针对玉米精密播种机使用导种管的结构不合理导致株距均匀性差的问题，该文介绍了一种应用逆向工程设计软件Geomagic Design设计导种管的方法，研制性能优良的导种管。利用悬臂式三坐标测量机对进口曲线型导种管结构进行扫描，获取三维点云数据；通过三维逆向工程软件Geomagic Design减少噪音点、合并、简化、对齐等数据预处理获得网格数据；依照网格数据逐个创建特征重构导种管的三维几何模型；对重建的三维几何模型与网格数据进行误差分析实现三维几何模型的优化；依照所优化的三维几何模型生成工程图纸，完成导种管试制。在丰美2BQX-6玉米免耕精密播种机上进行了试制导种管、进口导种管和无导种管的性能对比试验，结果表明：试制导种管、进口导种管和无导种管的段粒数合格率分别为95%、97%和67%，空段率分别为3%、3%和33%，说明导种管可有效提高播种质量，且本研究试制的导种管与进口导种管性能相当。应用逆向工程设计导种管相对传统的理论研究和试验研究，可以缩短设计周期，降低设计成本；所建的三维几何模型为后续导种管结构研究和改进优化提供了一定参考。%In order to improve the performance of seed tube and solve the problem of bad uniformity of seed spacing caused by unreasonable seed tube structure, this study introduced a method of applying reverse engineering design software Geomagic Design to design seed tube. Reverse engineering is a kind of technology that builds engineering model of products or parts according to prototypes of current products or parts, and then analyzes and improves them. As a new product design method, it plays an important role in absorbing advanced manufacturing technology at home and abroad, shortening product development cycle and reducing production cost. Seed tube is mainly applied in precision planter, which is used to shorten the distance between metering point and dropping point, reduce seed horizontal speed variance between different metering speeds and reduce seed bounce in dropping and falling processes, in order to realize zero-speed dropping seed and make sure of good uniformity of seed spacing. The length of linear part, the angle between linear part and horizontal direction, the curvature of arc part, the central angle of arc part, the cross-sectional area and the smooth degree etc all have significant impact on seed dropping performance. The imported curve-type seed tube was scanned by non-contact laser scanning method of three-coordinate measuring instrument and the three-dimensional (3D) point clouds were obtained. The front and back of the seed tube were scanned respectively in order to get the complete point cloud data; to make the point clouds better matched with the scanned seed tube, unrelated scanned data were deleted through 3D reverse engineering software Geomagic Design, data preprocessing like reducing noise, merging, simplifying, alignment etc. was done, and then the mesh data of seed tube were got. Through the application of 3D reverse engineering software Geomagic Design, based on the mesh data, and by the application features design tools in “design” interface, coordinate system, tube body, semicircle groove, hanger and strip rib and other features were created one by one, and the 3D geometrical model of seed tube was re-built. Error analysis for the re-built 3D geometrical model and the mesh data was done in “measure” interface, and different colors were used to distinguish different errors. If there were large errors, then back to “design” interface and adjust the corresponding features to reduce error and optimize 3D model. The seed tube was trial-produced according to the engineering drawings which were generated from the optimized 3D geometric model. According to the national standard GB/T 20865-2007, the test was done with Fengmei 2BQX-6 corn no-tillage precision seeder, and the performances were compared among the trial seed tube, imported seed tube and without seed tube. Taking the qualified rate of seed number and the no-seed rate in seed channel as the test indices, make a continuous measurement of 100 segments, and the theoretical length of a segment was 250 mm. The results showed that the qualified rates of seed number in seed channel for the trial seed tube, imported seed tube and without seed tube were 95%, 97% and 67% respectively; the no-seed rates in seed channel were 3%, 3% and 33% respectively. It can draw the conclusions that seed tubes can effectively improve seeding quality, and the performance of the trial seed tube is good and equivalent to the imported seed tube. This research can be successfully applied on seed tube design. Applying reverse engineering for designing the seed tube can shorten the design time and reduce the design cost compared with theoretical study and experimental study. The built 3D geometric model provides a certain reference for the improvement and optimization of seed tube.
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