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ARES, a variable stiffness actuator with embedded force sensor for the ATLAS exoskeleton

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Abstract

Purpose – The purpose of this study is to present a variable stiffness actuator, one of whose main features is that the compliant elements simultaneously allow measuring of the torque exerted by the joint. Conceived as a force-controlled actuator, this actuator with Adjustable Rigidity and Embedded Sensor (ARES) is intended to be implemented in the knee of the ATLAS exoskeleton for children to allow the exploitation of the intrinsic dynamic during the locomotion cycle. Design/methodology/approach – A set of simulations were performed to evaluate the behavior of the actuator mechanism and a prototype of the variable impedance actuator was incorporated into the exoskeleton’s knee and evaluations of the torque measurements capabilities along with the rigidity adjustments were made. Findings – Mass and inertia of the actuator are minimized by the compact design and the utilization of the different component for more than one utility. By a proper match of the compliance of the joint and the performed task, good torque measurements can be achieved and no bandwidth saturation is expected. Originality/value – In the actuator, the compliant elements simultaneously allow measuring of the torque exerted by the join. By a proper match of the compliance of the joint and the performed task, good torque measurements can be achieved and no bandwidth saturation is expected.
... From the last one and a half decades, various robotic aided lower extremity exoskeleton devices (LEEDs) have been developed to achieve active and passive therapeutic measures [8][9][10]. Conventionally, LEEDs are classified into three categories based on the application: assistive [10][11][12], rehabilitation [13][14][15][16], and strength augmentation devices [17]. Mohan et al. [10] introduced a passive exoskeleton ANKUR-LL II with a RRR configuration, which is augmented to a vertical manipulator having a parallel arrangement of 2PRP-2PPR. ...
... This lower extremity exoskeleton system is specifically designed to assist the patients in the sagittal plane. Cestari et al. [11] presented an assessment of the compliant actuation system in ATLAS exoskeleton to assist the children during flexion/extension of hip and knee joints. The ankle's dorsiflexion/plantarflexion movement is delivered via an attached link between the shank and thigh. ...
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The objective of this work is to design a neuro-fuzzy compensated PID control for passive gait rehabilitation using a lower extremity exoskeleton system. A prototype of 6-DOFs exoskeleton device is developed to assist the children of age 8-10 years old. A dummy having a well-matched body attributes to a healthy child (10 years) is utilized in this work to carry out the experimental runs. Kinect-LabVIEW setup is employed to compute the desired joint angles in the sagittal plane for a healthy gait trajectory. The Euler-Lagrange method is utilized to formulate the dynamic analysis of the exoskeleton system. As the performance of existing control strategies for gait rehabilitation devices is still debatable; therefore, a robust neuro-fuzzy compensated PID control strategy is designed in this work. The asymptotic stability of the proposed control scheme is proved mathematically by Lyapunov theorem. Thereafter, the proposed control strategy is implemented on the exoskeleton-dummy setup in real-time and compared with the classical PID control strategy. From experimental runs, the root mean square error (RMSE) for proposed control scheme is found to be less by 40% nearly while tracking the desired gait trajectory. The robustness of the proposed controller is also validated by varying lower limb masses of dummy and by providing an external disturbance. It is observed that proposed controller is more robust to deal with the input disturbance as compared to parametric uncertainty. Finally, the low values of settling time in both the directions ensures the fast convergence of proposed controller.
... Kim et al. [13] developed a 14-DOFs lower-limb exoskeleton to provide gait assistance, having a 3-DOFs hip joint, a 1-DOF knee joint, and a 3-DOFs ankle joint for each limb. Cestari et al. [14] presented the ATLAS exoskeleton to assist the children during flexion/extension of hip, knee, and ankle joints. At the introductory level, a dummy with body features of 10 years human child was used to test the exoskeleton system. ...
Preprint
The main purpose of this work is to design a robust adaptive backstepping (RABS) control strategy for a pediatric exoskeleton system during passive-assist gait rehabilitation. The nonlinear dynamics of the exoskeleton system have ill-effects of uncertain parameters and external interferences. In this work, the designed robust control strategy is applied on the exoskeleton to assist children of 10-12 years, 25-40kg weight, and 115-125cm height. The dynamic model of the coupled human-exoskeleton system is established using the Euler-Lagrange principle. An appropriate Lyapunov function is selected to prove the uniform boundedness of the control signals. The 'explosion of terms' is avoided by establishing a virtual control law without the dynamical system parameters. A Microsoft Kinect-LabVIEW experiment is carried out to estimate the desired gait trajectory. The robustness of the proposed control is validated by varying the limb segment masses and inducing the periodic external disturbances. The proposed control strategy is compared with the decentralized modified simple adaptive-PD (DMSA-PD) control strategy. From simulation results and improved performance index, it is observed that RABS control outperforms the contrast control (DMSA-PD) to track the desired gait during passive-assist rehabilitation under the effect of model uncertainties and external disturbances.
... Aggogeri et al. [10] presented a modular and reconfigurable mechanism for rehabilitating ankle joints of different subjects. Cestari et al. [11] introduced the ATLAS exoskeleton to assist the children during flexion/extension of the hip, knee, and ankle joints. At the preliminary level, a dummy with body features of a 10-year-old child was used to test the exoskeleton system. ...
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... This is to enable compliant behavior in the actuated joint in an otherwise non-backdrivable system. Examples include the ARES actuator joint on the ATLAS 2020 [26] and the WAKE-up exoskeleton [31]. ...
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