Robust Locomotion Control of a Self-Balancing and Underactuated Bipedal Exoskeleton: Task Prioritization and Feedback Control

Soliman, Ahmed Fahmy; Uğurlu, Barkan

doi:10.1109/lra.2021.3082016

Cited by 10 publications

(3 citation statements)

References 30 publications

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“…Interaction control is a robust solution that renders the desired device admittance/impedance against the environment. In position-controlled devices, force/torque sensors are required at the interaction interfaces (feet and hands) to implement admittance control on the contact forces or impedance control on the ZMP [13], [14]. Torque-controlled devices on the contrary are compliant by construction and impedance control can be implemented without any additional sensor, while model inaccuracies compromise tracking.…”

Section: A State Of the Art In Lle Balance Controlmentioning

confidence: 99%

Implementation and Tuning of Momentum-Based Controller for Standing Balance in a Lower-limb Exoskeleton with Paraplegic User

Prieto,

Keemink,

Asseldonk

et al. 2024

Preprint

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Lower limb exoskeletons (LLEs) are wearable devices that can restore the movement autonomy of paraplegic users. LLEs can restore the users’ ability to stand upright and walk. However, most of the commercially available and clinically used LLEs rely on the user maintaining balance through the use of crutches. Recent improvements in the design and control of LLEs and other legged robots allow for autonomous balance control. In this work, we implement and evaluate a momentum-based standing balance controller in the Symbitron LLE, consisting of eight active (torque-controlled) and two passive joints. We first investigate how gain tuning of the center of mass tracking control law, part of a multi-task optimal controller, affects balancing performance. We apply pushes on different device locations while in parallel-stance, compare the response for different gains, and derive heuristic guidelines for controller tuning given the control architecture, high-level goals, and hardware limitations. Next, we show how this controller successfully prescribes joint torques to the LLE to maintain balance with a paraplegic user. The LLE can autonomously balance the user and reject mediolateral and anteroposterior pushes in the order of 60 N at hip height (and 40 N at shoulder height) while standing in parallel-stance, staggered-stance with both feet at the same height, and staggered-stance with a height difference of 0.05 m between the feet. This work presents a viable control strategy for torque-controlled light-weight under-actuated LLEs to keep the balance of paraplegic users during stance, which is a necessary starting point towards autonomous balance control during gait.

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Section: A State Of the Art In Lle Balance Controlmentioning

confidence: 99%

Implementation and Tuning of Momentum-Based Controller for Standing Balance in a Lower-limb Exoskeleton with Paraplegic User

Prieto,

Keemink,

Asseldonk

et al. 2024

Preprint

View full text Add to dashboard Cite

show abstract

“…As these control approaches do not provide balance support, balance impaired users often have to use external stabilizers such as crutches or walkers that limit function [ 7 ]. For applications in spinal cord injury patients where the exoskeleton takes over from the user, some lower limb exoskeletons that support balance have been developed [ 10 ]. However, such exoskeletons only support walking using a control strategy that is not necessarily compatible with the human balance control strategy.…”

Section: Introductionmentioning

confidence: 99%

Assisting walking balance using a bio-inspired exoskeleton controller

Afschrift

Asseldonk

Mierlo

et al. 2023

J NeuroEngineering Rehabil

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Background Balance control is important for mobility, yet exoskeleton research has mainly focused on improving metabolic energy efficiency. Here we present a biomimetic exoskeleton controller that supports walking balance and reduces muscle activity. Methods Humans restore balance after a perturbation by adjusting activity of the muscles actuating the ankle in proportion to deviations from steady-state center of mass kinematics. We designed a controller that mimics the neural control of steady-state walking and the balance recovery responses to perturbations. This controller uses both feedback from ankle kinematics in accordance with an existing model and feedback from the center of mass velocity. Control parameters were estimated by fitting the experimental relation between kinematics and ankle moments observed in humans that were walking while being perturbed by push and pull perturbations. This identified model was implemented on a bilateral ankle exoskeleton. Results Across twelve subjects, exoskeleton support reduced calf muscle activity in steady-state walking by 19% with respect to a minimal impedance controller (p < 0.001). Proportional feedback of the center of mass velocity improved balance support after perturbation. Muscle activity is reduced in response to push and pull perturbations by 10% (p = 0.006) and 16% (p < 0.001) and center of mass deviations by 9% (p = 0.026) and 18% (p = 0.002) with respect to the same controller without center of mass feedback. Conclusion Our control approach implemented on bilateral ankle exoskeletons can thus effectively support steady-state walking and balance control and therefore has the potential to improve mobility in balance-impaired individuals.

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“…Admittance control (Chen et al, 2021) and impedance control (Soliman and Ugurlu, 2021) are more widely used in lower limb exoskeletons, due to the fact that they allow the motor to always move in the direction where the human-robot interaction force becomes smaller, ensuring flexibility between the human and the robot (Losey and O'Malley, 2017). In active patient rehabilitation training, the coupling and interaction between the human and the robot change at any time, and therefore the controller should be able to adjust the appropriate parameters according to these changes (Cousin et al, 2021;Wang et al, 2021;Guo et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

Autonomous motion and control of lower limb exoskeleton rehabilitation robot

Gao

Zhang

Peng

et al. 2023

Front. Bioeng. Biotechnol.

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Introduction: The lower limb exoskeleton rehabilitation robot should perform gait planning based on the patient’s motor intention and training status and provide multimodal and robust control schemes in the control strategy to enhance patient participation.Methods: This paper proposes an adaptive particle swarm optimization admittance control algorithm (APSOAC), which adaptively optimizes the weights and learning factors of the PSO algorithm to avoid the problem of particle swarm falling into local optimal points. The proposed improved adaptive particle swarm algorithm adjusts the stiffness and damping parameters of the admittance control online to reduce the interaction force between the patient and the robot and adaptively plans the patient’s desired gait profile. In addition, this study proposes a dual RBF neural network adaptive sliding mode controller (DRNNASMC) to track the gait profile, compensate for frictional forces and external perturbations generated in the human-robot interaction using the RBF network, calculate the required moments for each joint motor based on the lower limb exoskeleton dynamics model, and perform stability analysis based on the Lyapunov theory.Results and discussion: Finally, the efficiency of the APSOAC and DRNNASMC algorithms is demonstrated by active and passive walking experiments with three healthy subjects, respectively.

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Robust Locomotion Control of a Self-Balancing and Underactuated Bipedal Exoskeleton: Task Prioritization and Feedback Control

Cited by 10 publications

References 30 publications

Implementation and Tuning of Momentum-Based Controller for Standing Balance in a Lower-limb Exoskeleton with Paraplegic User

Implementation and Tuning of Momentum-Based Controller for Standing Balance in a Lower-limb Exoskeleton with Paraplegic User

Assisting walking balance using a bio-inspired exoskeleton controller

Autonomous motion and control of lower limb exoskeleton rehabilitation robot

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