星间光通信无信标捕跟瞄技术

无信标捕跟瞄技术以通信光为信标光,无需额外的信标光激光器,在重量和功耗受限的卫星光通信应用中更具优势。针对低轨小卫星平台星间光通信,对直接探测方式下的捕跟瞄链路进行功率预算分析,研究光通信终端的无信标捕跟瞄技术,设计捕跟瞄流程,并深入分析视轴抖动对捕获时间和捕获概率的影响,提出剩余不确定区域计算方法。结果表明:所设计的无信标捕跟瞄方法所需最大激光发射功率为0.135 W,捕获时间为30 s,捕获概率为95%,能够满足低轨星间光通信链路要求。     

卫星平台振动对星间激光链路的影响和解决方案

分析了振动对卫星光通信的影响以及卫星平台振动产生原因和特点,找出了卫星平台振动规律。针对振动对卫星光通信系统影响问题,定义了补偿因子以描述补偿效果;对于影响较大的低频振动情况,设计并建立了模拟振动补偿系统。实验结果表明,采用前馈补偿技术的模拟振动补偿系统对于10Hz低频振动的补偿效果显著,补偿大约80%的振动。     

光电跟瞄系统瞄准精度测试技术

为了提高多传感器光电跟瞄系统瞄准精度,提出了多传感器光电跟瞄系统瞄准精度测试的3种方法:像纸法、CCD法和靶标法。系统采用宽光谱大口径平行光管,结合光电跟瞄系统的激光、红外和电视分系统,实现激光与红外/电视瞄准线高精度测试。详细介绍了每种测试方法的工作原理和主要误差来源,建立了实验测试环境,分别用像纸法、CCD法和靶标法对同一光电跟瞄系统红外、电视、激光传感器的瞄准线之间的偏差进行了测试和误差分析。结果表明,靶标法测试误差源少,精度能够达到4″,适用于高精度光电跟瞄系统瞄准精度测试。     

终端与平台耦合运动对卫星光通信系统粗瞄影响的仿真研究

通过分析二维转台与卫星平台的耦合运动引起粗瞄误差的变化规律,讨论耦合运动对信标光光场分布的影响,进而提出补偿方案以保证卫星光通信系统的性能.通过数值仿真得到:对于主转动惯量小于100kg·m2的卫星平台耦合运动引起的粗瞄误差较大,导致目标卫星接收到的信标光功率下降,系统冗余大幅度下降,应采取补偿方法消除粗瞄误差保证系统性能:对于主转动惯量为l00kg·m2:1000kg·m2的卫星平台,当瞄准角较小时耦合运动引起的粗瞄误差较小,可不予补偿,瞄准角较大时耦合运动引起的粗瞄误差较大,应采取相应的补偿措施;对于主转动惯量为＞1000kg·m2的卫星平台耦合运动引起的粗瞄误差可忽略不计.     

激光发散角测量的误差分析

为了研究产品装调过程中,套孔法和CCD成像法得到的激光发散角偏差较大原因,采用ZEMAX仿真进行了理论分析,并结合相关试验进行了验证。结果表明,在CCD白光观瞄系统中利用CCD成像法测量激光光斑大小时,由于白光与激光间存在光程差,计算激光发散角时,需要消除光程差导致的图像误差的影响。激光光斑大小与距离符合双曲线规律变化。近场条件下不成线性关系,CCD成像法测量得到的激光光斑图像偏大,计算得到的激光发散角远大于套孔法的测量值;远场条件下近似成线性关系,套孔法及CCD成像法测算得到的激光发散角数值基本一致。该研究可以根据产品的设计参量,消除光程差对激光激光束散角的影响,提高测量精度。     

ATP跟瞄精度与最佳信号光发射角的研究

激光星间通信中捕获、跟踪、瞄准(ATP)技术是保障通信正常进行的关键一环，在完成捕获进入跟踪状态下，ATP的跟瞄精度是一个重要指标。然而．在实际系统中，ATP的跟瞄精度受到很多因素的制约．只能达到一定的精度。在这种条件下．信号光束发散角的选取对通信系统的整体性能影响很大。提出了影响光束发散角的三种因素，并进一步分析了在给定跟瞄精度的条件下．信号光束的发散角并不是越小越好而是存在一个最佳发散角．该发散角可以在满足通信系统指标的情况下．对发射端的功率需求最小。     

