Rotation Angle Control Strategy for Telescopic Flexible Manipulator Based on a Combination of Fuzzy Adjustment and RBF Neural Network

The length of fexible manipulators with a telescopic arm alters during movement.The dynamic parameters of telescopic fexible manipulators exhibit signifcant time-varying characteristics owing to variations in length.With an increase in the manipulators’length,the nonlinear terms caused by fexibility in the manipulators’dynamic equations cannot be ignored.The time-varying characteristics and nonlinear terms of telescopic fexible manipulators cause fuctuations in rotation angles,which afect the operation accuracy of end-efectors.In this study,a control strategy based on a combination of fuzzy adjustment and an RBF neural network is utilized to improve the control accuracy of fexible telescopic manipulators.First,the dynamic equation of the manipulators is established using the assumed mode method and Lagrange’s principle,and the infuence of nonlinear terms is analyzed.Subsequently,a combined control strategy is proposed to suppress the fuctuation of the rotation angle in telescopic fexible manipulators.The variation ranges of the feedforward PD controller parameters are determined by the pole placement strategy and length of the manipulators.Fuzzy rules are utilized to adjust the controller parameters in real-time.The RBF neural network is utilized to identify and compensate the uncertain part of the dynamic model of the fexible manipulators.The uncertain part comprises time-varying parameters and nonlinear terms.Finally,numerical simulations and prototype experiments prove the efectiveness of the combined control strategy.The results prove that the proposed control strategy has a smaller standard deviation of errors.Therefore,the combined control strategy is more suitable for telescopic fexible manipulators,which can efectively improve the control accuracy of rotation angles.

Attitude tracking control of flexible spacecraft with large amplitude slosh

This paper is focused on attitude tracking control of a spacecraft that is equipped with flexible appendage and partially filled liquid propellant tank. The large amplitude liquid slosh is included by using a moving pulsating ball model that is further improved to estimate the settling location of liquid in microgravity or a zero-g environment. The flexible appendage is modelled as a three-dimensional Bernoulli–Euler beam, and the assumed modal method is employed.A hybrid controller that combines sliding mode control with an adaptive algorithm is designed for spacecraft to perform attitude tracking. The proposed controller has proved to be asymptotically stable. A nonlinear model for the overall coupled system including spacecraft attitude dynamics,liquid slosh, structural vibration and control action is established. Numerical simulation results are presented to show the dynamic behaviors of the coupled system and to verify the effectiveness of the control approach when the spacecraft undergoes the disturbance produced by large amplitude slosh and appendage vibration. Lastly, the designed adaptive algorithm is found to be effective to improve the precision of attitude tracking.

Position Control of a Flexible Manipulator Using a New Nonlinear Self-Tuning PID Controller

In this paper, a new nonlinear self-tuning PID controller(NSPIDC) is proposed to control the joint position and link deflection of a flexible-link manipulator(FLM) while it is subjected to carry different payloads. Since, payload is a critical parameter of the FLM whose variation greatly influences the controller performance. The proposed controller guarantees stability under change in payload by attenuating the non-modeled higher order dynamics using a new nonlinear autoregressive moving average with exogenous-input(NARMAX) model of the FLM. The parameters of the FLM are identified on-line using recursive least square(RLS) algorithm and using minimum variance control(MVC) laws the control parameters are updated in real-time. This proposed NSPID controller has been implemented in real-time on an experimental set-up. The joint tracking and link deflection performances of the proposed adaptive controller are compared with that of a popular direct adaptive controller(DAC). From the obtained results, it is confirmed that the proposed controller exhibits improved performance over the DAC both in terms of accurate position tracking and quick damping of link deflections when subjected to variable payloads.

Modeling and controlling of a flexible hydraulic manipulator

A mathematical model was developed combining the dynamics of an Euler-Bernoulli beam, described by the assumed-mode method and hydraulic circuit dynamics. Only one matrix, termed drive Jacobian, was needed in the modeling of interaction between hydraulic circuit and flexible manipulator mechanism. Furthermore, a new robust controller based on mentioned above dynamic model was also considered to regulate both flexural vibrations and rigid body motion. The proposed controller combined sliding mode and backstepping techniques to deal with the nonlinear system with uncertainties. The sliding mode control was used to achieve an asymptotic joint angle and vibration regulation by providing a virtual force while the backstepping technique was used to regulate the spool position of a hydraulic valve to provide the required control force. Simulation results are presented to show the stabilizing effect and robustness of this control strategy.

