空间遥感相机桁架机身接头结构的设计和分析

大型空间相机需要使用力学特性强、质量轻以及体积小的机身结构对光学系统和其他系统进行支撑与固定,以保证镜头的成像质量。分析了铰链连接和螺栓连接一胶接方案的特点,并对比了各方案的力学性能。根据支杆材料和机身框架材料的性能,优先选择钛合金作为连接结构的制作材料。考虑到复合材料制造52艺的复杂性以及胶接的高强度和高刚度要求,制定了合理的胶接工艺以避免和控制胶接所产生的应力。最后通过静／动力学试验验证了接头设计方案的有效性。结果表明,螺栓一铰接设计方案是一种优化、合理的设计方案。     

某空间可见光相机的机身桁架结构设计

作为空间可见光相机的主要承载结构,机身桁架结构对于保证机身的力学性能至关重要。为了保证空间相机机身的结构刚度和稳定性,针对机身桁架结构设计进行了研究。研究了桁架的基本结构,分析了支杆力学性能的影响因素,探讨了支杆长度和角度对该机身桁架力学性能的影响。分析了支杆数量、支撑位置和分布形式对机身力学性能的影响,并分析了"△"型和"X"型桁架结构的特点。通过选择合理的支杆数量和分布形式,保证了机身桁架的力学性能。然后在设计分析的基础上进行了力学试验,验证了机身的力学性能。试验结果表明,该桁架结构的设计能够获得较好的力学性能,满足机身结构的设计要求。     

空间相机桁架杆接头结构研究

在大跨度空间结构中广泛应用的桁架结构在大尺寸空间相机主支撑结构中的应用越来越多.桁架杆与安装光学元件的框架之间的连接接头是桁架式主支撑结构的重要组成部分之一.综合比较了桁架杆接头的几种常用结构形式,结合复合材料零件与金属零件的3种连接方式,提出了一种一端与桁架杆胶接、另一端与框架螺钉连接的桁架杆接头.该桁架杆接头设计有...     

基于全空域跟踪的椭球型天线桁架设计及标校方法

为满足某卫星工程的测控需求，进一步提高测控网综合测控能力和覆盖范围，提出了一种新型空间椭球天线桁架结构形式及标校方法，满足了全空域、大跨度和高精度的要求。依据大跨度空间桁架理论及有限元分析结果，采用单层空间椭球面网壳的天线桁架构型，通过优化杆件截面、网架形式、跨度和高度等参数实现了对天线桁架承载力的有效分配，合理设计了空间椭球桁架结构及连接方式，并进行了椭球型天线桁架的加工。通过现场测试标定与系统联调，设计加工的椭球型天线桁架达到了系统整体的接收G/T值、第一旁瓣、差波束零深、位置精度和高刚度要求，解决了大型阵列长期运行中定期频繁标校难题，对大尺度阵列天线桁架的设计具有一定的参考意义。     

长焦距空间相机主次镜间桁架支撑结构设计

为了满足长焦距空间相机主次镜间支撑结构高刚度、高强度、高热稳定性和轻量化的设计要求,从材料选择、结构形式、连接工艺和参数优化等方面分析了空间相机主次镜间支撑结构设计中需要考虑的问题。针对某7 m焦距,相对孔径1∶6,采用卡塞格林光学系统的空间相机,设计了一种采用碳纤维复合材料的3层27杆式主次镜间桁架支撑结构,并基于有限元法对其进行了优化设计。分析结果表明,设计的桁架结构质量减轻了38 kg,一阶固有频率可达80 Hz,在径向自重和5℃均匀温升载荷作用下,次镜最大倾角为4.6″,表明所设计的支撑桁架合理可行,能够满足长焦距空间相机的使用要求。     

