外文翻譯數(shù)控機床的核心及動力測量值的幾何誤差

1、畢業(yè)設計(論文)外文資料翻譯系部： 機械工程系 專 業(yè)： 機械工程及自動化 姓 名： 學 號： 外文出處： proceedings of spie vol. 4222 (2000) 0277-786x! 附 件： 1.外文資料譯文；2.外文原文。 指導教師評語： 簽名： 年 月 日附件1：外文資料翻譯譯文數(shù)控機床的核心及動力測量值的幾何誤差摘 要 在這篇論文中，介紹了一個用于測量數(shù)控機床上所有動力學方面幾何誤差的系統(tǒng)，并且給出了一些實驗結果。這些實驗結果表明了一些靜態(tài)與動態(tài)誤差特性間的重要差異。通過關于在動態(tài)信號運動或暫停時的分析，會發(fā)現(xiàn)數(shù)控機床上一些錯誤的方法。另外，用這個系統(tǒng)任何一種形態(tài)的

2、輪廓誤差可以被直接地測量而不需要用到一個球型金屬塊或者別的什么裝置，它可以提供一個簡單而又實用的估計數(shù)控機床輪廓誤差的方法。關鍵詞：機床用具度量衡 幾何誤差 動態(tài)測量1序言 在過去的幾年中，機床的校準對于機床的制造方和使用方來說變得愈加重要，每個國家都有它承認的標準去評估數(shù)控機床的性能13。然而，在這些標準中幾乎所有的幾何誤差都是在靜態(tài)或類似靜態(tài)的情形下被測量出的。換句話說，機器的軸被移動到特定的位置，停止轉動的時候被測量記錄的。這個過程明顯很耗費時間，也可能很耗費勞力。現(xiàn)今很多如惠普5529a激光測量系統(tǒng)和雷尼紹激光干涉系統(tǒng)的現(xiàn)代化測量系統(tǒng)提高了校準效率。這些校準包括自動收集信息，自動調調整

3、校準部分程序和機械補償參數(shù)。這些工具可以簡化校準過程，費較小的勞力。但是他們也不能克服只能在靜態(tài)情況下測量的限制。很長的測量周期加購買測量器械的花費使得整個校準過程異常昂貴。如果機械很大而且可能出現(xiàn)誤差的地方又多的話將會花費更多。眾所周知，一臺三軸機床有21處可能出現(xiàn)幾何誤差的地方需要測量。另外，當數(shù)控機床在工作狀態(tài)加工零件時，機床的靜態(tài)幾何誤差并不是表現(xiàn)出來的那么正確。機床是由機械部分、電部分和數(shù)字化部分等組成，每個組成部分都在一定的條件下起作用，比如速度，加速度，摩擦力，牽引力，能量變化等。所有因素都影響機床的正常工作狀態(tài)，并且機床的動力傳輸都假定在靜態(tài)狀態(tài)下。因此，有必要評估機床的動態(tài)性

4、能并且去研究精確地測量機床動態(tài)幾何誤差2動態(tài)測量系統(tǒng) 為了評估機床的動態(tài)性能，一個比較研究被正式納入從兩個基本調查中得出的結果。首先，機床的靜態(tài) 幾何誤差由惠普激光干涉儀測量。其次，同一臺機床的動態(tài)幾何誤差由house-built數(shù)據(jù)采集系統(tǒng)同時圖1 機床的動態(tài)幾何測量工作示意圖 采集，高轉速，基于時間的測量，來比較編碼器讀數(shù)與激光干涉儀讀數(shù)。圖1顯示了機床的動態(tài)幾何測量誤差的相關機構4。在這一動態(tài)測量系統(tǒng)中，使用zygo axiom 2/20激光干涉儀，因為它可以允許數(shù)控機床的工作臺或軸的移動速度達到1 .8m/min ，它是惠普激光系統(tǒng)的5倍速度。同時，house-built數(shù)據(jù)收集和處理

