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板栗收獲拍打式落果裝置設(shè)計(jì)與試驗(yàn)

2021-11-24 10:02宗望遠(yuǎn)黃木昌肖洋軼鄧丁霖
關(guān)鍵詞:搖桿曲柄落果

宗望遠(yuǎn),黃木昌,肖洋軼,李 茂,鄧丁霖

?農(nóng)業(yè)裝備工程與機(jī)械化?

板栗收獲拍打式落果裝置設(shè)計(jì)與試驗(yàn)

宗望遠(yuǎn)1,2,黃木昌1,肖洋軼1,2,李 茂1,鄧丁霖1

(1. 華中農(nóng)業(yè)大學(xué)工學(xué)院,武漢 430070;2. 農(nóng)業(yè)農(nóng)村部長(zhǎng)江中下游農(nóng)業(yè)裝備重點(diǎn)實(shí)驗(yàn)室,武漢 430070)

針對(duì)板栗人工收獲效率低、高空落果易傷人等問(wèn)題,該研究設(shè)計(jì)了一種板栗收獲拍打式落果裝置。裝置采用無(wú)急回特性的搖桿機(jī)構(gòu),建立拍打搖桿的角位移、角速度和角加速度運(yùn)動(dòng)學(xué)方程,進(jìn)行動(dòng)力學(xué)數(shù)值仿真。通過(guò)板栗樹果實(shí)與樹枝的分離力試驗(yàn),得出不同拉力角的分離力變化規(guī)律,0°~90°,隨著拉力角的增大分離力逐漸減小,拉力角為0°時(shí)最大分離力為65.24 N。對(duì)4種常用材料的拍打條分別進(jìn)行三因素三水平正交試驗(yàn)。結(jié)果表明,聚氨酯材料的拍打力小于板栗與樹枝的分離力,鐵片和玻璃纖維拍打力滿足要求但作用力過(guò)大容易損傷板栗樹枝,最佳拍打條材料為低密度聚乙烯,最優(yōu)組合為電機(jī)轉(zhuǎn)速600 r/min、拍打條長(zhǎng)度350 mm、拍打角度20°,此時(shí)拍打力大小為70.71 N。田間試驗(yàn)結(jié)果表明,該落果裝置能有效采摘板栗果實(shí),平均落果率為90.5%,且對(duì)板栗樹枝損傷較小。該設(shè)計(jì)滿足板栗果實(shí)的采摘要求,對(duì)板栗收獲機(jī)的研發(fā)提供了理論依據(jù)。

農(nóng)業(yè)機(jī)械;收獲;板栗;落果裝置;數(shù)值仿真;分離力;拍打

0 引 言

板栗中富含淀粉,還有蛋白質(zhì)、脂肪、B族維生素等多種營(yíng)養(yǎng)物質(zhì),素有“干果之王”的美稱。中國(guó)是板栗第一生產(chǎn)大國(guó),種植面積和產(chǎn)量均居世界第一,到2020年,中國(guó)板栗種植面積達(dá)183.24萬(wàn)hm2,產(chǎn)量為214.91萬(wàn) t[1-3]。國(guó)內(nèi)板栗種植主要分布在丘陵山地,其中湖北是板栗主產(chǎn)區(qū)之一,湖北羅田板栗于2007年被國(guó)家質(zhì)量監(jiān)督檢驗(yàn)檢疫總局認(rèn)定為地理標(biāo)志產(chǎn)品[4]。在當(dāng)前國(guó)家糧食安全戰(zhàn)略背景下,提高板栗生產(chǎn)機(jī)械化水平對(duì)促進(jìn)板栗果實(shí)深加工產(chǎn)業(yè)發(fā)展具有重要現(xiàn)實(shí)意義[5-6]。

