陳學深,馬 旭,※2,武 濤,曾令超,李康毓,陳林濤
虎杖根系脫土滑梳式輥指的設計與試驗
陳學深1,馬 旭1,※2,武 濤1,曾令超1,李康毓1,陳林濤1
(1. 華南農業(yè)大學工程學院,廣州 510642;2. 華南農業(yè)大學南方農業(yè)機械與裝備關鍵技術教育部重點實驗室,廣州 510642)
根系脫土是中藥虎杖收獲的重要環(huán)節(jié),采用直線梳刷式脫土輥指實現根土分離極為有效,然而直輥與根系作用時,常出現相互勾連、扯拉等不良狀況,致使脫土功耗顯著增加,為此該文融入滑切方式,設計了一種曲線滑梳式脫土輥指。根據滑切理論,確定了輥指滑梳的臨界條件,利用對數螺線方程建立了輥指梳刃的曲線方程,通過輥指的動力學分析,建立了輥指作業(yè)的功耗模型,確定了輥指轉速、輥指作業(yè)長度、輥指滑切角為功耗的主要影響因素,并根據摩擦角與滑切角關系,利用Matlab軟件得到摩擦角和滑切角與功耗的偽彩色能量圖,確定功耗最小所對應的輥指滑切角為67°。進行功耗及脫凈率試驗,利用多目標優(yōu)化設計方法對試驗結果進行綜合評價。結果表明:在輥指轉速為350 r/min、輥指作業(yè)長度為30 mm、輥指滑切角為67°時,脫土輥指的作業(yè)性能較優(yōu),此時脫凈率為93.03%,功耗為76.73 W。研究結果可為虎杖根土分離部件的結構改進設計和作業(yè)參數優(yōu)化提供依據。
農業(yè)機械;藥;收獲;根土分離;滑切;梳刷;虎杖
中藥虎杖屬蓼科植物,具有祛風利濕、散瘀定痛、止咳化痰功效,近年藥理研究發(fā)現,其含有的白藜蘆醇具有抗艾滋病作用,掀起了虎杖研發(fā)熱,也使種植規(guī)模大為提高[1-3]。但相應收獲機具的研發(fā)滯后,特別是收獲脫土環(huán)節(jié),完全依靠效率低、強度大、成本高的人工方式,嚴重制約了虎杖藥用規(guī)?;a業(yè)化發(fā)展。因此,亟需解決虎杖根系的機械化脫土問題。
根土分離是中藥虎杖收獲、加工的關鍵環(huán)節(jié),傳統的根莖類藥材根土分離,主要是將根莖與土壤一起收集,然后通過一系列的振動、篩分機構實現根土分離[4-12]。采用這種方法的裝置結構復雜、效率低、功耗大,且作業(yè)對象多為根構簡單的根莖類或塊莖類藥材。而虎杖根構復雜,主根、支根與土壤組成錨固固土方式,縱橫交錯的細小須根與土壤形成網絡加筋固土方式,通過根系與土體間的摩擦、咬合、粘附等作用,使虎杖根系與土壤形成牢固的根土復合體[13-14],這些根系猶如鋼纖維對土體起到阻裂、橋聯作用,從而提高土體的強度、增加土體的塑性和韌性,使傳統的根土分離機械難以獲得理想的分離效果。本課題組在文獻[15]中采用直線梳刷式脫土輥指實現虎杖根土分離,雖可獲得較好的根系脫凈率,但因徑直的梳刷輥指與根系的沖擊、勾連、扯拉等負面影響,相對于曲線的滑梳輥指,在同等條件下,脫土功耗增加近80%。類似的根土復合體分離裝置,還有玉米根茬土壤分離裝置,如楊新義[16]采用碾壓碎土滾筒與抖動桿條鏈實現根土分離;徐寶庫[17]采用碾輥柵板去土機構實現對根土復合體的碾壓、沖擊、揉搓;Quan等[18-22]運用碾壓輥與抖動升運鏈進行玉米根茬土壤分離;武濤等[23]采用雙輥碾壓脫土機構和雙組柔性飛錘擊打脫土機構聯合作用進行玉米根茬土壤分離。以上脫土裝置采用多級脫土模式,雖獲得較高脫凈率,但機構復雜、作業(yè)功耗較大、損傷率高,限制了此類裝置的應用推廣。
本文在文獻[15]研究的基礎上,將徑直的梳刷輥指改為曲線的滑梳輥指,使脫土方式融合了滑切、梳刷作用,減少了輥指與細長根系的勾連、扯拉,緩和了輥指與粗壯根系的沖擊,有效地提高了虎杖根土分離品質,降低了功耗。
設計的虎杖脫土試驗裝置,結構如圖1所示。主要由變頻調速系統1、電動機2、滑梳輥總成3、柵板4、滑梳輥指5、機架6、翻轉輥總成7、扭矩傳感器8和傳動系統等組成。工作時,物料放置在滑梳輥與翻轉輥之間的柵板上,柵板下方高速旋轉的滑梳輥指伸出柵板對物料底部進行沖擊、梳刷實現根土分離,柵板上方的翻轉輥指的旋轉運動對物料側面有卷起、抬升作用,因兩輥同向旋轉,來自底部和側面的作用力產生翻轉力矩,使物料翻轉的同時,實現逐層脫土。因梳指的曲線結構,物料從接觸輥指到脫離輥指,會有一個明顯向上抬升的過程,此過程產生的慣性作用可以緩和梳指與虎杖粗根的沖擊;同時,減少與細根的相互勾連、扯拉,使物料的損傷、功耗都得到降低。梳指的結構特點,也使輥指在與物料接觸作用時有一個明顯向前推進的過程,此過程產生的慣性作用可使物料獲得沖擊、梳刷,實現根土分離;同時,使物料緊靠在翻轉輥上,更有利于物料翻轉。
圖1 虎杖根系脫土試驗裝置結構圖Fig.1 Structure diagram of roots-soil separating device of Polygonum cuspidatum
2.1 滑梳輥結構
