基才滑模PI控制交流变频钻机旋转系统

钻井过程中钻头粘滑振动会导致钻头失速,钻杆组合故障,增加钻井成本。为此,提出了滑模PI控制策略用于电动钻机交流变频旋转系统。在建立钻机旋转系统模型基础上,将滑模控制与PI控制相结合,用于提高系统的鲁棒性．抑制钻头的粘滑振动。仿真结果表明：基于滑模PI控制的钻机交流变频旋转系统,可有效地控制钻头失速,减少钻柱疲劳损坏．改善旋转系统的动态和静态响应特性。     

压电粘滑驱动系统中温度变化的实验研究

压电粘滑驱动系统具有长行程(几十毫米或更多,取决于机械结构)和高精度(几纳米)的特点.摩擦在粘滑驱动器中具有积极的作用.但在驱动器运行中,摩擦也可能造成"明显的"温度变化,在微运动中,该温度变化可能影响驱动器的精度.本次研究的目的是开发一种温度测量系统来测量粘滑驱动器在运行中的温度变化.其关键技术在于如何妥善处理如此小信噪比物理信号.实验表明,通过设计合理的滤波器和选择合适的高分辨率传感器,这里开发的温度测量系统可以很好的测量出温度变化.通过实验发现,压电粘滑驱动器中温度变化既来自于摩擦又来自于压电陶瓷自身发热.由压电陶瓷自身发热导致的温度变化呈非线性,而由摩擦导致的温度变化呈线性.     

环境湿度下硅材料表面的黏着与黏滑机理

首先采用湿法刻蚀处理硅110面,得到按一定规律排列的圆形、三角形凹坑修饰硅表面;然后在自行开发的微摩擦黏着实验机上,对光滑硅表面和凹坑修饰硅表面在湿度环境下的黏着和摩擦性能进行了测试,发现经过规则形貌修饰的硅表面可以明显地降低由于毛细作用引起的黏着．摩擦力测试中光滑硅表面在湿度超过70％后有明显的黏滑现象,而经过修饰的硅表面对黏滑有抑制作用．在此基础上,从硅表面液桥形成及断裂的角度探讨了环境湿度对黏着与黏滑的作用机理,建立了球面接触模式下不同湿度下的黏着力（pull-off force）与黏滑峰值力的计算模型与公式,并结合实验结果进一步改善了计算模型．可为控制硅袁面的毛细黏着与黏滑提供模型依据．     

钻柱粘滑振动仿真和控制策略研究

在深井和超深井钻探过程中存在钻柱粘滑振动,不仅造成机械钻速降低,驱动能量浪费,而且会加速钻具的老化和失效,严重威胁钻井安全。以钻柱旋转系统为研究对象,建立转盘、BHA(Bottom-Hole Assembly)和钻头的二自由度钻柱系统扭转模型。该模型考虑了扭转刚度、粘滞阻尼和岩石钻头相互作用等高度非线性摩擦。通过MATLAB/Simulink仿真模块对该模型进行仿真试验,分析了实际钻井过程中钻柱产生的粘滑振动特性。为抑制钻柱的粘滑振动,设计1套基于PID控制策略的双闭环控制系统。该研究结论对工程实践中钻柱粘滑振动的抑制具有重要意义。     

摩擦动力系统中两种非光滑现象及其算法研究

摩擦引起的振动在很多工业应用中都是很严重的问题,因此是目前国内外普遍关注的问题之一。讨论摩擦动力系统中的两类非光滑现象:stick-slip运动和碰摩现象,并对其进行比较细致的描述。采用事件驱动方法对实例进行数值分析,并与其他通用数值方法进行比较。结果指出采用方法的优越性。     

Anisotropic stick-slip friction of highly oriented thin films of poly(tetrafluoroethylene) at the molecular level

Lateral force microscopy (LFM) studies of poly(tetrafluoroethylene) (PTFE) films with molecular resolution are reported. Thin PTFE layers with a high degree of orientation were obtained by pressing and sliding a block of polymer on a clean, heated muscovite mica substrate. LFM nanographs obtained on these films by scanning at directions between ca. 40 and 90° with respect to the film orientation direction, i.e. with respect to the direction of the polymer chains, showed a stick-slip type frictional motion of the LFM probe tip at the molecular level. The friction force observed at constant load decreased with decreasing scan angles. Chain-chain packing distances obtained by LFM and contact-mode atomic force microscopy were the same to within the experimental error and had a value of 5.8 Å. Dual-mode contact AFM/LFM imaging was also performed by scanning in the chain direction. Here LFM nanographs showed no distinct stick-slip phenomenon. The contact mode AFM images, however, exhibited clear molecular resolution with the expected chain-chain periodicity. The disappearance of the stick component in LFM scans performed in the chain direction was attributed to the smooth surface of PTFE on the molecular scale.     

利用振动抑制爬行的方法

文章对机床导轨爬行机理进行理论分析，并利用该机理，提出了一种解决机床导轨爬行的有效方法，即用外加振荡器与基本摩擦振荡器构成闭环控制，并通过该外加振荡器来调节法向力的大小，使机床导轨之间的摩擦力被控制在较小的范围内，并通过仿真试验验证了该方法的有效性。     

Time Dependent Crack Growth and Loading Rate Effects on Interfacial and Cohesive Fracture of Adhesive Joints

Double cantilever beam fracture specimens were used to investigate rate dependent failures of model epoxy/steel adhesively bonded systems. Quasi-static tests exhibited time dependent crack growth and the maximum fracture energies consistently decreased with debond length for constant crosshead rate loading. It was also possible to cause debonding to switch between interfacial and cohesive failure modes by simply altering the loading rate. These rate dependent observations were characterized using the concepts of fracture mechanics. The time rate of change of the strain energy release rate, dG/dt, is introduced to model and predict failure properties of different adhesive systems over a range of testing rates. An emphasis is placed on the interfacial failure process and how rate dependent interfacial properties can lead to cohesive failures in the same adhesive system. Specific applications of the resulting model are presented and found to be in good agreement when compared with the experimental data. Finally, a failure envelope is identified which may be useful in predicting whether failures will be interfacial or cohesive depending on the rate of testing for the model adhesive systems.     

基于自抗扰算法的钻杆黏滑控制方法研究

石油钻井过程中钻柱系统产生的黏滑是一类自激转矩振荡。黏滑过程中,钻头处于或转或停"黏滞-滑动"的状态,钻杆转矩振荡大,不仅影响钻井效率也威胁钻井作业安全。钻柱系统具有非线性、不确定性等特点,难以得到其精确模型。基于以上考虑,设计了自抗扰控制器,该控制算法可以对模型不确定因素以及外扰进行补偿,具有较好的鲁棒性。通过不断地整定自抗扰控制器的参数,在仿真实验中得到了良好的控制效果,能够有效地抑制黏滑振荡,具有广阔的工程应用前景。     

Lateral Displacement of an AFM Tip Observed by In-Situ TEM/AFM Combined Microscopy: The Effect of the Friction in AFM

When the lateral displacement of an AFM tip due to friction is comparable to or larger than the scan size, for example during atomic-scale friction measurement, the interpretation of the friction image is different from the situation where the scan size is much larger than the lateral displacement of the tip and the image is a simple direct mapping of the friction value. This is because, due to the lateral displacement of the tip, the tip is not at the position where the scan indicates, as can be clearly observed by an in-situ TEM/AFM combined microscopy and atomic-scale friction analysis. This lateral displacement of the tip at the nanometer scale affects the shape of the force-distance curve. We discuss the effect of the tip lateral displacement in AFM data and its normal load dependence.