This paper applies the topology optimization (TO) technique to the design of custom compression casts/braces on two-manifold mesh surfaces. Conventional braces or casts, usually made of plaster or fiberglass, have the drawbacks of being heavy and unventilated to wear. To reduce the weight and improve the performance of a custom brace, TO methods are adopted to optimize the geometry of the brace in the three-dimensional (3D) space, but they are computationally expensive. Based on our observation that the brace has a much smaller thickness compared to other dimensions and the applied loads are normal forces, this paper presents a novel TO method based on thin plate elements on the two-dimensional manifold (2-manifold) surfaces instead of 3D solid elements. Our working pipeline starts from a 3D scan of a human body represented by a 2-manifold mesh surface, which is the base design domain for the custom brace. Similar to the concept of isoparametric representation, the 3D design domain is mapped onto a two-dimensional (2D) parametric domain. An Finite Element Analysis (FEA) with bending moments is performed on the parameterized 2D design domain, and the Solid Isotropic Material with Penalization (SIMP) method is applied to optimize the pattern in the parametric domain. After the optimized cast/brace is obtained on the 2-manifold mesh surface, a solid model is generated by our design interface and then sent to a 3D printer for fabrication. Compared with the optimization method with solid elements, our method is more efficient and controllable due to the high eciency of solving FEA in the 2D domain.
Subramanian Chidambaram*, Yunbo Zhang*, Venkatraghavan Sundararajan, Niklas Elmqvist, Karthik Ramani, In Proceedings of ACM SIGCHI Conference on Human Factors in Computing Systems (CHI 2019), May 4–9, 2019, Glasgow, Scotland, UK. [pdf] [Video] (* Equal Contribution Authors, acceptance rate 23.8%)
Current Computer-Aided Design (CAD) tools lack proper support for guiding novice users towards designs ready for fabrication. We propose Shape Structuralizer (SS), an interactive design support system that repurposes surface models into structural constructions using rods and custom 3Dprinted joints. Shape Structuralizer embeds a recommendation system that computationally supports the user during design ideation by providing design suggestions on local refinements of the design. This strategy enables novice users to choose designs that both satisfy stress constraints as well as their personal design intent. The interactive guidance enables users to repurpose existing surface mesh models, analyze them in-situ for stress and displacement constraints, add movable joints to increase functionality, and attach a customized appearance. This also empowers novices to fabricate even complex constructs while ensuring structural soundness. We validate the Shape Structuralizer tool with a qualitative user study where we observed that even novice users were able to generate a large number of structurally safe designs for fabrication.
Yunbo Zhang, Tsz-Ho Kwok, In Proceedings of the 46th SME North American Manufacturing Research Conference, NAMRC 46, College Station, Texas, USA, June 18-22, 2018. [pdf]
In this paper, we apply Augmented Reality (AR) technologies to develop a design and interaction interface for Smart Manufacturing (SmartMFG). This work is motivated by the lack of appropriate human-machine-interaction (HMI) tools to support interaction and customization in SmartMFG environment. Trying to address this research problem, we hypothesize that AR-based design interfaces that communicate with Machine Control Unit (MCU) directly will increase the degree of interaction and the complexity of instructions performed in Manual Data Input (MDI) systems. To test this hypothesis, we developed a prototyping system consisting of an AR-tablet device as the input interface and an Ultimaker 3 printer as the machine tool. Firstly, this AR-based system has sensing, design and control capabilities to interact and communicate with the machine tool via Wifi. Secondly, a set of sketch-based computational tools is developed for users to design shapes on existing objects easily and efficiently within the AR environment. Finally, The customized design is converted to machine code, which is also customized based on the machine tool and the registration of the virtual model and the existing object. We tested our system by designing two customized shapes onto an existing shape in the AR environment and generating the G-code to control the printer to fabricate them onto the physical object.
