Grasping impact force control of a flexible robotic gripper using a piezoelectric actuator

This paper presents robust force tracking control of a flexible beam during a grasping operation using a piezoceramic actuator. Equations describing the motion of the gripper in conditions of contact and noncontact are derived based on the cantilever beam. In this study, contact force is regulated, in addition to the impact force generated at the instant of contact, based on variable structure model reference adaptive control theory using only force measurements. For the derivation of the control law, it is assumed that parameters of the beam and the stiffness of the object are unknown. Computer simulations show the effectiveness the controller. This work was presented, in part, at the Fourth International Symposium on Artificial Life and Robotics, Oita, Japan, January 19–22, 1999     

Active noise control of flexible linkage mechanism with piezoelectric actuators

An active noise control method for flexible linkage mechanism systems with piezoelectric actuators and strain gauge sensors is studied. By employing a set of wave number transformations on the original equations of motion of the flexible linkage mechanisms, a new set of equations of motion is obtained, in which the unknown variables can describe the structural acoustic radiation level of the mechanism system directly. On the basis of the new equations, the active noise control of the flexible linkage mechanism system with piezoelectric actuators is discussed. Firstly, the optimal control forces are determined based on the optimal control theory. Secondly, the controller of the system that consists of the output feedback and the disturbance feed-forward control laws is presented. Simulations show that the method presented in this paper is valid.     

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.     

Force control of a two-linke planar manipulator with one flexible link

Force control of a two-link planar manipulator with one flexible link is considered in this study. The equations of motion are derived using the extended Hamilton's principle with only structural flexibility effects included in the dynamic model. The linear quadratic Gaussian/loop transfer recovery (LQG/LTR) design methodology is exploited to design a robust feedback control system that can handle modelling errors and sensor noise, and operate on Cartesian space trajectory errors. The LQG/LTR compensator together with a feedforward loop is used to simultaneously control the force exerted by the flexible manipulator normal to the environment and the position of the end-point in a direction tangent to the environment. Simulated results are presented for a numerical example.     

Intelligent fault-tolerant system of vibration control for flexible structures

This paper describes an intelligent fault-tolerant control method for vibration control of flexible structures. We consider a case where the fault phenomena of the control system for flexible structures can be treated as a change of system parameters. Therefore, the adaptive control method can be applied to a vibration control system for flexible structures with a fault. In this paper, a neural network (NN) adaptive control system is used to compensate for the change in the parameters of a plant with a fault. When the characteristics of the plant and of a nominal model have been agreed by a NN adaptive control system, the control method designed for the nominal model, such as decoupling feedback control or linearizing feedback control, can be used even if the change in the system parameters has been caused by a fault. To confirm the effectiveness of the proposed fault-tolerant control method, the simulational results from a 5-link robotic arm are shown at the end of the paper. This work was presented, in part, at the Fourth International Symposium on Artificial Life and Robotics, Oita, Japan, January 19–22, 1999     

Vibration damping of a flexible car body structure using piezo-stack actuators

Active vibration damping of a railway car body is accomplished by actuator forces acting directly on the flexible car body structure. In this work piezo-stack actuators mounted in consoles are utilized to introduce bending moments into the flexible structure, thus achieving a significant increase in ride comfort. For a heavy metro vehicle the complete design of the active vibration damping system is presented. Analytic modeling, system identification, and robust controller design are presented. The excellent performance of the proposed method is documented by both extensive experimental results and co-simulation studies.     

Designing feedforward command shapers with multi-objective genetic optimisation for vibration control of a single-link flexible manipulator

This paper presents investigations into the design of a command-shaping technique using multi-objective genetic optimisation process for vibration control of a single-link flexible manipulator. Conventional design of a command shaper requires a priori knowledge of natural frequencies and associated damping ratios of the system, which may not be available for complex flexible systems. Moreover, command shaping in principle causes delay in system's response while it reduces system vibration and in this manner the amount of vibration reduction and the rise time conflict one another. Furthermore, system performance objectives, such as, reduced overshoot, rise time, settling time, and end-point vibration are found in conflict with one another due to the construction and mode of operation of a flexible manipulator. Conventional methods can hardly provide a solution, for a designer-oriented formulation, satisfying several objectives and associated goals as demanded by a practical application due to the competing nature of those objectives. In such cases, multi-objective optimisation can provide a wide range of solutions, which trade-off these conflicting objectives so as to satisfy associated goals. A multi-modal command shaper consists of impulses of different amplitudes at different time locations, which are convolved with one another and then with the desired reference and then used as reference (for closed loop) or applied to system (for open loop) with the view to reduce vibration of the system, mainly at dominant modes. Multi-objective optimisation technique is used to determine a set of solutions for the amplitudes and corresponding time locations of impulses of a multi-modal command shaper. The effectiveness of the proposed technique is assessed both in the time domain and the frequency domain. Moreover, a comparative assessment of the performance of the technique with the system response with unshaped bang–bang input is presented.     

