外文翻譯---三坐標測量機測頭的誤差校準

1、<p><b>　　附錄2</b></p><p>　　Study and Design no Automation Control System of the Thermal Power Unit from the System Point of view.</p><p>　　Tian Jianyan liu sifeng Pan lizh

2、en</p><p>　　（1. Nanjing University of Aeronautics and Astronautics ,Nanjing 210016 China)</p><p>　?。?. Taiyuan University of Technology ,Taiyuan 030024 China)</p><p>　　Abstract: Fr

3、om the system point of view, the feature of the thermal power unit and the demand on its control system are analyzed and research in details in this paper. The character that the boils and the steam turbine are a whole o

4、f relative independence is fully considered. By coordinate control, the purpose of the optimal whole operating effect of the system is realize adopting the key techniques of communication, computer and intelligent inform

5、ation process etc.... The adaptation and whole p</p><p>　　1Introduction</p><p>　　The system is an organic whole certain structure and function ,which consists of several element with interrelati

6、on , interdependence and interplay .The thermal power unit is a typical system ,composed of generator ,steam turbine ,boiler and many anxiliary equipment .Its main function is to produce the power load according to powe

7、r network requirement .System engineering is the science used to study and design the complex system .In the meantime, It is also the theory and method used to deal wi</p><p>　　2 Study and Design on Automati

8、on Control System of the Thermal Power unit from the System Point of View </p><p>　　2.1 Function of Automation Control System of the Power unit </p><p>　　At first the thermal power unit as the c

9、ontrolled object is deeply studied before its automation control system is studied and designed .The thermal power unit is a huge group of equipments ,which is composed of generator, ,steam turbine ,boiler and many auxil

10、iary equipments. Its process flow is complex and pipelines intervenient .Especially the large-scale power unit is a typical coupling ,nonlinear ,varying complex controlled object with multi-input and multi-output .Thous

11、ands of parameters a</p><p>　?。?.）Load control :Along with the increase of the unit capacity ,early load control mode of “boiler follows steam turbine ”or “steam turbine follows boiler ” has not already sati

12、sfied the requirements so we must adopt more suitable load control scheme ,which is the unit coordinate control .</p><p>　?。?.）Reliability: The design of system must be reliable, ensuring safe and economic

13、operation of the unit .In addition, The tolerance fault, redundant technology ,self-diagnosis of software and hardware must be adopted to improve the reliability of system .</p><p>　?。?.）Communication and m

14、an-machine interface: Because there are many parameters need to be measured and controlled and its varying speed is quick when the large scale unit is running , communication system must have quick real-time response an

15、d high reliability ;man-machine interface must be good at the operator station including operating terminal and large-area display that provides synthetic menus and information about the whole production process for the

16、operators. </p><p>　　2.2 Structure of Automation Control system of the power unit </p><p>　　The design of automation control system of thermal power unit mainly includes control, alarm monito

17、r, protect etc . In accordance with the above analysis .So we divide the complex system into several subsystems in order to make the whole system optimal .</p><p>　?。?.）Data acquisition system(DAS):It is in

18、formation center of whole system and provides credible rapid objective operating records ,which is the base of safe and economical operating of equipments .Function of ,print of accident list and incident review ,prope

19、rty calculate ,operate guidance etc…</p><p>　?。?）Boiler control system :Boiler control system such as boiler combustion ,steam temperature ,feedwater ,auxiliary control system and the boiler safe supervisor

20、y system and boiler combustion management system. There subsystem coordinate each other and make boiler operate in safe ,efficient and steady state to satisfy the load instruction of power network in various operating mo

21、des .</p><p>　?。?.）Steam turbine control system :Steam turbine control system realizes load control and rotative velocity control of steam turbine by DEH (Digital Electro-Hydraulic ).In addition ,the auxilia

22、ry system of steam turbine include the deoxygenation water lever control ,deoxygenation pressure control ,the condenser hot well water level control and the heater water lever control etc </p><p>　　（4.）Aux

23、iliary system :Besides the main systems mentioned above ,the auxiliary system also has by-pass control system etc…</p><p>　　The main system and auxiliary system are a organic whole through close connection o

24、f information communication network .They are inter-permeable and .Inter-dependent so as to form the main part of the automation control system of the large-scale unit.</p><p>　　2.3 Design of Automation Cont

