En radiologie interventionnelle, l’assistance robotisée permet de limiter l’exposition du praticien aux rayons X et d’apporter plus de précision pour effectuer des opérations complexes. La présence de robots dans un environnement humain pose alors la question de la sécurité du patient et de l’équipe médicale, que ce soit lors d’interactions ou de manipulations. Dans cette thèse, nous nous intéressons dans un premier temps aux problématiques de sûreté. Une structure d’actionnement intrinsèquement sûre est proposée. Le prototype réalisé permet d’effectuer des tâches de positionnement en mode automatique. Parallèlement, une stratégie de guidage basée sur une approche passive est proposée. Un système à raideur variable permet d’imposer un effort résistif variable à l’utilisateur en vue de contraindre son geste. Dans une deuxième partie, nous étudions la possibilité d’intégrer de tels systèmes sur un dispositif à plusieurs degrés de liberté, répondant au problème de placement d’aiguille. / In the context of interventional radiology, robotic-assisted surgery limits practitioners’ exposure to radiations and brings more accuracy to perform complex interventions. However, the presence of robot in the environment is a potential danger for the patient and the medical staff in case of unexpected interactions and manipulations.In this PhD thesis, we first focus on safety problems. An intrinsically safe mechanism is proposed. The achieved prototype allows to follow both planned trajectories and moving environments.Secondly, a guidance mechanism based on a passive approach is suggested. With a variable stiffness system, using a compliant mechanism, a resistive force is applied to the user which allows him to be guided in his gesture.Based on medical needs, we then study the possibility to integrate and generalize such systems to multiple degrees of freedom.

<p dir="ltr">To ensure safety, traditional industrial robots must operate within cages to separate them from human workers. This requirement has led to the rapid development of collaborative robots (cobots) designed to work closely to humans. However, existing cobots often prioritize <a href="" target="_blank">performance </a>aspects, such as precision, speed, and payload capacity, or prioritize safety, leading to a challenging balance between them. To address this issue, this dissertation introduces innovative concepts and methodologies for variable stiffness mechanisms. These mechanisms are applied to create easily fabricated cobot components to allow for controllable trade-offs between safety and performance in human-robot collaboration intrinsically. Additionally, the end-effectors developed based on these mechanisms enable the flexible and adaptive gripping of objects, enhancing the utility and efficiency of cobots in various applications.</p><p dir="ltr">This article-based dissertation comprises five peer-reviewed articles. The first essay introduces a reconfigurable variable stiffness parallel-guided beam (VSPB), whose stiffness can be adjusted discretely. An accurate stiffness model is also established, capable of leveraging a simple and reliable mechanical structure to achieve broad stiffness variation. The second essay discusses several discrete variable stiffness actuators (DVSAs) suitable for robotic joints. These DVSAs offer high stiffness ratios, rapid shifting speeds, low energy consumption, and compact structures compared to most existing variable stiffness actuators. The third essay introduces a discrete variable stiffness link (DVSL), applied to the robotic arm of a collaborative robot. Comprising three serially connected VSPBs, it offers eight different stiffness modes to accommodate diverse application scenarios, representing the first DVSL in the world. The fourth essay presents a variable stiffness gripper (VSG) with two fingers, each capable of continuous stiffness adjustment. The VSG is a low-cost, customizable universal robotic hand capable of successfully grasping objects of different types, shapes, weights, fragility, and hardness. The fifth essay introduces another robotic hand, the world's first discrete variable stiffness gripper (DVSG). It features four different stiffness modes for discrete stiffness adjustment in various gripper positions by on or off the ribs. Therefore, unlike the VSG, the DVSG focuses more on adaptability to object shapes during grasping.</p><p dir="ltr">These research achievements have the potential to facilitate the construction and popularize of next-generation collaborative robots, thereby enhancing productivity in industry and possibly leading to the integration of personal robotic assistants into countless households.</p>