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毕业设计(论文)中期报告题目:数控卧式镗铣床刀库机械手升降机构设计与分析系 别 机电信息系 专 业 机械设计制造及其自动化 班 级 姓 名 学 号 导 师 2013年 3 月 20 日1.设计(论文)进展状况 : 本毕业设计的主要内容是了解刀库机械手升降机构的性能要求,了解刀库机械手升降机构的工作原理,进行结构设计和计算分析,从一开始拿到任务书正式开始毕业设计以来,按照任务书的要求,我的工作进展还较为顺利。至今为止,通过大量查阅相关资料,我了解了课题的背景和发展状况,完成了对课题的分析,对升降机构的装配图有了认识,并提出了自己的方案,完成了开题报告和对外文文献的翻译,对升降机构有了一定的认识。图1 升降机构自动换刀机械手由升降丝杠1、滑座2、横梁3、液动机4、装刀手5、手架6、卸刀手7组成并与刀库8(由四排带刀套的链条组成,每条链条上均有15个刀套)组成自动换刀装置。升降机构由液动机、滚珠丝杠、螺旋副间隙调整垫、导向柱、减速齿轮和无触点行程开关等组成。当接受使手架上升或下降(找刀排)指令后,压力油进到液动机中,液动机带动滚珠丝杠转动,使手架带着装、卸刀手升降。因刀库有四排刀排,手架可上下移动3*420毫米的距离,当手架上下运动接近所选刀排位置时,其上的悬臂感应块使安装在刀排相应位置的无触点行程开关发信,控制手架升降油路的调速阀作用使手架减速,当到达所选刀排要求准确定位时,装在减速齿轮上的感应块无触点行程开关(12XK或20XK)发信,切断手架升降油路, 液动机停止转动,手架即停在所规定的位置上。 滚珠丝杠和螺母间隙,可用修磨调整垫来达到。导向柱除起导向作用外,并使滚珠丝杠在传动中免受弯曲力距的作用,使手架升降运动平稳可靠。图2 机械手升降机构装配图数控卧式镗铣床刀库机械手升降机构由液动机,滚珠丝杠副,手架,减速离合器2,减速齿轮,讯号盘3,讯号开关5导向柱6等组成。2.存在问题及解决措施: 由于毕业设计涉及的范围很广,几乎囊括了在大学里所学的全部知识,很多在大一、大二学习的知识由于很久没有接触造成了这些知识的模糊甚至淡忘,所以在某些细节方面总是会有多多少少的问题,给设计带来了不小的麻烦。下面是我设计过程中遇到的问题以及解决方案。问题(1):液动机带动滚珠丝杠转动,那么滚珠丝杠副的工作原理是什么?在设计过程中,通过翻阅大量资料,我首先想到的是看图册,和同学讨论,在查阅相关资料,目前基本了解了滚珠丝杠副的工作原理。图3 滚珠丝杠副基本结构从图可知滚珠丝杠副就是指在具有螺旋槽的丝杠与螺母之间,连续填满滚珠作为中间体的螺旋传动。其工作原理如上当螺母2(或丝杠1)转动时在丝杠与螺母间布量的滚珠3依次沿螺纹滚道滚动同时滚珠3促使丝杠1(或螺母2)作直线运动。为了防止滚珠沿螺纹滚道滚出,在螺母上设有滚珠循环返回装置(返向器)4,构成一个滚珠循环通道。借助于这个返回装置,可以使滚珠沿滚道面运动后,经通道自动地返回到其工作的入口处,从而使滚珠能在螺纹滚道上继续不断地参与工作。为了消除间隙和提高传动精度及刚度滚珠螺母常由两段组成。问题(2):刀库机械手升降机构的性能要求是什么?目前知道了刀库机械手升降机构的工作原理,但对它的性能要求不了解,正在翻阅资料,以便之后对它进行计算分析。问题(3):升降机构中电机是如何受力的?当手抓接到上升找刀排的指令后,电动机带动滚珠丝杠向使手抓上升的方向转动,带动手抓上升到接近所选刀排位置时,手臂支架上的感应块,使刀库上与刀排位置相应的无触点开关发出讯号,电动机变速,手架随之减速,装在讯号盘上的定位块转到使讯号开关同时发出讯号时,电动机停转,摩擦片式离合器吸合,丝杠制动,手抓准确地停在预定的换刀位置上。手架下降找刀排过程与上升情况基本相同,只是电动机带动丝杠时旋转的方向相反。问题四:结构设计和计算分析?在设计中,不知道用哪些计算公式来计算升降机构,正在网上查阅相关文献,来完成结构设计和计算分析。3.后期工作安排:(1)1011周: 在了解了性能要求后,翻阅资料,查找公式;(2)1112周: 完成详细的设计并计算;(3)1213周: 根据计算数据以及所选机构画出零件图和装配图;(4)1314周: 编写设计说明书以及校核图纸,交给导师查阅;(5). 1415周: 准备完成最后答辩。 指导教师签字: 年 月 日4叉车升降机构的创新设计清华大学精密仪器和机械学部门, 100084, 北京,中国文章历史:2010年6月17收到题目,2010年8月3日开始修订到2010年8月4日,2010年9月1日网上可用。关键词:叉车,空间多连杆机构,连杆摘要:在物流中叉车是一种最重要的工具。然而,一个叉车采用通用桅杆系统,不仅影响驾驶员的视野,而且增加了卡车的重量,从而降低了燃油经济性。因此,本文主要对叉车升降机构进行创新设计。首先,提议一个空间多连杆升降机构。然后,根据约束条件、流动性、在理论上研究了叉架。最后,确定升降机构,在计算机上模拟,证明运动的可行性。此多连杆式升降机构利用了灵活的电缆驱动和连杆,不仅给驾驶员提供了更大范围的视野,也降低了叉车重量,因此提高了燃油经济性。1. 介绍: 叉车通常用于火车站、仓库、港口和工厂装卸与运输。叉车由底盘和工作装置组成,可倾斜吊和垂直吊。然而,一般的叉车有以下主要缺点。首先,桅杆系统由几个大组件组成且在司机前面,将严重影响司机的视野。许多叉车碰撞行人的事故本质上都是由于可见性1、2。此外,在支持负载和指导叉架垂直提升时,桅杆系统扮演一个重要的角色,所以它的强度和刚度必须足够好,它的自重也必须增加。后面的重量平衡装置也增加,这就造成不必要的浪费。扩大驾驶员的视野一直是一个重要的研究项目。一些类型的叉车已经通过改变桅杆2、3,而加大了司机的视野范围,而其他的利用视觉制导方法空间操作4或计算机指导5,6加大视野范围。这些叉车司机有更好的视野,但是对于通用桅杆结构的不足和自重问题,他们不是根本的解决方案。为了提高驾驶的舒适性和驾驶员的安全,减少能源消耗,重点考虑叉车升降机构的创新设计。先提出一个升降机构的设计方案,然后确定他的可行性,最后确定方案.这种机制不仅扩展了司机的视野,也减少了车辆的重量。2. 机构的提升: 众所周知,三个转动副和两个链接,生成平面运动。假设两个这样的平面以非零的角度放置,如图1。两端的两个连杆机构都与同一刚体连接并转动,如图1所示。连杆1是基础,连杆4是连杆1通过两个平行的连杆机构ABC和DEF从而传递运动。很容易发现,这两个连杆机构之间有很紧密的联系。因此,刚体4必须平行于俩个连杆机构所在的平面和。即刚体4只能是直的。机制和机理论45(2010)1892 1896 图1空间多连杆结构曲柄滑块机构是一种常见的开链结构。在汽油和柴油引擎7中被广泛使用。然而,在曲柄滑块机构中,死点是一个致命的缺点。