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Gait disorders are major problems among patients with cerebellar ataxia (CA) and Parkinson’s disease (PD). Little is known on how damages to the cerebellum or the basal ganglia affect the recovery responses to external gait perturbations. Six patients with CA, six patients with PD and six healthy controls (HC) were exposed to 9 blocks of 8 antero-posterior (AP) and medio-lateral (ML) perturbations. AP and ML Base of support (BoS) were compared between groups at perturbation onset and the following five heel strikes. HCs showed longer AP BoS than the CA and PD groups. Patients with CA showed a wider ML BoS than the HC and PD groups. Patients with PD were unable to take longer or larger steps when necessary (i.e., in reaction to anterior and medial perturbations). These findings could help to design specific perturbation-based training in patients with different degenerative neurological diseases.

This paper presents an upper-body motion mode recognition method based on inertial measurement units (IMUs) using cascaded classification approaches and integrated machine learning algorithms. The proposed method is designed to be applied on a dynamic spine brace in the future to assess its usability. This study focuses on the problem of classifying upper-body motion modes by using four IMUs worn on the upper-body of the subjects. Six locomotion modes and ten locomotion transitions were investigated. A quadratic discriminant analysis (QDA) classifier and a support vector machine (SVM) classifier were deployed in our study. With selected cascade classification strategies, the system is demonstrated to achieve a satisfactory performance with an average of 96.77%(QDA) and 97.64%(SVM) recognition accuracy. The obtained results prove the effectiveness of the proposed method.

Recording 3D ground reaction forces through instrumented crutches can assist patients undergoing ambulatory rehabilitation as well as help roboticists develop new assistive controllers for their exoskeletons. Current methods to measure the amount of weight a patient exerts on their limbs are either inaccurate, or not feasible outside of ideal laboratory conditions. This paper introduces Smart Crutches, an instrumented crutch system capable of measuring the weight that a patient places on his/her lower extremities and providing vibratory feedback in response to the measured weight. The device was calibrated using a motion capture system and force plates. Linear regression and support vector regression (SVR) were used for calibration, and 10-fold cross-validation was applied to estimate the system's accuracy. Results indicate that machine learning regression methods may lead to improved accuracy, but the choice of the kernel function is critical. Gaussian kernel yielded root-mean-square errors (RSME) of 2.5N or less relative to force plates, while other kernel functions produced more inconsistent and less accurate results. Instrumented crutches may be a valid alternative to force plates for estimating ground reaction forces in crutch gait.

Ahstract- 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.

This paper presents a method of stride identification, extraction, and analysis of data sets of time-series contact force data for ambulating subjects both with and without Parkinson's disease (PD). This method has been made robust with the use of seeded K-Means clustering, fast Fourier transformation (FFT) spectral analysis, and minimum window size rejection. These methods combine to produce well selected strides of active walking data. We are able to calculate quality of walking measures of stride duration, stance duration (as percent of gait cycle - %GC), swing duration (%GC), time to maximum heel force (%GC), time to maximum toe force (%GC), time spent in heel contact (%GC), and time spent in toe contact (%GC).

A novel robot-aided assist-as-needed gait training paradigm has been developed recently. This paradigm encourages subjects’ active participation during training. Previous pilot studies demonstrated that assist-as-needed robot-aided gait training (RAGT) improves treadmill walking performance post-stroke. However, it is not known if there is an over-ground transfer of the training effects from RAGT on treadmill or long-term retention of the effects. The purpose of the current study was to examine the effects of assist-as-needed RAGT on over-ground walking pattern post-stroke. Nine stroke subjects received RAGT with visual feedback of each subject’s instantaneous ankle malleolus position relative to a target template for fifteen 40-minute sessions. Clinical evaluations and gait analyses were performed before, immediately after and 6 months post-training. Stroke subjects demonstrated significant improvements and some long-term retention of the improvements in their self-selected over-ground walking speed, Dynamic Gait Index, Timed Up and Go, peak knee flexion angle during swing phase and total hip joint excursion over the whole gait cycle for their affected leg (p

