Abstract
The twenty-first century is the century of marine resources. The ocean is a treasure of biological resources, energy, water resources and mineral resources, and it would gradually become the “second space” of mankind. In the next few years, it would be more and more relevant to human life. Many scholars have realized the importance of the ocean and began to vigorously develop and use the ocean. Underwater robot is a means for human beings to explore and develop the ocean, and it would be widely used in this field. The development and promotion of underwater vehicles are of great significance to resource development, economic development, and national security. With the increasing shortage of land resources, the development and utilization of marine resources have received increasing attention. The direct exploitation of marine resources by humans would have adverse effects, so the underwater robot technology has developed rapidly in recent years. However, at present, most underwater robots are driven by electric turbines. The underwater working environment requires that the underwater motor has good sealing performance, so its structure is complex and expensive, and it is rarely used in ordinary underwater operations. In recent years, intelligent robots have been used more and more, but because of the complexity and uncertainty of the underwater working environment, there are many uncertain factors. Therefore, it is very meaningful to carry out stability control for it. The research results showed that the displacement, stability, and other corresponding test curves of each component can be obtained by establishing a simple model with software and through ADAMS (Automatic Dynamic Analysis of Mechanical Systems) simulation analysis. This can simulate the movement of real objects in the real environment and find the existing problems, so as to provide a reference for the actual underwater robot design. In this way, the development cycle and production costs can be reduced. This article analyzed the structure and control system of the underwater vehicle based on ADAMS simulation. The results showed that the dynamic stability of the underwater vehicle based on ADAMS simulation analysis was improved by 4.67% compared with the underwater vehicle before optimization.
1 Introduction
Today, with the development of science and technology, the application of automation and intelligent equipment is the inevitable trend of enterprise development. In order to improve the working efficiency of the underwater vehicle, it is necessary to strengthen the design of its control system and introduce a modular control system on this basis to improve its working efficiency. By using modular technology, different products can be divided into modules to achieve different functions. Through the combination and collocation of various functional modules, the design of the system is realized, so as to improve the working efficiency of the underwater robot.
There are some related research studies on underwater robots. Cong Yang’s research believed that robot technology is a comprehensive technology integrating motion, dynamics, and artificial intelligence, while underwater robots need to complete multiple tasks independently. It is not enough to rely solely on them to complete various tasks. Therefore, a complete cooperative work system should be established to ensure the information exchange between various components, so as to realize the functions of various system components [1]. Cui’s research found that the underwater robot usually has six degrees of freedom of action, which can realize multiple actions such as forward and backward, side shift, lifting, swinging, etc., and has a lot of nonlinear and time-varying characteristics. Therefore, its control technology is very important and complex [2]. Petillot found that current underwater robots mainly include cabled underwater robots and cableless underwater robots. Traditional underwater vehicles use propellers and impellers as propulsion devices, and they are driven by conventional energy. They have poor maneuverability, slow response, and great interference with the water environment. They are difficult to use in narrow, dynamic, complex, and fragile environments [3]. Gu et al. proposed that the underwater robot is just a carrier. If people want to operate underwater, they need to carry equipment. It can be said that in the underwater operation system, various types of underwater operations can be carried out according to the work objectives by taking it as the center. It has the characteristics of being able to carry underwater operation system, thus expanding its application field [4]. Lima et al. proposed that the underwater robot is mainly composed of machinery, drive, sensor, etc., and combines a variety of technologies. At present, it is a leading topic in the development of underwater robot technology and combines bionic, interactive, intelligent, and other technologies [5]. In a word, the working environment of Autonomous Underwater Vehicle (AUV) is unpredictable, so the design of its software and software system is very difficult. Therefore, the test must be carried out on the simulation platform to reduce the occurrence of faults.
