多功能農(nóng)業(yè)機械手結(jié)構(gòu)設(shè)計（含三維SW及仿真）

多功能農(nóng)業(yè)機械手結(jié)構(gòu)設(shè)計（含三維SW及仿真）,多功能,農(nóng)業(yè),機械手,結(jié)構(gòu)設(shè)計,三維,SW,仿真 附件5 本科生畢業(yè)設(shè)計（論文）開題報告 學(xué) 院 智能工程學(xué)院 年 級 2020級 學(xué) 號 姓 名 指導(dǎo)教師 年 月 日　 廣西城市職業(yè)大學(xué)本科生畢業(yè)設(shè)計（論文）開題報告 學(xué)院（全稱）： 專業(yè)（全稱）： 機械設(shè)計制造及其自動化 姓名 學(xué)號 年級 2020級 班級 2班 設(shè)計（論文） 題目 多功能農(nóng)業(yè)機械手機械結(jié)構(gòu)設(shè)計 指導(dǎo)教師姓名 職稱 未定職 擬完成時間 　　年　月　 日 論文（設(shè)計）類別 t項目設(shè)計制作類　　 囗項目設(shè)計策劃類 囗實踐操作類　 囗課堂教學(xué)與設(shè)計類　　囗學(xué)位論文類　 命題來源 t教師命題 囗學(xué)生自擬 囗教師科研課題 是否在實驗實訓(xùn)、實習(xí)、工程實踐和社會調(diào)查等社會實踐中完成 囗是 t否 一、選題依據(jù)及意義（不少于300字） 在農(nóng)業(yè)生產(chǎn)中果蔬采摘作業(yè)是果蔬生產(chǎn)鏈中最耗時,最費力的一個環(huán)節(jié),果蔬收獲期間需投入的勞力約占整個種植過程所用勞力的50%-70%。隨著社會經(jīng)濟的發(fā)展和人口老齡化,很多國家農(nóng)業(yè)勞動力嚴(yán)重短缺,導(dǎo)致果蔬生產(chǎn)勞動力成本增加,為降成本,提高勞動效率,果實采摘的自動化成為待解決的問題（圖1-1采摘機器人）。近年來,隨著電子技術(shù)特別是電子計算機的廣泛應(yīng)用,機械手的研制和生產(chǎn)已成為高科技技術(shù)領(lǐng)域內(nèi)迅速發(fā)展起來的一門新興技術(shù)。它更加促進了機械手的發(fā)展,使得機械手能更好地實現(xiàn)與機械化和自動化的有機結(jié)合。 圖1-1 蘋果采摘機器人 目前,機械手雖然還不如人手那樣靈活,但它具有可不斷重復(fù)工作、能在條件比較惡劣的環(huán)境下工作、載重量大、定位精確等特點,因此受到了農(nóng)業(yè)部門的重視。它可以在惡劣的環(huán)境中收割作物,提高收割精度和產(chǎn)量,使機械手在農(nóng)業(yè)方面越來越廣泛地得到了應(yīng)用。鑒于此，我們以多功能農(nóng)業(yè)機械手設(shè)計為課題進行了多功能農(nóng)業(yè)機械手的相關(guān)結(jié)構(gòu)設(shè)計改進。為后續(xù)設(shè)計該多功能農(nóng)業(yè)機械手提供可靠的數(shù)據(jù)依據(jù)。 二、研究目的與主要內(nèi)容（含設(shè)計（論文）提綱，不少于500字） 本次多功能農(nóng)業(yè)機械手設(shè)計，我們以抓取番茄為目標(biāo)。該裝置由末端執(zhí)行器、機械臂、及傳感器組成。通過兩指抓手對番茄莖進行抓取。該機械手通過夾取番茄莖對其進行采摘。該機器手在穩(wěn)定工作的過程中摘取番茄的速度大約是6個每分鐘。該機械手擁有豐富的自由度，非常適合農(nóng)業(yè)作物中對番茄的采摘。由于果實位置及成熟度不同，所以我們將機械手抓取位置設(shè)置為根莖處，可極大程度避免對果實的損壞。 圖2-1 多功能農(nóng)業(yè)機械手原理圖 多功能農(nóng)業(yè)機械手手爪與機械手的整個裝置是一體的,一個機械手系統(tǒng)只有一個手型,這種機械手只能抓取范圍很小的一類東西。特別是對于現(xiàn)在農(nóng)業(yè)生產(chǎn)中產(chǎn)品小批量、多品種的發(fā)展趨勢,以往的這種機械手暴露出很多弊端。當(dāng)作物變化時,企業(yè)不得不花費大量的資金來買新的機械手。買來的機械手可能用不了多久隨著作物品種的更換,這些機械手就被廢棄了,造成企業(yè)資金的嚴(yán)重浪費。 針對以往機械手適應(yīng)性不強的弊端,為使其靈活適應(yīng)不同的工作要求,在設(shè)計機械手的手部時,保證手的活動部位的活動原理不變,而手的根部和手指之間采用可拆卸的螺栓連接,也就是手爪部設(shè)計成大小、形狀、材料不同的產(chǎn)品,分系列生產(chǎn),以靈活適應(yīng)工作要求的變化,實現(xiàn)一個機械手多用的目的。遇到特殊情況,可以自己設(shè)計爪部,并安裝到機械手的根部。在農(nóng)業(yè)收割中,當(dāng)需要用機械手抓取的農(nóng)作物表面質(zhì)量要求較高、不能損害時,可以把機械手手部面積設(shè)計得較大些,增加作物的受力面積,在保證受力不變的情況下減小壓強,這樣,可使作物在夾緊過程中被抓物體的受力從開始到加緊有一個緩慢的過程,從而保護被抓物體的表面。 本論文主要研究內(nèi)容是運用三維軟件對多功能農(nóng)業(yè)械手進行結(jié)構(gòu)設(shè)計。在設(shè)計過程中，了解多功能農(nóng)業(yè)械手的結(jié)構(gòu)特征和三維軟件的使用要領(lǐng)。其研究內(nèi)容包括： （1）各部分功能分析與方案設(shè)計； （2）結(jié)構(gòu)設(shè)計與三維造型； （3）傳動部分設(shè)計與計算； （4）各個結(jié)構(gòu)部件的可靠性； （5）能夠?qū)崿F(xiàn)的功能； 三、研究方法和手段 1、調(diào)查研究設(shè)計內(nèi)容，進行理論分析。 2、通過查詢圖書資料以及相關(guān)文獻(xiàn)、文檔，了解的方案。 3、與指導(dǎo)老師及同學(xué)共同分析和探討所要設(shè)計的內(nèi)容含義等。 4、理論結(jié)合實際，對設(shè)計方案進行整體分析研究，得出結(jié)論。 5、繪制裝配圖與主要零件圖。 6、寫出畢業(yè)論文，仔細(xì)檢查修改。 7、指導(dǎo)老師檢查，錯誤的修改直到完成設(shè)計。 四、文獻(xiàn)綜述（在對選題涉及的研究領(lǐng)域的文獻(xiàn)進行廣泛閱讀或調(diào)查的基礎(chǔ)上，對該領(lǐng)域的研究現(xiàn)狀、發(fā)展動態(tài)等內(nèi)容進行綜述，并提出自己的見解和研究思路。不少于700字） 近年來,農(nóng)業(yè)生產(chǎn)正朝著規(guī)?；⒍鄻踊?、精確化方向發(fā)展,農(nóng)業(yè)勞動力的成本迅速上升,勞動力不足的現(xiàn)象日趨明顯,多功能農(nóng)業(yè)機械手技術(shù)越來越受到關(guān)注但是,由于采摘對象的復(fù)雜性和工作環(huán)境的非結(jié)構(gòu)化, 目前國內(nèi)的采摘自動化程度仍然很低,尤其是采摘機械手的關(guān)鍵部位--機械手,其結(jié)構(gòu)復(fù)雜、控制繁瑣等因素,造成工作效率低、生產(chǎn)成本較高,故不能在農(nóng)業(yè)生產(chǎn)中得到普遍的適用.