保持基座稳定的双臂空间机器人轨迹规划研究

针对双臂空间机器人在轨执行任务中需要利用平衡臂稳定基座的问题, 提出了两种典型应用需求——基座质心位置稳定、基座姿态和质心位置同时稳定的协调规划方法.首 先,提出了“系统质心等效机械臂”的概念并推导其运动学模型,基于此模型的位置级反解规 划平衡臂的运动轨迹,使基座质心位置稳定在期望位置;其次,根据角动量守恒定律确定反作用飞 轮的运动速度,将飞轮与平衡臂的运动相结合,同时稳定基座姿态和质心位置;最后,建立双臂空间机器人系统的多体动力学模型并开展仿真研究.所提出的方法克服了以往基于微分运动学所无法回避的奇异问题,且不对平衡臂的质量特性和安装位置作特殊规定,仿真结果证明了方法的有效性.     

机械臂的位姿分离求逆和改进RRT-connect算法研究北大核心CSCD

针对机械臂逆解求取过程中存在大量矩阵变换、计算成本高的问题,采用位姿分离法对逆运动学求解过程进行改进,并提出基于自适应步长的RRT-connect路径规划算法。首先建立六自由度机械臂连杆坐标系模型,采用Standard Denavit-Hartenberg(D-H)方法对机械臂进行正运动学分析,得到机械臂末端执行器位姿相对于基座的齐次变换矩阵。然后引入位姿分离法改进了机械臂的逆运动学求解方法,将机械臂运动学逆解分为位置逆解和姿态逆解两部分,分别用几何法和解析法进行求解,减少了整体计算量。再者提出基于自适应步长的改进RRT-connect路径规划算法,解决了扩展速度慢的问题。最后通过仿真验证所提出方法的正确性和有效性。     

基于PSO的空间机械臂轨迹规划技术研究

研究机器人的机械臂轨迹优化问题,空间机器人系统的机械臂和基座之间存在动力学耦合,基座姿态稳定性容易受到机械臂运动的反作用干扰.为了使空间机器人系统的姿态稳定性不受的影响,提出了一种基于PSO(粒子群优化算法)的参数化5-3-5轨迹规划方法.利用PSO的优化能力找到合适的参数组合,进行关节空间轨迹规划.通过对比实验,运用动力学仿真对方法的有效性进行了验证.仿真结果表明,方法规划出的轨迹运动光滑,且按段轨迹运动机械臂对基座姿态的扰动符合预期要求,证明规划轨迹的有效性.     

改进末端跟随运动的超冗余蛇形臂机器人运动学逆解

针对超冗余蛇形臂机器人运动学逆解中计算量大、超关节极限和位形偏移量大的问题,提出了一种改进末端跟随运动的逆解算法．在末端跟随法中引入蛇形臂弯曲角度的约束,调整关节位置的更新方式,使关节在蛇形臂轴线上运动．通过依次更新关节的空间位置,将超冗余多节蛇形臂的运动学逆解转化为2自由度单节蛇形臂的运动学逆解．仿真分析了蛇形臂机器人在基座移动和基座固定条件下的轨迹跟踪效果,对比了同一目标位置下不同方法的性能．结果表明,改进后的算法能保证蛇形臂的弯曲角度不超过给定范围,关节的运动量从末端到基座依次减小,机器人的运动更协调;与基于雅可比矩阵的数值法和现有启发式方法相比,该方法运算量降低,机器人整体位形偏移量减小,能用于蛇形臂机器人的实时控制．     

一种笛卡儿空间的自由漂浮空间机器人路径规划方法

针对自由漂浮空间机器人工作时需保证载体姿态稳定的问题,提出了一种笛卡儿空间内载体姿态无扰的自由漂浮空间机器人非完整路径规划方法．首先,基于自由漂浮空间机器人特征方程和角动量守恒方程得到广义雅可比矩阵;其次,出于路径规划的需要,分析了载体姿态无扰的自由漂浮空间机器人可达工作空间;最后,引入相关系数,设计了笛卡儿空间内的无扰向量合成算法．仿真得到的路径规划结果表明机械臂末端达到目标点的同时确保了载体姿态无扰动,从而验证了所提方法的可行性和有效性．     

