基于并行计算的平面可调五杆机构动力学解析模型与仿真

基于凯恩动力学方程、数字-符号方法和并行计算建立了杆长和惯性参数可变平面可调五杆机构的动力学解析模型,并对驱动构件质量和杆长对驱动力/力矩的影响进行了仿真分析。将动力学模型的推导问题转化为特定条件下运用运动学和动力学计算公式求解机构驱动力矩的问题,并将广义坐标以及驱动构件杆长和惯性参数作为符号量,导出了模型矩阵元素数字-符号表达式。     

基于旋量理论的开链机器人动能的探讨

定义了空间坐标系下的惯性张量和广义惯性矩阵,给出了该坐标系下的刚体动能表示式：推导出物体坐标系下的惯性张量和广义惯性矩阵与空间坐标系下的惯性张量和广义惯性矩阵的关系,分析了空间坐标系下的广义惯性矩阵的特点;推导了开链机器人的动能表达方式,从而为建立机器人动力学方程奠定了基础。     

可倾瓦轴承的完整动力分析模型及计算方法

提出求解可倾瓦径向滑动轴承完整动力特性的解析模型和计算方法,给出可倾瓦轴承完整动力特性系数矩阵的简明表达形式.基于瓦块和轴颈间的运动耦合关系,建立瓦块局部坐标系统.与瓦块和轴颈运动相关的全局广义位移矢量可以通过简练的步骤转换为局部动坐标系下轴颈的位移矢量;利用求解固定瓦轴承动力特性的方法求得的局部动坐标系下的油膜力及其Jocabian矩阵,该油膜力矢量可以精确地转换为全局广义坐标系下的表达形式.在轴承的平衡位置处,全局坐标系下的油膜力矢量关于广义位移和广义速度的Jocabian矩阵为轴承完整动力特性系数矩阵的负值.给瓦块一个设定的扰动频率,就可以得到简化的当量动力特性系数矩阵.此解析方法求解简单方便,可用于分析可倾瓦轴承-转子系统.     

柔性机械系统动力学的变形耦合方法

采用弹性广义坐标耦合形式描述柔性构件的变形场 ,引入非线性位移 -应变关系确定新的形函数 ,使柔性体广义变形坐标 -应变成为线性关系 ,采用这种线性形式描述柔性体的应变能。将含变形广义坐标二阶项保留到求出偏 (角 )速度后再线性化 ,根据Kane方程建立了基于小变形的柔性机械系统动力学一致线性化模型。对含柔性梁的急回机构动力学进行了仿真研究。仿真结果表明曲柄在一些特定转速下 ,柔性梁出现失稳 ;在某些转速时 ,柔性梁动响应具有拍频特征。     

机械臂挠性的一种模拟方法

采用有限段刚体对挠性进行离弹性小变形情况下，应用广义欧拉角描述臂的弯曲和扭转变形，用线位移描述剪切和纵向变形，这种描述通过建立在各段质心的附体坐标系的空间关系来实现。利用Ｋａｎｅ方法分析模拟系统的动力学特性进而建立梁式构件的多刚体模拟系统的动力学方程。采用Ｃ语言编制计算机程序，在微分方程组的求解中，应用四阶Ｒｕｎｇｅ－Ｋｕｔｔａ积分程序，计算了梁式构件的人武部动态历程。以欧拉梁为例验证了该模拟方法     

材料力学课程中内力求解方法研究

为了提高材料力学中内力求解的准确率,提高内力图绘制的效率,以材料力学课程中内力的求解方法与内力图的绘制方法为研究对象,通过对拉压杆、轴和梁等构件的内力求解方法与内力图绘制方法进行分析,以揭示3种不同构件内力的变化规律和内力图的形状特征。结合内力的突变特征、内力图的形状特征以及内力方程的边界条件,提出了一种内力求解的新方法——"突变-形状-边界"法。利用该方法,学生只需对约束力进行计算,便可以根据内力突变特征、内力图形状特征和边界条件等快速准确地确定构件的内力和内力图。     

