基于波动法的框式结构功率流主动控制方法与实验研究

为了研究扰动影响下框式结构中的功率流传播与主动控制,首先采用波动方法建立了框式结构的动力学模型并获得了其在扰动下的精确动力学响应,进一步得到结构中传播的功率流,并以此为目标函数,优化得到了最优控制力的大小与相位,然后对结构施加最优控制力,实现了框式结构的功率流主动控制.对框式结构功率流主动控制方法进行了数值计算分析与实验验证.结果表明:采用波动方法计算框式结构的动力学响应精确可靠;通过数值计算与实验研究可知功率流主动控制可以明显降低框式结构全频域内的抖动,验证了基于波动方法功率流主动控制的正确性与有效性.     

非线性建筑结构振动控制研究

为了反映建筑结构的非线性特征,本文引入了bouc-wen模型.由于所采用的非线性模型很难降阶,同时考虑到直接对模型进行控制器设计也很难,为此,本文提出了一种基于能量的新的振动主动控制策略.该方法是通过比较允许能量与实际能量来确定结构控制力的大小,而其方向是通过对能量求导确定.由于不需要求解线性矩阵不等式,所以计算简单,操作方便.并且当采用同样容量限的多个作动器时,控制输出力一致,从而避免设计多个控制系统,简化了控制器设计.此外,由于采用阶跃控制,控制系统便于实现.最后,以八层建筑物为例来说明本文方法的可行性.     

卫星平台扰动对星载原子干涉重力梯度仪测量影响分析

面向未来空间应用,分析了卫星平台扰动对星载原子干涉重力梯度仪测量噪声的影响。其中卫星平台平动自由度的干扰加速度导致梯度仪质心偏差和梯度仪基线长度变化,卫星平台转动自由度的干扰加速度带来拉曼激光方向偏离,引入额外的离心力与科里奥利力。分析结果表明,对于卫星平动自由度,其干扰加速度贡献的原子干涉重力梯度仪测量噪声较小,可忽略不计;对于卫星转动自由度,可通过对卫星角运动的测量和补偿,将原子干涉重力梯度仪的测量噪声在0.1?Hz以下的测量频带内抑制到1?mE/Hz1/2。所述研究将对未来原子干涉重力梯度仪的星载应用提供理论支撑。     

星载原子干涉重力梯度仪测量方法与噪声分析

原子干涉重力梯度仪在星载环境下可获得较长的干涉时间,有效规避了原子触碰容器壁的风险,因此可实现高精度的测量,同时利于星载仪器的小型化。目前原子干涉重力梯度仪地面测量技术成熟,尚未得到空间应用。根据星载失重的特殊条件,提出一种适用于空间微重力环境的原子干涉重力梯度测量方法,并对其测量精度进行了分析。结果表明,在卫星重力测量关注的0.1 Hz以下的测量频带内,星载原子干涉重力梯度仪的潜在测量精度可达到1 mE/Hz~(1/2)。该测量方法为未来原子干涉重力梯度仪的星载应用提供重要的技术基础。     

一种能量与前馈杂交控制新方法

振动能量大小可以反映结构振动控制的效果。为此,本文提出了一种简单的基于能量的振动控制策略,通过比较允许能量与实际能量来确定系统控制力的大小,利用能量导数来确定控制力的方向。同时,考虑到实际地震波的随机性,本文引入了前馈控制策略。通过附加前馈增益、状态方程离散及代换把两种控制方法有机地结合在一起。此外,直接引入前馈增益对控制系统的控制效果影响较小,为此本文提出了调整因子的概念。本文方法计算简单,操作方便。最后,以六层建筑物为例说明了本文方法的可行性。     

整星被动多杆隔振平台研究

整星振动隔离是降低作用于卫星的振动载荷的有效方法.本文了采用多杆隔振平台来实现整星隔振,利用牛顿欧拉法建立了考虑基础运动和支杆转动惯量的隔振平台的动力学模型,分析了平台放置刚性卫星和柔性卫星的振动传递率,分析结果表明隔振平台可以有效的隔离来自于基础的振动.     

