Optimal control of stretching process of flexible solar arrays on spacecraft based on a hybrid optimization strategy

The optimal control of multibody spacecraft during the stretching process of solar arrays is investigated,and a hybrid optimization strategy based on Gauss pseudospectral method(GPM) and direct shooting method(DSM) is presented. First, the elastic deformation of flexible solar arrays was described approximately by the assumed mode method, and a dynamic model was established by the second Lagrangian equation. Then, the nonholonomic motion planning problem is transformed into a nonlinear programming problem by using GPM. By giving fewer LG points, initial values of the state variables and control variables were obtained. A serial optimization framework was adopted to obtain the approximate optimal solution from a feasible solution. Finally, the control variables were discretized at LG points, and the precise optimal control inputs were obtained by DSM. The optimal trajectory of the system can be obtained through numerical integration. Through numerical simulation, the stretching process of solar arrays is stable with no detours, and the control inputs match the various constraints of actual conditions.The results indicate that the method is effective with good robustness.     

动态规划求解空间双臂机器人非完整运动最优控制问题

通过自适应动态规划研究自由漂浮空间双臂机器人运动的最优控制问题．针对空间双臂机器人的非完整性运动,采用自适应动态规划(Adaptive Dynamic Programming, ADP)方法求解其最优控制问题．根据多体动力学理论,推导了载体位置、姿态均无控制条件下,双臂空间机器人满足的系统动量守恒关系的非完整约束方程,并将其转化为控制系统的状态方程,从而将双臂空间机器人的非完整运动规划问题转化为对非线性系统的控制问题．文中根据自适应动态规划网络结构,利用神经网络来近似性能指标函数,进而用龙格库塔法求解状态变量．并给出了适合该类问题的一种效用函数具体表达式,保证了空间双臂机器人到达期望位置后不再继续运动．实现了对空间双臂机器人非完整运动规划的最优控制．数值仿真实验验证了ADP对求解空间双臂机器人非完整运动规划最优控制问题的有效性．     

自由下落猫姿态最优控制的混合优化策略

研究猫自由下落时的转体运动对探索宇航员在太空失重状态下的空间运动规律具有重要的参考价值.针对猫自由下落时四肢先着地现象的姿态最优控制问题,提出一种由Gauss伪谱法求解可行解与直接打靶法求解最优精确解相结合的混合优化策略.首先,根据猫在自由下落过程中的角动量守恒原理,推导出简化后的两对称刚体系统的非完整姿态运动方程;然后基于Gauss伪谱法将此无漂移系统的姿态非完整运动规划问题离散为非线性规划问题,并在不考虑实际性能指标函数的条件下利用序列二次规划算法求解此非线性规划问题在较少节点时对应的控制变量可行解,再通过三次样条插值获取较多节点时的控制变量值;最后基于直接打靶法将插值得到的控制值作为序列二次规划算法的初始猜测值,从而求解得到最优的控制输入,再代入系统姿态运动方程,通过数值积分得到落体猫的转体姿态运动曲线.通过数值仿真,求解得到的姿态运动曲线是光滑的,能以较高的精度到达预定的目标姿态;最优控制输入也能满足预先设计的零边界控制要求以及最大控制要求;结果表明了此混合优化策略具有较强的鲁棒性和有效性.     

Detumbling strategy and coordination control of kinematically redundant space robot after capturing a tumbling target

This paper focuses on the motion planning to detumble and control of a space robot to capture a non-cooperative target satellite. The objective is to construct a detumbling strategy for the target and a coordination control scheme for the space robotic system in post-capture phase. First, the dynamics of the kinematically redundant space robot after grasping the target is presented, which lays the foundation for the coordination controller design. Subsequently, optimal detumbling strategy for the post-capture phase is proposed based on the quartic B\(\acute{\text{ e }}\)zier curves and adaptive particle swarm optimization algorithm subject to the specific constraints. Both detumbling time and control torques were taken into account for the generation of the optimal detumbling strategy. Furthermore, a coordination control scheme is designed to track the designed reference path while regulating the attitude of the chaser to a desired value. The space robot successfully dumps the initial velocity of the tumbling satellite and controls the base attitude synchronously. Simulation results are presented for detumbling a target with rotational motion using a seven degree-of-freedom redundant space manipulator, which demonstrates the feasibility and effectiveness of the proposed method.     

