Background. High-intensity repetitive training is challenging to provide poststroke. Robotic approaches can facilitate such training by unweighting the limb and/or by improving trajectory control, but the extent to which these types of assistance are necessary is not known. Objective. The purpose of this study was to examine the extent to which robotic path assistance and/or weight support facilitate repetitive 3D movements in high functioning and low functioning subjects with poststroke arm motor impairment relative to healthy controls. Methods. Seven healthy controls and 18 subjects with chronic poststroke right-sided hemiparesis performed 300 repetitions of a 3D circle-drawing task using a 3D Cable-driven Arm Exoskeleton (CAREX) robot. Subjects performed 100 repetitions each with path assistance alone, weight support alone, and path assistance plus weight support in a random order over a single session. Kinematic data from the task were used to compute the normalized error and speed as well as the speed-error relationship. Results. Low functioning stroke subjects (Fugl-Meyer Scale score = 16.6 ± 6.5) showed the lowest error with path assistance plus weight support, whereas high functioning stroke subjects (Fugl-Meyer Scale score = 59.6 ± 6.8) moved faster with path assistance alone. When both speed and error were considered together, low functioning subjects significantly reduced their error and increased their speed but showed no difference across the robotic conditions. Conclusions. Robotic assistance can facilitate repetitive task performance in individuals with severe arm motor impairment, but path assistance provides little advantage over weight support alone. Future studies focusing on antigravity arm movement control are warranted poststroke.

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 single-session 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 rigid-link 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 ( ). 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%). 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.

Robotic rehabilitation devices have gained significant popularity in the past decade. Over-ground leg exoskeletons commonly use traditional rigid link architectures or support the weight of a user by strapping the user in a harness. This results in bulky and large architectures which are cumbersome and restrictive. C-ALEX is a leg exoskeleton without a rigid link structure which has been used in gait training on a treadmill. In this paper, we explore the feasibility of using the C-ALEX exoskeleton over-ground. We converted C-ALEX into a carted system for over-ground use. We tested the architecture on eight healthy subjects to compare the controller's RMS joint torque errors, the effects on step height, joint angles and the deviation of ankle trajectories from target trajectories. The results show that C-ALEX's controller and tension planner have comparable RMS torque errors with no significant difference between the two use cases. C-ALEX is able to increase the step height, affect knee flexion in both walking conditions with no significant difference. There is significant difference between C-ALEX's ability to control hip flexion angles and deviation area over-ground and on a treadmill.

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 providing 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 min 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.

Various leg exoskeletons have been designed for gait rehabilitation. The transparency of these exoskeletons is crucial to their effectiveness in gait training. The weight and inertia of an exoskeleton are two important factors affecting its transparency. In this study, using a light-weight leg exoskeleton C-ALEX, we conducted a series of experiments to explore the effect of exoskeleton weight and inertia on the natural walking of twelve healthy subjects. They walked in C-ALEX under three levels of mass added to the leg: (i) no added mass, (ii) 1.8 kg, and (iii) 3.6 kg, and three different setups of C-ALEX: (i) freewalking without C-ALEX, (ii) with C-ALEX, and (iii) with C-ALEX compensating for the weight of the added mass. The result shows that increasing exoskeleton mass increases step length, decreases step height, and reduces maximum knee flexion. After weight compensation, the step height, and the maximum knee flexion partially restored, but the step length did not, implying that the inertia is responsible for the change in step length. The study demonstrates that compensating for weight alone cannot eliminate the changes due to exoskeleton mass. On the other hand, reducing the overall mass of the exoskeleton can better preserve the natural gait of the subjects.

The training for both translation and rotation of the hand is desirable for patients with impairments. This paper focuses on the design and control of a 7-degree-of-freedom cable-driven arm exoskeleton (CAREX-7), used for dexterous motion (including translation and rotation) training or assistance of the whole-arm. The CAREX-7 includes an additional wrist module compared with CAREX, and eight cables are routed through the exoskeleton cuffs to drive the whole-arm motion. Based on the “assist-as-needed” paradigm, a novel wrench-field controller was designed to regulate a needed wrench (force and torque) on the hand for assisting its dexterous manipulation. Healthy subjects participated in path-tracking experiments while wearing CAREX-7. The experimental results show that the CAREX-7 with the new wrench-field controller can help the subjects to follow the path more closely, and this demonstrates the effectiveness of the device. The current design of CAREX-7 is unique and offers significant improvements and new functionality over the existing CAREX. The novel features are the following: 1) CAREX-7 is an exoskeleton for the full human arm, including shoulder, elbow, and the wrist, with new design issues; and 2) controller of CAREX-7 builds on a screw-theoretic approach and assists both translation and rotation of the hand, allowing for dexterous hand reorientation, which is required in everyday tasks.

