多杆空间柔性机器人递推Lagrange动力学建模和仿真

研究了多杆空间柔性机器人的动力学问题.运用Lagrange方法,结合齐次变换矩阵,推导得到了多杆空间柔性机器人动力学方程,在推导过程中采用了运动学递推策略以提高计算效率.建模时除考虑柔性构件的横向弯曲变形外,还计及了构件的扭转变形.基于上述理论研制了多杆空间柔性机器人动力学仿真软件,并对一空间柔性机器人进行了动力学仿真计算,验证了理论和软件的先进性能.     

柔性杆柔性铰机器人动力学分析

研究由N柔性杆和N柔性铰组成的空间机器人的动力学问题．把柔性铰简化成一个线性扭转弹簧,采用假设模态法表示杆件的弹性变形,运用Kane方法对全柔机器人进行动力学建模,推导出完整的系统动力学方程组．通过一个数值仿真算例,验证所做工作的可行性,并分析了柔性效应对机器人动力学响应的影响．     

微分求积法求解悬臂L梁固有振动特性研究北大核心CSCD

悬臂L梁结构由于具有柔性大、可设计性强、空间利用充分,振动过程中变形方式多样等独特优势而受到了广泛的关注与研究.该文提出了一种基于微分求积法求解末端附加质量块的矩形等截面均质悬臂细长L梁的各阶固有频率和模态的方法.在双坐标系下,基于Euler-Bernoulli梁理论建立了悬臂L梁的动力学方程,然后通过选取Chebyshev多项式的根作为节点坐标、选取Lagrange插值基函数、求解各阶权系数、处理边界条件等步骤,最终利用求解矩阵广义特征值问题的方法求得结构各阶固有频率及模态.在边界条件的处理上,直接将边界条件施加于边界点上,通过对比研究验证了该文固有频率理论解的正确性.最后分析了末端质量、内外梁的长度比、宽度、厚度对各阶固有振动特性的影响.该方法可以进一步应用推广到相关结构振动的研究中.     

基于四元数方法的绳系机器人姿态控制

为进一步提升空间绳系机器人在轨服务能力，研究了空间绳系机器人抓捕目标后的复合体姿态控制问题.首先，基于四元数原理，描述了空间绳系机器人在抓捕目标后组成的复合体姿态，建立了空间绳系机器人系统的动力学方程；其次，针对带约束的动力学控制方程，结合投影技术和Runge Kutta方法，构造了一种保四元数范数的显式投影方法；最后，通过数值实验，验证了所提出数值方法的有效性，同时分析了采用系绳和推力器同时控制，采用系绳、推力器相互切换控制，以及单独采用推力器进行控制这3种方式对空间绳系机器人抓捕目标后的复合体姿态的控制效果和能量消耗.     

基于二次B样条的时间最优轨迹规划

轨迹规划是机器人运动中的基本问题,文章给出带动力学限制的时间最优二次B样条轨迹的规划方法.算法首先搜索可见性图的对偶图得到初始折线路径.在此基础上可以求解带有避障条件的二次B样条拟合问题,到无碰撞光滑的运动轨迹.在此基础上,联合动力学限制建立新的时间最优模型,并用"Bang-Bang-Singular"控制策略求解得到运动轨迹.数值实验表明,文章方法可以求得符合动力学限制的时间最优运动路径.     

浅析多动点轨迹方程的求法

多动点轨迹方程的求法,是学生感到比较困难的问题.事实上一个轨迹命题中,不管有多少个动点,总可以分成两类,即主动点和从动点,从动点随主动点的运动而运动.主动点的轨迹方程往往为已知或者容易求出,而从动点的轨迹方程是待求的.下面介绍几种常用的多动点轨迹方程的求法.1 代入法在多动点轨迹问题中,如果主动点只有一个,其它动点都是从动点.此时,只要能找出主动点与从动点(待求的)之间的联系,并用从动点的坐标去表示主动点的坐标,然后代入主动点所满足的方程,化简整理即可.     

一类柔性臂机器人的稳定性

本文研究了一类柔性臂机器人的控制问题,且柔性臂的弯曲振动与扭转振动的耦合作用表现在边界方程中。本文运用算子谱理论、算子半群理论等,得到系统的主算子生成的C0-半群的具体表示式,并证明了半群的解析性、非紧性及非一致指数稳定性。     

基于模态自适应的大变形多体系统动力学分析

柔性大变形系统在进行模态降阶时，若模态选取不当，会影响求解精度甚至导致求解结果发散.对此，提出了基于绝对节点坐标法(ANCF)的柔性大变形系统模态自适应选择方法.通过ANCF梁单元建立系统的动力学模型；利用全模态稀疏表示内部区域的坐标；根据Latin超立方抽样构建采样矩阵，作用于动力学方程，以减少方程的数量；以采样后的动力学方程作为约束，构造模态坐标范数优化问题；求解优化问题可以得到具有重大贡献的模态.通过两个实例表明：数值计算结果与常用方法的结果高度吻合并且求解效率显著提升.     

