【終稿全套】QTZ500塔式起重機(jī)——臂架優(yōu)化設(shè)計【12張CAD圖紙+文檔】

喜歡就充值下載吧。。。資源目錄里展示的全都有，，下載后全都有,,請放心下載，原稿可自行編輯修改=====================喜歡就充值下載吧。。。資源目錄里展示的全都有，，下載后全都有,,請放心下載，原稿可自行編輯修改=====================喜歡就充值下載吧。。。資源目錄里展示的全都有，，下載后全都有,,請放心下載，原稿可自行編輯修改=====================

河北建筑工程學(xué)院 畢業(yè)設(shè)計（論文）任務(wù)書 課題 名稱 QTZ500塔式起重機(jī)——臂架優(yōu)化設(shè)計 系： 機(jī)械工程系 專業(yè)： 機(jī)械設(shè)計制造及其制動化 班級： 機(jī)053班 姓名： 張勇杰 學(xué)號： 2005307322 起迄日期： 2009年3月23日~ 2009年 6月26日 設(shè)計（論文）地點: 河北建筑工程學(xué)院 指導(dǎo)教師： 李常勝 劉春東 輔導(dǎo)教師： 發(fā)任務(wù)書日期： 2009年2月 23 日 1、畢業(yè)設(shè)計（論文）目的： 畢業(yè)設(shè)計是對機(jī)械專業(yè)學(xué)生在畢業(yè)前的一次全面訓(xùn)練，目的在于鞏固和擴(kuò)大學(xué)生在校所學(xué)的基礎(chǔ)知識和專業(yè)知識，訓(xùn)練學(xué)生綜合運用所學(xué)知識分析和解決問題的能力。是培養(yǎng)、鍛煉學(xué)生獨立工作能力和創(chuàng)新精神之最佳手段。畢業(yè)設(shè)計要求每個學(xué)生在工作過程中，要獨立思考，刻苦鉆研，有所創(chuàng)新、解決相關(guān)技術(shù)問題。通過畢業(yè)設(shè)計，使學(xué)生掌握塔式起重機(jī)的總體設(shè)計、吊臂的設(shè)計、整體穩(wěn)定性計算等內(nèi)容，為今后步入社會、走上工作崗位打下良好的基礎(chǔ)。 2、畢業(yè)設(shè)計（論文）任務(wù)內(nèi)容和要求（包括原始數(shù)據(jù)、技術(shù)要求、工作要求等）： （1） 設(shè)計任務(wù)： ① 總體參數(shù)的選擇（QTZ500級別） ② 結(jié)構(gòu)形式 （2） 總體設(shè)計 ① 主要技術(shù)參數(shù)性能 ② 設(shè)計原則 ③ 平衡重的計算 ④ 塔機(jī)的風(fēng)力計算 ⑤ 整機(jī)傾翻穩(wěn)定性的計算 （3） 吊臂的設(shè)計和計算 ① 吊臂的形式及尺寸（變截面）（雙吊點） ② 吊臂的強(qiáng)度、穩(wěn)定性及剛度驗算 （4） 設(shè)計要求 ① 主要任務(wù)：學(xué)生應(yīng)在指導(dǎo)教師指導(dǎo)下獨立完成一項給定的設(shè)計任務(wù)，編寫符合要求的設(shè)計說明書，并正確繪制機(jī)械與電氣工程圖紙，獨立撰寫一份畢業(yè)論文，并繪制有關(guān)圖表。 ② 知識要求：學(xué)生在畢業(yè)設(shè)計工作中，應(yīng)綜合運用多學(xué)科的理論、知識與技能，分析與解決工程問題。通過學(xué)習(xí)、鉆研與實踐，深化理論認(rèn)識、擴(kuò)展知識領(lǐng)域、延伸專業(yè)技能。 ③ 能力培養(yǎng)要求：學(xué)生應(yīng)學(xué)會依據(jù)技術(shù)課題任務(wù)，完成資料的調(diào)研、收集、加工與整理，正確使用工具書；培養(yǎng)學(xué)生掌握有關(guān)工程設(shè)計的程序、方法與技術(shù)規(guī)范，提高工程設(shè)計計算、圖紙繪制、編寫技術(shù)文件的能力；培養(yǎng)學(xué)生掌握實驗、測試等科學(xué)研究的基本方法；鍛煉學(xué)生分析與解決工程實際問題的能力。 ④ 綜合素質(zhì)要求：通過畢業(yè)設(shè)計，學(xué)生應(yīng)掌握正確的設(shè)計思想；培養(yǎng)學(xué)生嚴(yán)肅認(rèn)真的科學(xué)態(tài)度和嚴(yán)謹(jǐn)求實的工作作風(fēng)；在工程設(shè)計中，應(yīng)能樹立正確的生產(chǎn)觀、經(jīng)濟(jì)觀與全局觀。 ⑤ 設(shè)計成果要求： 凡給定的設(shè)計內(nèi)容，包括說明書、計算書、圖紙等必須完整，不得有未完的部分，不應(yīng)出現(xiàn)缺頁、少圖紙現(xiàn)象。 1） 對設(shè)計的全部內(nèi)容，包括設(shè)計計算、機(jī)械構(gòu)造、工作原理、整機(jī)布置等，均有清晰的了解。對設(shè)計過程、計算步驟有明確的概念，能用圖紙完整的表達(dá)機(jī)械結(jié)構(gòu)與工藝要求，有比較熟練的認(rèn)識圖紙能力。對運輸、安裝、使用等也有一定了解。 2） 說明書、計算書內(nèi)容要精練，表述要清楚，取材合理，取值合適，設(shè)計計算步驟正確，數(shù)學(xué)計算準(zhǔn)確，各項說明要有依據(jù)，插圖、表格及字跡均應(yīng)工整、清楚、不得隨意涂改。制圖要符合機(jī)械機(jī)械制圖標(biāo)準(zhǔn)，且清潔整齊。 3） 對國內(nèi)外塔式起重機(jī)情況有一般的了解，對各種塔式起重機(jī)有一定的分析、比較能力。 其他各項應(yīng)符合本資料有關(guān)部分提出的要求。 3、畢業(yè)設(shè)計（論文）成果要求（包括圖表、實物等硬件要求）： ① 計算說明書一份 內(nèi)容包括：設(shè)計任務(wù)要求的選型、設(shè)計計算內(nèi)容、畢業(yè)實習(xí)報告等。作到內(nèi)容完整，論證充分（包括經(jīng)濟(jì)性論證），字跡清楚，插圖和表格正規(guī)（分別進(jìn)行統(tǒng)一編號）、批準(zhǔn)，字?jǐn)?shù)要求不少于2萬字；撰寫中英文摘要；提倡學(xué)生應(yīng)用計算機(jī)進(jìn)行設(shè)計、計算與繪圖。 ② 圖紙一套 1） 總圖一張（0號） 2） 臂架裝配圖一張（0號） 3） 臂架結(jié)構(gòu)圖五張（2號） 4） 零件圖若干張（4號） 4、主要參考文獻(xiàn)： [1] 哈爾濱建筑工程學(xué)院主編.工程起重機(jī).北京：中國建筑工業(yè)出版社 [2] 董剛、李建功主編.機(jī)械設(shè)計.機(jī)械工業(yè)出版社 [3] 機(jī)械設(shè)計手冊.化學(xué)工業(yè)出版社（5冊） [4] GB/T9462—1999 塔式起重機(jī)技術(shù)條件 [5] GB/T13752—1992 塔式起重機(jī)設(shè)計規(guī)范 [6] GB5144—1994 塔式起重機(jī)安全規(guī)程 5、本畢業(yè)設(shè)計（論文）課題工作進(jìn)度計劃： 起 迄 日 期 工 作 內(nèi) 容 2009.3.23-2009.3.28 2009.3.29-2009.4.13 2009.4.14-2009.4.20 2009.4.21-2009.5.15 2009.5.16-2009.6.5 2009.6.6-2009.6.19 2009.6.20-2009.6.26 熟悉整理資料 方案選擇及總體設(shè)計 繪制總圖 臂架設(shè)計 繪制臂架裝配及結(jié)構(gòu)圖紙 繪制零件圖紙 準(zhǔn)備論文及答辯 教研室審查意見： 教研室主任簽字： 年 月 日 系審查意見： 系主任簽字： 年 月 日 河北建筑工程學(xué)院 畢業(yè)實習(xí)報告 系 別 機(jī)械工程系 專 業(yè) 機(jī)械設(shè)計制造及其自動化 班 級 機(jī)053班 姓 名 張勇杰 學(xué) 號 22 實習(xí)日期 3月18日——5月5日 實習(xí)周數(shù) 一周 實習(xí)地點 沈陽、張家口 實習(xí)單位沈陽某建筑工地、張家口建筑機(jī)械廠 指導(dǎo)教師 李常勝 職稱 高級工程師 劉春東 職稱 講師 實習(xí)成績 畢業(yè)實習(xí)報告 時間過得真快，轉(zhuǎn)眼大學(xué)四年就要過去了，我們大多數(shù)人對機(jī)械專業(yè)還是不夠了解,然而畢業(yè)設(shè)計是我們加深對專業(yè)知識了解的一個很好的渠道。我們懂得的只是一些課本上所學(xué)的理論知識，為了讓我們更直接、更深入的了解對我們設(shè)計的塔式起重機(jī)，李老師和劉老師特地安排我們?nèi)チ艘恍┧狡鹬貦C(jī)的作業(yè)工地和生產(chǎn)廠家進(jìn)行參觀學(xué)習(xí)。實習(xí)是讓我們把理論與實際結(jié)合的最好的方法。這次實習(xí)，我們先后去過了沈陽皇姑區(qū)一家大型建筑工地和生產(chǎn)QTZ500塔式起重機(jī)的張家口建筑機(jī)械廠。 1.實習(xí)目的 畢業(yè)實習(xí)是畢業(yè)設(shè)計最為關(guān)鍵的環(huán)節(jié)之一，是我們理論聯(lián)系實際、擴(kuò)大知識面的一個過程，可以通過實地參觀對塔式起重機(jī)設(shè)計有一個感性認(rèn)識，了解機(jī)器的實際結(jié)構(gòu)，綜合運用所學(xué)理論知識和方法為完成畢業(yè)設(shè)計打下了堅實的基礎(chǔ)；同時實習(xí)又是鍛煉和培養(yǎng)學(xué)生能力及素質(zhì)的重要渠道，培養(yǎng)我們具有吃苦耐勞的精神，也是我們接觸社會、了解產(chǎn)業(yè)狀況、了解國情的一個重要途徑，逐步實現(xiàn)由學(xué)生到社會的轉(zhuǎn)變，培養(yǎng)我們工作的能力、了解企業(yè)管理的基本方法和技能。培養(yǎng)面對現(xiàn)實問題的正確態(tài)度和獨立地分析解決問題的基本能力；通過實習(xí)，認(rèn)識社會的需要，發(fā)現(xiàn)自身差距，培養(yǎng)銳意創(chuàng)新進(jìn)取的精神；培養(yǎng)良好的職業(yè)精神，適應(yīng)畢業(yè)后實際工作的要求。 我此次畢業(yè)設(shè)計的題目是：QTZ500塔式起重機(jī)——臂架優(yōu)化設(shè)計。通過畢業(yè)實習(xí)，結(jié)合畢業(yè)設(shè)計深入工廠企業(yè)實地參觀與調(diào)查，在這個基礎(chǔ)上把所學(xué)的專業(yè)理論知識與實踐緊密結(jié)合起來，提高實際工作能力與分析能力，以達(dá)到學(xué)以致用的目的。