25、rol System of the Thermal Power Unit </p><p>　　From the system point of view, we analyze and study the principle of two basic feedback control method early that “boiler follows steam turbine” and “steam turb

26、ine follows boiler” in order to find out the existent problem ad be able to design more reasonable control method.</p><p>　　2.3.1 Boiler follows steam turbine mode </p><p>　　This kind of control

27、 mode is first to let steam turbine trail the needs of power network load ,then let boiler trail steam turbine .Its advantage is to be able to fully use the heat accumulation of boiler ,make the unit meet the change of p

28、ower network load comparatively quickly.. But because the inertia and delay of boiler are greater ,the regulation of former turbine pressure pt cannot follow the speed of load regulation, thus pt has greater fluctuation,

29、 which is disadvantageous to the steady </p><p>　　2.3.2. Steam turbine follows boiler mode </p><p>　　This kind of control mode is first to let boiler train the needs of power network load, then

30、let steam turbine train boiler .It can be better to maintain steam pressure stabilize and beneficial to boiler steady operation .But it do not fully utilize the heat accumulation f boiler to regulate the unit’s output ,i

31、t is more slowly that the unit meets the load’s demand ,so this control mode is only to be applied to the unit undertaking basic load .</p><p>　　2.3.3 Coordinate control mod</p><p>　　According t

32、o the analysis above, it must use the heat accumulation of boiler fully and reasonably when the unit has better adaptability to power network load in safe operation. That is to let former turbine pressure changes, then t

33、o coordinate the interaction between two loops of power regulation and pressure regulation reasonably, so that unit's output meets the needs of the power network load promptly, and guarantee the control demand of uni

34、t steady operation. The practical method is to lead i</p><p>　　2.3.3.1. Basic function of coordinate control system. </p><p>　　Coordinate control system of the thermal power unit should usually

35、have following function:(l) select different load instruction according to the unit operating condition and the requirement of power network for the unit.(2) restrict the change rate of load instruction.(3). Calculate th

36、e biggest possible output of the unit and restrict the biggest and minimum amplitude of load.(4). Have the function of RUNBACK.(5). Select different running mode according to the unit operating condition.(6). Calc</p&

37、gt;<p>　　2.3.3.2 Basic composition of coordinate control system of the unit.</p><p>　　Now the coordinate control system of the unit is composed of two parts, which are load instruction process and coo

38、rdinate control of boiler and steam turbine, shown as fig.1. </p><p>　　Fig.1 Unit Coordinate Control System</p><p>　　In which, load instruction process is composed of unit calculation loop, unit

39、 Allowed load calculation loop and load restriction loop. Coordinate and steam turbine controller.</p><p>　　2.3.3.3. Implementation of coordinate control system of the thermal power unit Modern large-scale t

40、hermal power unit adopts distributed control system to realize the unit automation control that guarantees safe economic operation of the unit. TEKEPERM-ME of SIEMENS is chosen to realize coordinate control system of the

41、 thermal power unit including several parts shown as Fig.2.</p><p>　　Fig 2 Implementation diagram of unit coordinate control system</p><p>　　When each subsystem of the unit normally run, start t

42、he mode of coordinate control mode. In this mode , steam turbine and boiler accept load instruction in parallel. Boiler maintains main steam pressure through changing combustion rate, and steam turbine pressure and set v

43、alue. When the deviation of former turbine pressure and set value exceeds certain limit value, open degree instruction of steam value given by steam turbine main control loop is restricted, up to this deviation within th

44、e press</p><p>　　3. Conclusion. </p><p>　　In one word, from the system point of view, the automation control system of the thermal power unit is divided into several subsystems as well as the de

45、sign and implementation of unit coordinate control system is demonstrated in this paper. The large scale unit coordinate control has faster trailing performance and better stability and robustness. The purpose of the opt

46、imal whole operation effect of the unit is realized by coordinate the subsystems.</p><p><b>　　Reference</b></p><p>　　[1]Xiong Shuyan , Wangxingye ,Tianyan .Distributed Control System

47、 of thermal power plant ,Scientific Press .</p><p>　　Beijing P.R China ,20003 </p><p>　　[2] Zhong xinyuan .Application of DEB Coordinated Control System in Thermal power plants ,electric power S

48、cience And Engineering ,2003(3):50-53.</p><p>　　Author Biographies </p><p>　　Jianyan Tian , associate professor ,is a Doctoral student in Nanjing University of Aeronautics and Astronautics .Her