Proxy-based position control of manipulators with passive compliant actuators: Stability analysis and experiments

In this work we introduce a position control scheme which is targeted at the enhancement of the safety of compliant joint robots. In addition to the necessity for accuracy and robustness that both serve as prerequisites for the successful performance of various tasks, the ability to safely handle unexpected events, such as communication failures or unintended interactions which may endanger the robot/human safety, is a paramount requirement. To achieve a smooth motion behaviour of compliant systems under different circumstances, damping control actions are essential. To this end, a novel proxy-based approach for compliant joint robots, integrated into a passivity-guaranteed controller, is proposed. The stability analysis of the proposed scheme is presented and the global asymptotic convergence, as well as the passivity of the control scheme, are analytically proven. The performance of the proposed approach is practically evaluated by means of experiments on a spatial robotic arm with passive compliant actuators, and is compared with that of a classical PD approach. Experimental results validate the ability of the proposed approach to inject damping in order to provide smooth and damped recovery when an interruption in task execution occurs.     

Modeling and control of hysteresis in magnetostrictive actuators

A novel dynamic model is proposed for the hysteresis in magnetostrictive actuators by coupling a Preisach operator to an ordinary differential equation, and a parameter identification method is described. An efficient inversion algorithm for a class of Preisach operators with piecewise uniform density functions is then introduced, based upon which an inverse control scheme for the dynamic hysteresis model is presented. Finally the inversion error is quantified and l₁ control theory is applied to improve the robustness of inverse compensation. Simulation and experimental results based on a Terfenol-D actuator are provided.     

Robust control of flexible structures with stable bandpass controllers

In this paper, a control law for the active vibration control of mechanical flexible systems is considered. The proposed strategy minimizes an index and results in a stable stabilizing controller with bandpass frequency shape, due to the presence of zeros at the origin. The control authority is thus effective in a chosen band of frequency, resulting in a selective broadband control action, as opposed to narrow-band (tonal) vibration reduction. Moreover, the explicit closed-form solution of the controller is also obtained, thus avoiding numerical calculation of the solution of the Riccati equations, which can be ill-conditioned in the case of very high-order, poorly damped flexible systems. The parametrization of all the controllers is also given and a family of controllers with the above properties is deduced. The case is also obtained as a byproduct. The controller is based on a colocated actuators/sensors pair strategy and numerical simulations are presented, showing the robustness of the proposed approach even for systems with zero damping. Finally, experimental results on a skin panel of a Boeing 717 aircraft also prove the effectiveness of the proposed approach in practical complex applications, with global vibration reduction performances.     

采用MFC压电作动器对复合材料悬臂板振动主动控制

针对复合材料层合悬臂板,在其上表面铺设压电纤维复合材料MFC作为作动器,同时在下表面对称铺设压电薄膜(PVDF)作为传感器,应用速度反馈控制方法研究其主动振动控制.运用Hamilton原理和假设模态法推导含多个MFC作动器的复合材料层合板的力电耦合结构运动方程,其中考虑了MFC作动器作为悬臂板附加质量及刚度的影响.基于模态控制力/力矩最大化的原则,将多对MFC作动器/PVDF传感器铺设在层合悬臂板前几个低阶模态应变最大的区域,通过算例得出结构受控前后的时域和频域响应以及各MFC作动器所需的控制电压曲线.讨论复合材料层合板纤维铺设角度不同情况下,作动器MFC铺设位置及压电纤维铺设方向的相应变化.     

采用扰动估计的气动人工肌肉系统非线性控制

气动人工肌肉系统凭借其材质轻便、输出力大及柔顺性好等优势, 其运动控制研究近年来逐渐成为热点问题. 然而, 气动人工肌肉(pneumatic artificial muscle, PAM)系统所固有的特性(如迟滞、蠕变、非线性时变等), 为其控制方法设计与实现带来了挑战. 考虑到实际工作过程中, 系统往往遭受未知干扰的影响, 本文针对气动人工肌肉系统, 提出了一种基于干扰估计的非线性控制策略, 可在系统存在持续不确定干扰的情况下, 在线进行扰动抑制, 实现精确的跟踪控制. 具体而言, 本文先通过模型变换, 将系统不确定性、未建模动态、外部扰动等处理成集总扰动的形式. 随后, 结合自适应更新律及正则化最小二乘算法, 在线估计未知系统参数及扰动; 在精确扰动代数估计的基础上, 通过所提基于干扰估计的非线性控制器, 消除未知扰动对系统造成的影响, 并确保跟踪误差收敛至零. 此外, 经稳定性分析证明了跟踪误差的渐近收敛性. 最后, 通过硬件实验验证了本文方法的有效性及鲁棒性.     

Dynamic modelling, simulation and control of a manipulator with flexible links and joints

The paper presents a dynamic modelling technique for a manipulator with multiple flexible links and flexible joints, based on a combined Euler–Lagrange formulation and assumed modes method. The resulting generalised model is validated through computer simulations by considering a simplified case study of a two-link flexible manipulator with joint elasticity. Controlling such a manipulator is more complex than controlling one with rigid joints because only a single actuation signal can be applied at each joint and this has to control the flexure of both the joint itself and the link attached to it. To resolve the control complexities associated with such an under-actuated flexible link/flexible joint manipulator, a singularly perturbed model has been formulated and used to design a reduced-order controller. This is shown to stabilise the link and joint vibrations effectively while maintaining good tracking performance.     