Impact vibration reduction for flexible manipulators via controllable local degrees of freedom

When performing operation tasks, the interaction between a flexible manipulator and a grasped object usually results in an impact. In this paper, a new way is suggested to alleviate impact vibration of a flexible manipulator via its structural characteristic when capturing a moving object. Controllable local degrees of freedom are introduced to the topological structure of the flexible manipulator, and used as an effective tool to combat impact vibration through dynamic coupling. A corresponding method is put forward to reduce impact vibration responses of the flexible manip- ulator via the controllable local degrees of freedom. By planning motion of the controllable local degrees of freedom, appropriate control force can be constructed to increase the modal damping and stiffness and eliminate the exciting force simultaneously, thereby reducing impact vibration responses of the flexible manipulator. Simulations are conducted and results are shown to prove the presented method.

Active Disturbance Rejection Control for a Multiple-Flexible-Link Manipulator

The control problem of multiple-flexible-link manipulators( MFLMs) is studied in this paper.The dynamic model of MFLM is derived and separated into two-time scale by utilizing the singular perturbation technique. The active disturbance rejection control( ADRC) is adopted to the slow subsystem to track a desired trajectory. The proposed ADRC structure preshapes the desired trajectory by utilizing the tracking differentiator,estimates the disturbance and internal states with an extended state observer,and guarantees a robust performance by combining a feedback controller with a feedforward term. Two types of feedback controllers are designed,proportional derivative( PD) controller and nonlinear PD( NPD) controller. For the fast subsystem,a fast stabilizing control is designed according to the standard linear quadratic regulator approach. Simulations are performed to evaluate the proposed control scheme.Results show that,compared with the traditional PD controller,the ADRC structure based control scheme has smaller overshot and shorter settling time,suppresses vibration quickly,and is robust to the maneuver speed. In general,the control scheme utilizing ADRC structure and NPD feedback controller shows better performance.

Dynamic Tracking Control of Space Robot Flexible Arm

An inverse dynamic model is deve1oped through further deduction from the dynamic model of a flexible arm based upon the lagrangian formula,and a dynamic non-linear tracking control scheme,which combines an inverse dynamic method with PD control and non-linear compensator,is proposed for flexible arms.Simulation reaults show this non-linear control scheme can put the flexible arm system under effective control and realize accurate trajectory tracking.

Adaptive Tracking Control of Mobile Manipulators with Affine Constraints and Under-actuated Joints

Adaptive motion/force tracking control is considered for a class of mobile manipulators with affine constraints and under-actuated joints in the presence of uncertainties in this paper. Dynamic equation of mobile manipulator is transformed into a controllable form based on dynamic coupling technique. In view of the asymptotic tracking idea and adaptive theory, adaptive controllers are proposed to achieve the desired control objective. Detailed simulation results confirm the validity of the control strategy.

Fuzzy Supervisory Control and GPC Applied to a Flexible Single-Link Manipulator

This paper presents the development of a classical and intelligent control approaches applied to a flexible single-link manipulator robot and compared in terms of input tracking and vibration suppression. Lagrange＇s equations and finite elements method are combined to compute dynamic model of a flexible link manipulator with one rigid joint. Next, dynamics are itemized to explain flexible link behavior. Then a fuzzy supervisory controller is developed and introduced in the high level of the closed-loop of the flexible manipulator. A generalized predictive controller is then developed and introduced in the flexible system closed-loop to minimize end-point residual vibrations. Simulation results obtained are compared to a GPC （generalized predictive controller） in terms of end-point vibration suppression, input tracking and disturbance rejection. A conclusion encloses the paper.

