Control of Elastic Soft Robots based on Real-Time Finite Element Method

International audienceIn this paper, we present a new method for the control of soft robots with elastic behavior, piloted by several actuators. The central contribution of this work is the use of the Finite Element Method (FEM), computed in real-time, in the control algorithm. The FEM based simulation computes the nonlinear deformations of the robots at interactive rates. The model is completed by Lagrange multipliers at the actuation zones and at the end-effector position. A reduced compliance matrix is built in order to deal with the necessary inversion of the model. Then, an iterative algorithm uses this compliance matrix to find the contribution of the actuators (force and/or position) that will deform the structure so that the terminal end of the robot follows a given position. Additional constraints, like rigid or deformable obstacles, or the internal characteristics of the actuators are integrated in the control algorithm. We illustrate our method using simulated examples of both serial and parallel structures and we validate it on a real 3D soft robot made of silicon

Bézier Shell Finite Element for Interactive Surgical Simulation

International audienceThere is a strong need, in surgical simulations, for physically based deformable model of thin or hollow structures. The use of shell theory allows to have a well-founded formulation resulting from continuum mechanics of thin objects. However, this formulation asks for second order spatial derivatives so requires the use of complex elements. In this paper, we present a new way of building the interpolation: First, we use the trianular cubic Bézier shell to allow for a good continuity inside and between the elements and second, we build a kinematic mapping to reduce the degrees of freedom of the element from 10 control points with 3 Degrees of Freedom ($=30$ DOFs) to only 3 nodes with 6 DOFs ($=18$ DOFs). This reduction allows for good computation performance. This new shell model description is also used to map a smooth surface (for the collision detection and response) on a coarse mechanical mesh to account for the complex contacts that take place during surgical procedures. We demonstrate the convergence and the computational efficiency of our approach as well as its use in two different simulation cases: the planning of surgery for congenital heart disease correction and a preliminary simulation of childbirth

Six Degree-of Freedom Haptic Rendering for Dental Implantology Simulation

International audienceDental implantology procedures are among the most com- plex surgical procedures executed by dentists. During the critical part of the procedure, the jawbone is drilled at the location of the missing tooth (or the missing group of teeth). This asks for specic skills from the dentists, who need to be well trained. In this paper we present a virtual reality based training system for im- plantology and we mainly focus on the simulation of drilling. We have two main contributions: The rst one is a method for precise haptic rendering of contacts between the drilling tool and the jawbone model issued from a CT-scan. The second one is the real-time simulation of the jawbone erosion during drilling which is compatible with the haptic rendering of contacts

A Shell Model for Real-time Simulation of intra-ocular Implant Deployment

International audienceWith 30 million interventions a year worldwide, cataract surgery is one of the most frequently performed procedures. Yet, no tool currently allows teaching all steps of the procedure without putting pa- tients at risk. A particularly challenging stage of this surgery deals with the injection and deployment of the intra-ocular lens implant. In this paper we propose to rely on shell theory to accurately describe the com- plex deformations of the implant. Our approach extends the co-rotational method used in finite element analysis of in-plane deformations to incor- porate a bending energy. This results in a relatively simple and compu- tationally efficient approach which was applied to the simulation of the lens deployment. This simulation also accounts for the complex contacts that take place during the injection phase

Connective Tissues Simulation on GPU

International audienceRecent work in the field of medical simulation have led to real advances in the mechanical simulation of organs. However, it is important to notice that, despite the major role they may have in the interaction between organs, the connective tissues are often left out of these simulations. In this paper, we propose a model which can rely on either a mesh based or a meshless methods. To provide a realistic simulation of these tissues, our work is based on the weak form of continuum mechanics equations for hyperelastic soft materials. Furthermore, the stability of deformable objects simulation is ensured by an implicit temporal integration scheme. Our method allows to model these tissues without prior assumption on the dimension of their of their geometry (curve, surface or volume), and enables mechanical coupling between organs. To obtain an interactive frame rate, we develop a parallel version suitable for to GPU computation. Finally we demonstrate the proper convergence of our finite element scheme

Asynchronous haptic simulation of contacting deformable objects with variable stiffness