Sang Ho Yoon, Ke Huo, Yunbo Zhang, Guiming Chen, Luis Paredes, Subramanian Chidambaram, Karthik Ramani, In Proceedings of the 30th Annual ACM Symposium on User Interface Software & Technology (UIST 2017) , Quebec City, Canada, Oct 22-25, 2017. [pdf] [Highlighted by ACM Interactions Magazine Link] [Video@youtube] (Acceptance rate 22.5%)
Abstract: We present iSoft, a single volume soft sensor capable of sensing real-time continuous contact and unidirectional stretching. We propose a low-cost and an easy way to fabricate such piezoresistive elastomer-based soft sensors for instant interactions. We employ an electrical impedance tomography (EIT) technique to estimate changes of resistance distribution on the sensor caused by fingertip contact. To compensate for the rebound elasticity of the elastomer and achieve real-time continuous contact sensing, we apply a dynamic baseline update for EIT. The baseline updates are triggered by fingertip contact and movement detections. Further, we support unidirectional stretching sensing using a model-based approach which works separately with continuous contact sensing. We also provide a software toolkit for users to design and deploy personalized interfaces with customized sensors. Through a series of experiments and evaluations, we validate the performance of contact and stretching sensing. Through example applications, we show the variety of examples enabled by iSoft.
Min Liu*, Yunbo Zhang*, Jing Bai, Yuanzhi Cao, Jeffrey Alperovich, Karthik Ramani, In Proceedings of the ACM Conference on Human Factors in Computing Systems (CHI 2017), Denver, CO, May 6-11, 2017. [pdf] [Video@youtube] (* Equal Contribution Authors, acceptance rate 25%)
Abstract: We propose WireFab, a rapid modeling and prototyping system that uses bent metal wires as the structure framework. WireFab approximates both the skeletal articulation and the skin appearance of the corresponding virtual skin meshes, and it allows users to personalize the designs by (1) specifying joint positions and part segmentations, (2) defining joint types and motion ranges to build a wire-based skeletal model, and (3) abstracting the segmented meshes into mixed-dimensional appearance patterns or attachments. The WireFab is designed to allow the user to choose how to best preserve the fidelity of the topological structure and articulation motion while selectively maintaining the fidelity of the geometric appearance. Compared to 3D-printing based high-fidelity fabrication systems, WireFab increases prototyping speed by ignoring unnecessary geometric details while preserving structural integrity and articulation motion. In addition, other rapid or low-fidelity fabrication systems produce only static models, while WireFab produces posable articulated models as user’s desire.
Abstract: Additive Manufacturing (AM) enables the fabrication of three-dimensional (3D) objects with complex shapes without additional tools and refixturing. However, it is difficult for user to use traditional computer-aided design tools to design custom products. In this paper, we presented a design system to help user design custom 3D printable products based on some reference freeform shapes. The user can define and edit styling curves on the reference model using our interactive geometric operations for styling curve. Incorporating with the reference models, these curves can be converted into 3D printable models through our fabrication interface. We tested our system with four design applications including a hollow patterned bicycle helmet, a T-rex with skin frame structure, a face mask with Voronoi patterns, and an AM-specific night dress with hollow patterns. The executable prototype of the presented design framework used in the customization process is publicly available.
Sang Ho Yoon, Yunbo Zhang, Ke Huo, Karthik Ramani, To Appear in Proceedings of the 29th Annual ACM Symposium on User Interface Software & Technology (UIST'16) , Tokyo, Japan, 2016. (Acceptance rate 20.6%) [pdf] [video@youtube]
Abstract: We present TRing, a finger-worn input device which provides instant and customizable interactions. TRing offers a novel method for making plain objects interactive using an embedded magnet and a finger-worn device. With a particle filter integrated magnetic sensing technique, we compute the fingertip’s position relative to the embedded magnet. We also offer a magnet placement algorithm that guides the magnet installation location based upon the user’s interface customization. By simply inserting or attaching a small magnet, we bring interactivity to both fabricated and existing objects. In our evaluations, TRing shows an average tracking error of 8.6 mm in 3D space and a 2D targeting error of 4.96 mm, which are sufficient for implementing average-sized conventional controls such as buttons and sliders. A user study validates the input performance with TRing on a targeting task (92% accuracy within 45 mm distance) and a cursor control task (91% accuracy for a 10 mm target). Furthermore, we show examples that highlight the interaction capability of our approach.