具體了解吊臂的結(jié)構(gòu)特征，以完成此次的畢業(yè)設(shè)計。 2.實習(xí)內(nèi)容 本次畢業(yè)實習(xí)，我們首先到沈陽皇姑區(qū)正在進(jìn)行生產(chǎn)作業(yè)的某建筑工地參觀實習(xí)，初步了解塔式起重機(jī)的整體結(jié)構(gòu)。然后到張家口市建筑機(jī)械廠對此次設(shè)計的QTZ500型塔式起重機(jī)進(jìn)行具體的學(xué)習(xí)。 3月21日，我們在李老師和劉老師的帶領(lǐng)下，來到了皇姑區(qū)一家大型建筑工地，這家工地矗立著四座塔式起重機(jī)，都在進(jìn)行作業(yè)。這是我第一次正式地參觀塔式起重機(jī)作業(yè)，看著這些塔機(jī)的每一個機(jī)構(gòu)遠(yuǎn)轉(zhuǎn)，我對塔機(jī)有了初步的認(rèn)識。李老師給我們介紹了塔機(jī)的整體情況和各個機(jī)構(gòu)的特點。 塔式起重機(jī)是現(xiàn)代工業(yè)與民用建筑的主要施工機(jī)械之一。高層建筑施工中，它的幅度利用率比其他類型起重機(jī)高，其幅度利用率可達(dá)全幅度的80%。我們這次設(shè)計的QTZ500自升式塔式起重機(jī)是為滿足高層建筑施工、設(shè)備安裝而設(shè)計的新型起重運輸機(jī)械，性能先進(jìn)，結(jié)構(gòu)合理，操作使用安全可靠。其主要特點是起升高度大，工作幅度大。塔機(jī)上部能借助于液壓頂升機(jī)構(gòu)，根據(jù)施工的建筑物的增高而相應(yīng)的升高，使司機(jī)操作方便，視野寬闊并始終保持高清晰。QTZ500塔式起重機(jī)有多種形式，設(shè)計正在不斷的完善中。此次設(shè)計的形式為固定上回轉(zhuǎn)液壓頂升自動加節(jié)，最大起升高度可達(dá)100米（附著狀態(tài)）。隨著更高層建筑的出現(xiàn)，塔式起重機(jī)必然朝著更完美的方向發(fā)展。 塔式起重機(jī)由金屬結(jié)構(gòu)、工作機(jī)構(gòu)和電氣系統(tǒng)三部分組成。金屬結(jié)構(gòu)包括塔身、動臂和底座等。工作機(jī)構(gòu)有起升、變幅、回轉(zhuǎn)和頂升四部分。電氣系統(tǒng)包括電動機(jī)、控制器、配電柜、連接線路、信號及照明裝置等。 塔式起重機(jī)的起升和變幅機(jī)構(gòu)均由電動機(jī)、聯(lián)軸器、制動器、減速器和卷筒等部件組成。為提高塔機(jī)的生產(chǎn)效率，加快吊裝的施工進(jìn)度，各工作機(jī)構(gòu)均應(yīng)具備較高的工作速度，并要求啟動和制動過程中都能平緩進(jìn)行，避免產(chǎn)生急劇沖擊，對金屬結(jié)構(gòu)產(chǎn)生破壞性影響。另外，工作機(jī)構(gòu)與金屬結(jié)構(gòu)之間的關(guān)系協(xié)調(diào)，互不相碰。 起升機(jī)構(gòu)：起升機(jī)構(gòu)是起重機(jī)機(jī)械的主要機(jī)構(gòu)，用以實現(xiàn)重物的升降運動。起升機(jī)構(gòu)通常由原動機(jī)、減速器、卷筒、制動器、鋼絲繩、滑輪組和吊鉤組成。 回轉(zhuǎn)機(jī)構(gòu):塔機(jī)是靠起重臂回轉(zhuǎn)來保障其工作覆蓋面的?；剞D(zhuǎn)運動的產(chǎn)生是通過上、下回轉(zhuǎn)支座分別裝在回轉(zhuǎn)支承的內(nèi)外圈上并由回轉(zhuǎn)機(jī)構(gòu)驅(qū)動小齒輪。小齒輪與回轉(zhuǎn)支承的大齒圈嚙合，帶動回轉(zhuǎn)上支座相對于下支座運動。我們設(shè)計的QTZ500塔式起重機(jī)的回轉(zhuǎn)機(jī)構(gòu)設(shè)成單回轉(zhuǎn)式，通常由回轉(zhuǎn)電動機(jī)、液力耦合器、回轉(zhuǎn)制動器、回轉(zhuǎn)減速器和小齒輪組成。 變幅機(jī)構(gòu):變幅機(jī)構(gòu)是實現(xiàn)改變幅度的工作機(jī)構(gòu)，用來擴(kuò)大起重機(jī)的工作范圍，提高起重機(jī)的生產(chǎn)率。變幅機(jī)構(gòu)由電動機(jī)、減速器、卷筒和制動器組成。功率和外形尺寸較小。變幅機(jī)構(gòu)按其構(gòu)造和不同的變幅方式分為運行小車式和吊臂俯仰式。 塔機(jī)都設(shè)有安全保護(hù)裝置，包括：起升高度限制器、起重量限制器、力矩限制器。 此次我設(shè)計吊臂，所以主要了解了吊臂。塔式起重機(jī)起重臂簡稱臂架或吊臂，按構(gòu)造形式可分為：小車變幅水平臂架；俯仰變幅臂架，簡稱動臂；伸縮式小車變幅臂架；折曲式臂架。本次設(shè)計采用小車變幅水平臂架，小車變幅水平臂架又概分為三種不同形式：單吊點小車變幅臂架、雙吊點小車變幅臂架和起重機(jī)與平衡臂架連成一體的錘頭式小車變幅臂架。單吊點小車變幅臂架是靜定結(jié)構(gòu)，而雙吊點小車變幅臂架則是超靜定結(jié)構(gòu)。雙吊點小車變幅臂架結(jié)構(gòu)自重輕，據(jù)分析與同等起重性能的單吊點小車變幅臂架相比，自重均可減輕5%-10%。小車變幅臂架拉索吊點可以設(shè)在下弦處，也可設(shè)在上弦處，現(xiàn)今通用小車變幅臂架多是上弦吊點，正三角形截面臂架。這種臂架的下弦桿上平面均用作小車運行軌道。塔機(jī)臂架的截面形式有三種：正三角形截面、倒三角形截面和矩型截面。小車變幅水平臂架大都采用正三角形截面。小車臂架常用的標(biāo)準(zhǔn)節(jié)長度有6、7、8、10、12m五種，為便于組合成若干不同長度的臂架，除標(biāo)準(zhǔn)節(jié)之外，一般都配有1-2個3-5m長的延長節(jié)，吊臂長50米，采用標(biāo)準(zhǔn)節(jié)長度6米，配有1個2米長的延長節(jié)。 這次設(shè)計的QTZ500型塔式起重機(jī)是一種采用水平臂架，小車變輻，上回轉(zhuǎn)的自升塔式起重機(jī)，該塔機(jī)采用液壓頂升，起升機(jī)構(gòu)采用變頻調(diào)速技術(shù)，可獲得理想的起升速度及荷重慢就位；回轉(zhuǎn)機(jī)構(gòu)、牽引機(jī)構(gòu)采用變頻器控制變頻電機(jī)帶動行星減速器傳動，實現(xiàn)無級調(diào)速。 李老師為我們詳細(xì)地講解以后，我對自己的設(shè)計又有了更加直觀深入的了解。 5月5日上午，我們幾個同學(xué)一行人又來到了張家口建筑機(jī)械廠實習(xí)。張家口建筑機(jī)械廠是一家主要生產(chǎn)塔式起重機(jī)的老國有企業(yè)。我們找到了廠里的一位姓鄭的女工程師為我們講解塔機(jī)的各部件情況。鄭工為我們詳細(xì)的講解了塔機(jī)每一個機(jī)構(gòu)的生產(chǎn)情況和工作原理，在我們對塔機(jī)整體了解上又進(jìn)一步加深了。后來我們獨自又仔細(xì)看了看我們各自設(shè)計的那一部分的具體結(jié)構(gòu)。對自己要設(shè)計的部分有了更直觀的認(rèn)識。 我重點了解了吊臂的情況，通過老師給我們的講解和我仔細(xì)觀看了吊臂的具體結(jié)構(gòu)，我對自己設(shè)計的部分——吊臂，基本對吊臂有了很全面的了解。我們在張家口建機(jī)廠收獲頗多。 3. 實習(xí)結(jié)果 通過這次參觀實習(xí)，我們受益頗多。以下是我在實習(xí)參觀時所得出的的一些體會： 1.了解了QTZ500塔式起重機(jī)的總體結(jié)構(gòu)，重點對吊臂的結(jié)構(gòu)有了全面的了解； 2. 知道了塔機(jī)用頂升機(jī)構(gòu)進(jìn)行頂升時，利用液壓缸的作用把上面的所有機(jī)構(gòu)頂起，然后加入標(biāo)準(zhǔn)節(jié)。 3. 明白了塔機(jī)的起升機(jī)構(gòu)和變幅機(jī)構(gòu)是用不同的鋼絲繩分開控制的； 4.實習(xí)總結(jié) 畢業(yè)實習(xí)結(jié)束了，時間雖然不長，但通過以實習(xí)，我們擴(kuò)充了視野，開闊了大腦思維，鞏固和闊充了我們在學(xué)校學(xué)不到的實踐知識，使我們收益頗深。培養(yǎng)、鍛煉了我們獨立工作的能力和創(chuàng)新的精神；進(jìn)一步鞏固和深化了所學(xué)的理論內(nèi)容，彌補(bǔ)了以前理論學(xué)習(xí)的不足，更加深刻地體會到了自己學(xué)習(xí)上的不足。感謝老師們不辭辛苦地為我們聯(lián)系實習(xí)單位，并親自帶領(lǐng)我們?nèi)嵙?xí)地參觀講解，感謝老師們給予我們的幫助。 河 北 建 筑 工 程 學(xué) 院 本科畢業(yè)設(shè)計（論文） 題 目 QTZ500塔式起重機(jī)——臂架優(yōu)化設(shè)計 學(xué) 科 專 業(yè) 機(jī)械設(shè)計制造及其自動化 班 級 機(jī)053班 姓 名 張勇杰 指 導(dǎo) 教 師 李常勝 劉春東 輔 導(dǎo) 教 師 河北建筑工程學(xué)院 畢業(yè)設(shè)計（論文）開題報告 課題 名稱 QTZ500塔式起重機(jī)——臂架優(yōu)化設(shè)計 系 別： 機(jī)械工程系 專 業(yè)： 機(jī)械設(shè)計制造及其自動化 班 級： 機(jī)053班 學(xué)生姓名： 張勇杰 學(xué) 號： 2005307322 指導(dǎo)教師： 李常勝 劉春東 課題來源 社會實踐 課題類別 工程設(shè)計 一、 論文資料的準(zhǔn)備 (一) 塔式起重機(jī)概述 塔式起重機(jī)是一種塔身樹立起重臂回轉(zhuǎn)的起重機(jī)械，簡稱塔機(jī)，也叫塔吊，起源于西歐。具有工作效率高、使用范圍廣、回轉(zhuǎn)半徑大、起升高度大、操作方便以及安裝與拆卸比較簡便等特點。主要完成在高層建筑施工中預(yù)制構(gòu)件及其他建筑材料與工具等吊裝工作。塔式起重機(jī)必須具備下列特點： ① 起升高度和工作幅度較大、起重力矩大； ② 工作速度高，具有安裝微動性能及良好的調(diào)速性能； ③ 要求拆裝運輸方便迅速，以適應(yīng)頻繁轉(zhuǎn)移工地的需要。 (二) 我國塔式起重機(jī)的發(fā)展現(xiàn)狀 塔式起重機(jī)在我國的生產(chǎn)與應(yīng)用已經(jīng)有50余年的歷史，經(jīng)歷了以個從測繪仿制到自行設(shè)計制造的過程，特別是進(jìn)入20世紀(jì)90年代以后，我國塔式起重機(jī)行業(yè)隨著全國范圍建筑任務(wù)的增加而進(jìn)入了一個興盛時期，年產(chǎn)量連年猛增，而且有部分產(chǎn)品出口到國外。 