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A previously developed pneumatic muscles’ (PMs) actuated gait exoskeleton (with only knee joint) has been demonstrated in achieving appropriate actuation torque, range of motion (ROM), and control bandwidth for task-specific gait training. While the adopted multi-input–multi-output (MIMO) sliding mode (SM) strategy has preliminarily implemented simultaneous control of the exoskeleton’s angular trajectory and compliance, its efficacy with human users during gait cycles has not been investigated. This article presents an improved bi-joint gait rehabilitation exoskeleton (BiGREX) with integrated human hip and knee joints. The results with 12 healthy subjects demonstrated that the system’s compliance can be effectively adjusted while guiding the subjects walking in predefined trajectories. Note to Practitioners—This article was motivated by achieving compliant interaction between PM-actuated exoskeletons and human when conducting task-specific gait training. Due to the intrinsic nonlinearity of PM, it is challenging to establish a mathematical model to precisely predict real-time compliance of the powered joints. This article suggests a new strategy that adopts the average pressure of flexor and extensor PMs as the feedback to synchronously realize the joint position control and compliance regulation. A novel experimental approach was adopted to validate the system capability on adjusting the compliance from human users’ perception. This article provides a new insight between the controlled PM pressure and the desired joint compliance, which would be essential for the future design of PM-actuated exoskeletons. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive review of high-level control techniques for upper-limb robotic training. It aims to compare and discuss the potentials of these different control algorithms, and specify future research direction. Included studies mainly come from selected papers in four review articles. To make selected studies complete and comprehensive, especially some recently-developed upper-limb robotic devices, a search was further conducted in IEEE Xplore, Google Scholar, Scopus and Web of Science using keywords ('upper limb*' or 'upper body*') and ('rehabilitation*' or 'treatment*') and ('robot*' or 'device*' or 'exoskeleton*'). The search is limited to English-language articles published between January 2013 and December 2017. Valuable references in related publications were also screened. Comparative analysis shows that high-level interaction control strategies can be implemented in a range of methods, mainly including impedance/admittance based strategies, adaptive control techniques, and physiological signal control. Even though the potentials of existing interactive control strategies have been demonstrated, it is hard to identify the one leading to maximum encouragement from human users. However, it is reasonable to suggest that future studies should combine different control strategies to be application specific, and deliver appropriate robotic assistance based on physical disability levels of human users. [ABSTRACT FROM AUTHOR]

Assist-as-needed control strategy is an emerging approach to improve the effectiveness of gait rehabilitation training. We have proposed a pneumatic muscle (PM) driven Gait Rehabilitation Exoskeleton (GAREX) implemented with a multi-input–multi-output (MIMO) sliding mode control system to actively adjust the assistance level provided during gait rehabilitation. To realize the assist-as-needed control strategy, a specific algorithm is imperative to assess the active participation or effort of wearers and adapt the amount of assistance accordingly. We sought to establish a fuzzy logic compliance adaptation (FLCA) controller to form a novel cascade control system. We evaluated the feasibility of implemented FLCA controller on the performance of adjusting the compliance of GAREX's knee joint according to the online assessment of the wear's active participation level once in every gait cycle. Using controlled, treadmill-based walking tests involved three healthy subjects, we demonstrate that FLCA controller could effectively distinguish the capability/effort levels of wearers and enable the exoskeleton to adapt the knee joint compliance accordingly. Obtained results reveal that FLCA controller can collaborate well with MIMO sliding mode controller in a system and indicate the novel method of realizing assist-as-needed concept with the pneumatic muscle powered mechanisms. • Proposed fuzzy logic compliance adaption controller possesses the capability of dealing with multivariable inputs, and an assist-as-needed training has been realized. • This method also allows designing the adaptation law using predefined training principles directly from clinical practice in natural language terms. • We demonstrate the contributions of this work as following: (1) provides a novel approach to establish a cascade control system with fuzzy logic and sliding mode control for PM driven devices; (2) proposed controller is model-free and robust. [ABSTRACT FROM AUTHOR]