stewart平臺(tái)電液驅(qū)動(dòng)機(jī)構(gòu)設(shè)計(jì)【六自由度運(yùn)動(dòng)平臺(tái)全套含cad圖紙】
stewart平臺(tái)電液驅(qū)動(dòng)機(jī)構(gòu)設(shè)計(jì)【六自由度運(yùn)動(dòng)平臺(tái)全套含cad圖紙】,六自由度運(yùn)動(dòng)平臺(tái)全套含cad圖紙,stewart,平臺(tái),驅(qū)動(dòng),機(jī)構(gòu),設(shè)計(jì),自由度,運(yùn)動(dòng),全套,cad,圖紙
附錄
美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)對(duì)并聯(lián)運(yùn)動(dòng)機(jī)床過(guò)去、現(xiàn)在、未來(lái)的研究
摘要
并聯(lián)運(yùn)動(dòng)機(jī)床在突破了控制器局限性的限制后，其在制造業(yè)方面的應(yīng)用開(kāi)始產(chǎn)業(yè)化。并聯(lián)機(jī)床由于其投放市場(chǎng)后的商業(yè)價(jià)值，在1994年芝加哥國(guó)際制造業(yè)展覽會(huì)上出現(xiàn)了新發(fā)明的數(shù)控并聯(lián)機(jī)床。與傳統(tǒng)機(jī)床相比，并聯(lián)驅(qū)動(dòng)技術(shù)在加工制造方面具有許多優(yōu)點(diǎn)，比如：較高的剛度——體積比、較高的速度、較高的精度、安裝次數(shù)少，夾具簡(jiǎn)單。在美國(guó)，一些機(jī)床制造者正在研發(fā)并聯(lián)驅(qū)動(dòng)技術(shù)，同時(shí)并聯(lián)驅(qū)動(dòng)技術(shù)的潛在用戶——加工制造商正企劃這種新型的多軸加工技術(shù)在操作領(lǐng)域的用途。
NAMT、NIST的研究員及來(lái)自各行業(yè)、大學(xué)的合作者正在研究這個(gè)新型工具的獨(dú)特性能。其工作包括對(duì)1995年五月搭建的八面體、六驅(qū)動(dòng)器機(jī)床的大范圍的實(shí)驗(yàn)。研究領(lǐng)域包括機(jī)床測(cè)量、性能測(cè)試方法及標(biāo)準(zhǔn)、性能拓展方法、仿真試驗(yàn)工具和開(kāi)放式體系結(jié)構(gòu)控制界面。本論文給出了美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)對(duì)并聯(lián)運(yùn)動(dòng)機(jī)床的研究現(xiàn)狀及歷史的綜述。并聯(lián)運(yùn)動(dòng)的優(yōu)點(diǎn)、所面臨的挑戰(zhàn)、將來(lái)的研發(fā)方向也被提到。
1簡(jiǎn)介
提高產(chǎn)品質(zhì)量、降低產(chǎn)品成本、縮短產(chǎn)品開(kāi)發(fā)周期是企業(yè)保持競(jìng)爭(zhēng)力的迫切需要。這些決定競(jìng)爭(zhēng)力的關(guān)鍵因素要求機(jī)床的加工精度、速度、多功能性不斷發(fā)展、提高。這就對(duì)機(jī)床研究領(lǐng)域提出了挑戰(zhàn)。鞭策機(jī)床研發(fā)單位為設(shè)計(jì)新機(jī)床而演化基本的機(jī)構(gòu)。因此，基于并聯(lián)運(yùn)動(dòng)機(jī)構(gòu)的機(jī)床模型——并聯(lián)運(yùn)動(dòng)機(jī)床研發(fā)成功。六自由度杰出代表——Stewart平臺(tái)是并聯(lián)運(yùn)動(dòng)機(jī)床的機(jī)構(gòu)模型，最近許多新機(jī)床的設(shè)計(jì)都是基于Stewart平臺(tái)機(jī)構(gòu)模型?；赟tewart平臺(tái)機(jī)構(gòu)模型的并聯(lián)機(jī)床的經(jīng)典結(jié)構(gòu)組成：動(dòng)平臺(tái)與固定的基礎(chǔ)平臺(tái)之間由六個(gè)同樣的能活動(dòng)的可伸縮桿聯(lián)接。高的力容積比、高的結(jié)構(gòu)剛性、低動(dòng)量是Stewart平臺(tái)機(jī)構(gòu)的優(yōu)點(diǎn)。從加工應(yīng)用的角度考慮，Stewart平臺(tái)的缺點(diǎn)在于工作空間復(fù)雜、運(yùn)動(dòng)方向受到限制、對(duì)于五自由度工作（磨、鉆、簡(jiǎn)單操作）需要六個(gè)驅(qū)動(dòng)器驅(qū)動(dòng)。一些基于Stewart平臺(tái)的機(jī)床機(jī)構(gòu)模型通常叫做并聯(lián)機(jī)械機(jī)構(gòu)。
