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大學(xué)
畢業(yè)論文(設(shè)計(jì))中期檢查記錄表
年 4 月 20 日
學(xué)生姓名
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課題名稱
分區(qū)式殘膜回收機(jī)的設(shè)計(jì)
課題完成進(jìn)度(學(xué)生自述)
已經(jīng)完成了機(jī)械各零部件和總裝配圖的三維模型設(shè)計(jì),下一步將進(jìn)行
二維圖的設(shè)計(jì)以及說明書的書寫。
存在的問題及整改措施(學(xué)生自述)
問題1:切膜盤的設(shè)計(jì)問題?
整改措施:通過老師的指導(dǎo),應(yīng)該將切膜盤設(shè)計(jì)成垂直于地膜的形狀,不應(yīng)該設(shè)計(jì)成一側(cè)想內(nèi)凹凸的,因?yàn)檫@樣會(huì)具有翻土效果,與設(shè)計(jì)不符。
問題2:怎樣保證膜在回收過程中不斷?
整改措施:設(shè)計(jì)一個(gè)引導(dǎo)裝置,將中間膜與邊膜匯聚成一股,然后通過回收輥回收,這樣就可以保證膜不斷。
指導(dǎo)教師意見(課題進(jìn)展情況、優(yōu)缺點(diǎn)、整改措施等)
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負(fù)責(zé)人簽名
年 月 日
大學(xué)
畢業(yè)論文(設(shè)計(jì))任務(wù)書
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班級(jí)
學(xué)生姓名
學(xué)號(hào)
課題名稱
分區(qū)式殘膜回收機(jī)的設(shè)計(jì)
起止時(shí)間
指導(dǎo)教師
職稱
副教授
課題內(nèi)容
設(shè)計(jì)與小型拖拉機(jī)配備的分區(qū)式殘膜回收機(jī),并完成圖紙與設(shè)計(jì)說明書。
擬定工作進(jìn)度(以周為單位)
2015年11月5日-11月25日,查閱相關(guān)資料、文獻(xiàn),撰寫開題報(bào)告。
2015年11月26日-2016年1月20日,完成機(jī)器草圖設(shè)計(jì)。
2016年1月21日-4月17日,繪制機(jī)器各零件圖。
2016年4月18日,中期檢查。
2016年4月19日-5月9日,完成各零件圖,裝配圖,撰寫設(shè)計(jì)說明書。
2016年5月10日,審閱畢業(yè)設(shè)計(jì)相關(guān)資料。
2016年5月11日-5月24日,修改設(shè)計(jì),準(zhǔn)備答辯。
主要參考文獻(xiàn)
1.農(nóng)業(yè)機(jī)械設(shè)計(jì)手冊 中國農(nóng)業(yè)科學(xué)技術(shù)出版社
2.農(nóng)業(yè)機(jī)械學(xué) 中國農(nóng)業(yè)出版社
3.機(jī)械設(shè)計(jì)手冊 機(jī)械工業(yè)出版社
任務(wù)下達(dá)人(簽字)
年 月 日
任務(wù)接受人意見
任務(wù)接受人簽名
年 11 月 27 日
注:1、此任務(wù)書由指導(dǎo)教師填寫,任務(wù)下達(dá)人為指導(dǎo)教師。
2、此任務(wù)書須在學(xué)生畢業(yè)實(shí)踐環(huán)節(jié)開始前一周下達(dá)給學(xué)生本人。
3、此任務(wù)書一式三份,一份留學(xué)院存檔,一份學(xué)生本人留存,一份指導(dǎo)教師留存。
果園開溝施肥機(jī)的設(shè)計(jì)
摘要:是一個(gè)棉花種植大省,隨著時(shí)間的積累,塑料殘膜對(duì)棉田地的污染越來越嚴(yán)重。解決殘膜污染問題已成為當(dāng)下重中之重。為了提高殘膜的回收效率,并結(jié)合棉田地貌特點(diǎn)以及國內(nèi)外對(duì)殘膜回收機(jī)械的研究現(xiàn)狀,設(shè)計(jì)了一款分區(qū)式殘膜回收機(jī)械,該機(jī)械降低了收膜過程中殘膜的破損程度,提高了殘膜回收的效率。
本文首先敘述了目前我國殘膜污染的現(xiàn)狀,闡述了本文選題的目的、意義及選題背景。通過對(duì)國內(nèi)外殘膜回收機(jī)機(jī)械的研究比較,借鑒了現(xiàn)有殘膜回收機(jī)械的優(yōu)點(diǎn),避免了以往殘膜回收機(jī)械的不足。重點(diǎn)研究了收膜裝置。其次,對(duì)牽引裝置的速度和收膜裝置進(jìn)行了試驗(yàn)研究,通過 origin 軟件對(duì)試驗(yàn)數(shù)據(jù)進(jìn)行處理,得到了牽引速度在4.5km/h,滾齒長度為 80mm 的時(shí)候?yàn)樽罴呀M合,殘膜回收率可以達(dá)到 90%以上。最后總結(jié)了本論文的創(chuàng)新點(diǎn)和設(shè)計(jì)成果。
關(guān)鍵詞:殘膜回收;機(jī)構(gòu);牽引速度;殘膜回收機(jī)
中圖分類號(hào):TD451 文獻(xiàn)標(biāo)識(shí)碼:A
0引言
地膜覆蓋種植技術(shù)改善和優(yōu)化了農(nóng)業(yè)生產(chǎn)種植條件,克服了一些不良條件和不良環(huán)境對(duì)農(nóng)業(yè)生產(chǎn)種植的影響,所以,地膜覆蓋種植技術(shù)被認(rèn)為是一種能使農(nóng)作物早熟、高產(chǎn)、高效、優(yōu)質(zhì)的先進(jìn)農(nóng)業(yè)技術(shù)。
從上個(gè)世紀(jì) 50 年代開始,日本在農(nóng)業(yè)生產(chǎn)方面利用地膜覆蓋種植技術(shù)的農(nóng)作物種類就非常之多了,并且這種技術(shù)在日本國家普及非常之快。在世界上的其他一些國家,如美國、英國、法國、德國等國家也同樣重視地膜覆蓋種植技術(shù),投入了大量的人力、物力、財(cái)力對(duì)此項(xiàng)技術(shù)研究完善并取得了豐厚的回報(bào)
我國是從 70 年代通過技術(shù)交流的方式,從日本引進(jìn)了地膜覆蓋技術(shù)。在引進(jìn)之初,我國僅僅把這種技術(shù)應(yīng)用于一些瓜果、蔬菜類生產(chǎn)。20 世紀(jì) 80 年代,我國把覆膜技術(shù)開始推廣到棉花、花生、玉米、小麥等經(jīng)濟(jì)作物。目前在我國的東北、西北地區(qū)地膜覆蓋技術(shù)應(yīng)用尤為廣泛。到目前為止我國使用地膜的耕地已達(dá)到上千萬公頃,每年的地膜用量已接近幾百萬噸。我國在地膜覆蓋種植技術(shù)上的研究探索是與中國的國情緊密相連的,一切從實(shí)際出發(fā)。雖然我國引進(jìn)的地膜覆蓋技術(shù)比較晚,但是在實(shí)踐應(yīng)用領(lǐng)域上較國外有重大發(fā)展。
1總體設(shè)計(jì)思路
分區(qū)式殘膜回收機(jī)主要由機(jī)架、切膜裝置、起膜裝置、引導(dǎo)裝置、回收裝置等部分組成。
1.1 設(shè)計(jì)原理
機(jī)具與拖拉機(jī)三點(diǎn)懸掛聯(lián)接,作業(yè)時(shí)拖拉機(jī)液壓系統(tǒng)置于懸浮狀態(tài),該分區(qū)式殘膜回收機(jī)上的四個(gè)邊架將該分區(qū)式殘膜回收機(jī)分為中間收膜部分和兩邊收膜部分。在四個(gè)邊架上裝有切膜盤,將在距離棉桿根部 20mm 處的薄膜切開,安裝在兩邊架之間的收膜裝置將切斷的兩壟之間的殘膜回收起來。對(duì)于收取邊膜的部分也是同樣在拖拉機(jī)的牽引下,切膜盤將薄膜在距離棉桿根部20mm 的地方切斷,然后起膜鏟將埋在土里的邊膜鏟于地表,通過邊膜引導(dǎo)裝置,將其與中間膜一起匯聚在收膜裝置上,通過收膜裝置將膜回收到收集箱里面,待拖拉機(jī)到達(dá)田間地頭的時(shí)候,液壓系統(tǒng)將分區(qū)式殘膜回收機(jī)提升起來進(jìn)行卸膜,完成一次收膜過程。
1.2 設(shè)計(jì)總體結(jié)構(gòu)
分區(qū)式殘膜回收機(jī)的總體結(jié)構(gòu)示意圖,如圖1所示。
該分區(qū)式殘膜回收機(jī)的機(jī)架主要有兩個(gè)部分組成,一部分是牽引架,另一部分是支架。在工作的工程中,牽引架與拖拉機(jī)采用三點(diǎn)懸掛式連接,這種懸掛的連接方式機(jī)動(dòng)性好,可以非常方便的將機(jī)具升起、降落,對(duì)殘膜的收取和卸膜工作有很大的益處。對(duì)于支架部分,一共有四條支架,內(nèi)邊架兩個(gè),外邊架兩個(gè)。邊架與牽引架的連接是通過 U 型卡螺栓與螺母將支架與牽引架緊固接。
1.切膜盤 2.連接桿 3.機(jī)架 4.鏈接套筒 5.回收輥軸
6.鏈條 7.集膜箱 8.地輪 9.引導(dǎo)裝置 10.起膜鏟
圖1 分區(qū)式殘膜回收機(jī)整體結(jié)構(gòu)圖
2關(guān)鍵部件的設(shè)計(jì)
2.1切膜裝置的設(shè)計(jì)
為了能夠更簡單高效的完成收膜作業(yè),本分區(qū)式殘膜回收機(jī)添加了圓盤式切膜裝置,在殘膜回收機(jī)工作的時(shí)候,先由切膜裝置以作物壟上膜為界限將殘膜切割成為中間膜和邊膜。這種分開的好處有兩點(diǎn):一是可以縮短收膜的時(shí)間,因?yàn)橛眠@種分區(qū)式殘膜回收機(jī)不會(huì)受作物秸稈處理與否的影響,這樣就可以提前一段時(shí)間進(jìn)行收膜,也就減縮短了外力對(duì)殘膜破壞的時(shí)間,相比之下提高了殘膜的完整程度,對(duì)殘膜的回收大有益處。二是該切膜裝置把殘膜分開,跳過破損最嚴(yán)重的壟上膜,去除秸稈等外力對(duì)中間膜和邊膜的破壞,因此使殘膜回收率大大的提高。
2.2 起膜裝置設(shè)計(jì)
起膜鏟在結(jié)構(gòu)上的設(shè)計(jì)對(duì)把地膜鏟于地表和鏟斷地膜纏繞連接的須根都起著非常重要的作用,
起膜鏟設(shè)計(jì)的好壞直接影響到整個(gè)分區(qū)式殘膜回收機(jī)對(duì)邊膜的回收效果。通過對(duì)國內(nèi)外起膜鏟方面
的文獻(xiàn)查詢,發(fā)現(xiàn)對(duì)起膜鏟相關(guān)描述說明是比較少的,只有簡單的說明了一下收膜裝置的前方放有
起膜鏟,起膜鏟放置的大體位置為前面高后面低。分區(qū)式殘膜回收機(jī)的起膜鏟是機(jī)架的左右兩側(cè)各
