球坐標(biāo)工業(yè)機(jī)械手設(shè)計(jì)
球坐標(biāo)工業(yè)機(jī)械手設(shè)計(jì),球坐標(biāo)工業(yè)機(jī)械手設(shè)計(jì),坐標(biāo),工業(yè),機(jī)械手,設(shè)計(jì)
MCB －工業(yè)的機(jī)械手論文
巴雷特機(jī)械手爪－可編程式可彎曲部分的搬運(yùn)和組裝
摘要
本文詳細(xì)介紹了巴雷特機(jī)械手爪BH8 – 250型的設(shè)計(jì)和運(yùn)行，一個(gè)智能的，靈活的八軸夾具, 一個(gè)可以隨時(shí)進(jìn)行自我完善,改變或者中斷各種危險(xiǎn)行為的工具。機(jī)械手爪帶來(lái)巨大的價(jià)值-工廠自動(dòng)化,因?yàn)樗?降低所需機(jī)器人工作單元的數(shù)量和尺寸 (平均每項(xiàng)90,000美元不包括高成本的占地面積),從而提高了工廠的生產(chǎn)能力,通過(guò)一個(gè)可編程平臺(tái)控制整合了各種各樣的機(jī)械手抓;漸漸的改進(jìn)和推出新產(chǎn)品介紹，通過(guò)工廠里的軟件進(jìn)行國(guó)際聯(lián)網(wǎng)。
介紹
本文介紹了一種新的方法來(lái)進(jìn)行材料處理，零件分類(lèi)和構(gòu)件組裝，我們稱(chēng)它為“抓”，即一個(gè)單一的嵌入式智能可重構(gòu)機(jī)械手爪，取代了獨(dú)特的，固定形狀的夾子和整個(gè)換刀庫(kù)。指導(dǎo)的目的是為了感謝巴雷特機(jī)械手爪的設(shè)計(jì)，今天我們必須探討什么是錯(cuò)誤的機(jī)器人技術(shù)，機(jī)器人在未來(lái)的巨大潛力，以及以前遺留下來(lái)的行不通的手爪的解決方案。
為了實(shí)現(xiàn)機(jī)器人的優(yōu)秀解決方案，可編程的靈活性，需要沿著整個(gè)機(jī)器人的設(shè)計(jì)史，從它的誕生，到現(xiàn)在。機(jī)器人手臂能夠從基礎(chǔ)的編程升級(jí)到靈活性的鈑金，讓機(jī)器人的外殼越來(lái)越薄。但即使要讓這些機(jī)器人的外殼變薄，也必須嵌入智能軟件Excel，以確保每個(gè)機(jī)器人能正常運(yùn)轉(zhuǎn)和適應(yīng)新的復(fù)雜的功能。就像在串行鏈中最薄弱環(huán)節(jié)，不靈活的爪子限制了整個(gè)工作單元機(jī)器人的生產(chǎn)力。
機(jī)械爪子已經(jīng)進(jìn)行了獨(dú)特的設(shè)計(jì)，但是固定顎板的形狀還沒(méi)有確定。在設(shè)計(jì)的過(guò)程中，一般難以預(yù)計(jì)硬盤(pán)成本和進(jìn)度的范圍。一般來(lái)說(shuō)，機(jī)器人的每個(gè)形狀、方向和接近角的預(yù)期的變化，需要其他自定義，但是爪子固定的位置，存放爪子的地方和更換爪子的器械，是不容許擅自改變和增加的。
相比之下，巴雷特的專(zhuān)利機(jī)械手爪如圖1所示，機(jī)械結(jié)構(gòu)，自動(dòng)重新配置和高度可編程性，不到一秒鐘匹配，地工作單元不停頓的數(shù)據(jù)交換量，交換手爪的幾乎任意形狀的變換功能。
對(duì)于需要處理的可變等多種有效載荷的方向，提出了高度靈活性的任務(wù)，一個(gè)能讓機(jī)械手爪更安全，更快捷的安裝，以及比定做加工夾具更低的成本和大容量的存儲(chǔ)機(jī)架。
不間斷運(yùn)行時(shí)，工作單元只有一個(gè)或兩個(gè)備用機(jī)械手爪可以作為應(yīng)急備份，而一個(gè)或兩個(gè)備用的手抓，是要求每個(gè)手爪都能變化 - 可能每個(gè)工作單元需要幾十人。而且，悲劇的是如果兩個(gè)手爪都系統(tǒng)備份，如果失敗，因?yàn)樗鼤?huì)存儲(chǔ)前幾天的可以識(shí)別的數(shù)據(jù)，很多自定義形狀，裝運(yùn)和自身裝配，所以會(huì)影響后面的操作。與此相反，由于機(jī)械手爪是數(shù)據(jù)相同，他們總是可以通過(guò)特定的軟件及時(shí)提供無(wú)限量的數(shù)據(jù)。
傳統(tǒng)夾具
今天的機(jī)器人，裝配零件的處理大部分是通過(guò)夾具。如果表面的條件允許，真空吸力和電磁鐵也可以應(yīng)用，例如：處理汽車(chē)擋風(fēng)玻璃和車(chē)身。作為部分尺寸開(kāi)始超過(guò)100gms，顎板的自定義形狀，以確保安全運(yùn)行。由于處理和裝配耐用的主體，這些工具沒(méi)有什么變化，因?yàn)闄C(jī)器人是從三十年以前才開(kāi)始的。
夾具，可以看做簡(jiǎn)單的類(lèi)似鉗子的動(dòng)作，有兩個(gè)或三個(gè)非鉸鏈?zhǔn)种?，被稱(chēng)為“鉗口”，保持平行或者進(jìn)行打開(kāi)或者觀關(guān)上的運(yùn)動(dòng)，如2所示。良好的組織目錄可從制造商那里得到客戶(hù)所匹配（除了自定義形成的素具）的各種組成手爪所需要的部分任務(wù)和部分參數(shù)。
