李永磊,徐澤昕,萬里鵬程,趙 虎,陳海軍,宋建農(nóng)
批次式種子清選機橡膠球清篩裝置激振力模擬分析
李永磊1,徐澤昕1,萬里鵬程1,趙 虎1,陳海軍2,3,宋建農(nóng)1
(1. 中國農(nóng)業(yè)大學(xué)工學(xué)院,北京 100083;2. 農(nóng)業(yè)農(nóng)村部規(guī)劃設(shè)計研究院,北京 100125;3. 農(nóng)業(yè)農(nóng)村部農(nóng)產(chǎn)品產(chǎn)后處理重點實驗室,北京 100125)
橡膠球清篩裝置清篩性能對批次式種子清選機作業(yè)效率與質(zhì)量具有重要影響,橡膠球?qū)Y面的激振力是決定清篩性能的關(guān)鍵因素。針對橡膠球隨機彈性碰撞清篩過程理論解析困難、橡膠球激振力難以精準獲取等問題,該研究介紹了橡膠球清篩裝置結(jié)構(gòu)與工作原理,分析了橡膠球彈跳產(chǎn)生條件與激振力作用機制;采用Hertz-Mindlin接觸模型建立了篩分裝置EDEM-MBD耦合仿真模型,并搭建了橡膠球激振力測定裝置,單個橡膠球平均激振力、最大激振力模擬值與實測值相對誤差分別小于5%、10%,形成了橡膠球激振力模擬方法;采用四因素三水平Box-Behnken試驗?zāi)M了不同工況下清篩裝置激振力,建立了平均激振力、最大激振力與振幅、振動頻率、篩面傾角、球格球數(shù)等參數(shù)的數(shù)學(xué)關(guān)系;以篩面卡種數(shù)量為指標開展了玉米種子清選清篩性能試驗,獲得了不同振動頻率下篩面卡種數(shù)量與清篩裝置激振力的對應(yīng)關(guān)系。試驗結(jié)果表明:振動頻率為7.2 Hz時篩面無卡種,清篩裝置平均激振力8.87 N、最大激振力18.78 N;批次式玉米種子清選作業(yè)各工況清篩裝置激振力應(yīng)滿足條件:平均激振力≥9 N、最大激振力≥19 N。研究結(jié)果可為橡膠球清篩裝置清篩機理研究及其結(jié)構(gòu)參數(shù)優(yōu)化提供研究方法與設(shè)計參考。
自動化;模擬;種子清選;清篩裝置;橡膠球;激振力
批次式種子清選機是為滿足試驗小區(qū)種子特殊加工要求而研制的專用裝備,減少或避免篩孔卡種及篩面種子殘留是提高清選質(zhì)量和作業(yè)效率的重要技術(shù)措施[1-2]。篩孔堵塞是顆粒物料振動篩分設(shè)備常見問題,被堵塞的篩孔無法實現(xiàn)物料有效透篩,從而引起篩分效率下降進而影響篩分效率與作業(yè)質(zhì)量[3-4]。種子清選機等篩分設(shè)備通常設(shè)置擊打式、架刷式、橡膠球式等清篩裝置[5],其中橡膠球清篩裝置因清篩過程柔和、故障率低等優(yōu)點得以廣泛應(yīng)用。
橡膠球清篩裝置作為篩分設(shè)備的輔助裝置并未得到研究人員的足夠重視,橡膠球清篩技術(shù)多源于生產(chǎn)實踐和經(jīng)驗設(shè)計。有關(guān)學(xué)者圍繞農(nóng)業(yè)顆粒物料篩分效率提升需求主要從篩分結(jié)構(gòu)設(shè)計、運動參數(shù)優(yōu)化等方面開展研究[6-8],戴飛等[9]設(shè)計了雙風(fēng)道風(fēng)篩式胡麻脫粒物料分離清選裝置實現(xiàn)了不同組分脫粒物料的分離清選作業(yè);王升升等[10]設(shè)計了由內(nèi)流式圓筒篩、橫流風(fēng)機等組成的大白菜種子清選裝置并優(yōu)化了工作參數(shù);周澗楠[11]基于風(fēng)選篩選復(fù)式作業(yè)原理設(shè)計了適用禾谷類種子的清選機械;劉鵬等[12]分析了魚鱗篩、貝殼篩、網(wǎng)篩、圓孔篩等不同篩片組合的篩分裝置對大豆清選的適應(yīng)性;金誠謙等[13]針對小麥清選損失率、含雜率高等問題優(yōu)化了喂入量、風(fēng)門開度、風(fēng)機轉(zhuǎn)速等主要作業(yè)參數(shù)。橡膠球清篩裝置研究方面,周治國[14]根據(jù)煤炭分選需求設(shè)計了剛?cè)狁詈蠌椥院Y并分析了聚氨酯擊打球?qū)Y面堵孔顆粒的作用機理;常榮[5]研究分析了硅膠橡膠球數(shù)量對清篩效果及蕎麥分級的影響;李永磊等[2]探索采用變頻振動清篩技術(shù)提高批次式種子清選機橡膠球清篩裝置清篩效果,以期減少或避免篩孔卡種及篩面種子殘留。
