農(nóng)機(jī)機(jī)械外文翻譯--馬鈴薯播種機(jī)的性能評(píng)估

1、<p><b>　　中文5020字</b></p><p>　　本科畢業(yè)論文外文資料翻譯</p><p>　　系 別： </p><p>　　專 業(yè)： </p><p>　　姓 名：

2、 </p><p>　　學(xué) 號(hào)： </p><p>　　20** 年 03月 10 日</p><p><b>　　外文資料翻譯譯文</b></p><p>　　出處：Biosystems Engineering (2006) 95 (1), 35–41&l

3、t;/p><p>　　馬鈴薯播種機(jī)的性能評(píng)估</p><p>　　H. Buitenwerf1，W.B. Hoogmoed1，P. Lerink3， J. Muller</p><p>　　大多數(shù)馬鈴薯播種機(jī)都是通過勺型輸送鏈對(duì)馬鈴薯種子進(jìn)行輸送和投放。當(dāng)種植精度只停留在一個(gè)可接受水平的時(shí)候這個(gè)過程的容量就相當(dāng)?shù)?。主要的限制因素是：輸送帶的速度以及取薯勺的?shù)量和位置。假

4、設(shè)出現(xiàn)種植距離的偏差是因?yàn)槠x了統(tǒng)一的種植距離，這主要原因是升運(yùn)鏈?zhǔn)今R鈴薯播種機(jī)的構(gòu)造造成的.</p><p>　　一個(gè)理論的模型被建立來確定均勻安置的馬鈴薯的原始偏差，這個(gè)模型計(jì)算出兩個(gè)連續(xù)的馬鈴薯觸地的時(shí)間間隔。當(dāng)談到模型的結(jié)論時(shí)，提出了兩種假設(shè)，一種假設(shè)和鏈條速度有關(guān)，另一種假設(shè)和馬鈴薯的形狀有關(guān)。為了驗(yàn)證這兩種假設(shè)，特地在實(shí)驗(yàn)室安裝了一個(gè)種植機(jī)，同時(shí)安裝一個(gè)高速攝像機(jī)來測(cè)量?jī)蓚€(gè)連續(xù)的馬鈴薯在到達(dá)土壤表層時(shí)

5、的時(shí)間間隔以及馬鈴薯的運(yùn)動(dòng)方式。</p><p>　　結(jié)果顯示：（a）輸送帶的速度越大，播撒的馬鈴薯越均勻；（b）篩選后的馬鈴薯形狀并不能提高播種精度。</p><p>　　主要的改進(jìn)措施是減少導(dǎo)種管底部的開放時(shí)間，改進(jìn)取薯杯的設(shè)計(jì)以及其相對(duì)于導(dǎo)種管的位置。這將允許杯帶在保持較高的播種精度的同時(shí)有較大的速度變化空間。</p><p><b>　?。苯榻B說明

6、</b></p><p>　　升運(yùn)鏈?zhǔn)今R鈴薯種植機(jī)（圖一）是當(dāng)前運(yùn)用最廣泛的馬鈴薯種植機(jī)。每一個(gè)取薯勺裝一塊種薯從種子箱輸送到傳送鏈。這條鏈向上運(yùn)動(dòng)使得種薯離開種子箱到達(dá)上鏈輪，在這一點(diǎn)上，馬鈴薯種塊落在下一個(gè)取薯勺的背面，并局限于金屬導(dǎo)種管內(nèi).</p><p>　　在底部，輸送鏈通過下鏈輪獲得足夠的釋放空間使得種薯落入地溝里。</p><p>　　圖一

7、，杯帶式播種機(jī)的主要工作部件：（1）種子箱；（2）輸送鏈；（3）取薯勺；（4）上鏈輪；（5）導(dǎo)種管；（6）護(hù)種壁；（7）開溝器；（8）下鏈輪輪；（9）釋放孔；（10）地溝。</p><p>　　株距和播種精確度是評(píng)價(jià)機(jī)械性能的兩個(gè)主要參數(shù)。高精確度將直接導(dǎo)致高產(chǎn)以及馬鈴薯收獲時(shí)的統(tǒng)一分級(jí)(McPhee et al, 1996；Pavek & Thornton, 2003)。在荷蘭的實(shí)地測(cè)量株距（未發(fā)表的數(shù)

8、據(jù)）變異系數(shù)大約為20%。美國(guó)和加拿大早期的研究顯示，相對(duì)于玉米和甜菜的精密播種，當(dāng)變異系數(shù)高達(dá)69%(Misener, 1982；Entz & LaCroix, 1983；Sieczka et al, 1986)時(shí)，其播種就精度特別低。</p><p>　　輸送速度和播種精度顯示出一種逆相關(guān)關(guān)系，因此，目前使用的升運(yùn)鏈?zhǔn)椒N植機(jī)的每條輸送帶上都裝備了兩排取薯勺而不是一排。雙排的取薯勺可以使輸送速度加倍而且

