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機(jī)床專題報(bào)告
近幾年，機(jī)床企業(yè)越來越重視產(chǎn)品技術(shù)水平的提高和品種的增長，重視提高為國家重點(diǎn)建設(shè)項(xiàng)目提供關(guān)鍵設(shè)備的能力，研制開發(fā)出一批為發(fā)電設(shè)備、造船、航空航天、國防軍工、交通運(yùn)輸?shù)炔块T的重大工程項(xiàng)目所需要的重大裝備。改變了我國重點(diǎn)工程建設(shè)需要的關(guān)鍵設(shè)備主要依靠進(jìn)口，花費(fèi)國家大量外匯，且受制于人的局面。
重點(diǎn)工程關(guān)鍵設(shè)備的國產(chǎn)化:
武重為加工三峽工程水輪機(jī)生產(chǎn)的關(guān)鍵設(shè)備CKX53160型數(shù)控單柱移動立式銑車床，其技術(shù)要求高，制造難度大，要求既能車削加工，還能銑削加工，工作臺可精確分度。自重近700噸，創(chuàng)國內(nèi)機(jī)床重量之最。加工直徑16米，加工高度6.3米，工作臺承重550噸，承重為國內(nèi)第一“大力士”，一次裝卡完成車、銑、鏜、鉆、攻絲、磨削全部加工工序。保證了號稱世界最大的三峽電站550噸重巨型水輪機(jī)轉(zhuǎn)輪的加工完成。該機(jī)床的研制成功，代表了我國超重型機(jī)床的生產(chǎn)能力和水平，標(biāo)志著我國自主版權(quán)產(chǎn)品達(dá)到世界先進(jìn)水平，成為世界上少數(shù)幾個超重型機(jī)床供應(yīng)國之一。同時也為設(shè)計(jì)、制造更多的銑車復(fù)合系列機(jī)床打下了基礎(chǔ)。CKX53160型數(shù)控單柱移動立式車床被評為2004年中國機(jī)械工業(yè)科技進(jìn)步一等獎第一名，也是機(jī)床行業(yè)惟一獲得一等獎的產(chǎn)品。
齊齊哈爾第一機(jī)床廠設(shè)計(jì)制造的DH4300/250-25×18000-1型數(shù)控重型臥式車床，是為哈爾濱電機(jī)廠提供的三峽工程的配套設(shè)備，加工直徑4.3米，加工長度18米，最大承重250噸，機(jī)床可實(shí)現(xiàn)工件自動測量，機(jī)內(nèi)對刀。在加工三峽機(jī)組水輪機(jī)轉(zhuǎn)子時，一次裝卡重達(dá)200噸的工件，完成對工件的全部加工。該機(jī)床的研制成功，標(biāo)志著重型臥式車床制造能力邁上新臺階。
武重研制的XK9720×400型數(shù)控龍門移動式鏜銑床，龍門間距3200mm，工作臺長40500mm，龍門移動行程41000mm。主要用于大號碼高速道岔的加工，是目前國內(nèi)加工鐵路道岔的最大加工設(shè)備，為提高鐵路道岔的加工能力和火車運(yùn)行提速提供了技術(shù)保障。
武重為船舶螺旋槳廠提供的CKX5680重型七軸五聯(lián)動車銑復(fù)合加工機(jī)床，機(jī)床最大加工直徑8000mm，最大加工高度2000mm，承重100噸，專門用于艦船螺旋槳的加工，具有五軸聯(lián)動車、銑復(fù)合加工、在線測量等功能，可實(shí)現(xiàn)工作臺自動精確分度，能一次裝卡完成螺旋槳的全部工序的加工，是我國自行研制的首臺大型螺旋槳數(shù)控五軸聯(lián)動立式加工機(jī)床，達(dá)到當(dāng)代國際先進(jìn)水平，有助于提高我國艦船的制造水平和國防作戰(zhàn)能力。
齊齊哈爾第一機(jī)床廠于2005年6月5日在鞍鋼重型機(jī)械有限公司安裝成功并交付用戶使用了DMVT1600X55/250L-NC數(shù)控重型龍門移動立式車銑床。該產(chǎn)品是采用了龍門移動技術(shù)和大型立式車床工作臺C軸技術(shù)的全功能車銑床，具有自主知識產(chǎn)權(quán)。產(chǎn)品最大車削直徑16.2米，最大加工高度5.5米，最大承重250噸，具有車、銑、鉆、鏜、磨等復(fù)合功能。世界也只有少數(shù)幾個國家能夠生產(chǎn)此類產(chǎn)品。
從近幾年重型機(jī)床進(jìn)口情況分析，我國重型立式車床已經(jīng)完全不用進(jìn)口，產(chǎn)品技術(shù)水平已經(jīng)進(jìn)入世界先進(jìn)行列。
