Optimum Design of the Hydraulic Excavator’s Working Device Based on ADAMS.doc

学术会议英语A3班 专业：机械工程Optimum Design of the Hydraulic Excavators Working Device Based on ADAMSXu Dan摘要：挖掘机工作装置设计是否合理直接影响装载机作业效率、使用寿命及操作人员舒适性和视野。挖掘机工作装置优化设计的约束条件多，结构复杂，用虚拟样机软件ADAMS可以很好地对装载机工作装置进行优化设计。因此，本文以典型的装载机工作装置机构反转四连杆机构为例，对挖掘机工作装置机构的各杆的位置和方向对机构各项参数的影响进行了定性分析。在ADAMS中建立和参数化挖掘机模型后以驱动液压缸驱动力最小为目标函数以各设计要求为约束进行运动学和动力学仿真和优化，减小了液压缸的最大驱动力，得到最优的驱动力。关键词：ADAMS，挖掘机工作装置，仿真，优化Abstract: In this paper, first a virtual prototype of hydraulic excavators working device model is built. Then a qualitative analysis on the working device about the mechanism is made, which shows how to affect the kinematical and dynamical characteristics of each links location and direction. At last, we make a dynamical simulation and optimization on the virtual model by using the ADAMS software. The results indicate that the driving force has been optimized.Keywords: ADAMS; working device of excavator; simulation; optimization1 IntroductionHydraulic excavator is widely used in agriculture，construction traffic and some other industries (Lv Chao, 2010:03). It plays an important role in improving the work efficiency and reducing the workers burden. The working device is the direct assignment section of an excavator. Its performance and reliability will directly affect the whole machines performance. Therefore, it is the research and development foundation of the whole machine control to study on the working device. The optimization of the working device can make the whole machine digging capacity raise and lengthen the using time. Virtual prototype technology (Zhen Jianrong, 2002:65-97) can shorten the cycle of design，reduce the cost of product research and development. So we can quickly design the product which meets the market demand quiet well. This paper will have some kinematics and dynamics simulations and optimizations of the hydraulic excavators working device by using ADAMS software. 2 Qualitative Analysis of Excavator Working Device Fig.1 Components of the Working DeviceThe excavators working device work on the same principle as the arms action. Its transmission mechanism substantially is a three-degree of freedom planar mechanism, and the planar mechanism is connected in series with four four-bar linkages. (In Fig.1) The numeral 1 stands for the movable arm hydraulic cylinder, the numeral 2 stands for the movable arm, the numeral 3 stands for the boom hydraulic cylinder, the numeral 4 stands for the bucket hydraulic cylinder, the numeral 5 stands for the boom mechanism, the numeral 6 sands for the bucket, and the numeral 7 stands for the power link mechanism.Excavators working condition contains seven parts，they are digging, full lifting, unloading, empty returning, adjusting and maintaining, the whole machine moving and other auxiliary functions. Because we do not consider the excavators revolving movement, this paper only analyzes on the former four conditions optimization.3 Model Establishment and the Optimization3.1 Building Excavators Working Device ModelThrough the qualitative analysis we obtain the position of each working pole, then build the model in ADAMS and add constraints of kinematic pair (Wei Hangxin et al, 2002:11-13). As shown in Fig. 2, there are three cylindrical joints, five revolute joints, three spherical joints, three translational joints, one inline primitive joint and three motions. Add driving functions and forces as follows:Fig. 2 Excavators Working Device ModelThe arm cylinder: STEP (time, 0, 0, 0.5,-70) + STEP (time, 1, 0, 120) + STEP (time, 3, 0, 4, 120)The boom cylinder: STEP (time, 0.5, 0, 1, 140) + STEP (time, 0, 2.5, 2, 180) + STEP (time, 4, 0, 4.5,-180) + STEP (time, five, 0, 6, 200)The bucket cylinder: STEP (time, 0, 5, 1, -110) + STEP (time, 2.5, 0, 3.5, 130) + STEP (time, 4.5, 0, 5, 135) + STEP (time, five, 0, 6, 150)3.2 The Kinematics Optimization of Excavators Working Device Fig. 3 POINT Vs Motion TrackTo describe the positions of the points on an excavator, we parameterize the working