Feedback control of a flexible cylindrical manipulator

Flexible robotic manipulators have been the subject of numerous studies in the past few years. Past studies, however, have concentrated on flexible manipulators with only revolute joints. This paper considers the case of a structurally flexible manipulator with prismatic and revolute joints; specifically, an algorithm for controlling a structurally flexible three-degree-of-freedom cylindrical manipulator is presented. The control algorithm involves two steps. Using nonlinear feedback, the equations of motion are first decoupled into three subsystems representing the three rigid degrees of freedom together with their associated ‘flexible equations’, if any. Then, using linear optimal control theory, controllers are designed for the three subsystems independently. Computer simulated results for an example system are presented.     

一种柔性机器人的子杆法建模方法

本文实现了一种用虚拟刚性子杆及被动关节模型模拟柔性杆,进而对空间多杆柔性 机器人建模的方法;采用遗传算法解决了子杆参数的优化辨识问题;讨论了这一建模方法的 适用范围;并通过Raleigh阻尼的引入完善了这一方法;最后通过仿真初步验证了这一方法 的有效性和正确性．     

Robust adaptive controller design for flexible joint manipulators

In this paper the control problem for robot manipulators with flexible joints is considered. A reduced-order flexible joint model is constructed based on a singular perturbation formulation of the manipulator equations of motion. The concept of an integral manifold is utilized to construct the dynamics of a slow subsystem. A fast subsystem is constructed to represent the fast dynamics of the elastic forces at the joints. A composite control scheme is developed based on on-line identification of the manipulator parameters which takes into account the effect of certain unmodeled dynamics and parameter variations. Stability analysis of the resulting closed-loop full-order system is presented. Simulation results for a single link flexible joint manipulator are given to illustrate the applicability of the proposed algorithm.     

一种多机械手(指)自适应协调控制的递推算法

提出了一种多机械手(指)的自适应协调控制递推算法.原系统的控制问题转化为各 子系统的控制问题.各子系统之间的动态关联在Lyapunov意义下表示为在各分解点处的 "虚功率流".机械手指的点接触问题处理成被动关节的控制问题.原系统的渐近稳定性在 Lyapunov意义上得到保证.计算机数字仿真验证了理论结果.     

受限柔性机器人基于遗传算法的自适应模糊控制

研究一类平面双连杆受限柔性机器人的混合位置/力控制问题,提出一种自适应 模糊逻辑控制方案,利用遗传学习算法对控制器中的参数进行学习和修正,达到提高系统控 制精度、改善系统鲁棒性的目的.计算机仿真结果表明这种控制器设计方案具有很好的特性.     

冗余度卫星搭载机械臂神经网络优化控制

研究了节点变换函数参数可调的多层神经网络,并将这种神经网络用于控制冗余度卫星搭载机器人系统;提出了卫星位姿最小摄动的冗余度机器人臂神经网络控制方案,在这种方案中将系统的正运动学方程作为神经网络学习的对象,由神经网络学习拟合系统运动学,实现了机器人臂运动和卫星运动的解耦,在机器人臂的运动和卫星本体解耦的基础上,基于带动量项的BP解法,实现了系统的最小动能优化控制,利用平面4关节星载机器人系统进行了仿真,取得比较理想的效果。     

Optimal Trajectory Planning for Minimum Vibration of Flexible Redundant Cooperative Manipulators

The optimal path planning for two flexible cooperating manipulators carrying a solid object on a prescribed tip trajectory has been studied using kinematic resolution. The formulation has been derived using the Pontryagin minimum principle that results in a two-point boundary value problem. Also, a numerical technique based on converting the abstract optimization to parametric optimization problem has been proposed. The problem has been solved and compared for globally minimized elastic deformation of flexible links and joints as well as minimization of joints velocities while the end-effector moves along the specified path.     

Fuzzy tuning control approach to perform cooperative object manipulation by a rigid–flexible multibody robot

We study cooperative object manipulation control of rigid–flexible multibody systems in space. During such tasks, flexible members like solar panels may get vibrated. Which in turn may lead to some oscillatory disturbing forces on other subsystems and consequently produce errors in the motion of the end-effectors of the cooperative manipulating arms. Therefore, to design and develop capable model-based controllers for such complicated systems, deriving a dynamics model is required. However, due to practical limitations and real-time implementation, the system dynamics model should require low computations. So, first, to obtain a precise compact dynamics model, the rigid–flexible interactive dynamics modeling (RFIM) approach is briefly introduced. Using this approach, the system is virtually partitioned into two rigid and flexible portions, and a convenient model for control purposes is developed. Next, a fuzzy tuning manipulation control (FTMC) algorithm is developed for a simple conceptual model for cooperative object manipulation. In fact, a suitable setup is designed for practical implementation of this controller. After that, a wheeled mobile robot (WMR) system with flexible appendages is considered as a practical case that necessitates delicate force exertion by several end-effectors to move an object along a desired path. The WMR system contains two cooperative manipulators, appended with two flexible solar panels. To reveal the merits of the developed model-based controller, the maneuver is deliberately planned such that flexible modes of solar panels get stimulated due to arms motion. The obtained results show an effective performance of the proposed approach as will be discussed.     

