An Integrated Force Probe and Quartz Crystal Microbalance for High-Speed Microtribology

We have developed a technique for measuring frictional forces and contact areas, over a wide range of applied loads, at microscopic contacts reaching high sliding speeds near 1 m/s. Our approach is based on integrating two stand-alone methods: nanoindentation and quartz crystal microbalance (QCM). Energy dissipation and lateral contact stiffness are monitored by a transverse shear quartz resonator, while a spherical indenter probe is loaded onto its surface. Variations in these two quantities as functions of shear amplitude, with the normal load held fixed, reveal a transition from partial to full slip at a critical amplitude. Average values of both the threshold force for full slip and the kinetic friction during sliding are determined from these trends, and the contact area is inferred from the lateral stiffness at low shear amplitudes. Measurements are performed at loads ranging from 5 µN to 8 mN using an electrostatically actuated indenter probe. For the materials chosen in this study, we find that the full slip threshold force is about a factor of two larger than kinetic friction. The forces increase sublinearly with load in close correspondence with the contact area, and the shear strengths are found to be relatively insensitive to pressure. The threshold shear amplitude scales in proportion to the contact radius. These results demonstrate that the probe–QCM technique is a versatile and full-featured platform for microtribology in the speed range relevant to practical applications.     

Lubricant Flow and Accumulation on the Slider’s Air-Bearing Surface in a Hard Disk Drive

Lubricant accumulation on the slider’s surface of a hard disk drive (HDD) has a detrimental effect on its read/write performance. Air flow through the slider-disk clearance moves some of the lubricant from the air-bearing surface (ABS) toward the slider’s lateral walls where it accumulates. In this article, we show by numerical simulations that the lubricant accumulation characteristics are strongly dependent on the slider’s flying height, skew angle and ABS design. The lubricant flow on the slider’s surface is quantified numerically. Air shear stress, air pressure and disjoining pressure are used as driving forces in the simulations. The lubricant thickness profile and volume evolution are calculated for two states of the HDD: operating and at rest. In the first state, lubricant is driven by air shear stress toward the trailing edge of the slider where it accumulates on the deposit end. In the second state, lubricant from the deposit end flows back into the ABS driven by the action of disjoining pressure. Lubricant accumulation on the four lateral walls of the slider is taken into account. The lateral walls are unfolded to study the flow using a two-dimensional lubrication model. The effects of flying height, skew angle and slider design on the accumulation removal of lubricant from the ABS are determined for the two states of the drive.     

一种管道机器人的自适应主动螺旋式驱动机理分析

对变径管道的机器人爬行工况进行分析,提出了一种由液压驱动的主动螺旋式自适应爬行结构。该驱动系统分别实现了驱动轮及其螺旋转角的三轴差速运动,并通过限流系统限制了驱动轮打滑和空转时的功率输出,使系统保持稳定的驱动力。提出了以系统内部压力感知机构运动的负载变化,并通过控制各驱动轮转角来调节整体负载能力的机理,实现了由传统驱动到螺旋式驱动的相互转化。最后通过虚拟样机技术对提出的负载调节和差速运动过程进行了数值模拟。     

Analysis of Micropolar and Power Law Fluid–Lubricated Slider and Journal Bearing with Partial Slip–Partial Slip Texture Configuration

An analysis of micropolar and power law fluid–lubricated partial slip–partial slip texture slider and journal bearings is presented. The nondimensional pressure and shear stress expressions for a partial slip texture configuration are analyzed using narrow groove theory. The parameters used in the analysis are nondimensional partial slip length, nondimensional partial slip–partial slip texture length, nondimensional depth of recess, ratio of land with slip to recess, nondimensional slip coefficient, coupling number; ratio of characteristic length to film gap, and power law index. A partial slip configuration with a higher slip coefficient yields an improvement in load capacity and reduction in coefficient of friction compared to a partial slip texture configuration for micropolar and power law shear thinning (pseudoplastic) fluid-lubricated slider and journal bearings.     

