无引线镀金表面贴装器件搪锡技术

针对无引线镀金表面贴装器件(如CLCC等封装类型器件)的手工智能焊台搪锡技术、手工锡锅搪锡技术、返修工作站搪锡技术进行了介绍和讨论,并比较了三种搪锡技术的性能特点,给出了适合无引线镀金表面贴装器件搪锡的最佳方案。     

脉冲等离子体源控制航天器表面充电电位的研究

在空间环境运行的航天器存在表面充电现象,而航天器表面充电引发的静电放电是导致航天器异常及故障的重要原因之一。因此,在航天器设计和应用中,必须对航天器表面电位采取必要的控制和防护措施。文章介绍了用脉冲等离子体源进行航天器表面充电电位主动控制的研究。通过模拟实验和实验数据分析,证实了用脉冲等离子体源能有效地控制航天器表面充...     

Sliding mode control of reaction flywheel-based brushless DC motor with buck converter

Reaction flywheel is a significant actuator for satellites’ attitude control. To improve output torque and rotational speed accuracy for reaction flywheel, this paper reviews the modeling and control approaches of DC-DC converters and presents an application of the variable structure system theory with associated sliding regimes. Firstly, the topology of reaction flywheel is constructed. The small signal linearization process for a buck converter is illustrated. Then, based on the state averaging models and reaching qualification expressed by the Lee derivative, the general results of the sliding mode control (SMC) are analyzed. The analytical equivalent control laws for reaction flywheel are deduced detailedly by selecting various sliding surfaces at electromotion, energy consumption braking, reverse connection braking stages. Finally, numerical and experimental examples are presented for illustrative purposes. The results demonstrate that favorable agreement is established between the simulations and experiments. The proposed control strategy achieves preferable rotational speed regulation, strong rejection of modest disturbances, and high-precision output torque and rotational speed tracking abilities.     

Evaluating the feasibility of GPS measurements of SSH on board a ship along the Portuguese West Coast

Aiming to validate coastal altimetry data, an exploratory experiment was carried out, using a survey ship with onboard GPS and motion compensation systems. The ship navigation plan followed a track as coincident as possible with the passage of two altimetry satellites, Envisat and Jason-1, along the Portuguese coast, in June 2007.     

Reconfigurable Flight Control Design for Combat Flying Wing with Multiple Control Surfaces

With control using redundant multiple control surface arrangement and large-deflection drag rudders,a combat flying wing has a higher probability for control surface failures.Therefore,its flight control system must be able to reconfigure after such failures.Considering three types of typical control surface failures(lock-in-place(LIP),loss-of-effectiveness(LOE) and float),flight control reconfiguration characteristic and capability of such aircraft types are analyzed.Because of the control surface redundancy,the aircraft using the dynamic inversion flight control law already has a control allocation block.In this paper,its flight control configuration during the above failures is achieved by modifying this block.It is shown that such a reconfigurable flight control design is valid,through numerical simulations of flight attitude control task.Results indicate that,in the circumstances of control surface failures with limited degree and the degradation of the flying quality level,a combat flying wing adopting this flight control reconfiguration approach based on control allocation could guarantee its flight safety and perform some flight combat missions.     

光线追踪求交算法的研究及其实现

本文对光线追踪求交算法进行了深入讨论。文中结合形体设计实例说明了此算法的正确性和实用性。     

Performance of a small and low-cost chamber to simulate lunar surface environment

The performance of a small and low-cost metal chamber built to simulate the pressure and temperature conditions of lunar surface was assessed and the results are presented. This chamber is intended for studying the physical properties of lunar surface and subsurface (using soil simulants) and also to validate the technology readiness of certain newly developed payloads planned for future lunar surface missions (Lander/Rover). It is possible to reach down to ∼10⁻⁷ Pa under specific conditions and maintain the temperature of the sample under investigation to lunar day and night temperatures. The designed system has been subjected to various tests to evaluate its performance and suitability for carrying out experiments in a simulated lunar environment.     

CMM曲线曲面测量领域的关键问题

分析了三坐标测量机曲线曲面测量领域涉及到的测量路径的生成、测球半径的补偿和曲线曲面数学模型的建立等几个关键问题和技术．阐述了ＣＭＭ测量路径的生成方法和设计原则，分析了计算曲线曲面法失的常用方法以及给出了基于样条理论曲面拟合建模的一般数学模型．     

纳米硅薄膜的氧化特性

将ｎｃ－Ｓｉ：Ｈ薄膜进行等离子和高温氧化处理，测量了样品的氢，氧含量，Ｒａｍａｎ谱，红外吸收谱，光致发光（ＰＬ），结果表明两种氧化方式都将氧掺入薄膜中，但不同处理方式氧在薄膜中的键合形式不同Ｒａｍａｎ谱表明氧化处理对薄膜中晶粒大小及晶态比没有影响，用晶粒－表面模型对氧化引起的光致发光（ＰＬ）蓝移进行了解释。     

内埋电阻丝阵列检测复合材料表面裂伤初探

探讨了用层间埋置Ｎｉ－Ｃｒ合金丝构成局部网络实现对复合材料表面损伤位置和损伤程度检测。对表面裂纹尖端附近的应力场分布进行了分析，并将试验结果与预测结果进行了比较。实验结果表明：Ｎｉ－Ｃｒ合金丝阵列可以在玻纤／环氧树脂复合材料中用作传感元件，合金丝阵列所反映的裂端附近应力场分布是合理的。