遗传算法在柔性臂控制中的应用

提出了一种双连杆柔性机械臂的控制方法.首先运用拉格朗日法建立双连杆柔性机械臂的动力学模型,并利用奇异摄动方法将柔性臂系统分解为慢变和快变子系统后,设计了组合控制器.对慢变子系统利用遗传算法确定两杆的PD控制参数,而时快变子系统采用最优H2综合策略设计控制器后,对柔性臂系统施加组合控制律.仿真结果表明了所设计控制器的有效性.     

一种双连杆柔性臂动力学模型的研究

针对末端位置受约束的双连杆柔性机械臂,通过哈密顿原理得到系统的分布参数模型,推导了描述关节角,柔性杆振动和接触力之间关系的动力学模型.根据3个假设条件推导柔性臂简化的集中参数动力学模型及准静态方程,利用了计算力矩法设计的控制器对模型进行控制,通过Matlab进行仿真,利用Matlab的符号运算功能,编制M文件实现数学模型自动推导,整个建模和运算过程简单、直观和高效,并绘制了参数轨迹图像,验证了模型的有效性,已应用到小波神经网络控制算法研究中.     

线驱动柔性机械臂的运动学分析

与传统的由连杆和关节构成的刚性机械臂不同,设计的柔性机械臂无任何刚性结构,外围驱动装置通过嵌在机械臂内部的拉线与柔性机械臂相联系,控制拉线长度的变化量即可调整柔性机械臂末端执行器的位置和姿态。柔性机械臂由弹性材料制作而成,拥有无穷多个自由度,在确保了高安全性、高灵活性的同时,随之也带来运动学和动力学建模复杂、控制难度大等问题。基于分段常曲率的假设,提出了一种运动学建模方法,通过建立3个空间,即驱动空间、虚拟关节空间、任务空间,以及两个映射,即驱动空间-虚拟关节空间映射、虚拟关节空间-任务空间映射,将拉线长度的变化量和柔性机械臂末端执行器的位置和姿态关联起来。仿真结果表明,提出的线驱动柔性机械臂的运动学模型,能较为真实地模拟柔性机械臂在拉线长度变化时的形态,计算末端执行器的位置和姿态。     

基于遗传算法的柔性机械臂的同时优化设计

针对单连杆柔性机械臂系统,采用同时设计的方法,对包含柔性机械臂结构参数、传感器参数和控制器参数的系统模型进行整体优化设计,改进的遗传算法用于参数的全局寻优.仿真结果显示,优化设计后的单连杆柔性机械臂为变截面梁,可以仅采用简单的控制器(PD控制器)达到减小梁末端振动的效果.     

柔性机械臂动力学建模研究进展

刚性机械臂由于其较高的工作精度和重复性、较强的承载能力,已广泛应用于危险或相对单一、重复性高工作场景.但刚性机械臂的结构及运作方式不够灵活,无法适用于不定型、非标准、狭窄空间等生产场景.最近几年,柔性机械臂因其结构柔性、作业空间大、人机交互安全等优点而受到广泛关注,有希望应用于医疗、服务和智能制造等领域.但柔性机械臂结构柔软,运动比较自由,在作业过程中柔性效应不可忽略,这对其高精度控制提出了重大挑战.柔性机械臂控制的核心科学问题之一是建立包含结构柔性特征和动态特性的高精度动力学模型.为此,本文对柔性机械臂运动学建模和动力学建模研究进行了综述.作为动力学建模的基础,本文首先综述了柔性机械臂的运动学建模方法,主要介绍了曲率法、伪刚体运动学(PRB)方法、基于Cosserat杆的运动学建模方法、结构几何分析方法、Denavit Hartenberg(D H)法及坐标法、数据驱动和机器学习方法等.随后,本文详细综述了柔性机械臂的动力学建模方法,主要包括集中参数系统法、假设模态法、有限元法.最后,本文简述了目前柔性机械臂动力学研究的主要内容,并对未来研究做出展望.     

