检测数控机床圆周运动误差的一种新方法和新仪器外文文献翻译、中英文翻译
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检测数控机床圆周运动误差的一种新方法和新仪器外文文献翻译、中英文翻译,检测,数控机床,圆周运动,误差,一种,新方法,仪器,外文,文献,翻译,中英文
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A new method and instrument for measuring circular motionerror of NC machine toolsH.L. Liua,b,*, H.M. Shia, B. Lia, X. LiaaNational CNC Control System Research Center, Mechanical Department, Huazhong University of Science and Technology, Wuhan 430074, ChinabZhanjiang Ocean University, Zhanjiang, Guangdong 524025, ChinaReceived 31 August 2004; accepted 13 January 2005Available online 16 February 2005AbstractA new method andinstrument formeasuring circular motionerror of numerical control (NC) machine tools are described inthis paper. Theinstrument consists of a linear displacement transducer bar with two balls at each end and a high accuracy rotary encoder. The radiusvariations are detected by the transducer and the rotation angle of the bar is measured by the rotary encoder while the machine is moving in acircular path. The measuring area is circular except for a small area around the center of the disc. The bar can be expanded and contractedalong its axis for different application. The instrument has a compact structure and can be installed on a machine tool simply and quickly. It isshownby the experimental results that the instrument hasgood repeatability andhighprecision ofmeasuring circular motiontrajectories. Theinstrument can be widely used especially in the error-compensation and error-source project in the industrial application.q 2005 Elsevier Ltd. All rights reserved.Keywords: NC machine tool; Motion error; Measurement instrument; Circular measurement1. IntroductionIn recent years, the precision machining process hasattracted much attention from numerous investigators. Oneof its important tasks for error-compensation and errorsource diagnosis is to map the volumetric errors of amachine tool 1. Current techniques have the ability tomeasure parametric error function for each of the machinesaxes, for instance, the positioning and linear motionaccuracy. However, it is still difficult to measure preciselythe circular motion error let alone a more general motiontrajectory.Several devices and methods are usually used to measurethe trajectory accuracy of circular motions, and described asfollows:(1) A test bar and a one-dimensional probe 2.(2) A disk (or a ring gage) and a two-dimensional probe 3.(3) The double ball bar system (DBB) consists of a flexuralbar at each end and two magnetic balls constrained byspecial sockets with a spherical surface. The deviationof the relative distance between balls is measured usingthe flexural bar while the machine moves in circularmotion 4,5.(4) The double-bar linkage and two rotary encoders are setat the root end of the link separately to detect therotation angles of the links 6,7.(5) The KGM circular test system 8.The above-mentioned instruments and methods havereally used to assess the trajectory accuracy of circularmotion and some usefully results have been gained. Thereexist some problems to some extent in their practicalapplications as those pointed out by several researchers1,6. In (1) and (2), there is limitation by its own strandeddisk accuracy. High accuracy can be obtained by (3) butonly in the radius direction. Although circular motion errorsalong x axis and y axis in XY plane (two-dimensional error)can be got in (4), the instrument is very complicated and willbe made hardly. KGM circular test system, also calledcross-grid encoder, has an excellent performance, but it isvery costly and the biggest measuring zone is merely acircular of about radius 120 mm.0890-6955/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.ijmachtools.2005.01.012International Journal of Machine Tools & Manufacture 45 (2005) 13471351/locate/ijmactool* Corresponding author.Tel.:C86 27 87542513; fax: C86 27 87545256.E-mail