机载摄影稳定平台的自抗扰控制

针对航空摄影稳定平台中非线性、多干扰的控制问题,采用自抗扰控制方法对三框架稳定平台进行分散独立控制。利用拉格朗日定理建立了考虑外部干扰的三框架结构稳定平台的动力学方程。设计独立的扩张状态观测器对每个环架的未知模型动态与外部扰动进行动态估计和补偿,采取非线性状态反馈控制以提高系统的控制性能。通过仿真和实验证明采用该方法设计的控制器不仅能满足系统稳态精度的要求,而且有效抑制了负载变化和不确定性扰动对系统的影响,提高了系统的稳定性和适应性。     

光电跟踪系统力矩波动的自抗扰控制

为解决光电跟踪伺服系统受电机力矩波动影响产生的速度波动问题,提出了一种改进的自抗扰控制策略进行力矩波动补偿。该算法主要由两部分组成:通过扩张状态观测器辨识出系统扰动,然后将该扰动前馈到系统控制量中去,构成复合校正系统;反馈通道中采用两参数的比例微分控制器,可以保证系统的稳定性和良好的动态特性。仿真分析和实验结果表明:与同等闭环控制带宽的PI控制器相比,自抗扰控制器可以提高系统对扰动力矩的抑制能力,采用自抗扰补偿时,速度误差的峰值由1.88%降低到0.65%,速度误差的均方根值由0.8%降低到0.2%。实验结果证明提出的方法能够有效降低电机力矩波动的影响,提高速度平稳性。     

光电平台伺服系统自抗扰滑模控制

提出一种基于参考模型的自抗扰滑模控制器,它包括一个自抗扰控制器和一个全局滑模控制器.根据参考模型,利用跟踪微分器设计自抗扰控制器,控制参考模型的输出精确跟踪指令输入信号.全局滑模控制器控制伺服系统被控对象的输出高精度跟踪参考模型的输出.光电平台伺服系统的实验结果证明该新型控制器能有效补偿系统的参数不确定性和非线性扰动,提高了伺服系统的跟踪精度.系统具有全局鲁棒性.     

大口径光电望远镜风阻力矩自抗扰补偿研究

光电望远镜口径超过5m以后,应该补偿风阻力矩干扰,以提高光电望远镜跟踪精度.本文首次将自抗扰控制器应用于光电望远镜的伺服系统中,根据自抗扰控制器可以动态补偿系统模型扰动和外部扰动,将作为负载扰动的风阻力矩归为外部扰动,利用扩张观测器对包括风阻力矩的各项扰动进行观测和补偿.该方法能有效地抑制风阻力矩对系统的影响,同时提高伺服系统速度环的响应速度,减小了稳态误差且无超调.仿真结果表明,具有自抗扰控制器的调速系统,当随机风阻力矩在±100N.m之间变化时,系统稳态误差的均值为1.8×10-5rad/s,标准差为9.87×10-4rad/s,最大值约为5.7×10-3rad/s,其抗扰性能明显优于PID调速系统.     

机载光电跟踪平台伺服系统自抗扰控制

摩擦非线性造成机载光电跟踪平台伺服系统低速不平稳性,增加了系统的稳态误差.常规PID控制难以满足光电跟踪平台高精度伺服系统的性能要求.采用一种新的二阶离散系统最速控制函数设计自抗扰控制器,将它作为机载光电跟踪平台伺服系统的位置环控制器.实验结果表明,当系统跟踪幅值为0.5°、频率为0.159 Hz的正弦输入信号时,在0...     

基于ADRC的网络化运动控制系统高精度轮廓跟踪控制

本文研究了具有重复任务性质的网络化运动控制系统高精度轮廓跟踪控制问题。首先,分析了网络时延给系统带来的影响,基于自抗扰控制设计了单轴跟踪控制器,将时变时延带来的不确定性建模为系统总和扰动的一部分,设计扩张状态观测器对总和扰动进行估计,并在前馈通道中对其进行补偿,消除时变时延影响,得到稳定的单轴跟踪控制。其次,基于迭代学习交叉耦合控制设计了轮廓误差补偿控制器,实现高精度轮廓跟踪控制。最后,通过实验验证了所提方法的有效性。这种控制方法在设计过程中不依赖于系统模型信息,为网络化运动控制系统轮廓跟踪控制方法的研究及应用提供了一种新的思路。     

