Keywords: Exoskeletons, Design and development in rehabilitation robotics, Control strategies in rehabilitation robotics
Abstract: This paper presents a model inversion procedure for a viscoelastic compliant element contained within a rotary series elastic actuator (SEA). Model inversion plays an important role in enabling accurate model-based control of physical human-robot interaction (HRI) with SEAs. If the compliant element of the SEA is elastomeric, analytically inverting its model is non-trivial due to the presence of complex non-linear terms. This paper applies an alternative inversion procedure, by coupling a partially analytical inverse model with a disturbance observer (DOB). Results of inverting without a DOB are given as a baseline and compared to the analytical inversion + DOB with two different types of filter. To quantify the accuracy of the inversion, the output of the inversion procedure is passed back through the forward model to identify the ‘actual setpoint’, the signal that would be generated if the output of the inversion procedure was tracked accurately. The inversions for five desired torque signals are presented; in all cases, the root-mean square (RMS) error between the desired setpoint and actual setpoint is lower when the DOB inversion procedure is used, compared to the RMS error incurred when the DOB is omitted. The results suggest that the proposed inversion procedure provides an accurate and mathematically tractable inverse of the complex viscoelastic elastomer model.

Keywords: Integrated diagnostic and therapeutic systems, Biomechanics and robotics in physical rehabilitation
Abstract: Clinical assessment of abnormal neuro-mechanics is typically performed by manipulation of the affected limbs; a process with low inter- and intra-rater reliability. This paper aims at formalizing a framework that closes the loop between a clinician’s expertise and computational algorithms, to enhance the clinician’s diagnostic capabilities during physical manipulation. The framework’s premise is that the dynamics that can be measured by manipulation of a limb are distinct between movement disorders. An a priori database contains measurements encoded in a space called the information map. Based on this map, a computational algorithm identifies which probing motions are more likely to yield distinguishing information about a patient’s movement disorder. The clinician executes this movement and the resulting dynamics, combined with clinician input, is used by the algorithm to estimate which of the movement disorders in the database are most probable. This is recursively repeated until a diagnosis can be confidently made. The main contributions of this paper are the formalization of the framework and the addition of the information map to select informative movements. The establishment of the framework provides a foundation for a standardized assessment of movement disorders and future work will aim at testing the framework’s efficacy.

Keywords: Clinical evaluation in robot-aided rehabilitation, Integrated diagnostic and therapeutic systems, Robotic platforms in neuroscience
Abstract: Although motor and sensory impairments of the upper limb after stroke have been widely studied, the relationship between sensory deficits and motor functions has been less thoroughly explored. In this ongoing study, we investigated the relationship between proprioceptive impairments and motor functions with 20 chronic stroke survivors. Their proprioceptive abilities were assessed with a passive joint position matching test using H-Man and their motor functions were assessed with ARAT (Action Research Arm Test) and FMA (Fugl Meyer Upper Extremity Assessment) clinical scores. The assessments were conducted before, during and after the therapy. Results indicated a significant difference between the proprioceptive outcomes of healthy and stroke participants (at baseline) in both matching accuracy (absolute error, p = 0.02) and precision (variability of the signed error, p = 0.03). Significant correlations were found between the proprioceptive assessment outcomes (assessed before the beginning of the motor rehabilitation) of stroke participants with impaired proprioception and their ARAT clinical scores assessed at the first follow-up (week 12) (rho = -0.74 and p = 0.047 for the absolute error; rho = -0.78 and p = 0.03 for the variability of the signed error). The results from this preliminary study indicated a significant relationship between proprioceptive impairments and motor function performances in proprioceptively impaired chronic stroke participants.

Keywords: Exoskeletons, Biomechanics and robotics in physical rehabilitation, Wearable robotic systems
Abstract: Robotic exoskeletons are a promising technology for rehabilitation and locomotion following musculoskeletal injury, but their adoption outside the physical therapy clinic has been limited by relatively primitive methods for identifying and incorporating the user’s gait intentions. Various intent detection approaches have been demonstrated using electromyography and electroencephalography signals. These technologies sense the human directly but introduce complications for donning/doffing the device and in measurement consistency. By contrast, sensors onboard the exoskeleton avoid these complications but sense the human indirectly via the human-robot interface. This pilot study examines if onboard sensors alone may enable identification of user intent. Joint positions and commanded motor currents are compared prior to and after changes in the user’s intended gait speed. Preliminary experimental results confirm that these measures are significantly different following intent changes for both able-bodied and non-able-bodied users. The findings suggest that intent detection is possible with onboard sensors alone, but the intent signals depend on exoskeleton control settings, user ability, and temporal considerations.

Keywords: From lab to market - Usability evaluation, Design and development in rehabilitation robotics
Abstract: The increasing number of strokes goes hand in hand with the need for new effective rehabilitation systems. In this contribution the methods and results of a series of user surveys comprising methods of qualitative research are presented. The goal of these surveys was to elicit requirements clinical personnel poses on rehabilitation devices to enable an effective, efficient and satisfying use in a rehabilitation environment. The analysis of the survey concluded that the use of a rehabilitation device should be time-effective and bring joy and that the device should be customizable and provide feedback.

Keywords: Exoskeletons, Wearable robotic systems, New technologies and methodologies in human movement analysis
Abstract: Trunk exoskeletons are an emerging technology that could reduce spinal loading, guide trunk motion, and augment lifting ability. However, while they have achieved promising results in brief laboratory studies, they have not yet been tested in longer-term real-world studies – partially due to reliance on stationary sensors such as cameras. To enable future real-world evaluations of trunk exoskeletons, this paper describes two preliminary studies on using inertial measurement units (IMUs) to collect kinematic data from an exoskeleton wearer. In the first study, a participant performed three activities (walking, sit-to-stand, box lifting) while trunk flexion angle was measured with both IMUs and reference cameras. The mean absolute difference in flexion angle between the two methods was 1.4° during walking, 3.6° during sit-to-stand and 5.2° during box lifting, showing that IMUs can measure trunk flexion with a reasonable accuracy. In the second study, six participants performed five activities (standing, sitting straight, slouching, ‘good’ lifting, ‘bad’ lifting), and a naïve Bayes classifier was used to automatically classify the activity from IMU data. The classification accuracy was 92.2%, indicating the feasibility of automated activity classification using IMUs. The IMUs will next be used to obtain longer-term recordings of different activities performed both with and without a trunk exoskeleton to determine how the exoskeleton affects a person’s posture and behavior.

Keywords: Exoskeletons, Wearable robotic systems, Design and development in rehabilitation robotics
Abstract: To be successful, hand exoskeletons require customisable low encumbrance design with multi-compliant materials. This paper details the modification and testing of a fused filament fabrication printer to produce three categories of multi-compliant material that can be incorporated into the design of hand exoskeletons. Demonstration of the multi-compliant material for some common problems in hand exoskeleton design are presented. This method of manufacturing multi-compliant materials could result in widespread use of exoskeleton design in both the rehabilitation and assistive fields.

Keywords: Exoskeletons, Orthotics - modeling and simulation
Abstract: Introduction: People with arthrogryposis multiplex congenita (AMC) often have muscle weakness in the biceps that makes elbow flexion difficult. An elbow-flexion assist orthosis was designed using the force of springs, combined with a sliding joint, to apply appropriate elbow torque to aid a user in lifting her hand to her mouth. The sliding joint allows an increasing elbow torque despite a decreasing spring force. Methods: The device was prototyped for a user with AMC. An occupational therapist measured the user’s flexion with and without the device. Benchtop torque measurements were also determined and compared with user trials. Results: The assist orthosis applied an increasing torque as the elbow flexed, thereby allowing the subject to reach her mouth for feeding and then extend her elbow to a position of no applied torque. Without the device, the subject had active elbow flexion of 87 degrees. With the device, this flexion increased to 120 degrees. Conclusion: The novel prototype is a lightweight, spring-powered flexion orthosis which can be made relatively easily and is potentially concealed under clothing. It provides the appropriate torque to move the hand against gravity and increases elbow-flexion of the user.

Keywords: Exoskeletons, Design and development in rehabilitation robotics, Assistive robotics
Abstract: Recent commercial availability of a stacked dielectric elastomer actuator (SDEA) has opened up possibilities of their use as “artificial muscles” for rehabilitation robots and powered exoskeleton devices. Made by CTsystems, this actuator (CT_SDEA) is made from soft materials, and offers a lightweight and acoustically noiseless alternative to DC motor actuators used in conventional rehabilitation robotic systems. The purpose of the present work was to benchmark the electromechanical properties of CT-SDEAs to assess its capabilities and limitations for mechanizing rehabilitation robots. The CT-SDEAs tested in this study showed 21 ms electrometrical delay, and their calculated strain-rate was 660 %/s. They could generate 21.74 N of force and have a 426 W/kg power-to-mass ratio. Their longitudinal strain was measured at 3.3%. Additionally, their steady state current consumption was measured 39 µA. CT-SDEAs’ fast response, short electromechanical delay and high strain-rate, make them highly suitable for closed-loop control. Additionally, their force generation capability, fast response, high power-to-mass ratio, and low steady state power consumption make them a strong candidates for exoskeleton applications. It’s longitudinal strain (3.3%) however, was less than that of skeletal muscle (20%). Depending on the application, their use may require the addition of mechanical linkages, for force to displacement conversion.

Keywords: Exoskeletons, Assistive robotics, Control strategies in rehabilitation robotics
Abstract: Exoskeletons are human-robot interfaces that have enormous potential to assist people with everyday tasks. To improve the design of exoskeletons for use in clinical populations, it is important to further our understanding of how exoskeleton design and control parameters lead to sub-optimal effectiveness. Here we simulated the effect of three factors, gait variability, wearer-exoskeleton delays, and exoskeleton inertia, have on the predicted energy assistance provided by an exoskeleton with a finite-state controller trained on a set of stroke survivors’ free walking gait data. Results indicate that larger errors between the wearer’s desired ankle trajectory and the exo’s estimated ankle trajectory result in statistically large reductions in the actual assistance provided. Specifically lags on the order of even 10 ms can illustrate statistically sub-optimal performance. Likewise subjects that exhibit large gait variability will have a statistical reduction in actual assistance. However, reasonably low exoskeleton inertias are not significant as a factor in terms of sensitivity to wearer assistance. Therefore, to improve cooperative control algorithms for exoskeletons and achieve true assistance based on wearer induced motion, this work implies that designers should prioritize minimizing delays and wearers should train to reduce variability in order to maximize energy savings.

Keywords: Exoskeletons, Design and development in rehabilitation robotics, Control strategies in rehabilitation robotics
Abstract: Robot-assisted rehabilitation in children and young adults with Cerebral Palsy (CP) is expected to lead to neuroplasticity and reduce the burden of motor impairments. For a lower-limb exoskeleton to perform well in this context, it is essential that the robot be "transparent" to the user and produce torques only when voluntarily-generated motor outputs deviate significantly from the target trajectory. However, the development of transparent operation modes and assistance-as-need control schema are still open problems with several implementation challenges. This paper presents a theoretical approach and provides a discussion of the key issues pertinent to designing a transparent operation mode for a lower-limb exoskeleton suitable for children and young adults with CP. Based on the dynamics of exoskeletons as well as friction models and human-robot interaction models, we propose a control strategy aimed to minimize human-machine interaction forces when subjects generate motor outputs that match the target trajectory. The material is presented as a conceptual framework that can be generalized to other exoskeleton systems for overground walking.