龍門式鏜銑床、落地式銑鏜床、重型加工中心以及提供成套設(shè)備等系列產(chǎn)品，在技術(shù)上與國外先進(jìn)技術(shù)比較，還有一定的差距。我國需要的關(guān)鍵重型機(jī)床產(chǎn)品中，進(jìn)口比例仍占多數(shù)。主要技術(shù)差距是在速度、精度、復(fù)合柔性化和多功能性上，其中最主要的差距在可靠性能上，包括電氣、機(jī)械部分的可靠性與保持性。世界著名重型機(jī)床生產(chǎn)廠家德國瓦德里希·科堡(WALDRICH-COBURG)公司，最近推出的新產(chǎn)品不但在高速、高精、高效方面有很大提高，并且在多功能、復(fù)合化方面也有很大突破。工作臺寬度4500～6000mm龍門移動式的固定工作臺上配置數(shù)控車、銑復(fù)合旋轉(zhuǎn)工作臺增加車削功能。最近的MULTITEC型龍門加工中心系列，工作臺寬度1250～3000mm，在移動的工作臺上也配置數(shù)控車、銑復(fù)合旋轉(zhuǎn)工作臺，完成車、銑、磨等工序的復(fù)合加工。根據(jù)用戶要求還可提供帶交換工作臺的龍門加工中心，縮短輔助時間，提高生產(chǎn)效率。法國費(fèi)雷斯特-里內(nèi)公司(FOREST-LINE)生產(chǎn)的AEROMINUMAC型高速龍門銑床為了高效地適應(yīng)航空、航天工業(yè)產(chǎn)品鋁合金、鈦合金多維曲面框架結(jié)構(gòu)的主體零件加工，在移動橫梁上安裝兩個或多個銑頭同時進(jìn)行精密高速加工，主軸最高轉(zhuǎn)速40000r/min，主電機(jī)最大功率100kW，快移速度30m/min。意大利的JOBS橋式龍門銑加工寬度在2200mm時的移動速度為70m/min;加工寬度在4000mm時快移速度為40m/min;主軸轉(zhuǎn)速24000r/min；在中小產(chǎn)品上，快速移動達(dá)到了100m/min的線性驅(qū)動；2.5秒的換刀時間；18000轉(zhuǎn)主軸在1.6秒內(nèi)即可從靜止達(dá)到最高轉(zhuǎn)速；線性驅(qū)動(X/Y/Z)可在0.17秒加速到100m/min.。可見國外先進(jìn)技術(shù)發(fā)展很快。
我國在主機(jī)的關(guān)鍵部件、關(guān)鍵技術(shù)以及功能部件等方面，還是以進(jìn)口為主要來源，自己開發(fā)還有一定的差距和不足。而最主要的是機(jī)床使用壽命短和可靠性差，是國產(chǎn)重型機(jī)床的通病。我國重型機(jī)床技術(shù)水平要想盡快趕上世界先進(jìn)水平，必須做好幾件踏實(shí)的基礎(chǔ)工作。
其一，我國主要重型機(jī)床制造廠家，都是在“一五”期間建設(shè)投產(chǎn)的，自身的設(shè)備、廠房都已老化。有的重型機(jī)床制造廠家，機(jī)加設(shè)備數(shù)控化率只有可憐的3%左右，仍然維持傳統(tǒng)的生產(chǎn)方式在組織生產(chǎn)，完全不能適應(yīng)現(xiàn)代工業(yè)發(fā)展需要。用戶對產(chǎn)品技術(shù)水平和交貨期的要求，已經(jīng)很難予以滿足和保證。企業(yè)急需進(jìn)行自身技術(shù)改造，已經(jīng)形成企業(yè)的共識。用國產(chǎn)數(shù)控機(jī)床武裝自身設(shè)備，既滿足技術(shù)改造的需要，又能提升產(chǎn)品開發(fā)水平，是值得認(rèn)真推廣的好經(jīng)驗(yàn)。只有首先裝備好自己，才能更好地裝備用戶，最終完成用“中國裝備”裝備中國的大任.
其二，新產(chǎn)品開發(fā)和試制，離不開新技術(shù)的應(yīng)用。新技術(shù)的產(chǎn)生，必須走科學(xué)實(shí)驗(yàn)的道路。承受上百次、上千次甚至上萬次的考驗(yàn)，才能滿足用戶需要，讓用戶放心使用。關(guān)鍵技術(shù)和關(guān)鍵部件經(jīng)過科研實(shí)驗(yàn)達(dá)到設(shè)計(jì)標(biāo)準(zhǔn)，整機(jī)的可靠性才能有保證。開發(fā)有自主知識產(chǎn)權(quán)、有特色的產(chǎn)品，開展基礎(chǔ)技術(shù)研究和實(shí)驗(yàn)工作，必須引起我國重型機(jī)床廠家高度重視。
其三，在產(chǎn)品設(shè)計(jì)方面進(jìn)行模塊化管理是提高產(chǎn)品開發(fā)速度的好辦法，有的企業(yè)已經(jīng)重視和執(zhí)行，并取得成效。生產(chǎn)周期縮短，交貨期加快是我國重型機(jī)床企業(yè)在產(chǎn)品市場競爭中必須面臨的一個新的形勢，因此企業(yè)應(yīng)該加快新產(chǎn)品開發(fā)速度、交貨速度。
其四，技術(shù)引進(jìn)、合作生產(chǎn)是提高企業(yè)技術(shù)水平的一條捷徑，但不是目的。企業(yè)只有自己開發(fā)出具有特色的產(chǎn)品，并且不斷更新和進(jìn)步，才能站穩(wěn)市場，立于不敗之地。為達(dá)到此目的，企業(yè)必須注重培養(yǎng)一支過硬和相對穩(wěn)定的產(chǎn)品開發(fā)隊(duì)伍，培養(yǎng)一支熟練的技術(shù)操作和裝配能手隊(duì)伍。這樣的企業(yè)才會有無限的生命力和發(fā)展?jié)摿Α?