放一把,對(duì)稱放置。在拖拉機(jī)的牽引下,分區(qū)式殘膜回收機(jī)的起膜鏟隨著運(yùn)動(dòng)而進(jìn)入邊膜的下面,一方面鏟斷與邊膜纏繞的棉桿根部的須根,另一方面就是將邊膜從地下鏟于地表,為了能夠更好的分析研究分區(qū)式殘膜回收機(jī)的起膜裝置,把起膜機(jī)構(gòu)設(shè)計(jì)成了分體的機(jī)構(gòu),這個(gè)起膜機(jī)構(gòu)主要是由圓柱形的力臂和梯形的鏟板組成。因?yàn)榉謪^(qū)式殘膜回收機(jī)在起膜之前,是先要由切膜裝置將邊膜與棉桿根部距離 2-3cm 的地方切開,所以此起膜裝置主要是處理一些沒有被徹底切開的須根和把邊膜鏟于地表,對(duì)于主根系,起膜鏟是不用處理的,且起膜鏟與主根系是有距離的。這種切割方式可以延長起膜鏟的壽命,如果選用上磨刃的切割方式進(jìn)行切割,就會(huì)大大的縮短起膜鏟的使用時(shí)間,上磨刃的切割方式會(huì)使起膜鏟在很短的時(shí)間內(nèi)就被磨鈍,這樣一來就不能有效的切除須根的纏繞為了保證纏繞在邊膜上的須根順利被滑切,起膜鏟鏟板的放置與分區(qū)式殘膜回收機(jī)行進(jìn)的方向所成夾角不大于 。根據(jù)以上分析,本課題把分區(qū)式殘膜回收機(jī)的起膜鏟設(shè)計(jì)成倒八字鏟。
為了能夠降低起膜裝置對(duì)牽引車的阻力,就必須減小起膜鏟的鏟板沿收膜方向入土的投影面積。 起土角η和頂角φ的幾何關(guān)系如下:
在研究的過程中,入土角λ是必不可少的,同時(shí)也是可以確定的,因此起土角η則有下列計(jì)算
公式
2.3 回收裝置設(shè)計(jì)
收膜裝置是采用地輪通過鏈條帶動(dòng)膠輥轉(zhuǎn)動(dòng)收膜,這樣在分區(qū)式殘膜回收機(jī)前進(jìn)的過程中,收膜裝置的膠輥就會(huì)在地輪的帶動(dòng)下轉(zhuǎn)動(dòng),這樣地表上的殘膜就會(huì)被收集到后面的集裝箱。分區(qū)式殘膜回收機(jī)的收膜裝置分為兩個(gè)部分,一部分是地輪帶動(dòng)膠輥裝置,另一部分是后面的集裝箱部分。在這過程中,中間殘膜裸露于地表,所以在收膜的過程中,不需要進(jìn)行特殊處理,兩邊邊膜因?yàn)閴涸谕晾锏模赃@需要起膜鏟先將邊膜鏟于地表之后,然后通過人工輔助,將地膜的中間和兩邊部分通過膜的引導(dǎo)裝置匯聚到一起放到膠輥上,再通過拖拉機(jī)帶動(dòng)機(jī)械前進(jìn),用地輪帶動(dòng)膠輥轉(zhuǎn)動(dòng),達(dá)到收膜的目的。所以,對(duì)于分區(qū)式殘膜回收機(jī)在作業(yè)的過程中,起關(guān)鍵作用的就是收膜裝置。
分區(qū)式殘膜回收機(jī)的收膜裝置主要包括引導(dǎo)裝置、橡膠輥、鏈輪、轉(zhuǎn)動(dòng)軸、支撐架、集膜箱等幾部分組成。
設(shè)計(jì)的集膜箱主要功用是盛放從收膜輥中出來的地膜,其設(shè)計(jì)要求為:具有足夠大的盛放容積,本文設(shè)計(jì)了一種上大下小抽屜式的集膜箱,其主要包括集膜箱壁、抽板和螺栓等組成,如圖 4-3 所示。它利用厚度為 3mm 的鋼板焊接而成,長度×寬度×高度=890mm×440mm×300mm,利用 4個(gè)20的螺栓固定于機(jī)架的尾部。當(dāng)收集的地膜放滿集膜箱時(shí),靠人工拉動(dòng)集箱底部的抽板進(jìn)行卸膜。
3總結(jié)
本文首先介紹了我國目前的殘膜污染的情況以及殘膜對(duì)我們?nèi)粘I畹奈:?。并總結(jié)了我國目前的所研制出來的殘膜回收機(jī)械的幾大類型,春播前殘膜回收機(jī),秋收后殘膜回收機(jī),苗期殘膜回收機(jī)。通過研究比較我國殘膜回收機(jī)的優(yōu)缺點(diǎn),而最終確定了研制一款分區(qū)式殘膜回收機(jī),來提高殘膜的回收效率,減少殘膜對(duì)我國環(huán)境和土地的影響。本機(jī)具有以下特點(diǎn):
(1) 本機(jī)器結(jié)構(gòu)簡單、緊湊,各個(gè)零件的要求較低,便于生產(chǎn)加工;
(2)該機(jī)器工作可靠,能較好地滿足殘膜的回收工作,最大限度的保證殘膜的完整性回收,可以實(shí)現(xiàn)較高的工作效率。
本文介紹的分區(qū)式殘膜回收機(jī)成本低,效率較高,和小型四輪拖拉機(jī)配合使用,具有操作簡單,占地面積小等諸多優(yōu)勢。能較好的滿足承包戶的經(jīng)濟(jì)要求,以及實(shí)際生產(chǎn)要求。
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為農(nóng)業(yè)機(jī)械提供位置數(shù)據(jù)測量
Herman Speckmann
原文來源:Federal Agricultural Research Centre Braunschweig (FAL), Institute for Biosystems Engineering, Bundesallee 50, D-38116 Braunschweig, Germany
摘要
農(nóng)業(yè)機(jī)械、車輛需要位置數(shù)據(jù)來指導(dǎo)和控制執(zhí)行最佳工作位置。位置數(shù)據(jù)也被需要用在像精細(xì)農(nóng)作這樣的應(yīng)用上。位置數(shù)據(jù)的必要的準(zhǔn)確性、分辨率和頻率依照不同的應(yīng)用而變化。只有一個(gè)系統(tǒng),安裝在中央車輛(例句、拖拉機(jī)),應(yīng)該提供對(duì)每項(xiàng)任務(wù)的位置數(shù)據(jù)。
提出的關(guān)于中央系統(tǒng)的基本概念是位置數(shù)據(jù)按照特定應(yīng)用程序計(jì)算并且直接被傳送到它需要被應(yīng)用到的那個(gè)點(diǎn)上。這片論文闡述了測量的基本原理和位置數(shù)據(jù)的計(jì)算,還對(duì)現(xiàn)有的傳送數(shù)據(jù)的農(nóng)業(yè)網(wǎng)絡(luò)進(jìn)行了簡要介紹。它集中建議了一個(gè)提供和轉(zhuǎn)移位置數(shù)據(jù)的網(wǎng)絡(luò)服務(wù)。被討論的解決方案是以農(nóng)業(yè)BUS(總線)系統(tǒng)為基礎(chǔ)(DIN 9684, ISO 11783). ? 2000 Elsevier Science B.V. 版權(quán)所有.
1.前言
位置指導(dǎo)的目的是給生長在農(nóng)田里一個(gè)固定的區(qū)域上的莊稼帶來增產(chǎn)的方法。莊稼或者它們在農(nóng)田里所處的位置是指導(dǎo)的重要參照。
位置數(shù)據(jù)被用來指導(dǎo)農(nóng)用車、實(shí)現(xiàn)控制和支持精耕農(nóng)業(yè)。準(zhǔn)確性、分辨率和頻率取決于他們的具體應(yīng)用。
必須強(qiáng)調(diào)的是本文沒有合適的解決這個(gè)問題的傳感器來產(chǎn)生數(shù)據(jù)。更確切的說,這里研究的問題是參照移動(dòng)單位的一定的位置進(jìn)行了一個(gè)位置信號(hào)產(chǎn)生,但是這個(gè)位置和需要的位置數(shù)據(jù)并不是完全一致的。此外,位置信息有可能在同一時(shí)間被需要用于幾種目的, 車輛和工具組合的結(jié)構(gòu)可能會(huì)經(jīng)常改變。
正如 Freyberger 和 Jahns (1999), Wilson (1999)所提到的, 測量系統(tǒng)可以是一個(gè)絕對(duì)定位系統(tǒng),比如Bell(1999)描述的衛(wèi)星系統(tǒng),或者是一個(gè)相對(duì)的系統(tǒng),比如Debain et al. (1999), Hague et al. (1999)描述的機(jī)器視覺系統(tǒng)。它可能也包括輔助傳感器。
傳感器只有在參考具體位置情況下測量位置,比如相機(jī)的安裝點(diǎn)、天線的底部。在接下來的描述中,這個(gè)位置被稱為測量點(diǎn)。由于各種原因,這位置測點(diǎn)的是預(yù)先設(shè)定好的,意味著衛(wèi)星天線將盡可能安裝在拖拉機(jī)的車頂上以便減少測量不到的區(qū)域。攝像機(jī)將會(huì)安裝在有保障最佳視覺的位置。粗糙或傾斜的表面引起的運(yùn)動(dòng)可能導(dǎo)致測量位置和運(yùn)動(dòng)表面的位置不同。例如,一輛車頂上裝有衛(wèi)星天線的車輛,大約3.5m,駕駛在10°的斜坡表面,傾斜方向造成的區(qū)別相差60cm。圖1闡述了這個(gè)情形。在這個(gè)例子中,計(jì)算一個(gè)參考點(diǎn)的位置可能更適當(dāng)一些。貝爾(1999)提出把拖拉機(jī)的后方軸的中點(diǎn)作為參考點(diǎn)。表面上的一個(gè)點(diǎn),例如,后方軸中間的下垂直面似乎顯得更適合與某些應(yīng)用。像一些應(yīng)用,比如控制實(shí)現(xiàn),工具的一定點(diǎn)的位置可能最終重要。這個(gè)點(diǎn)將被稱作目標(biāo)點(diǎn)。
在某些情況下位置數(shù)據(jù)需要用于不同的目的,分別為每個(gè)目的以一種獨(dú)立的測量系統(tǒng)測量位置不是很有效。當(dāng)位置測量只有一次時(shí)多個(gè)硬件可以避免,同時(shí)工具上其他點(diǎn)的位置或者工具也被計(jì)算。假如位置和方法被測量,實(shí)驗(yàn)測量和空間向量之間的地點(diǎn)測點(diǎn)的計(jì)算是眾所周知的,那么這種情況是可能的。如果兩個(gè)點(diǎn)嚴(yán)格耦合,這意味著兩點(diǎn)都在拖拉機(jī)上、兩點(diǎn)之間的向量是常數(shù),一個(gè)簡單的矩陣運(yùn)算就能產(chǎn)生結(jié)果。如果這些點(diǎn)沒被嚴(yán)格耦合,這意味著,例如,一處拖拉機(jī),另一個(gè)是在附加工具上,矢量是可變的。額外的測量成為必要用來建立兩點(diǎn)之間的向量或必須應(yīng)用其他原理計(jì)算目標(biāo)點(diǎn)的位置。
2.數(shù)據(jù)處理和數(shù)據(jù)轉(zhuǎn)移
通過計(jì)量點(diǎn)上的測量位置和方法,在車輛或工具上任何點(diǎn)的位置數(shù)據(jù)可以被計(jì)算出來。計(jì)算結(jié)果可以被測量系統(tǒng)(中央數(shù)據(jù)處理)或由請(qǐng)求目標(biāo)位置數(shù)據(jù)的各個(gè)系統(tǒng)(分布式數(shù)據(jù)處理)計(jì)算出來。
2.1 分布式數(shù)據(jù)處理
在分布式數(shù)據(jù)的情況下,測量系統(tǒng)僅作為智能傳感器服務(wù)。它測量需要的位置和計(jì)算,和提供這些未經(jīng)處理的數(shù)據(jù)。頻率和精度等特點(diǎn)取決于請(qǐng)求的單位。這個(gè)單位執(zhí)行所有處理來計(jì)算位置。單位必須知道測點(diǎn)的位置和各有關(guān)參數(shù)。這樣處理的好處是測量裝置可以相對(duì)簡單。另一方面,每個(gè)請(qǐng)求的單位需要的充分的能力來履行這一運(yùn)算。
2.2 中央數(shù)據(jù)處理
