1,721,139 research outputs found
Vibrotactile feedback to control the amount of weight shift during walking - A first step towards better control of an exoskeleton for spinal cord injury subjects
Get PDFPeople with Spinal Cord Injury do not only lack the ability to control their muscles, but also miss the sensory information from below the level of their lesion. Therefore, it may become difficult for them to perceive the state of the body during walking, which is however often used to control wearable exoskeletons. In the present study the possibilities of providing vibrotactile feedback about the Center of Mass (CoM) during walking were investigated. The results showed that healthy subjects could successfully interpret the provided vibrotactile cues and change their walking pattern accordingly. Vibrotactile stimulation was either provided in a concurrent (over the complete CoM movement) or terminal (only when the desired CoM displacement was reached) way. The latter led to a better accuracy and can be easily implemented in a wearable exoskeleton where a certain amount of CoM displacement is needed to initiate stepping
Automatic versus manual tuning of robot-assisted gait training in people with neurological disorders
Get PDFBackground: In clinical practice, therapists choose the amount of assistance for robot-assisted training. This can result in outcomes that are influenced by subjective decisions and tuning of training parameters can be time-consuming. Therefore, various algorithms to automatically tune the assistance have been developed. However, the assistance applied by these algorithms has not been directly compared to manually-tuned assistance yet. In this study, we focused on subtask-based assistance and compared automatically-tuned (AT) robotic assistance with manually-tuned (MT) robotic assistance. Methods: Ten people with neurological disorders (six stroke, four spinal cord injury) walked in the LOPES II gait trainer with AT and MT assistance. In both cases, assistance was adjusted separately for various subtasks of walking (in this study defined as control of: weight shift, lateral foot placement, trailing and leading limb angle, prepositioning, stability during stance, foot clearance). For the MT approach, robotic assistance was tuned by an experienced therapist and for the AT approach an algorithm that adjusted the assistance based on performances for the different subtasks was used. Time needed to tune the assistance, assistance levels and deviations from reference trajectories were compared between both approaches. In addition, participants evaluated safety, comfort, effect and amount of assistance for the AT and MT approach. Results: For the AT algorithm, stable assistance levels were reached quicker than for the MT approach. Considerable differences in the assistance per subtask provided by the two approaches were found. The amount of assistance was more often higher for the MT approach than for the AT approach. Despite this, the largest deviations from the reference trajectories were found for the MT algorithm. Participants did not clearly prefer one approach over the other regarding safety, comfort, effect and amount of assistance. Conclusion: Automatic tuning had the following advantages compared to manual tuning: quicker tuning of the assistance, lower assistance levels, separate tuning of each subtask and good performance for all subtasks. Future clinical trials need to show whether these apparent advantages result in better clinical outcomes.Biomechatronics & Human-Machine Contro
Cooperative ankle-exoskeleton control can reduce effort to recover balance after unexpected disturbances during walking
Get PDFBACKGROUND: In the last two decades, lower-limb exoskeletons have been developed to assist human standing and locomotion. One of the ongoing challenges is the cooperation between the exoskeleton balance support and the wearer control. Here we present a cooperative ankle-exoskeleton control strategy to assist in balance recovery after unexpected disturbances during walking, which is inspired on human balance responses. METHODS: We evaluated the novel controller in ten able-bodied participants wearing the ankle modules of the Symbitron exoskeleton. During walking, participants received unexpected forward pushes with different timing and magnitude at the pelvis level, while being supported (Exo-Assistance) or not (Exo-NoAssistance) by the robotic assistance provided by the controller. The effectiveness of the assistive strategy was assessed in terms of (1) controller performance (Detection Delay, Joint Angles, and Exerted Ankle Torques), (2) analysis of effort (integral of normalized Muscle Activity after perturbation onset); and (3) Analysis of center of mass COM kinematics (relative maximum COM Motion, Recovery Time and Margin of Stability) and spatio-temporal parameters (Step Length and Swing Time). RESULTS: In general, the results show that when the controller was active, it was able to reduce participants' effort while keeping similar ability to counteract and withstand the balance disturbances. Significant reductions were found for soleus and gastrocnemius medialis activity of the stance leg when comparing Exo-Assistance and Exo-NoAssistance walking conditions. CONCLUSIONS: The proposed controller was able to cooperate with the able-bodied participants in counteracting perturbations, contributing to the state-of-the-art of bio-inspired cooperative ankle exoskeleton controllers for supporting dynamic balance. In the future, this control strategy may be used in exoskeletons to support and improve balance control in users with motor disabilities.Biomechatronics & Human-Machine Contro
Effects of selectively assisting impaired subtasks of walking in chronic stroke survivors