9、不必增加輸送帶的速度。因此在相同的精度上具有更高的性能是可行的。</p><p>　　該研究的目的是調(diào)查造成勺型帶式種植機(jī)精度低的原因，并利用這方面的知識(shí)提出建議，并作設(shè)計(jì)上的修改。例如在輸送帶的速度、取薯杯的形狀和數(shù)量上。</p><p>　　為了便于理解，建立一個(gè)模型去描述馬鈴薯從進(jìn)入導(dǎo)種管到觸及地面這個(gè)時(shí)間段內(nèi)的運(yùn)動(dòng)過程，因此馬鈴薯在地溝的運(yùn)動(dòng)情況就不在考慮之列。由于物理因素對(duì)農(nóng)業(yè)設(shè)

10、備的強(qiáng)烈影響(Kutzbach, 1989)，通常要將馬鈴薯的形狀考慮進(jìn)模型中。</p><p>　　兩種零假設(shè)被提出來了：（1）播種精度和輸送帶速度無關(guān)；（2）播種精度和篩選后的種薯形狀（尤其是尺寸）無關(guān)。這兩種假設(shè)都通過了理論模型以及實(shí)驗(yàn)室論證的測(cè)試。</p><p><b>　?。膊牧霞胺椒?lt;/b></p><p><b>　　

11、播種材料</b></p><p>　　幾種馬鈴薯種子如圣特、阿玲達(dá)以及麻佛來都已被用于升運(yùn)鏈?zhǔn)讲シN機(jī)測(cè)試，因?yàn)樗鼈?lt;/p><p>　　有不同的形狀特征。對(duì)于種薯的處理和輸送來說，種薯塊莖的形狀無疑是一個(gè)很重要的因素。許多形狀特征在結(jié)合尺寸測(cè)量的過程中都能被區(qū)分出來(Du & Sun, 2004； Tao et al, 1995； Zödler, 1969)。

12、在荷蘭，馬鈴薯的等級(jí)主要是由馬鈴薯的寬度和高度（最大寬度和最小寬度）來決定的。種薯在播種機(jī)內(nèi)部的整個(gè)輸送過程中，其長(zhǎng)度也是一個(gè)不可忽視的因素。</p><p>　　形狀因子S的計(jì)算基于已經(jīng)提到的三種尺寸：</p><p>　　此處l是長(zhǎng)度，w是寬度，h是高度（單位：mm），且h<w<l。還有球形高爾夫球（其密度和馬鈴薯密度大致相同）作為參考。同是，在研究中用到的馬鈴薯的形狀特征

13、通過表一給出</p><p>　　表一 實(shí)驗(yàn)中馬鈴薯及高爾夫球的形狀特征</p><p>　　2.2 建立數(shù)學(xué)模型</p><p>　　數(shù)學(xué)模型的建立是為了預(yù)測(cè)升運(yùn)鏈?zhǔn)讲シN機(jī)的播種精度和播種性能，該模型考慮了滾軸的半徑和速度，取薯勺的尺寸和間距，以及它們相對(duì)于導(dǎo)種管壁的位置和地溝的高度（如圖二）。模型假設(shè)馬鈴薯在下落的過程中并沒有相對(duì)于取薯勺移動(dòng)或者相對(duì)于軸轉(zhuǎn)動(dòng)。

14、</p><p>　　圖二，模型模擬過程，當(dāng)取薯杯到達(dá)A點(diǎn)的時(shí)候模擬開始。釋放時(shí)間是開啟一個(gè)足夠大的空間讓土豆順利通過所需的時(shí)間。該模型同時(shí)也計(jì)算出兩個(gè)連續(xù)的馬鈴薯之間的時(shí)間間隔以及馬鈴薯到達(dá)地面（自由下落）的時(shí)間。rc 代表鏈輪半徑、帶的厚度以及取薯杯長(zhǎng)度之和；xclear ，取薯勺與導(dǎo)種管壁之間的間距；xrelease 釋放的間距；αrelease ，釋放角度；ω, 鏈輪的角速度；C點(diǎn)，地溝。</p&

15、gt;<p>　　田間作業(yè)速度和輸送帶速度可設(shè)定為達(dá)到既定的作物間距的要求。馬鈴薯離開導(dǎo)種管底部的頻率fpot 通過如下公式計(jì)算：</p><p>　　式中：vc 是勺型輸送帶的速度（單位：m s?1），xc 是帶上兩個(gè)取薯勺之間的距離（單位：m）.槽輪的角速度ωr（單位：rad s?1）計(jì)算如下：</p><p>　　導(dǎo)種管的間距必須足夠大以使得馬鈴薯能通過并被

