Hybrid task priority-based motion control of a redundant free-floating space robot

This paper presents a novel hybrid task priority-based motion planning algorithm of a space robot. The satellite attitude control task is defined as the primary task, while the leastsquares-based non-strict task priority solution of the end-effector plus the multi-constraint task is viewed as the secondary task. Furthermore, a null-space task compensation strategy in the joint space is proposed to derive the combination of non-strict and strict task-priority motion planning,and this novel combination is termed hybrid task priority control. Thus, the secondary task is implemented in the primary task's null-space. Besides, the transition of the state of multiple constraints between activeness and inactiveness will only influence the end-effector task without any effect on the primary task. A set of numerical experiments made in a real-time simulation system under Linux/RTAI shows the validity and feasibility of the proposed methodology.     

空间绳系机器人逼近目标协调控制方法

 为了节省空间绳系机器人的末端执行装置在逼近目标卫星过程中推力器所使用的燃料,本文提出一种利用推力器、反作用轮及空间系绳的协调控制方法。首先利用二次型最优控制器(LQR)算法计算出末端执行装置逼近目标所需的理想轨道控制力,然后利用模拟退火算法将所需轨道控制力优化分配到推力器及空间系绳,同时利用时间延迟算法通过反作用轮补偿空间系绳产生的姿态干扰力矩。仿真结果表明,利用该协调控制方法能显著节省末端执行装置上推力器的燃料消耗,有效抑制空间系绳协调控制力产生的姿态干扰,使末端执行装置保持相对稳定的姿态。     

过驱动轮控卫星的动态控制分配方法

反作用飞轮在卫星姿态控制中具有重要作用,配置3个以上飞轮的卫星构成一类过驱动系统,能够提高姿态控制系统的可靠性.针对期望控制力矩到冗余飞轮的指令分配问题,提出了一种基于伪逆法的动态控制分配方法,并针对传统伪逆法难以考虑飞轮最大力矩等物理约束问题,采用零空间方法对传统伪逆法给出的分配结果进行了修正.基于稳定控制模式下姿态...     

Detumbling strategy based on friction control of dual-arm space robot for capturing tumbling target

The rotational motion of a tumbling target brings great challenges to space robot on successfully capturing the tumbling target. Therefore, it is necessary to reduce the target’s rotation to a rate at which capture can be accomplished by the space robot. In this paper, a detumbling strategy based on friction control of dual-arm space robot for capturing tumbling target is proposed. This strategy can reduce the target’s rotational velocity while maintaining base attitude stability through the establishment of the rotation attenuation controller and base attitude adjustment controller. The rotation attenuation controller adopts the multi-space hybrid impedance control method to control the friction precisely. The base attitude adjustment controller applies the dual-arm extended Jacobian matrix to stabilize the base attitude. The main contributions of this paper are as follows: (1) The compliant control method is adopted to achieve a precise friction control, which can reduce the target angular velocity steadily; (2) The dual-arm extended Jacobian matrix is applied to stabilize the base attitude without affecting the target capture task; (3) The detumbling strategy of dual-arm space robot is designed considering base attitude stabilization, realizing coordinated planning of the base attitude and the arms. The strategy is verified by a dual-arm space robot with two 7-DOF (degrees of freedom) arms. Simulation results show that, target with a rotation velocity of 20 (°)/s can be effectively controlled to stop within 30 s, and the final deflection of the base attitude is less than 0.15° without affecting the target capture task, verifying the correctness and effectiveness of the strategy. Except to the tumbling target capture task, the control strategy can also be applied to other typical on-orbit operation tasks such as space debris removal and spacecraft maintenance.     

