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.     

双螺杆压缩机转子齿形三坐标测量的半径补偿

双螺杆压缩机转子齿形进行三坐标测量机测量时,需要对球形测头半径进行半径补偿.结合转子螺旋曲面的几何特点,对转子型线测量数据点进行半径补偿计算,得到三坐标测量机球形测头真实接触点,再将空间分布的真实接触点旋转到相同横截面上得到转子型线数据点.通过实例验证该方法的有效性,可以应用于双螺杆压缩机转子型线的检测及逆向工程等工作中.     

Variation risk analysis: MEMS fabrication tolerance for a micro CMM probe

This paper describes a methodology of variation risk analysis for microsystems using analytical modelling and simulation, a key characteristic (KC) method and statistical analysis considering MEMS fabrication tolerances. This methodology is applied to an innovative design for a micro co-ordinate measuring machine (CMM) probe utilising piezoelectric actuation and sensing currently being developed at the National Physical Laboratory. Analytical modelling is used to investigate the individual effects of dimensional parameters on the sensors’ open-circuit voltage output, which is a KC of the micro CMM probe. A computer simulation is performed using the finite-element method and compared with the analytical model. The KC variation is predicted and the variation contribution of the probe manufacturing processes is presented. This KC is mainly influenced by the thickness of the piezoelectric layer associated with the composite sol gel deposition process. Variation risk analysis results can be used to implement a variation risk mitigation strategy.     

Volumetric distortion assessment of a five-axis machine by probing a 3D reconfigurable uncalibrated master ball artefact

In this paper, a method is proposed that uses an artefact assembled in situ and exploiting the on-machine probing capability to perform a rapid volumetric distortion assessment of a five-axis machine. The 3D reconfigurable uncalibrated master ball artefact (RUMBA) is an assembly of the machine pallet and an adjustable number of master balls located within the machine working and probing envelop. The artefact design philosophy allows flexibility in the number and positions of the balls thus conferring the reconfigurability attribute. Reconfigurability allows adaptation of the artefact to the machine topology and geometry and its construction around a fixture and workpiece to reduce disruption to machine production. On the down side, the artefact is uncalibrated as its construction concept hinders precise knowledge of its geometry. During a test, combinations of all the machine axes are used to move and probe the master balls. A mathematical model is developed in order to identify the setup errors of each master ball and the probe. Simultaneous identification of the rotary axes’ linear offset with the setup errors is proposed to improve the parameter estimation and volumetric distortion prediction. The machine contribution to the volumetric distortion is then computed from the ball centre data excluding the setup errors. Tests are conducted in a laboratory on a horizontal machining centre. The results show that the proposed mathematical procedure is capable of removing the influence of the uncalibrated artefact geometry, excluding scale, and that the proposed design is suited to the machine environment.     

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.     

便携式坐标测量仪的最佳测量位姿研究

提出了一种利用现有五自由度便携式坐标测量仪提高工件测量精度的测量方法。该方法在已知设备关节转角随机误差量及测量点的情况下,通过反求各关节处可能的角度值,并在相应的各关节转角组合下,加入转角的随机误差量,重构相应姿态下的测头坐标,然后与已知测量点比较得出该姿势下受角度随机误差影响的最大值,不同的位姿对应不同的最大值,把最小的一个最大值对应的位姿作为最优测量位姿。文中通过引入两球模型和间接球法,大大的减少了反求角度过程中的计算量。     

NON-CONTACT MEASUREMENT OF SCULPTURED SURFACE OF ROTATION

A method for measuring the sculptured surface of rotation by using coordinate measuring machine (CMM) and rotary table is proposed. The measurement is realized during the continuous rotation of the workpiece mounted on the rotary table while the probe moves along the generatrix of the surface step by step. This method possesses lots of advantages such as simplicity of probe motion, high reliability and efficiency. Some key techniques including calibration of the effective radius of the probing system, determination of the position of axis of rotation, auto-centering of the workpiece, data processing algorithm, are discussed. Approaches for determining the coordinates on measured surface, establishing workpiece coordinate system and surface fitting are presented in detail. The method can be used with contact or non-contact probes. Some fragile ceramic and plaster parts are measured by using the system consisting of a CMM, rotary table, motorized head and non-contact laser triangulation probe. The measurin     

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.     

Reduced configuration set for the multi-step method applied to machine and probe error separation on a CMM

This paper presents a refinement and further analysis of an application of the multi-step method for the separation of machine and probe errors on a CMM using multiple redundancy probing of the machine’s own master ball. The objective is to reduce the amount of data required and so minimize the test time in order to reduce the industrial cost of such periodic verifications.     

Software compensation of rapid prototyping machines

This paper addresses accuracy improvement of rapid prototyping (RP) machines by parametric error modeling and software error compensation. This approach is inspired by the techniques developed over the years for the parametric evaluation of coordinate measuring machines (CMM) and machine tool systems. The confounded effects of all errors in a RP machine are mapped into a “virtual” parametric machine error model. A generic artifact is built on the RP machine and measured by a master CMM. Measurement results are then used to develop a machine error function and error compensation is applied to the files which drive the build tool. The method is applied to three test parts and the results show a significant improvement in dimensional accuracy of built parts.     

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.     