現(xiàn)在我國的建筑用塔式起重機(jī)已越來越普遍，從普通的多層民用建筑、房地產(chǎn)工程、高層建筑到大型的鐵路工程、橋梁工程、電力工程、水利工程等，到處都有塔機(jī)的應(yīng)用。近20年來，市場的需求，有力的促進(jìn)了技術(shù)的進(jìn)步，通過研究開發(fā)、技術(shù)創(chuàng)新、引進(jìn)消化，我們的設(shè)計手段和配套件生產(chǎn)能力也有了很大的進(jìn)步，計算機(jī)輔助設(shè)計、微電子技術(shù)、程控語言控制技術(shù)都在塔機(jī)上得到了應(yīng)用。當(dāng)然也不可否認(rèn)，我國的塔機(jī)產(chǎn)品的技術(shù)性能、制作質(zhì)量和品種型號規(guī)格，與發(fā)達(dá)國家產(chǎn)品相比，仍然存在較大的差距，特別是基礎(chǔ)零部件的可靠性、電氣元件、液壓元件、工藝安裝、生產(chǎn)設(shè)備和檢測手段等，差距更大。這就影響了我們整機(jī)產(chǎn)品的質(zhì)量和可靠性，增加了事故隱患。對此我們絕不可以掉以輕心，要加倍努力、敢于創(chuàng)新、嚴(yán)格把關(guān)、趕超國際水平。 (三) 我國塔式起重機(jī)的發(fā)展趨勢 我國大規(guī)模經(jīng)濟(jì)建設(shè)已有二十來年的歷史，這二十來年里，大量建筑物的涌現(xiàn)和大型工程的興建，鐵路、公路橋梁的建設(shè)，給塔式起重機(jī)提供了良好的市場。我國的塔式起重機(jī)發(fā)展趨勢可以分以下幾個方面： ① 我國塔機(jī)產(chǎn)品的品種、型號、規(guī)格應(yīng)向多樣化發(fā)展，以適應(yīng)不同工程、不同用戶的需求。就目前現(xiàn)實而言，我國塔式起重機(jī)幾乎是上回轉(zhuǎn)一統(tǒng)天下，下回轉(zhuǎn)塔機(jī)很少。 這正好說明我國塔機(jī)品種單一化，實際上只要是有技術(shù)創(chuàng)新，下回轉(zhuǎn)塔機(jī)在我國完全是可以大有作為的。 ② 適當(dāng)發(fā)展動臂式自升塔機(jī)和折曲式兩用臂架自升塔機(jī)的生產(chǎn)，以適應(yīng)塔機(jī)出口市場和國內(nèi)大中型城市內(nèi)某些特定工程和鋼結(jié)構(gòu)高層建筑施工的需要。 ③ 更多的采用組裝式結(jié)構(gòu)，做到產(chǎn)品系列化，部件模數(shù)化，以不同模數(shù)塔身、臂架標(biāo)準(zhǔn)節(jié)組合成的變斷面塔身和臂架，這不僅能提高塔身、臂架的力學(xué)性能，減輕塔式起重機(jī)自重，而且可明顯減少使用單位塔架、臂架的儲備量，為單位節(jié)約成本。便于產(chǎn)品更新?lián)Q代，簡化設(shè)計制造，提高塔機(jī)使用的經(jīng)濟(jì)效益。 (四) 國外塔式起重機(jī)的發(fā)展現(xiàn)狀 ① 組合塔機(jī)或稱模塊塔機(jī)：所謂組合塔機(jī)，就是以塔身結(jié)構(gòu)為核心，按結(jié)構(gòu)和功能特點，將塔機(jī)分解為若干部分，并依據(jù)系列化和通用化要求，遵循模數(shù)制原理將各部分劃分并設(shè)計成若干模塊。根據(jù)參數(shù)要求，選用適當(dāng)模塊分別組成具有不同技術(shù)性能特點的塔機(jī)，以滿足施工的具體要求。 ② 一些超重型塔機(jī)相繼問世：近年來由于大功率電站、高壩、近海石油鉆井平臺、天然氣鉆井平臺以及石油化工業(yè)發(fā)展的需要，對重型和超重型塔機(jī)提出了更多更高的要求。如今，幅度70～90m、最大起重量50～60t、起升高度100～300m的塔機(jī)已非罕見。 ③ 適應(yīng)都市改建需要的城市塔機(jī)應(yīng)運而生，并得到發(fā)展，其特點是：采用短平衡臂、可在4m×4m～6m×6m尺寸范圍內(nèi)進(jìn)行X形底架、運輸方便快捷、安裝架設(shè)速度快、采用較完善的調(diào)速、操縱系統(tǒng)和電子儀表。 (五) QTZ500型塔式起重機(jī)的簡單介紹及其市場前景 QTZ500型塔式起重機(jī)簡稱QTZ500型塔機(jī)，是500kN·m上回轉(zhuǎn)自升式塔機(jī)，是一種結(jié)構(gòu)合理，性能比較優(yōu)異的產(chǎn)品，比較國內(nèi)同規(guī)格同類型的塔機(jī)具有更多的優(yōu)點，能夠滿足高層建筑施工的需要，可用于建筑材料和預(yù)制構(gòu)件的吊運和安裝，并能在市內(nèi)狹窄地區(qū)和丘陵地帶建筑施工。 該機(jī)屬于快裝塔機(jī)和城市塔機(jī)，用于中小城市公用建筑、學(xué)校建筑和多層住宅的施工建設(shè)。以基本高度（獨立式）36米。如果用戶需要高層附著施工，只需提出另行訂貨需求，即可增加某些部件實現(xiàn)本機(jī)的最大設(shè)計高度100m，也就是附著高層施工，可建32層以內(nèi)的高樓。 近年來，隨著建設(shè)工程量的不斷擴(kuò)大，起重安裝工程量也越來越大，尤其是現(xiàn)代化大型石油、化工、冶煉、電站及高層建筑的安裝作業(yè)逐年增加，因此，對工程起重機(jī)特 別是大規(guī)模的起重機(jī)需求日益增加，隨著當(dāng)代科學(xué)技術(shù)的發(fā)展，各種新技術(shù)、新材料、新工藝、新結(jié)構(gòu)在工程起重機(jī)上得到廣泛的應(yīng)用，所有這些因素都有力的促進(jìn)了工程起重機(jī)的發(fā)展。目前中小城市居民樓建設(shè)主要以10層以內(nèi)的為多，而我們的產(chǎn)品QTZ500型塔式起重機(jī)主要針對城市12層以內(nèi)高樓的建設(shè)以及設(shè)備安裝工作，適合當(dāng)前市場的需要，因此設(shè)計生產(chǎn)這一型號的塔式起重機(jī)是可行的。 二、本課題的目的（重點及擬解決的關(guān)鍵問題） 本次畢業(yè)設(shè)計是對機(jī)械專業(yè)學(xué)生在畢業(yè)前的一次全面訓(xùn)練，目的在于鞏固和擴(kuò)大我們在校所學(xué)的基礎(chǔ)知識和專業(yè)知識，訓(xùn)練我們綜合運用所學(xué)知識分析和解決問題的能力。是培養(yǎng)、鍛煉我們獨立工作能力和創(chuàng)新精神之最佳手段。畢業(yè)設(shè)計要求我們在設(shè)計過程中，要獨立思考，刻苦鉆研，有所創(chuàng)新，解決相關(guān)技術(shù)問題。通過畢業(yè)設(shè)計，使我們掌握塔式起重機(jī)的總體設(shè)計，吊臂的設(shè)計，整體穩(wěn)定性計算，有限元分析等內(nèi)容，為今后步入社會、走上工作崗位打下良好的基礎(chǔ)。通過此次設(shè)計使我們獲得基本塔機(jī)結(jié)構(gòu)設(shè)計，理論聯(lián)系實際，擴(kuò)大知識面；同時也是鍛煉和培養(yǎng)自身能力及素質(zhì)的重要渠道，也是我們逐步實現(xiàn)由學(xué)生到社會的轉(zhuǎn)變，培養(yǎng)我們初步擔(dān)任技術(shù)工作的能力、初步了解企業(yè)管理的基本方法和技能，體驗企業(yè)工作的內(nèi)容和方法。 三、主要內(nèi)容、研究方法、研究思路 (一) 主要內(nèi)容 （1） 設(shè)計任務(wù)： ① 總體參數(shù)的選擇（QTZ500級別） ② 結(jié)構(gòu)形式 （2） 總體設(shè)計： ① 主要技術(shù)參數(shù)性能 ② 設(shè)計原則 ③ 平衡重的計算 ④ 塔機(jī)的風(fēng)力計算 ⑤ 整機(jī)傾翻穩(wěn)定性的計算 （3） 吊臂的設(shè)計和計算： ① 吊臂的形式及尺寸（變截面）（雙吊點） ② 吊臂的強(qiáng)度、穩(wěn)定性及剛度驗算 (二) 研究方法 ① 類比法：參考國內(nèi)同類型塔式起重機(jī)設(shè)計； ② 有限元分析法：利用有限元分析軟件對臂架進(jìn)行優(yōu)化設(shè)計。 (三) 研究思路 塔式起重機(jī)的機(jī)構(gòu)是有起升機(jī)構(gòu)、回轉(zhuǎn)機(jī)構(gòu)、小車變幅機(jī)構(gòu)、行走機(jī)構(gòu)四大傳動機(jī)構(gòu)組成，另外還要重點注意該機(jī)的金屬結(jié)構(gòu)，塔機(jī)的金屬結(jié)構(gòu)又分為塔身、臂架、平衡臂、塔頂、以及頂升套架。我們應(yīng)該不僅設(shè)計好塔機(jī)的機(jī)構(gòu)，更重要的也要設(shè)計好塔機(jī)的金屬結(jié)構(gòu)，所以我們這次設(shè)計分塊分工完成。 我負(fù)責(zé)設(shè)計的部分是塔式起重機(jī)金屬結(jié)構(gòu)中臂架的優(yōu)化設(shè)計，臂架是由若干個臂架標(biāo)準(zhǔn)節(jié)組成的，所以我以臂架標(biāo)準(zhǔn)節(jié)節(jié)為單位進(jìn)行參數(shù)化設(shè)計，提出參數(shù)化模型，并利用三維制圖軟件制成三維圖，并利用有限元分析軟件對塔式起重機(jī)進(jìn)行動力學(xué)和靜力學(xué)分析，以對結(jié)果進(jìn)一步優(yōu)化設(shè)計。 四、總體安排和進(jìn)度（包括階段性工作內(nèi)容及完成日期） 2009.3.23-2008.3.28 熟悉整理資料 2009.3.29-2009.4.13 方案選擇及總體設(shè)計 2008.4.14-2008.4.20 繪制總圖 2008.4.21-2008.5.15 臂架設(shè)計 2008.5.16-2008.6.5 繪制臂架裝配及機(jī)構(gòu)圖紙 2008.6.6-2008.6.19 繪制零件圖紙 2008.6.20-2008.6.26 準(zhǔn)備論文及答辯 五、主要參考文獻(xiàn) [1] 哈爾濱建筑工程學(xué)院主編.工程起重機(jī).北京：中國建筑工業(yè)出版社 [2] 董剛、李建功主編.機(jī)械設(shè)計.機(jī)械工業(yè)出版社 [3] 機(jī)械設(shè)計手冊.