所以對采摘機械手的設(shè)計及控制研究對于今后農(nóng)業(yè)生產(chǎn)具有深遠(yuǎn)意義。在日本、美國等發(fā)達(dá)國家,農(nóng)業(yè)人口較少。隨著農(nóng)業(yè)生產(chǎn)向規(guī)模化、多樣化、精確化的方向邁進,勞動力不足的現(xiàn)象越來越明顯。許多作業(yè)項目如蔬菜、水果的挑選與采摘,蔬菜的嫁接等都是勞動力密集型的工作,再加上時令的要求,勞動力缺乏的問題很難解決。正是基于這種情況,這些發(fā)達(dá)國家大力進行農(nóng)業(yè)生產(chǎn)機械手的研究,并取得了很好的成果。 國內(nèi)在多功能農(nóng)業(yè)機械手方面的研究始于20世紀(jì)90年代中期,相對于發(fā)達(dá)國家起步較晚,但是發(fā)展很快,很多院校、研究所都在進行多功能農(nóng)業(yè)機械手和智能農(nóng)業(yè)機械相關(guān)的研究。中國農(nóng)業(yè)大學(xué)張鐵中教授率先在我國開展了自動化嫁接技術(shù)的研究工作,先后成功開發(fā)了自動插接法、自動旋切貼合法嫁接技術(shù),填補了我國自動化嫁接技術(shù)的空白,形成了具有我國自主知識產(chǎn)權(quán)的自動化嫁接技術(shù)。上海交通大學(xué)機械手研究所的曹其新等人進行了用于精確農(nóng)業(yè)的智能農(nóng)業(yè)機械的研究工作,已經(jīng)完成了智能化聯(lián)合收割機、蔬菜工廠化育苗播種流水線樣機的研制,正在進行草莓挑選機械手、黃瓜采摘機械手的研究。浙江大學(xué)應(yīng)義斌教授研究的水果自動分級機械手系統(tǒng)得到國家"863"計劃的支持。吉林大學(xué)王榮本、于海業(yè)在90年代中期開始進行農(nóng)用自動引導(dǎo)行走車的研究。南京農(nóng)業(yè)大學(xué)姬長英、沈明霞等人,浙江工業(yè)大學(xué)青芳、張立斌等人,在進行多功能農(nóng)業(yè)機械手的視覺研究。江蘇大學(xué)紀(jì)良文、吳春篤進行了噴藥機械手的研究,他們采用超聲測距作為噴藥機械手的輔助視覺系統(tǒng)"還有吉林工業(yè)大學(xué)與吉林農(nóng)業(yè)研究所研制的鋤草機械手",中國農(nóng)業(yè)大學(xué)楊麗博士研制的組培苗分割移植機械手系統(tǒng),江蘇大學(xué)的陳樹人、尹建軍等在對西紅柿的視覺研究亦取得很大的成果,還有周云山和李強等人研究的蘑菇來摘機械手也處于是國內(nèi)領(lǐng)先水平,西北農(nóng)林科技大學(xué)對蘋果采摘機械手手臂控制進行了研究,東北林業(yè)大學(xué)的陸懷民研制了林木球果采摘機械手。 雖然在許多的農(nóng)業(yè)作業(yè)已經(jīng)實現(xiàn)了機械化，但仍有許多危險的、勞動強度大的和單調(diào)乏味的工作不適合人去做，需要一定的與人一樣的智能去完成，要使農(nóng)業(yè)持續(xù)下去，農(nóng)村勞動力的匱乏勢必導(dǎo)致勞動力成本的提高，急需大量的農(nóng)業(yè)機械或者自動機械參與到農(nóng)業(yè)生產(chǎn)中以實現(xiàn)農(nóng)業(yè)生產(chǎn)機械化和自動化，也提高在生產(chǎn)加工速度，綜上所述，可以看出，機械手的發(fā)展前景非常廣闊，但其發(fā)展需要我們進一步推動，來提高現(xiàn)代化生產(chǎn)的效率，簡化人工操作、降低運營成本、提高經(jīng)濟效益。 研究思路 五、參考文獻(xiàn)目錄（作者、書名或設(shè)計（論文）題目、出版社或刊號、出版年月或出版期號） [1] 方傳青.尹麗娟.仿真設(shè)計(ADAMS)在農(nóng)業(yè)機械手設(shè)計中的應(yīng)用[J].農(nóng)業(yè)裝備與車輛工程, 2008(02):20-22. [2] 鄭岳智.崔志鵬.采摘機械手在農(nóng)業(yè)方面研究分析[J]. 現(xiàn)代園藝, 2016, 000(002):207. [3] 姚金.一種農(nóng)業(yè)摘果機械手: CN208047328U[P]. 2018. [4] 黃浩乾.采摘機械手的設(shè)計及其控制研究[D]. 南京農(nóng)業(yè)大學(xué). [5] 陳樹人.戈志勇.王新忠.基于MATLAB的番茄采摘機械手運動學(xué)仿真研究[C]// 中國農(nóng)業(yè)機械學(xué)會學(xué)術(shù)年會.2006. [6] 黎波.辜松.初麒.等.葉菜椰糠培育種苗移植機械手設(shè)計與試驗簡[J].農(nóng)業(yè)工程學(xué)報.2017. [7] 姬偉.程風(fēng)儀.趙德安.等.基于改進人工勢場的蘋果采摘機械手機械手避障方法[J]. 農(nóng)業(yè)機械學(xué)報, 2013, 44(011):253-259. [8] 張望岐.機械手花生谷物播種機:, CN2144914Y[P]. 1993. [9] 周小燕.農(nóng)業(yè)機械手無碰運動規(guī)劃技術(shù)的研究[D]. 浙江工業(yè)大學(xué), 2009. [10] 趙東輝.農(nóng)業(yè)機械手的設(shè)計與分析[J]. 農(nóng)機化研究, 2010, 32(010):75-77,82. [11] 釧相艷.一種農(nóng)業(yè)機械手:. [12] 王玉榮.劉云泉, 潘榮晴.農(nóng)業(yè)果蔬采摘機械手機械手設(shè)計[J].電視技術(shù). 2019. 043(015):73-75. [13] 龔智強.楊沖.周智文. 一種多功能果蔬采摘機械手: CN206686628U[P]. 2017. [14] 郭甜甜. 一種具有控制器的農(nóng)業(yè)澆注機械手臂:, CN107309417A[P]. 2017. [15] 劉凡.楊光友.楊康.農(nóng)業(yè)采摘機械手柔性機械手研究[J]. 中國農(nóng)機化學(xué)報, 2019, 040(003):173-178. [16] 謝黎.基于3D的椰子采摘機械手設(shè)計[J]. 數(shù)碼設(shè)計（上）, 2018, 000(009):111. [17] 常新.采摘機械手結(jié)構(gòu)設(shè)計分析[J]. 科技尚品, 2016(4). [18] 李永強.黃瓜采摘機械手的定位與采摘研究[D]. 吉林大學(xué). 六、工作進度安排（時間、內(nèi)容、步驟） 2021.9.15－2021.9.28?