滑梳輥為脫土核心部件,為保證滑梳效果,減小功耗,輥指軸向間距不易過密。同時,考慮物料個體大小差異及在機具上的作業(yè)空間,軸向布置了8排輥指;為保證輥指作業(yè)平穩(wěn),輥指周向布置排數應合理,過少會增大間歇作業(yè)沖擊,過多也使功耗增加,本文根據文獻[15]的前期試驗基礎,輥指周向布置4排,以軸向相鄰2排輥指為一組,軸向相鄰兩組輥指在圓周上錯開45°,結構如圖2所示。此類螺旋布置結構可使輥指交替作用在物料上,使根系滑梳脫土更為平穩(wěn),功耗更小。
圖2 滑梳輥總成結構圖Fig.2 Structure diagram of slide-combing roller
2.2 滑梳輥指梳刃曲線方程的建立
為使輥指與物料滑梳平穩(wěn),降低作業(yè)功耗,采用等
滑切角刃口曲線作為輥指的梳刃?;彷佇D中心為極坐標原點O,梳刃上的2點M、M'以及M在OM'上的投影E'所組成的三角形(如圖3所示),滿足公式(1)。
式中τ'為M'的極徑與割線MM'的夾角,(°);Δρ為M'與M的極徑之差,mm。
當M趨于M'時,該兩點的極角差Δθ趨于0,直線ME'趨近于弧ME,因此滑切角τ滿足公式(2)。
式中ρ為刃口任一點的極徑,mm;θ為梳刃任意兩點間的極徑夾角,(°)。由公式(2),解得梳刃等滑切角曲線的對數螺線方程為
式中ξ為積分常數。
圖3 滑梳輥指曲線分析Fig.3 Curve analysis of slide-combing roller finger
根據對數螺線方程的性質,隨著輥指長度(輥指根部到末端的曲線長度)的增加,曲率半徑逐漸增大,輥指末端越趨于直線。按輥指與物料接觸作用次序,接觸點由輥指曲線部分逐漸向直線部分過渡,此結構緩沖了直線輥指與物料的直接作用,有利于降低功耗、增強作業(yè)穩(wěn)定性。
2.3 輥指滑梳最小滑切角確定
物料受到滑梳輥指滑切作用時,更有利于緩沖與根系的直接沖擊,降低功耗,但相對于直輥指的砍切,曲線輥指的滑切弱化了脫土強度。因此,需合理確定的滑切角范圍,以保證脫土效果。
回轉中心O與輥指曲線上任意點D及該點處的曲率中心OD組成的三角形,如圖4所示。根據三角形正弦定理,滿足如下關系化簡得到
式中τ為D點的滑切角(梳刃上某點的速度矢量和梳刃曲線法平面之間的夾角[24]),(°);r1為滑梳輥指曲線上任意點D的曲率半徑,mm;α為回轉中心與輥指曲線任意點D及該點處曲率中心OD所成的直線夾角,(°);l為D點曲率中心與O點的距離,mm。
由式(5)得到最小滑切角公式為
圖4 滑梳輥指梳刃曲線Fig.4 Combing blade curve of slide-combing roller finger
將上述任意滑切角代入公式(6),得到l和r1的確定關系,遞增l值,可得到對應的r1值,l和r1又重新組建一個三角形,以此類推,通過對2組值組成的三角形簇進行旋轉描點擬合,可確定輥指的曲線形狀,如圖5所示。
圖5 滑梳輥指形狀曲線生成示意圖Fig.5 Spanning graph of curve of slide-combing roller finger
根據滑切理論,最小滑切角等于物料間的摩擦角,但虎杖根系為根土復合材料,具有各向異性特點,理論摩擦角應介于20°~36°[25-26](木與鋼、土與鋼摩擦角),為了深入探討滑切角對滑梳性能的影響,本機分別取摩擦角20°、25°、30°、35°采用圖5的方法設計出具有不同滑切角的4種滑梳輥指。在物料含水率、輥指回轉長度及轉速相同的情況下進行脫土試驗,借助高速攝像慢速回放功能量化輥指與根系勾連、扯拉發(fā)生的概率,發(fā)現滑切角超過30°時,物料在柵板上的脫土作業(yè)已相對平穩(wěn)。因此,針對中藥虎杖這種特殊的根土復合材料,選擇最小滑切角為30°即可實現鋼質輥指的滑梳脫土。
2.4 輥指滑梳最大滑切角確定
根據文獻論述的結論,隨滑切角遞增,功耗呈先小后大變化趨勢[27]。因此,需建立輥指滑梳功耗模型,尋找功耗轉換點,約束滑切角的遞增界限,進而確定輥指與物料作用的最大滑切角。
物料與滑梳輥指相互作用的受力如圖6所示。
圖6 滑梳輥指受力分析Fig.6 Force analysis of slide-combing roller finger
式中m為物料的質量,kg;g為重力加速度,m/s2;s為輥指長度,mm;φ是物料和輥指之間的摩擦角,(°);L為輥指根部到末端的曲線段。
輥指與物料作用時,對滑梳輥指回轉中心O,產生的總阻力矩Mr(N·m)為
式中dρ為輥指的有效擊打半徑,mm;r為輥的半徑,mm。聯立式(7)、(8)得到
單位時間產生的阻力功耗P滿足
由式(9)、(10),得到功耗P與摩擦角φ、滑切角τ以及轉速ω的函數關系