5、系統(tǒng)被使用。它主要由一個ariel dsp的接口卡與全局總線+數(shù)字接口和l6m的隨機存儲器，house-built控制電子，和一個使用c和visual basic軟件的pc接口組成。在機床動態(tài)測量的實驗中，模型monarch 45數(shù)控銑床加工中心被用作對象的測試。在開始測量前，當monarch數(shù)控銑床加工中心通電并處于一個靜態(tài)的情況下，整個數(shù)據(jù)采集系統(tǒng)開始收集數(shù)據(jù)。測量出的背景噪聲代表了測量系統(tǒng)本身的誤差和主軸的振動。許多實驗表明，當機床已適當調整過后，最大誤差小于0.5微米。3 .實驗結果和討論3.1靜態(tài)和動態(tài)測量值的對比 靜態(tài)測量，使用惠普5528激光干涉儀，三套的雙向測量是采取為每個線性

6、軸間隔50毫米。這些通過所有測量均在同一點的數(shù)據(jù)作為靜態(tài)測量的結果并為參照來和動態(tài)測量的結果作比較。對于動態(tài)測量，選擇不同的原料來找出是否一些動態(tài)幾何誤差與工作臺的移動速度有關系。在下面的動態(tài)實驗中，在工作臺以一個穩(wěn)定的速度移動后收集數(shù)據(jù)，以便消除工作臺加速度的影響。事實上，圖2 動態(tài)與靜態(tài)線性位移測量值的比較 加速度會產(chǎn)生巨大的動態(tài)誤差，尤其是當有一個更大的abbe偏移和一個更大的加速度。圖通常表明一些顯著性差異靜態(tài)和動態(tài)測量誤差的線性位移。圖2表明了一些靜態(tài)和動態(tài)測量誤差直線位移的差異。3.2噪聲測量 一個動態(tài)和靜態(tài)測量最明顯的區(qū)別是動態(tài)測量比靜態(tài)測量有更大的隨機變化，尤其是在圖2所示測量

7、直線位移誤差。這些隨機變化可稱為測量噪聲。噪音是由數(shù)控機床上許多不同種類的誤差引起的，如滾珠絲杠和螺母節(jié)距誤差，編碼器讀數(shù)誤差，工作臺傾斜引起的abbe誤差，激光測量系統(tǒng)誤差，主軸振動等。它可被視為一個反映了機床動態(tài)特性的參數(shù)。在我們的實驗中，在這臺機床上以不同運動速度，從100mm/mim至4000mm/mim，做同樣的實驗，這超過了獲得一個高定位精度的正常速度。通過所有這些實驗，我們發(fā)現(xiàn)測量噪聲與機床的進給速度幾乎沒有任何關系。通過fft分析，如圖3所示，我們發(fā)現(xiàn)測量噪聲的空間頻率約2.84毫米，這個現(xiàn)象可以進一步驗證圖3a是圖2的一部分。它可以得出結論， 滾珠絲杠或螺母可能是測量噪聲主要

8、來源。 a .動態(tài)測量噪聲 b.測量噪聲的fft分析 圖3 動態(tài)測量噪聲和fft分析3.3跳動誤差 當工作臺以一定的速度沿著x軸從0毫米位置至100毫米的位置， 停止移動一到兩秒鐘，然后回到0毫米的位置。以不同的速度重復幾次這個過程，我們反復觀察到約2微米的跳動誤差。從這些實驗中，也觀測到跳動誤差與工作臺的移動速度幾乎沒有任何關系。這個誤差是工作臺初始角度重新調整的動力引起的。當工作臺前后移動時，角度和直線測量的結果也顯示一個在水平方向上的跳動誤差。正因為導軌之間存在間隙，特別是在水平方向，動力方向引起工作臺傾向相反的方向傾斜，產(chǎn)生abbe跳動誤差。 3.4輪廓誤差 圖4. 用這個系統(tǒng)得到的輪

