Dynamic behaviour analysis of planar mechanical systems with clearance in revolute joints using a new hybrid contact force model

In this study, the dynamic behaviour of planar mechanical systems including revolute joints with clearance is investigated using a computational methodology. The contact model in revolute joint clearance is established using a new nonlinear continuous contact force model, which is a hybrid contact force model, and the friction effect is considered using modified Coulomb friction model. And then, the dynamic characteristics of planar mechanical system with revolute joint clearance are analysed based on the new contact model. Numerical results for two simple planar mechanisms with revolute clearance joints are presented and discussed. The correctness and validity of the new contact force model of revolute joint clearance is verified through the demonstrative application examples. Clearance size and friction effect are analysed separately. The numerical simulation results show that the proposed contact force model is a new method to predict the dynamic behaviour of planar mechanical system with clearance in revolute joints.     

Dynamic and motion consistency analysis for a planar parallel mechanism with revolute dry clearance joints

The aim of the research was to introduce a methodology for dynamic response and motion consistency research on multibody system with multiple revolute clearance joints. An improved impact force model and a modified friction force model were introduced to evaluate the effects of impact and friction in clearance joints. A planar parallel mechanism which has two clearance joints in the left wing and the right wing was also used as an example. From the results based on different conditions, clearance has slight influence on the angular displacement and angular velocity, but obvious effect on angular acceleration. And with same clearance values of left wing and right wing, the motion consistency of the parallel mechanism is very good, which means the dynamic response of two wings is almost symmetrical. When the two clearance joints have different clearance values, the motion consistency and relative error between two wings are much obvious, especially the angular acceleration.     

Study on the dynamic interaction of multiple clearance joints for flap actuation system with a modified contact force model

Journal of Mechanical Science and Technology - To analyze the effects of clearance joint number and dynamic interaction on responses of the flap actuation system, a dynamic analysis model is...     

用矢量网络法实现平面动态机械系统的图形仿真

介绍了一种运用多体动力学进行机械系统仿真的新方法——矢量网络法,包括建模方法和其常规公式化的解题程序。结合具体实例编写了仿真程序并进行了结果分析。说明了矢量网络法应用性强的优点。     

Precise positioning problems using piezo-electric actuators with force transmission through mechanical contact

Mechanical actuators composed of material possessing piezo-electric properties have been tested with a view to assessing quantitatively the effectiveness of these actuators for use as displacement and/or correction devices in precise mechanical systems. Specifically, a mechanical system involving the Burleigh PZ40 pusher and PZ70 HV DC Op Amp was tested. Input-output measurements presented demonstrate the distortion, gain, and nonlinearities inherent in the application of these actuators to mechanical systems. Important parameters are considered and applicability is discussed.     

Stochastic modeling of friction force and vibration analysis of a mechanical system using the model

The squeal noise generated from a disk brake or chatter occurred in a machine tool primarily results from friction-induced vibration. Since friction-induced vibration is usually accompanied by abrasion and lifespan reduction of mechanical parts, it is necessary to develop a reliable analysis model by which friction-induced vibration phenomena can be accurately analyzed. The original Coulomb’s friction model or the modified Coulomb friction model employed in most commercial programs employs deterministic friction coefficients. However, observing friction phenomena between two contact surfaces, one may observe that friction coefficients keep changing due to the unevenness of contact surface, temperature, lubrication and humidity. Therefore, in this study, friction coefficients are modeled as random parameters that keep changing during the motion of a mechanical system undergoing friction force. The integrity of the proposed stochastic friction model was validated by comparing the analysis results obtained by the proposed model with experimental results.     