device model which we have established (Chen Liping, 2005:47-62). Then taking the biggest driving force of excavators bucket cylinder for the target function, conduct the kinematics simulation to the working devices sequential working by using ADAMS software. We can get the excavators working range envelope curve (Fig. 3), it is also the optimized bucket teeth-point V track. From the envelope curve, we can easily find out the movement regulation. In the process of optimization we measure the main working sizes, such as the biggest mining radius, the biggest digging depth and height, the maximum unloading height and so on. After the optimization, the largest digging radius becomes 7 meter, the largest digging depth rises to 6.5 meter, the largest digging height is 3.26 meter，the biggest unloading height is 5.456 meter. 3.3 The Dynamics Optimization of Excavators Working Device 3.3.1 The Digging Resistance AnalysisFig. 4 The Digging Resistance and Its DecompositionThe digging resistance is made up of several parts. This paper we main consider the resistance when the working device is in digging mode. Use a resistance F to stand for all the parts resultant force. F can be decomposed into two directional forces, one is Fn which is pointing along the tangent of the teeth-path curve, the other is Ft which is perpendicular to the tangent direction (Fig. 4).Ft = K0bh （1）Fn = W1 （2）According to Fig. 4, we use the following formulas to calculate the resistance Ft and Fn, then we can obtain the buckets resistance F by experience calculation method.K0 -resistance, unit: N/m2; b -cutting width (bucket wide), the unit: mm;h -mining depth, general h = (0.1 0.33) b, unit: mm;-mining resistance coefficient.3.3.2 The Dynamics Optimization of Excavators Working Device There are some redundant constraints in the model, and the ADAMS software cannot auto-delete all of them, so we need to remove them by hand. Through the previous optimization analysis we know that the coordinates of point A, C, F, Q, are more sensitive to the buckets hydraulic cylinder driving force change. Increasing point As x-coordinate or decreasing the y-coordinate between A and C all can make the driving force reduce. Add three forces at the bucket as follows (Hao Caohui et al, 2010:18-23), and then, take the minimum value of the excavators biggest bucket cylinder driving force as the target function, start the optimization design. The bucket resistance: step (time, 0, 2.5, 2, 9000) + step (time, 2.5, 0, 3, 9000)Insert the resistance: step (time, 0, 2.5, 2, 8000) + step (time, 2.5, 0, 3, 8000)Material gravity: step (time, 3, 0, 4,-12000) + step (time, 4, 0, 5, 12000)(b) Point C(a) Point A(c) Point F(d) Point QFig. 5 Stress Changes: (a) Point As Force Change; (b) Point Cs Force Change; (c) Point Fs Force Change; (d) Point Qs Force ChangeFig. 5 is some important points stress changing curve after the optimization within one work cycle. At 2.5 seconds the excavator finished putting the arm down action. When the bucket went into the digging site, the arm hydraulic cylinder and the boom hydraulic cylinder and the bucket hydraulic cylinder act at the same time. Each points stress change is quite obviously. When in digging, the bucket teeths force change is increasing. For unloading completely, the excavator unloads very fast, so the points force change dramatically. This change results in the force curve producing a peak, and the force first increases, then decreases, until completely unload. And this is in line with the actual working condition. After the unloading, the excavator starts to collect the bucket and drop the arm, then goes into the next work cycle.4 The optimization conclusionFirst we find the points coordinates when they are in the upper limit unload condition, this provides some basic parameters to manufacture various spare parts. Then we analyze each points stress, so we can further to analyze the parts internal force. By means of the finite element analysis software, we also can do some structure optimi