3-RRRT并联机器人正向动力学仿真

研究一种3-RRRT新型高速搬运机器人动力学建模及正向动力学求解实现方法。以支链构件相对运动坐标和动平台绝对运动坐标作为广义坐标,结合拉格朗日第一类方程建立了3-RRRT型并联机器人的运动学与动力学模型。阐述了运用违约修正法对动力学模型(微分/代数方程组)进行求解的过程,并利用Matlab软件平台进行了动力学正向数值仿真,结果表明此数值积分方法速度快、精度高,适合于3-RRRT并联机器人动力学正向求解。     

基于全加速度计惯性测量单元的微震颤测量技术研究

对基于全加速度计惯性测量单元的微震颤测量技术进行研究和分析,设计了测量系统的方案并研制了实验样机,惯性测量单元采用9加速度计的配置形式;推导了加速度计输出的比力方程,提出了将积分法和开方法结合起来求解角速度的算法;给出了利用四元数求解捷联矩阵的数值求解方法和在惯性坐标系下载体系上任意位置在任意时刻坐标的数值求解方法。     

数控平面磨床主轴减振方法研究

将一类数控平面磨床主轴系统简化为耦合双弹性梁结构,分别建立了非齐次边界条件下的机架子系统Euler梁和转子子系统Rayleigh梁解析模型,给出了各子系统在模态坐标下的广义动、势能.利用拉格朗日方程进行子系统综合,构造了广义坐标下的系统动力学模型.据此,考虑实际工况,设计了一动力减振器.模拟仿真和试验结果表明,在系统加入动力减振器后,主轴末端振动幅值可得到有效减小.     

虚拟环境下的活动线缆物理特性建模与运动仿真技术

针对活动线缆的布线工艺可靠性差的问题,提出一种基于弹性细杆力学模型的活动线缆物性建模与运动仿真方法.该方法针对活动线缆的柔性及连续性特性,通过建立固定的惯性坐标系、与活动线缆微元固连的Ftenet坐标系和主轴坐标系等三套坐标系,并对活动线缆微元进行平衡状态下的受力分析,得到活动线缆在平衡状态下的Kirchhoff方程,...     

基于ADAMS的腕力传感器动态性能分析

腕力传感器是智能机器人中最重要的传感器之一,作为反馈控制系统中的检测元件,要能迅速反映力和力矩的变化,应具有良好的动态特性。利用机械系统动力学软件ADAMS对一种新型的并联六维腕力传感器的弹性体进行瞬态动力学分析,得到了它的动态响应曲线,由此计算出传感器的动态性能指标,为此类传感器的进一步研究提供了一种新的途径和方法。     

The simulation of elastic mechanisms using kinematic constraints and Lagrange multipliersLa simulation de mecanismes elastiques par emploi de contraintes cinematiques et multiplicateurs de lagrange

In the Lagrange multiplier method, the motion of each element is represented in terms of its own rigid-body and flexible body generalized coordinates. The elements are treated as uncoupled from each other except for the application of interaction forces (the Lagrange multipliers) which enforce constraint conditions between the elements. Rather than eliminating the multipliers and obtaining coupled system coordinates, the values of the Lagrange multipliers are solved in time as part of a numerical technique. The multipliers are applied in turn to the individual elements and the simulation proceeds to the next point in time using numerical integration.The method of solution is applied to an illustrative example, a slider-crank mechanism. Modeling considerations and appropriate kinematic constraints are discussed. The author hopes to present numerical results for this example at the conference.     

