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

A new method and instrument for measuring circular motionerror of NC machine toolsH.L. Liu*, H.M. Shi, B. Lia, X. LiNational CNC Control System Research Center, Mechanical Department, Huazhong University of Science and Technology, Wuhan 430074, ChinaZhanjiang Ocean University, Zhanjiang, Guangdong 524025, ChinaAbstract A new method and instrument for measuring circular motion error of numerical control (NC) machine tools are described in this paper. The instrument consists of a linear displacement transducer bar with two balls at each end and a high accuracy rotary encoder. The radius variations are detected by the transducer and the rotation angle of the bar is measured by the rotary encoder while the machine is moving in a circular path. The measuring area is circular except for a small area around the center of the disc. The bar can be expanded and contracted along its axis for different application. The instrument has a compact structure and can be installed on a machine tool simply and quickly. It is shown by the experimental results that the instrument has good repeatability and high precision of measuring circular motion trajectories. The instrument 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. Introduction In recent years, the precision machining process has attracted much attention from numerous investigators. One of its important tasks for error-compensation and errorsource diagnosis is to map the volumetric errors of a machine tool 1. Current techniques have the ability to measure parametric error function for each of the machines axes, for instance, the positioning and linear motion accuracy. However, it is still difficult to measure precisely the circular motion error let alone a more general motiontrajectory. Several devices and methods are usually used to measure the trajectory accuracy of circular motions, and described as follows:(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 by special sockets with a spherical surface. The deviation of the relative distance between balls is measured using the flexural bar while the machine moves in circular motion 4,5.(4) The double-bar linkage and two rotary encoders are set at the root end of the link separately to detect the rotation angles of the links 6,7.(5) The KGM circular test system 8. The above-mentioned instruments and methods have really used to assess the trajectory accuracy of circular motion and some usefully results have been gained. There exist some problems to some extent in their practical applications as those pointed out by several researchers 1,6. In (1) and (2), there is limitation by its own stranded disk accuracy. High accuracy can be obtained by (3) but only in the radius direction. Although circular motion errors along x axis and y axis in XY plane (two-dimensional error) can be got in (4), the instrument is very complicated and will be made hardly. KGM circular test system, also called cross-grid encoder, has an excellent performance, but it is very costly and the biggest measuring zone is merely a circular of about radius 120 mm. A new method and instrument for measuring the circular motion error of NC machine tools is presented in this paper. When the machine is stopped at points along the circular path where radius and angle information can be gained and commanded and actual points can be compared, errors of x and y axis can be measured which is a two-dimensional error. Moreover, this method is simple and convenient in practical application, while the instrument is of a compact structure with low cost.2. Outline of the measurement instrument A schematic diagram of the presented prototype measurement instrument is shown in Fig. 1. This instrument consists of a linear transducer bar with two balls at each end of the bar similar to DBB and a rotary encoder, which is set at 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 NC machine tool to be measured, for example, xy stage of the machine center. The rotation plane of the linear transducer bar is parallel to xy plane of the machine table and perpendicular to the rotation axis of the spindle. The measuring coordinate frame can be set as that the rotation axis of the encoder on the root of ball 1 is defined as the zaxis, which is parallel to the rotation axis of the spindle denoted as Z. The x and y axes are set to be parallel respectively to the machine tool and denoted as X, Y, so the xy plane is located on the rotation plane of the linear transducer bar Fig. 2 is a photograph of the prototype measurement instrument.3. Principle of the measurement method In order to avoid the velocity lag of the axis servo, which always cause the actual point dropping behind the commanded point in machine moving, machine must be programmed to move in such a way that a point P(x,y) is moved along a circle and stopped at an actual point P(X,Y) after a few seconds, while the position data of this point gotby the linear transducer and rotary encoder are transferred t a personal computer. The resolution of the linear transducer is 0.1 m. The type of the rotary encoder made in HEIDENHAIN is ROD 280, which can send out 18000 sine wave pulses. The signals are transferred to a personal computer through IK220 interpolator which can equally divided one original sine wave pulse into maximum 4096square pulses. Therefore, the periphery resolution of the angle signal is less than 0.1 m. Motion error of point P(x,y) can be expressed as:In which, the coordinates of the actual point P(X,Y) in the circular path is given as:where, R is rotation radius of the moving circle which is the distance between the two balls,is rotation angle of the linear transducer bar which is measured by the rotary encoder, and R is radius variations of the actual path which is obtained by the linear transducer. In order to eliminate motion vibration in measuring process, machine is programmed to move at low speed. Because the connected link attached to the linear transducer bar can be changed, the actual working range can be defined as:where r is distance from the measuring point to the original o of the measuring coordinate, R and Rmax are minimum and maximum length of the linear transducer