Improvement of coordinate measuring machine probing accessibility

In this paper, the probe accessibility of coordinate measuring machines (CMM) in dimensional inspection is studied. Based on the previous methods of the accessibility map, the influence of the actual configuration of the probe on the accessibility is analyzed in detail. A method, which takes the effects of the probe length and volume into account, is proposed so that the shortcomings of abstracting the probe as an infinite half-line could be overcome completely. Finally, a feasible and efficient algorithm is given.     

A general method for analysing the accessibility of features using concentric spherical shells

This paper presents a general method for features accessibility analysis used in the dimensional inspection of mechanical parts by CMMs (coordinates measuring machines). It is based on the intersection of concentric spherical shells (ICSS) centred at the measurement point. This method can be applied to any type of solid or surface and is not limited by continuity or derivability constraints. Accessibility domains can be generated easily as a limit case of the ICSS. This method has been generalised to include inspection with bent probes to take into account the actual shape of the probe. It may be used to analyse the accessibility or probe approach directions for any point within or outside any object. It is also possible to determine the common accessibility domain for a set of points directly or by comparing the accessibility domain of each point. This method has potential applications in fields such as machining and robotics.     

An Object Oriented Planner for Inspection of Prismatic Parts – OOPIPP

Coordinate measuring machines (CMMs) have been widely accepted and are increasingly used for carrying out inspections. With the increase in complex designs and tighter tolerances, the inspection process involving a CMM has become critical and there is a need to plan it effectively. In the present work, an object oriented planner for the inspection of prismatic parts (OOPIPP) has been developed. It incorporates interactive feature recognition and carries out all the essential steps of inspection planning, that is, selection of the most stable part orientation, arriving at number and distribution of inspection points, feature accessibility analysis, sequencing of probe orientations, removal of duplicate faces, and, finally, sequencing of faces. Various relationships between different entities of the system and distinct features of OOM have been used to develop the algorithms of different modules. Fuzzy logic for decision making has also been applied and a suitable method of combining fuzzy sets has been used for the selection of part orientation and for sequencing probe orientations.     

复杂曲面零件加工精度的原位检测误差补偿方法

为提高复杂曲面零件的数控机床原位检测精度,分析影响接触式检测系统精度的各项因素及其误差补偿方法。对检测系统的主要误差来源如机床几何误差、测头预行程误差和测头半径误差进行分析研究。在对数控机床的几何误差进行分析和建模的基础上,采用激光干涉仪进行三轴数控机床的单项误差测量和补偿;针对测头检测过程中存在的预行程误差,提出基于径向基函数(Radial basis function, RBF)的预行程误差预测方法,获得测头预行程误差分布图,并对检测系统进行实时预行程误差的补偿;提出改进的三角网格模型顶点法矢计算方法,有效进行三维测头的半径补偿。通过实例零件的加工精度原位检测试验及其与三坐标测量机CMM检验结果的比较,验证了原位检测方法的有效性。     

Efficient inspection planning for coordinate measuring machines

The coordinate measuring machine (CMM) has been recognized as a powerful tool for dimensional and geometric tolerance inspection in the manufacturing industry. The power of the CMM depends heavily on an efficient inspection plan that measures a part in minimal time. This paper proposes CMM inspection planning that can minimize the number of part setups and probe orientations and the inspection feature sequence. In our planning, a greedy heuristic method is adopted to obtain the minimal number of part setups and probe changes. Meanwhile, a continuous Hopfield neural network is developed to solve the inspection feature-sequencing problem. The proposed method was successfully implemented and tested using a machine spindle cover part. The results show that the proposed method can achieve excellent performance compared to the other methods.     

复杂曲面快速测量、建模及基于测量点云的RP和NC加工

坐标测量在制造领域中有着广泛的应用。评述了坐标测量及相关技术中所涉及的多传感器集成测量、测量点规划、测头路径规划、测头半径补偿、测量点云分割、曲面拟合以及基于测量点云的直接NC和RP加工等关键技术的研究现状,并对一些瓶颈问题的解决方案作了探讨,提出了几点建议。     

基于多传感器集成的三坐标测量机自动检测规划系统研究

为了充分发挥多传感器集成的优势，提高检测自动化水平，提出了该环境下三坐标测量机自动检测规划系统的体系结构。构建了专家规则库来制定检测策略，选择检测设备。重点分析了接触式测量检测规划的流程，提供了零件定位、测点自动生成等模块的解决方案。讨论了光学自动检测规划的要点。通过中性文件的使用和映射，实现了CAD与三坐标测量系统的集成，从而为产品的自动检测和质量控制提供了保障。     

CMM Probing Accessibility in a Single Slot

This study presents a novel mathematical method for resolving the accessibility of a through slot when using coordinate measuring machines. The proposed method considers the actual shape of a probe consisting of a motor column, a stylus, and a probe tip. Also derived herein is a mathematical method to derive the feasible probe orientation of the measurement point in the bottom of a slot using a geometrical relationship between the probe and the slot.     