Adaptive stabilization of mobile manipulators

This paper considers the motion control problem for uncertain mobile manipulator systems comprised of a robotic arm mounted on a wheeled mobile platform. More specifically, we address the problem of stabilizing mobile manipulators in the presence of uncertainty regarding the system dynamic model. It is proposed that a simple and effective solution to this problem can be obtained by combining ideas from homogeneous system theory and adaptive control theory. Thus each of the proposed control systems consists of two subsystems: a (homogeneous) kinematic stabilization strategy, which generates a desired velocity trajectory for the mobile manipulator, and an adaptive control scheme, which ensures that this velocity trajectory is accurately tracked. This approach is shown to provide arbitrarily accurate stabilization to any desired configuration and can be implemented without knowledge of the details of the system dynamic model. Moreover, it is demonstrated that exponential rates of convergence can be achieved with this methodology. The efficacy of the proposed stabilization strategies is illustrated through computer simulations with two mobile manipulators. © 1998 John Wiley & Sons, Inc.     

SLIDING-MODE ADAPTIVE CONTROL FOR FLEXIBLE-LINK MANIPULATORS USING A COMPOSITE DESIGN

ABSTRACT

A robust adaptive control scheme for flexible link robotic manipulators is presented. The design is based on considering the flexible mechanical structure as a singular perturbed system, which allows us to assume the existence of slow (rigid) and fast (flexible) modes that separately can be controlled. The rigid dynamics are controlled by means of a robust sliding adaptive approach with well-established stability properties. The flexible dynamics can be controlled using H _∞ or optimal designs, which successfully handle the actual interaction between the slow and fast subsystems. This composite approach achieves good closed-loop tracking properties, both in simulation and experimental results on a laboratory-flexible arm.     

柔性臂漂浮基空间机器人建模与轨迹跟踪控制

利用拉格朗日法和假设模态方法建立了末端柔性的两臂漂浮基空间机器人的非线性动力学方程．通过坐标变换,推导出一种新的以可测关节角为变量的全局动态模型,并在此基础上运用基于模型的非线性解耦反馈控制方法得到关节相对转角与柔性臂的弹性变形部分解耦形式控制方程．最后,讨论了柔性臂漂浮基空间机器人的轨迹跟踪问题,并通过仿真实例计算,表明该模型转换及控制方法对于柔性臂漂浮基空间机器人末端轨迹跟踪控制的有效性．     

平面双连杆受限柔性机器人臂的自适应模糊力/位置控制

本文对一类平面双连杆受限柔性机器人的力／位置控制问题进行研究,提出了一种新的自适应模糊控制方案．利用结构分解技术对模糊推理系统进行简化,用梯度法对参数进行自适应调整,从而实现对受限柔性机器人系统末端的混合力／位置控制．计算机仿真结果表明,本文提出的控制方案是合理、有效的     

Dynamic state feedback control of two cooperative manipulators

Dynamic coordinated control of two robot manipulators that rigidly grasp a common object is studied. A dynamic coordinated control model for the two manipulators is derived that is suitable for system analysis and design in state space. The model takes into account kinematic and dynamic constraints between the two manipulators, and is explicitly described by non-linear state equtions and non-linear output equations in the state space. Since coordinated control requires the control of forces applied to the object by manipulators, the output equations include both position components and force components. While robotic systems with position outputs can be linearized using a static state feedback, systems with force outputs, such as the present two robot system, require a dynamic non-linear state feedback for exact linearization. By using dynamic non-linear feedback, coordinated control of two robotic manipulators is converted into a control problem of linear systems.     

Optimal design for robust control of uncertain flexible joint manipulators: a fuzzy dynamical system approach

A novel fuzzy dynamical system approach to the control design of flexible joint manipulators with mismatched uncertainty is proposed. Uncertainties of the system are assumed to lie within prescribed fuzzy sets. The desired system performance includes a deterministic phase and a fuzzy phase. First, by creatively implanting a fictitious control, a robust control scheme is constructed to render the system uniformly bounded and uniformly ultimately bounded. Both the manipulator modelling and control scheme are deterministic and not IF-THEN heuristic rules-based. Next, a fuzzy-based performance index is proposed. An optimal design problem for a control design parameter is formulated as a constrained optimisation problem. The global solution to this problem can be obtained from solving two quartic equations. The fuzzy dynamical system approach is systematic and is able to assure the deterministic performance as well as to minimise the fuzzy performance index.     