基于Rayleigh算法的空间相机桁架结构设计与优化

为了满足空间相机主支撑结构在强度、刚度和稳定性等方面的要求,根据能量守恒原理,采用基于Rayleigh算法的单位力法,推导了空间相机三角形桁架单元的频率计算公式,研究了桁架杆间夹角对相机主支撑结构频率的影响。以某种桁架式空间相机为例,结合有限元方法对理论计算结果进行了分析验证,并以此为基础对相机的桁架结构进行了优化。结果表明:优化后的相机结构较原方案在X和Y向的频率分别提高了18.01 Hz和27.38 Hz,增加了相机结构刚度,为以后的空间相机主支撑结构设计提供了重要依据。     

压电驱动三支链六自由度微动机器人机构设计

为简化6支链并联微动机器人结构、减小其装配误差,提出了压电陶瓷驱动的3支链6自由度并联微动机器人结构。采用整体式下平台和3条两端带有柔性球铰链和单轴直圆柔性铰链的支杆,使结构紧凑并有利于提高精度。在分析逆解的基础上,根据工作空间要求设计了整体尺寸。根据柔性铰链选取原则,对直角平板和支杆处柔性铰链进行尺寸选择,采用有限元分析对整体刚度进行分析和安全校验。样机测试结果表明了设计的可行性。     

铝钛异种合金的激光熔钎焊

提出了一种连接Al/Ti异种合金的新工艺，即采用激光为热源，AlSi12为填充材料，实现了Ti-6Al-4V钛合金和LF6铝合金的激光熔钎焊连接。激光熔钎焊是一种局部加热焊接过程，通过调整激光加热参数，控制填充材料的润湿铺展及界面金属间化合物的形态和数量，从而控制接头质量。在实验过程中，填充焊丝实时送入，通过改变激光功率、间隙大小、光斑尺寸、焊接速度、送丝速度、激光辐照位置等工艺参数，以获得对接头的不同加热效果。研究了不同参数下的钎缝成形规律、接头界面特点及接头拉伸强度。结果表明，采用激光熔钎焊工艺连接Al/Ti异种合金可以获得成形良好、强度较高的接头，但焊接过程对工艺参数要求严格;接头厚度方向不同位置的界面金属间化合物的厚度和形态各不相同;热输入较低情况下，钎料与钛合金材料作用不充分，接头易从界面处断裂;热输入较高时，接头容易从铝合金侧熔合区附近断裂。     

GH99高温合金环形和C形激光焊接对比研究

发动机火焰筒主要材料为GH99高温合金,其传统焊接方法为电阻点焊。为提高焊接效率,减少机加工序以及焊接缺陷,对比研究了两种激光焊接方式(环形和C形焊),从焊缝成形、微观组织、力学性能等方面揭示激光焊接替代电阻焊的可行性。此外,利用有限元方式,对接头局部和整体构件的焊后应力分布及变形情况进行分析。结果表明,两种焊接方式均能获得良好的焊缝成形,接头性能较原有的电阻焊接头分别高出15.4%和22.1%。有限元计算结果显示C形焊后局部和整体的应力及变形较小。     

空间桁架横梁分布式光纤变形监测与误差修正

空间桁架结构是一种具有低频、密模、非线性等复杂动力学特征的大型挠性空间结构,针对此类结构服役状态的智能辨识对于目前开展高轨深空探测研究具有重要意义。为此,该文提出了一种基于分布式光纤光栅传感技术的空间桁架横梁结构变形监测与反演方法。借助ANASYS有限元分析法,数值模拟得到横梁结构在不同载荷作用下的应变、位移分布特征,研究了基于位移算法的桁架横梁结构变形反演算法,计算得到空间桁架结构不同位置的挠度信息。在此基础上,构建了单边固支桁架横梁分布式光纤变形监测与反演系统,平均相对误差约为2.4%。最后,提出了一种用于横梁结构变形反演精度提升的误差分离修正方法,修正后平均相对误差下降了41.7%。研究结果表明,该文所提方法具有精度高,实时性好等优点,能为及时准确获取空间桁架结构展开形态,实现桁架形态自适应调节与主动控制提供有力保障。     

