| The seedling picking mechanism is a key component of an automatic transplanting machine to achieve automatic transplanting.To achieve efficient operation,the precise seedling picking and large pushing angle of the seedling picking mechanism are important links in the seedling picking process of the seedling picking mechanism.The non circular gear planetary gear train transmission can achieve automatic seedling picking and pushing actions of the transplanting and seedling picking mechanism.Compared to other seedling picking mechanisms mainly composed of various rod mechanisms,the planetary gear train transmission mechanism,due to its symmetrical rotation distribution,operates smoothly.One rotation can achieve two seedling picking and pushing actions,resulting in high seedling picking efficiency,therefore,the planetary gear system seedling harvesting mechanism has advantages in seedling harvesting efficiency and work stability that cannot be compared to various rod structures of seedling harvesting mechanisms.Due to the constraints of small curvature radius and non-circular gear design with sharp point pitch curve,as well as the limitations of seedling trajectory error caused by mechanism transmission,traditional non circular gear design methods and non-circular gear system seedling picking mechanisms cannot achieve precise seedling picking and large seedling pushing angle design.This article innovatively proposes a seedling picking mechanism for non-circular complete gear planetary gear trains with large contact angles.The main content includes:establishing a design method for non-circular gears with variable involute variable cycloid combination tooth profile,with the goal of designing a seedling picking mechanism with a large pushing angle and precise seedling picking,and developing software for designing non circular gears with small curvature radius and sharp pitch curve;revealing the variation law of non-circular gear contact ratio due to the dual factors of tooth shape and tooth direction,and proposing a design method for non-circular complete gears with high contact ratio.A seedling picking mechanism with a large pushing angle(greater than 80 °)was developed,and the kinematics of the seedling picking mechanism and the error model of the seedling picking track were constructed.Finally,a seedling harvesting experiment by the seedling harvesting mechanism was carried out.(1)Propose a design method for non-circular gears with involute–cycloid composite tooth profile and Variable-Involute and Variable-Cycloid composite tooth profile.Aiming at the phenomenon of involute tooth profile undercutting in non-circular gears with small curvature radius pitch curves,a composite tooth profiles of involute and cycloid was used to design non-circular gears with small curvature radius pitch curves.The mathematical models of involute–cycloid composite tooth profile and Variable-Involute and Variable-Cycloid composite tooth profile(VIVC-CTF)were derived,and active non-circular gears were designed.The envelope method was used to design driven non-circular gears.Based on the equal pressure angle design of the tooth profile connection point and the equal left and right partial derivatives,the smooth continuity of the joint of the composite tooth profile is studied,and the design software of the small curvature radius pitch curve composite tooth profile non-circular gear is developed.The meshing characteristics of the composite tooth profile such as pressure angle and contact ratio are studied,and the flank clearance and transmission ratio of the involute–cycloid composite tooth profile and VIVC-CTF non-circular gears are measured.(2)Propose a design method for the composite of variable–involute and incomplete variable–cycloid composite tooth profiles.Aiming at the design problem of non-circular gear with cusp pitch curve,the design method of variable involute and incomplete variable cycloid composite tooth profile is proposed(VIIVC-CTF).First,the mathematical model of VIIVC-CTF is constructed,and the research on the smoothness continuity of the joint of composite tooth profile was carried out.The design software of non-circular gear with cusp pitch curve was developed.The variation on the profile shape,pressure angle and contact ratio of the VIIVC-CTF was studied about the relationship between the radius of rolling,elliptical eccentricity and amplitude coefficient of.The research on the meshing characteristics and transmission characteristics of non-circular gear transmission mechanism with sharp pitch curve was carried out,and the measurement test of its backlash and transmission ratio was carried out.(3)A design method for non-circular gears with high contact ratio tooth profile based on dual factors of tooth profile and tooth direction.In view of the transmission error caused by the tooth side clearance affecting the accuracy of the seedling picking track of the seedling picking mechanism,and ultimately affecting the success rate of the seedling picking mechanism,it is proposed to design the non-circular gear with high contact ratio profile by increasing the tooth height coefficient,negative displacement,reducing the pressure angle of the bar curve,and the tooth profile factors of the high contact ratio composite tooth profile.The non-circular gear with high contact ratio profile is designed by the tooth orientation factors of the non-circular superposition gear,and the elliptic eccentricity,radius of rounding the tooth profile factors of pitch curve proportion,negative modification coefficient and pitch curve pressure angle,as well as the tooth alignment factors of spiral angle and rolling radius on the change law of non-circular gear contact ratio,pressure angle and sliding rate characteristics,and the tooth side clearance measurement test was carried out.(4)Develop a non-circular gear planetary gear train seedling picking mechanism with a high contact ratio composite tooth profile and a large seedling pushing angle(greater than 80 °),and conduct error analysis and seedling picking experiments on the seedling trajectory.First,a quadratic unequal transmission ratio curve is designed based on Fourier function,and the variation law of Fourier function coefficient on the seedling picking characteristics and movement characteristics of the seedling picking mechanism is analyzed.Based on expert experience,seedling picking track that meets the seedling picking requirements and had a large seedling pushing angle was designed,and the transmission ratio curve and design parameters of the seedling picking mechanism were determined,and the kinematics model of the seedling picking mechanism;Second,the error model of the seedling picking track and the movement variance model were constructed.Kinematics for the seedling picking mechanism and error analysis of the seedling picking track based on the tooth side clearance and center distance error were carried out;Finally,the idle running test of the seedling picking mechanism based on the high-speed camera technology,measure the seedling picking angle and pushing angle of the seedling picking mechanism and seedling picking test research on the platform of the seedling picking mechanism with different sun gear input shaft speeds were carried out.This dissertation combines theoretical analysis,transmission experiments,and application experiments to study the design method and experimental verification of involute–cycloid composite tooth profile,VIVC-CTF,VIIVC-CTF,and high contact ratio overlap non circular gears.This provides certain theoretical guidance for the design of small curvature half diameter pitch curve non circular gears and pointed pitch curve non circular gears,as well as the design of precise seedling picking mechanisms. |
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