Keywords: Exoskeletons, Control strategies in rehabilitation robotics, Wearable robotic systems
Abstract: In this paper, we present a novel concept that can enable the human aware control of exoskeletons through the integration of a soft suit and a robotic lower body exoskeleton. Unlike the state-of-the-art exoskeleton controllers which mostly rely on lumped human-robot models, the proposed concept makes use of the independent state measurements concerning the human user and the robot. In order to realize such a system from the hardware point of view, we propose a system integration frame that combines a soft suit for human state measurement and a rigid exoskeleton for human assistance. We identify the technological requirements that are necessary for the realization of such a system with a particular emphasis on the soft suit integration. We also propose a template model, named scissor pendulum, that may encapsulate the dominant dynamics of the human-robot combined model to synthesize a controller for human state regulation. A series of simulation experiments were conducted so as to check the controller performance. As the result, satisfactory tracking results were obtained, adequately confirming the fact that the proposed integrated system could potentially improve the performance of lower body exoskeletons.

Keywords: Control strategies in rehabilitation robotics, Assistive robotics - home robots, Cognitive robotics in rehabilitation
Abstract: Motor learning issues for hemiplegics not only include motor impairments such as spastic paralysis, but reportedly also an inability to appropriately recognize somatic sensations. In this regard, biofeedback of movement information through visual information and auditory information has been found effective as a method for drawing attention to appropriate somatic sensations. In this context, here, we propose a novel eccentric training system utilizing visual biofeedback of force information. We first develop a compact and highly portable rehabilitation robot for home use. The robot estimates the force on the tiptoe without the use of a force sensor, and a display connected to the robot presents the force information to the trainee. Clinical trials with two chronic hemiplegics have been conducted. The results show that the timed up and go tests of both trainees are shortened after training twice a week for three weeks (six times in total). Simultaneously, the co-contraction index scores of the tibialis anterior and gastrocnemius muscles decrease. These findings in conjunction with previous results suggest that training with visual biofeedback of force information may enhance reciprocal inhibition of the tibialis anterior muscle and reduces co-contraction.

Keywords: Cognitive robotics in rehabilitation, Clinical evaluation in robot-aided rehabilitation, Design and development in rehabilitation robotics
Abstract: Robot-based neurorehabilitation strategies often ignore cognitive performance during treatment, but this is a need in populations dealing with a wide variety of cognitive and motor impairments, such as the stroke and HIV populations, for which an association between the two have been established. In this study, we concurrently measure cognitive and motor performance on a robotic cognitive-motor task and quantify cognitive-motor interference. We apply this method to a pilot group of healthy, stroke, and HIV-stroke subjects, and we demonstrate the potential of smoothness and correct response rate as metrics to capture motor and cognitive-related dual-task effects.

Keywords: Exoskeletons, Control strategies in rehabilitation robotics, Assistive robotics
Abstract: Lower limb exoskeletons (LLEs) are susceptible to falls, and users are at risk of head and/or hip injuries. To address concerns regarding the safety of LLE users, optimization techniques were used to study safe-fall control strategies. Simulation results of these studies showed promising performance that leads to head impact avoidance and mitigation of hip impact velocity. The motivation for the current research was to extend the application of previously developed optimization techniques to study more realistic human-LLE fall conditions. We examined a range of feasible fall durations for the human-LLE model and found the optimal fall duration for which the user’s safety is maximized. Next, we used a range of coefficients of friction to examine fall strategies on different ground surface conditions. We found that the effectiveness of a safe-fall strategy is higher when falling on less slippery surfaces compared to more slippery ones. The simulation results were implemented in a half-scale physical model of a three-link inverted pendulum, which represented a human-LLE model. Results of our experiments verified that the optimal safe-fall strategy could be implemented in a mechanical test setup. The hip linear velocity at impact was found to have similar values in both the experimental (2.04 m/s) and simulation results (2.09 m/s). Further studies should be conducted with appropriate software and hardware platforms to successfully implement safe-fall strategies in an actual LLE.

Keywords: Clinical evaluation in robot-aided rehabilitation, Technologies for neurodegenerative disorders, Design and development in rehabilitation robotics
Abstract: Vibration stimulation seems to be an affordable easy-to-use rehabilitation tool. Focal muscle vibration (FV) has potential to reduce spasticity and enhance muscle strength and performance. Combined with robotic assisted movement therapy, the rehabilitation can benefit from improvement of more than one aspect. For example, FV could firstly decrease abnormally increased muscle tone and joint rigidity by tackling volitional control for easier robotic movement exercise. Exactly this approach is evaluated within a clinical trial presented in this paper. FV were applied to relaxed spastic wrist flexor and extensor muscles for 15min. Subsequently, the wrist was engaged in a robotic-assisted game-playing. Results from two cases who completed the trial showed short-term decrease in wrist stiffness as assessed by clinical spasticity measurement Modified Ashworth Scale (MAS). Active range of motion (AROM) and engineering joint stiffness (JS) measurements were estimated using a robotic apparatus and the results complemented previous observations. The AROM increased and JS decreased for both cases when compared at the beginning and at the end of each interventional session. These results are a part of an ongoing clinical trial but show promise for reducing repercussions of spasticity in incomplete spinal cord injury.

Keywords: Exoskeletons, Wearable robotic systems, Robotic orthoses - design and development
Abstract: Robotic exoskeletons have the capability to improve community ambulation in aging individuals. These exoskeleton controllers utilize different environmental information such as walking speeds and slope inclines to provide corresponding assistance. Several numerical approaches for estimating this environmental information have been implemented; however, they tend to be limited during dynamic changes. A possible solution is a machine learning model utilizing the user’s electromyography (EMG) signals along with mechanical sensor data. We developed a neural network-based walking speed and slope estimator for a powered hip exoskeleton and explored the EMG signal contributions in both static and dynamic settings while wearing the device. We also analyzed the performance of different EMG electrode placements. The resulting machine learning model achieved error rates below 0.08 m/s RMSE and 1.3° RMSE. Our study findings from four able-bodied and two elderly subjects indicate that EMG can improve the performance by reducing the error rate by 14.8% compared to the model using only mechanical sensors. Additionally, results show that using EMG electrode configuration within the exoskeleton interface region is sufficient for the EMG model performance.

Keywords: Exoskeletons, Assistive robotics, Human-machine interfaces and robotic applications
Abstract: Assistive exoskeletons that utilize trajectory following control have been shown to produce stable gait for users. These however, do not allow intuitive tuning to customize gait to users’ preferences. When persons walk on their own, they balance a variety of needs such as speed, comfort, and energy. Providing user tuning by optimizing between different gait performance measures gives an intuitive flexibility. We have shown the optimization between natural walking and gait energy produces stable bipedal gait through simulation in a virtual constraint framework. This verification shows validity of the methodology and framework for improving tuning and customization of assistive exoskeletons.

Keywords: Exoskeletons, Assistive robotics, From lab to market - Usability evaluation
Abstract: Despite the growing interest, the adoption of industrial exoskeletons may still be held back by technical limitations. To enhance versatility and promote adoption, one aspect of interest could be represented by the potential of active and quasi-passive devices to automatically distinguish different activities and adjust their assistive profiles accordingly. This contribution focuses on an active back-support exoskeleton and extends previous work proposing the use of a Support Vector Machine to classify walking, bending and standing. Thanks to the introduction of a new feature - forearm muscle activity - this study shows that it is possible to perform reliable online classification. As a consequence, the authors introduce a new hierarchically-structured controller for the exoskeleton under analysis.

Keywords: Clinical evaluation in robot-aided rehabilitation, Biomechanics and robotics in physical rehabilitation, Robot-aided mobility
Abstract: To maximize the benefits of the newly developed powered prosthetic legs, amputees must rely on tuning experts (TE) from manufacturers to tune these devices based on their specific physical conditions. Because TEs are hard to train, it is difficult to access the TEs and the cost of customization is high. If the knowledge used by the TEs could be extracted, it is possible to reduce the tuning cost by automating the tuning procedure or developing efficient TE training programs. In this paper, we preliminarily identified kinematic features that are sensitive to the control parameter change of the powered prosthetic leg. Using data collected from three transtibial amputee subjects with four levels of push-off power, we tested whether a change of push-off power could generate a significant difference on 13 preselected kinematic features during level ground walking at self-selected walking speed. Six features across three joints on the prosthesis side were demonstrated to be sensitive to the change of push-off power.

Keywords: Clinical evaluation in robot-aided rehabilitation, Technologies for neurodegenerative disorders, Robotic platforms in neuroscience
Abstract: Postural responses to unstable conditions or perturbations are important predictors of the risk of falling and can reveal balance deficits in people with neurological disorders, such as Parkinson’s Disease (PD). However, there is a lack of evidences related to devices and protocols providing a comprehensive and quantitative evaluation of postural responses in different stability conditions. We tested ten people with PD and ten controls on a robotic platform capable to provide different mechanical interactions and to measure the center of pressure displacement, while trunk acceleration was recorded with a sensor placed on the sternum. We evaluated performance while maintaining upright posture in unperturbed, perturbed, and unstable conditions. The latter was tested while standing and sitting. We measured whether the proposed exercises and metrics could highlight differences in postural control. Participants with PD had worse performance metrics when standing under unperturbed or unstable conditions, and when sitting on the unstable platform. PD subjects in response to a forward perturbation showed bigger trunk oscillations coupled with a sharper increase of the CoP backward displacement. These responses could be due to higher stiffness of lower limb which leads to postural instability. The exercises and the proposed metrics highlighted differences in postural control, hence they can be used in clinical environment for the assessment and progression of postural impairments.

Keywords: Exoskeletons, Wearable robotic systems, Body-machine interfaces
Abstract: In this paper, we present a hybrid exoskeletal-soft glove for the application of on-axis angle sensors that can be placed close to the center of rotation of the digit joints. 3D printed exoskeletal digit segments that run medially on most digits connect to low friction bearings. Exoskeletal segments and bearings provide rigid fixation points for a variety of traditional angle sensors, while a combination of textile and rigid structure fixate exoskeletal digits to the digits and hand. Exoskeletal digits are designed modularly so that only required digits are used and to reduce difficulty in donning and doffing. On-axis measurement may prove useful in control or assessment tasks in rehabilitation. The articulation of the digits while wearing the glove is demonstrated, albeit without sensors, showing little restriction at an early stage of the design process. Exoskeletal metacarpophalangeal joints of the 3rd and 4th digits require more work as the flexion/extension joint axis is inaccessible and moves when the digits are articulated. The proposed device must be customized for an individual and will facilitate an alternative approach to existing hand posture monitoring techniques.

Keywords: Integrated diagnostic and therapeutic systems, New technologies and methodologies in human movement analysis, New technologies and methodologies in biomechanics
Abstract: This paper analyses the time-window size required to achieve the highest accuracy of the convolutional neural network (CNN) in classifying periodic upper limb rehabilitation. To classify real-time motions by using CNN-based human activity recognition (HAR), data must be segmented using a time window. In particular, for the repetitive rehabilitation tasks, the relationship between the period of the repetitive tasks and optimal size of the time window must be analyzed. In this study, we constructed a data-collection system composed of a smartwatch and smartphone. Five upper limb rehabilitation motions were measured for various periods to classify the rehabilitation motions for a particular time-window size. 5-fold cross-validation technique was used to compare the performance. The results showed that the size of the time-window that maximizes the performance of CNN-based HAR is affected by the size and period of the sample used.

