Calibration of an smt robot assembly cell

A new calibration method for an assembly robot cell is described. The proposed method is a combination of a model-free, numerical, relative robot calibration procedure and a procedure for the robot periphery calibration. Two important simplifications based on the study of an assembly process are introduced into the calibration strategy. A robot is calibrated in a task (Cartesian) space. The robot workspace and the number of calibrated degrees of freedom (dof) in the task space are reduced in accordance with the difficulty measure of the task. An automatic measurement system for measuring the relative robot accuracy was developed. An original principle of transforming the robot endpoint approach distance into the one-dimensional position displacement error is introduced. The accuracy errors of each particular calibrated dof in the task space is measured separately. The error tables are used in a direct robot calibration procedure that is based on the linear interpolation of the discrete position-error functions. An iterative inverse calibration algorithm used in a particular robot cell is described. An efficient sensor-based system for an additional simultaneous robot periphery calibration is presented. The implementation of the proposed calibration methodology in the pick-and-place robot cell for Surface Mount Technology (SMT) is presented. © 1994 John Wiley & Sons, Inc.     

机械臂绝对定位精度标定关键技术综述

目前我国飞机和卫星装配仍主要采用人工装配,装配技术陈旧、机器人绝对定位精度低等问题难以满足飞机和卫星高精度、高性能的要求,阻碍了工业机器人在航空制造行业的发展,因此,在机器人柔性自动化装配过程中,如何提高机械臂绝对定位精度的标定技术已成为学术界和工业界广泛关注的焦点。为了系统地分析和总结现有的研究成果,对绝对定位精度标定方法进行了分类探讨,归纳了国内外机械臂标定技术的研究现状,详细分析了误差不确定性、冗余参数的消除及最优测量结构选择性等关键技术,并对机械臂绝对定位精度标定技术的未来发展趋势进行了构想和展望。     

利用平面单应分解实现服务机器人视觉伺服

智能空间中家庭服务机器人所需完成的主要任务是协助人完成物品的搜寻、定位与传递。而视觉伺服则是完成上述任务的有效手段。搭建了由移动机器人、机械臂、摄像头组成的家庭服务机器人视觉伺服系统,建立了此系统的运动学模型并对安装在机械臂末端执行器上的视觉系统进行了内外参数标定,通过分解世界平面的单应来获取目标物品的位姿参数,利用所获取的位姿参数设计了基于位置的视觉伺服控制律。实验结果表明,使用平面单应分解方法来设计控制律可简单有效地完成家庭物品的视觉伺服任务。     

Automatic work objects calibration via a global–local camera system

In a human–robot collaborative manufacturing application where a work object can be placed in an arbitrary position, there is a need to calibrate the actual position of the work object. This paper presents an approach for automatic work-object calibration in flexible robotic systems. The approach consists of two modules: a global positioning module based on fixed cameras mounted around robotic workspace, and a local positioning module based on the camera mounted on the robot arm. The aim of the global positioning is to detect the work object in the working area and roughly estimate its position, whereas the local positioning is to define an object frame according to the 3D position and orientation of the work object with higher accuracy. For object detection and localization, coded visual markers are utilized. For each object, several markers are used to increase the robustness and accuracy of the localization and calibration procedure. This approach can be used in robotic welding or assembly applications.     

一种多传感器反直升机智能雷伺服跟踪系统

讨论一种基于多传感器的反直升机智能雷AHM(Anti-Helicopter Mine)系统.为了提高智能雷的全自动智能跟踪能力和打击精度,在传统的被动声探测技术的基础上,结合图像传感器的视觉信息和激光测距仪的深度信息,提出一种基于声-光-电多传感器联合的自动目标探测、识别、跟踪算法.首先将五元十字声源定位技术用于低空目...     