篩面物料運動是極其復(fù)雜的、篩孔堵塞是隨機的、橡膠球彈性撞擊是無序的,只有各結(jié)構(gòu)與工作參數(shù)得以合理匹配才能夠提高物料透篩概率和實現(xiàn)最佳清篩效果。前期研究表明:橡膠球?qū)Y面的激振力與篩分物料特性、篩分裝置結(jié)構(gòu)參數(shù)與運動特性等相關(guān),其能夠表征清篩裝置清篩性能。橡膠球隨機彈性碰撞清篩過程理論解析較為困難、橡膠球激振力難以精準獲取等問題制約了橡膠球清篩機理研究及清篩裝置優(yōu)化設(shè)計。隨著數(shù)值模擬技術(shù)發(fā)展,離散元法在顆粒物料篩分領(lǐng)域得到廣泛應(yīng)用[15-19],離散元耦合仿真技術(shù)為相關(guān)研究提供了新方法[20-25]。
本文在前期研究基礎(chǔ)上,圍繞批次式種子清選機清篩需求,分析橡膠球激振力產(chǎn)生條件與作用機制,建立篩分裝置EDEM-MBD耦合仿真模型并搭建橡膠球激振力測定裝置,試驗?zāi)M了不同工況下橡膠球激振力,獲得了不同振動頻率下篩面卡種數(shù)量與清篩裝置激振力的對應(yīng)關(guān)系,提出基于清篩裝置激振力數(shù)值模擬的清篩性能評估方法,以期為橡膠球清篩裝置清篩性能研究與結(jié)構(gòu)參數(shù)優(yōu)化奠定基礎(chǔ)。
清篩裝置是批次式種子清選機篩分裝置[2]的重要組成部分。篩分裝置主要包括上篩框、篩片、清篩裝置、篩框支架、驅(qū)動裝置、傾角調(diào)節(jié)裝置、安裝板、安裝底板、彈性板、安裝底座、出料口等,如圖1所示。上篩框、篩片、清篩裝置組成的篩分單體(長430 mm,寬250 mm)安裝在篩框支架上;篩片安裝在上篩框與清篩裝置之間;驅(qū)動裝置由驅(qū)動電機、偏心軸、連桿等組成,驅(qū)動篩分單體近似往復(fù)直線運動完成種子篩分。篩面傾角0°~10°無級調(diào)節(jié),振幅5~7 mm,振動頻率5.6~7.2 Hz。
1.球框 2.篩片 3.橡膠球 4.球架
1.Ball frame 2.Sieve 3.Rubber ball 4.Ball rack
圖2 清篩裝置結(jié)構(gòu)簡圖
Fig.2 Structure diagram of sieve-cleaning device
清篩裝置隨篩分單體近似往復(fù)直線運動,橡膠球在球格內(nèi)隨機彈性碰撞并不斷撞擊篩片。篩孔內(nèi)滯留物料在橡膠球撞擊力、篩片受迫振動等效沖擊力、重力、慣性力、摩擦力、種子間作用力等復(fù)合作用下被彈出篩孔實現(xiàn)清篩。因單粒種子質(zhì)量較小,橡膠球撞擊力和篩片受迫振動等效沖擊力為主要作用力。
圖3 清篩裝置運動分析簡圖
Fig.3 Analysis diagram of sieve-cleaning device motion
圖4 橡膠球受力分析簡圖
Fig.4 Force analysis diagram of rubber ball
采用振動強度(球架最大加速度與重力加速度之比)表征清篩裝置振動強弱,如式(6)所示。
由式(5)、(7)可得:
種子清選采用概率篩分基本原理,篩面種子應(yīng)保持足夠的活躍度從而實現(xiàn)松散、分層及透篩過程。振動的篩分裝置為種子運動提供動能,傾斜的篩面為種子運動提供一定的重力勢能,而種子運動過程中碰撞和摩擦則帶來能量的損耗。當(dāng)種子過量堆積或受摩擦阻力影響滯留在篩孔中時,種子和篩片位置相對靜止,種子動能下降且無法獲得有效外部能量補充,從而產(chǎn)生篩孔卡種堵塞現(xiàn)象。因單粒種子質(zhì)量較小,其重力及慣性力也相對較小,多數(shù)情況下無法克服篩孔摩擦力及篩孔夾持力等外力。通過外部激勵為篩孔滯留種子補充能量并提高其動能是實現(xiàn)清篩及提高篩分效率的基本途徑。橡膠球激振力的作用表現(xiàn)為:橡膠球?qū)Y孔內(nèi)種子的直接撞擊作用力,篩片受迫振動等效沖擊力對種子的間接作用力。
1)橡膠球直接撞擊受力分析
當(dāng)篩孔滯留種子受到橡膠球直接撞擊作用時,種子受到自身重力、慣性力、篩孔摩擦力、橡膠球激振力等力的綜合作用,如圖5所示。堵塞種子脫離篩孔瞬間種子法向合力為0,力學(xué)方程如式(9)所示。
注:為篩面種子流動方向;為篩面法向方向;為種子重力,N;為種子重力向分力,N;為種子重力向分力,N;為種子慣性力,N;為慣性力向分力,N;為慣性力向分力,N;為橡膠球 向合力,N;為種子所受激振力,N;為篩孔摩擦力。