Keywords: Exoskeletons
Abstract: This paper proposes a robotic exoskeleton chair, named ChairX, for providing sitting assistance for the industrial workers who need to carry out tasks at different crouched postures repetitively. It can act as a customizable chair to support bodyweight for relieving the lower extremity and provide freedom for ambulation when moving between workstations. In comparison to the predecessors, the ChairX is designed to assist the user for assuming crouched positions with forward- as well as backward-inclined leg angles. Moreover, it is flexible to provide sitting assistance at different heights to ensure ergonomics at work. The ChairX includes a knee-centered locking mechanism on the lateral side and an active linkage mechanism on the posterior of the leg to support the weight of the user at various seated positions. A mathematical model was formulated to optimize the system parameters and a prototype was built to carry out the physical tests. The results revealed that ChairX can maintain stability and reduce the musculoskeletal strains effectively, thus has the potential to improve the quality of work

Keywords: Exoskeletons, Control strategies in rehabilitation robotics, Robotic orthoses - design and development
Abstract: This paper investigates sensorimotor adaptation strategies of sagittal postural control in healthy subjects under kinematic constraints. A passive exoskeleton named CAPTUR, with locked ankle joints and legs motion restrained to the sagittal plane is used to restrict and measure participant's movements. The aim is to assess the role of the orientation of the shank and the trunk segments in maintaining the body center of mass above its support base, while the ankle strategy is inhibited. Five young healthy participants were asked to keep standing, while their balance was challenged by five experimental conditions. Participants mainly regulated quiet standing balance by flexing/extending the knees, in order to affect the shank and feet angles, and move the contact patch along the sagittal axis. In this case, the orientation of the trunk segment changes synchronously with the shank angle to keep an upright posture. Responses to more dramatic excursions of the center of pressure are ensured by changing the trunk tilt angle in opposition of phase with the shank angle. These observations could be used to implement a bioinspired balance controller for such constrained lower-limb exoskeletons.

Keywords: Exoskeletons, Robot-aided mobility, Control strategies in rehabilitation robotics
Abstract: This paper presents a framework to address three dimensional (3-D) dynamic walking for a bipedal exoskeleton with underactuated legs. To achieve this goal, the framework is constructed via a trajectory generator and an optimized inverse kinematics algorithm that can cope with underactuation. In order to feasibly attain task velocities with underactuated legs, the inverse kinematics algorithm makes use of a task prioritization method via the exploitation of null space. In doing so, the tasks with lower priority, e.g., swing foot orientation, are attained as much as possible without disrupting the higher priority tasks, such as, CoM trajectory. Meanwhile, the trajectory generator utilizes the ZMP concept analytically and ensures the acceleration continuity throughout the whole walking period, regardless of the contact and phase changes. The proposed method is verified via a lumped human-bipedal exoskeleton model that is developed and simulated in MSC.ADAMS simulation environment. As the result, we obtained feasible and dynamically balanced 3-D walking motion, in which no oblique foot landing or exaggerated torso orientation variations were observed, despite the underactuated nature of the robot legs.

Keywords: Exoskeletons, Design and development in rehabilitation robotics
Abstract: In this paper, we present our research study concerning the design and development of an exoskeleton that aims to provide 3D walking support with the minimum number of actuators. Following a prior simulation study, the joint configuration was primarily determined. In order for the exoskeleton to possess advanced characteristics, the following design criteria were investigated: i) all the actuators (hip/knee/ankle) were deployed around the waist area to decrease leg weight and improve wearability, ii) custom-built series elastic actuators were used to power system for high fidelity torque-controllability, iii) 3D walking support is potentially enabled with reduced power requirements. As a result, we built the first actual prototype to experimentally verify the aforementioned design specifications. Furthermore, the preliminary torque control experiments indicated the viability of torque control.

Keywords: Exoskeletons, Control strategies in rehabilitation robotics, Human-machine interfaces and robotic applications
Abstract: In physical rehabilitation, exoskeleton assistive devices aim to restore lost motor functions of a patient suffering from neuromuscular or musculoskeletal disorders. These assistive devices are classified as operating in one of two modes: (1) passive mode, in which the exoskeleton passively moves its joints through the full range (or a subset) of the patient's motion during engagement, or (2) assist-as-needed (AAN) mode, in which the exoskeleton provides assistance to the joints of the patient, either by initiating the movements or assisting the patient's movements to complete the task at hand. Achieving high physical human-robot interaction (pHRI) transparency is an open problem for multiple degrees-of-freedom (DOFs) redundant exoskeletons. Using the EXO-UL8 exoskeleton, this study compares two multi-joint admittance control schemes (hyper parameter- based, and Kalman Filter-based) with comfort optimization to improve human-exoskeleton transparency. The control schemes were tested by three healthy subjects who completed reaching tasks while assisted by the exoskeleton. Kinematic information in both joint and task space, as well as force- and torque-based power exchange between the human arm and exoskeleton, are collected and analyzed. The results show that the preliminary Kalman Filter-based control scheme matches the performance of the existing hyper parameter-based scheme, highlighting the potential of the Kalman Filter-based approach for additional performance.

Keywords: Design and development in rehabilitation robotics, Assistive robotics, Exoskeletons
Abstract: In this paper, we present a prototype of an innovative portable shoulder exoskeleton for human assistance and augmentation. The device provides torques to flexion/extension movements of the shoulder, compensating for gravitational forces, and is passively compliant along the remaining degrees of freedom letting the shoulder moving along them. The novelty of our system is a flexible link, made of a hyper-redundant passive structure, that avoids joint misalignment by adapting to the complex movements of the humerus head, similarly to a soft component. The flexible link is compliant to rotations around one axis but rigid around the other two axes, allowing transmission of flexion/extension torque but kinematically transparent along the remaining degrees of freedom. The device is light weight and allows to cover around the 82% of the shoulder flexion/extension range of motion. The exoskeleton was tested on a cohort of 5 healthy subjects, monitoring shoulder kinematics, interaction forces and acquiring the electromyography of three major muscles contributing to shoulder flexion. During both static postures and dynamic movements, assistance from the exoskeleton resulted in a significant reduction of muscular effort in the anterior (-32.2% in static, -25.3% in dynamic) and medial deltoid (-56.9% in static, -49.6% in dynamic) and an average reduction of the biceps brachii.

Keywords: Exoskeletons, Assistive robotics, Control strategies in rehabilitation robotics
Abstract: Industrial active exoskeletons have recently achieved considerable interest, due to their intrinsic versatility compared to passive devices. To achieve this versatility, an important open challenge is the design of appropriate control strategies to automatically modulate the physical assistance according to the activity the user is performing. This work focuses on active back-support exoskeletons. To improve the assistance provided in dynamic situations with respect to state-of-the-art methods, a new strategy making use of the angular acceleration of the user’s trunk is presented. The feasibility and effectiveness of the proposed strategy were tested experimentally on a prototype in a load handling task. The main advantages in terms of assistive torque profiles emerge during the transition phases of the movement (i.e. beginning and end of lowering and lifting) indicating an appropriate adaptation to the dynamics of the execution. In this preliminary evaluation, the data on peak muscular activity at the spine show promising trends, encouraging further developments and a more detailed evaluation.

Keywords: Integrated diagnostic and therapeutic systems, Human-machine interfaces and robotic applications
Abstract: Currently, driver rehabilitation involves use of fixed-base simulators. Such simulators are used infrequently and with little success. We hypothesize that the absence of motion feedback may be limiting the therapeutic effectiveness of driving simulation. During real, motor vehicle driving, the driver receives motion feedback that provides rich and real-time information about acceleration, deceleration and turning of the vehicle. Thus, motion feedback may be a key missing component that could dramatically increase the clinical pragmatism of simulator-based driver rehabilitation. In this pilot study, six young adult drivers participated in simulated driving tasks with or without motion feedback. Participants who received motion feedback completed faster laps on a racetrack and committed fewer driving infractions on a highway. They reported being more motivated and aware of the pressure of high speed driving. Particularly, they experienced substantially fewer symptoms of simulator sickness, a primary impediment to widespread use of driving simulators for driver rehabilitation. These preliminary finding motivate a full investigation of the impacts of motion feedback during simulated driving, and of the efficacy of lower cost, two degree of freedom driving simulators for clinical use.

Keywords: Clinical evaluation in robot-aided rehabilitation, Integrated diagnostic and therapeutic systems, Design and development in rehabilitation robotics
Abstract: Harmony is a bimanual upper-limb exoskeleton designed for post-stroke rehabilitation. It moves the subject’s shoulders and arms through their entire ranges of motion while maintaining natural coordination, is capable of force/torque control of each joint, and is equipped with sensors to measure motions and interaction forces. With these capabilities Harmony has the potential to assess motor function and create individualized therapy regimens. As a first step, five stroke survivors underwent rehabilitation sessions practicing multi-joint movements with the device. Each participant performed a total of 1130 motions over seven hours of therapy with no adverse effects reported by participants or the attending therapist, supporting the suitability of Harmony for use in a clinical setting. Donning and doffing time averaged 3.5 minutes and decreased with therapist experience. Reported levels of stress, anxiety, and pain indicate that the Harmony safely assisted in the completion of the trained movements and has great potential to motivate and engage patients. We developed a novel methodology for assessing coordination capability and results from the study indicate that Harmony can enable therapists to identify neuromuscular weakness and maladaptive coordination patterns and develop targeted interventions to address these aspects of upper-limb function. The results suggest Harmony’s feasibility and show promising improvements, motivating future study to gain statistical support.

Keywords: Integrated diagnostic and therapeutic systems, Clinical evaluation in robot-aided rehabilitation, Human-machine interfaces and robotic applications
Abstract: The concept of augmenting error in interactive reaching training has shown promise, but the possibility of doing this robot-free, with only visual feedback, has not been tested. Here we present very early results from a visual distortion environment that shifts the subject’s cursor in the direction of instantaneous error as if it is being pushed by a robot. This clinical test asked chronic stroke survivors to visit the laboratory three times a week for three weeks as they practiced a bimanual virtual reality task for approximately one hour. Results show that both treatment and control patients improved from the practice (Fugyl Meyer average increase of 4.2), and a slight advantage is seen at this point in the treatment group. These vision-only results may prove compelling because removing the robot reduces expenses, intimidation, complexity, confounding effects, and failure modes.

Keywords: Clinical evaluation in robot-aided rehabilitation, From lab to market - Usability evaluation, Biomechanics and robotics in physical rehabilitation
Abstract: Interpersonal rehabilitation games, which allow patients to compete or cooperate with other patients or unimpaired loved ones, have demonstrated promising short-term results, but have not yet been tested in longer-term studies. This paper thus presents a preliminary 9-session evaluation of interpersonal rehabilitation games for post-stroke arm exercise. Two pairs of stroke survivors were provided with a system that included one competitive and one cooperative rehabilitation game, and exercised with it for 9 sessions in addition to their conventional therapy. They were able to choose the game they wanted to play in each session, and had to exercise for at least 10 minutes per session. Both pairs completed the protocol without any issues, reporting high levels of motivation and consistent levels of exercise intensity (measured using inertial sensors) across the sessions. Furthermore, the maximum difficulty levels reached in the cooperative game increased over time, and improvements of 1-8 points were observed on the Box and Block test. These results indicate that 2 different interpersonal games are sufficient to promote high levels of motivation and exercise intensity for 9 sessions performed over a 3-week period. As the next step, our system will be expanded with additional competitive, cooperative and single-player games, then tested in full clinical trials in both clinical and home environments.