Due to the complexity of the human musculoskeletal system and intra/intersubjects variability, powered exoskeletons are prone to human–robot misalignments. These induce undesired interaction forces that may jeopardize safe operation. Uncompensated inertia of the robotic links also generates spurious interaction forces. Current design approaches to compensate for misalignments rely on the use of auxiliary passive degrees of freedom that unavoidably increase robot inertia, which potentially affects their effectiveness in reducing undesired interaction forces. Assessing the relative impact of misalignment and robot inertia on the wearer can, therefore, provide useful insights on how to improve the effectiveness of such approaches, especially in those situations where the dynamics of the movement are quasi-periodic and, therefore, predictable such as in gait. In this paper, we studied the effects of knee joint misalignments on the wearer's gait, by using a treadmill-based exoskeleton developed by our group, the ALEX II. Knee joint misalignments were purposely introduced by adjusting the mismatch between the length of the robot thigh and that of the human thigh. The amount of robot inertia reflected to the user was adjusted through control. Results evidenced that knee misalignment significantly changes human–robot interaction forces, especially at the thigh interface, and this effect can be attenuated by actively compensating for robot inertia. Misalignments caused by an excessively long robot thigh are less critical than misalignments of equal magnitude deriving from an excessively short robot thigh.

Cable-driven parallel robots (CDPRs) possess a number of promising advantages over conventional rigid-link robots, such as light weight, large payload handling capacity, considerably large workspace, and simpler dynamics. However, since cables can only pull but not push its attachment point on the end-effector, it is usually challenging for the wrench-feasible workspace (WFW) of CDPRs to meet the design requirements. Therefore, redundant cables or load on the end-effector is used to attain the required workspace. In this paper, springs are added between the end-effector and a base with the goal to modulate the workspace. The effects of different parameters of the spring on CDPR's wrenches are investigated and an optimization is proposed to determine the feasible spring parameters. Workspaces of two planar and spatial examples are presented. A reshaped workspace validation experiment was conducted. These results show that springs, with properly chosen parameters, can increase or reshape the WFW of CDPRs to meet the specified design requirements.

This paper proposes a novel method for analyzing linear series elastic actuators (SEAs) in a parallel-actuated Stewart platform, which has full six degrees-of-freedom (DOF) in position and orientation. SEAs can potentially provide a better human–machine interface for the user. However, in the study of parallel-actuated systems with full 6DOF, the effect of compliance in series with actuators has not been adequately studied from the perspective of wrench capabilities. We found that some parameters of the springs and the stroke lengths of the linear actuators play a major role in the actuation limits of the system. This is an important consideration when adding SEAs into a Stewart platform or other parallel-actuated robots to improve their human usage.

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.

This paper proposes a novel methodology for the design of series elastic actuators in parallel-actuated platforms which have full six degrees-of-freedom in position and orientation. Series elastic actuators can potentially contribute to lower power consumption and provide a better human-machine interface for the user. This is an important consideration in the use of a robotic spine exoskeleton for human subjects, which motivates this work. In the study of parallel-actuated systems with full six degrees-of-freedom, the effect of compliance in series with actuators has not been adequately studied from the perspective of kinematics and wrench capabilities. These analyses are performed in this paper with the goal to improve the design of the robotic spine exoskeleton (ROSE) and its human usage.

This paper presents a modular, computationally-distributed "multi-robot" cyberphysical system designed to assist children with developmental delays in learning to walk. The system consists of two modules, each assisting a different aspect of gait: a tethered cable pelvic module with up to 6 degrees of freedom (DOF), which can modulate the motion of the pelvis in three dimensions, and a two DOF wearable hip module assisting lower limb motion, specifically hip flexion. Both modules are designed to be lightweight and minimally restrictive to the user, and the modules can operate independently or in cooperation with each other, allowing flexible system configuration to provide highly customized and adaptable assistance. Motion tracking performance of approximately 2 mm root mean square (RMS) error for the pelvic module and less than 0.1 mm RMS error for the hip module was achieved. We demonstrate coordinated operation of the two modules on a mannequin test platform with articulated and instrumented lower limbs.