基于自适应反作用零空间控制的大型非合作目标动力学参数实时辨识仿真

针对小型空间机器人抓捕大型空间非合作目标时被抓捕目标初始动量未知且不为0、实时辨识过程中基座姿态受扰动较大的问题,采用自适应反作用零空间控制方法保证在轨实时参数辨识阶段基座姿态受到的扰动最小,建立含有目标动力学参数的动量增量方程,根据在轨实时测量的基座线速度、角速度和机械臂关节角度、角速度求解目标的未知动力学参数.数值仿真结果表明,该方法在辨识过程中可实现空间机器人基座姿态较小的扰动,而且在初始动量未知且不为0的情况下能够实时高精度辨识出大型非合作目标的动力学参数.     

外部扰动下空间机器人基于扰动观测器的鲁棒控制

针对参数不确定及存在外部扰动的情况下,载体位置不控、姿态受控的漂浮基空间机器人末端抓手轨迹跟踪控制问题,提出了一种基于扰动观测器的鲁棒控制方法.结合动量守恒定律,采用拉格朗日第二类方程建立了系统动力学方程.假设外部扰动是随时间变化的未知量,设计了扰动观测器估计由外部干扰和参数不确定构成的总扰动,并基于估计的总扰动引入扰动补偿项,保证了系统的控制性能.根据Lyapunov稳定性理论,证明了文中所提出控制律的稳定性.该控制律能补偿由于参数不确定和外部扰动引起的总扰动,从而提高了系统的轨迹跟踪性能.所提出的控制方案与传统鲁棒控制方案相比,具有控制器结构简单,不需要测量机械臂角加速度及基座的位置、移动速度、移动加速度,系统所需的传感器数量少等优点.最后通过数值仿真模拟,验证了上述控制方案的有效性.     

基于局部支撑姿态的逆运动学求解

逆运动学(Inverse Kinematics)是虚拟角色运动控制的一种基本方法,它根据用户指定肢体末端的位置计算出虚拟角色各个关节的旋转.传统算法求解时没有考虑人体姿态的运动规律,因此其结果不能完全令人满意.文中提出了一种利用捕获的运动数据辅助求解逆运动学问题的新方法.通过自组织映射(Self-Organizing Map,SOM)对姿态数据学习和聚类,获得一组刻画人体姿态空间的支撑姿态,然后通过对问题所在局部空间的支撑姿态加权优化来求解逆运动学问题.该方法克服了传统方法结果不自然、计算效率较低的缺点.实验结果也表明了该文方法的有效性.     

可运动解耦的连续体单孔手术机器人设计与控制

提出一种可拓扑解耦的连续体单孔手术机器人,通过设计中间联动连续体段可以实现多段驱动间的解耦,并且机器人的末端姿态仅取决于远端形变段,实现了位姿分离.基于该运动解耦构形,设计了一种基于空间十字交叉曲面盘的连续体骨架结构来实现具有6自由度的多段连续体机器人,建立了机器人的正运动学,并给出了逆运动学的直接求解法.最后进行了机器人驱动解耦与轨迹跟踪控制实验,经过测试,机器人解耦运动的平均角度误差为2.39?,在20 mm/s的速度及无负载条件下轨迹跟踪误差为1.46 mm.实验表明机器人具有较好的驱动空间解耦能力,并能够基于逆运动学直接求解法实现机器人稳定的运动控制.     

垂直起降无人机基于图像的目标跟踪控制

针对安装有惯性测量单元和摄像机的低成本四旋翼无人机,研究无位置、速度、航向测量情况下的机动目标基于图像的跟踪控制方法.首先,结合无人机的动力学方程在图像空间中推导了系统的误差方程.其次,为克服无航向测量的问题,设计了一种位置控制器,使用图像矩作为反馈输入并输出油门和姿态指令.最后,针对缺少图像速度测量问题,设计了一种super-twisting滑模观测器和控制器,生成的期望姿态和拉力指令无颤振,并通过李雅普诺夫理论证明了控制系统的稳定性.最终无人机通过调整倾斜姿态实现了跟踪飞行,且避免了响应慢的航向调整.跟踪机动目标的仿真结果验证了所提出方法的有效性.     

