Enhance performance of inspection process on Coordinate Measuring Machine

Coordinate Measuring Machine (CMM) has been an important inspection tool in quality control for several years owing to its high accuracy and precision. Effectiveness of inspection plan generated by CMM greatly depends on measurement cycle time. Lesser the inspection time taken by CMM to measure a given part better will be the performance of inspection process. Therefore, it has been critical to reduce measurement time for efficient performance of inspection process. In this paper, methodologies to generate most suitable measurement path resulting into minimum inspection time has been introduced. These methodologies are based on different algorithms to reduce measurement cycle time for CMM. The different algorithms have successfully been explored and compared to show their effectiveness in minimizing inspection time for stationary CMM equipped with touch trigger probe. The proposed methodologies have also been implemented and tested on real-world mechanical part with certain number of features to demonstrate their applicability.     

Integrated laser/CMM system for the dimensional inspection of objects made of soft material

The applications of the coordinate measuring machines (CMMs) with a contact trigger probe to the dimensional inspection of manufactured products are restricted to the parts made of hard material, such as steel. By combining the laser and CMM, the applications of the CMMs can be extended to the inspection of objects made of soft materials, such as foils, plastics, wood, wax and clay materials. In this research, replacing the contact probe with an inexpensive laser sensor is attempted so as to eliminate the possible deflection of the component being measured when using contact probe. By combining a laser sensor with the existing automated inspection environment, a CAD-directed, three-dimensional coordinate sampling system which can perform non-contact dimensional inspection is developed.     

基于检测状态模型的飞机结构件在线检测路径规划

针对飞机结构件在线检测路径规划中零件工艺模型伴随加工过程动态变化、检测工艺复杂的难点,提出了基于检测状态模型的飞机结构件在线检测路径规划方法。检测状态模型以特征为载体,以干涉特征和虚路径表达干涉规避、路径优化等知识和经验,并随着加工过程动态扩充。基于检测状态模型,按照检测操作级、检测特征级、特征自身级三级实现了在线检测路径规划。根据以上研究,基于CATIA V5开发的在线检测数据自动生成系统已在某大型航空企业中得到成功应用。     

Evaluation of a multi-sensor horizontal dual arm Coordinate Measuring Machine for automotive dimensional inspection

Multi-sensor coordinate measuring machines (CMM) have a potential performance advantage over existing CMM systems by offering the accuracy of a touch trigger probe with the speed of a laser scanner. Before these systems can be used, it is important that both random and systematic errors are evaluated within the context of its intended application. At present, the performance of a multi-sensor CMM, particularly of the laser scanner, has not been evaluated within an automotive environment. This study used a full-scale CNC machined physical representation of a sheet metal vehicle body to evaluate the measurement agreement and repeatability of critical surface points using a multi-sensor horizontal dual arm CMM. It was found that there were errors between CMM arms and with regard to part coordinate frame construction when using the different probing systems. However, the most significant effect upon measurement error was the spatial location of the surface feature. Therefore, for each feature on an automotive assembly, measurement agreement and repeatability has to be individually determined to access its acceptability for measurement with a laser scanner to improve CMM utilisation, or whether the accuracy of a touch trigger probe is required.     

On-machine measurement using a noncontact sensor based on a CAD model

Once a machining process is finished, an inspection process is carried out to check whether the part is within dimensional tolerances. A coordinate measuring machine (CMM) is a general metrological device for assessment of dimensions on the shop floor. It cannot be ignored, however, that CMM measurements require significant resources in operating time and cost, which has led to many studies into on-machine measurement (OMM) systems. This study aims to develop an OMM system with a noncontacting laser displacement sensing apparatus and a computer-aided design (CAD) model for ease of operation, improved operating speed, and free form profiling. The system is composed of two software modules, one for sensor alignment with the machine tool and the other for measurement based on CAD/CAM (computer-aided machining). Consequently, the system was verified on the shop floor at a numerical control (NC) machining center.     

Analysis of the geometrical features detectability constraints for laser-scanner sensor planning

This paper presents a planning approach for automatic synthesis of the viewpoint locations of a laser scanner that satisfy the detectability constraints of the geometrical features of a given object. Dominant constraints taken into consideration were the laser scanner field of view, depth of view, and the maximum permissible view angle. The approach is task driven and sensor model based. Information is given about the scanned object and its selected features, as well as about the optical characteristics of the sensor. Planning is presented as an optimisation problem where the optimal laser-scanner viewpoint must satisfy all the constraints simultaneously. The approach is demonstrated by scanning a 2D feature, and through planning an experiment in which robotic assembly of a car door is assisted by a laser scanner.     

Novel adaptive laser scanning sensor for reverse engineering measurement

In this paper, a series of new techniques are used to optimize typical laser scanning sensor. The integrated prototype is compared with traditional approach to demonstrate the much improved performance. In the research and development, camera calibration is achieved by extracting characteristic points of the laser plane, so that the calibration efficiency is improved significantly. With feedback control of its intensity, the laser is automatically adjusted for different material. A modified algorithm is presented to improve the accuracy of laser stripe extraction. The fusion of data extracted from left and right camera is completed with re-sampling technique. The scanner is integrated with a robot arm and some other machinery for on-line measurement and inspection, which provides a flexible measurement tool for reverse engineering.     

