考虑滑动副间隙空间机构的动力学研究

本文进行了含间隙滑动副（Ｐ副）空间机构的动力学研究。以ＲＳＳＰ机构为例,建立了机构的动力学方程并给出了数值解,计算结果表明,间隙对机构速度、加速度影响比较小,不象其它间隙运动副如圆柱副、回转副那样,对速度影响较小,而对加速度影响较大。     

含球面副间隙的空间并联机构动力学特性分析

为了掌握含间隙4-UPS-RPU并联机构的动力学特性,建立了含球面副间隙空间并联机构的刚体动力学模型,实现了机构的动力学分析。首先假定并联机构的驱动支链与动平台相连的球面副元素之间存在间隙,基于"接触—分离"二状态模型,建立了球面副间隙的运动学模型;然后基于Lankarani-Nikravesh接触力模型和修正的库伦摩擦力模型,利用拉格朗日方程建立了考虑球面副间隙的4-UPS-RPU并联机构的刚体动力学模型;利用数值仿真方法分析了考虑球面副间隙并联机构的动力学特性。研究结果表明,球面副间隙对机构动平台质心点的加速度和碰撞力有较大影响,而且球面副间隙值越大,对机构动态特性的影响越明显。本研究为预测球面副对机构动力学行为的影响,掌握含间隙并联机构的实际动力学行为以及间隙补偿控制提供了理论依据。     

考虑关节间隙的五杆机构动力学建模

利用含间隙关节元素之间的几何关系建立了该机构的间隙模型,写出了该机构的位置方程并对其进行了运动学分析,采用连续接触碰撞力模型描述了该机构间隙副的法向接触力,并以修正的Coulomb摩擦力模型建立了该机构的间隙副的切向接触力,利用第二类拉格朗日方程建立了该机构含间隙副的完整动力学模型,并结合ADAMS动力学仿真软件分析了运动副间隙对该机构动态特性的影响。为该机构的间隙补偿与控制策略提供了理论依据。     

用连续接触模型进行含间隙转动副的空间机构动力学分析

本文建立了间隙Ｒ副的连续接触模型，并对含间隙Ｒ副的空间机构进行了动力学研究。采用希林（ｓｃｈｉｅｎｌｅｎ）方法建立了机构的动力学方程，通过数值解研究了运动副元素的分离特性和Ｒ副的运动特性。数值计算结果表明：Ｒ副元素的分离时间很短，这说明在研究含间隙Ｒ副机构的动力学问题时，采用连续接触模型是可行的。     

考虑构件弹性和转动副间隙的空间机构动力学研究

对同时考虑构件弹性和转动副间隙的空间机构进行了动力学研究。提出了一种新型空间间隙转动副的连续接触模型。以此模型采用有限元法,建立了同时考虑构件弹性和转动副间隙的刚弹耦合方程,并给出了数值解。计算结果显示,间隙对弹性构件的振动有较大影响。     

含间隙隔膜泵曲柄滑块机构动力学研究

采用二状态模型,考虑了运动副元素接触表面的线弹性变形和阻尼,建立了含间隙隔膜泵曲柄滑块机构的动力学模型,并调用Matlab中的ode45对动力学模型进行数值仿真,得出运动副间隙对机构动态特性的影响,指出由于存在间隙,运动副元件在初始阶段会产生猛烈的冲击和碰撞.     

含间隙多连杆机构刚柔耦合动力学建模与分析

针对间隙和柔性构件对多连杆机构动力学响应的影响，研究了一种适用于多连杆机械式压力机的平面六杆机构。建立了转动副间隙矢量模型，通过Lankarani-Nikravesh法向接触力模型和改进的库伦摩擦力模型建立了转动副间隙处的碰撞力模型。基于绝对节点坐标法建立了柔性梁单元模型，通过拉格朗日乘子法建立了含间隙机构的刚柔耦合动力学方程，并通过Adams虚拟仿真软件验证了动力学模型和理论分析的正确性。研究间隙值和摩擦系数对机构动力学响应的影响，利用相图、Poincare映射图和分岔图对机构的非线性特性进行分析，结果表明，随着间隙值的增大和摩擦系数的减小，机构受到的影响越大，产生的响应峰值越高，同时转动副间隙处的混沌现象有所增强。     

