OPTIMAL CONTROL FOR VIBRATING SYSTEMS

A linear regulator problem for mechanical vibrating systems is studied in the second-order formulation. We exploit the second-order form of the differential equations involved, and solve the problem without the traditional use of a Riccati equation. In its natural representation, the optimal control problem gives rise to minimisation of a functional depending on second derivatives. The Euler–Lagrange equations and the transversality conditions developed lead to a linear fourth-order differential equation that determines the optimal control. The results are demonstrated by examples.     

汽车主动安全控制液压执行器的性能与原理

介绍目前汽车主动安全系统(汽车制动防抱系统、汽车驱动力控制系统、汽车电子稳定控制系统、汽车主动悬架、汽车四轮转向系统)上所应用的液压执行器,并重点分析目前先进的汽车主动安全系统——汽车电子稳定控制程序(Electronic stability program,ESP)上的液压执行器的结构、工作原理、工艺特点及其高速响应的性能特点。ESP所使用的液压执行器的响应速度在10 ms以内,其响应特性与液压执行器的各部分结构参数、被控车辆制动系统的参数等有紧密的联系,需要进行综合考虑和选择。介绍所采用的对汽车制动防抱系统液压执行器进行动态特性分析和参数匹配的建模分析方法,此方法同时也适用于对其他类型汽车主动安全系统的动态特性分析与参数匹配。最后对未来的汽车主动安全系统执行器的发展进行展望。     

形状记忆合金增强弹性梁主动振动控制中的驱动器布局研究

以往对形状记忆合金结构振动控制的研究通常限于均匀对称外铺层SMA驱动器的情况，而对其他驱动器布局方式研究较少。本文通过理论分析和实验测试对SMA驱动器在复合材料主动控制中的布局进行研究，除了对振动抑制进行研究外，还对利用SMA驱动器对结构进行激励进行了探讨，最后指出了SMA驱动器在应用上存在的问题和相应的改进方法。     

协同式CO2焊短路过渡模糊控制系统研究

介绍了一种在波形控制基础上,采用电弧自身传感的协同式模糊控制方法对焊接过程参数进行实时控制的逆变式CO2焊机控制系统.它通过电弧自身传感对CO2焊接过程有重要影响的短路过渡频率的检测,通过模糊处理和模糊判决之后,实时的对电弧电压进行控制,以保持焊接过程中规范参数的协同匹配关系.试验结果表明,采用该控制系统的焊机,实现了焊接规范参数的自动匹配和自动调节,同时明显改善了焊缝成形和降低了焊接过程中的飞溅.     

PARAMETRIC TIME-DOMAIN METHODS FOR THE IDENTIFICATION OF VIBRATING STRUCTURES—A CRITICAL COMPARISON AND ASSESSMENT

A critical comparison of four stochastic (PEM, 2SLS, LMS, IV) and three deterministic (LS, Prony, ERA) methods for the parametric time-domain identification of vibrating structures from random excitation and noise-corrupted response signals is presented. Concise summaries of the methods, highlighting their principles and realisations, are provided, while the study is based upon a six-degree-of-freedom structural model characterised by two closely spaced modes, two weak modes and a wide range of modal damping. Monte-Carlo experiments under two different (wideband/narrowband) noise environments are performed, along with comparisons with non-parametric frequency domain identification.The stochastic methods—most notably PEM, LMS and IV—are, at the price of increased complexity, shown to lead to potential advantages in non-negligible noise cases, while deterministic methods—most notably Prony and ERA—may suffice under negligible noise. In addition: (a) Model order estimation is shown not to be straightforward, and significant overdetermination is required (especially by the LS). (b) A weak closely spaced mode is hard to identify, while being completely missed by the deterministic methods and the 2SLS. (c) A highly damped mode presents some difficulty as well (mainly for the LS). (d) False modes are exhibited, primarily by the LS (wideband noise) and the ERA (narrowband noise). (e) The achievable estimation accuracy is generally high for the natural frequencies, lower for the damping ratios, and even more so for the residues (mode shapes). Furthermore, accuracy is somewhat lower for the closely spaced modes and significantly lower for the two highly damped modes. (f) PEM, LMS and IV achieve lower bias errors and good overall accuracy, followed by the 2SLS, Prony, ERA and, finally, LS. (g) Unstable modes are mainly exhibited by the IV and ERA. (h) All methods appear sensitive to the selected model order and design parameters, and user expertise is necessary.     

Formation mechanisms of low-friction tribo-layers on arc-evaporated TiC1−xNx hard coatings

A detailed correlation of the tribological performance of arc-evaporated TiC_1−xN_x coatings with testing temperature, atmosphere as well as variation in load and sliding velocity is presented in this paper. The low-friction behavior in combination with its mechanical integrity are the reasons for the extensive industrial application of TiC_1−xN_x over the last decades. Still the tribo-mechanisms behind this performance are not yet completely understood. The present study adds further understanding, as the low-friction behavior degrades at elevated temperatures and dry or inert environments, which is related to the different constitution of the tribo-layer formed as investigated by Raman spectroscopy. Surprisingly, the wear rate of the coatings does not correlate with the coefficient of friction indicating the presence of different wear regimes.     

