Biologically inspired underwater propulsion and adhesion mechanisms

Abstract

The ultimate objective of this research is to develop an innovative underwater pipe inspection robot with both swimming and crawling capabilities as opposed to conventional in-pipe robots with wheeled designs or driven by propellers. The contents of this thesis include two different parts: a propulsion mechanism using a passive compliant tail and a reversible underwater adhesion mechanism. The propulsion mechanism is the primary concern of this research. The hypothesis of this part of research is that a continuous passive compliant tail structure with an optimized stiffness profile in its longitudinal direction along with the proper control of a single actuator can allow the undulatory motion of this mechanism to resemble real fish swimming locomotion. This approach is in contrast to conventional approaches where multiple joints are actuated to create traveling waves to emulate propulsion mechanisms of fish. Four iterations of experiments are developed in total to verify the hypothesis, take measurements and improve the performance of the propulsion mechanism. It is proven that a continuous passive compliant structure driven by a DC motor through a four bar linkage can generate sufficient propulsion to drive a moving unit forward along a guide rail. The experiments with a simple prototype demonstrate that the propulsion mechanism is promising to drive a robot forward along a prescribed path without a guide rail. It is demonstrated that the stiffness profile in the longitudinal direction is one of the critical factors that affects the performance of the propulsion mechanism. A simulation model is developed to guide the design process of the passive compliant structure, mainly to optimize its stiffness profile along the tail structure. Special measures are implemented into the experiments to extract data to compare with simulated results. The reversible underwater adhesion mechanism is another critical component of the underwater pipe inspection robot that is under development. The goal of developing a reversible underwater adhesion mechanism is to provide adequate traction to various surfaces while the robot operates in water. This reversible underwater adhesion mechanism allows a robot to stick and crawl in water pipes even across the stream. This mechanism may enable recharging capability extracting energy from kinetic energy of the pipe flow. Two generations of robot prototypes are developed to demonstrate the crawling and propulsion mechanisms.