为了提高稳定性,避免死点,本文取代了曲柄滑块机构中的运动链,是由两个转动副和运动副组成, 可以在没有死点的前提下生成平面运动。假设两个垂直平面,滑块及运动链位于与纵向对称的平面内。两个运动链如图2。对空间多连杆升降机构的运动原则进行理论分析。研究叉架的自由度,可以建立一个笛卡尔坐标系,来确定A和D对轴的转动,A和D的交点为原点,轴的转动副a为x轴 .坐标系如图3。假设轴对D的转动角度用(0180)表示,与 A和D坐标系统的起源是相同的。D的坐标可以表示为(a 0 0)和(acos asin所示,两者之间的对角用(0bb180)表示。每个运动链包括两个转动副和一个运动副、一连杆和滑道。连杆和滑道都连接在一个运动副中,叉架有两个运动链。在这个空间多连杆结构中,轨道和叉架是在一条直线的。此外, 在每一个垂直平面中添加另一个类似的运动链可以提高强度和刚度。在该滑块的位置,连接叉架和叉车底盘,与此同时,上下运动链是连接约束棒的。随着轨道的上下运动,约束棒提供约束,提高刚度和稳定性,从而提升8的承载能力0)。C、F的坐标可以表示为(a yc zc)和(xF yF zF)。不难发现,A和C对轴的转动是平行的,所以研究D和F对轴的转动。A和C对轴的转动用s1 =(1 0 0)T表示, D和F对轴的转动用s2 =(cos sin 0)T表示, B对矢量方向的位移用s3 =(0 yc zc)T表示,E对矢量方向的位移用s4 =(xFbcos yF bsin zF)T表示。1894 j- y wang etal。/机制和机理论45(2010)1892 - 1896图2升降机构1叉;2叉架;3挤压转动副;4连杆;5约束杆;6导轨;7支持块根据螺旋理论9,终端约束螺旋矩阵可以得到方程:$TE$ = 0其中$是一个螺旋矩阵,$是终端约束螺旋。ABC是这个运动螺旋矩阵的一个运动链,可以表示为:$ABC = $A $B $C= 1 0 0 0 0 0 t 0 0 0 0 yC zC 1 0 0 0 zC yC依照Eq.(1)可以得到,终端约束螺旋矩阵由一组基本的终端约束螺旋组成。$ABC =1 0 0 0 0 0 t 0 0 0 0 1 0 0 0 0 0 0 1 图3笛卡尔坐标系依照Eq.(1)可以得到,终端约束螺旋矩阵由一组基本的终端约束螺旋组成。图4 计算机模拟升降机构 1叉架;2前皮带轮;3前支持杆;4后支持杆;5电缆;6回轮同样得到终端约束螺旋矩阵的运动链:$DEF = cos sin 0 0 0 0 t 0 0 0 sin cos 0 0 0 0 0 0 1因此,终端约束螺旋矩阵在CF上可以表示为:$CF = $ABC $DEF根据Eq. (1), 只要0180CF可以表示为:$CF =(0 0 0 0 0 1)t由此证明了:叉架沿z轴方向只有一个自由度,即叉架为一条直线。在此约束下的升降机构中,叉架垂直于地面。3. 实现升降机构:在计算机上模拟叉车升降机构的运动。如上所述, 升降机构的轨迹和叉架在一条直线上。在不影响司机视野的前提下,为了提升货物可以使用锚机和软钢电缆,结构如图4所示。锚机在叉车的后面,回轮和支持杆在顶部,每个电缆的一端连接叉架,另一端固定在锚机上。当锚机运动时,电缆将带动叉架上下运动。为了验证这种叉车是否能实现预期的运动,特别是保证叉架的垂直运动,用Proe来模拟它的运动,如图4中(a)、(b)(c)显示不同的位置时叉架的运动。可以看出叉架是在垂直于地面的一条直线上运动。此外,没有桅杆系统,司机可以有一个更好的视野范围。 这种升降机构有柔性电缆和刚体使它有更好的结构性能。钢丝绳牵引的机械手以其独特的优势,如低惯性、低重量等,被广泛应用。货物的重量主要由电缆支持,因此对升降机构的强度和刚度要求是较低的,它的重量也可以减轻。通用叉车的组件,如气缸、链条、链轮子和支架系统,锚机、电缆和连杆,他们的重量和重心向后移动。因此,后面的重量平衡装置,大大减小了整个卡车的重量。所以提出的叉车升降机构降低了能耗,提高了车辆的燃油经济性。4. 结论:本文基于空间多连杆升降机构,提出了一种新型的叉车升降机构。为了验证升降机构的可行性,对其进行了理论分析和计算机模拟。升降机构由灵活的电缆驱动和连杆组成,降低了自重。与一般的叉车对比,司机有一个更广泛的视野, 明显的提高了叉车的可靠性和驾驶舒适性。此外对升降机构的强度和刚度要求低,使的整个叉车的重量大大降低。提高了叉车的燃油经济性。致谢:作者在中国国家自然科学基金的资助下,设计的这个升降机构,被授予全国优秀博士论文。Short communicationInnovative design of the lifting mechanisms for forklift trucksJian-Yi Wang, Jing-Shan Zhao, Fu-Lei Chu, Zhi-Jing FengDepartment of Precision Instruments and Mechanology, Tsinghua University, Beijing 100084, PR Chinaa r t i c l ei n f oa b s t r a c tArticle history:Received 17 June 2010Received in revised form 3 August 2010Accepted 4 August 2010Available online 1 September 2010Forklift truck is one of the most important tools in logistics. However, the general mast systemof a forklift truck not only restrains the drivers vision, but also increases the whole weight of atruck and decreases the fuel economy. Therefore, this paper focuses on the innovative design ofa new lifting mechanism for forklift truck. Firstly, a spatial multi-link lift-guidance mechanismis proposed. And then, under the constraints of this mechanism, the mobility of the fork andfork frame is investigated in theory. Lastly, a new lifting mechanism based on it is presentedand computer simulation is used to demonstrate the feasibility of motion. This multi-link liftingmechanism takes advantage of flexible cable drive and rigid body guidance, which not onlyprovides the operator with a wider field of vision but also reduces the equilibrate weight of avehicle and therefore improves the fuel economy. 