| China is the largest producer of vegetables and rapeseed in the world.Seedling transplanting is the main planting form for dryland economic crops including vegetables and rapeseeds,which has a lot of advantages,such as solving the seasonal contradiction,full utilization of light and heat resources,increase of multiple cropping index,easy to manage,cost reduction and the impact reduction of natural disasters.Therefore,it has great scientific significance and application value to deeply study on the key scientific problems and technology of dryland plug seedling transplanter.At present,the semi-automatic transplanting mechanisms with low efficiency are mainly used for transplanting plug seedlings in the world,and there are some defects on the automatic transplanting mechanisms,such as complex structure,high cost,low efficiency,large vibration and not suitable for domestic transplanting operations,etc.Also three generation rotary pick-up mechanisms for plug seedling we have studied have some problems,including rigid contact with high impact for intermittent transmission mechanism with the locking arc,trajectory and dynamic performance unsatisfactory for continuously transmission mechanism of planetary gear train with two-order general non-circular gears.So in the paper,an innovative type of rotary plug seedling pick-up mechanism of planetary gear train with non-uniform and continuously transmission was put forward,which includes an innovative transmission mechanism of combined incomplete non-circular gears with the performance of two times of transmission ratio fluctuation continuously and sharply in a motion period,and easy to form the ideal working trajectory and posture.Then the working principle,design methods and tests of the mechanism were studied.The main research contents and results are as follows.1)Based on the analysis and research of the working principle of the existing rotary pick-up mechanism for plug seedling,a new combined incomplete non-circular gear mechanism with two time unequal amplitude of transmission ratio was put forward to solve the rigid impact of lock-up device in the existing seedling pick-up mechanism.The kinematics characteristics and design of the combined incomplete non-circular gear mechanism,and the configuration synthesis and kinematics characteristics of rotary seedling pick-up mechanism of planetary gear train based on the preceding mechanism were carried out.The kinematics model of the rotary seedling pick-up mechanism was established.2)According to the kinematics model of the seedling pick-up mechanism,the analysis and optimization software of the mechanism based on human-computer interaction has been developed by using Visual Basic 6.0.By using this software,the effects on the seedling pick-up trajectory by parameters of the mechanism were analyzed,and a set of optimized parameters of the mechanism were finally achieved which can meet the design requirements.3)According to the optimized parameters,the tooth profile design of non-circular gears used in the drive part of the mechanism was carried out,while the whole structure design of seedling pick-up mechanism,the corresponding improvement design of the device of eliminate backlash and the seedling pushing cam were completed.4)Three-dimensional entity modeling and virtual assembly of the mechanism were completed by applying UG8.0 and the assembly was then imported into ADAMS to carry out kinematics simulation tests.The simulation motion trajectory and velocity curve of seedling needle cusp of the mechanism were obtained.Compared with the theoretical analysis results,the correctness of parameter optimization method and results of the mechanism were verified.5)Physical prototype was manufactured to be installed on the self-developed test bench for conducting high-speed photography kinematics tests.Transplanting trajectory and posture of the mechanism were obtained and compared with the relevant theoretical results.The experimental results are almost in agreement with the theoretical results,which shows that the kinematics modeling and optimization design of the mechanism are correct,and also prove the feasibility for the mechanism to be applied in the actual transplanter. |
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