張季琴,劉 剛,胡 號(hào),黃家運(yùn)
排肥單體獨(dú)立控制的雙變量施肥控制系統(tǒng)研制
張季琴1,2,劉 剛1,3※,胡 號(hào)1,3,黃家運(yùn)1,3
(1. 中國(guó)農(nóng)業(yè)大學(xué)現(xiàn)代精細(xì)農(nóng)業(yè)系統(tǒng)集成研究教育部重點(diǎn)實(shí)驗(yàn)室,北京 100083;2. 寧夏大學(xué)機(jī)械工程學(xué)院,銀川 750021;3. 中國(guó)農(nóng)業(yè)大學(xué)農(nóng)業(yè)農(nóng)村部農(nóng)業(yè)信息獲取技術(shù)重點(diǎn)實(shí)驗(yàn)室,北京 100083)
針對(duì)當(dāng)前變量施肥機(jī)無(wú)法根據(jù)實(shí)際田塊尺寸調(diào)整作業(yè)行數(shù),進(jìn)而調(diào)節(jié)作業(yè)幅寬的問(wèn)題,該研究通過(guò)改造玉米播種施肥機(jī)的排肥驅(qū)動(dòng)方式,設(shè)計(jì)了一種排肥單體獨(dú)立控制的雙變量施肥控制系統(tǒng)。首先通過(guò)二次多項(xiàng)式擬合方法,構(gòu)建了排肥單體的雙變量控制模型;然后對(duì)排肥單體的定位方法進(jìn)行了分析,提出排肥單體獨(dú)立控制系統(tǒng);最后對(duì)各行排肥量一致性、不同車速下的排肥量控制準(zhǔn)確性以及各行獨(dú)立控制性能進(jìn)行試驗(yàn)研究。結(jié)果表明,在排肥軸轉(zhuǎn)速為10~60 r/min的區(qū)間內(nèi),各行平均排肥量一致性變異系數(shù)為3.35%;在目標(biāo)排肥量為350 kg/hm2,作業(yè)車速為7 km/h的條件下,排肥量控制精度達(dá)到97.6%;對(duì)于凸、凹和S形3種不同形狀的施肥邊界,各行排肥滯后距離相對(duì)于作業(yè)幅寬的變化率均小于15%。系統(tǒng)具有較高的控制準(zhǔn)確性和穩(wěn)定性,能夠適應(yīng)復(fù)雜施肥邊界,可為玉米基肥變量施用裝備的創(chuàng)新性研發(fā)提供技術(shù)參考。
農(nóng)業(yè)機(jī)械;玉米;基肥;雙變量;排肥單體;獨(dú)立控制
變量施肥技術(shù)能夠根據(jù)土壤養(yǎng)分或作物長(zhǎng)勢(shì)進(jìn)行按需施肥,在降低肥料用量的同時(shí),能夠提高肥料利用率,提高產(chǎn)量,減少溫室氣體排放和對(duì)環(huán)境的污染[1-4]?,F(xiàn)有變量施肥機(jī)的排肥方式主要包括離心式、轉(zhuǎn)盤式、螺旋式和外槽輪式等[5-7]。其中,基于外槽輪的變量施肥機(jī),通過(guò)改變排肥軸轉(zhuǎn)速來(lái)實(shí)現(xiàn)施肥量調(diào)節(jié)[8-10],普遍存在施肥量調(diào)節(jié)范圍小,低速排肥時(shí)脈動(dòng)顯著,排肥均勻性差等缺點(diǎn)[11]。
為了克服單一變量控制的缺點(diǎn),提高變量施肥作業(yè)精度和穩(wěn)定性,近年來(lái),國(guó)內(nèi)外學(xué)者在雙變量施肥機(jī)的整機(jī)結(jié)構(gòu)設(shè)計(jì)、控制系統(tǒng)集成等方面做了大量研究,并取得一定成果。劉成良等[12]研發(fā)了一種排肥軸轉(zhuǎn)速、排肥口開(kāi)度雙調(diào)節(jié)的變量施肥機(jī)。吳金林[13]設(shè)計(jì)了一種液壓驅(qū)動(dòng)的雙變量排肥裝置,通過(guò)在排肥主軸兩側(cè)安裝主軸馬達(dá)和開(kāi)口馬達(dá),帶動(dòng)主軸上所有外槽輪轉(zhuǎn)動(dòng)和左右移動(dòng),實(shí)現(xiàn)雙變量調(diào)節(jié)。Su等[14-15]將手動(dòng)調(diào)節(jié)開(kāi)度的庫(kù)恩氣吸式點(diǎn)播機(jī)改造為有效工作長(zhǎng)度可通過(guò)伺服電機(jī)自動(dòng)調(diào)整的變量施肥機(jī),經(jīng)試驗(yàn)驗(yàn)證,在5個(gè)不同開(kāi)度下,7個(gè)排肥器各行平均排肥量一致性變異系數(shù)為8.4%。戚武振等[16-17]設(shè)計(jì)了一種絲杠排肥軸連接機(jī)構(gòu),以步進(jìn)電機(jī)為動(dòng)力,帶動(dòng)排肥軸做軸向移動(dòng)實(shí)現(xiàn)所有排肥器開(kāi)度的自動(dòng)調(diào)節(jié)。Alameen等[18]搭建了一個(gè)可以通過(guò)氣缸調(diào)節(jié)所有排肥器開(kāi)度的雙變量施肥試驗(yàn)臺(tái),室內(nèi)試驗(yàn)結(jié)果表明,該試驗(yàn)臺(tái)具有較好的準(zhǔn)確性、穩(wěn)定性和調(diào)節(jié)快速性。施印炎等[19-20]設(shè)計(jì)了一種基于光譜探測(cè)的小麥精準(zhǔn)追肥機(jī),該機(jī)采用軸分段式執(zhí)行機(jī)構(gòu),8個(gè)排肥器分2組,每組4個(gè)排肥器通過(guò)一個(gè)直流電機(jī)控制轉(zhuǎn)速,一個(gè)步進(jìn)電機(jī)控制開(kāi)度,作業(yè)時(shí),根據(jù)光譜傳感器獲取小麥冠層歸一化植被指數(shù),生成目標(biāo)追肥量,通過(guò)對(duì)兩組排肥器的開(kāi)度、轉(zhuǎn)速的實(shí)時(shí)調(diào)整,實(shí)現(xiàn)追肥量的精確控制,田間試驗(yàn)控制精度達(dá)到90%以上[21-22]。
