基于压电陶瓷动态信息的结构裂纹识别方法

利用压电陶瓷的动态特性和压电系统的动态信息,对铝梁的裂纹损伤进行了分析研究。随着梁裂纹尺寸的增加,压电陶瓷片的导钠幅值下降,且系统固有频率减小。利用导钠幅值的变化和系统的动态信息,可以对裂纹的位置和尺寸大小进行识别。实验证明该方法的有效性。     

劈刀和肋环夹持工况对超声键合换能系统电学特性的影响

通过实验分析了肋环夹持松紧度和劈刀存在两个因素对超声键合换能系统电学导纳特性的影响规律。对换能系统在悬挂有无劈刀和夹持8个松紧度等各个情况下进行谐振频率附近的导纳圆测量,确定换能系统等效电路各特征参数的变化情况。由实验结果的分析可知,劈刀的附加质量以及肋环松紧程度对换能系统谐振频率的影响不大,但劈刀的存在改变了换能系统的能量分布和耗散,是影响换能系统各特征参量的主要因素之一。这些结论有助于超声键合换能系统的优化。     

Safe and intuitive manual guidance of a robot manipulator using adaptive admittance control towards robot agility

Key areas of robot agility include methods that increase capability and flexibility of industrial robots and facilitate robot re-tasking. Manual guidance can achieve robot agility effectively, provided that a safe and smooth interaction is guaranteed when the user exerts an external force on the end effector. We approach this by designing an adaptive admittance law that can adjust its parameters to modify the robot compliance in critical areas of the workspace, such as near and on configuration singularities, joint limits, and workspace limits, for a smooth and safe operation. Experimental validation was done with two tests: a constraint activation test and a 3D shape tracing task. In the first one, we validate the proper response to constraints and in the second one, we compare the proposed approach with different admittance parameter tuning strategies using a drawing task where the user is asked to guide the robot to trace a 3D profile with an accuracy or speed directive and evaluate performance considering path length error and execution time as metrics, and a questionnaire for user perception. Results show that appropriate response to individual and simultaneous activation of the aforementioned constraints for a safe and intuitive manual guidance interaction is achieved and that the proposed parameter tuning strategy has better performance in terms of accuracy, execution time, and subjective evaluation of users.     

负荷模型对电力系统混合仿真误差的影响

电力系统仿真的准确度直接关系到系统的安全经济运行,其中负荷模型对仿真结果有显著的影响。大型电力系统仿真软件PSS/E所具有的高度模块化的结构,以及其模型库中所提供的丰富的设备模型,特别是其自带的二次开发语言IPLAN使得它能够完成各种各样的仿真任务。基于PSS/E,用接地时变导纳的动态等值方法对系统进行混合仿真,即注入实测数据代替某部分电网,发现采用不同的负荷模型对混合仿真误差有很大的影响,最后分析了原因。     

均质土中部分埋入粘弹性桩的瞬态波动响应

基于回传射线矩阵法,得到均质土中部分埋入粘弹性桩在单位脉冲作用下的桩顶速度导纳,然后利用Fourier逆变换和卷积定理得到了在瞬态半正弦激振力作用下的桩顶速度时域响应,与全埋入粘弹性桩作对比,分析桩身材料阻尼、外露桩长、桩侧土阻尼和刚度及桩底土阻尼和刚度对桩顶速度导纳和反射波的影响.结果表明:桩材料阻尼、外露桩长、桩侧土阻尼和桩底土阻尼对桩顶频域及时域速度响应有显著影响;桩侧土刚度和桩底土刚度只对速度导纳曲线的低频部分有影响,且桩底土刚度对导纳曲线的相位和反射波的形状及幅值有显著的影响.     

Haptic force control based on impedance/admittance control aided by visual feedback

This paper demonstrates a haptic device for interaction with a virtual environment. The force control is added by visual feedback that makes the system more responsive and accurate. There are two popular control methods widely used in haptic controller design. First, is impedance control when user motion input is measured, and then, the reaction force is fed back to the operator. The alternative method is admittance control, when forces exerted by user are measured and motion is fed back to the user. Both, impedance and admittance control are also basic ways for interacting with a virtual environment. In this paper, several experiments were performed to evaluate the suitability of force-impedance control for haptic interface development. The difference between conventional application of impedance control in robot motion control and its application in haptic interface development is investigated. Open loop impedance control methodology is implemented for static case and a general-purpose robot under open loop impedance control was developed as a haptic device, while a closed loop model based impedance control was used for haptic controller design in both static and dynamic case. The factors that could affect to the performance of a haptic interface are also investigated experimentally using parametric studies. Experimental results for 1 DOF rotational motion and 2 DOF planar translational motion systems are presented. The results show that the impedance control aided by visual feedback broaden the applicability of the haptic device and makes the system more responsive and accurate.

正确认知射频导纳液位计

以DREXELBROOK公司的射频导纳液位计为例，从概念、结构、原理和应用几方面对射频导纳液位计进行了一系列剖析，以便使人们了解射频导纳液位计的本质，消除一些错误认识，从而更好地发挥其作用。     

基于零序补偿导纳的小电流接地系统单相故障保护新方法

在深入分析零序导纳选线算法的基础上,提出基于零序补偿导纳的小电流接地系统单相接地保护新方法。该方法有效地利用了电网中的已知参数,通过补偿的实施,将故障线和健全线原本很小的区分裕度进行了有效的放大,以方便整定。结合工程实际的考虑,将电纳误差和补偿导纳角综合为一种小电流接地系统单相故障保护新算法。ATP仿真证明:该方法对线路故障有很好的分辨能力,而且对系统运行方式、故障方式、过渡电阻等因素的变化具有较高的鲁棒性, 在较大程度上提高了选线的正确率。     

Finite–infinite element for dynamic analysis of axisymmetrically saturated composite foundations

The formulations of axisymmetrically infinite elements for dynamic analysis of vertical vibration problems in unbounded saturated composite foundations are presented. The theoretical basis as well as the implementation of the elements is discussed, and the element decay functions are derived using the analytical solutions of axially symmetric configurations. Using the proposed finite–infinite element method, the surface vertical displacements of air‐saturated soil (‘dry’ soil) and of water‐saturated soil with extremely low permeability subjected to a surface point excitation (called as the Lamb's problem) are calculated and the results agree very well with the existing theoretical solutions of single‐phase elastic media. As an application, the velocity admittances of a concrete block resting on cement mixing‐pile or gravel‐pile saturated composite foundations are calculated. The influence of soil permeability and pile rigidity on the dynamic response of the composite foundations is investigated. The method proposed by this paper is a simple and reliable numerical one that could be used to study axisymmetrically dynamic problems of layered saturated media and to get the mechanism of dynamic testing on single‐pile saturated composite foundations. Copyright © 2006 John Wiley & Sons, Ltd.     

基于补偿法的电网图形化开断分析

电网开断分析在整定计算及运行方式设定具有重要意义,该文通过电网图形局部拓扑分析,采用后补偿模式只对部分支路进行修正,大大提高了整定效率,并根据此原理在整定计算程序中对各种电网开断方式进行了研究。