Coupling numerical deformable models in global and reduced coordinates for the simulation of the direct and the inverse kinematics of Soft Robots

International audienceIn this paper, we propose a method to combine the Finite Element Method (FEM) with Discrete Cosserat Modeling (DCM) to capture the mechanics and the actuation of soft robots. The FEM is used to simulate the non-linear behavior of the volume of the soft structure while the cable/rod used for the actuation is modeled using the DCM. The two models are linked using kinematic constraints without imposing meshing rules. We demonstrate that both direct and inverse kinematic models can be obtained by quadratic optimization. The originality of this coupling is that the FEM model uses global coordinates (the position of the nodes of its mesh in space) where the Cosserat model uses local coordinates (successive strain values). The coupling of these mechanical models allows to combine the best of each parametrization. On the one hand, FEM allows to capture the behavior of the volume structure of the robot while accounting for its geometry with a complex mesh. On the other hand, the DCM allows efficient modeling of 1D structures such as rods, (concentric) tubes, cables, etc. that are used to deform the volume structure of the soft robots. DCM handles large deformation, torsion and (in)-extensibility and is efficient to compute. Moreover, the approach is compatible with complementarity constraints introduced when modeling contact and friction of the robot with its environment as well as the self-collision

Physical validation of simulators in Computer Graphics: A new framework dedicated to slender elastic structures and frictional contact

International audienceWe introduce a selected set of protocols inspired from the Soft Matter Physics community in order to validate Computer Graphics simulators of slender elastic structures possibly subject to dry frictional contact. Although these simulators were primarily intended for feature film animation and visual effects, they are more and more used as virtual design tools for predicting the shape and deformation of real objects; hence the need for a careful, quantitative validation. Our tests, experimentally verified, are designed to evaluate carefully the predictability of these simulators on various aspects, such as bending elasticity, bend-twist coupling, and frictional contact. We have passed a number of popular codes of Computer Graphics through our benchmarks by defining a rigorous, consistent, and as fair as possible methodology. Our results show that while some popular simulators for plates/shells and frictional contact fail even on the simplest scenarios, more recent ones, as well as well-known codes for rods, generally perform well and sometimes even better than some reference commercial tools of Mechanical Engineering. To make our validation protocols easily applicable to any simulator, we provide an extensive description of our methodology, and we shall distribute all the necessary model data to be compared against

Soft robots locomotion and manipulation control using FEM simulation and quadratic programming

International audienceIn this paper, we propose a method to control the motion of soft robots able to manipulate objects or roll from one place to another. We use the Finite Element Method (FEM) to simulate the deformations of the soft robot, its actuators, and surroundings when deformable. To find the inverse model of the robot interacting with obstacles, and with constraints on its actuators, we write the problem as a quadratic program with complementarity constraints. The novelty of this work is that friction contacts (sticking contact only) are taken into account in the optimization process, allowing the control of these specific tasks that are locomotion and manipulation. We propose a formulation that simplifies the optimization problem, together with a dedicated solver. The algorithm has real-time performance and handles evolving environments as long as we know them. To show the effectiveness of the method, we present several numerical examples, and a demonstration on a real robot

Soft robots locomotion and manipulation control using FEM simulation and quadratic programming

International audienceIn this paper, we propose a method to control the motion of soft robots able to manipulate objects or roll from one place to another. We use the Finite Element Method (FEM) to simulate the deformations of the soft robot, its actuators, and surroundings when deformable. To find the inverse model of the robot interacting with obstacles, and with constraints on its actuators, we write the problem as a quadratic program with complementarity constraints. The novelty of this work is that friction contacts (sticking contact only) are taken into account in the optimization process, allowing the control of these specific tasks that are locomotion and manipulation. We propose a formulation that simplifies the optimization problem, together with a dedicated solver. The algorithm has real-time performance and handles evolving environments as long as we know them. To show the effectiveness of the method, we present several numerical examples, and a demonstration on a real robot