2010 Elsevier Ltd. All rights reserved.Keywords:Forklift truckSpatial multi-link mechanismRigid body guidanceFlexible driving method1. IntroductionForklift trucks are usually used at railway stations, warehouses, ports and factories for loading, unloading and conveying. Ageneral weight-balanced forklift truck consists of a chassis and a work device which can be tilted and lifted vertically.However, the general forklifts have the following major disadvantages. First, the mast system composed of several largecomponents will badly affect the drivers field of vision because it locates in front of the driver. Many accidents involving collisionsbetween pedestrians and trucks are due to inherently bad visibilities of the forklift trucks 1,2. In addition, the mast system playsan important role in supporting the loads and guiding the fork frame to lift vertically. So its strength and stiffness must be highenough and its self-weight has to be increased. The weight of the rear equilibrator is increased as a result, which surely improvesthe unnecessary waste of energy.Expanding the drivers vision has always been an important research project. Some kinds of trucks have improved visibility viachanging the forms of the mast 2,3, while others utilize the visual guidance methods of mobile camera-space manipulation 4 orcomputer vision guidance 5,6. These trucks have better visibility for drivers but they are not fundamental solutions to overcomethe shortages of the general mast structures, and the problem of high self weight has not been cracked completely either.In order to improve the driving comfort and safety for the drivers and to reduce energy consumption, this paper focuses on theinnovative design of the lifting mechanism for forklift trucks. A spatial multi-link lift-guidance mechanism is proposed, and then anew kind of lifting mechanism based on it is presented. This mechanism not only expands the vision field of the driver but alsoreduces the whole weight of the vehicle.2. Proposition of a lift-guidance mechanismAs is well known, a planar RRR-open-chain linkage that consists of three revolute pairs and two links generates planar motions.Suppose that two such planar RRR-linkages are placed in two planes with a certain nonzero subtended angle. The ends of the twoRRR-open-chain linkages are connected with a same rigid body through revolute pairs shown in Fig. 1. Link 1 is the base and rigidMechanism and Machine Theory 45 (2010) 18921896 Corresponding author. Fax: +86 10 62788308.E-mail address: jingshanzhao (J.