空间光学相机结构中的机械结合面模型分析

机械结合面是影响结构动力学特性的重要因素,但在空间相机结构设计和分析中却很少应用。着重研究了两种螺栓结合面模型的动力学特性。首先,基于弹簧一阻尼单元模型和虚拟材料模型理论,建立了试验件的两种模型,并确定模型的参数。弹簧阻尼单元参数采用理论和实验结合的方法确定,虚拟材料模型的参数根据模型理论公式确定。然后,通过有限元计算,对比分析了两种模型在有限元情况下的试验件模态。最后比较了两种模型动力学特性的优缺点。结果表明,弹簧阻尼单元模型的振型与实际模态情况较吻合,虚拟材料模型的低阶固有频率值与实际模态情况较吻合。结果为结合面动力学模型在空间相机结构分析中的应用提供了依据。     

Effects of toe stiffness on ankle kinetics in a robotic transtibial prosthesis during level-ground walking

Robotic transtibial prostheses are gaining popularity, as they significantly improve amputees’ locomotion. Existing studies mainly concentrate on the importance of ankle joints in these prostheses. However, there are few studies that focus on the effects of prosthetic toe joints. Different from human feet, most prosthetic feet are single-segment structures without toe joints. In order to develop more human-like prostheses with ankle and toe joints, it is of great importance to investigate the effects of toe stiffness on ankle kinetics, as it contributes to the design and control optimizations. In this paper, we analyze the effects of toe stiffness on ankle kinetics in a robotic transtibial prosthesis we have built recently. Dynamic models of the prosthesis’ ankle and toe joints are built. The imposed plantar pressures and objective joint angles of these models are obtained from locomotion experiments on able-bodied subjects. Simulation results indicate when the toe joint is fixed, the ankle energy consumption in one gait cycle is almost 1.2 times of that when the toe joint is driven to track the able-bodied toe motion. Experiments of the prosthesis prototype are carried out on an amputee subject with a transtibial amputation. The results show that compared with the fixed toe joint either the active toe joint or the passive toe joint can reduce the ankle output moment and power consumption. This means adding a toe joint to the foot can reduce the designing requirements of the ankle joint. In addition, the active toe joint can help the prosthesis perform more human-like behaviors compared with the passive toe joint. On the other hand, the passive toe joint can simplify the prosthesis structures and reduce the total weight compared with the active toe joint.     

Development of numerical algorithm to guide solder joint structure and component structural design during manufacturing

In order to improve the production technology of the lead-free BGA (Ball Grid Array) assembly, a numerical method is developed to predict the yield of the soldering process based on calculated stand-off stiffness curves and component warpage. The stand-off stiffness curve which reflects the relationship of the force and height of solder joints is obtained by solving the differential equations of the solder joint shapes of BGA solder joints using the Runge-Kutta method. The analytical expression of thermal warpage of component in free boundary constraint conditions is proposed based on the lamination theory of the elastic mechanics. The expression can reflect the material parameter variation with temperature and provide an effective calculation method to analyze component warpage with large changing temperature during soldering reflow process. Considering the manufacture deviation of volumes and the randomness of the positions of the solder joints, combined with the stand-off stiffness curves and the component warping deformation, the yield of the soldering process can be predicted. According to the types and positions of the failure solder joints, the production technology can be improved. Based on the stand-off curves of solder joints, the influence of the deviation rate of volume of the solder joint and diameter of pad on the yield of self-assembly are simulated. The optimal matching relations of the solder joint volume and the diameter of the pad with the 0.35 mm pitch and 0.3 mm pitch are analyzed.     

A new creep–fatigue life model of lead-free solder joint

Life prediction plays an important role in reliability design of electronic product. Solder joint failure is one of the most common failure modes for electronic packaging structure. Current creep–fatigue life models of solder joints are unable to distinguish the creep damage and fatigue damage. In this work, a new creep–fatigue life model was proposed for solder joint tested under high strain rate, where the creep damage was based on Monkman–Grant equation and the fatigue damage was evaluated employing the Coffin–Manson model. Then, linear damage rule was utilized to build the new model. Creep test, fatigue test and creep–fatigue test were conducted respectively in order to determine the parameter in the new model. At last, the experimental result was compared with the predicted result, which shows that the calculation life meets well with the experimental life under high strain rate.     