16、釋放。xrelease是當(dāng)取薯勺以一定的角度αrelease徑向通過鏈輪時(shí)的時(shí)間間距。釋放角（圖二）按以下公式進(jìn)行計(jì)算：</p><p>　　rc（單位：m）是鏈輪半徑，鏈條的厚度以及取薯勺長(zhǎng)度之和；xclear（單位：m）是取薯勺端面與導(dǎo)種管管壁之間的間隙。</p><p>　　當(dāng)馬鈴薯的各種參數(shù)已確定的情況下，釋放馬鈴薯的所需角度可以通過計(jì)算得到。除了形狀和尺寸，護(hù)種壁的馬鈴薯的位置也

17、具有訣定性的作用，因此，這個(gè)模型區(qū)分了兩種狀態(tài)：（a）最小需求間距等于馬鈴薯的高度；（b）最大需求間距等于馬鈴薯的高度。</p><p>　　釋放角度αo所需的時(shí)間trelease的計(jì)算公式如下：</p><p>　　當(dāng)馬鈴薯釋放后，將直接落到地溝。由于每個(gè)馬鈴薯都是在一個(gè)特定的角度釋放的，通常那時(shí)都有一個(gè)高于地面的高度（圖二）。由于小一點(diǎn)的馬鈴薯釋放得早，因此通常將小塊馬鈴薯放在大塊馬鈴

18、薯的上方。</p><p>　　該模型計(jì)算出馬鈴薯剛好落到地溝時(shí)的速度υend（單位：m s?1）。假定垂直方向的初速度等于取薯勺線速度的垂直分量：</p><p>　　釋放高度的計(jì)算公式為：</p><p>　　yrelease=yr-rcsinαrelease</p><p>　　yr（單位：m）是鏈輪中心和地溝的距離</

19、p><p>　　自由下落時(shí)間的計(jì)算公式為：</p><p>　　g（9.8 m s?2）是自由落體加速度，v0（單位: m)是馬鈴薯釋放時(shí)垂直下落的初速度。終止速度的計(jì)算公式為：</p><p>　　馬鈴薯從A點(diǎn)移動(dòng)到釋放點(diǎn)的時(shí)間trelease還應(yīng)該加上tfall。該模型計(jì)算出以不同的方式在取薯勺上定位的兩個(gè)連續(xù)馬鈴薯之間的時(shí)間間隔。最大的誤差區(qū)間將出現(xiàn)在馬

20、鈴薯由縱向定位趨向軸向定位的過程中，反之亦然。</p><p><b>　　實(shí)驗(yàn)室裝置</b></p><p>　　一個(gè)標(biāo)準(zhǔn)的播種機(jī)可以替換片狀導(dǎo)種管底部的類似透明丙烯酸的材料（圖三）。輸送鏈通過鏈輪被變速電動(dòng)機(jī)驅(qū)動(dòng)，其速度可以通過一個(gè)旋轉(zhuǎn)的紅外檢測(cè)儀測(cè)得。此裝置只能觀察一排取薯勺。</p><p>　　實(shí)驗(yàn)室實(shí)驗(yàn)臺(tái)：片狀導(dǎo)種管底端的右下部被透

21、明的丙烯酸金屬片替代；右上端正對(duì)一個(gè)高速攝像機(jī)。</p><p>　　這個(gè)攝像機(jī)通過透明的導(dǎo)種管對(duì)種薯的運(yùn)動(dòng)進(jìn)行攝像記錄，并測(cè)量?jī)蓚€(gè)連續(xù)馬鈴薯之間的時(shí)間間隔。一張坐標(biāo)圖被安放在導(dǎo)種管的開口處，X軸平行于地面。當(dāng)種薯的中點(diǎn)通過地面的時(shí)候時(shí)間就被記錄下來了。連續(xù)種薯之間的時(shí)間間隔的標(biāo)準(zhǔn)偏差被用來衡量作物間距的精度。</p><p>　　為了便于測(cè)量，測(cè)量系統(tǒng)的記錄速率設(shè)置為1000幀每秒。平均

22、自由下落的速度是2.5 m s?1時(shí)，種薯每幀的移動(dòng)距離是2.5 mm，足夠小到可以記錄準(zhǔn)確的位置。</p><p>　　為了測(cè)試鏈速的影響，進(jìn)料速度被分別設(shè)置為300、400、500個(gè)種薯每分鐘。（fpot =5,6.7和8.3 s?1），對(duì)應(yīng)的鏈速為0.33,0.45,0.56（m s?1）。這些速度分別對(duì)應(yīng)的是3、2、1排取薯杯。每分鐘400個(gè)種薯的進(jìn)料率（0.45 m s?1

