Research On Motion Control Of The Spherical Underwater Robot

With the development of underwater robotics and robot-related science and technology,the researches on underwater robots have made many remarkable achievements, at present,there are many countries in the world are committed to the research and development ofunderwater robots. Underwater robots show significant potential of being applied in the fieldsof industry, fishery, exploration, and military and so on. Underwater robots have become oneof the most important tools to exploit and use marine resources. The control of underwaterrobots is one of the key technologies for these kinds of robots, and the control problems ofunderwater robots involve many aspects. The difficulty of underwater robot control lies in itsworking environment is underwater, underwater various disturbances and uncertainties, aswell as the inconvenience of the experimental environment is bound to add the difficulty ofunderwater robot control. The resultant performance cannot satisfy our requirements whenusing some traditional methods to design the controller of underwater robots. Therefore, it isnecessary to investigate more efficient and easy to implement motion control methods.The developed autonomous spherical underwater robots will be seemed as an object ofstudy, and the three sets of water jet propulsion system which is the combination of the waterjet thrusters and servo motors were as the way of vectored water jet propulsion. The relatedstudy about propulsion system modeling and dynamic modeling will be carried on, and got anintelligent control algorithm which is fit for the vectored water jet propulsion sphericalunderwater robots on the basis of the model. The control algorithm should be more suitable toimplement a stable motion control in the complicated underwater environments; also, itshould be simple and has a low requirement of the model, which can be easily implemented inproject applications. This paper aimed to choose the fuzzy control as the main research point,and combined the self-adaptive control and sliding mode control to design a controller whichis more suitable for the spherical underwater robots.The main research work of this paper are as follows: First, we carried mechanical designon the developed autonomous vectored water jet propulsion spherical underwater robots, andwe also carried electrical design on the inner control circuit of the spherical underwater robots,so that people can understand the overall framework and working principle of the autonomousvectored water jet propulsion spherical underwater robots. Second, we discussed the designand distribution of the propulsion system in detail, and we calculated the resultant actuatingforce, also we carried on modeling and identification research on a single and multiple water jet propulsion systems respectively in order to realize the thrust forecast of the propulsionsystems. The thrust forecast mainly uses the method of combining experimentalmeasurements and theoretical analysis, and the derived water jet propulsion system model isthe control input vector of underwater spherical robots dynamic model. Third, we analyzedthe kinematics and dynamics of the underwater robots on the basic concepts of the fluidmechanics, and built the dynamics model of the whole system. According to the analysisresults of kinematics and dynamics, we carried the dynamics statement on the vectored waterjet propulsion spherical underwater robots, thus we realized the necessary calculationssimplified and gained the simplified dynamics model based on the spherical underwaterrobots finally. We also carried on model simulation, and compared the simulation results withthe actual underwater experimental results in order to verify the validity of the model. Inaddition, we discussed the hydraulics analysis of three underwater motions, surge, heave, andyaw of the spherical underwater robots and obtained the impact of the spherical underwaterrobots structure on velocity and pressure. Fourth, we studied the control algorithm of thespherical underwater robots based on the model of water jet thrusters and sphericalunderwater robots, and we carried research on the PID control and the fuzzy sliding modecontrol for forward movement of spherical underwater robots firstly, then based on the fuzzycontrol, the self-adaptive control, and the sliding mode control, we proposed an improvedadaptive fuzzy sliding mode controller for the developed spherical underwater robots, and wecarried on simulation studies with disturbance, at the same time we compared its results withthe simulation results of the designed PID controller and fuzzy sliding mode controller inorder to prove the excellence of the improved adaptive fuzzy sliding mode controller. Finally,we carried out a series of experiments on three degrees of freedom of movement, surge, heave,and yaw, by adopting sensor-based feedback controller which can be adjusted online based onfuzzy control idea. Also, we carried on the common surge motion experiments of multipleunderwater robots in order to prove the feasibility and validity of the developed sphericalunderwater robots.