現(xiàn)代組合機(jī)床已經(jīng)逐漸打破了通常認(rèn)為只適用于箱體類零件加工的模式，其功能和應(yīng)用范圍正在不斷地延伸和擴(kuò)展。
組合機(jī)床加工旋轉(zhuǎn)體零件的情況下，采用組合機(jī)床加工軸類和盤類零件具有明顯的優(yōu)越性。一些軸件，尤其是大型軸件，可以用旋轉(zhuǎn)夾具夾持中部，在組合機(jī)床或?qū)Ｓ脵C(jī)床上進(jìn)行兩端同時加工，其優(yōu)點(diǎn)是工序集中，省去調(diào)頭加工，增加了刀具及其驅(qū)動部件的布置空間。
現(xiàn)代成批大量生產(chǎn)的儀表、精密機(jī)械、家用電器、鐘表等工業(yè)部門，常有小型箱體類、蓋罩類、連桿撥叉類、雜件等小型異形零件。這類零件由于廣泛采用先進(jìn)高效的毛坯制造工藝，金屬切除量較小，且大部分零件的材質(zhì)是鋁合金或銅合金，加工時，切削力較小。由于生產(chǎn)節(jié)拍短，要求有極高的生產(chǎn)率。用組合機(jī)床加工這類零件時，要作專門的設(shè)計(jì)，以適應(yīng)這類零件構(gòu)造和加工上的特殊性。通常加工這類零件的組合機(jī)床稱為小型組合機(jī)床，自成體系，發(fā)展迅速。
CNC 機(jī)床的性能測驗(yàn)的系統(tǒng)發(fā)展和平面的編碼器測量的應(yīng)用
W. Jywe
自動化工程學(xué)部， 國立Huwei科技研究所, Huwei, 林云,臺灣
在這個文章中，平面的編碼器的測定的裝置是為了發(fā)展測試 CNC 機(jī)床的表現(xiàn)。在計(jì)算機(jī)的協(xié)助下，這一個系統(tǒng)能被使用進(jìn)行2 D 的 CNC畫 輪廓測試和 3D立體定位測試。根據(jù)系統(tǒng)的結(jié)構(gòu)和原則,可以進(jìn)行一般的 2 D 的應(yīng)用畫輪廓測試，漂流物測試, 和指定的幾何學(xué)的部份路徑測試。 一個真實(shí)的個案是研究改良一個凸輪的機(jī)制準(zhǔn)確性的描述。 最后, 示范了一個新的使用光學(xué)的編碼器的 3D立體放置方法。
關(guān)鍵字: 球狀校核系統(tǒng); 機(jī)床; 幾何學(xué)的部份路徑; 平面的編碼器; 熱的漂流物測試; 三維空間的定位; 二維空間的畫輪廓
1. 介紹
機(jī)床的表現(xiàn)和一致性-對機(jī)器制造的質(zhì)量的起主要作用。 系統(tǒng)地檢查機(jī)床的表現(xiàn)對于直接的質(zhì)量校核或?yàn)檫@不確定補(bǔ)償是重要的。1932年 , 低空飛機(jī)遠(yuǎn)程警戒雷達(dá)網(wǎng) 首先為機(jī)器提供一個系統(tǒng)的方法。這個方法成為國際標(biāo)準(zhǔn)組織標(biāo)準(zhǔn)發(fā)展的基礎(chǔ)。在 1959年，Tlusty使用了電和感應(yīng)來測試紗錠準(zhǔn)確性。 Tlusty，Koenigsberger和 Burdekin為機(jī)床指出了新的測試方法。 Burdekin檢查了機(jī)床的運(yùn)動準(zhǔn)確性和機(jī)器加工部份的關(guān)系。 Tlusty計(jì)劃了一個不切割的測試方法。然后機(jī)床表現(xiàn)的測試分為一個直接的切斷之內(nèi)分類測試和一個間接的切斷測試。Ericson首先描述了機(jī)床的工作地域。布賴恩和皮爾森解釋了斜度，旋轉(zhuǎn)，偏離的測量程度的定義和方法。 在商業(yè)的激光干涉計(jì)的使用之后,測定體積誤差的分析可以被描述了。Voutsudopoulos 和 Burdekin指出坐標(biāo)測量機(jī)需要校正的模型。 Fan使用一個激光干涉計(jì)和個人計(jì)算機(jī)校正不同類型的機(jī)床的裝置。 Zhang和 Hockey 通過測量位置錯誤 獲得了 的 21個錯誤成份。為了找出 21個錯誤成份, Zhang 和 Zang設(shè)計(jì)1-D球狀隊(duì)列，然后 Zhang描述了一個迅速獲得筆直錯誤的方法。 在2000年, Jywe 描述了一個使用球狀校核系統(tǒng)的方法證明了CNC機(jī)床 的測定體積錯誤。圓形的測試被發(fā)展用來檢查幾何學(xué)和畫輪廓錯誤。 為了準(zhǔn)確性評估，Burdekin[20] 描述了使用圓形的路徑的方法作切斷測試。 布賴恩為畫輪廓測試發(fā)展了第一個球狀校核系統(tǒng)。