Get PDFBackground: Recently developed controllers for robot-assisted gait training allow for the adjustment of assistance for specific subtasks (i.e. specific joints and intervals of the gait cycle that are related to common impairments after stroke). However, not much is known about possible interactions between subtasks and a better understanding of this can help to optimize (manual or automatic) assistance tuning in the future. In this study, we assessed the effect of separately assisting three commonly impaired subtasks after stroke: foot clearance (FC, knee flexion/extension during swing), stability during stance (SS, knee flexion/extension during stance) and weight shift (WS, lateral pelvis movement). For each of the assisted subtasks, we determined the influence on the performance of the respective subtask, and possible effects on other subtasks of walking and spatiotemporal gait parameters. Methods: The robotic assistance for the FC, SS and WS subtasks was assessed in nine mildly impaired chronic stroke survivors while walking in the LOPES II gait trainer. Seven trials were performed for each participant in a randomized order: six trials in which either 20% or 80% of assistance was provided for each of the selected subtasks, and one baseline trial where the participant did not receive subtask-specific assistance. The influence of the assistance on performances (errors compared to reference trajectories) for the assisted subtasks and other subtasks of walking as well as spatiotemporal parameters (step length, width and height, swing and stance time) was analyzed. Results: Performances for the impaired subtasks (FC, SS and WS) improved significantly when assistance was applied for the respective subtask. Although WS performance improved when assisting this subtask, participants were not shifting their weight well towards the paretic leg. On a group level, not many effects on other subtasks and spatiotemporal parameters were found. Still, performance for the leading limb angle subtask improved significantly resulting in a larger step length when applying FC assistance. Conclusion: FC and SS assistance leads to clear improvements in performance for the respective subtask, while our WS assistance needs further improvement. As effects of the assistance were mainly confined to the assisted subtasks, tuning of FC, SS and WS can be done simultaneously. Our findings suggest that there may be no need for specific, time-intensive tuning protocols (e.g. tuning subtasks after each other) in mildly impaired stroke survivors.Biomechatronics & Human-Machine Contro
Advances on mechanical designs for assistive ankle-foot orthoses
Get PDFAssistive ankle-foot orthoses (AAFOs) are powerful solutions to assist or
rehabilitate gait on humans. Existing AAFO technologies include passive,
quasi-passive, and active principles to provide assistance to the users, and
their mechanical configuration and control depend on the eventual support they
aim for within the gait pattern. In this research we analyze the
state-of-the-art of AAFO and classify the different approaches into clusters,
describing their basis and working principles. Additionally, we reviewed the
purpose and experimental validation of the devices, providing the reader with a
better view of the technology readiness level. Finally, the reviewed designs,
limitations, and future steps in the field are summarized and discussed.Comment: Figures appear at the end. Article submitted to Frontiers in
Bioengineering and Biotechnology (currently under review
Trans-spinal direct current stimulation for the modulation of the lumbar spinal motor networks
Get PDFTrans-spinal Direct Current Stimulation (tsDCS) is a noninvasive neuromodulatory tool for the modulation of the spinal neurocircuitry. Initial studies have shown that tsDCS is able to induce a significant and lasting change in spinal-reflex- and corticospinal information processing. It is therefore hypothesized that tsDCS may be a useful tool in the rehabilitation of spinal cord dysfunctions or injuries. However, to efficiently utilize tsDCS as a tool in neurorehabilitation, more knowledge is necessary about its mechanisms of action, as well as how tsDCS needs to be applied to ensure the desired outcome. This dissertation focuses on the use of tsDCS for the modulation of the lumbar spinal motor circuitry, for a possible application in spinal cord injury rehabilitation. This is investigated using theoretical as well as experimental techniques. Chapter 2 focusses on simulating the electric field (EF) generated during tsDCS and its interaction with the targeted neural structures. This includes visualization and analysis of the generated EF as well as the identification of the most likely neural target. Furthermore, a comparison with existing human tsDCS studies and the possible effects of electrode misplacement during application are discussed. After having established a theoretical basis of some of the underlying mechanisms of action, the following two chapters deal with experimentally assessing the effects of tsDCS for different protocol variations. Chapter 3 deals with experimentally assessing the effects of tsDCS applied with different EF directions, as well as the repeatability of results previously obtained by others. The central question was to assess whether the tsDCS outcome is dependent on EF direction. Chapter 4 compares the effects of tsDCS during active movement and rest, to investigate during which of the two conditions the application of tsDCS leads to larger modulatory effects. The underlying hypothesis is, that the modulatory effect of tsDCS can be significantly increased when paired with ongoing neural activity. Lastly, chapter 5 investigates important safety aspects, when tsDCS is applied in the presence of metallic spinal implants. The presence of metallic implants in the body is still a safety concern, in connection with electrical stimulation procedures. Since spinal implants are expected to be present in at least part of the targeted population with spinal cord injury, it is necessary to explore the safety and application specific consequences of tsDCS with the presence of a spinal metallic implant
Towards postural balance control of exoskeletons