Keywords: Clinical evaluation in robot-aided rehabilitation, New technologies and methodologies in human movement analysis, Biomechanics and robotics in physical rehabilitation
Abstract: This study utilized a 3-degree of freedom robotic device (Wristbot) to examine wrist proprioception and eye-hand coordination in a cross-sectional sample of sixty-three young adults (19-29 years), 20 older young adults (30-49), and 17 older adults (50 years and older). Results indicated differences in the emergence of age-related declines in sensorimotor functioning depending on the tested motor skill component. While young adults exhibited smaller matching error and lower variability compared to older young adults and older adults on the proprioception task, we observed lower times-on-target and higher Linearity indices for participants older than 50 years of age compared to both young adults and older young adults. The present results provide necessary quantitative information on sensorimotor function in adulthood, and have implications for the early diagnosis and effective management of sensorimotor dysfunction in clinical settings using a commercially available robotic device.

Keywords: Integrated diagnostic and therapeutic systems, Neural processes in rehabilitation, Clinical evaluation in robot-aided rehabilitation
Abstract: Proprioceptive deficits are common among stroke survivors and are associated with slower motor recovery, poorer upper limb motor function, and decreased self-care ability. Somatosensory feedback augmenting proprioception should enhance motor control after stroke, but available evidence is inconclusive. This study evaluated the effects of a robot-aided somatosensory-focused training on proprioceptive acuity and motor performance in individuals with chronic stroke. Twelve stroke survivors completed two training sessions on two consecutive days. During training, participants used a haptic robotic wrist exoskeleton and made continuous, goal-directed wrist ab/adduction movements to a visual target while receiving vibro-tactile feedback. Proprioceptive acuity and active movement errors were assessed before, immediately after, and two days after intervention. Results showed significantly improved proprioceptive acuity at posttest and retention. Motor accuracy measures showed improvements, however these were not statistically significant. This study demonstrates feasibility of robot-aided somatosensory training in chronic stroke survivors.

Keywords: Robotic prostheses - neural interfaces, Control strategies in rehabilitation robotics, Human-machine interfaces and robotic applications
Abstract: Non-negative Matrix Factorization (NMF) has been effective in extracting commands from surface electromyography (EMG) for the control of upper-limb prostheses. This approach enables Simultaneous and Proportional Control (SPC) over multiple degrees-of-freedom (DoFs) in a minimally supervised way. Here, like with other myoelectric approaches, robustness remains essential for the clinical adoption, with device donning/doffing being a known cause of performance degradation. Previous research has demonstrated that NMF-based myocontrollers, trained on just single-DoF activations, permit a certain degree of user adaptation to a range of disturbances. In this study, we compare this traditional NMF controller with its sparsity constrained variation that allows initialization using both single and combined-DoF activations (NMF-C). The evaluation was done on 12 able-bodied participants through a set of online target-reaching tests. Subjects were fitted with an 8-channel bipolar EMG setup, which was shifted by 1cm in both transversal directions throughout the experiments without system retraining. In the baseline condition, NMF performed somewhat better than NMF-C, but it did suffer more following the electrode repositioning, making the two perform on pair. With no significant difference present across the conditions, results suggest that there is no immediate advantage from the naïve inclusion of more comprehensive training sets to the classic synergy-inspired implementation of SPC.

Keywords: Robotic prostheses - neural interfaces, Control strategies in rehabilitation robotics, New technologies and methodologies in human movement analysis
Abstract: Multichannel electromyography (EMG) can be used to decode the intended motor command, based on distributed muscle activation patterns. In this regard, the high density EMG (HD-EMG) approach allows for enhancement of the spatiotemporal resolution for motor intention detection. Despite the advantages of relying on several EMG channels, the challenge of HD electrode systems is the changing electrode-skin contact impedance, which affects a number of electrodes over the time of data acquisition. This can result in low-quality EMG recordings with an artifact pattern distributed over the electrode grid. To address this issue, we propose a novel online approach for adaptive information extraction and enhancement for automatic artifact detection and attenuation in HD-EMG-based myocontrol of prosthetic devices. The method is based on an adaptive weighting scheme that modifies the contribution of each HD-EMG channel considering the spectral information content. The technique (named IE-HD-EMG) was tested as an online pre-conditioning step for a 4-finger activation classification problem. It is shown that the IE-HD-EMG technique led to a superior performance in finger activation recognition (79.25% accuracy, 89% sensitivity, 89.15% specificity) in comparison to the conventional HD-EMG recording under the same conditions (56.25% accuracy, 61.3% sensitivity, 67% specspecificity). Therefore, the proposed technique carries the potential to expand the clinical viability of HD-EMG systems.

Keywords: Control strategies in rehabilitation robotics, Exoskeletons
Abstract: The nominal gait of each individual is unique and varies with the walking speed of the person. This poses a difficult problem for powered rehabilitative orthoses since control strategies often require a reference trajectory and give little control to the patient. This paper describes a simple control approach which applies torque resistive to joint movement that is unnatural for healthy individuals in the hip and knee joints during the swing phase of gait. The controller uses a configuration-dependent orthonormal basis to represent vectors in terms of components which are tangent and normal to healthy gait patterns for a continuum of gait speeds. The controller damps motion in the normal direction, thereby resisting movement which is unnatural for healthy individuals. With this control law, subjects are not restricted to a particular reference trajectory and have a large degree of volition over spatiotemporal gait parameters (e.g., stride length, swing time, and cadence). Experiments are conducted to check the feasibility of the control law in a provisional powered pediatric lower-limb orthosis. The gait guidance controller is used in conjunction with a human controller representing an individual with gait impairment. The main results compare gait shape quality when the gait guidance controller is enabled versus disabled, and show how the gait guidance controller is able to reshape gait to more closely resemble that of a healthy individual for various cadences.

Keywords: Robotic prostheses - design and development, Robotic prostheses - modeling and simulation
Abstract: This paper presents a compliant, underactuated finger for the development of anthropomorphic robotic and prosthetic hands. The finger achieves both flexion/extension and adduction/abduction on the metacarpophalangeal joint, by using two actuators. The design employs moment arm pulleys to drive the tendon laterally and amplify the abduction motion, while also maintaining the flexion motion. Particular emphasis has been given to the analysis of the mechanism. The proposed finger has been fabricated with the hybrid deposition manufacturing technique and the actuation mechanism's efficiency has been validated with experiments that include the computation of the reachable workspace, the assessment of the exerted forces at the fingertip, the demonstration of the feasible motions, and the presentation of the grasping and manipulation capabilities. The proposed mechanism facilitates the collaboration of the two actuators to increase the exerted finger forces. Moreover, the extended workspace allows the execution of dexterous manipulation tasks.

Keywords: Control strategies in rehabilitation robotics, Brain-machine interfaces, Technologies for neurodevelopmental disorders
Abstract: For individuals with severe motor deficiencies, controlling external devices such as robotic arms or wheelchairs can be challenging, as many devices require some degree of motor control to be operated, e.g. when controlled using a joystick. A brain-computer interface (BCI) relies only on signals from the brain and may be used as a controller instead of muscles. Motor imagery (MI) has been used in many studies as a control signal for BCIs. However, MI may not be suitable for all control purposes, and several people cannot obtain BCI control with MI. In this study, the aim was to investigate the feasibility of decoding covert speech from single-trial EEG and compare and combine it with MI. In seven healthy subjects, EEG was recorded with twenty-five channels during six different actions: Speaking three words (both covert and overt speech), two arm movements (both motor imagery and execution), and one idle class. Temporal and spectral features were derived from the epochs and classified with a random forest classifier. The average classification accuracy was 67±9 % and 75±7 % for covert and overt speech, respectively; this was 5-10 % lower than the movement classification. The performance of the combined movement-speech decoder was 61±9 % and 67±7 % (covert and overt), but it is possible to have more classes available for control. The possibility of using covert speech for controlling a BCI was outlined; this is a step towards a multimodal BCI system for improved usability.

Keywords: Control strategies in rehabilitation robotics, Wearable robotic systems, Biomechanics and robotics in physical rehabilitation
Abstract: We present a novel control method for an omnidirectional robotic platform for gait training. This mobile platform or ``walker'' provides trunk support and allows unrestricted motion of the pelvis simultaneously. In addition to helping the user maintain balance and preventing falls, the walker combines two types of therapeutic intervention: forward propulsion of the trunk and partial body weight support (BWS). The core of the walker's control is an admittance controller that maximizes the platform's horizontal mobility by optimizing the virtual mass of the admittance model. Said mass represents the best tradeoff between a low-frequency oscillation mode that becomes more damped as the virtual mass decreases, and a high-frequency mode that becomes less damped simultaneously and hence could destabilize the system. Forward propulsion of the trunk is aided by a horizontal force that is modulated with the patient's gait speed and turning rate to ensure easy adaptation. BWS is provided by a second, independent admittance controller that generates a spring-like upward force. In an initial study, a stroke patient was able to walk stably in the platform, as evidenced by the absence of oscillations associated with an excessively low virtual mass. A progressive increase in the patient's self-selected speed, along with greater uniformity in the instantaneous velocity, suggest that forward propulsion was effective in compensating the patient’s own propulsion deficit.

Keywords: Socially interactive robotics - design and development, Biomechanics and robotics in physical rehabilitation, Assistive robotics
Abstract: A successful rehabilitation after surgery in hip endoprosthetics comprises self-training of the lessons taught by physiotherapists. While doing this, immediate feedback to the patient about deviations from physiological gait patterns during training is important. Such immediate feedback also concerns the correct usage of forearm crutches in three-point gait. In the project ROGER, a mobile Socially Assistive Robot (SAR) to support patients after surgery in hip endoprosthetics is going to be developed. The current implementation status of the robotic application developed for the use in a real-world scenario is presented below.

Keywords: Control strategies in rehabilitation robotics, Design and development in rehabilitation robotics, Robotic orthoses - design and development
Abstract: In order to provide an effective system for rehabilitation of walking, a new rotational orthosis for walking with arm swing, called ROWAS II, was developed. This study focused on development and implementation of admittance control of the ankle mechanism in the ROWAS II system for promoting active training. Firstly, the mechanical structure of the ankle mechanism is briefly introduced. Then the algorithms of the closed-loop position control and the admittance control for the ankle mechanism are described in detail. Four able-bodied participants were recruited to use the ankle mechanism running in passive and active modes. The experimental results showed that the ankle mechanism well tracked the target trajectory in passive mode. In active mode, the participants interacted with the ankle mechanism, and adjusted their ankle movement based on their active force. The ankle mechanism has the technical potential to meet the requirements of passive and active training in the ankle movement for patients in different post-stroke stages.