然而，在這一個系統(tǒng)中，不確定是很高的,其主要原因是在球和磁性插口之間的摩擦和沒有準(zhǔn)確測量和制造它的的半徑.Knapp's 的系統(tǒng)是 在機(jī)床上用一個圓形的比較標(biāo)準(zhǔn)圓盤展開和 2 D 測量。這一個系統(tǒng) 的問題是在 2 D 之間摩擦的存在和系統(tǒng)對高速的畫輪廓測試是無法使用圓盤, 小帶寬和2 D 測試的高費(fèi)用。 Kakinov 提供了使用一個球狀校核系統(tǒng)校準(zhǔn)一個同等的CNC機(jī)床。 Knapp描述了一條減少預(yù)定黏住–滑等的錯誤的規(guī)則.Burdekin 和Park通過使用四坐標(biāo)聯(lián)動的方式修改了原始的球狀校核系統(tǒng)。 Burdekin 和 Jywe[31]提供通過一個診斷畫輪廓錯誤和調(diào)整 CNC 機(jī)床的參數(shù)來優(yōu)化機(jī)床的方法。 Ziegert 和 Mize描述了一個激光球校核系統(tǒng)。 所有的這些球校核系統(tǒng), 包括Renishaw側(cè)面的系統(tǒng) 提供只有在畫輪廓測試期間的半徑錯誤, 都限制了外形制造錯誤的分析即使每個軸存在共有的不是各自的錯誤。為了獲得每個軸的外形制造錯誤, Jywe[34]使 用了二個位置硅探測器來測試.。 一個激光源發(fā)出激光光線,激光光線進(jìn)入二條垂直的線之內(nèi)被分離并且射在二臺垂直放置機(jī)床的硅探測器上。 Heidenhein格子編碼器也提供畫輪廓2 D測試, 但是非常費(fèi)用很高。在半導(dǎo)體和電子制造儀器應(yīng)用平面的編碼器系統(tǒng)。這個有很好的電動反應(yīng)系統(tǒng)能測量 0.1 m 的數(shù)量級.但最重要的是低費(fèi)用。 然而,那最初的平面編碼器為人工的操作而設(shè)計(jì),用來進(jìn)行CNC 機(jī)床的外形測試是不適當(dāng)?shù)?由于下列的考慮:
1. 最初的系統(tǒng)只包括了一個編碼器和探測器。 沒有相關(guān)的接口和驅(qū)動。
2. 如此沒有相關(guān)的畫輪廓軟件和測試-方法。因此,即使有了相關(guān)的軟件,使用和整合一個新的計(jì)算機(jī)輔助平面編碼器中系統(tǒng)來測試兩者的動態(tài)表現(xiàn)和CNC機(jī)床的幾何錯誤也僅僅在紙上,。最重要的是與Heidenhein 格子編碼器系統(tǒng)相比較,畫輪廓測試的裝置 能減少90% 費(fèi)用。從早先的研究，已經(jīng)發(fā)現(xiàn)了那個測試裝置總是不適合的對3D幾何錯誤測試。 此外，這些裝置不適合的對一個自由形態(tài)的 2 D畫輪廓測試的。書中設(shè)計(jì)和發(fā)展了一個裝置的簡單測量裝置來檢查每個輸出軸的制造外形。 同時一個3D位置的測試也發(fā)展了。
2. CNC機(jī)床的2 D 平面編碼器畫輪廓測量系統(tǒng)
2.1 平面的編碼器的原則
一個平面的編碼器系統(tǒng)例如 Renishaw RGX系統(tǒng)已經(jīng)在半導(dǎo)體和電子制造儀器產(chǎn)業(yè)發(fā)展了, 系統(tǒng)使用一個有二個直角可以 測試X 和 Y 方向感應(yīng)器的探測器
.系統(tǒng)有一個好動態(tài)的反映而且在方向上達(dá)到了0.1 m的數(shù)量級。 V -B被用來編輯測定的軟件程序。圖 1 使用簡單的平面編碼器測試的外形輪廓。 這平面的編碼器提供每個軸的2 D 畫輪廓的定位數(shù)據(jù)。 在測試中, 平面的編碼器與 CNC 機(jī)床不兼容而且探測器經(jīng)常需要修理。 計(jì)算機(jī)軟件經(jīng)由一張柜臺卡片能讀抽取樣品數(shù)據(jù)。
Fig.1
3. 測定的系統(tǒng)不確定
3.1 由于抽取樣品程序的不確定
完善的軟件出現(xiàn)了下列的因素:
1.采樣必須都是在外形附近和合理地獨(dú)立計(jì)算機(jī)速度
2. 充份的抽取樣品數(shù)據(jù)對顯示和分析高辨識率的錯誤是必要的。
3. 抽取樣品數(shù)據(jù)應(yīng)該與畫輪廓速度,計(jì)算機(jī)速度和畫輪廓半徑無關(guān)。
3.2 由于熱的效果不確定
為測試考慮系統(tǒng)的熱效果,如果平面的編碼器的溫度不同于那機(jī)床平臺,半徑誤差將會被影響。 如果那平面的編碼器本身的溫度不是統(tǒng)一的, 那在外圓誤差將會被影響。 雖然平面的編碼器的擴(kuò)充系數(shù)相當(dāng)小,到了極小的影響,編碼器也應(yīng)該不時的放到測試機(jī)床平臺來減少溫度差異和讓編碼器的溫度穩(wěn)定。