There currently exist no practical tools to identify functional movements in the upper extremities (UEs). This absence has limited the precise therapeutic dosing of patients recovering from stroke. In this proof-of-principle study, we aimed to develop an accurate approach for classifying UE functional movement primitives, which comprise functional movements. Data were generated from inertial measurement units (IMUs) placed on upper body segments of older healthy individuals and chronic stroke patients. Subjects performed activities commonly trained during rehabilitation after stroke. Data processing involved the use of a sliding window to obtain statistical descriptors, and resulting features were processed by a Hidden Markov Model (HMM). The likelihoods of the states, resulting from the HMM, were segmented by a second sliding window and their averages were calculated. The final predictions were mapped to human functional movement primitives using a Logistic Regression algorithm. Algorithm performance was assessed with a leave-one-out analysis, which determined its sensitivity, specificity, and positive and negative predictive values for all classified primitives. In healthy control and stroke participants, our approach identified functional movement primitives embedded in training activities with, on average, 80% precision. This approach may support functional movement dosing in stroke rehabilitation.

Many robotic devices in rehabilitation incorporate an assist-as-needed haptic guidance paradigm to promote training. This error reduction model, while beneficial for skill acquisition, could be detrimental for long-term retention. Error augmentation (EA) models have been explored as alternatives. A robotic Tethered Pelvic Assist Device has been developed to study force application to the pelvis on gait and was used here to induce weight shift onto the paretic (error reduction) or nonparetic (error augmentation) limb during treadmill training. The purpose of these case reports is to examine effects of training with these two paradigms to reduce load force asymmetry during gait in two individuals after stroke (>6 mos). Participants presented with baseline gait asymmetry, although independent community ambulators. Participants underwent 1-hr trainings for 3 days using either the error reduction or error augmentation model. Outcomes included the Borg rating of perceived exertion scale for treatment tolerance and measures of force and stance symmetry. Both participants tolerated training. Force symmetry (measured on treadmill) improved from pretraining to posttraining (36.58% and 14.64% gains), however, with limited transfer to overground gait measures (stance symmetry gains of 9.74% and 16.21%). Training with the Tethered Pelvic Assist Device device proved feasible to improve force symmetry on the treadmill irrespective of training model. Future work should consider methods to increase transfer to overground gait.

Normal aging is associated with decline in both physical and cognitive functions. This contributes to an increased risk for falls, one of the most common and serious problem in late life. Physical exercise can marginally improve balance, gait and cognitive functions. In order to specifically target the neuromuscular skills required for fall prevention, new training paradigms that strengthen the control of compensatory responses after balance perturbations are required. To date, it is unknown if these training paradigms are also able to improve the cognitive functioning.

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.

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.

Orthoses are devices used for rehabilitation of the patients having muscle weakness at their limbs. People with motor-incomplete motion can train their weak limbs using appropriate orthoses to improve their muscle activity and walking performance. In this paper, we propose a lower leg planar external passive orthosis to assist the patients with lower leg disabilities during swing phase of gait on treadmill. This orthosis attaches to the shank of the leg and its other end is connected to a walking frame. In this work, we optimize the physical and geometrical parameters of external orthosis together with the parameters of two torsional springs located at its joints or two linear springs connected to its links, to obtain a desired swing motion of the leg without existence of any actuators or making any effort by the user. Applying kinematic constraints of the closed-loop system consisting of the human leg and the external orthosis in addition to dynamic equations of motion, optimization process is accomplished using Genetic Algorithm approach through computer simulation. The simulation results show that the actual trajectories of hip and knee joint angles of the leg are very close to the desired ones during swing phase of gait on treadmill.

In this paper, we study the human locomotor adaptation to the action of a powered exoskeleton providing assistive torque at the user's hip during walking. To this end, we propose a controller that provides the user's hip with a fraction of the nominal torque profile, adapted to the specific gait features of the user from Winter's reference data . The assistive controller has been implemented on the ALEX II exoskeleton and tested on ten healthy subjects. Experimental results show that when assisted by the exoskeleton, users can reduce the muscle effort compared to free walking. Despite providing assistance only to the hip joint, both hip and ankle muscles significantly reduced their activation, indicating a clear tradeoff between hip and ankle strategy to propel walking.

Previous work has shown that training with the "assist-as-needed" method using a force-feedback joystick can improve the driving performance of children and adults. This paper is the first study to evaluate training with a repelling force versus an assisting force for learning of a line following task in a wheelchair through a force-feedback joystick. We designed a robotic training wheelchair, that can accurately localize itself in the training environment, and implemented assisting and repelling force fields on the force-feedback joystick. The training protocol included three groups. The control (CT) group received no force feedback. The assisting force (AF) group was trained using the "assist-as-needed" paradigm. The repelling force (RF) group was trained with the repelling force field. We observed that both the AF and RF groups improved their driving skills. The error reductions of both groups were not statistically different under the current setting. We believe that this pilot study could provide a promising foundation regarding the effects of a robotic wheelchair training algorithm on motor learning.