基于80C196KC的CO2焊逆变电源数字波控系统

论述了基于Intel 80C196KC 16位单片机控制基础之上,采用波形控制的CO2焊逆变电源机系统,包括系统构成、电流波形控制策略、参数设置与显示、送丝及时序控制等.该系统根据CO2焊短路过渡的特点,软件上采用各种灵活措施对CO2焊焊接电流和电压波形进行较为精确的控制.并给出了该系统短路过渡CO2焊焊接电流电压波形.试验结果表明本CO2焊逆变电源数字控制系统具有良好的控制性能,而且结构简单和容易操作.     

波控短路过渡CO2焊接恒频自适应控制系统

针对短路过渡CO2焊接工艺的特殊性,基于熔滴与熔池短路阶段电源输出回路电阻的变化特征,确定了有利于消除瞬时短路及提高熔滴过渡规则性的焊接电源输出电流波形.在对短路过渡频率及焊丝伸出长度进行实时检测的基础上,采用MC68HC11A1单片机为主控CPU,建立了焊丝伸出长度变化前馈补偿-短路过渡频率负反馈控制的波控短路过渡CO     

A surface motor-driven planar motion stage integrated with an XYθZ surface encoder for precision positioning

This paper describes a surface motor-driven XY planar motion stage equipped with a newly developed XYθ_Z surface encoder for sub-micron positioning. The surface motor consists of four linear motors placed on the same surface, two pairs in the XY-axes. The magnetic array and the stator winding of the linear motor are mounted on the platen (the moving element) and the stage base, respectively. The platen can be moved in the X-direction by the X-linear motors, and in the Y-direction by the Y-linear motors. It can also be rotated about the Z-axis if the X- or Y-linear motors generate a moment about the Z-axis. The surface encoder consists of two two-dimensional angle sensors and an angle grid with two-dimensional sinusoidal waves on its surface. The angle grid is mounted on the platen of the stage which is levitated by air-bearings. The angle sensors and the air-bearing pads are fixed on the stage base so that the motion of the platen is not affected by the electronic cables and air hoses. The XY-positions and θ_Z rotation of the platen can be obtained from the angle sensor outputs with resolutions of approximately 20 nm and 0.2′′, respectively. The surface encoder is placed inside the stage so that the stage system is very compact in size. Experimental results indicate that precision positioning can be carried out independently in X, Y and θ_Z with resolutions of 200 nm and 1′′, respectively.     

高速开关式位置伺服系统的模糊控制器的研究

四个高速开头阀经过恰当的组合,用PWMA方法可以对双作用油缸的位置和方向进行控制。为了克服液压系统建模的复杂性和阀控缸的非线性对传统控制算法的影响,设计了一种模糊控制器,实现了PWM高速开头阀控液压缸位置系统的精确控制。试验证明：模糊控制是对高速开头阀进行控制的有效工具,它为高速开关阀在工程中的应用开辟了广阔的前景。     

Comment on “Pulsed Laser Deposition and Properties of Mn+1AXx Phase Formulated Ti3SiC2 Thin Films”

A recent paper by Hu et al. claimed synthesis of the MAX-phase Ti₃SiC₂at 100–300 °C using pulsed laser deposition. In this comment, we find that the evidence presented by Hu et al. is insufficient to show Ti₃SiC₂ formation. In fact, there is a simpler interpretation of their results from X-ray diffraction and transmission electron microscopy, namely that the material produced is a cubic TiC-based compound.     

TOX^R板件冲压连接技术

介绍了TOX板件冲压连接技术原理、强度分析、适用范围及应用。     

基于程序升温GC的EA-IRMS联机系统在氮、碳和硫同位素组成测定中的应用

基于具有程序升温气相色谱（GC）的元素分析-稳定同位素比率质谱仪（EA-IRMS）联机系统,初步建立了总氮、总碳和总硫稳定同位素比率的快速分析方法。分析结果表明：EA-IRMS联机系统运行状态良好,δ¹⁵N、δ¹³C和δ³⁴S标准曲线在时间上无显著漂移,质量控制标准的长时间测量精度优于0.3‰,准确度优于0.1‰。在18 mm的反应管内不存在³⁴S记忆效应,25 mm的反应管在加入空锡囊燃烧后可基本消除³⁴S记忆效应。利用该联机系统分析了不同类型的食品和环境样品。对于C/N、C/S质量比都小于200的样品,δ¹⁵N、δ¹³C和δ³⁴S的测定精度均优于0.15‰,能够满足实验室测试要求。对于C/N或C/S质量比极高的木材和琥珀样品,在N₂和SO₂信号强度都小于0.5 V的情况下,δ¹⁵N和δ³⁴S也获得了较好的重现性,其测定精度分别优于0.6‰和0.2‰。该研究可为EA-IRMS技术的应用与发展提供基础数据和科学依据。     

