区域逼近与动态图形法求解大行程液压支撑机构参数及优化

为实现一种作业与运输兼用型地轮机构的状态转换,针对其结构特点研究一种非端部支撑的新型液压支撑方案,以满足在有限的安装空间内实现大工作行程的要求。在建立该机构力学及运动学模型的基础上,通过几何关系及动力约束条件进行参数的区域逼近;确定液压缸安装位置和参数的可行域后,运用动态图形模拟摆梁步进旋转时机构的运动情况,观测参数取值域曲线的运动状态,得出与可行边界线的交点,从而确定在液压系统压力16 MPa条件下,安装臂长度175 mm,安装臂距旋转点357 mm,液压缸缸体长度为916 mm,缸体内径为71 mm。研究及样机试用表明,非端部支撑对置双缸体液压支撑机构能够满足地轮状态转换的需要,且具有结构紧凑、工作行程大的特点。同时,该研究探索并证实了区域逼近与动态图形求解法在解决此类机构的优化与参数求解方面的可行性与有效性。

Parameters solving and optimization of long working stroke hydraulic support mechanism using regional approximation and dynamic graphical solution

Abstract: As a result of substantial improvements in agricultural mechanization in China, large farm implements have been widely utilized. However, a problem has arisen concerning how to guarantee safety, effectiveness and convenience when such wide-breadth farm implements switch between road transport and operational modes. At present, there are 3 methods of resolution: Folded frames, which can be subdivided into supero-inferior fold, horizontal fold and lifting fold; a trailer for longitudinal traction along the girder of a wide-breadth farm implement; and combined double-frame agricultural implement with common mechanism for raising/lowering and rotating a lift frame about a vertical axis. Nevertheless, folded frames have complex structures and are expensive to manufacture; a dedicated shoring trailer has to be furnished, and field operation is very inconvenient; and the complex structure of combined double frames are more expensive. To address these technical problems, a high-mobility universal frame platform for wide-breadth farm implements, which can benefit operation and transport, was designed at Northeast Agricultural University. Its land wheel mechanism outperforms conventional land wheels on the frames of farm implements that only have depth-limiting and transmission functionality. The land wheel mechanism ensures easy tilling depth adjustment, good conformality, the ability to produce a large driving force, and convenient and quick switch modes. To realize the mode switching of land wheel mechanism for operation and transport purposes, a novel hydraulic support scheme was selected based on a part of trunnion mounted cylinder on a common rod. It adapted to the structural characteristics of the land wheel actuation device that required a long working stroke within a limited mounting space. Toward mechanics and kinematic models for this mechanism, support structure parameters were regionally approximated according to a spatial geometric relationship and subject to dynamic constraints. After the feasible region of the mounting position and dimensions of the hydraulic cylinder were determined, a dynamic graphical solution was used to simulate the motion situation of mechanism. As the swing arms rotated stepwise, the curve describing the cylinder length on one side was observed to find its point of intersection with a feasible boundary. The optimal solutions for the mounting position and cylinder dimensions could be determined using this information. When the hydraulic system pressure was 16 MPa, the length of the mounting arm was found to be 175 mm, the mounting arm was 357 mm away from the pivot point, the length of the hydraulic cylinder was 916 mm, and the inside diameter of the cylinder was 71 mm. The study and prototype trial indicate that the non-end supported opposed twin-cylinder hydraulic support mechanism enables the land-wheel mode to switch and is characterized by a compact structure and a long working stroke. The study also demonstrates that regional approximation and dynamic graphical solutions can be effectively used in the optimization and parameter solving for such mechanisms.