M. Bächer, B. Hepp, F. Pece, P. G. Kry, B. Bickel, B. Thomaszewski, O. Hilliges
Proceedings of ACM CHI (San Jose, USA, May 7-12, 2016), ACM Transactions on Computer-Human Interaction.Abstract We propose to embed piezoresistive sensing elements into flexible 3D printed objects. These sensing elements are then utilized to recover rich and natural user interactions at runtime. Designing such objects manually is a challenging and hard problem for all but the simplest geometries and deformations. Our method simultaneously optimizes the internal routing of the sensing elements and computes a mapping from low-level sensor readings to user-specified outputs in order to minimize reconstruction error. We demonstrate the power and flexibility of the approach by designing and fabricating a set of flexible input devices. Our results indicate that the optimization based design greatly outperforms manual routings in terms of reconstruction accuracy and thus interaction fidelity.
M. Bächer, S. Coros, B. Thomaszewski
Proceedings of ACM SIGGRAPH (Los Angeles, USA, August 9-13, 2015), ACM Transactions on Graphics, vol. 34, no. 4.Abstract We present a method for interactive editing of planar linkages. Given a working linkage as input, the user can make targeted edits to the shape or motion of selected parts while preserving other, e.g., functionally-important aspects. In order to make this process intuitive and efficient, we provide a number of editing tools at different levels of abstraction. For instance, the user can directly change the structure of a linkage by displacing joints, edit the motion of selected points on the linkage, or impose limits on the size of its enclosure. Our method safeguards against degenerate configurations during these edits, thus ensuring the correct functioning of the mechanism at all times. Linkage editing poses strict requirements on performance that standard approaches fail to provide. In order to enable interactive and robust editing, we build on a symbolic kinematics approach that uses closed-form expressions instead of numerical methods to compute the motion of a linkage and its derivatives. We demonstrate our system on a diverse set of examples, illustrating the potential to adapt and personalize the structure and motion of existing linkages. To validate the feasibility of our edited designs, we fabricated two physical prototypes.
M. Bächer, E. Whiting, B. Bickel, O. Sorkine-Hornung
Proceedings of ACM SIGGRAPH (Vancouver, CAN, August 10-14, 2014), ACM Transactions on Graphics, vol. 33, no. 4.Abstract Spinning tops and yo-yos have long fascinated cultures around the world with their unexpected, graceful motions that seemingly elude gravity. We present an algorithm to generate designs for spinning objects by optimizing rotational dynamics properties. As input, the user provides a solid 3D model and a desired axis of rotation. Our approach then modifies the mass distribution such that the principal directions of the moment of inertia align with the target rotation frame. We augment the model by creating voids inside its volume, with interior fill represented by an adaptive multi-resolution voxelization. The discrete voxel fill values are optimized using a continuous, nonlinear formulation. Further, we optimize for rotational stability by maximizing the dominant principal moment. We extend our technique to incorporate deformation and multiple materials for cases where internal voids alone are insufficient. Our method is well-suited for a variety of 3D printed models, ranging from characters to abstract shapes. We demonstrate tops and yo-yos that spin surprisingly stably despite their asymmetric appearance.
M. Bächer, B. Bickel, D. L. James, H. Pfister
Proceedings of ACM SIGGRAPH (Los Angeles, USA, August 5-9, 2012), ACM Transactions on Graphics, vol. 31, no. 4.
B. Bickel, M. Bächer, M. A. Otaduy, H. R. Lee, H. Pfister, M. Gross, W. Matusik
Proceedings of ACM SIGGRAPH (Los Angeles, USA, July 25-29, 2010), ACM Transactions on Graphics, vol. 29, no. 4.
B. Bickel, M. Bächer, M. A. Otaduy, W. Matusik, H. Pfister, M. Gross
Proceedings of ACM SIGGRAPH (New Orleans, USA, August 3-7, 2009), ACM Transactions on Graphics, vol. 28, no. 3.
C. Ledergerber, G. Guennebaud, M. Meyer, M. Bächer, H. Pfister
IEEE Transactions on Visualization and Computer Graphics (Proceedings of Visualization 2008), 14(6):1372-1379, 2008.Abstract The method of Moving Least Squares (MLS) is a popular framework for reconstructing continuous functions from scattered data due to its rich mathematical properties and well-understood theoretical foundations. This paper applies MLS to volume rendering, providing a unified mathematical framework for ray casting of scalar data stored over regular as well as irregular grids. We use the MLS reconstruction to render smooth isosurfaces and to compute accurate derivatives for high-quality shading effects. We also present a novel, adaptive preintegration scheme to improve the efficiency of the ray casting algorithm by reducing the overall number of function evaluations, and an efficient implementation of our framework exploiting modern graphics hardware. The resulting system enables high-quality volume integration and shaded isosurface rendering for regular and irregular volume data.
H. Zhang, J. K. Lai, M. Bächer
The 4th Human Computation Workshop (HCOMP), 2012.
A. Peters Randles, M. Bächer, H. Pfister, E. Kaxiras
Statistical Atlases and Computational Models of the Heart (STACOM), 2012.Abstract In this paper, we propose a system to determine the pressure gradient at rest in the aorta. We developed a technique to efficiently initialize a regular simulation grid from a patient-specific aortic triangulated model. On this grid we employ the lattice Boltzmann method to resolve the characteristic fluid flow through the vessel. The inflow rates, as measured physiologically, are imposed providing accurate pulsatile flow. The simulation required a resolution of at least 20 microns to ensure a convergence of the pressure calculation. HARVEY, a large-scale parallel code, was run on the IBM Blue Gene/Q supercomputer to model the flow at this high resolution. We analyze and evaluate the strengths and weaknesses of our system.
Ph.D. Thesis, Advisor: H. Pfister, Harvard University, 2013.
Master Thesis, Advisor: B. Bickel, Supervisor: M. Gross, Swiss Federal Institute of Technology, 2008.
M. Bächer, B. Bickel, D. L. James, H. Pfister
U.S. Patent. Pub. No.: US 2015/0187134, Pub. Date: July, 2, 2015.
P. A. Beardsley, M. Bächer
U.S. Patent. Pub. No.: US 2009/0297020 A1, Pub. Date: Dec. 3, 2009.
Harvard University, 2009.