SELFORGANIZING ASSEMBLY MODELING BASED ON RELATIONAL CONSTRAINTS

On the research of assembly modeling of mechanical products, current CAD systems can only support the design process of componettoassembly. It is difficult to realize the design process of assemblyto component. The theory of selforganizing assembly modeling based on relational constraints is proposed, which implements the product design of assembly to component commencing with conceptual design and supporting abstract design and sepnice refinement design.     

Universal mechanism modeling method in virtual assembly environment

Motion simulation and performance analysis of mechanism are important methods for analyzing assembly quality after finishing assembly simulation in virtual assembly environment. However, most simulation systems have no function of mechanism motion simulation due to the randomicity of mechanism and lack of universal mechanism modeling method. In order to realize the simulation of any mechanism after finishing assembly simulation in a virtual environment, a new universal mechanism modeling method is presented. Two main models are contained in the mechanism model: information model and mathematical model. Firstly, the information model of mechanism is proposed to describe the data structure of mechanism which contains bottom geometry data, information of constraint, link, kinematic pair and physical data. Because the object of mechanism simulation is the assembly, which is assembled during the process of assembly simulation, the information of mechanism can be obtained automatically through mechanism automatic search method. Secondly, mathematical model of mechanism is presented. The mathematical model uses mathematical method to express the mechanism. In order to realize the automatic expression of any random mechanism, basic constraint library is presented, consequently random mechanism can be described based on the basic constraint library. Finally, two examples are introduced to validate the method in the prototype system named VAPP(Virtual Assembly Process Planning). The validation result shows that the mechanism modeling provides a universal modeling method for mechanism motion simulation in virtual assembly environment. This research has important effect on the development both of mechanism motion simulation and virtual assembly.     

VIRTUAL EXPERIMENTAL ANALYSIS ON CLEANING ELEMENT OF SUGARCANE HARVESTER

The laws of influence of different factors have been analyzed in order to enhance the working efficiency and fatigue life of the cleaning element in brush shape of the sugarcane harvester. Based on the principle of orthogonal experiment design,the virtual-orthogonal-experimental analysis for the cleaning element is carried out on the finite element analysis (FEA) software-ANSYS after analyzing the nonlinear structural behavior in the working procedure.The results are analyzed with the overall balancing method,and then the optimal combination is got,which is made up of different levels of different factors.Also the optimal combination of design parameters of the cleaning element received from the virtual experimental analysis is conducted an experiment to confirm that the virtual analysis model and results are right,and the effect of factors on the function of the cleaning element is obtained by more analysis and further optimizing.     

RESEARCH OF MOVEMENT NAVIGATION BASED ON ASSEMBLY CONSTRAINT RECOGNITION

0 INTRODUCTIONThe traditional assembly design stresses the final result of assembly modeling, but pays little attention to the process of assembly simulation. Nonetheless, the procedure of assembly is a cardinal element that determines the quality of assembly modeling. These drawbacks hinder the advancement of the speed and quality of assembly design. Moreover, in the traditional mode of product development, designers make prototypes to evaluate the function and appearances of products. P…     

Virtual Reality Toolkit for the Assembly of Nanotube-based Nano-electro-mechanical Systems

Nano assembly and manipulation technologies are the basis for nano-electro-mechanical systems(NEMS). Atomic force microscope(AFM) is widely used to manipulate nanotubes to assemble NEMS. Manipulating nanotubes with AFM is a challenging and difficult task. One of the major reasons is the deficiency of visual information during the manipulation process. To address these difficulties, this research aims to put forward novel virtual tools and assembly strategies to improve the efficiency, accuracy and ease of the assembly process of NEMS. This paper begins by the discussion of the principles and implementation of a virtual nano-assembly simulator, which serves as a benchmark to test the proposed NEMS assembly techniques and virtual tools. Then, a general framework of nanotube-based NEMS assembly is proposed. Several nano-assembly strategies and virtual tools, such as automated path planning for NEMS assembly, a four-step scheme of nanotube manipulation, virtual fixtures for assembly finalization and safe manipulation, are introduced. These virtual tools and methods are experimented for justification. An assembly task of moderate complexity was performed in our virtual nano-assembly simulator with and without the help of the proposed toolkit. Experimental results suggest that the proposed methods tend to greatly enhance the efficiency and accuracy of nanotube-based NEMS assembly. In general, the proposed virtual reality toolkit not only ensures the safety, but also enhances the accuracy and efficiency of the assembly of nanotube-based NEMS.     