化學(xué)工業(yè)出版社（5冊） [4] GB/T9462—1999 塔式起重機(jī)技術(shù)條件 [5] GB/T13752—1992 塔式起重機(jī)設(shè)計規(guī)范 [6] GB5144—1994 塔式起重機(jī)安全規(guī)程 指導(dǎo)教師意見： 指導(dǎo)教師簽名： 日期： 教研室意見： 教研室主任簽名： 日期： 系意見： 系領(lǐng)導(dǎo)簽名： 日期： 系蓋章 目 錄 第1章 前言··········································································1 1.1 概述··············································································1 1.2 發(fā)展趨勢·······································································1 第2章 總體設(shè)計····································································2 2.1 概述···········································································2 2.2 確定總體設(shè)計方案························································2 2.3 總體設(shè)計原則·····························································29 2.4 平衡臂與平衡重的計算················································31 2.5 起重特性曲線·····························································32 2.6 塔機(jī)風(fēng)力計算·····························································34 2.7 整機(jī)的抗傾覆穩(wěn)定性計算·············································43 2.8 固定基礎(chǔ)穩(wěn)定性計算···················································49 第3章 吊臂的設(shè)計計算·······················································51 3.1 分析單吊點與雙吊點的優(yōu)缺點·······································51 3.2 吊臂吊點位置選擇······················································51 3.3 吊臂結(jié)構(gòu)參數(shù)參數(shù)······················································53 3.4 有限元模型建立過程的幾點簡化····································53 3.5 吊臂結(jié)構(gòu)的有限元分析計算··········································54 3.6 計算結(jié)果分析····························································70 3.7吊臂強(qiáng)度校核······························································75 3.8 吊臂穩(wěn)定性校核·························································75 畢業(yè)設(shè)計小結(jié)······································································84 致謝··················································································85 參考文獻(xiàn)············································································86 附：英文原文 英文翻譯 畢業(yè)實習(xí)報告 Abstract Refers to the similar tower crane, this design is composed by the system design and the lazy arm design to the QTZ500 tower crane. In the lazy arm design progress, it has carried Finite Element method on the analysis computation, and used ANSYS10.0 software. According to the entire machine main performance parameter, various organizations type and the steel structure pattern has been determined. The design parameter of operating modes which are composed of nose increase, the cross center increase and the root increase. Through the suitable simplification to the lazy arm, the lazy arm finite element model is establishment applied ANSYS10.0 software, and then exerted various operating modes load, carried on the solution. Then ANSYS10.0 software can calculate various pitch points stress situation, various units receive the axial stress size, and the lazy arm distortion size under various operating modes. Also it can demonstrate the animation in the process of the lazy arm increase. It has clearly displayed the lazy arm stress performance under various operating modes. Through the revision for model parameter, the analysis comparison is carried on the different model. Because the stress condition and rigidity condition of different model is compared under the same operating mode, and the generalized analysis intensity and the rigidity condition is carried on, a most reasonable model parameter can be obtained, though the intensity and the rigidity examination regarding this model, then the final parameter result of the lazy arm can be obtained. Key words: QTZ500 tower crane Lazy arm Finite element analysis ANSYS10.0 MR imaging at high magnetic fields Masaya Takahashi a, *, Hidemasa Uematsu b , Hiroto Hatabu a a Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA 02115, USA b Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, PA, USA Received 12 November 2002; received in revised form 13 November 2002; accepted 14 November 2002 Abstract Recently, more investigators have been applying higher magnetic field strengths (3C1/4 Tesla) in research and clinical settings. Higher magnetic field strength is expected to afford higher spatial resolution and/or a decrease in the length of total scan time due to its higher signal intensity. Besides MR signal intensity, however, there are several factors which are magnetic field dependent, thus the same set of imaging parameters at lower magnetic field strengths would provide differences in signal or contrast to noise ratios at 3 T or higher. Therefore, an outcome of the combined effect of all these factors should be considered to estimate the change in usefulness at different magnetic fields. The objective of this article is to illustrate the practical scientific applications, focusing on MR imaging, of higher magnetic