自由漂浮空间机器人路径优化的Legendre伪谱法

基于Legendre 伪谱法研究自由漂浮空间机器人非完整路径规划的最优控制问题. 自由漂浮是空间机器人执行任务常用的工作模式,其路径优化是空间机器人完成复杂空间任务的基础. 由于空间机器人不具有固定基座,机械臂和载体之间存在非完整约束,使得自由漂浮空间机器人路径规划完全不同于地面机器人而变得具有挑战性. 本文提出自由漂浮空间机器人路径规划的最优控制伪谱方法. 首先,利用多体动力学理论建立自由漂浮空间机器人动力学模型,给定系统的初始和目标位形,选取机械臂关节耗散能最小为性能指标,并考虑实际控制输入受限,建立其路径规划的Bolza 问题. 然后,应用Legendre 伪谱法,将状态和控制变量在Legendre-Gauss-Lobatto (LGL) 点上离散,并构造Lagrange 插值多项式逼近系统状态和控制变量,将连续路径优化问题离散化为非线性规划问题求解. 最后通过数值仿真表明,应用Legendre 伪谱法求解自由漂浮空间机器人非完整路径规划问题,得到的机械臂和载体最优运动轨迹,较好地满足各种约束条件,且计算精度高、速度快,并具有良好的实时性.      

Optimal control of attitude for coupled-rigid-body spacecraft via Chebyshev-Gauss pseudospectral method

The attitude optimal control problem(OCP) of a two-rigid-body spacecraft with two rigid bodies coupled by a ball-in-socket joint is considered. Based on conservation of angular momentum of the system without the external torque, a dynamic equation of three-dimensional attitude motion of the system is formulated. The attitude motion planning problem of the coupled-rigid-body spacecraft can be converted to a discrete nonlinear programming(NLP) problem using the Chebyshev-Gauss pseudospectral method(CGPM). Solutions of the NLP problem can be obtained using the sequential quadratic programming(SQP) algorithm. Since the collocation points of the CGPM are Chebyshev-Gauss(CG) points, the integration of cost function can be approximated by the Clenshaw-Curtis quadrature, and the corresponding quadrature weights can be calculated efficiently using the fast Fourier transform(FFT). To improve computational efficiency and numerical stability, the barycentric Lagrange interpolation is presented to substitute for the classic Lagrange interpolation in the approximation of state and control variables. Furthermore, numerical float errors of the state differential matrix and barycentric weights can be alleviated using trigonometric identity especially when the number of CG points is large. A simple yet efficient method is used to avoid sensitivity to the initial values for the SQP algorithm using a layered optimization strategy from a feasible solution to an optimal solution. Effectiveness of the proposed algorithm is perfect for attitude motion planning of a two-rigid-body spacecraft coupled by a ball-in-socket joint through numerical simulation.     

基于能力评估的空间翻滚目标抓捕策略优化

由于目标的翻滚运动, 空间双臂机器人对动态目标的抓捕相比于静态目标更具有挑战性. 对抓捕策略进行优化可以提高空间双臂机器人对翻滚目标的操作能力以保证任务的成功. 本文提出了一种基于能力评估的抓捕策略优选方法. 空间双臂机器人捕获目标时, 双臂末端执行器与目标同时接触形成闭链系统, 闭链约束的引入使操作能力的评估更加复杂. 在对双臂空间机器人协调操作翻滚目标的运动学与动力学分析基础上, 建立了考虑闭链约束的协调工作空间, 并分析了基于任务兼容度的消旋能力评估指标. 建立的协调工作空间同时包含位置和姿态信息, 可以用于灵巧度的计算. 接着, 基于协调工作空间的全局灵巧度指标确定机械臂末端执行器对目标的最优抓捕点, 以及考虑相机视角约束和末端执行器对目标速度跟踪约束下的力任务兼容度指标确定空间双臂机器人捕获翻滚目标时的最优抓捕构型. 利用能力评估确定抓捕策略可以充分利用双臂的协调性以增加对动态目标的操作能力, 通过仿真验证了所提抓捕策略的可行性和有效性.      

基于Clamped B样条的空间非合作目标抓捕策略研

空间机械臂技术是未来实施在轨服务与维护任务的关键技术之一. 利用机械臂对空间非合作目标, 特别是翻滚目标的抓捕仍然存在巨大的挑战. 本文提出一种基于Clamped B样条的空间非合作目标抓捕策略方案. 在对非合作目标与空间机械臂运动学与动力学分析的基础上, 结合非合作目标被空间机械臂抓捕后的动静态对偶性分析, 构建抓捕后的力可操作度椭球作为抓捕策略设计的优化指标. 其次, 考虑目标的运动预测和空间机械臂的抓捕能力图谱构建, 确定空间机械臂应对目标的最优抓捕时机与抓捕终端状态. 基于Clamped B样条对空间机械臂各关节轨迹进行时间归一化参数描述, 并对抓捕过程中的机械臂关节角、速度、避撞、抓捕走廊等约束进行数学变换, 最终将抓捕策略转换为多约束、多目标的非线性优化问题, 利用自适应惯性权重的粒子群优化算法进行求解. 将所设计的抓捕策略应用于空间七自由度运动学冗余机械臂, 实现了对空间中翻滚目标的成功捕获, 验证了所提抓捕策略的可行性与有效性.      