用解析法讨论共点线与共线点的问题

一、预备知识平面几何中的共点线与共线点是一类重要课题,本文用解析法(坐标法)讨论这一类问题.解析法虽计算量不一定小,但比起综合法来还是容易思考的.关键问题是共线点问题,要求出直线     

基于最小二乘法的飞机发动机安装节动态力识别

飞机舱内噪声与振动控制的一个关键技术是获取发动机安装节处的动态力,从而实现对发动机振动引发的机体结构振动和舱内噪声进行预测和控制.但对于飞机,在飞行状态下不可能对发动机安装节处的动态力进行直接测量.通过采用最小二乘法正则化逆运算,利用地面状态下发动机安装节至吊挂或发动机安装节至安装节上的结构频率响应函数,以及飞行状态下吊挂或发动机安装节上相同位置处的振动加速度响应,对发动机安装节上的动态力进行识别.通过对比逆运算过程中的矩阵条件数,判定两组动态力识别的相对准确度.通过对两组数据识别的动态力均方根值进行对比,确认通过最小二乘法识别的发动机安装节动态力满足工程使用要求.     

Computation of program controls performed nonstop by gyrodynes

A new method for calculating space vehicle (SV) attitude controls ensuring their effective implementation by a system of collinear pairs of single-gimbal forced unrestrained gyros (gyrodynes) has been proposed. The novelty of the method consists in a virtual kinematic configuration of the gyro system, i.e., the precession of gyro units in the collinear pairs of gyrodynes is coupled in a nonmechanical manner. In addition, the angular momentum of the system as a state variable for describing the dynamics of the SV permanent rotation was used for the first time at the stage of computing controls performed nonstop by gyrodynes. In the general formulation, when the desired final state of the SV is arbitrary, the SV attitude control problem can be reduced to a sequence of permanent rotations. The performance of the method is demonstrated as applied to the calculation of program gyrodyne controls with a permanent reduction in the SV angular velocity around its center of mass with a nonzero SV angular momentum after its discharge.

     

Cell-to-cell mapping method for time-optimal trajectory planning of multiple robot arm systems

This paper presents the results obtained by applying the cell-to-cell mapping method to solve the problem of the time-optimal trajectory planning for coordinated multiple robotic arms handling a common object along a specified geometric path. Based on the structure of the time-optimal trajectory control law, the continuous dynamic model of multiple arms is first approximated by a discrete and finite cell-to-cell mapping on a two-dimensional cell space over a phase plane. The optimal trajectory and the corresponding control are then determined by using the cell-to-cell mapping and a simple search algorithm. To further improve the computational efficiency and to allow for parallel computation, a hierarchical search algorithm consisting of a multiple-variable optimization on the top level and a number of cell-to-cell searches on the bottom level is proposed and implemented in the paper. Besides its simplicity, another distinguishing feature of the cell-to-cell mapping methods is the generation of all optimal trajectories for a given final state and all possible initial states through a single searching process. For most of the existing trajectory planning methods, the planning process can be started only when both the initial and final states have been specified. The cell-to-cell method can be generalized to any optimal trajectory planning problem for a multiple robotic arms system.     

Adaptive control of kinematically redundant robots

A redundant robot has more degrees of freedom than those neededto position the Robert end-effector uniquely. In a usual robotictask, only end-effector position trajectory is specified. Thejoint position trajectory is unknown, and it must be selectedfrom a self-motion manifold for a specified end-effector. Inmany situations, the robot dynamic parameters such as the linkmass, inertia, and joint viscous friction are unknown. The lackof knowledge of the joint trajectory and the dynamic parametersmake it difficult to control redundant robots. In this paper we show, through careful formulation of the problem,that the adaptative control of redundant robots can be addressedas a reference-velocity traking problem in the joint space.A control law ensures bounded estimation of the unknown dynamicparameters of the robot, and the convergence to zero of thevelocity traking error is derived. To ensure the joint motionon the self-motion manifold remains bounded, a homeomorphictransformation is found. This transformation decomposes thedynamics of the velocity tracking error into a cascade systemconsisting of the dynamics in the end-effector error coordinatesand the dynamics on the self-motion manifold. The dynamics onthe self-motion manifold is shown to be related to the conceptof zero dynamics. In the shown that, if the reference jointtrajectory is selected to optimize a certain type of objectivefunction, then stable dynamics on the self-motion manifold result.This ensures the overall stability of the adaptive system. Detailedsimulations are given to test the theoretical developments.The proposed adaptive scheme does not require measurements ofthe joint acceleration or the inversion of the inertia matrixof the robot.     

