Wearhap

FP7-ICT-2011-9. Duration 2013-2017.

The complexity of the world around us is creating a demand for cognition-enabled interfaces that will simplify and enhance the way we interact with the environment. Project WEARHAP, aims at laying the scientific and technological foundations for wearable haptics, a novel concept for the systematic exploration of haptics in advanced cognitive systems and robotics that will redefine the way humans will cooperate with robots. The challenge of this new paradigm stems from the need for wearability which is a key element for natural interaction. This paradigm shift will enable novel forms of human intention recognition through haptic signals and novel forms of communication and cooperation between humans and robots. Wearable haptics will enable robots to observe humans during natural interaction with their shared environment. Research challenges are ambitious and cross traditional boundaries between robotics, cognitive science and neuroscience. Research findings derived from distributed robotics, biomechanical modeling, multisensory tracking, underaction in control and cognitive systems will be integrated to address the scientific and technological challenges imposed in creating effective wearable haptic interaction. To highlight the enabling nature, the versatility and the potential for industrial exploitation of WEARHAP, the research challenges will be guided by representative application scenarios. These applications cover robotics, health and social scenarios, stretching from human-robot interaction and cooperation for search and rescue, to human-human communication, and interaction with virtual worlds through interactive games.

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Strain Limiting for Soft Finger Contact Simulation

The command of haptic devices for rendering direct interaction with the hand requires thorough knowledge of the forces and deformations caused by contact interactions on the fingers. In (Perez et al. 2013), we propose an algorithm to simulate nonlinear elasticity under frictional contact, with the goal of establishing a model-based strategy to command haptic devices and to render direct hand interaction. The key novelty in our algorithm is an approach to model the extremely nonlinear elasticity of finger skin and flesh using strain-limiting constraints, which are seamlessly combined with frictional contact constraints in a standard constrained dynamics solver. We show that our approach enables haptic rendering of rich and compelling deformations of the fingertip.

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Simulation of Hyperelastic Materials Using Energy Constraints

Real-world materials exhibit highly nonlinear mechanical behavior, but computer animation often neglects such nonlinearities. Hyperelasticity, or strain-dependent material stiffness, is one of the clear sources of nonlinearity. Correctly modeling real-world materials would require capturing strain-dependent elasticity, but hyperelasticity induces stiff differential equations that may complicate simulation, in particular for real-time computer animation. In (Perez et al. 2013), we propose a method based on constrained optimization for the simulation of hyperelastic materials. The key novelty of our method lies on limiting elastic energy to model extremely nonlinear elasticity within a common linear co-rotational formulation. Our method is designed on a hexahedral FEM discretization to avoid locking phenomena, and is capable of solving together energy-limiting and frictional contact constraints. We show that our approach enables the simulation of a large range of hyperelastic material behaviors.

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Anisotropic Strain Limiting

Many materials exhibit a highly nonlinear elastic behavior, such as textiles or finger flesh. An efficient way of enforcing the nonlinearity of these materials is through strain-limiting constraints, which is often the model of choice in computer graphics. Strain-limiting allows to model highly non-linear stiff materials by eliminating degrees of freedom from the computations and by enforcing a set of constraints. However, many nonlinear elastic materials, such as composites, wood or flesh, exhibit anisotropic behaviors, with different material responses depending on the deformation direction. This anisotropic behavior has not been addressed in the past in the context of strain limiting, and naïve approaches, such as applying a different constraint on each component of the principal axes of deformation, produce unrealistic results. In (Hernandez et al. 2013), we enable anisotropic behaviors when using strain-limiting constraints to model nonlinear elastic materials. We compute the limits for each principal axis of deformation through the rotation and hyperbolic projection of the deformation limits defined in the global reference frame. The limits are used to formulate the strain-limiting constraints, which are then seamlessly combined with frictional contact constraints in a standard constrained dynamics solver.

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