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Prototype Design of a Kind of Biomimetic Cuttlefish Underwater Robot Actuated by SMA Wires
Abstract
Cuttlefish can swim with great maneuverability by undulating their fins and can swim with high speed by jetting. To mimic the muscle structure of the cuttlefish, a kind of flexible fin unit which can bend to both sides and a kind of biomimetic mantle which can flexibly contract and expand, are developed with the structure that SMA (shape memory alloy) wires are embedded into the flexible silicone rubber. Then a kind of biomimetic undulating fin and a kind of biomimetic jet propeller based on the former design are developed to mimic the swimming mechanism of cuttlefish. And the thrust performance of both of the propellers is tested. At last, a prototype of biomimetic cuttlefish robot is developed and the swimming experiments are carried out.
In order to improve the performances of microfluidic actuators, a microfluidic actuating way based on the shape memory alloy(SMA) is presented, which is applied for the liquids circulation of a microfluidic colour-changing system. A SMA spring is used as the main actuating part, a microfluidic actuating device based on the SMA spring is designed and fabricated. The models for the SMA spring and the whole SMA actuated microfluidic system are established, the experimental platform is built. The temperature properties, output displacement performances and pressure responses of the present system are simulated and tested under different experimental conditions. Comparing with traditional microfluidic actuating systems, the SMA actuated microfluidic colour-changing system is driven by using DC power, small in size, convenient in operation, and has fast response speed and high reliability.
A shape control algorithm for soft robot inspired by octopus is presented. Because of the infinite degrees of freedom of soft robot, the control algorithm for the rigid robot is not applicable. According to the movement characteristics of soft robot, the shape control parameters are derived. Then the kinematics model of the soft robot is developed, and the relation between soft robot shape parameters and driving cables length is deduced. From this relation, a shape control algorithm is designed. The stability of the shape control algorithm is proved through Lyapunov theory. Finally, the effectiveness of the shape control algorithm is verified by experiments.
Investigations on dynamics and motion control for a crablike robot in floating gait are conducted, in order to achieve the waypoint-tracking control of the leg-paddle coupling crablike robot disturbed by unknown current and flow. Firstly, dynamic model of the robot subject to complex underwater environment is established with consideration of the effects of the gravity, the buoyancy, the thrust produced by the swimming leg and the hydrodynamic force. On this basis, a sliding mode variable structure controller based on exponential approach law is designed. The phase difference between the flapping motion and the feathering motion is taken as the controlled variable to achieve the yaw rate control. And the globally asymptotic stability of the control system is proved by the Lyapunov direct method. Simulations and experiments of single and multiple target tracking are carried out, and the results show that the presented controller has strong waypoint tracking ability and robustness against the variations and disturbances of the system dynamics.
This paper mainly discusses the design and realization of the test model for a bionic underwater vehicle, which is propelled by undulations of a long flexible fin. Firstly, design principles and architecture of the test model are briefly introduced. Then we focus on the design method, the components and the operational procedure of the bionic long flexible fin, the control and communication module, as well as the motion control subsystem. Finally, some conclusions are drawn from the test data and experimental results of the test model, and the necessities to improvements and further research are also proposed. Realization of this test model verifies that propulsion by undulations of a long flexible fin may be effectively applied to the propulsion control system of underwater vehicles from the view of principles and technologies.
In order to improve the maneuverability of underwater biomimetic fish-like propulsor, we recently study black ghost knifefish which typically uses undulatory locomotion of ventral ribbon fin to produce thrust. The morphology and kinematics of this ribbon fin is analyzed. Meanwhile, the fin model is simplified, and a robotic fish fin driven by shape memory alloy (SMA) is developed. Then, the mechanical structure and corresponding control circuit of this biomimetic robot fin are introduced. Particularly, the swimming velocity and thrust generated by undulatory motion of the developed robotic fin are analyzed theoretically. Furthermore, a computational fluid dynamics (CFD) method is used to show pressure distribution on robotic fin surface as well as the periodical change of generated swimming thrust with time. These computational results are compared with previous experimental value, indicating that these computational results are reasonable and correct. All these results show that it's a very-interesting and feasible to study the SMA driven robotic fish fin.