Cecil Piya, Vinayak, Yunbo Zhang, Karthik Ramani, In Proceedings of Graphics Interface 2016, Victoria, BC, Canada. [pdf] [video@youtube]
Abstract: We present RealFusion, an interactive workflow that supports early stage design ideation in a digital 3D medium. RealFusion is inspired by the practice of found-object-art, wherein new representations are created by composing existing objects. The key motivation behind our approach is direct creation of 3D artifacts during design ideation, in contrast to conventional practice of employing 2D sketching. RealFusion comprises of three creative states where users can (a) repurpose physical objects as modeling components, (b) modify the components to explore different forms, and (c) compose them into a meaningful 3D model. We demonstrate RealFusion using a simple interface that comprises of a depth sensor and a smartphone. To achieve direct and efficient manipulation of modeling elements, we also utilize mid-air interactions with the smartphone. We conduct a user study with novice designers to evaluate the creative outcomes that can be achieved using RealFusion.
Yunbo Zhang, Wei Gao, Luis Paredes, Karthik Ramani, In Proceedings of the ACM 2016 CHI Conference on Human Factors in Computing Systems, May 7-12, San Jose, CA USA, pages 897-907, 2016. (Acceptance rate 23.4%) [pdf] [video@youtube][Media]
Abstract: Computer-aided design of flat patterns allows designers to prototype foldable 3D objects made of heterogeneous sheets of material. We found origami designs are often characterized by pre-synthesized patterns and automated algorithms. Furthermore, augmenting articulated features to a desired model requires time-consuming synthesis of interconnected joints. This paper presents CardBoardiZer, a rapid cardboard based prototyping platform that allows everyday sculptural 3D models to be easily customized, articulated and folded. We develop a building platform to allow the designer to 1) import a desired 3D shape, 2) customize articulated partitions into planar or volumetric foldable patterns, and 3) define rotational movements between partitions. The system unfolds the model into 2D crease-cut-slot patterns ready for die-cutting and folding. In this paper, we developed interactive algorithms and validated the usability of CardBoardiZer using various 3D models. Furthermore, comparisons between CardBoardiZer and methods of Autodesk® 123D Make, demonstrated significantly shorter time-to-prototype and ease of fabrication.
Abstract: A flattenable mesh surface is a polygonal mesh surface that can be unfolded into a planar patch without stretching any polygon. This paper presents a new method for computing a slightly stretched flattenable mesh surface M from a piecewise-linear surface patch P in 3D, where the shape approximation error between M and P is minimized and the strain of stretching on M is controlled. Prior approaches result in either a flattenable surface that could be quite different from the input shape or a (discrete) developable surface has relative simple shape. The techniques investigated in this paper overcome these difficulties. First, we introduce a new surface modeling method to conduct a sequence of nearly isometric deformations to morph a flattenable mesh surface to a new shape which has a better approximation of the input surface. Second, in order to get better initial surfaces for fitting and overcome topological obstacles, a shape perturbation scheme is investigated to obtain the optimal surface fitting result. Last, to improve the scalability of our optimal surface fitting algorithm, a coarse-to-fine fitting framework is exploited so that very dense flattenable mesh surfaces can be modeled and boundaries of the input surfacescan be interpolated.
