飞摄陌生故土

四川，我是再熟悉不过了，因为它是我的家乡，但当我们飞凌高空，它变得陌生了，不再是平时我的脚所熟悉的土地了。     

An inertial parameter identification method of eliminating system damping effect for a six-degree-of-freedom parallel manipulator

A new simple and effective inertial parameter identification method based on sinusoidal vibrations of a six-degree-of-freedom parallel manipulator is proposed. Compared with previously known identification algorithms, the advantages of the new approach are there is no need to design the excitation trajectory to consider the condition number of the observation matrix and the inertial matrix can be accurately defined regardless of the effect of viscous friction. In addition, the use of a sinusoidal exciting trajectory allows calculation of the velocities and accelerations from the measured position response. Simulations show that the new approach has acceptable tolerance of dry friction when using a simple coupling parameter modified formula. The experimental application to the hydraulically driven Stewart platform demonstrates the capability and efficiency of the proposed identification method.     

一种QFN封装器件焊接故障分析

结合工程实践,介绍了QFN封装器件的优点和结构特点,从印制电路板裸板制板工艺、装联工艺两方面分析了一种QFN器件产生故障的原因,并给出了解决办法。通过改变制板工艺、改进网板设计等手段,有效解决连焊等问题并增强元器件的装联可靠性。介绍了其返修过程中应注意的工艺问题,并给出了QFN器件的可靠装联工艺。     

网带炉温度及运行时间的测量方法

介绍网带炉在静态不充气、充气及动态充气等状态下，温场的测量方法；并就冷态空载、负载运行时间及加热空载、负载运行时间的测量进行了讨论和分析。     

宇航用瓷介电容表面处理工艺优化研究与实践

系统研究了宇航用瓷介电容表面处理工艺存在的问题,分析了工艺影响因素及机理,并由此开展了工艺优化路线研究,从四个方面进行了优化实践,实现了宇航工艺控制目标。对今后开展宇航产品工艺优化研究及过程控制体系完善,具有参考意义。     

Optimal acknowledgment frequency over asymmetric space-internet links

The acknowledgement (ACK) strategy of transmission control protocol (TCP) has been modified to delay the ACKs for a configurable period of time that is related to the round-trip time (RTT) to improve its performance in asymmetric links such as space communications. A general relationship between the asymmetric channel ratio and the optimal ACK frequency to achieve maximum throughput is not available. This paper studies the optimal ACK frequency with respect to the channel RTT to achieve the maximum throughput over various asymmetric, geo-stationary earth orbit (GEO)-satellite links using a test-bed. It is found that when the asymmetric channel ratio is as high as about 100/1, the optimal ACK frequency must be increased with an increase in asymmetric ratio to complement the impact of the reduction of ACK channel rate. As a rule of thumb, every two-fold increase in asymmetric ratio requires the optimal ACK frequency to be increased by one ACK per RTT. A regression model was built to reflect the relationship between the optimal ACK frequency and the asymmetric channel ratio and has been validated     

真空实验舱数字式压力控制系统设计与验证

针对脉冲等离子体推力器测试所需的容积大于60m3的大型真空实验舱对气压控制的要求,设计了数字式压力控制系统.该控制系统采用旋片泵组和罗茨泵构成两级串联的组合抽气方式对实验舱进行抽真空,具有较高的效率.基于双曲正切函数构建了变增益函数,从而实现对不同压力范围的变增益比例、积分和微分(PID)调节.试验结果表明,这一数字式...     

Calibration of robotic drilling systems with a moving rail

Industrial robots are widely used in aircraft assembly systems such as robotic drilling systems. It is necessary to expand a robot＇s working range with a moving rail. A method for improving the position accuracy of an automated assembly system with an industrial robot mounted on a moving rail is proposed. A multi-station method is used to control the robot in this study. The robot only works at stations which are certain positions defined on the moving rail. The calibration of the robot system is composed by the calibration of the robot and the calibration of the stations.The calibration of the robot is based on error similarity and inverse distance weighted interpolation.The calibration of the stations is based on a magnetic strip and a magnetic sensor. Validation tests were performed in this study, which showed that the accuracy of the robot system gained significant improvement using the proposed method. The absolute position errors were reduced by about 85%to less than 0.3 mm compared with the maximum nearly 2 mm before calibration.     

飞机在尾旋中侧滑和坡度的分析

分析了在飞机在尾旋中产生侧滑和坡度的根本原因，论述了侧滑和坡度在尾中的变化的规律，影响侧滑和坡度的因素，以及侧滑和坡度变化对尾旋动态的影响，同时就尾旋中偏滚对尾旋侧滑的影响，绕铅垂旋轴对坡度的影响等进行了讨论分析，最后通过分析ＪＪ６飞机和ＪＪ５飞机尾旋的测试曲线，进一步说明了ωｘ和ωｙ对坡度的影响，可为飞行员掌握尾旋特性，提高飞行技术和保证飞行安全提供参考。