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液压挖掘机正铲工作装置仿真设计[含三维PROE]【全套9张CAD图纸和WORD毕业论文】

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目录
1 前言 (1)
1.1课题研究的背景和意义 (1)
1.2 液压挖掘机研究现状及发展动态 (1)
1.2.1 国外的研究现状及发展动态 (2)
1.2.2 国内的研究现状及发展动态 (3)
1.3 本文研究的主要内容 (5)
2液压正铲挖掘机工作装置的运动分析 (6)
2.1 液压正铲挖掘机的基本组成和工作原理 (6)
2.2 工作装置结构方案的确定 (7)
2.3 工作装置运动分析 (10)
2.3.1动臂运动分析 (10)
2.3.2斗杆运动分析 (12)
2.3.3斗齿尖的几种特殊工作位置的计算 (13)
3 工作装置尺寸的设计确定 (17)
3.1应用举例 (17)
  3.1.2动臂及斗杆长度确定 …………………………………………………(17)
3.1.2机构转角范围确定 (18)
3.2 油缸铰点及行程确定 (19)
3.2.1动臂油缸的铰点及行程确定 (19)
3.2.2 斗杆油缸铰点及行程确定 (19)
3.2.3 铲斗油缸铰点及行程确定 (19)
3.3工作装置的位置模型建立 (19)
3.3.1 动臂与平台铰点位置C的确定 (20)
3.3.2 动臂及斗杆长度的确定 (20)
3.3.3 机构转角范围确定 (20)
3.4工作装置油缸铰点及行程确定 (25)
3.4.1动臂油缸的铰点及行程确定 (25)
3.4.2斗杆油缸铰点及行程确定 (28)
3.4.3铲斗油缸铰点及行程确定 (31)
3.5液压正铲挖掘机三维模型 (32)
4 结论 (34)
参考文献 (35)
致谢 (36)

1 引言
1.1课题研究的背景和意义
目前我国露天矿的开采规模逐渐扩大,为了适应日益增大的矿用汽车铲装的需要,这就需要较大斗容的挖掘机,由于挖掘机愈大,每单位土石方的施工成本愈低,而液压挖掘机较机械式挖掘机有很多优点,但是国内对大型液压正铲挖掘机的研究较少,液压挖掘机工作装置是完成挖掘机各项功能的主要构件,其结构的合理性直接影响到挖掘机的工作性能和可靠性,对其研究是整机开发的基础,对工作装置进行优化,目的在于缩短研究和开发周期,降低产品成本,提高设计质量,本课题的任务就在于此。
现代化建设速度,在很大程度上取决于各种工程建设速度,而工程机械水平的高低,又直接对工程建设速度发挥着促进或抑制作用。传统研发管理及设计方法只是被动地重复分析产品的性能,而不是主动地设计产品的参数。作为一项设计,不仅要求方案可行、合理,而且应该是某些指标达到最优的理想方案。随着电子计算机的应用,在机械设计领域内,已经可以用现代化的设计方法和手段进行设计,来满足对机械产品提出的要求。利用优化设计方法,人们就可以从众多的设计方案中寻找出最佳设计方案,从而大大提高设计效率和质量。可靠性是我国工程机械的致命弱点,我们要正视差距,增强科研开发力度,提高技术水平,更多地发展具有自主知识产权的高质量产品,进一步促进工程机械的发展。

1.2 液压挖掘机研究现状及发展动态
     挖掘机作为一种典型的土石方施工设备,在基础设施建设中起着十分重要的作用,因此加强对挖掘机的研究具有十分重要的意义,随着能源的紧缺和人们对环保意识的增强,节能技术研究成为同行学者关注的焦点没随着人类空间获活动的延伸,以及人类对挖掘机工作环境与功能要求的延伸,在遥控挖掘机和机器人化挖掘机研究方面正进行不懈努力,遥控挖掘机的研究离实用化已经不远,开发智能化的多功能挖掘机并使之成为真正的挖掘机器人还是人们追求的目标。由于挖掘作业中负载变化剧烈,有些学者已经开始将振动挖掘方式运用于减少挖掘阻力,减低功率消耗以及延长机器使用寿命方面的研究。近年来,随着人类对自然的开发,挖掘机也朝着大型化大功率化发展,从而满足人类对大型工程的需求。
1.2.1 国外的研究现状及发展动态
1)国外产品发展趋势
1950 年在意大利生产了第一台液压挖掘机,由于其挖掘能力强、生产率高、通用性好、操纵轻便等特点,在工程建设施工中起着重要的作用。六十年代,随着西方经济的发展,液压挖掘机需求数量急剧上升,但大多数属于中小型液压挖掘机。七十年代开始,随着科学技术的进步和大型水电工程及大型露天矿建设的需要,液压挖掘机向高速、高压、大斗容、大功率发展。随着液压挖掘机产量的提高和使用范围的扩大,世界上著名的挖掘机生产商纷纷采用各种高新技术,来提高产品的竞争力。国外的一些公司开始研制大型矿用液压挖掘机,其中以德国、法国产品居多。
在液压挖掘机产品功能方面,液压挖掘机工作装置向多功能化的方向发展。当液压挖掘机配置不同的作业装置时,可以用来吊、夹、推、刮、松、挖、装、铣削、拆除、清除和压实等作业,且大都采用快换装置,驾驶员在驾驶室内就可以完成作业装置的更换,一般在2分钟内就可以完成作业装置的更换。工作装置中动臂、斗杆结构变化多样,扩展了主机的使用功能。随着传统型和通用型产品样机减少,一些有特殊构造的、有特色的产品和多功能的产品备受用户的青睐,这些多用途作业装置大大扩展了液压挖掘机的功用,提高了产品的施工适用性。同时也体现了各厂家市场差异化的产品发展战略和各自的技术水平。所以,研究专业性的挖掘机设计理论、方法甚至是专用软件,以便缩短设计周期、提高产品性能和可靠性,快速响应市场和用户的要求。
2)国外液压挖掘机设计方法研究现状
(1)设计理论和方法研究及应用。国外生产企业在产品的设计和研制过程中,广泛推广采用有限寿命设计理论,以替代传统的无限寿命设计理论和方法,并将疲劳


内容简介:
