Development and Innovative Design Research of Underwater Bionic Fish Products under Hybrid Propulsion Technology

Abstract

For a long time, underwater robot has been used as a scientific research tool and a teaching platform, but the real application products have not been well explored. The successful case of UAV gives underwater robot a higher expectation. How to apply underwater robot and enter the market has become a hot spot of underwater robot research at present. This paper mainly introduces a bionic fish-shaped robot, redefines underwater robot with innovative thinking, determines product functions from the perspective of the market, and develops product functions and designs and realizes the structure of each part according to the existing scientific research experience. Main innovation points of this design are to adopt the way of the hybrid propulsion for underwater robot movement, through the form of a hybrid propulsion and long range and the contradiction between the rapid maneuver, at the same time of umbilical cord cable, using float design improvement, and through the highly integrated ground station for the system operation control.

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1. Introduction

After 66 years of development, the technology of underwater robot has gradually matured, which is mainly reflected in the miniaturization of its main body, diversification of accessories, and modularization of functions. This paper mainly introduces a hybrid propulsion bionic fish system based on underwater robot technology. The system consists of three parts: the robot body, the fin communication system, and the ground station control system. According to the design requirements of the subject, the mechanical structure design of the system and the stress analysis of key bearing parts are carried out by using Unigraphics NX 10.0. The fluid mechanic analysis of the bionic fish is carried out by combining with Solidworks 2018. The overall design, production, and debugging of the system are carried out according to the basic parameters of the design task book. In order to further develop its functions and enter the application market, the feasibility of underwater bionic robot in the market is explored.

As a tool for exploring underwater space, the main difference between underwater robot and land and air robot lies in the huge difference of working environment medium. As an important technical means and equipment for ocean research and development, underwater robots have been increasingly widely applied in various fields of ocean research and development [1, 2]. When the robot enters the water, the two problems that must be considered are the influence of water on the normal operation of electronic devices in the robot work and the absorption and shielding of electromagnetic waves by water. Of course, after so many years of development, low-cost solutions for civil use gradually take shape. With the structural upgrading and technological improvement of waterproof sealing chamber, a 300-meter pressure-resistant chamber only needs more than 1,000 yuan. Subsea powertrain solutions are also being miniaturized and productized. At present, a high-power and high-thrust thruster only costs 2,000 yuan. All the signs indicate that the potential for the application market of underwater robots is gradually improving.

This paper mainly studies a hybrid propulsion bionic fish. The original plan is to use uncabled underwater robot (AUV), but the team still has not solved the problem of low-cost underwater communication; so, the current research stage is still stuck in the level of cabled underwater robot (ROV). During the discussion and development of the scheme, draw lessons from the “Haizheng ii” ARV designed by China Ship Science Research Center. It has three modes of autonomy, remote control, and monitoring for timely selection in complex environment. It has its own energy and is connected with the mother ship through optical fiber. It can conduct search, fixed-point observation and light underwater operations in a medium range [2]. We are looking forward to a new way of thinking to solve the limitations of umbilical cord on the robot’s movement space and range, so as to improve its maneuverability and facilitate the market promotion and application of underwater robots.

2. Research Status: The Development History of Bionic Robots

People are very famous for the exploration of the bionic robot can be traced back to the earliest of The Three Kingdoms period MuNiu LiuMa, humans have been found in the long process of evolution, biological many details remain very worth learning, and this greatly inspired the exploration of human desire; since September 1960, the first world conference on bionics was held in the United States air force base, Ohio. In the decades since, a host of bionic technologies and devices has emerged. For example, Boston Dynamics, the most familiar company, has been conducting research and development of bionic robots since its establishment in 1992 [3, 4]. All the robots released have generated a great sensation, from Big Dog to Handle, which has provided great impetus for the development of bionic robots.