field strength. First, we will discuss previous literature and our experiments to demonstrate several changes that lead to a number of practical applications in MR imaging, e.g. in relaxation times, effects of contrast agent, design of RF coils, maintaining a safety profile and in switching magnetic field strength. Second, we discuss what will be required to gain the maximum benefit of high magnetic field when the current magnetic field (5/1.5 T) is switched to 3 or 4 T. In addition, we discuss MR microscopy, which is one of the anticipated applications of high magnetic field strength to understand the quantitative estimation of the gain benefit and other considerations to help establish a practically available imaging protocol. # 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Magnetic resonance imaging; Higher magnetic field strength; Contrast agent 1. Introduction Thanks to recent technological development, whole- body magnetic resonance (MR) scanners at higher magnetic field strengths (/3T)have been introduced into research and clinical settings. In the beginning, one of the main reasons to install higher fields was its higher sensitivity to the blood oxygenation level-dependent effect for functional MR imaging of the brain 1. Recently, more investigators applied these higher mag- netic field strengths to both research and conventional clinical settings. The expectation for higher magnetic fields in MRI is the improvement in signal-to-noise ratio (SNR) due to higher signal intensity (SI), where the most significant benefit is to decrease the length of time required to obtain images. Then, higher spatial resolu- tion may be achievable. One question is how it improves or practically how beneficial it is when we switch the current magnetic field (5/1.5 T) to 3 or 4 T. Several studies have reported and discussed the advantages of higher magnetic field in, for example, delineation of various brain lesions 1 or cardiac structures 2,3. Dougherty et al. 2 reported that the SNR of the anterior myocardium at 4 T was 2.9 times higher than that of the same region at 1.5 T. Bernstein et al. demonstrated contrast enhanced imaging at 3 T and concluded that higher spatial resolution at 3 T could improve diagnostic accuracy 4. In addition, if higher magnetic field can provide better image quality, it may be reasonable to expect a reduction in total injection of contrast agent, for example, in MR angiography which needs to cover a larger area of the peripheral artery 5 or the lung 6,7. However, such speculation would be difficult to prove as higher magnetic fields change other imaging aspects besides SNR. Many theoretical and experimental studies havebeen employed to demonstrate the magnetic field dependen- cies. Besides SNR, the magnetic field-dependence is * Corresponding author. Tel.: C27/1-617-667-0198; fax: C27/1-617-667- 7021. E-mail address: mtakahascaregroup.harvard.edu (M. Takahashi). European Journal of Radiology 46 (2003) 45C1/52 0720-048X/02/$ - see front matter # 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 7 2 0 - 0 4 8 X ( 0 2 ) 0 0 3 3 1 - 5 well-documented in tissue relaxation times 8C1/10,as well as in MR contrast agent effects (e.g. R1, R2 or R2* relaxivities) 11,12. SNR depends upon imaging para- meters, RF coil sensitivity and machine adjustments, such as magnetic field homogeneity, accuracy in excita- tion/refocusing pulse settings, etc. These theoretical and experimentally proven properties suggest that imaging parameters must be reconfigured for different magnetic fields. Unlike relaxation time and MR contrast agent effects, the benefit to signal intensity at higher magnetic field should be compared under nearly identical experi- mental conditions. Therefore, it is imperative to quan- tify the practical differences in terms of SNR and contrast-to-noise ratios (CNR) between higher and lower (B/1.5 T) magnetic fields. However, the studies of direct comparisons between SNRs and CNRs as an outcome of the combined effect of several magnetic field-dependent parameters at different fields compared with the theoretical values are substantially sparse. Hence, it is still unclear how much benefit we can gain in SNR or what we can/should do in switching a current magnetic field strength (5/1.5 T in most cases) to a higher magnetic field. In this article, we consider the magnetic field dependent alterations, e.g. MR signal on the image, relaxation times, effects of contrast agent, design of RF coil and safety profile. Then, we evaluate the scientific expectations for MR imaging on a higher magnetic field to quantify the scientific and technical issues relative to safe human experimentation. Further, the feasibility of MR microscopy, which is one of the expectations of higher fields, is discussed. 