address: huanlao_liu (H.L. Liu).A new method and instrument for measuring the circularmotion error of NC machine tools is presented in this paper.When the machine is stopped at points along the circularpath where radius and angle information can be gained andcommanded and actual points can be compared, errors of xand y axis can be measured which is a two-dimensionalerror. Moreover, this method is simple and convenient inpractical application, while the instrument is of a compactstructure with low cost.2. Outline of the measurement instrumentA schematic diagram of the presented prototypemeasurement instrument is shown in Fig. 1. This instrumentconsists of a linear transducer bar with two balls at each endof the bar similar to DBB and a rotary encoder, which is setat root end of ball 1 to detect rotation angles of the bar.Ball 2 is connected to machine tool spindle by ball holder.The base of the instrument is fixed on table of an NCmachine tool to be measured, for example, xy stage of themachine center. The rotation plane of the linear transducerbar is parallel to xy plane of the machine table andperpendicular to the rotation axis of the spindle. Themeasuring coordinate frame can be set as that the rotationaxis of the encoder on the root of ball 1 is defined as the z-axis, which is parallel to the rotation axis of the spindledenoted as Z. The x and y axes are set to be parallelrespectively to the machine tool and denoted as X, Y, so thexy plane is located on the rotation plane of the lineartransducer bar.Fig. 2 is a photograph of the prototype measurementinstrument.3. Principle of the measurement methodIn order to avoid the velocity lag of the axis servo, whichalways cause the actual point dropping behind thecommanded point in machine moving, machine must beprogrammed to move in such a way that a point P(xi,yi) ismoved along a circle and stopped at an actual point P(Xi,Yi)after a few seconds, while the position data of this point gotby the linear transducer and rotary encoder are transferred toa personal computer. The resolution of the linear transduceris 0.1 mm. The type of the rotary encoder made inHEIDENHAIN is ROD 280, which can send out 18000sine wave pulses. The signals are transferred to a personalcomputer through IK220 interpolator which can equallydivided one original sine wave pulse into maximum 4096square pulses. Therefore, the periphery resolution of theangle signal is less than 0.1 mm.Motion error of point P(xi,yi) can be expressed as:EXiZxiKXi(1)EYiZyiKYi(2)In which, the coordinates of the actual point P(Xi,Yi) in thecircular path is given as:XiZRicosqi(3)YiZRisinqi(4)RiZRCDRi(5)where, R is rotation radius of the moving circle which is thedistance between the two balls, qiis rotation angle of thelinear transducer bar which is measured by the rotaryencoder, and DR is radius variations of the actual path whichis obtained by the linear transducer. In order to eliminateFig. 1. Schematic diagram of the prototype measurement.Fig. 2. Photograph of the measurement instrument.H.L. Liu et al. / International Journal of Machine Tools & Manufacture 45 (2005) 134713511348motion vibration in measuring process, machine is pro-grammed to move at low speed. Because the connected linkattached to the linear transducer bar can be changed, theactual working range can be defined as:Rmin!r!Rmax(6)where r is distance from the measuring point to the originalo of the measuring coordinate, Rminand Rmaxare minimumand maximum length of the linear transducer bar respect-ively. Rmin, which has been confirmed by experimental, isless than 80 mm. Rmaxshould not more than 500 mm.Therefore, the whole working range is of annulus formaround the original o whose inner radius is 80 mm and outerradius is 500 mm.4. Center-offset error compensationIn practice, the center point of the ball 1, on the xoy planedenoted by O may not be coincided with the center of thecircular motion which the machine tool is commandedmoving. This will cause center-offset error, as shown inFig. 