| This paper takes the pneumatic precision metering device for rapeseed as the investigation object. Theoretical analysis, computer simulation analysis and experimental study were carried out via kinematics and dynamics analysis of the metering process, ANSYS/CFX simulation, seeding performance on a laboratory seeder test-rig and high-speed video camera system experiment. The major points were generalized as follows:1) In order to study the relationship between vacuity and structural and operational parameters of positive and negative pressure precision metering device for rapeseed, dynamics analysis was conducted on sucking process to establish mathematical model of maximum vacuity Hmax, pressure ratio coefficient K of outlet and interface was put forward. Based on the kinematics and dynamics analysis on dropping process of positive and negative pressure precision metering device for rapeseed, the influence of positive pressure on dropping speed of rapeseed and influencing factors of advance dropping process, timely dropping process and delayed dropping process were clarified.2) The influence factors of K were studied through air current simulation of vacuum chamber with ANSYS/CFX. Simulation results show that the cone angle of the nozzle has a very significant effect on K, but nozzle numbers of the seed disc and the vacuity have no significant effect on K. K is5.36,2.02, and1.56when the nozzle with cone angle of60°,90°, and120°respectively. K increases with increasing cone angle.3) Single factor test of structural parameters on structure of seed-throwing mouth and mounting direction of disc were carried out so as to define the reasons of them affecting the seeding performance. The improving measure of the seed-throwing mouth was proposed. Single factor test of operating parameters on rotational speed of the disc, vacuity, pressure were conducted in order to obtain the range as well as the seeding performance influencing rules of the operating parameters.4) Based on the single factor test, orthogonal design and uniform design method were developed. The order of the factors influencing the test index was cleared. It was obtained that the rotational speed of the disc affects the test index little when the ratio of vacuity and pressure is reasonable.5) The ratio R of vacuity and pressure experiment showed that when R is30to40, the seeding performance of the seed-metering device is good; when R is less than20, the eligible index decreases and the miss index increases with the increasing rotational speed of the disc; when R is more than50, the eligible index decreases with the increasing rotational speed of the disc, and the miss index and multiple index increases with the increasing rotational speed of the disc.6) We analyzed the dropping process of the pneumatic precision seed-metering device for rapeseed via high-speed video camera system technique for the first time. Based on the seed dropping videos, the following phenomena was observed:timely seed dropping, a nozzle sucking multiple seeds, advance seed dropping, failed seed dropping, delayed seed dropping, enforcement seed dropping, timely seed dropping seed impinging against delayed seed dropping seed and nozzle with no seed turning over the seed throwing area. The reasons leading to missing seeding and multiple seeding were found out, which verify and supplement and perfect the theory of the seed-dropping process. Improvement measures for structure of positive pressure chamber and seed-throwing mouth were put forward. |
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