Influence of measured objects parameters on CMM touch trigger probe accuracy of probing

Influence of the measured objects parameters on coordinate measuring machine (CMM) touch trigger probe inaccuracy of probing is investigated. Factors such as material stiffness of measured workpiece, its surface shape and roughness are taken into consideration. The measuring method out off CMM, based on a rotary table and a reference axis is applied for tests. 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 of a precise rotary table. The statistical analysis of variance and regression is applied for data analysis.     

零件轮廓测量机安全监测系统的设计

为适应现代先进制造业质量检测自动化的需要,研究开发能够在线非接触、高精度自动检测的智能三坐标测量机已经成为制造业发展的必然趋势,其中机器视觉检测技术的应用为实现复杂自由曲面的自动化检测提供了技术支持。介绍了零件轮廓测量机的工作原理,分析了回转工作台和偏心调整机构在回转体零件测量系统中的作用。采用合理的图像处理技术,完成了包括测量工位上异常物体的检测、工件类型识别和工件位置检测等功能在内的图像识别系统的设计。     

Effect of slice thickness on the profile accuracy of model maker rapid prototyping measured by a circular triangulation laser probe

The objective of this research is to investigate the effect of slice thickness on the profile accuracy of the model maker (MM) rapid prototyping (RP) system, layer by layer, through non-contact laser probe measurement. A circular triangulation laser probe, model OTM-3A20, made by Wolf & Beck Co., was mounted on a coordinate measuring machine (CMM), as the non-contact sensor. An adjustment device for the laser probe was designed to minimise the cosine error caused by assembly inaccuracy. The alignment test of the measuring laser beam was carried out using a calibrated specimen. The systematic accuracy of the circular triangulation laser probe with respect to the surface roughness and the surface slope of the RP workpiece was investigated using a HP5529A laser interferometer system. The maximum error of 21/2D RP part profile accuracy can be improved from 220 μm to 131 μm, and the average error can be improved from 78 μm to 46 μm as the slice thickness changed from 0.127 mm (0.005 in.) to 0.0127 μm (0.0005 in). However, the machining time increases by about seven fold based on the experimental results. An overall error of 197 μm as measured by the laser probe is attainable using the finest slice thickness 0.0127 mm (0.0005 in.) for the 3D profile accuracy. To verify the accuracy of non-contact laser probe measurement, the 3D profile of the RP part was also measured by a CNC CMM, with good consistency.     

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.     

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.     

大尺寸工件在机视觉测量的图像拼接方法

大型工件在制造过程中需要拆卸到坐标测量机上进行测量,造成效率低下、质量不易控制等问题。本文提出一种用于大尺寸工件在机视觉测量的图像拼接方法。将摄像机安装在数控机床上,通过控制机床工作台移动,摄取多幅图像,并对其进行高精度拼接。探讨了图像拍摄规则、重叠图像对的合理定义、角点提取和射影变换矩阵的计算问题。尺寸测量结果验证了该方法的有效性和高精度、高效率。     

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.     

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     

三坐标机探针测头的选用

三坐标测量机作为高端精密测量仪器之一,选择合适的探针测头,可以有效的提高测量精度和测量效率。本文首先采用正交试验,从探头的半径与长度、探头的旋转角度、探头的接近距离、物体的大小四个方面分析,确定探头的半径与长度对精度影响比较大。其次采用半径筛选法,以叶片背弧面为例,确定最佳测头半径。该方法已用于叶片测量中,改变了以往传统多次试测选择测头的方式,提高了测量的准确性和测量效率。     

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.     

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.     

Intermittent Process Measurement of a Freeform Surface Profile with a Circular Triangulation Laser Probe on a Machining Centre

This paper describes the development of a non-contact type system for measuring a freeform surface on a machine tool. A laser probe, model OTM-3A20 made by Wolf & Back Co., was integrated into a CNC machining centre as a non-contact sensor. An adjustment device for the laser probe was designed to minimise the cosine error caused by assembly inaccuracy. An alignment test of the measuring laser beam was carried out using a calibrated specimen. The systematic accuracy of the circular triangulation laser probe and a standard triangulation laser probe, with respect to the surface roughness, surface slope, and coating colour of the workpiece, was investigated by using an HP5529A laser interferometer system. The measuring system, which consists of a personal computer, a CNC controller of a machining centre, a Renishaw MP10 touch-trigger probe system, and the controller of the laser probe system, was integrated information-technically. Automatic measuring software was developed for the purpose of measuring path simulation, generation of NC codes, and error analysis of the measured data. The profile error of the tested object, measured by the laser probe and the coordinate measuring machine respectively was found to be within 45 μm. In this case, the tolerance of the designed part is about 50 μm, so the developed system can be applied to the inspection of mould production in bakelite according to the experimental results. ID="A1"Correspondance and offprint requests to: Dr Fang-Jung Shiou, Department of Mechanical Engineering, National Taiwan University of Science and Technology, No. 43, Section 4, Keelung Rd. 106 Taipei, Taiwan. E-mail: shiou@mail.ntust.edu.tw     

Surface probing simulator for the evaluation of CMM probe radius correction software

Scanning coordinate metrology is largely based on recording the position of a spherical tip which is maintained in contact with the surface to be measured. The coordinate measuring machine (CMM) software converts these tip coordinates into coordinates of points on the measured surface, a process called probe radius correction. In order to investigate the probe radius correction accuracy of specific CMM software in scanning measurements, a surface probing simulator is developed. It calculates the coordinates of probe tip center points (virtual indicated measured points) as raw measurement data by numerically probing a known virtual surface. An iterative solution based on geometric criteria is used to achieve the necessary tangential contact conditions. Various sculptured surface profiles, probe radii, and scanning increments can then be simulated. These raw data are then fed to the CMM software where the probe radius correction is performed. The CMM results are then compared with the known surface to evaluate the probe radius correction accuracy of the CMM built-in algorithm. The simulator allows a rapid CMM software capability check for a variety of situations and may pinpoint shortfalls that may be avoided through alternative measurement procedures. It may also be used to motivate the development of new probe radius correction techniques and assist in their evaluation. Tests were conducted on a Zeiss and a Mitutoyo CMM to demonstrate the usefulness of the simulator.     