2. SI, SNR and CNR The question of optimum field strength has been a subject of intense controversy for over a decade. The interest in higher fields stems from the fact that SNRs increase with field strength (v), where SI and noise have different magnetic field-dependencies. SI8(number of spins) C29(voltage induced by each spin) (1) As shown in Eq. (1), theoretically, the signal intensity from a MR experiment is proportional to the square of the static magnetic field (v 2 ) since both number of spins that can be observed and voltage induced by each spin increase linearly as magnetic field (v) increases. Noise is proportional to the static magnetic field (v), when all noise comes from a sample, resulting in an SNR that is proportional to v in the case. On the other hand, noise is proportional to one-quarter of v (v 1/4 ) when all noise comes from the RF coil, resulting in an SNR that is proportional to v 7/4 . Therefore, SNR can be expected to increase more than 2.7 (C30/4/1.5) times at 4 than at 1.5 T. If this is true, since the SNR scales as the square root of the number of image averages, the time needed to obtain the same SNR is reduced by a factor of 8. To confirm this theory, we imaged the brain in a subject at both fields. To make our comparison between the magnetic fields as direct as possible, the same sets of experiments in the same subjects were conducted at both 4 and 1.5 T on the commercially supplied whole-body MR scanners (Signa TM , General Electric Systems, Mil- waukee, WI) with the equipped head coils. Fig. 1 shows the T1-weighted images (top) and T2-weighted images (bottom) obtained in the same level of the brain of the same subject. Each image was obtained with a conven- tional spin echo sequence with the same imaging parameters at 1.5 and 4 T, respectively. These images showed different tissue contrast between the magnetic fields even though the images were acquired with the same set of imaging parameters. In the quantitative measurements of SI, we found that 4 T increased the SI in both white and gray matter (Fig. 1). In addition, those enhancement ratios were also different between the imaging parameters (T1-WI and T2-WI). Thus, 4 T provides a different tissue contrast compared with 1.5 T using the same set of imaging parameters, which might be inconsistent with theoretical values. 3. Relaxation times As discussed above, SNR in biological tissue was found to be in approximate proportion to field strength. However, the practically achievable SNR gain may be somewhat less since the above theory assumes that all parameters except the magnetic field are consistent. One reason for the discrepancy is the increase in T1 relaxa- tion time with increasing field strength. SI is a function of relaxation time that is, in turn, magnetic field- dependent 3. In theory, T1 value increases in a magnetic field-dependent manner in most biological tissues of which the correlation time (t c ) of tissue water is :/10 C288 s 13, whereas T2 value does not change (Fig. 2). Comparisons of relaxation times in humans have been published in the literature. Jezzard et al. and Duewell et al. presented a comparison of T1 and T2 relaxation times in human subjects between 1.5 and 4 T in the brain and several peripheral regions 9,10 (Table 1). In any tissue, T1 relaxation times are prolonged at a higher magnetic field, while T2 relaxation times are somewhat shortening. Those results are consistent with previous reports (Fig. 2). To confirm this phenomenon, we conducted the same set of phantom experiments at both 4 and 1.5 T on the same whole-body MR scanners with head coils 14. Phantoms included different con- centrations of Gd-complex aqueous solution with each phantom representing tissue with a different T1 relaxa- M. Takahashi et al. / European Journal of Radiology 46 (2003) 45C1/5246 tion time. In this study, the trains of spin echo images with varied TRs or TEs were obtained with the same commercial clinical scanners with the head coils de- scribed above. The relaxation times (T1, T2) for all phantoms were determined at both 1.5 and 4 T from the fitting curves. The results in this confirmatory study demonstrated that any T1 relaxation times were pro- longed (1.10C1/1.47 times) at 4 T compared with those at 1.5 T, while T2 values were identical or slightly shortened (Table 2). Further, a standard contrast-enhanced MR angio- graphic sequence (3D spoiled gradient recalled acquisi- tion or SPGR) sequence with the same imaging parameters was utilized to confirm changes in SI. Peak SNRs at 4 T increased at least 