FLEXIBLE ASSEMBLY FIXTURING LAYOUT MODELING AND OPTIMIZATION BASED ON GENETIC ALGORITHM

There are many welding fixture layout design problems of flexible parts in body-in-white assembly process, which directly cause body assemble variation. The fixture layout design quality is mainly influenced by the position and quantity of fixture locators and clamps. A general analysis model of flexible assembles deformation caused by fixture is set up based on "N-2-1" locating principle, in which the locator and clamper are treated as the same fixture layout elements. An analysis model for the flexible part deformation in fixturing is set up in order to obtain the optimization object function and constraints accordingly. The final fixture element layout could be obtained through global optimal research by using improved genetic algorithm, which effectively decreases fixture elements layout influence on flexible assembles deformation.     

Contact state estimation based on surface-matching in virtual assembly

Contact problems are one of the most challenging fields in virtual assembly.Information of contact states could be utilized to realize compliant motion of work pieces,to analyze the contact stress,to assist positioning parts and so on.Some methods have already been proposed to estimate contact states between objects and in most of these methods contact states between objects are simplified in order to realize real-time visual reality animation.While in virtual assembly contact states between parts are required to analyze contact stress,deformation and quality.Besides the contact state estimation method for virtual assembly should be able to handle a number of complex parts in real time.There are rarely known methods which could meet this requirement till now.In this study a contact state estimation algorithm based on surface-matching for virtual assembly is proposed.Contacts between parts are categorized into six basic types according to contact region of surfaces.Based on continuous collision detection of polyhedral models a novel contact state identification algorithm which is based on surface matching is proposed.Then contact evolution algorithm,which utilizes the extern force and contact information,is implemented to handle evolution of contact state.Finally a prototype system is developed to verify the above technologies.Experiment results reveal that contact state between parts could be estimated correctly in real time virtual assembly.The proposed contact state estimation algorithm provides a complete solution to obtain the contact state between parts in virtual assembly.Information of contact state between parts could be utilized to realize contact dynamic,contact stress analysis,assembly quality analysis,and so on.     

Non-linear torsional vibration characteristics of an internal combustion engine crankshaft assembly

Crankshaft assembly failure is one of the main factors that affects the reliability and service life of engines.The linear lumped mass method,which has been universally applied to the dynamic modeling of engine crankshaft assembly,reveals obvious simulation errors.The nonlinear dynamic characteristics of a crankshaft assembly are instructionally significant to the improvement of modeling correctness.In this paper,a general expression for the non-constant inertia of a crankshaft assembly is derived based on the instantaneous kinetic energy equivalence method.The nonlinear dynamic equations of a multi-cylinder crankshaft assembly are established using the Lagrange rule considering nonlinear factors such as the non-constant inertia of reciprocating components and the structural damping of shaft segments.The natural frequency and mode shapes of a crankshaft assembly are investigated employing the eigenvector method.The forced vibration response of a diesel engine crankshaft assembly taking into account the non-constant inertia is studied using the numerical integral method.The simulation results are compared with a lumped mass model and a detailed model using the system matrix method.Results of non-linear torsional vibration analysis indicate that the additional excitation torque created by non-constant inertia activates the 2nd order rolling vibration,and the additional damping torque resulting from the non-constant inertia is the main nonlinear factor.The increased torsional angular displacement evoked by the high order excitation torque relates to the non-constant inertia.This research project is aimed at improving nonlinear dynamics theory,and the confirmed nonlinear parameters can be used for the structure design of a crankshaft assembly.     

