Design and analysis of ℋ∞ force control of a series elastic actuator for impedance control of an ankle rehabilitation robotic platform

Purpose This paper aims to present an impedance control method with mixed H2/H∞ synthesis and relaxed passivity for a cable-driven series elastic actuator to be applied for physical human–robot interaction. Design/methodology/approach To shape the system’s impedance to match a desired dynamic model, the impedance control problem was reformulated into an impedance matching structure. The desired competing performance requirements as well as constraints from the physical system can be characterized with weighting functions for respective signals. Considering the frequency properties of human movements, the passivity constraint for stable human–robot interaction, which is required on the entire frequency spectrum and may bring conservative solutions, has been relaxed in such a way that it only restrains the low frequency band. Thus, impedance control became a mixed H2/H∞ synthesis problem, and a dynamic output feedback controller can be obtained. Findings The proposed impedance control strategy has been tested for various desired impedance with both simulation and experiments on the cable-driven series elastic actuator platform. The actual interaction torque tracked well the desired torque within the desired norm bounds, and the control input was regulated below the motor velocity limit. The closed loop system can guarantee relaxed passivity at low frequency. Both simulation and experimental results have validated the feasibility and efficacy of the proposed method. Originality/value This impedance control strategy with mixed H2/H∞ synthesis and relaxed passivity provides a novel, effective and less conservative method for physical human–robot interaction control.

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Impedance Control of Hydraulic Series Elastic Actuator with a Model-Based Control Design

2020 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM) ◽

10.1109/aim43001.2020.9158817 ◽

2020 ◽

Author(s):

Pauli Mustalahti ◽

Jouni Mattila

Keyword(s):

Impedance Control ◽

Control Design ◽

Model Based Control ◽

Series Elastic Actuator ◽

Model Based ◽

Series Elastic

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Fuzzy impedance-based control with fast terminal sliding mode force control loop for a series elastic actuator system

Transactions of the Institute of Measurement and Control ◽

10.1177/01423312211043661 ◽

2021 ◽

pp. 014233122110436

Author(s):

Seyed Ali Moafi ◽

Farid Najafi

Keyword(s):

Force Control ◽

Fuzzy Logic Controller ◽

Sliding Mode ◽

Control Loop ◽

Terminal Sliding Mode ◽

Control Approach ◽

Series Elastic Actuator ◽

Control Scheme ◽

Fast Terminal Sliding Mode ◽

Series Elastic

This paper proposes a robust control scheme to accomplish the interaction control problem between a series elastic actuator (SEA) and a flexible environment. The adaptability of the controller to unknown variations and robustness of the controller during interaction of the system with environment are the main aims. The control scheme is based on a fuzzy impedance control approach and consists of an inner fast terminal sliding mode force control loop. An experimental setup is designed to prove the efficiency of the developed controller. The experimental results confirm that the proposed fuzzy logic controller guarantees the sensitivity of the controlled system to unpredictable variations. Moreover, by applying the fast terminal sliding mode algorithm for the inner force control loop, the system has faster convergence to the reference path compared with similar control methods found in the literature.

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