There are also many scholars’ research studies on Automatic Dynamic Analysis of Mechanical Systems (ADAMS) simulation analysis. Alwan and Sarhan established the inverse kinematics model of the manipulator using ADAMS software. ADAMS can analyze it from different angles, and then output the data of the corresponding machinery [6]. In order to develop high-precision performance test equipment, Liu established the coaxiality geometric delay model of RV (Rotary Vector) reducer using geometric methods and combined it with ADAMS dynamics simulation software to dynamically simulate the coaxiality of the model transmission system within different error ranges [7]. Hosseini et al. used the ADAMS simulation method to simulate the fault of a brushless DC motor and applied it to chemical, aerospace, power, and other industries [8]. On this basis, Xu established a virtual prototype simulation model of the rear reducer with ADAMS software and made a detailed analysis of the factors such as the angle between the shafts and the stiffness of the middle support [9]. Mitra modeled and verified the vehicle suspension system through ADAMS software. The results showed that there was good consistency between the model and the experimental platform, which provided a basis for future analysis and optimization [10]. ADAMS mechanical system simulation technology has been used more and more in mechanical design and has gradually become an indispensable technology for mechanical engineering technicians. It has a close relationship with a variety of basic theory courses.
With the development of marine science and technology, the demand for national defense construction and intelligent control is growing. Underwater robot is an intelligent system, which must be able to independently execute the operator’s instructions according to the changes in the external environment. Therefore, it is of practical significance to carry out in-depth research on it and research on underwater vehicle technology.
2 Concept and basic modules of ADAMS
2.1 Concept of ADAMS
ADAMS is a computer simulation software with high mechanical and dynamic performance. It constructs a set of complete mechanical modeling of parametric mechanics by means of an interactive graphical environment, part library, constraint library, force library, and other technologies. It uses the Lagrange function method to carry out static and dynamic simulation and gives the calculation formulas of corresponding motion data. ADAMS software simulation system can test system performance, disturbance range, collision, peak load, input load, etc.
2.2 Basic module of ADAMS
The software of the ADAMS system includes basic module, expansion module, professional domain module, and other modules. Users can use basic modules to simulate general machines or specific modules to quickly and effectively simulate and handle specific industrial problems. The modules included in these basic components are shown in Figure 1.
Basic module of ADAMS software.
2.2.1 User module
It has a large number of functions such as geometry library, constraint library, moment library, graphic shortcut key, menu shortcut key, etc. It takes 3D geometry parts as the center, and it supports Boolean operation with a friendly interface and convenient operation. During the modeling process, ADAMS would process the surrounding environment with various colors according to the actual situation. The default material of the model is steel, and the default center point of each component is located in its center. The entity size is calculated by default through ADAMS and can be adjusted according to the actual situation so that the size and direction of the gravity acceleration can be adjusted.
2.2.2 Solution module
This model can simulate and analyze rigid bodies and elastic bodies. When analyzing the finite element and control system, not only the parameters defined by the model itself, such as displacement, velocity, acceleration, and force but also the user’s own design parameters should be output. Users can add a variety of constraints to the motion, such as motion incentives, user-customized sub-items, and so on. According to this principle, users can achieve the desired purpose by solving the forces and reactions between various actions.
2.2.3 Processing module
The processing module is mainly used to process the simulation result data and display the simulation animation. It can work independently in the module environment of a user interface or without it. The main functions of the system include: using fast and high-quality animation to better understand the effect of the design scheme visually. For example, data processing and document output functions have complete data statistics functions.
3 Overview and research progress of underwater vehicle technology
3.1 Overview of underwater robot
Underwater robot is a kind of complex unmanned driving system that can replace human beings to engage in complex and dangerous work. The previous underwater detection was mostly based on the exploration of divers, and most of the time, it was judged by the experience of divers. However, under water, complicated factors such as water flow and line of sight would also affect their judgment. With the continuous development of computer technology, optoelectronic technology, and data processing technology, underwater robots have made great breakthroughs in many important technical fields [11]. Among them, the underwater vehicle is a new type of auxiliary observation method and has been widely used.
3.2 Research progress of underwater vehicle technology
Initially, the designer based on the robot detection system, and used annular sonar and high-definition underwater photography technology to monitor the cracks less than 1 mm in the water transmission pipeline of the water transmission and storage power station, which provided a new technical means for the tilt monitoring of the water transmission pipeline of the water transmission and storage power station [12]. According to the characteristics of dam detection, an automatic diver with a high-precision automatic positioning system is designed, which can automatically detect the structural state of the dam body. Moreover, a comprehensive description of the dam has laid a solid foundation for further research on the complexity of the dam. The designer has made an in-depth analysis of the use of hydraulic tunnels. Underwater robots were used to conduct all-round underwater monitoring, and DGPS (Differential Global Positioning Service) was used to detect undersea buildings (especially tunnels) with water depth, long channels, long operation time, complex environment, and unknown environments, which provided a new idea for the detection of undersea buildings (especially tunnels) with water depth, long path, long operation time, and complex and unknown environment.
