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题名: 重载强扰动搅拌摩擦焊机器人动态特性分析与优化设计
其他题名: Optimal Design of Friction Stir Welding (FSW) Robot under Heavy-Load and Strong-Disturbance Conditions
作者: 骆海涛
导师: 周维佳 ; 王洪光
分类号: TP242
关键词: 搅拌摩擦焊机器人 ; 典型工况 ; 结合部刚度 ; 动态优化设计 ; 数值模拟
索取号: TP242/L99/2014
页码: 190页
学位专业: 模式识别与智能系统
学位类别: 博士
答辩日期: 2013-12-04
授予单位: 中国科学院沈阳自动化研究所
作者部门: 空间自动化技术研究室
中文摘要: 搅拌摩擦焊是上世纪90年代以来发明的一种特别适用于低熔点高强轻质合金材料的先进固态焊接工艺,它优点众多且可以实现同种或异种低熔点合金材料的固态连接,尤其是那些用传统方法不能焊接的材料。如:高强铝合金、有色金属和复合材料等。为此,该种焊接工艺备受焊接领域的青睐,特别是航空航天领域对上述材料和复杂空间焊缝的焊接有强烈要求。搅拌摩擦焊首先是将一个旋转的焊头插入被焊工件,然后通过焊头与被焊工件之间接触产生的摩擦热来软化材料(材料不会熔化),最后焊头会沿着焊缝方向发生移动,焊缝区域的材料就会混合在一起(也叫搅拌)。在整个焊接过程中,焊头将会承受着巨大的力和力矩,并且这些外载是时刻发生变化的。因此,为了使焊缝焊后达到想要的机械强度和焊接质量,需要焊接设备本体具有优良的静动态性能的同时,又使重量增加最小化。而如何保证所研制的搅拌摩擦焊机器人既能实现给定任务的焊接作业又能满足焊后焊缝的焊接精度,这是我们所追求的最终目标。 本文以国家重大科技专项“大型薄壁高精度搅拌摩擦焊设备技术研究”(课题编号:2010ZX04007-011)为依托,针对我国目前尚无专用搅拌摩擦焊机器人的现状,通过采用机器人多体系统的相关理论和产品结构性能动态优化设计的分析方法,旨在研发出一种能够抗干扰、高刚性和满足复杂空间曲面焊接要求的机器人化搅拌摩擦焊设备,最终以达到增强机器人的动态性能,提高焊接精度和焊缝质量的目的。具体阐述如下: (1) 首先给出了搅拌摩擦焊机器人的总体构型,各部分系统组成和功能指标。介绍了机器人用于实际焊接任务的五种典型工况,为后续的机构分析和结构设计提供了边界约束。基于机器人理论的分析方法,建立了机构的运动学和动力学模型,并进行了典型工况下的仿真分析,获得了机器人在关节空间和末端工具空间内的各参数随机时间的变化关系。 (2) 建立了滚珠-滚道的赫兹点接触理论模型,给出了采用牛顿科特斯(Newton-Cotes)公式计算椭圆偏心率的求解流程,得到了接触区的弹性趋近量和最大接触应力。在此基础上,分别建立了角接触球轴承、滚珠丝杠副和直线导轨副的刚度计算模型,并以实际型号为例进行了理论计算。针对角接触球轴承,用模态测试的手段验证了基于有限元方法刚度分析的准确性。通过角接触球轴承动刚度的有限元仿真,得出了滚珠-滚道结合部在低速运行状态下的动态刚度近似等于静刚度的结论。三种结合部刚度计算的数学模型和分析方法具有普遍的适用性,所获得的结合部刚度数据是进行机器人整机静动态特性分析和刚柔耦合动力学仿真的前提条件。 (3) 提出了一种基于结构分解的动态设计优化方法,以组成结构的外部框架和内部单元为出发点,研究它们的材料分配、结构样式、几何尺寸与力学性能之间的关系。综合考虑结构的质量、应力、位移和固有频率等约束条件,合理配置材料的分布、结构框架尺寸和基本单元样式以其改善结构的静动态特性。分别对机器人的底座、立柱和滑枕大件结构进行了仿真分析,获得了以结构的柔度最小和一阶固有频率最高的多目标拓扑优化结果。通过对组成结构内部的筋格单元进行尺寸优化分析,找到了适用于加强不同大件内部结构的基本单元样式。最终,通过比较优化前后的分析结果,保证了从微观和宏观上所设计出的产品具有较优的动态性能。 (4) 建立了搅拌头的力学模型并进行了焊接过程的数值仿真,得到了作用于搅拌头上的各种机械载荷。精确地模拟了机器人空载以及在五种典型工况下的受载状态,获得了整机刚度和强度的结果数据。进行了整机的模态分析和频响分析,得到了用于评价整机动态性能的结果数据,其中模态试验验证了有限元分析的精度。最后,通过多体系统的刚柔耦合动力学仿真,得到了在考虑了结合部的刚度以及滑枕结构柔度条件下的搅拌摩擦焊机器人焊接精度,验证了整个结构设计方案的可行性。
英文摘要: Friction stir welding (FSW) processes, invented in the late 90’s by TWI, are widely recognized as advanced solid-state welding methods particularly suitable for low-melting temperature, high-strength and low-weight alloy. It has many advantages over the conventional fusion welding methodologies and most significantly, can weld almost all low-melting temperature alloys that are typically non-weldable using the traditional welding methods, such as high-strength aluminum alloys, non-ferrous metal, composite material, etc. Therefore, the FSW processes are considerable as one of the most favorable processes in space and aerospace industry for joining similar or dissimilar aerospace-grade aluminum alloy together and can yield much better mechanical characteristics than any other conventional joining process. FSW process involves plunging a rotating tool into the workpieces, which generates frictional heat between the tool and workpiece materials to cause the materials being plasticized (i.e., soft but not melting); when the tool traverses in the direction of a to-be-jointed seam, plasticized materials from the workpieces are mixed together (called “stir”) to form a joint. During the entire process, the FSW tool is subject to an enormous force and torque as well as considerable amount of variation in them. Therefore, in order to assure demanded surface quality and mechanical characteristics, the welding facility must have sound structures. The overall goal of this research is to design a FSW Robot providing desired static and dynamic performances specified by the welding applications, and at the same time, satisfying minimal weight objective. This research was Sponsored by the National Science and Technology Major Project, “Research on large-scale and high-precision friction stir welding equipment for thin-shell structures” (2010ZX04007-011). A high-payload capacity, high-stiffness, and disturbance-resistance FSW robot is developed using multibody system dynamics theory and structure-performance-based dynamic optimal design method, which yields overall system performances satisfying load, precision and surface quality requirements specified for complex 3D-joint welding in its working space. In view of the fact that china does not have such dedicated FSW robot, this research is considered as