-S. Zhao).0094-114X/$ see front matter 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.mechmachtheory.2010.08.002Contents lists available at ScienceDirectMechanism and Machine Theoryjournal homepage: /locate/mechmtbody 4 is connected with the base through two parallel RRR-kinematic chains, ABC and DEF. It is easy to find that, these twokinematicchainsarebothplanarRRR-kinematiclinkages.Thereforethetrackofrigidbody 4must beparalleltoboth ofplane andplane . That is, rigid body 4 can only make a free translation parallel to the intersection line, mn, of the two planes. As a result, thetrack of rigid body 4 is a straight line.Slider-crank mechanism is a common mechanism that applies RRR-open-chain structure. It is widely used and examples of itsapplications are easily found in gasoline and diesel engines 7. However, in the applications of slider-crank mechanism, deadpoints possibly lead to actuating failure. In order to improve the stability and avoid the dead points, this paper replaces the RRR-kinematic chains with RPR-kinematic chains, which are composed of two revolute pairs and one prismatic pair and can also onlygenerate planar motions without dead points.Suppose the two vertical planes that the support blocks and their RPR-kinematic chains located are symmetrical withrespect to the longitudinal symmetrical plane of the vehicle. As is shown in Fig. 2, the subtended angle between the twoplanes is denoted by (0bb180). Two RPR-kinematic chains are placed in the two planes, respectively. Every RPR-kinematic chain includes two revolute pairs and one prismatic pair, a connecting rod and a slideway. The connecting rod andthe slideway are connected through a prismatic pair. The fork frame has two extruded revolute pairs connected with theends of the two RPR-kinematic chains. As is discussed above, in such a spatial multi-link structure, the track of the forkframe is in a straight line.In addition, one can improve the strength and stiffness by adding another similar kinematic chain in each vertical plane, inwhich the support blocks located, to connect the fork frame and the truck chassis. Meanwhile, the upper and lower kinematicchains are connected by constraint rods. As the track of the upper and lower kinematic chains are parallel, the constraint rodsprovide redundant restraints and improve the stiffness and stability of the lift-guidance mechanism and the load-carryingcapacity 8.Now the kinematic principles of the spatial multi-link lift-guidance mechanism can be analyzed in theory. In order toinvestigate the degree of freedom (DoF) of the fork frame, one can establish a Cartesian coordinate system, where xoy-plane is theplane determined by the axes of revolute pairs A and D, the origin of coordinate system is the intersection point of axes of A and D,x-axis is the axis of revolute pair A. The coordinate system is shown in Fig. 3.Assume that the subtended angle of the axes of revolute pair D and revolute pair A is denoted by (0obb180o), the