Positioning variation synthesis for an automated drilling system in wing assembly

Tight position tolerance is required for fastener holes in wing manufacturing. Automated drilling system with high positioning accuracy is the key to achieve the requirement. The paper seeks to determine allowable values of variation sources and guarantee the hole position tolerance. The process of reference hole positioning and the compensation of drilling positions are firstly explored and formalized for an automated drilling system integrated with an industrial camera. Based on this, a positioning variation model for automated drilling considering positioning error measurement and compensation is built. After that, positioning variation synthesis being imposed engineering constraints on is mathematically modeled based on the theory of mathematical statistics. In the positioning variation synthesis, imperfect camera installation, nonideal measurement conditions, equipment positioning error, etc. are included. The positioning variation model and involving synthesis strategy have been used to develop an automated drilling system for wing assembly. Experiments conducted on the developed drilling system show that the fastener holes’ desired position tolerance 0.3 mm will not be exceeded, which is a necessary condition of the satisfactory drilling quality of the aircraft wing.     

基于WMPS的飞机大部件对接测控技术

现有的飞机大部件对接系统主要利用激光跟踪仪对部件位姿进行测量定位,可以达到较高精度.但由于激光跟踪仪每次只能测量一个靶球,故在效率上满足不了对接需求.工作空间测量定位系统(WMPS,Workspace Measuring and Positioning System)作为一种新型的、采用光平面交会原理的大尺寸三维坐标测量系统,具有测量精度高、测量效率高、测量范围大等特点,在大尺寸数字化测量及装配等领域具有重要应用价值.提出了一种基于wMPS系统进行飞机大部件对接的测控技术,能够同时满足对接过程中测量精度和测量效率的要求.     

Guidance of an ultrasound probe by visual servoing

A new visual servoing technique based on two-dimensional (2-D) ultrasound (US) image is proposed in order to control the motion of an US probe held by a medical robot. In opposition to a standard camera which provides a projection of the three-dimensional (3-D) scene to a 2-D image, US information is strictly in the observation plane of the probe and consequently visual servoing techniques have to be adapted. In this paper the coupling between the US probe and a motionless crossed string phantom used for probe calibration is modeled. Then a robotic task is developed which consists of positioning the US image on the intersection point of the crossed string phantom while moving the probe to different orientations. The goal of this task is to optimize the procedure of spatial parameter calibration of 3-D US systems.     

Development of a monocular vision system for robotic drilling

Robotic drilling for aerospace structures demands a high positioning accuracy of the robot, which is usually achieved through error measurement and compensation. In this paper, we report the development of a practical monocular vision system for measurement of the relative error between the drill tool center point （TCP） and the reference hole. First, the principle of relative error measurement with the vision system is explained, followed by a detailed discussion on the hardware components, software components, and system integration. The elliptical contour extraction algorithm is presented for accurate and robust reference hole detection. System calibration is of key importance to the measurement accuracy of a vision system. A new method is proposed for the simultaneous calibration of camera internal parameters and hand-eye relationship with a dedicated calibration board. Extensive measurement experiments have been performed on a robotic drilling system. Experimental results show that the measurement accuracy of the developed vision system is higher than 0.15 mm, which meets the requirement of robotic drilling for aircraft structures.     

Uncalibrated Eye-to-Hand Visual Servoing Using Inverse Fuzzy Models

A new uncalibrated eye-to-hand visual servoing based on inverse fuzzy modeling is proposed in this paper. In classical visual servoing, the Jacobian plays a decisive role in the convergence of the controller, as its analytical model depends on the selected image features. This Jacobian must also be inverted online. Fuzzy modeling is applied to obtain an inverse model of the mapping between image feature variations and joint velocities. This approach is independent from the robot's kinematic model or camera calibration and also avoids the necessity of inverting the Jacobian online. An inverse model is identified for the robot workspace, using measurement data of a robotic manipulator. This inverse model is directly used as a controller. The inverse fuzzy control scheme is applied to a robotic manipulator performing visual servoing for random positioning in the robot workspace. The obtained experimental results show the effectiveness of the proposed control scheme. The fuzzy controller can position the robotic manipulator at any point in the workspace with better accuracy than the classic visual servoing approach.     