板栗收獲主要通過(guò)落果收集與掛果采摘2種方法完成[7-9]。落果收集法是待板栗果實(shí)完熟后自然落地,再人工撿拾收集,或使用簡(jiǎn)易的機(jī)械設(shè)備輔助撿拾收集。此種方法操作簡(jiǎn)便,但果實(shí)落地太久易脫水風(fēng)干,影響其品質(zhì)和儲(chǔ)藏時(shí)間。掛果采摘是在板栗成熟期采用外力擊打或振動(dòng)作用實(shí)現(xiàn)落果,再人工或機(jī)械撿拾收集。國(guó)內(nèi)板栗機(jī)械收獲研究還處于起步階段,相關(guān)研究包括便攜式堅(jiān)果采摘機(jī)的設(shè)計(jì)[10],其操作簡(jiǎn)單,但勞動(dòng)強(qiáng)度高。板栗落果裝置研究可參考其他林果采摘機(jī)械經(jīng)驗(yàn),國(guó)外類似研究包括Rezaei等[11]設(shè)計(jì)的氣動(dòng)執(zhí)行器,可短時(shí)間收獲杏仁;Larbi等[12]設(shè)計(jì)的櫻桃收獲機(jī),能通過(guò)末端執(zhí)行器快速撞擊樹干實(shí)現(xiàn)果實(shí)脫落;此外,橄欖、開心果和草莓等皆可通過(guò)相應(yīng)機(jī)械設(shè)備實(shí)現(xiàn)高效率收獲[13-15]。國(guó)內(nèi)果樹以丘陵山地種植模式居多,相較于國(guó)外平原種植模式,國(guó)內(nèi)機(jī)械采摘發(fā)展較緩慢[16-17],饒洪輝等[18]設(shè)計(jì)的液壓驅(qū)動(dòng)式油茶果采摘機(jī),伍德林等[19]設(shè)計(jì)的搖枝式油茶果采摘機(jī),采摘機(jī)構(gòu)都較為靈活,在提高收獲效率的同時(shí)還能降低花苞損傷率;陳軍等[20]設(shè)計(jì)的振刷式枸杞采收機(jī),可完成枸杞高效收獲;王克奇等[21]設(shè)計(jì)的擊打式松果采摘機(jī)器人,可實(shí)現(xiàn)復(fù)雜林間環(huán)境下對(duì)松果精準(zhǔn)采摘;徐麗明等[22]設(shè)計(jì)的臍橙采摘機(jī)器人末端執(zhí)行器可滿足無(wú)損采摘的要求,且采摘機(jī)器人智能化程度較高。

針對(duì)板栗果實(shí)帶刺、落果易傷人、采摘難度較大等問(wèn)題,結(jié)合現(xiàn)有采摘機(jī)械的研究現(xiàn)狀,本文設(shè)計(jì)了一種板栗收獲拍打式落果裝置,適于丘陵山地等復(fù)雜地區(qū)板栗采收,以期為板栗收獲機(jī)械研制提供有力支撐。

1 整機(jī)結(jié)構(gòu)與工作原理

1.1 整機(jī)結(jié)構(gòu)

板栗收獲機(jī)基本結(jié)構(gòu)如圖1所示,主要由履帶底盤、電器控制箱、升降液壓臺(tái)、定位結(jié)構(gòu)、落果裝置和電源等組成。落果裝置安裝于定位結(jié)構(gòu)前端,用于采收板栗果實(shí);電器控制箱內(nèi)裝有控制器,可實(shí)現(xiàn)手動(dòng)或遙控操作;定位結(jié)構(gòu)通過(guò)安裝板固定在升降液壓臺(tái)上,主要由電機(jī)、電動(dòng)推桿和伸縮架組成,可帶動(dòng)落果裝置在6個(gè)自由度上運(yùn)動(dòng)。升降液壓臺(tái)固定在履帶底盤上,通過(guò)液壓驅(qū)動(dòng)帶動(dòng)工作部件上下移動(dòng),最高作業(yè)高度可達(dá)8 m。

履帶底盤有高速、低速和倒擋3個(gè)檔位,最大爬坡角度為35°,最小轉(zhuǎn)彎半徑為1.1 m,丘陵山地板栗種植地區(qū)地面坡度多為6°~25°,種植間距為3~5 m,因此板栗收獲機(jī)可以在板栗種植地區(qū)正常行駛;履帶底盤上裝有柴油機(jī)、液壓泵和電源等供能設(shè)備,底盤上方的支撐架用于支撐非工作狀態(tài)下的定位結(jié)構(gòu),可增強(qiáng)機(jī)器在行走過(guò)程中的平穩(wěn)性,底盤兩邊用于支持地面的4個(gè)螺旋桿用于保證整體機(jī)器在作業(yè)時(shí)的穩(wěn)定性。板栗收獲機(jī)主要作業(yè)參數(shù)如表1所示。