Wei Gao*, Yunbo Zhang*, Diogo C. Nazzetta, Karthik Ramani, Raymond J. Cipra, In Proceeding of the 28th Annual ACM Symposium on User Interface Software & Technology (UIST'15), Nov 8-11, Charlotte, NC USA, Pages 437-446, 2015. (* Equal Contribution Authors, acceptance rate 23.6%). [pdf][Video][Presentation][Media]
Abstract: In recent years, 3D printing has gained significant attention from the maker community, academia, and industry to support low-cost and iterative prototyping of designs. Current unidirectional extrusion systems require printing sacrificial material to support printed features such as overhangs. Furthermore, integrating functions such as sensing and actuation into these parts requires additional steps and processes to create “functional enclosures”, since design functionality cannot be easily embedded into prototype printing. All of these factors result in relatively high design iteration times. We present “RevoMaker”, a self-contained 3D printer that creates direct out-of-the-printer functional prototypes, using less build material and with substantially less reliance on support structures. By modifying a standard low-cost FDM printer with a revolving cuboidal platform and printing partitioned geometries around cuboidal facets, we achieve a multidirectional additive prototyping process to reduce the print and support material use. Our optimization framework considers various orientations and sizes for the cuboidal base. The mechanical, electronic, and sensory components are preassembled on the flattened laser-cut facets and enclosed inside the cuboid when closed. We demonstrate RevoMaker directly printing a variety of customized and fully-functional product prototypes, such as computer mice and toys, thus illustrating the new affordances of 3D printing for functional product design.
Tsz-Ho Kwok, Charlie C.L. Wang, Dongping Deng, Yunbo Zhang, Yong Chen, ASME Transactions - Journal of Mechanical Design, Special Issue on Design for Additive Manufacturing, 137(11), 111413, 2015. [pdf] [doi:10.1115/1.4031023] [video@Youtube]
Abstract: A self-folding structure fabricated by additive manufacturing can be automatically folded into a demanding 3D shape by actuation mechanisms such as heating. However, 3D surfaces can only be fabricated by self-folding structures when they are flattenable. Most generally designed parts are not flattenable. To address the problem, we develop a shape optimization method to modify a non-flattenable surface into flattenable. The shape optimization framework is equipped with topological operators for adding interior/boundary cuts to further improve the flattenability. When inserting cuts, self-intersection is locally prevented on the flattened 2D pieces. The total length of inserted cuts is also minimized to reduce artifacts on the finally folded 3D shape.
Wei Gao, Yunbo Zhang, Devarajan Ramanujan, Karthik Ramani, Yong Chen, Christopher B. Williams, Charlie C.L. Wang, Yung C. Shin, Song Zhang, Pablo D. Zavattieri, Computer-Aided Design, Special Issue on Geometric and Physical Modeling for Additive Manufacturing, 69, 65-89, 2015. (Top 1 most cited articles from Computer-Aided Design since 2014; Top 1 the most downloaded articles from Computer-Aided Design in the last 90 days). [doi:10.1016/j.cad.2015.04.001]
Abstract: Additive manufacturing (AM) is poised to bring about a revolution in the way products are designed, manufactured, and distributed to end users. This technology has gained significant academic as well as industry interest due to its ability to create complex geometries with customizable material properties. AM has also inspired the development of the maker movement by democratizing design and manufacturing. Due to the rapid proliferation of a wide variety of technologies associated with AM, there is a lack of a comprehensive set of design principles, manufacturing guidelines, and standardization of best practices. These challenges are compounded by the fact that advancements in multiple technologies (for example materials processing, topology optimization) generate a “positive feedback loop” effect in advancing AM. In order to advance research interest and investment in AM technologies, some fundamental questions and trends about the dependencies existing in these avenues need highlighting. The goal of our review paper is to organize this body of knowledge surrounding AM, and present current barriers, findings, and future trends significantly to the researchers. We also discuss fundamental attributes of AM processes, evolution of the AM industry, and the affordances enabled by the emergence of AM in a variety of areas such as geometry processing, material design, and education. We conclude our paper by pointing out future directions such as the “print-it-all” paradigm, that have the potential to re-imagine current research and spawn completely new avenues for exploration.