大型液壓夾鉗的有效載荷的尺寸范圍從微克至100+公斤。驅(qū)動(dòng)是典型的氣動(dòng)或液動(dòng),用簡(jiǎn)單的開(kāi)/關(guān)閥控制切換全開(kāi)或全閉狀態(tài)。鉗口通常移動(dòng)1cm就可以全開(kāi)至全關(guān)。這兩只手，兩個(gè)或三個(gè)手指，被稱(chēng)為“鉗口”。對(duì)鉗口部分的制造目標(biāo)是可移動(dòng)的機(jī)械軟鋼或鋁，被稱(chēng)為“軟鉗口”。
在特殊的情況下，工具專(zhuān)家設(shè)計(jì)師決定要對(duì)矩形軟鉗口件進(jìn)行自定義加工。一旦加工形狀完成，軟鉗口夾持器就要連接到各自的機(jī)構(gòu)進(jìn)行測(cè)試。這一過(guò)程可以采取任何數(shù)量的迭代和調(diào)整，直到系統(tǒng)正常工作。模具設(shè)計(jì)者需要時(shí)間來(lái)重復(fù)整個(gè)過(guò)程中每一個(gè)新的形態(tài)。
隨著消費(fèi)者需求產(chǎn)品選擇的多元化，更加頻繁的產(chǎn)品介紹，對(duì)可調(diào)節(jié)自動(dòng)化的需求前所未有地強(qiáng)烈。然而，并沒(méi)有使機(jī)械手爪更全面，在過(guò)去幾年中機(jī)器人產(chǎn)業(yè)一直遵循的工具自動(dòng)來(lái)交換數(shù)控磨刀具技術(shù)的例子。
但是，應(yīng)用換模型串行工具連接機(jī)器人證明是昂貴的和無(wú)效的。不同于使用標(biāo)準(zhǔn)規(guī)范外的銑床工具進(jìn)行成品切割，機(jī)器人工具設(shè)計(jì)者必須定制每一套機(jī)械爪的形狀 ， 一個(gè)耗時(shí)多、昂貴且難以確定范圍的任務(wù)。雖然機(jī)械手爪只便宜了500美元，但是每個(gè)工人努力制造機(jī)械手爪會(huì)耗資數(shù)倍。通過(guò)上面的例子，如果你要增加12個(gè)爪子的換刀架和刀具庫(kù)，那么花費(fèi)就不止10,000美元，而是劇增到20,000美元至60,000元。
更嚴(yán)重的是，在定制過(guò)程中準(zhǔn)確的預(yù)測(cè)成本將是未知數(shù)。因此，客戶(hù)必須提交一份包括初裝費(fèi)、所需時(shí)間和材料的成本在內(nèi)的采購(gòu)訂單，這是是交易的基礎(chǔ)。雖然在美國(guó)售價(jià)30,000美元，智能機(jī)械手爪并不便宜。然而，人們可以“定制”在某一天運(yùn)行一個(gè)小時(shí)軟件來(lái)驗(yàn)證的系統(tǒng)的性能。如果系統(tǒng)的性能不能達(dá)到目標(biāo)要求，那么那一天的勞動(dòng)是白費(fèi)的。如果系統(tǒng)成功，那么按照原訂單將沒(méi)有任何隱藏的費(fèi)用。
除了成本、轉(zhuǎn)換機(jī)制的物理重量，在末端串行連接的機(jī)械臂外，限制了有效載荷和整個(gè)系統(tǒng)的動(dòng)態(tài)響應(yīng)。該轉(zhuǎn)換長(zhǎng)度增加了額外的有效載荷中心，運(yùn)動(dòng)的靈活性，動(dòng)態(tài)響應(yīng)和關(guān)鍵的安全距離。
巴雷特機(jī)械手爪的說(shuō)明
靈活性和耐久性的簡(jiǎn)潔介紹
巴雷特機(jī)械手爪在靈活性的基礎(chǔ)上，按圖3中確定的八種聯(lián)合軸連接。只有四個(gè)直流伺服電動(dòng)機(jī)，如圖4所示，需要控制所有八個(gè)關(guān)節(jié)，由智能機(jī)械耦合增強(qiáng)。由此產(chǎn)生的機(jī)械手爪是自身總共只有一點(diǎn)一八公斤重，只有8mm直徑的連接電纜提供直流電源，建立雙向串行通訊連接到機(jī)器人的主要工作單元控制器中。該機(jī)械手爪的通訊電子，五微處理器，傳感器，信號(hào)處理電路，電子換相，電流放大器，和伺服電機(jī)都整齊的安裝在機(jī)械手的體內(nèi)。
巴雷特機(jī)械手爪的手掌有三個(gè)手指關(guān)節(jié)，如圖5所示，通過(guò)聯(lián)系手掌及每個(gè)手指，協(xié)調(diào)他們的動(dòng)作，能讓他們?cè)谀繕?biāo)范圍內(nèi)，牢牢的抓住物體。
每個(gè)巴雷特機(jī)械手爪的三根手指都是由三個(gè)獨(dú)立伺服電機(jī)控制，如圖6所示。除了F1手指和F2手指的伸展動(dòng)作, 都是由伺服電動(dòng)機(jī)驅(qū)動(dòng)，F(xiàn)1、F2、F3 三個(gè)手指的內(nèi)外部的機(jī)械結(jié)構(gòu)都是用一樣的鉸鏈連接的。
三個(gè)手爪的每個(gè)馬達(dá)都必須驅(qū)動(dòng)兩個(gè)關(guān)節(jié)軸。通過(guò)專(zhuān)用通道來(lái)控制扭矩，扭矩控制器如圖7所示，這些關(guān)節(jié)的作用是能讓爪子在抓東西時(shí)更安全。如圖8所示，當(dāng)手爪第一次接觸物體時(shí)，需要傳遞簡(jiǎn)單的扭矩，確定他們的接合處，關(guān)閉電機(jī)電流，并等待手抓內(nèi)部的微處理器發(fā)出進(jìn)一步的指示命令。
