Saturated Adaptive Control of Antagonistic Muscles on an Upper-Limb Hybrid Exoskeleton | IEEE Conference Publication | IEEE Xplore

Saturated Adaptive Control of Antagonistic Muscles on an Upper-Limb Hybrid Exoskeleton


Abstract:

Functional electrical stimulation (FES) is a viable rehabilitation method for individuals affected by neurological injuries. When FES is combined with a powered exoskelet...Show More

Abstract:

Functional electrical stimulation (FES) is a viable rehabilitation method for individuals affected by neurological injuries. When FES is combined with a powered exoskeleton, a hybrid exoskeleton is created. To control hybrid exoskeletons, a user’s muscles must be stimulated while simultaneously activating the exoskeleton’s motors. In this paper, an adaptive position-based controller is developed to stimulate a user’s biceps and triceps muscle groups on an upper-limb hybrid exoskeleton. For user comfort and stability, the stimulation input is saturated and the remainder is redirected into the exoskeleton’s motor. The motor is actuated using a robust feedback controller along with the excess input from the user’s saturated muscle controller. A Lyapunov stability analysis is conducted to prove that the closed-loop position error system is uniformly ultimately bounded using the two controllers. This approach showcases a novel way to safely limit stimulation without sacrificing overall performance via a conditionally offloaded neural network on hybrid exoskeletons. Experiments were conducted on four participants without injuries for validation and to demonstrate the efficacy of the proposed approach.
Date of Conference: 08-10 June 2022
Date Added to IEEE Xplore: 05 September 2022
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Conference Location: Atlanta, GA, USA

I. Introduction

Every year, nearly 800,000 people have a stroke with over 600,000 of them being first time strokes [1]. These injuries can result in mobility impairments, with strokes being the leading cause of long-term disability with effects ranging from gait instability to falls, especially for people 65 and older [1], [2]. While there are many options for rehabilitative therapy, functional electrical stimulation (FES) is a common option, especially for people with extremely limited or non-existent muscular control. FES has been shown to impart a number of beneficial effects ranging from increased strength to endurance [3]. Precise control of FES however, is extremely difficult for specific rehabilitative motion due to dynamic nonlinearities and inherent inefficiencies such as fatigue [3], [4]. These effects can be compensated for by combining FES with motorized actuators in an exoskeleton, creating a hybrid exoskeleton [5], [6].

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