23、的杯帶速度）作為一個(gè)固定速度來對(duì)馬鈴薯形狀的影響進(jìn)行測(cè)評(píng)。</p><p>　　為了評(píng)估時(shí)間間隔的正態(tài)分布，30個(gè)種薯將被重復(fù)使用5次。在另一個(gè)測(cè)試中20個(gè)種薯將被重復(fù)使用3次。</p><p><b>　　2.4. 統(tǒng)計(jì)分析</b></p><p>　　對(duì)上述假設(shè)進(jìn)行了Fisher測(cè)試，分析表明：總體呈正態(tài)分布。尾部進(jìn)行單因素上限分析的Fis

24、her測(cè)試被用來檢驗(yàn)頻率a為5%第一類誤差，然而一個(gè)正確的零假設(shè)被錯(cuò)誤地拒絕了。其置信區(qū)間等于(100?a)%</p><p><b>　　3 結(jié)果與討論</b></p><p><b>　　3.1 輸送帶速度</b></p><p>　　3.1.1 實(shí)證結(jié)果</p><p>　　測(cè)得的連續(xù)種薯觸地

25、的時(shí)間間隔呈正態(tài)分布。進(jìn)料速度為300、400、500的標(biāo)準(zhǔn)偏差</p><p>　　σ分別為33.0、20.5、12.7 ms。通過F檢驗(yàn)可知進(jìn)料率的差異顯著。三種進(jìn)料率的正態(tài)</p><p>　　分布如圖四所示。當(dāng)變異系數(shù)分別為8.6%、7.1%和5.5%的時(shí)候，杯帶的速度越大則播種機(jī)的精度越高。</p><p>　　圖四，三種馬鈴薯進(jìn)料速率時(shí)間間隔的正態(tài)分布圖

26、</p><p>　　3.1.2 結(jié)果模型預(yù)測(cè)</p><p>　　圖五顯示了開口形成時(shí)間對(duì)升運(yùn)鏈速度的影響。鏈條的速度與沉積時(shí)偏離了時(shí)間間隔的種薯的準(zhǔn)確性呈線性關(guān)系。形成開口的時(shí)間越短，偏差越小。計(jì)算結(jié)果見表二：</p><p>　　表二 模型計(jì)算出來的連續(xù)種薯之間的時(shí)間間隔</p><p>　　升運(yùn)鏈脫離導(dǎo)種管壁的速度是很重要的一個(gè)因素

27、。相對(duì)提高輸送帶速來說，取薯勺線速度可以通過降低鏈輪的半徑來增大。實(shí)驗(yàn)中使用的鏈輪半徑是0.055米,是播種機(jī)的一般標(biāo)準(zhǔn)。為了使取薯勺的線速度達(dá)到最高的升運(yùn)鏈速度，鏈輪半徑必須通過最低的鏈條速度計(jì)算。由此得出種薯進(jìn)料率為每分鐘300個(gè)和400個(gè)的半徑分別為0.025米和0.041米。與此相比，實(shí)驗(yàn)室測(cè)量的結(jié)果是一條呈線性變化的直線，最大的半徑約為0.020米</p><p>　　數(shù)學(xué)模型預(yù)測(cè)的結(jié)果呈一種線性關(guān)系。

28、鏈輪的半徑和種薯沉積的精確度呈線性關(guān)系。該模型用來估計(jì)進(jìn)料率為每分鐘300個(gè)種薯的標(biāo)準(zhǔn)差。其結(jié)果如圖六所示，該模型的預(yù)測(cè)值與實(shí)測(cè)數(shù)據(jù)相比，其精度逐漸減小。顯然0.025米可能是技術(shù)上可行的最小半徑，相對(duì)于原來的半徑的標(biāo)準(zhǔn)差為75%。</p><p>　　圖六顯示了鏈輪半徑與沉積的種薯時(shí)間間隔標(biāo)準(zhǔn)差之間的關(guān)系。當(dāng)滿足r>0·01 m</p><p>　　時(shí)，這種關(guān)系是線性的。

29、● ，測(cè)量數(shù)據(jù)；，數(shù)學(xué)模型的數(shù)據(jù)； ■，延長(zhǎng)到R < 0 ? 01米； -，線性關(guān)系；R2，決定系數(shù)。</p><p>　　3.2 馬鈴薯的尺寸和形狀</p><p>　　實(shí)驗(yàn)數(shù)據(jù)由表三給出。顯示固定進(jìn)料率為每分鐘400個(gè)種薯的時(shí)間間隔的標(biāo)準(zhǔn)偏差。這</p><p>　　些結(jié)果與期望值剛好相反，即高的標(biāo)準(zhǔn)偏差將使得形狀因子增加。球狀馬鈴薯的結(jié)果尤其令人吃驚：球