The design of cable-driven manipulators is complicated by the unidirectional nature of the cables, which results in extra actuators and limited workspaces. Furthermore, the particular arrangement of the cables and the geometry of the robot pose have a significant effect on the cable tension required to effect a desired joint torque. For a sufficiently complex robot, the identification of a satisfactory cable architecture can be difficult and can result in multiply redundant actuators and performance limitations based on workspace size and cable tensions. This work leverages previous research into the workspace analysis of cable systems combined with stochastic optimization to develop a generalized methodology for designing optimized cable routings for a given robot and desired task. A cable-driven robot leg performing a walking-gait motion is used as a motivating example to illustrate the methodology application. The components of the methodology are described, and the process is applied to the example problem. An optimal cable routing is identified, which provides the necessary controllable workspace to perform the desired task and enables the robot to perform that task with minimal cable tensions. A robot leg is constructed according to this routing and used to validate the theoretical model and to demonstrate the effectiveness of the resulting cable architecture.

Designing an effective cable architecture for a cable-driven robot becomes challenging as the number of cables and degrees of freedom of the robot increase. A methodology has been previously developed to identify the optimal design of a cable-driven robot for a given task using stochastic optimization. This approach is effective in providing an optimal solution for robots with high-dimension design spaces, but does not provide insights into the robustness of the optimal solution to errors in the configuration parameters that arise in the implementation of a design. In this work, a methodology is developed to analyze the robustness of the performance of an optimal design to changes in the configuration parameters. This robustness analysis can be used to inform the implementation of the optimal design into a robot while taking into account the precision and tolerances of the implementation. An optimized cable-driven robot leg is used as a motivating example to illustrate the application of the configuration robustness analysis. Following the methodology, the effect on robot performance due to design variations is analyzed, and a modified design is developed which minimizes the potential performance degradations due to implementation errors in the design parameters. A robot leg is constructed and is used to validate the robustness analysis by demonstrating the predicted effects of variations in the design parameters on the performance of the robot.

This study presents the development of second spine, an upper body assistive device for human load carriage. The motivation comes from reducing musculoskeletal injuries caused by carrying a heavy load on the upper body. Our aim was to design a wearable upper body device that can prevent musculoskeletal injuries during human load carriage by providing a secondary load pathway—second spine—to transfer the loads from shoulders to pelvis while also allowing a good range of torso motion to the wearer. Static analysis of the backpack and the second spine was first performed to investigate the feasibility of our concept design. The development of second spine had two considerations: load distribution between shoulders and pelvis, and preserving the range of torso motion. The design was realized using load bearing columns between the shoulder support and hip belt, comprising multiple segments interconnected by cone-shaped joints. The performance of second spine was evaluated through experimental study, and its biomechanical effects on human loaded walking were also assessed. Based on the findings from second spine evaluation, we proposed the design of a motorized second spine which aims to compensate the inertia force of a backpack induced by human walking through active load modulation. This was achieved by real-time sensing of human motion and actuating the motors in a way that the backpack motion is kept nearly inertially fixed. Simulation study was carried out to determine the proper actuation of motors in response to the human walking kinematics. The performance of motorized second spine was evaluated through an instrumented test-bed using Instron machine. Results showed a good agreement with simulation. It was shown that the backpack motion can be made nearly stationary with respect to the ground which can further enhance the effectiveness of the device in assisting human load carriage.

Laparoscopic surgery is a challenging task for surgeons. The challenges include: (i) lack of depth perception, (ii) inverted motion of the hand instrument. In this paper, we investigate the possibility of using CAREX-M, a Cable-driven Arm Exoskeleton - Mobile, to train subjects using laparoscopic tool to do a simple task. CAREX-M uses an assist-as-needed controller that generates assistive force that helps the subjects to move the laparoscopic tool along a prescribed trajectory. An experiment was conducted which trains the subjects to use the laparascopic tool to follow a straight path. Two groups of subjects (experiment and control) participated in the experiment. The experiment group received assistance from CAREX-M during the training, while the control group did not receive any assistance. The results show that the experiment group gained significantly larger performance improvement from training than the control group. This shows that CAREX-M is effective in training of laparascopic tool manipulation. A further analysis shows that the improvement in the performance comes from the reduced error along the depth direction. This suggests that CAREX-M can improve the depth perception of the subjects.