Measurement error analysis and accuracy enhancement of 2D vision system for robotic drilling

Robotic drilling for aircraft structures demands higher accuracy on industrial robots than their traditional applications. Positioning error measurement and compensation based on 2D vision system is a cost-effective way to improve the positioning accuracy in robotic drilling. In this paper, we first discuss the principle of error measurement and compensation with a 2D vision system for robotic drilling and the determination of tool center point of the vision system so that the Abbe errors are eliminated in the measurement process. Measurement errors due to nonideal measurement conditions, i.e. nonperpendicularity of the camera optical axis to the workpiece surface and incorrect object distance, are mathematically modeled and experimentally verified. A method utilizing four laser displacement sensors is proposed to ensure perpendicularity of the camera optical axis to the workpiece surface and correct object distance in the measurement process, and hence to achieve high accuracy in 2D vision-based measurement. Experiments performed on a robotic drilling system show that the 2D vision system can achieve an accuracy of approximately 0.1 mm with the proposed method.     

Binocular visual servoing based on linear time-invariant mapping

We propose a simple visual servoing scheme based on the use of binocular visual space. When we use a hand-eye system which has a similar kinematic structure to a human being, we can approximate the transformation from a binocular visual space to a joint space of the manipulator as a linear time-invariant mapping. This relationship makes it possible to generate joint velocities from image observations using a constant linear mapping. This scheme is robust to calibration error, especially to camera turning, because it uses neither camera angles nor joint angles. Some experimental results are also shown to demonstrate the positioning precision remained unchanged despite the calibration error,     

Automatic robotic tasks in unstructured environments using an image path tracker

This paper describes a new method to perform automatic tasks with a robot in an unstructured environment. A task to replace a blown light bulb in a streetlamp is described to show that this method works properly. In order to perform this task correctly, the robot is positioned by tracking secure previously defined paths. The robot, using an eye-in-hand configuration on a visual servoing scheme and a force sensor, is able to interact with its environment due to the fact that the path tracking is performed with time-independent behaviour. The desired path is expressed in the image space. However, the proposed method obtains a correct tracking not only in the image, but also in the 3D space. This method solves the problems of the previously proposed time-independent tracking systems based on visual servoing, such as the specification of the desired tracking velocity, less oscillating behaviour and a correct tracking in the 3D space when high velocities are used. The experiments shown in this paper demonstrate the necessity of time-independent behaviour in tracking and the correct performance of the system.     

Visual servoing based on efficient histogram information

The robustness of a visual servoing task depends mainly on the efficiency of visual selections captured from a sensor at each robot’s position. A task function could be described as a regulation of the values sent via the control law to the camera velocities. In this paper we propose a new approach that does not depend on matching and tracking results. Thus, we replaced the classical minimization cost by a new function based on probability distributions and Bhattacharyya distance. To guarantee more robustness, the information related to the observed images was expressed using a combination of orientation selections. The new visual selections are computed by referring to the disposition of Histograms of Oriented Gradients (HOG) bins. For each bin we assign a random variable representing gradient vectors in a particular direction. The new entries will not be used to establish equations of visual motion but they will be directly inserted into the control loop. A new formulation of the interaction matrix has been presented according to the optical flow constraint and using an interpolation function which leads to a more efficient control behaviour and to more positioning accuracy. Experiments demonstrate the robustness of the proposed approach with respect to varying work space conditions.

     

工业机器人定位误差规律分析及基于ELM算法的精度补偿研究

针对工业机器人应用于飞机零部件自动化钻孔时绝对定位精度较差的问题,提出利用极限学习机（ELM）算法建立机器人法兰中心点理论位置与实际位置之间的误差模型,并优化补偿机器人定位精度的方法．首先基于空间网格采样方法,获得了机器人绝对定位误差沿机器人基坐标系不同方向的误差变化规律,分析了建模补偿的可行性;其次建立基于ELM算法的误差补偿模型,并针对误差模型训练中隐含层神经元个数取值问题进行了分析优化．实验结果表明,机器人绝对定位误差值沿其坐标系不同方向存在不同的变化规律,补偿前绝对定位误差分布范围为0.29 mm~0.58 mm,平均误差为0.41 mm;补偿后定位误差分布范围降低到0.04 mm~0.32 mm,平均误差为0.18 mm;采用ELM算法建模的补偿速度快,泛化性能好．     

A machining accuracy informed adaptive positioning method for finish machining of assembly interfaces of large-scale aircraft components