選題，查閱資料，擬定大綱，填寫開題報告 2021.9.27－2021.10.10撰寫論文初稿并以班級為單位上交學(xué)院 2021.10.11－2021.10.22在指導(dǎo)老師指導(dǎo)下修改論文 2021.10.22－2021.10.28繼續(xù)修改論文，并定稿打印，送交論文，等待答辯 七、預(yù)期成果 1、完成三維軟件建模； 2、 完成二維圖紙； 3、 完成的工程圖繪制； 4、完成運動模擬； （以上內(nèi)容在教師指導(dǎo)下由學(xué)生填寫）　學(xué)生簽名：　　 年　　月　　日 八、指導(dǎo)教師審核意見： 　　　　 　　 　　　　　　　　　　　 指導(dǎo)教師簽名： 年　　月　　日 　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　 　　 九、學(xué)院畢業(yè)設(shè)計（論文）領(lǐng)導(dǎo)小組審核意見： 　　　　　　　 領(lǐng)導(dǎo)小組簽名： 年　　月　　日 說明：本表由學(xué)生填寫，指導(dǎo)教師和學(xué)院簽署意見，一式三份，分別存于教務(wù)處、學(xué)院、學(xué)生個人檔案。 外文翻譯資料 旋轉(zhuǎn)泵 旋轉(zhuǎn)泵應(yīng)用于不同的設(shè)計中，在流體動力系統(tǒng)中極其常用。今天最常用的旋轉(zhuǎn)泵是外齒輪泵、內(nèi)齒輪泵、擺線轉(zhuǎn)子泵、滑動葉片泵和螺旋泵。每種類型的泵都有優(yōu)點，適合于特定場合的應(yīng)用。 直齒齒輪泵，這種泵有兩個嚙合的齒輪在密封殼體內(nèi)轉(zhuǎn)動。第一個齒輪即主動輪的回轉(zhuǎn)引起第二個齒輪即從動輪的回轉(zhuǎn)。驅(qū)動軸通常連接到泵上面的齒輪上。 當(dāng)泵首次啟動時，齒輪的旋轉(zhuǎn)迫使空氣離開殼體進入排油管。這種泵內(nèi)空氣運動使泵吸入口處形成了真空，于是外部油箱的液體在大氣壓的作用下，由泵的入口進入，聚集在上下齒輪和泵殼體之間，齒輪連續(xù)的旋轉(zhuǎn)使液體流出泵的出口。 直齒齒輪泵的壓力的升高是由擠壓嚙合齒輪和腔體內(nèi)的液體產(chǎn)生的。當(dāng)齒輪脫開嚙合時，腔內(nèi)形成真空，使更多的液體被吸入泵內(nèi)。直齒齒輪泵是定排量的元件，當(dāng)軸轉(zhuǎn)速不變時，輸出流量恒定。只有一種方法即改變輸入軸的轉(zhuǎn)速，能調(diào)節(jié)這種直齒齒輪泵的排量。現(xiàn)代應(yīng)用在流體動力系統(tǒng)的齒輪泵的壓力可達(dá)3000psi。 圖示為直齒齒輪泵的典型特性曲線。這些曲線表明了泵在不同速度下的流量和輸入功率。當(dāng)速度給定時，流量曲線接近于一條水平的直線。泵的流量隨出口壓力的升高而稍有降低，這是由于泵的出油口到吸油口的齒輪徑向泄漏所增加而造成的。滲漏有時定義為泄漏，泵出口壓力的增加也會使泄漏增加。表征泵的出口壓力和流量之間關(guān)系曲線常叫做水頭流量曲線或泵的HQ曲線；泵的輸入功率和泵流量關(guān)系曲線叫做功率流量特性曲線或PQ曲線。 直齒齒輪泵的輸入功率隨輸入速度和出口壓力的增加而增加。隨著齒輪泵速度的增加，流量（加侖/分）也增加。于是在出口壓力為120psi，轉(zhuǎn)速為200rpm時，輸入功率是5馬力。在轉(zhuǎn)速為600rpm時，輸入功率是13馬力?？v坐標(biāo)壓力是120psi，橫坐標(biāo)是200rpm和600rpm時，在HQ曲線上可以讀出相應(yīng)的流量分別為40gpm和95gpm。 圖示是直齒齒輪泵在粘度不變時的情況。隨著流體粘度的增加（即流體變稠，不易流動），齒輪泵的流量降低。粘稠的流體在油泵高速運轉(zhuǎn)時，因為這種流體在油泵中不能迅速進入泵體完全充滿真空區(qū)，所以油流量受到限制。圖示為在流體動力系統(tǒng)中流體粘度的增大對旋轉(zhuǎn)泵工作情況的影響。當(dāng)流體的粘度值為100SSU，出口壓力為80psi時，泵流量為220gpm。當(dāng)流體的粘度值為500SSU時，泵流量減少到150gpm。由功率特性曲線可知，泵輸入功率也會增加。 可以用齒輪或其他內(nèi)部元件每轉(zhuǎn)一圈輸出多少加侖來表示泵的流量。如果封閉定量泵的出口，則出口壓力將會增加，直至驅(qū)動馬達(dá)停止或泵內(nèi)其他部分或排油管破裂。由于存在著破裂的危險，幾乎所有的流體動力系統(tǒng)都安裝壓力溢流閥。這種溢流閥可安裝在泵內(nèi)，也可安裝在排油管路。 滑動式葉片泵 這些泵有大量的葉片，葉片能在轉(zhuǎn)子的槽內(nèi)自由的滑進滑出。當(dāng)驅(qū)動轉(zhuǎn)子時，離心力，彈簧或壓力油使葉片伸出槽子，頂在泵殼體的內(nèi)腔或凸輪環(huán)上。隨著轉(zhuǎn)子的旋轉(zhuǎn)，葉片之間的流體經(jīng)過吸油口時，完成吸油。流體順著泵殼體到達(dá)排出口。在排出口，流體被排出，進入排油管。 圖示的滑動式葉片泵中的葉片安裝在橢圓形的腔內(nèi)。當(dāng)轉(zhuǎn)子開始旋轉(zhuǎn)時，離心力使葉片伸出槽子。同時葉片又受到其底部腔內(nèi)壓力油的作用力，壓力油來源于槽子端部的配流盤。吸油口通過A和A1口相通，他們位于直徑的相對位置。同樣兩排油口位于類似的位置。油口這樣配置，使葉片轉(zhuǎn)子保持壓力平衡，從而使軸承不受重載影響。當(dāng)轉(zhuǎn)子逆時針旋轉(zhuǎn)時，從吸油管出來的流體進入A和A1口，聚集在葉片之間，沿周向流動后，通過B和B1口排出。這樣設(shè)計的泵壓力可達(dá)2500psi。的泵必須分級才能達(dá)到這么大的壓力，而現(xiàn)在用一級泵即可達(dá)到。在轉(zhuǎn)子上應(yīng)用均流均壓閥可以達(dá)到高壓。轉(zhuǎn)速通常限制在2500rpm這是因為考慮到離心力和凸輪環(huán)表面葉片之間的磨損。圖示為泵在轉(zhuǎn)速為1200rpm粘度在100F的條件下的特性曲線。 每個槽內(nèi)安裝兩個葉片可以控制其作用于殼體內(nèi)部和凸輪環(huán)上的力。雙葉片會產(chǎn)生更緊的密封，能減少從排油口到吸油口之間的泄漏這種入口和出口相對應(yīng)的設(shè)計也能維持液壓平衡。這些都是定量泵。 不改變轉(zhuǎn)速就不能改變?nèi)~片泵的流量，除非油泵采用特殊設(shè)計。圖示為滑動式變量葉片泵。它不用雙吸油和排油口。轉(zhuǎn)子在壓力腔內(nèi)轉(zhuǎn)動，轉(zhuǎn)子形成的偏心量是可調(diào)的。隨著偏心的程度或偏心率的變化，流體的流量也隨著變化。圖示為轉(zhuǎn)子在旋轉(zhuǎn)180°范圍內(nèi)，產(chǎn)生一真空度以便于油液進入，同時壓油區(qū)也在180°范圍內(nèi)旋轉(zhuǎn)。吸油區(qū)和壓油區(qū)的起始段梢有重疊。 圖示，在最小的工作壓力下可以得到最大的流量。隨著壓力的升高，流量按預(yù)設(shè)的規(guī)律減少。當(dāng)流量減到最小值，壓力增大到最大值。泵只需要提供補充回路中元件滑動配合間隙中泄漏流體。 這種變量泵的設(shè)計可以保護管路，溢流閥不是必須的。