基于D-H法的果园作业平台工作空间分析与试验

针对蒙特卡洛方法分析果园作业平台工作空间存在边界不清、点浪费等问题，该研究采用D-H法建立了作业平台运动学模型，利用U形反正弦分布函数改进了蒙特卡洛方法，得到其工作空间点云图。考虑农机农艺融合和工作人员舒适度，分析了平台理想工作空间；采用网格化算法对改进前后生成的工作空间进行分析，改进后最底层与最顶层边界层面积分别增大180.70 %和102.69 %，表明边界清晰度明显提高；改进后在X、Y、Z三个方向的空间差异系数较改进前分别降低了6.92 %、8.99 %、2.64 %。利用高速摄像机对平台参考点跟踪测试，平台参考点的实测值与计算值最大差值仅为6.2 mm；实际果园试验结果表明，平台参考点实际工作空间与可达工作空间在X、Y、Z方向最大值、最小值均值的差异系数分别为0.27 %、0.76 %和0.01 %，改进方法有效。该研究为果园作业平台结构参数优化、智能控制和同类农业机械工作空间分析提供理论参考。

Workspace analysis and experiments of orchard platform based on D-H method

Abstract: In recent years, due to the transfer of rural labor and the increase of labor cost, there have be more and more researches and applications on the orchard platform which was used for assisting artificial works. The workspace is an important index to measure the organic integration of orchard platform and orchard planting mode. The researcher about kinematics and workspace analysis of agricultural machinery or agricultural robots was few. The values of the samples with the traditional Monte Carlo method are evenly distributed. In the course of the mapping process, the non-linear equation ''stretches'' or ''compresses'' the uniformly distributed intervals, which results in uneven distribution of the boundary position of platform reference point. The sparse point cloud and large ''noise'' makes the workspace boundary inaccurate and thereby affects the optimization of mechanical parameters of orchard platform and other follow-up researches. In order to improve the utilization rate of orchard platform''s workspace and make the operators more comfort, a kinematic model of orchard platform based on the D-H method was established to deduce the positive solution of the platform reference point kinematics of orchard platform and analyze the workspace. In view of the problems, such as workspace boundary fuzziness of orchard platform and point waste etc, an improved Monte Carlo method in which the domain of definition was of the U-shaped arcsine distribution was proposed, and a gridding algorithm was used to analyze the workspace generated by the ones before and after improved, then a cuboid was constructed which was divided into several subspaces along the direction of axis Z-Y-X contained all simulation points. The boundary definition therein was obviously improved, the number of boundary distribution points of workspace was increased by 23.74 %, and the area of the bottom and the top boundary layer was increased by 180.70 % and 102.69 % respectively. By taking the mean value of the workspace generated multiple times as the reachable workspace of orchard platform, the spatial difference coefficients in three directions were reduced 6.92 %, 8.99 % and 2.64 % respectively compareed with those before improved, which indicated that the workspace after improved was closer to the ideal workspace. Through the platform reference point position tracking test, the measured value of platform reference point basically agreed with the calculated value. When Z was 1 314.4 mm, the maximum difference of Y direction was 1.2 mm; when Y was 763.6 mm, the maximum difference of Z direction was 6.2 mm. The results showed that the kinematic model and the solution method were correct. On the actual workspace test of platform reference point, there was larger difference between the actual workspace and the ideal workspace of platform reference point, which was maximum in the direction Y and it was 10.27 %, but which between actual workspace and reachable workspace was less and they were respectively 0.27 %, 0.76 % and 0.01 % in three directions, indicating the one of analyzing workspace by improving the Monte Carlo method was effective. The research can provide the theoretical reference for orchard operation platform''s structural parameter optimization, smart control and workspace analysis of similar type of agricultural machinery.