| An amphibious robot is a robot which should be adapted to various environmental conditions inland and underwater. It also could pass through complex medium terrain at the transitional zone between the land and water. Such a robot can find broad applications in resource exploration, disaster rescue, and reconnaissance, etc. Developing amphibious robots constitute a challenging research topic that has gained much attention from worldwide researchers. Current researches of amphibious robot are mainly focused on the design of the composite propulsion mechanism and the experimental study in the land and water. But the capability and effectiveness of the amphibious robot when locomoting at the transitional zone between the water and the land to which relatively little attention has been paid. In the real world, various complex terrains at the transitional zone are always not easily to be conquered with regard to a robot. In all of the complex terrains, the soft substrates which are common at the transitional zone is more difficult to the robot. This kind of complex terrain is quite a nightmare for most of the current amphibious robots. Furthermore, the selection of the amphibious propulsion methods also plays an important role in the construction of amphibious robot. Above all, it is meanful to understand the mechanism of interaction between the propulsion performer and soft substrates. In the like manner, we also need to promote the technology of amphibious composite propulsion method.In this paper, preliminary theoretical and simulation analysis are presented to explore the dynamics between the arched foot and soft substrates. An orthogonal experiment is conducted to study the locomotion performance of the propulsion unit equipped with arched feet in the sandy and muddy terrain with different water content. We presented the detailed structural design of the transformable foot-flipper propulsion mechanism and its driving module. Finally, basic propulsion experiments of the robot are launched, which verifies that the transformable foot-flipper mechanisms have enabled the amphibious robot to pass through rough land, soft substrate, and underwater, simultaneously. The main research contents and contributions of this thesis are listed as follows:(1) By testing three kinds of common water-land transitional environment medium’s shear strength resistance (dry sand, wet sand, mud), we obtain the soil mechanical properties preliminarily. we use infinitesimal method to analysis the stress situation of the arc foot moving in soft medium, and take advantage of the experiment of the bar to achieve the mechanical model parameters, then calculate the variation of the propulsive force, supporting force and torque in one rotation period when the arc feet of different configuration parameters moving in the sand medium. We also make the arched foot motion simulation analysis in the same condition by using the Particle Flow Code (PFC), and the trends of the variation of different foot types are similar. It implies that the theoretical analysis method is feasible and the results of the theoretical analysis can provide design reference for the amphibious robots’ mechanism design and control method.(2) We built the soft medium experimental platform which is in water-land transitional environment autonomously, and we do research on propulsion performance of different types of arc feet with different motion control parameter in sand medium and mud medium with different moisture content. Because of the large number of variables and the difficulty of experiment, in order to optimize the energy consuming, the speed of moving and the value of centroid fluctuation, we adopt the way of orthogonal test and range analysis to analysis the law of the different variables influence on propulsion performance from considering the results of the theory analysis and simulation, we can understand the relationship between the arc feet and the soft medium in water-land transitional environment deeper,and achieve the best combination of parameters under the conditions of different optimization goal.(3) It is suitable to adopting the arched foot as the propulsion performer in the soft substrates due to the balance of supportive force and forwarding force compared with the wheeled and straight leg methods. According this result, we proposed a novel amphibious robot with the foot-flipper composite propulsion mechanism. When proceeding terrestrial locomotion, the robot occupies six arc shaped legs and walks like a cockroach. By switching the legs to the flipper state, the robot could swim in the water and perform various maneuvering. The electrical system design of the robot is introduced. We also developed a neural control system using the central pattern generator (CPG) based on the Hopf model. It can easily generate the gait signals which are designed for the propulsion in land and underwater. The gait conversion between triple gait and synchronous gait is also realized.(4) Experimental study on the motion performance of six foot-flipper amphibious robot is carried out. In land, the maximum walking speed is up to approximately0.49m/s (0.58times of body length). The maximum angle of slope that can be conqued by the robot is about35degrees. The robot could go over a obstacle with the vertical height less than180mm and climb up continuous stairs with the single stair height less than160mm. In water, the robot could realize a linear maneuvering at about maximum speed of0.25m/s (0.3times of body length) because of the non-streamline of the body case. Thanks to the cooperation of six flippers, the robot can realize the motion including pivot turning, ascending, diving and braking. A landing motion has also been performed to verify the movement of the robot at soft muddy terrain between the water and land. |
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