构架式可展天线机构自由度分析——拆杆等效法

针对四面体构架式可展天线机构的多环耦合特性,提出了一种空间多环耦合机构的自由度分析方法——拆杆等效法。首先拆除四面体基本可展单元机构的耦合约束链,将剩余部分视为一个并联机构,然后应用螺旋理论分析各输出节点的自由度数目及性质,进而构造各输出节点与定节点之间的等效串联运动链,最后复原拆除的耦合约束链得到四面体基本可展单元的等效机构,应用修正的G-K公式计算等效机构的自由度数目,并基于反螺旋理论分析等效机构的自由度性质,从而获得四面体基本可展单元的运动特性。根据四面体基本可展单元的等效机构及其组合方式对最小组合单元及大尺寸构架式可展天线机构的结构进行了化简,并根据其几何特征约束方程推导了最小组合单元及大尺寸构架式可展天线机构的自由度。建立了由27个四面体基本可展单元组成的构架式可展天线机构的仿真模型,对该机构的自由度进行了验证,结果表明提出的拆杆等效法求得的自由度正确,为进一步分析此类天线机构的运动学和动力学奠定了基础,同时为其他类型的空间多环耦合机构的自由度分析提供了一种新的思路。     

Design and analysis of a truss deployable antenna mechanism based on a 3UU-3URU unit

Space deployable structures with large calibers, high accuracy, and large folding ratios are indispensable equipment in the aerospace field. Given that the single-DOF 3RR-3RRR deployable unit cannot be fully folded, this study proposes a 3UU-3URU deployable unit with two kinds of DOF: folding movement and orientation adjustment. First, based on the G-K formula, the DOF of the 3UU-3URU unit is analyzed. Then, the 3UU-3URU unit is used to construct a deployable truss antenna with a curved surface, and the DOF of the whole deployable antenna containing multiple 3UU-3URU units is calculated. The structural design of a deployable antenna with two loops is carried out with specific parameters and geometric relations. Next, a DOF simulation of a basic combination unit composed of three 3UU-3URU units is performed. Finally, a prototype of the basic combination unit is manufactured, and the DOF of the mechanism is experimentally verified.     

3R-3URU可展单元机构及其在构架式可展天线中的应用

提出了一种空间单自由度(DOF)可展单元机构3R-3URU。首先,基于螺旋理论和修正的G-K公式分析了RURUR单闭环机构的自由度,建立了该机构中主动关节和被动关节速度之间的解析关系式,基于此关系式和3个RURUR机构共用首尾转动副的结构特点推导了3R-3URU单元机构的自由度,得到了3R-3URU机构具有1个自由度时各运动副的方向和位置满足的几何关系式。其次,将3R-3URU机构应用于3RR-3RRR四面体可展单元及其组成的球面构架式可展天线中,得到了具有收拢和调姿两种自由度的新型可展机构。最后,利用Adams软件对3R-3URU可展单元机构的自由度和其在四面体构架式可展天线中的应用进行了仿真验证。该3R-3URU可展单元机构具有单自由度、铰链种类少、结构简单等优点,可用于曲面构架式可展天线的支撑机构中,实现大折叠比。     

Design and analysis of truss deployable antenna mechanism based on a novel symmetric hexagonal profile division method

As the deployment, supporting, and stability mechanisms of satellite antennas, space-deployable mechanisms play a key role in the field of aerospace. In order to design truss deployable antenna supporting mechanisms with large folding rate, high accuracy, easy deployment and strong stability, aiming at the geometric division of the parabolic reflector, a novel method based on symmetric hexagonal division and its corresponding modular truss deployable antenna mechanism is proposed, and the original method based on asymmetric triangular division and its corresponding mechanisms are presented for comparative analysis. Then, the screw theory is employed to analyze the mobility of different mechanisms. Furthermore, the improved three-dimensional mesh method is used to divide the reflector surface of a large parabolic antenna designed by the two different methods, and the profile accuracy and the type of links are taken as the evaluation indexes to quantitatively analyze the division results. Finally, a three-dimensional model of the modular deployable mechanism based on the symmetric hexagonal design is developed, and the deployable mechanisms with different configurations based on the two design methods are compared and analyzed from the mechanical perspective. The research results provide a good theoretical reference for the design of deployable truss antenna mechanisms and their application in the aerospace field.     