With increasing populations of the elderly in our society, robot technology will play an important role in providing functional mobility to humans. From the perspective of human safety, it is desirable that controllers for walk-assist robots be dissipative, i.e., the energy is supplied from the human to the walker, while the controller modulates this energy. The simplest form of a dissipating controller is a brake, where resistive torques are applied to the wheels proportional to their speeds. The fundamental question that we ask in this brief is how to modulate these proportional gains over time for the two wheels so that the walker can perform point-to-point motions. The unique contribution of this brief is a novel way in which the theory of differential flatness is used to plan the trajectory of these braking gains. Since the user input forces are not known a priori , the trajectory of the braking gain is computed iteratively during the motion. Simulation and experimental results show that the walk-assist robot, along with the structure of this proposed control scheme, can guide the user to reach the goal.

Identifying noninvasive treatments to alleviate the symptoms of Parkinson's disease (PD) is important to improving the quality of life for those with PD. Several studies have explored the effects of visual, auditory, and vibratory cueing to improve gait in PD patients. Here, we present a wireless vibratory feedback system, called the PDShoe, and an associated intervention study with four subjects. The PDShoe was used on two control subjects, one subject with PD who experienced freezing of gait (FOG), and one subject with PD with an implanted deep brain stimulator (DBS). This short intervention study showed statistically significant improvements in peak heel pressure timing, peak toe pressure timing, time on the heel sensor, and stance to swing ratio after just one week of twice-daily therapy. Thus, step-synchronized vibration applied to the feet of patients with PD may be an effective way to improve gait in those subjects.

As our robotics community advances its understanding toward the optimal design of robotic exoskeletons for human gait training, the question we ask in this paper is how the anterior lunge degree of freedom in the robotic exoskeleton affects human gait training. Answering this question requires both novel robotic design and novel protocols for human gait training to characterize this effect. To the best of the authors' knowledge, this is the first study to characterize the effect of an exoskeleton's degrees of freedom on human gait adaptation. We explored this question using the Active Leg EXoskeleton (ALEX) II. The study presented was performed using ALEX II under the following two configurations: 1) locking the anterior/posterior translation in the exoskeleton, while allowing other degrees-of-freedom (labeled as locked mode) and 2) keeping the anterior/posterior degree of freedom unlocked (labeled as unlocked mode). Healthy subjects walked at self-selected speeds on a treadmill and were trained to walk with a new gait template, scaled down from their normal template. While both groups showed adaptation and retention over a 26-min period following training, the unlocked group showed better performance in terms of adaptation and retention compared with the locked group.

In this paper, a planar underactuated cable-driven micro-macro robot is presented. The system consists of two-link passive serial manipulator attached to a cable-suspended parallel robot. The system is conceived for applications requiring point-to-point motions inside large workspaces in the presence of obstacles: The serial arm allows us to reach points close to the obstacles that would not be reachable by the cable robot alone due to cable-obstacle interference. The kinematic and dynamic models are presented and the differential flatness framework is applied to make the system controllable for point-to-point movements. In addition, a multiobjective optimization framework is presented, which allows us to choose the design parameters that minimize two conflicting objective functions (movement time and control effort) for a given movement task. This novel approach allows designers to infer useful information about the influence of the design parameters on the dynamic performance of the system.

Adaptive cable-driven parallel robots can adjust the position of one or more pulley blocks to optimize performance within a given workspace. Because of their augmented kinematic redundancy, adaptive systems have several advantages over their traditional counterparts featuring the same numbers of cables. In this paper, we explore the application of adaptive cable-driven robots to cable-suspended camera systems. Performance of the traditional and of the adaptive designs are analyzed, using dexterity and stiffness as performance metrics. Results show superior performance of the adaptive design compared to the traditional system. An illustrative design problem for adaptive cable-suspended camera systems is also presented and solved.

This paper demonstrates that for certain choices of mass distribution and addition of springs, an underactuated two-degree-of-freedom (2-DOF) \bm PRRRP system is static feedback linearizable, i.e., differentially flat as well. This paper is original and provides a ground breaking study in underactuated dynamical systems.