采矿作业的机械化及自动化采石挖掘机工作装置的模型 E. V. Gaisler, A. P. Mattis, E. A. Mochalov,and S. V. Shishaev我们用由安装在一面墙上的冲级快驱动装有刀片的桶开发出了一个露天矿场使用的挖掘机数学模型。铲斗操作如下:当铲斗与岩石表面接触时,它被破坏的力大于铲齿所受的总摩擦力和驱动装置给于它的驱动力,使冲击块带有动能。冲击块的运动导致铲齿铲入岩石中,并在岩石表面形成深深的痕迹。减小位于铲齿下方的受力面积,于是就形成了所谓的“破坏结合区”。破坏这个区所需要的力比破坏完整的块要小的多利用这些活动的块,岩石将可以在不利用preloosening的情况下被挖掘描述铲斗开挖过程中的主要参数包括岩石的力学性能,外力影响下各力学属性的变化,驱动装置的工作特性和设备的参数,在挖掘过程中产生的两种破坏方式:切割和冲击破坏作用在各铲齿表面的几何方向上的力表现在挖入过程中的阻力,映射在冲击块轴向的力的总和为P1。垂直轴方向的力的总和为P2.垂直于铲齿运动方向上的 力的中和为零。因为压裂是块的主要破坏方式。以下是为了描述铲斗运动的数学模型的设想:-铲斗内岩石的重心和铲斗的重心是相对固定的-铲齿是连续分开排列的-各铲齿的负载相等的-铲齿切入岩石的瞬间冲击-铲斗内部物体的阻力忽略-相对于动臂旋转轴的瞬间摩擦力忽略通过以上假设,铲斗的运动就可以用在外力作用下的二维运动机构来表示,它包括压力装置的驱动力和提升装置的产生的力,重力和岩石表面产生的阻力。任一时间段斗的位置由坐标r(t)来定义,距离(oc)和(t)-斗杆与boom之间的角度,该装置的动力由 = ( + m) ,- + JT (1)来表示。其中m1表示岩石和铲斗的重量,m2表示斗杆和空铲斗的质量,J表示铲斗加岩石和斗杆相对于其旋转轴的瞬间惯性。Y = ml (r + lCBii)+ J + mi(r- rl) 2 + IGA), (2)其中J1是指空斗与斗杆的转动惯量,r-r1是空斗重心与斗杆重心的在坐标内的距离。在铲斗中的岩石的质量m取决于铲斗前沿的运动路线和岩石表面的初始形状。为了写出一个表示岩石质量增长率的表达式。我们将考虑使用图2中的方案,入股铲斗前沿在时间t内的运动路线用曲线 f2 (r2, 2)来表示,岩石的初始形状用曲线 f3 (r3, 3)表示,r2, , r3, 3是在零点位置的极坐标,在时间t内,铲斗前沿走过了ICDI的闭合路线:在这种情况下,当d 2 = d 3在时间t内质量的增长则有dm1=1/2pb(OCOD-OAOB)sind来决定。dm = T ,B (I OC l I OD I -I OA . I OB I) sin da 2,其中o是岩石的密度,B是铲斗边缘的宽度。我们从简图中可以看出:loci = r, ION = r= dr, IOAI = r, IOBI = r dr3.考虑到sin da da 2和忽略面积的微小变量,我们写出以下公式:增量da2等于斗臂在时间t内的角速度和时间增量t的乘积。i.e., d 2 = da 3 = &dt.,于是质量的增长率则由.3表达出来了。单位时间t内陷入铲斗中的岩石质量则由表达,这里面的m1只是时间t的一个函数。利用一个质量变化动力学的基本方程式,我们可以证明拉格朗日方程式是适合关联重心的绝对速度等于零的变量点机械运动力学系统的。考虑到一个机械运动系统包含n个由以速度vi运动的质量为m1,m2的材料的重心。拉格朗日方程式中的m1=在2, p. 340中衍生出的常数。考虑到m i = mi(t)的情况,在下述的2中,我们引入广义的坐标 q,于是。其中ri是质心的位置向量,于是其中qj是广义速度,在任何时间的机械系统的动能由表示我们发现关于整个坐标的动能的偏导数qj广义速度.qj: 我们区分这相对于时间的表达式考虑到第一数据,考虑到动态变量的基本方程-相关联块质心的绝对速度为零2, p. 143 其中P是作用于点而产生的力,通过材料的变量,我们得出其中R是适用于its点的反作用力,于是得出 第二数据是,实际上,8T/Sqj 2, p. 342。我们得出: 对于具有固定的完美约束系统QjR = 0它是包含变量的机械系统的拉格朗日方程相关联块的绝对速度为零的假想质心,这等同于派生恒体积的材质分属于机械系统的拉格朗日方程这一机制的拉格朗日运动方程其中Q1,Q2是作用于替代的和,如下: 图1活动斗挖掘机的设计方案图2铲斗内岩石质量增量的计算 其中是F1和F2两个力之间的角度由驱动器和升降机构产生的力挖掘机驱动装置和提升装置的参数确定了瞬间作用在电机轴和其转速的关系。所以f1() 和 f2(, &)的函数组成取决于驱动器的特性和压力机制与提升机制间的传动比。Ql 和Q2的表达式包括力 Pl 和 P2。他们是挖掘阻力的组成,他们可以利用数学模型来估算-泽莱宁、 韦特罗夫,巴洛夫涅夫和费德罗三世等的逻辑模型。通常,挖掘阻力取决于土层的物理性质,铲齿的几何形状,挖掘角度和剪切层的密度,我们应该考虑到最后两个参数必须绝对的取决于时间: 计算出动能的导数之后,将他们代入拉格朗日方程式内,我们得出:其中Q1和Q2已在方程式6中定义。该机制的运动可由方程式8表达出来。这些方程式的初始条件为: 表一:特别的破坏能量地面温度.t /C含水率斗杆能量特别破坏的能量E01*1/100KWH/m3参考砂42516231.50.09700.30386壤土砂42511211.50.08030.41416壤土粘土42516401.50.18070.35216粘土42518311.50.29910.40156壤土粘土71.30.2048*壤土砂71.30.1026*壤土砂71515182.20.13570.19797煤6.07.00.17000.17048-来自采矿协会,西伯利亚分院,苏联科学研究院的研究资料。 在岩壁的工作中,有三种主要的操作模式:1.在完整的岩床上切割,2.冲击和移动铲斗以铲齿侵入一定的深度,3.切割干扰结合区域。等式2-8及初始条件9组成一个数学模型用来描述在切割的挖掘方式的工作过程。我们将描述在操作模式2中铲斗的运动,在时间t1间从模式1到模式2的状态的转变是其中u是摩擦系数。这个行程是在时间t2=t1+T1+T2中完成的。T1是装置的启动时间,T2冲击的循环时间,当产生冲击的时候,铲齿铲入岩石内部的一段长度为岩石的一个性质函数,铲齿的几何形状,和冲击能量。现场研究和在实验室测量在冲击时铲齿的铲入情况,由采矿研究院,工程机械研究院,Skochinski研究院和卡拉干达理工学院【4-6】进行指导,建议用岩床被压裂的特殊情况来评估压裂效果的某些特征。对于压裂的能量单位这种特征可以利用和衡量每单位岩床的能量e.g.。岩石的最终抗压强度,i.e.。其中A是独立的冲击能量,J,K0是岩床上冲击能量的传递系数。X是一次冲击时铲齿的穿透深度。m;F3是压裂的横切面积m的平方。a是岩石的最终抗压强度,千牛/平方米。 E0的估算取决于岩床的机械性能和它的环境。