一类基于四面体组合单元的模块化构架式可展开天线机构

针对现有基于四面体单元的构架式天线机构结构复杂、收拢率低、运动副数量多等问题，基于3RR-3RRR四面体组合单元和基于3RR-3URU四面体对称组合单元分别提出了两种新型模块化可展结构。以3个组合单元组成的模块化结构为分析对象，首先，详细介绍了模块化结构的组成及虎克铰轴线布置，并利用组合单元本身的自由度数目及性质，采用拆杆-等效-复原的思想，应用螺旋理论和G-K公式分别对提出的两种模块化结构进行了自由度分析，得到了自由度数目及性质。其次，应用Adams动力学仿真软件对两种模块化结构进行运动仿真，仿真结果验证了自由度分析的正确性。以完全展开和完全收拢时机构所占的空间体积比值表征该机构的收拢率，计算现有基于四面体单元的非模块化机构与提出的模块化机构的收拢率。最后，对比分析非模块化机构与模块化机构的自由度数目、运动副数目及收拢率。分析结果表明，基于3RR-3URU四面体对称组合单元的模块化结构既能实现较大收拢率，自由度及运动副数目也相对减少，且组成大型天线时杆件类型较少。研究结果为该类模块化构架式可展天线结构的设计与分析提供一定理论依据。     

Deployment dynamic analysis of deployable antennas considering thermal effect

Dynamic analysis of flexible multibody systems is complex. Several successful methods have been demonstrated. However, few works discussed the dynamic performance of the flexible multibody under different temperatures. This paper uses the absolute nodal coordinate formulation to analyze the flexible body dynamics of deployment structures under different temperatures to simulate space environments. The dynamic equations of finite element in temperature field are developed. Then a computer-aided simulation of flexible multibody systems in temperature field is implemented. A general four-bar mechanism under different temperatures as a simulation example is demonstrated, and the deployment characteristics of a special four-bar mechanism as a basic module of the hoop truss deployable antenna is analyzed under different temperatures in order to evaluate the dynamic performance of the deployable antenna in space environments. The simulation results indicate the influence factors of deployment dynamic characteristics include the structural form, material properties, geometric parameters and deployment planning in ambient and thermal/vacuum environments.     

Structural design and model fabrication of cable-rib tensioned deployable parabolic cylindrical antenna

Deployable mechanisms with light weight and high storage ratio have received considerable attention for space applications. To meet the requirements of space missions, a parabolic cylindrical deployable antenna based on cable-rib tension structures is proposed and verified by a physical prototype. The parabolic cylindrical antenna adopts simple parallel four-bar mechanisms to construct the basic deployable unit, and the cylindrical direction dimension can be easily extended by modularization, which has obvious advantages in storage ratio and area density. Considering the complexity of the entire antenna structure design, including cable networks and flexible trusses, the form-finding design optimization model of a parabolic cylindrical antenna is established using the force density sensitivity method, and then the kinematics analysis of the deployable mechanism is carried out. Finally, a single-module prototype with a deployable diameter of 4 m × 2 m was designed and fabricated. The results of the ground deployment process test and surface accuracy measurements show that the antenna has good feasibility and practicability.     

Configuration synthesis of planar folded and common overconstrained spatial rectangular pyramid deployable truss units

Compared with non-overconstrained deployable units, overconstrained deployable units are widely used in space missions for their higher stiffness characteristics. Besides the performance of a three-step topological structural analysis and design of the rectangular pyramid deployable truss unit(PDTU), conducting a structural synthesis of an overconstrained deployable unit requires the determination of the relative position and direction of each kinematic axis. The structural synthesis of an overconstrained deployable unit is investigated based on screw theory and its topological structure. The possible overconstrained cases of the rectangular PDTUs are analyzed, and corresponding screw expressions are obtained. Thus, the rectangular PDTUs, which can be folded into a plane, are synthesized systemically, and a series of overconstrained rectangular PDTUs is obtained. Furthermore, the feasibility of the folded and deployed motions under one degree of freedom for those deployable units is verified in dynamical simulation by using ADAMS 2010.     

Optimizing accuracy of a parabolic cylindrical deployable antenna mechanism based on stiffness analysis

Accuracy of the fitted surface is of great importance to the performance of deployable antennas utilized in space. This paper proposes a stiffness analysis based fitting accuracy optimization method for achieving the optimal parameters of the parabolic cylindrical deployable antenna mechanism. The stiffness matrix of the proposed cylindrical antenna mechanism is established by assembling the stiffness of beams and tension cables. Structural deformations of the mechanism are calculated where the tensioned cable is substituted by a 2-node truss element and an equivalent force acting on the joint. Consideration of the tensity of tension cables, namely tensioned or slack, is transformed into a typical linear complementarity problem. Comparison between structural deformations of the mechanism fixed at different points is performed. Sensitivities of the geometric and structural parameters on fitting accuracy are investigated. Influence of force of the driven cable on structural deformations of antenna operated in different orbits is conducted. A fitting optimization method is proposed to minimize the structural deformations subject to constraints on volume and mass. Simulation result shows that the fitting accuracy of the antenna mechanism is improved significantly through the optimization. The proposed method can be utilized for the optimal design of other deployable mechanisms constructed by joining rigid links.     

