Abstract
In this study, a model-free adaptive sliding mode control method was developed in combination with the prescribed performance method. On this basis, this study attempted to fulfill the joint position tracking trajectory task for the one-degree of freedom (DOF) upper-limb exoskeleton in passive robot-assisted rehabilitation. The proposed method is capable of addressing the defect of the initial error in the controller design and the application by adopting a tuning function, as compared with other prescribed performance methods. Moreover, the method developed here was not determined by the dynamic model parameters, which merely exploit the input and output data. Theoretically, the stability exhibited by the proposed controller and the tracking performance can be demonstrated. From the experimental results, the root mean square of the tracking error is equal to 1.06 degrees, and the steady-state tracking error converges to 1.91 degrees. These results can verify the expected performance of the developed control method.
Highlights
Unlike the original model-free adaptive control (MFAC)-sliding mode control (SMC)-PP control framework, a tuning function, which can be exploited to overcome the technical difficulty of the initial tracking error limitation in prescribed performance method, is introduced into the proposed control method to manipulate a one-degree of freedom (DOF) upper-limb exoskeleton driven by pneumatic artificial muscle (PAM)
MFAC-SMC-PP controller was designed as the comparison method, and its controller parameters are selected to be identical to the proposed controller except for the prescribed performance function (i.e., ρ0 = 5, v = 0.05, and ρ∞ = 0.05)
This study proposed a novel MFAC-SMC-PP control method for the one-DOF upper-limb exoskeleton robot driven by the PAM to fulfill passive robot-assisted rehabilitation tasks when the initial tracking error is out of the boundary
Summary
The exoskeleton refers to a wearable robot system comprising an external structural mechanism with joints and links corresponding to the human body [1]. Inspired by the mentioned observations, this study is focused on the PP method in the tracking trajectory issue of the upper-limb exoskeleton It primarily discusses a new MFAC-SMC-PP control method to address the initial position that does not meet the performance boundary condition, which often occurs during the restart of the exoskeleton. Unlike the original MFAC-SMC-PP control framework, a tuning function, which can be exploited to overcome the technical difficulty of the initial tracking error limitation in prescribed performance method, is introduced into the proposed control method to manipulate a one-DOF upper-limb exoskeleton driven by PAMs. On that basis, this study attempted to mimic passive rehabilitation training.
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