Supernumerary robotic limbs (SRL) are wearable extra limbs intended to help humans perform physical tasks beyond conventional capabilities in domestic and industrial applications. However, unique design challenges are associated with SRLs as they are mounted on the human body. SRLs must 1) be lightweight to avoid burdening the user, 2) be fast enough to compensate for human unpredictable motions, 3) be strong enough to accomplish a multitude of tasks, 4) have high force-bandwidth and good backdrivability to control interaction forces between the user and the environment. This paper studies the potential of a remotely actuated 3-DOF supernumerary robotic arm equipped with a 3 fingers soft gripper, both powered by magnetorheological (MR) clutches and hydrostatic transmission lines. The tethered configuration allows the power-unit to be located on the ground, which minimizes the deported mass (4.2 kg) on the user. MR clutches minimize the actuation inertia in order to provide fast dynamics and good backdrivability. An experimental open-loop force-bandwidth of 18 Hz is founded at each joint and the maximal speed reached by the device end-effector is 3.4 m/s, which is sufficient for compensating human motions. Also, the two first joints provide 35 Nm and the third joint, 29 Nm, which is strong enough to hold manual industrial tools. Finally, the SRL is put in real practical situations, as fruit and vegetables picking, painting, tools holding and badminton playing. The capability of the proposed MR-Hydrostatic SRL to successfully perform various tasks with high speed and smoothness suggests a strong potential of SRLs to become future commonly used devices.

In the last decade, the development of simple and easy-to-use robotics has provided a significant step towards the democratization of collaborative robots, which can now work closely alongside humans. However, state-of-the-art cobots still provide safety at the cost of work-speed, which is purposely limited to avoid high-energy collisions. In order to increase safety and work speed simultaneously, force/impedance-controlled actuators with high dynamic performance, backdrivability and low-reflected inertia are of interest. In this letter, a novel robotic actuator architecture with two independent magnetorheological (MR) power chains is proposed, built and experimentally characterized. The modular 30 Nm robotic joint is shown to have similar size (85 X 85 X 124 mm), weight (1.1 kg) and torque density (27 Nm/kg) as the Universal Robot (UR) size 1 robotic joint, which relies on a Harmonic Drive (HD) gearbox, but with 150 times less inertia, high backdrivability (0.7% of max torque), high torque bandwidth (>70 Hz) and inherent torque-limiting that makes it immune to impacts. The dual MR power chain allows ultra-fast transparent interactions with bluezero backlash over half its torque range and peak torque when motor reversal is allowed. To illustrate the force/impedance control performance, a 3-DOF robotic arm is built and used to simulate virtual objects in both open and closed loop.

Precise and high-fidelity force control is critical for new generations of robots that interact with humans and unknown environments. Mobile robots, such as wearable devices and legged robots, must also be lightweight to accomplish their function. Hydrostatic transmissions have been proposed as a promising strategy for meeting these two challenging requirements. In previous publications, it was shown that using magnetorheological (MR) actuators coupled with hydrostatic transmissions provides high power density and great open-loop human-robot interactions. Still, the open-loop force fidelity at low and high frequencies are decreased by the transmission's dynamics and by nonlinear friction. This paper compares control strategies for MR-hydrostatic actuator systems to increase its torque fidelity, defined as the bandwidth (measured vs desired torque reference) and transparency (minimizing the undesired forces reflected to the end effector when backdriving the robot). Four control approaches are developed and compared experimentally: (1) Open-loop control with friction compensation; (2) non-collocated pressure feedback;(3) collocated pressure feedback; (4) LQGI state feedback. A dither strategy is also implemented to smoothen ball screw friction. Results show that approaches (1), (2) and (3) can increase the performances but are facing compromises, while approach (4) can simultaneously improve all metrics. These results show the potential of using control schemes for improving the force control performance of robots using tethered architectures, addressing issues such as transmission dynamics and friction.

Active suspension systems for automotive vehicles were developed in the past using hydrostatic, electric, magnetic and magnetorheological (MR) technologies to control road vibrations and vehicle dynamics and thus improve ride comfort and vehicle performance. However, no such systems were developed for heavy equipment, trucks and off-highway vehicles. For instance, agricultural tractors are still equipped with minimal suspension systems causing discomfort and health problems to drivers. The high suspension loads due to the massive weight of these vehicles are a challenge since high forces are needed to achieve efficient active suspension control. This paper presents an experimentally validated feasibility study of a hydrostatic, MR clutch-driven system of actuators. The scope of this paper is to evaluate the preliminary performance of the actuator for future vibration control. The hydraulic system allows the actuators to be remotely located from the wheels or cabin of the heavy vehicle and conveniently placed on the vehicle’s suspended frame. The design includes two MR clutches driven in an antagonistic configuration to push and pull on the end effector. Experiments on a laboratory prototype show that the low-inertia characteristics of the clutches allow a high blocked-output force bandwidth of 20 Hz with peak output forces exceeding 15 kN.

Patient transfer devices allow for passive movement of patients in hospitals and care centers. Instead of hoisting the patient, it would be beneficial in some cases to assist their movement, enabling them to move by themselves and reducing hospitalization time. However, patient assistance requires devices capable of precisely controlling output forces at significantly higher speeds than those used for patient transfers alone, and a single-motor solution would be over-sized and would show poor efficiency for accomplishing both functions. This paper presents a ceiling robot, using a dual-motor actuator and adapted control schemes, that can be used to transfer patients, assist patients in their movement, and help prevent falls. The prototype is shown to be able to lift patients weighing up to 318 kg and to assist a patient with a desired force of up to 100 kg with a precision of 7.8%. Also, a smart control scheme to manage falls is shown to be able to stop a patient who is falling by applying a desired deceleration.