Transparency analysis and delay compensation scheme for haptic-based networked virtual environments

Haptic-based NVEs (networked virtual environments) with CS (client/server) communication architectures support better consistency but induce larger end-to-end delays than those with P2P (peer-to-peer) communication architectures. Unfortunately, large delay severely deteriorates the transparency (i.e., reality) of haptic interaction. To improve the haptic interaction quality for haptic-based NVEs with CS communication architectures, in this paper the degradation of haptic interaction quality is analyzed according to network delays. Based on the analysis, the maximum allowable delay bound is predicted and unrealistic force feedback caused by the network delay is compensated. Experimental results confirm that the proposed analysis provides an acceptable quantification method about haptic interaction quality and that the proposed delay-compensation scheme effectively improves haptic interaction quality with respect to network delays.     

Application of an intelligent classification method to mechanical fault diagnosis

A new method for intelligent fault diagnosis of rotating machinery based on wavelet packet transform (WPT), empirical mode decomposition (EMD), dimensionless parameters, a distance evaluation technique and radial basis function (RBF) network is proposed in this paper. In this method, WPT and EMD are, respectively, used to preprocess vibration signals to mine fault characteristic information more accurately. Then, dimensionless parameters in time domain are extracted from each of the original vibration signals and preprocessed signals to form a combined feature set. Moreover, the distance evaluation technique is utilised to calculate evaluation factors of the combined feature set. Finally, according to the evaluation factors, the corresponding sensitive features are selected and input into the RBF network to automatically identify different machine operation conditions. An experiment of rolling element bearings is carried out to test the performance of the proposed method. The experimental result demonstrates that the method combining WPT, EMD, the distance evaluation technique and the RBF network may accurately extract fault information and select sensitive features, and therefore it may correctly diagnose the different fault categories occurring in the bearings. Furthermore, this method is applied to slight rub fault diagnosis of a heavy oil catalytic cracking unit, the actual result shows the method may be applied to fault diagnosis of rotating machinery effectively.     

Smooth Switching Output Tracking Control for LPV Systems

This paper is concerned with the problem of smooth switching state feedback controller design for aircraft dynamic systems with multiple operating points. Based on the theory of robust control, a single state feedback controller which considers smooth switching is constructed. With the constant controller, the output response can be considerably improved in the switching process when the flight condition changes. An example for autopilot design of an F‐18 aircraft is given to illustrate the effectiveness of the proposed approach.     

小卫星共轨式轨道转移策略

针对小卫星与共轨目标星之间的交会问题,设计制导策略使小卫星在预期时间内与目标星相遇。利用均匀中心引力场模型,推导了一个关于两星相对运动状态和转移时间的二次方程,求解该方程能够得到固定燃料转移问题的最优推力时间和推力方向的解析解。在自由滑行段采用Lambert变轨算法代替解析算法,提出了一种改进制导算法。应用该改进制导算法进行大量仿真实验,并利用STK仿真软件对仿真结果进行验证,表明本文算法是有效的。     

Application of the sun line-of-sight vector in the optimal attitude estimation of deep-space probe

This paper proposed an optimal algorithm using the sun line-of-sight vector to improve the probe attitude estimation accuracy in deep-space mission.Firstly,the elaborate analysis of the attitude estimation error from vector observations was done to demonstrate that the geometric relation between the reference vectors is an important factor which influences the accuracy of attitude estimation.Then,with introduction of the sun line-of-sight vector,the attitude quaternion obtained from the star-sensor was converted into a pair of mutually perpendicular reference vectors perpendicular to the sun vector.The normalized weights were calculated according to the accuracy of the sensors.Furthermore,the optimal attitude estimation in the least squares sense was achieved with the quaternion estimation method.Finally,the results of simulation demonstrated the validity of the proposed optimal algorithm based on the practical data of the Deep Impact mission.     

工艺参数对2195铝锂合金搅拌摩擦焊接头力学性能的影响

文中采用不同搅拌摩擦焊工艺对2195铝锂合金的可焊性进行了研究.结果表明,接头抗拉强度随旋转频率的提高先增后减,随焊接速度的提高先增后减.当旋转频率为600 r/min、焊接速度为200 mm/min时,接头抗拉强度最高,为432.8 MPa,是母材强度的77.3%.接头区域的硬度低于母材.热影响区内临近HAZ/TMAZ界面的区域是整个接头中软化程度最大的区域.根据热输入的变化,断裂方式可以分为两种:模式1:断裂发生在热影响区,呈现塑性断裂特征,断口特征为等轴韧窝;模式2:断裂发生在焊核区,断裂方式为韧-脆混合型断裂.     

MT300/KH420碳纤维/聚酰亚胺树脂复合材料层合圆柱壳高温承载性能

基于Donnell-Mushtali近似理论及热弹性理论,考虑结构热变形和材料高温性能衰减等温度影响因素,对MT300/KH420碳纤维/聚酰亚胺树脂复合材料圆柱壳在常温、420℃及周向210~420℃不均匀温度场等热载工况下的承载性能进行了理论分析。并引入一阶屈曲模态缺陷作为几何初始扰动,利用ABAQUS,采用非线性显式动力学方法完成对MT300/KH420复合材料圆柱壳在以上热载工况下的轴压稳定性有限元仿真计算,计算结果与理论分析较为一致。设计并开展MT300/KH420复合材料圆柱壳力-热载荷联合轴压试验,获得圆柱壳在以上热载工况下的破坏载荷和破坏模式。研究表明:高温工况下,力学性能衰减和温场不均匀引起的结构热变形是影响MT300/KH420复合材料圆柱壳轴向失稳载荷的主要因素。      

重型运载火箭及其应用探讨

提出中国重型运载火箭发展原则,根据这些原则,进行重型运载火箭构型分析,初步确定了火箭的直径以及发动机的推力量级,形成了基于大推力液氧煤油发动机和基于大推力固体助推器的两种重型运载火箭总体技术方案,并对重型运载火箭的关键技术进行了梳理.结合重型运载火箭的特点对未来的潜在应用需求进行了分析,结果表明重型运载火箭对于提升中国...     

车载导弹光学辅助数学传递对准方法

从发射准备时间和对准精度等方面分析现代战争环境下车载导弹对初始对准的要求,提出利用自准直仪进行光学辅助数学传递对准的方法。给出光学辅助数学传递对准系统搭建方案,推导主、子惯导方位光学传递关系,将光学准直得到的相对方位测量角引入到“角速度+加速度”匹配模式中构成新的量测方程,对主、子惯导安装角进行滤波估计。在实验室条件下对方位光学传递算法的正确性和精度进行了验证,并对光学辅助数学传递对准方法进行了数学仿真分析,仿真结果表明,该方法具有较快的对准速度和较高的对准精度,能够满足现代车载导弹快速高精度初始对准的要求。     

An interaction controller formulation to systematically avoid force overshoots through impedance shaping method with compliant robot base

Nowadays, light-weight manipulators are widely adopted in many applications requiring manipulation/interaction with compliant/fragile objects. Reduced inertia and controlled compliance, indeed, make such manipulators particularly attractive when compliant mountings (or mobile platforms) are adopted and contact force overshoot may compromise the application. The here presented work proposes the design of a force-tracking controller for interaction tasks allowing to systematically avoid any force overshoot for lightweight robots mounted on compliant bases. The developed algorithm allows to compensate for the compliant robot base dynamics that affects the interaction. The control gains are calculated to track a target force reference through the estimation of the robot base state and the interacting environment stiffness. Closed-loop stability and control gains calculation are described. The control law has been validated in a probing task involving a compliant robot base and a compliant environment to show the obtained performance.