這些并聯(lián)機(jī)床與傳統(tǒng)機(jī)床相比具有許多優(yōu)點(diǎn)。它們還提出了一些重要的問(wèn)題。這些機(jī)床的性能如何描述？計(jì)算工作空間的最好方法是什么？機(jī)床可以達(dá)到的加工精確程度？實(shí)際應(yīng)用時(shí)什么是最好的控制算法？在成本方面是否具有競(jìng)爭(zhēng)力？這些機(jī)床最適合于何種加工方式？這些機(jī)床的模塊化程序設(shè)計(jì)如何最優(yōu)化？何種結(jié)構(gòu)在低成本的前提下又具有較多的功能？這些都是從并聯(lián)機(jī)床方面提出的重要問(wèn)題，自從1990年美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)在并聯(lián)機(jī)床的許多領(lǐng)域進(jìn)入了研究。這一論文概述了美國(guó)國(guó)家標(biāo)準(zhǔn)與技術(shù)研究對(duì)于并聯(lián)運(yùn)動(dòng)機(jī)床的過(guò)去、現(xiàn)在、未來(lái)的研究，提出了一些依然具有挑戰(zhàn)性的課題。本論文的討論圍繞著六自由度的Stewart平臺(tái)機(jī)械機(jī)構(gòu)、并聯(lián)運(yùn)動(dòng)機(jī)床的機(jī)構(gòu)模型。然而，還有一些并聯(lián)機(jī)構(gòu)的排列方式也許更適合于作為機(jī)床的機(jī)構(gòu)模型（可能優(yōu)于Stewart平臺(tái)機(jī)構(gòu)本身）。
工業(yè)機(jī)器人問(wèn)世以來(lái), 采用串聯(lián)機(jī)構(gòu)的操作器一直占主導(dǎo)地位，它結(jié)構(gòu)簡(jiǎn)單，工作空間大，因而獲得廣泛應(yīng)用。與之相比,并聯(lián)機(jī)器人活動(dòng)空間小，活動(dòng)上平臺(tái)遠(yuǎn)不如串聯(lián)機(jī)器人手部靈活。但是，并聯(lián)機(jī)器人也有其獨(dú)特的優(yōu)點(diǎn)：
并聯(lián)式結(jié)構(gòu)其末端件上平臺(tái)同時(shí)經(jīng)由6 根桿支撐，與串聯(lián)的懸臂梁相比，剛度大，而且結(jié)構(gòu)穩(wěn)定；由于剛度大，并聯(lián)式較串聯(lián)式在相同的自重或體積下，有高得多的承載能力；串聯(lián)式末端件上的誤差是各個(gè)關(guān)節(jié)誤差的積累和放大，因而誤差大、精度低，并聯(lián)式則沒(méi)有那樣的誤差積累和放大關(guān)系，誤差小、精度高；串聯(lián)式機(jī)器人的驅(qū)動(dòng)電機(jī)及傳動(dòng)系統(tǒng)大都放在運(yùn)動(dòng)著的大小臂上，增加了系統(tǒng)的慣量，惡化了動(dòng)力性能，而并聯(lián)式則很容易將電機(jī)置于機(jī)座上，減小了運(yùn)動(dòng)負(fù)荷；位置求解上，串聯(lián)機(jī)構(gòu)正解容易, 但反解十分困難, 而并聯(lián)機(jī)構(gòu)正解困難，反解卻非常容易。由于機(jī)器人的在線實(shí)時(shí)計(jì)算是要計(jì)算反解的，這對(duì)串聯(lián)式十分不利,而并聯(lián)式卻容易實(shí)現(xiàn)。
并聯(lián)機(jī)構(gòu)的出現(xiàn)，擴(kuò)大了機(jī)器人的應(yīng)用范圍。隨著對(duì)并聯(lián)機(jī)器人研究的不斷深入，其應(yīng)用領(lǐng)域也越來(lái)越廣闊。并聯(lián)機(jī)器人的應(yīng)用大體分為六大類：運(yùn)動(dòng)模擬器、并聯(lián)機(jī)床、工業(yè)機(jī)器人、動(dòng)機(jī)構(gòu)、醫(yī)用機(jī)器人和操作器。
運(yùn)動(dòng)模擬器 作為運(yùn)動(dòng)模擬器,其最廣泛的應(yīng)用是飛行模擬器。訓(xùn)練用飛行模擬器具有節(jié)能、經(jīng)濟(jì)、全、不受場(chǎng)地和氣象條件限制、訓(xùn)練周期短、效率高等突出優(yōu)點(diǎn),目前已成為各類飛行員訓(xùn)練的必備工具。同時(shí)，這種運(yùn)動(dòng)模擬器也是研究和開(kāi)發(fā)各種運(yùn)載設(shè)備的重要工具。通過(guò)模擬器可以在早期發(fā)現(xiàn)問(wèn)題、減少風(fēng)險(xiǎn)、進(jìn)行綜合系統(tǒng)驗(yàn)證，解決各系統(tǒng)間的動(dòng)態(tài)匹配關(guān)系、加速系統(tǒng)實(shí)驗(yàn)過(guò)程，縮短研制周期，降低開(kāi)發(fā)費(fèi)用。