測量單位被擴(kuò)展包括計(jì)算目標(biāo)位置的各個(gè)組件。這個(gè)測量和處理系統(tǒng)形成了一個(gè)所謂的位置和導(dǎo)航服務(wù)的單元,這個(gè)單元提供任何目標(biāo)點(diǎn)的最終位置數(shù)據(jù)。在這種情況下,只有一個(gè)測量與處理系統(tǒng)是必要的,即使位置數(shù)據(jù)必須被更多的用戶要求。這樣做,只有PNS必須知道所有相關(guān)的參數(shù)來進(jìn)行計(jì)算。
2.3 數(shù)據(jù)傳送
無論數(shù)據(jù)在哪里處理,一個(gè)數(shù)據(jù)傳輸是必要的。對(duì)于這樣一個(gè)數(shù)據(jù)傳輸,一個(gè)標(biāo)準(zhǔn)的網(wǎng)絡(luò)是適當(dāng)?shù)摹榱擞糜谵r(nóng)業(yè)領(lǐng)域,存在一個(gè)在移動(dòng)單位和固定農(nóng)場電腦之間傳輸數(shù)據(jù)的汽車。農(nóng)業(yè)總線系統(tǒng)(LBS)也已被標(biāo)準(zhǔn)化以便能在網(wǎng)路的各個(gè)電子單元(LBS節(jié)點(diǎn)或BUS節(jié)點(diǎn))之間進(jìn)行信息交換。這個(gè)標(biāo)準(zhǔn)定義了物理層網(wǎng)絡(luò),網(wǎng)絡(luò)協(xié)議,系統(tǒng)管理,數(shù)據(jù)對(duì)象和常見任務(wù)的服務(wù)程序(Speckmann andJahns, 1999)。
LBS以DIN9684(DIN,1989–1998)作為標(biāo)準(zhǔn)。目前,正在努力建立一個(gè)國際標(biāo)準(zhǔn)(Nienhaus,1993),ISO 11783,為了這個(gè)目的,像LBS,ISO 11783也將定義一個(gè)農(nóng)業(yè)BUS作為一個(gè)農(nóng)業(yè)機(jī)械交換數(shù)據(jù)的開放系統(tǒng),特別是在拖拉機(jī)-執(zhí)行工具的組合和從移動(dòng)單位到靜止不動(dòng)的農(nóng)場計(jì)算機(jī)。這個(gè)標(biāo)準(zhǔn)是基于控制器區(qū)域網(wǎng)絡(luò)數(shù)據(jù)協(xié)議(CAN; BOSCH, 1991)。市場上有相應(yīng)的硬件設(shè)備。
在LBS中,為一般位置數(shù)據(jù)(地理位置:經(jīng)度、緯度、高度,或軌道位置)的傳輸定義了數(shù)據(jù)對(duì)象。這標(biāo)準(zhǔn)允許定義的額外的數(shù)據(jù)對(duì)象,例如多維的距離,方向和速度。沒有幾何實(shí)施參數(shù)的數(shù)據(jù)對(duì)象目前存在在LBS中。ISO 11783提供,在第7部分(信息實(shí)現(xiàn)應(yīng)用層),實(shí)施航行偏移的第一個(gè)定義?,F(xiàn)行標(biāo)準(zhǔn)沒有定義數(shù)據(jù)在哪里進(jìn)行處理。因此,關(guān)于BUS中哪個(gè)單元計(jì)算目標(biāo)點(diǎn)的數(shù)據(jù),哪個(gè)或那些單元測量數(shù)據(jù)不具體。
LBS提供所謂的LBS服務(wù)來執(zhí)行常見任務(wù)。LBS服務(wù)是為LBS的參與者頻繁地執(zhí)行復(fù)發(fā)的任務(wù)的功能單元。LBS用戶站就是這樣的一項(xiàng)服務(wù)。這是一個(gè)為用戶提供輸入和輸出BUS上節(jié)點(diǎn)(BUS參與者)處置的數(shù)據(jù)中央接口。另一項(xiàng)服務(wù)提供在移動(dòng)單位和固定的電腦,農(nóng)場的電腦之間的數(shù)據(jù)交換。一些服務(wù)在LBS中被定義但尚未有詳細(xì)的標(biāo)準(zhǔn),例如診服務(wù)斷或“Ortung und Navigation”(位置和導(dǎo)航),將在下面作為PNS被討論。在圖2中,一個(gè)典型的農(nóng)業(yè)網(wǎng)絡(luò)的簡化方案展示了一個(gè)拖拉機(jī)-噴霧器的組合。這個(gè)圖表包括物理BUS線路,即骨干網(wǎng)絡(luò)。在這個(gè)BUS上,參與單元如拖拉機(jī)的電子控制單元(ECUs)、霧化器被連接協(xié)作起來。另外,兩項(xiàng)LBS服務(wù)也被連接到BUS上。一項(xiàng)服務(wù)代表LBS用戶站。另外一項(xiàng)是位置和導(dǎo)航服務(wù),即位置數(shù)據(jù)的測量和處理系統(tǒng)。
2.4 分布式和中央數(shù)據(jù)處理的比較
一個(gè)分布式數(shù)據(jù)處理,農(nóng)業(yè)BUS,根據(jù)DIN 9684 或者ISO 11783, 定義了在測量系統(tǒng)和任何參賽者之間必要的數(shù)據(jù)交換;獨(dú)自地,任何一個(gè)ECU。每一個(gè)ECU怎樣得到計(jì)算機(jī)位置數(shù)據(jù)計(jì)算必要的幾何和運(yùn)動(dòng)參數(shù)的問題保持開放。每一個(gè)ECU知道從各自的結(jié)合點(diǎn)到目標(biāo)點(diǎn)的參數(shù),但它不知道從結(jié)合點(diǎn)到測量點(diǎn)的參數(shù)。這些參數(shù)必須由其他ECU提供。沒有標(biāo)準(zhǔn)定義相應(yīng)的數(shù)據(jù)對(duì)象或請(qǐng)求數(shù)據(jù)的程序。對(duì)于分布式數(shù)據(jù)處理,這些定義必須補(bǔ)充。
另外,對(duì)于中央數(shù)據(jù)處理,一定要知道測量點(diǎn)和目標(biāo)點(diǎn)之間所有的運(yùn)動(dòng)參數(shù)。此外,方法必需被定義以便使用中央服務(wù)計(jì)算目標(biāo)點(diǎn)的位置數(shù)據(jù)。一個(gè)位置和導(dǎo)航服務(wù)需要擴(kuò)展標(biāo)準(zhǔn),但以下的優(yōu)點(diǎn)在實(shí)際使用中是至關(guān)重要的。
● 為了確定目標(biāo)點(diǎn)的位置數(shù)據(jù),相應(yīng)的控制單元(ECU)只有一個(gè)對(duì)話伙伴網(wǎng)絡(luò)。它獨(dú)立工作于各自的網(wǎng)絡(luò)配置,僅僅發(fā)送自己的參數(shù)和只接受它特定位置數(shù)據(jù)。
● PNS從所有的ECU上接受參數(shù)。它知道所有一切幾何條件和車輛-工具組合的運(yùn)動(dòng)參數(shù)。因此,任何目標(biāo)點(diǎn)位置的確定是可能的。
● 這個(gè)標(biāo)準(zhǔn)的定義了計(jì)算程序和明確的提出了目標(biāo)點(diǎn)的位置數(shù)據(jù)。
● 計(jì)算位置數(shù)據(jù)的計(jì)算性能完全由PNS提供。沒有計(jì)算能力需要用于這個(gè)目的。
在前一節(jié)提到,提供位置和導(dǎo)航數(shù)據(jù)的服務(wù)已經(jīng)在LBS的計(jì)劃中。在下文中,將提到PNS的一個(gè)試?yán)鉀Q方案。
3.一項(xiàng)定位和導(dǎo)航服務(wù)的提議
此時(shí),應(yīng)當(dāng)指出,下面的PNS的介紹是一項(xiàng)建議。它提供了一個(gè)平臺(tái)進(jìn)行討論,這可能導(dǎo)致這個(gè)服務(wù)標(biāo)準(zhǔn)化。
3.1 PNS的主要特征
PNS的特征首先依賴于它的使用目的。從前面所講的,很明顯的是,測量的位置數(shù)據(jù)在一個(gè)地點(diǎn),用在不同的地點(diǎn)。為了提供需要的數(shù)據(jù)來指導(dǎo)車輛,控制工具的位置和協(xié)助任何一種精耕農(nóng)業(yè),下面的條件必須滿足:
PNS提供有關(guān)測量點(diǎn)的數(shù)據(jù)。
PNS提供有關(guān)參考點(diǎn)的數(shù)據(jù)。
PNS提供有關(guān)目標(biāo)點(diǎn)的數(shù)據(jù)。
這項(xiàng)服務(wù)的特點(diǎn)如下:
1.數(shù)據(jù)的請(qǐng)求和傳播的方式已經(jīng)標(biāo)準(zhǔn)化,數(shù)據(jù)被LBS (DIN 9684)定義和將被ISO 11783標(biāo)準(zhǔn)化。因此,它將不會(huì)在此討論。在下面,LBS將作為一種標(biāo)準(zhǔn)化的農(nóng)業(yè)BUS系統(tǒng)被使用。
2.數(shù)據(jù)的容量、準(zhǔn)確性、頻率和范圍是由數(shù)據(jù)的目的決定的。
3.滿足這些要求的硬件和軟件不應(yīng)被規(guī)范,應(yīng)該取決于生產(chǎn)廠家。
3.2關(guān)于位置數(shù)據(jù)測量和計(jì)算方法標(biāo)準(zhǔn)的影響
各種測量系統(tǒng)和PNS中用于決定位置數(shù)據(jù)的方法不再標(biāo)準(zhǔn)的范圍之內(nèi)?;谛l(wèi)星,機(jī)器視覺、慣性導(dǎo)航、地磁或這些情況的組合可能被應(yīng)用。作為一種結(jié)果,生產(chǎn)企業(yè)可以決定如何產(chǎn)生位置數(shù)據(jù),只要他滿足了規(guī)定的要求和準(zhǔn)確性。
3.3 PNS在農(nóng)業(yè)BUS系統(tǒng)中的整合
在LBS中整合定位和導(dǎo)航服務(wù)存在一些好處,因?yàn)樵S多特性已經(jīng)被定義。LBS已經(jīng)包括在PNS的選項(xiàng)作為試驗(yàn)的標(biāo)準(zhǔn)。它允許實(shí)現(xiàn)服務(wù)作為一個(gè)獨(dú)立的物理單位或者為另外一個(gè)物理單位的邏輯單位。BUS接口和BUS協(xié)議的物理性能(DIN 9684, part 2)已經(jīng)被標(biāo)準(zhǔn)定義。為LBS中服務(wù)的集成,系統(tǒng)的功能的定義是果斷的(DIN 9684,part3)。他們在LBS中定義節(jié)點(diǎn)的性能。第三部分也給了LBS服務(wù)一般的定義。
一項(xiàng)LBS服務(wù)形成與LBS參與者點(diǎn)對(duì)點(diǎn)的連接。LBS參與者使用服務(wù)時(shí)不會(huì)被其它使用者影響,一個(gè)LBS參與者也不能影響其他參與者對(duì)服務(wù)的使用。所有進(jìn)一步PNS的定義還不規(guī)范。
3.4 PNS操作的一般模式
PNS設(shè)計(jì)應(yīng)用以下的基本假設(shè):
