Haptic joysticks for man-machine interaction used in aerospace flight control have highly demanding requirements of reliability, force density, and high dynamics that can hardly be met with conventional electromagnetic actuators. This work explores the potential of using an alternative actuation strategy based on hyper-redundant MR clutches that modulate the force of a tendon-driven 2-degree-of-freedom spherical gimbal. A system design and its closed-loop force control scheme are proposed. Experimental results for an open-loop characterization, static force control and dynamic force control are set out and compared with typical requirements for such devices from the literature. Results show that the proposed architecture leads to one of the lightest systems reported in the literature that has the potential to meet reliability requirements by providing a jam-free design with duplex fault tolerance, and yet, can generate high force levels while providing enough force resolution. The approach is promising and can extend to high-performance collaborative robot applications.

Supernumerary Robotic Limbs (SRLs) are wearable robots augmenting human capabilities by acting as a co-worker, reaching objects, support human arms, etc. However, existing SRLs lack the mechanical backdrivability and bandwidth required for tasks where the interaction forces must be controlled such as painting, drilling, manipulating fragile objects, etc. Being highly backdrivable with a high bandwidth while minimizing weight presents a major technological challenge imposed by the limited performances of conventional electromagnetic actuators. This paper studies the feasibility of using magnetorheological (MR) clutches coupled-to a low-friction hydrostatic transmission to provide a highly capable, but yet lightweight, force-controllable SRL. A 2.7 kg 2-DOFs wearable robotic arm is designed and built. Shoulder and elbow joints are designed to deliver 39 and 25 Nm, with 115 and 180°of range of motion. Experimental studies conducted on a one-DOF test bench and validated analytically demonstrate a high force bandwidth (>25 Hz) and a good ability to control interaction forces even when interacting with an external impedance. Furthermore, three force-control approaches are studied and demonstrated experimentally: open-loop, closed-loop on force, and closed-loop on pressure. All three methods are shown to be effective. Overall, the proposed MR-Hydrostatic actuation system is well-suited for a lightweight SRL interacting with both human and environment that add unpredictable disturbances.

Replacing aircraft hydraulic actuators with ElectroMechanical Actuators (EMAs) is seen as a necessary step towards the development of safer and more efficient aircraft with minimal environmental impact. EMAs are commonly used in a wide range of applications as they have improved efficiency over hydraulic actuators. However, in their current form, EMAs do not comply with the stringent weight and reliability requirements of primary flight control applications. This paper describes an Active Torque Distribution (ATD) system that could meet flight control reliability requirements, be lightweight, and increase the dynamic performance of current flight controls. The proposed ATD system uses magneto-rheological clutches to modulate the torque transferred from a centralized velocity source to various control surfaces. The fundamental advantage of this approach is found in the fluidic nature of magneto-rheological clutch interfaces which transmit torque without any solid mechanical contact thus preventing wear and failure causing mechanical seizure. The analytical study used to scale an ATD system and an analogue EMA system based on a representative flight control application shows that the proposed ATD system is 42% lighter than a system composed of EMAs and has a weight similar to that of current hydraulic actuators. Furthermore, this study demonstrates that ATD systems add ~100x less inertia to flight surfaces than EMAs allowing implementation of load alleviation control algorithms requiring high frequency motion (~30 Hz). A proof-of-concept clutch and controller confirm the analytical predictions and validate the possibility of using magneto-rheological clutches for flight control actuation.