并聯(lián)機(jī)床 用作并聯(lián)機(jī)床是并聯(lián)機(jī)構(gòu)最具吸引力的應(yīng)用。并聯(lián)機(jī)床結(jié)構(gòu)簡(jiǎn)單，傳動(dòng)鏈短,剛度大、質(zhì)量輕、成本低，容易實(shí)現(xiàn)“6軸聯(lián)動(dòng)”，能加工更加復(fù)微雜的三維曲面。還具有環(huán)境適應(yīng)性強(qiáng)的特點(diǎn)，便于重組和模塊化設(shè)計(jì)，可構(gòu)成形式多樣的布局和自由度組合。德國(guó)Micromat 公司生產(chǎn)的6X 并聯(lián)機(jī)床，這種機(jī)床采用伸縮桿的長(zhǎng)度變化驅(qū)動(dòng)主軸部件，實(shí)現(xiàn)加工軌跡所需的運(yùn)動(dòng)，工件固定在工作臺(tái)上不動(dòng)。
工業(yè)機(jī)器人 隨著工業(yè)現(xiàn)代化發(fā)展的高速進(jìn)程,以及加工業(yè)工藝的不斷完善，技術(shù)的不斷進(jìn)步，工業(yè)機(jī)器人的應(yīng)用被越來(lái)越多的企業(yè)認(rèn)識(shí)和接受。工業(yè)機(jī)器人既保證了產(chǎn)品質(zhì)量,又減少了特殊環(huán)境工作的危險(xiǎn)和實(shí)現(xiàn)對(duì)人員的勞動(dòng)強(qiáng)度的降低和人員勞動(dòng)保護(hù)意識(shí)的提高。
微動(dòng)機(jī)構(gòu) 作為微動(dòng)機(jī)構(gòu)是并聯(lián)機(jī)器人的一個(gè)重要應(yīng)用方面。這種微動(dòng)機(jī)構(gòu)發(fā)揮了并聯(lián)機(jī)構(gòu)的特點(diǎn)，工作空間不很大但精度和分辨率都非常高。
醫(yī)用機(jī)器人 醫(yī)療機(jī)器人已經(jīng)成為醫(yī)學(xué)外科學(xué)會(huì)和機(jī)器人學(xué)會(huì)共同關(guān)注的新興技術(shù)領(lǐng)域。近年來(lái)，醫(yī)療機(jī)器人技術(shù)引起美、法、德、意、日等國(guó)家學(xué)術(shù)界的極大關(guān)注，研究工作蓬勃興起。醫(yī)療機(jī)器人具備選位準(zhǔn)確、動(dòng)作精細(xì)、避免病人感染等特點(diǎn)。
操作器 作為操作器, 并聯(lián)機(jī)器人可以用作飛船和空間對(duì)接器的對(duì)接機(jī)構(gòu)，上下平臺(tái)中間都有通孔作為對(duì)接后的通道，上下平臺(tái)作為對(duì)接環(huán)，由6 個(gè)直線驅(qū)動(dòng)器驅(qū)動(dòng)以幫助飛船對(duì)正;對(duì)接機(jī)構(gòu)還能完成吸收能量和減振，以及主動(dòng)抓取、對(duì)正拉緊、柔性結(jié)合、最后鎖住卡緊等工作。對(duì)于困難的地下工程，如土方挖掘、煤礦開(kāi)采，也可以采用這種強(qiáng)力的并聯(lián)機(jī)構(gòu)。Arai 等1991 年提出將并聯(lián)機(jī)構(gòu)裝于履帶式或步行式可移動(dòng)的小車上，挖掘頭裝于并聯(lián)機(jī)構(gòu)的上平臺(tái)，強(qiáng)有力的并聯(lián)機(jī)構(gòu)可以承受巨大的挖掘力。
其他方面應(yīng)用 此外,Stewart 平臺(tái)還在其他方面應(yīng)用，如力或位移傳感器，造船起重機(jī),主動(dòng)式振動(dòng)控制器，體感模擬娛樂(lè)機(jī)械等。
并聯(lián)機(jī)器人具有很多傳統(tǒng)串聯(lián)機(jī)器人不具備的優(yōu)點(diǎn),并聯(lián)機(jī)器人還有很多理論問(wèn)題需要進(jìn)一步的研究和完善，適用于不同工作要求的新型的并聯(lián)機(jī)構(gòu)有待于進(jìn)一步開(kāi)發(fā)。目前,并聯(lián)機(jī)器人研究所要解決的問(wèn)題應(yīng)包含以下內(nèi)容：
不同自由度的新型并聯(lián)機(jī)構(gòu)的研究。研究新型的并聯(lián)機(jī)構(gòu)，并研究相應(yīng)的運(yùn)動(dòng)學(xué)、動(dòng)力學(xué)等理論，必將會(huì)進(jìn)一步豐富并聯(lián)機(jī)構(gòu)領(lǐng)域的研究成果，并進(jìn)一步擴(kuò)大并聯(lián)機(jī)構(gòu)的應(yīng)用范圍。
并聯(lián)機(jī)器人運(yùn)動(dòng)學(xué)正解數(shù)值算法的研究。主要是提高位置正解的計(jì)算速度，這項(xiàng)工作是并聯(lián)機(jī)器人軌跡規(guī)劃的基礎(chǔ)。并聯(lián)機(jī)器人動(dòng)力學(xué)模型研究。建立通用的適用于控制系統(tǒng)設(shè)計(jì)的并聯(lián)機(jī)器人動(dòng)力學(xué)數(shù)學(xué)模型，這項(xiàng)工作是計(jì)開(kāi)發(fā)出具有優(yōu)良動(dòng)力學(xué)性能的并聯(lián)機(jī)構(gòu)，對(duì)不同類型并聯(lián)機(jī)構(gòu)進(jìn)行動(dòng)力學(xué)分析的基礎(chǔ)。