1.每一個(gè)ECU的只知道它自己的參數(shù),包括參考點(diǎn)、目標(biāo)點(diǎn)、結(jié)合點(diǎn)位置、車輛類型或軸距的坐標(biāo)和數(shù)量。
2.只有ECU根據(jù)工作條件可以定義必要的時(shí)間間隔,準(zhǔn)確度和位置數(shù)據(jù)的分辨。
3.每一個(gè)ECU的可以選擇不同的任意時(shí)刻的位置數(shù)據(jù)。
4.參數(shù)和計(jì)算和提供的位置數(shù)據(jù)的方法將會(huì)在田野機(jī)械開始運(yùn)作過程之前被定義。
5.PNS提供了一些程序?yàn)閷?shí)施標(biāo)準(zhǔn)和車輛類型計(jì)算位置數(shù)據(jù)。
6.位置數(shù)據(jù)自動(dòng)(周期性)地或根據(jù)需求被提供。
為了滿足這些要求,服務(wù)窗口提供適當(dāng)?shù)墓ぞ?,同時(shí) ECUs 決定如何使用及使用哪個(gè)工具。這意味這它們定義一個(gè)或者多個(gè)任務(wù)。這樣一項(xiàng)任務(wù)基本上代表了一個(gè)命令表,包括激活具體工具使用的命令。這些任務(wù)被送到PNS,隨后PNS執(zhí)行這些任務(wù)。一個(gè)ECU的不同的任務(wù)相互獨(dú)立的被執(zhí)行。
圖3闡明了PNS與一個(gè)ECU之間的數(shù)據(jù)傳遞。同時(shí),也顯示了PNS的主要部分。PNS的這些工具包括位置測量系統(tǒng)和測量點(diǎn)的數(shù)據(jù),以及一系列處理這些數(shù)據(jù)的程序方法。程序如下:
1. 計(jì)算位置數(shù)據(jù)(位置程序);
2. 計(jì)算位置數(shù)據(jù)值的平均值,最大值、最小值和積分的方法(算術(shù)程序);
3. 輸入和輸出數(shù)據(jù)(傳輸程序);
4. 傳遞數(shù)據(jù)到ECU(傳遞程序);
5. 控制數(shù)據(jù)處理(數(shù)據(jù)控制程序);
為了這些方法的執(zhí)行,ECU必須定義相應(yīng)的參數(shù)。它同時(shí)也定義位置數(shù)據(jù)的數(shù)據(jù)對(duì)象。
PNS的主要工具是一項(xiàng)執(zhí)行ECU定義的任務(wù)的程序系統(tǒng)。簡而言之,程序系統(tǒng)解釋任務(wù)指令,調(diào)動(dòng)相應(yīng)的方法,計(jì)算要求的位置以及把數(shù)據(jù)送到ECU(電子控制單元)。
為了一項(xiàng)任務(wù)的定義,ECU生成一個(gè)任務(wù)庫。一個(gè)務(wù)庫主要是一系列調(diào)動(dòng)PNS的程序法或者調(diào)動(dòng)內(nèi)嵌的任務(wù)庫的指令。各種參數(shù)被定義并且放置在參數(shù)庫里。為了存儲(chǔ)被計(jì)算的位置數(shù)據(jù),ECU必需定義數(shù)據(jù)庫。數(shù)據(jù)庫必需在激發(fā)相應(yīng)任務(wù)程序之前通過BUS從ECU傳送到達(dá)PNS。
3.5 PNS預(yù)定義的程序
PNS預(yù)定義的程序是一些處理位置數(shù)據(jù)或者控制數(shù)據(jù)處理的程序。不同的程序執(zhí)行不同的功能。不同的程序被一些獨(dú)特的標(biāo)識(shí)符區(qū)別。這些程序被稱為“內(nèi)部任務(wù)”(任務(wù)庫)。他將會(huì)成為標(biāo)準(zhǔn)的一部分用來定義標(biāo)識(shí)符,功能規(guī)格和調(diào)用程序規(guī)格。
3.5.1 位置程序
位置程序(計(jì)算位置數(shù)據(jù)的程序)是計(jì)算目標(biāo)點(diǎn)位置數(shù)據(jù)的數(shù)據(jù)。這些方法計(jì)算從最初的位置(輸入位置數(shù)據(jù)、資料的參考點(diǎn)的數(shù)據(jù)或以前計(jì)算的數(shù)據(jù))到一種新的點(diǎn)的位置(輸出的位置數(shù)據(jù)、數(shù)據(jù)的目標(biāo)點(diǎn)或作為中間結(jié)果)。位置程序能夠滿足不同結(jié)構(gòu)位置的計(jì)算(考慮一、二或三維模型,嚴(yán)格耦合點(diǎn),幾個(gè)基本類型車輛的不嚴(yán)格耦合點(diǎn),工具和車輛-工具的結(jié)合)。這些程序從有關(guān)ECU執(zhí)行定義的參數(shù)庫得到他們的實(shí)際參數(shù)(目標(biāo)點(diǎn)的坐標(biāo),車輛的長度、寬度、高度、類型或軸距)這是確定的有關(guān)實(shí)施ECU的。
圖4顯示了使用一個(gè)位置程序的一段任務(wù)庫。PNS的程序系統(tǒng)執(zhí)行這個(gè)程序庫。在任務(wù)庫的某一點(diǎn)上,它發(fā)現(xiàn)調(diào)用位置程序的指令。這個(gè)調(diào)用指令包括特定程序的標(biāo)識(shí)符和有關(guān)參數(shù)庫的引用。這時(shí),程序系統(tǒng)擁有由以上的操作產(chǎn)生的實(shí)際位置數(shù)據(jù)?,F(xiàn)在它使用這些實(shí)際數(shù)據(jù)作為輸入數(shù)據(jù),和引用參數(shù)庫用于位置程序。然后,它執(zhí)行特定的程序。該程序使用指定的參數(shù)計(jì)算輸出的位置數(shù)據(jù)。然后,它返回到程序系統(tǒng)。位置程序的輸出數(shù)據(jù)成為新的實(shí)際位置數(shù)據(jù)。程序系統(tǒng)繼續(xù)執(zhí)行下面的指令。
3.5.2 算術(shù)程序
算術(shù)方法被用來計(jì)算位置數(shù)據(jù)的平均值,最大值、最小值或者積分值。一個(gè)算術(shù)程序從程序系統(tǒng)的實(shí)際位置數(shù)據(jù)或從特定數(shù)據(jù)庫得到位置輸入數(shù)據(jù)。它使用在調(diào)用指令里決定的參數(shù)庫中的參數(shù)計(jì)算輸出位置數(shù)據(jù)。然后,計(jì)算結(jié)果數(shù)據(jù)被存儲(chǔ)在一個(gè)被定義的數(shù)據(jù)庫里。
圖5展示了一個(gè)算術(shù)程序使用的例子。在任務(wù)庫的某一點(diǎn)上,它發(fā)現(xiàn)調(diào)用算術(shù)程序的指令。這個(gè)調(diào)用包括具體程序的標(biāo)識(shí)符,一個(gè)有關(guān)參數(shù)庫的引用,一個(gè)目的數(shù)據(jù)庫的引用和源數(shù)據(jù)庫選擇性的引用。這個(gè)程序系統(tǒng)采用實(shí)際數(shù)據(jù)和參考數(shù)據(jù)用于程序計(jì)算。根據(jù)調(diào)用規(guī)格,算術(shù)程序從程序系統(tǒng)(沒有定義的數(shù)據(jù)庫參考)或一種數(shù)據(jù)資源(數(shù)據(jù)資源I)得到輸入數(shù)據(jù)。它計(jì)算被要求的值并把計(jì)算結(jié)果存儲(chǔ)在一個(gè)數(shù)據(jù)庫里(數(shù)據(jù)庫II)。計(jì)算參數(shù)是從定義的參數(shù)庫中得到的。程序發(fā)揮到程序系統(tǒng)并繼續(xù)執(zhí)行。實(shí)際的位置數(shù)據(jù)沒有被改變。
3.5.3 傳輸程序
PNS定義了三種類型的傳輸程序。輸入程序是用來裝載作為實(shí)際位置數(shù)據(jù)的確定的數(shù)據(jù)庫位置數(shù)據(jù)到PNS的程序系統(tǒng)。輸出程序存儲(chǔ)實(shí)際位置數(shù)據(jù)到一個(gè)在調(diào)用指令里預(yù)先定義了的數(shù)據(jù)庫。輸入/輸出程序被用來從一個(gè)源數(shù)據(jù)庫到目的數(shù)據(jù)庫之間傳輸數(shù)據(jù)。
圖6顯示了一個(gè)使用輸入和輸出程序的例子。輸入程序的調(diào)用指令包括具體程序的標(biāo)識(shí)符和源數(shù)據(jù)庫的引用。在執(zhí)行輸入程序之前,程序系統(tǒng)為程序提供源數(shù)據(jù)庫的引用。然后,程序執(zhí)行和得到位置數(shù)據(jù),并將它作為實(shí)際位置數(shù)據(jù)返回給程序系統(tǒng)。以前的實(shí)際位置數(shù)據(jù)被損壞。系統(tǒng)繼續(xù)進(jìn)行。對(duì)于輸出程序的使用,實(shí)際位置數(shù)據(jù)與目的位置數(shù)據(jù)庫提供參考。輸出程序?qū)?shí)際數(shù)據(jù)放到目的數(shù)據(jù)庫并返回到程序系統(tǒng)。實(shí)際位置數(shù)據(jù)仍然有效。
3.5.4 傳遞程序
傳遞程序發(fā)送具體的位置數(shù)據(jù)到ECU。源數(shù)據(jù)在調(diào)用指令(或一個(gè)數(shù)據(jù)庫或程序系統(tǒng)的實(shí)際數(shù)據(jù))里被定義。當(dāng)執(zhí)行一個(gè)傳遞程序時(shí),它得到具體的位置數(shù)據(jù)并傳送到ECU。
3.5.5 數(shù)據(jù)控制程序
數(shù)據(jù)控制程序控制一個(gè)任務(wù)庫的執(zhí)行。程序流程是控制時(shí)間或距離。PNS的程序系統(tǒng)調(diào)查任務(wù)庫。假如確定的時(shí)間間隔已過期或已超出距離限制,程序?qū)?zhí)行下列指令。否則,程序系統(tǒng)跳到數(shù)據(jù)庫的結(jié)尾。
