Global robust distributed output consensus of multi-agent nonlinear systems: An internal model approach

This paper studies the problem of global robust distributed output consensus of heterogeneous leader–follower multi-agent nonlinear systems by general directed output interactions. For a class of minimum-phase single-input single-output nonlinear agents having unity relative degree, it is shown that the problem is solvable by an internal model approach under certain mild conditions. A Lyapunov function based output-feedback control law is developed by converting the global output consensus into a global distributed stabilization problem for an augmented network.     

基于PMAC的开放式机器人控制系统

以IPC+DSP作为六轴工业机器人的控制器,设计了一种基于可编程多轴控制器PMAC(ProgrammableMulti-AxisCon-troller)的开放式机器人控制系统。系统采用双微机分级控制方式和模块化结构软件设计,上级IPC负责整个系统管理和路径规划,下级PMAC则实现对各个关节的位置伺服控制和多个关节的协调控制。实践证明这种机器人控制系统运行平稳,具有良好的开放性和扩展性。     

基于扩张状态观测器的二质量系统非奇异快速终端滑模控制

针对含未知负载信息的二质量伺服系统,提出一种基于有限时间扩张状态观测器的非奇异快速终端滑模控制方法.首先,利用电机侧位置信息设计有限时间扩张状态观测器估计系统的扰动,并将估计值融入到控制器中作为前馈项对系统的未知扰动进行补偿;然后,引入一种新型的滑模趋近律,该趋近律能够避免传统滑模控制中存在的奇异性问题,据此设计非奇异快速终端滑模控制器,保证系统状态在有限时间内收敛到原点,并根据李雅普诺夫稳定性理论分析闭环系统的稳定性;最后,通过仿真和实验验证所提出方法的优越性.结果表明,与传统的PID等控制相比较,所提出的基于扩张状态观测器的有限时间滑模控制方法能够提高系统的跟踪性能,并有效增强二质量伺服系统的抗扰动能力.     

机器人视觉伺服中CMAC学习控制系统研究

根据小脑模型关联控制器（CMAC）收敛速度快,适于实时控制系统的特点,设计了一种基于CMAC学习控制方法的机器人视觉伺服系统。在该系统中,CMAC被用作前馈视觉控制器对常规反馈控制器进行补偿。所提出的CMAC控制器替代图像雅可比矩阵来获得目标图像特征和机器人关节运动之间2D/3D变换关系,通过其在线学习,可以使系统对摄像机标定误差不敏感,从而提高系统的鲁棒性。实验证明了所设计控制系统的有效性。     

Nonlinear disturbance observer design for robotic manipulators

Robotic manipulators are highly nonlinear and coupled systems that are subject to different types of disturbances such as joint frictions, unknown payloads, varying contact points, and unmodeled dynamics. These disturbances, when unaccounted for, adversely affect the performance of the manipulator. Employing a disturbance observer is a common method to reject such disturbances. In addition to disturbance rejection, disturbance observers can be used in force control applications. Recently, research has been done regarding the design of nonlinear disturbance observers (NLDOs) for robotic manipulators. In spite of good results in terms of disturbance tracking, the previously designed nonlinear disturbance observers can merely be used for planar serial manipulators with revolute joints [Chen, W. H., Ballance, D. J., Gawthorp, P. J., O'Reilly, J. (2000). A nonlinear disturbance observer for robotic manipulators. IEEE Transactions on Industrial Electronics, 47 (August (4)), 932–938; Nikoobin, A., Haghighi, R. (2009). Lyapunov-based nonlinear disturbance observer for serial n-link manipulators. Journal of Intelligent & Robotic Systems, 55 (July (2–3)), 135–153]. In this paper, a general systematic approach is proposed to solve the disturbance observer design problem for robotic manipulators without restrictions on the number of degrees-of-freedom (DOFs), the types of joints, or the manipulator configuration. Moreover, this design method does not need the exact dynamic model of the serial robotic manipulator. This method also unifies the previously proposed linear and nonlinear disturbance observers in a general framework. Simulations are presented for a 4-DOF SCARA manipulator to show the effectiveness of the proposed disturbance observer design method. Experimental results using a PHANToM Omni haptic device further illustrate the effectiveness of the design method.     

A geometric approach to H∞ control of nonlinear Markovian jump systems

This paper first discusses the H_∞ control problem for a class of general nonlinear Markovian jump systems from the viewpoint of geometric control theory. Following with the updating of the Markovian jump mode, the appropriate diffeomorphism can be adopted to transform the system into special structures, which establishes the basis for the geometric control of nonlinear Markovian jump systems. Through discussing the strongly minimum-phase property or the strongly γ-dissipativity of the zero-output dynamics, the H_∞ control can be designed directly without solving the traditional coupled Hamilton–Jacobi inequalities. A numerical example is presented to illustrate the effectiveness of our results.     