International audienceAbstract--This paper presents a new asynchronous approach for haptic rendering of deformable objects. When stiff nonlinear deformations take place, they introduce important and rapid variations of the force sent to the user. This problem is similar to the stiff virtual wall for which a high refresh rate is required to obtain a stable haptic feedback. However, when dealing with several interacting deformable objects, it is usually impossible to simulate all objects at high rates. To address this problem we propose a quasi-static framework that allows for stable interactions of asynchronously computed deformable objects. In the proposed approach, a deformable object can be computed at high refresh rates, while the remaining deformable virtual objects remain computed at low refresh rates. Moreover, contacts and other constraints between the different objects of the virtual environment are accurately solved using a shared Linear Complementarity Problem (LCP). Finally, we demonstrate our method on two test cases: a snap-in example involving non-linear deformations and a virtual thread interacting with a deformable object

Computation and Visualization of Risk Assessment in Deep Brain Stimulation

International audienceDeep Brain Stimulation is a neurosurgical approach for the treatment of pathologies such as Parkinson's disease. The basic principle consists in placing a thin electrode in a deep part of the brain. To safely reach the target of interest, careful planning must be performed to ensure that no vital structure (e.g. blood vessel) will be damaged during the insertion of the electrode. Currently this planning phase is done without considering the brain shift, which occurs during the surgery once the skull is open, leading to increased risks of complications. In this paper, we propose a method to compute the motion of anatomical structures induced by the brain shift. This computation is based on a biomechanical model of the brain and the cerebro-spinal fluid. We then visualize in a intuitive way the risk of damaging vital structures with the electrode.La stimulation cérébrale profonde est une procédure neurochirurgicale pour le traitement de pathologies comme la maladie de Parkinson. La procédure consiste à implanter une électrode dans une région profonde du cerveau. Pour atteindre la cible sans risque, le chirurgien procède à une plannification minutieuse pour s'assurer qu'aucune structure vitale (vaisseaux sanguins, ventricules) ne se retrouve sur le chemin de l'électrode. Actuellement, la plannification ne considère pas les déformations intra-opératoires, qui se produisent une fois que le crâne est ouvert. Cela peut entraîner des compolications. Dans ce papier, nous proposons une méthode pour calculer le risque de mouvement des structures anatomiques causés par ces déformations. Le calcul s'appuie sur un modèle biomécanique du cerveau et du fluide céphalo-rachidien. Nous visualisons ensuite intuitivement le risque d'endommager une structure vitale avec l'électrode

Unified processing of constraints for interactive simulation

International audienceThis paper introduces a generic way of dealing with a set of different constraints (bilateral, unilateral, dry friction) in the context of interactive simulation. We show that all the mentioned constraints can be handled within a unified framework: we define the notion of generalized constraints, which can be derived into most classical constraints types. The solving method is based on an implicit treatment of constraints that provides good stability for interactive applications using deformable models and rigid bodies. Each constraint law is expressed in constraint subspace, making constraint evaluation much easier. A global solution is calculated using an iterative process that takes into account the mechanical coupling between the constraints. Various examples, from basic to more complex, show the practical advantage of using generalized constraints, as a way of creating heterogeneously constrained systems, as well as the scalability of the proposed method

Toward the use of proxies for efficient learning manipulation and locomotion strategies on soft robots

Soft robots are naturally designed to perform safe interactions with their environment, like locomotion and manipulation. In the literature, there are now many concepts, often bio-inspired, to propose new modes of locomotion or grasping. However, a methodology for implementing motion planning of these tasks, as exists for rigid robots, is still lacking. One of the difficulties comes from the modeling of these robots, which is very different, as it is based on the mechanics of deformable bodies. These models, whose dimension is often very large, make learning and optimization methods very costly. In this paper, we propose a proxy approach, as exists for humanoid robotics. This proxy is a simplified model of the robot that enables frugal learning of a motion strategy. This strategy is then transferred to the complete model to obtain the corresponding actuation inputs. Our methodology is illustrated and analyzed on two classical designs of soft robots doing manipulation and locomotion tasks.Comment: Accepted at IEEE Robotics and Automation Letters (RAL) in October 202

Shell Model for Reconstruction and Real-Time Simulation of Thin Anatomical Structures

International audienceThis paper presents a new modelling technique for the defor- mation of thin anatomical structures like membranes and hollow organs. We show that the behaviour of this type of surface tissue can be ab- stracted with a modelling of their elastic resistance using shell theory. In order to apply the shell theory in the context of medical simulation, our method propose to base the geometrical reconstruction of the organ on the shape functions of the shell element. Moreover, we also use these continuous shape functions to handle the contacts and the interactions with other types of deformable tissues. The technique is illustrated using several examples including the simulation of an angioplasty procedure