Effective locomotion training with robotic exoskeletons requires identification of optimal control algorithms to better facilitate motor learning. Two commonly employed training protocols emphasize use of training stimuli that either augment or reduce performance errors. The current study sought to identify which of these training strategies promotes better short-term modification of a typical gait pattern in healthy individuals as a framework for future application to neurologically impaired individuals. Ten subjects were assigned to each of a performance-based error-augmentation or error-reduction training group. All subjects completed a 45-min session of treadmill walking at their preferred speed with a robotic exoskeleton. Target templates prescribed an ankle path for training that corresponded to an increased step height. When subjects’ instantaneous ankle positions fell below the inferior virtual wall of the target ankle path, robotic forces were applied that either decreased (error-reduction) or increased (error-augmentation) the deviation from the target path. When the force field was turned on, both groups walked with ankle paths better approximating the target template compared to baseline. When the force field was removed unexpectedly during catch and post-training trials, only the error-augmentation group maintained an ankle path close to the target ankle path. Further investigation is required to determine if a similar training advantage is provided for neurologically impaired individuals.

In this paper, a new cable-suspended parallel robot (CSPR) with reconfigurable end-effector is presented. The system has been conceived for pick and place operations in industrial environments where the ability to avoid obstacles and to maximize the performance are the main requirements. The proposed system has the capability of dynamically modifying the configuration of the cable anchor points on the end-effector to avoid collisions with obstacles in the approaching/departing phases, while reducing the movement time in the rest of the trajectory. Kinematic and dynamic models of the reconfigurable CSPR are derived and an optimal design of the end-effector is presented. The optimization aims at minimizing the force required by the linear actuator to modify the position of the cable anchor points during a pick and place task. The results reveal the predominant effect of the end-effector mass distribution on the force exerted by the linear actuator.

Balance recovery during an unexpected disturbance is a complex motor task, where part of the variability depends on the type of the perturbation itself. Despite of this, little is known to what extent adaptation mechanisms to repeated perturbations are dependent on the direction and the amplitude of the applied disturbances. Here, we used a modified version of the Active Tethered Pelvic Assist Device (A-TPAD) to apply unexpected force-controlled multidirectional waist-pull perturbations while subjects were walking. Healthy young subjects were divided into two groups and were exposed to a single training session. Each group received perturbations of different amplitudes along the Medio-Lateral (ML) or the Antero-Posterior (AP) direction. Dynamic stability was determined in both the AP and ML directions in terms of base of support (BoS) and margin of stability (MoS). Results showed: 1) an adaptation of the balance recovery reactions only for perturbations delivered along the AP directions; 2) aftereffects able to modify the control of stability during the post-training session of which type and extent depends on the direction of the perturbations previously applied; and 3) a directional and amplitude effect on the dynamic stability at the end of the balance recovery reactions., by Dario Martelli,Vineet Vashista, Silvestro Micera and Sunil K. Agrawal

Objective: Body Weight Supported Treadmill Training (BWSTT) with therapists’ assistance is often used for gait rehabilitation post-stroke. However, this training method is labor-intensive, requiring at least one or as many as three therapists at once for manual assistance. Previously, we demonstrated that providing movement guidance using a performance-based robot-aided gait training (RAGT) that applies a compliant, assist-as-needed force-field improves gait pattern and functional walking ability in people post-stroke. In the current study, we compared the effects of assist-as-needed RAGT combined with functional electrical stimulation and visual feedback with BWSTT to determine if RAGT could serve as an alternative for locomotor training. Methods: Twelve stroke survivors were randomly assigned to one of the two groups, either receiving BWSTT with manual assistance or RAGT with functional electrical stimulation and visual feedback. All subjects received fifteen 40-minutes training sessions. Results: Clinical measures, kinematic data, and EMG data were collected before and immediately after the training for fifteen sessions. Subjects receiving RAGT demonstrated significant improvements in their selfselected over-ground walking speed, Functional Gait Assessment, Timed Up and Go scores, swing-phase peak knee flexion angle, and muscle coordination pattern. Subjects receiving BWSTT demonstrated significant improvements in the Six-minute walk test. However, there was an overall trend toward improvement in most measures with both interventions, thus there were no significant between-group differences in the improvements following training. Conclusion: The current findings suggest that RAGT worked at least as well as BWSTT and thus may be used as an alternative rehabilitation method to improve gait pattern post-stroke as it requires less physical effort from the therapists compared to BWSTT.