Computers and Electronics in Agriculture 25 (2000) 87106 Providing measured position data for agricultural machinery Hermann Speckmann Federal Agricultural Research Centre Braunschweig (FAL), Institute for Biosystems Engineering, Bundesallee 50, D-38116 Braunschweig, Germany Abstract Agricultural machinery and vehicles require position data for guidance and to control implements for optimal working positions. Position data are also needed for such applica- tions as precision farming. The necessary accuracy, resolution and frequency of position data vary according to the specific application. Only one system, installed at a central vehicle (e.g. the tractor), should provide position data for each task. The basic concept for the proposed central system is that position data are calculated in accordance with the application and transferred directly to the point at which they will be used. The paper describes the fundamentals of measurement and calculation of position data, and gives a short introduc- tion to the existing agricultural networks to transfer these data. It concentrates on a proposal for a network service to provide and transfer position data. The solution discussed is based on the agricultural BUS (DIN 9684, ISO 11783). 2000 Elsevier Science B.V. All rights reserved. Keywords: Local area network; Controller area network; Agricultural BUS system; LBS; Calculation of position; Calculation of direction; LBS service :locate:compag 1. Introduction The purpose of position guidance is to bring the means of production to the plants, which grow at a fixed location on the field. The plants, or rather their location on the field surface, are the reference for guidance. Position data are needed to guide agricultural vehicles, to control implements and to support precision farming. Accuracy, resolution and frequency depend on their application. E-mail address: hermann.speckmannfal.de (H. Speckmann) 0168-1699:00:$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S0168-1699(99)00057-5 H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 8710688 It must be emphasized that this paper does not address the problem of suitable sensors to generate the data. Rather, the problem studied here is that a position signal is generated with reference to a certain location on the mobile unit, but this position is not identical with the location where the position data are needed. Moreover, position information may be needed for several purposes at the same time, and the configuration of the vehicleimplement combination may change frequently. As mentioned by Freyberger and Jahns (1999), Wilson (1999), the measuring system can either be an absolute position system, such as the satellite system described by Bell (1999), or a relative system, such as the machine vision systems described by Debain et al. (1999), Hague et al. (1999). It may also include auxiliary sensors. Sensor systems measure position only in reference to a specific location, such as the mounting point of the camera or the foot of the aerial. In the following presentation, this location is called the measuring point. For various reasons, the location of this measuring point is predetermined, meaning the satellite antenna will be mounted as high as possible on the roof of the tractor cab to minimize shading. A camera will be mounted where optimal view is guaranteed. Movement caused by rough or sloping field surfaces may cause the measured position and the position on the field surface to differ widely. For example, for a vehicle with a satellite antenna mounted on top of the cab, at about 3.5 m, driving on a sloping surface of 10, the difference in direction of the inclination will be about 60 cm. Fig. 1 illustrates this scenario for one dimension. In this example, it may be appropriate to calculate the position of a reference point. Bell (1999) proposes the middle rear axes of the Fig. 1. Difference in position for two locations due to sloping terrain. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87106 89 tractor as a reference point. A point in the field surface, for example, vertical under the middle of the rear axis seems more appropriate for some applications. For certain applications, such as the control of implements, the position of a certain point of the implement may be of final importance. This point will be called the target point. In cases where position data are needed for different purposes, it is not very efficient to measure the position for each purpose separately with an independent measuring system. Multiple hardware can be avoided when the position is measured only once, and the positions of the other points on the vehicle or implements are calculated. This is possible if position and attitude are measured, and the spatial vector between the measuring point and the point to be calculated is known. If both points are rigidly coupled, meaning that both points are on the tractor, the vector between these points is constant, and a simple matrix calculation yields the result. If these points are not rigidly coupled, meaning, for example, that one point is on the tractor and the other is on an attached implement, the vector is variable. Additional measurements become necessary to establish the vector between these two points or other principles to calculate the position of the target point must be applied. 