49、research is aimed at intelligent control ,System Engineering and Grey System theory .</p><p>　　Lizhen pan is a student for Master Degree in 2002 .Her research is aimed at intelligent control theory and its

50、application.</p><p><b>　　附錄3</b></p><p>　　三坐標測量機測頭的誤差校準</p><p>　　內容摘要:經過幾十年的快速發(fā)展，坐標測量技術已臻成熟，測量精度得到極大提高，測量軟件功能更加強大，操作界面也日益完善，生產廠家遍布全球，開發(fā)出了適于不同用途的三坐標測量機型。幾十年的發(fā)展充分證明，現(xiàn)代三坐標測

51、量系統(tǒng)打破了傳統(tǒng)的測量模式，具有通用、靈活、高效等特點，可以通過計算機控制完成各種復雜零件的測量，符合機械制造業(yè)中柔性自動化發(fā)展的需要，能夠滿足現(xiàn)代生產對測量技術提出的高精度、高效率要求。 除用于空間尺寸及形位誤差的測量外，應用坐標測量機對未知數學模型的復雜曲面進行測量，提取復雜曲面的原始形狀信息，重構被測曲面，實現(xiàn)被測曲面的數字化，不僅是坐標測量機應用的一個重要領域，也是反求工程中的關鍵技術之一，近年來也得到快速發(fā)展。<

52、;/p><p>　　關鍵詞：補償誤差 探針 找正 校準 三維特性 觸發(fā)</p><p><b>　　坐標測量機及其特點</b></p><p>　　坐標測量機是一種具有很強柔性的尺寸測量設備，CMM在工業(yè)界的應用開始于對棱柱零件的快速、精確測量。但隨著CMM各方面技術的發(fā)展（如回轉工作觸發(fā)式測頭的產生），特別是計算機的CMM的出現(xiàn)，目前

53、，CMM已廣泛應用于對各類零件的自動檢測。與投影儀、輪廓測量儀、圓度測量儀、激光測量儀等比較，CMM具有適應性強，功能完善等特點。坐標測量機的出現(xiàn)，不僅提高了檢測設備的水平，而且在自動化檢測中也是一個生重要的突破。</p><p>　　CMM在自動化程度方面有很大的差別。計算機控制的CMM具有自動執(zhí)行檢測、分析檢測數據和輸出檢測結果的功能，而一般的CMM僅有手動控制功能或手動控制加示教功能。目前，隨著計算機硬件性

54、能的提高和價格降低，絕大部分CMM均配有計算機，利用計算機可對測量所得的數據進行在線分析，以判別被控件是否合格。同時也可以使用統(tǒng)計技術來確定工藝能力是否滿足，分析誤差等來源。</p><p>　　除了再質量檢測方面使用CMM外，CMM還可以用于對實物的仿物的信制加工中，即所謂逆向工程。在這種情況下，由CMM測量實際工件，并將測量所得的數據傳到系統(tǒng)中，由CAD/CAM系統(tǒng)對這些數據進行加工處理，建立CAD模型，并進

55、一步生成加工指令來指導加工。 CMM測頭</p><p>　　測頭是CMM非常重要的部件，可以這樣說，測頭的發(fā)展先進程度就標志著CMM的發(fā)展先進程度。CMM可以配置不同類型的測頭傳感器。接觸類的測頭主要包括觸發(fā)式、模擬式兩種。非接觸式包括激光三角測量、激光成像、機器視覺等。最初人們使用CMM時，由操作人員移動坐標軸，所用的測頭是剛性的，當剛性測頭以一定的接觸力接觸到被測表面時，人為記錄下各坐標軸的坐標值

56、。這種初期的 CMM不可能具有自動檢測的能力，使用范圍受到了極大的限制。但是由于它具有了三坐標的雛形，在使用測頭鉆孔的位置時也相當有效。</p><p>　　CMM能被廣泛地應用，其主要的一個原因是發(fā)明了觸發(fā)式測頭，觸發(fā)式測頭的最大功能是它的觸發(fā)功能，即當探針接觸被測表面并有一定的微笑位移時，測頭就發(fā)出一電信號，利用此信號可以立即鎖定當前坐標軸的位置，從而自動記錄坐標值。觸發(fā)式測頭是由雷尼紹公司發(fā)明的，現(xiàn)在該公司

