Six d.o.f. displacement measuring device based on a modified Stewart platform

Acquisition of the displacements and deformations of a loaded component is generally a not easy operation. This is especially the case as the component often presents a complex geometry and the deformations involve more degrees of freedom or a combination of them.Measurement devices used for this kind of application often allow to obtain simplified measurements.This paper presents a novel measurement device, consisting of six displacement sensors mounted as a parallel mechanism, capable to measure the global deformation of a component in terms of translations and rotations. The deformations are obtained by applying the direct kinematic equations to convert the six displacements read from the six sensors into the three translations and rotations representing the deformation of the component.The geometry of the device leads to write simplified equations for the direct kinematic that can be solved with a semi-numerical procedure implemented in a program written in Matlab environment.The results given by this procedure have been validated with the positions obtained from a 3D CAD model of the device, showing perfect agreement between the results.A prototype has been made and tested on a workbench.     

一种三自由度Stewart并联平台重心稳定分析及Simulink仿真

以三自由度Stewart并联平台为研究对象,提出了一种Stewart并联平台重心稳定的分析方法,并对其进行Simulink仿真。利用三维建模软件Creo建立三自由度Stewart平台的三维模型。通过Creo里的接口,将Stewart平台三维模型导入Simulink中生成对应的Simmechanics模块,包括3条运动支链,每条支链由铰链、电动缸、驱动杆、动、定平台等组成。在Simulink的仿真环境中,对3条支链的电动缸添加驱动模块,再使用Fcn函数编程,使驱动模块对电机施加驱动,从而产生驱动杆不同的伸长量,达到动平台的预定运动轨迹。在Simulink环境下,通过编程实现三自由度Stewart并联平台动平台的一种特殊运动,即动平台与水平面成一定的二面角旋转一周,而动平台自身的重心保持稳定。     

被动式Stewart隔冲平台的刚度特性

建立了Stewart隔冲平台的运动微分方程,分析了隔冲平台3个方向的动态刚度特性,讨论了刚度大小对平台抗冲击性能的影响,对隔冲平台进行了落锤式冲击试验,并与仿真结果进行了对比。研究结果表明:被动式Stewart隔冲平台的三向动态刚度近似呈线性;隔冲平台的横向冲击隔离率大于纵向冲击隔离率,纵向冲击隔离率大于垂向冲击隔离率;试验所得的冲击隔离率达到86.39%以上。研究成果可为Stewart隔冲平台在船舶设备抗冲击中的实际应用提供理论和试验依据。     

基于LabVIEW的Stewart平台传感与控制系统建模与测试

为了设计面向柔性自动化装配的Stewart机器人传感与控制系统,并且提高系统建模与测试的效率,在Windows环境下,基于Lab VIEW,以Stewart平台为控制对象,进行机器人六维力测量和运动学逆解的建模与计算,然后以PC+运动控制卡(IMC3062E)和PC+数据采集卡(PCI8605)的硬件平台为实验平台,对系统进行开发与测试。结果表明,所开发的传感与控制系统可以有效对六维力/力矩进行测量,并实现对动平台的速度控制。     

Recombinant Landscapes in the American City

How are urban actors, such as landscape designers, community groups, developers and local politicians, actively restructuring their environments to meet the challenges of the American city in the new global context? Grahame Shane outlines the approaches to landscape that have been emerging since the mid-20th century and are set to recombine urban assemblages whether they are located in historic city centres, postindustrial waterfronts or suburban sprawl. Copyright © 2007 John Wiley & Sons, Ltd.     

基于Kane方法的Stewart传感器动力学及固有频率分析

通过线性化动力学方程并应用Kane方法,研究了Stewart传感器的固有频率．将Stewart传感器的上平台、上连杆、敏感元件及下连杆作为独立的子结构分别处理,依据矢量和张量理论对其运动学方程和动力学方程进行系统的推导,并经过简化导出Stewart传感器简洁的固有频率方程形式．为验证Kane方法的有效性,提供了MATHEMATICA数值算例．相比于传统的牛顿一欧拉方法及拉格朗日方法,Kane方法既简洁又高效,特别适合于计算机计算．     

BKX-Ⅰ型并联机床的谐响应分析

应用有限元分析软件(ANSYS),对BKXⅠ型并联机床进行谐响应分析,分别得到了机床各节点沿机床的虚拟轴X、Y和Z向的位移谐响应曲线。在此基础上,还分析了该机床的谐响应规律,并明确了谐响应的特点,为改善此类机床的动态特性提供了一定的参考依据。     

Orientationability analyses of a special class of the Stewart–Gough parallel manipulators using the unit quaternion representation

This paper addresses the orientation-singularity and orientationability analyses of a special class of the Stewart–Gough parallel manipulators whose moving and base platforms are two similar semi-symmetrical hexagons. Employing a unit quaternion to represent the orientation of the moving platform, an analytical expression representing the singularity locus of this class of parallel manipulators in a six-dimensional Cartesian space is obtained. It shows that for a given orientation, the position-singularity locus is a cubic polynomial expression in the moving platform position parameters, and for a given position, the orientation-singularity locus is an analytical expression but not a polynomial directly with respect to the mobile platform orientation parameters. Further inspection shows that for the special class of parallel manipulators, there must exist a nonsingular orientation void in the orientation space around the orientation origin for each position in the position-workspace. Therefore, a new performance index referred to as orientationability is introduced to describe the orientation capability of the special class of manipulators at a given position. A discretization algorithm is proposed for the computation of the orientationability of the special class of manipulators. Moreover, effects of the design parameters and position parameters on the orientationability are investigated in details. Based on the orientationability performance index, another novel performance index referred to as practical orientationability is presented which represents the practical orientation capability of the manipulator at a given position. The practical orientationability not only can satisfy all the kinematic demands and constraints of such class of manipulators, but also can guarantee that the manipulator is nonsingular.     

并联机床的历史、现状及展望

本文介绍了并联机床的基本概念、分类方法及其基本特性，详细地阐述了并联机床在国内外的发展历史、研究状况以及关键基础零部件的发展状况，在此基础上，分析了并联机床结构上的优缺点，表明了并联机床走向实用化所面临的一些问题，本文的最后对并联机床的发展趋势作了展望。     

基于Stewart平台的空间对接动力学模拟的稳定性研究

在地面进行空间对接动力学的模拟实验是实现空间对接不可或缺的过程。本文利用Stewart平台实现由动力学方程解算得到的两航天器相对运动轨迹，提出用质量-弹簧-阻尼系统来研究空间两航天器对接动力学过程模拟中的稳定性问题。建立了基于Stewart平台位置内环的动力学回路系统模型，推导出为使模拟系统稳定的动力学参数之间的配置关系，论证了Stewart平台的频率特性与动力学系统谐振频率之间的关系。为空间对接动力学过程的模拟奠定了理论基础。