Robust dynamic surface control of flexible joint robots using recurrent neural networks

A robust neuro-adaptive controller for uncertain flexible joint robots is presented. This control scheme integrates H-infinity disturbance attenuation design and recurrent neural network adaptive control technique into the dynamic surface control framework. Two recurrent neural networks are used to adaptively learn the uncertain functions in a flexible joint robot. Then, the effects of approximation error and filter error on the tracking performance are attenuated to a prescribed level by the embedded H-infinity controller, so that the desired H-infinity tracking performance can be achieved. Finally, simulation results verify the effectiveness of the proposed control scheme.     

Geometric stiffening of flexible link system with large overall motion

In the conventional hybrid-coordinate formulation, the Cartesian deformation variables are employed with a linear Cauchy strain measure. It has been found that such modeling method fails to capture the motion-induced stiffness terms and provides erroneous dynamic results in case of high rotating speed. In this paper, geometric stiffening of flexible link system is investigated. Using a non-Cartesian deformation variable, the equations of motion of each link, which include the stiffening terms, are obtained based on the virtual power principle, and forward recursive formulation is employed to derive the equations of flexible link system. Relative generalized coordinates are employed to derive the equations of motion of the link system. Numerical examples are presented to investigate the stiffening effect on large overall motion as well as deformation of the flexible link system and to testify the accuracy and efficiency of the formulation.     

A self-organizing fuzzy logic controller for the active control of flexible structures using piezoelectric actuators

This paper proposes an on-line self-organizing fuzzy logic controller (FLC) design applied to the control of vibrations in flexible structures containing distributed piezoelectric actuator patches. In this methodology, the fuzzy rules are generated using the history of input/output (I/O) pairs without using any plant model. The generated rules are stored in the fuzzy rule space and updated on-line by a self-organizing procedure. The validity of the proposed fuzzy logic control has been demonstrated experimentally in a steel cantilever test beam and a set of experimental tests are made in the system to verify the efficiency of the on-line self-organizing fuzzy controller.     

垂直气动人工肌肉系统的模型参考自适应逆补偿控制

与传统刚性驱动系统相比, 气动人工肌肉系统具有质量轻、人机交互友好等优势, 近年来在生产生活中受到广泛关注. 然而, 该类系统的运动呈现出复杂的迟滞特性, 这给针对该类系统的跟踪控制研究带来了挑战. 本文针对垂直气动人工肌肉系统, 提出一种模型参考自适应逆补偿控制策略, 可有效克服迟滞特性以及控制过程中外界扰动和参数摄动等不确定因素对系统运动状态的影响, 实现系统高精度跟踪控制. 具体而言, 本文首先对系统的运动特性以及影响系统控制精度的不确定因素进行分析; 然后, 基于分析结果建立一个描述系统运动特性的参考模型; 进而采用逆补偿思想, 通过对所建立的参考模型求逆来构造一个逆补偿控制器, 克服迟滞特性对系统运动状态产生的影响; 随后, 基于最小均方误差算法设计自适应律, 在线辨识参考模型的权值, 同时估计逆补偿控制器的设计参数, 克服外界扰动和参数摄动等不确定因素对系统运动状态的影响; 最后, 通过实验验证所提控制策略的有效性.     

Robust adaptive vibration control for an uncertain flexible Timoshenko robotic manipulator with input and output constraints

The problems of the constraints and the vibration suppression are investigated for the flexible Timoshenko robotic manipulator in this paper. Robust adaptive boundary control laws with the disturbance observes are designed to guarantee the convergence of the feedback flexible Timoshenko robotic manipulator system with the uncertain parameters and the states are proven to be uniform bounded. In addition, the proposed boundary controls are verified to be effectiveness by the numeral experiments.     

受时变约束柔性臂鲁棒RBF神经网络力/位置控制

研究了受时变约束的柔性臂系统，建立了分布参数模型，通过奇异摄动方法将该模型划分为表征系统刚性运动的集中参数子系统和表征系统振动的分布参数子系统．设计了集中参数子系统的鲁棒RBF神经网络力／位置控制算法和分布参数子系统的鲁棒自适应振动抑制控制算法．理论分析及仿真结果验证了该方法的有效性．     

Partial differential equation modeling and vibration control for a nonlinear 3D rigid‐flexible manipulator system with actuator faults

In this paper, modeling and controlling problem for a two‐link rigid‐flexible manipulator in three‐dimensional (3D) space is studied under actuator faults. For modeling, the dynamics of the 3D mechanical system is represented by nonlinear partial differential equations, which is first derived in infinite dimension form. Based on the nonlinear model, the controller is proposed, which can achieve joint angle control and vibration suppression control in the presence of actuator faults. The stability analysis of the closed‐loop system is given based on LaSalle invariance principle. Numerical simulations illustrate the effectiveness of the proposed controller. This study will promote the development of nonlinear flexible manipulator systems in 3D space.