Through the acousto-optic imaging system installed on the underwater robot, the underwater patrol can be carried out within the depth range of 0–300 meters, and the complex underwater environment can be measured, so as to obtain high-definition three-dimensional acoustic images of underwater buildings and real-time high-definition optical images, which can better understand the underwater situation. At the same time, using the navigation and positioning devices carried by the underwater robot, the defective parts of the underwater building were accurately determined, which provided a basis for the subsequent defect evaluation and repair work [13].
4 Structural design and problems of underwater robot
In recent years, due to the rapid development of computer technology and the requirements of an underwater working environment, underwater robots are widely used in underwater detection, construction, data acquisition, maritime rescue, underwater equipment inspection, and maintenance. There are mainly two kinds of underwater robots: one is the underwater robot with cable, and the other is the underwater robot without cable, namely the so-called autonomous submarine, which can navigate autonomously on the predetermined channel [14]. With the continuous development of underwater robot technology, new types of fishing equipment and equipment have also been greatly developed, with a wide range of applications and great market demand.
4.1 Robot structure design
In order to enhance the autonomy of the underwater vehicle and enable it to perform various tasks in complex waters, it is necessary to design its system structure [15]. The research on its system architecture can improve its self-learning, integration, security, and reliability. The design of a policy determines that the architecture, behavior, and function of the whole system can be controlled, which is called architecture. The design architecture of the robot is mainly composed of five parts, as shown in Figure 2.
Five main structures of the robot system.
In the control of the underwater robot, it is mainly composed of machinery, circuit, drive, etc. In the complex sea area, divers can complete a variety of special surveillance work, which is not easy. On this basis, it is necessary to propose an underwater robot based on motion control, attitude adjustment, and information collection. In the design process of underwater vehicles, at the top level, the planned control is the reasonable configuration of time and space, which is similar to the multiple work processes of computers. The driving control of the bottom layer is mainly mechanical, fluid mechanics, signal acquisition, inertial navigation, etc. It is similar to the acquisition of computer keyboards, cameras, and other mechanisms.
4.2 Functional module division
According to the classification principle of modules, they can be divided into generic and proprietary. Among them, general modules are characterized by strong universality, wide application fields, and comprehensive management of all system modules. It is not only applicable to underwater operators but also applicable to other electronic equipment. The proprietary module is the underwater control module. When developing the system, the corresponding system functions should be set according to the special needs of users to improve the flexibility of the system.
4.2.1 Software control system
The main control part adopts programming software, and each function has its own control system, which can maximize the use of the functions and functions of each module. In terms of software and hardware, the existing serial interface should be detected first, and then, the scanning frequency and check code should be set according to the relevant serial parameters. If the mechanical arm cannot be detected, it needs to be detected again, and the baud rate and serial interface parameters should be adjusted. In order to improve the motion stability and fluency of the robot, a simple control system composed of five functions: AI (Analog input), AO (Analog output), DI (Digital input), DO (Digital output), and underwater lighting control must be established. After pressing the corresponding module information on the operating system, the function of each module can be completed. For example, on the AI module detection interface, the analog voltage of four channels can be detected and displayed on the system screen. Fundamentally, the hardware module of the system is the basic function of the software system, while other hardware needs to be controlled by software. The control of each module can not only reduce the difficulty of operation but also facilitate the expansion of the module. At the same time, with the progress of science and technology, the performance of the underwater robot would become better and better. In order to reduce the maintenance and upgrading of the system, it is necessary to have greater expansion capacity to further improve the performance of the underwater robot, so as to achieve better results.
4.2.2 Hardware design
As the hardware mainly includes AI, AO, DI, DO, etc., the combination of these modules can achieve various functions. AI and DI modules are designed to acquire temperature, water leakage, heading and other data through sensors, and automatically process the collected data. The function of AO and DO components is to receive control from the main equipment, so as to control the connecting components of on-off valves, motors, etc. The underwater control module is mainly used to achieve the purpose of lighting. Under water, the light is very dark, so its brightness needs to be guaranteed.
