| With the gradual decrease of unrenewable resources on land,the exploration and exploitation of marine space which is rich in energy and resources has drawn attention from more and more nations.As an essential equipment for underwater vehicle in working process,the research and application of underwater manipulator has encountered many emerging problems due to the complexity of working environment and high autonomy of working requirements.Up until now,most underwater manipulators are actuated either by electricity or by oil hydraulic power.On account that the dimensions of joints in electrically actuated manipulator are usually very large as a result of the output shaft in actuating motor needs to be motively sealed,and oil hydraulic powered manipulator is prone to cause leakage pollution which at the same time would lead to very low control accuracy,therefore,it is of great research significance and practical value to study underwater manipulator actuated by water-hydraulic power and its control technology.The following research work were carried out in this paper:(1)The current achievements of research on underwater manipulator actuated by oil hydraulic power and water hydraulic power were summarized at home and abroad.By analyzing the advantages and disadvantages of each type,the foundation was laid for the study of water-hydraulic power actuated underwater manipulator in this paper.Through summarizing the different control methods currently applied in underwater manipulator and analyzing the characteristics of each method,theoretical and technical support were provided for the research on control technology of underwater manipulator.(2)Considering the control target of motion accuracy for underwater manipulator designed in this paper,the control target of flux accuracy for the hydraulic system were analyzed?By analyzing the characteristics of water hydraulic transmission and studying the control and realization methods of micro-flow,theoretical reference and technical guidance were provided for the design of high-precision water-hydraulic system in underwater manipulator in this paper?Through analyzing the function needed to be met by the hydraulic system of the underwater manipulator developed in this paper,the designing scheme of water-hydraulic system was proposed and improved ? A two-way single-piston pump was developed as a power source of water hydraulic system and achieved the minimal flow output.(3)Considering the control mode of the actuating motor of the bidirectional single piston pump in the hydraulic system of the underwater manipulator developed in this paper,the overall design of the control system was designed based on the master-slave control idea,and the hardware circuit modular was specially designed.The driving motor of bidirectional single piston pump and its control module ? the joint angle sensor and its signal acquisition module was analyzed and designed in detail.Two ARM microprocessors was applied in each control module as the core information processing unit,to improve information processing efficiency and control performance,and to avoid mutual interference.On the basis of hardware control system platform,the software of main and slave controller was designed,software programming was completed.(4)According to the manipulator developed in this paper,the kinematics and dynamics of performance were studied,and trajectory planning was carried out.In this paper,the link coordinates of the freedom redundant manipulator was established.The forward kinematics was derived using D-H method,and inverse kinematics equations was derived from the anti-conversion laws;The dynamics equation was derived according to Lagrange method,and considering factors such as hydrodynamic effect on its underwater operations,underwater dynamic equation was improved.On the basis of the robot kinematics and dynamics model,five interpolation function and linear interpolation method were used for robot motion planning of deployment and recovery processes and working process.(5)Motion control technology of underwater manipulator was studied after the establishment the general mathematical model of single joint control system.In accordance with the hysteresis phenomenon in the starting process and reversing process caused by dead zone of the hydraulic system,the characteristic of the dead zone and the dead-zone compensation control method was studied.In this paper,the compensation control method of conventional PID controller was applied by adding the dead zone compensation part in the closed-loop control system,for the actuator to quickly cross the dead zone.The simulation was performed to verify that the control method can effectively reduce the start-up and shorten the action lag when the components reverse in the hydraulic system.The response speed and trajectory tracking accuracy were improved.The influence of amplitude and reversing frequency on the tracking performance of different controllers were analyzed.(6)In order to ensure that the hydraulic system of underwater manipulator developedin this paper can work reliably,the experimental study of its pressure sealing performance was performed,including the external pressure and internal pressure static sealing and dynamic sealing performance.In order to get the pressure loss in the hydraulic system,experiments on the influence for the hydraulic medium,pipe length,the impact of the inside diameter on the pipe pressure loss in the hydraulic circuit were conducted and determine the ultimate use of the medium and pipe size range in the hydraulic system were determined.Tracking experiments of step signal and sinusoidal signal under conventional PID control method and PID control method with dead-time compensation were carried out both on land and in water,and the effectiveness of the PID control method with dead-time compensation applied in this paper was proved by the experiment results. |
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