9、廓誤差 眾所周知，循環(huán)試驗提供了一個快速和高效的方式來測量機床沿圓形輪廓的輪廓精度。圓形輪廓提供一個最好的檢查輪廓的表現(xiàn)，當機床沿圓形軌跡加工時每根軸上都有一個正弦加速度，速度和位置的變化。因此，在所有的評估數(shù)控機床的標準中，圓形輪廓測試是一個關鍵組成部分。球型金屬塊被廣泛使用于這項測試。還有圓形擋板，十字網(wǎng)格編碼器等其他設備和工具。在這里，我們使用我們的發(fā)展動態(tài)測量系統(tǒng)，用x和y編碼器讀數(shù)作為時間函數(shù)，來獲得任何形狀的輪廓誤差。3.5數(shù)控機床的不完整運動當工作臺是移動到一個理想的位置，例如，不作任何停頓地移動到x軸100mm位置然后返回，實際上工作臺并沒有達到100mm點。實驗還表明，工作臺

10、的移動速度越來越高，實際位置和理想的位置之間的偏移量也隨之變得越來越大。停頓幾毫秒時間的控制模式可使工作臺移動到理想的位置。4.結束語使用商用激光干涉儀系統(tǒng)和house-built數(shù)據(jù)收集和處理系統(tǒng)，成功地檢測出了機床的靜態(tài)和動態(tài)幾何誤差。實驗結果顯示了一些靜態(tài)和動態(tài)誤差特性的重大差異。隨著對機床誤差而導致的測量噪聲改進，其他一些誤差被觀測出來，比如因為數(shù)控機床軸來回移動而產(chǎn)生的跳動誤差，因此有必要對數(shù)控機床的動態(tài)特性進行測量和評估。附件2：外文原文：quick and dynamic measurements of geometric errors of cnc machinesabstra

11、ctin this paper, a system that is used to measure dynamically all kinds of geometric errors of cnc machines is introduced, and some experiment results are given. the experiment results showed some significant differences between the static and dynamic error characteristics. through analyses of the d

12、ynamic signals in both time and space fields, some error resources of the cnc machines can be found. in addition, any shape of contouring errors can be directly measured by this system without using a ball bar or other devices, which provides a simple and practical way to evaluate contouring errors

13、of cnc machines. key words： machine tool metrology, geometric errors, and dynamic measurement1. introductioncalibration of machine tools has become increasingly important for both machine tool builders and users over the past few years, and each country has its own standard to evaluate the performan

14、ce of cnc machines 13 however, in these standards almost all the geometric errors are measured when cnc machines are in a static state or a quasi-static state. that is, the machine axis is moved to target positions, stopped and a measurement recorded. this process is obviously very time-consuming, a

15、nd may be labor-intensive. nowadays, many modern measurement systems, such as hp 5529a laser measurement system and renishaw laser interferometer system, provide features to improve the efficiency of calibration. these include automatic data collection facilities, and automatic generation and transf

16、er of the calibration part program and machine compensation parameters. these facilities can streamline the calibration process and make it less laborious, but they do not overcome the inherent time-intensive nature of the static calibration method. long measurement periods, together with the relati

17、vely high capital cost of the measurement equipment and machine, can make the whole calibration process costly. the problem is obviously compounded if the machine is large and many error components are to be measured. it is well known that for a three-axis machine tool, there are 21 potential geomet

18、ric errors that could be measured. in addition, parts are machined when cnc machines are in a dynamic state, measuring static geometric errors of machine tools does not totally represent the performance of them. as machine tools are a synthesis of mechanical, electrical, digital components etc., eac

19、h of these components reacts in a time-dependent way, such that, velocities, accelerations, frictional forces, drive forces, power source variations etc. all these influence the active state of the machine and the dynamic performance of the machine is hypothesized to be sufficiently distinct from th

20、e static in process control and inspection for industry, shulian zhang, wei gao, editors, proceedings of spie vol. 4222 (2000) 0277-786x!oo/$1 5.00performance. so it is necessary to evaluate the dynamic performance of machine tools and to study the methods of measuring the dynamic geometric errors o

21、f machine tools for precision applications.2. dynamic measurement system in order to evaluate the dynamic performance of machine tools, a comparative study is formalized incorporating the results from two basic inquiries. first, static geometric errors of the machine tool are ascertained using a hew