并聯(lián)機(jī)機(jī)器人工作空間研究。研究各種奇異性對(duì)工作空間的影響，可以提高我們對(duì)并聯(lián)機(jī)構(gòu)運(yùn)動(dòng)機(jī)理的認(rèn)識(shí)，是進(jìn)行并聯(lián)機(jī)構(gòu)無(wú)奇異路徑規(guī)劃和實(shí)現(xiàn)運(yùn)動(dòng)的可控性的基礎(chǔ)。
并聯(lián)機(jī)器人誤差分析。建立實(shí)用的、完整的并聯(lián)機(jī)構(gòu)誤差數(shù)學(xué)模型，分析并聯(lián)機(jī)構(gòu)輸入誤差因子對(duì)動(dòng)平臺(tái)位資誤差的影響，從而通過(guò)控制敏感輸入誤差因子，提高并聯(lián)機(jī)器人精度。
少自由度并聯(lián)機(jī)構(gòu)的研究由于少自由度并聯(lián)機(jī)構(gòu)具有結(jié)構(gòu)簡(jiǎn)單、造價(jià)低廉等特點(diǎn)，有著廣闊的應(yīng)用前景。但少自由度并聯(lián)機(jī)構(gòu)在某些時(shí)候的運(yùn)動(dòng)、動(dòng)力分析反而變得更復(fù)雜。
2美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)制造工程實(shí)驗(yàn)室對(duì)于并聯(lián)運(yùn)動(dòng)機(jī)床的研究歷史
美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)制造工程實(shí)驗(yàn)室對(duì)Stewart平臺(tái)機(jī)械機(jī)構(gòu)的創(chuàng)新應(yīng)用的研究興趣要追溯到19世紀(jì)80年代中期，當(dāng)時(shí)詹姆士和他的從事機(jī)器人系統(tǒng)（現(xiàn)在的智能系統(tǒng)）研究的同事研制了一個(gè)新項(xiàng)目——繩索機(jī)器人吊車，這臺(tái)機(jī)械采用的是Stewart平臺(tái)的機(jī)械結(jié)構(gòu)模型。用六個(gè)絞車控制的電纜的方式來(lái)控制平臺(tái)，這臺(tái)繩索機(jī)器人吊車最初研發(fā)的目的像傳統(tǒng)的吊車那樣是用來(lái)穩(wěn)定的起重貨物的。在制造業(yè)和建筑業(yè)領(lǐng)域，為了穩(wěn)地過(guò)地搬運(yùn)貨物、直升機(jī)的救援工作、有害廢物的再利用，許多不同型號(hào)的這種繩索機(jī)器人吊車被研發(fā)出來(lái)應(yīng)用。這種繩索機(jī)器人吊車在控制負(fù)載的位置和姿態(tài)方面明顯的優(yōu)于傳統(tǒng)的起重機(jī)。
美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)對(duì)Stewart平臺(tái)的深入研究生產(chǎn)了這種創(chuàng)新的機(jī)械結(jié)構(gòu)繩索機(jī)器人吊車。這種八面體結(jié)構(gòu)包括三個(gè)用來(lái)懸掛工作平臺(tái)的上支點(diǎn)，采用三個(gè)上支點(diǎn)是為了本身是較輕的結(jié)構(gòu)卻能提供足夠的結(jié)構(gòu)剛度。詹姆士和克萊頓認(rèn)為這種Stewart平臺(tái)結(jié)構(gòu)和八面體空間結(jié)構(gòu)的結(jié)合在機(jī)床應(yīng)用方面具有潛在的優(yōu)點(diǎn)?；谶@一思想，他們?cè)?991 年提出了“新型機(jī)床”，并且建造了樣機(jī)。模型結(jié)構(gòu)表明該機(jī)床是由三個(gè)可運(yùn)動(dòng)的Stewart平臺(tái)串連嵌套，第四個(gè)Stewart平臺(tái)固定的結(jié)構(gòu)組合而成。與傳統(tǒng)的設(shè)計(jì)相比，這種機(jī)構(gòu)的優(yōu)點(diǎn)在于提高了剛度和精度。
在建立這種新型機(jī)床設(shè)計(jì)的機(jī)構(gòu)模型啟動(dòng)計(jì)劃的過(guò)程中，美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)的研究員意識(shí)到：形成一種商業(yè)性的并聯(lián)機(jī)床的過(guò)程也就是利用相似原理搭建成一樣機(jī)的過(guò)程。美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)認(rèn)為商業(yè)性的并聯(lián)機(jī)床樣機(jī)為將來(lái)的研究提供一個(gè)好的起點(diǎn)，并且獲得了一個(gè)試驗(yàn)樣機(jī)，該機(jī)床樣機(jī)原型來(lái)自 Ingersoll 銑床公司。這種八面體機(jī)構(gòu)，被公司改進(jìn)后的二代產(chǎn)品，于1995年5月在美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)安裝。該機(jī)床大約高5米，六個(gè)同樣的絞桿，每個(gè)絞桿功率11千瓦、絞的轉(zhuǎn)速范圍0轉(zhuǎn)/分鐘~6000轉(zhuǎn)/分鐘，機(jī)床上還配備有一個(gè)同樣的備用絞桿。