但是，當(dāng)扭矩控制器如圖9所示時(shí)，為使安全和控制，扭矩控制機(jī)制第一次接觸物體時(shí)，用事先設(shè)置好的扭矩的上限值，再次確定物體螺紋的聯(lián)系，并當(dāng)手爪第二次接觸時(shí)，在一毫秒之內(nèi)更改第一次接觸時(shí)的所有扭矩信息。接觸順序快速確定，沒(méi)有高速攝像機(jī)的幫助下你將無(wú)法想象其中的過(guò)程。當(dāng)機(jī)械手爪放開(kāi)被抓對(duì)象時(shí)，它會(huì)讓扭矩控制器對(duì)每個(gè)手爪的扭矩的上限值進(jìn)行設(shè)定，而可控扭矩可以讓機(jī)械的停止的爪子再一次打開(kāi)。當(dāng)扭矩達(dá)到最高，那就是它的上限。這樣的話，機(jī)械手爪就有一個(gè)可抓起物體重量的準(zhǔn)確范圍。
與傳統(tǒng)的機(jī)械手爪不同，這種手抓里的連接，容許每個(gè)手指的兩個(gè)一致的獨(dú)立接觸點(diǎn)來(lái)穩(wěn)固的抓住物體的表面。不管位置，速度，加速度，還是扭矩，都可以通過(guò)所有17,500種型號(hào)的編碼器進(jìn)行控制處理。當(dāng)速度和加速度設(shè)置為最大時(shí)，每個(gè)手指可以在不到一秒鐘的時(shí)間內(nèi)向任何一個(gè)的方向上進(jìn)行運(yùn)動(dòng)。通過(guò)測(cè)量，每個(gè)手指都能夠迅速的產(chǎn)生2公斤的力。一旦確定穩(wěn)定的抓住物體時(shí)，則鏈接將自動(dòng)鎖定，并關(guān)掉電機(jī)，這樣可以節(jié)省電源，直到需要重新調(diào)整或者放開(kāi)物體時(shí)，電機(jī)會(huì)自動(dòng)打開(kāi)。
雖然手抓的張開(kāi)與收縮是擬人化，但如圖10所示，清楚的顯示了機(jī)器的非擬人化。機(jī)器伸展的動(dòng)作非常近似于靈長(zhǎng)類(lèi)動(dòng)物的手指（拇指）的動(dòng)作，但是又不能替代，巴雷特機(jī)械手爪還有一種類(lèi)似的手爪，整個(gè)手爪可以旋轉(zhuǎn)180度，手指中心對(duì)稱(chēng)且平行于連接軸，是一種可以抓住各種夾具形狀的多功能手爪。
在1/2秒內(nèi)可控制的機(jī)器在 [3000]位置中任意伸展。不同的是機(jī)械鎖定了手爪伸縮的運(yùn)動(dòng)，使伸縮運(yùn)動(dòng)變回了可驅(qū)動(dòng)狀態(tài)，允許其控制手爪的位置，速度，加速度和扭矩。通過(guò)允許手爪的伸縮運(yùn)動(dòng)，使手指緊密的感應(yīng)物體，機(jī)械手爪的主要目的是找到一個(gè)接觸面積最大的同時(shí)耗能又是最小的地方。
電子和機(jī)械的優(yōu)化
可編程機(jī)器人智能靈巧的控制是成功的關(guān)鍵，不論是控制機(jī)械手臂，自動(dòng)引導(dǎo)工具，還是機(jī)械手爪。雖然智能機(jī)器人驅(qū)動(dòng)電機(jī)控的制通常是與處理器相關(guān)聯(lián)，很多生物系統(tǒng)，包括人類(lèi)的手，一定程度上是通過(guò)大腦控制來(lái)處理一些反饋上來(lái)的獨(dú)立信號(hào)。實(shí)際上，巴雷特機(jī)械手爪通過(guò)結(jié)合現(xiàn)實(shí)世界中生物的靈活動(dòng)作，制作了一個(gè)機(jī)械程度相當(dāng)高的智能可編程微處理器，來(lái)處理反饋的信號(hào)。
通過(guò)嚴(yán)格的數(shù)學(xué)定義，要求關(guān)節(jié)軸通過(guò)智能電機(jī)的控制，使每一個(gè)獨(dú)立關(guān)節(jié)都能非常靈活。如果想讓機(jī)器人變得靈活，至少需要N個(gè)獨(dú)立的伺服電機(jī)，有時(shí)會(huì)多達(dá)N+1個(gè)或者2N個(gè)，每個(gè)關(guān)節(jié)軸都需要驅(qū)動(dòng)器控制。能讓機(jī)器人靈活的最重要的組成是伺服電機(jī)，可惜的是，這個(gè)家伙非常大，非常復(fù)雜，同時(shí)也是非常昂貴的。所以，理想中的想法可能是美好的，但放到現(xiàn)實(shí)中確實(shí)一個(gè)不切實(shí)際的設(shè)計(jì)。
根據(jù)定義，靈活的既不是你的手，也不是巴雷特機(jī)械手爪。當(dāng)然，其本身的良好定義是多功能的。其次，如果嚴(yán)格的定義巴雷特機(jī)械手爪的靈活性，它需要八至16個(gè)馬達(dá)，使過(guò)于笨重的，復(fù)雜的，和不牢固的機(jī)械手變得靈活起來(lái)，但實(shí)際應(yīng)用起來(lái)卻并非如此。但是，通過(guò)利用四個(gè)智能的聯(lián)合耦合機(jī)制，僅需要4個(gè)伺服電機(jī)基本上就可以讓巴雷特機(jī)械手爪變得靈活起來(lái)。