Wuyuan Xie, Yunbo Zhang, Charlie C.L. Wang, C.-K. Chung, 2014 IEEE Conference on Computer Vision and Pattern Recognition, Columbus, Ohio, June 24-27, 2014 (Oral presentation paper - with acceptance rate as 5.75%). [pdf] [doi:10.1109/CVPR.2014.282] [Video@TechTalks][Video@Youtube] [Video2@Youtube] [Project Page with Code]
Abstract: In this paper, we propose an efficient method to reconstruct surface-from-gradients (SfG). Our method is formulated under the framework of discrete geometry processing. Unlike the existing SfG approaches, we transfer the continuous reconstruction problem into a discrete space and efficiently solve the problem via a sequence of least-square optimization steps. Our discrete formulation brings three advantages: 1) the reconstruction preserves sharp-features, 2) sparse/incomplete set of gradients can be well handled, and 3) domains of computation can have irregular boundaries. Generally, these strengths of our method help overcome the unwanted distortions during the surface reconstruction. Our formulation is direct and easy to implement, and the comparisons with state-of-the-arts show the effectiveness of our method.
Abstract: Techniques have been developed to deform a mesh with multiple types of constraints. One limitation of prior methods is that the accuracy of demanded metrics on the resultant model cannot be guaranteed. Adding metrics directly as hard constraints to an optimization functional often leads to unexpected distortion when target metrics differ significant from what are on the input model. In this paper, we present an effective framework to deform mesh models by enforcing demanded metrics on length, area and volume. To approach target metrics stably and minimize distortion, an iterative scale-driven deformation is investigated, and a global optimization functional is exploited to balance the scaling effect at different parts of a model. Examples demonstrate that our approach provides a user-friendly tool for designers who are used to semantic input.
Tsz-Ho Kwok, Yunbo Zhang, Charlie C.L. Wang, Graphical Models, Special Issue of 2012 Geometric Modeling and Processing (GMP) conference, June 20-22, 2012, Mount Huang, Volume 74, Issue 4, July 2012, Pages 152-163. [pdf] [doi:10.1016/j.gmod.2012.03.012] [Project Page with Executable Program]
Abstract: In this paper, we propose a novel algorithm to construct common base domains for cross-parameterization constrained by anchor points. Based on the common base domains, a bijective mapping between given models can be established. Experimental results show that the distortion in a cross-parameterization generated on our common base domains is much smaller than that of a mapping on domains constructed by prior methods. Different from prior algorithms that generate domains by a heuristic of having higher priority to link the shortest paths between anchor points, we compute the surface Voronoi diagram of anchor points to find out the initial connectivity for the base domains. The final common base domains can be efficiently generated from the initial connectivity. The Voronoi diagram of the anchor points gives better cues than the heuristic of connecting shortest paths greedily, therefore resulting in an efficient and reliable algorithm for construction of common base domains that bring to low distortion in constrained cross-parameterization.
Tsz-Ho Kwok, Yunbo Zhang, Charlie C.L. Wang, IEEE Transactions on Visualization and Computer Graphics, vol.18, no.10, pp.1678-1692, Oct. 2012. [pdf] [doi:10.1109/TVCG.2011.115] [Project Page with Executable Program]
Abstract: Given a set of corresponding user-specified anchor points on a pair of models having similar features and topologies, the cross-parameterization technique can establish a bijective mapping constrained by the anchor points. In this paper, we present an efficient algorithm to optimize the complexes and the shape of common base domains in cross-parameterization for reducing the distortion of the bijective mapping. The optimization is also constrained by the anchor points. We investigate a new signature, Length-Preserved Base Domain (LPBD), for measuring the level of stretch between surface patches in crossparameterization. This new signature well balances the accuracy of measurement and the computational speed. Based on LPBD, a set of metrics are studied and compared. The best ones are employed in our domain optimization algorithm that consists of two major operators, boundary swapping and patch merging. Experimental results show that our optimization algorithm can reduce the distortion in cross-parameterization efficiently.