綜上可知,現(xiàn)有雙變量施肥機(jī)一般通過(guò)一個(gè)驅(qū)動(dòng)軸驅(qū)動(dòng)多個(gè)排肥器同時(shí)作業(yè),無(wú)法根據(jù)實(shí)際需要調(diào)整作業(yè)行數(shù),最小作業(yè)寬度為機(jī)具幅寬。但田間作業(yè)區(qū)域大多形狀不規(guī)則,且田塊寬度一般不是作業(yè)幅寬的整數(shù)倍,在田塊邊緣易發(fā)生作業(yè)區(qū)域的重疊或造成壟溝邊界的肥料浪費(fèi)[23],無(wú)法進(jìn)行跨處方圖柵格作業(yè)。因此,本文擬改造現(xiàn)有玉米播種施肥機(jī)的排肥驅(qū)動(dòng)方式,設(shè)計(jì)一種排肥單體獨(dú)立控制的雙變量施肥控制系統(tǒng),以實(shí)現(xiàn)各行獨(dú)立作業(yè),作業(yè)幅寬可調(diào),提高變量施肥機(jī)對(duì)田間復(fù)雜環(huán)境的適應(yīng)能力。
雙變量施肥機(jī)實(shí)物如圖1所示,整機(jī)主要由RTK- GNSS(Real Time Kinematic-Global Navigation Satellite System)定位系統(tǒng)、排肥單體獨(dú)立控制的雙變量施肥控制系統(tǒng)、施肥執(zhí)行裝置等組成。RTK-GNSS定位系統(tǒng)主要包括天線和接收機(jī);控制系統(tǒng)包括車載終端、下位機(jī)控制器、伺服電機(jī)、減速器、電子推桿、電子位移傳感器等;施肥執(zhí)行裝置主要包括肥箱、螺旋外槽輪排肥器、開(kāi)度調(diào)節(jié)擋板、排肥管、開(kāi)溝器、地輪等。該機(jī)與拖拉機(jī)采用三點(diǎn)懸掛方式連接,設(shè)有2個(gè)肥箱,每個(gè)肥箱配2個(gè)排肥器,每個(gè)排肥器為一個(gè)獨(dú)立的控制單元,可實(shí)現(xiàn)排肥口開(kāi)度、排肥軸轉(zhuǎn)速的獨(dú)立控制。最大作業(yè)行數(shù)為4行,作業(yè)幅寬為0.6~2.4 m,可根據(jù)實(shí)際作業(yè)需求調(diào)整,主要技術(shù)參數(shù)如表1所示。
作業(yè)時(shí),首先根據(jù)GNSS系統(tǒng)采集的坐標(biāo)位置信息,計(jì)算獲得單體排肥器的位置,查詢處方圖,得到各排肥單體的目標(biāo)施肥量,再根據(jù)控制模型計(jì)算得到排肥器轉(zhuǎn)速、開(kāi)度控制信息,最后發(fā)送控制指令到下位機(jī)執(zhí)行裝置,實(shí)現(xiàn)變量施肥作業(yè)。該系統(tǒng)采用CAN(Controller Area Network)通信方式、各排肥器獨(dú)立控制??刂葡到y(tǒng)原理如圖2所示,RTK-GNSS接收機(jī)獲取整機(jī)當(dāng)前位置經(jīng)緯度信息、車速信息以及航向角信息,并通過(guò)RS232串口發(fā)送給車載計(jì)算機(jī);車載計(jì)算機(jī)根據(jù)當(dāng)前位置信息以及RTK-GNSS天線的安裝位置等信息,計(jì)算每個(gè)排肥單體的位置坐標(biāo),通過(guò)查詢處方圖,得到每個(gè)排肥器的目標(biāo)施肥量信息,結(jié)合作業(yè)車速,形成單體排肥器的開(kāi)度、轉(zhuǎn)速控制決策,最后將控制指令發(fā)送給并聯(lián)在CAN通信網(wǎng)絡(luò)上的各排肥單體控制器,控制器通過(guò)對(duì)伺服電機(jī)和電子推桿的控制,實(shí)現(xiàn)對(duì)排肥器轉(zhuǎn)速、開(kāi)度的控制,最終實(shí)現(xiàn)精準(zhǔn)施肥作業(yè)。
該排肥單體獨(dú)立控制的雙變量施肥機(jī)以單個(gè)排肥器為獨(dú)立控制單元,通過(guò)雙變量調(diào)節(jié)裝置,實(shí)現(xiàn)排肥軸轉(zhuǎn)速、排肥口開(kāi)度的調(diào)節(jié)[24]。車載計(jì)算機(jī)通過(guò)CAN總線控制多個(gè)排肥器。各排肥單體的工作原理相同,因此,以一個(gè)排肥單體為例,對(duì)其施肥量的控制模型及田間精準(zhǔn)定位方法進(jìn)行分析。
