柔性机械手加速度反馈消振的进一步研究

在柔性机械手的控制中,加速度反馈的方法是一种消除末端振动的有效而简便途径。然而,目前对其有效性尚无严格的理论证明和分析。本文将通过非约束模态分析方法对单柔性臂机械手的动力学方程进行了分析,以此为基础对加速度反馈的理论和实现进行了研究和讨论,得到了一些重要的结论。     

柔性关节柔性连杆机械臂的动力学建模

柔性关节柔性连杆机械臂是典型的非线性、强耦合、欠驱动系统,其控制难度高.对于这类系统,选择合适的动力学模型进行控制器设计对于提高控制性能是非常有帮助的.为此,研究了具有柔性关节柔性连杆机械臂的动力学建模问题,并提出了一种改进的建模方法.在该方法中,连接柔性连杆的柔性关节首先被简化为刚性关节和柔性连杆的弹性约束边界.然后,根据结构动力学理论、哈密顿原理和假设模态法建立系统的刚柔耦合动力学方程.相较于将柔性关节简化为刚性关节和扭簧的传统处理方式,所采用的简化方式一方面可以降低系统的自由度,另一方面可以得到更适合控制器设计的动力学模型.最后,通过数值仿真验证了本文方法的有效性和优势.     

机器人非线性连续变增益H∞控制器设计

本文针对n关节的刚性机器人,提出了一种设计连续变增益控制器的新方法．这种方法结合 了变增益和H∞理论,通过在平衡点附近线性化系统,利用具有极点配置的状态反馈H∞ 技术,对应每个运动区域,设计满足H∞性能和动态特性的状态反馈增益,这些增益通过 泰勒级数展开拟合成与运动点有关的连续函数．随着系统状态的变化,拟合成的增益函数可 使控制器获得连续的增益,使得所设计的控制器同样适合系统状态变化较快的对象,而且系 统随状态的变化始终具有很高的动态性能,克服了传统变增益控制器中存在的不足．仿真结 果验证了此控制器的有效性．     

含铰链间隙的刚-柔机械臂动力学模型

根据Hertz接触定律和Coulomb摩擦定律,建立了含间隙平面旋转铰的力学模型;采用几何变形约束法和模态缩聚技术描述柔性机械臂的非线性变形;同时考虑两个旋转铰的间隙特性和柔性臂的弹性变形,最终采用Kane方程建立了含铰链间隙的刚-柔机械臂系统的动力学模型．     

柔性机械臂的双时间尺度组合控制

本文研究柔性机械臂的轨迹跟踪和振动抑制问题. 首先, 利用Lagrange法和假设模态法建立柔性机械臂的动态模型, 进而利用奇异摄动理论得到柔性机械臂的双时间尺度模型. 然后, 基于慢时间尺度模型利用滑模控制理论设计轨迹跟踪控制器; 借助于快时间尺度模型利用自适应动态规划设计参数不精确已知情况下的最优振动抑制控制器; 将二者相结合, 构造双时间尺度组合控制器, 利用奇异摄动理论证明闭环系统稳定. 最后, 在Matlab/Simulink环境下进行实验, 与现有方法相比, 本文设计的控制器对柔性振动具有更好的振动抑制效果, 跟踪精度更高.     

柔性倒立摆的模糊控制算法

针对直线柔性一级倒立摆多变量的特性,提出了基于融合函数的模糊控制算法,解决了"规则爆炸"问题.利用最优控制理论计算出使系统稳定的反馈增益矩阵,由反馈增益矩阵构造融合函数,由此减少了模糊控制器的输入变量维数.仿真和实际实验结果证明该方案的有效性和正确性.     

利用状态反馈增益变化设计广义系统H∞可靠控制器

通过对状态反馈两种增益变化形式的分析,研究广义系统H∞可靠控制器的设计问题.给出基于状态反馈增益变化的广义系统H∞可靠控制器的定义,得到了执行器故障模型.用线性矩阵不等式(LMI)方法,研究两种状态反馈增益变化的广义系统H∞控制器存在的充分条件和设计方法.进而,针对执行器的不同故障情形,用LMI方法给出广义系统存在基于状态反馈增益变化的H∞可靠控制器的充分条件.最后,给出了优化广义系统H∞可靠控制器的设计算法.     

