Comparison of some modeling and control issues for a flexible two link manipulator

The nonlinear dynamics of a flexible two link manipulator presents a challenging modeling and control problem with its lumped actuator dynamics coupled with distributed link dynamics. Issues related to modeling uncertainty and control robustness as well as a good understanding of the experimental issues are essential for advanced modeling and control for such systems. This paper reports some of the advanced modeling, control, and experimental issues for a flexible two link manipulator, including some novel approaches developed by the authors.     

Analytical dynamic solution of a flexible cable-suspended manipulator

Cable-suspended manipulators are used in large scale applications with, heavy in weight and long in span cables. It seems impractical to maintain cable assumptions of smaller robots for large scale manipulators. The interactions among the cables, platforms and actuators can fully evaluate the coupled dynamic analysis. The structural flexibility of the cables becomes more pronounced in large manipulators. In this paper, an analytic solution is provided to solve cable vibration. Also, a closed form solution can be adopted to improve the dynamic response to flexibility. The output is provided by the optimal torque generation subject to the actuator limitations in a mechatronic sense. Finally, the performance of the proposed algorithm is examined through simulations.     

软腔体柔性机械臂的T-S模糊建模与控制

针对柔性机械臂强非线性、强耦合性及不确定性的特点，利用Takagi—Sugeno模糊模型其规则前件是模糊变量，而规则后件的结论是输入输出线性函数的特点，对柔性机械臂进行了建模。在验证了模型准确性的基础上，进行了广义预测控制方法的研究，最后，对比分析了广义预测控制和传统PID控制，实验结果表明，基于T—S模糊模型的广义预测控制能很好的实现对柔性机械臂的控制。为柔性机械臂的模糊建模和进一步研究提供了理论指导及重要的前提条件。     

Dynamic modeling and control of flexible space structures

This paper presents a global mode modeling of space structures and a control scheme from the practical point of view. Since the size of the satellite has become bigger and the accuracy of attitude control more strictly required, it is necessary to consider the structural flexibility of the spacecraft. Although it is well known that the finite element (FE) model can accurately model the flexibility of the satellite, there are associated problems: FE model has the system matrix with high order and does not provide any physical insights, and is available only after all structural features have been decided. Therefore, it is almost impossible to design attitude and orbit controller using FE model unless the structural features are in place. In order to deal with this problem, the control design scheme with the global mode (GM) model is suggested. This paper describes a flexible structure modeling and three-axis controller design process and demonstrates the adequate performance of the design with respect to the maneuverability by applying it to a large flexible spacecraft model.     

Improved dynamic equations for the generally configured Stewart platform manipulator

In this paper, a Newton-Euler approach is utilized to generate the improved dynamic equations of the generally configured Stewart platform. Using the kinematic model of the universal joint, the rotational degree of freedom of the pods around the axial direction is taken into account in the formulation. The justifiable direction of the reaction moment on each pod is specified and considered in deriving the dynamic equations. Considering the theorem of parallel axes, the inertia tensors for different elements of the manipulator are obtained in this study. From a theoretical point, the improved formulation is more accurate in comparison with previous ones, and the necessity of the improvement is clear evident from significant differences in the simulation results for the improved model and the model without improvement. In addition to more feasibility of the structure and higher accuracy, the model is highly compatible with computer arithmetic and suitable for online applications for loop control problems in hardware.     

空间刚柔耦合并联机构的逆动力学建模与控制

为了提高3-RRRU空间刚柔耦合并联机构的轨迹跟踪精度,提出了一种基于瞬态刚体校正法的逆动力学模型求解方法来构建该机构的非线性控制策略。首先,利用自然坐标法和绝对节点坐标法建立该机构的非线性逆动力学模型,它考虑了各支链柔性空间梁单元的剪切效应,并能描述柔性梁的大范围非线性弹性变形。然后,通过分析刚柔耦合动力学模型在求解过程中出现的相容性问题,结合自然坐标法与理想运动学模型,提出了瞬态刚体校正法并求出逆动力学模型的稳定数值因果解。最后,基于该数值解构建并联机构的非线性控制策略,通过仿真与实验验证了该方法的可行性与有效性。仿真与实验结果表明:逆动力学方程组的求解精度为10-6,约束方程的相容误差为10-8;与刚性并联机构的控制方法相比,该方法在圆形轨迹下的最大跟踪误差降低了0.465mm,圆度误差降低了0.416mm。结果表明:该求解方法解决了闭链机构多体动力学方程的违约问题,有效地改善了系统的综合收敛性能,所构建的控制策略提高了并联机构的轨迹跟踪精度。     

Trajectory tracking of a spatial flexible link manipulator using an inverse dynamics method

Discussed in this paper is the problem of trajectory tracking of a spatial flexible link manipulator. To solve this problem, an inverse dynamics method is proposed, based on which computed joint torques can be determined and used to drive the endpoint of a spatial flexible link manipulator to follow its given trajectory.     