An assembly interface of a large-scale aircraft component is a joint surface to connect adjacent large components. To guarantee the final assembly accuracy of the large components, the assembly interface is finish machined on site before the final assembly to cut the observed machining allowance. Thus, aiming at realizing the high efficiency and high quality in the finish machining operation, in this paper we propose an adaptive positioning method that integrates comprehensive engineering constrains (including Positioning Accuracy Constraints (PACs) of the large component and Machining Accuracy Constraints (MACs) of the assembly interface). In this method, the key Measurement Points (MPs) of a component are assigned to obtain its initial pose. Then the measurement data and the initial pose are used as input data to obtain the optimal pose parameters of the component based on an improved Particle Swarm Optimization Simulated Annealing (PSO-SA) algorithm. The optimal pose parameters can provide data support for the adaptive positioning of the large component, the function of which is implemented based on IEC 61499 Function Block (FB) technology. Finally, a positioning experiment of a vertical tail of a large passenger aircraft is used to validate the proposed method. The experimental results illustrate that the proposed method can improve the efficiency and positioning accuracy of the large component, compared to the traditional method.     

Developing robust vision modules for microsystems applications

In this work, several robust vision modules are developed and implemented for fully automated micromanipulation. These are autofocusing, object and end-effector detection, real-time tracking and optical system calibration modules. An image based visual servoing architecture and a path planning algorithm are also proposed based on the developed vision modules. Experimental results are provided to assess the performance of the proposed visual servoing approach in positioning and trajectory tracking tasks. Proposed path planning algorithm in conjunction with visual servoing imply successful micromanipulation tasks.     

Kinematic calibration of modular reconfigurable robots using product-of-exponentials formula

A modular reconfigurable robot system is a collection of individual link and joint components that can be assembled into different robot geometries for specific task requirements. However, the machining tolerance and assembly errors at the module interconnections affect the positioning accuracy of the end-effector. This article describes a novel kinematic calibration algorithm for modular robots based on recursive forward dyad kinematics. The forward kinematic model derived from the Product-of-Exponentials formula is configuration independent. The error correction parameters are assumed to be in the relative initial positions of the dyads. Two calibration models, namely the six- and seven-parameter methods, are derived on the grounds of the linear superposition principle and differential transformation. An iterative least square algorithm is employed for the calibration solution. Two simulation examples of calibrating a three-module manipulator and a 4-DOF SCARA type manipulator are demonstrated. The result has shown that the average positioning accuracy of the end-effector increases two orders of magnitude after the calibration. © 1997 John Wiley & Sons, Inc.     

基于机器视觉的航空散热器智能定位钻孔技术

因某型航空散热器再制造的需要,需对产品大量的散热管进行重复的钻孔工作,为解决人工钻孔不便开发的问题开发出一种利用带机器视觉装置的工业机器人对散热器进行定位钻孔的技术。根据产品的特点选用了相应功能的工业机器人与机器视觉装置硬件,给出了智能定位钻孔系统的设计技术方案,建立了系统控制以及软件结构框架。通过最小二乘法对机器视觉采集的图像进行处理,给定了系统坐标标定的过程和方法,明确了机器人定位精度及视觉精度的计量方法。试验结果表明,该系统提高了钻孔效率和精度,可应用于实际生产。     

基于图像矩与神经网络的机器人四自由度视觉伺服

针对传统的视觉伺服方法中图像几何特征的标记、提取与匹配过程复杂且通用性差等问题,本文提出了一种基于图像矩的机器人四自由度(4DOF)视觉伺服方法.首先建立了眼在手系统中图像矩与机器人位姿之间的非线性增量变换关系,为利用图像矩进行机器人视觉伺服控制提供了理论基础,然后在未对摄像机与手眼关系进行标定的情况下,利用反向传播(BP)神经网络的非线性映射特性设计了基于图像矩的机器人视觉伺服控制方案,最后用训练好的神经刚络进行了视觉伺服跟踪控制.实验结果表明基于本文算法可实现0.5 mm的位置与0.5°的姿态跟踪精度,验证了算法的的有效性与较好的伺服性能.