然而,通過常規(guī)代數方法,難以確定功耗與3個變量的關系,因此,采用數值解析方法,在轉速ω一定的情況下,依次求解各摩擦角和滑切角組合下的功耗,并通過Matlab軟件繪制出偽彩色能量圖,通過顏色差別反映功耗大小,其中功耗數值以扭矩Mr的具體數值與該轉速ω的乘積表達。如圖7所示,隨滑切角的逐漸增大,功耗呈現先減小后增大的變化趨勢,此趨勢與文獻[27]的結論一致。根據滑梳的臨界條件,當輥指與物料摩擦角為30°時,功耗最小所對應的滑切角為67°~77°,超過此范圍梳刷阻力雖可減小,但在滑梳過程中物料相對于梳刃滑過的路徑也相應增加,從而導致功耗有所上升;同時,相對而言較大的滑切角也弱化了輥指梳刃與物料的作用力,降低了脫土作業(yè)的效果。因此,滑切角取67o更有利于裝置作業(yè)性能。
圖7 功耗的偽彩色能量圖Fig.7 Pseudo-color energy figure about relationship among energy consumption, friction angle and slide-cutting angle
通過以上分析,根據最小滑切條件及功耗最小所對應的滑切角,可確定滑切角最小值為30°,最大值為67°,最優(yōu)滑切角設計應在此范圍內,即可獲得較好的脫凈率,又不至功率消耗過大。
3.1 試驗條件
試驗地點為華南農業(yè)大學工程試驗中心,試驗材料取自廣東省肇慶市懷集縣冷坑鎮(zhèn)虎杖種植基地。為適應脫土裝置和作業(yè)要求,試驗前去掉虎杖的莖葉,并將根塊分割成適當大??;為控制損傷率,參考文獻[15]的試驗方法,將滑梳輥轉速設定在580 r/min以下;同時,通過自然風嗮,使虎杖根系裹夾土壤的含水率在15%~20%之間,使之更有利于土壤松碎,實現根土分離[28]。
試驗設備為自行研制的虎杖根土分離試驗裝置,試驗樣機如圖8所示。脫土作業(yè)中承土盤放在輸土鏈桿上用于計收根系脫落土壤的質量,輥指的轉速由變頻調速系統控制,扭矩由安裝于試驗臺驅動軸上的扭矩傳感器測量(型號:ZRN503,量程:±0~200 N·m,電源:±15 VDC,輸出:10±5 kHz,北京中瑞能儀表技術有限公司)。
3.2 試驗方法與指標選取
3.2.1 試驗方法
根據滑梳輥指與物料作用分析,在翻轉輥轉速為200 r/min、作業(yè)時間為15 s的情況下,選取輥指轉速、輥指滑切角、輥指作業(yè)長度(滑梳輥指伸出柵板的最大長度)為試驗因素,并考慮各因素間的交互影響,采用有交互作用的正交試驗方法設計試驗,試驗因素與水平如表1所示。試驗中每60根虎杖為1組,數據取平均值,分別計算脫凈率Y1、功耗Y2。試驗時人工投放物料,通過變頻器調節(jié)電動機轉速,通過更換不同滑切角的輥指改變滑梳角度,通過調整柵板高度控制輥指作業(yè)長度。
表1 試驗因素及水平Table1 Experimental factors and levels
3.2.2 試驗指標選取
脫凈率為裝置脫去的土壤與投入裝置前根系所包裹土壤的質量百分比,計算方法為
式中Y1為根系脫凈率,%;W1為投入裝置的根土復合體總質量,kg;W2為經裝置脫土后含殘余土壤的根系總質量,kg;W3為不含土壤的根系質量,kg。
為減小空轉轉速差異引起的功耗誤差,實測功耗為在一定轉速下整機作業(yè)功耗與該轉速整機空轉功耗的差值。根據材料力學可知,功耗Y2(W)、扭矩M(N·m)和轉速nw(r/min)之間的關系為
3.3 結果與分析
試驗結果如表2所示,方差分析如表3所示。
表2 正交試驗結果Table2 Results of orthogonal experiment
表3 性能指標方差分析Table3 Variance analysis of performance indexes
方差分析表明:對于脫凈率指標,在95%的置信度下,輥指轉速和輥指作業(yè)長度影響極顯著,輥指滑切角度影響顯著,3個因素的交互項對脫凈率影響均不顯著。各因素對脫凈率影響由大到小依次是:輥指轉速>輥指作業(yè)長度>輥指滑切角>輥指轉速×輥指滑切角度>輥指轉速×輥指作業(yè)長度>輥指作業(yè)長度×輥指滑切角度。對于功耗指標,在95%的置信度下,輥指轉速、輥指滑切角度、輥指作業(yè)長度影響均極顯著,3個因素的交互項對功耗影響均不顯著。各因素對功耗影響由大到小依次是:輥指作業(yè)長度>輥指轉速>輥指滑切角>輥指轉速×輥指滑切角度>輥指轉速×輥指作業(yè)長度>輥指滑切角度×輥指作業(yè)長度。
3.3.2 多目標分析
為選取較優(yōu)的因素水平組合,需兼顧脫凈率以及功耗2個指標,因此采用模糊數學中的加權評分方法對2個指標進行綜合評價[29-30]。考慮到脫凈率和功耗2個指標的量綱不同,需對二者進行無量綱化處理,轉換為指標隸屬度值。
對于脫凈率指標,采用升半正態(tài)分布映射
式中μ1(y1i)是脫凈率的映射評分函數,值域為[0,1],y1i是第i次試驗脫凈率的值,%;y1max是試驗結果中脫凈率的最大值,%,y1min是試驗結果中脫凈率的最小值,%,脫凈率越大,評分越高。