Robotic rehabilitation devices are attractive to physical therapists. Various leg exoskeletons have been developed during the past decade and have been used in gait training. Traditional exoskeletons usually have a complex structure and add extra inertia to the wearer's leg, which may change their natural gait. In this paper, we present the design of a cable-driven active leg exoskeleton (C-ALEX) for human gait training. The advantages of cable-driven designs are that they have a simpler structure, add minimal inertia to the human limbs, and do not require precise joint alignment. C-ALEX employs the "assist-as-needed" control strategy to help the ankle center move along a prescribed path. An experiment with 6 healthy subjects was conducted who walked with C-ALEX on a treadmill. The results showed that C-ALEX is capable of helping the subjects better track a prescribed ankle path.

Exoskeletons have been used successfully for functional training of human motions. Our designs of the Cable-driven Arm Exoskeleton (CAREX) are targeted to improve arm function in patients with stroke. In this study, we focus on how muscle activation patterns of subjects change during movements with and without CAREX. Our goal was to evaluate whether CAREX distorts the natural pattern of EMG activity in healthy human subjects during arm movements. Eight healthy subjects performed point-to-point reaching tasks under two conditions: (a) with or without CAREX, and (b) with or without a 5 lb weight attached to their wrist. The EMG signals of 10 muscles were recorded and processed. The results showed that (i) EMG pattern of the subjects while wearing CAREX and while not wearing CAREX showed a high correlation, suggesting little alteration to normal EMG patterns while wearing CAREX; (ii) The subjects showed significantly lower muscle activation when they wore CAREX; (iii) The high correlation and the lower activation were observed in both the no weight condition and the 5 lb weight condition. Overall, the results suggest that CAREX can help subjects reduce the magnitude of muscle activation while preserving normal muscle activation patterns.

In recent years, the authors have proposed lightweight exoskeleton designs for upper arm rehabilitation using multi-stage cable-driven parallel mechanism. Previously, the authors have demonstrated via experiments that it is possible to apply “assist-as-needed” forces in all directions at the end-effector with such an exoskeleton acting on an anthropomorphic machine arm. A human-exoskeleton interface was also presented to show the feasibility of CAREX on human subjects. The goals of this paper are to 1) further address issues when CAREX is mounted on human subjects, e.g., generation of continuous cable tension trajectories 2) demonstrate the feasibility and effectiveness of CAREX on movement training of healthy human subjects and a stroke patient. In this research, CAREX is rigidly attached to an arm orthosis worn by human subjects. The cable routing points are optimized to achieve a relatively large “tensioned” static workspace. A new cable tension planner based on quadratic programming is used to generate continuous cable tension trajectory for smooth motion. Experiments were carried out on eight healthy subjects. The experimental results show that CAREX can help the subjects move closer to a prescribed circular path using the force fields generated by the exoskeleton. The subjects also adapt to the path shortly after training. CAREX was also evaluated on a stroke patient to test the feasibility of its use on patients with neural impairment. The results show that the patient was able to move closer to a prescribed straight line path with the “assist-as-needed” force field.

The Second Spine is a vest intended to prevent musculoskeletal injuries caused by heavy backpack loads, while also maintaining the range of motion of the wearer. The vest is formed by multiple segments between the shoulder and a pelvic belt. In normal “off” configuration, the segments are disconnected from each other and the vest is flexible providing full range of motion to the upper body. With the pull of a string in the “on” configuration, the vest becomes semi-rigid creating a secondary pathway to transfer loads between the shoulder and a pelvic belt. The device was evaluated by a subject who walked on a treadmill while carrying a backpack load of 25% of his body weight (BW). Experiment results showed that the semi-rigid vest reduces the force exerted on the shoulders and induces a more erect posture. Muscle activations in the lower limbs indicate that loads were successfully transferred from the shoulders to the waist while bypassing the vertebral column. These results show that the device can be used to mitigate potential risks of musculoskeletal injuries caused from backpack loads.

An active Tethered Pelvic Assist Device (A-TPAD) has been presented in this paper. TPAD is a cable robot for studying force adaptation in human walking by applying external forces and moments on the human pelvis. A two stage control strategy was implemented to apply the desired force-moment profile. The controller includes (i) a quadratic programming based optimization scheme, (ii) a real-time human motion monitoring system and (iii) a PID feedback loop to plan and implement the required cable tensions. The control strategy was validated first by testing it on a dummy pelvis setup. A pilot experiment was then conducted with a human walking on a treadmill with A-TPAD. The goal was to apply a vertical downward force vector equivalent to 10% of subject's body weight (BW) at the pelvis. Results showed that the applied vertical force was acting downwards over the full gait cycle and was between 8-13% of the BW. Other force-moment components were maintained within a specified range during the experiment. Increased foot pressure was reported in the presence of vertical force. In summary, A-TPAD provides the capability of applying and controlling a desired force-moment profile on the human pelvis over a gait cycle.