3美國(guó)的六條腿機(jī)床(Hexapod)用戶群
在美國(guó)，隨著對(duì)并聯(lián)運(yùn)動(dòng)機(jī)床研究興趣的上升，桑蒂亞國(guó)家實(shí)驗(yàn)室、麻省理工學(xué)院、美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)等各大組織形成一個(gè)強(qiáng)大的六條腿機(jī)床(Hexapod)用戶群，這一用戶群包括機(jī)床制造商、機(jī)床用戶、對(duì)并聯(lián)機(jī)床的研發(fā)感興趣的研究機(jī)構(gòu)，大約34個(gè)企業(yè)，大學(xué)和政府組織的代表已經(jīng)參與了第一個(gè)六條腿機(jī)床(Hexapod)用戶會(huì)議，該會(huì)議在于1996 年八月在麻省理工學(xué)院舉行。第二次會(huì)議于1997年3月在美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)舉行，后來(lái)還有一些非正式會(huì)議在召開(kāi)，美國(guó)機(jī)械工程師交流(ASME) 暨美國(guó)機(jī)械工程技術(shù)研討和展覽會(huì) (IMECE) 在 1997年十一月、1998年六月、1998年九月舉行, 這些非正式的會(huì)議為共享并聯(lián)運(yùn)動(dòng)機(jī)床的試驗(yàn)結(jié)果、研發(fā)方向的想法和計(jì)劃、確定行業(yè)需求提供了寶貴的機(jī)會(huì)。當(dāng)然，在六條腿機(jī)床(Hexapod)用戶群這一組織成立以前，并聯(lián)機(jī)床的研發(fā)還吸引了許多院校及其他組織對(duì)并聯(lián)運(yùn)動(dòng)機(jī)械裝置（大多為機(jī)器人應(yīng)用領(lǐng)域）的研究。
4美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所對(duì)并聯(lián)運(yùn)動(dòng)機(jī)床現(xiàn)在研究領(lǐng)域的研究
美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)對(duì)并聯(lián)運(yùn)動(dòng)機(jī)床現(xiàn)狀的研究突出在以下幾點(diǎn)：
對(duì)并聯(lián)運(yùn)動(dòng)機(jī)床特性的更深層次的理解；
評(píng)價(jià)并聯(lián)運(yùn)動(dòng)機(jī)床性能的測(cè)試方法及檢測(cè)手段的標(biāo)準(zhǔn)；
冷卻液走向的排布問(wèn)題；
與應(yīng)用、研發(fā)、測(cè)試并聯(lián)運(yùn)動(dòng)機(jī)床相關(guān)的建模和仿真問(wèn)題；
完成同一工作過(guò)程中的協(xié)同工作、遠(yuǎn)程控制能力的提高；
控制檢測(cè)的綜合問(wèn)題。
因此，并聯(lián)運(yùn)動(dòng)機(jī)床的研發(fā)問(wèn)題圍繞著達(dá)到以下設(shè)計(jì)目標(biāo)而進(jìn)行： 精確測(cè)量、性能拓展、及對(duì)并聯(lián)機(jī)床協(xié)同研發(fā)、測(cè)量學(xué)的應(yīng)用、遠(yuǎn)程控制、仿真工具的探討、論證。這一工作的完成要依賴于各個(gè)學(xué)科的有機(jī)綜合及政府、企業(yè)、大學(xué)各個(gè)合作部門(mén)的共同努力。美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)的并聯(lián)運(yùn)動(dòng)機(jī)床研究項(xiàng)目被美國(guó)制造工程實(shí)驗(yàn)室引進(jìn)為先進(jìn)制造基礎(chǔ)項(xiàng)目（NAMT）。以下部分是美國(guó)國(guó)家標(biāo)準(zhǔn)和技術(shù)研究所(NIST)對(duì)并聯(lián)運(yùn)動(dòng)機(jī)床項(xiàng)目的最新研究成果。
4.1并聯(lián)運(yùn)動(dòng)機(jī)床的工作性能描述及測(cè)量
4.2并聯(lián)運(yùn)動(dòng)機(jī)床的校準(zhǔn)
4.3并聯(lián)運(yùn)動(dòng)機(jī)床中伸縮桿的測(cè)量
4.4并聯(lián)運(yùn)動(dòng)機(jī)床的機(jī)構(gòu)剛度及測(cè)量
4.5并聯(lián)運(yùn)動(dòng)機(jī)床的建模和仿真