distancefrom revolute pairs A and D to the origin of coordinate system are equal and denoted by a. The coordinates of A and D area00 andacosasin 0, respectively. In addition, the coordinates of C and F can be expressed asayCzC andxFyFzF, individually.It is not difficult to find that, the axes of revolute pairs A and C are parallel, and so are the axes of revolute pairs D and F.s1=100Tdenotes the direction vector of the axes of revolute pairs A and C, s2=cos sin 0Tdenotes the unitdirection vector of the axes of revolute pairs D and F, s3=0yCzCTdenotes the direction vector of prismatic pair B ands4=xFbcos yFbsin zFTdenotes the direction vector of prismatic pair E.Fig. 1. Spatial multi-link structure.1893J.-Y. Wang et al. / Mechanism and Machine Theory 45 (2010) 18921896According to the screw theory 9, the terminal constraint screw matrix of a kinematic chain can be obtained by solving thereciprocal screw equation$TE$= 01where $ is a kinematic screw matrix and $is the terminal constraint screw.The kinematic screw matrix of a kinematic chain, ABC, can be expressed as$ABC= $A$B$C? =1000000000yCzC1000zCyC2435T2Therefore, in accordance with Eq. (1), one can obtain the terminal constraint screw matrix composed of a set of base screws ofthe terminal constraint screw system.$ABC=1000000000100000012435T3Fig. 2. A new lift-guidance mechanism. 1fork; 2fork frame; 3extruded revolute pair; 4connecting rod; 5constraint rod; 6slideway; 7support block.Fig. 3. Cartesian coordinate system.1894J.-Y. Wang et al. / Mechanism and Machine Theory 45 (2010) 18921896Similarly, the terminal constraint screw matrix of kinematic chain DEF is obtained:$DEF=cossin0000000sincos00000012435T4Consequently, the terminal constraint screw matrix on CF can be expressed as$CF=$ABC$DEF?5According to Eq. (1), so long as 0bb180, the kinematic screw matrix of the frame CF can be solely obtained$CF=000001T6It proves that the fork frame has only one DoF along z-direction, i.e., the track of the fork frame is restricted to a straight line.Under the constraints of the lift-guidance mechanism, the fork frame can be lifted up and down perpendicular to the ground.3. Implementation of a new lifting mechanismThis section will present a new lifting mechanism for forklift truck based on the lift-guidance mechanism proposed above andsimulate its motion in a computer.As is discussed above, the lift-guidance mechanism restrains the track of the fork frame in a straight line. In order to lift goodswhilenotaffectingthedriversfield ofvision,onecanusewindlassandsoftsteelcablesto lifttheforkandforkframe.The structureis shown in Fig. 4(a). One can set a windlass at the rear of the forklift truck and places some pulleys and supporting rods on the topof the cab. One end of each cable is connected with the fork frame and the other end is fixed to the windlass. When the windlassworks, the cables will lift or drop the fork frame.In