為了實(shí)現(xiàn)雙變量施肥機(jī)的精確控制,建立一個(gè)排肥單體的雙變量控制模型是關(guān)鍵。根據(jù)外槽輪排肥器的排肥原理,變量施肥機(jī)每公頃施肥量為[25]
式中為目標(biāo)施肥量,kg/hm2;為單個(gè)排肥器單位時(shí)間排肥量,g/min;為排肥器個(gè)數(shù);為變量施肥機(jī)作業(yè)車速,km/h為作業(yè)行距,即相鄰2個(gè)排肥器之間的距離,m;k為機(jī)具打滑率。
由于該系統(tǒng)采用GNSS測(cè)速,伺服電機(jī)驅(qū)動(dòng)排肥軸,機(jī)具打滑對(duì)排肥器的影響可忽略,即k=1,同時(shí)由于該控制系統(tǒng)以單個(gè)排肥器為一個(gè)獨(dú)立控制單元,即=1,則式(1)可簡(jiǎn)化為
由式(2)可知,要實(shí)現(xiàn)施肥量的精確控制,必須獲取單位時(shí)間排肥量與控制參數(shù)即排肥口開(kāi)度(mm)和排肥軸轉(zhuǎn)速(r/min)的關(guān)系。經(jīng)過(guò)標(biāo)定試驗(yàn),獲取不同開(kāi)度、轉(zhuǎn)速條件下的單位時(shí)間排肥量,利用Matlab軟件進(jìn)行二次多項(xiàng)式擬合,得到、與滿足如下關(guān)系:
=-13.5+9.153+19.89-0.0982+1.756-0.3072(3)
擬合方程決定系數(shù)為0.9992,擬合度較高。根據(jù)目標(biāo)施肥量范圍確定開(kāi)度后,代入式(3)即可獲得排肥軸轉(zhuǎn)速與的二次方程,通過(guò)解二次方程即可獲得目標(biāo)排肥轉(zhuǎn)速。
作業(yè)時(shí),通過(guò)處方圖獲取目標(biāo)施肥量,確定開(kāi)度,實(shí)時(shí)獲取變量施肥機(jī)作業(yè)速度,代入式(2),計(jì)算可得單位時(shí)間排肥量,代入式(3)即可獲得目標(biāo)轉(zhuǎn)速,進(jìn)而控制伺服電機(jī)帶動(dòng)排肥器動(dòng)作,實(shí)現(xiàn)施肥量的精確控制。
為了實(shí)現(xiàn)排肥單體的準(zhǔn)確定位,需要根據(jù)GNSS系統(tǒng)獲取的變量施肥機(jī)的當(dāng)前經(jīng)緯度信息,實(shí)時(shí)計(jì)算各排肥器的位置坐標(biāo)。GNSS系統(tǒng)遵循NMEA-0183協(xié)議,利用ASCII碼傳遞信息[26],本文截取包含位置、速度以及航向角的$GPRMC格式信息。為了實(shí)現(xiàn)排肥單體在平面上的準(zhǔn)確定位,基于大地坐標(biāo)系(WGS84)的經(jīng)緯度信息通過(guò)墨卡托投影法(Mercator)轉(zhuǎn)化為平面坐標(biāo)信息。
作業(yè)時(shí),GNSS天線安裝在拖拉機(jī)駕駛室的上方,與各排肥器中心連線的垂直距離為(m),GNSS天線的平面位置坐標(biāo)為(,),則第個(gè)排肥單體的平面坐標(biāo)(x,y)的計(jì)算公式為[27]
式中θ為向量[x-x y-]T與平面坐標(biāo)軸的夾角,(°)。d為第個(gè)排肥單體與GNSS天線之間的距離,m,計(jì)算方法如式(5)~(6)所示。
式中為航向角,(°),∈[1,]。
作業(yè)過(guò)程中,設(shè)備基本參數(shù)如GNSS天線與各排肥器中心連線的垂直距離、相鄰2個(gè)排肥器之間的距離以及排肥單體個(gè)數(shù)等由用戶根據(jù)設(shè)備實(shí)際情況通過(guò)控制軟件輸入。GNSS天線的平面位置坐標(biāo)(,)以及航向角由對(duì)GNSS信息的解析和變換獲得。為防止$GPRMC字段截取不完整造成定位信息丟失,本文采用C#正則表達(dá)式進(jìn)行字段匹配。
基于排肥單體獨(dú)立控制的雙變量施肥機(jī)控制系統(tǒng)主要實(shí)現(xiàn)對(duì)GNSS信息的采集、解析、存儲(chǔ),作業(yè)參數(shù)設(shè)置以及排肥單體的獨(dú)立控制。系統(tǒng)采用CAN通信方式,以單個(gè)排肥器為一個(gè)獨(dú)立控制單元,具有很好的可擴(kuò)展性??刂葡到y(tǒng)硬件系統(tǒng)組成如圖3所示。
本系統(tǒng)采用的GNSS設(shè)備是基于NovAtel公司的OEM615核心板卡開(kāi)發(fā)的,支持北斗雙頻差分定位,RTK水平定位精度達(dá)到0.01 m。采用APC-3082工業(yè)平板作為車載終端,經(jīng)串口由USB/CAN-IIC分析儀連接到CAN網(wǎng)絡(luò),實(shí)現(xiàn)人機(jī)交互、作業(yè)參數(shù)設(shè)置以及作業(yè)控制。電機(jī)選用MOTEC公司的ARES-8015-E-AC系列直流伺服電機(jī),額定功率100 kW,額定轉(zhuǎn)速3 000 r/min,根據(jù)MOTECIAN通信協(xié)議發(fā)送控制指令到伺服電機(jī)驅(qū)動(dòng)器,驅(qū)動(dòng)伺服電機(jī)轉(zhuǎn)動(dòng)進(jìn)而實(shí)現(xiàn)對(duì)排肥軸轉(zhuǎn)速的控制,與之配套的減速器減速比為1∶32。