An efficient motion generation method for redundant humanoid robot arms based on motion continuity

This paper proposes a novel method of motion generation for redundant humanoid robot arms, which can efficiently generate continuous collision-free arm motion for the preplanned hand trajectory. The proposed method generates the whole arm motion first and then computes the actuators’ motion, which is different from IK (inverse kinematics)-based motion generation methods. Based on the geometric constraints of the preplanned trajectory and the geometric structure of humanoid robot arms, the wrist trajectory and elbow trajectory can be got first without solving inverse kinematics and forward kinematics. Meanwhile, the constraints restrict all feasible arm configurations to an elbow-circle and reduce the arm configuration space to a two-dimension space. By combining the configuration space and collision distribution of arm motion, collision-free arm configurations can be identified and be used to generate collision-free arm motion, which can avoid unnecessary forward and inverse kinematics. The experiments show that the proposed method can generate continuous and collision-free arm motion for preplanned hand trajectories.     

Kinematic control of redundant free-floating robotic systems

This paper is aimed at presenting solution algorithms to the inverse kinematics of a space manipulator mounted on a free-floating spacecraft. The reaction effects of the manipulator's motion on the spacecraft are taken into account by means of the so-called generalized Jacobian. Redundancy of the system with respect to the number of task variables for spacecraft attitude and manipulator end-effector pose is considered. Also, the problem of both spacecraft attitude and end-effector orientation representation is tackled by means of a non-minimal singularity-free representation: the unit quaternion. Depending on the nature of the task for the spacecraft/manipulator system, a number of closed-loop inverse kinematics algorithms are proposed. Case studies are developed for a system of a spacecraft with a six-joint manipulator attached.     

Hybrid predictive dynamics: a new approach to simulate human motion

A new methodology, called hybrid predictive dynamics (HPD), is introduced in this work to simulate human motion. HPD is defined as an optimization-based motion prediction approach in which the joint angle control points are unknowns in the equations of motion. Some of these control points are bounded by the experimental data. The joint torque and ground reaction forces are calculated by an inverse algorithm in the optimization procedure. Therefore, the proposed method is able to incorporate motion capture data into the formulation to predict natural and subject-specific human motions. Hybrid predictive dynamics includes three procedures, and each is a sub-optimization problem. First, the motion capture data are transferred from Cartesian space into joint space by using optimization-based inverse kinematics (IK) methodology. Secondly, joint profiles obtained from IK are interpolated by B-spline control points by using an error-minimization algorithm. Third, boundaries are built on the control points to represent specific joint profiles from experiments, and these boundaries are used to guide the predicted human motion. To predict more accurate motion, the boundaries can also be built on the kinetic variables if the experimental data are available. The efficiency of the method is demonstrated by simulating a box-lifting motion. The proposed method takes advantage of both prediction and tracking capabilities simultaneously, so that HPD has more applications in human motion prediction, especially towards clinical applications.     

航天器姿轨耦合非线性同步控制

研究航天器飞行稳定控制建模问题。航天器动力学模型的精确建立,要求采用单独建立轨道或姿态的模型无法满足任务高精度要求,从非线性相对轨道动力学方程和修正罗德里格斯参数(MRP)表示的姿态运动学方程出发,建立了航天器六自由度的相对耦合动力学方程。为了给出姿轨运动的基准,分别设计了航天器理想姿态和椭圆加指数接近轨道。针对耦合非线性动力学方程设计了非线性同步控制律,并通过Lyapunov证明闭环系统的全局渐近稳定性。通过仿真结果可以看出,非线性同步控制算法能使轨道和姿态误差逐步趋于零,为航天器姿轨耦合设计提供了依据。     

Tracking of a moving ground target by a quadrotor using a backstepping approach based on a full state cascaded dynamics