An accurate probe pre-travel error compensation model for five-axis on-machine inspection system

On a five-axis CNC machine tool, the pretravel errors of touch-trigger probes are severely affected by gravity and must be compensated to ensure the required measurement accuracy. The situation is more complex than that of the three-axis on-machine inspection system. This paper proposes a simple and accurate modeling and compensation method for the probe pretravel error of a five-axis on-machine inspection system. First, the pretravel error for the 5-axis CNC tool is decoupled into three parts, which are analyzed based on the probe's mechanical structure. Then, a new calibration point selection strategy is proposed to obtain the accurate reference sphere center. Finally, we carry out calibration tests to validate the proposed method. The compensation results show that the proposed compensation method for the probe pretravel error under the influence of gravity (PPEUG) can improve the accuracy considerably.     

CNC加工动态基准视觉检测新工艺研究

由于CNC加工过程中工序间误差累积,严重影响数控加工精度。为此提出一种CCD视觉检测新工艺来实现加工动态基准的在线检测和误差补偿。研究动态基准的视觉特征提取方法,获取加工基准位置和误差;采用嵌入式控制技术,实现视觉图像的在线采集和处理;视诊测头像普通刀具一样通过标准锥柄安装在加工中心刀库中,通过CNC程序代码实现一体化控制功能。针对汽车关键件的验证,得出视诊测头检测精度达到0.03 mm,与基于触发式测头的CNC在线检测方法相比,检测效率提高近3倍,证明了该检测工艺在检测精度及效率上均能够满足生产线自动化检测需求。     

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.     

A computer-aided inspection planning system for on-machine measurement — Part II: Local inspection planning —

As a part II of theis research, new local inspection planning strategy is proposed in this paper based on the proposed inspection feature extraction method. In the local inspection planning stage, each feature is decomposed into its constituent geometric elements for more effective inspection planning. The local inspection planning for the decomposed features are performed to determine: (l) the suitable number of measuring points, (2) their locations, and (3) the optimum probing paths to minimize measuring errors and times. The fuzzy set theory, the Hammersley’s algorithm and the TSP method are applied for the local inspection planning. Also, a new collision checking algorithm is proposed for the probe and/or probe holder based on the Z-map concept. Finally, the results are simulated and analyzed to verify the effectiveness of the proposed methods.     

绝对式科赫分形平面涡流传感器裂纹检测性能研究

针对传统涡流传感器会忽略特殊方向短裂纹的缺点,提出了一种绝对式科赫分形平面涡流传感器,其激励线圈和信号拾取线圈均采用基于分形自相似理论的科赫雪花曲线。首先,对具有相同尺寸的科赫和圆形传感器进行有限元分析。然后,针对不同长度、方向、宽度和深度的裂纹,对比分析两种传感器响应信号的差异。最后,搭建实验系统对有限元分析结果进行验证。研究结果表明,对于不同长度、方向和宽度裂纹的探测,有限元分析结果与实验结果定性一致;在3和5 mm长的裂纹检测中,科赫传感器输出信号变化量比圆形传感器至少高出40%;在不同方向裂纹检测中,对于难检测方向的90°裂纹,科赫传感器比圆形传感器至少高出49%;在不同宽度裂纹检测中,科赫传感器的信号变化量比圆形传感器至少高出29%;在不同深度裂纹检测中,科赫传感器比圆形传感器至少高出6%;相对圆形传感器,科赫传感器对短裂纹探测的优势更加显著。该研究结果对平面柔性涡流传感器电磁感应结构的设计具有重要的参考意义。     

用接触式坐标测量进行自由曲面反求的方法研究

分析了逆向工程中自由曲面的反求过程 ,对接触式和非接触式测量方法进行了比较。针对工程实际应用的要求 ,提出了一种等距面指导的精度可控 ,测量过程能够自动进行的数字化方法。该方法采用接触式测量的 CMM作为数字化设备 ,解决了已往接触式测量不易进行精确控制以及人工操作劳动强度大的缺点。     