其他回路中，為阻止局部壓力超過正常壓力水平，可以用安全閥或溢流閥來控制。 為了自動控制流量，采用可變彈簧負(fù)載調(diào)節(jié)器。安裝這種調(diào)節(jié)器，泵的出口壓力作用于活塞或定子內(nèi)表面，壓縮的彈簧產(chǎn)生位移。如果泵的出口壓力高于調(diào)節(jié)器彈簧的設(shè)定值時，彈簧被壓縮。這使壓力環(huán)（定子）移動，減少相對于定子的偏心量，于是，泵的流量減少，得到所需的壓力。這種油泵設(shè)計的出口壓力在100psi和2500psi之間。 圖示為變量泵補償器的特性，標(biāo)出輸入功率值，可以準(zhǔn)確計算所需的輸入功率。變量泵可以預(yù)先設(shè)定不同壓力值的變化規(guī)律。高低壓泵控制既能提供有效的卸荷回路，也能為先導(dǎo)控制回路提供足夠壓力。 圖示陰影區(qū)域為變量泵在背壓100psi壓力下的閉式回路。油液以100psi卸荷閥或溢流閥排出，可以維持正常的控制回路壓力，這些是消耗的功率。兩級壓力控制回路包括：先導(dǎo)液壓控制和電磁控制。圖示負(fù)號表示電磁鐵不帶電，先導(dǎo)控制油回油箱。于是泵排出的控制油的力小于調(diào)節(jié)器彈簧力，所以得到最小壓力。圖示正號為電磁鐵帶電，控制油的力大于調(diào)節(jié)器彈簧力。與簡單的溢流閥原理一樣，小球和彈簧決定控制力的大小。這樣預(yù)先設(shè)定最大工作壓力。 另一種兩級壓力控制系統(tǒng)是利用所謂的差動卸荷調(diào)節(jié)器。它應(yīng)用于高低壓或雙泵回路中。調(diào)節(jié)器通過壓力傳感器自動卸荷大流量泵以達(dá)到最小的空載壓力設(shè)定值?？蛰d壓力指的是由于變量泵控制機構(gòu)工作所形成的特定壓力。泵的實際空載流量等于系統(tǒng)的泄漏量與控制流量之和。當(dāng)泵空載時，即使液壓系統(tǒng)在提供加緊或保壓作用，也不會需要較大的功率。 調(diào)節(jié)器是液壓操縱的，差動活塞帶有雙壓力控制，當(dāng)外部控制壓力作用于控制卸荷口時，差動活塞允許完全卸荷。 空載壓力的最小設(shè)定值由調(diào)節(jié)器主彈簧A控制。最大壓力由溢流閥調(diào)節(jié)點B控制。調(diào)節(jié)器的操作壓力由大容積泵提供，從小孔C進入。 為了說明如何使用這種裝置，假設(shè)回路需要1000psi的最大壓力，由一個5-gpm來提供。在壓力達(dá)到500psi時，需要大流量（40gpm），繼續(xù)上升到1000psi，流量減少。由流量為40-gpm的帶有卸荷調(diào)節(jié)器的泵組成的雙泵系統(tǒng)可滿足要求。 我們可以把40-gpm的泵從500psi卸荷壓力調(diào)整至200psi最小設(shè)定壓力（或另一需求值），這樣5-gpm泵可以使回路達(dá)到1000psi或更高壓力。 圖中為雙泵系統(tǒng)控制壓力源。由一個40-gpm的泵提供調(diào)節(jié)器腔內(nèi)壓力，就可以達(dá)到最大設(shè)定壓力。彈簧設(shè)定力加上調(diào)節(jié)器的腔內(nèi)壓力共同決定了40-gpm泵的最大壓力。第二個控制源是特殊的回路，它能達(dá)到1000psi?？刂朴屯ㄟ^小孔D進入調(diào)節(jié)器作用于卸荷活塞E。活塞E面積比安全閥中提動閥F的有效面積大15％。因此卸荷差動力大約為15％。調(diào)節(jié)器將在500psi卸荷，會在500psi以下15％或425psi時起作用。這里所謂的卸荷，指的是40-gpm的泵無輸出量。 隨著回路中壓力從0到500psi的增加，調(diào)節(jié)器腔內(nèi)的壓力也隨著增加，直到溢流閥的設(shè)定值時，溢流閥打開，流體流出油箱。 調(diào)節(jié)器腔內(nèi)的壓力降是最大的疊加值，允許油泵達(dá)到卸荷狀態(tài)。同時，當(dāng)系統(tǒng)壓力繼續(xù)增加超過700psi時，導(dǎo)致活塞E最底部的壓力比頂部的壓力大?；钊固嵘yF完全打開，溢流提升閥全部開啟導(dǎo)致調(diào)節(jié)器腔內(nèi)壓力進一步下降至零。流體通過小孔C進入調(diào)節(jié)器腔，經(jīng)過溢流提升閥直接回油箱，不增加調(diào)節(jié)器腔內(nèi)的壓力。40-gpm的泵卸荷壓力可以減小至更低的設(shè)定值。調(diào)整卸荷調(diào)節(jié)器，40-gpm的泵達(dá)到卸荷。隨著壓力到1000psi，回路的流量減至5gpm。在1000psi時，5-gpm泵也達(dá)到卸荷設(shè)定，于是流量僅僅維持系統(tǒng)壓力。在500psi時，40-gpm的油泵卸荷。需要600psi的系統(tǒng)壓力把40gpm的泵卸荷到最小壓力200psi。600psi的先導(dǎo)控制油通過孔D進入并作用于差動活塞E。在500psi時，泵流量減少到零。100psi的附加壓力需要完全打開提升閥，使調(diào)節(jié)器腔內(nèi)的壓力減小至零。當(dāng)回路壓力減小時，兩個泵以同樣的方式來工作。 ? ? ? ? - 4 - 外文資料翻譯 Rotary pumps These are built in many different designs and are extremely popular in modern fluid-power system. The most common rotary-pump designs used today are spur-gear, generated-rotary , sliding-vane ,and screw pump ,each type has advantages that make it the most suitable for a given application . Spur-gear pumps. these pumps have two mating gears are turned in a closely fitted casing. Rotation of one gear ,the driver causes the second ,or follower gear, to turn . the driving shaft is usually connected to the upper gear of the pump . When the pump is first started ,rotation of gears forces air out the casing and into the discharge pipe. this removal of air from the pump casing produces a partial vacuum on the pump inlet ,here the fluid is trapped between the teeth of the upper