57、生產一系列的觸發(fā)式測頭，可用于CNC加工中心，雷尼紹公司的生產的CMM測頭現(xiàn)已成為行業(yè)標準配置，廣泛地用于各大生產廠家的CMM上。</p><p>　　常見的測頭再運動學上，探針處于由三個圓柱棒6個球組成的6個觸點唯一確定的位置上，用一個輕型的有參緊力的彈簧維持這一位置。6個 觸點圖中的方式依次連接，并接一個恒定電流電源。當探針接觸被測表面，并產生微小位移時，6個觸點中將有一個或一個以上的觸點斷開，從而使回路中的

58、電阻迅速增大。當回路中的電阻增大到一定數值時，兩端超過一定數值的電壓將將起到開關電路發(fā)出信號。利用此信號就可以讀取當前的測量位置數據。這種測頭的特點是具有三維特性，即X,Y,Z三個方向的移動接觸均能引起觸發(fā)。因此，可以從不同的方向接觸被測表面，而不會影響測量結果。</p><p>　　在觸發(fā)式測頭進行測量的過程中，探針必須偏移一個固定的數量才會觸發(fā)開關，因此，測量結果中要對這段偏移進行補償。探針接觸被測表面后，為

59、了避免移動過量而折段，探針需要反方向退出一定距離。因此測量速度比硬探頭掃描測量速度低。</p><p>　　CMM是用探針端部球的中心坐標值作為點的輸入數據。因此，在測量時必須用恰當的方法推斷測頭端部球與被測零件的觸點位置。在非CAD指導的檢測系統(tǒng)中，通常在觸點附近作三點測量，從而近似地找出通過該三點的平面法線，這不僅要耗費很多時間，從而測量精度也比較低。在CAD指導的檢測系統(tǒng)中可以根據被測工件的CAD模型直接計

60、算出被測點法向，讓測頭從法向接觸被測點，這樣就比較容易判斷觸點的位置。如圖所為觸點坐標，為測頭端部球心坐標，8，a分別為測點法向與z軸夾角及法向在xy平面內投影與y軸夾角，則接觸點的坐標可表示為：</p><p>　　x=x’-R sinB.sina</p><p>　　y=x’-R sinb.sina</p><p>　　z=X’-R sinb.sina</

61、p><p>　　圖所示為探針的形狀。它的作用是為紅寶石球提供一個固定的支撐，當探針接觸被測表面時，探針的微笑移動可觸發(fā)開關，從而發(fā)出信號。探針有不同的類型。如圖所示，根據不同的需要可以選擇不同的類型的探針。為了獲得較高的測量精度，建議在實際測量時遵循以下兩條原則：1、盡量使用長度短的和剛性好的探針。測量時探針的彎曲越大，偏移越大，測量的重復精度就越低。2、盡量選用直徑大的紅寶石探針。選用直徑大的紅寶石探針，一方面可以

62、減小加工表面缺陷時測量精度的影響，另一方面可以增大探針的有效工作長度。如圖7-8所示。</p><p>　　1 測頭的分類 測量頭作為測量傳感器，是坐標測量系統(tǒng)中非常重要的部件。三坐標測量機的工作效率、精度與測量頭密切相關，沒有先進的測量頭，就無法發(fā)揮測量機的卓越功能。坐標測量機的發(fā)展促進了新型測頭的研制，新型測頭的開發(fā)又進一步擴大了測量機的應用范圍。按測量方法，可將測頭分為接觸式（觸發(fā)式）和非接觸式兩

63、大類。觸發(fā)式測量頭又分為機械接觸式測頭和電氣接觸式測頭；非接觸式測頭則包括光學顯微鏡、電視掃描頭及激光掃描頭等。本文討論的重點為觸發(fā)式測頭。 (1)機械接觸式測頭 接觸式測頭又稱為“剛性測頭”、“硬測頭”，一般用于“靜態(tài)”測量，大多作為接觸元件使用。這種測頭沒有傳感系統(tǒng)，無量程、不發(fā)訊，只是一個純機械式接觸頭。機械接觸式測頭主要用于手動測量。由于人工直接操作，故測頭的測量力不易控制，只適于作一般精度的測量。由于其明顯

64、的缺點，目前這種測頭已很少使用。 (2)電氣接觸式測頭 電氣接觸式測頭又稱為“軟測頭”，適于動態(tài)測量。這種測頭作為測量傳感器，是唯一與工件接觸的部件，每測量一個點時，測頭傳感部分總有一個“接觸—偏轉—發(fā)訊—回復”的過程，測頭的測端與</p><p><b>　?。?）探針的校準</b></p><p>　　在對工件進行實際檢測之前，首先要對測量過程