Keywords: Control strategies in rehabilitation robotics, New technologies and methodologies in human movement analysis, Wearable robotic systems
Abstract: In robotic rehabilitation, knowledge of human joint torques is very important to provide reliable data for clinical assessment and to provide feedback information about the user in order to design safe robotic control strategies. Nevertheless, their measurement can be complex and requires a high-cost implementation. Estimation approaches based on disturbance observers have been well studied for human joint torque estimation in robotic rehabilitation systems, most of them, for upper-limb devices. This paper represents our initial effort toward applying disturbance observer techniques for estimation of patient torque for lower-limb robotic rehabilitation. Three disturbance observer approaches for torque estimation are evaluated on a test scenario consisting of a robotic wearable device for ankle rehabilitation attached to a physical mock-up that replicates the ankle movement in the sagittal plane. The results obtained demonstrate the feasibility of the proposed methods and encourage us to test them with voluntary users.

Keywords: Control strategies in rehabilitation robotics, Biomechanics and robotics in physical rehabilitation, Robot-aided mobility
Abstract: In EU-funded BALANCE project, developing a stability index which can be employed to estimate actual state of balance of both healthy and neurologically impaired humans’ walking in exoskeleton was one of scientific tasks. In the task, Centroidal Momentum (CM), referring to linear and angular momenta at Center of Mass (CoM), has raised as a potential index for such purpose. While our past studies have presented analysis results of CM in offline and online (real time) manners for walking of healthy human and stroke patients, in this study, we present real time computation of CM in exoskeleton-supported walking, specifically with healthy subjects. Experimental setup consists of LOPES II, a treadmill-based robotic gait training exoskeleton for lower limbs rehabilitation developed by Twente University, and commercially available IMUs (Inertial Measurement Units)-based full body motion capture suits from Xsens. CM was computed and demonstrated in two walking conditions: unperturbed walking and walking with unexpected pelvic perturbations in lateral direction. While electromagnetic fields (EMF) from LOPES II exoskeleton affected signals of IMUs in the motion capture suit, the results show the potential applicability of the CM as a sort of stability index for human walking in the exoskeleton.

Keywords: Control strategies in rehabilitation robotics, Human-machine interfaces and robotic applications
Abstract: Lower limb amputations impair normal locomotion. This calls for the use of prosthetic devices to restore the lost or disabled functionality. Most of the commercially available prostheses offer only passive assistance with limited capacity. On the other hand, active prostheses may better restore movement, by supporting missing muscle function with additional motor power. The control algorithms of such embedded motors must understand the users locomotive intention to produce the required locomotion similar to that of an able-bodied individual. For individuals with transtibial amputation, the control algorithm should produce the desired locomotion by controlling an active ankle joint to generate appropriate ankle angle and ankle moment. In this paper, a strategy is proposed for the continuous estimation of ankle angle and ankle moment during walking using a support vector regression approach. Experimentally obtained hip and knee joint motion data were provided as the inputs to the support vector regression model. It is shown that, for level ground walking at self-selected speed, the proposed method could predict the ankle angle and moment with high accuracy (mean R² value of 0.98 for ankle angle and 0.97 for ankle moment).

Keywords: Robotic prostheses - modeling and simulation, Robotic prostheses - design and development
Abstract: Predictive simulation of gait is a promising tool for robotic lower limb prosthesis design, but has been limited in its application to models of existing design types. We propose a modeling approach to find optimal prosthesis dynamics in gait simulations without constraining the prosthesis to follow kinematics allowed by a specific joint mechanism. To accomplish this, we render a transtibial prosthetic device as the composition of its resultant forces and moments as they act upon the prosthetic foot and socket and allow 3 degree-of-freedom planar motion. The model is implemented into a human musculoskeletal model and used to solve dynamic optimizations of muscle and prosthesis controls to minimize muscle effort and loading on the residual limb during walking. The emphasis on muscle effort vs. limb loading is varied in the minimization objective and the resulting optimal prosthesis dynamics are compared. We found that muscle effort and socket loading measures were reduced for our prosthesis model compared to a revolute joint prosthesis model. We interpret large displacements in the linear axes to transfer energy to the plantarflexion action before toe-off and reduce loading at the socket-limb interface. Our results suggest this approach could assist in the design of non-biomimetic prostheses but requires experimental validation to assess our modeling assumptions, as well as progress toward increased fidelity of predictive simulation approaches more generally.

Keywords: Robotic prostheses - design and development
Abstract: Design of rehabilitation and physical assistance robots that work safely and efficiently despite uncertain operational conditions remains an important challenge. Current methods for the design of energy efficient series elastic actuators use an optimization formulation that typically assumes known operational requirements. This approach could lead to actuators that cannot satisfy elongation, speed, or torque requirements when the operation deviates from nominal conditions. Addressing this gap, we propose a convex optimization formulation to design the stiffness of series elastic actuators to minimize energy consumption and satisfy actuator constraints despite uncertainty due to manufacturing of the spring, unmodeled dynamics, efficiency of the transmission, and the kinematics and kinetics of the load. To achieve convexity, we write energy consumption as a scalar convex-quadratic function of compliance. As actuator constraints, we consider peak motor torque, peak motor velocity, limitations due to the speed-torque relationship of DC motors, and peak elongation of the spring. We apply our formulation to the robust design of a series elastic actuator for a powered prosthetic ankle. Our simulation results indicate that a small trade-off between energy efficiency and robustness is justified to design actuators that can operate with uncertainty.

Keywords: Socially interactive robotics - design and development, Design and development in rehabilitation robotics, Socially interactive robotics - humanoids
Abstract: We introduce Lil'Flo, an affordable robot for pediatric upper extremity rehabilitation. We present the design and fabrication methodology of the head and face of the robot, the central design element for emotional expression. Through a guided interview with 10 subjects, a number of faces which have a clear sentiment associated with them are identified. The data suggest that a digital face, characterized by eyes and a mouth, can express sadness, happiness, surprise, and mischievousness well, but that finer emotions, e.g., differentiating between happy and very happy can be difficult. The data fail to show that a robot with a dynamic face is viewed more positively than one with a static face. The results of numerical sentiment analysis and open ended questions provide a design direction for our face and a general idea of simple face designs which have a clear sentiment.

Keywords: Control strategies in rehabilitation robotics, Human-machine interfaces and robotic applications
Abstract: One of the main challenges in robotic neurorehabilitation is to understand how robots should physically interact with trainees to optimize motor leaning. There is evidence that motor exploration is crucial to boost motor learning. Furthermore, effectiveness of a robotic training strategy depends on several factors, such as task type and trainee’s skill level. We propose that Model Predictive Controllers (MPC) can satisfy many training/trainee’s needs simultaneously, without restricting trainees to a fixed trajectory. We designed two MPCs to support training of a pendulum task with a delta robot. These MPCs differ from each other in terms of the application point of the intervention force: to the virtual pendulum mass (ballMPC), and the virtual rod holding point (eeMPC). The effect of the MPCs on task performance, physical effort, motivation and sense of agency was evaluated in 14 healthy participants. We found that the location of the applied controller force affects the task performance; ballMPC significantly reduced performance errors and sense of agency during training; eeMPC did not, probably due to low force saturation limits and slow optimization speed of the solver. Participants applied significantly more forces with eeMPC, probably because they reacted against the robotic assistance. Although MPCs look very promising for neurorehabilitation, further steps have to be taken to improve their technical limitations, and their effects on motor learning should be evaluated.

Keywords: Control strategies in rehabilitation robotics, Human-machine interfaces and robotic applications, Assistive robotics
Abstract: Motivation plays a crucial role in motor learning and neurorehabilitation. Participants’ motivation could decline to a point where they may stop training when facing a very difficult task. Conversely, participants may perform well and consider the training boring if the task is too easy. In this paper, we present a combination of a virtual reality environment with different robotic training strategies that modify task functional difficulty to enhance participants’ motivation. We employed a pneumatically driven robotic stepper as a haptic interface. We first evaluated the use of disturbance observers as acceleration controllers to provide high robustness to unmodeled dynamics and unknown disturbances associated with pneumatic control. The task to be learned consisted of steering a recumbent bike to follow a desired path by changing the movement frequency of the dominant leg. The motor task was specially designed to engage implicit learning. A haptic assistance strategy was developed to reduce the task difficulty during practice. In a feasibility study with eight healthy participants, we found that the haptic assistance successfully contributed to improve task performance during training, especially for less skilled participants. Furthermore, we found a negative correlation between participants' motivation and performance error when training with haptic assistance, suggesting that assistance has a great potential to enhance motivation during motor training.

Keywords: Control strategies in rehabilitation robotics, Exoskeletons, Assistive robotics
Abstract: This paper introduces an adaptive integral sliding mode controller for exoskeletons. The controller design is based on the hypothesis that only classical properties are known such as parameters’ bounds, and all other functions are unknown. To ensure the convergence in position, velocity and acceleration for desired trajectories, disturbances are supposed to be bounded. The closed-loop stability of the system in the sense of Lyapunov is demonstrated. The effectiveness of the proposed approach is proved in real time using a 2-DOF upper limb exoskeleton in the rehabilitation context taking into account the security and the safety of the user.

Keywords: Robotic prostheses - modeling and simulation, Robotic prostheses - neural interfaces
Abstract: Although remarkable improvements have been made, the natural control of hand prostheses in everyday life is still challenging. Changes in limb position can considerably affect the robustness of pattern recognition-based myoelectric control systems, even if various strategies were proposed to mitigate this effect. In this paper, we investigate the possibility of selecting a set of training movements that is robust to limb position change, performing a trade-off between training time and accuracy. Four able-bodied subjects were recorded while following a training protocol for myoelectric hand prostheses control. The protocol is composed of 210 combinations of arm positions, forearm orientations, wrist orientations and hand grasps. To the best of our knowledge, it is among the most complete including changes in limb positions. A training reduction paradigm was used to select subsets of training movements from a group of subjects that were tested on the left-out subject's data. The results show that a reduced training set (30 to 50 movements) allows a substantial reduction of the training time while maintaining reasonable performance, and that the trade-off between performance and training time appears to depend on the chosen classifier. Although further improvements can be made, the results show that properly selected training sets can be a viable strategy to reduce the training time while maximizing the performance of the classifier against variations in limb position.

Keywords: Control strategies in rehabilitation robotics, Assistive robotics, Exoskeletons
Abstract: Advanced control strategies that can adjust assistance based volitional effort from the user may be beneficial for deploying exoskeletons for overground gait training in ambulatory populations, such as children with cerebral palsy (CP). In this study, we evaluate the ability to predict biological knee moment during stance phase of walking with an exoskeleton in two children subjects with crouch gait from CP. The predictive model characterized the knee as a rotational spring with the addition of correction factors at knee extensor moment extrema to predict the instantaneous knee moment profile from the knee angle. Our model prediction performance was comparable to previous studies for weight acceptance (WA) and mid-stance (MS) phases in both assisted (Assist) and non-assisted (Zero) modes based on normalized root mean square error (RMSE), demonstrating the feasibility of joint moment estimation during exoskeleton walking. RMSE was highest in late stance phase, likely due to the non-linear knee stiffness exhibited during this phase in one participant. Overall, our results support real-time implementation of the joint moment prediction model for control of exoskeleton knee extension assistance in children with CP.