在冻土层用对称的契状工具每次冲击的破坏能量的变化,由工程设计研究院给出的单一的冲击密集度来确定。已在表一中给出,铲斗的侵入深度可以用一下公式定义:此外,E0可以由实验测得也可以从【7-9】的报告中的数据来估算。冲击之后,铲斗的运动再次用方程式2和8来表达。但是由于条件的限制,直到铲斗前沿的运动距离X。 图3斗杆的旋转角度相对时间的坐标系(1-冲击后不对C进行削弱调整的挖掘,2-一次弱化的C,3-二次弱化的C,4-实验数据,1-3-岩石(f=5,C1=30*1000000H/平方米,。)。4-粉砂岩,【】。 方式3中的条件转变表示为:(12)满足条件(12)后,方式3中的切割就开始了。 岩石的抗破坏阻力通常由非正式的表达式表达: .(13)其中是标准压强,是内摩擦角,C是岩石的粘合力,莫尔-可以通过函数方程式10计算的破坏载荷作用下的主应力的库伦准则: .(14)其中是相对于应力应变曲线的最大主应力。根据和还有方程(13)(14)来表示的 和。我们获得一个关于粘结力最终单轴抗压强度的函数表达式C:(15)表达式(15)体现了岩石体在冲击后主要特征粘结力的变化是降低的,岩床的结合力可由一下方程式表达: .(16)其中C1是一块岩石的结合力,是岩床的削弱系数。它是一个平均块大小的函数,主要的破裂网络和在方程式8中提出的挖掘方向。冲击之后,结合力其中是代表冲击载荷作用下的岩床上附加的削弱系数。在冲击载荷作用点上,岩石被压碎,根据定理(7),2.在冲击之后的的影响降至0.0005,铲齿铲过破坏结合区时,在特定模式下它提升到的初始值(研究C=f(x)的特性是一门独立的学科)。在第一次逼近的时候,该区域的面积和结合力的大小可以通过表达式7-9估算出来,铲斗在破坏结合区的那一刻可以用表达式2-10表达,加上加在C(岩石结合力)上的附加系数。随着C的递增,P1和P2的数值也逐渐增大,铲斗的下一步运动是遵循模式1还是2,取决于是否满足条件(10).方程式2-8适用于所有铲斗的运动模式,加上P1。,P2和C的各自参数的限制,模式的转换取决于是否满足条件9和10。由等式4,6,8组成的描述挖掘机铲斗的工作进程的数学模型,由非线性的微分方程组组成。可以自动进行选择和能精确控制的一个改良版的莫森运算法则被用来解决这个系统中的问题。这个模型已被互交换模式的计算机进行程序化,在解决的过程中,铲斗的运动轨迹可有所选择的升降机构和压力机构的驱动器的负载特性进行调整。i.e.。通过选择适当的函数式:。它相当于控制挖掘机的实际进程。 几个可供选择的方案用于估算这个模型,结果在图三中很明确的表示出来了。 在第一种情况下,压裂完全是由冲击载荷引起的。单一的冲击能量是不足以创建“破坏结合去”的(曲线1).其他两种情况是不同形式的的在“破坏结合区”的弱化衔接(2.一次弱化3.二次弱化)。模拟结果是:与在kemerovougol的克拉斯诺戈尔斯克区分部的粉砂岩层进行现场实验的数据(图三中的虚线)比较,在实际进程与模型之间观察到相似之处(误差不超过30%)。最小的差异是通过在“破坏结合区”结合力的线性削弱得出的。通过这个数学模型,我们可以调查各种不同工作进程中的参数,这些机构的挖掘条件设置应满足不同的技术和经济参数和挖掘目标。 参考资料1. A. I. Fedulov and V. N. Labutin, Impact Coal Destruction in Russianl, Nauka, Novosibirsk(1973).2. A. A. Yablonskii, A Course in Theoretical Mechanics, 5th reved. in Russian,Vysshaya Shkola, Moscow (1977).3. V. I. Balovnev, Modeling of the Interaction of Actuator Elements of Road ConstructionMachines with the Surrounding Media in Russian, Vysshaya Shkola, Moscow (1981).4. V. A. Sidorov, A study of the process of destruction of permafrost grounds with solidinclusions by a frequent-stroke working element (with special reference to the Norilskindustrial region), Candidates Dissertation, Technical Sciences, VNIIstroidormash,Moscow (1977).5. A. F. Kichigin and E. I. Safankov, Test ground studies of an active bucket of an E-652 excavator, in: Construction Machines and Mechanisms in Russian, Politekh.Inst., Karaganda (1972).6. N. G. Antsiferova, A. M. Demenok, A. A. Korablev, et al., Experimental studies offorce and kinematic parameters of a high-power dynamic installation, in: Technologyand Mechanization of Coal Mining in Russian, A. A. Skochinskii IGD (1971).7. S. T. Sofronov and O. N. Egorova, Theoretical evaluation of an impact destructionzone, in: Methods of Solution of Problems of Mathematical Physics in Russian,Yakutsk (1980).8. Yu. I. Belyakov, Improved Technologies for Mining and Haulage in Open