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     

Measuring external profiles of porous objects using CMM

Coordinate measuring machine (CMM) has been extensively used in surface measurement and inspection. CMM produces more accurate and reliable results compared with non-contact measurement devices, since CMM measures target surfaces in a tactile way and is not affected by surface reflection quality. However, when there is porosity on the outside surfaces, CMM measurement will have errors because part of the probing stylus will come into the porosity spaces. This paper presents a method of using CMM to measure external profiles of objects with external porosity spaces. The center of a CMM probing stylus will be compensated to avoid porosity spaces and located above external surface areas along surface normal directions. Such a probing strategy can be implemented in both computer-aided design (CAD)-guided mode and non-CAD-guided mode. When the CAD model is available, the probing styli are guided to approach the surface along its normal directions successively to identify and avoid porosity spaces. When the CAD model is unavailable, surface normal directions will be estimated first and then adjusted. The presented method is able to avoid porosity spaces in CMM measurement regardless of the availability of CAD models.     

Metrological feasibilities of CMM touch trigger probes. Part I: 3D theoretical model of probe pretravel

New 3D model of the inaccuracy of a touch trigger probe used to collect coordinates of a measured object by coordinate measuring machine (CMM) is proposed. The analysis is performed both for one and two stage types of probes. The influence of a stylus length and diameter, a spring force and direction of a contact point approach are taken into consideration. The effects of frictional interaction between the stylus ball and a measured surface are also taken into consideration. The theoretical analysis of a tough trigger probe hysteresis is presented. Finally a computer simulation of mathematical modeling in the XYZ space is shown.     

用于工业三维点测量的接触式光学探针

为了快速、准确地获得大尺寸工业产品或带有深槽孔工件的关键点三维坐标,本文基于工业近景摄影测量理论、立体视觉技术等,研究并实现了两种工业便携式、接触式光学探针测量系统。研究了测量系统涉及的探针设计、探针标定以及三维点解算等关键技术,设计了点阵式和手持相机式两种适用于不同工业场合的工业探针。针对点阵式探针的测量,提出了一种用于解算探针坐标系与世界坐标系相对关系的点云匹配方法。此外,采用拟合虚拟球的方法准确标定了两种探针的内部参数。最后,通过对比标准球与三坐标测量机的测量结果,得到系统的测量精度可达0.1 mm/m。该精度满足一般大、中型工件的三维点测量精度标准。     

5m大螺纹磨床丝杠临床动态测量机械探测系统研究及应用

本文论述5m大螺纹磨床长丝杠工件临床动态测量中如何解决机械探测系统的布局和设计。论述的临床动态检测法是一种成功的方法,不需用专门的5m长丝杠动态检测仪器。轻巧挠性探头能手携方便地装卸,利用红宝石圆柱探针及红宝石球探针能对滚珠丝杠及矩形、角度丝杠等进行测量,极为经济合算。本法为丝杠动态测量提供了前景广阔的新思路。     

Simple master artefact for CMM dynamic error identification

The proposition in this paper is a new method applying a simple master artefact for testing the dynamic performance of coordinate measuring machines (CMM). The principle of the method is presented and the method is used for identification and evaluation of dynamic error sources. The validity of the method is experimentally confirmed on a Zeiss ACCURA bridge coordinate measuring machine equipped with a Vast Gold active scanning probe, as well as Vast XXT passive scanning probe.     

5m大螺纹磨床丝杠临床动态测量机械探测系统研究及应用

本文论述5m大螺纹磨床长丝杠工件临床动态测量中如何解决机械探测系统的布局和设计。论述的临床动态检测法是一种成功的方法,不需用专门的5m长丝杠动态检测仪器。轻巧挠性探头能手携方便地装卸,利用红宝石圆柱探针及红宝石球探针能对滚珠丝杠及矩形、角度丝杠等进行测量,极为经济合算。本法为丝杠动态测量提供了前景广阔的新思路。     

A new technique for directly measuring the position errors of a 3-axis machine. Part 2: application

To expand the measurement range of the method introduced in part 1 of this paper series, a pyramid array artifact is proposed and calibrated on a CMM. In the calibration procedure, the distance between the pyramids is presented by data from three groups. Then in the measurement procedure, the position changes are calculated from both calibration and measurement data. In addition, the error induced by manufacture can be reduced or erased in these two procedures. After calibration by a high-accuracy CMM or machine tools, the developed device can also have the same accuracy as these tools. The developed device has been tested using an actual machine tool. The measurement results of the proposed device were checked by other high-accuracy measuring systems, and the comparison showed good agreement.     

Self-centering probes with parallel kinematics to verify machine-tools

In this paper, a new type of self-centering probe is presented to verify the performance of machine-tools in an efficient and rapid way using ball artifacts. A self-centering probe is placed in the spindle of the machine-tool and a ball artifact on the work table. The probe is moved to the calibrated center positions of the balls of the reference artifact. The probe touches these balls and, in a single measurement, it provides the X, Y, Z offset of the actual machine position from the desired (programmed) position. A non-conventional probe design has been chosen: three independently movable probe styli form a miniature coordinate measuring machine with parallel kinematics. The development process of two variants of such a self-centering probe is presented in this paper. The results obtained in laboratory tests show a repeatability of less than 0.5 μm and an error range of less than 2 μm throughout the large measurement range (2 mm × 2 mm × 2 mm) of the probe.