在某些情況下反射控制甚至比刻意控制要好?；趯?duì)自身有兩個(gè)例子可以說(shuō)明這一點(diǎn)。假設(shè)你的手不小心摸了非常燙的表面，它本能的會(huì)立刻回縮，通過(guò)條件反射來(lái)彌補(bǔ)主觀控制。如果沒(méi)有這種反射行為，你的手將邊燃燒邊等待疼痛的感覺(jué)通過(guò)神經(jīng)纖維緩慢的從你的手傳送到到你的大腦，然后你的大腦通過(guò)相同的神經(jīng)纖維緩慢的指揮你的手臂，手腕，手指的肌肉收縮。
至于第二個(gè)例子，試著動(dòng)食指的某一個(gè)關(guān)節(jié)而不出動(dòng)其他關(guān)節(jié)。如果你還是正常人的話，你將不能完成，因?yàn)槟愕氖值年P(guān)節(jié)是聯(lián)系在一起的。你的肌肉和肌腱為了精簡(jiǎn)而失去了某些靈活的功能。
巴雷特機(jī)械手爪承諾，微處理器和機(jī)械智能集成的功能設(shè)計(jì)將滿(mǎn)足智能靈活的要求。
電子控制
在巴雷特機(jī)械手爪中，包含了中央監(jiān)控微處理器，協(xié)調(diào)四個(gè)專(zhuān)門(mén)的運(yùn)動(dòng)控制微處理器通過(guò)RS232線進(jìn)行對(duì)I / O的控制。在圖4所示部分控制電路是在70針底板上建立并運(yùn)行的。每個(gè)控制微處理器都是傳感器電子進(jìn)行相關(guān)的運(yùn)動(dòng)，電機(jī)換向電子和電機(jī)功率，手指或擴(kuò)散的動(dòng)作電流放大器的電子產(chǎn)品。
微處理器通過(guò)I/O命令監(jiān)視高速通過(guò)的信息，通過(guò)行業(yè)標(biāo)準(zhǔn)的RS232串行通信連接到PC的工作單元 或 控制器進(jìn)行通訊。機(jī)器人的兼容性允許使用任何RS232控制器，只有8毫米直徑的電纜同時(shí)對(duì)所有電力和通信進(jìn)行限制。通過(guò)使用公開(kāi)出版的機(jī)械手爪通訊語(yǔ)言（GLS）優(yōu)化了通信速度、帶寬和所需要的時(shí)間，并處理了機(jī)械手爪遇到特殊情況所出現(xiàn)的延遲問(wèn)題。重要的是要認(rèn)識(shí)到，機(jī)械手爪一般在工作周期中是最活躍的，而其執(zhí)行手臂運(yùn)動(dòng)，手臂在一個(gè)估計(jì)的軌跡兩端活動(dòng)時(shí)所用時(shí)間是最短的。
當(dāng)然機(jī)械臂在整個(gè)周期需要高控制帶寬，機(jī)械手抓就有足夠的時(shí)間接受安裝信息，因?yàn)樗咏哪繕?biāo)比較大。然后，用精確定時(shí)的控制器發(fā)布一個(gè)“觸發(fā)器”命令，如ASCII字符“C”，在幾個(gè)毫秒內(nèi)開(kāi)始執(zhí)行。
機(jī)械手爪的控制語(yǔ)言(GCL)
該機(jī)械手爪可以傳達(dá)和接受任何機(jī)器人的工作控制器命令，個(gè)人電腦，蘋(píng)果機(jī)，UNIX box，甚至是通過(guò)標(biāo)準(zhǔn)的ASCII RS232 - C的掌上電腦進(jìn)行串行通信 他們都有共同的通信協(xié)議。雖然強(qiáng)大，相比USB或火線的標(biāo)準(zhǔn)， RS232有一個(gè)慢速帶寬的說(shuō)法，但其的簡(jiǎn)單導(dǎo)致了數(shù)據(jù)有一個(gè)短時(shí)間的小延遲。通過(guò)簡(jiǎn)化GCL，我們已經(jīng)實(shí)現(xiàn)了只需要以毫秒為單位就可以執(zhí)行和反饋一個(gè)命令（從控制器傳輸?shù)綑C(jī)械手爪，然后再傳回控制器）。通過(guò)最初的努力，建立了一個(gè)高度優(yōu)化的機(jī)械手爪語(yǔ)言，這樣的標(biāo)準(zhǔn)基礎(chǔ)協(xié)議意味著GCL的行業(yè)標(biāo)準(zhǔn)兼容協(xié)議的未來(lái)是美好的。
該機(jī)械手抓有兩種控制模式：監(jiān)管模式和即時(shí)模式。監(jiān)督是通過(guò)正常的模式來(lái)控制機(jī)械手爪。它是通過(guò)一個(gè)簡(jiǎn)單的指揮體系，為了實(shí)現(xiàn)最佳的性能。
監(jiān)管模式具有以下幾種語(yǔ)法結(jié)構(gòu)：
對(duì)象（前綴） - 動(dòng)作（命令） - 主體（參數(shù)） - 限定（數(shù)值）.
前綴是指通過(guò)1-4臺(tái)電機(jī)的ASCII數(shù)值1，2，3，4來(lái)分別對(duì)應(yīng)F1,F2,F3,F4四個(gè)手指。任何前綴號(hào)碼，可用于任何命令。如果前綴被省略，那么機(jī)械手爪的命令適用于所有可用的軸。
