机电伺服系统有限时间自适应反步控制方法研究

机电伺服系统存在未建模动态及不可避免的未知扰动,会严重影响系统的伺服性能。针对未知扰动下机电伺服系统惯性负载的角位移跟踪控制问题,考虑未建模动态对系统的影响,提出一种基于有限时间的模糊自适应指令滤波反步控制方法,能有效补偿系统中的未知扰动和未建模动态,具有良好的惯性负载角位移跟踪控制效果。针对系统中存在的未知外部扰动及未建模动态,结合滤波反步法和模糊控制理论,使用模糊逻辑系统逼近未知非线性动态同时构造自适应控制器。考虑到微分计算带来的计算爆炸问题,构建有限时间指令滤波器,降低了系统的计算复杂度,并通过设计滤波误差补偿机制,对滤波误差项进行补偿,保证滤波信号的逼近能力,提升系统跟踪控制性能。通过稳定性分析,证明所设计的控制器能够保证系统的跟踪误差在有限时间内收敛。最后通过仿真实验,验证了所提控制方法的有效性。     

负载扰动的电液比例位置系统鲁棒控制策略研究

针对带有负载扰动的电液比例位置系统,提出了一种可以实现高精度位置跟踪的动态面鲁棒控制策略。该控制策略在设计过程中引入动态面方法避免了传统反步法设计鲁棒控制器时带来的"计算膨胀"的问题,提高了控制策略在实际系统中的可使用性。通过Layapunov方法证明了鲁棒控制器作用下电液比例位置系统的所有信号有界稳定且具有渐近跟踪性能。最后,通过MATLAB仿真,验证了该控制策略的有效性。     

基于滑模变结构控制的鲁棒控制器设计

为了有效抑制状态变量的超调,加快转子的收敛速度,增强系统的抗干扰性,提出了一种基于滑模变结构控制方法的鲁棒控制器。与传统PID控制器不同,该控制器采取最终滑动模态的极点配置方式对系统的期望闭环动态以及选择滑模面进行设计,然后采取基于李亚普诺夫稳定性理论的控制方法来设计滑模控制器,使系统在设计的滑模面上具有期望闭环动态,在执行器动态变化导致误差的情况下,所述系统依旧可以在有限时间内收敛到设计的滑模面。该控制可以代替PID控制器应用于永磁同步直线电机,验证所设计的控制器在系统参数(动子质量、粘滞摩擦系数)发生较大变化和负载扰动情况下,都保持良好的跟踪性能,实现系统对不确定性扰动下的强鲁棒性。     

四旋翼飞行器的动态滑模轨迹跟踪控制研究

为了提高四旋翼飞行器在外界扰动影响下的飞行性能,提出了一种结合动态滑模与反步法的轨迹跟踪控制策略。首先,利用牛顿-欧拉方程推导了四旋翼的动力学模型,明确系统输入输出关系。其次,根据时间尺度原理,将系统分为位置与姿态两个控制环,分别设计了基于反步法的动态滑模控制器,并对建模的不精确性与外界扰动的影响进行了补偿。最后,通过仿真算例与飞行实验对文中所提控制策略的有效性进行了验证,结果表明该控制策略表现出比传统反步法与滑模控制更优的控制性能,能有效抑制外界扰动,实现四旋翼的轨迹跟踪控制。     

液压位置系统扰动消除设计方法的研究

针对液压系统建模困难,模型误差影响系统动态性能和负载干扰难于抑制的问题,基于X-滤波自适应逆系统结构提出了一种对模型误差不敏感的液压位置自适应逆扰动消除系统.针对该系统结构特点,提出一种适用于X-滤波结构的自适应算法,利用该算法得到不受模型误差影响的较为精确的液压位置逆模型,为液压位置扰动消除系统中控制器和扰动消除器的建立莫定基础.仿真结果表明:液压位置自适应逆扰动消除系统在建模误差较大的情况下,具有良好的动态响应和干扰抑制能力.     

基于扩张状态观测器的双永磁同步电机同步抗扰控制北大核心

对于双永磁同步电机系统中由于参数摄动和随机摩擦扰动引发的转速失同步现象,提出了一种新的双永磁同步电机滑模控制方法。首先,设计了扩张状态观测器去估计系统状态与实时扰动,并结合滑模跟踪控制器来提高电机在扰动作用下的跟踪性能;其次,将交叉耦合结构与滑模同步控制器结合,对电机转速的同步误差进行抗扰控制并且提升系统的同步性能。仿真结果表明,扩张状态观测器能准确估计电机系统机械角、转速及系统总扰动;设计的滑模控制器能够有效提高电机系统在扰动作用下的跟踪与同步控制性能。     

永磁直线同步电机智能分数阶动态面控制

针对永磁直线同步电机(PMLSM)存在的参数变化、外界扰动等不确定因素影响位置跟踪精度的问题，提出一种基于径向基函数(RBF)神经网络的分数阶动态面控制方法。在反步控制器设计的基础上，引入动态面控制技术，避免了反步控制存在的“微分爆炸”问题；在虚拟控制量中加入分数阶微积分项，增加了系统的参数自由度；利用RBF神经网络逼近补偿系统的不确定因素。基于Lyapunov稳定性理论，对所控制的系统进行稳定性分析证明。仿真结果表明，所提出的控制方法能减小系统的跟踪误差，提升鲁棒性，加快系统的响应速度。     

XY平台伺服系统的零相位鲁棒控制

针对直接驱动XY平台伺服系统的位置控制进行设计,考虑到系统的扰动、摩擦等因素引起的误差,采用零相位误差跟踪控制器和干扰观测器相结合的控制方法,通过零相位误差跟踪控制器来减小系统的跟踪误差,并通过干扰观测器来减小扰动对系统的影响,从而同时提高系统的跟踪性能和鲁棒性能。仿真实验结果表明,所提出的控制方案对提高伺服系统的定位精度有一定的作用。     

基于动力学补偿的并联机器人鲁棒轨迹跟踪控制研究

针对6-DOF并联机器人系统存在动力学建模误差和外界不确定性因素干扰的问题,提出了一种基于动力学补偿的并联机器人鲁棒轨迹跟踪控制策略。在充分研究了机器人系统动力学模型特点的基础上,基于Lyapunov方法获得了并联机器人的鲁棒控制率,提出了一种鲁棒轨迹跟踪控制方法,采用逆动力学对内回路进行补偿,外回路采用PD控制,然后对并联机器人进行了鲁棒控制器的设计,最后通过MATLAB进行了系统的轨迹跟踪控制仿真分析。仿真结果表明:当系统存在外界周期干扰的状况时,系统轨迹跟踪误差仍然一致终值有界,在一定程度上提高了系统的鲁棒稳定性。     

流量控制式ECHPS系统的自适应动态面控制策略

针对商用车普遍采用的液压动力转向系统(HPS)助力特性不可变的缺点,提出了一种旁通流量控制式电控液压转向系统。设计了这种转向系统的助力控制策略,研究其核心部件电液比例阀的结构原理和数学模型,采用动态面控制方法设计了一个鲁棒自适应动态面控制器。理论推导证明所设计的控制器不仅能够保证闭环系统半全局渐近稳定,输出渐近跟踪期望轨迹,而且对于系统不确定参数和外界干扰具有较强的鲁棒性。仿真结果表明,所设计的自适应动态面控制器不仅响应快、跟踪效果好、控制精度高,而且能够实现汽车低速时的转向轻便性和高速时的良好路感要求。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。