| With the popularization of super hybrid rice planting technology,the efficiency and seeding accuracy requirements of factory seedling planting equipment have gradually increased.Among the precision seeder for super rice,vacuum-vibration precision seeder has broad application prospects with low seed injury rate and high seeding accuracy.The existing vacuum-vibration seeding assembly line adopts a two-degree-of-freedom Cartesian coordinate manipulator to drive the suction plate to complete seeding.However,the Cartesian coordinate manipulator has low space utilization and poor flexibility,so it is unable to coordinate the assembly line longitudinally and carry out dynamic motion planning,resulting in the suspension of the assembly line and waiting for seed metering,which affects the seeding efficiency.A fixed suction height can easily lead to a decrease in seed suction rate,which in turn reduces the seeding eligible rate.Therefore,in order to improve the seeding efficiency and accuracy of the vacuum-vibration precision seeder,the six-axis manipulator was used to replace the Cartesian coordinate manipulator to realize the cycle motion of suction,carrying and rowing continuously on the assembly line.The following motion control method of seeding manipulator was proposed,and the motion control system of precision seeding manipulator was built,which followed the suction height,had the constraint of the seed-carrying speed and the continuous seeding process.This system could change the fixed-position suction method into the following suction method,and the plane intermittent sowing method into the space following sowing method,so as to improve the work efficiency and seeding eligible rate.The main research works of this paper are as follows:(1)The overall scheme design of the following motion control system of the seeding manipulator.Aiming at the problems existing in the seeding process of the Cartesian coordinate manipulator combined with three-stage assembly line,the following motion control system of six-axis seeding manipulator was designed.According to the periodic motion law of suction,carrying and discharging,the performance requirements of seeding and the control requirements of following suction and discharging were proposed.The following motion control system of the manipulator was composed of information perception layer,regional decision-making layer,motion planning and motion control layer.The control system was carried on the vacuum-vibration precision seeding test platform.The bottom soil and coating surface soil device were set on the whole section of the assembly line,and the electromagnetic vibration seed feeding device was used for discrete seeds.According to the visual test results,the manipulator was controlled by remote communication to drive the suction plate to complete the function of following suction and discharging.(2)Kinematics analysis of six-axis seeding manipulator.The manipulator pose description method and link coordinate system were determined,and the kinematics model was established.The forward kinematics of the manipulator was analyzed by using the D-H parameter method,and the end pose of the manipulator was solved.According to the end pose,the positions of each joint were obtained by the algebraic method to solve the inverse kinematics of the manipulator.The connecting rod model of the manipulator was established in MATLAB,and the reachable workspace of the manipulator was obtained by Monte Carlo random sampling,which lain a theoretical foundation for the study of obstacle avoidance motion planning and following motion control method of the manipulator.(3)Research on motion planning method of seeding manipulator based on sub-regional motion planning strategy.The sub-regional motion planning algorithm was composed of collision detection,decision-making layer and planning layer.The mixed bounding box model was established,and the collision-free workspace was calculated by using the line-surface collision detection.A decision system based on position sampling and time calibration was established to judge the motion state of the manipulator.According to the decision results,the point-to-point off-line motion planning and RRT*online obstacle avoidance motion planning were carried out,and the parabolic transition interpolation method was used to smooth the trajectory to obtain the desired trajectory.(4)The following motion control strategy design of seeding manipulator.The following motion control strategy mainly included the following control strategy of the suction height in the suction process,the kinematic constraint in the seed-carrying process,and the following control strategy in the seeding process.The theoretical relationship between suction height and seed layer thickness was determined by EDEM simulation,and the mapping relationship between seed layer thickness and actual suction height was established by bench test.The force of seeds in the carrying process was analyzed,and the mathematical model between the inertial force and the adsorption force was established.The acceleration of the suction plate should be less than 40.866m/s~2,and the seed-carrying motion strategy of the suction plate was constructed.In order to improve the output frequency of the image detection algorithm,the motion state of the seedling tray was detected by image,and the posture information was interpolated.The ARIMA model was used to predict the motion state of the seedling tray after being occluded by the manipulator.The error feedback motion control strategy based on position and orientation guidance was established,and the position and orientation of the suction plate were adjusted according to the feedback value to realize the function of following seed suction and discharge.(5)Simulation and test of the following motion control method of the seeding manipulator.The simulation platform was built by V-REP to prove the correctness of the motion planning algorithm and control logic.Vacuum-vibration precision seeding test platform was built.In the base coordinate system of the manipulator,when the speed of the assembly line was-0.12m/s,the dynamic positioning error range of the seedling tray attitude estimation system on X axis was[-3.0 mm,3.8 mm],and the attitude error was[-0.9°,0°].The experimental results on the performance of the manipulator following motion control system showed that when the vibration frequency of the vibrating seed tray was 11Hz,the amplitude was 5mm,the negative pressure of suction plate was 4.5k Pa,and the seed layer thickness was 12mm～20mm,the seed suction following motion control model can maintain the seed suction rate above 96.5%.When the running speed of the assembly line was-0.12m/s and the time interval for providing seedling trays was 6s,the efficiency was about 600 discs/h,and the eligible rate was 94.70%,the replay rate was 2.77%and the hole rate was 2.53%.In addition to ensuring a higher qualified rate of sowing,the seeding efficiency was improved to meet the expected effect of the system.This system can provide an effective basis for the intelligent development of precision seeding technology for super rice. |
PDF Full Text Request