新型轨道自动检测系统研究

近年来,起重机轨道的检测系统测量准确性不高并且效率较低.为了提高现有起重机轨道检测的测量准确性,提高检测效率,提出了一种新型轨道检测系统.在系统中综合使用基站搭载的激光扫描仪,实时追踪小车位置,根据扫描仪采集的数据重构出轨道顶面中心线的空间形状,检测轨道变形程度.系统测量精度可以满足现有标准要求,同时相对于传统检测设备...     

储罐底板自动漏磁检测小车的路径规划与运动控制

针对储罐底板现有检测装备自动化程度不高、检测劳动强度大、检测效率低等问题,设计了储罐底板自动化漏磁检测系统。介绍了系统的结构组成,分析了基于双目激光测距的小车自动定位原理。根据储罐底板的结构特征和漏磁检测的特点,规划了检测小车的运动路径,研究了小车运动速度增量式PID控制算法和小车运动方向差动式控制算法,并进行了实验研究。结果表明,小车能够根据设定的PID控制参数沿规划路径扫查,小车在直线寻迹时30°方向偏差纠偏时间约为1.7s,轨迹跟踪性能良好。     

Tool probe for measuring dimensional wear and X-coordinate of turning edge

This paper presents an original method of direct measurement of turning tool wear at the tip of the cutting edge, made automatically on an NC lathe by a probe, which also allows for determining the X-coordinate of the cutting edge. In the initial solution, this measurement, patented by one of the authors, was carried out using a special probe with two-touch trigger sensors or a one-touch trigger sensor and a displacement sensor. The improved probe has only one displacement sensor. Not only does the new solution simplify the probe, but it also makes tool wear measurement more accurate.     

Magnetic resonance imaging-compatible tactile sensing device based on a piezoelectric array

Minimally invasive surgery is a widely used medical technique, one of the drawbacks of which is the loss of direct sense of touch during the operation. Palpation is the use of fingertips to explore and make fast assessments of tissue morphology. Although technologies are developed to equip minimally invasive surgery tools with haptic feedback capabilities, the majority focus on tissue stiffness profiling and tool-tissue interaction force measurement. For greatly increased diagnostic capability, a magnetic resonance imaging-compatible tactile sensor design is proposed, which allows minimally invasive surgery to be performed under image guidance, combining the strong capability of magnetic resonance imaging soft tissue and intuitive palpation. The sensing unit is based on a piezoelectric sensor methodology, which conforms to the stringent mechanical and electrical design requirements imposed by the magnetic resonance environment The sensor mechanical design and the device integration to a 0.2 Tesla open magnetic resonance imaging scanner are described, together with the device's magnetic resonance compatibility testing. Its design limitations and potential future improvements are also discussed. A tactile sensing unit based on a piezoelectric sensor principle is proposed, which is designed for magnetic resonance imaging guided interventions.     

曲面工件自动超声检测轨迹规划

航空发动机叶片是典型复杂曲面结构,为实现叶片的自动化超声检测,提出基于曲面点云数据重建的自动化检测轨迹规划方法,在此基础上实现7轴联动复杂曲面自动扫描成像。叶片点云采用线激光轮廓仪配合工件旋转轴自动扫描获取,数据拼接整理后采用数据拟合方法获得曲面轮廓方程,基于曲面上的曲线方程规划加减速扫描轨迹,进一步对各扫描轨迹点进行多轴运动分解,获得包括六轴机械手和工件旋转轴在内的各轴轨迹。实际检测试验表明,轨迹规划算法可以实现叶片自动扫描,获得清晰C扫描图像。     

新型自由曲面三维激光扫描系统

从机械结构、控制系统及操作系统结构等几个角度介绍一种三维激光扫描系统设计方案。系统集成了先进的数据处理技术、激光扫描技术、先进控制技术及机器人技术,有效地借助于光机电一体化技术实现了表面检测及三维表面模型重构智能化及自动化。系统由具有电驱动装置的激光测头、C形滑臂、升降旋转台、电控系统及主控计算机组成。通过所设置测量参数,系统能够对不同的被测物体进行扫描路径规划,进而通过激光测头、C形滑臂及转台的全自动协调控制完成无盲点三维表面测量任务。试验结果表明,该三维激光扫描系统的扫描精度达到0.1 mm,速度为10 000点/s,能够应用于小型工件及模型、模具表面数据检测及模型重构。     

Error Compensation for Three-Dimensional Line Laser Scanning Data

In this paper, the problem of compensation of 3D line laser scanning data for improved inspection accuracy is addressed. This problem is important, as a 3D line laser scanner is about one order less accurate than a touch probe. The approach taken is to compensate through error characterisation. In other words, a software compensation is performed, instead of a hardware compensation, which is probably more expensive. To do so, the errors associated with a 3D line laser scanning system are first characterised. With error characterisation, an empirical formula is obtained relating the errors to the influencing factors including the projected angle and the scan depth. This empirical formula is used to compensate for the digitised surface data obtained by the corresponding laser scanning system. The results show that the proposed approach effectively improves inspection accuracy.     