4. 圓形的畫輪廓路徑測試結(jié)果
在一個 有0 M Fanuc 校核器并且垂直 CNC機(jī)床上進(jìn)行XY方向 上進(jìn)行了一個簡單的畫輪廓測試.畫輪廓結(jié)果顯示在圖 2中。 那逆時針方向的和順時針方向的在 20 毫米半徑畫輪廓測試能滿足ISO 230-1 和 230-2的需求。 從結(jié)果來看,絕對的半徑錯誤能被容易地發(fā)現(xiàn)。 對于一般的畫輪廓系統(tǒng),僅僅沒有給了圓度。 此外, 如果有需要的話,每個軸的錯誤也能被個別地發(fā)現(xiàn)。對于分析的目的這是有用的。
Fig.2
5. 熱的漂流物
畫輪廓系統(tǒng)提供例如非連絡(luò)畫輪廓測試。 對于像球校核系統(tǒng)的畫輪廓系統(tǒng), 由于問題信號電纜的卷繞只有一個的有限制數(shù)字運(yùn)行。 在這個試驗(yàn)里, 測試運(yùn)行是無限的。 因此, 一個熱的漂流物測試能在沒有另外的固定物時容易地運(yùn)行。 經(jīng)過八小時的連續(xù)順時針方向畫輪廓運(yùn)行, 畫輪廓結(jié)果在圖 3 中以每個二小時的周期被顯示。 畫輪廓中心在圖 4 中每個30分鐘被顯示。在 8 小時中 畫輪廓中心漂流物是重要的。不僅給的畫輪廓中心漂流物還有也獲得每次運(yùn)行畫輪廓錯誤的形式都是很重要的。 從這一個測試中, 這一個系統(tǒng)很容易顯示連續(xù)運(yùn)行的表現(xiàn)。
Fig.3
Fig.4
Fig.5
6.平面編碼的方形錯誤測試
使用平面編碼器方形錯誤可能容易地被檢測到。編碼器被設(shè)置在被測試的平面上。探測器沿著編碼器的正方形邊緣。CNC 機(jī)床被測試了并且結(jié)果被顯示在圖5. 制造外形的測試。
7. 激光 二極管和象限傳感器塑造外形的系統(tǒng)[ *
使用激光 二極管和象限傳感器塑造外形的系統(tǒng)可能核實(shí)平面編碼器塑造外形的系統(tǒng)。使用一條2 毫米順時針制造外形的半徑, 圖6 顯示塑造外形收效使用象限傳感器, 當(dāng)圖7 給近似結(jié)果。
Fig. 6.
Fig. 7.
Fig. 8.
Fig. 9.
Fig. 10.
沒有傳感器, 被連接到被測試的CNC 機(jī)床的平臺和二到個各自的球和磁性插口探測器。球校核在平臺的球的中心的是3D 測量和目標(biāo)分析。當(dāng)目標(biāo)后, 在平面編碼器第一樣品被放在在它的第一個位置。沒有移動目標(biāo), 平面編碼器被移動向鄰居點(diǎn)并且第二個樣品被采取。終于, 其他鄰居點(diǎn)被抽樣如同第三個樣品。每個三個樣品包括第2 個座標(biāo),個可能被分析目標(biāo)的3D 座標(biāo)。因而各3D 運(yùn)動將由這個1 點(diǎn)和3 步(1P3S) 方法獲得。這個方法可能被描述如下。
為了獲得3D 安置的座標(biāo)x, Y 和Z, 一個簡單的模型被開發(fā)在下圖,
已知:
圖13. 模型為分析x, y, z 座標(biāo)。 x, y, z 是被分析座標(biāo)
x1, y1, z1, x2, y2, z2, x3, y3, z3 是被提供第一, 第二個和第三個步樣品的2D光學(xué)標(biāo)度座標(biāo)
L1, L2, L3 是球禁止系統(tǒng)提供的長度.然后,
解等式:
這里, 發(fā)現(xiàn)了二種可能的解答。你是在平面編碼器的上面, 而另一個是在它之下。因而,在這種應(yīng)用唯一座標(biāo)在球板材的上面被使用。在同等的z 被發(fā)現(xiàn)之后, x 和y 可能并且被發(fā)現(xiàn)。在這種應(yīng)用,長度是固定, 因而L1 L2 L3 。擴(kuò)大運(yùn)作的范圍一個標(biāo)準(zhǔn)或激光 球校核系統(tǒng)與一個長的運(yùn)轉(zhuǎn)的范圍位移傳感器可能被使用。在那個案件, L1, L2, L3 可能由那個傳感器獲得。為了使費(fèi)用減到最小,使用了 在這種應(yīng)用只一套平面編碼器和一個簡單的球校核系統(tǒng)。因而, 一個平面編碼器測量的系統(tǒng)為CNC 機(jī)床27 座標(biāo)x1, y1, z1, x2, y2, z2, x3, y3, z3 必須由平面編碼器獲得在三個各自的樣品。