利用能量/动量飞轮的偏置动量姿态控制系统

研究偏置动量姿态控制系统中的集成能量与姿态控制问题。利用一对正 反转飞轮提供偏置角动量并同时储 /放能以满足星载设备的能源需求。滚动 /偏航运动由俯仰轴磁矩控制。设计了力矩形式的飞轮的控制律 ,使之提供期望的俯仰控制力矩 ,并以给定的功率储 /放能。保持两只飞轮正 反转可以完全避免飞轮控制律中的系统奇异。提出了利用动能反馈的飞轮储能功率规划方案 ,以使系统维持能量平衡 ,避免由于能量过剩引起的飞轮饱和。飞轮的最小转动惯量受最大偏置角动量和最小能量的限制 ,结合几何方法对这种限制条件进行了分析。数值仿真结果证明了控制方案的有效性。     

跟踪弹道导弹时预警卫星姿态前馈协同控制

基于角动量守恒定理,推导了跟踪弹道导弹时,具有活动部件的预警卫星姿态前馈协同控制。该控制算法基于角动量守恒方程估计红外相机运动产生的角动量扰动以及为抑制该扰动所需的期望飞轮转速,将期望飞轮转速与实际转速的偏差作为前馈信号加入到传统控制系统中,推导出预警卫星姿态前馈控制模型。最后通过数值仿真验证了控制方法,仿真结果与理论分析具有很好的一致性。并且该控制方法简单、可靠,能够适应卫星在轨实时控制。     

冗余飞轮构型下力矩分配策略设计与分析

 主要研究了航天器姿控系统中冗余飞轮构型的力矩分配问题。在阐明该问题的基础上,首先给出了能量最优的力矩分配策略,并考虑飞轮力矩约束对其进行了限幅处理;接着基于静态最优化理论和飞轮系统性质,对四飞轮和多飞轮情况分别设计了相应的力矩最优分配策略,由于可有效地输出飞轮系的最大力矩,其有重要的工程应用价值;最后研究并对比了几种典型构型下两种分配策略所能输出的力矩包络,表明了所设计方法的有效性。     

基于星敏感器的卫星姿态估计方法研究

以星敏感器姿态信息作为测量数据,结合卫星姿态动力学方程组,采用增广卡尔曼滤波方法对无陀螺卫星姿态进行估计。研究发现,干扰力矩的变化会降低卫星姿态估计结果的精度,为此提出两种改进的姿态估计算法:增广自适应卡尔曼滤波方法和增广强跟踪卡尔曼滤波方法;仿真表明,两种算法都能很好地克服干扰力矩变化导致的精度下降现象。     

漂浮基空间机器人捕获卫星过程动力学模拟及捕获后混合体运动的RBF神经网络控制

 讨论了漂浮基空间机器人在轨捕获目标卫星过程的碰撞动力学建模,以及捕获操作结束后空间机器人与卫星混合体的稳定控制问题。首先采用多刚体动力学建模方法并结合空间机器人捕获目标卫星过程中的碰撞动力学特性,建立了漂浮基空间机器人在轨捕获漂浮卫星过程的动力学模型,并在此基础上计算出完成捕获操作后空间机器人与目标卫星混合体关节的运动速度。然后针对卫星及空间机器人系统惯性参数均是未知的复杂情况,应用上述模型、神经网络控制理论和Lyapunov稳定性理论,设计了空间机器人与卫星混合体在捕获过程碰撞冲击影响下稳定运动的高斯径向基函数神经网络控制方案,以达到对捕获卫星的有效控制。此外,高斯径向基函数神经网络控制方案具有不需要测量和反馈载体位置、移动速度与加速度的显著优点。系统数值仿真证实了上述控制方案的有效性。     

基于泵式流体回路的小卫星姿控/热控一体化执行机构设计

 主要研究了小卫星姿控/热控一体化执行机构的设计问题.首先,根据流体回路中液体流速变化对小卫星产生力矩实现姿态控制、液体流动吸/散废热实现热控制的原理,提出一种姿控/热控一体化执行机构设计方案.然后针对该设计方案,利用以电机转速为变量的流体回路内压强和电磁力矩方程,推导了一体化执行机构姿控力矩模型;利用散热量随流体回路流速的变化,建立了一体化执行机构热控模型.最后,针对某小卫星设计了基于姿控/热控一体化执行机构的闭环控制系统,并针对该一体化执行机构设计了一种姿控/热控解耦算法,对其姿控/热控能力进行数学仿真验证,仿真结果证明了该一体化执行机构的有效性.     