蔡氏电路混沌系统的单状态延时反馈控制

基于时滞系统的Hopf分叉理论，设计了仅考虑单个状态变量的时滞反馈控制器，实现了将蔡氏电路系统的混沌运动稳定到某周期轨道上．首先论证了蔡氏电路系统的混沌动力学行为及平衡点的稳定性，然后详细分析了系统在x，y，z三个不同的单状态时滞反馈下增益参数的可控取值范围，最后数值仿真结果验证了理论分析的正确性．     

基于分布参数机械臂协调操作柔性负载双时标控制

基于分布参数系统理论,建立机械臂协调操作柔性负载系统的动力学模型.利用奇异摄动方法,对动力学模型进行双时标分解,得到一个表征系统大范围刚性运动的集中参数慢变子系统和表征系统弹性振动的分布参数快变子系统.分别设计了自适应模糊滑模慢变控制器和振动反馈快变控制器,并通过分析快变子系统主算子及其生成C_O半群的特性,证明了分布参数闭环子系统的渐近稳定性.最后,通过仿真实验验证了所提出方法的有效性.     

机器人多胞变增益输出反馈H∞控制

针对n类关节的刚性机器人，提出一种设计包含极点配置的多胞变增益输出反馈H∞控制器的新方法．利用平衡族附近的线性化，机器人系统可化为一关于平衡族的连续线性变参数系统，通过引入滤波器得到易于设计变增益控制器的增广对象，并将其凸分解为多胞表示，基于二次D-稳定和二次H∞性能概念，利用多胞特性将整个控制器设计转化为对胞体顶点控制器的设计，然后利用LMI方法，对多胞的各顶点分别设计满足H∞性能和动态特性的输出反馈控制器，最后综合顶点控制器得到具有同样多胞结构的全局连续变增益控制器．实验结果验证了此控制器的有效性和先进性。     

Decoupling and tracking control for elastic joint robots with coupled joint structure

The paper deals with the modeling, identification, and control of a flexible joint robot developed for medical applications at the German Aerospace Center (DLR). In order to design anthropomorphic kinematics, the robot uses a coupled joint structure realized by a differential gearbox, which however leads to strong mechanical couplings inside the coupled joints and must be taken into account. Therefore, a regulation MIMO state feedback controller based on modal analysis is developed for each coupled joint pair, which consists of full state feedback (motor position, link side torque, as well as their derivatives). Furthermore, in order to improve position accuracy and simultaneously keep good dynamic behavior of the MIMO state feedback controller, a cascaded tracking control scheme is proposed, based on the MIMO state feedback controller with additional feedforward terms (desired motor velocity, desired motor acceleration, derivative of the desired torque), which are computed in a computed torque controller and take the whole rigid body dynamics into account. Stability analysis is shown for the complete controlled robot. Finally, experimental results with the DLR medical robot are presented to validate the practical efficiency of the approaches.     

On the Robust Nonlinear Motion Position and Force Control of Flexible Joints Robot Manipulators

The design of a robust nonlinear position and force controller for a flexible joints robot manipulator interacting with a rigid environment is presented. The controller is designed using the concept of feedback linearization, sliding mode techniques, and LQE estimation methodologies. It is shown that the nonlinear robot manipulator model is feedback linearizable. A robust performance of the proposed control approach is achieved by accounting for the system parameters uncertainties in the derivation of the nonlinear control law. An upper bound of the error introduced by parametric uncertainties in the system is computed. Then, the feedback linearizing control law is modified by adding a switching action to compensate the errors and to guarantee the achievement of the desired tracking performance. The relationship between the minimum achievable boundary layer thickness and the parametric uncertainties is derived. The proposed controller is tested using an experimental flexible joints robot manipulator, and the results demonstrate its potential benefits in reducing the number of sensors required and the complexity of the design. This is achieved by eliminating the need for nonlinear observers. A robust performance is obtained with minimum control effort by taking into account the effect of system parameter uncertainties and measurement noise.     

Constrained motion control of flexible robot manipulators based on recurrent neural networks

In this paper, a neural network approach is presented for the motion control of constrained flexible manipulators, where both the contact force everted by the flexible manipulator and the position of the end-effector contacting with a surface are controlled. The dynamic equations for vibration of flexible link and constrained force are derived. The developed control, scheme can adaptively estimate the underlying dynamics of the manipulator using recurrent neural networks (RNNs). Based on the error dynamics of a feedback controller, a learning rule for updating the connection weights of the adaptive RNN model is obtained. Local stability properties of the control system are discussed. Simulation results are elaborated on for both position and force trajectory tracking tasks in the presence of varying parameters and unknown dynamics, which show that the designed controller performs remarkably well.     

