Alias, Nor Akmal (2023) Trajectory tracking control of nonholonomic differential drive wheeled mobile robot for rehabilitation purpose. Doctoral thesis, Universiti Tun Hussein Onn Malaysia.

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Abstract

The over ground gait rehabilitation is one of the popular rehabilitation devices to enhance rehabilitation outcome while reducing therapist’s workload. However, in practice, it is a challenging task to design a system that is easily affected by uncertainties and external disturbances from the wheeled mobile robot (WMR). Thus, it is hard to maintain its stability and robustness when dealing with patients who are disabled to walk. It is very risky to let off this concern. The strategies of trajectory tracking control of the WMR can provide better motion and steer ability while assisting patients through gait treatment to improve rehabilitation outcomes. Therefore, a suitable controller is designed to ensure stability in human-robot interactions. In this work, a new control law has been proposed by improving the switching law of the sliding mode controller (SMC) to eliminate the chattering effect in the control system called Terminal Super Twisting Sliding Mode Control (TSTSMC). The enhanced TSTSMC uses sliding mode control techniques to achieve high-precision tracking of a reference signal with Cuckoo optimisation. The proposed TSTSMC algorithm enhances control law for the trajectory tracking control while reducing the chattering effect in the control system. The TSTSMC was tested for external disturbance and uncertainties to evaluate the chattering suppression of the controllers. The TSTSMC was benchmarked with SMC (SMC), Terminal SMC (TSMC) and super twisting SMC (STSMC), and terminal Super Twisting SMC (TSTSMC) without optimisation. A simulation study shows that the TSTSMC algorithm improves the chattering and steady error by up to 35% and 25%, respectively. The translational velocity from the data sampling that has been used in the control law simulation gives results within an average normal gait speed. The average speed performed by the WMR is 1.25ms-1 which is lesser than the normal speed. The proposed controller algorithm has been proven to provide trajectory robustness and stability for WMR and can be extended for future improvement for gait assistive devices

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