英语翻译原文-基于交叉网格编码为数控机床的运动精度的多步测量方法的发展

1、编号： 毕业设计(论文)外文翻译原文Development of a multi-step measuring method for motion accuracy of NC machine tools based on cross grid encoder基于交叉网格编码为数控机床的运动精度的多步测量方法的开展院 系： 机电工程学院 专 业： 机械设计制造及其自动化 学生姓名： 学 号： 指导教师单位： 机械制造及其自动化教研室 姓 名： 职 称： 教授 2012 年 5 月 21 日Development of a multi-step measuring method for moti

2、on accuracy of NC machine tools based on cross grid encoderAbstractMachining accuracy is directly influenced by the quasi-static errors of a machine tool. Since machine errors have a direct effect on both the surface finish and geometric shape of the finished work piece, it is imperative to measure

3、the machine errors and to compensate for them. A revised geometric synthetic error modeling, measurement and identification method of 3-axis machine tool by using a cross grid encoder is proposed in this paper. Firstly a revised synthetic error model of 21 geometric error components of the 3-axis NC

4、 machine tools is developed. Also the mapping relationship between the error component and radial motion error of round work piece manufactured on the NC machine tools are deduced. Aiming to overcome the solution singularity shortcoming of traditional error component identification method, a new mul

5、ti-step identification method of error component by using the cross grid encoder measurement technology is proposed based on the kinematic error model of NC machine tool. Finally the experimental validation of the above modeling and identification method is carried out in the 3-axis CNC vertical mac

6、hining center. The entire error components have been successfully measured by the above method. The whole measuring time of 21 error components is cut down to 12 h because of easy installation, adjustment, operation and the characteristics of non- contact measurement. It usually takes days of machin

7、e down time and needs an experienced operator when using other measuring methods. Result shows that the modeling and the multi-step identification methods are very suitable for on machine measurement.Keywords: Cross Grid Encoder； Geometric motion error； Modeling Sequential identification； CNC Machin

8、e tool1 IntroductionNC machine tools are one of the most important components in modern manufacturing facilities and high-performance machines are required. Machine-tool motion accuracy has a significant influence on the quality of the machining operations and, therefore, the development of a curren

9、t measurement and evaluation methods has become a significant research subject. Generally, there are three major types of errors, which are known as geometric, thermal and cutting-force induced errors. However, geometric errors make up the major part of the inaccuracy of a machine tool. Thus modelin

10、g and identification of geometric errors are the key steps in error measurement and compensation for machine tools. The style of error model and accuracy of error identification greatly affect the precision of error measurement and compensation.For NC machine tools, the radial error of circular moti

11、on is the comprehensive function result of all the error components of link: worktable, sliding table and main spindle block. How to identify each single error component from the radial error is the key to find the error sources. Therefore a great amount of work, over the last decade, has gone into

12、this area. Studies on machine accuracy tests have been carried out by many authors.Week HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib1#bib1 1 developed a method using a laser beam and a four quadrant photodiode to measure the radial error-motion of a rotating table of a gea

13、r hobbing machine, and the parallelism between the rotating axis and a linear guide-way. Thus, Zhang et al. HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib2#bib2 2 developed a displacement method to assess the 21 error components based on laser interferometer. Charles Wang HY

14、PERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib3#bib3 3 developed this measuring method using laser interferometer, named Laser Doppler Displacement Meter (LDDM), and invented a new error identification methodstepped volumetric diagonal measuring method based on this measuremen

15、t system. A hybrid on-line and off-line method for identifying machine geometric error components was presented by Ni and Wu HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib4#bib4 4. The method utilizes a multi-degree-of-freedom optical laser system, to simultaneously measure

16、multiple geometric errors. I was awa et al. developed a circular motion measurement device that employs an optical fiber-type laser displacement interferometer HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib5#bib5 5. The capability of the measurement instrument was demonstrat

17、ed for not only circular motion but also positioning accuracy measurement in a two-dimensional plane.Chen et al. HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib6#bib6 6 and Florussen HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib7#bib7 7 gave a displa

18、cement measurement approach for machine geometric error assessment in 2001 respectively. Lee and Yang HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib8#bib8 8 measured the geometric errors in a miniaturized machine tool using capacitance sensors in 2005.The double ball bar (DB

19、B) method HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib9#bib9 9 and HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib10#bib10 10 is widely used for dynamic circle path measurement of NC machine tools. The DBB method seems to be an excellent measurement

20、 method, because it is simple and versatile, and has been adopted as circular test method in standards and directives for inspecting machine tools, such as ISO 230-4 ,VDI/DGQ 3441 and GB/T 17421-4. Furthermore, multi-axis NC machine tools have recently come into wide use. Therefore, accuracy evaluat

21、ion using the DBB method requires much more complicated measurement procedures and analytical methods. More recent research is by Lai et al. HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib11#bib11 11 who proposed the identification method of 3-axis machine tool based on Doubl