由式(9)、式(10)可得:
2)篩片受迫振動等效沖擊受力分析
注:為橡膠球作用區(qū)域;為橡膠球撞擊點;為撞擊點變形最大位移;為卡種位置;為等效沖擊力,N;為橡膠球激振力,N;為撞擊點與卡種位置距離;為簡支梁長度的1/2。
綜上分析,橡膠球直接撞擊作用力及篩片受迫振動等效沖擊力均可有效作用于篩孔滯留的種子,為種子提供一定能量從而克服篩孔對種子的束縛產(chǎn)生清篩效果。
為準確獲取橡膠球激振力,采用Hertz-Mindlin接觸模型建立篩分裝置EDEM-MBD耦合仿真模型,并搭建橡膠球激振力測定裝置,對比激振力模擬值與實測值,以期形成有效的橡膠球激振力模擬方法。
3.1.1 篩分裝置仿真模型建立
為方便獲取橡膠球激振力,以條形鋼板(250×40×1 mm)代替篩片,采用INVENTOR軟件繪制篩分裝置三維結(jié)構(gòu)圖,使用RecurDyn軟件建立多體動力學(xué)模型,從RecurDyn中將球架、球框及鋼板導(dǎo)入EDEM軟件中建立篩分裝置EDEM-MBD仿真模型,在EDEM中使用顆粒工廠建立直徑24 mm的橡膠球模型,使用Hertz-Mindlin(no slip)接觸模型建立橡膠球與球架、鋼板互作關(guān)系。篩分裝置仿真模型如圖7所示。球架及條形鋼板本征參數(shù)參考文獻[26]確定為:泊松比0.28、密度7 890 kg/m3、剪切模量8.2×1010Pa。
3.1.2 橡膠球仿真參數(shù)確定
本征參數(shù):
橡膠球密度采用質(zhì)量體積法測定為1 258 kg/m3,泊松比參考文獻[27]取值為0.47,橡膠球硬度采用邵氏硬度計測定為55 HA,剪切模量由式(13)計算為6.09×105Pa。
接觸參數(shù):
表1 e1試驗數(shù)據(jù)
表2 e2試驗數(shù)據(jù)
表3 試驗數(shù)據(jù)
表4 仿真試驗因素水平編碼表
3.1.3 單球模擬仿真及結(jié)果分析
采用上文仿真模型,以平均激振力、最大激振力為指標,以振動頻率為因素開展單因素五水平模擬仿真試驗。振動頻率設(shè)置為5.6、6、6.4、6.8、7.2 Hz,仿真時間10 s,瑞利時間步長設(shè)置為20%,保存間隔為0.002 s,每組試驗重復(fù)3次。
表5 仿真試驗方案設(shè)計與結(jié)果
表6 仿真試驗方差分析表
注:“**”極顯著(≤0.01);“*”顯著(0.01<≤0.05);下同。
Note: “**”highly significant (≤0.01); “*” significant (0.01<≤0.05).
使用EDEM軟件后處理功能Result Data命令提取條形鋼板受到的力,結(jié)果如表7所示。平均激振力、最大激振力均隨振動頻率增加而增大,且隨著碰撞次數(shù)增多平均激振力較最大激振力有更高的增大速率,7.2 Hz時單個橡膠球平均激振力約1.912 N、最大激振力約3.159 N。
表7 平均激振力與最大激振力模擬結(jié)果
3.2.1 試驗裝置搭建
1)測試原理與方法
橡膠球激振力測定采用應(yīng)變式測力原理[29],應(yīng)變片排布及電橋接法如圖12所示。改造批次式種子清選機篩分單體,以條形鋼板代替篩片,將貼片后的鋼板夾持在上篩框與清篩裝置之間,球格內(nèi)放置1個橡膠球并設(shè)置有效工作區(qū)域,使用HP-DS8X25動態(tài)信號測試分析系統(tǒng)采集數(shù)據(jù)并處理,如圖13所示。
2)傳感器標定
表8 標定試驗數(shù)據(jù)表
3.2.2 橡膠球激振力測定
試驗裝置振動頻率設(shè)置為5.6、6、6.4、6.8、7.2 Hz,共開展5組試驗,每組重復(fù)3次;HP-DS8X25動態(tài)信號測試分析系統(tǒng)采樣頻率為500 Hz,應(yīng)用式(17)將測得的全橋形變量轉(zhuǎn)換為橡膠球激振力,測得橡膠球平均激振力、最大激振力,試驗結(jié)果如表9所示。
3.2.3 橡膠球激振力測定值與模擬值對比分析
橡膠球激振力測定值與模擬值對比分析結(jié)果如表10所示。受鋼板形變、橡膠球撞擊次數(shù)及測量誤差等影響,平均激振力模擬值與實測值的相對誤差為2.1%~4.6%、最大激振力相對誤差為2.4%~8.4%。