Pits in Russian,Nedra, Moscow (1977).9. O. D. Alimov, V. K. Manzhosov, and V. . Eremyants, Impact: Propagation of DeformationWaves in Impact Systems in Russian, Nauka, Moscow (1985).10. R. Goodman, Hard Rock Mechanics Russian translation, Stroiizdat, Moscow (1987). MECHANIZATION AND AUTOMATION OF MINING OPERATIONS A MODEL OF THE WORKING OPERATIONS OF A QUARRY EXCAVATOR E. V. Gaisler, A. P. Mattis, E. A. Mochalov, and S. V. Shishaev We develop a methematical model of the process of open-pit mining with a quarry ex- cavator using a bucket that has active blades driven by impact blocks installed in the front wall. The bucket operates as follows. When the bucket comes in contact with a rock area that can be broken by a force greater than the sum of the forces of friction of the tool on the sleeve and the force of activation of the starting device, the impact blocks are energized. The action of these blocks causes the bucket blades to enter the rock to a depth X, weakening the zone located directly under the blades and forming the so-called disrupted bonding zone i. This zone requires much less force to be broken than an in- tact mass. With such active buckets, strong rocks can be excavated without preloosening. The main parameters describing the movements of the bucket during excavation include the mechanical properties of the rock, the variation of these properties under the effect of the impact, the working characteristics of the drives of the actuator mechanisms, and the parameters of the equipment. Two types of destruction take place during the course of excavation: cutting and impact breaking. The geometric sum of forces acting on all the faces of a blade represents the resist- ance to intrusion. The projection of this sum onto the axis of the impact block is Pl; the projection onto the direction perpendicular to the axis is P2. The sum of forces act- ing perpendicularly to the bucket-traveling plane is equal to zero because block fracturing is mainly performed. The following assumptions are made for a mathematical model describing the motions of the bucket: ? - the center of mass of the rock in the bucket is stationary relative to the bucket; - chips are separated continuously; - the loads on the bucket blades are equal; - the blades penetrate the rock instantaneously upon impact; -the resistance to the bucket-filling is disregarded; - the moment of friction relative to the rotation axis of the arm is disregarded. With these assumptions, the motion of the bucket can be interpreted as the motion of a two-dimensional mechanism under the effect of external forces, which includes the force developed by the drives of the pressure mechanism