The team DEFROST aims to address the open problem of control and modelling methods for deformable robots by answering the following challenges:
Our research crosses different disciplines: numerical mechanics, control design, robotics, optimisation methods and clinical applications. Our organisation aims at facilitating the team work and cross-fertilisation of research results in the group. We have three objectives (1, 2 and 3) that correspond to the main scientific challenges. In addition, we have two transverse objectives that are also highly challenging: the development of a high performance software support for the project (Objective 4) and the validation tools and protocols for the models and methods (Objective 5).
The objective is to find concrete numerical solutions to the challenge of modelling soft robots with strong real-time constraints. To solve continuum mechanics equations, we will start our research with real-time Finite Element Method (FEM) or equivalent methods that were developed for soft-tissue simulation. We will extend the functionalities to account for the needs of a soft-robotic system:
The focus of this objective is on obtaining a generic methodology for soft robot feedback control. Several steps are needed to design a model based control from FEM approach:
Even if the inherent mechanical compliance of soft robots makes them safer, more robust and particularly adapted to interaction with fragile environments, the contact forces need to be controlled by:
Expected research results of this project are numerical methods and algorithms that require high-performance computing and suitability with robotic applications. There is no existing software support for such development. We propose to develop our own software, in a suite split into three applications:
The implementation of experimental validation is a key challenge for the project. On one side, we need to validate the model and control algorithms using concrete test case example in order to improve the modelling and to demonstrate the concrete feasibility of our methods. On the other side, concrete applications will also feed the reflexions on the objectives of the scientific program.
We will build our own experimental soft robots for the validation of Objectives 2 and 3 when there is no existing “turn-key” solution. Designing and making our own soft robots, even if only for validation, will help the setting-up of adequate models.
For the validation of Objective 4, we will develop “anatomical soft robot”: soft robot with the shape of organs, equipped with sensors (to measure the contact forces) and actuators (to be able to stiffen the walls and recreate natural motion of soft-tissues). We will progressively increase the level of realism of this novel validation set-up to come closer to the anatomical properties.
Robotics in the manufacturing industry is already widespread and is one of the strategies put in place to maintain the level of competitiveness of companies based in France and to avoid relocation to cheap labor countries. Yet, in France, it is considered that the level of robotization is insufficient, compared to Germany for instance. One of the challenges is the high investment cost for the acquisition of robotic arms. In recent years, this challenge has led to the development of “generic” and “flexible” (but rigid) robotic solutions that can be mass produced. But their applicability to specific tasks is still challenging or too costly. With the development of 3D printing, we can imagine the development of a complete opposite strategy: a “task-specific” design of robots. Given a task that needs to be performed by a deformable robot, we could optimize its shape and its structure to create the set of desired motions. A second important aspect is the reduction of the manufacturing cost: it is often predicted that the cost of deformable robots will be low compared to classical rigid robots. The robot could be built on one piece using rapid prototyping or 3D printers and be more adapted for collaborative work with operators. In this area, using soft materials is particularly convenient as they provide a mass/carried load ratio several orders of magnitude higher than traditional robots, highly decreasing the kinetic energy thus increasing the motion speed allowed in presence of humans. Moreover, the technology allows more efficient and ergonomic wearable robotic devices, opening the option for exo-skeletons to be used by human operators inside the factories and distribution centers. This remains to be put in place, but it can open new perspectives in robotic applications. A last remarkable property of soft robots is their adaptability to fragile or tortuous environments. For some particular industry fields (chemistry, food industry etc.) this could also be an advantage compared to existing rigid solutions. For instance, the German company festo, key player in the industrial robotics field, is experimenting with deformable trunk robots that exhibit great compliance and adaptability, and we are working on their accurate control.
Personal and service robotics are considered an important source of economic expansion in the coming years. The potential applications are numerous and in particular include the challenge of finding robotic solutions for active and healthy aging at home. We plan to develop functional orthosis for which it is better not to have a rigid exoskeleton that is particularly uncomfortable. These orthosis will be ideally personalized for each patient and built using rapid prototyping. On this topic, the place of our team will be to provide algorithms for controlling the robots. We will find some partners to build these robots that would fall in the category of “wearable robots”. With this thematic we also connect with a strong pole of excellence of the region on intelligent textiles (see Up-Tex) and with the strategic plan of INRIA (Improving Rehabilitation and Autonomy).