取樣步驟(1P3S) 是: 1. 讓機(jī)床行動向被測試的位置(一點(diǎn)) 。 2. 采取樣品由平面編碼器(步驟1) 。 3. 移動閱讀器向一個鄰居位置與平面編碼器有關(guān); 被測試的機(jī)器不被移動。采取樣品由平面編碼器(步驟2) 。
11. 討論和結(jié)論
在本文里, 一個平面編碼器系統(tǒng)被使用了為CNC 機(jī)床的一個塑造外形的測試。它證明, 這個系統(tǒng)能成功地被使用為制造外形的測試。這種應(yīng)用好處可能被總結(jié)
如下: 1. 在塑造外形的測試期間, 塑造外形的錯誤為各個單獨(dú)軸可能被獲得。這不是可能的使用一個一般球校核系統(tǒng)。這個作用為分析提供更加有用的信息塑造外形的錯誤。2 。系統(tǒng)可能被使用為長期間熱量漂泊測試, 但傳統(tǒng)球校核系統(tǒng)不能實(shí)現(xiàn), 因?yàn)樵谶@中沒有可能受傷的纜繩。
2. 為塑造外形復(fù)雜的曲線的組合譬如凸輪, 系統(tǒng)可能被使用當(dāng)一個一般球校核系統(tǒng)不實(shí)現(xiàn)。表1 。平面編碼器的證明結(jié)果為3D 安置
以這個第2 個光學(xué)測量的系統(tǒng), 3D 位置誤差測試可能成功地并且執(zhí)行。因而這臺光學(xué)編碼器可能被使用為動態(tài)表現(xiàn)和對CNC 機(jī)床的幾何學(xué)錯誤測試。審查工作由國際科 委員會進(jìn)行,格蘭特?cái)?shù)字支持了NSC-88-2212-E-150-0的工作.
叁考
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2. J. Tlusty,測試機(jī)床的系統(tǒng)和方法 Microtechnic ,1959.
3. J. Tlusty 和 F. Koenigsberger ，機(jī)床規(guī)格和測試，，曼徹斯特,1970.
4. G. Schlesinger ， F. Koenigsberger 和 M. Burdekin,Testin,機(jī)床， 機(jī)器出版公司,倫敦,1978.
5. M. Burdekin," 切斷準(zhǔn)確性評估測試 ", 1980.
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7. C. Ericson,"機(jī)器制造對準(zhǔn)–第一個邁向的步伐"， ASTME,1966.
8. J. B. 布賴恩和 J. W. 皮爾森， "機(jī)床度量衡學(xué) ",Lawr國立實(shí)驗(yàn)室，加州,1968.
9. Hewlett- Packard， " 機(jī)床的口徑測定 ".
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The Development and Application of a Planar Encoder Measuring
System for Performance Tests of CNC Machine Tools
W. Jywe
Department of Automation Engineering, National Huwei Institute of Technology, Huwei, Yunlin, Taiwan
In this paper, a measuring device with a planar encoder is developed to test the performance of a CNC machine tool. With the assistance of a PC, this system can be employed for both 2D contouring tests and 3D positioning tests for a CNC machine tool. The structure and the principle of the system, the applications for the general 2D contouring test, the drift test, and the specified geometric part path tests. An actual case study on improving the accuracy of machining a cam are
described. Finally, a new 3D positioning method using the optic encoder is demonstrated.