Near Optimal Measuring Sequence Planning and Collision-Free Path Planning with a Dynamic Programming Method

A near optimal measuring sequence was introduced to complete the entire measuring process and reduce the measuring time of a coordinate measuring machine (CMM) for a workpiece whose shape consists of several geometric elements. The number and positions of the measuring points of the workpiece were planned by a CAD/CAM software system. A weight matrix of the number of probe spins and the concept of the angle difference matrix were proposed for the measured feature face using the assumptions in this paper, for the purpose of dynamic programming. First, a dynamic programming method was carried out to plan the optimal measuring sequence of the feature face of the geometric elements. Then, a measuring point distance difference matrix was established for an individual feature face. Then, a dynamic programming method was used to plan the measuring path of the measuring points for solving the approximated shortest path. A collision-free interference inspection method established in this paper was also used to include a collision-free path for paths with interference. The entire measuring path planning was thus completed. With the help of CAD/CAM software and the powerful computation and analytical capability of computers, the system was able to achieve an appropriate measuring sequence in a short time.     

基于球形目标的激光位移传感器光束方向标定

搭建了非接触式的三坐标测量系统以便精密测量三维型面。将激光位移传感器通过具有两个回转轴的回转体安装在测量机的Z轴上,从而可根据待测表面的形状来调整传感器的方位。为了使传感器在各个方位上实现测量功能,提出了基于球形目标的光束方向标定方法,并详细阐述了其数学原理。标定时,驱动测量机使传感器分别沿测量机的X,Y和Z轴做等间距步进,根据步长和激光束长度的变化建立方程组求解出激光束所在直线的单位方向向量。最后,多次测量尺寸参数已知的六面体标准块规,检验了该测量系统的重复性。结果显示,该系统的测量不确定度为0.048mm;测量另一直径已知的被测球时,传感器在各个方位上的误差小于0.05mm,表明所提出的标定方法使测量系统达到了逆向工程的使用要求。得到的数据表明,本文所提出的方法有较高的标定精度和较好的重复性,为实现三维型面的快速扫描测量奠定了基础。     

激光三角法扫描测头特性的研究

在分析了激光三角法位移测量原理的基础上,以ＩＢ－１２型激光三角法位移传感器为实例,研究了激光三角法位移传感器的使用特性,补偿非线性误差、倾斜角误差,提高了测量精度,使其能够作为非接触式扫描测头用在三坐标测量机上,完成空间自由曲面的非接触扫描测量。     

An innovative algorithm for statistic sampling of measured points and simplifying measuring probe orientation for sculpture surfaces

As living standards have improved, the requirements of appearance modeling variables have also increased. Although several CAD systems can design and modeling needed products with complicated geometric, but the questions of measuring methods and workpiece error-detection are also growing. For the contact measuring method, besides measuring collision and probe orientation, the sampling points and their distributed locations are the important factors that influence measuring time as well as precision. In this paper, the sampling statistics technique was used to calculate the minimum number of sampling points, which will tally the contour tolerance requirements of the measured surface. Next, the suitable locations for sampling points will be carried out using the one-half sampling distribution method. Finally, the 2D space picture of measuring characteristic of five-axis CMM (CMM-space) was developed for measuring probe’s orientation in the measuring process. As a result, an algorithm of measuring characteristic matrix of five-axis CMM (CMM-matrix) and the minimum times of the measuring probe’s placement was derived to reduce the measuring time and improve the measuring efficiency.     

基于激光位移传感器的非接触三坐标测量机的设计

针对采用接触测头进行测量的三坐标测量机的测量效率低、不能对易变形物体进行测量等问题,设计了一种基于激光位移传感器的非接触三坐标测量系统,以PLC和工控机为主控,通过运动模组带动激光位移传感器定位,实现对工件表面特征点尺寸和数据的快速测量,且用户可通过触摸显示屏对设备进行操作。通过对待测工件进行实测表明,该设备能满足生产测量需求,具有实用性和有效性。     

Real-Time Prediction of Workpiece Errors for a CNC Turning Centre, Part 1. Measurement and Identification

This paper analyses the error sources of the workpiece in bar turning, which mainly derive from the geometric error of machine tools, i.e. the thermally induced error, the error arising from machine–workpiece–tool system deflection induced by the cutting forces. A simple and low-cost compact measuring system combining a fine touch sensor and Q-setter of machine tools (FTS FQ) is developed, and applied to measure the workpiece dimensions. An identification method for workpiece errors is also presented. The workpiece errors which are composed of the geometric error, thermal error, and cutting force error can be identified according to the measurement results of each step. The model of the geometric error of a two-axis CNC turning centre is established rapidly based on the measurement results by using an FTSFQ setter and coordinate measuring machine (CMM). Experimental results show that the geometric error can be compensated by modified NC commands in bar turning.     

双目视觉检测技术在自由曲面测量中的应用

提出一种由三坐标测量机和视觉形貌测头组成的自由曲面非接触测量系统。利用虚拟三维靶标完成了包括水平方向不确定比例因子和主点坐标在内的摄像机各项参数的标定。对圆柱正截面和量块表面的测量试验验证了该测量系统对自由曲面和金属强反射表面测量的可行性。