-form sub-structures, paneling, sun and rain protectors, pavilions, etc.

However, so far these structures have only been investigated using small-scale desktop models. We investigate the scalability of such structures, presenting a medium sized model. It was designed by an architecture student without expert knowledge on elastic structures or differential geometry, just using the elastic geodesic grids design-pipeline. We further present a fabrication-process for EGG-models. They can be built quickly and with a small budget.

Geometry-based structural form-finding to design architected cellular solids

In this paper, we introduce a geometry-based structural design method as an alternative approach for designing low-density structures applicable to material science and mechanical engineering. This method will provide control over internal force-flow, boundary condition, and applied loads. The methodology starts with an introduction to the principles of geometric equilibrium and continues by introducing multiple design techniques to generate truss cellular, polyhedron cellular, and shell cellular (or Shellular) materials by manipulating the geometry of the equilibrium of force. The research concludes by evaluating the mechanical performance of a range of cellular structures designed by this approach.

SESSION: Session 2

Representing Crochet with Stitch Meshes

Crochet is a fabrication technique in which a 3D surface is created from yarn by interlacing loops formed with a special hook. Crochet patterns are typically represented using a standardized set of abstract pictorial symbols. Unfortunately, while this notation is enough for someone well-versed in the individual stitches, it does not directly show the yarn layout of stitches. This lack of specification makes it difficult for both novice users and computer programs to parse, visualize, and design crochet patterns.

We demonstrate how to represent crochet patterns within the “stitch mesh” paradigm. That is, the pattern is represented using a library of tiles, where each tile contains yarn geometry, and tiles connect along their edges. In order to adapt stitch meshes to crochet, we introduce a special edge type which captures the idea of the current loop – the loop of yarn held on the crochet hook during fabrication. We also create a library of mesh face types which model commonly-used crochet stitches. We illustrate the richness of the crochet stitch faces by showing a number of examples including patterns generated from 3D models.

Self-shaping Curved Folding:: A 4D-printing method for fabrication of self-folding curved crease structures

Curved folding, a method to create curved 3D structures from a flat sheet, can be used to produce material and manufacturing efficient, static or dynamic structures. However, the complex assembly and folding sequence of curved crease patterns is the bottleneck in their fabrication process. This paper presents Self-shaping Curved Folding: a material programming approach to create curved crease origami structures that self-assemble from flat into 3D folded state upon exposure to external stimuli. We propose a digital fabrication process via the 3D-printing of shape-changing materials, accompanied by a computational design workflow in which the geometry of a crease pattern is correlated with the printing toolpaths and the layup of stimuli-responsive and passive materials to achieve a target shape-change. We demonstrate our method by producing multiple prototypes and documenting their shape-change upon actuation. Lastly, we explore the functional and performance benefits of self-shaping curved folding under three application scenarios relevant to the field of industrial design and architecture.

SESSION: Session 3

Print Paths Key-framing: Design for non-planar layered robotic FDM printing

We present a method to design non-planar layered print paths for robotic fused deposition modeling (FDM) printing of single-shell surfaces. The advent of robotic arms has created great potential in the 3D printing industry for the realization of non-planar print paths that allow transitioning between different orientations during the print. However, this potential is often not fully realized due to the various challenges associated with the design of feasible non-planar print paths. Inspired by the ubiquitous key-framing technique in animation, where an input of limited degrees of freedom is used to describe a complex behavior, we propose a method to generate non-planar layered print paths subject to the input of the designer, by specifying a series of target curves on the surface of a mesh. Our method generates intermediary print paths with a direction that interpolates that of the targets while respecting the sequence and distances between neighboring paths imposed by fabrication constraints. The resulting print paths have variable layer height, and their realization relies on variable end-effector orientation. We present several examples and fabricated prototypes and make qualitative comparisons to planar slicing, to showcase the capabilities of our method.

Coupling Programs and Visualization for Machine Knitting

To effectively program knitting machines, like any fabrication machine, users must be able to place the code they write in correspondence with the output the machine produces. This mapping is used in the code-to-output direction to understand what their code will produce, and in the output-to-code direction to debug errors in the finished product. In this paper, we describe and demonstrate an interface that provides two-way coupling between high- or low-level knitting code and a topological visualization of the knitted output. Our system allows the user to locate the knitting machine operations generated by any selected code, as well as the code that generates any selected knitting machine operation. This link between the code and visualization has the potential to reduce the time spent in design, implementation, and debugging phases, and save material costs by catching errors before actually knitting the object. We show examples of patterns designed using our tool and describe common errors that the tool catches when used in an academic lab setting and an undergraduate course.

SESSION: Session 4

Automated Generation of Multi-Material Structures Using the VoxelFuse Framework

Multi-material fabrication allows for the creation of individual parts which combine several distinct materials. It can make use of materials with very different properties, allowing for mechanisms to be integrated into monolithic components. However, multi-material structures can be difficult to design using traditional CAD programs due to high material counts or surface complexity. VoxelFuse was previously introduced as an extensible modeling framework to simplify the process of designing manufacturing-ready multi-material components. This paper presents our efforts to expand the VoxelFuse framework with approaches for generating structures including primitive solids, lattice structures, triply periodic surfaces, and dithered material distributions. We introduce two example applications that demonstrate the utility of this framework for generating an infill structure and a graded material transition. This framework provides a foundation for future work in material-aware design automation.