基于自抗扰的快速刀具伺服系统复合控制

快速刀具伺服(fast tool servo, FTS)系统是实现微机械零件加工的关键部件。以压电陶瓷型FTS系统为研究对象,将迟滞状态时滞模型、时变时滞模型以及未建模动态非线性模型引入到FTS系统模型设计中以描述颤振现象,并基于神经网络控制提出具有迟滞时滞补偿功能的复合自抗扰控制方案,以实现FTS系统的颤振控制。其中,线性自抗扰控制将内部不确定性及迟滞时滞非线性和其他干扰视为总扰动并实时估计补偿,自适应BP(back propagation)神经网络用来对扰动估计误差进行逼近。与传统模型求逆方法相比,复合控制方案无需精确的数学模型易于初始设计。与线性自抗扰相比,复合控制方案减少了需要整定的参数数目,在相同带宽下具有更高的跟踪精度。仿真结果表明,所设计的复合控制具有更好的鲁棒性,能够实现压电陶瓷型FTS系统的快速精密跟踪控制。     

基于神经网络优化的交流自抗扰伺服系统控制

目的 为了解决传统交流永磁同步电机伺服自抗扰控制系统中外界扰动、非线性特性和本身自抗扰控制中参数较多且整定难的问题.方法 利用小波神经网络对自抗扰控制中的扩张状态观测器的误差校正系数进行在线整定,设计出基于小波神经网络优化的自抗扰控制器及相关的控制系统,以实现对整体控制系统的性能优化,并通过在Matlab/SIMULINK仿真实验与传统PID伺服控制系统和未进行优化的交流自抗扰伺服系统进行对比验证.结果 仿真结果表明,基于小波神经网络优化的交流永磁同步电机伺服自抗扰控制系统对目标位置动态响应快、稳态误差小、抗干扰能力强,稳态时转矩脉动小.结论 与常规未优化自抗扰伺服系统和传统PID伺服系统相比,基于小波神经网络优化后的自抗扰伺服系统,能有效地提高伺服系统控制性能和鲁棒性.     

基于模糊控制的微操作平台位置精度补偿方法

由于压电式微操作平台的迟滞非线性会导致其位置精度和动态性能下降,且难以建立精确的迟滞非线性模型,采用一种基于模糊控制策略的位置精度补偿方法,以摆脱对迟滞模型的依赖。以一种一维压电式微操作平台为对象,以平台的位置偏差与偏差变化率为模糊输入,压电驱动器输入电压变化量为模糊输出,提出采用基于PID控制的实验数据获取经验来制定模糊规则的方法。通过模糊推理和解模糊过程,建立平台输入量与输出量之间的模糊关系,实现了可消除迟滞现象的自适应补偿。为了说明所提出的位置精度补偿方法的可行性,通过实验与PID控制进行比较,分析平台跟踪不同频率正弦信号的位置误差。实验结果表明,所提出的模糊控制方法能使平台具有更高的位置跟踪精度和更快的跟踪速度,并具有较好的自适应性。     

柔性关节空间机械臂奇异摄动自抗扰控制仿真研究

针对不同重力环境条件下考虑摩擦、关节刚度非线性与外扰影响的柔性关节空间机械臂的控制问题,提出了一种基于奇异摄动理论的自抗扰控制方法。首先建立了柔性关节空间机械臂在地面重力和空间微重力环境下的动力学模型;然后采用奇异摄动法将系统模型分为快变子系统和慢变子系统,针对快变子系统设计速度反馈控制律来抑制柔性关节的振动,针对慢变子系统设计加入前馈补偿的自抗扰控制器(ADRC)来抵抗系统的内外扰动,并对系统进行了稳定性分析;最后对设计的控制器进行了仿真验证与对比研究。仿真结果表明,采用该方法,在不同重力环境下柔性关节空间机械臂均能实现很好的轨迹跟踪和抖振抑制,且能有效抵抗内外扰动,系统具有鲁棒性。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...