Atomic Orbital Search Optimization Based Fractional Order PID Controller for 4 DoF Lower Limb Exoskeleton

This paper presents a design of fractional order Proportional-Integral-Derivative (FOPID) controller for a 4 degree-of-freedom (DoF) lower limb exoskeleton (LLE) for motion assistance. The exoskeleton consists of four actuators, each responsible for hip flexion/extension and knee flexion/extension. The ankle is considered a passive one in this design. The exoskeleton dynamic modeling is derived using the Euler-Lagrange method. The fractional order PID controller is used to improve the stability and performance of the exoskeleton by incorporating the advantages of integer order PID controllers and fractional order calculus. To improve the performance of the controller, an atomic orbital search (AOS) optimization algorithm is used to tune the controller parameters. The effectiveness of the proposed fractional order PID controller is evaluated by introducing disturbance in the angular position of a 4 DoF LLE. The dynamic simulation results show promising potential for improving the quality of life for paraplegic patients by tracking the reference trajectory and highlighting the need for further refinement.