大型可展开天线太空结构频率预测

由于空间大型可展开天线口径较大,在地面模拟太空环境难度高,使得直接在天线原型上进行性能测试非常困难或不可能。为了解决该问题,提出了一种“两步法”,利用空间大型可展开天线的缩比模型进行地面性能测试,以预测天线原型在太空中的工作性能。据此对周边桁架可展开天线太空工作的结构固有频率进行性能预测研究,首先推导了结构固有频率的相似准则,然后考虑结构参数畸变的影响,得出其相似性经验公式,最后研究了温度变化对结构频率的影响,得出了预测大型天线太空工作性能的经验公式。仿真结果验证了该方法的有效性,该方法可应用于其他空间结构的设计和性能预测。     

星载平面可展天线支撑桁架的结构效率优化

针对折展结构性能存在多指标且这些指标之间又相互制约的特点,把结构效率引入到可展结构的优化设计中,应用多因素正交试验法对一种空间可展开平板天线支撑桁架的优化问题进行了研究。对其关键几何设计参数进行了分析,建立了桁架结构的优化数学模型,以结构效率最大化作为优化目标,对可展桁架进行了结构优化,得到了支撑桁架各杆件的设计参数。结果表明:结构效率综合考虑了质量和刚度的影响,使结构质量和刚度同时得到优化;长宽比(l/w)是影响可展桁架结构性能的主要因素,对不同优化目标产生影响的次要因素有所不同;截面积对结构效率影响不显著(置信度p=90%),在相同杆长参数配置下,等截面可展桁架的结构效率仅次于变截面方案,但工程经济性最佳。该研究方法有助于在概念设计阶段从系统设计的角度进行空间桁架结构的快速设计与优化。     

Form-finding methods for deployable mesh reflector antennas

Deployable high-frequency mesh reflector antennas for future communications and obser- vations are required to obtain high gain and high directivity. In order to support these new missions, reflectors with high surface accuracy are widely required. The form-finding analysis of deployable mesh reflector antennas becomes more vital which aims to determine the initial surface profile formed by the equilibrium prestress distribution in cables to satisfy the surface accuracy requirement. In this paper, two form-finding methods for mesh reflector antennas, both of which include two steps, are pro- posed. The first step is to investigate the prestress design only for the cable net structure as the circum- ferential nodes connected to the supporting truss are assumed fixed. The second step is to optimize the prestress distribution of the boundary cables connected directly to the supporting truss considering the elastic deformation of the antenna structure. Some numerical examples are carried out and the simulation results demonstrate the proposed form-finding methods can warrant the deformed antenna reflector surface matches the one by design and the cable tension forces fall in a specified range.     

四棱锥单元平板式可展开收拢机构的

 基于7杆闭环机构提出一种新型四棱锥单元,其可作为一种基本可展机构单元,组合成大型可展机构。利用机构学方法研究,分析了单元机构的自由度、运动学和奇异性,给出了单元组合方法并基于四棱锥单元机构设计了一平板式可展开收拢机构,最后计算了机构的伸缩比。分析结果表明,这种单元机构组合方便简单,组合后的机构自由度为1,便于机构的展开收拢控制。当机构完全展开时,由于其奇异特性,机构有较好的力学性能。利用这种单元可以设计出新型大型可展开收拢机构,在航空航天领域有很好的应用前景。     

空间对称型7R机构运动特性分析及组合应用

提出了一种空间对称型7R机构，可利用此机构组合构造空间可展开机构。通过旋量拓扑图分析了其整体自由度，得到了其运动副轴线方位变化时整体机构自由度数目的变化情况；基于反螺旋理论分析了运动副轴线方位不同的情况下运动输出构件的自由度数目和性质，并针对其瞬时性做了判别，发现其在不同运动副轴线方位布置情况下会出现局部自由度与瞬时自由度；分析了机构在不同驱动情况下的奇异特性，得到了机构在不同的驱动下处于奇异位形时的几何条件；最后选定自由度为1时的空间对称型7R机构组合构造了一类单自由度多棱锥型空间可展开机构，通过设置其运动副轴线方位，可以使其具有较大收拢率，同时当机构完全展开时，奇异特性使得其具有较好的力学性能。通过多个棱锥型空间可展开机构的组合，可以构造出新型大尺度空间可展开机构，在航空航天领域具有较好的应用前景。     

