一类非线性系统基于滑模原理的模糊自适应控制

针对一类非线性系统，设计出了一种自适应控制方案，用模糊逻辑逼近非线性函数，根据滑模原理及李雅普诺夫函数设计出自适应控制器。然后，用模糊推理进行修正，以克服一般滑模控制具有的抖动现象，保证闭环系统的稳定性和跟踪误差收敛于零的某邻域内。     

Adaptive sliding mode approach for learning in a feedforward neural network

An adaptive learning algorithm is proposed for a feedforward neural network. The design principle is based on the sliding mode concept. Unlike the existing algorithms, the adaptive learning algorithm developed does not require a prioriknowledge of upper bounds of bounded signals. The convergence of the algorithm is established and conditions given. Simulations are presented to show the effectiveness of the algorithm.     

Recent Advances in Disordered and Nanostructured Carbon Coatings for Superl Ubricity and Wearless Sliding

Increasingly more demanding and very stringent operating conditions envisioned for future mechanical and tribological systems will certainly require new materials and coatings that are superhard and at the same time self-lubricating.For example, dry machining is a much desired practice in manufacturing sector, but it is currently very difficult to realize mainly because of high friction and severe wear losses. However, recent advances in surface engineering and coating technologies may enable design and production of novel coatings architectures that can combine superhardness with self-lubricating properties in both the disordered or nanostructured forms. Recently developed nearly frictionless carbon films, ultrananocrystalline diamond and carbide derived carbon films can dramatically lower friction and at the same time reduce wear under very harsh sliding conditions. These coatings can be formulated in such a way that they can substantially increase the load-bearing capacity of sliding surfaces and hence improve their resistance to scuffing. It is also possible to design nano-composite coatings that can form self-replenishing and-lubricating tribofilms on their sliding surfaces and thus help increase the overall lubricity of these surfaces. In this paper, an overview of recent advances in disordered and nanostructured carbon films will be presented. Specific examples will be given to demonstrate the superior performance and durability of such novel coatings under a very wide range of tribological conditions. The major emphasis is placed on super low friction carbon films. The fundamental tribological mechanisms that control their exceptional friction and wear behaviors are also discussed.     

Variable structure control of a class of uncertain systems

This brief paper proposes a method for tuning the parameters of a variable structure controller. The approach presented extracts the error at the output of the controller and applies a nonlinear tuning law using this error measure. The adaptation mechanism drives the state tracking error vector to the sliding hypersurface and maintains the sliding mode. In the simulations, the approach presented has been tested on the control of Duffing oscillator and the analytical claims have been justified under the existence of measurement noise, uncertainty and large nonzero initial errors.     

A study of contact-start-stop wear tracks by TOF SIMS

In magnetic hard disk drive system, an ultra thin layer of lubricant is coated to the thin film media surface to prevent wear. Under the condition of relative motion, the displacement and replenishment of the lubricant at the head and media contact area are the factors that control the friction and wear behavior of the system. In this study, we investigate the sliding wear disk surface prepared by contact-start-stop (CSS) test using TOF SIMS (Time of Flight Secondary Ion Mass Spectrometry). TOF SIMS is a power tool for surface analysis with both high spatial and high mass resolution. Our investigations show that the lubricant thickness variation of the disk media at the contact area can be captured by sharp ion map images of TOF SIMS, and the thickness can be inferred based on the relative ion fragment intensity. In addition, the composition variation of the slider material and the magnetic layer materials can also be monitored. Finally the sliding effect is analyzed.     

Improved single neuron controller for multivariable stochastic systems with non-Gaussianities and unmodeled dynamics

In this paper, a new adaptive control approach is presented for multivariate nonlinear non-Gaussian systems with unknown models. A more general and systematic statistical measure, called (h,?)$(h,?)$-entropy, is adopted here to characterize the uncertainty of the considered systems. By using the “sliding window” technique, the non-parameter estimate of the (h,?)$(h,?)$-entropy is formulated. Then, the improved neuron based controllers are developed for multivariate nonlinear non-Gaussian systems by minimizing the entropies of the tracking errors in closed loops. The condition to guarantee the strictly decreasing entropy of tracking error is presented. Moreover, the convergence in the mean-square sense has been analyzed for all the weights in the neural controllers. Finally, the comparative simulation results are presented to show that the performance of the proposed algorithm is superior to that of PID control strategy.     