柔性关节机器人高精度自适应反步法控制

为实现多连杆柔性关节机器人的高精度运动控制,首先对其建立完整的动力学模型,包含了连杆和关节动力学的耦合项、LuGre动态摩擦模型和关节回差等因素．然后针对该模型设计带观测器的自适应反步法控制器,对不可测项进行在线估计和补偿．理论分析证明了观测器的收敛性和闭环系统的稳定性．该方法在一个3DOF（degree of freedom）柔性关节机器人上进行仿真,仿真结果验证了观测器的有效性,并表明该控制器能够降低连杆跟踪误差,实现良好的轨迹跟踪效果．     

随机激励下单杆柔性关节机械臂的建模与控制

机械系统如移动机器人、机械臂等在运动过程中通常会受到随机干扰.针对随机激励下单连杆柔性机械臂的数学建模和控制问题,目前还没有相关的研究.本文引入随机干扰,建立了一个具有未知参数的随机动力学模型.然后通过坐标变换,将该模型化成一个4阶系统.在此基础上,结合自适应理论,动态面方法和Lyapunov方法,设计了一种新的控制器.这种控制器有效地避免了传统方法中的过参数估计和复杂性爆炸的问题,同时可以保证跟踪误差在均方意义下任意小,且闭环系统的所有信号依概率有界.最后通过一个仿真例子验证了本文理论的有效性.     

柔性连杆机器人的多速率神经网络混合控制器设计

提出了一种用于动力学部分已知柔性连杆机器人的多速率神经网络自适应混合控制器，基于奇异摄动方法和两时标分解，柔性连杆机器人的模型分解成两个子系统；慢子系统和快子系统。这样可以根据每个分立的子系统设计系统的慢和快控规律，然后组合成一个混合控制。系统的慢控制由基于神经网络的自适应控制器实现，用于控制等效的刚性连杆机器人，而快控制用于在慢子系统建立的平衡轨迹附近稳定快子系统。     

双连杆柔性臂轨迹跟踪的鲁棒控制

研究了双连杆柔性臂轨迹跟踪的鲁棒控制问题·基于假设模态法和奇异摄动法,导 出了双连杆柔性臂系统的动力学方程,并将系统模型分离为慢变和快变两个子系统.针对柔 性臂的特点,提出了关节角的补偿控制思想,并且给出了补偿控制算法.对两个子系统分别采 用滑模变结构控制和H∞控制,由此得到的组合控制使系统精确跟踪目标轨迹.研制了双连 杆柔性臂实验台,并对文中提出的方法进行了实验.     

基于PMSM驱动的柔性关节空间机械臂轨迹跟踪控制方法

针对目前柔性关节空间机械臂轨迹跟踪控制方法忽略了不同重力影响下的机械臂驱动力变化,导致柔性关节空间机械臂轨迹跟踪控制效果较差的问题,提出了基于PMSM驱动的柔性关节空间机械臂轨迹跟踪控制方法。基于构建PMSM驱动数学模型,采用PMSM的矢量控制方法,分析驱动力矩矢量。根据驱动力矩矢量分析结果,分析不同重力环境下有、无摩擦时的驱动力矩。构建柔性关节模型,分析其在不同重力环境下遇到的重力释放问题,使用自适应反演滑膜控制方法,设计控制率,保证机械臂能够按照既定的方向运动,使机械臂具有鲁棒性。根据柔性关节空间机械臂动力学特性,分析不同重力环境下基于PMSM驱动力矩,确定重力项是随之发生改变的。设计控制器,构建动力学模型,确保空间阶段能够最大限度跟踪运动轨迹。实验结果表明,所提方法X轴、Y轴的末端跟踪结果均与实际运动轨迹一致,误差为0。关节控制力矩在时间为3s时,出现了最大为0.5N.m的误差,说明所提方法的跟踪控制效果较好。     

A distributed parameter model for the dynamics of flexible-link robots

In this paper a model is developed for kinematic and dynamic analysis of flexible robots undergoing general three-dimensional motion. For modeling robotic links, distributed mass and flexibility are considered without discretization. Some modeling issues are discussed, and parameters characterizing the real design of a robot are introduced into the analysis. The concept of a fictitious rigid link is presented to consider the rigid body motion of a link separately, and to account for possibly complex link shapes. Based on Jourdain's principle, an alternative formulation is proposed to derive the dynamic equations of flexible robots. The equations of motion are developed and analyzed in detail. The vibrations of links are described by linear, inhomogeneous partial differential equations, with homogeneous, nonlinear, time-dependent boundary conditions. © 1998 John Wiley & Sons, Inc.     

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.     