振动对空间光-光纤耦合效率影响及补偿实验研究

利用现有成熟光纤通信技术是目前卫星光通信技术的重要发展方向,但需首先解决空间光-光纤耦合这一关键问题。文中对卫星平台振动对空间光-光纤耦合效率的影响进行了理论分析;在此基础上针对卫星光通信终端,建立以CCD 为探测器,高速偏转镜为补偿器件的卫星平台微振补偿系统,并进行了实验研究。实验结果表明:所采用的基于反馈控制技术的主动补偿系统能有效地抑制低频振动。在振动频率介于1～50 Hz,振动幅度介于75～300 rad 之间时,补偿系统对耦合效率的最大改善率可达54.73%,验证了补偿方案的可行性及有效性,为在卫星光通信系统中应用各种光纤通信技术打下基础。     

卫星相干光通信跟瞄误差对链路性能的影响

以星间相干激光通信链路的接收机相干效率为研究对象,分析了动态跟瞄误差对相干效率的影响,将相干效率引入到星间相干激光通信链路方程,推导了跟瞄误差波前失配条件下的相干光通信链路的误码率概率表达式,对卫星激光通信链路中跟瞄对准误差导致的相干效率下降、链路误码性能劣化情况进行了仿真计算。结果表明,由于跟瞄对准误差波前失配的影响,相干激光通信接收终端具有一个优化的接收孔径,在本仿真条件下,LEO-GEO星间链路动态跟瞄误差为0.5μrad时,优化接收孔径为0.5 m,链路可获得最佳误码性能。     

卫星光通信终端CCD成像光斑弥散圆尺寸选择

利用CCD对自由空间传输的激光进行成像,可得到入射光束的角度信息以实现对发射光束的控制。卫星光通信中,提高对入射光束角度偏差实时测量的精度,可以有效地提高终端的光束跟踪性能,进而有效地保持激光链路的稳定。通过分析角度偏差检测原理,建立了卫星光通信中跟瞄装置测角性能分析模型。分析了测角精度与CCD成像光斑弥散圆尺寸之间的关系,并通过模拟实验进行了验证。结果表明,在卫星光通信系统设计中,综合考虑测角精度要求、终端功耗限制等因素,选择CCD成像光斑相对尺寸在2到3之间为最佳。     

基于星敏感器的跟瞄系统在轨标定方法

为分析空间跟瞄机构光轴误差问题,建立了星上跟瞄系统模型,介绍了跟瞄系统不同坐标系间的转换形式,分析了跟瞄机构光轴的误差形式,提出了多星敏光轴标定算法,介绍了标定过程中的坐标转换过程和误差计算方法,通过仿真验证了算法的正确性,并比较了随机误差对光轴标定的影响,同时在引入星敏感器全天识别算法的情况下对双星敏标定算法的正确性进行了验证,对精确度进行了分析。经仿真,双星敏算法标定精确度可达25”以内,比例系数K值小于0.01,在跟瞄相机与星敏同时工作的情况下解决了跟瞄相机的在轨标定问题。     

钢丝绳传动的三轴转台伺服控制的设计

针对某机载平台中钢丝绳传动带来的非线性误差及外部扰动等因素直接影响平台相机成像质量的问题,提出一种模糊自适应前馈补偿的控制策略.首先对钢丝绳传动机构和高精度直流伺服电机进行了建模,并建立了摩擦模型,为转台速度环控制回路引入模糊自适应PID控制器.设计出前馈补偿和模糊自适应控制器的复合控制策略.Matlab仿真结果以及实...     

基于速度矢量模型的圆轨道空间相机偏流角实时补偿

偏流角是影响线阵CCD 相机推扫成像性能的重要因素。为实现在轨有限计算资源环境下偏流角的快速计算,根据圆轨道卫星飞行与地物随地球自转的速度矢量运动关系,建立了适用于圆轨道正视与前后视成像的偏流角模型,给出卫星飞行过程中星下点相对地物的运动速度矢量作角向振动的数学表达式。根据该模型提出基于旋转CCD 方式的偏流实时补偿方案,并搭建偏流校正成像模拟平台进行了实验验证。仿真和实验表明,速度矢量模型具有更高的计算效率,计算精度和稳定性与坐标变换模型和轨道要素模型一致,能够将偏流导致的图像MTF 下降抑制到5%。该方案适用于 TDICCD 相机与三线阵CCD 立体测绘相机的偏流实时调整机构开发工作。     

Calibration and compensation of cogging effect in a permanent magnet linear motor