Composite beam–columns with interlayer slip—Approximate analysis

An approximate second order analysis procedure for composite beam–columns with interlayer slip subjected to transverse loading and axial compressive loads is developed. The magnification factors to be applied to the first order solutions in order to estimate the deflections and internal forces obtained by the second order analysis approach are presented. The method of applying magnification factors to internal axial forces is discussed. The approximate second order analysis procedure is developed for the four Euler cases with various transverse load conditions. The procedure is applied to and the accuracy is illustrated for simply supported partially beam–columns of steel and concrete, and timber and concrete with different bending stiffness and interlayer slip properties. The deflections and internal forces obtained by the approximate method compared extremely well, except for slip forces in case of very flexible shear connectors, with those obtained by the more rigorous second order analysis approach for different composite action (partial interaction) parameters (shear connector stiffness values). The study also shows that the magnification factor associated with the deflections can be utilized to estimate also the internal actions, except shear forces in case of very flexible shear connectors, in the second order case with minimal error for simply supported beam–columns. Thus, for members with shear connector stiffness of structural significance the proposed approximate method can be used in general for simply supported beam–columns. For other boundary and loading conditions, the approximate method needs to be re-evaluated. The approach of using one magnification factor greatly simplifies the analysis task for those components.     

MB-CVT电液控制系统智能优化设计

为了提高配有金属带式无级变速器车型燃油经济性,提出基于滑模极值搜索理论的控制算法和基于滑模极值搜索控制与传统夹紧力控制相结合的一体化式联合控制方法;设计了滑模极值搜索控制和传统液压控制合为一体化的联合控制系统。建立具有非线性、离散性的数学模型;分析无级变速器传动效率和金属带滑差率在一定速比下存在特殊曲线关系;测试主/从动轮夹紧力比值系数,完成了速比跟踪控制器及变化率控制流程设计。依据滑模极值搜索算法原理,完成了滑模极值搜索控制器设计。在具有环境仓的转鼓试验台上进行整车试验,试验结果表明:采用一体化式控制的金属带式无级变速器车型油耗为7.18L/100km,比传统控制系统的油耗降低约5.64%;主、从动压力安全系数倒数指标均小于1。满足整车提高燃油经济需求的可靠性、稳定性及优化性能。     

轮毂电机驱动汽车侧向稳定性底盘协同控制

轮毂电机驱动汽车可以通过差动驱动抑制车辆横摆和侧倾运动,从而提高车辆侧向稳定性,但受轮毂电机力矩和地面附着力约束的限制,作用效果薄弱。为提升车辆侧向稳定性控制效果,提出综合差动驱动、主动转向和主动悬架的车身横摆与侧倾稳定性底盘协同控制方法。根据轮毂电机驱动汽车特点,对其侧向失稳机理进行分析,基于模型预测控制设计前轮主动转向控制器;利用所提出的变系数指数趋近率求解期望横摆控制力矩,基于最优控制算法计算侧倾控制力矩;最后,构建集成差动驱动、主动转向和主动悬架的侧向稳定性控制器并完成整车侧向稳定性协同控制仿真验证。研究表明,所提出的底盘协同侧向稳定性控制方法可以有效控制车辆的横摆和侧倾运动,使其收敛于理想控制域,为轮毂电机驱动车辆的主动安全性控制提供了理论支持。     

应用铜基粉末冶金摩擦片的粘液传动的承载能力分析

铜基摩擦材料已经在各种机械和工业车辆的离合器和制动器的摩擦衬面中广泛应用,根据表明,湿式摩擦式的性能对动摩擦系数和承载能力有很大的影响。粘液传动是利用主动和从动摩擦片间的油膜剪力来传递运动和转矩实现无级变速的一种新型传动。本文将着重讨论采用带油槽的铜基粉末冶金摩擦力的粘液传动的传动机理,分析摩擦片间油膜的承截能力,并进一步讨论油槽深度和油槽数目对承载能力的影响。     

锁止离合器液粘传动机理分析

液粘传动是利用主动和从动摩擦片间的油膜剪切力来传递运动和转矩,实现无级变速和同步运行的一种新型传动装置.本文运用流体动力润滑理论,对锁止离合器液粘油膜传动机理进行了理论分析,建立了带径向油槽摩擦片间油膜传动的数字模型,得到了油槽数目、深度、宽度对液粘传动性能的影响;并考虑油液离心力对传动性能的影响;获得了锁止离合器油膜温度场的分布.     