基于分段连续ANCF缆索单元的输电线缆动力学建模与仿真

在绝对节点坐标缆索单元和Bézier/B样条几何体关系的基础上,构造了分段连续的ANCF缆索单元。单元形函数为分段连续函数,给出了其递推形式的定义式。单元在内节点处的连续性取决于单元节点坐标的选取以及形函数的定义方式。给出了单元弹性力及其对节点坐标雅可比矩阵的定义。进而采用该单元,建立了输电线缆架设过程中断线工况的动力学分析模型。可以实现用一个单元表示整条电缆线,从而在动力学仿真程序中避免了反复进行的单元到系统的集成及系统到单元的离散过程。用静力学分析计算得到输电线缆在重力、张紧力等外力共同作用下达到平衡时的节点坐标值,将其作为初值输入给动力学仿真程序,以模拟张紧力对输电线缆动力学行为的影响。建立了静、动力学仿真算例验证了单元的准确性,并给出了输电线缆的动力学仿真结果。     

A continuous force model for the impact analysis of flexible multibody systems

A new continuous impact model applicable to multibody systems consisting of interconnected rigid and flexible bodies is presented. The continuous impulsive force that acts during the short-lived interval of impact is written in terms of the relative displacement and velocity of the impacting bodies. In the method developed in this paper, the material compliance and damping coefficients are determined from energy balance relations. In order to account for the kinematic constraints between the two impacting bodies and other bodies in the system, an effective mass compensation is proposed. Flexible bodies in the system are discretized using the finite element methods. The generalized impulsive forces associated with the system generalized coordinates are then derived using the virtual work and are written in terms of a coupled set of reference and modal elastic coordinates. Numerical examples are presented in order to demonstrate the feasibility of the mathematical model developed in this paper.     

Synthetic analysis of flexible multibody system including a very flexible body

The progress in developing a dynamic analysis solver has different aspects of improvement in the sense of simulating the behavior of the parts. Among them, dynamics in flexible body and large deformable body have been an issue in recent decades. A modal coordinate formulation has been developed and used for analyzing the flexible body dynamics with a commercial dynamic solver, like in ADAMS. Flexible body dynamics using modal coordinates are reliable when the system’s deflection is relatively small, and generally its accuracy depends on how many relevant modes are used for the system. Conversely, to simulate the behavior of the large deflected body, absolute nodal coordinate formulation is derived and developed. The theory presents the mixed equations of motion, which consider both the absolute nodal coordinates and absolute cartesian orientation coordinates to simulate the large deflection. Its reliability is proved by many researches and experimental data. In this study, a dynamic solver which can handle the flexible bodies is developed. Three kinds of bodies, rigid, flexible and large deformable body, can be simulated. Its validity is verified by comparison with a commercial analysis program. For further studies, the constraints and force elements between different coordinates will be developed. Solving efficiency would be another major concern to be improved. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Ji Won Yoon received B.S. and M.S. degrees in Mechanical Engineering from Ajou University in 2004 and 2006, respectively. Mr. Yoon is currently a Ph.D student at the School of Mechanical Engineering at Ajou University in Suwon, Korea. He is serving as an instructor for undergraduate students. Mr. Yoon’s research interests are in the area of multibody dynamics, flexible body dynamics, and fatigue analysis.     

Evaluation of loop constraints for kinematic and dynamic modeling of general closed-chain robotic systems

In this article, the two algorithms evaluating loop constraints are presented for kinematic and dynamic modeling of general closed-chain robotic systems in terms of a system minimum set of coordinates. These procedures are based on higher order kinematic relationships between hypothetically open chain reference coordinates (system Lagrangian coordianates) and a set of independent closed-chain coordinates (system generalized coordinates). These relationships, along with principle of virtual work, allow for the determination of a system generalized coordinate based dynamic model in terms of the system Lagrangian coordinate based dynamic model in terms of the system Lagrangian coordinate based dynamic model(s). The proposed algorithms for determining/evaluating these relationships, both numerically and symbolically, are investigated and discussed with respect to their relative computational merits.     