order to verify whether this kind of forklift truck can achieve the desired movements, especially insure the fork frame to beraised vertically, Pro/engineer software is utilized to simulate its motion. Fig. 4(a), (b) and (c) show different positions when themechanism lifts the fork and fork frame up. From the simulation one finds that the track of the fork and fork frame is a straight lineperpendicular to the ground. In addition, without the mast system, the driver has a better vision forwards and backwards.This kind of lifting mechanism consists of the flexible cable drive and rigid body guidance with better structural performances.Cable-driven manipulators have been widely investigated in applications for their unique advantages such as low inertia, lightweight and so on 10. It is not difficult to find that the weight of goods is supported mostly by the cables. Therefore, therequirement for strength and stiffness of the lift-guidance mechanism is lower, and the weight of it can be decreased as a result.Meanwhile, compared with components of the general forklift trucks, such as cylinder, chains, chain wheels and the mast system,this kind of lifting mechanism utilizes windlass, cables and several connecting rods. Their weight is lower and the gravity center ofthem moves backwards. Consequently, the weight of rear equilibrator is greatly decreased and the whole weight of the truckbecomes much lower. So the proposed forklift truck reduces energy consumption and improves the fuel economy of the vehicle.Fig. 4. Implementation of the new lifting mechanism and computer simulations. 1fork frame; 2front pulley; 3front supporting rods; 4back supporting rods;5cables; 6back pulley.1895J.-Y. Wang et al. / Mechanism and Machine Theory 45 (2010) 189218964. ConclusionsThis paper proposes a new kind of lifting mechanism, which is based on a spatial multi-link lift-guidance mechanism, forforklift trucks. Theoretical analysis and computer simulations are used to verify the single DoF of the fork frame under theconstraints of the mechanism. The lifting mechanism consists of flexible cable drive and rigid body guidance, and therefore shouldseparate the lifting from the guidance which decreases the self weight of a mast system. Compared with the general forklift trucks,the driver has a wider field of vision without the mast system and hence both the reliability of a truck and the driving comfort areenhanced obviously. In addition, because of lower requirement of strength and stiffness for every link of the new liftingmechanism, the whole weight of a truck is greatly decreased. Consequently, it improves the fuel economy of the vehicle.AcknowledgementsThis research was supported by the National Natural Science Foundation of China under Grant 50805083 and a Foundation forthe Author of National Excellent Doctoral Dissertation
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