下位機(jī)控制器采用Arduino的Mega2560控制板,通過(guò)MCP2515模塊連入CAN通信網(wǎng)絡(luò),可實(shí)現(xiàn)對(duì)電子位移傳感器數(shù)據(jù)的采集和電子推桿的控制。電子推桿采用TB6600型驅(qū)動(dòng)器,推力250/N、速度12 mm/s,主要實(shí)現(xiàn)排肥口開(kāi)度大小調(diào)節(jié)。電子位移傳感器選用米郎RTK系列,量程為75 mm,測(cè)量精度達(dá)到0.1 mm。GNSS設(shè)備和工業(yè)平板均采用12 V、60 Ah的鋰電池供電。排肥控制單體的電源選用同型號(hào)鋰電池,通過(guò)升壓器轉(zhuǎn)化為24V電壓給伺服電機(jī)和電子推桿供電,通過(guò)降壓器轉(zhuǎn)轉(zhuǎn)化為5 V電壓給控制器供電。電子位移傳感器由控制器的5 V電壓輸出引腳供電。每個(gè)排肥單體配備一塊鋰電池。
使用C#語(yǔ)言,基于VS2012開(kāi)發(fā)平臺(tái)結(jié)合SQL2008數(shù)據(jù)庫(kù),開(kāi)發(fā)上位機(jī)控制軟件。軟件系統(tǒng)在VS2012軟件開(kāi)發(fā)平臺(tái)開(kāi)發(fā)主體程序,利用SQL2008數(shù)據(jù)庫(kù)實(shí)現(xiàn)GNSS信息的上傳和存儲(chǔ),主要包括通信模塊、參數(shù)設(shè)置模塊和作業(yè)控制模塊。其中,作業(yè)控制模式分為手動(dòng)和自動(dòng)控制模式,自動(dòng)控制模式的軟件工作界面如圖4所示。
系統(tǒng)通訊模塊使用CAN總線通訊技術(shù),通過(guò)對(duì)CAN分析儀的二次開(kāi)發(fā),實(shí)現(xiàn)串口信號(hào)到CAN信號(hào)的轉(zhuǎn)換。參數(shù)設(shè)置模塊主要實(shí)現(xiàn)對(duì)設(shè)備信息和所用肥料信息的設(shè)置和存儲(chǔ)。作業(yè)控制模塊實(shí)現(xiàn)對(duì)排肥器的自動(dòng)控制,控制方式主要有手動(dòng)模式和自動(dòng)模式??刂屏鞒倘鐖D5所示。
作業(yè)時(shí),首先啟動(dòng)系統(tǒng),進(jìn)行GNSS設(shè)備和CAN分析儀的通信連接,包括對(duì)通信端口的配置和波特率的選擇,其中,GNSS設(shè)備波特率為115 200 b/s,CAN分析儀波特率為500 kb/s。然后進(jìn)行系統(tǒng)作業(yè)參數(shù)設(shè)置,輸入GNSS天線到排肥口的安裝距離,相鄰2個(gè)排肥器之間的距離以及排肥器個(gè)數(shù),以便系統(tǒng)對(duì)各個(gè)排肥單體進(jìn)行定位。完成參數(shù)設(shè)置后進(jìn)入作業(yè)控制界面,根據(jù)實(shí)際作業(yè)需要選擇手動(dòng)或自動(dòng)控制模式。
在手動(dòng)模式下,用戶可以根據(jù)實(shí)際情況選中需要作業(yè)的排肥器編號(hào),然后輸入排肥口目標(biāo)開(kāi)度和排肥軸目標(biāo)轉(zhuǎn)速值,并設(shè)定排肥時(shí)間,啟動(dòng)系統(tǒng)作業(yè),到達(dá)設(shè)定時(shí)間后,排肥自動(dòng)停止。該功能模塊可實(shí)現(xiàn)對(duì)不同肥料標(biāo)定。在自動(dòng)模式下,系統(tǒng)通過(guò)解析GNSS信息,獲得機(jī)具當(dāng)前位置坐標(biāo)、航向角以及車速信息,實(shí)時(shí)計(jì)算單體排肥器位置坐標(biāo),再根據(jù)處方圖目標(biāo)施肥量信息,結(jié)合施肥控制模型生成控制序列,形成控制指令并發(fā)送給下位機(jī)控制器,實(shí)現(xiàn)自動(dòng)施肥。
為了檢驗(yàn)該雙變量施肥樣機(jī)的作業(yè)性能,于2020年11月中旬,在中國(guó)農(nóng)業(yè)大學(xué)上莊試驗(yàn)站進(jìn)行田間試驗(yàn)。采用GB/T 35487—2017《變量施肥播種機(jī)控制系統(tǒng)》對(duì)該樣機(jī)的各行排肥量一致性、施肥量控制準(zhǔn)確性進(jìn)行檢驗(yàn)。另外,針對(duì)該機(jī)的各行獨(dú)立控制性能,設(shè)計(jì)了施肥邊界為凸、凹、S三種形狀的道路排肥試驗(yàn)。試驗(yàn)肥料采用撒可富“22-8-10”復(fù)合肥,堆積密度為964 kg/m3。
