Collaborative robots are more and more used in applications requiring robots and humans to work in proximity or direct contact. However, conventional collaborative robots powered by servo-geared actuators are intrinsically dangerous due to their high reflected inertia. Recent studies have shown that low inertia and high bandwidth (> 30 Hz) magnetorheological (MR) actuators have the potential to improve the safety of collaborative robots without reducing their force and speed capabilities. The main contribution of this paper is to provide a quantitative assessment of how MR actuators can contribute to reducing the impact forces with humans, and thus increase the safety of collaborative robots. Dynamic models, validated with simplified 1 DOF experiments, show that the safety level of collaborative robots can be increased by a factor up to 3 only by changing the conventional servo-geared actuator architectures for MR actuators with no other changes. The paper also presents a simple, reliable, and fast collision detection method based on joint angular velocity band-pass filtering, a method exploiting the unique low inertia and clean dynamics properties of MR actuators. Finally, an experimental comparison of representative collaborative robots demonstrates an impact force reduction of 10 times using MR actuators, fast collision detection, and passive foam padding.

Wearable robots are limited by their actuators performances because they must bear the weight of their own power system and energy source. This paper explores the idea of leveraging hybrid modes to meet multiple operating points with a lightweight and efficient system by using hydraulic valves to dynamically reconfigure the connections of a hydrostatic actuator. The analyzed opportunities consist in 1) switching between a highly geared power source or a fast power source, 2) dynamically connecting an energy accumulator and 3) using a locking mechanism for holding. Based on a knee exoskeleton case study analysis, results show that switching between gearing ratio can lead to a lighter and more efficient actuator. Also, results show that using an accumulator to provide a preload continuous force has great mass-saving potential, but does not reduce mass significantly if used as a power booster for short transients. Finally, using a locking valve can slightly reduce battery mass if the work cycle includes frequent stops. The operating principles of the proposed multimodal schemes are demonstrated with a one-DOF prototype.

Collaborative robots need to work closely and safely with users while being fast and strong. Fulfilling both these needs simultaneously presents a significant challenge, if not a roadblock, for conventional geared motor technology. Magnetorheological (MR) actuation is an alternative technology that has the potential to exhibit both safety and speed at the same time in a compact and cost-effective envelope. MR actuation has demonstrated great potential for low-DOF mechatronic devices in close collaboration with humans such as exoskeletons and flight control systems but its potential for high-DOF collaborative robots remains widely unexplored. This paper presents the design and experimental validation of a 6 DOF manipulator prototype actuated by semi-delocalized MR clutches. The manipulator is designed with the objective of matching or exceeding the performance requirements of today's cobots in order to verify the potential of MR actuation for such applications. Experimental results show that the prototype has a mass in motion of 5.3 kg and can move a 4.5 kg payload at 1 m/s in a range of 0.885 m. Force bandwidth is above 50 Hz and backdriving forces less than 10% of the joints maximum torque, assuring excellent dynamic performance. Furthermore, the manipulator prototype is shown to be inherently safe and impact-tolerant. In all, results suggest that semi-delocalized MR actuation is a promising solution for high performance cobots although future work is needed for the MR technology to reach full-maturity in robotics.

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.

Tendon-Driven Manipulators (TDM) have been used in various applications requiring low inertia robots having multiple degrees-of-freedom (DOF) and redundancy. TDMs are generally actuated by gear electric motors placed at the base of the robot, and consequently require complex cable tension feedback from force sensors or dynamic modelling to maintain cables under tension. This paper presents a high performance TDM actuated by magneto-rheological clutches along with a specialized motion control algorithm, termed Projected PID, that requires no tension feedback. A 2-DOF proof-of-concept TDM powered by magneto-rheological clutches is used to demonstrate overall controller performance, and a reconfigurable 2-DOF TDM powered by direct-drive electric motors is used to demonstrate the controller's ability to compensate for configuration variations and actuator failure. Experimental results also demonstrate the ability of Projected PID to control magneto-rheological cable-driven TDMs with high accuracy.