This article details the design, fabrication, and application of a mechatronic arm exoskeleton for firearm aim stabilization (MAXFAS), which senses and damps involuntary tremors in the arm. Human subject experiments were carried out using the device in a simulated shooting and aiming task. Results indicate that MAXFAS reduced arm tremors and improved shooting performance while wearing the device. Residual performance improvement after removing the device and possible training function of MAXFAS will also be discussed.

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.

Robotic spine brace based on parallel-actuated robotic system is a new device for treatment and sensing of scoliosis, however, the strong dynamic coupling and anisotropy problem of parallel manipulators result in accuracy loss of rehabilitation force control, including big error in direction and value of force. A novel active force control strategy named modal space force control is proposed to solve these problems. Considering the electrical driven system and contact environment, the mathematical model of spatial parallel manipulator is built. The strong dynamic coupling problem in force field is described via experiments as well as the anisotropy problem of work space of parallel manipulators. The effects of dynamic coupling on control design and performances are discussed, and the influences of anisotropy on accuracy are also addressed. With mass/inertia matrix and stiffness matrix of parallel manipulators, a modal matrix can be calculated by using eigenvalue decomposition. Making use of the orthogonality of modal matrix with mass matrix of parallel manipulators, the strong coupled dynamic equations expressed in work space or joint space of parallel manipulator may be transformed into decoupled equations formulated in modal space. According to this property, each force control channel is independent of others in the modal space, thus we proposed modal space force control concept which means the force controller is designed in modal space. A modal space active force control is designed and implemented with only a simple PID controller employed as exampled control method to show the differences, uniqueness, and benefits of modal space force control. Simulation and experimental results show that the proposed modal space force control concept can effectively overcome the effects of the strong dynamic coupling and anisotropy problem in the physical space, and modal space force control is thus a very useful control framework, which is better than the current joint space control and work space control.

Magnetic-inertial measurement units (MIMUs) are often used to measure the joint angles between two body segments. To obtain anatomically meaningful joint angles, each MIMU must be computationally aligned (i.e., calibrated) with the anatomical rotation axes. In this paper, a novel four-step functional calibration method is presented for the elbow joint, which relies on a two-degrees-of-freedom elbow model. In each step, subjects are asked to perform a simple task involving either one-dimensional motions around some anatomical axes or a static posture. The proposed method was implemented on a fully portable wearable system, which, after calibration, was capable of estimating the elbow joint angles in real time. Fifteen subjects participated in a multi-session experiment that was designed to assess accuracy, repeatability and robustness of the proposed method. When compared against an optical motion capture system (OMCS), the proposed wearable system showed an accuracy of about 4° along each degree of freedom. The proposed calibration method was tested against different MIMU mountings, multiple repetitions and non-strict observance of the calibration protocol and proved to be robust against these factors. Compared to previous works, the proposed method does not require the wearer to maintain specific arm postures while performing the calibration motions, and therefore it is more robust and better suited for real-world applications.

To study stress in fathers of preterm infants admitted in a neonatal intensive care unit. Questionnaire-based study. Questionnaire included domains on infant’s health, maternal illness, staff behavior, parental role, home affairs and finances. Eligible fathers were repeatedly interviewed on day 7 (n=80), day 17 (n=59) and day 27 (n=28). Raw and standardized stress scores were calculated. Financial burden was the main stressor at all times. Stress related to staff behavior and altered parental role reduced with time. Birthweight and father’s age, occupation and education independently predicted stress. Fathers of preterm infants admitted in hospital are stressed, primarily due to financial burden.

This paper presents studies of an upper body assistive device designed to aid human load carriage. The two primary functions of the device are: (i) distributing the backpack load between the shoulders and the waist and (ii) reducing the dynamic load of a backpack on the human body during walking. These functions are targeted to relieve stress applied on the shoulders and the back, and also reduce the dynamic loads transferred to the lower limbs during walking. These functions are achieved by incorporating two modules—passive and active—within a custom fitted shirt integrated with motion/force sensors, actuators, and a real-time controller. The relevant modeling and controller design are presented for dynamic load compensation. Preliminary evaluation of the device was first performed on a single subject, followed by a pilot study with ten healthy subjects walking on a treadmill with a backpack. Results show that the device can effectively transfer the load from the shoulders to the waist and also reduce the dynamic loads induced by the backpack during walking. Reduction in peak and total normal ground reaction forces, leg muscle activations, and oxygen consumptions was observed with the device. This suggests that the device can potentially reduce the risk of musculoskeletal injuries and fatigue on the lower limbs associated with carrying heavy loads and provide some metabolic benefits.