考虑球面副润滑间隙的空间并联机构动力学建模与响应分析

为了分析含球面副润滑间隙的空间并联机构动力学响应特性,以2RPS-SPR(R转动副,P移动副,S球面副)空间并联机构为研究对象,结合Reynolds方程和Gümbel边界条件,建立了含多个球面副润滑间隙的空间并联机构动力学模型,对比分析了含润滑间隙、不考虑间隙的理想情况和含干摩擦间隙的机构动力响应特性,以及分析了不同动力粘度、不同间隙值对润滑状况下的机构动力学响应的影响。结果表明,润滑间隙相比于干摩擦间隙能有效改善并联机构的动力特性,且随着润滑油动力粘度的增大以及间隙值的减小,机构运行状况越好。该研究为含球面副润滑间隙并联机构动力学响应特性分析提供了理论方法,为指导实际生产提供了理论依据。     

含全运动副间隙的机构动力学特性研究

以曲柄滑块机构为研究对象,考虑机构除驱动转动副以外的所有运动副间隙,即剩余两处转动副间隙和滑块与轨道间移动副间隙,利用动力学分析软件ADAMS对机构进行动力学仿真分析,并将仿真结果与含有双转动副间隙的曲柄滑块机构动力学仿真结果进行对比,以确定全运动副间隙对机构动力学特性的影响。结果表明:与含双转动副间隙相比,全运动副间隙增加了机构震荡的次数,降低了机构的稳定性。在机构设计时要综合考虑机构除驱动运动副以外的所有运动副间隙以提高机构的动力学性能。     

含间隙RU-RPR解耦并联机构动力学建模及混沌现象辨识

为适应高速、重载、精密等工程需求,机构动力学特性及其蕴含的混沌现象日益引起重视。以自主提出的RURPR(R为转动副,U为虎克铰,P为移动副)两转动解耦并联机构为研究对象,针对运动副存在间隙状况,应用拉格朗日法建立间隙机构动力学方程,并采用Runge-Kutta(龙格-库塔)法予以求解;分析不同间隙大小对机构动态特性的影响,并借助相轨迹图、庞加莱(Poincare)截面映射法及李雅普诺夫(Lyapunov)指数进行机构混沌现象辨识。研究结果表明含间隙解耦并联机构动力学响应中存在混沌现象,并且随着间隙的增大,混沌现象愈加明显。所作工作是并联机构混沌动力学特性研究的有益尝试,对解耦并联机构动力学深入研究及进一步的样机研制与控制具有指导意义和实践价值。     

含间隙的变拓扑多体系统动力学建模分析

分析了含间隙多体系统的变拓扑结构特性,引入了基本约束变结构约束概念。在动力学建模中将系统拓扑结构的变化表示为含间隙处约束关系的变化,即变结构约束的增加与删除,给出了拓扑结构切换点的识别方程,建立了含间隙多体系统动力学的广义模型,对典型含间隙系统进行了仿真研究,验证了本理论模型的正确性。     

多间隙运动副四杆机构运动特性研究

运动副存在间隙会造成机构精确度的降低,为了研究运动副间隙对机构运动可靠性的影响,以含间隙转动副的平行双曲柄四杆机构为研究对象。根据运动副对目标构件的作用特性定义了运动副的性质,利用ADAMS研究了间隙运动副对机构不同目标构件运动特性的影响。结果表明:二级驱动间隙副比一级驱动间隙副对目标杆Ⅲ运动特性的影响更明显,但杆Ⅲ长度增加会减弱二级驱动间隙副的影响;另外,驱动间隙副比约束间隙副对目标杆Ⅱ的速度影响更大。     