22、e Ball Bar in 1997. Meanwhile, Schmitz and Ziegert developed an instrument HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib12#bib12 12 capable of measuring arbitrary, dynamic CNC tool paths through three-dimensional space by simultaneous trilateration with three laser ball bar

23、s (LBBs) HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib13#bib13 13. This method allows for the measurement of step, corkscrew, and oblique circle paths.In an effort to shorten machining time, high-feed machining has become common, particularly in die manufacturing. Thus, a m

24、easuring method that incorporates a cross grid encoder, which uses a cross grid scale, has been developed for arbitrary tool-path measurements in a two-dimensional plane HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib14#bib14 14. Rehsteiner and Weikert employed the cross grid

25、 scale to measure the motion accuracy of machine tools HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib15#bib15 15. A cross-grid encoder is a very precise measurement instrument, but its use is limited to two-dimensional planes. W. Knapp HYPERLINK :/ sciencedirect /science/art

26、icle/pii/S0890695509002387 l bib16#bib16 16 developed this measuring method named KGM+ system; he equipped an optical sensor in the Z-axis, which can measure the distance vibration in the Z-axis.In recent years, many Multi-Degree-of-Freedom Measuring Systems (MDFMS) HYPERLINK :/ sciencedirect /scien

27、ce/article/pii/S0890695509002387 l bib17#bib17 17 have been developed and applied in many industrial areas. A 6 degree measuring system (6DMS) HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib18#bib18 18 is developed in Taiwan Univ., which can measure all the errors of the 6 de

28、grees at the same time on the linear work table. Tohoku Univ. invented an atomic force microscope (AFM) HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib19#bib19 19 system, which is useful for large-area measurement with a spiral scanning strategy. What is more, a measurement i

29、nstrument developed by Qiu et al. HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib20#bib20 20 and HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib21#bib21 21 resembles an instrument in the point that both use rotary encoders. Nakao et al. developed an in

30、strument capable of measuring three-dimensional tool paths by means of a parallel mechanism HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib22#bib22 22. However, this instrument is unsuitable for accuracy measurement of a rapidly varying dynamic motion, because the upper part

31、of the parallel mechanism, which is rather heavy, is attached to the machine-tool spindle.In the field of error components identification, Zhang and Zang HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib23#bib23 23 gave a new machine tool geometric error identifying method with

32、 one-dimensional balls array. In 1994, Kruth HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib24#bib24 24 proposed a self-calibration method. It makes use of a two-dimensional ball disk to realize the CMM geometric errors identification. In 1995, Mou and Liu HYPERLINK :/ scienc

33、edirect /science/article/pii/S0890695509002387 l bib25#bib25 25 estimated the machine tools geometric errors by measuring the size and shape of the work piece. 9 HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib26#bib26 26, 14 HYPERLINK :/ sciencedirect /science/article/pii/S08

34、90695509002387 l bib27#bib27 27, 15 HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib28#bib28 28 and 22 HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib29#bib29 29 lines error identification methods had been proposed sequentially in the last century. In 1

35、999, Chen et al. HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib30#bib30 30 developed a laser interferometer automatic alignment device, which can increase the measuring speed in use of 22 lines error identification method. Charles Wang et al. HYPERLINK :/ sciencedirect /scie

36、nce/article/pii/S0890695509002387 l bib31#bib31 31 put forward a sequential volumetric diagonal measuring method, which improved the displacement error identification speed dramatically. Hong et al. HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib32#bib32 32, successfully dete

37、cted each motion error resource in use of standard test barmicro-displacement encoder sensor measuring system. To sum up, most of the error identification methods mentioned above are based on the least square method (LSM) in setting the mathematical model of the machine tools HYPERLINK :/ sciencedir

38、ect /science/article/pii/S0890695509002387 l bib10#bib10 10 and HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib33#bib33 33. However the matrix of measurement equation is not full rank, which causes the solution to be not unique. In addition the complete mapping of all geometr

39、ic error components is very time consuming.The measuring methods mentioned above are extensively applied in machine error measurement, yet all of them have some disadvantages. For example, laser interferometer has large measuring length, vertical and horizontal, yet laser wave length considerably de

40、pends on the temperature, humidity, air pressure and air circulation. The result is extremely dependent on the environmental conditions. In use of Double Ball Bar to measure an arbitrary tool path is not possible, because the extensible range of the bar hold with two magnetic sockets is only about 2

41、0 mm. The system cannot evaluate servo-induced errors in machine tools in small-radius circular and square corner programmed test paths. Geometrical deviations such as squareness error between two axes must be evaluated by circular deviation, because the extensible range of the bar is small. On the

