1,721,315 research outputs found
Introducing a Modular, Personalized Exoskeleton for Ankle and Knee Support of Individuals with a Spinal Cord Injury
Get PDFIn the Symbitron Project, one of the main objectives is to develop a safe, bio-inspired, and personalized wearable exoskeleton that enables individuals with a spinal cord injury (SCI) to walk without additional assistance, by complementing their remaining motor function. The first target group of five subjects, have enough hip control to keep themselves upright, but need support around the ankle and/or knee joint. This paper gives an overview of the design features of the newly developed exoskeleton and shares some details about the design process.</p
Towards Exoskeletons with Balance Capacities
Get PDFCurrent exoskeletons replay pre-programmed trajectories at the actuated joints. Towards the employment of exoskeletons with more flexible and adaptive behavior, we investigate human balance control during gait. We study human balance control by applying brief force pulses at the pelvis in different directions, with different amplitude, and applied at different phases of the gait phase. The observed changes were dependent on the phase at which the perturbation was applied and the walking velocity. From the results we concluded that foot placement was the dominant strategy in the frontal plane, center of pressure (CoP) modulation in the double support phase was utilized in the sagittal plane, and the duration of the swing and double support phase changed. Without the ability to control the CoP through an ankle torque, humans also used a foot placement strategy in the sagittal plane. The center of pressure with respect to the center of mass at the end of the double support phase was linearly related to velocity of the center of mass at the end of the preceding swing phase, which is in agreement with extrapolated center of mass or capture point based stepping strategies previously applied in simple models.</p
Improving the Standing Balance of People with Spinal Cord Injury Through the Use of a Powered Ankle-Foot Orthosis
Get PDFIn this study, our goal was to improve the standing balance of people with a Spinal Cord Injury (SCI) by using a powered Ankle-Foot orthosis acting in the sagittal plane. We tested four different controllers on two SCI subjects that have a lesion at a low level. In the experiments the subjects repeatedly had to recover from pelvis perturbations, while receiving ankle assistive torques from the orthosis. We found that the controllers that use centroidal dynamics as input parameters were able to provide proper support to the subjects after a perturbation had been applied, even though they worked against the subjects after they had recovered from the perturbation. These preliminary results show the potential of balancing controllers that operate in Center of Mass-space.</p
Joint-Level Responses to Counteract Perturbations Scale with Perturbation Magnitude and Direction
Get PDFTo realize a lower extremity exoskeleton that can provide balance assistance in a natural way, an understanding of human balance control is a necessity. In this study, we investigated how the angle, torque and power of the ankle, knee and hip joints changed in response to balance perturbations during walking. Nine healthy young adults walked on an instrumented treadmill and received pelvis perturbations of various magnitudes and directions at the instance of toe-off right. An open source musculoskeletal modeling package (OpenSim) was used to perform inverse kinematics and inverse dynamics. Subjects modulated the ankle torque in the (left) stance foot with the magnitude and direction of the perturbation. Also in gait phases following foot placement, subjects addressed ankle torques to mitigate the remaining effects of the perturbation. The results presented here support the use of ankle actuation in lower extremity orthoses for natural and cooperative balance control.</p
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
Haptic Physical Human Assistance
Get PDFThis dissertation covers three aspects of upper-extremity exoskeleton design: 1) Kinematics & motion: How to support the full range of motion of the human shoulder? We present a 2D visualization method that can show coupling between the range of motion (ROM) of rotations of the glenohumeral joint. This visualization helps in communication, comparison, design and analysis of human and assistive device ROM. We furthermore provide a conceptual design and differential inverse kinematics method for a redundant 4 degree of freedom (DOF) shoulder-exoskeleton. The extra DOF allows for movement redundancy to steer away from body collisions and kinematic singularity. 2) Haptics & Control: How to get devices such robots or exoskeletons to behave as some defined impedance in a stable manner when interacting with human users; how to implement stable admittance control with inertia reduction? We analyze the energetic behavior of the control method ‘admittance control’. During admittance control an interaction force with a human user is measured, which is used in a dynamical mechanical model that prescribes a motion for the exoskeleton to follow. Such a method is inherently active (i.e. it generates energy that can result in coupled instability) when it is used to reduce the apparent inertia of the exoskeleton. We provide insight into why this energetically active behavior occurs, and provide guidelines to design a controller that is (close to) passive and is therefore (almost) always stable when in contact with a human limb. 3) Human Factors: How do humans respond to dissipative shared control forces? Passive and active exoskeletons can apply forces to the human user to steer or help the person and share control authority. A passive force that only dissipates energy is a damping force. We investigate how position dependent damping forces around reaching targets influence human reaching time and kinematics. Results show that humans increase their accelerations and decrease their reaching time when assisted in this manner. We pose the hypothesis that damping forces attenuate neural activation dependent motor noise. Without the damping, this higher noise for higher accelerations would have had too much of a negative effect on the required task accuracy
Arm-based control of a lower limb exoskeleton: Proof of concept of a novel approach based on the shoulder kinematics
No full textRecognising the user’s locomotive intentions is crucial for the correct functionality of exoskeletons and active orthoses. For gait applications, extrapolating control inputs from the arm swing may be worthwhile, since arm oscillations naturally occur during human locomotion. A similar method would be unaffected by severe impairments of the lower limbs, and there is evidence suggesting enhanced results of gait rehabilitation when arms and legs exercise together. In this thesis, we propose a control algorithm to drive online a lower limb exoskeleton through the arm swing. Contrary to a previous EMG-based approach by La Scaleia et al. (2014), our algorithm exploits shoulder kinematic data to mimic “single swinging”, a natural mode of human interlimb coordination which is characterised by each arm swinging in-phase with the contralateral leg. Our proposed control architecture relies on two major modules: an Arm Observer and a Gait Generator. The Arm Observer consists of an adaptive frequency oscillator which extrapolates the frequency and phase of the arm swing by receiving online measurements of the angular shoulder position in the sagittal plane. This data is used by the Gait Generator to compute lower limb trajectories, based on regression models from a previous study by Koopman et al. (2014). We validated our controller through human-subject experiments, involving three participants walking on a treadmill with and without a lower limb exoskeleton, the Lopes II. When feed by data associated with natural walking, our adaptive frequency oscillator could very precisely replicate the arm swing frequency, stride cadence and timing of shoulder flexion peaks when walking faster than 0.5 m/s. When wearing the exoskeleton, our algorithm allowed the participants to cope with constant and variable treadmill velocities in the range of 0.5-1.25 m/s. As such, the results of this thesis show that our proposed approach can extend the applicability of arm-based control to walking speeds suitable for gait rehabilitation and assistance.Mechanical Engineering | BioMechanical Desig
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
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