各行之間的排肥量一致性反映了變量施肥機(jī)的施肥均勻性,采用各行一致性變異系數(shù)進(jìn)行評(píng)價(jià)。使用變量施肥控制軟件的手動(dòng)模式控制排肥。首先選中4個(gè)排肥器,設(shè)置排肥口開(kāi)度為常用工作開(kāi)度35 mm,調(diào)整排肥軸轉(zhuǎn)速10~60 r/min,調(diào)節(jié)步長(zhǎng)5 r/min,排肥時(shí)長(zhǎng)1 min,系統(tǒng)達(dá)到設(shè)定時(shí)間自動(dòng)停止。將4個(gè)排肥器依次從左到右編號(hào),在每個(gè)排肥口放置小桶收集肥料并稱量統(tǒng)計(jì),每個(gè)轉(zhuǎn)速條件下進(jìn)行3次重復(fù)試驗(yàn),取均值作為試驗(yàn)結(jié)果,試驗(yàn)結(jié)果如表2所示。
表2 各行排肥量一致性試驗(yàn)結(jié)果
由表2可知,當(dāng)排肥軸轉(zhuǎn)速為10 r/min時(shí),各行排肥量一致性變異系數(shù)為5.37%,隨著轉(zhuǎn)速的提高,各行之間的排肥一致性提高,排肥穩(wěn)定性增加。各行最小變異系數(shù)為2.99%,平均一致性變異系數(shù)為3.35%,整機(jī)具有較好的排肥穩(wěn)定性。
排肥量控制準(zhǔn)確性是評(píng)價(jià)變量施肥機(jī)作業(yè)性能的重要指標(biāo)。田間試驗(yàn)在Jhon Deere的5E-904型拖拉機(jī)的牽引下進(jìn)行,在排肥口掛小桶對(duì)排肥進(jìn)行收集并稱質(zhì)量,分別在車速3、5、7 km/h[29]的條件下進(jìn)行施肥作業(yè)50 m,每種車速條件下進(jìn)行3次重復(fù)試驗(yàn),取均值作為試驗(yàn)結(jié)果。排肥量控制精度采用式(7)計(jì)算,試驗(yàn)現(xiàn)場(chǎng)如6所示。
排肥量控制精度計(jì)算公式[28]為
式中為排肥量控制精度,%;1為實(shí)際排肥總質(zhì)量,g;2為理論排肥總質(zhì)量,g。
理論排肥質(zhì)量2按照下式計(jì)算:
2=2/10 (8)
式中為作業(yè)面積,m2;2為目標(biāo)排肥量,kg/hm2。
試驗(yàn)結(jié)果見(jiàn)表3,在目標(biāo)排肥量35 0kg/hm2下,排肥量控制準(zhǔn)確性隨著作業(yè)車速的增加而增加,排肥精度在車速為7 km/h 時(shí)達(dá)到97.6%,滿足GB/T 35487—2017的要求。
表3 排肥量控制準(zhǔn)確性試驗(yàn)結(jié)果
各行獨(dú)立控制性能是評(píng)價(jià)排肥單體獨(dú)立控制的變量施肥機(jī)對(duì)不規(guī)則形狀施肥邊界適應(yīng)能力的重要指標(biāo)。如果各行獨(dú)立控制,則通過(guò)不規(guī)則施肥邊界時(shí),各行落肥位置與施肥邊界的滯后距離不會(huì)發(fā)生變化;如果各行同步控制,則通過(guò)不規(guī)則施肥邊界時(shí),各行落肥位置與落肥邊界的之間的滯后距離會(huì)有較大差異,因此,用實(shí)際落肥滯后距離相對(duì)于作業(yè)幅寬的變化率V來(lái)評(píng)價(jià)各行獨(dú)立控制性能[30],計(jì)算公式如下:
4.3.1 試驗(yàn)原理
為了對(duì)該機(jī)各行獨(dú)立控制性能進(jìn)行評(píng)價(jià),設(shè)計(jì)了直徑為2.5m的半圓形凸、凹、S形的道路排肥試驗(yàn)。試驗(yàn)原理如圖7所示。
以凸邊為例,在平面坐標(biāo)系內(nèi),假設(shè)4個(gè)排肥器的初始位置為1~4,以第2行排肥器為例,在時(shí)刻的位置與初始位置的距離為d,并隨著整機(jī)沿作業(yè)方向行駛不斷增大。當(dāng)d=10 m時(shí),2、3行排肥器到達(dá)施肥邊界,發(fā)送2、3行排肥控制指令,啟動(dòng)排肥,當(dāng)d=10.35 m時(shí),1、4行排肥器達(dá)到施肥邊界,發(fā)送1、4行排肥控制指令,啟動(dòng)排肥。
經(jīng)過(guò)對(duì)邊界形狀的幾何運(yùn)算和分析可得,對(duì)于凹邊排肥過(guò)程,1、4行排肥器先到達(dá)施肥邊界,啟動(dòng)1、4行排肥,繼續(xù)行駛0.35 m后,2、3行到達(dá)施肥邊界,啟動(dòng)2、3行排肥;對(duì)于S邊排肥過(guò)程,作業(yè)時(shí),3、4行先到達(dá)施肥邊界,啟動(dòng)3、4行排肥,繼續(xù)行駛1.1 m后,1、2行達(dá)到施肥邊界,啟動(dòng)1、2行排肥。因此,通過(guò)實(shí)時(shí)計(jì)算排肥器當(dāng)前位置與初始位置的距離d,即可實(shí)現(xiàn)對(duì)不同形狀排肥邊界的準(zhǔn)確識(shí)別和對(duì)排肥的精確控制。試驗(yàn)現(xiàn)場(chǎng)如圖8所示。
注:1~4為排肥器行數(shù),ds為任意時(shí)刻排肥口與初始位置的距離,m。下同。
4.3.2 試驗(yàn)結(jié)果