2.1. Technical Difficulties and Market Analysis of Bionic Underwater Robot

Biomimetic fish remained in the theoretical stage before the design and production of robofish “RoboTuna” in 1994. Since then, a large number of biomimetic fish have gradually entered the public view, and their shapes are gradually diversifying. With the slow progress of technology, many low-cost waterproof and sealing schemes and reliable communication schemes have been developed, and the bionic fish has also begun to be commercialized. The “KenFish-A-Series” series of Lewisdom Robot is very representative (See Figure 1), providing users with a set of kits that can be built quickly through modular products [5, 6]. This robot uses a steering gear to carry out single-joint movement to provide power to the robot. From the perspective of dynamic structure, the efficiency of this mode of movement is low. In practical use, the movement speed of single-joint bionic fish is less than 0.5 m/s. The waterproof and sealed shell made of engineering plastic cannot withstand enough water pressure, and communication signal transmission through Wi-Fi cannot solve the problem of underwater communication; so, the robot is summarized.

[figure omitted; refer to PDF]

The overall maximum height is 200 mm and the maximum width is 350 mm. According to these two parameters, the diameter of the chip cabin barrel is 160 mm. According to the minimum principle of camera cabin, select 90 mm camera cabin. [9]

According to the above dimensional analysis, the overall structure diagram can be obtained, and the preliminary layout is shown in Figure 5:

The prototype’s frame is made of aluminum profile, which has the advantages of easy processing, standardization, ease of procurement, and low cost. It uses a standard connection mode with good internal and external angles, which greatly improves connection strength accuracy. At the same time, the prototype’s surface has corrosion resistance characteristics after high temperature oxidation and sand blasting treatments. It is the ideal material for bionic fish frame. The disadvantage of this flexibility is that the solution is not optimal in terms of cost and energy consumption, but a good compromise can be found [10]. The preliminary design of the bionic fish frame is shown in Figure 6.

[figure omitted; refer to PDF]

Robot KenFish lexrev company team will be the water according to the different parts of functional division, KenFish single joint suite is a multipurpose water robot contest teaching platform, and the platform is given priority to with sensing, control, and able to meet the needs of all kinds of colleges and universities students to learn and practice, but also suitable for students in extracurricular development challenge, innovation, competition, and subject. KenFish single joint kit meets the requirements of the International Underwater Robot Competition project team and obtains the product authorization letter from the International Underwater Robot Alliance. The mechanical movement part of KenFish single-joint kit uses bionics technology to simulate the swimming mode of fish, so that the robot can move continuously and freely in water, with propeller propulsion mechanism, sensing mechanism, rotating mechanism, and other mechanical structure, so that the robot can carry out more ways of movement. Equipped with a vision cabin, it can transmit 720P HD video in real time and store images. Suite is divided into single joint head tank processor module, a standard module of balancing module, oscillating propulsion control module, sensor module, the propeller propulsion module, module through standard PH2.0 4 p port connection between modules, include the power cord and CAN bus communication, convenient communication between each module, can be flexible enough to increase or decrease in hull, and convenient user study and extracurricular expanding. It provides an efficient and reliable platform for users to carry out underwater applications. The rapid increase and decrease of the cabin are the characteristics of this robot; so, a reliable and convenient waterproof method has become the core of this function. Through the deep understanding of this sealing principle, we refer to this structure for floating waterproof sealing structure design.

The principle of this sealing method is to add a layer of soft silica gel ring between the two connectors, through the compression force to make the soft silica gel deformation, so as to fill the gap between the two connectors, and this process in how to produce effective positive pressure between the two parts becomes the main point of consideration. We need to add a sealing structure at the bottom of the float, so as not to damage the overall structure of the upper end of the float and not to damage its external streamline overall more beautiful.

According to the above argument, the floating structure is divided into two parts: (1) upper fin shape and bracket structure and (2) lower sealing cover structure. The two structures are connected by screws, and the positive pressure generated after screw tightening is used to deform the soft silica gel ring, thus creating a closed space. The fin shape assembly effect is shown in Figure 16.