1.5m口径垂直状态短筒长焦距平行光管次镜支撑系统设计

非球面次镜相对于主镜的位置和稳定性对光管的检测和校验性能起着非常重要的作用。从原理上分析了次镜支撑系统,同时建立改进的支撑桁架动力学模型;然后,使用降维处理的方法通过有限元分析对结构进行优化设计;最后,分析温度变化对1.5 m光管性能的影响。结果表明,采用的切向三翼支撑结构,减小了系统的遮拦比而且保证了结构的刚度,改进桁架的比刚度得到改善,从而使整个支撑系统的一阶谐振达到62 Hz;改变局部结构材料降低了温度变化对光学系统的影响,使波像差由/20减小为/30。提出的设计方案精度高,稳定性好,可以满足设计要求。     

基于扭转载荷的微尺度CSP焊点应力应变分析与优化

建立了微尺度芯片尺寸封装焊点有限元分析模型并对其进行扭转应力应变仿真分析与实验验证.分析了焊点材料、焊点直径、焊盘直径和焊点高度对焊点扭转应力应变的影响;以焊点材料、焊点直径、焊盘直径和焊点高度为设计变量,采用响应面法设计了29组不同水平组合的焊点模型并获取了相应焊点扭转应力,建立了焊点扭转应力与焊点结构参数的回归方程,结合遗传算法对焊点结构参数进行了优化.结果表明：焊点材料为SAC305时扭转应力应变最大,焊点最大扭转应力应变随焊点直径和焊盘直径增加而减小、随焊点高度增大而增大;最优焊点结构参数水平组合为：焊点材料SAC305、焊点直径0.22mm、焊盘直径0.14mm和焊点高度0.14mm;仿真验证表明最优焊点最大扭转应力下降了3.7MPa.     

Modeling,observation, and control of hysteresis torsion in elastic robot joints

Hysteresis torsion in elastic robot joints occurs as a coupled nonlinearity due to internal friction, backlash, and nonlinear stiffness, which are coactive inside of mechanical transmission assemblies. The nonlinear joint torsion leads to hysteresis lost motion and can provoke control errors in relation to the joint output at both trajectories tracking and positioning. In this paper, a novel modeling approach for describing the nonlinear input–output behavior of elastic robot joints is proposed together with the observation and control method, which aim to compensate for the relative joint torsion without load sensing. The proposed modeling approach includes the recently developed 2SEP dynamic friction model and Bouc–Wen-like hysteresis model, which is originated from structural mechanics, both arranged according to the assumed torque transmitting structure. The proposed method is evaluated with experiments using the laboratory setup which emulates a single rotary joint under impact of nonlinear elasticities, friction, and gravity.     

Characterization of multijoint finger stiffness: dependence onfinger posture and force direction

The two-dimensional static stiffness of the index finger was measured with the interphalangeal joints in flexed and extended postures. The stiffness of the relaxed finger was compared with the stiffness when voluntary force was exerted in different directions. The finger stiffness was found to be anisotropic, with the direction of greatest stiffness being approximately parallel to the proximal phalange of the finger. This direction was relatively unaffected by finger posture or direction of finger force. Finger stiffness was more anisotropic when the interphalangeal joints were extended than flexed. The stiffness was most anisotropic when the interphalangeal joints were extended and force was being exerted in the direction of pointing, while it was least anisotropic when the interphalangeal joints were flexed and force was being exerted in directions normally associated with pinching and tapping actions. The stiffness of the individual finger joints was computed and the relation between stiffness and joint torque was examined. Previous studies, which examined single finger joints in isolation, had found that joint stiffness varied in a linear fashion with net joint torque. In contrast, the authors did not find a monotonic relation between joint stiffness and net joint torque, which they attributed to the need to vary the amount of cocontraction of antagonistic muscles when controlling the direction of finger force