and lower gears and the pump casing .continued rotation of the gears forces the fluid out of the pump discharge . Pressure rise in a spur-gear pump is produced by the squeezing action on the fluid ad it is expelled from between the meshing gear teeth and casing ,.a vacuum is formed in the cavity between the teeth ad unmesh, causing more fluid to be drawn into the pump ,a spur-gear pump is a constant-displacement unit ,its discharge is constant at a given shaft speed. the only way the quantity of fluid discharge by a spur-gear pump of type in figure can be regulated is by varying the shaft speed .modern gear pumps used in fluid-power systems develop pressures up to about 3000psi. Figure shows the typical characteristic curves of a spur-gear rotary pump. These curves show the capacity and power input for a spur-gear pump at various speeds. At any given speed the capacity characteristic is nearly a flat line the slight decrease in capacity with rise in discharge pressure is caused by increased leakage across the gears from the discharge to the suction side of the pump. leakage in gear pumps is sometimes termed slip. Slip also increase with arise pump discharge pressure .the curve showing the relation between pump discharge pressure and pump capacity is often termed the head-capacity or HQ curve .the relation between power input and pump capacity is the power-capacity or PQ curve . Power input to a squr-gear pump increases with both the operating speed and discharge pressure .as the speed of a gear pump is increased. Its discharge rate in gallons per minute also rise . thus the horsepower input at a discharge pressure of 120psi is 5hp at 200rpm and about 13hp at 600rpm.the corresponding capacities at these speed and pressure are 40 and 95gpm respectively, read on the 120psi ordinate where it crosses the 200-and 600-rpm HQ curves . Figure is based on spur-gear handing a fluid of constant viscosity , as the viscosity of the fluid handle increases (i.e. ,the fluid becomes thicker and has more resistance to flow ),the capacity of a gear pump decreases , thick ,viscous fluids may limit pump capacity t higher speeds because the fluid cannot into the casing rapidly enough fill it completely .figure shows the effect lf increased fluid biscosity on the performance of rotary pump in fluid-power system .at 80-psi discharge pressure the pp has a capacity lf 220gpm when handling fluid of 100SSU viscosity lf 500SSU . the power input to the pump also rises ,as shown by the power characteristics. Capacity lf rotary pump is often expressed in gallons per revolution of the gear or other internal element .if the outlet of a positive-displacement rotary pump is completely closed, the discharge pressure will increase to the point where the pump driving motor stalls or some part of the pump casing or discharge pipe ruptures .because this danger of rupture exists systems are filled with a pressure –relief valve. This relief valve may be built as of the pump or it may be mounted in the discharge piping. Sliding-Vane Pumps These pumps