Ultra-local model-based predefined-time assist-as-needed control for upper limb patient-exoskeleton system under input and performance constraints

Honglin Xie; Yangchun Wei; Honglin Xie; Yangchun Wei

doi:10.3934/math.20251055

AIMS Mathematics

2025, Volume 10, Issue 10: 23738-23772. doi: 10.3934/math.20251055

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Research article

Ultra-local model-based predefined-time assist-as-needed control for upper limb patient-exoskeleton system under input and performance constraints

Honglin Xie ,
Yangchun Wei ^,

School of Data and Computer Science, Shandong Women's University, 2399 Daxuelu, Jinan, 250300, Shandong, China

Received: 16 July 2025 Revised: 05 October 2025 Accepted: 11 October 2025 Published: 20 October 2025
MSC : 93B52, 93C40, 93C85, 93D05

In this work, an ultra-local model-based predefined-time assist-as-needed controller (UPTAC) is presented for a upper limb patient-exoskeleton system (ULPES) under input and performance constraints. The designed UPTAC has a dual-loop control architecture. The outer impedance sub-control loop includes task performance function and impedance controller, which dynamically adjust the speed of rehabilitation exercises and obtain the desired assistive torque. Next, under the ultra-local model-based control framework, an inner torque sub-control loop was designed by combining barrier Lyapunov function and performance constraints, thereby achieving predefined time convergence and reducing the complexity of controller design. Finally, the effectiveness of UPTAC was verified through simulation.
- ultra-local model-based control,
- predefined-time control,
- assist-as-needed control,
- barrier Lyapunov function
Citation: Honglin Xie, Yangchun Wei. Ultra-local model-based predefined-time assist-as-needed control for upper limb patient-exoskeleton system under input and performance constraints[J]. AIMS Mathematics, 2025, 10(10): 23738-23772. doi: 10.3934/math.20251055

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Abstract

In this work, an ultra-local model-based predefined-time assist-as-needed controller (UPTAC) is presented for a upper limb patient-exoskeleton system (ULPES) under input and performance constraints. The designed UPTAC has a dual-loop control architecture. The outer impedance sub-control loop includes task performance function and impedance controller, which dynamically adjust the speed of rehabilitation exercises and obtain the desired assistive torque. Next, under the ultra-local model-based control framework, an inner torque sub-control loop was designed by combining barrier Lyapunov function and performance constraints, thereby achieving predefined time convergence and reducing the complexity of controller design. Finally, the effectiveness of UPTAC was verified through simulation.

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