Keywords: From lab to market - Usability evaluation, From lab to market - Market opportunities and economic impact, Robotic prostheses - design and development
Abstract: In war-affected regions in the world, limb loss is one of the leading injuries. The need for low-cost, low-maintenance prostheses arises. The rapid developments in 3D printing allows us to investigate robotic or prosthetic hand designs that can satisfy those basic requirements. 3D printed prosthetic hands are more affordable and lightweight alternatives for prostheses. In this paper, we investigate the flexibility of different designs of the soft joints of a low-cost 3D printed prosthetic hand with respect to the material type. We designed flexible joints from elastomeric materials instead of plastic joints. This modification can make the current 3D printed prosthesis designs more robust. As a drawback from these flexible joints, the prosthetic hand will not be in a full open palm position in its initial state, as compared to typical designs. We then converted this drawback to a beneficial feature by calculating the angles of the natural pose of the human hands and transfer those angles to the prosthetic hands with flexible joints. This work has implications in the design of 3D printed prosthetic hands that can be deployed for war-wounded refugees or for those in low-resource countries.

Keywords: Control strategies in rehabilitation robotics, Exoskeletons
Abstract: In this paper, we address the problem of assist-as-needed (AAN) control of rehabilitation robots. The objective is to develop a path tracking control scheme with the minimized intervention of the robot to gain active participation of impaired subjects while avoiding large position errors. We achieve these properties by constructing a velocity field encoding the desired path, and by considering a force field around the path. In particular, the proposed controller includes a normal force term to keep the robot position arbitrarily close to the path, and also contains velocity tracking components, which adaptively adjust the contribution of the controller by monitoring the tracking error. As a result, we gain the AAN property with adequate freedom in the timing of movement, which is a key factor in reducing the robot intervention. The performance of the controller is examined on a lower-limb robotic exoskeleton in following the gait pattern.

Keywords: Robotic prostheses - design and development, Control strategies in rehabilitation robotics, Robotic prostheses - modeling and simulation
Abstract: Prosthetic limb controllers employ discrete modes for well-defined scenarios such as stair ascent, stair descent, or ramps. General human locomotion, however, is a continuous motion, fluidly adapting to the environment and not always categorizable into modes. It exhibits strong inter-joint coordination and the movement of a single joint can be largely predicted based on the movement of the rest of the body. We show that using body motion from the intact limbs and trunk, a reference trajectory can be generated for a prosthetic joint for every instant in time.

Previously we demonstrated that a Recurrent Neural Network (RNN) can predict ankle angle trajectory for structured activities. In this study, we apply a similar network to more unstructured activities which are hard to categorize into modes. A wearable motion capture suit was worn by 10 healthy subjects to record full body kinematics during obstacle avoidance, sidestepping, weaving through cones, and backward walking. We used an RNN to predict right ankle kinematics from the other joint kinematics. The model was robust to subject-specific variations such as walking speed and step length. We present the performance for different activities and using different subsets of the sensors. This system demonstrates the potential for generating a reference trajectory for a prosthesis or other rehabilitation robot without explicit featurization of terrains or gait events.

Keywords: Robotic prostheses - design and development, Robotic prostheses - modeling and simulation, Wearable robotic systems
Abstract: A major challenge for upper limb amputees is discomfort due to improper socket fit on the residual limb during daily use of their prosthesis. Our work introduces the implementation of soft robotic actuators into a prosthetic socket. The soft actuators are a type of electrically-powered actuator. The actuator is driven through changes in internal temperature causing actuation due to vapor pressure, which results in high and reliable force outputs. A regression fit was generated to model how the smart polymer's temperature relates to force output, and the model was cross-validated based on training data collected from each actuator. A proportional integral (PI) controller regulated the force exerted by the actuators based off of tactile and temperature feedback. Results showed that a socket system can be integrated with smart polymers and sensors, and demonstrated the ability to control two actuators and reach desired forces from set temperatures.

Keywords: Design and development in rehabilitation robotics, Control strategies in rehabilitation robotics, Human-machine interfaces and robotic applications
Abstract: Several research groups have developed and stud- ied powered ankle exoskeletons to improve energetics of healthy subjects and the mobility of elderly subjects, or to reduce asymmetry in gaits induced by strokes. To achieve optimal effect, the timing of assistive torque has been proved to be of crucial importance. Previous studies estimated the onset timings mostly by extrapolating the time horizon from past gait events observed with sensors. Such methods have inherently limited performance when subjects are not walking at steady frequencies. To overcome such limitation and allow the use of exoskeletons in various scenarios in a daily life, we propose to estimate the gait phase as a continuous variable progressing over a gait cycle, hence allowing immediate response to fre- quency changes rather than iteratively correcting it after each cycle. Our method uses recurrent neural networks to estimate gait phases out of an inertial measurement unit (IMU) every 10 ms. By replacing foot sensors with an IMU we can obtain rich enough information to estimate gait phase continuously as well as avoid physical damage in sensors from ground impacts. Our preliminary tests with 2 healthy subjects showed qualitatively positive outcomes regarding the gait phase estimation and the assistive torque control.

Keywords: Robotic prostheses - design and development, Control strategies in rehabilitation robotics, Wearable robotic systems
Abstract: Upper limb loss is a devastating injury for which current prosthetic replacement inadequately compensates. A lack of wrist movement in prostheses due to mechanical design and control system considerations compels prosthetic users to employ compensatory movements using their upper back and shoulder that can eventually result in strain and overuse injuries. One possible means of easing this control burden is to allow a prosthetic wrist to self-regulate, keeping the terminal device of the prosthesis level relative to the ground when appropriate. This study aims to outline such a wrist control scheme, and evaluate its function in terms of compensatory movements, objective system performance, and subjective perception of system performance based on user feedback. Twelve able-bodied participants were recruited to control a body-mounted robotic arm using three different control schemes: fixed-wrist (FW), sequential switching (SS), and automatic levelling (AL). The resulting movement strategies were recorded for two different tasks using 3D motion-capture. SS and AL control schemes induced similar movement strategies and less compensation than FW for horizontal movements, while AL reduced shoulder flexion for vertical movements. However, AL was ranked less intuitive and less reliable than the FW. These results suggest that complex wrist control schemes may be able to eliminate harmful compensations, but that control must be reliable and simple or people will opt for an easier system.

Keywords: Control strategies in rehabilitation robotics, Human-machine interfaces and robotic applications, Assistive robotics
Abstract: Dyadic interaction between humans has gained great research interest in the last years. The effects of factors that influence the interaction, as e.g. roles or skill level matching, are still not well understood. In this paper, we further investigated the effect of skill level matching between partners on learning of a visuo-motor task. Understanding the effect of skill level matching is crucial for applications in collaborative rehabilitation. Fifteen healthy participants were asked to trace a path while being subjected to a visual-motor rotation (Novice). The Novices were paired with a partner, forming one of the three Dyad Types: a) haptic connection to another Novice, b) haptic connection to an Expert (no visual-motor rotation), or c) no haptic. The intervention consisted of a Training phase, in which the Novices were learning the task in the respective Dyad Type, followed by a Test phase in which the learning was assessed (haptic connection removed, if any). Results indicate that learning the task without haptic connection to a partner was most beneficial. Among the dyads with haptic connection to a partner, learning was better (in terms of duration and efficiency) when connected to a similarly skilled partner than to an Expert. However, interestingly during the training phase the dyads comprising an Expert clearly outperformed the dyads with matched skill levels. The results confirm previous findings in literature and can be explained by current motor-learning theories.

Keywords: Control strategies in rehabilitation robotics, Human-machine interfaces and robotic applications, New technologies and methodologies in human movement analysis
Abstract: Prosthetics need to incorporate the users sense of proprioception into the control paradigm to provide intuitive control, and reduce training times and prosthetic rejection rates. In the absence of functional tasks with a prosthetic, virtual cursor control tasks have been used to train users to control multiple degrees of freedom. In this study, A pro- portional position signal was derived from the cross-sectional ultrasound images of the users forearm. We designed a virtual cursor control task with one degree of freedom to measure the users ability to repeatably and accurately acquire different levels of muscle flexion, using only their sense of proprioception. The experiment involved a target acquisition task, where the cursors height corresponded to the extent of muscle flexion. Users were asked to acquire targets on a screen. Visual feedback was disabled at certain times during the experiment, to isolate the effect of proprioception. We found that as visual feedback was taken away from the subjects, position error increased but their stability error did not change significantly. This indicates that users are not perfect at using only their proprioceptive sense to reacquire a level of muscle flexion, in the absence of haptic or visual feedback. However, they are adept at retaining an acquired flexion level without drifting. These results could help to quantify the role of proprioception in target acquisition tasks, in the absence of haptic or visual feedback.

Keywords: Robotic prostheses - modeling and simulation, Human-machine interfaces and robotic applications
Abstract: Humans consistently coordinate their joints to perform a variety of tasks. Computational motor control theory explains these stereotypical behaviors using optimal control. Several cost functions have been used to explain specific movements, which suggests that the brain optimizes for a combination of costs and just varies their relative weights to perform different tasks. In the case of tunable human-machine interfaces, we hypothesize that the human-machine interface should be optimized according to the costs that the user cares about when making the movement. Here, we study how the relative weights of individual cost functions in a composite movement cost affect the optimal control signal produced by the user and the mapping between the user’s control signals and the machine’s output, using prosthesis control as a specific example. This framework was tested by building a hierarchical optimization model that independently optimized for the user control signal and the virtual dynamics of the device. Our results indicate the feasibility of the approach and show the potential for using such a model in prosthesis tuning. This method could be used to allow clinicians and users to tune their prosthesis based on costs they actually care about; and allow the platforms to be customized for the unique needs of every patient.

Keywords: Control strategies in rehabilitation robotics, Biomechanics and robotics in physical rehabilitation, Human-machine interfaces and robotic applications
Abstract: Falling has become a key factor that affects the quality of life of the elderly. Currently, the use of a few rehabilitation robots can contribute to the restoration of balance. In this paper, a walker-based rehabilitation robot with a gait-phase-dependent control algorithm is proposed to promote dynamic balance in the elderly. It has unique characteristics in that the level of the walker to resist the propulsion force exerted by a user can vary depending on the gait-phase that is estimated using the interaction force between the robot and the user. The robot efficiently improves the muscle power of various muscle groups of the user. Experiments with three young subjects were conducted to validate the effectiveness of the walker with the gait-phase-dependent control algorithm.

Keywords: Control strategies in rehabilitation robotics, Exoskeletons, Wearable robotic systems
Abstract: This paper presents a novel method to perform automatic standing balance in a full mobilization exoskeleton. It exploits the locked ankle and the curved foot sole of the exoskeleton TWIICE. The idea is to use the knees to roll the sole and change the position of the contact point with the floor, which allows to stabilize without an actuated ankle. This controller is biologically inspired, originating from a previous experiment with the passive exoskeleton CAPTUR and healthy subjects. Then, a simulation model was built to test the observed balance strategy. Finally, the controller was implemented on the actual actuated exoskeleton, without a wearer for the time being, to experimentally check the basic operation. The next planned step is to test its actual performance with healthy subjects, then paraplegic patients.