試驗結(jié)果表明,單個橡膠球平均激振力、最大激振力模擬值與實測值平均相對誤差分別小于5%、10%,篩分裝置EDEM-MBD耦合仿真模型有效,能夠滿足清篩裝置激振力模擬要求。
表9 平均激振力與最大激振力實測結(jié)果
表10 實測值與模擬值對比分析
批次式種子清選機主要篩分過程發(fā)生在下層篩分單體中,以該篩分單體為研究對象開展激振力模擬與玉米種子清選清篩性能試驗。通過激振力模擬建立清篩裝置激振力與振幅、振動頻率、篩面傾角、球格球數(shù)等參數(shù)的函數(shù)關(guān)系;根據(jù)清篩性能試驗獲得不同振動頻率條件下篩面卡種數(shù)量間接表征清篩裝置清篩性能,在此基礎(chǔ)得到篩面卡種數(shù)量與清篩裝置激振力的對應(yīng)關(guān)系。
在前期試驗研究基礎(chǔ)上并參考文獻[2],以平均激振力、最大激振力為指標,以振幅、振動頻率、篩面傾角、球格球數(shù)為因素開展四因素三水平Box-Behnken試驗,共29組試驗,每組重復(fù)3次取均值為指標值,試驗因素水平及編碼如表11所示,試驗方案及結(jié)果如表12所示。
表11 Box-Behnken試驗因素水平編碼表
表12 試驗方案及結(jié)果表
表13 平均激振力方差分析表
表14 最大激振力方差分析表
4.2.1 試驗方案
以篩面卡種數(shù)量為指標,以振動頻率為試驗因素開展了玉米種子清選清篩性能試驗。試驗于2021年8月在中國農(nóng)業(yè)大學(xué)工學(xué)院完成,所用批次式種子清選機為作者團隊研制,如圖15a所示;玉米種子品種稷秾101,容重616 kg/m3,初始凈度94%,含水率約9.2%,批次處理量為3 kg;其他儀器設(shè)備有電子稱、轉(zhuǎn)速計、傾角儀、計時器等。
圖15 清篩性能試驗
4.2.2 試驗結(jié)果與分析
試驗結(jié)果如表15所示。篩分裝置正常工作時橡膠球均可對篩面產(chǎn)生有效的撞擊,隨著振動頻率增加,清篩裝置平均激振力、最大激振力增大,清篩能力逐漸增強,篩面卡種數(shù)量持續(xù)減少。當(dāng)振動頻率為7.2 Hz時,篩面無卡種、清篩效果良好,此時清篩裝置平均激振力8.87 N、最大激振力18.78 N。據(jù)此可以預(yù)測,為實現(xiàn)良好的清篩效果,批次式玉米種子清選作業(yè)各工況下清篩裝置激振力模擬值應(yīng)滿足以下條件:平均激振力≥9 N、最大激振力≥19 N。
表15 卡種數(shù)量與激振力的對應(yīng)關(guān)系
由試驗結(jié)果可看出,橡膠球與篩面短時間接觸內(nèi)產(chǎn)生較高的能量轉(zhuǎn)換,橡膠球-篩面-種子間存在能量傳遞與耗散,在篩體慣性力、橡膠球激振力、種子料群動態(tài)載荷等作用下產(chǎn)生篩面彈性變形,篩面加速度顯著增大,從而促進種子料群松散分層與透篩,即便在較低振動頻率下也可以完成清選作業(yè),橡膠球激振力可為篩面與種子料群提供動能,在種子清選作業(yè)中十分重要,較大的激振力有利于物料透篩,并可防止篩面擁堵,篩面的受迫振動有利于篩分順利進行。當(dāng)篩面所受平均激振力大于8.87 N,最大激振力大于18.78 N時可實現(xiàn)玉米種子完全清篩,通過擬合方程可預(yù)估不同工作參數(shù)下清選裝置的清篩性能。
2)建立了篩分裝置EDEM-MBD耦合仿真模型,并采用應(yīng)變式測力原理搭建了橡膠球激振力測定裝置,單個橡膠球平均激振力模擬值與實測值的相對誤差為2.1%~4.6%、最大激振力相對誤差為2.4%~8.4%,能夠滿足清篩裝置激振力模擬要求。
3)開展了清篩裝置激振力模擬與玉米種子清選清篩性能試驗。建立了清篩裝置激振力與振幅、振動頻率、篩面傾角、球格球數(shù)等參數(shù)的函數(shù)關(guān)系,獲得了不同振動頻率條件下篩面卡種數(shù)量與清篩裝置激振力的對應(yīng)關(guān)系,提出了批次式玉米種子清選作業(yè)各工況清篩裝置激振力要求:平均激振力≥9 N、最大激振力≥19 N。
本研究以玉米種子清選為例建立了優(yōu)化工作參數(shù)、橡膠球激振力、清篩性能(篩面卡種數(shù)量)三者間的聯(lián)系,研究提出的基于清篩裝置激振力數(shù)值模擬的清篩性能評估方法可用于批次式種子清選機清選小麥、水稻等農(nóng)作物種子時的清篩性能預(yù)測,并為清篩裝置清篩機理研究及其結(jié)構(gòu)參數(shù)優(yōu)化提供方法與參考。
