Benchmarking the Effects on Human-Exoskeleton Interaction of Trajectory, Admittance and EMG-Triggered Exoskeleton Movement Control

Abstract

Nowadays, robotic technology for gait training is becoming a common tool in rehabilitation hospitals. However, its effectiveness is still controversial. Traditional control strategies do not adequately integrate human intention and interaction and little is known regarding the impact of exoskeleton control strategies on muscle coordination, physical effort, and user acceptance. In this article, we benchmarked three types of exoskeleton control strategies in a sample of seven healthy volunteers: trajectory assistance (TC), compliant assistance (AC), and compliant assistance with EMG-Onset stepping control (OC), which allows the user to decide when to take a step during the walking cycle. This exploratory study was conducted within the EUROBENCH project facility. Experimental procedures and data analysis were conducted following EUROBENCH's protocols. Specifically, exoskeleton kinematics, muscle activation, heart and breathing rates, skin conductance, as well as user-perceived effort were analyzed. Our results show that the OC controller showed robust performance in detecting stepping intention even using a corrupt EMG acquisition channel. The AC and OC controllers resulted in similar kinematic alterations compared to the TC controller. Muscle synergies remained similar to the synergies found in the literature, although some changes in muscle contribution were found, as well as an overall increase in agonist-antagonist co-contraction. The OC condition led to the decreased mean duration of activation of synergies. These differences were not reflected in the overall physiological impact of walking or subjective perception. We conclude that, although the AC and OC walking conditions allowed the users to modulate their walking pattern, the application of these two controllers did not translate into significant changes in the overall physiological cost of walking nor the perceived experience of use. Nonetheless, results suggest that both AC and OC controllers are potentially interesting approaches that can be explored as gait rehabilitation tools. Furthermore, the INTENTION project is, to our knowledge, the first study to benchmark the effects on human-exoskeleton interaction of three different exoskeleton controllers, including a new EMG-based controller designed by us and never tested in previous studies, which has made it possible to provide valuable third-party feedback on the use of the EUROBENCH facility and testbed, enriching the apprenticeship of the project consortium and contributing to the scientific community.

Keywords: EMG control; benchmarking; electromyography; exoskeleton; exoskeleton control; human–robot interaction.

Figure 1

Conceptual diagram of the Exo-H3 trajectory control.

Figure 2

Conceptual diagram of the Exo-H3 admittance control.

Figure 3

Conceptual diagram of EMG onset-based control loop designed for this experiment and implemented with Exo-H3.

Figure 4

Experimental setup.

Figure 5

Pictures of two different subjects while they walked with Exo-H3. Most of the experimental setup is represented in the two pictures.

Figure 6

Schematics of the experimental protocol followed for each participant.

Figure 7

Average ankle, knee and hip joint angles when walking with TC (continuous), AC (dashed) and OC (dotted) controllers.

Figure 8

Normalized and cycle-averaged EMG envelopes of Sol and ReFe muscles.

Figure 9

Average onset detection for the right and left Sol and ReFe.

Figure 10

Average muscle synergies (right leg).

Figure 11

Average scores of Attention, Energy expenditure, Fatigue and Stress PIs for TC, AC and OC controllers. Scores of each PI were updated for each minute of trial.