Yu Wang, Kai-Ming Yu, Charlie C.L. Wang, Yunbo Zhang, Computer-Aided Design, vol.43, no.8, pp.1001-1010, August 2011. [pdf] [doi:10.1016/j.cad.2011.04.011]
Abstract: This paper presents an automatic method for designing conformal cooling circuit, which is an essential component that directly affects the quality and timing for the products fabricated by rapid tooling. To reduce the time of cooling and control the uniformity of temperature and volumetric shrinkage, industry expects to have cooling channels that are conformal to the shape of products. We achieve the goal of automatically designing such conformal cooling circuit in twofold. First, the relationship between the conformal cooling and the geometry shape of cooling circuit is formulated. Based on that, we investigate a geometric modeling algorithm to design the cooling circuit approaching the conformal cooling. Simulations have been taken to verify the advantage of the cooling circuit generated by our algorithm.
Abstract: We present a method for refining n-sided polygons on a given piecewise linear model by using local computation, where the curved polygons generated by our method interpolate the positions and normals of vertices on the input model. Firstly, we construct a Bezier curve for each silhouette edge. Secondly, we employ a new method to obtain C1 continuous cross-tangent functions that are constructed on these silhouette curves. An important feature of our method is that the cross tangent functions are produced solely by their corresponding facet parameters. Gregory patches can therefore be locally constructed on every polygons while preserving G1 continuity between neighboring patches. To provide a flexible shape control, several local schemes are provided to modify the cross-tangent functions so that the sharp features can be retained on the resultant models. Because of the localized construction, our method can be easily accelerated by graphics hardware and fully run on the Graphics Processing Unit (GPU).
Abstract: Surface flattening has numerous applications in sheet manufacturing industries, such as garment industry, shoe industry, toy industry, furniture industry and ship industry. Motivated by the requirements of those industries, WireWarping approach presented in  is exploited to generate 2D patterns with invariant length of feature and boundary curves. However, strict length constraints on all feature curves sometimes cause large distortions on 2D patterns, especially for those 3D surfaces which are highly non-developable. In this paper, we present a flexible and robust extension of WireWarping by introducing a new type of feature curves named elastic feature, which brings flexibility to shape control of the resultant 2D patterns. On these new feature curves, instead of strictly preserving the exact lengths, only the ranges of their lengths are controlled. To achieve this function, a multi-loop shape control optimization framework is proposed to find the optimized 2D shape among all possible flattening results with different length variations on those elastic feature curves, while the lengths of other feature curves are kept unchanged. Besides, we also present a topology processing algorithm on the network of feature curves to eliminate cases that lead to numerical singularity. Experimental results show that the WireWarping++ can successfully flatten surface patches into 2D patterns with more flexible shape control and more robust numerical performance.
Charlie C.L. Wang, Yunbo Zhang, Hoi Sheung, IEEE Computer Graphics and Applications, vol.20, no.6, pp.74-85, November 2010. [pdf] [doi:10.1109/MCG.2009.155] [Application on WetSuit Design@Youtube] [Application in Facial Mask Design@YouTube] [exuskin.com]
Abstract: This article describes a geometric modeling system that generates industry required planar pieces for fabricating user-customized products from styling designs. The processing from style design to industrial patterns is automated. Prestored styling designs can be automatically mapped into different reference model shapes and then unfolded into planar pieces. Besides, a map-guided algorithm has been developed to locate unfolded pieces according to industrial requirement.
Hongwei Lin, Yunbo Zhang, Charlie C. L. Wang, Shuming Gao, ASME IDETC/CIE 2010 Conference, 30th Computers and Information in Engineering Conference, Montreal, Quebec, Canada, August 15-18, 2010. [pdf] [doi:10.1115/DETC2010-28301]
Abstract: Models represented by polygonal meshes have been more and more widely used in CAD/CAM systems. In sheet manufacturing industries, the flattenability of a model is very important. Prior methods for processing the flattenability of a mesh surface usually employ a constrained optimization framework, which takes the positions of all its non-boundary vertices as variables in computation. For a mesh surface with hundred thousands of vertices, solving such an optimization is very time-consuming, and may exceed the capacity of main memory. In this paper, we develop a controllable evolution method to process the flattenability of a given mesh patch. It decouples the global optimization problem into a sequence of local controllable evolution steps, each of which has only one variable. Therefore, mesh surfaces with large number of vertices can be processed.