4.2.3 Development direction of underwater robot
In the future, with the expansion of the scope of use, there would be a development trend of smaller, better compatibility and more intelligence, so as to solve the design problems of underwater robots and enable them to achieve better automation. Multimedia, telepresence, virtual technology, and other technologies would go beyond different types of underwater machinery, so that different types of underwater robots would be born. The development direction of underwater robot is shown in Figure 3.
Development direction of underwater robot.
4.2.3.1 Professional development
This requires both market and technology. Underwater robots of the same type are not competent for all tasks. They would be equipped with special equipment and perform specific tasks according to specific needs. Underwater robots would have more types, more divisions, and more specialties.
4.2.3.2 Remote development
On the basis of existing communication, navigation, control, perception, artificial intelligence, architecture, environment modeling, and other technologies, it is completely feasible to develop an AUV with a distance of more than 500 nautical miles. Now, however, three technologies have hindered the development of long-distance communication: energy, long-distance navigation, and real-time communication.
4.2.3.3 Intelligent development
The improvement of intelligent behavior of underwater vehicles has become the direction of joint efforts of many researchers in the world. At present, the development of intelligent robots depends on improving their emergency response ability. On this basis, robots no longer only follow the preset program of humans, but can continuously accumulate information and continuously improve the accuracy of behavior. However, the existing artificial intelligence technology has been unable to meet its intelligence needs, so in future research, the introduction of human intelligence would become the focus of its research.
4.2.3.4 Mass development
With the development of artificial intelligence methods, robot technology, and multi-agent integration technology, robots can cooperate among multiple robots under complex and uncertain conditions, so as to achieve real-time logic and cooperation for multiple robots. It is the future trend that multiple robots work together to accomplish more tasks.
4.2.3.5 Technical difficulties of underwater robot
Different from the aviation photography industry, there are not many kinds of underwater robots. After all, its research is much more difficult! For example, underwater visibility is far lower than that in the air; underwater resistance is greater than that in the air; underwater electromagnetic interference is weakened. Underwater robots have encountered many technical difficulties. The main technical difficulties of the underwater robot are shown in Figure 4.
Technical difficulties of underwater robot.
4.2.3.5.1 Underwater communication problems
In the underwater robot, there are cables that can complete communication well, but cables would make it unable to play its due role. At present, the control signal of underwater vehicles is mainly completed by underwater acoustic communication, but it is difficult to control it in real time because the underwater acoustic speed is slower than the speed of light. The transmission distance is also affected by the carrier frequency and transmission power. The current communication distance is only 10 km, and sound waves are easily affected by multipath. Although narrow wave speed can be used, problems such as beam alignment and tracking may also occur. In recent years, relevant scholars have carried out blue-green laser communication in the seabed 100 meters deep underwater, and the application of laser communication technology provides a new way for underwater large-scale communication. However, due to its large size, low efficiency, and large energy consumption, it cannot be applied to underwater robots without cable.
4.2.3.5.2 Energy supply
Underwater robots usually have no energy problem, but when working on the seabed, the more cables, the greater the communication loss. Although the voltage and frequency can be increased, there are also insulation and safety problems. For underwater vehicles, due to their lack of energy, fuel power can be considered. However, it has not yet been applied to underwater machinery, which requires more time to explore.
4.2.3.5.3 Automatic control problems
The underwater robot is relatively easy to operate, and the operator can conduct human–computer interaction on the console. However, due to the strong nonlinear coupling characteristics of the underwater vehicle itself when it moves freely in the water, its flow direction and velocity are random. This makes it difficult to use the rigidity of the control system, which leads to difficulties in information transmission of underwater vehicles. However, due to the large linearity and time variation of cross-coupling, its control technology is very complex and needs further research and development.
5 Structure and control system of underwater robot
5.1 Hydrodynamic performance analysis of underwater vehicle
When the underwater robot is moving, the drift angle
Among them,
Under the action of dimensionless hydrodynamic force, the central arm
The adaptive stability of the underwater vehicle is analyzed by studying its head angle change
According to Formulas (5) and (6), it can be obtained:
Among them,
It is assumed that
5.2 Hierarchical structure control system model of underwater vehicle
Aiming at the practical problems of the underwater vehicle, an optimization scheme of the structure control system of the underwater vehicle with three-layer hierarchical control is proposed. The hierarchical structure control system model of the underwater vehicle is shown in Figure 5.