have a number of vanes which are free to slide into or out of slots in the pup rotor . when the rotor is turned by the pump driver , centrifugal force , springs , or pressurized fluid causes the vanes to move outward in their slots and bear against the inner bore of the pump casing or against a cam ring . as the rotor revolves , fluid flows in between the vanes when they pass the suction port. This fluid is carried around the pump casing until the discharge port is reached. Here the fluid is forced out of the casing and into the discharge pipe. In the sliding-vane pump in Figure the vanes in an oval-shaped bore. Centrifugal force starts the vanes out of their slots when the rotor begins turning. The vanes are held out by pressure which is bled into the cavities behind the vanes from a distributing ring at the end of the vane slots. Suction is through two ports A and AI, placed diametrically opposite each other. Two discharge ports are similarly placed. This arrangement of ports keeps the rotor in hydraulic balance, reliving the bearing of heavy loads. When the rotor turns counterclockwise, fluid from the suction pipe comes into ports A and AI is trapped between the vanes, and is carried around and discharged through ports B and BI. Pumps of this design are built for pressures up to 2500 psi. earlier models required staging to attain pressures approximating those currently available in one stage. Valving , uses to equalize flow and pressure loads as rotor sets are operated in series to attain high pressures. Speed of rotation is usually limited to less than 2500rpm because of centrifugal forces and subsequent wear at the contact point of vanes against the cam-ring surface.. Two vanes may be used in each slot to control the force against the interior of the casing or the cam ring. Dual vanes also provide a tighter seal , reducing the leakage from the discharge side to the suction side of the pump . the opposed inlet and discharge port in this design provide hydraulic balance in the same way as the pump, both these pumps are constant-displacement units. The delivery or capacity of a vane-type pump in gallons per minute cannot be changed without changing the speed of rotation unless a special design is used. Figure shows a variable-capacity sliding-vane pump. It dose not use dual suction and discharge ports. The rotor rums in the pressure-chamber ring, which can be adjusted so that it is off-center to the rotor. As the degree of off-center or eccentricity is changed, a variable volume of fluid is discharged. Figure shows that the vanes create a vacuum so that oil enters through 180 of shaft rotation. Discharge also takes place through 180 of rotation. There is a slight overlapping of the beginning of the fluid intake function and the beginning of the fluid discharge. Figure shows how maximum flow is available at minimum working pressure. As the pressure rises, flow diminishes in a predetermined pattern. As the flow decreases to a minimum valve, the pressure increases to the maximum. The pump delivers only that fluid