and the lift mechanism, the gravity force, and the resistance force of the rock face. The position of the bucket at each point in time is defined by the coordinate r(t), the distance (OC), and (t) - the angle between the boom and the bucket stick. The kinetic energy of this mechanism is expressed as = ( + m) ,- + JT (1) where m 1 is the rock mass and the bucket; m 2 is the mass of the stick and the empty bucket; J is the moment of inertia of the bucket with rock and the stick relative to its rotation axis Institute of Mining, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk. Trans- lated from Fiziko-Tekhnicheskie Problemy Razrabotki Po!eznykh Iskopaemykh, No. 2, pp. 60-67, March-April, 1991. Original article .submitted September 25, 1990. 0038-5581/91/2702-0131512.50 ?9 1992 Plenum Publishing Corporation 131 Y = ml (r + lCBii)+ J + mi(r- rl) 2 + IGA), (2) where J1 is the moment of inertia of an empty bucket and the stick relative to the center of mass and r - rl is the coordinate of the center of mass of the empty bucket with the stick. The rock mass in the bucket m depends on the path traveled by the front edge of the bucket and the initial shape of the rock face. In order to write an expression for the rate of mass increment, we will consider the scheme in Fig. 2. Suppose that the path traveled by the bucket edge by the time t is described by the curve f2(r2, 2) The ini- tial shape of the face by the curve f3(r3, 3), where r2, , r3, 3 are polar coordinates with the origin at zero. During the time dt the bucket edge travels a distance ICDI; in that case, since d 2 = d 3 the mass increment within the time dt is specified by I dm = T ,B (I OC l I OD I -I OA . I OB I) sin da 2, where 0 is the rock density and B is the width of the bucket edge. We see from the diagram that loci = r, ION = r= dr, IOAI = r, IOBI = r dr3. Considering that sinda da 2 and disregarding the squares of the infinitesimal variables, we write 1 a, = r,z (, - d) a. The increment d 2 is equal to the product at the angular speed of the stick at the time t and the increment dt, i.e., d 2 = da 3 = &dt. The rate of increment of the mass is now ex- pressed as dNl o , = .-7- = _ ,i (d - ,.:,) =. (3) The mass falling into the bucket during the time t is defined by ! m, = J s ()dT 0 This mass m I is only a function of the time t. Making use of the fundamental equation of the dynamics of a variable-mass point (Mesh- cherskiis equation), we can demonstrate that Lagrangian equations are applicable to the mechanical system that consists of variable-mass material points if the absolute velocity of the associated mass is equal to zero. Consider a mechanical system comprised of n