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Impulsive force simulation of the rubber ball sieve-cleaning device for batch seed cleaners
Li Yonglei1, Xu Zexin1, Wan Lipengcheng1, Zhao Hu1, Chen Haijun2,3, Song Jiannong1
(1.,,100083,; 2.,,100125,; 3.,,100125,)
A batch seed cleaner is a piece of special equipment to meet the specific processing of plot breeding materials. A rubber ball sieve-cleaning device can usually be used as an accessory for a seed cleaner to keep sieve cleaning and avoid sieve-mesh blocking. The sieve-cleaning performance of rubber ball sieve-cleaning devices has an important influence on the operation efficiency and quality of batch seed cleaners. The impulsive force of the rubber ball on the sieve is the key factor to determining the cleaning performance. In this study, the structural and working principles of rubber ball sieve-cleaning devices were introduced to theoretically analyze the random elastic collision screening of rubber balls for the accurate acquisition of impulsive force. An EDEM-MBD coupling model was built for a batch seed cleaner using Hertz-Mindlin in contact mode. A piece of sieve-developed test equipment was utilized to measure the contact parameters, such as the restitution coefficient and friction coefficient for the contact model. A rubber ball impulsive force measurement device was built to obtain the real force of a single ball, according to strain-force measurement. The average and the maximum impulsive force of a single rubber ball were effectively obtained, with the acceptable relative errors between the simulation and measured value, less than 5 % and 10%, respectively. The Box-Behnken experiments with four-factor and three-level were conducted to simulate the impulsive force of sieve-cleaning devices under different working