Lower-extremity robotic exoskeletons are used in gait rehabilitation to achieve functional motor recovery. To date, little is known about how gait training and post-training are characterized in brain signals and their causal connectivity. In this work, we used time-domain partial Granger causality (PGC) analysis to elucidate the directed functional connectivity of electroencephalogram (EEG) signals of healthy adults in robot-assisted gait training (RAGT). Our results confirm the presence of EEG rhythms and corticomuscular relationships during standing and walking using spectral and coherence analyses. The PGC analysis revealed enhanced connectivity close to sensorimotor areas ( $ {\rm C}_{3}$ and $ {\rm CP}_{3}$ ) during standing, whereas additional connectivities involve the centroparietal ( $ {\rm CP}_{ {\rm z}}$ ) and frontal ( $ {\rm F}_{ {\rm z}}$ ) areas during walking with respect to standing. In addition, significant fronto-centroparietal causal effects were found during both training and post-training. Strong correlations were also found between kinematic errors and fronto-centroparietal connectivity during training and post-training. This study suggests fronto-centroparietal connectivity as a potential neuromarker for motor learning and adaptation in RAGT.

The broader goal of our research is to train infants with special needs to safely and purposefully drive a mobile robot to explore the environment. The hypothesis is that these impaired infants will benefit from mobility in their early years and attain childhood milestones, similar to their healthy peers. In this paper, we present an algorithm and training method using a force-feedback joystick with an “assist-as-needed” paradigm for driving training. In this “assist-as-needed” approach, if the child steers the joystick outside a force tunnel centered on the desired direction, the driver experiences a bias force on the hand. We show results with a group study on typically developing toddlers that such a haptic guidance algorithm is superior to training with a conventional joystick. We also provide a case study on two special needs children, under three years old, who learn to make sharp turns during driving, when trained over a five-day period with the force-feedback joystick using the algorithm.

Rehabilitation robots are, currently, being explored for training of neural impaired subjects or for assistance of those with weak limbs. Intensive training of neurally impaired subjects, with quantifiable outcomes, is the eventual goal of these robot exoskeletons. Conventional arm exoskeletons for rehabilitation are bulky and heavy. In recent years, the authors have proposed to make lightweight exoskeletons for rehabilitation by replacing the rigid links of the exoskeleton with lightweight cuffs fixed to the moving limb segments of the human arm. Cables are routed through these cuffs, which are driven by motors, to move the limb segments relative to each other. However, a scientific limitation of a cable-driven system is that each cable can only pull but not push. This paper is the first to demonstrate via experiments with cable-driven arm exoskeleton (CAREX) that it is possible to achieve desired forces on the hand, i.e., both pull and push, in any direction as required in neural training. In this research, an anthropomorphic arm was used to bench test the design and control concepts proposed in CAREX. As described in this paper, CAREX was attached to the limb segments of a five degree-of-freedom anthropomorphic arm instrumented with joint sensors. The cuffs of CAREX were designed to have adjustable cable routing points to optimize the “tensioned” workspace of the anthropomorphic arm. Simulation results of force field for training and rehabilitation of the arm are first presented. Experiments are conducted to show the performance of a CAREX force field controller when human subjects pull the end-effector of the anthropomorphic arm to travel on prescribed paths. The human-exoskeleton interface is also presented at the end of this paper to demonstrate the feasibility of CAREX on human arm.

It has been mathematically proven that a completely restrained n- degree-of-freedom (n-DOF) single rigid-bodied cable-driven platform requires a minimum of n + 1 cables with positive tension to fully constrain it. However, the force-closure analysis of open chains that are driven by cables is still an open question. For the case of an n -DOF cable-driven open chain, the following two important questions arise. 1) How can the force-closure analysis be carried out for a given cable routing configuration, while retaining the geometric insights of the problem? 2) Are n + 1 cables sufficient to fully constrain the entire chain? This paper addresses these issues by proposing a systematic and novel approach based on the reciprocal screw theory. The key idea is to express wrenches acting on the open chain as linear combinations of the reciprocal screws and determine the total required torques at each joint. This is followed by equating the joint torques that are provided by the cable forces with the joint torques, which are required by the external wrenches, and checking for force closure. The proposed methodology can analyze open chains with arbitrary cable routing configuration. The analysis shows that the entire n-DOF open chain requires a minimum of n + 1 cables to fully constrain it.