舉一個(gè)例子，在ASCII字符“c”表示命令，驅(qū)動(dòng)相關(guān)的發(fā)動(dòng)機(jī)，以默認(rèn)（或用戶(hù)定義）的速度和加速度開(kāi)始運(yùn)行，直到運(yùn)行夠默認(rèn)（或用戶(hù)定義）的時(shí)間后停止，并鎖定這個(gè)時(shí)候機(jī)械手抓的位置
?1C代表關(guān)閉F1號(hào)手指。
?2C代表關(guān)閉F2號(hào)手指
?12C代表關(guān)閉F12號(hào)手指。
?C相當(dāng)于1234C并關(guān)閉所有手指。
我們也有專(zhuān)門(mén)的命令“S”（取自于單詞“spread”）作為 “4”的快捷方式，“G” （取自于“grasp”）作為“123”的快捷方式，所以：
?GC是相當(dāng)于123C
?SC是相當(dāng)于4C。
有類(lèi)似的命令啟動(dòng)手指，移動(dòng)任何組合的四個(gè)軸的位置，打開(kāi)默認(rèn)或用戶(hù)定義的數(shù)據(jù)，讀取和設(shè)置用戶(hù)自定義的參數(shù)，并讀?。蛇x）相應(yīng)的三個(gè)手指。BH8-250型號(hào)的最新版本有21和28兩種命令設(shè)置參數(shù)，可以靈活的進(jìn)行各種設(shè)置。
在即時(shí)模式下，如過(guò)先進(jìn)的即時(shí)遙操作控制，并且經(jīng)常通過(guò)巴雷特的用戶(hù)友好的GUI訪問(wèn)運(yùn)行Windows95/98/NT電腦。在即時(shí)模式下，用戶(hù)指定一個(gè)已有的數(shù)據(jù)包括模式和結(jié)構(gòu)。巴雷特的個(gè)人電腦軟件為用戶(hù)提供了20個(gè)連續(xù)的模式，使用戶(hù)可以通過(guò)定量細(xì)化數(shù)據(jù)包里的信息內(nèi)容。
GUI可以快速的形成一個(gè)機(jī)械手抓的圖案，其中包括了速度和位置的控制。GUI也有新型“生成C + +代碼”按鈕，使一個(gè)沒(méi)有任何C或C + +編程知識(shí)人都可以成功的保存和讀取。但是，如果熟悉C + +編程，也可以根據(jù)需要自行編輯代碼。
一旦即時(shí)模式啟動(dòng)，數(shù)據(jù)將全部處于ASCII字符的控制，直到發(fā)出停止即時(shí)模式或監(jiān)管模式才能返回。則該系統(tǒng)已被證明有效，并將客戶(hù)的各種應(yīng)用進(jìn)行了強(qiáng)化。
結(jié)論
雖然巴雷特機(jī)械手爪BH8 - 250只在1999年推出商用，已在30個(gè)企業(yè)投入使用，在全球各地每個(gè)的價(jià)格統(tǒng)一30,000美元。購(gòu)買(mǎi)機(jī)械手爪最集中的產(chǎn)業(yè)是日本汽車(chē)行業(yè)的制造商和供應(yīng)商，包括本田，雅馬哈摩托車(chē)， NGK（催化改裝陶瓷基板）。在這個(gè)時(shí)候，這些廠家才剛剛開(kāi)始探索這種多功能設(shè)備的功能，而諸如Fanuc Robotics公司，美國(guó)和日本空間計(jì)劃的客戶(hù)，已成為回頭客。
附錄A
MCB – Industrial Robot Feature Article
The BarrettHand grasper – programmable flexible part handling and assembly
Abstract
This paper details the design and operation of the BarrettHand BH8-250, an intelligent, highly flexible eight-axis gripper that reconfigures itself in real time to conform securely to a wide variety of part shapes without tool-change interruptions. The grasper brings enormous value to factory automation because it: reduces the required number and size of robotic work cells (which average US$90,000 each – not including the high cost of footprint) while boosting factory throughput; consolidates the hodgepodge proliferation of customized gripper-jaw shapes onto a common programmable platform; and enables incremental process improvement and accommodates frequent new-product introductions, capabilities deployed instantly via software across international networks of factories.
