Research On Measurement Technology And Error Analysis For Center Of Gravity Of Autonomous Underwater Vehicle

Center of gravity of autonomous underwater vehicle(AUV)is not only the main technical parameter needed to be considered in the process of design,but also important technical indicator needed to be maintained in the control process for AUV.The accuracy was not satisfactory based on the traditional methods used to measure center of gravity of AUV,and those methods were too much complex.In the paper,a new gravity measurement method was studied for AUV.And according to the developed AUV prototype,the relative theory and experiments were performed.Firstly,the research about measurement of center of gravity was reviewed by the relative literature at home and abroad.And the paper analyzed the representative devices used to measure center of gravity in the world.Furthermore,the paper summarized the different measurement methods about center of gravity for different systems.Considering the practical characteristics of underwater vehicle,the overall scheme about measurement of center of gravity was determined based on the multi-point moment equilibrium balance principle.Secondly,in order to carry out experimental study for the proposed gravity measurement method,a gravity measurement test platform for AUV was developed.Mechanical body structure of the test platform was designed to measure center of gravity of AUV.And the sensing system and slave control system were presented.In order to meet the digital and intelligent design requirements,a human-computer interaction interface was developed in LabVIEW programming environment.Thirdly,a large number of experimental studies were carried out in the developed gravity measurement test platform for AUV,including the calibration experiments of weighing sensors and digital junction box,parameter calibration of the mechanical structure platform and weight and center of gravity measurement experiments.By weighing sensors and digital junction box,the input-output relationship of the measurement system was determined,which made the measurement accuracy satisfy the design requirements.After the parameter calibration of the mechanical structure platform,precision errors caused by machining and assembly were compensated.And from weight and center of gravity measurement experiment results,it demonstrated the proposed method had a good measurement accuracy,which satisfied the design requirements of the system.Fourthly,since the location and size of the regulating weight and buoyancy material could not be determined in advance,it may result in adding the unnecessary weight to AUV.In order to resolve the problem,the paper proposed an approach by combining gravity measurement test platform with three-dimensional modeling software to adjust the attitude of AUV.The weight and center of gravity were calculated according to the gravity measurement test platform,and the buoyant force and center were calculated by three-dimensional modeling software.The location and size of the regulating weight and buoyancy material were determined according the obtained weight and buoyant force and the relative location between center of gravity and buoyance center.Then,as for Autonomous underwater vehicle-manipulator system,the center of gravity and buoyancy are time-varying,which would affect the tracking accuracy and stability of underwater manipulator.The paper proposed a kind method to measure the center of gravity for underwater vehicle in real-time by making use of the gravity measurement test platform.The attitude of underwater vehicle was adjusted based on the obtained attitude,which required the measurement test platform had the ability to dynamically measure center of gravity.In order to study the performance of the developed gravity measurement test platform,the paper built an AUV prototype with the continuously variable center of gravity.According to the measurement results,the paper gave the measurement ability in the range of the rate of change of the center of gravity.Finally,in order to accurately evaluate the measurement accuracy of the developed gravity measurement test platform for AUV,the uncertainty of the experiment platform was analyzed based on the modern error theory.From the perspective of the measurement system error sources,the sources of the uncertainty of the experiment platform were analyzed.Then the mathematical model was established for the developed gravity measurement test platform.According to the uncertainty propagation law of the measurement system,the measurement uncertainty of weight and center of gravity for the developed measurement system were calculated.The experiment results demonstrated the proposed measurement method had a satisfactory accuracy for the measurement of center of gravity in AUV.