Dynamic contact stress analysis using a compliant sensor array

A flexible sensor array has been developed for the measurement of contact stress distribution between flexible bodies. The array incorporates 960 contact geometry modulation resistive (CGMR) transducers to provide a spatial resolution of 10 mm × 10 mm. The high flexibility of the array and its special structure enable it to comply with the very large displacements of the interface between the human body and a flexible cushion. In addition, a method and instrument have been developed to measure, digitize and record dynamic contact stress distributions with a sampling rate of up to 300 frames per second (960 sensors/frame). Measurements performed using this system under static and dynamic conditions are consistent with those performed through the contact pressure display (CPD) method. The new method has been used by the authers and their associates to obtain basic data required for the new field of cushioning mechanics.     

一类三自由度含间隙系统的动力学分析

建立了一类三自由度含间隙系统的力学模型,用变步长四阶Runge-Kutta法,通过理论分析和数值仿真结合,研究了该系统倍周期分岔、杈式分岔向混沌的演化路径,为实际应用中的三自由度含间隙机械系统的动力学优化提供了理论依据。     

风力发电机主轴的非线性接触有限元分析

使用非线性接触有限元方法对风力发电机主轴零件进行结构分析.模型模拟了轴承和轴套对主轴的非线性支承条件以及轴承的调心转动,给出静强度和疲劳寿命计算结果.分析结果表明,该主轴的强度、刚度和疲劳寿命满足设计要求.     

基于虚拟样机技术的含间隙转动铰建模与动力学仿真

对基于ADAMS的含间隙转动铰虚拟样机建模方法进行阐述,并建立具有多个含间隙转动铰的平面曲柄摇杆机构虚拟样机;通过动力学仿真,分析不同连接处的含间隙转动铰元素之间的相对运动关系,对三类运动铰间隙模型的适用性进行评价.     

Mode of zero wear in mechanical systems with dry contact

A theoretical and experimental analysis of a mechanical system with dry contact and subject to harmonic excitation is made. The adopted model is a two-degree-of-freedom system representing two sub-structures in dry contacts from their flat ground surfaces. It is theoretically shown that the two sub-structures move in phase with equal amplitudes at a particular frequency of oscillation. This particular frequency is called the frequency of virtual sticking and depends upon the physical properties of the two contacting sub-structures as well as the ratio between the amplitudes of external forces applied on these two structures in the direction of their friction sliding. Zero wear of contact surfaces can thus be established since relative velocity between encountered asperities of sub-structure surfaces becomes zero. It is shown, theoretically and experimentally, that when one of the applied harmonic forces is zero, the frequency of virtual sticking is equal to the natural frequency of the unforced sub-structure. The displacement ratio of the two contacting structures under the effect of harmonic excitation in their sliding direction is investigated within a frequency range up to 400 Hz. The tangential contact stiffness and the dynamic contact rigidity are theoretically determined and experimentally predicted from the measured forced displacement ratio.     

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。     

A new calibration method of the lateral contact stiffness and lateral force using modulated lateral force microscopy

We describe a new calibration method for lateral contact stiffness using modulated lateral force microscopy, a technique that offers some advantages with respect to the more classical friction force microscopy currently used for characterizing the friction properties of materials. The calibration method is based on the study of the lateral contact stiffness versus applied load and on the use of elasticity contact theories to determine by fit the calibration coefficient, allowing the scaling of experimental data. The method is tested by measuring the friction coefficient and shear strength of silicon and mica samples, respectively, and compared with results from the literature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Maximum finger force prediction using a planar simulation of the middle finger

Maximum isometric finger-grip forces were predicted using a biomechanical model for plane motion of the middle finger. In the course of this study, mathematical representations of tendon displacement, the moment arm of tendon at the finger joints and muscle force-length relationship were investigated. The information gathered was applied to the model to estimate the maximum grip force of the middle finger gripping cylinders of different sizes. Muscle force per unit physiological cross-section area of 30 N/cm2 resulted in good agreement with measured force. However, for finger postures having an acute proximal interphalangeal joint angle, the estimated force was greater than that measured. Various joint angles were applied to the model to simulate the wrist and finger postures not limited to the cylinder grip. In general the finger force was greatest with the wrist in its extended position and at acute flexion of the proximal interphalangeal joint. The maximum finger force occurred at reduced metacarpophalangeal joint angles as the wrist joint changed from an extended position to a flexed one. It is also postulated that muscle force-length relationship is an important factor in muscle force predictions. The data obtained by this research are useful for the design of handles and the current model is applicable to the analysis of hand postures for workers using hand tools.     

