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Soft actuators can be classified into five categories: tendon-driven actuators, electroactive polymers, shape-memory materials, soft fluidic actuators (SFAs), and hybrid actuators. The characteristics and potential challenges of each class are explained at the beginning of this review. Furthermore, recent advances especially focusing on SFAs are illustrated. There are already some impressive SFA designs to be found in the literature, constituting a fundamental basis for design and inspiration. The goal of this review is to address the latest innovative designs for SFAs and their challenges and improvements with respect to previous generations, and to help researchers to select appropriate materials for their application. We suggest seven influential designs: pneumatic artificial muscle, PneuNet, continuum arm, universal granular gripper, origami soft structure, vacuum-actuated muscle-inspired pneumatic, and hydraulically amplified self-healing electrostatic. The hybrid design of SFAs for improved functionality and shape controllability is also considered. Modeling SFAs, based on previous research, can be classified into three main groups: analytical methods, numerical methods, and model-free methods. We demonstrate the latest advances and potential challenges in each category. Regarding the fact that the performance of soft actuators is dependent on material selection, we then focus on the behaviors and mechanical properties of the various types of silicone that can be found in the SFA literature. For a better comparison of the different constitutive models of silicone materials proposed and tested in the literature, ABAQUS software is here employed to generate the engineering and true strain-stress data from the constitutive models, and compare them with standard uniaxial tensile test data based on ASTM412. Although the figures presented show that in a small range of stress–strain data, most of these models can predict the material model acceptably, few of them predict it accurately for large strain-stress values. Sensor technology integrated into SFAs is also being developed, and has the potential to increase controllability and observability by detecting a wide variety of data such as curvature, tactile contacts, produced force, and pressure values.

There is a growing body of evidences that brain surrogates will be of great interest for researchers and physicians in the medical field. They are currently mainly used for education and training purposes or to verify the appropriate functionality of medical devices. Depending on the purpose, a variety of materials have been used with specific and accurate mechanical and biophysical properties, More recently they have been used to assess the biocompatibility of implantable devices, but they are still not validated to study the migration of leaching components from devices. This minireview shows the large diversity of approaches and uses of brain phantoms, which converge punctually. All these phantoms are complementary to numeric models, which benefit, reciprocally, of their respective advances. It also suggests avenues of research for the analysis of leaching components from implantable devices.

In this article we define the criteria and present the methodology to choose a smart material in order to actuate a soft neurosurgery robot. These criteria are defined with the experience of a neurosurgeon.

International audience; This paper deals with the specific hysteretic effects of a multi-antagonistic shapememory alloy (SMA) actuation system in which each wire can be thermally activated individually (one or more at a time). A planar system with six SMA wires organized in a ternary rotational symmetry is studied numerically, via finite element calculation software. The objective is to analyze the functional characteristics of such mechanism, whose response during a thermal activation sequence is multi-antagonistic and hysteretic. Important points are highlighted, such as the avoidance of buckling and plasticity, the possibility of locking a configuration without energy input, and the "attraction" effect of any heating step on the following steps. The feasibility of reaching a given target in the workspace is also illustrated. Finally, the analysis shows the necessity to consider these multi-antagonistic and hysteretic aspects of the actuation in the future design and control of such type of mechanisms. The latter could be of interest as hollow shaft rotary actuators with additional (small) translation degrees of freedom in applications requiring long-term and stable positioning at ambient temperature.

The aim of this article is to study the consequences of the active stiffening of a compliant mechanism on the workspace created by the deformation of its structure. In connection with recent soft robotics research integrating shape-memory alloys (SMAs), the variation in stiffness over time is here obtained by the thermal activation of a nickel–titanium SMA spring. The workspace is created by the deformation (in the strength of materials sense) controlled by two rotary actuators acting on a structure comprising two angled flexible beams. In addition to a natural variation in the elasticity modulus of the SMA component during its thermal activation, its shape reconfiguration adds a structural deformation modifying the workspace. The existence of a common area between the workspaces of the mechanism corresponding to the non-activated and activated modes of the SMA is preserved. Several compliance maps are determined from measurements using a laser tracker targeting a given position of the loaded structure. The impact of SMA pre-stretch on stiffness variability is compared to that of a change in Young’s modulus. Variations in the stiffness distributions between the two modes reveal interesting properties (stiffness sign inversion, anisotropy) for the future optimal design of compliant mechanisms with high versatility, associating the spatial positions of the effector with variable stiffness values.

