Dynamic behavior of a hydraulic crane operating a freely suspended payload

Abstract

We describe an investigation of the dynamic behavior of a hydraulically driven crane with a freely suspended payload during luffing and slewing motions. To simplify the task, the two movements are considered separately. Taking into account only one motion at a time, the crane is regarded as a three-link kinematic chain with revolute joints. The forward dynamics problem is solved for a crane with three rotational degrees of freedom, two of which describe the load swinging. In both the cases studied, the links are driven by a torque applied via a hydraulic drive, i.e., a linear actuator for the luffing case and a rack and pinion mechanism for the slewing motion. To compose the set of differential equations for the forward dynamics problem, a method based on a general Newton-Euler algorithm is used. From these simulations the time histories of various parameters, namely the swinging angles, hydraulic pressures, and joint forces, are determined. The results obtained via simulations are confirmed experimentally and a good agreement between the two outputs is observed. The results also show that a hydraulic drive system using fast opening flow direction control valves increases the load swing and imposes extensive inertial forces and problems of fatigue and reliability.

中文概要

目 的

对载有自由悬浮载荷的液压驱动起重机的动态特 性分别在升降运动和回转运动两种工况下进行 研究, 建立动力学模型并验证其正确性。

创新点

1. 为了简化任务, 将两种运动分开讨论。一次只 考虑一种运动, 把起重机看作具有三个转动关节 连接的运动链; 2. 为起重臂的运动问题构造微分 方程, 使用了通用的牛顿-欧拉算法; 3. 对运动和 动力模型进行仿真, 得到摆动角度、液压压强和 连接作用力随时间的变化曲线, 并通过实验进行 了验证。

方 法

1. 建立系统的运动和动力模型, 分别对回转运动 和升降运动两种工况下的液压缸压强进行推导; 2. 在两种工况下, 对起重臂转角、液压缸压力和 最大行程前臂液压缸反作用力进行仿真计算; 3. 将实验获得的有关参数的曲线与仿真得到的 曲线进行对比, 验证模型的正确性。

结 论

1. 在液压起重机运动期间悬浮载荷的摆动对起重 机的机械系统和液压驱动系统本身具有强烈的 影响, 所以在系统设计中不能忽视; 2. 系统性能 提升的主要方向是安装控制系统以减小载荷摆 动(特别是在起重机回转运动时); 3. 本文建立 的考虑了负载的大角度摆动和液压驱动系统的 动力学模型得到了验证, 表明其对起重机运动仿 真的适用性。尽管分开考虑了两种典型运动, 但 所用的建模方法还是适合对起重机一般运动的 研究。