conditions. The mathematical relationships were established between the average or the maximum impulsive force and parameters, such as the amplitude, vibration frequency, screening inclination angle, and ball number. The impulsive force of the rubber ball sieve-cleaning device under different parameters was easily obtained using regression equations. The maize seeds cleaning test under different vibration frequencies was carried out with the index of blockage number, where the relationship was between the blockage number of sieve and impulsive force of the sieve-cleaning device. The test results show that the sieve-cleaning device presented an excellent performance with no blockage on the sieve, with an average impulsive force of 8.87 N and the maximum impulsive force of 18.78 N, when the vibration frequency was 7.2 Hz. An optimal combination was achieved for the screening performance if the average impulsive force not less than 9 N or the maximum impulsive force not less than 19 N. The finding can provide a strong design reference for the screening mechanism and parameter optimization of rubber ball sieve-cleaning devices.
automation; simulation; seed cleaning; sieve-cleaning device; rubber ball; impulsive force
李永磊,徐澤昕,萬里鵬程,等. 批次式種子清選機橡膠球清篩裝置激振力模擬分析[J]. 農(nóng)業(yè)工程學(xué)報,2021,37(20):23-33.doi:10.11975/j.issn.1002-6819.2021.20.003 http://www.tcsae.org
Li Yonglei, Xu Zexin, Wan Lipengcheng, et al. Impulsive force simulation of the rubber ball sieve-cleaning device for batch seed cleaners[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2021, 37(20): 23-33. (in Chinese with English abstract) doi:10.11975/j.issn.1002-6819.2021.20.003 http://www.tcsae.org
2021-09-02
2021-10-03
國家重點研發(fā)計劃項目(2017YFD070120503)
李永磊,博士,副教授,研究方向為現(xiàn)代農(nóng)機裝備設(shè)計及振動利用技術(shù)。Email:liyl0393@cau.edu.cn
10.11975/j.issn.1002-6819.2021.20.003
S225.7
A
1002-6819(2021)-20-0023-11