International audience; The development of rotary actuators is an important issue of the engineering applications of shape memory alloys (SMAs). This paper reviews about a hundred references on this topic, and presents around eighty actuators driven by SMAs. A classification is made according to the type of rotation (continuous or non-continuous), the single or reversible direction of the rotation, as well as the number of SMA elements involved in the device. Different issues are then discussed, such as the characteristics of the SMA elements, the heating and cooling system for the SMA, the control of the actuator, as well as the output torque and stroke which can be reached. This paper provides the first review focused on rotary actuators triggered by SMAs, highlighting the specificities and potentialities of such actuators for new applications in the future.

Resume Il y a une cinquantaine d’annee, au Japon, a ete decrit le phenomene de karoshi : la mort par infarctus ou par accident vasculaire cerebral en lien avec les conditions de travail. Differents troubles sont progressivement apparus dans le monde du travail en Occident comme le workaholism, l’epuisement compassionnel, le burn out ou encore le bore out. Ces troubles correspondent a des processus psychologiques qui se mettent en place en reponse a des facteurs de risque psychosociaux comme la surcharge de travail, la perte de sens au travail, la surexposition a l’empathie… et aboutissent au final a un epuisement physique et/ou psychique et/ou emotionnel et/ou compassionnel. Tous ces processus peuvent aboutir a des epuisements pouvant se compliquer sur le plan medical de pathologies qu’elles soient somatiques ou psychiatriques, et sur un plan plus general d’accidents ou d’erreurs professionnelles. Le terme de burn out est devenu le principal terme pour parler d’epuisement professionnel alors que d’autres processus d’epuisement existent n’incluant pas les memes types de facteurs de risques psychosociaux ni les memes profils psychologiques. Nous proposons une modelisation des differents processus d’epuisement professionnel avec leurs particularites et leurs proximites. Nous presentons les modalites de prises en charge psychotherapeutiques de ces processus d’epuisement.

This study deals with the evaluation of the compliance map variability of a flexible structure using an active material, namely a shape memory alloy (SMA). Compliance or stiffness maps are an important indicator of the performances of robotic structures or mechanisms, for instance to assess the positioning error for a production task. The paper carefully examines the impact of the combination of a compliant structure (here a closed-loop flexible structure) and a SMA spring. Various static compliance maps are simulated and analyzed with respect to the state of the SMA. Several aspects are discussed, such as the concept of pseudo-workspace deriving from the deformation of the structure, or the anisotropy and non-linearity of the compliance change, as well as the relevance of the large displacement framework (in the strength of materials sense) for the correct calculation of the compliance maps. The results enable us to validate the capability of the combination of a compliant structure and a SMA component to achieve variable compliance maps that could be used for polyvalent robotic tasks.

In line with the recent development of soft actuators involving shape-memory alloys (SMAs) embedded in compliant structures, this paper proposes a concept for a rotary actuator driven by a SMA wire placed inside a 3D-printed helical structure. The concept consists of using the one-way memory effect of the SMA (activated by Joule heating) to create the rotation of a material point of the structure, while the inverse rotation is obtained during the return to ambient temperature thanks to the structure's elasticity. The study was performed in three steps. First, a prototype was designed from a chain of design rules, and tested to validate the feasibility of the concept. Thermal and geometrical measurements were performed using infrared and visible-range stereo cameras. A clockwise rotation (250°) followed by an anti-clockwise rotation (−200°) were obtained, enabling us to validate the concept despite the partial reversibility of the movement. Second, finite element simulations were performed to improve rotation reversibility. The high compliance of the mechanical system required a framework of large displacements for the calculations (in the strength of materials sense), due to the high structural flexibility. Finally, a second prototype was constructed and tested. Attention was paid to the rotation (fully reversible rotation of 150° reached) as well as to parasitic movements due to overall structural deformation. This study opens new prospects for the design and analysis of 3D-printed soft actuators activated by smart materials.

In robotics, static stiffness maps are used as tools for the performance analysis of robots employed in production tasks, such as pick-and-place or manufacturing. This paper evaluates the relevance of a numerical tool built from a commercial finite element package to generate stiffness maps for any type of robot (serial, parallel, hybrid or compliant). The key points are the spatial resolution, the precision, and the calculation time of a stiffness map. The method for obtaining the 36 static stiffness maps of a 3-D robotic structure in its operational space is presented. The mechanical model is based on a finite element calculation using beam elements for the links and spring elements for the joints. The approach is first applied to a rigid-body mechanism. Numerical results show that a good compromise can be obtained between spatial resolution, precision, and calculation time. Then, the method is applied to a compliant structure requiring processing in a large displacement framework for the relevant estimation of a stiffness map. The numerical tool opens new prospects for the design of robotic structures, in terms of both optimization and use of various material behaviors.