[figure omitted; refer to PDF]

4.1.1. The Design of Upper Fin Shape and Bracket Structure and Lower Seal Cover Structure

The shape of the upper fin and the structure of the bracket are characterized by streamlined shape design to reduce the influence of fluid resistance on the normal movement of the float. The internal frame structure is supported to improve the strength of the outer shell, so that the shell has a certain compressive capacity, but also can provide the corresponding installation position for the hardware chip. At the bottom of the whole structure, we reserved a ring of M3 screw bottom holes around the edge of the shell. In order to facilitate the positioning and installation of the lower sealing cover structure, the design of step provides a positioning foundation, and the step can also produce a certain auxiliary sealing function after the coordination of the two parts of the structure.

The function of the lower seal cover structure is mainly two, one is to connect with the upper fin shape and bracket structure to form a sealed cavity, in order to accommodate the hardware chip circuit board. The second is to provide a certain number of threading screw holes, so that the umbilical cable out of the main body of the underwater bionic fish can be connected to the float and to provide a sealing test port to test the sealing performance. Cushion a layer of soft silica gel ring in the middle of the two structures, the two structures are connected and pressed by screws, and the compression force makes the soft silica gel ring deformation to fill the gap of the contact surface to meet the requirements of sealing.

4.1.2. Application Example and Effect of Net Bridge in Fish Fin

The video data generated by the underwater bionic fish in the underwater shooting needs to be transmitted through a device after the transmission of the power carrier module and the power carrier module on the fin. At this time, we need a communication transmission module to achieve this function. After comprehensive consideration in terms of production cost and other aspects, Wi-Fi communication is undoubtedly the most convenient, efficient, and simplest solution. However, its disadvantage is also fatal; that is, its effective transmission distance is very limited, which has a great impact on the normal movement of the bionic fish. On this basis, we searched materials. It is decided to use the bridge as the communication module between the bionic floating fish and the ground station.

A Bridge, also called a Bridge, is a storage/forwarding device that connects two LANs. It can divide a large LAN into multiple network segments or interconnect more than two LANs into a logical LAN so that all users on the LAN can access the server. Expansion of the most common method is to use the bridge; according to the survey, on the market, the vast ShuWang bridge of the communication ability is very strong, we have chosen a very high cost performance digital bridge, when used correctly, and its effective communication distance is 9 km, 900 m more than communication ability in the process of actual use. Of course, it should be noted that the network bridge needs to be used in pairs, and its use angle is horizontal ±30°, in the installation of the need to pay attention to the direction, in order to ensure the best use effect [20].

In terms of power, the bridge of the power supply must be up to standard and smooth, not smooth needs to choose higher power supply voltage, but now, the fins is used in electric power carrier module, and it is a power interface and can be used directly the output power to supply the normal work of the bridge; of course, we need a voltage regulator module to module of the output voltage of electric carrier for processing, in order to prevent the substandard power supply leading to the bridge equipment frequent offline.

In the process of actual use, we placed on the fins on each side of a bridge and to form a comprehensive range of delivery status, so whatever floats in which bearing always has the direction of the signal back to ground station layout bridge, back to the video is clear, keep within 0.5 1 seconds delay, picture frame loss ratio is very small, and this scheme is proved practical.

5. Conclusion

After indepth discussion and research, combined with the actual production, we explore a new type of abled underwater robot communication scheme, through the electronic carrier module to transmit the video signal to the floating, and then by the floating internal bridge transmission, realize the real-time transmission of video signal and real-time control signal receiving and execution. With the addition of the fin floating structure, the whole bionic underwater robot gets rid of the shackle between the traditional umbilical cable and the ground station, making the movement of the bionic fish more free under water. In addition, ROV’s real boat test is difficult and costs a lot of money and time. Many control studies, especially in China, only stay in the simulation stage. The application of fuzzy control [21, 22], neural network control ,and sliding mode control or their combination in ROV control is worth discussing and further deepening. After the completion of the whole system, according to the actual operation results, the hybrid propulsion underwater bionic fish has practical application value and has broad development prospects in the consumer market.

Acknowledgments

This work was supported by the “Structure Design of Wheeled Propeller of New Type Underwater Robot and Optimal Design of Open Water Performance” (Project No. CXY202014).

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