Index based optimal anatomy of a metamorphic manipulator for a given task

This paper introduces an approach for the determination of the best anatomy of a metamorphic manipulator for a given task at a given location. The location of the task is determined by maximizing the performance of a current industrial fixed anatomy robot. Two types of tasks are considered: a point to point task and a path following task, where in the first case the approximated minimum of the manipulability index is formed along the task points and in the second case the approximated minimum of the manipulator velocity ratio is formed along the line segments. These indexes are maximized in order to determine the best anatomy for the task. The proposed approach is tested and the results show that the determined best anatomy for each type of task acquired higher performance than the respective one achieved by the fixed anatomy manipulator.     

三连杆移动机械臂模型与运动规划

采用拉格朗日动力学方法和非完整动力学罗兹方程建立了三连杆移动机器臂运动学和动力学模型,并且利用该模型采用了人工势函数方法来驱动移动机械臂系统绕过障碍物到达目标位置.仿真的结果证明了该模型的正确性及其规划方法是有效的.     

Automatic safe motion control system for a robotic manipulator

This paper is devoted to improving the automatic safe motion control system of a robotic manipulator, in such a way that the system, in addition to its primary function of shutting down the power drives in the case of overload, becomes capable of checking the operability of all its components. The proposed modification of the control system’s architecture makes it possible to prevent large deviations from the programmed motion even if only some of the console controllers remain operational.     

基于速度观测模型的可重构机械臂补偿控制

针对可重构机械臂动力学中存在的模型参数摄动和外界扰动,本文阐述了一种基于速度观测模型的模糊RBF神经网络补偿控制算法.利用Lyapunov函数给出了网络的权值、隶属度函数中心和宽度倒数的在线更新律,并证明了所提出的观测模型及其补偿控制算法的最终一致有界性.最后以RRP(revolute-revolute-prismatic)构形的可重构机械臂为例,通过仿真研究了算法对轨迹跟踪问题的有效性,同时与基于速度观测模型的RBF神经网络补偿控制进行了仿真对比及分析,给出了神经网络和模糊神经网络在可重构机械臂轨迹控制应用中各自的优缺点.     

机械臂鲁棒自适应运动控制

针对具有不确定性的机械臂系统,文中阐述了一种基于势函数和Lyapunov稳定性理论的鲁棒自适应控制方法．它是通过合理选择与控制目标相关的势函数,并根据模型中不确定性的实时变化,在控制器中引入可在线可调参数,使得控制器机械臂能够跟踪给定的有界参考信号,跟踪误差收敛到包含零点的很小的邻域内．同时该闭环系统的所有状态半全局最终一致有界（SGUUB）．仿真研究表明该方法的有效性．     

Intelligent compliant force/motion control of nonholonomic mobile manipulator working on the nonrigid surface

The task under consideration is to control a mobile manipulator for the class of nonrigid constrained motion. The working surface is deformable. The geometric and physical model of the surface is unknown and all contact force is nonlinear and difficult to model. To accomplish a task of this kind, we propose a force/motion fuzzy controller based on the philosophy of the parallel approach in two decoupled subspaces. In one subspace, we control the constant contact force normal to the surface and estimate the end-effector tool’s deformable depth of the surface; in the other, we keep the end-effector’s constant velocity parallel to the tangential plane of the surface and suppress the tangential force of the surface deformation. The nonholonomic mobile base is utilized to avoid the singularity. Stability is established and conditions for the control parameters are derived. Performance of the proposed controller is verified through computer simulations compared with the model-based control.     

Stabilizing underwater vehicle motion using internal rotors

As a case study of a particular control methodology and as a practical contribution in the area of underwater vehicle control, we consider the problem of stabilizing an underwater vehicle using internal rotors as actuators. The control design method comprises three steps. The first step involves shaping the kinetic energy of the conservative dynamics. For the underwater vehicle, the control term from this step may be interpreted as modifying the system inertia. In the second step, we design feedback dissipation using a Lyapunov function constructed in the first step. In the third step, we include a general model for the viscous force and moment on the vehicle and we show that these effects enhance stability. We first apply this method to a vehicle whose centers of buoyancy and gravity coincide and then to a vehicle with noncoincident centers of buoyancy and gravity.     

渐进式约束扩展的机械臂运动规划算法

为了保证冗余机械臂带约束运动规划时的路径连续性,针对目前的直接插值和连续插值方法潜在的约束失效和路径失效问题,提出渐进式约束扩展的快速搜索随机树算法（PCE-RRT）。该算法在进行搜索树扩展时引入了一种渐进式约束扩展方法,该方法使用带有最近点信息的逆运动学计算策略,可以在保证任务约束的情况下迭代缩短最近点和扩展点的距离,让每一次扩展都能够保证搜索树的约束性和连续性。PCE-RRT可以使最终生成的搜索树很好地贴合于约束流形子空间,且树上任意两个相连节点都能满足连续条件。通过仿真实验对算法进行验证,实验结果表明该算法能够为机械臂带约束运动规划问题提供同时满足约束性和连续性条件的路径解。     

Trajectory for saving energy of a direct-drive manipulator in throwing motion

In this article, equations of motion of a closed-type manipulator, whose mechanism can easily be made lighter, are derived in consideration of the characteristics of the driving source. Considering the final condition of angular displacement and angular velocity in throwing motion, trajectories of velocity for saving energy are calculated by iterative dynamic programming, and the dynamic characteristics of manipulator control based on the trajectory for saving energy are analyzed theoretically and investigated experimentally. This work was presented in part at the 11th International Symposium on Artificial Life and Robotics, Oita, Japan, January 23–25, 2006     

Singularities in motion and displacement functions for a 7 degree-of-freedom manipulator

The authors propose a method for the determination of singularities in motion and displacement functions for a seven degree-of-freedom manipulator. The manipulator is considered, hereby, as a set of six degree-of-freedom manipulators. It is proven that two types of singularities in motion can occur at link positions that are independent and dependent with respect to the trajectory to be executed. The relations between the structure of singularity equations and displacement equations are discussed. The derivation of displacement equations for a manipulator with singularities of the second type is based on the idea of modeling of a manipulator by two open kinematic chains and invariants that may be found for these chains. The inverse kinematic equations and the equations of singularities in motion have been derived using a symbolic computer program which can handle manipulators of general structure (with five, six, and seven degrees-of-freedom). This program is written in the Symbolic Computation Language REDUCE.     