柔性空间展开机构动力学建模研究

介绍了柔性多体系统动力学中的三类建模方法：浮动坐标系描述法、迁移坐标系描述法和惯性坐标系描述法。对各类建模方法从总体上作了比较,结果表明,对具有小变形、低转速特点的空间可展开机构动力学,较适合于采用浮动坐标系描述方法建立模型。然后,分别对浮动坐标系描述方法中所涉厦运动学的描述,动力学方程的建立和模态综合技术等问题进行了讨论。     

机器人操作臂振动的最优控制理论研究

本文就操作臂的末杆在其运动终点的振动控制问题进行了理论研究。首先建立了末杆的力学模型,并用有限元法建立了该模型的动力学方程;然后建立了振动控制问题的框图,并给出了有关的传递函数和脉冲响应函数的表达式;进而建立了振动抑制问题的最优控制的数学模型;最后就该数学模型提出了一种近似解析方法,并给出了一示例。     

Discrete state space modeling and control of nonlinear unknown systems

A novel procedure for integrating neural networks (NNs) with conventional techniques is proposed to design industrial modeling and control systems for nonlinear unknown systems. In the proposed approach, a new recurrent NN with a special architecture is constructed to obtain discrete-time state-space representations of nonlinear dynamical systems. It is referred as the discrete state-space neural network (DSSNN). In the DSSNN, the outputs of the hidden layer neurons of the DSSNN represent the system's (pseudo) state. The inputs are fed to output neurons and the delayed outputs of the hidden layer neurons are fed to their inputs via adjustable weights. The discrete state space model of the actual system is directly obtained by training the DSSNN with the input–output data. A training procedure based on the back-propagation through time (BPTT) algorithm is developed. The Levenberg–Marquardt (LM) method with a trust region approach is used to update the DSSNN weights. Linear state space models enable to use well developed conventional analysis and design techniques. Thus, building a linear model of a system has primary importance in industrial applications. Thus, a suitable linearization procedure is proposed to derive the linear state space model from the nonlinear DSSNN representation. The controllability, observability and stability properties are examined. The state feedback controllers are designed with both the linear quadratic regulator (LQR) and the pole placement techniques. The regulator and servo control problems are both addressed. A full order observer is also designed to estimate the state variables. The performance of the proposed procedure is demonstrated by applying for both single-input single-output (SISO) and multiple-input multiple-output (MIMO) nonlinear control problems.     

一个双连杆平面柔性机械臂系统

介绍了双连杆平面柔性机臂系统的总体结构及工作原理,包括传感器接口,数据采集与处理,伺服电机的驱动,系统的保护和抗干扰等,实际运行表明系统性能良好。     

空间相机镜筒柔性支撑结构设计与动力学分析

为了减小卫星平台的随机振动对空间相机像质的影响,为空间相机的镜筒设计了一套柔性支撑结构,并对柔性结构的动力学特性进行了深入研究.首先,在镜筒及其支座之间放置2mm厚的橡胶环,使镜筒和支撑之间形成柔性连接.然后,应用参数识别的方法对柔性支撑的迟滞阻尼特性进行分析,得到其刚度系数和阻尼系数随频率变化的公式.最后,使用拉格朗日法建立整个系统的动力学方程,得到镜筒质心位置位移和转角随频率变化的曲线.动力学分析结果表明:当振动频率大于663Hz时,位移传递率小于0.6;当频率大于974Hz时,转角变化范围在(0.046±0.050)°之间;满足设计要求.柔性支撑结构对高频振动抑制效果显著,可以为空间相机提供一个稳定的工作环境.     

Simulating the dynamic reaction of manipulator supports

The static and dynamic components of the response of manipulator supports are considered. The dynamic component is investigated as a function of the angular velocity, load, and clamp inclination. Corrections to the tipping torque for the dynamic response are calculated.     