4.6在并聯(lián)運(yùn)動(dòng)機(jī)床上零件編程和加工的應(yīng)用
4.7控制器的發(fā)展
5結(jié)論、挑戰(zhàn)及并聯(lián)運(yùn)動(dòng)機(jī)床的研發(fā)方向
致謝
附錄
First European-American Forum on Parallel Kinematic Machines
Theoretical Aspects and Industrial Requirements
31 August – 1 September, 1998
Milan, Italy
Parallel Kinematic Machine Research at NIST:
Past, Present, and Future
Albert J. Wavering
Intelligent Systems Division
National Institute of Standards and Technology (NIST)
Gaithersburg, MD 20899, U.S.A.
Abstract
Unchained from the confines of controller limitations, the industrial application of parallel kinematic machines in manufacturing is beginning to emerge. The launch of commercially available hexapod machine tools at the 1994 International Manufacturing Technology Show in Chicago represented the first radical departure in machine tool design since the introduction of numerical controls. The parallel actuator technology promises to offer manufacturers a number of advantages relative to conventional machine tools, such as a higher stiffness-to-mass ratio, higher speeds, higher accuracy, reduced installation requirements, and mechanical simplicity.Several machine tool makers in the U.S. and around the world are pursuing parallel actuator technology, while their prospective customers—manufacturers—are beginning to contemplate what the novel multi-axis machining technology might mean for their operations.
As part of the Manufacturing Engineering Laboratory's National Advanced Manufacturing Testbed (NAMT), NIST researchers and collaborators from industry and universities are studying the new tools' unique capabilities. The work includes extensive tests on an octahedral hexapod machine tool that was installed at NIST in May 1995. Research areas include machine metrology, performance characterization test methods and standards, performance enhancement methods, simulation and remote experimentation tools, and open architecture controller interfaces. This paper will give an overview of history and current status of research in parallel kinematic machines at NIST. The merits and key challenges of parallel kinematic machine tools will also be addressed, and directions for future research will be identified.