65、中用到的探針進行校準。因為在許多尺寸的測量當中需要沿不同的方向進行探測，系統(tǒng)記錄的是探針中心的坐標而不是接觸點的坐標。為了獲得接觸點的坐標，必須對探針半徑進行補償。因此首先必須對探針進行校準。一般使用校準球來校準探針。校準球是一個已知直徑的校準球，校準探針的過程實際上就是對這個已知直徑的標準進行測量直徑的過程，如圖7-1所示。該球的測量值等于校準球的直徑加探針直徑，這樣也就可以確定探針直徑，將探針直徑除以2，得出探針半徑，系統(tǒng)用這個值就

66、可以對測量結果進行補償。校準的具體操作步驟一般如下：將探頭正確的安裝在CMM的主軸上；將探針在工件表面移動，看是否均能測得到，檢查探針是否清潔。記住，一旦探針的位置發(fā)生改變，就必須重新校準；將校準球裝在工作臺上，要確保不用移動校準球上打點，測點當選最少為五個；給定的點當數測完后，就可以得到測量所得的校準球的位置、直徑、形狀偏差，由此可以得到探針的半徑值。</p><p>　　測量過程中所有要用到的探針都要進行校準

67、，而且一旦探針改變位置，或者取下后下次再用時要重新進行校準，這樣一來在探針的校準方面要用去大量的時間。為解決這一問題，有的CMM上配有測頭庫和測頭自動交換裝置。測頭庫中的測頭經過一次校準后可重復交換使用而無需重新校準。</p><p><b>　　工件的找正</b></p><p>　　我們知道CMM有其本身的機器坐標系，而在進行檢測規(guī)劃時，檢測點數量及其分布的確定以

68、及檢測路徑的生成及信真等都是在CAD中工件坐標系下進行的。因此在進行實際檢測之前首先要確定工件坐標系在CMM機器坐標系中的位置關系。即首先要在CMM機器坐標系中對工件進行找正。通常采用6點找正法，即“3-2-1”方法對工件進行找正。如圖7-12所示，首先通過在指定平面上測量三點或三點以上的點校準基準面；其次通過測量兩點或兩點以上的點來校準基準軸；最后再測一點來計算原點。在以上三步操作中檢測點位置的確定都是依據工件坐標系來選擇的?！?lt

69、;/p><p>　　工件在工作臺上的擱置方式一般有兩種。一種是通過專用夾具或自動裝卸裝置，將工件放在工作臺沙鍋內的某儀固定位置。這樣，通過一次工件找正，再以后測量同批工件時，由于工件的位置基本上是確定的，故無須再對工件進行找正，直接就可進行測量；另一種是通過肉眼的觀察直接將工件放在工作臺的某一合適位置，在這種情況下每測一工件都必須首先對其在工作臺上進行找正。</p><p>　　(2)測球半徑

70、補償誤差 當測針接觸到工件時，三坐標測量機接收的的坐標值應是紅寶石球頭中心點坐標，顯然，測量軟件將自動沿著測針從接觸點回退的方向加上一個測球半徑值作為測量值。但該測量值是一個與測頭的機械慣性有關的動態(tài)值。實際上，測量作為一個動態(tài)過程，其測量值應該考慮到從測頭采點到實際向系統(tǒng)傳送該點坐標值時發(fā)生的機器空間移動距離。盡管這個距離極小，但對系統(tǒng)計算動態(tài)尺寸有一定影響。 在實際測量時，每測量一個元素，系統(tǒng)都可以自動區(qū)分測球半

71、徑的補償方向，計算正確的補償半徑。在采點開始后，測量軟件將在沿著測針接觸工件的方向上對測球進行半徑補償。但被補償點并非真正的接觸點，而是測頭沿著測針接觸工件方向的延長線上的一個點。這樣就造成了補償誤差，產生誤差的大小與測球的半徑及該工件被測面與笛卡爾坐標軸的夾角有關，夾角越大，誤差越大。 ①測球半徑r對補償誤差的影響 補償誤差δ與測球半徑r成正比關系，即測球半徑r越小，補償誤差δ也越小。因此當用三坐標測量機進行點位測