2. Data processing and data transfer Position data of any point on the vehicle or implement can be calculated from the position and attitude measured at a measuring point. This calculation can be made by the measuring system (central data processing) or by each system requesting target position data (distributed data processing). 2.1. Distributed data processing The measuring system serves only as an intelligent sensor in the case of distributed data. It measures position and attitude on request, and provides these data without any processing. Characteristics such as frequency and accuracy are determined by the requesting unit. This unit performs all processing to calculate the position. The unit must know the position of the measuring point and all relevant parameters to do this. The advantage of this procedure is that the measuring device can be relatively simple. On the other hand, each requesting unit needs the full capacity to perform this calculation. 2.2. Central data processing The measuring unit is extended by components to calculate the position of target points for any user. This measuring and processing system forms one unit of a so-called position and navigation service (PNS), which provides final position data of any target point. In this case, only one measuring and processing system is necessary even when position data are requested by more than one user. To do so, only the PNS must know all of the relevant parameters for the calculation. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 8710690 2.3. Data transfer A data transfer is necessary no matter where the data are processed. For such a data transfer, a standardized network is appropriate. For agricultural purposes, a BUS for data transfer between mobile units and stationary farm computers exists. The agricultural BUS system (LBS) has been standardized to exchange information between the electronic units (LBS participants or BUS nodes) in a network. The standard defines the physical layer of the network, network protocol, system management, data objects and central services for common tasks (Speckmann and Jahns, 1999). The LBS has been standardized as DIN 9684 (DIN, 19891998). Currently, efforts are being made to establish an international standard (Nienhaus, 1993), ISO 11783, for such purposes. Like LBS, ISO 11783 will also define an agri- cultural BUS as an open system to exchange data on agricultural machinery, particularly on tractorimplement combinations and from the mobile units to the stationary farm computer. The standards are based on the controller area network data protocol (CAN; BOSCH, 1991). Corresponding hardware is on the market. In the LBS, data objects are defined for the transmission of general position data (geographical positions: longitude, latitude, altitude, or position in a tramline). The standard allows definition of additional data objects such as multidimensional distances, directions and speeds. No data objects exist presently in the LBS for geometric implement parameters. ISO 11783 provides, in Part 7 (Implement Mes- sages Application Layer), the first definitions of implement navigational offsets. Current standards do not define where which data are processed. Therefore, it is immaterial on which unit the BUS calculates the data for the target point, and which unit or units measure the data. The LBS provides so-called LBS services to execute common tasks. LBS services are functional units, which perform frequently recurring tasks for LBS participants. Such a service is the LBS user station. This is a central interface to the user (operator) for input and output of data which is at the disposal of any node (LBS participant) on the BUS. Another service provides the data exchange between the mobile unit and the stationary computer, the farm computer. Some more services are named in the LBS but not yet stan- dardized in detail, such as for diagnosis services or the service Ortung und Navigation (position and navigation), which will be discussed in the following as PNS. In Fig. 2, an exemplary simplified scheme of an agricultural network is shown for a tractorsprayer combination. This scheme includes the physical BUS line, which is the backbone of the network. At this BUS, participants such as electronic control units (ECUs) of the tractor and sprayer are coupled. Additionally, two LBS services are connected on the BUS. One of these services represents the LBS user station. The other is the LBS service position and navigation, with the measuring and processing system for position data. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87106 91 Fig. 2. Scheme of an agricultural network in a tractorsprayer combination. 