A Cable-Driven Upper Limb Rehabilitation Robot With Muscle-Synergy-Based Myoelectric Controller

Surface electromyography (sEMG) signal has been used in upper limb rehabilitation robots (ULRR). However, existing ULRR based on myoelectric controllers suffers from limited generalization ability in estimating three-dimensional (3-D) motion intention. This article proposes a muscle-synergy-inspired approach to enhance the generalization ability of the myoelectric controller of a cable-driven ULRR. Low-dimensional commands are extracted from sEMG signals based on an EMG-to-muscle activation model and non-negative matrix factorization. The extracted commands are used to estimate the 3-D human force. Two different trajectory tracking tasks are selected to test the generalization ability. The system is trained based on training sets where participants perform one task. Then the system is tested using testing sets where participants perform the other task. Finally, the system is verified on real-time robotic control experiment. Results show that the proposed controller achieves better force estimating accuracy, better trajectory tracking accuracy, and lower interaction force than the myoelectric controller without considering muscle synergies, which means the proposed controller yields better generalization performance.

I. Introduction

Stroke is one of the leading causes of death and long-term disability [1], [2]. It is estimated that more than 80% of stroke survivors experience some degree of upper limb motor impairment, which impacts the patients’ activities in daily life and places a great burden on poststroke care [3]. With an annual increase of over 15 million cases of stroke [4], traditional rehabilitation treatments are insufficient due to a limited number of physical therapists and heavy workloads [5]. Robot-assisted rehabilitation has the advantage of providing intensive and quantitative treatment [6]. Recently, upper limb rehabilitation robots (ULRRs) have become a beneficial complement to therapist-led upper limb rehabilitation treatments for patients after stroke [7].