Keywords: Ball bar system; CNC machine tool; Geometric part path; Planar encoder; Thermal drift test; Three-dimensional positioning; Two-dimensional contouring
1. Introduction
Machine tool performance and consistency is the main determinant of the quality of parts machined by it. It is of importance to check the performance of the machine tool systematically
for direct quality control purposes or to compensate for this uncertainty. Schlesinger, in 1932 [1], first provided a systematic testing method for machine tools. This method was developed as the basis of the ISO standard. Tlusty, in 1959 [2], employed an electric level and sensor to test the spindle accuracy. Tlusty and Koenigsberger [3] and Burdekin [4] indicated new testing rules for machine tools. Burdekin [5] checked the relation between the motion accuracy of machine tools and the machined part. Tlusty [6] proposed a non-cutting testing method. The tests for machine tool performance were then classified into a direct cutting test and an indirect cutting test. Ericson [7] first described the work zone of machine tools. Bryan and Pearson [8] explained the definition and the way to measure the pitch, roll and yaw motion and straightness error. After the commercial laser interferometer [9] was available, the analysis of volumetric errors [10–13] was described. Voutsudopoulos and Burdekin [14] indicated a calibrating model for a coordinate measuring machine. Fan [15] used a laser interferometer and a related device with the assistance of a PC to calibrate different types of NC machine tools. Zhang and Hockey [16] obtained the 21 error components by measuring the position errors. Zhang and Zang [17] designed a 1-D ball array to find the 21 error components, then Zhang [18] described a rapid method to obtain the straightness error. In 2000, Jywe [19] described a method of employing a ball bar system for the verification of the volumetric error of CNC machine tools. Circular tests were developed to check both geometric errors and contouring errors. Burdekin [20] described cutting tests using circular paths for accuracy assessment. Bryan [21] developed the first ball bar system for the contouring test. However, in this system, the uncertainty is high due to the friction between the master balls and the magnetic sockets and no accurate contouring radius was given. Knapp’s system [22,23] used a circular comparison standard disc mounted on the test table of the machine tool and a 2D-probe. The problems for this system are the existence of friction between the 2D probe and the disc, its small bandwidth, which causes the system to be unusable for high-speed contouring tests, and the high cost of the 2D probe. Kakinov [24–27] provided a series of methods using a ball bar system to calibrate a coordinate measuring machine and CNC machine tools. Knapp [28,29] described a rule to reduce the errors due to stick–slip etc. Burdekin and Park [30] modified the original ball bar system by employing a four-rod linkage. Burdekin and Jywe [31] provided a method to diagnose the contouring error and to adjust the parameters of the CNC controller to optimise the performance of the tested CNC machine tool. Ziegert and Mize [32] described a laser ball bar system. All these ball bar systems, including the lateral Renishaw system [33] provide only the radius error during the contouring test. This limits the analysis of contouring error since no individual error in each axis is available. Jywe [34] used two position silicon detectors (PSD) for a contouring test to obtain the contouring error in each axis. One laser source emits a laser beam and the laser beam is split into two vertical lines and projected onto two positioning silicon detectors, which are set vertically to each other on the test machine table. The Heidenhein [35] grid encoder also provides a 2D contouring test, but at very high cost. A planar encoder system was developed [36] for applications such as semiconductor and electronics manufacturing equipment. The system, which has a good dynamic response, can provide up to a 0.1 m resolution in positioning, and it is of importance that it is of low cost. However, the original planar encoder was designed for manual operation. It is not suitable for the contouring test of CNC machine tools due to the following considerations:
1. The original system only included an encoder and a reading head. No related interface and driver are available.
2. Thus there were no related contouring software and testing methods. Thus, in this paper a new computer-aided planar encoder system has been employed and integrated, with the related software, for checking the both the dynamic performance and the geometric error of a CNC machine tool. It is of importance that 90% of the cost of the contouring testing device can be reduced compared to the equivalent Heidenhein grid encoder system. From the previous research, it has been found that the device for the circular test is not always suitable for a 3D geometric error test. Furthermore, these devices are not suitable for a free-form 2D contouring test. In this paper a simple measuring device is designed and developed to check contouring performance with a single axis output. The application for a 3D positioning test is also developed.
2. The 2D Planar Encoder Contouring Measuring System for CNC Machine Tools
2.1 Principle of the Planar Encoder
A planar encoder system, such as the Renishaw RGX grid plate, has been developed for applications such as semiconductor and electronics manufacturing equipment. The system uses a reading head with two orthogonal sensors that read a checkered grid in both the X and Y directions simultaneously. The system has a good dynamic response and can provide up to 0.1 m
resolution in positioning. The software in V-Basic is edited to carry out the measuring procedure.
Figure 1 shows the arrangement of the contouring test using the simple planar encoder. This planar encoder provides positioning information in each axis for 2D contouring. During the test, the planar encoder is set on the CNC machine tool, and the reading head is fixed in the spindle. The computer software can read the sampling data via a counter card.
3. Uncertainty of the Measuring System
3.1 Uncertainty Due to Sampling Procedure
The developed software incorporated the following factors:
1. Sampling must be uniform around the profile and reasonably
independent of the type and speed of the computer. A Planar Encoder Measuring System for CNC Machine Tools 21
2. Sufficient sampling data is required to display and analyse the error at high resolution.
3. Sampling data should be independent of contouring speed, computer speed and contouring radius.
3.2 Uncertainty Due to Thermal Effect
Considering the thermal effect of the system for the tests, if the temperature in the planar encoder is different from that of the machine tool table, the radius error will be affected. If the temperature of the planar encoder itself is not uniform, the out of roundness error will be affected. Although the thermal expansion coefficient of the planar encoder is rather small, to minimise the effects, the encoder should be put on the test machine table for some time to reduce the difference in the temperatures and to let the temperatures of the encoder stabilise.
4. Test Results of a Circular Contouring Path
A simple contouring test is carried out on the XY-plane of a vertical CNC machine tool with a 0M Fanuc controller. The contouring result is shown in Fig. 2. The anticlockwise and clockwise contouring tests at 20 mm radius can meet ISO 230-1 and 230-2 requirements. From the results, the absolute radius error can be found easily. For general contouring systems, only the out of roundness is given. Furthermore, the error for each axis can also be found individually if necessary. This is useful for analytical purposes.