基于欧拉摩擦的皮带内力分布及载荷变形关系

围绕圆轮的皮带在达到临界状态前外载增加或降低过程中,局部静摩擦力会发生大小和方向的改变. 皮带任一点处内力变化可以沿指数曲线增加或减小,取决于加载历史. 皮带本身是线弹性材料,但变形与力之间是非线性关系,且加载与卸载过程不同,形成滞回圈.滞回圈内每一点都是皮带可能出现的载荷和变形状态.     

用于星敏感器的马蹄形卡塞格伦反射式光学系统杂散光抑制方法（英文）

星敏感器是惯性天文组合导航系统的关键传感器,星敏感器的光学系统设计及对杂散光的抑制是决定其能否实现测星的主要因素。提出一种改进型的卡塞格伦反射光学系统,该系统通过摆镜折叠光路并实现扫描,压缩了系统的体积,增强了系统的灵活性。进而针对该系统设计了一种基于基生叶结构的遮光罩,利用光线追迹软件在不同方位和俯仰角度入射下对系统进行了仿真分析,结果表明规避角以外的点源透射比可以达到10?9以下,满足系统使用要求。此外,鉴于传统点源透射比方法的计算量较大,还引入了杂散光系数的概念,通过对镜像系统进行反向光线追迹可以将杂散光分离,从而计算出杂散光系数,表征系统对杂散光的抑制能力。该方法可降低计算量,提高设计效率。     

空间结构耦合模态控制及实验研究

智能结构以主动元件为传感器和驱动器,根据结构的动态响应和控制要求,自适应地改变结构的动态性能,实现结构特性的自调节功能,以增强结构适应于外界环境变化的能力.结构振动主动控制方法中常用的模态空间控制方法,就是将系统方程转化到模态坐标下,从而得到内部解耦的以模态坐标表示的方程组,然后根据一定的控制方法,计算出模态控制力,实现实时控制.该方法计算简单,效率高,能满足实时控制的需要.本文根据一个三层智能结构主动控制实验,介绍了耦合模态控制理论及实现方法,设计并阐述了压电主元杆件的工作原理,根据Riccati方程得到了主元杆件的最优布置.通过对实验数据运用五点滑动平均平滑法进行处理分析及频谱分析可以看到,智能结构通过主动控制,对相应的控制模态位移及加速度有很大的抑制作用,对应的模态阻尼系数得到了不同程度的提高.     

半球谐振陀螺星载惯性测量单元设计与实现

半球谐振陀螺是一种新型固体振动陀螺,具备功耗低、寿命长、稳定性高等特点,可完美适应卫星的姿态控制。针对微小卫星应用需求,利用半球谐振陀螺构建了星载惯性测量单元。首先,通过测量单元硬件结构设计,对其内部空间进行优化,并通过力学特性及力学试验仿真分析,验证其机械可靠性。其次,针对微小卫星应用环境优化半球谐振陀螺电路设计,提高惯性测量单元可靠性。最后,力学环境试验结果表明,三轴半球谐振陀螺的零偏稳定性均优于0.1°/h,敏感器件满足标度因数非线性度≤500ppm和零偏稳定性≤0.1°/h(1σ)的要求,实现了满足微小卫星应用需求的低成本、小体积、高可靠的半球谐振陀螺星载惯性测量单元。     

气动八作动器隔振平台的主动隔振研究

多自由度隔振平台可以有效地隔离运载器传递到卫星的振动载荷。本文采用气动八作动器隔振平台实现卫星的六自由度隔振。首先应用牛顿欧拉法建立了气动八作动器隔振平台的动力学模型,设计了平台的主动控制律,然后对平台的主、被动隔振特性进行了仿真分析。仿真分析和实验结果显示主动隔振使平台各方向的低频隔振性能均得到改善。     

Design of a curved surface constant force mechanism

A new curved surface constant force mechanism which mainly consists of a roller and a curved surface has been proposed. The magnitude and the direction of normal force caused by squeezing between the roller and the curved surface satisfy a certain relationship, thus the decomposed force of the normal force keeps constant in a certain direction all the times. According to the envelope theorem, the trajectory of the roller center and the profile of the curved surface are obtained by ignoring friction. Then, the influence of the friction is discussed in detail. In addition, the simulation is performed to verify the theoretical calculation. The simulation results show that the output force is relatively constant and the friction has little effect on the output force.     