In this paper, a tracking controller is formulated for a quadrotor to track a moving ground target. The quadrotor exhibits distinct hierarchical dynamics that allows its position to be controlled by its attitude. This motivates the use of backstepping control on the underactuated quadrotor. Most backstepping architecture controls the quadrotor position and attitude independently, and couples them with inverse kinematics. Inverse kinematics computes the attitude angles required to achieve a desired acceleration. However unmodeled effects are shown to cause inexact inversion resulting in tracking error. The approach proposed in this paper uses a re-formulated full state cascaded dynamics to eliminate the need for inverse kinematics in a full state backstepping control architecture. It is shown that zero steady state error is achieved in the presence of unmodeled aerodynamics effect and wind disturbance despite no integral action. In addition, a backstepping formulation is derived using contraction theory that guarantees the boundedness of state response under bounded disturbances such as wind. This improves the system performance. Numerical simulations are performed using the proposed controller to track a target moving along predefined paths and the results are compared with a benchmark controller derived using inverse kinematics. The results show that the proposed controller is able to achieve better tracking performance under unmodeled aerodynamic effects and wind disturbance as compared with the benchmark controller.     

航天飞机操作器的运动学研究

本文考虑了航天飞机与操作器之间的耦合运动,建立了航天飞机机器人的运动学方程,并提供了一种新的迭代计算法.使用该方法可方便地认操作器所握住的负载的位置和姿态求解操作器各关节的位移,从而顺利地解决了被认为较困难的运动学逆问题.     

空间机械臂本体与末端抓手协调运动的自适应控制方法

讨论了载体位置不受控制的漂浮基空间机械臂本体与末端抓手协调运动的自适应控制问题. 对系统的运动学、动力学分析表明, 结合系统动量守恒关系得到的系统动力学方程及协调运动的增广广义Jacobi矩阵可以表示为适当选择的组合惯性参数的线性函数. 以此为基础, 对于系统存在未知参数的情况, 设计了本体姿态与机械臂末端抓手惯性空间轨迹协调运动的自适应控制方案. 上述控制方案的显著优点在于: 不需要测量、反馈飞行器本体的位置、移动速度及移动加速度. 仿真运算, 证实了上述控制方案的有效性.     

Dynamics and control of space free-flyers with multiple manipulators

This paper studies the motion control of a multiple manipulator free-flying space robot chasing a passive object in near proximity. Free-flyer kinematics are developed using a minimum set of body-fixed barycentric vectors. Using a general and a quasi-coordinate Lagrangian formulation, equations of motion for model-based controllers are derived. Two model-based and one transposed Jacobian control algorithms are developed that allow coordinated tracking control of the manipulators and the spacecraft. In particular, an Euler parameter model-based control algorithm is presented that overcomes the non-physical singularities due to Euler angle representation of attitude. To ensure smooth operation, and reduce disturbances on the spacecraft and on the object just before grasping, appropriate trajectories for the motion of spacecraft/manipulators are planned. The performance of model-based algorithms is compared, by simulation, to that of a transposed Jacobian algorithm. Results show that due to the complexity of space robotic systems, a drastic deterioration in the performance of model-based algorithms in the presence of model uncertainties results. In such cases, a simple transposed Jacobian algorithm yields comparable results with much reduced computational burden, an issue which is very important in space.     

卫星姿态的状态转移控制

本文面向卫星的应用需求,对卫星姿态的运动学和动力学进行了分析与建模.利用反馈线性化,将姿态运动的高阶非线性项包含在姿态控制中,通过局部动态线性化,将动力学系统近似为定常系统.通过幂级数法对系统进行了状态转移过程的求解.采用模型预测的方法获得姿态角和姿态角速度的预期偏差.通过广义逆变换构造关于偏差的最小范数、最小二乘控制器.提出了一种基于状态转移的卫星姿态机动、跟踪与稳定控制的新方法.控制器的参数具有根据系统采样周期和当前状态时变自适应的特点.考虑帆板挠性及多种偏差和噪声影响,仿真验证了方法的可行性和有效性.     

一种新型爬壁机器人机构及运动学研究

提出了一种新型爬壁机器人机构，介绍了机构的构型及结构特点，推导了运动学正、逆解方程式，规划了直线行走、平面旋转及交叉面跨越三种运动模式．机构构型及运动模式的分析表明，该机构具有体积小、运动特性较好的特点．仿真结果证明，该机器人在运动过程中所需吸附力矩较小且占据的空间较少．