Research On The Path Following Control Of The Tracked Robot As A Mobile Node Of WSN

The application of wireless sensor network(WSN)in agriculture can effectively reduce the workload and improve the intelligent level.However,the traditional WSN nodes remain stationary,lacking flexibility and local execution.Mobile robot can carry high-precision sensors,have stronger maneuverability,run the complex algorithm and perform more complex tasks.Combined with mobile robot,WSN will have a certain capacity of calculation and execution at local scope.The mobile robot can also assist WSN nodes with dynamic programming and maintenance task.Moreover,it can also complete more complex decision-making and management.Mobile node can be used as a collecting point,and also as a gathering point.When a fixed route is broken,mobile node can replace it and continue to work so that the performance of WSN can be improved.Yet,due to the influence of ground soil,field planning and changed mechanical structure parameters,a slide phenomenon will occur when the tracked robot runs in a complex farmland environment,which may make robot's path have a deviation.In order to reflect the slide phenomenon on volume,real-time measurement and control of slide quantity should be done.By this way,tracked robot's path tracking will be realized and the stable operation of the mobile node can be ensured.For these,the main research contents and results in this paper go as following:1.The relationship between WSN and the mobile node was expounded in this paper.The mobile node's function requirements was analyzed and its overall structure was determined.From two aspects of hardware and software,the mobile node was designed.Welding,fabrication of the mobile node's PCB were accomplished and the communication protocol was defined.Meanwhile,the drivers and applications' codes were programmed and tested after a software development environment for ARM embedded Linux system was set up.For obtaining the tracked robot's pose data,a differential GPS system was configured and built.The formula of the coordinate system's data transformation and calculation example are given as a result of analyzing the relationship among the coordinate systems.2.To guarantee the mobile node's stability,accuracy and efficiency in node replacement and information acquisition task in farmland environment,a slide parameter calculation method based on the unscented Kalman filter(UKF)algorithm and slide modeobserver(SMO)was presented,according to the the kinematics modeling analysis of slide problem,which had an influence on the tracked robot's path following.Firstly,the pose of the robot was rebuilt by using UKF to fuse its state and measurement equations.Then,the SMO with hyperbolic tangent function as a switching function was constructed,which weakened the jitter caused by the SMO symbol switching function and realized a precise calculation of slide parameters.The simulation results show that this method can get accurate,high update rate of slide momentum and it can provide the data base for the control of agricultural tracked robot's path tracking.3.In view of the mobile node control system's precision was easily affected by its changeable structure parameters and the external interference,an adaptive slide mode control method called fuzzy slide mode control(FSMC),based on the theory of two-dimensional fuzz,was proposed by combining the slide mode control(SMC)with the fuzzy control.In this way,the influence of interference factors on the control system was suppressed,and slide phenomenon was also reduced when the tracked robot run in such fields: grassland and yielding ground.Thus,the mobile node's path following control was eventually realized.The simulation results show that compared with the SMC,FSMC has a more remarkable adaptability,high efficiency and robustness,.4.The mobile node's functions were tested.Normal communication between mobile node,coordinator and server was achieved according to the designed protocol.Data acquisition and transmission were correct.In three kinds of farmland environment,the path following trajectories of the FSMC were all relatively smooth regardless of the mobile node was turning or going straight,and the deviation between the following trajectory and the default path tended to be 0.On the contrary,the deflection caused by SMC was large.Especially when robot was turning,the path following trajectory's amplitude changed fast,which made the robot have a larger centrifugal force.By then,the slide phenomenon occurred.What's worse,when the external interference got serious,the deviation of SMC became larger accordingly and the path following deviation changed within the range of± 0.3m and(10)-.~.m450m250.But the deviation of FSMC slightly changed within a range of ± 0.1m and ±m2.0.For adoption of fuzzy approximation,the control output was softened and the accuracy of the control system was improved by the FSMC at the same time.