30、的標(biāo)準(zhǔn)偏差高過阿玲達(dá)馬鈴薯50%以上。時(shí)間間隔的正態(tài)分布如圖七所示，球和馬鈴薯之間的差異明顯。兩個(gè)不同品種的馬鈴薯之間的差異不明顯。</p><p>　　表三 馬鈴薯品種對(duì)種植間距的精確度的影響</p><p>　　圖七，固定進(jìn)料率下不同形狀的沉積的馬鈴薯時(shí)間間隔的正態(tài)分布。</p><p>　　球狀馬鈴薯的這種結(jié)果是因?yàn)榍蚩梢砸圆煌姆绞皆谌∈砩妆巢慷ㄎ?。臨近杯

31、中球的不同定位導(dǎo)致沉積精度降低。杯帶的三維視圖顯示了取薯勺與導(dǎo)種管之間的間隔的形狀，顯然獲得不同大小的開放空間是可行的。</p><p>　　圖八，取薯勺呈45度時(shí)的效果圖；馬鈴薯在護(hù)種壁的位置對(duì)其釋放具有決定性影響。</p><p>　　阿玲達(dá)塊莖種薯在沉積時(shí)比麻佛來的精度高。通過對(duì)記錄的幀和馬鈴薯的分析，結(jié)果表明：阿玲達(dá)這種馬鈴薯總是被定位平行于最長(zhǎng)的軸線的護(hù)種壁。因此，除了形狀因子外

32、，寬度與高度的高比例值也將造成更大的偏差。阿玲達(dá)的這個(gè)比例是1.09，麻佛來的為1.15。</p><p>　　3.3 實(shí)驗(yàn)室對(duì)抗模型測(cè)試平臺(tái)</p><p>　　該數(shù)學(xué)模型預(yù)測(cè)了不同情況下的流程性能。相對(duì)于馬鈴薯，該模型對(duì)球模擬了更好的性能，然而實(shí)驗(yàn)測(cè)試的結(jié)果卻恰然相反。另外實(shí)驗(yàn)室試驗(yàn)是為了檢查模型的可靠性。</p><p>　　在該模型里，兩個(gè)馬鈴薯之間的時(shí)間間

33、隔被計(jì)算出來。起始點(diǎn)出現(xiàn)在馬鈴薯開始經(jīng)過A點(diǎn)的時(shí)刻，終點(diǎn)出現(xiàn)在馬鈴薯到達(dá)C點(diǎn)的時(shí)刻。通過實(shí)驗(yàn)平臺(tái)，從A到C點(diǎn)的馬鈴薯的時(shí)間間隔被測(cè)出。每個(gè)馬鈴薯的長(zhǎng)度、寬度和高度也通過測(cè)量獲得，同時(shí)記錄了馬鈴薯的數(shù)量。測(cè)量過程中馬鈴薯在取薯杯上的位置是已經(jīng)確定好的。這個(gè)位置和馬鈴薯的尺寸將作為模型的輸入量，測(cè)量過程將阿玲達(dá)與麻佛來以400個(gè)馬鈴薯每分的速率下進(jìn)行。測(cè)量時(shí)間間隔的標(biāo)準(zhǔn)偏差如表四所示。測(cè)量的標(biāo)準(zhǔn)誤差與模型的標(biāo)準(zhǔn)誤差只是稍稍不同。對(duì)這種不同現(xiàn)

34、象的解釋是：（1）模型并沒有把圖八中出現(xiàn)的情況考慮進(jìn)去；（2）從A點(diǎn)到C點(diǎn)的時(shí)間不一致。塊狀馬鈴薯如阿玲達(dá)可能從頂部或者最遠(yuǎn)距離下落，這將導(dǎo)致種薯到達(dá)C點(diǎn)底部的時(shí)間增加6ms</p><p>　　表四 通過實(shí)驗(yàn)室測(cè)量和模型計(jì)算出來的開放時(shí)間的標(biāo)準(zhǔn)誤差的差異</p><p><b>　　4. 總結(jié)</b></p><p>　　這個(gè)模擬馬鈴薯從輸