bar respectively. R, which has been confirmed by experimental, is less than 80 mm. Rshould not more than 500 mm. Therefore, the whole working range is of annulus form around the original o whose inner radius is 80 mm and outer radius is 500 mm.4. Center-offset error compensationIn practice, the center point of the ball 1, on the xoy plane denoted by O may not be coincided with the center of the circular motion which the machine tool is commanded moving. This will cause center-offset error, as shown in Fig. 3.On considering the error characteristics of R, centeroffset error e can be expressed as:where a, b are the offset distance associated with the x- and y-axis respectively. An equation can be obtained:where i indicates measured points in a full revolution. Following equations can be obtained by the least square method:Fig. 3. The schematic diagram for center-offset error. The offset distance a and b can be obtained: To remove the effects of the center-offset error, Eqs. (1) and (2) can be revised as: From Eqs. (16) and (17), the circular error in a given point can be got.5. Results In this section, some measurement results with the prototype instrument are demonstrated and discussed. The NC machine tool used in these experiments is a new vertical machining center. A feed rate, 40 mm/min, was used in order to measure the center-offset error accurately. Measurement process is separated into two steps. The one is to measure the center-offset error, in which more than 1000 points can be measured at equal interval in one full revolution without stopping when the machine was commanded to move in a circular path. The other is circular motion error measurement, in which the machine tool can be stopped in a commanded point and total 36 point in one full revolution can be got. Results of measuring center-offset error is shown in Fig. 4, where radius is 156.2780 mmand the circle marked with the dotted line is the moving path which is the machine tool commanded to move. The circle marked with centerline is the raw date error trace before the center-offset error is compensated. The circle marked with solid line is error trace after the center-offset error is compensated. From above results, some conclusions can be drawn:(1) The instrument can be used to measure the circular motion error.(2) The center-offset error has great effect on the measurement results.(3) The method of center-offset error compensation is correct.(4) The circular motion error can be obtained through comparing coordinate magnitude between commanded and actual point after the center-offset error compensation.Fig. 4. Measuring results of center-offset. Then following experiments will only show results after center-offset error compensation. Experimental results of three times at the same location are shown in Fig. 5, where the feed rate is 40 mm/min and the radius is 156.2780 mm. It is demonstrated that the instrument is of very good repeatability and the magnitude is less than +1 m. Some similar results of circular motion error also can be observed in the paper 2. As a further verification, the results of the circular motion error measurement can be compared with that of KGM measurement system. Because of the limitation of the working range of the KGM, the connecting link on the instrument is changed. The measurement radius is 110.230 mm. In Fig. 6, the results of error trace measurement is compared using the instrument in three times with that of KGM measurement system. Two of results match one another very well, and difference value is less than +2 m. Therefore, it is confirmed that the measurement results with the instrument presented in this paper are sufficiently accurate and reliable.Fig. 5. The diagram of the repeatability results.Fig. 6. The diagram of the comparison accuracy results.6. Conclusions A new method and instrument to measure the circular motion error of NC machine tools is developed and presented. The major feature can be summarized as follows: The developed instrument is of simple and compact structure yet provides larger working range. To install the instrument for measuring is simple and quick. The measurement operation is easy and convenient in practical applications. The proposed method is suitable to measure while the machine is commanded to stop at points along a circular path so that the commanded and actual points could be compared. It is confirmed by experimental results that the instrument is of high precision and repeatability. The proposed method will find widely use to enhance the accuracy of NC machine tools, especially for error compensation and error source project in industrialapplication.Acknowledgements The research was supported by the national advanced technological plan projector (2002AA423260). The authors also would like to express their thanks to the HEIDENHAIN CO. for the free use of the KGM measurement system.References1 R. Ramesh, M.A. Mannnan, A.N. Poo, Error compensation in machine toolsa review. Part I: geometric, cutting-force induced and fixture-dependent errors, International Journal of Machine Tools and Manufacture 40 (2000) 12351256.2 S. Hong, Y. Shin, H. Lee, An efficient method for identification of motion error sources from circular test results in NC machines, nternational Journal of Machine Tools and Manufacture 37 (3) (1997) 327340.3 W. Knapp, Test of the three-dimensional uncertainty of machine tools and measuring machines and its relation to the machine errors, Annals CIRP 32 (1) (1983) 459464.4 J.B. Bryan, A simple method for testing measuring machines and machine tools, part 1: principles and application, Precision Engineering 4 (2) (1982) 6169.5 J.B. Bryan, A simple method for testing measuring machines and machine tools, 1251386 H. Qiu, Y. Li, Y. Li, A new method and device for motion accuracy measurement 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 accuracy measurement of NC machine tools. Part 2: device error identification 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 and Acceptance Testing December 2002, Germany.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(x,y)的运动误差可以表示为：从而可得点P(X,Y)所在圆的轨迹可表示为：其中R是圆周运动的半径既两个球的距离，是线性传感棒的旋转角度，R是由传感棒检测到的实际运动轨迹的半径误差。为了消除震动引起的检测误差，机床必须是低速旋转。由于连接棒的可伸缩性，圆周仪的