Design Of A Wireless Network Based Teleoperation System For Tractors

Due to poor working conditions and structure of agricultural machinery,drivers are prone to premature fatigue when working in the field,and lead to a degraded working quality or even accidents.The combination of teleoperation technology and agricultural production can effectively reduce the labor intensity and improve the working conditions for drivers.With the development of Internet,teleoperation based on the Internet has broken through distance limitation and attracted attention of reserachers at home and abroad.A teleoperation system was developed for tractors in the paper.Firstly,the general plan was designed for the teleoperation system of tractors.Then,a MY250 tractor was refitted and a teleoperation control system was designed.Finally,tests were carried out to detect the system's performances about communication,action and driving.The main contents of this article are shown below:1.General plan design.According to the requirements that teleoperation system should be met,the general plan was designed.Through wireless communication,the tractor's working environment can be transmitted with video to the teleoperation terminal where an operator is located,and the operator can send commands to drive tractor.2.Wireless communication.First,Teleoperation network structure,wireless communication,VPN and intelligent router system were introduced.Then,"4G+VPN(Virtual Private Network)" communication was chosen.Finally,VPN contruction and encrypted channel configuration were simply described.3.Actuators refit.According to the structure and function parameters of MY250 tractor,the tractor was refitted for remote steering,clutch,braking,throttle,flameout and ignition,by installing actuators of motors,electric putters,ignition delay and so on.4.Devices of teleoperation system.In order to control actuators and detect their movement state,and collect real-time image information of the working environment,angle sensor,displacement sensors,front camera,overhead camera,NVR(Network video recorder),router,and 4G wireless network card were chosen,a driver board was designed to control electric putters and ignition based on Protel 99 SE,and on-board control ECU was chosen to control actuators.5.Software design of teleoperation system.Teleoperation system's software includs protocol expantion,main program design,PWM program design and user interface design.The protocol was expanded based on MODBUS RTU,including address,function,data and check code.Main program was designed by Source Insight and C language,compiled by Linux,and debugged by PuTTY and comdebug.PWM program was designed and compiled by Atmel Studio and C language.User interface was designed by MFC module and C++language,and to realize remote access to NVR for acquiring video and sending commands by calling SDK's related functions.6.Performance tests.The results showed that teleoperation terminal and tractor part can communicate successfully,the average communication delay was 0.074 ms,and the maximum video delay was 373 ms,the maximum control error was 2.21%for all actuators,and the maximum absolute error was no more than 201.1 mm when the tractor was driven along a straight line at a speed of 2.08 km/h by the teleoperation system,with a maximum RMS error of 91.5 mm;the system could realize orthogonal turn.The system can basically meet the requirements of teleoperated system.