This study focuses on how the inertia force of a backpack induced by human walking can be compensated by active load modulation through a Second Spine, a device that provides an alternate pathway to transfer loads from the shoulder to the pelvis. Human walking induces periodic vertical acceleration of the upper body. A backpack worn on the upper body undergoes this same acceleration. Inertia force is induced. by this acceleration and the human body has to sustain this motion and provide necessary energy.Based on this knowledge and our previous studies on a passive Second Spine, we present studies on a motorized Second Spine that can actively modulate the vertical motion of a backpack such that the inertia forces can be reduced. This is realized by real-time sensing and actuation so that the backpack is kept inertially fixed. The performance of such a device was evaluated on an instrumented test-bed using an Instron machine, showing results in good agreement with simulation. It was shown that the backpack motion can be made nearly stationary with respect to the ground by active modulation using motors and the inertia force is reduced.

The target of this work is to experimentally validate the Second Spine, a wearable device recently developed by our group to transfer forces from shoulder to pelvis during loaded walking. A key-feature of the Second Spine compared to traditional framed backpacks is the adjustable stiffness of its structure, which allows the wearer to change the load-bearing behavior of the device. In line with previous studies on loaded walking, we investigate biomechanical and physiological variables on a small group of young healthy subjects, as they walked on a treadmill under 3 different conditions: free walking, walking with a backpack of 25% of subject's Body Weight (BW), and walking with the same backpack while wearing the device. Results indicate that wearing the Second Spine significantly reduces the pressure on shoulders and induces smaller deviations from unloaded walking in terms of gait timing and stride length. The activations of the rectus femoris and the gastrocnemius muscles, along with the kinematics of the knee joint, provide indirect evidence that dynamic loads were rigidly transmitted from the shoulder to the waist. We discuss how these preliminary findings might be relevant for the prevention of injuries related to load carriage, and how they set important guidelines for the next generation of the Second Spine.

Serial multi-body systems can be driven by cables routed through the links to achieve the desired range of motion. Placement and routing of the cables alter the performance characteristics of the manipulator There are possible applications for such mechanisms where low moving inertia is required One of the challenges in the design of cable-driven mechanisms is to keep cables in tension during the motion. In this article, the addition of springs and its impact on workspace is investigated. A 2-link cable-driven robot is used to illustrate changes in Wrench Feasible Workspace (WFW) as springs are added between the serial manipulator and the ground or between the. links.

In the past few years, the authors have proposed several prototypes of a Cable-driven upper ARm EXoskeleton (CAREX) for arm rehabilitation. One of the assumptions of CAREX was that the glenohumeral joint rotation center (GH-c) remains stationary in the inertial frame during motion, which leads to inaccuracy in the kinematic model and may hamper training performance. In this paper, we propose a novel approach to estimate GH-c using measurements of shoulder joint angles and cable lengths. This helps in locating the GH-c center appropriately within the kinematic model. As a result, more accurate kinematic model can be used to improve the training of human users. An estimation algorithm is presented to compute the GH-c in real-time. The algorithm was implemented on the latest prototype of CAREX. Simulations and preliminary experimental results are presented to validate the proposed GH-c estimation method.

Coordination of the grip force (GF) with a tangential force (TF, often referred to as load force) exerted along a certain line in space (i.e., one-dimensional tasks) during object manipulation has proved both to be high and based on feed-forward neural control mechanisms. However, GF–TF coordination deteriorates when the TF of one-dimensional task consecutively switches its direction (bidirectional task). In the present study, we aimed to explore GF–TF coordination in the generally neglected multi-dimensional manipulations. We hypothesized that the coordination would depend on the number of unidirectional and bidirectional orthogonal components of a two-dimensional TF exertion. Fourteen subjects traced various circular TF patterns and their orthogonal diameters shown on a computer screen by exerting a static TF. As expected, the unidirectional tasks revealed higher GF–TF coordination than the bidirectional ones (e.g., higher GF–TF correlations and GF gains, and lower GF/TF ratio). Regarding the circular tasks, most of the data were in line with the hypothesis revealing higher coordination associated with higher number of unidirectional components. Of particular importance could be that the circular tasks also revealed prominent time lags of GF with respect to TF, suggesting involvement of feedback mechanisms. We conclude that the force coordination in bidirectional static manipulations could be affected by changes in TF direction along either of its orthogonal components. The time lags observed from the circular tasks could be a consequence of the activity of sensory afferents, rather than of the visual feedback provided or the task complexity.