Dynamic Performance and Torque Optimization of a Bio-Inspired Tadpole-Like Flexible Underwater Robot: A Comparative Study of SMC, Type-1, and Interval Type-2 Fuzzy Controllers

Abstract

Bio-mimicry of underwater robots with high agility capabilities such as tadpole-like locomotion provide high propulsion efficiency. But, the incorporation of a flexible and under-actuated tail structure into these robots results in complicated and highly nonlinear dynamics which are hard to control in various aquatic environments. This paper provides a complete dynamical study and comparison among three different robust control systems: traditional sliding mode control (SMC), type-1 fuzzy sliding mode control (Type-1 FSMC), and interval type-2 fuzzy sliding mode control (IT2-FSMC), used on a dual motor tadpole-like flexible underwater robot. The main aim of this research is to study the control effort (torque) and trajectory tracking performance of the joint actuators for two different operating situations: nominal (0%) and parametrically extreme (50%) situations.

From numerical simulation studies, it can be seen that although the conventional SMC and Type-1 FSMC perform reasonably well at 0% uncertainty, they become dynamically unstable with high-frequency chattering effects at 50% uncertainty level, adding dangerous resonance energy (control spillover effect) to the flexible tail. In contrast, the innovative IT2-FSMC model, which utilizes the concept of Footprint of Uncertainty (FOU) along with Karnik-Mendel type reduction scheme, successfully copes with the severe disturbances. The IT2-FSMC is capable of producing an extremely smooth and chattering free torque control signal to the motors.