unique and fills the technology gap. Detailed descriptions are as follows: (1) Firstly , it defines the topological and geometrical configurations of the FSW robot, the system compositions, and corresponding functional specifications; it then introduces five representative welding modes and specifies the boundary constraints for the analysis and design of robot mechanism and structure; based on that, it derives the kinematic and dynamic models of the robot; and after that, it simulates robot motions and dynamic responses under given working conditions, and obtains the performance-related parameters as the functions of time in robot’s join space and tool space. (2) Secondly, it establishes a ball-raceway contact model using Hertz Point Contact theory and derives the analytical computation process for the ellipse eccentricity using Newton-Cotes Formula, which yields the approaching amount of elasticity and maximum contact stress in the contact region; based on this, the stiffness computational models for angular contact ball bearings, ball screw and nuts, and linear guide-way are established and validated via Finite Element Analysis (FEA) simulations, statically and dynamically; case studies of above motion-transmission units using commercially-off-the-shelf products are given. For angular contact ball bearings, the accuracy of FEA simulation is verified by modal tests. FEA-based dynamic stiffness analysis shows that (a) for the angular contact ball bearings, the dynamic stiffness in the ball-raceway contact region can be approximated using its static stiffness at low speed; (b) the computational models describing the stiffness in the contact region for three representative motion-transmission units as mentioned above have general applicability; and (c) data obtained from FEA-stiffness analysis as well as from modal tests are directly applied to the static and dynamic stiffness analysis and simulations of the FSW robot. (3) It presents a structural-decomposition based optimization method for the dynamic design of FSW Robot. This method analyzes the material distributions, structural shapes, and relationships between geometric dimensions and mechanical characteristics of all mechanical components, from robot’s outer frame to its inner elements while takes into account of all constraints of each component such as mass, stress, displacement, and natural frequency; it optimally allocates mass, sizes, and geometrical shapes to the basic elements to improve the static and dynamic performances of overall structures. Numerical simulation of FSW Robot’s X (base), Y (pillar), and Z (ram) axes, the largest and heaviest elements of the robot, shows that dynamic design approach in conjunction with multi-objective optimization can yield minimal flexibility and highest first-order natural frequency. In addition, this approach also finds the optimal rib shapes, sizes, and geometrical topologies for the structural design of large elements. Through comparison, the dynamic optimal design approach clearly demonstrates the capability of delivering much better static and dynamic performances while maintaining minimal weight. (4) By establishing the mechanics models of the friction stir welding head and simulating the representative welding processes, the mechanical loads (forces and torques) exerted on the FSW head as well as on FSW robot can be precisely generated, and thus, a complete description of FSW robot's strength and stiffness corresponding to no-load or load (welding mode) status can be obtained. By performing modal analysis and frequency response analysis, data for evaluating robot’s dynamic performances can be obtained and is verified by the modal tests. Lastly, after taking into account of contact stiffness as well as the flexibility of big structures, a rigid-flexible coupling dynamic simulation of multi-body system is performed to obtain FSW robot welding accuracy and to validate the feasibility of design method.
语种: 中文
产权排序: 1
内容类型: 学位论文
URI标识: http://ir.sia.cn/handle/173321/14819
Appears in Collections:空间自动化技术研究室_学位论文

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Recommended Citation:
骆海涛.重载强扰动搅拌摩擦焊机器人动态特性分析与优化设计.[博士学位论文].中国科学院沈阳自动化研究所.2013
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