Introduction
This paper introduces a new approach to material handling, part sorting, and component assembly called “grasping”, in which a single reconfigurable grasper with embedded intelligence replaces an entire bank of unique, fixed-shape grippers and tool changers. To appreciate the motivations that guided the design of Barrett’s grasper, we must explore what is wrong with robotics today, the enormous potential for robotics in the future, and the dead-end legacy of gripper solutions.
For the benefits of a robotic solution to be realized, programmable flexibility is required along the entire length of the robot, from its base, all the way to the target work piece. A robot arm enables programmable flexibility from the base only up to the tool plate, a few centimeters short of the target work piece. But these last few centimeters of a robot must adapt to the complexities of securing a new object on each robot cycle, capabilities where embedded intelligence and software excel. Like the weakest link in a serial chain, an inflexible gripper limits the productivity of the entire robot work cell.
Grippers have individually-customized, but fixed jaw shapes. The trial-and-error customization process is design intensive, generally drives cost and schedule, and is difficult to scope in advance. In general, each anticipated variation in shape, orientation, and robot approach angle requires another custom-but-fixed gripper, a place to store the additional gripper, and a mechanism to exchange grippers. An unanticipated variation or incremental improvement is simply not allowable.
By contrast, the mechanical structure of Barrett’s patented grasper, illustrated in Figure 1, is automatically reconfigurable and highly programmable, matching the functionality of virtually any gripper shape or fixture function in less than a second without pausing the work cell throughput to exchange grippers.
For tasks requiring a high degree of flexibility such as handling variably shaped payloads presented in multiple orientations, a grasper is more secure, quicker to install, and more cost effective than an entire bank of custom-machined grippers with tool changers and storage racks.
For uninterrupted operation, just one or two spare graspers can serve as emergency backups for several work cells, whereas one or two spare grippers are required for each gripper variation – potentially dozens per work cell. And, it’s catastrophic if both gripper backups fail in a gripper system, since it may be days before replacements can be identified, custom shaped from scratch, shipped, and physically replaced to bring the affected line back into operation. By contrast, since graspers are physically identical, they are always available in unlimited quantity, with all customization provided instantly in software.
Gripper legacy
Most of today’s robotic part handling and assembling is done with grippers. If surface conditions allow, vacuum suction and electromagnets can also be used, for example in handling automobile windshields and body panels. As part sizes begin to exceed the order of 100gms, a gripper’s jaws are custom shaped to ensure a secure hold. As the durable mainstay of handling and assembly, these tools have changed little since the beginning of robotics three decades ago.
Grippers, which act as simple pincers, have two or three unarticulated fingers, called “jaws”, which either pivot or remain parallel during open/close motions as illustrated in Figure 2. Well organized catalogs are available from manufacturers that guide the integrator or customer in matching various gripper components (except naturally for the custom jaw shape) to the task and part parameters.
Payload sizes range from grams for tiny pneumatic grippers to 100+ kilograms for massive hydraulic grippers. The power source is typically pneumatic or hydraulic with simple on/off valve control switching between full-open and full-close states. The jaws typically move 1cm from full-open to full-close. These hands have two or three fingers, called “jaws”. The part of the jaw that contacts the target part is made of a removable and machine ably soft steel or aluminum, called a “soft jaw”.
Based on the unique circumstances, an expert tool designer determines the custom shapes to be machined into the rectangular soft-jaw pieces. Once machined to shape, the soft-jaw sets are attached to their respective gripper bodies and tested. This process can take any number of iterations and adjustments until the system works properly. Tool designers repeat the entire process each time a new shape is introduced.
As consumers demand a wider variety of product choices and ever more frequent product introductions, the need for flexible automation has never been greater. However, rather than make grippers more versatile, the robotics industry over the past few years has followed the example of the automatic tool exchange technique used to exchange CNC-mill cutting tools.
But applying the tool-changer model to serial-link robots is proving expensive and ineffective. Unlike the standardized off-the-shelf cutting tools used by milling machines, a robot tool designer must customize the shape of every set of gripper jaws — a time-consuming, expensive, and difficult-to-scope task. Although grippers may seem cheap at only US$500 each, the labor-intensive effort to shape the soft jaws may cost several times that. If you multiply that cost times a dozen grippers as in the example above and throw in a tool changer and tool-storage rack for an additional US$10,000, the real cost of the “few-hundred-dollar” gripper solution balloons to US$20,000 to US$60,000.