2.21 times higher compared with those at 1.5 T. Moreover, peak CNRs at 4 T increased at least 1.59 times higher compared with those at 1.5 T in the range of Gd concentrations expected during clinical use. In addition, those enhance- ments of SNR and CNR were a function of a flip angle that we used. Based on those results, using higher Fig. 1. T1- and T2-weighted images of a human subject obtained at 1.5 and 4 Tesla. Each image was acquired with the same set of imaging parameters (TR/TE is indicated in the parentheses), respectively. Note that different magnetic fields provided different image contrast. Fig. 3. Cross-sectional T1-weighted image of a fixed excised spinal cord of the larval sea lamprey. Image was obtained at 9.4 T experimental machine; resolution was 9C29/9 mm resolution. See Ref. 27. Fig. 2. Magnetic field dependency in T1 and T2 relaxation times, modified from Ref. 13. M. Takahashi et al. / European Journal of Radiology 46 (2003) 45C1/52 47 magnetic fields seems to be beneficial in CNRs as well as in SNRs even without optimization of imaging para- meters at each magnetic field. A relationship between the SI of a gradient echo sequence, the relaxation time and the optimal flip angle (a o : Ernst angle), can be expressed as follows: SIC30bC215 1 C28 exp(C28TR=T1) C215 exp(C28TE=T2C31) C215 sin a 1 C28 exp(C28TR=T1) C215 cos a (2) and cos a o C30C28exp(TR=T1) (3) where b is the scaling factor and a is the flip angle. SI is determined by its relaxation times (T1 and T2*) in individual tissue conditions in any imaging sequence. This implies that the same intensity will not be obtained with the same set of imaging parameters due to the alternation of relaxation times at different magnetic field. Since T1 values at higher magnetic field are longer than those at lower magnetic field, the TR, presumably as well as the flip angle, should be longer (smaller for flip angle) to optimize the SNR of the same sample at the higher field. Using longer TR, the advantage in SI at a higher field would be less in unit time. In other words, since the primary limitation imposed by long T1 relaxation time at higher magnetic field strength is reflected in the TR, the SNR per unit time is optimized with an Ernst angle pulse and the shortest achievable value of TR/T1. The necessity of optimization of imaging parameters was presented in a previous work. Keiper et al. 15 compared the usefulness in the diagnosis of white matter abnormalities in multiple sclerosis patients following the optimization of imaging parameters between 1.5 and 4 T. Their results demon- strated that MR imaging at 4 T (512C29/256 matrix) could depict smaller lesions that could not be detected at 1.5 T (256C29/192 matrix), implying that the higher resolution at 4 T provides higher accuracy of diagnosis in the same patients with almost identical total scan time. Although T2 values were substituted for T2* in the phantom study because T2 and T2* values should be theoretically identical in phantoms in each magnetic field 16, it is considered to be different from the conditions in some tissues where the T2* value is much shorter than the T2 value in some tissues. A magnitude of susceptibility (g) is proportional to the magnetic field as shown in the following equation 17: gC30 C18 Dx 2 C19C18 B 0 RG z C19 (4) where Dx is the difference in magnetic susceptibility of adjoining substances, B 0 (C30/v) is the static magnetic field, R is the cross section radius and G z is the read-out gradient. However, this effect on T2* depends on T2 in tissue since 1/T2* is a function of T2 and T2? (R2*C30/ R2C27/R2?) 18. The shorter T2 and T2* values at a higher magnetic field may cause a larger decrease in the SNR and CNR than would be expected in some tissue, such as the lung. Previously, we found that the CNR increased in the central arteries of the lung, but did not increase in the pulmonary peripheral arteries at 4 T as the dose of contrast agent increased, ranging from 0.05 to 0.2 mmol/kg body weight 19. Therefore, the optimal imaging parameters for the clinical application should be carefully considered, particular when an undesirable T2* effect may be involved. 