数字前馈跟踪控制器的频域迭代设计方法

 数字前馈控制器用于提高伺服系统跟踪性能,在工程应用中通常包含如下设计环节：闭环对象参数辨识、闭环离散化和设计前馈控制器,上述各环节都会引入设计误差,最终导致所设计的前馈控制器跟踪性能变差.针对上述问题,利用闭环对象的实测频率特性数据,提出一种新型的频域迭代设计方法,能有效消除各环节误差.通过对设计过程的频率特性差值的变化分析,给出了迭代算法的步骤.该方法将反馈控制思想引入前馈控制器设计过程,根据频率特性差值,不断修正对象频率特性数据,通过设计过程的迭代,使跟踪误差显著减小.以某飞行转台伺服系统为例,进行数值仿真和应用研究,结果表明了该方法的有效性,能显著拓宽伺服系统的跟踪频带,减小对低频信号的跟踪误差．     

低频振动切削的实验研究及机理分析

为了深入揭示振动切削中切削裂纹萌生和成屑机理，建立并调试了低频振动切削实验系统；采用计算机控制的压电陶瓷为驱动元件的微驱动刀架，作为振动源，用SDC系列测力仪对切削力进行测量，由反馈信号测量系统得到真实刀尖的运动参数，便于修正理论给定参数值；进行相同刀具几何参数条件下的低频振动切削实验和普通切削实验，得出不同振动频率、不同切削速度对切削过程和结果（切削力、已加工工件表面）的影响，并与相同切削用量条件下普通切削实验相比较。     

评定直线度误差的最小二乘法与 最小包容区域法精度之比较

介绍了直线度误差评定的最小二乘法和最小包容区域法的算法模型与实现方法。在三坐标测量机上对八种不同被测直线进行了采样点坐标数据提取,分别用最小二乘法和最小包容区域法的基于搜索逼近-逐次旋转逼近法进行了给定平面内直线度误差的评定。结果表明:最小二乘法的评定结果与最小包容区域法的基于搜索逼近-逐次旋转逼近法的评定结果完全一致,即直线度误差的最小二乘法评定结果符合最小条件。     

Improvement of performance of dye-sensitized solar cells based on electrodeposited-platinum counter electrode

Platinum nanoparticle was electrodeposited on FTO conducting glass substrate as counter electrode for application in dye-sensitized solar cells (DSSCs). Images of transmission electron microscope (TEM) and Scanning Electron Microscope (SEM) showed that platinum nanoparticle was with the mean size of 20-30 nm and was homogeneously distributed on the surface of the FTO conductive glass sheet. Using such a counter electrode, DSSC showed a 6.40% overall energy conversion efficiency under one sun illumination. It exhibited the same high-performance as the DSSC with a platinum counter electrode prepared by electroplating. Furthermore, the present preparation method for the platinum counter electrode has the advantage of low platinum loading and transparence.     

分段沉积/雕铣成型的工艺规划

分段沉积/雕铣成型技术是快速原形结合传统加工方法的一种新的工艺,兼有快速原形的高柔性和传统加工的高精度。本文就分段沉积/雕铣成型技术中零件的分段、薄壁件的加工、尖角的加工、曲面的加工等一些特殊工艺进行合理的工艺规划,提出解决措施。     

L-脯氨酸/吡啶催化合成对甲氧基肉桂酸

以L-脯氨酸/吡啶为催化剂,茴香醛和丙二酸为原料,经Knoevenagel 缩合反应合成了对甲氧基肉桂酸.考察了带水剂种类、原料摩尔比、催化剂L-脯氨酸和吡啶用量、反应时间等对对甲氧基肉桂酸收率的影响.结果表明,在以正己烷为带水剂(用量50 mL),茴香醛用量5 mL(0.041 5 mol),丙二酸与茴香醛摩尔比1.2∶1,L-脯氨酸用量(以丙二酸质量计)4.0%,吡啶用量5 mL,反应时间3 h的条件下,对甲氧基肉桂酸重结晶收率达90.0%.     

Preparation and characterization of organic-inorganic poly(ethylene glycol)/WS2 nanocomposite

Layered nanocomposite PEG/WS₂, intercalating oligomeric poly(ethylene glycol) (PEG6000) into the tungsten disulfide host galleries, was synthesized using the exfoliation-adsorption technique. X-ray diffraction revealed that the intercalated oligomer within the host galleries is in a double-layer arrangement with an interlayer expansion of about 8.8 Å. The optimum conditions were explored to prepare the single-phase product with a composition of Li_0.12(PEG)_1.51WS₂. Thermal analyses suggested that the resulting material shows good thermal stability, with the decomposition of the interacted oligomeric chains within the disulfide galleries occurring at around 258 °C. Despite high conductivity of the host material, those of the PEG/WS₂ nanocomposite were found to be high in the order of 1 × 10⁻² S cm⁻¹ at ambient temperature, resulted from the host guest-host charge transfers.     

火灾早期过程特征的红外光谱探测和诊断

提出用CO作为早期火灾探测的观察对象,利用红外光谱法进行气体探测,并在此基础上建立了基于FTIR的试验系统.通过该方法成功获得CO的浓度值.并用时间序列分析方法建立二阶自回归模型,提取出特征参数进行分析,能在较短时间内将真假火灾区分开来.     

Zr-intercalated molybdenum disulfide: preparation, characterization and catalytic activity in nitrobenzene hydrogenation

Layered composites, Zr-intercalated MoS₂, have been prepared utilizing the exfoliation and restacking properties of Li _x MoS₂ under mild conditions and characterized by X-ray powder diffraction, differential scanning calorimetry and BET surface measurements. It showed the formation of two distinct products depending on the employed Zr:MoS₂ reaction stoichiometry. The interlayer expansions of about 4.4 Å and 9.2 Å suggested mono- or bi-layer arrangements of the hydroxyl–Zr oligocations into the interlayer galleries between the MoS₂ host layers. The composites exhibit good catalytic activities in the hydrogenation of nitrobenzene into aniline, due to their intercalated structures and great specific surface areas.     

Piezoresistive Behavior Study on Finger‐Sensing Silicone Rubber/Graphite Nanosheet Nanocomposites

A novel finger‐sensing nanocomposite with remarkable and reversible piezoresistivity is successfully fabricated by dispersing homogeneously conductive graphite nanosheets (GNs) in a silicone rubber (SR) matrix. Because of the high aspect ratio of the graphite nanosheets, the nanocomposite displays a very low percolation threshold. The SR/GN nanocomposite with a volume fraction of conductive nanosheets closest to that for the percolation threshold presents a sharp positive‐pressure coefficient effect of the resistivity under very low pressure, namely, in the finger‐pressure range (0.3–0.7 MPa), whereby the abrupt transition could be attributed to compressive‐stress‐induced deformation of the conducting network. The super‐sensitive piezoresistive behavior of the nanocomposite is accounted for by an extension of the tunneling conduction theory which provides a good approximation to the piezoresistive effect.