含非规则粗糙间隙表面铰链关节的平面柔性多连杆传动系统动态误差与运动副磨损周期行为分析

传统旋转间隙关节接触模型假定销轴和衬套接触面形状是规则的并忽略了磨损效应的影响,降低了机构动力学模型预测精度。提出了一种含非规则粗糙间隙表面铰链关节的平面柔性多连杆机构多体动力学建模、磨损预测和动态误差分析方法。为准确描述运动副元素间碰撞行为,考虑滑动轴承间隙关节的磨损效应,提出了一种非规则粗糙间隙表面铰链关节的改进接触模型。在此基础上,考虑柔性杆的影响,基于绝对节点坐标法建立了含非规则粗糙间隙表面铰链关节的平面柔性多连杆传动系统多体动力学模型。与基于传统光滑间隙模型的结果相比,基于非规则粗糙间隙改进模型的多连杆机构动态响应更接近于试验值,验证了所提出计算方法的有效性。仿真结果表明,选用CuSn10P和CuPb30作为铰链衬套材料能够有效降低多连杆机构滑块动态响应偏差和提高机构的运动精度;表面粗糙度过高会导致运动副磨损加剧,过低则会降低间隙表面微凸体对碰撞能量的吸收。此外,磨损加剧了间隙表面轮廓不规则度,导致机构动态响应的不稳定性增大,运动精度降低。     

Reduction of the joint clearance effect for a planar flexible mechanism

When the operating speed of mechanical systems is increased, unpredictable dynamic problems are induced due to joint clearances and link elasticity. To solve these problems, quantitative prediction of the effects of joint clearance and link flexibility on the system is needed. This study has two principal objectives. The first is to develop a design method for eliminating the loss of contract at joints with clearance. The method utilizes three dimensionless parameters which govern the dynamic behavior at the instance when contact loss is predicted. These parameters are determined to maintain joint contacts throughout the operating cycle. The links in this mechanism are assumed to be rigid. The second objective of this study is to investigate the influence of the flexibility of the links. Using a finite element method, we found that link flexibility decreases the possibility of contact loss as well as the impact force at joints with clearance.     

Dynamic analysis of planar mechanical systems with clearance joints using a new nonlinear contact force model

We investigated the dynamic behavior of planar mechanical systems with clearance joints. First, the contact effect in clearance joint was studied using a new nonlinear contact force model, and the rationality of this model was verified by the results of numerical simulations, which are based on a journal and bearing contact model. Then, the dynamic characteristics of a planar slider-crank mechanism with clearance were analyzed based on the new nonlinear contact force model, and the friction effect of clearance joint was also considered using modified Coulomb friction model. Finally, the numerical results of the influence of clearance size on the acceleration of slider are presented, and compared with the published experimental results. The numerical and experimental results show that the new nonlinear contact force model presented in this paper is an effective method to predict the dynamic behavior of planar mechanical system with clearance joints, and appears to be suitable for a wide range of impact situations, especially with low coefficient of restitution.     

Effects of joint on dynamics of space deployable structure

Joints are necessary components in large space deployable truss structures which have significant effects on dynamic behavior of these joint dominated structures.Previous researches usually analyzed effects of one or fewer joint characters on dynamics of jointed structures.Effects of joint stiffness,damping,location,number,clearance and contact stiffness on dynamics of jointed structures are systematically analyzed.Cantilever beam model containing linear joints is developed based on finite element method,influence of joint on natural frequencies and mode shapes of the jointed system are analyzed.Analytical results show that frequencies of jointed system decrease dramatically when peak mode shapes occur at joint locations,and there are cusp shapes present in mode shapes.System frequencies increase with joint damping increasing,there are different joint damping to achieve maximum system damping for different joint stiffness.Joint nonlinear force-displacement is described by describing function method,one-DOF model containing nonlinear joints is established to analyze joints freeplay and hysteresis nonlinearities.Analysis results show that nonlinear effects of freeplay and hysteresis make dynamic responses switch from one resonance frequency to another frequency when amplitude exceed demarcation values.Joint contact stiffness determine degree of system nonlinearity,while exciting force level,clearance and slipping force affect amplitude of dynamic response.Dynamic responses of joint dominated deployable truss structure under different sinusoidal exciting force levels are tested.The test results show obvious nonlinear behaviors contributed by joints,dynamic response shifts to lower frequency and higher amplitude as exciting force increasing.The test results are further compared with analytical results,and joint nonlinearity tested is coincident with hysteresis nonlinearity.Analysis method of joint effects on dynamic characteristics of jointed system is proposed,which can be used in optimal design of joint parameters     

