Soft exosuits stand out when it comes to the development of walking-assistance devices thanks to both their higher degree of wearability, lower weight, and price compared to the bulkier equivalent rigid exoskeletons. In cable-driven exosuits, the acting force is driven by cables from the actuation system to the anchor points; thus, the user’s movement is not restricted by a rigid structure. In this paper, a 3D inverse dynamics model is proposed and integrated with a model for a cable-driven actuation to predict the required motor torque and traction force in cables for a walking-assistance exosuit during gait. Joint torques are to be shared between the user and the exosuit for different design configurations, focusing on both hip and ankle assistance. The model is expected to guide the design of the exosuit regarding aspects such as the location of the anchor points, the cable system design, and the actuation units. An inverse dynamics analysis is performed using gait kinematic data from a public dataset to predict the cable forces and position of the exosuit during gait. The obtained joint reactions and cable forces are compared with those in the literature, and prove the model to be accurate and ready to be implemented in an exosuit control scheme. The results obtained in this study are similar to those found in the literature regarding the walking study itself as well as the forces under which cables operate during gait and the cable position cycle.

Exoskeletons can improve human mobility, but discomfort remains a significant barrier to their widespread adoption. This paper presents a comfort-centered mechatronics design of portable hip exoskeletons, comprising of three factors: (i) actuation, (ii) wearable interface, (iii) and assistive controller. We introduced an analytical multibody model to predict the human-exoskeleton contact forces during gait. Informed by this model, we designed a wearable interface that significantly improved the three considered objective metrics: (i) undesired contact forces at the wearable interface, (ii) wobbling, and (iii) metabolic reduction, and also the post-test evaluation via a System Usability Scale questionnaire as a subjective metric. Our experiments with two exoskeleton controllers (gait-based and reinforcement learning-based) demonstrated that the design of the wearable physical interface has a greater impact on reducing metabolic rate and minimizing wobbling than the choice of controller. Our actuation design method leads to highly backdrivable, lightweight quasi-direct drive actuators with high torque tracking performance. By leveraging this wearable design, we achieved up to 60% reduction in undesired contact forces, and a 74% reduction in exoskeleton wobbling in the frontal axis compared to a traditional configuration. Additionally, the net metabolic cost reduction was 18% compared to the no exoskeleton condition.

A novel, synergy-based design for lower-limb, gait assistance exosuits is proposed in this paper. The general design philosophy is followed by the mathematical model that leads to the exosuit’s actuation system design from a certain set of postural synergies, which may reduce the number of total required actuators and, thus, the overall system weight and price. Cable extensions are chosen as the design variable upon which the principal component analysis is performed, given the high resulting cumulative variance that is obtained with few principal components. Expressions for the pulley radii are then derived and a general exosuit design is proposed, along with a novel transmission system that can combine any number of actuators to follow the gait movements from a synergy perspective. A basic testbench is also presented with such a transmission system implemented and an empirical set of results are shown with a varying number of actuators, proving that cable extensions and synergy-based design provide an excellent solution when reducing the number of actuation units in a walking-assistance exosuit.

Older adults (aged 55 years and above) have greater difficulty carrying out activities of daily living than younger adults (aged 25–55 years). Although age-related changes in human gait kinetics are well documented in qualitative terms in the scientific literature, these differences may be quantified and analyzed using the analysis of motor control strategies through kinetic synergies. The gaits of two groups of people (older and younger adults), each with ten members, were analyzed on a treadmill at a constant controlled speed and their gait kinetics were recorded. The decomposition of the kinetics into synergies was applied to the joint torques at the hip, knee, and ankle joints. Principal components determined the similarity of the kinetic torques in the three joints analyzed and the effect of the walking speed on the coordination pattern. A total of three principal components were required to describe enough information with minimal loss. The results suggest that the older group showed a change in coordination strategy compared to that of the younger group. The main changes were related to the ankle and hip torques, both showing significant differences (p-value $<0.05$) between the two groups. The findings suggest that the differences between the gait patterns of the two groups were closely related to a reduction in ankle torque and an increase in hip torque. This change in gait pattern may affect the rehabilitation strategy used when designing general-purpose rehabilitation devices or rehabilitation/training programs for the elderly.