Positioning error correction using virtual coordinate system for mMTs

In this paper, a new calibration and correction method is proposed to effectively improve positioning accuracy of practical 3-DOF positioning devices of miniaturized machine tools (mMTs). The method is composed of correction of the machine’s coordinate system, which is distorted due to the effects of various error components, and correction of positioning errors at arbitrary points in workspace using this corrected coordinate system. If only positioning results could be measured and assessed three-dimensionally, squareness and scale errors of the mMTs’ coordinate system can be corrected using this method without any additional device or jig. The proposed method was applied to correct the positioning errors of a serial-type 3-DOF precision positioning device used for a micro/nano-pattering system. After correction of over 40 μm × 40 μm × 40 μm of its workspace, the positioning accuracy was successfully improved by about 98%.     

三自由度并联机构坐标测量机及其虚拟原型研究

介绍三自由度并联机构坐标测量机的结构、特点及工作原理,建立了该坐标测量机的测量模型,讨论了测量空间的计算方法,并对计算机仿真结果进行了分析,在Ｗｉｎｄｏｗｓ９５开发环境下,通过ＶｉｕａｌＣ＾＋＋５．０调用ＯｐｅｎＧＬ图形库中的函数,对并联坐标测量机的虚拟原型进行了参数化三维建模与仿真,从而为真实样机的制作尊定了基础     

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.     

Multiple orientation technique for the calibration of cylindrical workpieces on CMMs

Coordinate measuring machines (CMMs) are widely used in various fields of precision engineering and science. Although they are highly accurate instruments, for some tasks, e.g. calibration of reference artifacts, the accuracy even of the best available instruments is not sufficient.In this paper, we describe a highly accurate technique using a CMM for the measurement of cylindrical workpieces. The proposed method is a combination of multiple orientation and substitution techniques and compensates for all geometrical errors of a CMM, systematic probing effects and the bending of the workpiece due to gravity. We demonstrate the method on a cylinder gauge with flat ends that incorporates a number of different geometrical features. The evaluation of the measurement uncertainties for each characteristic was performed manually and using the Virtual CMM (VCMM) [Trapet E, Franke M, Haertig F, Schwenke H, Waeldele F, Cox M, et al. Traceability of Coordinate Measurements According to the Method of the Virtual Measuring Machine: Final Project Report MAT1-CT94-0076, PTB-Report F-35, Parts 1 and 2; 1999; Haertig F, Trapet E, Waeldele F, Wiegand U. In: Proceedings of the 5th IMEKO TC-14. Traceability of coordinate measurements according to the Virtual CMM concept; 1995. p. 245–54.]. The results show, that very low uncertainties can be achieved by the proposed measurement techniques. It is also demonstrated that the VCMM approach considers reversal effects correctly for the calculation of measurement uncertainties.     

基于串并联坐标测量机器人虚拟样机研究

基于UG建立串并联坐标测量机器人的虚拟样机,在UG下实现了坐标测量机的运动仿真,得到了测量机的运动仿真数据及工作空间.在ADAMS下对机构进行运动学正解与逆解的计算以及动力性能的分析.     

CMM uncertainty analysis with factorial design

The purpose of this research is to present a method to estimate the Coordinate Measuring Machine (CMM) measurement uncertainty. The approach is based on a performance test using a ball bar gauge and a factorial design technique. A factorial design was applied to carry out a performance test and to investigate CMM errors associated to orientation and length in the work volume. The CMM measurement uncertainty was estimated with components of variance obtained after statistical analysis of variance applied to volumetric measurement errors. An application was performed with a Moving Bridge CMM and the results were compared to the volumetric performance test proposed by ANSI/ASME B89.4.1 standard. The results showed that the proposed method is suitable to investigate CMM hardware performance and determine the contribution of machine variables to measurement uncertainty.     

基于UG的串并联机构坐标测量机虚拟样机设计与仿真

针对一种串并联机构坐标测量机进行机构分析,进而基于UG建立测量机虚拟样机,在UG下实现了坐标测量机的运动仿真,得到了测量机精确的运动数据及工作空间。     

坐标测量机的空间误差检测及21项几何误差分离的方法

对使用2维检县（球板或孔板）快速检测三坐标测量机的空间误差，进行了较深入的研究，为了高效，准确地实现测量机的误差修正，提出了分离坐标测量机的21项几何误差的算法，并以龙门式结构的三坐标测量机为例，建立了其误差模型。通过计算机数据仿真，验证了此方法的可行性。     

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。     

面向快速探测的坐标测量机动态误差分析

坐标测量机在快速探测时，由于惯性力和驱动力的作用，引起机体变形，从而导致了动态误差的产生。分析了引起坐标测量机动态误差的原因，建立了坐标测量机的动态误差模型。采用有限元方法分析计算了快速探测过程中惯性力和驱动力产生的动态误差，验证了动态误差模型的应用，分析结果是合理的，方法是可行性的。     

利用弹性网络算法求解大型三坐标测量机几何误差的方法

为提高大型三坐标测量机(CMM)的精度,修正空间几何误差,研究利用激光追踪仪多站位测量技术取代实物基准,提出了基于弹性网络算法求解CMM几何误差的方法。基于激光追踪仪多站位测量技术,结合L-M算法,实现CMM空间规划点体积误差的高精度测量,有效提高测量效率。利用弹性网络算法解算CMM准刚体模型,解决模型求解存在多重共线的难题,实现CMM几何误差的求解;将方程组中部分系数为0的项结合体积误差与单轴几何误差的关系模型来求解几何误差。实验搭建了激光追踪多站位测量系统,测量了CMM的空间待测点体积误差。实验结果表明,提出的方法可以有效求解大型CMM的几何误差。     

Standardised Reference Data Sets Generation for Coordinate Measuring Machine (CMM) Software Assessment