Time-optimal rendezvous transfer trajectory for restricted cone-angle range solar sails

The advantage of solar sails in deep space exploration is that no fuel consumption is required. The heliocentric distance is one factor influencing the solar radiation pressure force exerted on solar sails. In addition, the solar radiation pressure force is also related to the solar sail orientation with respect to the sunlight direction. For an ideal flat solar sail, the cone angle between the sail normal and the sunlight direction determines the magnitude and direction of solar radiation pressure force. In general, the cone angle can change from 0° to 90°. However, in practical applications, a large cone angle may reduce the efficiency of solar radiation pressure force and there is a strict requirement on the attitude control. Usually, the cone angle range is restricted less more than an acute angle （for example, not more than 40°） in engineering practice. In this paper, the time-optimal transfer trajectory is designed over a restricted range of the cone angle, and an indirect method is used to solve the two point boundary value problem associated to the optimal control problem. Relevant numerical examples are provided to compare with the case of an unrestricted case, and the effects of different maximum restricted cone angles are discussed. The results indicate that （1） for the condition of a restricted cone-angle range the transfer time is longer than that for the unrestricted case and （2） the optimal transfer time increases as the maximum restricted cone angle decreases.     

Cicada(Tibicen linnei) steers by force vectoring

To change flight direction, flying animals modulate aerodynamic force either relative to their bodies to generate torque about the center of mass, or relative to the flight path to produce centripetal force that curves the trajectory. In employing the latter, the direction of aerodynamic force remains fixed in the body frame and rotations of the body redirect the force. While both aforementioned techniques are essential for flight, it is critical to investigate how an animal balances the two to achieve aerial locomotion. Here,we measured wing and body kinematics of cicada(Tibicen linnei) in free flight, including flight periods of both little and substantial body reorientations. It is found that cicadas employ a common force vectoring technique to execute all these flights. We show that the direction of the half-stroke averaged aerodynamic force relative to the body is independent of the body orientation, varying in a range of merely 20 deg.Despite directional limitation of the aerodynamic force, pitch and roll torque are generated by altering wing angle of attack and its mean position relative to the center of mass. This results in body rotations which redirect the wing force in the global frame and consequently change the flight trajectory.     

A 6-DOF passive vibration isolator based on Stewart structure with X-shaped legs

By employing the nonlinear stiffness and damping characteristics of a bio-inspired X-shaped structure (XSS) with passive springs and the Stewart platform with six degrees of freedom, a passive 6-DOF vibration isolation platform is designed and experimentally studied for its vibration isolation performance. A three-layer asymmetrical XSS is adopted as legs to construct a passive Stewart platform. Because of the specially designed XSS, the stiffness and damping properties of the system can be adjusted by changing structural parameters and thus it is designable to achieve an excellent performance including excellent stability and high-static-low-dynamic-stiffness isolation effect in all six directions with satisfactory loading capacity in the vertical direction, without any active control. Analytical and extensive experimental analysis of static stiffness and vibration response of the system revealed that (a) the aXSS Stewart platform has very beneficial high static nonlinear stiffness which can provide sufficient loading capacity; (b) the platform can achieve very low dynamic stiffness in each direction without losing loading capacity; (c) both static and dynamic stiffness is adjustable and designable with structure parameters and very easy to implement in a pure passive manner.     

安装方向对角接触球轴承保持架动态特性的影响

利用二次开发后的有限元软件MSC Patran/Ls-dyna实现角接触球轴承的参数化建模与动态性能分析.通过与试验以及文献结果进行对比,验证了建立的有限元模型的正确性及仿真结果的可靠性.在此基础上研究了角接触球轴承不同安装方向对保持架动态特性的影响.结果表明：由于重力作用,保持架水平安装较竖直安装时更易形成圆形的质心轨迹.低速工况下,保持架竖直安装时最大应力发生在过梁位置,水平安装时最大应力发生在侧梁位置.高速工况下,保持架在两种安装方向的最大应力均发生在过梁位置.不同转速下保持架在轴承竖直安装时最大应力值均更大.     