Fuzzy chaos control for vehicle lateral dynamics based on active suspension system

The existing research of the active suspension system（ASS） mainly focuses on the different evaluation indexes and control strategies. Among the different components, the nonlinear characteristics of practical systems and control are usually not considered for vehicle lateral dynamics. But the vehicle model has some shortages on tyre model with side-slip angle, road adhesion coefficient, vertical load and velocity. In this paper, the nonlinear dynamic model of lateral system is considered and also the adaptive neural network of tire is introduced. By nonlinear analysis methods, such as the bifurcation diagram and Lyapunov exponent, it has shown that the lateral dynamics exhibits complicated motions with the forward speed. Then, a fuzzy control method is applied to the lateral system aiming to convert chaos into periodic motion using the linear-state feedback of an available lateral force with changing tire load. Finally, the rapid control prototyping is built to conduct the real vehicle test. By comparison of time response diagram, phase portraits and Lyapunov exponents at different work conditions, the results on step input and S-shaped road indicate that the slip angle and yaw velocity of lateral dynamics enter into stable domain and the results of test are consistent to the simulation and verified the correctness of simulation. And the Lyapunov exponents of the closed-loop system are becoming from positive to negative. This research proposes a fuzzy control method which has sufficient suppress chaotic motions as an effective active suspension system.     

四轮驱动汽车牵引力控制算法

提出了实用的四轮驱动汽车牵引力控制算法。在确定控制系统结构的基础上,设计了车速估算算法、油门位置PI控制器和制动门限控制算法。为实现牵引力控制算法的快速开发,建立由传感器、执行器、工控机、采集卡和输入输出电路组成的车载快速开发平台。硬件在环试验和道路试验表明:传感器能准确检测输入信号,控制算法能根据输入信号生成控制指令,执行器能快速、准确产生动作以消除驱动轮过度滑转。     

Shear force distance control in near-field optical microscopy: experimental evidence of the frictional probe-sample interaction

The properties of the probe-surface contact for a near-field optical microscope driven in the shear force mode have been studied applying lateral amplitudes of the probing fiber tip larger than 15 nm. Electric current measurements between a conductive tip and a conductive sample reveal a pulsed current behavior at the very beginning of the approach curve. In the upper part of the approach curve it turns to the quasiconstant current. From this observation a conclusion is drawn about the presence of permanent mechanical contact between the probe and the surface in the shear force mode. A shift of the approach curve along the z-axis as a function of dither amplitude was discovered. These results are in contradiction to the established conception of possible physical mechanisms of shear force interaction. To settle this issue the friction model is proposed according to which the damping of the probe vibrations is caused by the friction between the tip and the surface.     

Lubricant-Induced Spacing Increases at Slider–Disk Interfaces in Disk Drives

In this article, we explore the physical mechanisms for lubricant migration on recording head slider surfaces and how this migration leads to increased slider–disk spacing during disk drive operations. This is done using both a new experimental methodology, called the “droplet stress test,” and through simulation. In our simulations, we compare the air shear-induced lubricant migration modeled either as viscous flow of a continuum liquid film with zero slip or as wind driven slippage of molecules across the surface. The experimental data are best fitted using the viscous flow model to determine an effective viscosity for the sub-nanometer thick lubricant films. This effective viscosity tends to be somewhat less than the lubricant bulk viscosity due to air shear promoting the slippage of lubricant molecules across the surface. Our experimental results also indicate that the potential spacing increase from the pickup of disk lubricant on the slider is limited by the mobile fraction of the dewetting thickness of the lubricant film on the slider.     

基于LuGre模型的气动位置伺服系统摩擦补偿控制

气动伺服系统的摩擦力/驱动之比较大,摩擦力模型复杂、受影响因素较多且存在一定的不确定性,导致精确建模比较困难;另一方面,摩擦力和气体的低刚度、弱阻尼特性相互作用导致爬行、黏滑振荡现象,严重影响了伺服系统的动态及稳态性能的提升。在综合考虑摩擦力特征、系统自身非线性、未建模动态不确定性及摩擦力和系统性能相互影响的基础上,结合LuGre摩擦模型,采用双观测器估计摩擦力模型中的部分不确定性参数,提出非线性自适应反步摩擦补偿控制方法。通过在低速和高速工况下分别进行试验验证,并与PID控制方法进行比较,结果表明非线性自适应反步摩擦补偿控制方法有效改善了起步阶段的动态滞后现象,减少了低速工况下爬行及高速工况下的黏滑振荡现象,提高系统的响应速度及跟踪精度。     