Automated Surface Roughness Measurement

A non-contact roughness sensor is described that is suited for integration with a computer-controlled coordinate measuring machine (CMM). The sensor employs a fibre optic interferometer, electronic control system and data-processing software. The combination of the sensor and computer controlled CMM allows surface texture assessment to be made during scheduled dimensional inspections of complex curved surface components, such as turbine blades. The sensor system will measure surface roughness parameters, for example Ra, using a method that reflects standard procedures. The lightweight sensor head can be mounted on a touch probe arm and the associated articulated mounting head; this combination gives quasi 5-axis positioning ability to the overall sensor. This is suitable for automated surface finish inspection of compound curved surface blades. The sensor and its control unit are integrated with the CMM controller and its operation can be controlled through standard part-program commands used by the CMM.     

An integrated reverse engineering approach to reconstructing free-form surfaces

An integrated reverse engineering approach to generating free-form surfaces has been developed to create CAD-compatible free-form surface models with a coordinate measurement machine and a touch trigger probe. The approach integrates data digitization and surface modelling to obtain an efficient and accurate digitization process with a collisionfree exploration path, and to reconstruct least-squares bi-cubic B-spline surface models for rapid product prototyping. The whole approach is divided into two stages: the planning of boundary digitization; and the adaptive model-based digitizing process (AMDP). The planning of boundary digitization defines the exploration surface region. The AMDP then automatically explores the whole measured surface region with a collision-free exploration path, continuing until a satisfactory surface model corresponding to the user's specified digitizing accuracy is obtained. This approach significantly reduces the product development lead time and obtains a surface model with controlled digitizing accuracy. The validity and applicability of this approach are demonstrated by three practical industrial examples.     

Evaluation of system models for an endoscopic fringe projection system

To be able to perform inline inspection of complex geometries, which exhibit for example undercuts or internal structures, a new endoscopic micro fringe projection system has been developed. It is designed to perform areal measurements for tool inspection inside the limited space of metal forming presses by employing flexible image fibers to couple the measurement system’s camera and projector to a compact sensor head. The projector features a laser light source and a digital micro-mirror device to generate high-contrast fringe patterns. To increase the depth of field of the sensor heads, custom gradient-index lenses have been designed as an approximation to the Scheimpflug principle. Challenges arise for both calibration and phase measuring algorithms from the optics, as well as from the reduction in resolution introduced by the fiber bundles. This paper presents an evaluation of two different system models for the endoscopic fringe projection system, which are based on the pinhole camera model and a black box model. An automated calibration process, which gathers the calibration data for two calibration algorithms that are robust to artifacts introduced by the optical path, is demonstrated. Based on a comparison of measurements, differences between the two modeling approaches are discussed. Finally, results of measurements of a demonstrational metal forming tool are shown as an application example.     

Handheld 3-D Scanning with Automatic Multi-View Registration Based on Visual-Inertial Navigation

In this article an approach to a mobile 3-D handheld scanner with additional sensory information is proposed. It fully automatically builds a multi-view 3-D scan. Conventionally complex post processing or expensive position trackers are used to realize such a process. Therefore a combination of a visual and inertial motion tracking system is developed to deal with the position tracking. Both sensors are integrated into the 3-D scanner and their data are fused for robustness during swift scanner movements and for long term stability. This article presents an overview over the system architecture, the navigation process, surface registration aspects, and measurement results.     

基于CMM测量路径优化算法的研究

随着计算机集成制造系统(CIMS)的深入发展,计算机辅助检测工艺规划(CAIP)已成为CIMS中集成质量系统(IQS)的关键环节。本文研究了基于坐标测量机(CMM)的测量路径优化算法,对坐标测量机的测量路径优化问题进行了合理的描述,分析了已有路径优化算法存在的不足,提出并实现了将遗传算法和禁忌搜索算法结合的策略用于测量路径优化的GATS算法,取得了良好的效果。     

A simple method of accuracy enhancement for industrial manipulators

A robot calibration method which includes identification of kinematic parameters and error compensation is presented. The parameter identification process features an easy-to-perform measurement procedure using a low-cost, instrumented, articulated linkage, and with proper planning of the data collection process, the measurement of actual end effector positions can be performed automatically. The basis of the parameter identification approach is akin to that of closed-loop mechanism synthesis. For error compensation, a computation scheme based on the nominal model as opposed to the calibrated one is presented. The resulting algorithm, allowing the exploitation of the closed-form inverse kinematics solutions available for most industrial robots, is computationally efficient and therefore suited for on-line applications. Examples based on simulation studies, devised to include realistic operating conditions, are presented to demonstrate the feasibility of this method. The effects are also investigated of the number of measurements and of the sensor resolution on the overall quality of the identification.