Patient-cooperative control of variable impedance actuators (PatRiA)
Final Report Abstract
The overall aim of the PatRiA project was to develop methods for patient-cooperative control strategies of Variable-Impedance Actuators (VIA). For this purpose, the project was divided into 5 WPs regarding the abstraction level of the control design. In model analysis, we developed and parametrized models of variable stiffness actuators using Linear Parameter Varying modeling approach. The model enables the variable stiffness to be decoupled from the torque generation and includes non-linear friction effects. By combining an inner PI control loop and a robust ℋ∞ non-smooth gain-scheduled torque control over the entire VSA stiffness range with a ℋ∞ loop-shaping, we could keep the actuator output function positive-real and guarantee robustness against unknown environment. To overcome the fixed-load model assumption, we replaced the Kalman Filter by a Generalized Extended State Observer to estimate the internal states and the disturbances caused by the load and patient. Hence, a robust impedance controller parametrization was carried out and confirmed for both lowimpedance and high-impedance tasks, where the stability was tested using a fixed quadratic Lyapunov function and solving the Lyapunov linear matrix inequality. Finally, we analyzed methods for adapting movement support based on patient information by estimation of the interaction/subject torque and the physical stiffness of the VSA. For both cases of low- and high-impedance, our study successfully demonstrated the possibility to support the sit-to-stand task with the MeRia-based 2-DOF exoskeleton of up to 60% of the required torque.
Publications
- “Zero-torque control of an exoskeleton joint actuator using a disturbance observer,” in AIP Conference Proceedings, 2019, vol. 2140
L. Bergmann, L. Liu, C. Ngo, B. Misgeld, and S. Leonhardt
(See online at https://doi.org/10.1063/1.5121929) - “Impedance-Controlled Variable Stiffness Actuator for Lower Limb Robot Applications,” IEEE Trans. Autom. Sci. Eng., vol. 17, no. 2, pp. 991–1004, 2020
L. Liu, S. Leonhardt, C. Ngo, and B. J. E. Misgeld
(See online at https://doi.org/10.1109/TASE.2019.2954769) - “Implementation of LPV H ∞ Loop-Shaping Control for a Variable Stiffness Actuator,” in IFAC World Congress 2020, 2020
L. Bergmann, L. Liu, N. Pham, and B. Misgeld
(See online at https://doi.org/10.1016/j.ifacol.2020.12.2738) - “Low Impedance-Guaranteed Gain-Scheduled GESO for Torque-Controlled VSA, with Application of Exoskeleton-Assisted Sit-to-Stand” IEEE/ASME Trans. Mechatronics, vol. 4435, 2020
L. Liu, Z. Hong, B. Penzlin, B. Misgeld, C. Ngo, L. Bergmann, S. Leonhardt
(See online at https://doi.org/10.1109/TMECH.2020.3032372) - “Preliminary test of a zero-torque controlled exoskeleton on a treadmill,” Proc. Autom. Med. Eng., pp. 1–2, 2020
L. Bergmann, L. Liu, B. Penzlin, S. Leonhardt, and C. Ngo
(See online at https://doi.org/10.18416/AUTOMED.2020) - “Workflow for 3D modeling of compliant actuators for active exoskeletons,” Automed 2021 Conference, Basel, Switzerland
L. Bergmann, C. Moazzami, S. Leonhardt, and C. Ngo
(See online at https://doi.org/10.5281/zenodo.4922726)