Robots using cellular-like redundant binary actuators could outmatch electric-gearmotor robotic systems in terms of reliability, force-to-weight ratio, and cost. This paper presents a robust fault-tolerant control scheme that is designed to meet the control challenges that are encountered by such robots, i.e., discrete actuator inputs, complex system modeling, and cross-coupling between actuators. In the proposed scheme, a desired vectorial system output, such as a position or a force, is commanded by recruiting actuators based on their influence vectors on the output. No analytical model of the system is needed; influence vectors are identified experimentally by sequentially activating each actuator. For position control tasks, the controller uses a probabilistic approach and a genetic algorithm to determine an optimal combination of actuators to recruit. For motion control tasks, the controller uses a sliding mode approach and independent recruiting decision for each actuator. Experimental results on a four degrees of freedom binary manipulator with 20 actuators confirm the method's effectiveness and its ability to tolerate massive perturbations and numerous actuator failures.

Robots using cellular-like redundant binary actuators could outmatch modern robotic systems in terms of reliability, force-to-weight ratio and cost. This paper presents a robust control scheme that is designed to meet the challenges encountered by such robots, i.e., discrete actuator inputs, complex system modeling and cross-coupling between actuators. In the proposed scheme, a desired vectorial system output, such as a position or a force, is commanded by recruiting actuators based on their influence vectors on the output. No analytical model of the system is needed, influence vectors are identified experimentally by sequentially activating each actuators. Experimental results on a four-degrees-of-freedom binary manipulator with twenty actuators confirm the method effectiveness, for position and motion control, and its ability to tolerate massive perturbations and up to 50% actuator failures.

Jet-boats perform remarkably well at high-speed but lack low speed maneuverability for tight maneuvers such as ducking. This paper presents a low speed omnidirectional propulsion system controlled with a joystick for jet-boats. Two concepts are presented and evaluated. The first concept uses all original parts. The second concept uses a set of fix jet nozzles disposed around the hull. The position and angles of the nozzles are optimized with an index of omnidirectionality quality based on the projection of a set of force solutions on a shell with the shape of the desired force space. A 3D simulator backed by experimental results serves for the evaluation by potential customers of each design. The first concept exhibited poor maneuverability, as it offers ten times less force in sway than in surge. The optimized force space of the second concept is much more uniform, and was unanimously appreciated for its quality of low speed maneuverability. Both designs have been validated experimentally. The present work offers an omnidirectional propulsion system that is easy to enhance with advanced control laws. Velocity feedback control is given as example, and shows important improvement of maneuverability and robustness to miscalibration.

In this paper the performance of a high-precision parallel robot manipulator with bistable actuation is experimentally evaluated. The manipulator is for performing prostate cancer biopsy and treatment within the bore of a magnetic resonance imaging (MRI) system. The analysis and simulations have shown that this bistable manipulator is able to perform well with dielectric elastomer actuators that have been shown to be compatible with the high magnetic fields of an MRI. In this work an experimental prototype system was developed and tested. The results show that it provides the precise needle placement required by the medical task.

Planetary scientists are greatly interested in the caves present on the Moon and Mars, however these areas present major challenges to current space robots. A new space robotics concept, microbots, is presented and a possible reference mission to Mars is discussed. The feasibility of the mobility and power systems of the microbot are analyzed within the context of the reference mission. The results of this analysis are that the microbot system is a feasible concept for a development timeline of approximately 10 years.

MRI (magnetic resonance imaging) is a powerful medical diagnostic tool. Its value would be greatly increased if it were possible to physically manipulate objects within the MRI during imaging. However, the extraordinarily strong magnetic fields used by the MRI make conventional electromagnetic components, such as actuators and sensors, unusable. In this paper, it is shown that devices constructed using binary polymer based actuators, called electrostrictive polymer actuators (EPAM) are able to function effectively within the MRI without degrading its imaging performance. These actuators eliminate the need for conventional electromagnetic actuators and their associated electronics. The binary nature of the actuators eliminates the need for feedback sensors to control the devices motion. The basic concept called digital mechatronics is briefly summarized in this paper. Its application to a reconfigurable MRI surface-imaging coil (RMIC) is also presented. Experimental results are presented that show the EPAM RMIC is completely compatible in the MRI and can be used to enhance the diagnostic capabilities of MRI. The paper also suggests other applications of binary EPAM based actuators for use in MRI systems.