Optimal Design of Bicycle Frame Parameters Considering Biomechanics

With the development of technology and the change of market demands,the trend in middle and high grade bicycle manufacturing is developed toward small-volume,multi-species,and customer-oriented production.Therefore,human element should be fully considered in design so that the bicycle has the best cycling performance for the specific rider.Currently,customized design is difficult to achieve since feature parameters of the rider are not included in the design.The design of bicycle frame is the most important in bicycle design.The relative positions among the saddle,handlebar and central axis are defined as the bicycle three-pivot,they are the main parameters in bicycle frame design.In conventional bicycle design,frame parameters are merely relevant to bicycle types.On the basis of the principles of biomechanics and ergonomics knowledge,this paper presents a design method for bicycle three-pivot considering feature parameters of the rider by dynamic simulation.Firstly,a dynamic model of rider-bicycle system is built for a special rider,and a serial of simulation experiments is designed by uniform test method.Then,a mathematical model is built between the three-pivot position and the square of lower limb muscle stress by using simulation and regression analysis of the rider-bicycle system.The optimal three-pivot position parameters are obtained by setting the minimal of the square of the lower limb muscle stress as the objective.Therefore,the optimal parameters are gained for the specific rider.Finally,various results are gained for different riders based on the same design process.The function between feature parameters of the rider and the optimum three-pivot position parameters is built by regression.Bicycle design considering biomechanics can be divided into three main steps:calculating the three-pivot position,designing the geometrical structure of the bicycle frame and analyzing frame strength,and selecting appropriate parts and assembling the bicycle.Bicycle design considering biomechanics changes the conventional bicycle design and realizes customized design by considering human element in the design process.     

Error Modeling and Sensitivity Analysis of a Parallel Robot with SCARA（Selective Compliance Assembly Robot Arm） Motions

Parallel robots with SCARA（selective compliance assembly robot arm） motions are utilized widely in the field of high speed pick-and-place manipulation. Error modeling for these robots generally simplifies the parallelogram structures included by the robots as a link. As the established error model fails to reflect the error feature of the parallelogram structures, the effect of accuracy design and kinematic calibration based on the error model come to be undermined. An error modeling methodology is proposed to establish an error model of parallel robots with parallelogram structures. The error model can embody the geometric errors of all joints, including the joints of parallelogram structures. Thus it can contain more exhaustively the factors that reduce the accuracy of the robot. Based on the error model and some sensitivity indices defined in the sense of statistics, sensitivity analysis is carried out. Accordingly, some atlases are depicted to express each geometric error’s influence on the moving platform’s pose errors. From these atlases, the geometric errors that have greater impact on the accuracy of the moving platform are identified, and some sensitive areas where the pose errors of the moving platform are extremely sensitive to the geometric errors are also figured out. By taking into account the error factors which are generally neglected in all existing modeling methods, the proposed modeling method can thoroughly disclose the process of error transmission and enhance the efficacy of accuracy design and calibration.     

面向装配的跨零件特征造型的模型表示与实现

在产品设计中 ,许多典型的结构特征具有跨零件性 ,如螺钉、销联接等。在现代 CAD系统中 ,特征造型是面向单个零件的 ,在处理跨零件特征时不仅造型效率低 ,而且破坏了这类跨零件特征明确的工程意义。本文在研究这类特征内在的跨零件性、局部修改性及装配关系的基础上 ,将面向零件的特征造型向面向装配的跨零件特征造型延伸 ,提出了虚零件等概念 ,建立了其数学模型 ,表达了在装配建模时通过虚零件对装配对象实体模型自动进行局部修改的关系 ,根据这一模型提出了其实现技术。在自主开发的超人 CAD/ CAM软件和商业 CAD/ CAM系统 UG上开发了机械联接单元智能快速设计软件包。实践表明 ,提出的方法在创建跨零件特征造型时工程语意明确 ,具有高效性、方便性、自然性、智能性等特点 ,并且可以方便地同传统特征造型系统融合     

机械联接单元快速造型方法的研究

提出了一种基于虚零件的知识驱动的联接单元造型方法，虚零件的是被联接零件局部修改的补集，在装配建模时，通过对被联接零件与虚零件的布尔差运算实现对基体零件实体模型作局部修改，联接单元的造型和装配一次完成，同时通过虚零件封装联接单元的规则与知识，实现联接单元的知识辅助设计，提高了建模效率与质量。根据这一方法，在UG软件上开发了知识驱动的联接单元快速设计模块，取得了满意的效果。     

面向过程的虚拟环境中产品装配建模研究

提出了面向过程的虚拟装配建模方法,在虚拟环境中将装配建模与装配仿真相结合,建立装配关系模型的同时,实现了对装配过程的创建与仿真,从而,在虚拟环境中将面向结果的装配建模发展为面向过程的装配建模.设计者采用直接三维交互进行装配建模操作的同时,系统通过装配关系识别自动捕捉设计者的装配设计意图,通过装配约束运动确定零件的装配路径,通过虚拟装配建模过程信息重用为装配规划提供有效的支持.开发了面向过程的虚拟装配建模原型系统.实践表明,面向过程的虚拟环境中产品装配建模方法有效地提高了产品装配设计的质量与效率.     

