一种新的测量数控制机床圆形运动误差的方法和器械外文文献翻译、中英文翻译

A new method and instrument for measuring circular motionerror of NC machine toolsAbstractA 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.1. IntroductionIn 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 motion trajectory.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 flexural bar 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 practicalapplications 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 instrumentA 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 endof 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 andperpendicular 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 thexy plane is located on the rotation plane of the linear transducer bar.Fig. 1. Schematic diagram of the prototype measurement.3. Principle of the measurement methodIn 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 beprogrammed to move in such a way that a point P(xi,yi) is moved along a circle and stopped at an actual point P(Xi,Yi) after a few seconds, while the position data of this point got by the linear transducer and rotary encoder are transferred to a personal computer. The resolution of the linear transducer is 0.1 mm. 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 4096 square pulses. Therefore, the periphery resolution of the angle signal is less than 0.1 mm.Motion error of point P(xi,yi) can be expressed as: （1） （2）In which, the coordinates of the actual point P(Xi,Yi) in the circular path is given as: （3） （4） （5）where, R is rotation radius of the moving circle which is the distance between the two balls, qi is rotation angle of the linear transducer bar which is measured by the rotaryencoder, and DR 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: （6）where r is distance from the measuring point to the original o of the measuring coordinate, Rmin and Rmax are minimum and maximum length of the linear transducer bar respectively. Rmin, which has been confirmed by experimental, isless than 80 mm. Rmax should 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 outerradius 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 commaned moving. This will cause center-offset error, as shown in Fig. 3. On considering the error characteristics of DR, centeroffset error e can be expressed as: （7）where a, b are the offset distance associated with the x- and y-axis respectively. An equation can be obtained: （8）where i indicates measured points in a full revolution. Following equations can be obtained by the least square method: （9） （10） （11） （12）Fig. 3. The schematic diagram for center-offset error.The offset distance a and b can be obtained: （13） （14） （15）To remove the effects of the center-offset error, Eqs. (1) and (2) can be revised as: （16） （17）From Eqs. (16) and (17), the circular error in a given point can be got.5. ResultsIn 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 errorcompensation.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 G1 mm. 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 G2 mm. Therefore, it is confirmed that the measurement results with the instrument presented in this paper are sufficiently accurate and reliable.Fig. 4. Measuring results of center-offset.Fig.4. The diagram of the repeatability results. Fig.5. The diagram of the comparison accuracy results.6. ConclusionsA 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. he 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 industrial application.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, International 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, part 2: construction, Precision Engineering 4 (3) (1982) 125138.6 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.一种新的测量数控制机床圆形运动误差的方法和器械摘要本文描述的是一种新的测量数控机床圆形运动误差的的方法和器械。该器械由在每个末端的二个球状物和一个具有高精确旋转性编码器的线性位移传感器条组成。半径的变化由传感器测得，而且当机器移动到一条圆形的轨道时，传感器的旋转角度由旋转编码器测得。 测定的区域除了圆盘中心周围的一个小的区域外都是圆形的。 传感器能够扩张而且由于不同的应用还能沿着它的轴收缩。该器械结构紧凑且能简单、快速地安装在机床上。 实验结果显示该器械在测量圆形运动轨道上具有很好的重复性和很高的精密度。 本器械具有广泛地应用，尤其是在工业的误差补偿和误差来源上。 关键词: 数控机床; 运动误差; 测量工具; 圆形测量法1、绪论 近年来，精加工方法已经吸引了许多研究人员的注意。 它的一个重要工作就是根据误差补偿和误差来源的诊断绘制出机床的测定体积误差的图形 1。现在的技术能够为每一部机器的轴测量参数的误差函数，例如定位和线性运动的精确性。 然而，它仍然难以精确地测量一个比较普通的圆形运动轨道的误差。 一些装置和方法通常被用来测量圆形运动的轨道准确性,描述如下： (1) 一根测试传感器条和直线探针 2。(2) 一个磁盘片 (或一个圆形计量器) 和二维探针 3。(3) 由在每个末端的曲形传感器条和二个被球形表面的特殊孔固定的磁性球组成的双球形传感器条系统 (DBB) 。当机器运动到圆形运动的时候，球之間的背离距离被曲形传感器条 测量出来 4和5。(4) 复纵线联接和二个旋转编码器在分离链接的根端部被分开，以便于探测链接的旋转角度6和7。(5) KGM 圆形测试系统 8。上述的器械和方法已经被用于估算圆形运动轨道的准确性，并且已经获得了一些成果。 但是正如一些研究员所指出的它在实际应用方面还存在一些问题 1和6 。而且在(1)和(2）上, 磁盘片的准确性还有局限性。在(3)上，只有在半径方向才能获得高精确性。 虽然(4)能够获得沿X-Y平面的x轴和y轴上的圆形运动误差(二维误差)，但是该器械非常复杂，而且很难制造。KGM 圆形测试系统,也被称为十字栅格编码器,它具有优良的性能, 但是它非常昂贵，而且最大测量区域只是一个大约半径120mm的圆形。本文介绍的是一种新的测量数控机床圆形运动误差的的方法和器械。 当机器停在能获得并掌握半径和角度的圆形轨道上的不同的点上时，x 轴和 y 轴的二维误差就能被测量出来。 而且，这一个方法在实际应用中既简单又方便，并且该器械成本低，结构紧凑。2、测量器械的外形图1是测量器械原型的示意图。它由一个与DDB相似的在末端有二个球的线性传感器条和一个放置在球1根部以探测旋转角度的旋转编码器组成, 球2通过支架连接到机床上。机器的底部有规则地固定在数控机床的工作台上，例如以机器中心的X-Y平面为基准。线性传感器的旋转平面平行于机床工作台的X-Y平面，垂直于心轴的旋转轴。测量相同结构时，若球1根部编码器的旋转轴被定为Z轴，那么与该轴平行的心轴就是Z方向。而X轴、Y轴则分别与机床平行，并且就是X方向、Y方向，因此X-Y平面就在线性传感器上。图1 原型测量示意图3、测量方法的原理机器移动时实际点的位置总是比要求的落后，因此为了要避免轴的伺服系统的速度延迟, 机器必须按这样的程序移动：点P(xi,yi) 沿着一个圆周移动并且在数秒之后停在真实的点 P(Xi,Yi)上，同时把线性传感器和旋转编码器得到的该点的位置数据传到计算机上。该线性传感器的精度是0.1 m。在HEIDENHAIN制造的该类型的旋转编码器为ROD 280,它能发出18000个正弦脉冲波。信号通过能在最多为4096的平方个脉冲波中区分出原始的正弦脉冲的IK220分类机传到计算机上。因此，角度