道路試驗(yàn)在上莊試驗(yàn)站的一段水泥路面上進(jìn)行,準(zhǔn)備路段10 m,作業(yè)路段20 m。測(cè)得道路坐標(biāo)原點(diǎn)的緯度為40.138 760 62,經(jīng)度為116.176 540 078,施肥邊界采樣頻率為5 Hz。確定施肥邊界形狀,選取施肥邊界參數(shù),作業(yè)車速為=5 km/h,在準(zhǔn)備區(qū)啟動(dòng)控制軟件,到達(dá)施肥邊界后,系統(tǒng)自動(dòng)排肥。試驗(yàn)結(jié)束后測(cè)量各行實(shí)際落肥位置相對(duì)于施肥邊界的滯后距離,計(jì)算滯后距離變化率。每種邊界條件下進(jìn)行3次重復(fù)試驗(yàn),取均值。
在每種施肥邊界條件下,測(cè)量各行實(shí)際落肥位置相對(duì)于施肥邊界的滯后距離,利用式(9)計(jì)算得到各行獨(dú)立控制的滯后距離變化率,結(jié)果如表4所示。
表4 各行獨(dú)立控制排肥滯后距離變化率
由表4可知,對(duì)于凹、凸、形3種不同形狀的施肥邊界,該變量施肥機(jī)的各行排肥器實(shí)際排肥位置的滯后距離變化率分別為10%、14%、13%,均小于15%,且不受排肥邊界形狀的影響。雖然本試驗(yàn)在水泥路面上進(jìn)行,但各排肥器通過(guò)位置信息觸發(fā)排肥,各行獨(dú)立控制性能主要受處方圖邊界解析精度、定位精度和作業(yè)車速影響,該試驗(yàn)結(jié)果能反映田間作業(yè)情況。
綜上可知,該變量施肥機(jī)機(jī)有較好的各行獨(dú)立控制性能,能夠較好適應(yīng)復(fù)雜施肥邊界形狀,可減少施肥過(guò)程中田塊邊緣和壟溝邊界的肥料浪費(fèi),為進(jìn)一步細(xì)化田間區(qū)域施肥精度提供可能。
1)基于CAN總線通訊技術(shù),設(shè)計(jì)了一種排肥單體獨(dú)立控制的雙變量施肥控制系統(tǒng),建立了系統(tǒng)控制模型,并對(duì)排肥單體的定位方法進(jìn)行了分析,搭建了變量施肥機(jī)控制系統(tǒng)的硬件,開(kāi)發(fā)了上位機(jī)操作軟件。
2)為了檢驗(yàn)該雙變量施肥控制系統(tǒng)的作業(yè)性能,進(jìn)行了各行排肥量一致性排肥試驗(yàn)和排肥量控制控制準(zhǔn)確性試驗(yàn)。試驗(yàn)結(jié)果表明,在排肥軸轉(zhuǎn)速10~60 r/min的區(qū)間內(nèi),各行平均排肥量一致性變異系數(shù)為3.35%,各行之間排肥均勻、穩(wěn)定;對(duì)于同一目標(biāo)排肥量350 kg/hm2,排肥量控制精度隨著作業(yè)車速的提高而提高,排肥量控制精度在車速為7 km/h時(shí)達(dá)到97.6%,該系統(tǒng)具有較好的排肥穩(wěn)定性和準(zhǔn)確性。
3)為了檢驗(yàn)該雙變量施肥控制系統(tǒng)的各行獨(dú)立控制性能,開(kāi)展了直徑為2.5 m的半圓形凹、凸、S形3種不同形狀的施肥邊界的排肥試驗(yàn)。結(jié)果表明,在作業(yè)車速5 km/h的條件下,各行排肥器排肥位置的滯后距離變化率均小于15%,且不受施肥邊界形狀的影響。該排肥單體獨(dú)立控制的雙變量施肥控制系統(tǒng)能夠?qū)崿F(xiàn)各行獨(dú)立控制,能夠適應(yīng)復(fù)雜施肥邊界形狀,減少肥料在壟溝邊界的浪費(fèi),可根據(jù)實(shí)際作業(yè)需求調(diào)整工作的排肥器個(gè)數(shù),進(jìn)而調(diào)節(jié)作業(yè)幅寬,實(shí)現(xiàn)跨處方圖柵格作業(yè),為玉米基肥變量施用裝備的研發(fā)提供參考。
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Development of bivariate fertilizer control system via independent control of fertilizing unit
Zhang Jiqin1,2, Liu Gang1,3※, Hu Hao1,3, Huang Jiayun1,3
(1.,,,100083,;2.,,750021,;3.,,,100083,)
Current variable-rate fertilizer applicator generally drives all the fertilizer distributers through the same drive shaft at a fixed working width. Most fields are in an irregular shape during the operation of fertilization, particularly unsuitable for an integer multiple of working width. Severe overlap of working areas normally occurs at the edge of the field, resulting in a large amount of waste