2.4. Comparison of distributed and central data processing For a distributed data processing, the agricultural BUS, according to DIN 9684 or ISO 11783, defines the necessary data exchange between the measuring system and any participant; respectively, any ECU. The question how each ECU gets geometric and kinematic parameters that are necessary to compute position data remains open. Each ECU knows its own parameter from its coupling point to the target point, but it does not know the parameter from the coupling point to the measuring point. These parameters must be provided from other ECUs. None of the standards define corresponding data objects or procedures requesting the data. For distributed data processing, these definitions have to be supplemented. Also, for central data processing, all kinematic parameters between the measur- ing point and the target point must be known. In addition, methods are to be defined for the use of the central service with regard to the calculation of position data of target points. A position and navigation service requires an extension of the standards, but the following advantages in practical use are essential: To determine the position data of a target point, the corresponding ECU has only one dialogue partner in the network. It works independently from the respective network configuration, delivers only its own parameters and receives only its specific position data. The PNS receives parameters from all ECUs. It knows all geometric conditions and kinematic parameters of the vehicleimplement combination. Thereby, an unambiguous determination of the position of any target point is possible. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 8710692 The standard defines the procedures to calculate and present the position data of a target point unambiguously. The computing performance to calculate the position data is provided solely by the PNS. No computing capacity is needed for this purpose from the ECUs. As mentioned in the previous section, a service to provide position and naviga- tion data is already planned in the LBS. In the following, a sample solution of a PNS is presented. 3. Proposal for a positioning and navigation service At this time, it should be mentioned that the following description of a PNS is a proposal. It provides a platform for discussion, which may lead to the standard- ization of such a service. 3.1. Main features of a PNS The features of a PNS depend, first of all, on the purpose for which it will be used. From the foregoing, it is clear that position data are measured at one location and used at different locations. The following requirements must be fulfilled to provide the data needed to guide a vehicle, to control positions of implements and to assist any kind of precision farming: The PNS provides data related to the measurement point(s). The PNS provides data related to the reference point(s). The PNS provides data related to the target point(s). The characteristics of such a service are as follows: 1. The way the data are requested and transmitted is already standardized and defined by the LBS (DIN 9684) and will be standardized by ISO 11783. Therefore, it will not be discussed here. In the following, LBS will be used as a standardized agricultural BUS system. 2. The volume, accuracy, frequency and range of the data are determined by the purpose of the data. 3. The hardware and software to fulfil these demands should not be standardized, but be determined by the manufacturers. 3.2. Influence of the standard on measuring and calculation methods for position data The kinds of measuring systems and methods used to determine position data by the PNS is not in the scope of the standard. Systems based on satellites, machine vision, inertial navigation, geomagnetics or a combination of these may be applied. As a consequence, the manufacturer may determine how to generate the position data as long as he meets the stated requirements and accuracy. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87106 93 3.3. Integration of the PNS into an agricultural BUS system There are some benefits of integrating the positioning and navigation service into the LBS, because many characteristics are already defined. The LBS already includes the option of a PNS as part of the standard. It allows the realization of a service either as an independent physical unit or as a logical unit inside of another physical unit. The physical properties of the BUS interface and the BUS protocol (DIN 9684, part 2) are defined by the standard. For integration of the service into the LBS, the definitions of the system functions are decisive (DIN 9684, part 3). They define the performance of the nodes at the LBS. Part 3 also gives the general definitions of LBS services. An LBS service forms a point-to-point link with LBS participants. The use of a service by an LBS participant can neither be influenced by other users, nor can an LBS participant influence links between the service and other participants. All further definitions of the PNS are not yet standardized. 