基于Adams的剪式稳定架刚柔耦合分析

采用CATIA对剪式稳定架系统进行三维建模,基于ANSYS和Adams建立刚柔耦合动力学模型。考虑剪式稳定架的柔性特征,对刚柔耦合模型升降过程的3种工况进行动力学仿真分析,得到运动过程中剪式稳定架应力分布规律、连接铰点力和接触力。分析方法和结论可指导剪式稳定架的设计。     

Optimization of frame structures with flexible joints

In the traditional approach to analysing and optimizing frame structures, joints are assumed to be rigid. Research has shown, however, that flexibility in the joints of a structure has a great effect on its behaviour. In this paper we present a formal method for optimizing frame structures to account for joint flexibilities and their design parameter sensitivities. We also present a simplified method that accounts for joint flexibility in the initial configuration, but neglects sensitivities to the design parameters. In a case study on an automotive sub-frame structure we compare optimization results using the traditional rigid joint model and the flexible joint methods proposed here. Results suggest that the simplified flexible joint method is more accurate than the traditional rigid joint model, and provides a more conservative design than the full flexible joint method while saving physical and computational effort. Received January 18, 1999     

A cohesive modeling technique for theoretical and experimental estimation of damping in serial robots with rigid and flexible links

Dynamic model incorporating damping characteristics, namely joint damping and structural damping in flexible links, of the serial robots with rigid and flexible links is presented. A novel procedure, based on the unified approach of theoretical formulation and analysis of experimental data, is proposed for the estimation of damping coefficients. First, the dynamic model of a robotic system with rigid and flexible links is presented. Next, the modifications in the dynamic model due to the considerations of damping characteristics of joints and structural damping characteristics of the flexible links are presented. A systematic methodology based on analysis of data obtained from experiments is presented for estimation and determination of damping coefficients of rigid-flexible links. The determination of joint damping coefficients, is based on the logarithmic decay of the amplitude of the oscillations of robotic links, while the structural damping coefficients are estimated mainly using the modal analysis and the method of evolving spectra. The method of evolving spectra, based on the Fast Fourier Transform of the decay of the amplitude in structural vibrations of the robot links in progressive windows is used to estimate the structural damping ratios while the critical structural coefficients are determined using the modal analysis. The methodology is illustrated through a series of simple experiments on simple robotic systems. The experimental results are then compared with the simulation results incorporating the damping coefficients determined using the proposed procedure. The comparisons leads to the validation of the proposed dynamic modeling technique, modeling of the damping characteristics, and the method proposed for estimation of damping coefficients for rigid-flexible link robotic systems.     

Observer-based continuous finite-time attitude control for rigid–flexible coupling satellites

In this paper, a novel finite-time attitude control law is proposed for rigid–flexible coupling satellites in large angle manoeuver. First, the rigid–flexible coupling dynamic model is set up to reflect the coupling effect between the deformation of flexible appendages and the spatial movement of the rigid hub. Then an extended state observer (ESO) is designed to estimate and compensate the total perturbation including high-order flexible coupling terms, external disturbances and uncertain inertia. Following this, a continuous finite-time attitude controller is designed based on non-singular fast terminal sliding mode (NFTSM) and fast power reaching law, which is introduced to smooth the control input and eliminate the chattering. Numerical simulation is designed to verify the finite-time stability, high accuracy, disturbance rejectionand vibration damping of the proposed control scheme and then a ground experimental system is set to further test the controller's practicability.     

Dynamics and Noncollocated Model‐Free Position Control for a Space Robot with Multi‐Link Flexible Manipulators

In this paper, both the dynamics and noncollocated model‐free position control (NMPC) for a space robot with multi‐link flexible manipulators are developed. Using assumed modes approach to describe the flexible deformation, the dynamic model of the flexible space robotic system is derived with Lagrangian method to represent the system dynamic behaviors. Based on Lyapunov's direct method, the robust model‐free position control with noncollocated feedback is designed for position regulation of the space robot and vibration suppression of the flexible manipulators. The closed‐loop stability of the space robotic system can be guaranteed and the guideline of choosing noncollocated feedback is analyzed. The proposed control is easily implementable for flexible space robot with both uncertain complicated dynamic model and unknown system parameters, and all the control signals can be measured by sensors directly or obtained by a backward difference algorithm. Numerical simulations on a two‐link flexible space robot are provided to demonstrate the effectiveness of the proposed control.     

带Stewart平台的航天器刚柔耦合动力学建模与仿真分析

本文采用柔性多体系统单向递推组集的建模方法,基于速度变分原理建立了带Stewart平台、柔性帆板和CMG组件的航天器刚柔耦合动力学模型.由于该模型自由度较大,无法满足实时控制的需求,因此建立了简化的Stewart平台等效模型,并通过与柔性Stewart平台完整模型对比,验证了所建立的动力学简化模型的正确性与高效性.分析了星体平台运动及柔性帆板的振动对有效载荷动力学响应的影响,指出了设计Stewart平台的微振动抑制方案时不能忽略下平台的运动及柔性附件的振动.本研究为带Stewart平台的航天器的微振动减振设计与高精度指向提供了有效的技术支撑.