Grasping Strategy in Space Robot Capturing Floating Target

When the space robot captures a floating target, contact impact occurs inevitably and frequently between the manipulator hand and the target, which seriously impacts the position and attitude of the robot and grasping security. “Dynamic grasping area” is introduced to describe the collision process of manipulator grasping target, and grasping area control equation is established. By analyzing the impact of grasping control parameters, base and target mass on the grasping process and combining the life experience, it is found that if the product of speed control parameter and dB adjustment parameter is close to but smaller than the minimum grasping speed, collision impact in the grasping process could be reduced greatly, and then an ideal grasping strategy is proposed. Simulation results indicate that during the same period, the strategy grasping is superior to the accelerating grasping, in that the amplitude of impact force is reduced to 20%, and the attitude control torque is reduced to 15%, and the impact on the robot is eliminated significantly. The results would have important academic value and engineering significance.     

Observer-based control for the platform of a tethered space robot

This paper addresses the attitude control problem of a space tethered robot platform in the presence of unknown external disturbance caused by a connecting elastic tether. The tether-generated unknown disturbance leads to tremendous challenges for attitude control of the platform. In this work, the perturbed attitude dynamics of the platform are derived with a consideration of the libration of the elastic tether, and then with the purpose of compensating the unknown disturbance, major attention is dedicated to develop a nonlinear disturbance observer based on gyros measurements, after which, an adaptive attitude scheme is proposed by combining the disturbance observer with a sliding mode controller. Finally, benefits from the observer based on an adaptive controller are validated by series of numerical simulations.     

卫星姿态控制系统容错控制综述

主要针对卫星姿态系统容错控制研究领域已有的成果进行了回顾。总结了国内外卫星容错控制的现有成果,主要从卫星姿态控制系统的可重构性、单体卫星容错控制和卫星编队容错控制3个部分对相关的研究成果进行了归纳分析。其中,卫星姿态系统的可重构性从重构目标和系统功能要求两方面进行分析;对单体卫星容错控制现状的介绍主要从自适应技术、滑模理论、预设性能、干扰观测器、故障估计观测器几个方面展开;卫星编队容错控制方法从独立容错、协同容错、拓扑重构和组成重构的角度进行阐述。最后进行总结,并展望了卫星姿态控制系统容错控制领域未来可能出现的新问题和研究思路。     

轻型高精度卫星的变结构姿态控制器

针对某些小卫星高指向精度和高稳定精度的姿态控制要求,设计了能克服反作用轮转速过零扰动的变结构姿态控制器,并对反作用轮转速过零时低速摩擦对卫星姿态产生扰动的机理进行了分析,建立了仿真用反作用轮低速摩擦动力学模型。同 PID控制器相比,该变结构姿态控制器能有效抑制反作用轮的低速摩擦影响,并具有良好的鲁棒性。数学仿真进一步证明了该变结构姿态控制器的有效性,其指向精度和稳定精度分别可达 0.3°和 0.0 0 1°/     

Momentum wheel start-up method for HAUSAT-2 ultra-small satellite

This paper addresses a newly proposed start-up method of the HAUSAT-2 satellite momentum wheel. The HAUSAT-2 is a 25 kg class nanosatellite which is stabilized to an earth pointing attitude by 3-axis active control method. A momentum wheel performs two functions. It provides a pitch-axis momentum bias while measuring satellite pitch and roll attitude. Pitch control is accomplished in a conventional way by driving a momentum wheel in response to pitch attitude errors. Precession control and nutation damping are provided by operating the pitch-axis magnetic torquer. A momentum wheel is nominally spinning at a particular rate, and speed changes are made as needed. Spinning the momentum wheel redistributes the angular momentum to the spacecraft body. If the wheel is suddenly spun up to its nominal speed, the large momentum produced together with the existing momentum due to the nominal rotational motions will result in a high disturbance and unstable motion. This simulation study investigates the feasibility and performance of a proposed strategy for starting-up the wheel. A proposed strategy to start-up the wheel shows that its pitch momentum wheel can start-up successfully to its nominal speed from rest, and can be stabilized to nadir pointing within about three orbits.     