5. Thermal Drift
This contouring system provides a non-contacting contouring test. For general contouring systems such as a ball bar system, only a limited number of runs are executed, due to the problem of winding of the signal cable. In this application, the test run is unlimited. Thus, a thermal drift test can be carried out easily without additional fixtures. For eight-hour continuous clockwise contouring runs, contouring results are shown in Fig. 3 for each two-hour period. The contouring centre for each 30 minutes, is plotted in Fig. 4. The contouring centre drift is significant in the 8 hours. It is important that not only the contouring centre drift is given but also the contouring error form in each run can be obtained. From this test, the performance of continuous runs
can be monitored easily by this system.
Fig. 1. The optical measuring system for contouring performance test on a CNC machine tool.
Fig. 2. The clockwise and anticlockwise contouring test results with
Fig. 3. The thermo drift test results during 8 hours continuous the planar encoder measuring system.
Fig4.The thermal drift test results presented by the drift of the contouring centres.
Fig. 5. The squareness test result on a CNC machine tool with theplanar encoder measuring system.
6. Squareness Error Test by Planar Encoder
The squareness error can be tested easily with the planar encoder. Let the encoder be set on the tested plane. The reading head goes along the square of the encoder. A CNC machine tool was tested and the result is shown in Fig. 5. contouring test.
7. Laser Diode and Quadrant Sensor Contouring System [37]*
Using a laser diode and a quadrant sensor contouring system, the planar encoder contouring system can be verified. Using a 2 mm clockwise contouring radius, Fig. 6 shows the contouring
result using the quadrant sensor, while Fig. 7 gives similar results.
Fig. 6. The contouring test results for square path with the laser diode and quadrant sensor contouring system [37].*
Fig. 7. The contouring results for a square path with the planar encoder.
Fig. 8. The test result for a combination of various geometric shapes provided by the planar encoder measuring system.
Fig. 9. The geometric shape of a specified 2D cam.
Fig. 10. The test results of the path of the CNC machine tool with/without cutter radius compensation.
Fig. 11. The test results with self-calculated cutter radius compensation under different feed rates.
Fig. 12. The structure of a 3D positioning measuring device.
without sensors, is connected to the spindle of the tested CNC machine tool and to the reading head by two individual balls and magnetic sockets. The centre of the ball on the ball bar on the side of the spindle is the 3D measuring target to be analysed. When the target is reached, the first sample from the planar encoder is then taken at its first position. Without moving the target, the planar encoder is moved to a neighbouring point and a second sample is taken. Finally, the other
neighbouring point is sampled as the third sample. Each of the three samples includes 2D coordinates, the 3D coordinates of the target which can be analysed. Thus each 3D movement
will be obtained by this 1-point and 3-step (1P3S) method. This method can be described as follows. To obtain the 3D positioning coordinates X, Y and Z, a simple model is developed in Fig. 13,
where:
Fig. 13. The model for analysing coordinates of x, y, z.
x, y, z are the coordinates to be analysed.
x1, y1, z1, x2, y2, z2, x3, y3, z3 are the coordinates provided by
the 2D optical scale in the first, second and third step samples.
L1, L2, L3 are the lengths provided by the ball bar. Then,
Solving the equation,
where
Here, two possible solutions can be found. One is on the top of the planar encoder, while the other is below it. Thus, in this application only the coordinates on the top of the ball plate are used. After the coordinate z is found, x and y can also be found. In this application, the ball bar length is fixed, thus L1 L2 L3. To extend the working range a standard or laser ball bar system with a long working range displacement sensor can be employed. In that case, L1, L2, L3 can be obtained by that sensor. To minimise the cost, in this application only one set of planar encoders and a simple ball bar are considered. Thus, A Planar Encoder Measuring System for CNC Machine Tools 27 the coordinates x1, y1, z1, x2, y2, z2, x3, y3, z3 have to be obtained by the planar encoder in three individual samples.
The sampling procedure (1P3S) is:
1. Let the machine tool move to the tested position (one point).
2. Take the sample by the planar encoder (step 1).
3. Move the reading head to a neighbouring position related to the planar encoder; the tested machine is not moved. Take the sample by the planar encoder (step 2).
4. Move the reading head to the next neighbouring position, the tested machine is not moved. Take the sample by the planar encoder (step 3). z1, z2, z3 are affected by the flatness (?Zij) of the linear
XY stage. The flatness of the linear XY stage ?Zij is equal to the ith grid
on the X-axis and the jth grid on the Y-axis.
11. Discussion and Conclusions
In this paper, a planar encoder system was employed for a contouring test of a CNC machine tool. It was proved that this system could be employed successfully for the contouring test. The advantages of this application can be summarised
as follows:
1. During the contouring test, the contouring error for each individual axis can be obtained. This is not possible using a general ball bar system. This function provides more useful information for analysing the contouring error. 2. The system can be employed for a long-period thermal drift test, but the traditional ball bar systems cannot, because in this there is no cable which can be wound up.
2. For contouring a combination of complicated curves such as a cam, the system can be employed while a general ball bar system cannot. Table 1. The verification result of the planar encoder for 3D positioning
With this 2D optical measuring system, the 3D positioning error test can also be performed successfully. Thus this optical encoder can be employed for both dynamic performance and geometric error tests on CNC machine tools. Acknowledgements The work was supported by National Science Council, Taiwan, Republic of China, Grant Number NSC-88-2212-E-150-006.
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