Effects of restitution coefficient and material characteristics on dynamic response of planar multi-body systems with revolute clearance joint

To study the effects of restitution coefficient and material parameters on the dynamic characteristics of planar multi-body systems with revolute clearance joints, a comprehensive methodology for clearance revolute joints in a planar multibody system is presented and analyzed. A new nonlinear contact force model, which accounts for the axial length of bearing and has a wide suitable range of impact situation, is presented to evaluate the contact force between journal and bearing. Furthermore, a modified Coulomb friction force model also presented to consider the effect of friction in clearance joint. Then, a typical journal-bearing model and a planar slider-crank mechanism has revolute clearance joint are used as examples. From the main numerical results under the different restitution coefficient and material parameters, it can be concluded that coefficient of restitution has significant effects on dynamic response of multi-body systems with revolute clearance joint. Additionally, materials of journal and bearing with smaller Young’s modulus will cause obvious delay on dynamic response of multi-body systems.     

Prediction of vibration characteristics of a planar mechanism having imperfect joints using neural network

Clearance is inevitable in the joints of mechanisms due primarily to the design, manufacturing and assembly processes or a wear effect. Excessive value of joint clearance plays a crucial role and has a significant effect on the kinematic and dynamic performances of the mechanism. In this study, effects of joint clearances on bearing vibrations of mechanism are investigated. An experimental test rig is set up, and a planar slider-crank mechanism having two imperfect joints with radial clearance is used as a model mechanism. Three accelerometers are positioned at different points to measure the bearing vibrations during the mechanism motion. For the different running speeds and clearance sizes, this work provides a neural model to predict and estimate the bearing vibrations of the mechanical systems having imperfect joints. The results show that radial basis function (RBF) neural network has a superior performance for predicting and estimating the vibration characteristics of the mechanical system.     

Modeling and simulation of joint clearance effects on mechanisms having rigid and flexible links

In this study, kinematic and dynamic characteristics of a planar four-bar mechanism having joint clearance and link flexibility are investigated. Assuming that joint clearance as a virtual massless link, artificial clearances are developed at crank-coupler and coupler-follower joints. Contact model in joints with clearance is established using the nonlinear spring-damper model and the friction effect is considered using the Coulomb friction model. Then the simulation is implemented and the kinematic and dynamic characteristics of model mechanism are investigated. The computational methodology can predict the effects of clearance on planar mechanism having rigid and flexible links. The results are evaluated for the case of stationary phase, and naturally show that extreme values occur in output of the mechanism with clearances. Due primarily to the suspension effect of the flexible link, values of these peaks in the flexible mechanism decrease relative to that of the rigid mechanism. In addition, the flexibility has a significant effect on the vibration response of the mechanism with joint clearance.     

不同类型铰机构动态特性对比研究

机构铰接副处过大间隙将引起异常的振动与噪声,加强了疲劳与磨损,严重地影响了机器的动态性能。通过算例,对比分析了理想铰、间隙铰、挤压油膜铰及多孔状挤压油膜铰等各类机构的动态特性的影响,分析结果表明,间隙铰机构稳态性能大大降低,而挤压油膜铰与多孔状挤压油膜铰均可控制机构的间隙效应,并且多孔状挤压油膜阻尼器适用于控制精度要求不高的场合。