To aggravate matters, unknowns in the customization process confound accurate cost projections. So the customer must commit a purchase order to the initial installation fee on a time and materials basis without guarantee of success or a cost ceiling. While priced at US$30,000, intelligent graspers are not cheap. However, one can “customize” and validate the process in software in a matter of hours at the factory in a single day. If the system does not meet performance targets, then only a day’s labor is wasted. If the system succeeds, then there are not any hidden expenses following the original purchase order.
Beyond cost, the physical weight of tool changer mechanisms, located at the extreme outer end of a serial-link robotic arm, limits the useful payload and dynamic response of
the entire system. The additional length of the tool changer increases the critical distance between the wrist center and payload center, degrading kinematic flexibility, dynamic response, and safety.
Description of the BarrettHand
Flexibility and durability in a compact package
The flexibility of the BarrettHand is based on the articulation of the eight joint axes identified in Figure 3. Only four brushless DC servomotors, shown in Figure 4, are needed to control all eight joints, augmented by intelligent mechanical coupling. The resulting 1.18kg grasper is completely self-contained with only an 8mm diameter umbilical cable supplying DC power and establishing a two-way serial communication link to the main robot controller of the work cell. The grasper’s communications electronics, five microprocessors, sensors, signal processing electronics, electronic commutation, current amplifiers, and brushless servomotors are all packed neatly inside the palm body of the grasper.
The BarrettHand has three articulated fingers and a palm as illustrated in Figure 5 which act in concert to trap the target object firmly and securely within a grasp consisting of seven coordinated contact vectors — one from the palm plate and one from each link of each finger.
Each of the BarrettHand’s three fingers is independently controlled by one of three servomotors as shown in Figure 6. Except for the spread action of fingers Fl and F2, which is driven by the fourth and last servomotor, the three fingers, Fl, F2, and F3, have inner and outer articulated links with identical mechanical structure.
Each of the three finger motors must drive two joint axes. The torque is channeled to these joints through a patented, TorqueSwitch mechanism (Figure 7), whose function is optimized for maximum grasp security. When a fingertip, not the inner link, makes first contact with an object as illustrated in Figure 8, it simply reaches its required torque, locks both joints, switches off motor currents, and awaits further instructions from the microprocessors inside the hand or a command arriving across the communications link.
But when the inner link, as illustrated in Figure 9, makes first contact with an object for a secure grasp, the TorqueSwitch, reaches a preset threshold torque, locks that joint against the object with a shallow-pitch worm, and redirects all torque to the fingertip to make a second, enclosing contact against the object within milliseconds of the first contact. The sequence of contacts is so rapid that you cannot visualize the process without the aid of high-speed photography. After the grasper releases the object, it sets the TorqueSwitch threshold torque for each finger in anticipation of the next grasp by opening each finger against its mechanical stop with a controlled torque. The higher the opening torque, the higher the subsequent threshold torque. In this way, the grasper can accommodate a wide range of objects from delicate, to compliant, to heavy.
The finger articulations, not available on conventional grippers, allow each digit to conform uniquely and securely to the shape of the object surface with two independent contact points per finger. The position, velocity, acceleration, and even torque can all be processor controlled over the full range of 17,500 encoder positions. At maximum velocity and acceleration settings, each finger can travel full range in either direction in less than one second. The maximum force that can be actively produced is 2kg, measured at the tip of each finger. Once the grasp is secure, the links automatically lock in place allowing the motor currents to be switched off to conserve
power until commanded to readjust or release their grasp.
While the inner and outer finger-link motions curl anthropomorphically, the spread motion of Figure 10 is distinctly non-anthropomorphic. The spread motion is closest in function to a primate’s opposable (thumb) finger, but instead of one opposable finger, the BarrettHand has twin, symmetrically opposable fingers centered on parallel joint axes rotating 180 degrees around the entire palm to form a limitless variety of gripper-shapes and fixture functions.
The spread can be controlled to any of [3,000] positions over its full range in either direction within 1/2 second. Unlike the mechanically lockable finger-curl motions, the spread motion is fully back drivable, allowing its servos to provide active stiffness control in addition to control over position, velocity, acceleration, and torque. By allowing the spread motion to be compliant while the fingers close around an object, the grasper seeks maximum grasp stability as the spread accommodates its position, permitting the fingers to find their lowest energy states in the most concave surface features.
Electronic and mechanical optimization
Intelligent, dexterous control is key to the success of any programmable robot, whether it is an arm, automatically guided vehicle, or dexterous hand. While robotic intelligence is usually associated with processor-driven motor control, many biological systems, including human hands, integrate some degree of specialized reflex control independent of explicit motor-control signals from the brain. In fact, the BarrettHand combines reflexive mechanical intelligence and programmable microprocessor intelligence for a high degree of practical dexterity in real-world applications.
By strict mathematical definition, dexterity requires independent, intelligent
motor control over each and every articulated joint axis. For a robot to be dexterous, at least n independent servomotors, and sometimes as many as n + 1 or 2n, are required to drive n joint axes. Unfortunately, servomotors constitute the bulkiest, costliest, and most complex components of any dexterous robotic hand. So, while the strict definition of dexterity may be mathematically elegant, it leads to impractical designs for any real application.