material points with masses ml, m 2 . m i, ., m n, that move with velocities v i. Lagrangian equations for m i = const have been derived in 2, p. 340. Consider the case of m i = mi(t). In following 2, we introduce generalized coordinates q, such that i = ri(ql, q2, , qs, t), where r i is the position vector of the ith mass. Now, i = )1 )j, Oli Oi j I uqj Uqj Oq) where j is generalized velocity. The kinetic energy of the mechanical system at any time point is defined as 1 - T ?niViU i . We find partial derivatives of kinetic energy with respect to the generalized coordinate qj and the generalized velocity j: or = - oi aqj miUi -r- , i=l aqi 132 _ ih, i - Or i OT mivl mivi Oqj = i=1 Oqj i= Oqj We differentiate this expression with respect to time . Consider now the first sum, taking into account the fundamental equation of the dynamics of variable-mass point for the case where the absolute velocity of the associated mass is equal to zero 2, p. 143 , am v =F, m.-7 + - where P is the resultant of the forces applied to the point. For a nonfree material point with variable mass, we have elT, i dm - m l -77 + -d-f vi = F., + 7 , where Ri is the resultant of the reactions of constraints applied to the ith point. Now, 7, + m, - . , + 7, + 7, - , = i=1 S - - . Or i = (F+n)=Q+&. i=l The second sum is, in fact, 8T/Sqj 2, p. 342. We obtain dt = Qj + o + OT Oq) For a system with stationary perfect constraints QjR = 0 d OT 07 It is the Lagrangian equation for a mechanical system consisting of variable-mass material points under the assumption that the absolute velocity of the associated mass is equal to zero. As we see, it is identical to a Lagrangian equation derived for a constant mass of material points belonging to the mechanical system. The Lagrangian motion equations for this mechanism are r - u-7- = QJ 7 , ,A , - = Q (5) where QI, Q2 are generalized forces acting on displacements 6r and 6, respectively, l Q, = - , o, ( - /- ,-o., / o - + :,- ,.o I + + (m + m).gcos(- ), O, = l).r.sin(-OCD) r + I CDI/ ) .P.sin cos (n - OCD) / (6) 133 Fig. 1 Fig. i. Fig. 2. C D Fig. 2 Design scheme for an excavator with an active bucket. Evaluation of the increment of rock weight in the bucket. 12(t). t + P3, (10) where U is the coefficient of friction of the tool in the bucket sleeve Pa as the force of activation of the automatic starting device. The stroke is made at the time l= 11+ Tl+ T2, where T l is the actuation time of the device and T 2 is the impact cycle time. Upon impact, blades penetrate the rock to a length which is a function of the rock properties, the blade geometry, and the impact energy. Studies in situ and laboratory experiments measuring the penetration