The tribological performance of DLC coatings under oil-lubricated fretting conditions

Whether or not the process of fretting occurs is to a large extent dependent on the coefficient of friction, because the coefficient of friction directly affects the amount of shear stress. As a result, the key factor when it comes to reducing the amount of fretting damage is to reduce the coefficient of friction. Various surface coatings, and especially hard, diamond-like carbon (DLC) coatings, are known to be able to produce surfaces with a low level of friction. Despite some such attempts in the past, which did not result in major improvements, the developments and improvements in DLC coatings in recent years suggest the need for a re-evaluation of these coatings for fretting applications. Another way to reduce the amount of friction in mechanical components is to apply lubricants, and recent studies on the lubrication of DLC coatings suggest that this combination could be very successful in preventing failures under boundary-lubrication conditions. Therefore, in this work we present the results of friction and wear measurements from three types of fretting contacts: steel/steel, steel/DLC and DLC/DLC. Boundary oil-lubrication conditions were investigated and a wide range of displacement amplitudes, i.e., from 25 to 500 μm, were selected to assess the fretting and sliding behaviours. The results show a significant difference between the fretting and sliding regimes. In the fretting regime, the DLC-containing contacts, and especially the self-mated DLC/DLC contacts, performed much better than the steel/steel contacts, and significantly reduced both the wear (a 3–10 times reduction with steel/DLC and DLC/DLC) and the friction (a more-than-two-times reduction with DLC/DLC). In the sliding regime, the lubrication effects governed the tribological performance, making the results for all three material combinations very similar.     

海浪扰动下水下航行器的动力定位性能分析

水下航行器动力定位是通过对水下航行器的多个螺旋桨推进器的转速、推力进行控制调节以抵御外界环境扰动,体现了水下航行器在外界环境扰动下执行各种任务的能力.通过对随机波浪扰动下的水下航行器前向动力定位进行建模仿真,分析得到各个状态特性与环境扰动分量对水下航行器动力定位性能的影响.进行了水下航行器的运动方程和螺旋桨动力学特性的精确建模;再针对波频扰动下的变参数问题以及控制器的鲁棒性和自适应性要求,建立了水下航行器动力定位滑模控制器;最后,将PM谱的随机波浪扰动应用于动力定位仿真研究,仿真结果显示,螺旋桨的动力学特性、幅值限制以及波浪的流速与加速度信息直接影响了水下航行器的动力定位性能.     

爆炸喷涂Cr_3C_2-35NiCr涂层的组织及性能研究

采用爆炸喷涂技术(D-gun)制备Cr3C2-35NiCr涂层。采用扫描电子显微镜(SEM)、电子探针(EPMA)、X射线衍射仪(XRD)对涂层微观结构、成分和相组成进行了分析,此外采用光学显微镜、显微硬度仪、拉伸试验机、摩擦磨损试验机等设备分别对涂层的孔隙率、硬度、断裂韧度、结合强度、磨损性能和热震性能进行了测试分析。试验结果表明:爆炸喷涂制备的Cr3C2-35NiCr涂层孔隙率为0.52%,显微硬度为HV803,断裂韧度为4.55MPa?m0.5,结合强度大于87.5MPa;涂层磨损性能和热震性能的测试结果表明,Cr3C2-35NiCr涂层室温摩擦系数为0.6,经受750℃下50次热震(水冷试验)无剥落。     

双梁起重机滑触线粉尘清扫装置

在永磁铁氧体生产环境中 ,铁氧体粉尘在双梁起重机滑触线上沉积 ,造成起重机电机缺相运行事故的发生。在起重机天车上设计、安装了滑触线粉尘清扫装置 ,该装置由清扫刷、悬臂板、连结架等组合而成。随着起重机的运行 ,清扫装置自动进行滑触线的清扫作业 ,保证了起重机电机的安全