The cogging force significantly deteriorates positioning accuracy and tracking accuracy in the direct-drive system with a permanent magnet linear motor (PMLM) that has widely applied in electromechanical manufacturing industries. At present, the optimization design of motor construction and adequate control strategies are main measures to overcome the cogging force of PMLM. This paper proposes an experimental method with iterative process to calibrate the cogging compensation force that is used to counteract the cogging force effect. A compensation approach using linear interpolation is presented to make a real time feedforward compensation for the cogging force. The calibration of the cogging compensation force and the compensation of the cogging force are alternately executed. The experiments obtain gradually accurate cogging compensation force. The tracking errors of the motion system are compared with and without cogging force compensation. The results show that the positioning accuracy and tracking accuracy are improved greatly by applying the cogging compensation with the calibrated cogging compensation force. This demonstrates the effectiveness and feasibility of the proposed methods.     

Deadbeat Feedforward Compensation With Frequency Shaping in Fast and Precise Positioning

This paper presents a novel deadbeat feedforward compensation technique for fast and precise positioning control in mechatronic systems. The proposed compensation provides the desired frequency shaping in control input to suppress the residual vibration, under the constraint of a specified step number in position reference. A 2-DOF positioning controller with the deadbeat feedforward compensation can ensure the required settling performance with the specified steps regardless of the positioning amplitude in reference. The effectiveness of the proposed approach has been verified by numerical simulations and experiments using a prototype of a galvano scanner.     

Random vibration test control of inverter-fed electrodynamic shaker

The random vibration control of an inverter-fed electrodynamic shaker is presented in this paper. First, the dynamic model of the shaker is found and a current-controlled pulsewidth modulation inverter is designed and implemented. The feedback controller is augmented with a command feedforward controller and a disturbance feedforward controller to let the armature exciting current have low harmonic content and possess excellent waveform tracking performance. Then, an acceleration controller and its random vibration command are arranged. In the proposed acceleration control scheme, a command feedforward controller and a robust disturbance feedforward controller are also employed to let the shaker have close random acceleration command waveform tracking control performance, and the performance be insensitive to the system parameter variations. It follows that the acceleration control with desired frequency response in a vibration test could be achieved through properly setting the command signal. The effectiveness of the proposed control scheme is verified by simulation and measured results     

Real-time electro-hydraulic hybrid system for structural testing subjected to vibration and force loading

Real-time electro-hydraulic hybrid system (REHS) with shaking table and force loading simulator is an essential experimental facility for evaluating structural performance subjected to simultaneously vibration excitation and force loading. The key feature of this paper is combination of a feedforward force controller including modified force inverse model compensator (MFIMC) and velocity feedforward compensator (VFFC) with an internal model control (IMC) to compensate the surplus force disturbance caused by active motion of shaking table and to obtain high fidelity force loading tracking performance. An acceleration tracking controller is also designed with modified acceleration inverse model compensator (MAIMC) to extend the acceleration tracking frequency bandwidth and to improve the acceleration tracking performance. The acceleration/force closed-loop transfer function model and their inverse model are identified and designed by multi-step recursive extended least squares (RELS) algorithm and zero magnitude error tracking controller (ZMETC) technology respectively because the identified transfer function model of the acceleration and force loading closed-loop systems may be a nonminimum-phase (NMP) system and their inverse model are instable. An acceleration and force modeling error compensator (MEC) are utilized in MFIMC and MAIMC to minimize the effect of the inaccuracy of identified model and designed inverse model. Experimental results obtained on a real uniaxial REHS with xPC rapid prototyping technology clearly demonstrate the benefit of the proposed compensation method.     

Suppression control method for torque vibration of three-phase HB-type stepping motor utilizing feedforward control

This paper proposes a method to reduce the vibration of the three-phase HB-type stepping motor with cogging torque by the feedforward compensation control. The compensation signal to suppress the vibration of the motor frame is obtained by the repetitive controller installing an online Fourier transformer and utilizing an acceleration sensor attached to the motor frame or an acoustic sensor such as a microphone placed close to the frame. The sensor is used only for the acquisition of the feedforward compensation data. The feedforward compensation signal at an arbitrary operating point is derived from the amplitude and phase data of the frequency components and the operating point data. Compensation data obtained by the repetitive controller is applied to the operating point changed by reference frequency and load condition in steady state. The compensation signal for the new operating point will be generated from compensation data utilizing polynomial equation approximation and linear interpolation method. The effectiveness of this proposed method is confirmed by the experimental results.