Keywords: Control strategies in rehabilitation robotics, Design and development in rehabilitation robotics, Human-machine interfaces and robotic applications
Abstract: Enhanced neurorehabilitation using robotic and virtual-reality technologies requires a computational framework that can readily assess the time course of motor learning in order to recommend optimal training conditions. Error-feedback plays an important role in the acquisition of motor skills for goal-directed movements by facilitating the learning of internal models. In this study, we investigated changes in movement errors during sparse and intermittent “catch” (no-vision) trials, which served as a “proxy” of the underlying process of internal model formations. We trained 15 healthy subjects to reach for visual targets under eight distinct visuomotor distortions, and we removed visual feedback (no-vision) intermittently. We tested their learning data from no-vision trials against our so-called proxy process models, which assumed linear, affine, and second-order model structures. In order to handle sparse (no-vision) observations, we allowed the proxy process models to either update trial-to-trial, predicting across voids of sparse samples or update sample-to-sample, disregarding the trial gaps. We exhaustively cross-validated our models across subjects and across learning tasks. The results revealed that the second-order model with trial-to-trial update best predicted the proxy process of visuomotor learning.

Keywords: Robotic prostheses - design and development, Human-machine interfaces and robotic applications, Wearable robotic systems
Abstract: This paper presents a novel robotic finger prosthesis for partially amputated patients who have lost a thumb and index finger. The challenging issues were to design i) a three-degree of-freedom (DOF) underactuated mechanism that mimics intact finger movements including motion profiles and self-adaptation for unknown constraints, ii) an attachment socket for everyday life that allows ease of donning and doffing, and comfortable wearability, and iii) a shape to pack the selected components including an actuator, linkages, and sensors into a limited space avoiding motion interference with other intact fingers and wrist. This paper reports our effort to solve the challenging issues. The proposed three-DOF prosthetic finger can generate 4.6N pinch force and 99.4 degrees/sec angular velocity at the MCP joints. For command signals, surface-electromyogram (sEMG) sensors were used. This enables users to operate the fingers with certain configuration and grasping force. The performance of the proposed design was verified through the box-and-block test and bottle opening test with a patient who has a partially amputated hand.

Keywords: Robotic orthoses - design and development, Robotic prostheses - design and development, Exoskeletons
Abstract: Drawing inspiration from autonomous vehicles, using future environment information could improve the control of wearable biomechatronic devices for assisting human locomotion. To the authors knowledge, this research represents the first documented investigation using machine vision and deep convolutional neural networks for environment recognition to support the predictive control of robotic lower-limb prostheses and exoskeletons. One participant was instrumented with a battery-powered, chest-mounted RGB camera system. Approximately 10 hours of video footage were experimentally collected while ambulating throughout unknown outdoor and indoor environments. The sampled images were preprocessed and individually labelled. A deep convolutional neural network was developed and trained to automatically recognize three walking environments: level-ground, incline staircases, and decline staircases. The environment recognition system achieved 94.85% overall image classification accuracy. Extending these preliminary findings, future research should incorporate other environment classes (e.g., incline ramps) and integrate the environment recognition system with electromechanical sensors and/or surface electromyography for automated locomotion mode recognition. The challenges associated with implementing deep learning on wearable biomechatronic devices are discussed.

Keywords: Control strategies in rehabilitation robotics, Biomechanics and robotics in physical rehabilitation, Exoskeletons
Abstract: Robot assisted gait retraining is an increasingly common method for supporting restoration of walking function after neurological injury. Gait speed, an indicator of walking function, is correlated with propulsive force, a measure modulated by the posture of the trailing limb at push-off. With the ultimate goal of improving efficacy of robot assisted gait retraining, we sought to directly target gait propulsion, by exposing subjects to pulses of joint torque applied at the hip and knee joints to modulate push-off posture. In this work, we utilized a robotic exoskeleton to apply pulses of torque to the hip and knee joints, during individual strides, of 16 healthy control subjects, and quantified the effects of this intervention on hip extension and propulsive impulse during and after application of these pulses. We observed significant effects in the outcome measures primarily at the stride of pulse application and generally no after effects in the following strides. Specifically, when pulses were applied at late stance, we observed a significant increase in propulsive impulse when knee and/or hip flexion pulses were applied and a significant increase in hip extension angle when hip extension torque pulses were applied. When pulses were applied at early stance, we observed a significant increase in propulsive impulse associated with hip extension torque.

Keywords: Robotic prostheses - design and development
Abstract: Locomotion is paramount in enabling human beings to effectively respond in space and time to meet different needs. There are 2 million Americans living with an amputation and the majority of those amputations are of the lower limbs. Although current powered prostheses can accommodate walking, and in some cases running, basic functions like hiking or walking on various non-rigid or dynamic terrains are requirements that have yet to be met. This paper focuses on the mechanisms involved during human locomotion, while transitioning from rigid to compliant surfaces such as from pavement to sand, grass or granular media. Utilizing a unique tool, the Variable Stiffness Treadmill (VST), as the platform for human locomotion, rigid to compliant surface transitions are simulated. The analysis of muscular activation during the transition from rigid to compliant surfaces reveals specific anticipatory muscle activation that precedes stepping on the compliant surface. These results are novel and important since the evoked activation changes can be used for altering the powered prosthesis control parameters to adapt to the new surface, and therefore result in significantly increased robustness for smart powered lower limb prostheses.

Keywords: Robotic prostheses - design and development, Robotic prostheses - modeling and simulation, Wearable robotic systems
Abstract: This paper investigates the design of a robotic fabric-based, soft ankle module capable of generating 50% of the human ankle stiffness, in plantarflexion and dorsiflexion for walking. Kinematics, dynamics, and anatomy of the human ankle joint are studied to set the functional requirements of the module. The design of the compliant and lightweight soft ankle module uses fabric-based inflatable actuator arrays for actuation. Models for the human ankle stiffness, as well as a data-driven model of soft ankle module is presented. A high-level stiffness controller utilizing the human ankle and soft ankle model with a low-level pressure controller is implemented. We demonstrate the ability to closely follow the ankle stiffness trajectory using soft ankle module.

Keywords: Robotic prostheses - design and development, Design and development in rehabilitation robotics
Abstract: Current methods for describing and characterizing the mechanical behavior of running-specific prosthetic feet are incomplete, and this has limited our understanding of how design parameters impact athlete performance. Deflections induced by most ground reaction forces consist of vertical, horizontal, and angular components, but previous work has focused only on the vertical component. Furthermore, the deflection depends heavily on the direction of the force, which changes throughout stance phase of running. In this paper, we introduce several methods that can be used to more precisely describe and characterize the mechanics of running-specific prosthetic feet. We use a custom finite element model to simulate these methods, and validate them with a series of tests using a prototype foot in a universal testing machine.

Keywords: Robotic prostheses - neural interfaces, Biomechanics and robotics in physical rehabilitation, Control strategies in rehabilitation robotics
Abstract: In this study we aimed to investigate the potential for antagonistic residual muscles to generate anticipatory and compensatory postural adjustments and their benefit to postural control with proportional myoelectric control of a powered ankle prosthesis. We conducted this investigation using a predictable pendulum drop task with a single transtibial amputee. In two individual testing sessions the participant used his prescribed passive device and a powered device with pneumatic artificial muscles actuated proportionally to the activation of residual Tibialis Anterior (TA) and Lateral Gastrocnemius (GAS) muscles. Results demonstrated the transtibial amputee generated activations from the residual TA significantly earlier in the powered condition (p = 0.007). In the powered condition anticipatory center of pressure excursions were significantly higher (p = 0.017), and peak center of mass excursions were reduced (p = 0.021). Peak medio-lateral center of pressure excursions were also significantly less in the direction of the intact limb for the powered condition (p = 0.003). The results from this pilot study demonstrate the promise for transtibial amputees to generate anticipatory postural adjustments as well as the potential improvement of stability under expected perturbations. This pilot study provides an initial basis for future study using proportional myoelectric control via antagonistic residual muscles for the control of posture under expected perturbations.

Keywords: Control strategies in rehabilitation robotics, Human-machine interfaces and robotic applications, Cognitive robotics in rehabilitation
Abstract: This work presents a multimodal cognitive interaction strategy aiming at walker-assisted rehabilitation therapies, with special focus on post-stroke patients. Such interaction strategy is based on monitoring user's gait and face orientation to command the displacement of the smart walker. Users are able to actively command the steering of the walker by changing their face orientation, while their lower limbs movement affect the walker's linear velocity. The proposed system is validated using a smart walker and the results obtained point to the feasibility of employing such cognitive interaction in rehabilitation therapies.

Keywords: Socially interactive robotics - humanoids, Socially interactive robotics - design and development
Abstract: Socially Assistive Robotics (SAR) has shown to be an important tool to assist patients in physical rehabilitation. SAR is used to provide feedback about patient's state and performance to users and health professionals, therefore, patients are monitored by means of sensor interfaces. In this context, aiming to avoid over-training conditions, one of the most important parameter to monitor is the fatigue level. However, it is usually measured by subjective scales such as Borg scale, thus, there is a need to develop systems that are able to estimate fatigue with greater accuracy. It has been demonstrated that fatigue can be associated to the decreasing performance of the exercise. Hence, this work carried out a study to determinate which temporal and kinematic features are related to the fatigue level during a sit-to-stand test. The procedure consisted of sitting down and standing up from a chair while kinematic data were measured by a Kinect sensor, in order to relate kinematic data and fatigue. Results show that temporal features (time stand-to-stand and time sit-to-stand) and 3 kinematic features (max vertical-velocity of the spin base, max knee-flexo-extension velocity, and max hip-flexo-extension velocity), have a significant correlation with the fatigue level (p < 0.05).

Keywords: Robotic orthoses - design and development, Exoskeletons, Robot-aided mobility
Abstract: This paper presents the mechatronic design and initial validation of a partial-assist knee orthosis for individuals with musculoskeletal disorders, e.g., knee osteoarthritis and lower back pain. This orthosis utilizes a quasi-direct drive actuator with a low-ratio transmission (7:1) to greatly reduce the reflected inertia for high backdrivability. To provide meaningful assistance, a custom Brushless DC (BLDC) motor is designed with encapsulated windings to improve the motor's thermal environment and thus its continuous torque output. The 2.69 kg orthosis is constructed from all custom-made components with a high package factor for lighter weight and a more compact size. The combination of compactness, backdrivability, and torque output enables the orthosis to provide partial assistance without obstructing the natural movement of the user. Several benchtop tests verify the actuator's capabilities, and a human subject experiment demonstrates reduced quadriceps muscle activation when assisted during a repetitive lifting and lowering task.

Keywords: Wearable robotic systems, Robotic orthoses - design and development, Exoskeletons
Abstract: In this paper, we explore the effect of residual hip assistance in one above-knee amputee subject using a novel lightweight powered hip exoskeleton. Differently from a powered prosthesis, a powered hip exoskeleton adds mass proximally. Thus, we expect that the negative effect of the added mass will be lower for a powered hip exoskeleton than a powered ankle and knee prosthesis. Consequently, residual-hip assistance may more easily lead to a net reduction of metabolic effort. To preliminarily assess this hypothesis, we measured the physiological cost index (PCI) while an above-knee subject walked with and without a powered hip exoskeleton. Experimental results show 20.5% reduction of PCI when walking with the powered hip exoskeleton.