of fertilizer at the boundary. In addition, the cross-regional or cross-prescription raster operations are still lacking in the current fertilizer applicator. In this study, a bivariate fertilizer control system was designed to implement the independent control of fertilizer discharging unit in a modified applicator for corn fertilizing. The whole machine was composed mainly of a real-time kinematic (RTK) and global navigation satellite system (GNSS) positioning, a bivariate fertilization control system, and an executing device. Firstly, a calibration test was conducted at different active-feed roll lengths and rotational speeds of the drive shaft. A quadratic polynomial fitting was then used to obtain the bivariate control model for the distributing monomer of fertilizer. Specifically, the coefficient of determination reached 0.9992 in the fitting equation, indicating a high level of fitting. Secondly, an in-depth analysis was conducted for the positioning of each fertilization unit. Thirdly, the hardware and software of the control system were developed using the CAN bus communication to realize the collection, analysis and storage of GNSS information, the operation parameter setting, and the independent control of discharging unit. The hardware was composed of a GNSS navigation device, an industrial personal computer, a servo/stepping motor, a micro-controller, and an electronic ruler. The software was performed on a VS2012 platform with SQL2008 database using C# language. Three function modules were included: the communication, setting of working parameters, and working control in the manual and automatic mode. Finally, a systematic evaluation was completed on the comprehensive performance of the bivariate fertilizer control system, including the consistency of fertilizer discharge in each row, the accuracy of fertilization rate at different vehicle speeds, and independent control performance in each row. The results showed that the maximum coefficient of variation (CV) was 5.37% at the driving speed of 10 r/min within the range of 10-60 r/min of fertilizer shaft speed, as the speed of the driving shaft increased. The minimum CV of each row dropped to 2.99% at the driving speed of 55 r/min, indicating the average