High-speed thermo-microscope for imaging thermal desorption phenomena

In this work, we describe a thermo-microscope imaging system that can be used to visualize atmospheric pressure thermal desorption phenomena at high heating rates and frame rates. This versatile and portable instrument is useful for studying events during rapid heating of organic particles on the microscopic scale. The system consists of a zoom lens coupled to a high-speed video camera that is focused on the surface of an aluminum nitride heating element. We leverage high-speed videography with oblique incidence microscopy along with forward and back-scattered illumination to capture vivid images of thermal desorption events during rapid heating of chemical compounds. In a typical experiment, particles of the material of interest are rapidly heated beyond their boiling point while the camera captures images at several thousand frames∕s. A data acquisition system, along with an embedded thermocouple and infrared pyrometer are used to measure the temperature of the heater surface. We demonstrate that, while a typical thermocouple lacks the response time to accurately measure temperature ramps that approach 150 °C∕s, it is possible to calibrate the system by using a combination of infrared pyrometry, melting point standards, and a thermocouple. Several examples of high explosives undergoing rapid thermal desorption are also presented.     

Stick‐slip in the presence of a normal vibration

This paper presents a dynamic analysis of a contact system subjected to an applied normal vibration. The tangential motion of the system is found to exhibit stick‐slip behaviour dependent on the applied vibration, even in the absence of a difference in static and kinetic friction or a negative gradient in the friction‐velocity relation. The analysis leads to the development of a criterion for stick‐slip in the form of an equation defined in terms of the system and input parameters. This criterion is also presented graphically and is assessed through a series of experiments. The analysis and measurements show that stick‐slip occurs for a significantly wider drive velocity range when the normal vibration applied is near the natural frequency of the drive system. In addition, when stick‐slip occurs in the presence of a normal vibration, the frequency of stick‐slip is found to lock in to the frequency of the applied vibration.     

Noise Effect on Ice Surface Softening During Friction

The ice surface softening by friction is investigated considering the additive non-correlated fluctuations of the shear strain and stress, and the temperature. The premelting is construed by the Kelvin–Voigt equation for shear strain and by the relaxation equations of Landau–Khalatnikov type for shear stress and temperature. Taking into account the noises in these equations, the Langevin and Fokker–Planck equations are derived. Their analysis is based on the investigation of extrema of the distribution function, i.e., steady-state values of the shear strain using the Stratonovich interpretation. The phase diagrams are constructed, where the noises intensities and thermostat temperature determine the regions of ice, softened ice and their mixture (stick–slip rubbing). We present that domain of ice friction is bounded by relatively small background sliding block temperatures and fluctuation intensities of the stress and temperature. The ice film softens with growth of the stress noise intensity even at small thermostat temperatures. The friction force time series for all rubbing modes are calculated and compared with experimentally observed ones.     

Air-Bearing Shear Force in the Head–Disk Interface of Hard Disk

The air-bearing shear force in the head–disk interface (HDI) of hard disk drives is a dominant factor determining the motion and instability of the lubricant layer, which plays an important role in drive reliability. In this communication, an analytical formula, which is applicable to the flow of an arbitrarily rarefied gas in the HDI and is more general than that based on the first-order slip theory, is presented based on the Boltzmann equation. When a hard sphere model is used for the air molecules, the formula reduces to that based on the first-order slip theory, and it thus validates previous studies based on the latter formula.     

地铁线路上一种钢轨波磨现象的成因分析

针对地铁线路直缓点附近区间上的一种特殊钢轨波磨现象,根据现场条件建立车辆-轨道系统数值模型,并对模型的有效性进行了验证;运用数值模型分析上述线路区间的轮轨界面黏滑特性,解释了该类钢轨波磨的形成原因;结合轮轨系统动力响应特性,分析促使钢轨波磨生成和发展的波长固定属性的成立条件。结果表明：在线路直缓点附近区间,导向轮对和从动轮对内外侧轮轨界面均会发生横向黏滑运动,而轮轨界面发生纵向黏滑运动的概率较低,且黏滑运动的交替发生,导致了钢轨表面初始波磨的形成;当导向轮对和从动轮对内外侧车轮经过线路直缓点时,外侧轮轨接触表现为轮缘-轨距角接触,且接触形式的改变造成了轮轨系统法向力的波动,说明直缓点的存在赋予了轮轨横向黏滑运动的相位同步特征,能够保持钢轨波磨的波长固定属性,因此,钢轨波磨最终形成并不断发展,而且内轨表现为轨面波磨,外轨表现为侧面波磨,这与实测区间波磨现象一致。