Organic Open-cell Porous Structure Modeling

Open-cell porous structures are ubiquitous in nature and have been widely employed in practical applications. Additive manufacturing has enabled the fabrication of shapes with intricate interior structures; however, a computational method for representing and modeling general porous structures in organic shapes is missing in the literature. In this paper, we present a novel method for modeling organic and open-cell porous structures with porosities and pore anisotropies specified by users or stipulated by applications. We represent each pore as a transformed Gaussian kernel whose anisotropy is defined by a tensor field. The porous structure is modeled as a level surface of combined Gaussian kernels. We utilize an anisotropic particle system to distribute the Gaussian kernels concerning the input tensor field. The porous structure is then generated from the particle system by following the anisotropy specified by the input. We employ Morse-Smale complexes to identify the topological structure of the kernels and enforce pore connectivity. The resulting porous structure can be easily controlled using a set of parameters. We demonstrate our method on a set of 3D models whose tensor field is either predesigned or obtained from the mechanical analysis.

Reduced-Order Simulation of Flexible Meta-Materials

We propose a reduced-order simulation and optimization technique for a type of digital materials which we denote as geometric meta-materials. They are planar cellular structures, which can be fabricated in 2d and folded in 3d space and thus well shaped into sophisticated 3d surfaces. They obtain their elasticity attributes mainly from the geometry of their cellular elements and their connections. While the physical properties of the base material (i.e., the physical substance) of course influence the behavior as well, our goal is to factor them out. However, the simulation of such complex structures still comes with a high computational cost. We propose an approach to reduce this computational cost by abstracting the meso-structures and encoding the properties of their elastic deformation behavior into a different set of material parameters. We can thus obtain an approximation of the deformed pattern by simulating a simplified version of the pattern using the computed material parameters.

SESSION: Session 5

Multifunctional Mesostructures: Design and Material Programming for 4D-printing

Natural materials, such as in plant and bone organs, adapt to their surroundings with functionally graded underlying structures. Advances in extrusion-based 4D-printing have enabled the manufacture of bio-inspired systems with varying properties and self-shaping behaviors. However, tailoring the internal composition of such systems relies on specialized knowledge, as most computer-aided design (CAD) applications are based on a modeling paradigm that considers objects as surfaces or solids with no geometrical definition of the interior structure. We propose that engineered materials with differentiated and heterogeneous mesostructures can achieve nature-inspired functionality. We present a design approach for tailoring the internal topology of 4D-printed material systems, using intuitive geometric descriptions from existing CAD workflows. We introduce a material programming framework for assigning and tuning material properties such as elasticity and shape change with varying magnitudes and anisotropies throughout a volume. Our method translates the desired properties into an assembly of functional patterns for fabrication via anisotropic material deposition. To demonstrate this framework, we show several types of material behaviors, including self-shaping double curvature and embedded passive cooling. Finally, we produce a prototype of a wearable assistive device that highlights the integration of multiple functions. Through design and material programming, the resulting 4D-printed material systems underline how nature-inspired mesostructured material networks can be physically encoded with custom-designed behaviors, shape changes, and functionalities.

Tomographic color Schlieren refractive index mapping for computed axial lithography

Computed axial lithography, when used in polymeric systems, directly solidifies freeform three-dimensional geometries inside liquid or gelled materials. Currently, this patterning system operates in open loop where projections are designed prior to the print so identification of errors and corrections can only be done after the printed object has been processed. This work introduces an in-situ 3D refractive index monitoring system to track localized material conversion by performing tomographic reconstruction from color Schlieren images. Our system successfully reconstructed evolving phase objects inside resins and the reconstruction quality was verified by comparison with isosurface laser scans. The technique provides support for physics-based real-time pattern modification to improve print fidelity and reduce manual iteration time when experimenting with new materials.

SESSION: Session 6

RobotSculptor: Artist-Directed Robotic Sculpting of Clay

We present an interactive design system that allows users to create sculpting styles and fabricate clay models using a standard 6-axis robot arm. Given a general mesh as input, the user iteratively selects sub-areas of the mesh through decomposition and embeds the design expression into an initial set of toolpaths by modifying key parameters that affect the visual appearance of the sculpted surface finish. These parameters were identified and extracted through a series of design experiments, using a customized loop tool to cut the water-based clay material. The initialized toolpaths are fed into the optimization component of our system afterwards for optimal path planning, aiming to find the robotic sculpting motions that match the target surface, maintaining the design expression, and resolving collisions and reachability issues. We demonstrate the versatility of our approach by designing and fabricating different sculpting styles over a wide range of clay models.

Inverse Design Tool for Asymmetrical Self-Rising Surfaces with Color Texture

4D printing encodes self-actuating deformation during the printing process, such that objects can be fabricated flat and then transformed into target 3D shapes. While many flattening algorithms have been introduced for 4D printing, a general method customized for FDM (Fused-Deposition Modeling) printing method is lacking. In this work, we vary both the printing direction and local layer thickness; and extend the shape space to continuous-height-field surfaces without the requirement of symmetry. We introduce an end-to-end tool that enables an initially flat sheet to self-transform into the input height field. The tool first flattens the height field into a 2D layout with stress information using a geometry-based optimization algorithm, then computes printing tool paths with a path planning algorithm. Although FDM printing is the fabrication method in this work, our approach can be applied to most extrusion-based printing methods in theory. The results exemplify how the tool broadens the capabilities of 4D printing with an expanded shape space, a low-cost but precise coloring technique, and an intuitive design process.