一种单自由度平面多关节机械手臂的设计与研究

针对工业中片状材料自动化传输的应用需求和垂直方向占用空间小的要求,设计了一种成本低、工作空间大和占用空间小的单自由度多关节机械手臂。该机械臂是一种3关节3连杆式机械结构,采用减速机和二级同步带进行传动。利用多坐标系分析方法和角速度叠加原理求出了任意臂长、任意同步带传动比下的末端连杆位姿方程,求出了末端连杆做直线运动的臂长、传动比条件并进行了实验验证。利用拉格朗日方程求出了其动力学方程,并用ADAMS软件仿真验证了其正确性,求出了其在任意位形下的等效转动惯量。搭建了PID闭环控制系统,在一种梯形路径规划下对闭环控制下的驱动力矩进行了仿真研究。研究结果表明,末端连杆直线运动条件和动力学方程推导正确,在示例的路径规划下其驱动力矩要大于25 Nm,为选择驱动力矩元件提供了一种方法和参考。     

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.     

考虑间隙的发动机曲柄滑块系统动态特性仿真研究

发动机是汽车的核心部件,曲柄滑块机构是发动机中的重要的传递力和位移的机构。建立曲柄滑块系统的多刚体模型,并通过对系统的运动学机型分析,得到曲柄滑块系统的速度方程与加速度方程。分析转动副间的间隙,并通过建立系统的尺寸链,利用极限法计算得到考虑转动副间隙影响时滑块运动到上止点时的位置。分析发动机的压缩比,建立发动机压缩比计算公式,找到发动机压缩比与滑块上止点的位置、转动副间隙之间的关系。利用MATLAB/Simulink对曲柄滑块系统进行运动仿真,分别得到曲柄作匀速、匀加速运动时,滑块位移与输入的关系。根据仿真得到的滑块运动位移结果,分别计算考虑和忽略转动副间隙时发动机的压缩比。通过结果对比可以看出,由于转动副间隙的存在,减小了发动机压缩比,降低了发动机性能,不利于发动机燃油经济性。     

Dynamic analysis for peg-in-hole assembly with contact deformation

The dynamic model is established based on compliance contact mechanics in this paper. The relationship is obtained between parameters, such as input force/torque, reaction contact forces/moment, contact pressure, contact deformation, etc. The traditional rigid body dynamic model with friction contact is limited. Inconsistencies and ambiguities can arise in such a model and the frictional impact can lead to violating principles of energy conservation. However, in light of physical characteristic of the system, the compliant contact dynamic model of this system can overcome these problems. Jamming and wedging are two ill-poses in assembly operation. On the basis of the dynamic model, the no-jamming and no-wedging assembly strategies can be obtained.     

Dynamic analysis of cross shaft type universal joint with clearance

Cross shaft type universal joint is widely used in ground vehicles to transfer torque between two intersecting axes, and its transmission feature can make a great contribution to NVH performance of the vehicle. We looked at the assembling clearance at cross shaft neck, and presented a dynamic model of cross shaft type universal joint with clearance at cross shaft neck. Two-state model is applied to describe the contact force between the cross shaft and driving joint fork based on Hertz theorem, and lumped mass method is applied to build up the dynamic model of the universal joint. Based on this model, numerical analysis is carried out to discuss the transmission feature of the universal joint with clearance at cross shaft neck, and the influence of clearance on the dynamic behavior of the system is evaluated with numerical results based on time history, power spectrum, and phase portrait. The method and conclusions presented are helpful to improvement of the transmission feature of cross shaft type universal joint.