1 Introduction
Improving product quality, reducing product cost, and shortening the product development cycle have always been critical for companies to stay competitive. These competitive drivers result in a continuing need to achieve improvements in accuracy, speed, and versatility in machining operations. These pressing needs pose challenges to the machine tool research community, and have driven several machine tool companies to revisit some of their basic assumptions about machine tool design. As a result, prototypes of a new class of machine tools based on parallel kinematic structures, known as parallel kinematic machines (PKMs), have been introduced.
The six degree-of-freedom Stewart platform [1] is one PKM configuration that has been used recently in a number of new machine tool designs. A Stewart platform machine tool typically consists of a moveable spindle platform connected to a rigid base through six identically jointed and extensible struts. The Stewart platform mechanism is characterized by high force capacity,high structural rigidity, and low moving mass [2]. For machining applications, disadvantages of the Stewart platform include a complex work volume, limited orientation range of motion, and a requirement of six actuators for a five degree-of-freedom task (milling, drilling, and similar operations). Several prototypes of Stewart-platform-based machine tools, commonly called hexapods, have been produced in the U.S. by companies such as Giddings & Lewis1, Hexel Corporation, and the Ingersoll Milling Machine Company.
These machine tools promise some key advantages over conventional machine tools, but they raise important questions as well. How should the performance of these machines be characterized? What is the best way to describe the work volume? What degree of accuracy is achievable? What are the best control algorithms to employ? Can they be cost-competitive? What types of machining applications are best suited to these machines? How can part programs be optimized for them? What configurations provide the most versatility for the least cost? These are just a few of the important issues raised by hexapod machine tools. Since the early 1990’s, NIST has conducted research in a number of these areas. This paper summarizes the past, current, and future work at NIST in parallel kinematic machines, and examines some of the remaining challenges. In this paper, the discussion is focused on the six degree-offreedom Stewart platform mechanism, reflecting the configuration of the prototype machine at NIST. However, there are certainly other parallel kinematic arrangements that may be well suited for use as machine tools (perhaps even more so than the Stewart platform).
Since the development of industrial robots, using tandem with the operation has been dominated by its simple structure, work space, which was widely used. By comparison, parallel robot small space activities, activities on the platform are far less flexible series robot hand. However, the parallel robot has its unique advantages:
Parallel structure of its terminal on the platform at the same time through the six-support, compared with the series of cantilever, stiffness, and structural stability; because of stiffness, a series of parallel with the same dignity or volume, there is high And more carrying capacity; Series at the end of the error is the accumulation of error in all joints and enlarge, thus error, precision low, there is no parallel as the accumulation of errors and to enlarge relations, small error and high precision; Series Robot The drive motor and transmission system mostly on the size of the campaign arm, to increase the system's inertia, the deterioration of the dynamic performance, and the parallel is very easy to put motor-seat, reducing the exercise load; location for , The series of institutions is easy, but the anti-solution is very difficult, and parallel institutions are of the difficulties, the anti-solution is very easy. As the robot on-line real-time calculation is to calculate the anti-solution, which is very unfavorable Series, and the parallel is easy to achieve.
The emergence of parallel institutions, expanded the scope of application of robots. As the parallel robot in-depth research of its increasingly broad applications. The application of parallel robot can be divided into six major categories: Motion Simulator, parallel machine tools, industrial robots, moving bodies, and medical robot for operations.
Motion Simulator as a sports simulator, the most widely used is the flight simulator. Flight simulator training with energy, economy, all from the venue and weather conditions, short training period, the outstanding merits of high efficiency, all kinds of pilot training has become an indispensable tool. At the same time, this movement simulator is also research and develop an important tool for carrying equipment. Through the simulator can be found in the early problems, reduce risk, comprehensive verification system to solve all the dynamic matching system, speed up the process of experimental systems, shorten the development cycle and reduce development costs.
PMT for PMT parallel mechanism is the most attractive application. PMT structure is simple, short transmission chain, stiffness, light weight, low cost, easy to implement "six-axis", to processing more complex three-dimensional surface of the micro-hybrid. Adaptability also has the characteristics of the environment, facilitate restructuring and modular design, can constitute a variety of layout and composition of freedom. Germany Micromat company's 6 X parallel machine tools, such a telescopic machine-driven changes in the length of spindle components, to achieve the required processing track the movement of the workpiece fixed at the stage fixed.
With the modernization of industrial robots industrial development of high-speed process and increase the continuous improvement of industrial technology and technology advances in the application of industrial robots are more and more enterprises understand and accept. Industrial robots not only ensure the quality of products, and reduce the risk of the work of the special environment and realize the strength of the labor and personnel to reduce labor protection awareness raising.
Fretting institutions as a micro-robot body is an important parallel applications. Such fretting agencies played a parallel mechanism to the characteristics of the work space but not great precision and resolution are very high.