Vibration suppression control of 3D flexible robots using velocity inputs

Research on vibration suppression control of flexible robots has concentrated mainly on the one-link and two-link planar manipulators. Most of the techniques that have been presented cannot be easily extended to the case of a general 3D flexible robot. In this article we present a general control scheme based on hardware velocity servo cards. The velocity commands to move the robot are calculated by adding a vibration suppression term to the joint position feedback employed in “rigid” robots. Two different methods are proposed to calculate this term, one based on optimum quadratic control and the other based on pseudo-inverse nonlinear decoupling. These techniques are studied numerically in the case of a real two-link three-joint flexible robot, by computing the values of the closed-loop poles at different configurations. Experiments on position stabilization of the robot prove the validity of our methods.© 1997 John Wiley & Sons, Inc.     

Mitigation of symmetry condition in positive realness for adaptive control

Feasibility of nonlinear and adaptive control methodologies in multivariable linear time-invariant systems with state-space realization {A,B,C} is apparently limited by the standard strictly positive realness conditions that imply that the product CB must be positive definite symmetric. This paper expands the applicability of the strictly positive realness conditions used for the proofs of stability of adaptive control or control with uncertainty by showing that the not necessarily symmetric CB is only required to have a diagonal Jordan form and positive eigenvalues. The paper also shows that under the new condition any minimum-phase systems can be made strictly positive real via constant output feedback. The paper illustrates the usefulness of these extended properties with an adaptive control example.     

Composite hierarchical anti-disturbance control for robotic systems with multiple disturbances

Various sources of disturbances exist simultaneously in robotic systems, such as vibrations, frictions, measurement noises, and equivalent disturbances from unmodeled dynamics and nonlinearities. However, most results on anti-disturbance control focus on only one type of disturbances, which cannot reflect the real applications and may lead to design conservativeness due to partial use of the disturbance information. In this paper, we propose a composite hierarchical anti-disturbance control (CHADC) strategy for robotic systems in the presence of multiple disturbances as well as system uncertainties. Particularly, we assume the existence of two types of disturbances, where the first type represents disturbances from exogenous systems with model perturbations, while the second type includes other random disturbances satisfying the L2-norm bound condition. Accordingly, the CHADC control architecture is composed of a nonlinear disturbance observer (NDO) and an H _∞ based PID controller, where the NDO is constructed to estimate the first type of disturbances and provide feed forward compensation, while the feedback PID loop is optimized using H _∞ theory to minimize the second type of disturbances. Robustness against system uncertainties is also considered in this hierarchical control structure. The proposed control approach is applied to a two-link robotic manipulator and compared with the conventional DOBC (disturbance observer based control) strategies.     

Adaptive explicit force control of position-controlled manipulators

This article presents a new adaptive outer-loop approach for explicit force regulation of position-controlled robot manipulators. The strategy is computationally simple and does not require knowledge of the manipulator dynamic model, the inner-loop position controller parameters, or the environment. It is shown that the control strategy guarantees global uniform boundedness of all signals and convergence of the position/force regulation errors to zero when applied to the full nonlinear robot dynamic model. If bounded external disturbances are present, a slight modification to the control scheme ensures that global uniform boundedness of all signals is retained and that arbitrarily accurate stabilization of the regulation errors can be achieved. Additionally, it is shown that the adaptive controller is also applicable to robotic systems with PID inner-loop position controllers. Computer simulation results are given for a Robotics Research Corporation (RRC) Model K-1207 redundant arm and demonstrate that accurate and robust force control is achievable with the proposed controller. Experimental results are presented for the RRC Model K-1207 robot and confirm that the control scheme provides a simple and effective means of obtaining high-performance force control. © 1996 John Wiley & Sons, Inc.     

Nonlinear adaptive control for dynamic and dead-zone uncertainties in robotic systems

Accurate position tracking performance of robotic systems with both dynamic and dead-zone uncertainties is difficult to achieve by traditional adaptive control. In this paper, for nonlinear robotic systems in the presence of uncertain dynamics and dead-zone, an adaptive control scheme is employed to guarantee accurate and stable position tracking. The dynamics of the robot and dead-zone parameters are concurrently estimated in the adaptation laws and the estimated values are subsequently applied in the control law. In order to demonstrate the practicability of this paper, an experimental setup composed of Phantom Omni robots are built. The experimental results show that even when the dynamic and dead-zone uncertainties simultaneously appear, the robot can well track any desired position trajectory.

     

基于模糊神经网络的机器人关节驱动补偿控制器

本文提出了一种模糊神经网络控制器,该控制器用于工业机器人关节驱动的位置控制,克服了传统PID很难达到对非线性以及不确定因素的控制效果和简单模糊控制不能完全消除稳态误差的缺点,通过神经网络对模糊规则的学习优化,提高了机器人关节末端位置精度,具有较好控制效果。     

机器人视觉伺服研究进展:视觉系统与控制策略

视觉伺服控制是机器人系统的重要控制手段. 随着机器人应用需求的日益复杂多样,视觉伺服的研究面临着挑战. 视觉伺服系统的设计主要包括视觉系统、控制策略和实现策略三个方面. 文中对视觉伺服中存在的主要问题进行了分析,重点介绍了视觉系统中改善动态性能和处理噪声的主要技术手段,阐述了处理模型不确定性和约束的控制策略的改进方案,总结了提高视觉伺服系统的可实现性和灵活性的实现策略. 最后,基于当前的研究进展对未来的研究方向进行了展望.     