35、送帶開始釋放的運(yùn)動(dòng)的數(shù)學(xué)模型是一個(gè)非常有用的證實(shí)假設(shè)和設(shè)計(jì)實(shí)驗(yàn)平臺(tái)的工具。</p><p>　　模型和實(shí)驗(yàn)室的測(cè)試都表明：鏈速越高，馬鈴薯在零速度水平沉積得更均勻。這是由于開口足夠大使得馬鈴薯下降得越快，這對(duì)馬鈴薯的形狀和種薯在取薯杯上的定位有一定的影響，與鏈條速度的關(guān)系也就隨之明確，因此，在保持高的播種精度時(shí)，應(yīng)該提供更多的空間以減小鏈條的速度。建議降低鏈輪的半徑，直至低到技術(shù)上的可行度。</p>

36、<p>　　該研究顯示，播種機(jī)的取薯勺升運(yùn)鏈鏈對(duì)播種精度（播種的幅寬）有很大的影響。</p><p>　　更規(guī)格的形狀（形狀因子低）并不能自動(dòng)提高播種精度。小球（高爾夫球）在很多情況下沉積的精度低于馬鈴薯，這是由導(dǎo)向的導(dǎo)種管和取薯勺的形狀決定的。</p><p>　　因此建議重新設(shè)計(jì)取薯勺和導(dǎo)種管的形狀，要做到這一點(diǎn)還應(yīng)該將小鏈輪加以考慮。</p><p&g

37、t;<b>　　外文原文</b></p><p>　　Assessment of the Behaviour of Potatoes in a Cup-belt Planter</p><p>　　The functioning of most potato planters is based on transport and placement of the see

38、 potatoes by a cup-belt. The capacity of this process is rather low when planting accuracy has to stay at acceptable levels. The main limitations are set by the speed of the cup-belt and the number and positioning of the

39、 cups. It was hypothesized that the inaccuracy in planting distance, that is the deviation from uniform planting distances, mainly is created by the construction of the cup-belt planter. </p><p>　　To deter

40、mine the origin of the deviations in uniformity of placement of the potatoes atheoretical model was built. The model calculates the time interval between each successive potato touching the ground. Referring to the resul

41、ts of the model, two hypotheses were posed, one with respect to the effect of belt speed, and one with respect to the in?uence of potato shape. A planter unit was installed in a laboratory to test these two hypotheses. A

42、 high-speed camera was used to measure the time inte</p><p>　　The results showed that: (a) the higher the speed of the cup-belt, the more uniform is thedeposition of the potatoes; and (b) a more regular pota

43、to shape did not result in a higher planting accuracy. </p><p>　　Major improvements can be achieved by reducing the opening time at the bottom of the duct and by improving the design of the cups and its posi

44、tion relative to the duct. This will allow more room for changes in the cup-belt speeds while keeping a high planting accuracy. </p><p>　　1. Introduction </p><p>　　The cup-belt planter (Fig. 1)

45、 is the most commonly used machine to plant potatoes. The seed potatoes are transferred from a hopper to the conveyor belt with cups sized to hold one tuber. This belt moves upwards to lift the potatoes out of the hopper

46、 and turns over the upper sheave. At this point, the potatoes fall on the back of the next cup and are confined in a sheet-metal duct. At the bottom, the belt turns over the roller, creating the opening for dropping the

47、 potato into a furrow in the s</p><p>　　Capacity and accuracy of plant spacing are the main parameters of machine performance.High accuracy of plant spacing results in high yield and a uniform sorting of t

48、he tubers at harvest (McPhee et al., 1996; Pavek & Thornton, 2003). Field measurements (unpublished data) of planting distance in The Netherlands revealed a coefficient of variation (CV) of around 20%. Earlier studie

49、s in Canada and the USA showed even higher CVs of up to 69% (Misener, 1982; Entz & LaCroix, 1983; Sieczka et al., 1986</p><p>　　Travelling speed and accuracy of planting show an inverse correlation. Ther

50、efore, the present cup-belt planters are equipped with two parallel rows of cups per belt instead of one. Doubling the cup row allows double the travel speed without increasing the belt speed and thus, a higher capac

51、ity at the same accuracy is expected. </p><p>　　The objective of this study was to investigate the reasons for the low accuracy of cup-belt planters and to use this knowledge to derive recommendations for de

52、sign modifications, e.g. in belt speeds or shape and number of cups. </p><p>　　For better understanding, a model was developed, describing the potato movement from the moment the potato enters the duct up t

53、o the moment it touches the ground. Thus, the behaviour of the potato at the bottom of the soil furrow was not taken into account. As physical properties strongly in?uence the efficiency of agricultural equipment (Kutzba

54、ch, 1989), the shape of the potatoes was also considered in the model. </p><p>　　Two null hypotheses were formulated: (1) the planting accuracy is not related to the speed of the cup-belt; and (2) the planti

55、ng accuracy is not related to the dimensions (expressed by a shape factor) of the potatoes. The hypotheses were tested both theoretically with the model and empirically in the laboratory. </p><p>　　Fig 1.