CV of consistency was 3.35%. At the target fertilizer rate of 350 kg/hm2, the accuracies of fertilization control were 93.2%, 96.75%, and 97.60% under the working speed of 3, 5, and 7 km/h, respectively. The operating speed was generally around 4-12 km/h in the variable rate fertilizer applicator, meeting the national standard accuracy of fertilizer application. Three experiments were conducted on the road fertilization with irregular boundary shapes, such as the concave, convex and S boundary. The lag distance change rate fertilization correlated to the working width was less than 15% on average, indicating no influence by the shape of fertilization boundary. More specifically, the variation ratios of lag distance were 10%, 14%, and 13% at the concave, convex and S boundary, respectively. This applicator can be expected to well simulate the fertilization boundary shape, due to its high stability of fertilization, and control accuracy.The bivariate fertilizer applicator with independent control of fertilization monomer can realize the independent control of each row, suitable for the shape of complex fertilization boundary, while reducing fertilizer wastes at the boundary of the furrow. The finding can provide a potential technical reference for the innovative development of variable-rate equipment for basal fertilizer in corn production.
agricultural machinery; corn; basic fertilizer; bivariate; fertilizing unit; independent control
10.11975/j.issn.1002-6819.2021.10.005
S224.2
A
1002-6819(2021)-10-0038-08
張季琴,劉剛,胡號(hào),等. 排肥單體獨(dú)立控制的雙變量施肥控制系統(tǒng)研制[J]. 農(nóng)業(yè)工程學(xué)報(bào),2021,37(10):38-45.doi:10.11975/j.issn.1002-6819.2021.10.005 http://www.tcsae.org
Zhang Jiqin, Liu Gang, Hu Hao, et al. Development of bivariate fertilizer control system via independent control of fertilizing unit[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2021, 37(10): 38-45. (in Chinese with English abstract) doi:10.11975/j.issn.1002-6819.2021.10.005 http://www.tcsae.org
2020-12-19
2021-04-18
國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2017YFD0700503)
張季琴,講師,博士生,研究方向?yàn)榫?xì)農(nóng)業(yè)關(guān)鍵技術(shù)。Email:zhjq2010jasmine@163.com
劉剛,教授,博士生導(dǎo)師,研究方向?yàn)殡娮有畔⒓夹g(shù)在農(nóng)業(yè)中的應(yīng)用。Email:pac@cau.edu.cn