玉米果穗剥皮的运动仿真与高速摄像试验

Dynamic simulation and high-speed photography experiment on corn-ear husking

针对玉米剥皮田间试验和室内试验存在玉米品种多样、适收期短等问题,该文提出了采用理论分析、虚拟仿真技术与高速摄像技术相结合的方法,研究果穗在剥皮机构中的运动。首先,对玉米果穗在剥皮机构中的受力及运动进行了理论分析,得到影响果穗剥净率、剥皮效率以及剥皮损失的主要因素;其次,应用ANSYS/LS-DYNA建立了玉米果穗与剥皮机构相互作用有限元仿真模型,获取了剥皮辊不同转速下玉米果穗在剥皮机构中的运动速度、绕自身轴线的角速度和受力情况。仿真结果表明,随着剥皮辊转速的增大,果穗的运动速度由0.2增大到0.4 m/s;果穗绕自身轴线的旋转角速度增加,在0-15 rad/s之间变化;果穗的受力增大,且波动性更强,3种工况下最大受力分别为11.9、14.5和16.3 N。以玉米果穗沿剥皮辊的速度和加速度为验证参数,仿真数据与果穗剥皮高速摄像试验数据进行了对比。结果表明,仿真数据与高速摄像试验结果基本一致,证明了仿真模型可以较好地替代物理试验。该研究结果可为剥皮机构的设计与分析提供了参考。

The moisture content of corn kernel is generally 25%-40% when corn ear is harvested in China, which makes it not suitable for using direct way of threshing and harvesting. As an important part of harvesting, corn ear husking plays a great role in the harvest performance. At present, research on the performance of corn ear husker is commonly implemented by field experiments and bench tests. However, these approaches are restricted by the various kinds of corn and the shortage of harvesting time. Therefore, there are limitations on the test results. To deal with the problems mentioned above, a method combining theory analysis, virtual prototyping technology with high-speed photography was proposed in this paper to study the motion pattern of the corn ear on the husking device. First of all, to obtain the main influence factors of husking rate, efficiency and damage rate, the force and movement of corn ear in husking mechanism was analyzed in theory. Secondly, the three-dimensional（3D） model of husking mechanism was established using 3D design software, and then the 3D model was imported to ANSYS/LS-DYNA. After that the finite element model of corn ear and corn husker was set up by setting the material model and adding constraint and load. The velocity of corn ear in the direction of husking roller, the angular speed of corn ear around its own axis and the force of corn ear corresponding to the performance of the corn husker, were obtained by simulation analysis. The simulation results showed that the movement speed of corn ear along husking roller rose from 0.2 to 0.4 m/s with the increase of husking roller rotating speed; the angular velocity of corn ear ranged from 0 to 15 rad/s when the rotating speed of husking roller increased from 350 to 550 r/min; meanwhile, the force which was applied to corn ear increased and showed strong fluctuations, and the maximum stresses under three kinds of working conditions were about 11.9, 14.5 and 16.3 N, respectively. Finally, the husking test bench was built in the basis of the 3D model. The husking experiment was carried out with different rotating speeds of husking roller using high-speed photography. The test bench was made up of base frame, husking device, transmission mechanism, variable frequency motor（rated power of 3 kw）, frequency converter, NI National Instruments data acquisition card, computer and high-speed photography（Phantom v9.1）. The test condition was mainly consistent with the simulation condition. In order to avoid the influence of different sizes of corn ear, corn ear in the experiment was similar to that in the simulation in length and diameter size. At the same time, for reducing the influence of accidental factors on test results, the experiment was carried out three times. Taking the actual velocity and acceleration of corn ear in the direction of husking roller as validation arguments, the simulation data were compared with the high-speed photography test data. It was found that the simulation results agreed well with the actual results, which verified the validity and accuracy of the simulation model. The result also indicates that the simulation model could be a better alternative to the physical test, which can reduce the development cycle and the number of physical prototype test. The research output will play a significant role in carrying out the optimization design of the corn husker and provide a new method to develop a new husking mechanism.