Singular Perturbation Model of Robots with Elastic Joints and Elastic Links Constrained by Rigid Environment

A robot with distributed flexibility in the links and lumped flexibility in the joints is considered in this paper. First the model of the system in free motion is formulated as a set of ordinary differential equations, adopting a finite number of modes of the link deformation. Then algebraic constraint equations on the generalized coordinates of the system are added, to account for the loss of degrees of freedom due to the contact with rigid environment. A reduced order model, expressed in the residual degrees of freedom is then derived, based on a coordinate partitioning procedure. The singularly perturbed model of the system is finally computed, and the expression of the fast subsystem is given. The special cases of a robot with rigid joints or rigid links are also addressed.     

An Overview of Calibration Technology of Industrial Robots

With the continuous improvement of automation,industrial robots have become an indispensable part of automated production lines.They widely used in a number of industrial production activities,such as spraying,welding,handling,etc.,and have a great role in these sectors.Recently,the robotic technology is developing towards high precision,high intelligence.Robot calibration technology has a great significance to improve the accuracy of robot.However,it has much work to be done in the identification of robot parameters.The parameter identification work of existing serial and parallel robots is introduced.On the one hand,it summarizes the methods for parameter calibration and discusses their advantages and disadvantages.On the other hand,the application of parameter identification is introduced.This overview has a great reference value for robot manufacturers to choose proper identification method,points further research areas for researchers.Finally,this paper analyzes the existing problems in robot calibration,which may be worth researching in the future.     

基于神经网络与粒子滤波的柔性臂控制方法研究

基于奇异摄动法将单连杆柔性臂系统分解为慢变、快变子系统,采用混合控制方法;设计了基于粒子滤波的神经网络控制器来线性化慢子系统,使其跟踪期望轨迹;采用粒子滤波训练神经网络克服了BP算法收敛速度慢、易陷入局部极小值的缺陷,及扩展卡尔曼滤波方法带来的模型线性化损失;对于快变系统采用最优控制方法;仿真结果表明:在神经网络训练误差收敛速度及精度方面,粒子滤波要比BP及卡尔曼滤波要好;组合控制方法能有效地抑制柔性臂弹性振动,轨迹跟踪迅速准确,精度方面也是前者最优。     

Contact Conditions for Cylindrical,Prismatic, and Screw Joints in Flexible Multibody Systems

This paper focuses on the modeling of the contact conditionsassociated with cylindrical, prismatic, and screw joints in flexiblemultibody systems. In the classical formulation these joints aredeveloped for rigid bodies, and kinematic constraints are enforcedbetween the kinematic variables of the two bodies. These constraintsexpress the conditions for relative translation and rotation of the twobodies along and about a body-fixed axis, and imply the relative slidingand rotation of the two bodies which remain in constant contact witheach other. However, these kinematic constraints no longer implyrelative sliding with contact when one of the bodies is flexible. Toremedy this situation, a sliding joint and a sliding screwjoint are proposed that involves kinematic constraints at theinstantaneous point of contact between the sliding bodies. For slidingscrew joints, additional constraints are added on the relative rotationof the contacting bodies. Various numerical examples are presented thatdemonstrate the dramatically different behavior of cylindrical,prismatic, or screw joints and of the proposed sliding and sliding screwjoints in the presence of elastic bodies, and the usefulness of theseconstraint elements in the modeling of complex mechanical systems.     

考虑关节柔性的模块机器人动力学参数辨识

提出了一种基于3维运动测量系统Optotrak3020的柔性关节模块机器人动力学模型参数辨识方法.首先将机器人的动力学模型参数化为不包括刚度力矩的线性形式,避免了参数矩阵的标定问题.激励轨迹基于有限的傅里叶级数函数,采用自适应遗传算法得出了优化的傅里叶级数系数.机器人每一关节单独跟随优化激励轨迹进行运动,同时电机位置、...     

A Geometric Calibration Methodology for Single-Head Cone-Beam X-Ray Systems

During X-ray based quality inspection, accurate reconstruction of a 3D object model from a set of its 2D X-ray projections requires efficient geometric calibration, i.e., accurate estimation of the geometric parameters of the setup. We present a calibration methodology for the estimation of the geometric parameters of single-head cone-beam X-ray radiography systems. Our method is related to known approaches regarding camera calibration and geometric calibration of tomography/radiography systems, but performs better in terms of computational efficiency.     