Robots have a long history with entertainment and arts where animatronics have been used for decades for cinematographic shootings, theater, amusement parks (Disney's audio-animatronic) and performing arts. This year, we obtained an award for an Art Installation at the Exhibit Panorama 22. The installation “L'Érosarbénus”, which was produced at Le Fresnoy for the exhibition Panorama 22, is a collaboration between visual artist Yosra Mojtahedi and DEFROST. This installation, whose aesthetics are inspired by rocky, plant and human forms, is brought to life with the help of Soft Robotics devices. It was awarded the prize “Révélation Art Numérique — Art Vidéo 2020” by the ADAGP. See the ARTE video.
Soft robots have many medical applications as their natural compliance makes them safer than traditional robots when interacting with humans. Such robots can be used for minimally invasive surgery, to access and act on remote parts of the body through minimal incisions in the patient. Applications include laparascopic and brain surgery, treatment of several cancers including prostate cancer, and cardiology, for example percutaneous coronary interventions. As an example, we received an industry grant (CIFRE) with Robocath to work on autonomous catheter navigation. See Section 9.1.
Another application is cochlear implant surgery in the project ANR ROBOCOP.
This year, with the health situation, we have cancelled completely our trips. Even if this situation is temporary, it has enabled us to totally reduce the carbon footprint of our activities. In the future, even if we resume our activities, we will ensure that this carbon footprint is kept low.
Quentin Peyron was successfull at the 2021 campaign of Inria competitive recruitment procedure for researchers, normal class. He joins DEFROST at the start of 2022 to work on the topic of eco-design of soft robots.
Dewi Brunet, folding artist, was awarded an AIRLab funding by the Université de Lille to be in residence in the DEFROST team for 3 months from October 2021 till January 2022, as part of his project Plantoid-Ori. Dewi will collaborate with the team to create a piece of art inspired by plants, origami and soft robotics.
In collaboration with the Mimesis team at Inria Nancy and the company InfinyTech3D managed by Erik Pernod, DEFROST was laureate of an ANR PRCE that will be running from Jnauary 2022 till December 2024. The topic of the project will be the simulation of percutaneous liver tumor ablation in virtual reality.
At the Hamlyn Symposium, the poster describing the research and results obtained in the Cooperative Brachytherapy project 32 won the award for "Best Virtual Poster Presentation". DEFROST has notably contributed to this project with the development of a novel prostate phantom (see Sec.8.2). These results are encouraging for pursuing the research direction of creating anatomical soft robots, i. e. devices that represent human organs. Numerical modeling, control, sensing, and fabrication come together to create devices that mimic organs in their physical properties and behavior. The coupling with the numerical simulation is essential for providing control signals as well as interpreting the sensor readings.
Art-science collaboration between Yosra Mojtahedi and Stefan Escaida Navarro led to a piece of art that made the cover of the International journal Soft Robotics (SoRo).
Smooth the user experience with Sofa By integrating authoring features into runSofa so we can design simulation in an integrated environment. We should be able to model scenes, simulate & debug them.
This tool replaces the old “runSofa” interface, today deprecated but still in use by most SOFA users.
SofaQtQuick provides a fluid and dynamic user experience for SOFA, thanks to the integration of authoring tools to design complex simulations directly in the 3D environment, rather that scripting them as it is done today.
FEATURES: Scene graph editing Interactive modeling Project oriented approach Prefab as reusable and parametric object 2D Canvas Custom widgets per component Live coding Node base interface for data link debugging Everything with a non-linear workflow
Based on a code gift from Anatoscope, stringly inspired by Blender & Unity's workflow.
In the context of the Cooperative Brachytherapy (CoBra) project, a novel prostate phantom to study needle-insertion based interventions, such as LDR brachytherapy, was developed. This devices was conceived using soft robotics fabrication and modeling techniques previously researched within the team 3. In the corresponding paper 12, it is described how the phantom is equipped with sensors and coupled with the simulation in order to estimate external forces acting on the device. The deformation/motion of the phantom due to this forces is also captured and it was shown that they are plausible from a clinical point of view.