needed to replace clearance floes resulting from the usual slide fit in circuit components. A relief valve is not essential with a variable-displacement-type pump of this design to protect pumping mechanism. Other conditions within the circuit may dictate the use of a safety or relief valve to prevent localized pressure buildup beyond the usual working levels. For automatic control of the discharge , an adjustable spring-loaded governor is used . this governor is arranged so that the pump discharge acts on a piston or inner surface of the ring whose movement is opposed by the spring . if the pump discharge pressure rises above that for which the by governor spring is set , the spring is compressed. This allows the pressure-chamber ring to move and take a position that is less off center with respect to the rotor. The pump theb delivers less fluid, and the pressure is established at the desired level. The discharge pressure for units of this design varies between 100 and 2500psi. The characteristics of a variable-displacement-pump compensator are shown in figure. Horsepower input values also shown so that the power input requirements can be accurately computed. Variable-volume vane pumps are capacity of multiple-pressure levels in a predetermined pattern. Two-pressure pump controls can provide an efficient method of unloading a circuit and still hold sufficient pressure available for pilot circuits. The black area of the graph of figure shows a variable-volume pump maintaining a pressure of 100psi against a closed circuit. Wasted power is the result of pumping oil at 100psi through an unloading or relief valve to maintain a source of positive pilot pressure. Two-pressure –type controls include hydraulic, pilot-operated types and solenoid-controlled, pilot-operated types. The pilot oil obtained from the pump discharge cannot assist the governor spring. Minimum pressure will result. The plus figure shows the solenoid energized so that pilot oil assists compensator spring. The amount of assistance is determined by the small ball and spring, acting as a simple relief valve. This provides the predetermined maximum operating pressure. Another type of two-pressure system employs what is termed a differential unloading governor. It is applied in a high-low or two-pump circuit. The governor automatically, Through pressure sensing, unloads the large volume pump to a minimum deadhead pressure setting. Deadhead pressure refers to a specific pressure level established as resulting action of the variable-displacement-pump control mechanism. The pumping action and the resulting flow at deadhead condition are equal to the leakage in the system and pilot-control flow requirements. No major power movement occurs at this time, even though the hydraulic system may be providing a clamping or holding action while the pump is in deadhead position The governor is basically a hydraulically operated, two-pressure control with a differential piston that allows complete unloading when sufficient external pilot pressure is applied to