加工中心在线检测误差补偿技术研究

提出了加工中心在线检测误差通用数学模型,研究了测量系统误差参数辨识方法,实现了基于模型的加工中心在线检测软件误差补偿。对标准试件的检测及补偿结果表明,补偿后加工中心检测精度提高５３．８％以上,加工中心在线检测误差补偿实验结果证明了提出的误差补偿方法的可行性和有效性。     

Genetic Algorithm Modelling and Solution of Inspection Path Planning on a Coordinate Measuring Machine (CMM)

A multiple component inspection path planning problem (MCIPP) can be formulated as an optimisation problem, referred to as a non-deterministic polynomial complete problem (NP). An MCIPP consists of testing points, which will be visited by a CMM probe only once, and dummy points which are set to avoid collision and may be visited by a CMM probe more than once. This paper considers the application of genetic algorithms (GAs) acting as optimisers for optimal inspection path planning systems. The paper explores the techniques used in the GA optimal inspection path planning system. The paper also discusses the comparison of integer programming models and genetic models.     

Automated dimensional inspection planning using the combination of laser scanner and tactile probe

Combining multiple sensors on CMMs (Coordinate Measuring Machines) is useful to fulfil the increasing requirements on both complexity and accuracy in dimensional metrology. Yet, the methodology to plan measurement strategies for systems combining different types of sensors is still a major challenge. Such planning is commonly done in an interactive way. This paper presents a methodology which can create inspection plans automatically for CMM inspection combining a touch trigger probe and a laser scanner. The inspection features are specified based on the extracted geometry features and the associated PMI (Product and Manufacturing Information) items from a CAD model. A knowledge based sensor selection method is applied to choose the suited sensor for each inspection feature. For touch trigger measurements, the sampling strategy considers the measurement uncertainty calculated by simulation. A geometry-guide method is developed for collision-free probing path generation. For laser scan measurements, the required view angles and positions of the laser scanner are determined iteratively, based on which the scan path is generated automatically. The proposed methodology is tested for several cases and validated by measurement experiments. The methodology provides suited planning results and can be used for automated dimensional inspection, i.e. Computer Aided Quality Control (CAQC).     

基于激光电磁超声的裂纹检测研究

为检测内裂纹,建立了一套基于脉冲激光激发、电磁超声探头接收的非接触型超声检测系统。为避免在试件表面产生烧蚀损伤,采用热弹性模式激发超声,采用EMAT探头接收信号。利用出平面EMAT探头和内平面EMAT探头,分别研究了横波与纵波在半圆铝制试块的传播情况。最后,结合阴影法,使用该试验系统测量了试件背面的裂纹,检测得到的裂纹深度与实际深度非常接近。证明在热弹性模式下,激光激发、EMAT探头接收信号的方法对于内裂纹的检测是可行的。     

复杂曲面零件加工精度原位检测系统的残余误差补偿

复杂曲面零件数控加工后直接进行原位加工精度检测和误差补偿,是实现精密产品闭环制造模式的有效途径。原位检测系统的误差来源于测量系统误差和机床运动系统误差,经相关的误差分离与误差补偿后,仍存在较大的残余误差,影响检测精度及其推广应用。针对原位检测系统的检测精度问题,开展检测系统残余误差的回归建模与补偿研究,在机床几何误差、测头半径误差以及预行程等基本误差补偿的基础上,建立基于偏最小二乘回归分析算法的误差回归模型,实现曲面零件测点法矢方向的检测数据二次补偿。在算法实现的基础上,列举复杂曲面零件进行数控加工与在线检测的试验研究。试验结果表明,二次误差补偿方法可以进一步提高原位检测系统的检测精度。     

Practical way to measure large-scale 2D parts using repositioning on coordinate-measuring machines

In many situations it is required to perform an inspection of large flat parts on a coordinate-measuring machine (CMM) when it is impossible to probe all necessary surfaces from one position of the part. Or it is necessary to measure a large part which dimensions exceed the volume of an available CMM. For this purpose one needs to merge the data measured in two different positions of the workpiece into one coordinate system. Though most of geodesic software has out-of-the-box functionality to do that, a lot of popular CMM software lacks it. In this paper a practical approach is described to bring a repositioning functionality into a CMM software. The Calypso metrology software was studied. The proposed inspection method can be used both for the measurements of linear dimensions and location tolerances as common practice in Calypso.