Measurement of form error of a probe tip ball for coordinate measuring machine (CMM) using a rotating reference sphere

This study presents a method of measurement of the form error of the tip ball in the tactile probing systems of a coordinate measuring machine (CMM) by using a rotating reference sphere. The measurement of the form error of the CMM probe tip was conducted without the use of additional external measuring instruments or sensors. The form errors of the probe tip ball and the reference sphere were separated from the probing coordinates of CMM by rotation of the reference sphere. The effectiveness of the proposed method was evaluated based on an uncertainty analysis. The uncertainty in measurement of diameter of the probe tip ball was estimated to be less than 0.5 μm.     

Wear Measurement and Assessment of Explanted Cross-Linked PE Acetabular Cups Using a CMM

Wear has been considered the main limiting factor in the longevity of hip replacements. Wear analysis is thus essential for determining wear-related failure mechanisms and prediction of wear, which will consequently enable biomedical engineers to improve the design, material, and service life of the bearing components. This article presents wear measurement and assessment of the explanted conventional cross-linked polyethylene (XPE) and second-generation highly cross-linked polyethylene cups (X3) using a coordinate measuring machine (CMM). An expanded uncertainty analysis was performed to assess the performance of wear measurement. Wear measurement using the CMM method was validated with the gravimetric technique. The normalized error between volumetric wear measurement of the CMM method and that of the gravimetric technique was estimated to be always less than 1, suggesting that the CMM method applied to explanted hip wear measurements under the specific conditions was accurate and reliable. The approach to CMM measurement with uncertainty analysis was shown not only to locate 3D wear scar and wear direction but also to accurately quantify linear and volumetric wear with a maximum volumetric uncertainty of ±3.15 mm³ (95% confidence level). It is shown that identifying the key uncertainty components involved in the measurement process including validation, which contributes to an overall expanded uncertainty budget, is crucial to improve the confidence and the reliability of hip wear measurement results using a CMM.     

Ball array calibration on a coordinate measuring machine using a gage block

The distances between the balls of a ball array used in machine geometry calibration have to be very accurate. These distances can be calibrated using a laser measurement system, which requires specially designed optical devices and measuring probes. In this paper, a new and economical alternative method for calibrating the ball array is described. A single gage block is used for measuring the standard distance at the starting position. Then, the exact distances between the balls can be obtained by using the coordinate measuring machine (CMM) probe motion. This method does not depend on the accuracy of the CMM. Also, this method does not require expensive instruments or devices, but a CMM and a gage block. A simple “parallel-plane” bracket, mounted on to the measuring end of a CMM probe, is used to determine the centers of the balls automatically and accurately.     

三坐标测量机高速测量下的动态综合误差分析

综合众多学者对三坐标测量机各组成部分误差的研究成果,对三坐标测量机的主要动态误差源进行了归纳,并从气浮导轨系统、机体结构、测头系统和测量系统四个方面分析了三坐标测量机高速测量时动态误差的产生原因及对测量结果的影响,为误差修正提供了参考依据。     

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.     

Uncertainty analysis of a laser calibration system for evaluating the positioning accuracy of a numerically controlled axis of coordinate measuring machines and machine tools

This paper presents an uncertainty analysis of a Positional Error Calibrator based on a laser interferometer system. This laser calibration system is capable of evaluating the positioning accuracy of a numerically controlled axis of machine tools and coordinate measuring machines (CMM) under dynamic conditions. In order to assess the measurement uncertainty of this calibrator, an analysis of the uncertainty components that make up the uncertainty budget of this calibrator has been carried out. These uncertainty components can be classified into three categories as follows: (1) uncertainties intrinsic to the laser system; (2) uncertainties due to environmental effects; (3) measuring uncertainties due to the installation. The procedure for evaluating the uncertainty of this calibrator follows GUM (“Guide to the Expression of Uncertainty in Measurement”). This uncertainty analysis was carried out when this calibrator was used to assess the positional errors of the “X” axis of a moving bridge type CMM.     