According to the shortcomings of most robot fish, such as not incorporating elastic mechanism to improve energy efficiency and poor pressure resistance capability, squid/cuttlefish, which have excellent swimming capability and pressure-resistant structure, are studied. Swimming mechanism of squid/cuttlefish jetting and fin undulating propulsion is analyzed, and the equations of jet thrust, propulsive efficiency of jetting period and whole hydrodynamic propulsion cycle are given. The advantages of squid/cuttlefish compound swimming are good performance at both high and low speeds, being capable of changing swimming direction immediately, low noise, and that thrust can be generated even if jet velocity is slower than that of the surrounding fluid. In order to explain swimming mechanism in depth, the muscle arrangements and functions of mantle and fin muscular hydrostats, the two locomotory systems, are studied. The muscular hydrostats not only serve to the skeleton support of body, to carry out movement and to generate force, but also have considerable pressure-resistant capability. The hydrostatic pressure in and out of the mantle of most squid/cuttlefish is equal due to no gas filled tissue in their body, which improves their pressure-resistant capability further. During the movement, energetic efficiency is improved because energy is saved by the elastic spring mechanism. If the characteristics of swimming mechanism, muscular and elastic mechanism could be applied to biomimetic underwater robot, the robot would be more efficient, flexible and pressure-resistant.
The undulating fin propulsion system is an instance of the bio-inspired propulsion systems. In the current study, the swimming motion of a squid-like robot with two undulating side fins, mimicking those of a Stingray or a Cuttlefish, was investigated through flow computation around the body. We used the finite analytic method for space discretization and Euler implicit scheme for time discretization along with the PISO algorithm for velocity pressure coupling. A body-fitted moving grid was generated using the Poisson equation at each time step. Based on the computed results, we discussed the features of the flow field and hydrodynamic forces acting on the body and fin. A simple relationship among the fin's principal dimensions was established. Numerical computation was done for various aspect ratios, fin angles and frequencies in order to validate the proposed relationship among principal dimensions. Subsequently, the relationship was examined base on the distribution of pressure difference between upper and lower surfaces and the distribution of the thrust force. In efficiency calculations, the undulating fins showed promising results. Finally, for the fin, the open characteristics from computed data showed satisfactory conformity with the experimental results.
Compact zero-mass pulsatile jet actuators are proposed for low-speed maneuvering and station keeping of small underwater vehicles.1 The flow field of such jets are initially dominated by vortex ring formation. Pinched-off vortices characterize the extremum impulse accumulated by the leading vortex ring in a vortex ring formation process. Relevant parameters in this process are identified in order to design simple and low cost zero-mass pulsatile jet actuators. Thrust optimization of synthetic jets for maximal thrust generation is achieved by enforcing the jet formation number to be around 4. Prototypes of such actuators are built and tested for underwater maneuvering and propulsion. The actuators could be used in two ways: (i) to improve the low-speed maneuvering and station keeping capabilities of traditional propeller driven underwater vehicles, and (ii) as a synthetic jet for flow control and drag reduction at higher cruising speeds. A model for calculating the rotation rate of the underwater vehicle is also proposed and verified.
This paper proposes a new synthetic jet actuation
concept for small, low speed, highly maneuverable AUVs.
Synthetic jet thrusters, which produce jets of vortex rings,
are inspired by the pulsatile jet propulsion of salps, jellyfish, and squid. To assess the potential utility of this scheme, we developed synthetic jet actuator prototypes, and verified their function via both force measurement and flow visualization experiments. We used a genetic-algorithm based technique for optimizing the actuation profile of the thrusters. Also presented is an initial discussion of vehicle design. Our conclusion
is that synthetic jet thrusters are a viable propulsion method for small underwater vehicles.
Future underwater vehicles will be increasingly called upon to work in cluttered environments and to interact with their surroundings. These vehicles will need sensors that work efficiently at short range and be highly maneuverable at low speed. To obtain insights into principles and mechanisms of low-speed operation in cluttered environments, we examine a fish that excels in this regime, the black ghost knifefish Apteronotus albifrons. This fish hunts in dark or turbid water using a short-range self-generated electric field to sense its surroundings. Coupled with this unique mode of sensing is an unusual ribbon fin propulsion system that confers high multidirectional maneuverability at low speeds. To better understand the relationship between body morphology and common maneuvers of this fish, we utilized an idealized ellipsoidal body model, Kirchhoff's equations, and an optimal control algorithm for generating trajectories. We present evidence that common fish trajectories are optimal, and that these trajectories complement the sensory abilities of the fish. We also discuss prototypes of the sensing and propulsion systems of the fish with a view to providing alternative approaches for underwater vehicle design where high maneuverability in geometrically complex environments is needed.