机械臂D-H参数和减速比几何标定及误差补偿

针对机械臂D-H参数和关节电机减速比不精确导致机械臂绝对定位精度降低的问题,提出了在利用几何分析标定机械臂D-H参数的基础上,通过分析关节实际旋转角度和相应电机编码器码值的线性关系,标定关节电机减速比的方法;针对关节角误差微分补偿法计算量大的缺点,通过推导机械臂末端位姿矩阵误差和关节角误差之间的微分关系建立误差模型,求解关节补偿角,避免了雅各比矩阵的求取,提高了计算效率;最后采用三维激光跟踪仪搭建测量系统,完成了一种6自由度机械臂的标定及补偿实验;实验结果表明,通过参数标定及误差补偿,机械臂的绝对定位误差均值从标定前的2.83 mm和1.14°降低到0.54 mm和0.24°,验证了方法的有效性。     

激光线扫式形貌测量机器人的标定研究

为能够高效、高精度的获取大型自由曲面物体的形貌,研究了基于通用工业机器人和激光线扫描传感器的测量方法.论述了激光线扫式形貌测量系统的原理与结构,利用标准球及优化算法实现了机器人和激光扫描传感器位姿关系的精确解算,并针对机器人运动学误差对系统测量影响较大,通过对机器人运动学参数的修正有效减小了机器人的绝对定位误差.实验和分析结果表明,经标定和运动学参数校正后的测量系统对标准球的测量能达到较高精度,为采集高精度三维点云提供了保证.     

机器人柔性视觉检测系统现场标定技术

针对江淮车身厂的轿车车身提出了一种基于工业机器人的柔性视觉检测系统．通过控制机器人在空间的位姿变换,立体视觉传感器能够依次到达空间指定测量位置采集空间特征点的图像信息,并通过计算图像数据获得该点的三维坐标数据．利用双经纬仪和精密靶标对机器人视觉测量系统进行整体标定,同时完成了测试试验数据的采集及计算,取得了较好的测量效果．该系统柔性好、测量无死角,能适应生产线多车型检测的需要．     

On the Robust Nonlinear Motion Position and Force Control of Flexible Joints Robot Manipulators

The design of a robust nonlinear position and force controller for a flexible joints robot manipulator interacting with a rigid environment is presented. The controller is designed using the concept of feedback linearization, sliding mode techniques, and LQE estimation methodologies. It is shown that the nonlinear robot manipulator model is feedback linearizable. A robust performance of the proposed control approach is achieved by accounting for the system parameters uncertainties in the derivation of the nonlinear control law. An upper bound of the error introduced by parametric uncertainties in the system is computed. Then, the feedback linearizing control law is modified by adding a switching action to compensate the errors and to guarantee the achievement of the desired tracking performance. The relationship between the minimum achievable boundary layer thickness and the parametric uncertainties is derived. The proposed controller is tested using an experimental flexible joints robot manipulator, and the results demonstrate its potential benefits in reducing the number of sensors required and the complexity of the design. This is achieved by eliminating the need for nonlinear observers. A robust performance is obtained with minimum control effort by taking into account the effect of system parameter uncertainties and measurement noise.     

轴不对准角在挠性陀螺组合静态误差标定中的应用

陀螺组合的安装误差会引起陀螺漂移,从而对惯导系统产生影响。从挠性陀螺组合安装误差模型入手,推导出存在轴不对准角情况下的挠性陀螺组合静态误差标定模型,并给出静态误差标定的位置试验方案。提出的标定方案可以有效标定陀螺组合静态误差系数,从而减少陀螺漂移。     

一种基于点对的相机几何标定方法

提出了一种基于点对的几何标定方法,用于标定相机外部参数．该方法考虑点对而不是单个点与相机的几何关系．首先根据三个标定点对计算旋转矩阵且不需要任何点对的精确三维信息．然后根据相机和一个点对的几何关系计算平移且只需这个点对的相对位置是已知的．整个标定过程不需要任何点对的绝对位置信息．试验结果表明了该方法的有效性．     

一种新型机器人自标定装置及其算法

针对传统基于几何约束的机器人自标定装置仅能对局部工作空间内的机器人位型进行标定测量的问题,提出了一种由安装于机器人末端的球心位置测量装置和可移动球杆组成的新型便携式机器人自标定装置,通过利用球面约束和距离约束,可在较大工作空间内对机器人进行标定测量,从而提高标定结果的可靠性.根据可移动球杆的单、双球布置方式,分别建立了基于向量差和距离差的2种机器人自标定模型及其算法.通过采用局部指数积公式并引入位置伴随变换矩阵,简化了2种自标定模型,从而降低了对运动学方程线性化的计算量.最后,对一种6自由度串联机器人进行了仿真实验,实验结果表明2种自标定算法均能够快速收敛,验证了2种算法的有效性和鲁棒性.     

Observer-Based Optimal Control of Flexible Stewart Parallel Robots

The design and simulation of two optimal control schemes for a parallel flexible link manipulator of the Stewart type is presented. The first control scheme combines a nonlinear rigid model of the flexible manipulator with a linear rigid observer, whereas the second scheme uses a nonlinear flexible manipulator model with a linear flexible observer. The majority of the results available in the literature do not address the optimal control problem through the use of observers, as it is done in this paper, for the control of parallel robots. The simulation results have shown in both cases that indeed optimal state-obscrver-based control is a good candidate for controlling parallel-link manipulators in practice. As expected, the second scheme (flexible model plus flexible observer) gives better results than the first one, achieving faster trajectory tracking. The effects of white noises, applied forces, and zero gravity environment were taken under consideration.     