汽车差速器结构设计、三维建模与虚拟装配研究

简述了依据汽车设计规范对差速器各零件进行结构设计的主要思路，给出了在Pro／E软件中基于特征创建差速器各零件三维模型的思路与结果，阐述了建立差速器三维装配模型的方法和主要步骤。差速器各零件三维精确建模有助于提高其零件的数控加工精度，三维虚拟装配则有助于及时发现和解决结构设计中的问题，从而缩短差速器产品的研发周期，降低设计成本。     

虚拟装配中的混合设计建模方法研究

针对现有虚拟装配建模方法不能为装配序列规划提供完整模型信息的问题,分析了自底向上和自顶向下建模方法在虚拟装配应用中的优、缺点,根据装配序列规划的要求,结合两种建模设计方法的优点,提出了一种混合设计方法建立产品的装配模型。该方法采用自顶向下建模方法进行了产品总体设计,使装配模型具有产品的结构层次关系信息;在产品细节设计上采用了自底向上建模方法,使装配模型具有零部件的约束关系信息,得到了完整的产品装配模型信息。通过建模应用实例,验证了混合设计建模方法的可行性,以及模型信息的易提取性。研究结果表明,利用混合设计建模方法得到的模型,能够满足虚拟装配对产品装配模型的要求,可以为虚拟装配序列规划提供完整的模型信息。     

UG在机械设计中的应用

虚拟设计是机械设计的必然发展趋势。简述了大型CAD/CAE/CAM集成化软件UG的强大功能,结合柱塞泵设计实例,介绍了利用UG软件进行建模、装配和有限元分析的虚拟设计方法。     

基于适应性装配特征的自动装配技术研究

装配设计是现代CAD技术中的一个重要组成部分,但其中对零部件自动装配的研究还相对薄弱。笔者在研究参数化设计和装配建模的基础上,提出了基于适应性装配特征的零部件自动装配方法,根据适应性装配特征来确定零部件间装配关系和装配对象的主参数,以便适应调整装配对象姿态、完成自动装配、提高装配设计的速度和效率。根据以上研究开发的基于CATIA平台的导管焊接夹具自动装配模块,验证了该方法的有效性和实用性。     

面向装配的适应性特征建模研究

目前CAD系统中的特征建模主要是面向零件级的建模,不易直接建立和维护零件间存在的关联特征的协调性模型,如键与键槽、螺钉与螺钉孔等。针对上述问题,本文在研究了零件间特征映射关系的基础上,提出了一种面向装配的适应性特征建模方法。在零件间关联特征建模时,融入特征间的映射规则,构建出相应的映射虚特征,进而通过虚特征与基体零件进行布尔差运算,建立出对应的关联特征,从而实现零件间特征的快速建模。最后以模具设计为例,验证了上述方法的有效性和实用性。     

虚拟装配技术在自动引导车转向系统中的应用

阐述了虚拟装配技术基本原理、过程和方法,提出了基于SolidWorks三维建模软件,以自动引导车转向系统为设计对象,进行三维建模和虚拟装配设计.先通过虚拟装配关系识别捕捉设计者的意图,然后利用装配约束条件确定零件的装配路径,并完成其装配,最后对自动引导车转向系统进行相应的干涉检验,并进行动画制作,进一步检测虚拟装配的可靠性.实践表明,利用虚拟装配技术可有效地缩短产品研发周期,节约成本和提高产品装配质量.     

基于Pro/Engineer的热气机传动机构参数化设计与装配仿真的实现

介绍基于Pro／Engineer的热气机传动机构参数化特征建模及装配设计，基于主要零件驱动的修改设计。讨论了零件与装配体的联动设计，装配仿真和干涉性检验的途径和方法。该方法可为设计其它工业产品提供借鉴。