On a linearized model and adaptive controller implementation for manipulator motion

The detailed model for the motion of a manipulator system is linearized along a specific path. An on-line parameter estimation algorithm based on the least-squares criterion is used to determine the parameter values along the path at the operating instances. Based on the estimated parameter values, a self-tuning adaptive controller is designed by minimizing a chosen performance criterion. Simulation results as well as experimental results are presented to demonstrate the approach. Certain aspects of the implementation are discussed.     

Planning the subminimum-time motion of a robotic manipulator which avoids obstacles

A method of planning the programmed motion of a manipulator with configuration constraints due to the presence of an obstacle in the working zone is proposed. The constraints on control variables, whose number is equal to the number of freedom degrees, are assumed to be specified beforehand. The planned motions are nearly time-optimal in the same sense, in which a dynamic system can be close to a certain linear decomposed system.     

Stabilizing helicopter motion with respect to all variables

We solve the equilibrium stabilization problem for equations that describe the motion of a helicopter. We use transformations to a normal form, partial linearization with feedback, and the method of virtual outputs that let us stabilize the system with respect to all variables.     

Sampling-based motion planning of manipulator with goal-oriented sampling

Intelligent Service Robotics - A sampling-based planning algorithm is one of the most powerful tools for collision avoidance in the motion planning of manipulators. However, this algorithm takes a...     

Fault-tolerant motion planning and control of redundant manipulator

One important issue in the motion planning of a kinematic redundant manipulator is fault tolerance. In general, if the motion planner is fault tolerant, the manipulator can achieve the required path of the end-effector even when its joint fails. In this situation, the contribution of the faulty joint to the end-effector is required to be compensated by the healthy joints to maintain the prescribed end-effector trajectory. To achieve this, this paper proposes a fault-tolerant motion planning scheme by adding a simple fault-tolerant equality constraint for the faulty joint. Such a scheme is then unified into a quadratic program (QP), which incorporates joint-physical constraints such as joint limits and joint-velocity limits. In addition, a numerical computing solver based on linear variational inequalities (LVI) is presented for the real-time QP solving. Simulative studies and experimental results based on a six degrees-of-freedom (DOF) redundant robot manipulator with variable joint-velocity limits substantiate the effectiveness of the proposed fault-tolerant scheme and its solution.     

A simple algorithm for intelligent manipulator collision-free motion

The collision-free planning of motion is a fundamental problem for artificial intelligence applications in robotics. The ability to compute a continuous safe path for a robot in a given environment will make possible the development of task-level robot planning systems so that the implementation details and the particular robot motion sequence will be ignored by the programmer.A new approach to planning collision-free motions for general real-life six degrees of freedom (d.o.f.) manipulators is presented. It is based on a simple object model previously developed. The complexity of the general collision detection problem is reduced, and realistic collision-free paths are efficiently found onCS planes. A heuristic evaluation function with a real physical sense is introduced, and computational cost is reduced to the strictly necessary by selecting the most adequate level of representation. A general algorithm is defined for 6 d.o.f. robots that yields good results for actual robot models with complex design structures with the aid of various heuristic techniques. The problem of adaptive motion is also considered.     

大范围运动柔性机械臂斜碰撞动力学分析

对作大范围运动柔性机械臂系统,进行斜碰撞动力学分析.基于柔性多体系统刚柔耦合动力学理论,计入耦合变形项,全面考虑大范围刚体运动与弹性小变形运动的耦合,建立系统连续动力学方程.引入斜碰撞力学模型,将法向和切向碰撞力以广义力的形式加入动力学方程中,对系统进行斜碰撞动力学建模分析.法向碰撞模型选取基于连续接触力法的非线性弹簧阻尼模型,切向碰撞模型选取一种修正Coulomb摩擦模型,对切向摩擦力进行统一描述.给出接触、分离判据,实现不同状态的动力学模型转换与求解.对斜碰撞全局动力学进行了仿真验证,分析了柔性机械臂全局过程的动力学特性变化以及碰撞对大范围运动和小变形运动的作用,并对比了不同碰撞方向对大范围运动、变形、机械能、碰撞力等动力学参数的影响.     

基于ROS的六自由度机械臂运动规划

针对传统机器人在复杂环境下的安全问题以及运动规划问题,采用开源机器人操作系统ROS搭建了机器人仿真平台,并进行运动规划。在ROS平台下,利用URDF文件完成机械臂3D建模;利用Movelt配置助手(setup assistant)配置机械臂模型并且生成启动文件。在Rviz中显示三维模型;利用Movelt完成对六自由度机械臂的运动规划,以及避障轨迹规划。结果表明,通过Rqt_plot导出机械臂运动过程中六个关节的位置关系信息,可为进一步改善和研究机械臂轨迹规划提供更加直观的方法。