考虑偏差的刚柔耦合夹具气动机械手加载状态主动控制技术

当前刚柔耦合夹具气动机械手在夹取重量较大或形状复杂的工件时,加载状态会出现非线性震荡,造成控制偏差,降低控制平稳度。为了提升刚柔耦合夹具气动机械手加载状态主动控制效果,设计一种考虑偏差的刚柔耦合夹具气动机械手加载状态主动控制方法。考虑四种动界限情况计算刚柔耦合夹具气动机械手加载振荡;加载振荡下将偏差分为刚度偏差和柔度偏差,通过奇异函数和拉普拉斯变换计算等级刚度、挠度以及转角,获得气动机械手加载状态受力偏差;构建气动机械手和接杆的坐标系和运动坐标系,分析气动机械手终端位置矢量和驱动力矩的映射关联;通过PD反馈进行刚度偏差和柔度偏差补偿,完成加载状态主动控制。实验结果表明:该方法偏差补偿后,输出力矩更接近理想值,可准确计算刚柔耦合夹具气动机械手在加载状态中的挠度、回旋角度以及动态角度,使气动机械手加载状态主动控制更加平稳。

基于反演法的矿用机械臂关节位置控制方法

针对矿用机械臂关节内部的柔性元件可导致机械臂末端位置无法实现精准控制的问题,对机械臂柔性关节的位置控制方法进行研究,基于拉格朗日动力学模型构建方法,建立融入机械臂关节柔性特性的关节动力学模型,并且与反演法原理进行结合,创新性地提出基于反演法的矿用机械臂柔性关节位置控制方法(IM-PCM),使机械臂关节柔性造成的末端位置控制精确性不足问题得到改善。通过MATLAB软件中的SIMULINK平台对IM-PCM的控制效果进行仿真分析,结果表明IM-PCM能够使矿用机械臂末端位置得到精确控制。

一类基于RBF网络机械手的轨迹稳定跟踪控制

目的针对具有外界干扰不确定性的柔性关节机械手实际轨迹跟踪稳定性问题,提出一种自适应动态面控制与神经网络相结合的方法。方法对于非线性系统中的函数以及未知参数,根据径向基函数(RBF)神经网络的特点对其进行逼近,并对来自外界对系统的干扰项,通过设计阻尼项将其补偿,再根据动态面的相关知识对该非线性系统中的控制器进行设计且实现关节轨迹跟踪控制。结果仿真结果表明:在非线性系统中,该方法能够克服干扰不确定性项,实现机械手连杆转角q较好的跟踪效果,误差缩在5%以内,具有较强的跟踪稳定性,且随着时间的进行,跟踪误差愈发减小且趋向于0,对于参数的估计以及逼近都达到了理想的阈值。结论该方法保证了闭环非线性系统半全局稳定,又可利用参数调节的方式达到跟踪误差任意小,且设计的控制器不但保证了机械手的位置跟踪稳定性,而且很好地解决了跟踪抖动问题。

多自由度柔性机械臂非线性连续时变反馈控制方法

针对当前多自由度柔性机械臂控制过程中,机械臂定位控制系数选择合理性较低,导致多自由度柔性机械臂控制时延较长且运动轨迹与预设轨迹存在较大差异的问题,提出多自由度柔性机械臂非线性连续时变反馈控制方法。将拉格朗日算子作为计算基础,以能量的方式构建多自由度柔性机械臂动力学模型。考虑到机械臂的负载状态,计算机械臂的重力矩,识别机械臂非线性连续时变反馈控制参数。设定非线性连续时变反馈控制规则,构建机械臂非线性控制器,实现机械臂定位控制。构建实验环节,实验结果表明:该方法可有效提升机械臂运动轨迹与预设轨迹的一致性,缩短机械臂定位控制时延,进一步提升机械臂应用效果。

基于数字孪生技术的机械手视觉抓取轨迹动态控制仿真

为了有效规划与控制机械手抓取轨迹,提升机械手抓取效果,提出基于数字孪生技术的机械手视觉抓取轨迹动态控制仿真方法。数字孪生物理实体层通过相机、位置及激光传感器采集机械手图像以及相关参数数据,并执行数据预处理操作;数字孪生虚拟模型层利用物理实体层获取数据,通过SolidWorks以及Unity3D等软件构建机械手数字孪生虚拟模型;数字孪生核心控制层的机械手规划与控制模块基于数字孪生虚拟模型,应用B样条曲线轨迹规划方法完成机械手抓取轨迹动态控制。实验结果表明:该方法可有效控制机械手抓取轨迹,并通过虚拟方式视觉呈现机械手的抓取轨迹,轨迹控制准确性较高。将该方法应用到实际的机械手抓取工作中,可显著提升机械手抓取效果。