56、 Working components of the cup-belt planter: (1) potatoes in hopper; (2) cup-belt; (3) cup; (4) upper sheave; (5) duct; (6) potato on back of cup; (7) furrower; (8) roller; (9) release opening; (10) ground level </p&

57、gt;<p>　　2 .Materials and methods</p><p>　　2.1. Plant material </p><p>　　Seed potatoes of the cultivars (cv.) Sante, Arinda and Marfona have been used for testing the cup-belt planter, be

58、cause they show different shape characteristics. The shape of the potato tuber is an important characteristic For handling and transporting. Many shape features, usually combined with size measurements, can be distinguis

59、hed (Du & Sun, 2004; Tao et al., 1995; Zodler,1969).In the Netherlands grading of potatoes is mostly done by using the square mesh size (Koning de et al.,1994),which</p><p>　　A shape factor S based on a

60、ll three dimensions was introduced: </p><p><b>　　(1)</b></p><p>　　Where/ is the length, w the width and h the height of the potato in mm, with h<w<l. As a reference, also sph

61、erical golf balls (with about the same density as potatoes), representing a shape factor S of 100 were used. Shape characteristics of the potatoes used in this study are given in Table 1. </p><p>　　表一 實(shí)驗(yàn)中馬鈴

62、薯及高爾夫球的形狀特征</p><p>　　2.2. Mathematical model of the process </p><p>　　A mathematical model was built to predict planting accuracy and planting capacity of the cup-belt planter. The model took in

63、to consideration radius and speed of the roller, the dimensions and spacing of the cups, their positioning with respect to the duct wall and the height of the planter above the soil surface (Fig. 2). It was assumed that

64、the potatoes did not move relative to the cup or rotate during their downward movement. </p><p>　　The field speed and cup-belt speed can be set to achieve the aimed plant spacing. The frequency fpot of potat

65、oes leaving the duct at the bottom is calculated as </p><p><b>　　(2)</b></p><p>　　where v c is the cup-belt speed in m s?1and xc is in the distance in m between the cups on the belt.

66、 The angular speed of the roller ωr in rad s?1 with radius r r in m is calculated as </p><p><b>　　(3)</b></p><p>　　The gap in the duct has to b e large enough for a potato to pass an

67、d be released .This gap xrelease in m is reached at a certain angle αrelease in rad of a cup passing the roller. This release angle αrelease (Fig.2) is calculated as </p><p>　　where: rc is the sum in m of t

68、he radius of the roller, the thickness of the belt and the length of the cup; and xclear is the clearance in m between the tip of the cup and the wall of the duct. </p><p>　　When the parameters of the potato

69、es are known, the angle required for releasing a potato can be calculated. Apart from its shape and size, the position of the potato on the back of the cup is determinative. Therefore, the model distinguishes two positio

70、ns: (a) minimum required gap, equal to the height of a potato; and (b) maximum required gap equal to the length of a potato. </p><p>　　The time trelease in s needed to form a release angle a0 is calculated a

71、s </p><p>　　Calculating trelease for different potatoes and possible positions on the cup yields the deviation from the average time interval between consecutive potatoes.</p><p>　　Combined with

72、 the duration of the free fall and the field speed of the planter, this gives the planting accuracy. </p><p>　　When the potato is released, it falls towards the soil surface. As each potato is released on a

73、unique angular position, it also has a unique height above the soil surface at that moment (Fig. 2). A small potato will be released earlier and thus at a higher point than a large one. </p><p>　　The model

74、calculates the velocity of the potato just before it hits the soil surface υend in m s?1 The initial vertical velocity of the potato vo in m s is assumed to equal the vertical component of the track speed of the tip of t

75、he cup: </p><p>　　The release height yrelease in m is calculated as</p><p>　　yrelease=yr-rcsinαrelease</p><p>　　Where yr in m is the distance between the centre of the roller (line

76、A in Fig.2) and the soil surface.</p><p>　　The time of free fall tfall in s is calculated with</p><p>　　where g is the gravitational acceleration(9.8ms-2) and the final velocity vend is calculat

77、ed as</p><p>　　with vo in ms-1 being the vertical downward speed of the potato at the moment of release.</p><p>　　The time for the potato to move from Line A to the release point trelease has to

78、 be added to t fall. </p><p>　　The model calculates the time interval between two consecutive potatoes that may be positioned in different ways on the cups. The largest deviations in intervals will occur whe

79、n a potato positioned lengthwise is followed by one positioned heightwise, and vice versa.</p><p>　　Fig. 2. Process simulated by model, simulation starting when the cup crosses line A; release time represen