Rapid and accurate in-process measurement has recently become more common in product cycles, especially for producing parts having 3D contoured shapes. As a result, the ability to analyse large quantities of dimensional data requires today’s coordinate measuring machines (CMM) to employ their extreme functionality. With the increasing demand for performance of the software supplied for a CMM, the testing methods for these software packages must be rigorous, stable, and efficient. Motivated by the aforementioned demand, this work is intended to design and develop an algorithm and computer code to generate the reference data sets representing the coordinates of Gaussian associated features for CMM measured parts. These reference data sets can be used to test the CMM software submitted for approval to the National Institute of Standards and Technology (NIST). A generic algorithm for the development of the data sets is proposed and the program code is designed and developed by employing object oriented concepts. Dynamic errors during measurement are also accounted for, using Fourier harmonics representing the form errors and noise in the measured data. The data sets, being an integral part of the proposed International Standard – ISO 10360, will become a significant step towards the standardisation of software testing procedures for coordinate measuring machines.     

数控机床误差的多项式预报与补偿

建立了数控机床空间误差预报的多项式模型，该模型把机床的空间误差表示为机床运动坐标的多项式函数；提出了用激光球杆仪直接测量机床空间误差的方法；由机床工作空间有限定位点误差的测量数据，利用最小二乘法来决定误差预报模型的系数。在XK713数控加工中心上进行了误差的多项式建模和补偿实验，结果表明本误差预报和补偿方法省时，效果显著。     

A developed algorithm for simulation of blades to reduce the measurement points and time on coordinate measuring machine (CMM)

A 3D Coordinate Measurement Machine Facility (CMM) of the latest technology enables both researchers and industrial manufacturers to evaluate the precision of the different manufacturing techniques that are usually applied for the production of the mechanical component. Especially when the examined component is a blade, due to the geometrical complexity, larger errors can occur during the manufacturing procedure. These errors have a strong impact on the final performance. The high precision measurement with a CMM requires scanning with small steps, which means measuring several points that need long-time measurement.The aim of this paper is to develop a method for simulating objects by three-dimensional scanning, with a small number of points, while achieving the goal of a certain allowable deviation. The curves used are of a 3rd degree polynomial form.     

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 .     

Ball tip–stylus tilt correction for a stylus profilometer

Ball tip and stylus tilt are two error sources found in coordinate measurement machines (CMMs). The magnitude of these errors is dependent on the ball tip radius and the degree of misalignment between the stylus motion axis and lateral referencing plane determined by the x and y axes of the CMM used. It is shown that these two errors are actually coupled and that their correction can be accomplished in one process. The overall benefit and versatility of this correction routine on a more general basis are given.     

Calibration of a 3D-ball plate

The presented 3D-ball plate is used for testing machine tools with a workspace of 500 mm × 500 mm × 320 mm. The artefact consists of a 2D-ball plate which is either located by a kinematic correct coupling on a base plate or on a spacer. The spacers are placed between the base plate and the ball plate and are also kinematic coupled to the other elements of the artefact. The kinematic couplings provide a high repeatability of the measurement setup. Because of the specific application the known calibration procedures for 2D-ball plates are not applicable.A calibration method for the pseudo-3D-artefact on a coordinate measuring machine (CMM) is presented, with the aim to minimise the influence of geometric CMM errors. Therefore a computer simulation is used to analyse the effects of these disturbing errors on the calibration of the ball plate and the spacers. Using a reversal method, the plate is measured at four different horizontal positions after rotating the ball plate around its vertical axis. A couple of the CMM errors, e.g., a squareness error C0Y between the X- and Y-axis of the CMM, can be eliminated by that method—others have to be determined with additional measurements, e.g., the positioning errors EXX or EYY of the X- and Y-axis, respectively. The paper also contains a measurement uncertainty estimation for the calibration by use of experiments, tolerances and Monte Carlo-simulations. The achieved uncertainty for ball positions in the working volume is less than 2.1 μm (coverage factor k = 2).     

Error separation in CMM coordinate metrology

测量形状误差是精密制造业质量控制的关键部分。坐标测量机(CMM)是自动化精确测量维度尺寸和几何形状的机器。本文选用两种类型的坐标测量机触发探针进行标准工件测量,旨在研究不同的每转波数(UPR)时不可预见的动态固有误差的影响。整个实验过程使用探针类型和探针速度参数,采用快速傅立叶变换分析实验结果,得到受CMM机械结构和探针扫描速度影响而可预见的几何误差。实验结果表明,UPR的数量在进行圆形测量时对CMM准确度水平起非常重要的作用。本文对探针系统和坐标测量机结构响应的具体误差公式也进行了假设与分析,以经验数据来预测PRISMO-Bridge-CMM在NIS中的准确度。     

Five axis machine tool volumetric error prediction through an indirect estimation of intra- and inter-axis error parameters by probing facets on a scale enriched uncalibrated indigenous artefact

The volumetric accuracy of five-axis machine tools is affected by intra-axis geometric errors (error motions) and inter-axis geometric errors (axes relative position and orientation errors). Self-probing of uncalibrated facets on the existing machine tool table is proposed to provide the necessary data for the self-calibration of the machine error parameters and of the artefact geometry using an indirect approach. A set of 86 non-confounded coefficients are selected from the ordinary cubic polynomials used to model both the intra- and inter-axis errors. A scale bar is added to provide the isotropic scale factor. The estimated model is then used to predict the actual tool to workpiece position. Experimental trials are conducted on a five-axis horizontal machining centre using its original unmodified machine table as an artefact. For validation purposes only, the estimated artefact geometry is compared to accurate coordinate measuring machine (CMM) measurements. A study of the volumetric error predictive capability of the model for selected subsets of estimated error coefficients is also conducted.