飞行器作动系统驱动能源对比分析

随着电气技术的发展,飞行器作动领域用电能取代液压能的呼声越来越高.笔者对全电飞机和多电飞机进行了简单的介绍,从体积、重量、功率、散热、控制管理等方面对电力作动和液压作动技术进行了对比分析,给出了分析结论和机载液压系统发展的一些建议.     

Modeling of nanoscale friction using molecular dynamics simulation

利用分子动力学方法模拟了刚性金刚石压头在Ni单晶体上的滑动过程, 讨论了压入深度对 摩擦力的影响(压入深度对滑动过程中压头下方的微结构演化(能否发射位错环)有很大影响). 结 合摩擦过程中的塑性行为和能量耗散机制, 解释了产生摩擦力锯齿形曲线的原因, 证实了位错的形 核及湮灭是黏--滑机制的原因之一. 不同滑动速度对摩擦力影响的模拟表明, 压头的滑动速度决定 了压头下方位错环的运动和演化形式: 在高速滑动下, 形成的位错环依次沿着滑移面很快向Ni单晶 基体内扩展; 在低速滑动下, 压头下方产生的位错环互相发生作用, 在材料的亚表面形成较低能量的 大位错环, 由此产生的塑性变形主要集中在材料的亚表面.     

大口径光学元件斜入射反射波前误差测量和计算

针对测量高功率激光驱动装置中大口径矩形反射光学元件的波前误差时测量角度和使用角度不完全相同引入的测量误差,提出了将测量角度下的反射波前转换到使用角度的反射波前的换算及恢复方法。首先分析了将斜入射测量角度下的波前转换到使用角度下波前的余弦换算方法,得到了实际测量角度与实际使用角度下的波前误差计算关系;然后计算并分析了双三次插值算法本身引起的中频PSD1(功率谱密度)误差,指出在满足有效口径测量的情况下,选择的入射角度应该与实际使用的角度尽可能的相接近。最后,基于410mm×410mm的熔石英反射镜开展了误差分析和实验验证。利用该方法将0°反射波前换算到45°反射波前,并将得到的测试结果与45°直接测量得到的测试结果进行了比较。结果显示上述结果的PV值相差0.01λ,RMS值相差0.003λ,PSD1值相差0.08nm;表明该换算方法不仅能够准确计算出使用角度下反射波前的低频误差,而且能获得相对准确的中频段PSD1误差。     

轮腿式复合机器人设计及运动实现

通过机械结构和控制系统设计,研制了轮式和腿式独立运动的轮腿式复合机器人。应用PWM对机器人的关节控制进行了研究。分析了其腿式运动、轮式运动和轮腿变形的过程,并进行了实验验证。结果表明,研制的机器人具有结构简单、易于控制的特点,解决了现有轮腿式机器人运动时与地面摩擦力不够的问题,具有很好的应用前景。     

三视场红外地球敏感器导航算法数值分析及实验研究

红外地球敏感器广泛运用空间飞行器,尤其是在地球轨道附近。目前最新的静态地球敏感器使用焦平面探测器来覆盖整个地球红外辐射圆。若面向飞行在70km-100km处的临近空间飞行器,他们就需要有很大的视场(>120°)且相对分辨率很低。本文针对临近空间飞行器的天文导航运用,采用线阵CCD作为探测器,设计了一个三视场红外地球敏感器。他们按照二维角度均匀分布以确保每个光学头能够均匀的指向地球红外辐射圆上。每个CCD覆盖20°以便能够精确地分辨地球辐射和空间的边界点。综合考虑地球辐射模型和地球扁率等因素,利用地球敏感器观测的向量可以获得地心矢量和飞行高度。以70-100km飞行高度为示例,建立相应的数学模型,同时提出了相应的姿态和高度确定算法并进行了仿真。综上述分析,研制了一套三视场地球敏感器原理样机并进行相关测试。仿真和实验结果表明：高度测量精度优于200m,姿态测量精度优于0.002°。     

硫化机网络群控系统

对硫化机群采用分散控制-集中管理式中央监控系统.系统分底层网络和上层网络两部分.底层网络分二级控制,采集现场硫化机温度、压力等参数.上层网络用于对生产数据进行处理显示、打印报表等.各层控制系统实现相对独立,该系统运行多年,未发生异常现象.     

Processing and Thermal Conductivity of Sintered Reaction-Bonded Silicon Nitride. I: Effect of Si Powder Characteristics

This paper will present sintered reaction-bonded silicon nitride (SRBSN) material with a high thermal conductivity of 121 W·(m·K)⁻¹, which has been successfully prepared from a coarse Si powder with lower levels of oxygen and aluminum impurities, using a mixture of Y₂O₃ and MgSiN₂ as sintering additives, by nitriding at 1400°C for 8 h and subsequent post-sintering at 1900°C for 12 h at a nitrogen pressure of 1 MPa N₂. This thermal conductivity value is higher than that of the materials prepared from high-purity α-Si₃N₄ powder (UBE SN-E10) with the same additive composition under the same sintering conditions. In order to study the effects of Si powder characteristics on the processing, microstructure, and thermal conductivity of SRBSN, the other type of fine powder with higher native oxygen and metallic impurity (typically Al and Fe) contents was also used. The effects of Si particle size, native oxygen, and metallic impurities on the nitriding process, post-sintering process, and thermal conductivity of the resultant SRBSN materials were discussed in detail. This work demonstrates that the improvement in thermal conductivity of SRBSN could be achieved by using higher purity coarse Si powder with lower levels of oxygen and aluminum impurities. In addition, this work also shows that the nitriding temperature has no significant effect on the microstructure and thermal conductivity of SRBSN during post-sintering, although it does affect the characteristics of RBSN formed during nitridation.     

Effect of solution properties on nanofibrous structure of electrospun poly(lactic‐co‐glycolic acid)

Electrospinning of poly(lactic‐co‐glycolic acid) (PLGA) in chloroform or 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) was investigated, focusing on its solution parameters, to develop nonwoven biodegradable nanofibrous structures for tissue engineering. PLGA nanofibers were obtained by electrospinning of 15 wt % PLGA solution and the resulting average fiber diameters were varied with the range of 270–760 nm, depending on solution property. When small amounts of benzyl triethylammonium chloride (BTEAC) was added to the PLGA/chloroform solution, the average diameter was decreased from 760 to 450 nm and the fibers were densely amounted in a straight shape. In addition, the average fiber diameter (270 nm) of nanofibers electrospun from polar HFIP solvent was much smaller than that (760 nm) of nanofibers electrospun from nonpolar chloroform solvent. Therefore, it could be concluded that conductivity or dielectric constant of the PLGA solution was a major parameter affecting the morphology and diameter of the electrospun PLGA fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1214–1221, 2006     

Polyimide foams with ultralow dielectric constants

To explore ultralow dielectric constant polyimide, the crosslinked polyimide foams (PIFs) were prepared from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA), and 2,4,6‐triaminopyrimidine (TAP) via a poly(ester–amine salt) (PEAS) process. FTIR measurements indicated that TAP did not yield a negative effect on imidization of PEAS precursors. SEM measurement revealed the homogeneous cell structure. Through using TAP as a crosslinking monomer, the mechanical properties of PIFs could be improved in comparison with uncrosslinked BTDA/ODA based PIF. The crosslinked PIFs still exhibited excellent thermal stability with 5% weight loss temperatures higher than 520°C. In the field with frequency higher than 100 Hz, the dielectric constants of the obtained PIFs ranged from 1.77 to 2.4, and the dielectric losses were smaller than 3 × 10^?2 at 25–150°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1734–1740, 2006