80、ts time needed to create an opening sufficiently large for a potato to pass; model also calculates time between release of the potato and the moment it reaches the soil surface (free fall); r c, sum of the radius of the

81、roller, thickness of the belt and length of the cup; xclear, clearance between cup and duct wall; xrelease , release clearance; xrelease release angle ;w,angular speed of ro</p><p>　　2.3. The laboratory arra

82、ngement </p><p>　　A standard planter unit (Miedema Hassia SL 4(6)) was modified by replacing part of the bottom end of the sheet metal duct with similarly shaped transparent acrylic material (Fig. 3). The cu

83、p-belt was driven via the roller (8 in Fig. 1), by a variable speed electric motor. The speed was measured with an infrared revolution meter. Only one row of cups was observed in this arrangement. </p><p>　　

84、A high-speed video camera (SpeedCam Pro, Wein- berger AG, Dietikon, Switzerland) was used to visualise the behaviour of the potatoes in the transparent duct and to measure the time interval between consecutive potatoes.

85、A sheet with a coordinate system was placed behind the opening of the duct, the X axis representing the ground level. Time was registered when the midpoint of a potato passed the ground line. Standard deviation of the ti

86、me interval between consecutive potatoes was used as measure</p><p>　　For the measurements the camera system was set to a recording rate of 1000 frames per second. With an average free fall velocity of 2.5

87、 m s -1,the potato moves approx 2.5 mm between two frames, sufficiently small to allow an accurate placemen registration. </p><p>　　The feeding rates for the test of the effect of the speed of the belt were

88、set at 300, 400 and 500 potatoes min-1(fpot=5,6.7and8.3s-1) corresponding to belt speeds of 0.33,.0.45 and 0.56ms-1. These speeds would be </p><p>　　Typical for belts with 3, 2 and 1 rows of cups, (cup-belt

89、 speed of 0.45 m s -1) was used to assess the effect of the potato shape. </p><p>　　For th assessment of a normal distribution of the time intervals, 30 potatoes in five repetitions were used. In the other

90、 tests, 20 potatoes in three repetitions were used. </p><p>　　2.4. Statistical analysis </p><p>　　The hypotheses were tested using the Fisher test, as analysis showed that populations were norma

91、lly distributed. The one-sided upper tail Fisher test was used</p><p>　　and a was set to 5% representing the probability of a type 1 error, where a true null hypothesis is incorrectly rejected. The confiden

92、ce interval is equal to (100_a)%. </p><p>　　Fig.3. Laboratory test-rig; lower right—part of the bottom end of the sheet metal duct was replaced with transparent acrylic sheet; upper right—segment faced by th

93、e high-speed camera</p><p>　　3. Results and discussion </p><p>　　3.1. Cup-belt speed </p><p>　　3.1.1. Empirical results </p><p>　　The measured time intervals between c

94、onsecutive potatoes touching ground showed a normal distribution. Standard deviations s for feeding rates 300, 400 and 500 potatoes min-1were 33_0, 20_5 and 12_7 ms, respectively.</p><p>　　According to the F

95、-test the differences between feeding rates were significant. The normal distributions for all three feeding rates are shown in Fig. 4. The accuracy of the planter is increasing with the cup-belt speed, with CVs of 8.6%,

96、 7.1% and 5.5%, respectively. </p><p>　　3.1.2. Results predicted by the model </p><p>　　Figure 5 shows the effect of the belt speed on the time needed to create a certain opening. A linear relat

97、ionship was found between cup-belt speed and the accuracy of the deposition of the potatoes expressed as deviation from the time interval. The shorter the time needed for creating the opening, the smaller the deviations.

98、 Results of these calculations are given in Table 2. </p><p>　　The speed of the cup turning away from the duct wall is important Instead of a higher belt speed, an increase of the cup's circumferential s

99、peed can be achieved by decreasing the radius of the roller. The radius of the roller used in the test is 0.055 m, typical for these planters. It was calculated what the radius of the roller.</p><p>　　Fig.

100、4. Normal distribution of the time interval (x, in ms) of deposition of the potatoes (pot) for three feeding rates.</p><p>　　Fig.5. Effect of belt speed on time needed to create opening</p>

101、<p><b>　　Table 2 </b></p><p>　　Time intervals between consecutive potatoes calculated by the model (cv. Marfona)</p><p>　　Fig6. Relationship between the radius of the roller and

102、 the standard deviation of the time interval of deposition of the potatoes; the relationship is linear for radii r>0.01 m, ● measurement data; ▲data from mathematica model; ■,extended for r<0.01 m; —, linear rela

103、tionship; R2 , coefficient of determination </p><p>　　had to be for lower belt speeds, in order to reach the same circumferential speed of the tip of the cup as found for the highest belt speed. This result