This platform is mainly composed of three parts: actuation system, micro controller, position sensor system. It is made of controlling cable-driven soft robots, such as the soft trunk robot shown in Fig. 5. Some research work has been completed on this platform: 2124
In rigid robotics, self-collision are usually avoided since it leads to a failure in the robot control and can also cause damage. In soft robotics, the situation is very different, and self-collisions may even be a desirable property, for example to gain artificial stiffness or to provide a natural limitation to the workspace. However, the modeling and simulation of self-collision is very costly as it requires first a collision detection algorithm to detect where collisions occur, and most importantly, it requires solving a constrained problem to avoid interpenetrations. When the number of contact points is large, this computation slows down the simulation dramatically. In this work, we applied a numerical method to alleviate the contact response computation by reducing the contact space in a lowdimensional positive space obtained from experiments. We showed good accuracy while speeding up dramatically the simulation. We applied the method in simulation on a cable-actuated finger and on a continuum manipulator performing exploration. We also showed that the reduced contact method proposed can be used for inverse modeling. The method can therefore be used for control or design. This work was published in
14, and see Figure
6.
In the context of the Cooperative Brachytherapy (CoBra) project, a novel prostate phantom for the study of needle-insertion based interventions, such as LDR brachytherapy, was developed. This devices was conceived using soft robotics fabrication and modeling techniques previously researched within the team 3. In the corresponding paper 12, it is described how the phantom is equipped with sensors and coupled with the simulation in order to estimate external forces acting on the device during needle insertion. The deformation/motion of the phantom due to this forces is also captured and it was shown that they are plausible from a clinical point of view.
In 2021, a survey paper on the subject of proximity perception in human-centered robotics was finalized 13. Proximity sensors can help in closing the gap between visual and tactile perception (see Fig. 8) in robotics.
The content of this survey was inspired and based upon the discussions and exchanges that took place in the Workshops on Proximity Perception in Robotics which were held at IROS 2018-2021.
This work, published in IEEE Robotics and Automation Letters 21, demonstrates a gain-scheduling closed-loop method to control a soft trunk robot operating within its workspace by using Finite Element Method (FEM). The main idea of this method is to divide the workspace into several sub-workspaces where the most suitable gains are applied correspondingly in each sub-workspace. As a result, it becomes feasible to control the trunk by gain scheduling when crossing from one sub-workspace to another as well as considering its dynamic characteristics. The derivation of the method is presented accordingly. In the end, the proposed method is validated by experiments (See the illustration in Figure 9).
Compliant Mechanisms (CMs) are used to transfer motion, force and energy, taking advantages of the elastic deformation of the involved compliant members. A branch of special type of elastic phenomenon called (post) buckling has been widely considered in CMs: avoiding buckling for better payload-bearing capacity and utilizing post-buckling to produce multi-stable states. This work digs into the essence of beam’s buckling and post-buckling behaviors where we start from the famous Euler–Bernoulli beam theory and then extend the mentioned linear theory into geometrically nonliner one to handle multi-mode buckling problems via introducing the concept of bifurcation theory. Five representative beam buckling cases are studied in this paper, followed by detailed theoretical investigations of their post-buckling behaviors where the multi-state property has been proved. We finally propose a novel type of bi-stable mechanisms termed as Pre-buckled Bi-stable Mechanisms (PBMs) that integrate the features of both rigid and compliant mechanisms. The theoretical insights of PBMs are presented in detail (see Figure 10).