基于奇异摄动的柔性关节机械臂约束跟随控制研究

针对二连杆柔性关节机械臂,提出了一种基于奇异摄动理论和Udwadia-Kalaba(U-K)方法的控制方法.设计步骤主要分为两步:第一,基于奇异摄动法对系统进行降阶,把系统拆分为快、慢系统,不仅降低了求解系统的阶次,而且克服了系统柔性;第二,基于U-K方法设计了快、慢系统的状态反馈约束跟随控制律,能使快、慢系统约束跟随误差收敛到零,即使系统初始不满足约束条件,该方法不需要借助Lagrange乘子和伪广义速度等辅助变量,可以同时处理完整约束和非完整约束.将以上方法运用在二连杆柔性关节机械臂系统中,解决了二连杆柔性关节机械臂的柔性振荡和约束跟随的问题.使用MATLAB进行仿真,并且与传统PID控制进行了对比,验证了所提出的方法的有效性与优越性.

海流环境下二关节机械臂动力学建模及其跟踪控制

水下机械臂的水动力性能受海流载荷的影响较大,目前针对水下机械臂控制的相关研究中将水下环境做了静水的假设或将海流载荷仅仅作为一种简单的随机扰动来考虑,控制精度较低.该文分别基于Lagrange法和Newton-Euler法推导出均匀海流环境下二关节机械臂的动力学模型,考虑海流和机械臂的相对运动,引入Morison公式计算海流对机械臂的水阻力和惯性力.基于此动力学模型,利用滑模控制策略实现机械臂理想轨迹的精确跟踪.对比PD(proportional-derivative)控制,仿真结果表明滑模控制具有更优的控制效果.

双连杆柔性关节机械臂分数阶线性自抗扰控制

针对双连杆柔性关节机械臂的柔性振动和受外部干扰的问题,提出了一种复合控制器的控制策略。通过拉格朗日方程建立了考虑关节柔性的刚柔耦合的机械臂动力学模型,使用奇异摄动法对机械臂系统解耦,使其分解成代表刚性部分的慢速子系统和代表柔性部分的快速子系统;对于慢速子系统,设计了带有前馈补偿的分数阶线性自抗扰控制器来抵抗内外扰动,实现了机械臂的高精度的轨迹跟踪,对于快速子系统,采用微分补偿项补偿,来抑制关节的柔性振动,从而达到系统稳定。实验和仿真结果表明,系统可以有效地实现双连杆柔性关节机械臂的轨迹跟踪,并且相对于整数阶线性自抗扰控制器有着更好的动态性能和鲁棒性。

移动装配机器人手臂的滑模鲁棒控制方法

为了克服外界干扰、未知负载等不确定性和电机动态特性对移动装配机器人手臂末端空间轨迹跟踪的影响,提出了一种基于扩张状态观测器的滑模鲁棒控制律。首先建立了包含不确定性和电机动态特性的数学模型,然后设计了扩张状态观测器来准确估计不确定性,在此基础上提出了滑模鲁棒控制律,最终实现了对移动装配机器人手臂末端空间轨迹跟踪的高精度控制。仿真结果表明,所设计的滑模鲁棒控制律具有更优的控制效果,移动装配机器人手臂末端空间轨迹的最大跟踪误差仅为0.5 cm,所设计的扩张状态观测器能够准确估计不确定性,最大估计误差仅为0.2 N·m,估计精度较高。移动装配机器人手臂空间固定坐标定位实验结果表明,在基于扩张状态观测器的滑模鲁棒控制律的作用下,移动装配机器人手臂末端空间轨迹的最大跟踪误差仅为0.24 cm,平均每次定位的运行时间仅为1.55 s,表现出了更优的快速性、准确性和工程实用性。

Task Space Division and Trajectory Planning for a Flexible Macro-Micro Manipulator System

This paper deals with a flexible macro-micro manipulator system, which includes a long flexible manipulator and a relatively short rigid manipulator attached to the tip of the macro manipulator. A flexible macro manipulator possesses the advantages of wide operating range, high speed, and low energy consumption, but the disadvantage of a low tracking precision. The macro-micro manipulator system improves tracking performance by compensating for the endpoint tracking error while maintaining the advantages of the flexible macro manipulator. A trajectory planning scheme was built utilizing the task space division method. The division point is chosen to optimize the error compensation and energy consumption for the whole system. Then movements of the macro-micro manipulator can be determined using separate inverse kinematic models. Simulation results for a planar 4-DOF macro-micro manipulator system are presented to show the effectiveness of the control system.

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．本文从柔性机机械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．