pilot unload port. The minimum deadhead pressure setting is controlled by the main governor spring A. the maximum pressure is controlled by the relief-valve adjustment B. the operating pressure for the governor is generated by the large-volume pump and enters through orifice C. To use this device let us assume that the circuit require a maximum pressure of 1000psi, which will be supplied by a 5-gpm pump. It also needs a large flow (40gpm) at pressure up to 500psi; it continues to 1000pso at the reduced flow rate. A two-pump system with an unloading governor on the 40-gpm pump at 500psi to a minimum pressure setting of 200psi (or another desired value) , which the 5-gpm pump takes the circuit up to1000psi or more. Note in figure that two sources of pilot pressure are required. One ,the 40-gpm pump, provides pressure within the housing so that maximum pressure setting can be obtained. The setting of the spring, plus the pressure within the governor housing, determines the maximum pressure capacity of the 40-gpm pump. The second pilot source is the circuit proper, which will go to 1000psi. this pilot line enters the governor through orifice D and acts on the unloading piston E . the area of piston E is 15 percent greater than the effective area of the relief poppet F. the governor will unload at 500psi and be activated at 15percent below 500psi, or 425psi. By unloading, we mean zero flow output of the 40-gpm pump. As pressure in the circuit increases from zero to 500psi, the pressure within the governor housing also increases until the relief-valve setting is reached, at which time the relief valve cracks open, allowing flow to the tank. The pressure drop in the hosing is a maximum additive value, allowing the pump to deadhead. Meanwhile, the system pressure continues to rise above 700psi, resulting in a greater force on the bottom of piston E than on the top. The piston then completely unseats poppet F, which results in a further pressure drop within the governor horsing to zero pressure because of the full-open position of the relief poppet F. flow entering the housing through orifice is directed to the tank pass the relief poppet without increasing the pressure in housing. The deadhead pressure of the 40-gpm pump then decreases to the lower set value. Thus , at the flow rate to the unloading governor ,the 40gpm pump goes to deadhead. The flow rate to the circuit decreases to 5gpm as the pressure to 1000psi, the 5-gpm pump is also at its deadhead setting, thus only holding system pressure.The 4-gpm pump unloads its volume at 500psi. It requires a system pressure of 600psi to unload the 40-gpm pump to its minimum pressure of 200psi. the 600-psi pilot supply enters through orifice D and acts on the differential piston E. The pumps volume is reduced to zero circuit-flow output at 500psi. The additional 100-psi pilot pressure is required to open poppet F completely and allow the pressure within the housing to decrease to zero.As circuit pressure decreases ,both pumps come back into service in a similar pattern. - 6 -