焊缝自动跟踪微机系统的数字控制器

对焊缝自动跟踪微机系统中的数字控制器进行了分析研究。在焊缝自动跟踪系统中,除了电弧传感器之外,大部分的传感器都有检测点超前于焊接点的情况。本文针对这种有普遍意义的传感器超前检测的自动控制系统的结构特点,分别设计了最少拍数字控制器、数字ＰＩＤ控制器以及一种实用型的数字控制器。这些数字控制器的仿真试验结果表明,本文提出的实用数字控制器具有跟踪结构精度高,结果简单、计算方便等优点,因而是这类传感器超前检     

一种基于积分反推原理的非线性伺服控制方法

针对机械伺服系统,提出了一种基于积分反推原理的新型的伺服控制器。该控制器对外部扰动及系统参数变化具有较强的鲁棒性。对直流电机伺服系统进行了数字仿真,结果表明了这种新型控制器的有效性。     

基于DSP的脉冲MIG焊数字控制系统的建模与仿真

为实现一脉一滴熔滴过渡,采用了双阶梯外特性和脉冲MIG焊电参数控制策略.构建了基于DSP(digital signal processor)的脉冲MIG焊数字控制系统模型.建立了控制系统的仿真模型.借助MATLAB对控制系统进行了仿真研究,得到了数字控制器的最佳参数范围.进行了脉冲MIG焊数字控制器的仿真试验.结果表明,所设计的数字控制器可以实现电弧电压、焊接电流的实时准确快速调节,能够实现脉冲MIG焊双阶梯形外特性和熔滴过渡的控制.     

一种新型电阻焊机恒电压控制策略

针对电焊杌焊接时恒压控制的工艺要求,研制了一种基于恒压控制策略的DSP全数字控制器,详细介绍了数字控制器的控制原理、控制器结构以及控制程序设计.该数字控制器主要基于对阻焊变压器一次电压的监控以及负载特性的变化,当电网电压在一定范围内波动时,仍能保证一次电压恒定.其控制主电路通过双向晶闸管控制其触发导通角从而改变其输出电压,数字控制器采用TMS320F2812实现.实验表明该方法能有效地控制焊接时输出的恒电压.达到满意的效果.     

数字电液比例位置控制系统

本文提出一种数字电液比例位置系统，研究采用状态反馈改善系统的动态性能，给出参数辨识和极点配置计算方法。此外，本文还提出电液比例专用数字控制器，简化了控制结构，使控制器成本低廉，可靠性高。     

功率匹配泵的数字PID控制器的非线性控制寻优

本文把系统的动态性能指标转化为系统输出的约束条件,并以使约束的最大误差最小作为优化目标,从而使控制器的设计问题能够通过限定条件的非线性寻优算法得到解决。本文结合功率匹配泵,利用序列二次规划法对其数字PID控制器进行了非线性控制寻优,取得了很好的效果。     

电液数字阀的PLC直接控制及特性

采用可编程控制器(PLC)直接控制电液数字阀，可使液压系统的控制系统简洁、可靠、成本显著下降。介绍了PLC控制电液数字阀的方法，数字阀的伺服控制、驱动接日及PLC梯形图的控制逻辑。     

步进式液压数字阀用永磁式步进电动机的非线性控制

通过现代非线性理论如混沌动力学理论研究了永磁式步进电动机的非线性动力学。本文的研究对象是三相步进电动机。研究表明在高频情况下系统会经历一个动态的分又(Hopf分叉)。由于步进电动机作为步进式液压数字阀的电气一机械转换元件被广泛地应用于液压数字压力阀、液压数字流量阀、液压数字方向阀。本文提出了对三相步进电动机的不稳定性的控制,设计了非线性鲁棒控制器,阐明了在一些电动机参数不确定的情况下,如何使系统稳定,并且具有令人满意的性能。     

基于模糊自调整PID控制的智能数字流量阀研究

针对PID控制数字流量阀的局限性,设计模糊自调整PID控制器,实现数字流量阀控制系统PID参数在线自整定的智能化.仿真结果表明:与常规PID控制的数字流量阀相比,智能数字流量阀具有更小超调量、更快动态响应及更强抗干扰特性,取得了优于传统PID控制的效果.     

高精度气动伺服阀的状态空间建模及数字化设计

伺服阀的性能是影响高精度气动精确定位系统性能的决定性因素.为了提高气动系统性能,改善伺服阀的性能至关重要.分析一种新型的高精度气动伺服阀的结构特点,建立其状态空间模型,设计数字控制器并进行仿真.仿真结果表明:该数字控制器是有效的,显著改善了气动伺服阀的动、静态性能.     