Five-axis automated measurement by coordinate measuring machine

This research paper presents an analysis of the undercut interference and inclination interference caused by complicated 3D workpiece during measurement. The objective of this research is to propose a solution to the collision between measuring probe and workpiece for the purpose of automation and interference-free measurement. The fundamental procedure is based on the 3D CAD model of workpiece and five-axis coordinate measuring machine (CMM) measuring facility to generate an interference-free stylus orientation through three phases—adjustment of inclination angle under linear contour, adjustment of inclination angle under non-linear contour, and definition of rotation-free angle. Such manner not only solves the interference problems but also incorporates the minimization of counts of measuring probe rotation. In terms of methodology, the research adopts projection of cutting plane to determine the interference status of the measuring point, and based on the measuring inclination angle on the proposition of self-intersected contour and cross-intersected contour concepts, the range of safe rotation range can be determined by sweeping operation. Following the presented methods and procedures, the five-axis CMM simulation system for automated measurement is finally developed to validate the feasibility of proposed solution.     

Development and validation of a new reference cylindrical gear for pitch measurement

A new type of master gear, the Gauge Block Gear (GBG), was developed for the performance verification of coordinate measuring machines (CMMs), for the specific task of pitch and chordal tooth thickness measurement. Its main characteristic is the replacement of the teeth with gauge blocks to achieve direct traceability of the chordal tooth thickness. Mathematical models for the geometrical definition of cylindrical gears with involute toothing, data evaluation, and assessment of the task-related uncertainty, were formulated, and measuring strategies for CMMs were designed and implemented. The GBG was calibrated using the swing round method, and measurement uncertainties on chordal tooth thickness and total pitch deviation F_p were determined to be 0.9 μm and 1.4 μm, respectively. Assembly stability and flexibility of the artefact were verified with measurements performed on a CMM provided with general purpose software, one with dedicated gear measuring software, a form tester, and a conventional gear measuring center. Results confirm the correctness of the mathematical models developed to analyze CMM results as well as their compatibility with existing approaches. The Gauge Block Gear provides, therefore, for direct traceability of the chordal tooth thickness and allows the definition of the task-specific uncertainty of pitch and tooth thickness measurements of cylindrical gears as basis for the assessment of the metrological capability of measuring machines.     

Algorithm for measuring gears implemented with general-purpose spreadsheet software

Conventional methods to verify gears are based on manual measurement instruments, such as vernier caliper gauges, gear pitch micrometers, profilometers, among others. The use of these instruments is widely described in technical literature, while in the actual industrial arena the coordinate measurement machines (CMM) are commonly used to obtain, with the appropriate software, all the parameters including the tooth profile.Commercial software for measuring gears with a CMM is usually based on continuous touch of teeth’s flanks. In the educational centres is still common to find single-point probing point to point touch machines. To transform them into continuous touch machines, new software and accessories are required and costs can be excessive for instructional purposes.This paper presents the geometrical and mathematical principles to develop a software application for measuring gears and describes its implementation using general-purpose spreadsheet software. For this purpose, the conventionally used software of the CMM is supported by a spreadsheet that calculates the probe positions and direction of measurement. The communication between the spreadsheet and the CMM software is established by ASCII files. At the end of this process, the spreadsheet displays the measurement results, thanks to its graphical and computing power, making possible to improve the learning process of students or training professionals.     

Precision tracking control of a horizontal arm coordinate measuring machine in the presence of dynamic flexibilities

One of the major sources that affect measurement accuracy and limit the use of high motion speeds in coordinate measuring machines (CMM) is the position error. In fact, static and dynamic probe errors are more direct factors in measuring machine accuracy, but are not the subject of this research. However the accuracy of acquisition of component position errors using a CMM in motion is also of importance, hence the dynamics of a CMM need to be considered. Therefore, this research aims to model the dynamics of a horizontal arm CMM by considering drive flexibility at joints and evaluates the characteristics of the system for fine motion control purposes. Design of a precision tracking controller (PTC) to perform superior tracking for enhancing the measurement accuracy and the probing speed in providing less inspection time at high motion speeds is carried out. A dynamic model for the CMM is developed including drive flexibilities represented with lumped springs at the joints. Due to the non-collocated nature of the control scheme in the flexible CMM dynamics, a non-minimum phase system is observed in the proposed CMM model. Using the derived CMM model with joint flexibilities, tracking motion control simulations are conducted at different probing speeds for the cases where a PI controller and a feedback PTC are employed. A comparison of the PI controller with the feedback PTC is also performed. Results demonstrate that the effects of joint flexibilities on the contour error and probing speeds are significant and the PI controller is not capable of providing good accuracy during challenging tasks such as corner tracking. However, the simulation results indicated that by using the proposed feedback precision tracking controller, contour errors in corner tracking that are caused by joint flexibilities can be reduced effectively .     

