Despite advances in assistive technology, existing prosthetic knees still have some limitations, such as weight, low active and braking torque, and high energy consumption. This paper presents an active magnetorheological knee (AMRK) actuator developed for transfemoral prostheses. The system consists of a motor unit comprising an EC motor, harmonic drive and magnetorheological (MR) clutch. The motor unit provides active motion, working in parallel with an MR brake. With this configuration, the AMRK possesses multiple functions; it can work as a motor, clutch, or brake, reproducing movements similar to those of a healthy knee in different activities. All components of the prosthetic knee are protected to avoid risk of accidents and to provide an aesthetically appropriate structure. To reduce weight, energy consumption and volume, the MR clutch/brake geometric design was optimized using a particle swarm optimization algorithm. A prototype was fabricated and tested to evaluate the AMRK performance. Dynamic models of the MR clutch, MR brake and motor unit were analysed, and torque control was implemented. The results show that the AMRK is promising for the proposed applications, which require multiple functions with compact size, low weight, low energy consumption, high active and braking torque, and quick response time.

Robot-Assisted Therapy (RT) is an innovative approach to neurological rehabilitation that uses intensive, repetitive, interactive, and individualized practice. This systematic review aimed to investigate the effectiveness of RT on the body function and structure of people with upper limb impairments (PROSPERO registration: CRD42017054982). A search strategy conducted on seven databases identified randomized controlled studies. Methodological quality was assessed using the PEDro scale. When possible, the data were pooled, the strength of evidence was assessed using the GRADE system, and the effect sizes were assessed using Cohen coefficient. Subgroup analyses investigated the impact on the estimated effects of the following parameters: methodological quality; portion of the assessed upper limb; duration of stroke; and intervention dose and duration. Thirty-eight studies involving 1174 participants were included. Pooled estimates revealed small effects of RT on motor control and medium effects on strength compared with other intervention (OI) at a short-term follow-up. Standardized differences in means were as follows: 0.3 (95% CI 0.1 to 0.4) and 0.5 (95% CI 0.2 to 0.8). Effects at other time points and on other investigated outcomes related to body function and structure were not found (p>0.05). The strength of the current evidence was usually low quality. Subgroup analyses suggested that the methodological quality, and duration and dose of RT may influence the estimated effects. In conclusion, RT has small effects on motor control and medium effects on strength in people with limited upper limb function. Poor methodological quality, and lower treatment dose and duration may impact negatively the estimated effects.

This study analyses the energy consumption of an active magnetorheological knee (AMRK) actuator that was designed for transfemoral prostheses. The system was developed as an operational motor unit (MU), which consists of an EC motor, a harmonic drive and a magnetorheological (MR) clutch, that operates in parallel with an MR brake. The dynamic models of the MR brake and MU were used to simulate the system’s energetic expenditure during over-ground walking under three different working conditions: using the complete AMRK; using just its motor-reducer, to operate as a common active knee prosthesis (CAKP), and using just the MR brake, to operate as a common semi-active knee prosthesis (CSAKP). The results are used to compare the MR devices power consumptions with that of the motor-reducer. As previously hypothesized, to use the MR brake in the swing phase is more energetically efficient than using the motor-reducer to drive the joint. Even if using the motor-reducer in regenerative braking mode during the stance phase, the differences in power consumption among the systems are remarkable. The AMRK expended 16.3 J during a gait cycle, which was 1.6 times less than the energy expenditure of the CAKP (26.6 J), whereas the CSAKP required just 6.0 J.

Degenerative diseases and injuries that compromise hand movement reduce individual autonomy and tend to cause financial and psychological problems to their family nucleus. To mitigate these limitations, over the past decade, hand exoskeletons have been designed to rehabilitate or enhance impaired hand movements. Although promising, these devices still have limitations, such as weight and cost. Moreover, the movements performed are not kinematically compatible with the joints, thereby reducing the achievements of the rehabilitation process. This article presents the biomimetic design of a soft hand exoskeleton actuated using artificial tendons designed to achieve low weight, volume, and cost, and to improve kinematic compatibility with the joints, comfort, and the sensitivity of the hand by allowing direct contact between the hand palm and objects. We employed two twisted string actuators and Bowden cables to move the artificial tendons and perform the grasping and opening of the hand. With this configuration, the heavy part of the system was reallocated to a test bench, allowing for a lightweight set of just 232 g attached to the arm. The system was triggered by the myoelectric signals of the biceps captured from the user’s skin to encourage the active participation of the user in the process. The device was evaluated by five healthy subjects who were asked to simulate a paralyzed hand, and manipulate different types of objects and perform grip strength. The results showed that the system was able to identify the intention of movement of the user with an accuracy of 90%, and the orthosis was able to enhance the ability of handling objects with gripping force up to 1.86 kgf.

Lower limb exoskeletons (LLE) have been successfully used in robotic-assisted rehabilitation to reduce the burden of locomotor impairment of disabled people. However, the design limitations of LLE mechanisms, such as the lack of kinematic compatibility relative to the user’s joints and the use of high stiff or heavy actuators, limit the outcomes of treatment and increase the risk of injury. To address these shortcomings, in this work we present the design of the MRKneeExo, a highly backdrivable and kinematically compatible active knee exoskeleton. The powertrain of the system is composed of a BLDC 70 W motor associated with a harmonic drive gearbox and a customized magneto-rheological (MR) clutch. To improve kinematic compatibility with the user’s knee, a crossed four-bar linkage mechanism (FBLM) was optimally designed to follow the trajectory of the instant center of rotation (ICR) of the knee projected in the parasagittal plane where the joint is placed. The MR clutch is used to decouple the motor-reducer from the FBLM, thus enabling high backdrivability. The results showed a small error (<3 mm) between the FBLM and the knee ICR. Furthermore, the MR clutch allowed for low back-drive torque (1.28 N m) compared to the torque to back-drive the motor-reducer (18.51 N m). This paper is presented in a framework that can be generalized to support the design of other knee exoskeletons.