Nonlinear transient response analysis for double walls with a porous material supported by nonlinear springs using FEM and MSKE method

In this paper, we newly propose a fast computation method for the nonlinear transient responses including coupling between nonlinear springs and sound proof structures having porous materials using FEM. In this method, we extend our numerical method named as Modal Strain and Kinetic Method (i.e. MSKE method proposed previously by Yamaguchi who is one of the authors) from linear damping analysis to nonlinear dynamic analysis. We assume that the restoring force of the spring has cubic nonlinearity and linear hysteresis damping. To calculate damping properties for soundproof structures including elastic body, viscoelastic body and porous body, displacement vectors as common unknown variable are solved under coupled condition. The damped sound fields in the porous materials are defined by complex effective density and complex bulk modulus. The discrete equations in physical coordinate for this system are transformed into nonlinear ordinary coupled differential equations using normal coordinates corresponding to linear natural modes. Further, using MSKE method, modal damping can be derived approximately under coupled conditions between hysteresis damping of viscoelastic materials, damping of the springs and damping due to flow resistance in porous materials. The modal damping is used for the nonlinear differential equation to compute nonlinear transient responses.Moreover, using the proposed method, we demonstrate new vibration phenomena including nonlinear coupling between nonlinear springs and soundproof structures by use of a simplified model. As a typical numerical example of the soundproof structure, we adopt double walls with a porous material. The double walls are supported by nonlinear concentrated springs. We clarify influences of amplitude of the impact force on nonlinear transient responses. We focused on the vibration modes, which magnify the amplitudes of the double walls. In these modes, the internal air of the porous material played a role of a pneumatic spring. Under a very large impact force as a severe condition, there exist the complicated nonlinear couplings between these modes and the super harmonic components of the rigid modes of the whole structure with large deformations in the nonlinear springs.     

Mechanical Property Investigation of Soft Materials by Cantilever‐Based Optical Interfacial Force Microscopy

Cantilever‐based optical interfacial force microscopy (COIFM) was applied to the investigation of the mechanical properties of soft materials to avoid the double‐spring effect and snap‐to‐contact problem associated with atomic force microscopy (AFM). When a force was measured as a function of distance between an oxidized silicon probe and the surface of a soft hydrocarbon film, it increases nonlinearly in the lower force region below ∼10 nN, following the Herzian model with the elastic modulus of ∼50 MPa. Above ∼10 nN, it increases linearly with a small oscillatory sawtooth pattern with amplitude 1–2 nN. The pattern suggests the possible existence of the layered structure within the film. When its internal part of the film was exposed to the probe, the force depends on the distance linearly with an adhesive force of −20 nN. This linear dependence suggests that the adhesive internal material behaved like a linear spring with a spring constant of ∼1 N/m. Constant‐force images taken in the repulsive and attractive contact regimes revealed additional features that were not observed in the images taken in the noncontact regime. At some locations, however, contrast inversions were observed between the two contact regimes while the average roughness remained constant. The result suggests that some embedded materials had spring constants different from those of the surrounding material. This study demonstrated that the COIFM is capable of imaging mechanical properties of local structures such as small impurities and domains at the nanometer scale, which is a formidable challenge with conventional AFM methods. SCANNING 35:59‐67, 2013. © 2012 Wiley Periodicals, Inc.     

Recursive newton-euler formulation for flexible dynamic manufacturing analysis of open-loop robotic systems

The main objective of this paper is to develop a recursive formulation for the flexible dynamic manufacturing analysis of open-loop robotic systems. The nonlinear generalized Newton-Euler equations are used for flexible bodies that undergo large translational and rotational displacements. These equations are formulated in terms of a set of time invariant scalars, vectors and matrices that depend on the spatial coordinates as well as the assumed displacement fields. These time invariant quantities represent the dynamic manufacturing couplings between the rigid body motion and elastic deformation. This formulation applies recursive procedures with the generalized Newton-Euler equations for flexible bodies to obtain a large, loosely coupled system equation describing motion in flexible manufacturing systems. The techniques used to solve the system equations can be implemented in any computer system. The algorithms presented in this investigation are illustrated using cylindrical joints for open-loop robotic systems, which can be easily extended to revolute, slider and rigid joints. The recursive Newton-Euler formulation developed in this paper is demonstrated with a robotic system using cylindrical mechanical joints.