對于功耗指標,采用降半正態(tài)分布映射
式中μ2(y2i)是功耗的映射評分函數,值域為[0,1],y2i是第i次試驗功耗的值,W;y2max是試驗結果中功耗的最大值,W,y2min試驗結果中功耗的最小值,W,功耗越低,評分越高。
2016年第39屆國際標準化組織大會,國家主席習近平以“標準是人類文明進步的成果”為題向大會的召開發(fā)表賀信。賀信說道“標準是人類文明進步的成果。從中國古代的‘車同軌、書同文’,到現代工業(yè)規(guī)?;a,都是標準化的生動實踐。伴隨著經濟全球化深入發(fā)展,標準化在便利經貿往來、支撐產業(yè)發(fā)展、促進科技進步、規(guī)范社會治理中的作用日益凸顯。標準已成為世界‘通用語言’。世界需要標準協同發(fā)展,標準促進世界互聯互通?!盵7]對于標準是人類文明進步的成果的新內涵論述,給出了標準及標準化概念內涵的新延伸,需要我們深入解讀兩種成果的關系。
根據式(14)和式(15)得到的隸屬度值,可構成模糊關系矩陣Rr
本試驗以脫凈率大,功耗小為目標,由性能指標重要性,確定權重分配集W =[w1w2]T=[0.6 0.4]T,每組試驗的綜合加權評分矩陣Z表示為
綜合評分結果為
將綜合評分結果進行方差和極差分析,結果如表4和表5所示。
表4 綜合評分方差分析Table4 Variance analysis of comprehensive evalualtion
表5 綜合評分極差分析Table5 Range analysis of comprehensive evalualtion
方差分析表明,在95%的置信度下,輥指轉速對綜合指標影響具有極顯著性,輥指作業(yè)長度、輥指滑切角度×輥指作業(yè)長度對綜合指標影響具有顯著性。極差分析表明,各因素對綜合指標影響由大到小依次是:輥指轉速>輥指作業(yè)長度>輥指滑切角度×輥指作業(yè)長度>輥指轉速×輥指作業(yè)長度>輥指轉速×輥指滑切角度>輥指滑切角度。通過比較3個因素各水平指標的大小,得到最優(yōu)參數組合為A3B3C1,即輥指轉速為350 r/min,滑切角為67°,作業(yè)長度為30 mm,此時脫凈率為93.03%,功耗為76.73 W。
1)設計了一種具有滑梳功能的輥指,有效緩和了輥指對物料的沖擊、糾纏,使虎杖根系根土分離作業(yè)更加平穩(wěn)、功耗更小。
2)根據滑切理論和試驗分析,確立了輥指與物料滑梳的臨界條件為滑切角大于30°,利用對數螺線方程建立輥指梳刃的曲線方程,通過動力學分析,建立了輥指作業(yè)的功耗模型,確定了影響作業(yè)功耗的主要因素為輥指轉速、輥指長度、輥指滑切角,并根據輥指滑梳的功耗模型,得到功耗最小所對應的滑切角為67°。
3)影響綜合指標的主次因素順序為:輥指轉速>輥指作業(yè)長度>輥指滑切角。最優(yōu)組合參數為:輥指轉速為350 r/min,滑切角為67°,輥指作業(yè)長度為30 mm。此時脫凈率為93.03%,功耗為76.73 W。
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Design and experiment of slide-combing roller finger for Polygonum cuspidatum root-soil separation
Chen Xueshen1, Ma Xu1,2※, Wu Tao1, Zeng Lingchao1, Li Kangyu1, Chen Lintao1
(1. College of Engineering, South China Agricultural University, Guangzhou 510642, China; 2. Key Laboratory of Key Technology on Agricultural Machine and Equipment(South China Agricultural University), Ministry of Education, Guangzhou 510642, China)
Root-soil separation is a critical link in Polygonum cuspidatum harvesting. It has been shown that combing machines are very useful for separating soil from root. However, it is a common occurrence during this process for Polygonum cuspidatum to be entangled by the machine, which leads to excessive energy consumption. In order