Key Technologies Of Robot Squid Prototype Based On The Principle Of Muscular Hydrostat

Ocean resources are of more strategic importance as the earth resources are drying up in the 21st century. Unmanned underwater vehicles (UUVs) are the important devices to explore, to mine and to protect the ocean resources. The screw propelled UUVs suffer from low propulsive efficiency, awkward movements, noise, and the danger of screws to marine life, etc. As to these problems, biomimetic swimming robots, such as robot fish, are invented. However, they are of low pressure resistance capability. Squid/cuttlefish, the soft bodied animals, compete with fish successfully by their high-efficient, versatile compound swimming of jetting and fin undulating. Furthermore, due to muscular hydrostat, they can migrate from the surface to a depth of over 1000 m. Muscular hydrostat, a 3D array of closely packed fibers of muscles and connective tissues without rigid skeleton, can support body, generate movements and forces, and it is incompressible and pressure resistant. A shape memory alloy (SMA) actuated robot squid prototype mimicking the compound swimming of squid is proposed. Its quasi-soft movement structures, such as biomimetic mantle, biomimetic squid fin, biomimetic inlet and arm-fin, are based on the principle of muscular hydrostat to be high pressure resistant.Squid swimming mechanisms, and the musculatures of mantle and fin, the two key parts for swimming, are investigated. Structure specifications were obtained by the anatomy of the short-fin squids, Todarodes pacificus. Based on the principle of muscular hydrostat, simplified transverse sections models of fin and mantle segment are established and analyzed. During slow swimming of squid, the low frequency of either jetting or fin undulating is close to the frequency of SMA, while the strain of transverse muscles of squid fin is small and the mantle outer strain of about -8% is close to the maximum strain of SMA. These findss ensure the development of robot squid prototype. The movement structures of the prototype employ the elastic mechanism of animals to improve efficiency.The swimming movements of body and/or caudal fin propulsion (BCF) and rajiform swimmers are too complicated to be mimicked. If BCF movements are divided along the body, while rajiform movements along the fin width into enough units, of which the movement is simplified into flexible bending left and right, the corresponding movements can be imitated by integrating the bending units connected in series or in parallel. According to this hypothesis, flexible fin unit mimicking the squid fin structure was developed. SMA wires serve as"transverse muscles". Elastic mechanism of animals is incorporated into the movements to reduce energy consumption by storing and relaxing elastic energy. A bending model is established by combining Brinson constitutive model of SMA. Experimental results show that the flexible fin unit can bend and return flexibly both in air and in water. The flexible fin unit has the merits of large bending, simple structure, light weight, large force, silent actuation and modularization.The feasibility of the flexible fin unit for underwater propulsion is validated by a caudal-fin propelled micro robot fish employing a flexible fin unit. The robot fish, 146 mm in length (with a carp-like caudal fin) and about 30 g in weight, realized subcarangiform- and carangiform-like swimming, and the maximum speed was 112 mm/s while the minimum turning radius 136 mm. A squid-fin like propeller, a biomimetic inlet and an arm-fin were developed. The squid fin-like propeller mimicks the fin oscillation of shotfin squid by employing 10 dual-face flexible fin units. The maximum speed was 40 mm/s and the maximum turning speed 22°/s.The jetting of robot squid prototype is realized by mantle-like propeller. The biomimetic mantle, employing SMA wires as"circular muscles", contracts actively and inflates by elastic energy. The feasibility of jet propulsion is validated by an SMA spring-actuated single jet propeller. Two kinds of SMA wire-actuated biomimetic mantle, including parallel and vertical setup, are designed. A movement model is established by combining Brinson constitutive model. PWM pulses can be adopted to improve the contraction frequency and to reduce energy consumption. The maximum inner strains of the 5 boimimetic mantle structures developed all exceeded -6%. A mantle-like propeller, with a 799 g biomimetic mantle in parallel setup, was developed. In the experiments, the propeller reached a maximum strain of outside diameter of -8.8% and an average speed of 56 mm/s during 0.6-1.2 s.Key technologies of robot squid prototype are studied, and squid fin-like propeller, biomimetic inlet, arm-fin and mantle-like propeller were developed, which lay the foundation of the practical applications of robot squid.