Keywords: Robotic orthoses - design and development, New technologies and methodologies in biomechanics, Design and development in rehabilitation robotics
Abstract: Knee osteoarthritis (KOA) is a painful and debilitating condition that is associated with mechanical loading of the knee joint. Numerous conservative treatment strategies have been developed to delay time to total joint replacement. Unloader braces are commonly prescribed for medial uni-compartmental KOA, however their evidence of efficacy is inconclusive and limited by user compliance. Typical commercial braces transfer load from the medial to lateral knee compartment by applying a continuous brace abduction moment (BAM). We propose that brace deficiencies could be addressed with a robotic device that intelligently modulates BAM in real time over the course of a step, day, and year to better protect the knee joint, improve pain relief, and increase comfort. To this end, we developed a robotic unloader knee brace ABLE (active brace for laboratory exploration) to flexibly emulate and explore different active and passive brace behaviors that may be more efficacious than traditional braces. The system is capable of modulating BAM within each step per researcher defined unloading profiles. Frequency response and intra-step trajectory tracking during level-ground walking were evaluated in a single healthy human subject test to verify performance. The system tracked trajectories with a root mean square error of 0.18 to 0.58 Nm for conditions varying in walking speed, 85-115% nominal, and trajectory peak BAM, 2.7 to 8.1 Nm.

Keywords: Robotic orthoses - design and development, Wearable robotic systems, Exoskeletons
Abstract: For patients with lower limb paralysis, wearable robotic systems are becoming increasingly important for regaining mobility. The actuation of these systems is challenging because of the necessity to deliver high power within very limited space. However, not all patients need full support, as many patients have residual muscle function that can be applied for locomotion. This work introduces a microprocessor-controlled leg (hip-knee-ankle-foot) orthosis (mpLeg) with energy recuperation capabilities at the hip joint. The system redistributes motion energy generated by the patient during walking. In stance phase of walking, energy is stored in an elastic element at the hip joint. This energy can be released by computer control later in the gait phase, to support swing phase motion. This work aims at investigating the influence of the elastic element in the orthotic hip joint on a patient’s motion. Experiments conducted with a patient suffering from incomplete paraplegia demonstrated that the motion pattern during walking improved with activated energy recuperation. This observation was made over a wide range of system parameters. The patient used the energy recuperation capabilities of the mpLeg with up to 4.1 J recuperated energy per step, which resulted in a more natural swing phase motion during walking. Therefore energy recuperation at the hip joint is a feasible technology for future supportive devices.

Keywords: Wearable robotic systems, Robot-aided mobility, Clinical evaluation in robot-aided rehabilitation
Abstract: Wearable robots for the legs have been developed for gait rehabilitation training and as assistive devices. Most devices have been rigid exoskeletons designed to substitute the function of users who are completely paralyzed. While effective for this target group, exoskeletons limit their users’ contributions to movements. Soft wearable robots have been suggested as an alternative that allows and requires active contributions from users with residual mobility. In this work, we first tested if the MyoSuit, a lightweight, lower-limb soft wearable robot, affected the walking kinematics of unimpaired users. Secondly, we evaluated the assistance delivered to a patient with a gait impairment. In our first study, 10 unimpaired participants walked on a treadmill at speeds between 0.5 and 1.3 m/s. We found that wearing the MyoSuit in its transparency mode did not affect the participants’ walking kinematics (RMS difference of joint angles <1.6°). Step length and the ratio of stance-to-stride duration were not affected when wearing the MyoSuit. In our case study with one spinal cord injured participant, the MyoSuit supported the participant to increase his 10 MWT walking speed from 0.36 to 0.52 m/s, a substantial clinically meaningful improvement. Our results show that the MyoSuit allows user-driven, kinematically unaltered walking and provides effective assistance. Systems like the MyoSuit are a promising technology to bridge the gap between rigid exoskeletons and unassisted ambulation.

Keywords: Wearable robotic systems, Design and development in rehabilitation robotics
Abstract: Lymphedema is a non-curative chronic swelling caused by impairment of the lymphatic system, affecting up to 250 million patients worldwide. The patients suffer from low quality of life because of discomfort and reduced range of motion due to the swelling. Severe swellings can be immediately mediated with special massaging technique known as the Manual Lymphatic Drainage (MLD). Limitations of MLD involves long travel distances, the cost of regular treatment sessions, and the lack of lymphedema specialists. Since MLD is performed very gently, described as caressing a baby’s head, soft wearable robotics with its inherent compliance and safety is the perfect solution to creating a light and safe wearable lymphedema massaging device. In this paper, origami-inspired soft fabric pneumatic actuator is developed that creates not only normal force, but also shear force which is essential in the performance of MLD. The shear is created by the unfolding of the Z-shaped fold-lines as the actuator is inflated. One Z-folded actuator module of 30 x 60 mm dimension with a single fold of 15 mm fold height creates maximum shear force of about 1.5 N and stroke displacement of about 30 mm when subjected to compression loading of 5 N. The range of forces exerted can be tuned by varying the tension of the compressive clothing covering the actuators, and the stroke displacement can be varied by changing the parameter of the actuator module itself, such as the fold height and the number of the folds.

Keywords: Design and development in rehabilitation robotics, Clinical evaluation in robot-aided rehabilitation, Technologies for neurodegenerative disorders
Abstract: Robot-assisted rehabilitation of hand function is becoming an established approach to complement conventional therapy after stroke, particularly in view of its possible unsupervised use to promote an increase in therapy dose. Given their intensive therapy regime, robots may promote a temporary increase in muscle tone, which is often already altered in patients in the form of spasticity. This poses potential concerns regarding monitoring of the muscle tone conditions throughout therapy, as hand spasticity negatively affects the patients quality of life and recovery. For these reasons, a new exercise requiring limited supervision and including an online assessment of muscle tone has been developed on a robotic device for hand rehabilitation. The exercise has been tested in a pilot study with five non-spastic chronic stroke survivors and five healthy subjects to identify the range of potential physiological muscle tone change during a single exercise session. In both groups, the muscle tone level during hand opening is higher after fast 20mm ramp-and-hold perturbations (150ms) compared to slow (250ms) perturbations, and corresponds to a force change of approximately 4-5N. In the stroke group, the force change increases over exercise time up to 6.3N at the end of the exercise session. This information could be used as a basis to develop strategies to continuously adapt the exercise difficulty and activity level to monitor or control the muscle tone evolution over time.

Keywords: Control strategies in rehabilitation robotics, Orthotics - modeling and simulation, Assistive robotics
Abstract: In literature, much attention has been devoted to the design of control strategies of exoskeletons for assistive purposes. While several control schemes were presented, their performance still has limitations in minimizing muscle effort. According to this principle, we propose a novel approach to solve the problem of generating an assistive torque that minimizes muscle activation under stability guarantees. First, we perform a linear observability and controllability analysis of the human neuromuscular dynamic system. Based on the states that can be regulated with the available measurements and taking advantage of knowledge of the muscle model, we then solve an LQR problem in which a weighted sum of muscle activation and actuation torque is minimized to systematically synthesize a controller for an assistive exoskeleton. We evaluate the performance of the developed controller with a realistic non-linear human neuromusculoskeletal model. Simulation results show better performance in comparison with a well known controller in the literature, in the sense of closed loop system stability and regulation to zero of muscle effort.

Keywords: Wearable robotic systems, Control strategies in rehabilitation robotics, Human-machine interfaces and robotic applications
Abstract: Wearable robotic systems have shown potential to improve the lives of musculoskeletal disorder patients; however, to be used practically, they require a reliable method of control. The user needs to be able to indicate that they wish to move in a way that feels intuitive and comfortable. One proposed method for detecting motion intention is through the combined use of muscle activity, known as electromyography (EMG), and brain activity, known as electroencephalography (EEG). Other groups have developed various methods of fusing EEG/EMG signals for classification of motion intention, but a comprehensive evaluation of their performance has yet to be completed. This work evaluates EEG/EMG fusion methods during elbow flexion–extension motion while varying parameters, such as speed of motion, weight held, and muscle fatigue. Overall, the use of EEG/EMG fusion was found to not be more accurate than using just EMG alone (86.81 +/- 3.98%), with some fusion methods demonstrating equivalent performance to EMG (p=1.000). EEG/EMG fusion was, however, demonstrated to be less sensitive to changes in motion parameters, allowing it to perform more consistently across different speed/weight combinations. The results of this work provide further justification for the use of EEG/EMG fusion for control of a wearable robotic device.

Keywords: Control strategies in rehabilitation robotics, Design and development in rehabilitation robotics
Abstract: Movement patterns are commonly disrupted after a neurological incident. The correction and recovery of these movement patterns is part of therapeutic practice, and should be considered in the development of robotic device control strategies. This is an area which has limited exploration in rehabilitation robotics literature. This work presents a new strategy aiming at influencing the cost associated with a movement, based on the principle of optimal motor control. This approach is unique, in that it does not directly modify the movement pattern, but instead encourages this altered movement. This `Indirect Shaping Control' is applied in a preliminary experiment using an end-effector based device with 5 healthy subjects. The study concludes that such an approach may encourage changes in movement patterns which do persist to out-of-robot reaching actions, but this was not consistent over all subjects and further experiments are required.

Keywords: Design and development in rehabilitation robotics, Control strategies in rehabilitation robotics, Robot-aided mobility
Abstract: Rehabilitation robots reduce the physical burden on therapists, quantify training and allow greater dose of therapy on individuals with neurological impairments. Robots are also capable of precisely customizing therapy based on the user’s physiology and/or needs, for example, customizing a reference trajectory for gait training. While a number of methods for obtaining reference gait patterns have been proposed, these approaches lack the ability of altering the trajectories according to the varying walking speed in real-time. The objective of this paper is to develop an online algorithm that can provide a continuous, speed-dependent reference gait pattern for robotic gait training. We employed Fourier series and profile blending methods to generate natural transitions in gait patterns, and synchronized the gait cycle time according to the given arbitrary walking speed. The simulation results suggest that the algorithm can stably change the gait patterns with the given walking speed in a synchronous manner. We conclude that the method can provide online speed-dependent walking motion that can be used for general robotic gait training applications.

Keywords: Control strategies in rehabilitation robotics, Body-machine interfaces, Robotic prostheses - neural interfaces
Abstract: Clinical viability of powered lower-limb assistive devices requires reliable and intuitive control strategies. Stance and swing are the main phases of the gait cycle across different locomotion tasks. Hence, a reliable method to accurately identify these phases can decrease sensing complexity and assist in enabling high-level control of assistive devices. Ultrasound (US) imaging has recently been introduced as a new sensing modality that may provide a solution for intuitive device control. US images of the RF and VI muscles were collected in humans during level, incline, and decline ambulation tasks. Five low-level static features of US images were measured with respect to a reference image, including correlation coefficient, SAD, structural similarity index, SSD, and image echogenicity. Time-derivatives of the static features were also calculated as temporal features. Support vector machine classifiers were trained using these static features to identify the gait phase both dependent and independent of the ambulation tasks. The results indicate an accuracy of 88.3% in identifying the gait phases for task-independent classifiers when trained using only the static features. Performance of the classifiers improved significantly to 92.8% after using the temporal features (p < 0.01). The algorithm was efficient and the average processing speed was faster than 100 Hz. This study is the first demonstration on use of US imaging to provide continuous estimates of ambulation phase.