to overcome the imperfections and defects of this kind of machine, a new roller finger for root-soil separation was designed. By applying the slide-cutting theory, the critical slide-cutting angle of the roller finger was calculated. Considering the friction coefficient between between Polygonum cuspidatum and roller finger, the slide-cutting angle was found to be more than 30°. By solving the differential equation and the logarithmic spiral equation, the curve equation of the roller finger was established in polar coordinates. With a mechanical model between Polygonum cuspidatum and roller finger set up, a function involving energy consumption, rotational speed of roller, length of roller finger and slide-cutting angle of the roller finger was obtained. It was found that the optimal slide-cutting angle varied in energy consumption with the difference of the coefficient of friction between Polygonum cuspidatum and roller finger. A pseudo-color energy figure about the relationship among consumption, angle of friction and angle of slide-cutting was shown with the MATLAB (Matrix Laboratory) software by the function derivation of the slide-cutting angle. It turned out that the optimal slide-cutting angle increased slowly as the coefficient of friction grew. Utilizing the curve, the maximal slide-cutting angle was obtained. The rotational speed of roller (Factor A), the slide-cutting angle (Factor B) and the length of roller finger (factor C) were selected as 3 factors of the orthogonal simulation experiment in order to explore their impact on the rate of soil-detachment and energy consumption. The priority order of the factors for the rate of soil-detachment was A > C > B > A×B > A×C > B×C, and that for the energy consumption was C > A >B > A×B > A×C > B×C. The rotational speed of roller and the length of roller finger had an extremely profound effect on the rate of soil-detachment while the slide-cutting angle had a profound effect on it. Meanwhile, those 3 factors also had an extremely profound effect on the energy consumption. Although the 3 factors