Compliant Mechanisms (CMs) present several desired properties for mechanical designs. Conventional rigid-body mechanisms composed of rigid links connected at kinematic joints, serve as devices to transfer motion, force and energy by the movements of rigid links whereas CMs are able to present the same function only through deflection of flexible members. Most designs of CMs in the current literature employ straight beams as the elementary flexible members whereas initially curved beams (ICBs) also provide potential advantages for CMs such as large range of motion and small strain range. This work presents an efficient spatial compliance analysis method of general ICBs. The spatial compliance analysis of different types of ICBs (such as varying-curvature beams and varying-cross-section beams) was conducted, followed by Finite Element Analysis (FEA) verification. Next, the modeling and optimization of two types of CMs including ICB-based parallelogram mechanisms and ICB-based Ortho-planar springs were carried out by applying screw theory under the framework of position space concept and parameter normalization strategy where a class of anti-buckling translational parallelograms with high load-bearing capacity and a type of compact 2R1T (2 rotational DOF and 1 translational DOF) compliant kinematic joints were obtained. The corresponding FEA was conducted to verify the optimal results (see Figure
11).
This work investigates the workspace estimation of soft manipulators. Given a configuration of such a soft robot, with the bounded actuators, the Discrete Cosserat method is adopted to deduce the mathematical model of soft manipulators, based on which an optimization-based approach is proposed to estimate the workspace. Implemented to various soft manipulators’ configurations, numerical simulations are provided to highlight the feasibility of the proposed methodology (see Figure 12).
As a novel class of robots, soft robots have demonstrated many desirable mechanical properties than traditional rigid robots due to their nature of being compliant, flexible and hyperredundant, such as great adaptability to unknown environments, safe human robot interaction (HRI), energy-saving actuation and the maneuverability to display diverse mechanical properties. However, its inherent high-DoF nature would result in some complex nonlinear behaviors, and their kinematic or dynamic models are therefore harder to deduce than the ones of conventional rigid robots. In this work, we propose a trajectory tracking control strategy for a soft trunk robot based on Finite Element Method (FEM). We first plan a feasible trajectory for the studied robot in SOFA (a FEM-based simulator) by solving a model-prediction-control (MPC)-based optimization problem. The second step is to conduct linearization around the pre-designed trajectory, based on which an associated controller can be then developed. The detailed derivation of the mentioned work is explained accordingly. In the end, the results of experimental validation is presented to prove the feasibility of the proposed method (see Figure
13).
Considering a soft manipulator configuration, controlled via installed bounded actuators, this work addresses the end-effector workspace estimation problem for such a soft robot. For this, the Discrete Cosserat method is adopted to deduce the mathematical model of soft manipulators, based on which a continuation method that accounts for simple and multiple bifurcation points to solution curves is developed to map its workspace boundaries. Difficulties encountered in calculating tangents at simple and multiple bifurcation points are studied, and an efficient solution is provided. Numerical simulations applied to planar and spatial soft manipulator configurations are presented to emphasize the validity of the proposed methodology (see Figure 14).
Compliant Mechanisms (CMs) present several desired properties for mechanical applications only depending on elastic deformation of the involved compliant beams/flexures. As reported in the current literature, most CM designs utilize straight beams and initially curved beams (ICBs) as the fundamental flexible members. In CM research community, many great contributions regarding modeling these elementary flexible members have been achieved. In this work, a comprehensive modeling methodology, based on beam theory, has been established to characterize the static planar deflection of slender beam. Then such a methodology has been applied to solve 8 loading scenarios of large beam-deflection problems that exist in the design of CMs. Essentially speaking, all these beam-deflection problems are treated as a type of boundary value problems (BVPs) of an ordinary differential equation (ODE) and solved by a modified collocation method. After that, this methodology has been used to model some representative CMs with large-deflection strokes, such as compliant parallelograms (see Figure 15).
In this contribution, 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 positions of the nodes of the mesh are in global space) while 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. The Figure 16 shows the inverse simulation of a soft silicone tentacle modeled in FEM and actuated by 4 cables models in reduced coordinates by DCM.