According to the definition, neither your hand nor the BarrettHand is dexterous. Naturally, their superior versatility challenges the definition itself. If the BarrettHand followed the strict definition for dexterity, it would require between eight and 16 motors, making it far too bulky, complex, and unreliable for any practical application outside the mathematical analysis of hand dexterity. But, by exploiting four intelligent, joint-coupling mechanisms, the almost-dexterous BarrettHand requires only four servomotors.
In some instances reflex control is even better than deliberate control. Two examples based on your own body illustrate this point. Suppose your hand accidentally touches a dangerously hot surface. It begins retracting itself instantly, relying on local reflex to override any ongoing cognitive commands. Without this reflex behavior, your hand would burn while waiting for the sensations of pain to travel from your hand to your brain via relatively slow nerve fibers and then for your brain, through the same slow nerve fibers, to command your arm, wrist, and finger muscles to retract.
As the second example, try to move the outer joint of your index finger without moving the adjacent joint on the same finger. If you are like most people, you cannot move these joints independently because the design of your hand is optimized for grasping. Your muscles and tendons are as streamlined and lightweight as possible without forfeiting functionality.
The design of the BarrettHand recognizes that intelligent control of functional dexterity requires the integration of microprocessor and mechanical intelligence.
Control electronics
Inside its compact palm, the BarrettHand contains its central supervisory microprocessor that coordinates four dedicated motion-control microprocessors and controls I/O via the RS232 line. The control electronics, partially visible in Figure 4 are built on a parallel 70-pin backplane bus. Associated with each motion-control microprocessor are the related sensor electronics, motor commutation electronics, and motor-power current-amplifier electronics for that finger or spread action.
The supervisory microprocessor directs I/O communication via a high-speed, industry-standard RS232 serial communications link to the work cell PC or controller. RS232 allows compatibility with any robot controller while limiting umbilical cable diameter for all power and communications to only 8mm. The openly published grasper communications language (GSL) optimizes communications speed, exploiting the difference between bandwidth and time-of-flight latency for the special case of graspers. It is important to recognize that graspers generally remain inactive during most of the work cell cycle, while the arm is performing its gross motions, and are only active for short bursts at the ends of an arm’s trajectories.
While the robotic arm requires high control bandwidth during the entire cycle, the grasper has plenty of time to receive a large amount of setup information as it approaches its target. Then, with precision timing, the work cell controller releases a “trigger”command, such as the ASCII character “C” for close, which begins grasp execution within a couple milliseconds.
Grasper control language (GCL)
The grasper can communicate and accept commands from any robot-work cell controller, PC, Mac, UNIX box, or even a Palm pilot via standard ASCII RS232-C serial communication — the common denominator of communications protocols. Though robust, RS232 has a reputation for slow bandwidth compared to USB or FireWire standards, but its simplicity leads to small latencies for short bursts of data. By streamlining the GCL, we have achieved time of flight to execute and acknowledge a command (from the work cell controller to the grasper and then back again to the work cell controller) of the order of milliseconds. The initial effort to develop a highly optimized grasper language based on such a standard protocol means that the GCL is upwardly compliant with any future industry-standard protocol.
The grasper has two control modes: supervisory and real time. Supervisory is the normal mode used to control the grasper. It is made up of a simple command structure, designed for optimal performance and minimized learning curve.
Supervisory mode has the following grammatical structure:
Object (prefix) — Verb (command) — Subject (parameters) — Qualifiers (values)
The prefix refers to motors 1 through 4 with the ASCII values for 1, 2, 3, and 4 corresponding to the fingers Fl, F2, F3, and the spread motion. Any number of prefixes may be used in any order. If the prefix is omitted, then the grasper applies the command to all available axes.
As an example, the ASCII character “C” represents the command which drives the associated motor (s) at its individual default (or user defined) velocity and acceleration profile(s) until the motor(s) stops for the default (or user defined) number of milliseconds. As each motor reaches this state its position is locked mechanically in place.
? 1C closes finger Fl.
? 2C closes finger F2.
? 12C closes fingers Fl and F2.
? C is equivalent to 1234C and closes all three fingers and the spread motion.
We also have defined “S” (derived from “spread”) as a shortcut for “4” and “G” (from “grasp”) as a short cut for “123”, so that:
? GC is equivalent to 123C
? SC is equivalent to 4C
There are similar commands for opening fingers, moving any combination of the four axes to an array of positions, incremental opening and closing by default or user-defined distances, reading and setting user-defined parameter values, and reading the (optional) strain gages on the three fingers. The latest version of the BH8-250 firmware has 21 commands and 28 parameter settings, giving it almost unlimited flexibility.
The real time mode is reserved for advanced uses such as real time teleportation control and is frequently accessed through Barrett’s user-friendly GUI for PCs running Windows95/98/NT. In real time mode, the user specifies a tailored packet-structure in supervisory mode. Barrett’s PC software gives the user a histogram of 20 successive time-of-flight tests so that the user can refine the packet structure by quantitatively balancing information content with latency.
The GUI accelerates the prototyping of tasks and includes a pictorial of the grasper with sliders for position and rate control. The GUI also has a novel “Generate C++ Code” button which enables anyone to save and later recall successful algorithms without any knowledge of C or C++ programming. But, with
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