4. Relaxivities of Gd-complex The R1 relaxivity of MR contrast agent is dependent upon various parameters, such as the type of contrast agent 20, temperature and tissue environment as well as magnetic field strength 11,12. R1 relaxivity of a paramagnetic contrast agent is higher at lower field strength 11. R2 and R2* values should be theoretically identical in phantoms in each magnetic field 16. In the phantom study described above, the authors attempted to compare the effects of contrast agent. For an accurate determination of the efficacy of Gd-complex (R1, R2 and R2*), only some of the relaxation times Table 1 Comparison of T1 and T2 relaxation times in human subject 9,10 Tissue T1 (s) T2 (ms) 1.5 T 4 T 1.5 T 4 T Brain a Gray matter 0.9C1/1.3* 1.72 77C1/90 63 White matter 0.7C1/1.1* 1.04 62 C1/80 50 Muscle b 0.98 1.83 31 26 Fat b 0.31 0.39 47 38 Bone marrow b 0.29 0.42 47 42 a Lezzard et al. 9. b Duewell et al. 10. * From previous literature. Table 2 Comparison of T1 and T2 relaxation time in gadolinium doped water solution at room temperature, modified Ref. 14 Gd concentration (mmol/l) T1 (ms) T2 (ms) 1.5 T 4 T 1.5 T 4 T 0 2556 3636 1643 1504 0.125 1067 1566 911 862 0.5 419 562 348 351 1.25 191 253 160 160 2.5 123 142 84 83 5 67814342 At room temperature. M. Takahashi et al. / European Journal of Radiology 46 (2003) 45C1/5248 (T1, T2) that could be excellently fitted to the curve(rC21/ 0.995) were reciprocally plotted against the concentra- tions of Gd at both 4 and 1.5 T. As a result, R1 and R2 relaxivity values were determined to be 2.95 and 4.82 (lC215/ s C281 C215/mmol C281 ) at 4 T and 3.89 and 4.67 (lC215/s C281 C215/mmol C281 ) at 1.5 T, respectively. R1 at 4 T was lower (:/25%) than R1 at 1.5 T, while the R2 at 4 T was almost that at 1.5 T (Table 3). Hence, we found that R1 relaxivity decreases as the magnetic field strength increases, while R2 relaxivity does not change as much, which is consistent with previous reports 16. Unlike Gd-complex, R2 and R2* might be consider- ably changed depending upon the type of contrast agent (e.g. super paramagnetic iron oxide: SPIO), application root and/or tissues. This suggested that we should also consider the use of the MR contrast agent, though it is not clear whether this change is substantially effectivein current clinical usage at higher magnetic field. 5. RF coil The application of higher magnetic field strengths to MR imaging (particular in whole body imaging) is more demanding because of the difficulty in building RF coils since the penetration of radio frequency into the tissue becomes harder 3,21. It is necessary to understand the relationship between SNR and RF coil, since an incomplete RF coil may sacrifice the advantage in SNR at increased magnetic field strength. RF coil characteristics, especially a receive coil, significantly impact SNR. SNR increases with decreasing coil diameter. Thus, the coil sensitivity of the head coil is :/3-fold higher than that of the body coil. The surface coil with smaller diameter gains more sensitivity, whereas the SNR drops off very rapidly with increasing depth from the surface. To cover these difficulties, an array of surface coils must be developed. Reported by Wright et al. 22, another idea to increase coil sensitivity and further improve SNR is to reduce coil temperature, thus lowering its resistance and thermal noise voltages and increasing its Q, while keeping the sample at room temperature. The cryogenic SNR gain would be greatest for coil and sample configurations having Q L /Q U close to 1. 6. Safety consideration Theoretical calculations of the interaction of high magnetic fields with human subjects havebeenreviewed. To date, no hazardous physical or physiological phe- nomena have been shown. The mechanism considered included orientation of macromolecules and mem- branes, effects on nerve conduction, electrocardiograms and electroencephalograms, and blood flow. The most current clinical MR imagers at lower magnetic field (5/1.5 T) equip up to 25 mT/m. If higher magnetic fields are to be used to archive higher spatial resolution, the gradient strength must increase. In the combination of higher statistic magnetic field and gradients, strength may be an issue in some applications due to limitations in the current FDA guidelines for specific absorption rate (SAR). SAR is defined as follow: SARC30 sjEj 2 2r C18 t TR C19 N P N S (5) where s is conductivity, E is the electric field, r is tissue density, t is pulse duration and N P and N S are number of pulses and image slices, respectively. Since E is proportional to static magnetic field, SAR greatly increases at higher magnetic field, which may limit the application in number of slices, selection of flip angle, etc. Additionally, RF energy is absorbed more effec- tively at higher frequencies; RF absorption, as expressed by SAR, must be carefully monitored. This could be a major concern in any application at high field strength as Bottomley et al. previously suggested 21. 7. MR microscopy In using a higher magnetic field, the investigators expect images with higher spatial resolution to be more beneficial in research and clinical settings. Recent