3.On considering the error characteristics of DR, center-offset error e can be expressed as:e Zffiffiffiffiffiffiffiffiffiffiffiffiffiffiffia2Cb2p/r(7)where a, b are the offset distance associated with the x- andy-axis respectively. An equation can be obtained:RiZr CDR ZffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiXiKa2CYiKb2qi Z0;1;2;.;N K1:(8)where i indicates measured points in a full revolution.Following equations can be obtained by the least squaremethod:4r;a;b ZXNK1iZ0r CDR2Kr2? Zmin(9)v4r;a;bvrZ0(10)v4r;a;bvaZ0(11)v4r;a;bvbZ0(12)The offset distance a and b can be obtained:a Z1NXNK1iZ0Xi(13)b Z1NXNK1iZ0Yi(14)r Z1NXNK1iZ0ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiXiKa2CYiKb2q(15)To remove the effects of the center-offset error, Eqs. (1)and (2) can be revised as:ExiZxiKXiKa(16)EyiZyiKYiKb(17)From Eqs. (16) and (17), the circular error in a givenpoint can be got.5. ResultsIn this section, some measurement results with theprototype instrument are demonstrated and discussed. TheNC machine tool used in these experiments is a new verticalmachiningcenter.Afeedrate,40 mm/min,wasusedinorderto measure the center-offset error accurately. Measurementprocessisseparated intotwo steps.Theoneistomeasurethecenter-offset error, in which more than 1000 points can bemeasured at equal interval in one full revolution withoutstopping when the machine was commanded to move in acircular path. The other is circular motion error measure-ment, in which the machine tool can be stopped in acommanded point and total 36 point in one full revolutioncan be got. Results of measuring center-offset error is showninFig.4,whereradiusis156.2780 mmandthecirclemarkedwith the dotted line is the moving path which is the machinetool commanded to move. The circle marked with centerlineis the raw date error trace before the center-offset error iscompensated. The circle marked with solid line is error traceafter the center-offset error is compensated.From above results, some conclusions can be drawn:(1) The instrument can be used to measure the circularmotion error.(2) The center-offset error has great effect on the measure-ment results.(3) The method of center-offset error compensation iscorrect.(4) The circular motion error can be obtained throughcomparing coordinate magnitude between commandedFig. 3. The schematic diagram for center-offset error.H.L. Liu et al. / International Journal of Machine Tools & Manufacture 45 (2005) 134713511349andactualpointafterthecenter-offseterrorcompensation.Then following experiments will only show results aftercenter-offset error compensation.Experimental results of three times at the same locationare shown in Fig. 5, where the feed rate is 40 mm/min andthe radius is 156.2780 mm. It is demonstrated that theinstrument is of very good repeatability and the magnitudeis less than G1 mm. Some similar results of circular motionerror also can be observed in the paper 2.As a further verification, the results of the circular motionerror measurement can be compared with that of KGMmeasurement system. Because of the limitation of theworking range of the KGM, the connecting link on theinstrument is changed. The measurement radius is110.230 mm. In Fig. 6, the results of error trace measure-ment is compared using the instrument in three times withthat of KGM measurement system. Two of results matchone another very well, and difference value is less thanG2 mm. Therefore, it is confirmed that the measurementresults with the instrument presented in this paper aresufficiently accurate and reliable.6. ConclusionsA new method and instrument to measure the circularmotion error of NC machine tools is developed andpresented. The major feature can be summarized as follows: The developed instrument is of simple and compactstructure yet provides larger working range. To install