22、lett packard laser interferometer. second, dynamic geometric errors of the same machine tool are measured by using a house-built data acquisition system capable of simultaneous, high-speed, time-based measurements in order to compare encoder readings with laser interferometer readings. fig.1 shows t

23、he setup for dynamically measuring the geometric errors of machine tools4. in this dynamic measurement system, a zygo axiom 2/20 laser interferometer is used as it can permit the table or the axis of a cnc machine to move at a speed of 1 .8m/min, which is 5 times faster than a hp laser system. at th

24、e same time, a house-built data collecting and processing system is used. it mainly consists of an ariel dsp interface card with a globalbus+digital interface and l6mwords of ram, house-built control electronics, and a developed pc interface using c and visual basic software. in the experiment of dy

25、namic machine tool measurement, the model monarch 45 cnc milling center is used as the object of testing. before starting measurement, the whole data acquisition system starts to collect data with the monarch cnc milling machine center table being in a static status and with power on. the measuremen

26、t background noise represents the errors of the measurement system itself and the vibration of the spindle. many experiments showed that the maximum error is less than half a micrometer when the z driver has been adjusted properly.3. experiment results and discussions3.1 comparison between static an

27、d dynamic measurementsfor the static measurements, three sets of bi-directional measurements are taken for each linear axis at an interval of 50mm by using the hp 5528 a laser interferometer. the data through averaging all measurements at the same point is used as the result for the static measureme

28、nt and as a reference to compare with the dynamic measurement results. for the dynamic measurements, different feed rates are chosen to find out whether or not some dynamic geometric errors have a relationship with the speed of the moving table. in the following dynamic experiments, the data are col

29、lected after the table moves at a stable speed to eliminate the influence of the acceleration of the moving table. in fact, acceleration can produce great dynamic errors for cnc machines, especially when there is a greater abbe offset and a larger acceleration. fig.2 typically shows some significant

30、 differences between static and dynamic errors for measuring the linear displacement. 3.2 measurement noise one of the most obvious differences between dynamic and static measurement is that dynamic measurement has much larger random variations than static measurement, especially in the measurement

31、of linear displacement errors shown in fig.2. these random variations may be called measurement noise. the noise is produced by many different kinds of errors in cnc machines, such as, the pitch errors of the ballscrew and the nut, encoder reading errors, abbe error variations caused by the table ti

32、lt, laser measurement system errors, vibration of the spindle etc. it may be considered as one of parameters that reflect the dynamic characteristics of machine tools. in our case, the same kind of experiment is done with different moving speed ranging largely from 100mm/min to 4000 mm/min that exce

33、eds the normal speed of getting a good position accuracy in this machine. through all these experiments, it is found that measurement noise nearly has nothing to do with the feed rate of the machine. through a fft analysis, it is found that measurement noise has a spatial frequency of about 2.84mm s

34、hown in fig.3b, and this phenomena can be further verified in fig.3a that is one part of fig.2. it can be concluded that the ballscrew or the nut is likely the main source of the measurement noise.3.3 jump errorswhen the table is moving along the x-axis at a certain speed from 0mm position to 100mm

35、position, it stops for one or two seconds and then is traveling back to 0mm position. this procedure with different moving speeds is repeated several times and an obvious jump error of about two micrometers is observed repeatedly. from these experiments, it is also observed that the jump error has n

36、early nothing to do with the speed of the moving table. this error is mainly caused by the initial table angular readjustment induced by dynamic forces. the results of both angular and straightness measurements also show obviously an angular jump in horizontal direction at the return point when the

37、table moves forth and back. as there is a gap between the slides, especially in horizontal direction, the direction of the dynamic force induces a table tilt in the opposite direction and produces an abbe error jump.3.4 contouring errorsit is well known that circular tests provide a rapid and effici

38、ent way of measuring a machine tool's contouring accuracy along a circular contour. circular contours provide one of the best checks for contouring performance in that as a machine is traversing with multiple axes along a circular trajectory each axis goes through sinusoidal acceleration, velocity, and position changes. so in all standards for evaluating cnc machines, circular contour test is a key part. a ball bar is widely used for this purpose. other devices and instruments include circular masks, cross grid encoders. here, we use our