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介绍了运动机器人针对动态变化环境的运动控制与决策(如运动障碍物规避,运动 目标跟踪等)问题. 分别从速度空间控制决策的角度分析阐述了运动 决策的基本方法,以及各自的特点. 提出了关于随机运动障碍物与目标的避障问题以及解 决思路,从而建立起基于概率分析的全局优化的速度避障决策方案. 通过仿真试验说明了方 法的有效性,并与传统非概率分析的实时局部决策的方法进了比较与评价.     

机器人无标定视觉伺服控制研究进展

视觉伺服控制是机器人系统重要的控制手段. 相比传统的在标定条件下使用的视觉伺服系统,无标定视觉伺服系统具有更高的灵活性与适应性,是机器人伺服控制系统未来重要的发展方向和研究热点. 本文从目标函数选择、控制器设计、运动轨迹规划三方面综述了无标定视觉伺服控制系统近年来的主要研究进展. 首先根据目标函数的形式,分析了基于位置的视觉伺服、基于图像的视觉伺服以及混合视觉伺服各自的特点与应用;在控制器设计方面,根据是否在设计过程中考虑机器人的非线性动力学特性,分别介绍了考虑机器人运动学与考虑机器人动力学的无标定视觉伺服控制器的设计,重点突出了雅克比矩阵的构造与估计方法;针对无标定视觉伺服系统运动轨迹可能存在的问题,从空间轨迹优化与障碍规避的角度,阐述了已有的可行解决方案. 最后,基于当前的研究进展展望了无标定视觉伺服的未来研究方向.      

勒让德伪谱法求解三维刚体摆姿态运动最优控制问题

研究伪谱法求解三维刚体摆姿态运动最优控制问题. 针对三维刚体摆这类含有约束的力学模型,提出了基于勒让德伪谱法的三维刚体摆姿态最优控制方法. 利用插值逼近设计了三维刚体摆姿态运动最优控制算法,得到了三维刚体摆的姿态最优控制轨迹,并结合松弛参数来控制插值点的取值,寻找满足的可行解. 仿真结果表明,基于勒让德伪谱法的最优控制算法使得三维刚体摆能以较小的误差运动到期望的末端姿态,且计算速度快,能够获得精度较高的控制输入量.     

OPTIMAL MOTION PLANNING FOR A RIGID SPACECRAFT WITH TWO MOMENTUM WHEELS USING QUASI-NEWTON METHOD

An optimal motion planning scheme based on the quasi-Newton method is proposedfor a rigid spacecraft with two momentum wheels. A cost functional is introduced to incorporatethe control energy, the final state errors and the constraints on states. The motion planning fordetermining control inputs to minimize the cost functional is formulated as a nonlinear optimalcontrol problem. Using the control parametrization, one can transform the infinite dimensionaloptimal control problem to a finite dimensional one that is solved via the quasi-Newton methodsfor a feasible trajectory which satisfies the nonholonomic constraint. The optimal motion planningscheme was applied to a rigid spacecraft with two momentum wheels. The simulation results showthe effectiveness of the proposed optimal motion planning scheme.     

Dynamics and trajectory planning of a planar flipping robot

In this paper, a new planar one-legged robot model is firstly proposed, which, unlike previous one-legged robot with springy legs, consists of three revolute joints. Then a novel manner of one-legged locomotion (i.e., ballistic flip) is designed for this robot. A complete flipping gait cycle is composed of four phases: two stance phases and two flight phases. During flight phases, no active control is needed on the knee joint. Rotational motion and translational motion is decoupled from each other in flight phases. Landing of the robot is regarded as an inelastic impulsive impact. During stance phases, the robot model can be simplified as a two-degree-of-freedom rigid manipulator. Based on analysis of kinematics and dynamics of the flip robot, trajectory planning of cyclic flip gait is formulized as a problem of numerical optimization subject to nonlinear constraints such as positive reaction force of ground and finite torque of the joints. One potential application of the flipping robot is space exploration, which urgently requires the legged locomotive robots to be light-weighted and energy efficient.     