Formulas of Tension of Continuous Rolling Process

The development of computer controlled continuous rolling process calls for a mathematical expression that can express the inequality condition of "constant flow". Tension is the link of the continuous rolling process. From the condition of dynamic equilibrium, a differential equation of tension is given out. On the basis of the physical rules established from the industrial practice and experimental studies, the law of volume constancy, the linear relation of forward slip and tension, the state equation of continuous rolling, the formula of dynamic tension, and the formula of static tension have been obtained. These formulae reflect the functional relations between tensions, thickness, roll velocity, and time in the continuous rolling process. It is implied that the continuous rolling process is a gradually steady, controllable, and measurable dynamic system. An assumption of predicting the thickness of a steel plate using these tension formulae is also put forward.     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.     

Optimierung des Schweißprozesses hochlegierter Stähle und Verbesserung der Korrosionsbeständigkeit der Schweißverbindungen

Optimization of the welding process of high alloyed steels and improvement of corrosion behaviour of welded joints The optimization of welding processes is necessary to obtain a good durability of the welded joints connected with a minimization of the corrosion performance. Welding processes represent a considerable influence of the material. The formation of precipitations, strong structure changes, increasing of the residual stress and not at all undefined surface layers are possible. All these changes have a great influence on the corrosion behaviour. Particularly tempering tarnish changes the passive layer which is decisive for the corrosion resistance. But also surface treatment methods can influence the corrosion behaviour. Therefore both the welding process and an “after‐care” coordinated with the respective welding process had to be optimized. The optimization of the welding process was carried out by variation of the energy per unit length and the use of different protective gases. For a selection of a surface treatment method it has to be taken into account that an obvious remove of the tempering tarnish doesn't lead to an improvement in the corrosion behaviour. Traces of the working tool which can have a negative effect on the corrosion behaviour often remain on the surface. The influence of these different parameters on the corrosion property could be proved by electrochemical and surface analytical examinations. The investigations were carried out at specimens of two typical representatives of high alloyed austenitic steels and at welded joints, which had different surface treatments.     

Gerissener Stahlbeton: Wie korrosionsgefährdet ist die Bewehrung?

Cracked reinforced concrete: What about corrosion risk? The formation of cracks within the tension zone of the concrete is part of the design principle of reinforced concrete structures. The width of these cracks can be limited by means of crack limiting reinforcement. Already by the end of the fifties first examinations have been carried out to determine the influence of cracks and their width on the corrosion risk. Compared to uncracked concrete CO₂ and chlorides as corrosion promoting substances are able to move faster towards the reinforcement within a crack, leading to an earlier depassivation of the reinforcement within the cracks. Before Schießl published his results, from experiments and literature research, it had been assumed that the corrosion rate of reinforcement within cracks increases with increasing crack width. Hence a differentiated maximum crack width linked to exposure classes had to be complied according to the DIN 1045 until the version of 1988. For the first time the DIN 1045 version 1988 did not enclose this differentiation, for durability reasons a maximum crack width of 0.25 mm has been fixed for reinforced concrete. In the version of 2001 the calculated crack width has been raised from 0.25 mm to 0.30 mm. Therewith the findings of Schießl (published in book no. 370 by the Deutscher Ausschuss für Stahlbeton) have been implemented by now. The main contributing factors influencing the corrosion rate of cracked concrete are the concrete quality and the concrete cover and not the crack width, whereas horizontal structural parts exposed to chlorides have to protected generally by additional measures.     

Stress Analysis of the Aperture in Compound Pipeline by FEM

There is a cyclical aperture at a certain part of the fiberglass reinforced plastic compound pipeline with a stainless steel pipe as a liner, which becomes the weakness of the conduit. The field of stress and strain of the aperture was investigated using the nonliner finite element code Marc. The results of the finite element analysis showed that there were concentrations of stress and strain in the layer of stainless steel at the part of the pipeline where the aperture existed. The method to solve these problems was also discussed.     

