| China is a big country of peach production,and the planting area and output of peach rank first in the world.In recent years,with the expansion of the production scale of peach orchards in China,the standalone operating efficiency of traditional orchard machinery has been difficult to meet the actual production needs.Studying the multi-robot collaborative operation technology of peach orchards can essentially improve the working efficiency and intelligent level of robot systems.Communication is one of the key technologies for peach orchard multi-robot.However,the characteristics of dense orchards and no support of basic communication facilities seriously affect the performance of short-range wireless communication technology,thereby greatly reducing the multi-robot collaborative operation capabilities in peach orchards.In view of this situation,this paper develops a wireless communication system for dense peach orchard multi-robot by studying the Wi-Fi signal propagation characteristics and the routing protocol of Ad Hoc network.The main research contents and conclusions of this paper are as follows:(1)The overall scheme design of the wireless communication system for dense peach orchard multi-robot.The impact of dense peach orchard environment on the performance of multi-robot wireless communication system was estimated initially.Firstly,the requirements of the system were analyzed.Secondly,the main equipment selection and overall hardware framework design were completed based on the above requirements.Then,by comparing several wireless communication technologies,Wi-Fi was selected to design the wireless communication network for dense peach orchard multi-robot,and finally the overall architecture of software based on embedded Linux system was designed.(2)Research on the propagation characteristics of Wi-Fi signal in dense peach orchard.Wi-Fi signal receiving strength measurement test in dense peach orchard was carried out,firstly,the received Wi-Fi signal strength at different deployment heights(25,50,75,100cm)and different deployment azimuths(0 °,30 °,60 °,90 °)of the receiving and sending nodes were tested.Then,through regression analysis,a prediction model of Wi-Fi signal receiving strength at different deployment heights and different deployment azimuths of the receiving and sending nodes was established.The test result showed that:the optimal deployment height of sending node and receiving node in peach orchard is75 cm.The correlation coefficient fitted under different azimuths of the sending and receiving nodes is distributed between 0.849 and 0.969,and the Wi-Fi signal receiving strength conforms to the logarithmic path loss model.(3)Improved AODV routing protocol based on dense peach orchard environment.Firstly,the defects of traditional AODV routing protocol in dense peach orchard environment were analyzed.Secondly,the priority node and path signal strength threshold were introduced to optimize the routing discovery algorithm and routing selection algorithm of AODV protocol,and with the prediction model of Wi-Fi signal receiving strength in Chapter 3,an improved AODV-SP routing protocol was obtained.Finally,the simulation environment by using NS2 was configured,and a performance comparison test between the AODV protocol and the AODV-SP protocol was carried out.The experimental result showed that: When the maximum moving speed of the nodes is 5m/s,the routing initiation frequency and routing overhead of the AODV-SP protocol are 3.65% and 7.09%lower than that of AODV protocol.When the maximum moving speed of the nodes is 8m/s,the packet delivery rate of the AODV-SP protocol is increased by 0.59%,and the average end-to-end delay is reduced by 13.09%.(4)Software and hardware integration and functional test of the wireless communication system.First,the hardware circuits of the orchard robots were designed,such as relay control and motor drive.Secondly,the motion control strategy of following robot based on fuzzy control was studied.According to the requirements of maintaining the formation among robots in the system,a fuzzy controller was designed with the distance deviation and deviation change rate between the robots as input variables and the set value of following speed as the output variable.Then mobile phone remote control APP based on Android platform,character device driver and QT application program based on embedded Linux system were developed.Finally,in order to verify the function of the dense peach orchard multi-robot wireless communication system,a physical platform for the wireless communication system was built,and the Wi-Fi module,motion control strategies of following robot,communication system application and physical platform were tested respectively.The result showed that: the Wi-Fi module and communication system applications are all running normally,motion control strategies of following robot can achieve the following distance control of the dense peach orchard.Through the effective communication mechanism and motion control strategy,the system can maintain the formation of the robots in straight and steering movements. |