列车预装配柔性实验平台机械手设计研究

针对现有高速列车车厢预装配实验平台制造成本高,重复利用率低,定位精度差的问题,对装配对象结构特征、装配工艺需求等方面进行了研究,提出了一种基于曲面特征点离散化法及多点柔性夹持技术的列车预装配柔性实验平台机械手定位方法;设计了可重复利用、驱-动分离的自动化、低成本高铁车厢预装配柔性实验平台机械手;通过ANSYS有限元分析工具对机械手关键零部件的强度进行了分析,验证了机械手结构的安全可靠性,获得了机械手的优化结构。利用简易车体装配台对机械手定位方法的可行性及预装配柔性实验平台的装配效果进行了验证。研究结果表明,该柔性实验平台能实现真实模拟车厢装配环境、准确定位车厢关键零部件等多项功能,整机制造成本低、装配效率高。     

内置式机械手柔性加工单元的设计

内置式机械手相对桁架式机械手和关节式机械手的柔性加工单元具有结构简单、占地面积小、制造成本低等优点.根据某用户的需求,在的某型车削加工中心基础上,设计了内置式机械手柔性加工单元.设计了专用夹具;将原来的转塔刀架改为排刀结构;配备内置式气动上下料机械手和振动料仓,并具有自动检测功能.自动上下料时间可以控制在10秒钟以内,...     

空间五自由度机械手动力学的研究及仿真

动力学的计算在机械手臂设计阶段和运动控制阶段都有实际意义.本文对空间五自由度机械手进行动力学分析并采用拉格朗日动力学方法建立理想情况下,即没有考虑摩擦影响下的动力学模型并结合相应计算机算法完成该机械手的动力学逆解仿真计算研究.     

集装箱喷漆机械手工作空间分析与仿真

对5自由度集装箱喷漆机械手建立D-H坐标系,通过齐次变换法得到其正运动学方程,利用蒙特卡洛方法对机械手工作空间进行仿真分析.结果表明,集装箱喷漆机械手工作空间分布在一平行于集装箱内表面的平面区域内,能够满足集装箱喷漆工艺的要求.蒙特卡洛法求解速度快,能够简单、直观、形象地描绘出机械手的工作空间.     

基于时滞的柔性机械臂轨迹追踪

由于时滞的存在,系统的控制效果和稳定性会受到影响。针对存在时滞的柔性机械臂振动控制问题进行研究,首先,基于拉格朗日动力学理论建立了具有时滞的柔性机械臂动力学模型,然后,把时间滞后表示成一阶滞后,进行时滞补偿,通过设计自适应算法来校正柔性机械臂的系统参数。同时,基于反步法进行自适应控制器的设计,用Lyapunov的稳定性判定定理证明控制器能够满足设计要求。仿真结果表明,通过对控制器的增益进行调节,能够准确地追踪到预期轨迹,验证了控制方案具有有效性。     

Closed loop control of the planar flexible manipulator via Youla-Kucera parameterization

This work treats the problem of controlling a flexible robotic manipulator. The case study is a planar manipulator with a single flexible arm together with a clamped-free end and a tip lumped mass. To control the angular position of the flexible arm using an actuator, a controller method is developed which is based on Youla-Kucera parameterization. The main challenge in this approach is to obtain a Youla parameter with infinity dimensions. This parameter is approximated by a subspace with finite dimensions which makes the problem tractable. The developed approach exhibit advanced theoretical properties and good numerical convergence. In this paper, two sets of orthogonal bases such as FIR and Laguerre bases are used for system identification. The results of the present case study indicate that the proposed method is very efficient and robust for the time-continuous instances. The characteristics of an optimization problem are finally formulated for larger systems with hundreds of variables and solved with the interior point method.     

Nonlinear modeling and dynamic analysis of flexible structures undergoing overall motions employing mode approximation method

This paper presents a nonlinear modeling method for dynamic analysis of flexible structures undergoing overall motions that employs the mode approximation method. This method, different from the naive nonlinear method that approximates only Cartesian deformation variables, approximates not only deformation variables but also strain variables. Geometric constraint relations between the strain variables and the deformation variables are introduced and incorporated into the formulation. Two numerical examples are solved and the reliability and the accuracy of the proposed formulation are examined through the numerical study.