周边桁架可展天线展开过程动力学分析及控制

 基于多刚体系统动力学的Lagrange方法,采用独立的Lagrange广义坐标,考虑耗散力、铰链处扭簧的驱动力及索网预张力对展开过程的影响,建立了周边桁架可展天线展开过程的动力学模型,给出了基于力控制的展开过程控制策略,得出了展开过程驱动力的变化与天线位形变化之间的关系,根据所规划好的天线展开运动得出相应的驱动力。编制了仿真程序进行算例分析,研究了初速度、阻尼及重力对天线展开过程的影响,实现了考虑驱动扭簧的刚度、关节中的阻尼、重力及索网预张力影响的周边桁架可展天线展开过程的动力学分析与控制。实验仿真结果验证了该方法的有效性。     

完全解耦3T2R并联机器人构型综合方法

针对并联机构内部耦合性带来运动学和动力学分析困难的问题,基于G_F集理论提出一种简单而有效的三移动两转动(3T2R)完全解耦构型综合方法。首先,阐述G_F集并联机器人构型理论;其次,根据G_F集的求和运算和转动轴线迁移定理,给出了机构输入运动副选择原则以及解耦支链设计准则;按照完全解耦并联机构设计步骤,列举出了3T2R并联机构各解耦分支运动链,综合出了含有单、双驱动支链的3T2R五自由度完全解耦并联机构,得到了大量新构型;通过所综合出的一种新型并联机构,运用约束螺旋法对机构的自由度数目和运动特性进行分析,根据机构输入与输出参数间关系式,求解得到机构雅可比矩阵,验证了机构的解耦特性,进一步证明了该构型方法的有效性。研究对解耦并联机构的构型设计具有理论指导意义。     

Visual analysis in a deployable antenna experiment [satellite antenna]

To establish a large deployable antenna, monitoring and collimation are essential for reliable and precise deployment. We have developed an analysis method to detect shifts in several images, in which the combination of cross-correlations between images and approximations at subpixel precision enables us to detect shifts in images with a precision of up to 0.01 pixels. The LDREX mission; which was a preliminary experiment for a large deployable antenna, ETS-VIII, was performed in December 2000. During this experiment, anomalies occurred in the antenna, and deployment was aborted. To understand the cause of the anomalies, we used our visual analysis method. Using this analysis, we detected vibrating features in the antenna, which were useful for explaining the anomalies. We outline our visual analysis method and discuss its application in monitoring the deployable antenna.     

一种星载伞天线展开机构研究

天线展开机构使用动力绳实现天线展开和收拢过程中易出现动力绳松弛、脱槽现象。以星载高精度伞状天线展开机构为研究对象，分析天线展开机构的工作原理；利用解析法获得展开机构的运动方程，结合天线展开机构运动部件结构参数，得到天线展开过程中展开机构动力绳的松弛规律；建立以展开机构结构参数为设计变量，以动力绳松弛量最小为目标的展开机构结构优化模型，通过模拟退火法进行求解，得到优化的展开机构结构参数，通过优化前后的展开机构展开、收扰功能试验，测试了机构工作时动力绳的松弛量，验证了展开机构优化的正确性。结果表明：优化后的展开机构动力绳松弛量较优化前降低了90%，优化效果显著。     

ATS-6 Parabolic Antenna for Mounting Solar Cells

Calculations are made to obtain the raw electrical power that can be generated by using an ATS-6 type deployable parabolic dish as a surface for mounting solar cells without seriously interfering with its normal function as an antenna. A minimum of a few hundred watts to a maximum of a few kilowatts are generated during the apparent course of the Sun around the spacecraft. Academically, it seems that deployable solar cell panels along with their booms can be avoided.     

铰链对含铰结构非线性动力学特性影响分析

针对可展结构中铰链带来的展开后非线性动力学问题,建立了含铰结构的动力学模型。基于铰链侧向和径向的几何约束关系,分析了不同约束条件下的铰链非线性特性。基于谐波平衡法（HBM）,对含铰结构的非线性变量进行一次谐波展开,得到铰链非线性力的谐波展开表达式,将含铰可展结构的非线性动力学方程转化为代数方程。分析了铰链在不同非线性特性下各参数对结构动态特性的影响,得到结构固有频率随铰链间隙、刚度和激振力的变化规律。考虑铰链的非线性特性,通过固有频率脊线求解,得到结构固有频率极值随铰链数量、位置和刚度的变化曲面,并对其进行非线性拟合,得到铰链参数对结构固有频率的影响函数,其计算方法和结果在多维复杂结构中具有一定的扩展性,为可展结构的设计和研究提供参考。利用龙格库塔法对非线性结构进行数值仿真,得到结构的固有频率变化曲线,仿真结果表明了利用HBM进行含铰结构动力学分析的正确性。