System modeling and tracking control of mobile manipulator subjected to dynamic interaction and uncertainty

Trajectory tracking of a mobile manipulator is a challenging research because of its complex nonlinearity and dynamics. This paper presents an adaptive control strategy for trajectory tracking of a mobile manipulator system that consists of a wheeled platform and a modular manipulator. When a robot system moves in the presence of sliding, it is difficult to accurately track its trajectory by applying the backstepping approach, even if we employ a non-ideal kinematic model. To address this problem, we propose using a combination of adaptive fuzzy control and backstepping approach based on a dynamic model. The proposed control scheme considers the dynamic interaction between the platform and manipulator. To accurately track the trajectory, we propose a fuzzy compensator in order to compensate for modeling uncertainties such as friction and external disturbances. Moreover, to reduce approximation errors and ensure system stability, we include a robust term to the adaptive control law. Simulation results obtained by comparing several cases reveal the presence of the dynamic interaction and confirm the robustness of the designed controller. Finally, we demonstrate the effectiveness and merits of the proposed control strategy to counteract the modeling uncertainties and accurately track the trajectory.     

Mechanical response of a tensegrity structure close to its integrity limit submitted to external constraints

The response to an external constraint of a symmetrical tensegrity structure made of elastic and rigid elements has been studied by numerical experiments. Two non-linear effects have been found when the structure is close to its integrity limit above which it collapses. The first one is that the mechanical power response of the tensegrity structure can be modulated according to the magnitude of the applied force. This effect indicates that the structure may act as a mechanical power amplifier. The second one is that a slightly prestressed tensegrity structure can offer a greater resilience to an applied force than more prestressed equivalent structures. This paradoxical stiffening effect indicates that increasing the prestress may not always be the most efficient way to keep the stability of the structure.     

形状记忆合金单晶细观本构关系的一种相变动力学模型及算法

形状记忆合金是由马氏体相和奥氏体相组成的非均质材料,热力载荷及相变不可避免地在材料中引起残余微应力场,它与外界驱动力的叠加可能导致低应力水平下发生马氏体相变或逆相变.论文假设马氏体相变及逆相变的驱动力是马氏体体积分数的连续函数,发展了形状记忆合金伪弹性的本构描述及相应的数值分析方法.分析表明,所发展的方法与理想相变模型间的误差远小于已有工作中引入的容许误差.对形状记忆合金单晶伪弹性响应的计算结果与试验结果或已有模型计算结果的比较表明所发展的方法具有较高的精度.此外,所发展的方法具有明晰的物理背景,且无需对每个变体的相变发生与否及其方向进行判断,简化了计算过程,提高了计算效率和收敛性.     

Dynamics analysis of a parallel hip joint simulator with four degree of freedoms (3R1T)

For a hip joint simulator with a 3SPS+1PS spatial parallel manipulator as the core module, a formulation based on the Kane equation was derived for the dynamic characteristics of the simulator from the kinematics analysis of the model. The relationships of the velocities and accelerations between the moving platform and active branched-chains were deduced. The velocity and angular velocity components of the moving platform were served as the generalized velocities. And the dynamic model was established by obtaining the generalized active forces and inertial forces. Then the driving forces and powers of the active branched-chains and the constraint reaction forces of the intermediate branched-chain were simulated in the numerical method. The results showed that the active driving forces of the branched-chains reached their respective maximum when the moving platform rotated into 0.13^° around X-axis, 2^° around Y-axis, and 18^° around Z-axis. And the intermediate branched-chain needed to balance the driving and inertia forces, as well as support the moving platform and load the force of hydraulic cylinder. Therefore, the maximum constraint reaction force of the intermediate branched-chain is along the Z-axis. The research works provided a theoretical basis for the design of the active branched-chains driving system and the structural parameters of the intermediate branched-chain, as well as for the control system.