Hierarchical control structure diagram of an underwater vehicle.
5.2.1 Task allocation control
In the hierarchical task allocation control system, this is an organizational-level concept. Under the concept of hierarchical control, the organizational level is the main concept of the control system, while artificial intelligence is the control function, which generates a series of general tasks through existing knowledge. However, at present, “autonomous” underwater robots are just a preset program, and most of them do not really realize intellectualization.
5.2.2 Position control
Position control is a coordination stage, which is based on the tasks and parameters extracted by the task controller while taking into account the safety, efficiency, navigation accuracy, current navigation conditions, etc., so as to provide a reference position and attitude for the implementation level control. The positioning control system can realize the functions of three-dimensional trajectory tracking, obstacle avoidance, area search, positioning, and positioning, and ensure its safety in navigation. For different sensor structures and navigation performance, designers can design corresponding positioning algorithms.
5.2.3 Command control
The main work of the system is to control the reference heading angle and reference depth of the input signal and analyze their transverse and longitudinal directions. At present, in the control of underwater vehicles, the executive-level control algorithm has been a hot topic. In the control design of underwater vehicle, two contradictory design requirements should be taken into account at the same time. First, it is necessary to have enough complexity to ensure that the influence of unknown fluids can be overcome in complex and unknown environments, and various random events can be processed in real time to meet specific performance requirements. Second, its calculation amount should reach the calculation capacity of the control computer, so the control system should be simple.
6 Experimental evaluation of underwater vehicle structure and control system based on ADAMS simulation
In this article, the structure of the underwater vehicle was modeled. On this basis, the material density and quality attributes of each part were defined using ADAMS, and the main parameters were tested.
6.1 Simulation analysis
The design parameters of the structural control system of the underwater vehicle are shown in Table 1.
Design parameters of underwater vehicle attitude adjustment control system
| Index | Parameter |
|---|---|
| Air supply pressure | p = 8.5 MPa |
| Initial volume of diaphragm cylinder inlet chamber | V = 2.7 × 10−3 m3 |
| Working area of diaphragm | A = 0.05 m2 |
| Total length of underwater robot | L = 1.8 m |
Through the simulation and calculation of ADAMS, the unit step response curve before and after optimization was obtained, as shown in Figure 6. It can be seen from Figure 6 that the optimized system achieved a high response rate after the minimum time attenuation under the action of the unit step signal, which indicated that the optimized system has good dynamic characteristics and time domain indicators.
Unit step response diagram comparison before and after optimization.
6.2 Change of center of mass position
The position error of the underwater robot’s center of mass before and after optimization is shown in Figure 7. Ten groups of tests have been carried out in this article. The experimental results showed that the position error of the robot’s center of gravity after optimization was lower than the original algorithm, and the overall gait planning effect after improvement was much better.
Position error of underwater vehicle’s center of mass before and after optimization.
6.3 Dynamic stability
The dynamic stability is related to the kinematic model of the manipulator; that is, when the manipulator is moving or moving at a high speed, the vertical line of its center of gravity would be fixed on the bearing surface to achieve balance. The dynamic stability comparison of the AUV before and after optimization is shown in Figure 8. The experiment showed that the navigation of the optimized AUV was more accurate. Compared with that before optimization, its dynamic stability was improved by 4.67%.
Comparison of dynamic stability of underwater vehicle before and after optimization.
7 Conclusions
Robots have been widely used in recent years. Among them, the use of underwater robots to replace human work has become an important topic of current electric robots. The working environment of underwater vehicles is unpredictable, so the design of its software and software system is very difficult. Therefore, the test must be carried out on the simulation platform to reduce failures. In view of the flexibility, good man–machine interface and expandability of the underwater vehicle system, an underwater vehicle system based on a three-layer hierarchical control structure, was proposed, and its dynamic characteristics were analyzed. This method can greatly shorten the development time and increase the flexibility of the control system. In addition, it can reduce the repeated work of the software and provide a basis for future system design. It is hoped that the structure of this hierarchical control system would be applied to the design and development of underwater vehicles in the future, and would be further improved in future applications.
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Funding information: The authors state no funding involved.
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Author contributions: All authors contribute equally to the article.
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Conflict of interest: The authors declare that there is no conflict of interest with any financial organizations regarding the material reported in this manuscript.
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