Get PDFLower-limb wearable exoskeletons have been designed to assist people that have a spinal cord injury during standing and walking. However, because these people generally also have impaired balance, it is difficult, if not impossible for them to operate these exoskeletons without additional supporting aids, such as crutches. Ideally the exoskeleton supports its user’s balance, preferably in a human-like way to match the user's natural intention. Therefore, proper balance control of the exoskeleton is required. This work presents the first steps taken towards postural balance control of lower-limb wearable exoskeletons. The focus is specifically on standing balance control strategies for exoskeletons, inspired by human and humanoid standing balance. The first goal of this thesis was to explore balance control strategies for the application in a lower-limb exoskeletons, with a particular focus on human-like motion generation. In Chapter 2 the ability of the momentum-based controller to generate human-like feet-in-place balance recovery strategies was investigated. Besides feet-in-place balance recovery strategies, people also use a reactive stepping strategy to maintain balance. Therefore, in Chapter 3 it was investigated whether the occurrence of reactive stepping could be predicted using a classification-based method, and what features are most relevant for that prediction. The second goal of this thesis was to verify the effectiveness of exoskeleton balance support. Hence, the effects of an ankle exoskeleton and an ankle-knee exoskeleton on the balance of able-bodied users and (three) users with an incomplete spinal cord injury respectively were assessed in Chapters 4 and 5. By modeling human balance for the use in an exoskeleton on the one hand, and by analyzing and implementing existing balance control strategies on the other, the results presented in this thesis provide insight into how to impose standing balance on exoskeletons and their users
Haptic human-human interaction: motor learning & haptic communication
Get PDFHaptic interaction with a partner – interaction by exerting forces onto each other directly or through an object – plays an important role in our lives. It can help us to coordinate our actions and it can benefit learning of new motor tasks; for example, a therapist can physically support a patient during recovery of their motor functions after injury or disease. My research goal is to create a better understanding of whether haptic interaction between two humans improves individual motor learning and why haptic interaction would improve motor performance. We performed two experiments in which two partners learned novel motor tasks together: tracking a randomly-moving target in two novel environments. We haptically-connected the partners while they simultaneously learned a motor task. The partners were not made aware of the coupling. Although haptic interaction improved performance of both partners during interaction, this improvement was not retained when performing the task alone in both experiments. Hence, haptic interaction between humans does not improve individual motor learning in a collaborative motor task. Interestingly, we found that haptic interaction improved motor performance during interaction, even when being coupled to a worse-performing partner. To explain this result, we developed a computational model of the interaction in which we mechanically coupled two simulated partners who both independently performed the same motor task. The model assumed that the partners were unaware of the haptic connection. Hence, the simulated partners were only mechanically influenced by the interaction force; they did not exchange any information about each other or the task through the interaction force to improve their performance. This model accurately predicted the improvement due to interaction observed in the experimental data. Additional model analysis suggested that haptic interaction improved performance because the compliant connection partially compensated for each partner's motor output variability, which includes tracking errors such as overshoots. The worse-performing partners additionally benefited from the haptic guidance provided by their better-performing partners. Similarly, we observed that partners did not coordinate reaching movements through the interaction force in another experiment. In conclusion, our findings suggest that haptically-coupling two humans does not necessarily result in any exchange of information or motor coordination through the interaction force
Foot placement in balance recovery: complex humans vs simple model
Get PDFMaintaining balance in daily life is very common to us. For a healthy individual, a fall is simply not supposed to happen. Unfortunately, various conditions such as stroke, spinal cord injury, or aging can lead to balance problems and affect a person's mobility. Robotic devices such as powered orthoses, often referred to as exoskeletons, might provide an outcome for these balance problems. In case of a lower-extremity exoskeleton, the user wears a construction around the legs that should provide support during standing and walking. This support can be to various purposes, such as to reduce the energetic costs of walking, to assist in gait rehabilitation, or to fully take over the walking motion. Although the purpose of the device might differ, most lower-extremity exoskeletons have one thing in common: they have no sense of balance. The exoskeleton cannot react to unexpected disturbances. Because of that, the user has to take the lead in making a balance recovery. This is especially troublesome when the user has balance impairments. To tackle these issues, the control of exoskeletons needs to be improved. Specifically, if the device can assist in balance control in a way that feels natural and intuitive to the user, the device is less likely to conflict with the user's intention. To realize such human-like balance controllers, we must first understand what human balance is, and investigate the way healthy humans regain their balance when it is lost. This might be investigated by applying perturbations to experimental subjects. Disturbances will lead to a balance recovery response involving various balance strategies, such as adjustments in foot placement, or modulation of ankle and hip moments. The focus of this thesis is on human balance recovery in response to external perturbations during walking. Because we mainly deal with walking, foot placement adjustments are expected to be a major, crucial strategy in balance control. This strategy might be replicated using simple inverted pendulum models of walking, which could provide a basis for predicting human-like responses
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