Review on Control Strategies for Lower Limb Rehabilitation Exoskeletons

Abstract

Research on lower limb exoskeleton (LLE) for rehabilitation have developed rapidly to meet the need of the population with neurologic injuries. LLEs for rehabilitation include therapeutic LLEs that aim to restore walking ability for patients, and assistive LLEs that offer support on activities in daily life. A substantial part of them can serve both purposes. However, these devices are yet to reach the final goal of performing human-machine joint movement agilely and smartly. Control strategy plays an important role in achieving their designed goal. At present, control strategies face three major challenges: how to detect human intention, how to do motion control with given intentions, and how to optimize control parameters to suit different individuals. As a contribution, this paper offers an overview on the state-of-the-art control strategies for rehabilitation LLEs by classifying them into eight categories, each of which is presented with a technical summary and tabulated information of representative papers. Moreover, current approaches addressing the three challenges are discussed in a macroscopic perspective. Finally, it has been explored which requirements the future control strategies should meet for maximizing the performance of rehabilitation LLEs.

Coordination Between Partial Robotic Exoskeletons and Human Gait: A Comprehensive Review on Control Strategies

“…Independent of the synchronization strategy followed, successful coordination between robot action and user’s gait will lead to the embodiment of the technology. Devices capable of matching their action with the one expected by the user will lead in integrating the exoskeleton into the body schema so it will be treated as part of the body instead of an external tool ( Li et al, 2021 ). However, a research effort is required to demonstrate the capability of this technology of being embodied, as it has already been demonstrated for wheelchairs ( Arnhoff and Mehl, 1963 ; Pazzaglia and Molinari, 2016 ) or prostheses ( Penner et al, 2019 ; Bekrater-Bodmann, 2020 ).…”

“…The review proposed by Yan et al also focused on control strategies for lower-limb exoskeletons, more specifically, on strategies that assisted user’s gait ( Yan et al, 2015a ). Similarly, Li et al also reviewed control strategies for lower-limb exoskeletons but centered on rehabilitation purposes ( Li et al, 2021 ).…”

“…Proper delivery of the assistance is required to ensure that the user can benefit from the exoskeleton’s assistance, but also, a predictable timing that matches the user’s pre-estimation is required to achieve the exoskeleton’s embodiment. This would lead wearers to assimilate the robot’s action; so the exoskeleton would not be used as a tool but as a part of the user’s body ( Li et al, 2021 ).…”

An Approach to Investigate Public Opinion, Views, and Perspectives Towards Exoskeleton Technology

“…The device was equipped with three motors and utilized a spatial mechanism with a redundant degree of freedom to recognize humanrobot axes' alignment. Li et al (Li et al 2021) developed a system that employed ordinal and preference feedback, as well as Bayesian posteriors, to estimate the utility landscape of users across four distinct exoskeleton gait parameters. In (Nasiri et al 2021), the authors developed an adaptive controller that optimized the support provided by an exoskeleton in rehabilitation tasks without prior knowledge of the user's motor capabilities.…”

A review of the design of load-carrying exoskeletons

“…Although there have been many literature reviews on the structure [15,16], actuation [15,16], functional performance [3,17,18], and control [17,19] of wearable robots for locomotion improvements, as well as the corresponding human physiological response [1,[20][21][22], few reviews have systematically discussed the design of exoskeletons for loadcarrying augmentation. This paper, therefore, focuses on the human physiological basis of load-bearing and four types of load-carrying exoskeletons.…”