轮式移动机器人非完整运动规划的最优控制方法

本文讨论轮式动机器人非完整运动的最优规划问题,利用约束与最优控制理论建立数学模型,考虑系统的非完整约束特性,提出轮式移动机器人运动规划的最优控制算法。通过数值仿真,表明该方法的有效性。     

Based on wavelet analysis to optimal control of motion planning of space manipulator

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配置柔顺机构空间机器人双臂捕获卫星操作力学模拟及基于神经网络的全阶滑模避撞柔顺控制

讨论了空间机器人双臂捕获卫星操作过程避免关节冲击破坏的避撞柔顺控制问题. 为此在关节电机与机械臂之间设计了一种旋转 型串联弹性执行器(rotatory series elastic actuator, RSEA)--柔顺机构,其作用在于:(1) 通过其内置弹簧的拉伸或压缩变形来吸收捕获操作过程中被捕获卫星对空间机器人关节产生的冲击能量;(2) 可以利用合理设计的与之配合的避撞柔顺控制策略来保证关节冲击力矩受限在安全范围. 首先,利用第二类Lagrange方程分别建 立了捕获操作前含柔顺机构双臂空间机器人的开环分系统动力学模型与目标卫星的分系统动力学模型;之后,基于系统动量 守恒关系、闭链系统位置与速度几何约束关系,获得了捕获操作后空间机器人与被捕获卫星闭链混合体系统综合动力学方程; 最后,基于RBF神经网络提出了一种捕获操作后两者混合体系统镇定运动的全阶终端滑模避撞柔顺控制方案. 所提方案结合柔 顺机构在有效吸收、缓冲被捕获卫星冲击能量的同时,还在冲击能量过大时适时开、关空间机器人关节驱动器,以避免关节驱 动器过载、破坏;此外,还通过最小权值范数法分配了机械臂各关节力矩,以保证双臂协调操作. Lyapunov稳定性理论证明了 系统的全局稳定性,系统计算机数值仿真也验证了上述避撞柔顺控制策略的有效性.      

TRAJECTORY TRACKING CONTROL FOR DUAL-ARM SPACE ROBOT WITH BOUNDED INPUT TORQUES

讨论基座姿态、位置均不控的自由漂浮双臂空间机器人在关节驱动力矩受限下其关节协调运动的控制问题. 运用拉格朗日第二类方程并耦合动量守恒关系建立动力学方程. 尔后,设计了基于饱和函数的控制方案,该方案引入具有饱和特性的双曲正切函数来控制关节力矩幅值. 最后,根据奇异扰动系统稳定性理论将系统分为降阶系统和边界层系统,分别利用李雅普诺夫函数证明其在原点呈指数稳定. 数值仿真进一步表明该方案的有效性和优越性.     

An evolutionary approach for the motion planning of redundant and hyper-redundant manipulators

The trajectory planning of redundant robots is an important area of research and efficient optimization algorithms are needed. The pseudoinverse control is not repeatable, causing drift in joint space which is undesirable for physical control. This paper presents a new technique that combines the closed-loop pseudoinverse method with genetic algorithms, leading to an optimization criterion for repeatable control of redundant manipulators, and avoiding the joint angle drift problem. Computer simulations performed based on redundant and hyper-redundant planar manipulators show that, when the end-effector traces a closed path in the workspace, the robot returns to its initial configuration. The solution is repeatable for a workspace with and without obstacles in the sense that, after executing several cycles, the initial and final states of the manipulator are very close.     

漂浮基柔性关节空间机器人自适应滑模运动控制及振动主动抑制

讨论了关节柔性且系统参数不确定的漂浮基空间机器人系统的动力学建模过程、运动轨迹跟踪控制算法设计及系统柔性振动的主动抑制问题。利用系统动量、动量矩守恒关系和拉格朗日法对系统动力学进行分析,并建立系统动力学方程。基于奇异摄动法将系统分解为表示系统刚性运动部分的慢变子系统和表示系统柔性运动部分的快变子系统。针对慢变子系统提出了一种自适应滑模控制算法。该控制算法是由基于滑模面的等效控制项、自适应控制项和PID反馈控制项组成。因此,它集合了滑模控制、自适应算法和PID技术的优点,且弥补了三种算法各自的缺点。该控制算法能够有效地补偿系统的转动误差和不确定参数,提高控制系统的精度。针对快变子系统,提出基于速度差值的反馈控制算法来抑制柔性关节引起的系统柔性振动,保证系统的稳定性。最后,通过仿真实验证明了提出的混合控制算法的有效性。