Abstract: This paper presents dynamic modelling and control of a linear prismatic series of elastic actuator. The capability of generating large torques is why this actuator is increasingly used in human-assistive robotic systems. Due to having human in the loop, the actuator requires precise control. A fractional PID controller known for its improved performance is used for the control, due to having additional degrees of freedom than the classical PID. The actuator has one servo driver and five controller gains to be tuned. The gains are optimized using both Particle Swarm Optimization (PSO) and Imperialist Competitive Algorithms (ICA). Comparison of the results from the two optimization methods illustrates that the PSO tuned FOPID controller has a slightly better performance, faster convergence and better settling time. Next, the PSO tuned controller is compared with a Genetic Algorithm (GA) tuned PID controller. It is shown that the PSO tuned FOPID controller continues to offer better performance, especially in terms of its rise time and settling time.Keywords: Series elastic actuator, Fractional order PID, Imperialist competitive algorithm, Particle swarm optimization, Control تفاصيل المقالة

This paper starts with developing kinematic and dynamic model of a snake shape robot in serpentine locomotion and finishes with actual experimentation. At the beginning the symmetrical and unsymmetrical serpenoid curves are introduced. Kinematics and dynamics of a snake robot on flat and inclined surfaces are obtained for a general n-link robot. SimMechanics toolbox of MATLAB software is employed to simulate the snake robot. Effects of serpenoid curve parameters on joint torques and progression of the snake robot are also investigated. Results indicate that by increasing the inclination angle of the surface, link length and numbers of links, joint torques are increased. NSGA multi optimization method is next utilized to obtain the unsymmetrical curve parameters resulting in minimum joint torques and maximum snake progression. Optimal solutions are presented in the form of Pareto front optimal. The optimization shows that the required range of parameters of snake robot's body curve for higher progression and less torque, is limited. Additionally, it is shown that by employing the unsymmetrical serpenoid curves the efficiency of snake robot can be increased. Finally, FUM-Snake I robot is employed to validate the theoretical results on a flat surface. The experimental results show that the proposed kinematics and dynamics model are reasonable. تفاصيل المقالة