柔性机械臂建模理论与控制方法研究综述

针对柔性机械臂进行有效和精确的建模以及对其进行有效的控制一直是国内外学者研 究的重要课题．由于柔性机械臂本身所具有的高度非线性、强耦合和时变的特点，建立精确 的动力学模型成为柔性臂研究的一个重点．而随着系统和控制领域理论和技术的不断发展， 针对柔性机械臂的控制，也形成了许多不同的控制策略．本文从柔性机械臂建模理论和控制 方法两方面，对国内外学者的研究工作分别加以介绍，并对各种方法的优缺点进行分析和比 较，并对今后的研究方向进行了展望．     

Hybrid Control Scheme for Robust Tracking of Two-Link Flexible Manipulator

The hybrid control scheme is proposed to stabilize the vibration of a two-link flexible manipulator while the robustness of Variable Structure Control (VSC) developed for rigid manipulators is maintained for controlling the joint angles. The VSC law alone, which is designed to accomplish only the asymptotic decoupled joint angle trajectory tracking, does not guarantee the stability of the flexible mode dynamics of the links. In order to actively suppress the flexible link vibrations, hybrid trajectories for the VSC are generated using the virtual control force concept, so that robust tracking control of the flexible-link manipulator can also be accomplished. Simulation results confirm that the proposed hybrid control scheme can achieve more robust tracking control of two-link flexible manipulator than the conventional control scheme in the presence of payload uncertainty.     

Hybrid Control Scheme for Robust Tracking of Two-Link Flexible Manipulator

A hybrid control scheme is proposed to stabilize the vibration of a two-link flexible manipulator while robustness of Variable Structure Control (VSC) developed for rigid manipulators is maintained for controlling the joint angles. The VSC law alone, which is designed to accomplish only the asymptotic decoupled joint angle trajectory tracking, does not guarantee the stability of the flexible mode dynamics of the links. In order to actively suppress the flexible link vibrations, hybrid trajectories for the VSC are generated using the virtual control force concept, so that robust tracking control of the flexible-link manipulator can also be accomplished. Simulation results confirm that the proposed hybrid control scheme can achieve more robust tracking control of two-link flexible manipulator than the conventional control scheme in the presence of payload uncertainty.     

Two-time scale control and observer design for trajectory tracking of two cooperating robot manipulators moving a flexible beam

In this paper, we present two-time scale control design for trajectory tracking of two cooperating planar rigid robots moving a flexible beam, which does not require vibration measurement for the beam. First, the kinematics and dynamics of the robots and the object are derived. Then, using the relations between different forces acting on the object by the manipulators’ end-effectors, dynamics equations of the robots and the object are combined. The resulting equations show that the coupled dynamics including beam vibration and the rigid motion take place in two different time domains. By applying two-time scale control theory on the combined dynamics, a composite control scheme is elaborated which makes the beam orientation and its center of mass position track a desired trajectory while suppressing the beam vibration. For the controller algorithm, first a slow controller is utilized for the slow (rigid) subsystem and then a fast stabilizing controller is considered for the fast (flexible) subsystem. To avoid requiring measurement of beam vibration for the fast control law, a linear observer is also designed. The simulation results show the efficiency of the proposed control scheme.     

Observer-Based Optimal Control of Flexible Stewart Parallel Robots

The design and simulation of two optimal control schemes for a parallel flexible link manipulator of the Stewart type is presented. The first control scheme combines a nonlinear rigid model of the flexible manipulator with a linear rigid observer, whereas the second scheme uses a nonlinear flexible manipulator model with a linear flexible observer. The majority of the results available in the literature do not address the optimal control problem through the use of observers, as it is done in this paper, for the control of parallel robots. The simulation results have shown in both cases that indeed optimal state-obscrver-based control is a good candidate for controlling parallel-link manipulators in practice. As expected, the second scheme (flexible model plus flexible observer) gives better results than the first one, achieving faster trajectory tracking. The effects of white noises, applied forces, and zero gravity environment were taken under consideration.     

一种基于多视角图像的目标物体定位方法

在遥操作机械臂时,为了能有一个更加友好的人机交互界面,往往需要在控制界面中构建一个虚拟的机械臂以及机械臂工作空间,所以,在虚拟工作空间中标示出目标物体与虚拟机械臂的相对位置,给操作人员一个直观的提示,是虚拟工作空间重构的关键问题.针对机械臂遥操作,提出了一种基于不同视角图像的快速高效的定位方法,该方法根据目标物体在多个不同视角图像中的位置,计算出目标物体在实际工作空间中的位置,从而在虚拟机械臂工作空间中标示出目标物体与虚拟机械臂的相对位置.最后,构建了机械臂遥操作实物系统,验证了该方法的正确性.