performed differently on the rate of soil-detachment and energy consumption, by utilizing a fuzzy comprehensive evaluation method, a comprehensive evaluation on the results of the rate of soil-detachment and energy consumption was carried out by the multi-objective optimization design method. Results reflected the important differences between the rate of soil-detachment and energy consumption, and a weight matrix was set for fuzzy calculation. According to the comprehensive evaluation, the sequence of the influence of the factors on the comprehensive result was A > C > B×C > A×C > A×B > B, and the rotational speed of roller had an extremely profound effect on the comprehensive result while both the length of roller finger and the slide-cutting angle × length of roller finger had a profound effect on it. The results of fuzzy calculation showed that the optimal parameters were as follows: the rotational speed of roller of 350 r/min, the slide-cutting angle of 67°, and the length of roller finger of 30 mm, and under these conditions the rate of soil-detachment was 93.03% and the energy consumption was 76.73 W.
agricultural machinery; medicine; harvesting; root-soil separation; slide-cutting; combing; Polygonum cuspidatum
10.11975/j.issn.1002-6819.2017.05.007
S225
A
1002-6819(2017)-05-0048-08
陳學深,馬 旭,武 濤,曾令超,李康毓,陳林濤. 虎杖根系脫土滑梳式輥指的設計與試驗[J]. 農業(yè)工程學報,2017,33(5):48-55.
10.11975/j.issn.1002-6819.2017.05.007 http://www.tcsae.org
Chen Xueshen, Ma Xu, Wu Tao, Zeng Lingchao, Li Kangyu, Chen Lintao. Design and experiment of slide-combing roller finger for Polygonum cuspidatum root-soil separation[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2017, 33(5): 48-55. (in Chinese with English abstract) doi:10.11975/j.issn.1002-6819.2017.05.007 http://www.tcsae.org
2016-05-23
2016-12-20
國家自然科學基金資助項目(51175188)
陳學深,男,漢族,吉林省遼源人,博士,副教授,主要從事現代農業(yè)技術裝備研究。廣州 華南農業(yè)大學工程學院,510642。
Email:chenxs@scau.edu.cn.
※通信作者:馬 旭,男,漢族,黑龍江哈爾濱人,教授,博士生導師,主要從事現代農業(yè)技術裝備方面的研究。廣州 華南農業(yè)大學南方農業(yè)機械與裝備關鍵技術教育部重點實驗室,510642。Email:maxu1959@scau.edu.cn中國農業(yè)工程學會高級會員:馬 旭(E041200004S)