theinstrument for measuring is simple and quick. Themeasurement operation is easy and convenient inpractical applications. The proposed method is suitable to measure while themachine is commanded to stop at points along a circularpath so that the commanded and actual points could becompared. Itis confirmed by experimental results that theinstrument is of high precision and repeatability. The proposed method will find widely use to enhance theaccuracy of NC machine tools, especially for errorcompensation and error source project in industrialapplication.AcknowledgementsThe research was supported by the national advancedtechnological plan projector (2002AA423260). The authorsalso would like to express their thanks to the HEIDENHAINCO. for the free use of the KGM measurement system.References1 R. Ramesh, M.A. Mannnan, A.N. Poo, Error compensation inmachine toolsa review. Part I: geometric, cutting-force inducedand fixture-dependent errors, International Journal of Machine Toolsand Manufacture 40 (2000) 12351256.2 S. Hong, Y. Shin, H. Lee, An efficient method for identification ofmotion error sources from circular test results in NC machines,Fig. 4. Measuring results of center-offset.Fig. 5. The diagram of the repeatability results.Fig. 6. The diagram of the comparison accuracy results.H.L. Liu et al. / International Journal of Machine Tools & Manufacture 45 (2005) 134713511350International Journal of Machine Tools and Manufacture 37 (3) (1997)327340.3 W. Knapp, Test of the three-dimensional uncertainty of machine toolsand measuring machines and its relation to the machine errors, AnnalsCIRP 32 (1) (1983) 459464.4 J.B. Bryan, A simple method for testing measuring machines andmachine tools, part 1: principles and application, Precision Engineering4 (2) (1982) 6169.5 J.B. Bryan, A simple method for testing measuring machines andmachine tools, part 2: construction, Precision Engineering 4 (3) (1982)125138.6 H. Qiu, Y. Li, Y. Li, A new method and device for motion accuracymeasurement of NC machine tools. Part 1: principle and equipment,International Journal of Machine Tools and Manufacture 41 (2001)521534.7 H. Qiu, Y. Li, Y. Li, A new method and device for motion accuracymeasurement of NC machine tools. Part 2: device error identifi-cation and trajectory measurement of general planar motions,International Journal of Machine Tools and Manufacture 41 (2001)535554.8 HEIDENHAIN, Measuring System for Machine Tool Inspection andAcceptance Testing December 2002, Germany.H.L. Liu et al. / International Journal of Machine Tools & Manufacture 45 (2005) 134713511351检测数控机床圆周运动误差的一种新方法和新仪器摘要本文将介绍一种检测数控机床圆周运动误差的新方法和新仪器圆周仪。圆周仪由一个线性位移传感器和一个高精度的旋转编码器组成。当机床做圆周运动时，其运动的半径误差由传感器检测，旋转角度误差由旋转编码器检测。圆周仪的检测范围是除包围圆心的一个极小区域之外的一个圆形范围，其探测棒可以根据需要伸长或缩短。圆周仪结构简洁，可以方便快速的安装在机床上。实验结果表明圆周仪可以反复的测量并且保持较高的测量精度。圆周仪已经得到了广泛的应用，尤其是在自动补偿生产中。关键词：数控机床，运动误差、检测仪器、圆周运动检测一、 简介近年来，精密加工被越来越多的人关注，它的主要特色是对机床进行误差自动补偿和误差源分析。目前的生产技术可以检测机床的轴向参数，例如相对位置误差和线性运动精度。然而进行完整的圆周运动检测仍然是一个难题。常规的圆周运动检测装置如下所示：(1)一根探测棒和一根空间探针。(2)一个圆盘（或者一个元环）和两根空间探针(3)一根折棒和以两个用特殊的凹球面固定在它两端的两个磁性球。当检测圆周运动时调整折棒的弯曲程度以调整两个球的相对距离。(4)双球联接和两个分别装在联接根部的旋转编码器用以检测圆周运动的旋转角度。(5)KGM圆周检测系统上述装置已经实用于检测圆周运动精度并且取得了一定的效果，然而研究人员指出，在实际应用中这些装置在某种程度上还存在着很多的问题。(1) 和(2)的工作精度严重受其结构精度限制；(3)只可获得较高精度的半径检测；(4)虽然可以检测X-Y坐标的x轴和y轴误差（两维误差），但是因其复杂的结构而难以制造；KGM圆周检测系统也叫十字格栅编码器，它有很好的工作性能，但是成本很高，并且它的最的检测范围仅为半径120mm的圆。本文将呈现检测数控机床圆周运动误差的一种新型仪器圆周仪及其使用方法。当机床停在圆周轨迹的的某点上时其半径和角度信息都将被截取并和期望值进行比较，从而检测两维误差的x轴和y轴误差。并且圆周仪结构简单使用便利成本低廉。二、 圆周仪外形图1：圆周仪原理图圆周仪的原理图如图1所示，它的主要结构是一个旋转编码器和一根类似于DBB一样的线性位移传感棒，棒的两端有两个传感球，其中安装在下部的球1用于检测棒的角度，球2用一个固定器连接到机床的中心轴。圆周仪按标准安装在数控机床的工作台上，比如机床中心的X-Y坐标，传感棒的旋转平面平行于工作台的x-y平面。圆周仪的自身坐标定义如下：球1的旋转轴为z轴，x轴和y轴分别平行于机床的XY轴，这样线性传感棒的旋转平面就落在了x-y平面上。图2为圆周仪的照片图2：圆周仪照片三、 检测原理为了避免圆周仪的速度滞后于机床分侍服系统导致实际检测点落后于期望点，编程时必须使机床的运动滞后几秒钟，使圆周仪获取运动坐标并且通过旋转编码器将其转换为电脑中的存取数据。线性传感器的分辩率为0.1m，编码器是由HEIDENHAIN制造的ROD 280型，可以发送18000个正弦脉冲，脉冲通过IK220分类机输入电脑，所以所检测的机床角度信号达小于0.1m的数量级。点P(
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