Flexible Exoskeleton Control Based on Binding Alignment Strategy and Full-arm Coordination Mechanism

TL;DR

This work addresses disruption from donning offsets in a $9$-DoF upper-limb exoskeleton by introducing Binding Alignment Strategy (BAS) and Full-Arm Coordination Mechanism (FCM), integrated with an Intention Distinction Module (IDM) and dynamic feedforward compensation. By classifying interactive forces into Major, Assistant, Coordination, and Redundant components, BAS leverages nonlinear gain functions to align user intent with exoskeleton action, while FCM enables joint- and target-oriented coordination across the full arm, resolving conflicts via IDM. Experimental results across flexibility, adaptability, accuracy, speed, and fatigue demonstrate that BAS+FCM substantially reduces donning disturbances and enhances handling of high-dynamic arm movements, achieving improved transparency and precision. The framework holds promise for more natural, comfortable, and safe full-arm exoskeleton operation in rehabilitation, teleoperation, and data-collection contexts, with future work focusing on force-feedback control for even higher dynamics and human-robot skill transfer.

Abstract

In rehabilitation, powered, and teleoperation exoskeletons, connecting the human body to the exoskeleton through binding attachments is a common configuration. However, the uncertainty of the tightness and the donning deviation of the binding attachments will affect the flexibility and comfort of the exoskeletons, especially during high-speed movement. To address this challenge, this paper presents a flexible exoskeleton control approach with binding alignment and full-arm coordination. Firstly, the sources of the force interaction caused by donning offsets are analyzed, based on which the interactive force data is classified into the major, assistant, coordination, and redundant component categories. Then, a binding alignment strategy (BAS) is proposed to reduce the donning disturbances by combining different force data. Furthermore, we propose a full-arm coordination mechanism (FCM) that focuses on two modes of arm movement intent, joint-oriented and target-oriented, to improve the flexible performance of the whole exoskeleton control during high-speed motion. In this method, we propose an algorithm to distinguish the two intentions to resolve the conflict issue of the force component. Finally, a series of experiments covering various aspects of exoskeleton performance (flexibility, adaptability, accuracy, speed, and fatigue) were conducted to demonstrate the benefits of our control framework in our full-arm exoskeleton.

Figures (15)

• Figure 1: The operator uses the 9 DoF exoskeleton, which is implemented with the exoskeleton control framework based on a binding alignment strategy and a full-arm coordination mechanism proposed in this article, to achieve flexible and coordinated control performance during high-dynamic, large-scale movements of the entire arm.
• Figure 1: Causes of disturbance in unstable phenomenon
• Figure 2: Overview of the exoskeleton system. The exoskeleton is driven by nine motors, which include shoulder joint motors SC1, SC2, SH1, SH2; elbow joint motors EL1, EL2; and wrist joint motors WR1, WR2, WR3. $\text{FT}_\text{UA}$, $\text{FT}_\text{FA}$, and $\text{FT}_\text{HA}$ are F/T sensors at the upper arm, forearm, and hand, respectively.
• Figure 3: In the ideal state, the interaction forces between the exoskeleton and the human at attachment points. (a), (b), (c) are respectively for the upper arm, forearm, and hand binding attachment.
• Figure 4: (a) is the simplified model diagram illustrating mismatched sizes for wearing the exoskeleton on the user's upper arm and forearm. It is similar to two linked rods moving together in a sleeve. The model is further simplified to the rod model in (b). When the upper arm and forearm move together, there is a misalignment at the binding point between the upper arm and forearm rods of the user and the exoskeleton.