Global Output Tracking Control of Flexible Joint Robots via Factorization of the Manipulator Mass Matrix

This paper investigates the problem of global output feedback tracking control of flexible joint robots. Despite the fact that only link position and actuator position are available from measurements, the proposed controller ensures that the link position globally tracks the desired trajectory while keeping all the remaining signals bounded. The controller development uses a partial state-feedback linearization technique combined with the integrator backstepping control design method whereas a filter and an observer are utilized to remove the requirement of link and actuator velocity measurements. Partial state-feedback linearization of robot dynamics is performed by factoring the manipulator mass matrix into a quadratic form involving an integrable root matrix. The applicability of the proposed general design methodology is illustrated by an example of flexible joint planar robots. Numerical results for a two-link flexible joint planar robot are also provided.      

A nonlinear feedback controller for a single-link flexible manipulator based on a finite element model

In this article, a nonlinear dynamic model of a flexible manipulator is derived through finite element method associated with Lagrange approach. The flexible manipulator is modeled as an Euler-Bernoulli beam driven by a motor at its base and with a point mass tip payload. The generalized coordinates of the system are selected to be the displacements and rotations of the nodes on the considered flexible beam, and such that a state space model is obtained with all the state variables having physical meanings. Based on this model, an effective nonlinear feedback controller is developed to control the tip position. Furthermore, an efficient algorithm is developed to calculate the inverse of the system's inertia matrix for real-time implementation. Numerical simulation results are given to show the effectiveness of the controller and its robustness in handling payload variations. © 1997 John Wiley & Sons, Inc.     

Nonlinear feedback control of flexible joint manipulators: a singlelink case study

A nonlinear feedback control for a flexible joint manipulator is investigated. It is shown that if the elastic (parasitic) modes are weakly observable from the output of the system, a state-space coordinate transformation and a static state feedback and control space transformation will turn the flexible system into a linear controllable and observable system. In contrast, if the parasitics are strongly observable, a dynamic state feedback is required for input-output linearization. Numerical simulations for a single link flexible joint manipulator are reported, illustrating the application of the methodology     

Control of a single-link flexibe manipulator fabricated form composite laminates

An experimental investigation on the control performances of a single-link flexible manipulator fabricated from composite laminates is presented. The dynamic modeling of the flexible manipulator is accomplished by employing Hamilton's principle, prior to developing a finite element formulation. An output feedback controller associated with two collocated angular position and velocity sensors is designed and experimentally implemented. Comparative works are undertaken to demonstrate some of the advantages to be accrued from this proposed methodology. It is shown that the manipulator fabricated from composite laminates has superior performance characteristics, such as smaller tip deflections and a smaller input torque relative to the manipulator fabricated from aluminum. © 1995 John Wiley & Sons, Inc.     

Dynamic Modeling and Experimental Validation of a 3-PRR Parallel Manipulator with Flexible Intermediate Links

This paper presents the development of structural dynamic equations of motion for a 3-PRR parallel manipulator with three flexible intermediate links, based on the assumed mode method. Lagrange’s equation is used to derive the dynamic model of the manipulator system. Flexible intermediate links are modeled as Euler–Bernoulli beams with pinned–pinned boundary conditions. Dynamic equations of motion of a 3-PRR parallel manipulator with three flexible links are developed by adopting the assumed mode method. The effect of concentrated rotational inertia at both ends of intermediate links is included in this model. Numerical simulations of vibration responses, coupling forces and inertial forces are presented. The corresponding frequency spectra analysis is performed using the Fast Fourier Transform (FFT). Experimental modal tests are performed to validate the theoretical model through comparison and analysis of modal characteristics of the flexible manipulator system.     

Active vibration control of flexible structures using delayed position feedback

The paper discusses the use of a simple position control system approach to improve the performance of lightly damped dynamic systems. This approach uses a delayed position feedback signal to actively control the vibrations of flexible structures. A complete analysis of the stability of a single-link flexible manipulator under time delay control is presented and critical values of time delay for a given controller gain have been determined. The paper also presents a short comparison between the delayed feedback signal control and the linear quadratic regulator.