Properties of Mechanically Milled Nanocrystalline and Amorphous Mg–Y–Ni Electrode Alloys for Ni–MH Batteries

Nanocrystalline and amorphous Mg2Ni-type Mg20-xYxNi10(x = 0,1,2,3 and 4) electrode alloys were fabricated using mechanical milling.The effects of the Y content and milling time on the microstructures and electrochemical performances of the alloys were investigated in detail.X-ray diffraction and transmission electron microscopy analyses revealed that the substitution of Y for Mg yields an obvious change in the phase composition and micro morphology of the alloys.When the Y content x B 1,the substitution of Y for Mg does not change the major phase Mg2 Ni,but with a further increase in the Y content,the major phase of the alloys transforms into the YMg Ni4 YMg3 phase.A nanocrystalline and amorphous structure can be obtained by mechanical milling,and the amorphisation degree of the alloy visibly increases with increased milling time.Electrochemical measurements indicate that the discharge capacity of the alloys first increases and then decreases with increasing Y content and milling time.The substitution of Y for Mg dramatically ameliorates the cycle stability of the as-milled alloys,and the mechanical milling more or less impairs the cycle stability of the alloys.Furthermore,the high rate discharge ability,electrochemical impedance spectrum,Tafel polarisation curves and potential step measurements indicate that the electrochemical kinetic properties of the as-milled alloys first increase and then decrease with increasing Y content and milling time.     

Characterization of aluminized layer formation during annealing of Ti coated with an Al film

During annealing of the Ti surface coated by the Al film, different aluminide phases were formed as the result of reactions between Ti and Al. The structural formation of aluminide phases and the microstructure formed after annealing treatment depended on the thickness of the initial Al film. After annealing treatment up to 900 °C, the microstructure of the overlayer clearly showed contours of grain boundaries of the initial Ti substrate. The shapes, sizes and distribution of the particles in the overlayer depended on the microstructure of the initial Ti substrate as well. The microstructure of the initial Ti substrate had a great effect on the transformation kinetics. Retardation of the reaction was observed on the substrate with lamellar structure. After the elimination of the overlayer, a fine plate structure was formed. The change of the phase compositions of the overlayer led to change in the microhardness. The peak value of the microhardness was observed with the lamellar like morphology of overlayer.     

桥壳钢边部裂纹缺陷原因分析

桥壳钢边部出现线状裂纹缺陷,钢板开裂发生在距离边部 20mm范围之内。通过金相显微检验对裂纹产生的原因进行分析,检验结果表明：钢板传动侧与操作侧边部表层均观察到厚度约 150μm的贝氏体组织,钢板板宽方向的其他部位表层组织与试样正常组织相同,均为铁素体＋珠光体。由此可知,钢板边部冷速过快导致贝氏体组织出现,贝氏体塑性较铁素体＋珠光体差,在钢板卷取过程中导致开裂的发生。     

Relationships between the microstructure and properties of thermally sprayed deposits

Thermally sprayed deposits have layered structure composed of individual splats. The individual splats have quenching microstructure of quasi-stable preferred fine grains. However, this fine-grained microstructure of the deposits is usually not reflected by improved performance of the deposits because a layered structure with two-dimensional voids occurs between lamellar interfaces. The microstructure of the thermal spray deposits with the emphasis on the layer structural parameters is reviewed. Conventionally, one of the most common quantitative parameters used to characterize the microstructure of the thermally sprayed deposits is the porosity, measured by different methods. However, it is illustrated that the relationships between properties and porosity for bulk porous materials processed by conventional processes cannot be applied to thermally sprayed deposits owing to the two-dimensional characteristics of voids. The total porosity in the deposits is not meaningful from the viewpoint of prediction of the deposit properties. An idealized structural model and related parameters, instead of porosity, are proposed to characterize quantitatively the microstructure of the thermally sprayed deposit. The relationships between the properties and the structural parameters are presented for the plasma-sprayed ceramic deposits based on the proposed microstructure model. The properties include the Young’s modulus, fracture toughness, erosion resistance, and thermal conductivity of the plasma sprayed ceramic deposits. The correlations of theoretical relationships with reported experimental data are discussed. An agreement of theoretical with observed values suggests that the lamellar structure of the deposit with limited interface bonding is the dominant factor controlling the performance of the deposit. An erratum to this article is available at .     

壳聚糖载体对药物鼻腔吸收的促进作用

目的:研究伊文思蓝鼻腔给药壳聚糖载体的促吸收作用及其对鼻腔黏膜的毒性。方法:小鼠鼻腔给伊文思蓝的壳聚糖溶液后, 采用荧光显微镜观察脑部伊文思蓝的分布;紫外法测定小鼠脑部其含量;通过鼻腔黏膜切片考察壳聚糖对大鼠鼻腔黏膜毒性。结果:壳聚糖对伊文思蓝经鼻吸收入脑具有促进作用, 伊文思蓝在脑前、中、后部均有分布;壳聚糖载体对大鼠鼻黏膜毒性较小。结论:壳聚糖是水溶性药物经鼻吸收入脑的优良载体。