Measurement strategy impact on dimensional inspection by portable camera-based measuring systems

In dimensional inspection of large objects, portable measuring systems are greatly involved in a wealth of applications, such as automotive, motorsports and aerospace industries. Metris K-series Optical CMM (Coordinate Measuring Machine) system is one of the metrology solutions with relatively high accuracy and flexibility. This paper focuses on measurement strategy via repeatedly measuring a length using Metris K610 camera system. The paper proposes a link between measurement strategy and the system performance that can be achieved. The result of the statistical analysis are also given based on the uncertainty propagation of the CMM.     

三坐标机测量齿轮齿廓的不确定度评价

介绍了坐标测量中几种常用的不确定度评价方法.指出传统的三坐标测量机的测量不确定度评价方法大都不适用于评价坐标测量中面向对象的测量不确定度,并对使用蒙特卡洛方法评价测量不确定度进行了研究.首先,根据三坐标测量机详细标定文件及补偿策略说明建立测量模型.然后,将测量中的采样点通过测量模型生成大量测量结果,并以此评价测量不确定度.在齿廓评价实验中,评定齿廓误差的测量不确定度为0.96 μm时,多次评价结果之间的最大差值不超过0.03 μm,具有可靠的理论依据和较稳定的评定结果.文章指出,目前商用三坐标测量机大都不能为特定的测量对象提供测量不确定度报告,使用蒙特卡洛方法有希望改变此现状.     

On the calibration of surface plates

Calibration of large surface plates could be performed using different measuring systems. In this investigation an autocollimator system, a laser system and a coordinate measuring machine have been investigated. A comparison among these methods of calibration has been carried out. An Elcomat 3000 autocollimator of resolution 0.05 arcsecond, an Agilent 5529A laser interferometer system of resolution 0.05 arcsecond and a Prismo/Zeiss Computerized Numerically Controlled Coordinate Measuring Machine (CNC–CMM) respectively are used. Large reflecting mirror, angular retro reflector and sensitive probe are used with autocollimator, laser systems and CNC–CMM respectively to identify heights at each position on the tested surface plate. Repeated results from the different methods are carried out and presented in the paper. Uncertainties associated with the measurement results of each method have been estimated using the GUM procedures and given in the paper. The paper discusses the difficults and ease as well as accuracies associated with each method.     

CMM touch trigger probes testing using a reference axis

A new method of testing of touch trigger probes for coordinate measuring machines (CMM) has been proposed. The concept is based on measurements of the distance between reference and triggering points in various directions. The reference points are established by the rotation axis of a precise rotary table. The advantage of this method relies on easy realisation with application of a commercial device for roundness error measurement. The accuracy of the presented method is much higher in comparison with the existing procedures of CMM probes calibration.The mathematical principle of the method has been presented and used for evaluation of its uncertainty. The validity of the method was experimentally confirmed by means of one- and two-stage type probes.     

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.     

Diagonal in space of coordinate measuring machine verification using an optical-comb pulsed interferometer with a ball-lens target

This paper presents a new optical method of coordinate measuring machine (CMM) verification. The proposed system based on a single-mode fiber optical-comb pulsed interferometer with a ball lens of refractive index 2 employed as the target. The target can be used for absolute-length measurements in all directions. The laser source is an optical frequency comb, whose repetition rate is stabilized by a rubidium frequency standard. The measurement range is confirmed to be up to 10 m. The diagonals of a CMM are easier to verify by the proposed method than by the conventional artifact test method. The measurement uncertainty of the proposed method is also smaller than that of the conventional method because the proposed measurement system is less affected by air temperature; it achieves an uncertainty of approximately 7 μm for measuring lengths of 10 m. The experimental results show that the measurement accuracy depends on noise in the interference fringe, which arises from airflow fluctuations and mechanical vibrations.     

面向任务的测量不确定度评估原理和方法

坐标测量机是典型的面向任务的测量设备,测量任务的改变将引入不同的测量不确定度。怎样评估坐标机面向任务的测量不确定度,目前我国还没有这方面专门的技术规范。参考ISO/TS15530系列标准,介绍了坐标测量机面向任务的不确定度评估原理和方法。     

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.     

PH9/PH10回转测头系统的数学模型

提出了 PH9/ PH1 0回转体安装姿态的概念 ,建立了三坐标测量机回转测头系统的数学模型 ,根据模型可一次性标定测头 ,从而简化了测头转位测量的规程