| Variable rate seeding is a precision agricultural technology that can properly and accurately put the seeding rate according to factors such as soil nutrients,light,and water storage capacity,which can not only greatly increase the crop yield,but also save the amount of seed used.The control system of variable rate seeding,used as the carrier of variable rate seeding implementation,can be divided into real-time sensor type and prescription map type control systems according to their realization principles.The variable rate seeding control system with prescription map type integrates frontier technologies such as global positioning system(GPS)and geographic information system(GIS),which would be a mainstream of precision agriculture in the furture.Focusing on the present research of variable rate seeding control system,although in-depth domestic research has been conducted in seeding electric-drive control,there has not been applicable and completive control system of variable rate seeding carried out yet.The existing control system of variable rate seeding in foreign countries has a complex structure and is not suitable for domestic use in seed meter drive and control.Aiming at the above problems,this paper proposed a control method of variable rate seeding based on prescription map,and innovatively designed a control system of variable rate seeding with smooth driving and precise controling.Besides,in order to seed independently in each row with the control system and attain high control precision,the positioning model of seeding unit,sowing distance lag compensation algorithm,turn compensation algorithm,etc.were studied.The main research contents and innovative results can be summarized as follows:(1)A prescription map type variable seeding control method based on Android control terminal is proposed.Realized functions includes extracting GPS spatial positioning information using field tag matching method,loading MapView and displaying prescription maps,querying prescription map using QueryTask,marking and displaying planted area using GraphicsLayer,etc.At the same time,a mathematic model of the motor speed of seed metering device,the seeding amount,and the forward speed was constructed.Bench test shows that the seeding accuracy is greater than 98.87%and the variation coefficient of seeding rate is less than 0.85%at forward speeds of 6,8,10 km/h and a GPS positioning frequency of 5 Hz.Field test shows that the seeding accuracy is higher than 96%and the variation coefficient of seeding rate is less than 1.56%,indicating that the control method can stably and accurately control the seeding unit to planting variably.(2)Electric drive control system of variable seeding was constructed based on CAN-Bus.Different drive control methods of seed metering device were analyzed.Besides,based on the principle of gear strength design and check,it was proposed and designed a circumferential electric drive mechanism of gear and outer gear ring,which is applicable for pneumatic precision seed metering device with combined holes.Therefore,the seed plate could be driven and controlled smoothly and reliably.Using the principles of centralized management and distributed control of communication information,a communication controller based on STM32 was designed to realize rapid and accurate transmission of variable seeding information among various components of the control system.Further,based on the designed communication controller,a CAN communication algorithm under identifier list mode was developed to realize the accurate control of seeding rate in each seeding unit and the flexible expansion of the number of units.Meanwhile,the CAN communication node fault detection method was designed to monitor the communication status of the seeding nodes in each row,which ensures the stability and reliability of the control system communication.(3)In order to reduce the delay distance for the variable sowing control system in the forward travel prosess that the tractor travles along the direct line,the compensation model and algorithm was built based on the idea of advanced control.Meanwhile the travel speed and positioning frequency of GPS were taken into this compensation algorithm aiming to avoid the increase of delay distance caused by the high travel speed and less positioning frequency of GPS.Experimental method and theoretical analysis were conducted to calculate the time lag for the control system and then the time lag was considered to calculate the delay diatance of the planting.The bench test results illustrate that the compensation algorithm helps reduce the delay distance obviously and weaken the negative effect induced by the travel speed and positioning frequency of GPS.Moreover,the field test also proves the better performance of the control system applied with the compensation algorithm when compared to that without the compensation algorithm.The delay distance was decreased maximally by 1.95 m and kept less than 1 m.(4)The positional relationship between the GPS receiver and seeding units was analyzed to build the positioning model of straight going seeding unit in any forward direction.By calculating the single positioning coordinates of GPS reveiver,the control system could recognize the accuracy position of each seeding monomer and then adjust the seeding rate independly based on the techniques of CAN bus and QueryTask prescription drawing.Experiments demonstrated the fitting ratio was always of 0.07-0.63 and not be easily affected by the shape of the seeding boundary that was convex or concave boundry compaered to theoretical valueof 0.29,0.29,0.91,which illustares that the control system has better ability to independly control the seeding monomer.(5)For the tractor turning process that the tractor travels in the curve line,the positioning model for locating each seeding monomer was also built.First the positional relation between the planter and the tractor was analyzed on the basis of the ackerman steering principle and then the turning radius was calculated by three constant position signal of tractor acquired from GPS.Simultaneously,taken together the turning radius and travel speed the compensation algorithm during tractor turning process was provided so as to adjust the travel speed of each seeding monomer.The test results illustrated that the control system proved good performance by steady qualified index and variation index of sowing rate that were respectively more than 97%and less of 1.52%even as the turing radius decreased.Oppositely,the decrease of qualified index and the increased of variation index were obviously that was done without the control system,which indicates that the control system help obtain the consistant sowing rate for inside and outside line. |
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