42、other hand, most of the measuring methods are contact measuring methods, and can only be used in low speed motion. The dynamic characteristics of machine tools cannot be indentified accurately. Whats more, the installation, adjustment and operation are very difficult and time consuming.Aiming to ove

43、rcome the shortcoming of traditional error component identification methods, a new measuring methodcross grid encoder (KGM) measurement system and a revised synthetic error model is proposed. KGM measuring system is developed by HEIDENHAIN. For precision machining it is convenient to measure and com

44、pensate for deviations in high speed dynamic motion with a non-contact measuring method. Standards and directives for inspecting machine tools, such as ISO 230-2, ISO 230-3, ISO 230-4 and VDI/DGQ 3441, stipulate a number of measuring methods for determining static and dynamic deviations. In combinat

45、ion with evaluation software, measuring systems for inspection and acceptance testing of machine tools make precise and informative measurements of the machine possible with a minimum of mounting and adjustment efforts. Furthermore, the mapping relationship between the error components and radial mo

46、tion error of circular work piece manufactured on the NC machine tools are deduced. According the mapping relationship, a new error component multi-step identification method by using the cross grid encoder measurement technology is based on the kinematic error model of NC machine tool.The measureme

47、nt device enables arbitrary NC tool-path measurements in two-dimensional space. The simple mechanical structure of the device enables a lightweight configuration and low-cost manufacture. In the future, the instrument is expected to find application in measurement for modern multi-axis NC machine to

48、ols.2. Geometric error components of 3-axis NC machine toolThe positioning error in an arbitrary point within the machine working volume is composed of the positioning errors of the individual axes. In a rigid body motion there are six different geometric errors of a single axis as shown in HYPERLIN

49、K :/ sciencedirect /science/article/pii/S0890695509002387 l fig1#fig1 Fig. 1 (namely, the linear displacement error, the straightness errorshorizontal and vertical and the angular errorspitch, yaw and roll). The basic structure of machine tool can be simplified into three mutually perpendicular Coor

50、dinate axis, and through slideguide way system and the rotating component to achieve relative movement between cutting tool and the work piece. Hence for a three-axis machine tool there are 18 errors plus the three squareness errors in the individual machine coordinate planes. Therefore, there are t

51、otally 21 geometric error components in 3-axis CNC machine tool mentioned in HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l tbl1#tbl1 Table 1, where is the linear error, subscript gives the error direction and the position coordinate is inside the parenthesis; is the angular err

52、or, subscript is the axis of rotation and the position coordinate is inside the parenthesis.Fig. 1. Six error components in x-axis.Table 1. 21 geometric error components in 3-axis CNC machine tool.Error componentLinear displacement errorsAngular errors Roll, Pitch and Yawx-AxisX (x)Y (x)Z (x)X (x)Y

53、(x)Z (x)y-AxisX (y)Y (y)Z (y)X (y)Y (y)Z (y)z-AxisX (z)Y (z)Z (z)X (z)Y (z)Z (z)Squareness errorxy,yz,zx3. Kinematic modeling of 3-axis NC machine toolAssume that: (1) all the machine components are rigid bodies; (2) angular error in tow components is very small compared to the angle between the two

54、 components; (3) consider only the one degree terms of the error equation; (4) consider only the static errors.3.1. Homogeneous transformation matrix of 3-axis machine toolThe total displacement of a target point in the rigid body can be considered as the vector stacking of its angular displacement

55、and linear displacement of the reference point in the rigid body. In the process of analysis and synthesis, the homogeneous transformation matrix (HTM) method is widely used to describe relationship between two coordinates as it is easy to understand and calculate. Homogeneous transformation matrix

56、is a 44 matrix in three-dimensional space, which can be the transformation matrix of a point between two different coordinates.In the normal kinematic modeling process of NC machine tool HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib14#bib14 14, HYPERLINK :/ sciencedirect /s

57、cience/article/pii/S0890695509002387 l bib34#bib34 34 and HYPERLINK :/ sciencedirect /science/article/pii/S0890695509002387 l bib35#bib35 35, it is considered that squareness errors only affect the transformational matrices. However, in the high precision motion error measurement of NC machine tools

58、, the influence of rotational error component affected by squareness error should be considered. Therefore, the HTM coming from the squareness errors xy, yz, xz among the 3 slides can be expressed as follows:The typical 3-axis vertical NC machine tool is shown as HYPERLINK :/ sciencedirect /science/

59、article/pii/S0890695509002387 l fig2#fig2 Fig. 2, which includes worktable (X-slide), sliding table (Y-slide) and the main spindle block (Z-slide), etc. Define the absolute reference coordinate system AS on the bed of machine tool, and define the relative coordinate frames BS, CS and DS on the slidi

60、ng table, worktable and main spindle block, respectively. Suppose that error components exist widely in the sliding table, worktable and main spindle block. Therefore, when the sliding table goes along the Y-slide with moving distance y, the HTM TAB represents the transformation of sliding table coo