微操作机器人的视觉伺服控制

视觉伺服控制是微操作机器人实现精确运动,完成自动操作的必要手段．本文介绍 了实现微操作机器人视觉伺服控制的方法．首先论述了微操作机器人的视觉伺服结构,并以 建立的面向生物工程的双手微操作机器人系统为例,介绍了基于二维显微视觉信息的三自由 度柔性铰链微操作机器人的运动学建模方法,针对压电驱动器控制器的特点提出了基本的PI D视觉伺服控制规律实现方法,并进行了点到点运动和圆轨迹跟踪实验．实验结果表明,视 觉伺服控制克服了由于标定以及环境等因素导致的运动模型不准确而引入的误差．     

Direct Adaptive Dynamic Compensation for Minimum Phase Systems With Unknown Relative Degree

We consider parameter-monotonic direct adaptive control for single-input-single-output minimum-phase linear time-invariant systems with knowledge of the sign of the high-frequency gain (first nonzero Markov parameter) and an upper bound on the magnitude of the high-frequency gain. The first part of the paper is devoted to fixed-gain analysis of single-parameter high-gain-stabilizing controllers. Two novel fixed-gain dynamic compensators are presented for stabilizing minimum-phase systems. One compensator stabilizes systems with arbitrary-but-known relative degree, while the other utilizes a Fibonacci series construction to stabilize systems with unknown-but-bounded relative degree. Next, we provide a general treatment of parameter-monotonic adaptive control, including a result that guarantees state convergence to zero. This result is then combined with the high-gain-stabilizing controllers to yield parameter-monotonic direct adaptive dynamic compensation for minimum-phase systems with either arbitrary-but-known or unknown-but-bounded relative degree     

Fuzzy servo control of an inverted pendulum system

In this paper, an application of fuzzy servo control for stabilizing inverted pendulum system will be discussed. The inverted pendulum system is a simple system that consists of pendulum and cart but has strong nonlinearity and inherent instability. It is used as benchmark problem for study the performance and effectiveness of new control method. The idea behind this control method is to divide the operating region of nonlinear system into small areas, and to treat as a collection of local linear servo systems by using Davison?CSmith method. The control rule of each local linear servo systems is calculated using pole assignment method proposed by Hikita. Fuzzy method is applied to each local linear servo system and combines it as new control rule. The simulations have been done and the comparisons have been made between the fuzzy servo control and linear servo control. The simulation to study the effect of reference r????0 is done. The comparisons between different values of weight matrix Q _n for fuzzy membership function and disturbance also have been done. The results show that the proposed method can stabilize the system better than linear servo control and follow the reference given. The effect of variant value of values of weight matrix Q _n for fuzzy membership function and disturbance also can be observed.     

Constrained visual servoing under uncertain dynamics

In visual servoing, limitations in the field of view of the vision sensors are either ignored or treated at the kinematic level. The former can easily jeopardise task success, while the latter reduces the maximum achievable robotic motion speeds. In this work, the aforementioned literature gap is filled by designing and rigorously analysing a torque controller that guarantees prescribed transient and steady-state performance attributes on the image feature coordinate errors, while respecting the field-of-view constraints. No path planning and no information regarding the actual system dynamics are required. In addition, no approximation structures (i.e. neural networks, fuzzy systems, etc.) are utilised to acquire such knowledge. The proposed visual servo controller is static, involving very few and simple calculations to produce the control signal, making its implementation on embedded control platforms straightforward. Simulation studies are utilised to illustrate the motivation and to clarify–verify the theoretical findings.     

Augmented Sliding Mode Control for Flexible Link Manipulators

A method of sliding mode control (SMC) is proposed for the control of flexible, nonlinear, and structural systems. The method departs from standard sliding mode control by dispensing with generalized accelerations during the control law design. Global, asymptotic stability of rigid body motion is maintained if knowledge on the bounds of the neglected terms exists. Furthermore, this method provides damping for the measured flexible body modes. This paper investigates an augmented SMC technique for slewing flexible manipulators. A conventional sliding surface uses a first order system including a combination of error and error rate terms. The augmented sliding surface includes an enhanced term that helps to reject flexible degrees-of-freedom. The algorithms are theoretically developed and experimentally tested on a slewing single flexible link robot. The test apparatus is instrumented with a strain gauge at the root and an accelerometer attached at the tip. A DC motor and encoder are used to servo the link from an initial position to a final position. A standard cubic polynomial is employed to generate the reference trajectories. The augmented SMC algorithm showed improved performance by reducing the flexible link tip oscillations.     

电-气位置伺服控制系统的研究进展

由于气压驱动系统本身具有强非线性、固有频率低、刚度低和阻尼小等特点,实现高精度的位置伺服控制比较困难．针对我国在这方面所做工作相对较少的现状,从电-气位置伺服系统的控制方式和控制策略两方面综述了近年来的发展状况．并对各种方法的优缺点进行分析和比较,同时探讨了这一研究领域的发展方向和需要解决的问题．