典型安装方式的协作机器人基坐标系标定方法

针对地面式、侧墙式、顶棚式三种典型安装方式下的协作机器人的基坐标系标定问题,采用了一种新的操作步骤简单、标定结果精确的机器人基坐标系标定方法。该方法通过在协作机器人的公共空间中构造四点"握手"动作并分别记录接触点在每个机器人的基坐标系下的坐标,求解协作机器人基坐标系间的旋转矩阵和平移矩阵,从而得到协作机器人基坐标系间的位姿关系。针对工业机器人常见的地面式、侧墙式、顶棚式三种典型安装方式进一步分析了机器人基坐标系间的约束关系,并利用这些约束关系对标定结果做出进一步的优化处理。为验证提出的标定方法的有效性,基于Matlab的机器人工具箱完成了仿真实验,仿真实验的标定误差控制在2mm以内,该精度可满足一般弧焊、搬运、切割等生产过程的定位精度要求。仿真实验的结果验证了提出的标定方法的正确性,表明该方法可有效的解决生产环境下的协作机器人的基坐标系标定问题。     

基于改进型RLM算法的六轴机械臂运动学标定实验

六自由度机械臂为高维性、强耦合的非线性时变系统,其模型较复杂,参数辨识易受外界扰动影响,导致末端绝对定位精度低,精度一致性差等问题。以某型六轴机械臂为研究对象,根据微分运动学原理并忽略高阶项,获得末端线性误差模型,提出了收敛速度快且鲁棒性较强的改进型RLM算法进行几何参数的误差辨识,在此基础上搭建综合标定实验平台,利用静态测量精度较高的API T3三维激光跟踪仪采集工作空间中灵敏度较高的样本位姿点,根据国际标准ISO 9283中的位置精度评价标准,比较标定前后的位置误差分布区间,并对分析结果给出评价和总结,完成六自由度工业机械臂本体标定实验。     

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．     

柔性针的运动学建模及实验研究

针对在微创手术中传统采用的钢针的不足,如与组织作用,双方均产生较大变形,造成很大误差,严重影响治疗效果。另外在手术中常常遇到一些重要的组织和器官要避开,传统的钢针无法满足需要。本文采用带斜尖的柔性针,完全利用进针时斜尖与组织的侧向作用力使针轴产生弯转。这样不但可以更精确控制针的轨迹,而且还能绕过障碍物准确达到靶点。本文首先简化了WebsterIII等人提出的柔性针非完整约束系统的自行车模型,提出了自行车前、后轮模型。在此基础上,又提出了更符合实际的带返程度的自行车模型,并进行了运动学建模研究。以实验数据拟合了模型中各参数,同时验证了此模型的合理性和准确性。     

Active Vibration Control of Flexible Robots Using Virtual Spring-damper Systems

When using robots for heavy loads and huge operating ranges, elastic deformations of the links have to be taken into account during modeling and controller design. Whereas for conventional rigid multilink industrial robots modeling can schematically be done by standard techniques, it is a massive problem to obtain an accurate analytic model for multilink flexible robots. But an accurate analytic model is essential for most modern controller design techniques, and modeling errors can lead to instability of the controlled system due to spillover since the eigenvalues of the system are only slightly damped. A new approach to active damping control for flexible robots is presented in this paper where the actuators act like virtual spring-damper-systems. As the spring-damper-element is a passive energy dissipative device, it will never destabilize the system and thus the control concept will be very insensitive to modeling errors. Basically, the two parameters, spring stiffness and damping constant of this system, are arbitrary and model independent. To satisfy performance requirements they are adjusted using knowledge of the system model. The more it is known about the system model, the better these parameters may be adjusted. The new input of the controlled system is a virtual variation of the spring base. The paper illustrates this technique with the help of a simple and easy to model one link flexible robot which is also available as a real laboratory testbed.     

应用于机器人标定的主动式靶标装置设计与精度优化

激光跟踪仪是工业机器人标定技术中常用测量设备,但其测量范围受限于被动式靶标的激光光线接收角度,进而影响了机器人的标定精度。为解决该问题,设计了一种具有三自由度的主动式靶标装置,并提出了一种精度优化方法,有效地补偿因装置的装配而引入的测量误差。该方法利用圆点分析法初步辨识主动式靶标装置的DH参数,基于距离平方误差模型法对该装置进行DH参数的精辨识,并基于坐标系转换将主动式靶标装置的位置误差补偿到激光跟踪仪输出的位置向量,从而实现误差的补偿。通过实验验证了该主动式靶标装置能够有效地扩大工业机器人关节的被测范围。所提出的精度优化方法能够将该装置的测量误差降低9331%,实际定位精度为00507 mm,能够满足机器人标定的精度要求。