Robot has become a medical robot Institute of Medicine and Surgery Robot Institute of common concern emerging technology. In recent years, the medical robot technology from the United States, France, Germany, Italy, Japan and other countries of great concern to the academic, research have mushroomed. Medical robot with the election of accurate, precise movements, to avoid the characteristics of the patient.
Operators as the operation, parallel robot can be used for spacecraft and space docking with the docking mechanism, from top to bottom among all platforms through holes as the channel after docking, and docking ring as a platform from top to bottom, from six straight drive to help drive the spacecraft Is; can complete the docking mechanism of energy absorption and vibration, and take the initiative to crawl, the tension is, flexible integration, the last card locked tight, and so on. The difficulties of underground works, such as the Turkish side mining, coal mining, can also use this powerful parallel institutions. Arai, such as in 1991 proposed a parallel mechanism installed in or walk-tracked to a small mobile vehicles, in parallel with the first excavation of the bodies on the platform, a powerful parallel institutions can withstand the excavation of huge.
Other applications In addition, Stewart also other aspects of application platforms, such as force or displacement sensors, shipbuilding cranes, active vibration control, the sense of mechanical simulation, and other entertainment.
Parallel series robot has many traditional robots do not have the advantage of parallel robot there are many theoretical issues need further study and improve, apply to different job requirements of the new parallel mechanism to be further developed. At present, the Institute for parallel robot to solve the problem should include the following:
Different degrees of freedom parallel mechanism of the new study. New Study on the parallel institutions, and to study the corresponding kinematics, dynamics, and other theories, will be further enriched the field of parallel institutions research results and further expand the application of parallel institutions.
Parallel kinematics robot is the study of the numerical algorithm. Location is the main solution is to increase the computing speed, which is parallel robot trajectory planning base. Parallel robot dynamics model. The establishment of a common control system applicable to the design of the parallel robot dynamics model, the development of this work is to have excellent dynamic performance of parallel institutions, the different types of parallel institutions based on the analysis of the dynamics.
And on-line robot work space research. The study of the various singularity of the impact of the work space, we can improve on the parallel mechanism of awareness campaigns, a parallel mechanism is not singular path planning and realization of the controlled movement of the foundation.
Parallel Robot error analysis. The establishment of practical, complete parallel mechanism error mathematical model of parallel institutions enter error factor on moving platforms in the error-effects, thereby through control of sensitive input error factor, increased parallel robot accuracy.
Parallel institutions less freedom because of fewer degrees of freedom parallel mechanism is simple in structure, low cost, and other characteristics, have broad application prospects. But less freedom parallel mechanism at certain times of movement, dynamic analysis it has become more complex.
2 History of PKM Research at the NIST Manufacturing Engineering Laboratory
Interest within the NIST Manufacturing Engineering Laboratory (MEL) in innovative applications of Stewart platform mechanisms dates back to the mid 1980’s, when James Albus and his colleagues in the Robot Systems (now Intelligent Systems) Division developed a concept for a robot crane (Figure 1). The machine, now called the RoboCrane [3,4], is a Stewart platform configuration where six winch-actuated cables are used to suspend and control the platform. The RoboCrane was developed originally under a Defense Advanced Research Project Agency (DARPA) contract to stabilize loads on conventional cranes. Many different RoboCrane configurations have been developed for applications ranging from large-scale manufacturing and construction, to stabilized cargo handling, helicopter rescue, and hazardous waste remediation. The principal advantage of the RoboCrane over conventional crane systems is improved control of the position and orientation of the load.
NIST research into Stewart platforms also produced an innovative structure from which to
suspend the RoboCrane work platform. An octahedral structure containing the three upper support points necessary to suspend the work platform provides exceptional structural stiffness in a lightweight frame. This combination of a Stewart platform and an octahedral space frame was also recognized by NIST researchers James Albus and Clayton Teague to have potential advantages for machine tool applications. In 1991 they proposed a “New Class of Machine Tools” based on this concept, and built the model shown in Figure 2. The model configuration shown actually can be considered to be three Stewart platforms in series (lower motion platform, “virtual” Stewart platform for laser metrology, and upper fixed platform) nested within a fourth fixed Stewart platform that forms the structural frame. The benefits expected to result from this configuration included greatly improved stiffness and accuracy haracteristics compared with conventional designs.
During the course of pursuing a start-up project to build a prototype of this new machine tool design, NIST researchers became aware that a commercial machine tool builder was in the process of building a prototype machine with a very similar configuration. NIST decided that a commercial prototype would provide a good starting point for investigations, and procured an experimental prototype Octahedral Hexapod machine tool from the Ingersoll
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