Mélina Skouras

Computational design of actuated deformable characters

We present a method for fabrication-oriented design of actuated deformable characters that allows a user to automatically create physical replicas of digitally designed characters using rapid manufacturing technologies. Given a deformable character and a set of target poses as input, our method computes a small set of actuators along with their locations on the surface and optimizes the internal material distribution such that the resulting character exhibits the desired deformation behavior. We approach this problem with a dedicated algorithm that combines finite-element analysis, sparse regularization, and constrained optimization. We validate our pipeline on a set of two- and three-dimensional example characters and present results in simulation and physically-fabricated prototypes.

Physical face cloning

We propose a complete process for designing, simulating, and fabricating synthetic skin for an animatronics character that mimics the face of a given subject and its expressions. The process starts with measuring the elastic properties of a material used to manufacture synthetic soft tissue. Given these measurements we use physics-based simulation to predict the behavior of a face when it is driven by the underlying robotic actuation. Next, we capture 3D facial expressions for a given target subject. As the key component of our process, we present a novel optimization scheme that determines the shape of the synthetic skin as well as the actuation parameters that provide the best match to the target expressions. We demonstrate this computational skin design by physically cloning a real human face onto an animatronics figure.

Designing inflatable structures

We propose an interactive, optimization-in-the-loop tool for designing inflatable structures. Given a target shape, the user draws a network of seams defining desired segment boundaries in 3D. Our method computes optimally-shaped flat panels for the segments, such that the inflated structure is as close as possible to the target while satisfying the desired seam positions. Our approach is underpinned by physics-based pattern optimization, accurate coarse-scale simulation using tension field theory, and a specialized constraint-optimization method. Our system is fast enough to warrant interactive exploration of different seam layouts, including internal connections, and their effects on the inflated shape. We demonstrate the resulting design process on a varied set of simulation examples, some of which we have fabricated, demonstrating excellent agreement with the design intent.

Computational Design of Rubber Balloons

This paper presents an automatic process for fabrication‐oriented design of custom‐shaped rubber balloons. We cast computational balloon design as an inverse problem: given a target shape, we compute an optimal balloon that, when inflated, approximates the target as closely as possible. To solve this problem numerically, we propose a novel physics‐driven shape optimization method, which combines physical simulation of inflatable elastic membranes with a dedicated constrained optimization algorithm. We validate our approach by fabricating balloons designed with our method and comparing their inflated shapes to the results predicted by simulation. An extensive set of manufactured sample balloons demonstrates the shape diversity that can be achieved by our method.

aeroMorph - Heat-sealing Inflatable Shape-change Materials for Interaction Design

This paper presents a design, simulation, and fabrication pipeline for making transforming inflatables with various materials. We introduce a bending mechanism that creates multiple, programmable shape-changing behaviors with inextensible materials, including paper, plastics and fabrics. We developed a software tool that generates these bending mechanism for a given geometry, simulates its transformation, and exports the compound geometry as digital fabrication files. We show a range of fabrication methods, from manual sealing, to heat pressing with custom stencils and a custom heat-sealing head that can be mounted on usual 3-axis CNC machines to precisely fabricate the designed transforming material. Finally, we present three applications to show how this technology could be used for designing interactive wearables, toys, and furniture.

Interactive surface design with interlocking elements

We present an interactive tool for designing physical surfaces made from flexible interlocking quadrilateral elements of a single size and shape. With the element shape fixed, the design task becomes one of finding a discrete structure---i.e., element connectivity and binary orientations---that leads to a desired geometry. In order to address this challenging problem of combinatorial geometry, we propose a forward modeling tool that allows the user to interactively explore the space of feasible designs. Paralleling principles from conventional modeling software, our approach leverages a library of base shapes that can be instantiated, combined, and extended using two fundamental operations: merging and extrusion. In order to assist the user in building the designs, we furthermore propose a method to automatically generate assembly instructions. We demonstrate the versatility of our method by creating a diverse set of digital and physical examples that can serve as personalized lamps or decorative items.

Two-Scale Topology Optimization with Microstructures

In this article, we present a novel two-scale framework to optimize the structure and the material distribution of an object given its functional specifications. Our approach utilizes multi-material microstructures as low-level building blocks of the object. We start by precomputing the material property gamut—the set of bulk material properties that can be achieved with all material microstructures of a given size. We represent the boundary of this material property gamut using a level set field. Next, we propose an efficient and general topology optimization algorithm that simultaneously computes an optimal object topology and spatially varying material properties constrained by the precomputed gamut. Finally, we map the optimal spatially varying material properties onto the microstructures with the corresponding properties to generate a high-resolution printable structure. We demonstrate the efficacy of our framework by designing, optimizing, and fabricating objects in different material property spaces on the level of a trillion voxels, that is, several orders of magnitude higher than what can be achieved with current systems.

Computational discovery of extremal microstructure families

We report the first fully automatic method for discovering microstructure families with extremal physical properties. Modern fabrication techniques, such as additive manufacturing, can be used to create materials with complex custom internal structures. These engineered materials exhibit a much broader range of bulk properties than their base materials and are typically referred to as metamaterials or microstructures. Although metamaterials with extraordinary properties have many applications, designing them is very difficult and is generally done by hand. We propose a computational approach to discover families of microstructures with extremal macroscale properties automatically. Using efficient simulation and sampling techniques, we compute the space of mechanical properties covered by physically realizable microstructures. Our system then clusters microstructures with common topologies into families. Parameterized templates are eventually extracted from families to generate new microstructure designs. We demonstrate these capabilities on the computational design of mechanical metamaterials and present five auxetic microstructure families with extremal elastic material properties. Our study opens the way for the completely automated discovery of extremal microstructures across multiple domains of physics, including applications reliant on thermal, electrical, and magnetic properties.

Computational Design and Fabrication of Deformable Objects

Deformable objects have a plethora of applications: they can be used for entertainment, advertisement, engineering or even medical purposes to cite but a few examples. However it is precisely because they deform that such objects are difficult to design. Their creator must foresee and invert effects of external forces on the behavior of the figure in order to take the proper design decisions. In this thesis, we investigate approaches based on physics-based simulation and inverse optimization techniques which alleviate these difficulties and we propose a complete framework to design custom deformable objects by automating some of the most tedious aspects of the design process. This framework is tailored to various applications in which optimization of diverse variables comprising rest shape, materials and actuation system is alternately considered. Validation of our method is performed by fabricating representative sets of physical prototypes designed with our method and compared to the results predicted by simulation. We start by introducing the basic concepts of physics-based simulation and optimization on which our inverse modeling component, central to our approach, is built. We show how the optimization of the system’s degrees of freedom can be cast as a constrained minimization problem combining strict enforcement of physical consistency with target shape approximation. A method to automatically design and easily fabricate rubber balloons of desired inflated shapes is presented in the following part of the thesis. In that section we precisely describe the different stages of the pipeline including material modeling and fitting, rest shape optimization and physical fabrication. We then extend our framework to address the problem of creating physical replicas of twoand three-dimensional animated digital characters which can be actuated using pins, strings or posed by hand. Our approach automatically computes a sparse set of actuators as well as their locations on the surface and optimizes the internal material distribution such that the resulting character exhibits the desired deformation behavior. Fully automatic systems are not always desirable. Aesthetics considerations, for