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Lhommeau, P. (2025). Embrayages magnétorhéologiques miniatures par fabrication additive. Thesis.

Robotic systems are now ubiquitous in our society and are no longer confined to factories or assembly lines. Advances in electronics and computing allow robots to collect information about their environment and process it in real time to decide their actions. In fragile or uncertain environments, actuators must be able to react quickly to unexpected events while remaining safe for their surroundings. Electric actuators integrating magnetorheological (MR) clutches have demonstrated strong responsiveness and excellent human–robot interaction capabilities, thanks to the decoupling of motor inertia and friction. Their transparency therefore makes them well suited for applications requiring haptic actuators for force feedback or direct manipulation of the actuator. Applications could include teleoperation or rehabilitation, where high transparency is essential for practitioners. There is a growing need to miniaturize this technology, both for smaller-scale applications such as haptic robotic hands and for high torque-density applications in actuators with high gear reduction ratios. It is therefore necessary to develop miniature MR clutches to improve their integration into small-scale complex mechanical systems. However, miniaturizing a mechanical system is not straightforward using conventional manufacturing processes, as one quickly encounters the complexity and cost of precision machining at such small scales. This limitation could be overcome thanks to recent advances in additive manufacturing, which allow the printing of high-precision small-scale parts and enable geometries that were previously impossible to achieve using conventional machining processes. The objective of this thesis is therefore to evaluate the feasibility and relevance of using an additive manufacturing process to facilitate the miniaturization of MR clutches. An MR clutch was manufactured and tested, integrating both the advantages and challenges of additive manufacturing. The developed clutch weighs only 85 g and delivers a torque of 0.55 N·m, with the goal of being integrated into a high reduction ratio (120:1) robotic actuator. Experimental characterization of the actuator showed that it is well suited for high power-density applications while offering excellent haptic capabilities. The 1.3 kg actuator demonstrates a maximum torque of 110 N·m and opposes only 1% of this torque when backdriven in open loop, thanks to the low inertia and friction of the 3D-printed clutches. The challenges related to 3D printing of MR clutches are identified, and the different strategies used to overcome them are presented. Metal 3D printing has therefore proven its relevance for the manufacturing of miniature MR actuators, although several challenges must still be addressed before it can be considered for production.

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