of the blade upon impact, conducted by the Institute of Mining, the iInstitute of Construction Machines, the Skochinski Institute, and the Karaganda Polytechnic 4-6, suggest the existence of some characteristic of the bed being fractured which can be used to assess the fracturing efficacy. For such a characteristic the specific energ 7 capacity of fracturing can be used and measured per a unit of strength of the bed, e.g., the rocks ultimate uniaxial compressive strength, i.e., i A.K E, = .,./,.% 2.78t(I -, (11) where A is the single-impact energy, J; K 0 is the transfer coefficient of the impact energy to the bed; x is the penetration of the blade in one stroke, m; F is the transverse cross sectional area of the fracturing track m2; and o 0 is the ultimate uniaxial compressive strength of the rock, kN/m 2. The value of E 0 depends on the mechanical properties of the bed and its condition. The range of specific destructive energy capacity per stroke in certain permafrost grounds with a tool shaped as a symmetric wedge, measured by a single stroke of the density gauge devised by the Road Construction Research Institute, is indicated in Table i. The pene- tration of a blade can be defined by A.K.2.78.10-7 E,I ?9 I:. % :33.3 Besides, E 0 can be measured experimentally or estimated from the data reported in 7-9. After the impact, the movement of the bucket is described again by Eqs. (2) and (8), but with the condition P = 0, P2 = 0, until the front edge of the bucket travels the dis- tance x. 135 g, deg 4 5 , sec Fig. 3. Bucket stick rotation angle vs. time (i - digging without adjust- ment for C weakening after impact, 2, 3 - linear and quadratic weakening of C, respectively; 4 - experimental data; i-3 - rock (f = 5; C l = 30 x 106 H/m2; = 0.5), 4 - siltstone f = 5-6, C I = (32-36)106 N/m2; = 0.5. The condition for transition to mode 3 in time appears as 2 2 1 2 (t) + r2 (l) - 2 .r, (4).r (/:). cos ( (l) - (t) x . ( 12 ) After (12) is satisfied, cutting in mode 3 begins. The rock resistance to destruction is generally described by the familiar expression = o.tgp+ C, (13) where o is normal pressure, 0 is the internal friction angle, and C is the rock cohesion. The Mohr-Coulomb criterion can be formulated as a function of principal stresses under destructive load i0: o, = o0+ 03 ?9 tg2(5 + p/2), (14) where o I is the largest principal stress corresponding to the maximum of the stress-strain curve. Expressing o I and o 2 in terms of T and o and solving simultaneously Eqs. (13) and (14), we obtain an expression of the uniaxial compressive ultimate strength o 0 as a function of cohesion C: Oo= 2 .C .tg(45+ 0/2). Expression (15) shows that the