| Rice wide-narrow distance transplanting has more advantages in increasing production andpreventing disease than equal row spacing transplanting. The core component of wide-narrowdistance transplanter is called "transplanting mechanism". It can get spatial transplantingtrajectory which formed by endpoints of plant arms through relative rotation motion betweenplant arms and spatial planetary gear train. The two existing high-speed wide-narrowtransplanting mechanisms are the sideling transplanting mechanism composed of cylindrical gearand the vertical transplanting mechanism composed of spatial gears. Both of them cannot solvethe problems such as large horizontal offset of picking up seedling trajectory in inclined andshaping wider plant hole, which can cause high degree of damaging seedling and laying seedling.The sideling transplanting mechanisms cannot shorten the horizontal offset of picking upseedling trajectory, because the structure cannot change. The horizontal offset of the verticaltransplanting mechanism depends on the ratio of planetary gear train, and the higher the ratio thebetter. In order to obtain a spatial planetary gear train with higher transmission ratio, one kind ofspecial shaped non-circular bevel gears was put forward, and a wide-narrow distancetransplanting mechanism composed of special shaped non-circular bevel gears and crossedcylindrical gears was obtained. The pitch curve of special shaped non-circular bevel gears wasdesigned by two non-uniform B-splines with the continuous angles and discontinuous radius.The gear pair could continuously and smoothly work after adjusting the height of tooth profilecurve in the transition section of two non-uniform B-splines. The main research work of thispaper is as follows:(1) The home and abroad transplanting mechanism working principles were studied, andobtained an ideal planting trajectory. One kind of wide-narrow distance transplanting mechanismcomposed of special shaped non-circular bevel gears based on spherical curve was put forward,which can further shorten the large horizontal offset of picking seedling trajectory. (2) The transmission characteristics and impact factor of special shaped non-circular bevelgear were studied, and a mechanism kinematics mathematical model established basedon the theory of Denavit-Hartenberg transformation matrix.(3) A computer-aided analysis and simulation program was written to study the kinematicsproperty of transplanting mechanism after analyzed the position, posture and speed of plantingtrajectory. The effect of mechanism parameters and gear parameters to the horizontal offset ofpicking seeding trajectory and plant hole were analyzed based on the program. A set of optimalparameters meeting the working requirements of wide-narrow distance planting trajectory wasobtained by the method of human-computer conversation afterward.(4) The characteristics of tooth profile formation of special shaped non-circular bevel gearwere studied. Mathematics model about the transition curve of tooth top and root established,and the gear pair could continuously and smoothly work after adjusting the height of toothprofile curve in the transition section of two non-uniform B-splines. The computer aided designprogram was written based on the development platform of Matlab.(5) A three-dimensional model of wide-narrow distance transplanting mechanism wasobtained by the optimal parameters. Virtual prototype test was performed by the software namedAdams and a model machining of the transplanting mechanism as well as its testing was made,and the shape of tow trajectory was almost same. A wide-narrow distance transplanting test-beddeveloped which is used on rotary trial soil bin. Tests were carried out with seedling and theupright degree, damaged seedling, laid seedling of seedlings was measured. All of the inspectedresults agree with the theoretic calculation, which give a convincing proof to verify thecorrectness of the design method of the transplanting mechanism. |
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