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Simulation study on prescribed-time stabilization of 5-DOF exoskeletons using a regularized super-twisting approach
Elahe Moradi1, Mohammad Ali Labbaf Khaniki2, Saeed Amiri3
1Department of Electrical Engineering, YI.C., Islamic Azad University, Tehran, Iran. Elahe.moradi@iau.ac.ir.
Scientific Reports
|July 31, 2026
Summary
This study introduces an enhanced Prescribed-Time Super-Twisting Controller (PT-STC) for upper-limb exoskeletons. It ensures precise, fast, and smooth rehabilitation robot control, minimizing errors and preventing actuator saturation.
Area of Science:
- Robotics
- Control Systems Engineering
- Biomedical Engineering
Background:
- Upper-limb rehabilitation exoskeletons require precise and safe control for effective patient recovery.
- Conventional control methods can suffer from chattering, actuator saturation, and sensitivity to initial conditions and disturbances.
- Prescribed-time control offers finite-time convergence but can face gain explosion issues.
Purpose of the Study:
- To propose an enhanced Prescribed-Time Super-Twisting Controller (PT-STC) for 5-DOF upper-limb rehabilitation exoskeletons.
- To ensure tracking error convergence within a user-defined time, independent of initial conditions and disturbances.
- To eliminate singularities and chattering for safe and smooth human-robot interaction.
Main Methods:
- Introduction of a regularized scaling transformation for tunable error bounds.
- Implementation of a "Soft-Landing" mechanism to prevent gain explosion and actuator saturation.
- Integration of the Super-Twisting Algorithm in a scaled coordinate domain.
Main Results:
- Achieved a settling time of approximately 1.99s in simulations.
- Demonstrated significant reductions in settling time and total variation compared to conventional sliding mode control.
- Verified chattering-free torque profiles and safe operational limits under various conditions, including impact disturbances.
Conclusions:
- The proposed PT-STC offers a balanced approach to temporal precision and smooth actuation for rehabilitation robotics.
- The "Soft-Landing" mechanism effectively addresses singularity and saturation issues inherent in prescribed-time control.
- Simulation results are promising, highlighting the need for further experimental validation before clinical application.
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