Aspects on the Functional Optimization of an Industrial Robot Structure Implemented in Military Logistical Activities

The authors of the present paper outline aspects on the optimization of the a TR-type industrial robot structure movements in order to generate the manipulation space to a flexible manufacturing cell with a parallel organization designed for the pallet and container operation of paint-filled recipients. The paper contains the direct and inverted geometrical modelling of the robot structure using the 3*3 rotation matrix method and the algebra method. After knowing the characteristic point movement of the prehension device, graphics for the variation of the TR robot's general coordinates and for the trajectory of the prehension device's characteristic point of its work space were performed by using the Mathematica 6.0 soft. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Omnidirectional walking of legged robots with a failed leg

This paper studies omnidirectional walking of a hexapod robot with a locked joint failure by proposing crab gaits and turning gaits. Due to the reduced workspace of a failed leg, fault-tolerant gaits have limitations in their mobility. As for crab gaits, an accessible range of the crab angle is derived for a given configuration of the failed leg. As for turning gaits, the conditions on turning trajectories guaranteeing fault tolerance are derived for spinning gaits and circling gaits. Based on the principles of fault-tolerant gait planning, periodic crab gaits and turning gaits are proposed in which a hexapod robot realizes tripod walking after a locked joint failure, having a reasonable stride length and stability margin. The proposed fault-tolerant gaits are then applied to an obstacle avoidance problem of a hexapod robot with a locked joint failure. The kinematic constraints of fault-tolerant gaits should be considered in planning the robot trajectory.     

Path planning for robots under stochastic uncertainty *

In order to reduce large online measurement and correction expenses, the a priori informations on the random variations of the model parameters of a robot and its working environment are taken into account already at the planning stage. Thus, instead of solving a deterministic path planning problem with a fixed nominal parameter vector, here, the optimal velocity profile along a given trajectory in work space is determined by using a stochastic optimization approach. Especially, the standard polygon of constrained motion-depending on the nominal parameter vector-is replaced by a more general set of admissible motion determined by chance constraints or more general risk constraints. Robust values (with respect to stochastic parameter variations) of the maximum, minimum velocity, acceleration, deceleration, resp., can be obtained then by solving a univariate stochastic optimization problem Considering the fields of extremal trajectories, the minimum-time path planning problem under stochastic uncertainty can be solved now by standard optimal deterministic path planning methods     

Flatness‐Based Trajectory Tracking Control of an Underconstrained Cable Suspension Manipulator

Cable suspension manipulators support a payload platform in space by several spatially arranged cables with computercontrolled winches. The winches are mounted either fixed or on movable trolleys. Compared to conventional cranes, it is possible to control not only the translational motion of the payload but also its orientation in order to perform, for example, assembly tasks. By this, cable suspension manipulators combine the ability of cranes to support heavy payloads in a large workspace with the dexterity of robot manipulators. The present contribution treats nonlinear trajectory tracking control of cable suspension manipulators that are kinematically undetermined and statically determined. In particular, the cable suspension manipulator Cablev [4] is considered that has been developed at University of Rostock (Fig. 1). Its payload platform is supported by three cables with winches mounted on trolleys that move themselves on a gantry. Thus, the payload platform may perform sway motions with three degrees of freedom while the cable lengths are kept fixed. Applications are, for example, precise handling and assembling large and heavy components on construction sites or on shipyards. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

自由漂浮空间非合作目标的运动预测

空间非合作目标的运动预测是航天器在轨服务中的一个重要问题。在获得非合作目标的运动预测结果后,追踪星即可规划运动轨迹以接近目标并对其进行捕获。该文提出了一种自由漂浮空间非合作目标的运动预测方法。该方法的核心思想是首先辨识出目标的姿态动力学参数和目标的质心运动学参数,然后利用参数辨识结果和目标的动力学方程实现对目标的运动预测。在姿态动力学参数的辨识过程中,首先对目标的惯性参数进行初步辨识,然后采用自适应无迹Kalman滤波器对姿态动力学参数进行粗略辨识,最后通过最优化方法进一步提高姿态动力学参数的辨识精度。该文通过数值仿真验证了所提运动预测方法的有效性。仿真结果表明,无论目标是做单轴旋转还是翻滚运动,所提运动预测方法都能够实现对目标的长时间高精度的运动预测。     

The Lightweight Robot ElRob: Interesting Aspects in Modeling and Control

The articulated robot ElRob, consisting of flexible links and joints, is considered in several publications. Recent developments are presented in this work. The overall goal of the research is to decrease the effects of structural elasticities in lightweight robots. For this purpose model-based control concepts are investigated and very accurate and efficient kinematic and dynamic models are necessary. The robot is split into groups of bodies, the so called subsystems, with separated describing velocities and coordinate systems. To obtain structured equations of motion the Projection Equation is used. The beams are modelled using the floating frame of reference formulation and a Ritz-approach. Because of its flexibility, the examined robot is an underactuated system leading to special difficulties. As an example is it not possible to compute the desired joint angles with respect to a reference path in task space for the flexible system (inverse kinematic problem). Different methods to solve this drawback and other problems resulting from flexibility are discussed with special focus on feed forward control and different feedback control concepts. The resulting end point error, the necessary control input and other interesting results for the laboratory experiment are presented and compared. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)