| Rapeseed precision seeding has the advantages of saving seeds,saving labor and increasing efficiency.The even distribution of seeds is one of the cores of rapeseed precision seeding technology.The traditional rapeseed precision planters mostly use land wheel and chain to drive the seed metering device to complete the seeding.During high-speed operation,problems such as ground wheel slippage,suspension,and chain jumping are prone to occur,resulting in missed seeding,which seriously affects the quality of seeding.Adopt the manual transmission with fixed gear to adjust the seeding amount,it is difficult to realize the stepless adjustment of the seeding amount and meet the requirements of precision seeding.This paper based on the 2BFQ series rapeseed precision combined seeding machine,designed and developed a speed-dependent seeding control system for rapeseed,and clarifyed the basic structure and working principle of the control system.Starting from the system design requirements,the circuit part of the control system was designed,and the installation and fixing of each device were completed;the hardware drivers,the wechat applet interaction program of the system and the overall control program were developed,and the closed-loop motor control mathematical model was built.Through the calibration test of each sensor,the respective errors were determined,and the correction coefficient was introduced for correction;the working effect of the system was verified through the bench and field tests,indicating that the system can achieve precise control of rapeseed seeding space and stepless adjustment of seeding amount.The main research substances are as follows:（1）On the foundation of comparative analysis of precision seed metering equipment and systems at home and abroad,combining with the technical requirements of rape precision seed metering,and aiming at the control of rapeseed seeding space and stepless adjustment of seeding amount,the data interaction logic of the speed-dependent seeding control system of rape precision combined direct seeding machine（abbreviated as the speed-dependent seeding control system）is determined.It obtained the forward speed through the dual-mode of Beidou receiver and land wheel encoder,seed metering device driven by stepping motor,and data interaction through wechat applet.The overall scheme design of the control system was carried out,mainly including the hardware circuit and software program design and parameter analysis of the transmission system,motor and various sensors.（2）The overall scheme design of the speed-dependent seeding control system was proposed.The main factors affecting the precision seeding effect of rape were systematically analyzed.Aiming at realizing the uniformity of rapeseed seeding space and stepless adjustment of seeding amount,a method was proposed,which used STM32 single chip microcomputer as the main controller,wechat applet as the human-computer interaction end,closed-loop stepping motor driven seed metering,ground wheel coder and Beidou receiver to obtain the forward speed,the differential pressure transmitter to obtains the real-time negative pressure at the negative pressure conveying head to control start-stop of the motor.The working principle and control logic of the system were described in detail.The system could display real-time data of6 kinds of sowing operations,set 7 operation parameters to adapt to different planters,and configure two working modes of constant speed and speed-dependent seeding to adapt to different operation requirements.（3）The hardware functional requirements and parameter analysis of the speed seeding control system wre carried out,and the selection and circuit design wre carried out on this basis.Stm32f103vet6 single chip microcomputer with multi-channel timer,communication interface,analog-to-digital converter（ADC）and clock frequency up to 72mhz was selected as the main controller of the system.The test determined that the negative pressure range at the negative pressure conveying head is-1477～-4563pa when 2BFQ-6 direct seeding machine works normally,and YZ1301 differential pressure transmitter with a range of 0～5kPa was selected to obtain real-time wind pressure.In the experiment,E6B2 CEZ1X encoder and atgm332d Beidou receiver wre used to obtain the forward speed of the tractor,and the encoder support was developed to realize coaxial rotation with the ground wheel.The system selected HC-08Bluetooth module and useed TTL level to communicate with MCU through serial port,which is used as a bridge to connect MCU and wechat applet.In order to adapting to different types of seed metering devices,the motor support was designed for stepping motor transmission.According to the demand torque of 1.92N·m at the maximum working speed of 800r/min,the stepping motor model was determined as 86HBS120.Taking the single chip microcomputer as the core,the hardware connection circuit was designed to connect the hardware and realize the power and data transmission.（4）The software driver of the seeding control system was designed.The software driver was programmed based on visonil 5.Based on JavaScript language,wechat developer tools were used to program interactive software.The control flow of the main control end was sorted out,and the motor control command was generated according to the preset parameters and the real-time digital of the sensors.The motor drive switch was designed to open when(（1）≥1477Pa.The speed source switching logic was designed,and the main controller could select the best speed source according to the real-time speed.A signal decoding program was designed,which could convert the string transmitted by the applet into numbers for program use.The mathematical model of motor control command generation was constructed,and the command generation was controlled by multiple parameters including tractor forward speed.The interactive program was developed,which could set 7 parameters such as target grain spacing and ground wheel diameter,and display 6 parameters such as seeding area and seeding amount.（5）The experiment and analysis of the speed-dependent seeding control system were carried out.The transmission error and corresponding transmission time were calibrated,and the transmission correction coefficient was 1.055 and the motor control frequency was 5Hz.The suitable speed measurement intervals of the two speed measurement methods were calibrated,and 3.68km/h was determined as the critical speed of speed source switching.The test results showed that the seeding performance of this system was better than that of constant speed seeding,and the qualified index of seeding space was higher than 87%,which can realized the seeding at the speed of 2.6～7.8km/h.The field experiment of precision seeding was carried out.The experimental results showed that the seeding amount error of the system was less than 3.9%at different operating speeds of 1.44～4.33km/h,the qualified rate of grain spacing was higher than 84%and the coefficient of variation ofseeding uniformity was lower than 16.67%;the precision hole seeder suitable for small-diameter seeds has a good sowing effect under the constant speed mode,and the qualified rate of hole spacing is 81.54%;both met the seeding quality indexes specified in the standard,and can realize the stepless adjustment of seeding amount and speed-dependent seeding control on seed metering devices,which could provide reference for the improvement of the structure of rapeseed speed-dependent seeding control system. |
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