Structure of electrodeposited graded composite coatings of Ni–Al–Al2O3

The structure of electrodeposited composite coatings of Ni–Al–Al₂O₃, with Ni as the matrix and Al and Al₂O₃ as second-phase particles, was investigated using light microscopy and scanning electron microscopy. Ni coatings with no particles, which were used as reference samples, had progressively coarser structures with increasing current density. Co-deposition with Al resulted in refinement of the Ni matrix structure at high (>10 A dm⁻²) current densities. For single-particle baths, the co-deposition of Al₂O₃ was more strongly affected by current density and bath particle content than was the co-deposition of Al. However, for baths containing both Al and Al₂O₃ the amount of incorporated Al₂O₃ no longer depended on current density. With the choice of appropriate conditions, coatings of Ni with up to 39 vol.% Al₂O₃ were made. Similar experiments with Al yielded a maximum of 17.5 vol.% only. Uniform and graded mixed-particle coatings were also produced. When coatings containing Al were annealed, the reaction of the two elements resulted in the formation of either single-phase γ or two-phase γ–γ' alloys, in agreement with the equilibrium phase diagram.     

基于QFT的开关阀控气动位置伺服系统鲁棒控制

考虑开关阀的滞后特性,建立了高速开关阀控气动位置控制系统的非线性模型,并在原模型的基础上,将系统模型处理为包含滞后环节的数学模型。针对该模型对象参数不确定、摄动量大和负载变化范围大等问题,采用包含小闭环的2自由度控制结构,用定量反馈理论,进行系统的鲁棒稳定性、干扰抑制和跟踪性能设计,设计了具有鲁棒性能的控制器,并且设计了有效的摩擦力补偿器。经过试验验证,系统不仅具有较好的稳定鲁棒性,还具有很好的动态性能和位置精度。     

Measurement failure robustness in H2/H∞ reliable controller synthesis

Attention has returned towards the design of closed loop control systems which remain stable under measurement (or actuator) failure. Engineers wish to introduce reliability into the closed loop system by including redundant measurements. These systems are designed to be robust to measurement failures in terms of retaining closed loop stability and desirable system performance. Two methods of denoting measurement failure within a system are introduced. The existing design procedures for designing reliable H_∞ controllers are considered before re-formulating the reliability issue in the H₂ framework. The system performance for different measurement failure structures can be measured in terms of the bound on the H_∞ norm or the H₂ cost.     

Study of the heating rate effect on the glass transition properties of (60 − x)V2O5–xSb2O3–40TeO2 oxide glasses using differential scanning calorimetry (DSC)

The glass-transition temperature (T_g) and crystallization temperature (T_Cr) have been determined for the system (60 − x)V₂O₅–xSb₂O₃–40TeO₂ with 0 < x < 10 (in mol%) using differential scanning calorimetry (DSC) at heating rates φ = 3, 6, 9 and 13 K/min. The effect of the heating rate and the Sb₂O₃ content on T_g is discussed. It was observed that the transition region shifts to higher temperatures when the measuring time is reduced (or, conversely, when the applied temperature rate is increased). Using differential scanning calorimetry, the compositional dependence of T_g has been determined and so, an empirical equation has been deduced which relates the glass-transition temperature with the Sb₂O₃ content.     

Interfacial reactions and silicate formation in highly dispersed Lu2O3– SiO2 system

Solid state interface reactions in highly dispersed Lu₂O₃– SiO₂ binary oxide system were studied at 600–1100 °C with X‐ray powder diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM) and Fourier Transform Infrared spectroscopy (FTIR). The results show that at 600–900 °C an amorphous, nanometer thick Lu‐O‐Si layer covering SiO₂ particles exists in the system. At higher temperatures the breakage of the layer into amorphous islands occurs and crystalline silicates with various structures are formed. In particular, Lu₄[Si₃O₁₀][SiO₄] silicate, analogue of B‐type Dy – Tm disilicates, forms at 1000 °C.     

Defects formed within hardness indenter interaction zone in Al2O3–ZrO2 composite

The Al₂O₃?10 wt% ZrO₂ composites were subjected to hardness tests using a Vickers diamond indenter up to 98.1 N. The microstructure observation using a transmission electron microscopy technique helped to identify up to four zones differing in defect level and character. The densest dislocation tangles, twins accumulation and frequent presence of three slip systems were found in regions that were in contact with the sides of the diamond pyramid. The second zone, characterized by two, or at least one, active slip systems, started at the bottom of the indentation mark and extended up to a distance comparable with the depth of indentation. In the third zone, with a thickness comparable to that above, only some α‐Al₂O₃ crystallites showed the presence of dislocations, whereas other crystallites were defect free. In the last zone the alumina crystals were left unaffected but the ZrO₂ crystallites showed twinning characteristic of strain‐induced transformation.