Design And Testing Of A Sowing Rate Monitoring And Control System For Cole Direct Seeding Machines

Canola precision seeding machine is widely used because of its high operational efficiency and the advantages of cost saving and efficiency,etc.The monitoring of sowing volume and precision seeding control in the sowing process is one of the trends in the development of sowing intelligence.However,it is difficult to detect rape seeds directly because of their small particle size,light quality,high sowing rate and closed seeding process.At present,the sowing volume index of cole rape precision sowing is mainly obtained indirectly through the change of seed volume in the seed box or the projection of the rotational speed and the number of type holes of the seed rower,and the complex operating environment and malfunction in the field will inevitably lead to the randomness of the cole rape precision seed rower to miss sowing,which affects the crop yield.Therefore,it is necessary to design a monitoring device that can detect the amount of rape sowing in real time and design a rape precision sowing control system on this basis to improve the quality of rape sowing.The main research contents and results are as follows.(1)The existing rape direct seeding machine was modified automatically,and the driving method of the seed row shaft of the rape direct seeding machine was changed from the traditional ground wheel chain drive to DC motor drive to realize the matching of the seed row shaft speed and the forward speed of the machine,and to realize the infinitely adjustable seed row shaft speed.On this basis,the forward speed of the machine and the real-time speed of the seed row shaft are obtained by means of incremental encoders installed on the seed sower distance measuring wheel and the seed row shaft.It effectively solves the seeding errors such as reseeding and omission caused by the traditional ground wheel which is easy to idle and slip.(2)A PVDF piezoelectric film-based oilseed rape monitoring system was designed to achieve real-time sensing and counting of small seeded oilseed rape seeds.Based on the characteristic piezoelectricity and sensor principle of rape seed collision signal,a sink substrate-piezoelectric film sensing structure was used to reduce the seed collision signal convergence time,and a dual-sensor detection method was used to reduce the field vibration environmental interference.The key structural parameters of the sensing device,such as the inner diameter of the conduit of 5mm,the inclination angle of the piezoelectric film of 52°,and the length of the conduit of 119 mm,were designed,and the relevant tests on its detection accuracy and vibration resistance performance were conducted.Under the conditions of26.5～42.2 r-min-1 seed row shaft speed,the sowing detection accuracy of the system is higher than 96.4% when there is no vibration interference in the sowing operation,and the minimum sowing leakage detection accuracy is Under the condition of vibration interference from 8 to 16 Hz,the detection accuracy of double sensor is not less than 95.2%,and the detection accuracy is higher than that of single sensor detection by 63.4%.The test results show that the designed monitoring system has high detection accuracy and strong antivibration interference capability,which can meet the requirements of actual production.(3)Study a closed-loop control system based on seeding volume information.The control system obtains the real-time vehicle speed through the encoder installed on the speed measuring wheel and calculates the target motor speed by combining the seeding volume information detected by the seeding axis speed and the monitoring device,and then uses the PID control algorithm to control the motor speed in real time.The test was conducted on the load carrying capacity and sowing control accuracy of the control system.The minimum motor speed control accuracy was 94.71% under the conditions of applying 7.5,10 and 12.5N-m torque load to the motor and setting the target speed of the sowing motor at 26.5,34.3and 42.2 r-min-1.The average hole spacing error did not exceed 7.5% and the average coefficient of variation of the spacing was 15.75% when the target spacing was set at 8,12 and 16 cm and the conveyor belt speed was 0.85,1.1 and 1.35 m-s-1,respectively.The above results show that the control system can work stably under different load conditions,with good synchronization,and can realize precise control of seeding volume.