Individuals with chronic hemiparesis post-stroke exhibit gait impairments that require functional rehabilitation through training. Exoskeletal robotic assistive devices can provide a user with continuous assistance but impose movement restrictions. There are currently devices that allow unrestricted movement but provide assistance only intermittently at specific points of the gait cycle. Our design, a cable-driven active leg exoskeleton (C-ALEX), allows the user both unrestricted movement and continuous force assistance throughout the gait cycle to assist the user in new walking patterns. In this study, we assessed the ability of C-ALEX to induce a change in the walking patterns of ten post-stroke participants using a singlesession training protocol. The ability of C-ALEX to accurately provide forces and torques in the desired directions was also evaluated to compare its design performance to traditional rigidlink designs. Participants were able to reach 91% ± 12% of their target step length and 89% ± 13 % of their target step height. The achieved step parameters differed significantly from participant baselines (p < 0.05). To quantify the performance, the forces in each cable’s out of the plane movements were evaluated relative to the in-plane desired cable tension magnitudes. This corresponded to an error of under 2Nm in the desired controlled joint torques. This error magnitude is low compared to the system command torques and typical adult biological torques during walking (2-4%) [1]. These results point to the utility of using non-restrictive cable-driven architectures in gait retraining, in which future focus can be on rehabilitating gait pathologies seen in stroke survivors.

Adaptive cable-driven parallel robots are a special subclass of cable-driven systems in which the locations of the pulley blocks are modified as a function of the end-effector pose to obtain optimal values of given performance indices within a target workspace. Due to their augmented kinematic redundancy, such systems enable larger workspace volume and higher performance compared to traditional designs featuring the same number of cables. Previous studies have introduced a systematic method to optimize design and trajectory planning of the moving pulley-blocks for a given performance index. In this paper, we study the motions of the pulley blocks that optimize two performance indices simultaneously: stiffness and dexterity. Specifically, we present a method to determine the pulley blocks motions that guarantee ideal dexterity with the best feasible elastic stiffness, as well as those that guarantee isotropic elastic stiffness with the best feasible dexterity. We demonstrate the proposed approach on some practical cases of planar adaptive cable-driven parallel robots.

Robotic training of children with crouch gait improved posture and walking by enhancing muscle strength and coordination.

Exoskeletons for gait training commonly use a rigid-linked “skeleton” which makes them heavy and bulky. Cable-driven exoskeletons eliminate the rigid-linked skeleton, providing a lighter and transparent design. Current cable-driven exoskeletons are aimed only at gait assistance by provide short bursts of forces to the leg during walking. It has not yet been shown if these designs are suitable for gait retraining where rehabilitative forces need to be continuously applied to the leg in response to errors from a desired movement. The goal of this study is to investigate if a cable-driven leg exoskeleton can retrain the gait of human users. Nine healthy subjects were trained by a cable-driven leg exoskeleton to walk in a new gait pattern with 30% increase in step height from their natural gait. After 40 minutes of training, the gait of the subjects became significantly closer to the target gait than before the training. In three different post-training sessions, the step height of the subjects increased by 22%, 29% and 31% on an average. In a fourth post-training session when the subjects were instructed to ignore the training and walk naturally, the step height remained increased by 11%. These results confirm the potential of cable-driven designs in gait training applications.

Head drop is a symptom commonly seen in patients with Amyotrophic Lateral Sclerosis (ALS). These patients usually experience neck pain and have difficulty in swallowing and breathing. Static neck braces are used in current treatment. These braces, however, immobilize the head in a single configuration which causes muscle atrophy. This paper presents the design of a dynamic neck brace for the first time in the literature, which can both measure and potentially assist in the head motion of the human user. This paper introduces the brace design method and validates its capability to perform measurements. The brace is designed based on kinematics data collected from a healthy individual via a motion capture system. A pilot study was conducted to evaluate the wearability of the brace and the accuracy of measurements with the brace. This study recruited ten participants who performed a series of head motions. The results of this human study indicate (i) the brace is wearable by individuals who vary in size, (ii) the brace allows nearly 70% of the overall range of head rotations, (iii) the sensors on the brace give accurate motion of the head with an error of under 5 $^{\circ}$ when compared to a motion capture system. We believe that this neck brace can be a valid and accurate measurement tool for human head motion. This brace will be a big improvement in the available technologies to measure head motion as these are currently done in the clinic using hand held protractors in two orthogonal planes.