AR = aspect ratio a = dimensionless length from the leading edge to the pivot point b = design variable vector bi = design variable in the ith element b k = design variable vector at the cycle number k b k i = design variable at the cycle number k in the ith element b k 1 = design variable vector at the cycle number k 1 b k 1 i = design variable at the cycle number k 1 in the ith element b 0 = initial design variable vector bmin = lower bound of the design variable C b = viscous damping matrix CD = drag coefficient CD = time-averaged drag coefficient CL = lift coefficient CL = time-averaged lift coefficient CM = pitch moment coefficient CT = thrust coefficient CT = time-averaged thrust coefficient c = chord, m E = Young’s modulus, Gpa Ei = Young’s modulus of the ith element E0 = initial Young’s modulus Fx = x component of the resulting aerodynamics force acting on the airfoil, N Fy = y component of the resulting aerodynamics force acting on the airfoil, N f = frequency, Hz f = static load vector f t = dynamic load vector feq s = equivalent static loads vector f k eq s = equivalent static loads vector at the cycle number k fz = compliance h = reduced plunging amplitude with respect to the chord K b = stiffness matrix k = reduced frequency Ma = Mach number M b = mass matrix Re = Reynolds number S = reference area St = Strouhal number T = period, s u = far-field flow velocity, m=s V = total volume of the structure ve = volume of each element z s = static displacement vector z t = dynamic displacement vector "1 = specified value of density "2 = percent of the total design variable "3 = density value of design update = propulsive efficiency = angle between the chord and the far-field flow speed direction Received 5 August 2010; revision received 22 March 2011; accepted for publication 1 July 2011. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0001-1452/11 and $10.00 in correspondence with the CCC. ∗Graduate Student, Department of Mechanical Engineering. Postdoctoral Fellow, Department of Mechanical Engineering. Member AIAA. Professor, Department of Mechanical Engineering; gjpark@ hanyang.ac.kr. Senior Member AIAA (Corresponding Author). Professor, Department of Mechanical Engineering. Aerospace Engineer, Air Vehicles Directorate. Member AIAA. AIAA JOURNAL Vol. 49, No. 12, December 2011

An upper-arm wearable exoskeleton has been designed for the assistance and functional training of humans. One of the goals of this design is to provide passive assistance to a user by gravity balancing, while keeping the transmitted forces to the shoulder joints at a minimum. Consistent with this goal, this paper discusses: analytical gravity balancing design conditions for the structure of the exoskeleton; a possible implementation of these conditions into practical designs; the minimization of transmitted joint forces to the shoulder while satisfying the gravity balancing conditions; the numerical optimization of the system for gravity balancing and minimization of transmitted forces; and the effect of parameter variation on joint moments and joint forces via numerical optimization. An implementation of the design was undertaken using zero-free-length springs. The design idea presented in this paper may be useful in relieving the actuators effort of exoskeletons to support the weight of the arm and therefore the possibility of using small actuators and making the system light and portable or even a stand-alone passive support device can be developed based on these gravity balancing conditions.

Self-generated mobility is a major contributor to the physical, emotional, cognitive, and social development of infants and toddlers. When young children have disorders that hinder self locomotion, their development is at risk for delay. Independent mobility via traditional power mobility devices may prevent this delay, but do little to encourage the child's development of gross motor skills. This research aims to develop a bio-driven mobile-assistive device that is controlled and driven by moving the feet, which may encourage the development of gross motor skills. In this study, system feasibility is shown by experiments on five typically developing toddlers and one special needs toddler with spastic cerebral palsy. Children were placed in the bio-driven device and instructed to navigate through a maze. All subjects were able to successfully complete the maze in multiple trials. In addition, two toddlers showed evidence of improved driving skill by completing the maze in shorter times in successive trials on a given testing day. The results suggest that such a device is feasible for purposeful driving. Recommendations are given for the device and protocol redesign for related future testing.