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This paper presents Artificial Neural Network (ANN) as an optimization tool in tuning Proportional-Integral-Derivative (PID) controller's gain of a multi-joints Lower Limb Exoskeleton (LLE) for gait rehabilitation. The interest in wearable post-stroke and spinal cord injury rehabilitation devices such as LLE has been increasing due to the demand for assistive technologies for paralyze patients and to meet the concerns in the increasing number of ageing society. The dynamic of three degree of freedom LLE was determined using Euler-Lagrange equation, and PID parameters were initially tuned using the Ziegler-Nichols (ZN) method. The paper compares different ANN-based algorithms in tuning PID controller's gain for LLE applications. The method compared and evaluated with other methods and dynamic systems in the literature. ANN-based algorithms, Gradient Descent, Levenberg-Marquardt, and Scaled Conjugate Gradient, are utilized for PID tuning of each joint in the LLE model. The result shows faster convergence and improves step response characteristics for each controlled joint model. The overshoot values found to be 0.3126%, 0.6335%, and 0.2619% compared to the ZN method with 10.5582%, 15.1643%, and 11.8511% for hip, knee, and ankle joints, respectively. It can be ascertained that the PID controlled of LLE has been optimally tuned significantly by different ANN methods, which reduced its steady-state errors.

A "Stroke" is a neurological disease due to poor blood flowing to the brain, resulting in body cell death. It is ranked second as the most common cause of death globally. The "World Health Organization" estimates that about 15 million people suffer a stroke annually. Most stroke survivors have gait disorders, and most patients cannot walk without assistance. Physiotherapy is crucial for stroke patients to recover and maintain their mobility, functionality, and well-being. In the last 20 years, the replacement of physiotherapists with wearable robotics has become essential due to the developing technology, the need for economic growth, and the challenging health circumstances around the world, such as the COVID-19 pandemic recently. Lower Limb Exoskeleton (LLE) represents the solution for stroke patients under such circumstances, though its performance is a critical challenge paid attention to in the industry. This challenge has motivated the researchers to investigate the application of gait rehabilitation. This review presents and discusses the developments in the control system of LLE over the last decade. It also explores the limitations, new directions, and recommendations in LLE development according to the literature.