基于MRP的全局稳定的PID刚体姿态控制

针对刚性航天器姿态控制问题,建立了由修正Rodrigues参数(MRP)表示的混杂姿态模型,并基于此模型设计了一种具有迟滞特性的非线性比例-积分-微分(PID)切换控制器.该控制器包含一个对克里奥利力矩和期望机动力矩的前馈补偿项和一个用于消除轨迹跟踪误差的PID反馈项.通过一个特别的Lyapunov函数分析得到了全局渐...     

一种多旋翼多功能空中机器人及其腿式壁面行走运动规划

 提出了一种既可实现飞行功能又可实现壁面运动的多旋翼多功能空中机器人。设计了机器人的结构,分析了其工作原理,研究了机器人腿式壁面行走模式下腿/足与壁面接触时的机体动力学。结合多旋翼推进的机理对机器人在壁面运动模式下的步态进行了规划,基于非线性轨迹线性化控制(TLC)法设计了空中机器人在步态过程中的姿态稳定控制器。在MATLAB环境下对机器人的腿式壁面运动进行了仿真分析研究,仿真结果表明了所设计的步态及其稳定控制方法的可行性。     

一种磁悬浮陀螺飞轮方案设计与关键技术分析

提出一种磁悬浮陀螺飞轮的设计方案,采用洛伦兹力磁轴承对陀螺飞轮转子进行五自由度支承以提供转动自由度,并利用洛伦兹力磁轴承磁力与电流的线性特性,间接测量陀螺仪的输入角速度.该装置作为姿态控制执行机构兼有敏感器功能,可同时进行三自由度姿态控制与两自由度姿态敏感.针对磁悬浮陀螺飞轮二自由度姿态敏感与三自由度姿态控制这两项关键...     

Momentum transfer-based attitude control of spacecraft with backstepping

A nonlinear control law design based upon the backstepping approach is addressed for attitude maneuver control of spacecraft by momentum transfer (MT) in the presence of disturbance. For MT, a traditional method usually applies constant torque as an input, which tends to produce significant residual oscillation. Enhanced methods such as optimal control can somewhat reduce the residual oscillation, but may not be enough for minimum residual motion. Feedback linearization technique can drive the final nutation angle small enough, but it is rather sensitive to parameter uncertainty. The proposed method here takes advantage of nonlinear control approach with small steady-state nutation angle. Sensitivity about parameter uncertainties by feedback linearization can be reduced by the backstepping technique. Stability of the resulting control law is guaranteed by the Lyapunov stability theory. Boundedness of the control law is presented to validate practical merit of the proposed control law.     

A view finder control system for an earth observation satellite

A real time TV view finder is used on-board a low earth orbiting (LEO) satellite to manually select targets for imaging from a ground station within the communication footprint of the satellite. The attitude control system on the satellite is used to steer the satellite using commands from the groundstation and a television camera onboard the satellite will then downlink a television signal in real time to a monitor screen in the ground station. The operator in the feedback loop will be able to manually steer the boresight of the satellite's main imager towards interested target areas e.g. to avoid clouds or correct for any attitude pointing errors. Due to a substantial delay (in the order of a second) in the view finding feedback loop and the narrow field of view of the main imager, the operator has to be assisted by the onboard attitude control system to stabilise and track the target area visible on the monitor screen.This paper will present an extended Kalman filter used to estimate the satellite's attitude angles using quaternions and the bias vector component of the 3-axis inertial rate sensors (gyros). Absolute attitude sensors (i.e. sun, horizon and magnetic) are used to supply the measurement vectors to correct the filter states during the view finder manoeuvres. The target tracking and rate steering reaction wheel controllers to accurately point and with high agility stabilise the satellite, will be presented. The controller reference generator for the satellite-to-target attitude and rate vectors, as used by the reaction wheel controllers, will be derived.