main characteristic of the alteration of rock properties after impact is a drop in cohesion. The cohesion in the bed is defined as (15) C = C,l, (16) where C I is rock cohesion in a lump; 11 is the structural weakening coefficient of the bed, which is a function of the average lump size, the main crack network, and the direction of the mine advance 8. After the impact, the cohesion C(t3) = C.2, where 12 is a coefficient representing additional weakening of the bed by impact loads. At the load application point, the material is crushed. According to Popov 7, k2 after the impact is reduced to 0.0005. As the blade moves through the disrupted bonding zone, the value rises to its initial level according to a certain pattern (studying the behavior of C = f(x) is a separate subject). In a first approximation, the size of the zone and the cohesion value can be estimated from the results of 7-9. The movement of the bucket in the disrupted bonding zone is described by (2)-(10), plus additional con- straints imposed on C (the rock cohesion). With increasing C, the values of Pl and P2 grow. The further movement of the bucket follows mode 1 or 2, depending on whether con- dition (i0) is met. 136 Equations (2)-(8) hold for all the modes of bucket movement, with the respective con- straints imposed on P1, P2, and C. Transitions between the modes occur depending on whether conditions (9) and (i0) are satisfied. A mathematical model composed of (4), (6), and (8), which describes the working process of an excavator with an active bucket, consists of a set of nonlinear differential equations. A modified Merson algorithm with an automatic step selection and accuracy control was used to solve this sytem. The model has been programmed for a computer in an interactive mode. In the course of solution, the trajectory of the bucket can be adjusted by selecting load characteristics of the drives of lift and pressure mechanisms, i.e., by choosing the appropriate functions fl(), f2(, &), which correspond to the actual process of excavator control. Several alternatives were computed to evaluate this model. The results are illustrated by solid plots in Fig. 3. In the first situation, the fracturing is caused entirely by impact loads. The energy of a single stroke is insufficient to create a disrupted bonding zone (curve i). The other two cases are characterized by different forms of weakening of cohesion in the dis- rupted bonding zone (2, linear weakening; 3, quadratic weakening). The modeling results were compared with the data of in situ experiments on siltstone in the Krasnogorsk section of Kemerovougol Enterprises
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