3.4. General mode of operation of the PNS For the design of the PNS, the following basic assumptions apply: 1. Each ECU knows only its parameters, meaning coordinates and numbers of reference points, target points, positions of couplings, vehicle types or wheelbases. 2. Only the ECU can define necessary time intervals, accuracy and resolution for position data, depending on the working conditions. 3. Each ECU can get different position data at arbitrary times. 4. Parameters and the way of calculating and providing position data will be defined before the working processes of the field machinery are started. 5. The PNS provides a library of procedures to calculate position data for standard implement and vehicle types. 6. Position data are provided automatically (cyclically) or on demand. To meet these requirements, the service provides the tools, and the ECUs determine how and which tools are used. This means they define one or several task(s). Such a task basically represents a list that includes commands to activate the specific tools. These tasks are sent to the PNS, which subsequently performs these tasks. Different tasks of one ECU are executed independently of each other. Fig. 3 illustrates the data transfer between the PNS and one ECU. It also shows the main parts of the PNS. The tools of the PNS include the system for measuring the position and attitude data of the measuring point, and a library of methods to process these data. Methods exist: to calculate position data (position methods); to calculate mean, maximum, minimum and integral values of position data (arithmetic methods); to export and import data (transport methods); to send data to the ECU (transmission methods); and to control the data processing (data control methods). H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 8710694 For some of these methods, the ECU has to define corresponding parameters. It also defines data objects for position data. The central tool of the PNS is the program system to execute the tasks defined by the ECU. Simplified, the program system interprets the instructions of the task, calls the corresponding methods, calculates the demanded position and sends the data to the ECU. For the definition of a task, the ECU generates a task resource. A task resource is mainly a list of instructions to call methods of the PNS or to call nested task resources. Parameters are defined by the ECU and placed in parameter resources. To store calculated position data, the ECU has to define data resources. The resources have to be transmitted from the ECU via the BUS to the PNS before activating corresponding tasks. Fig. 3. Strcture of a PNS and its data exchange with one ECU. H. Speckmann : Computers and Electronics in Agriculture 25 (2000) 87106 95 Fig. 4. Example of the use of a position method in the course of a task resource. 3.5. Predefined methods of the PNS Predefined methods of the PNS are procedures to process position data or to control this data processing. Methods exist to perform different functions. The different methods are distinguished by a unique designator. They are called within tasks (task resources). It will be a part of the standard to define the designators, function specifications and calling specifications of the methods. 3.5.1. Position methods Position methods (methods to calculate position data) are the basis for calculat- ing position data of target points. These methods calculate from an initial position (input position data, data of a reference point or previously computed data) the position of a new point (output position data, data of a target point or as an interim result). Position methods exist for different configurations (one-, two- or three-dimensional model considerations, rigidly coupled points, non-rigidly coupled points for several basic types of vehicles, implements and vehicleimplement combinations). These methods get their actual parameters (coordinates of the target point, vehicle length, width, height, type or wheelbases) from parameter resources which are defined by the concerned implement ECU. Fig. 4 shows a section of a task resource using a position method. The program system of the PNS executes this task resource. At a certain part of the task resource, it finds a calling instruction for a position method. This calling instruction includes the designator of the specific method and a reference to a relevant parameter resource. At this moment, the program system owns actual position data, which result from previous operations. Now it uses these actual data as input data, and the parameter resource reference for the position method. Then, it executes the specified method. This method calculat