In this contribution, we design in simulation and build a parallel soft robot with a 6 degrees of freedom (DOF) end-effector. We show that by using a 3D-printed meso-structured material which displays an anisotropic behaviour, we can modify the kinematics of the structure in order to control one additional DOF which is not possible to achieve using a standard isotropic and homogeneous material like silicone. The behaviour of the robot is simulated using numerical homogenization and the finite element method (FEM), which runs in real-time and can be used for control. We finally show that the parallel soft robot we have built is controllable in open loop thanks to the use of inverse simulation. We demonstrate its maneuverability by guiding a marble in a maze game.
is a French startup located in Rouen which is providing a robotic solution for catheter navigation to avoid exposure of the physician to X-rays. We have a collaboration through the CIFRE thesis of Pierre Schegg. The goal is to provide automatic planning for navigation of the guide and catheter for interventions in cardiology. We obtained significant results that are currently in submission. A patent has been filed by the company.
is a small french starting company which develops virtual reality solutions based on SOFA. As part of a contract Infinytech3D had with
Follouto integrate their medical haptic interface to SOFA, we proposed an expertise and consulting contract to InfinyTech3D. This allowed us to document a part of the SOFA code on collision detection, response and haptics. An ANR project has just been accepted in collaboration with this company and the Inria MIMESIS team in Strasbourg
is a startup company focusing on surgical robotics. Their aim is to revolutionize surgery with novel ground-breaking surgical robots. We are about to sign a contract (January 2022) for starting a collaboration through CIFRE PhD thesis.
ROBOCOP: Robotization of Cochlear implant. This is a 4-year project, supported by the ANR (French National Agency for Research) in the framework of PRCE, starting from 1 October 2019 until 30 September 2023. ROBOCOP aims at creating a new prototype of cochlear implant, and robotize (i.e. actuate and control) its insertion process to facilitate the work of surgeon, to increase the success ratio, and to decrease the probability of trauma.
Our contributions this year on the project can be divided into two points.
The associated GitLab project..
Cosseroot: Cosserat Rod Theory for Slender Robots. This is a 4 year project, supported by the ANR (French National Agency for Research) in the framework of PRC, starting from 1 November 2020 until 31 October 2024. The objective of COSSEROOTS project is to systematically investigate the relative parameterization modeling technique in order to create for the first time a toolbox dedicated to modeling and control of slender, flexible, continuous, bio-inspired robots that can undergo large, controlled deformations. associated GitHub project.
Contributions around this project this year can be grouped under two points.
In addition, new important features have been added to the software recently. Indeed, we have introduced the possibility of taking into account the plastic behavior of certain objects we use in our different simulations. A nonlinear model of the previous described model is currently under evaluation.
ADT Plan IA: The simulation of soft-robots is a growing field since it is a way to virtually train AI algorithms in taking decisions. To tackle this challenge, accurate modeling the interactions of the robots with their environment is key. This is already possible today, but at the cost of a (too) long calculation time or a significant simplification of the environment. A ADT started this year to modernize the matrix assembly in SOFA and to bring the solving algorithms up to standard. Results of this work are already visible in the latest SOFA release (v21.12) and its advances can be followed on the associated GitHub project.
Olivier GOURY was member of the jury for the selection of Chargé de recherche (Young research Scientist) and ISFP (Inria Starting Faculty Position) at Inria Lille Nord Europe in 2021.
The magazine 01Net did a portrait of Christian Duriez: L'homme qui désarticule les robots
On November 25th, 2021, Dewi Brunet, artist in residence in the DEFROST Lab, presented his exhibition "Embryon" at the Espace Culture in the Unversité de Lille. This exhibition will remain several months through 2022, and displays preliminary work link to the collaboration with the DEFROST team in Oribotics.
On December 8th, the event Portfolio #2 : Les simulacres du vivant took place at La Gaîté Lyrique in Paris. From the team, Christian Duriez and Stefan Escaida Navarro were invited to discuss with artists Jonathan Pêpe and Yosra Mojtahedi about the implications and impact of soft robotics technologies that imitate organic life. Both artists have created installations in collaboration with DEFROST in 2015 and 2020, respectively.
From the 25th to the 27th of November 2021, six members of the team (Alexandre Bilger, Yinoussa Adagolodjo, Tanguy Navez, Nina Tenenhaus, Paul Chaillou, Etienne Ménager) participated in the second edition of the HackATech in Lille. This event consists in helping a project leader to develop a startup based on an INRIA Technology. The project in soft-robotics consisted in developing a flexible robot that can perform dental operations, such as drilling for implant placement. The team modeled and simulated a technical solution to this problem, provided technical and organizational knowledge for the realization of a business plan and a pitch. Etienne Ménager was the technical referent for this event.