表1 板栗收獲機(jī)主要作業(yè)參數(shù)

1.2 工作原理

在采摘過(guò)程中,板栗收獲機(jī)行駛至采收地點(diǎn),對(duì)于不平整的工作地面,需將機(jī)身兩側(cè)4根螺旋桿支撐于地面,保證其在工作過(guò)程中的穩(wěn)定性。升降液壓臺(tái)與定位結(jié)構(gòu)協(xié)調(diào)作業(yè)實(shí)現(xiàn)落果裝置的移動(dòng),調(diào)節(jié)電機(jī)轉(zhuǎn)速,使落果裝置達(dá)到工作所需拍打頻率,在避免損傷板栗樹枝的情況下對(duì)板栗果實(shí)及樹枝不斷擊打。板栗果實(shí)主要通過(guò)2種情況脫離樹枝:當(dāng)拍打部件擊中果實(shí)時(shí)可直接將拍打力傳遞給果實(shí),若拍打力大于果實(shí)與樹枝的結(jié)合力,果實(shí)脫離樹枝;當(dāng)拍打部件擊中樹枝時(shí),樹枝受迫振動(dòng)給果實(shí)傳遞一個(gè)慣性力,若慣性力大于結(jié)合力時(shí)板栗也會(huì)脫離樹枝,從而實(shí)現(xiàn)采摘。

2 采收機(jī)關(guān)鍵部件設(shè)計(jì)

2.1 拍打機(jī)構(gòu)

拍打機(jī)構(gòu)是落果裝置在板栗收獲環(huán)節(jié)中實(shí)現(xiàn)板栗落果的關(guān)鍵部件,如圖2a所示,拍打機(jī)構(gòu)主要包括直角架、電機(jī)、聯(lián)軸器、箱體結(jié)構(gòu)、拍打條等結(jié)構(gòu)。電機(jī)和箱體結(jié)構(gòu)安裝在直角架上,兩者通過(guò)聯(lián)軸器連接;箱體內(nèi)部結(jié)構(gòu)如圖2b所示,由搖桿、連桿、銷、軸、偏心塊和軸承座等組成,偏心塊通過(guò)軸承座安裝于軸兩端,其上有與電機(jī)連接軸相偏置的安裝孔,安裝孔偏置距離即曲柄長(zhǎng)度;軸安裝于偏心塊安裝孔上,連桿一端連接在軸上,另一端通過(guò)銷連接搖桿,搖桿另一端安裝于箱體結(jié)構(gòu)鉸接處。箱體結(jié)構(gòu)兩側(cè)通過(guò)曲柄搖桿機(jī)構(gòu)組成一對(duì)可往復(fù)運(yùn)動(dòng)的拍打部件,共設(shè)計(jì)3對(duì)拍打部件,拍打條用螺栓固定于搖桿末端,工作時(shí),偏心塊在電機(jī)的驅(qū)動(dòng)下轉(zhuǎn)動(dòng),從而帶動(dòng)拍打條運(yùn)動(dòng),實(shí)現(xiàn)拍打功能。

2.2 無(wú)急回特性的曲柄搖桿機(jī)構(gòu)設(shè)計(jì)

拍打機(jī)構(gòu)工作條件為高空作業(yè),機(jī)構(gòu)運(yùn)動(dòng)的穩(wěn)定性需保證機(jī)器整體的性能要求,故設(shè)計(jì)一種無(wú)急回特性的曲柄搖桿機(jī)構(gòu),要求在運(yùn)動(dòng)時(shí)左右搖桿可滿足同時(shí)到達(dá)拍打最高點(diǎn)和最低點(diǎn)。結(jié)構(gòu)示意圖如圖3a所示。

對(duì)于上述成對(duì)存在的無(wú)急回特性曲柄搖桿機(jī)構(gòu),由于結(jié)構(gòu)呈對(duì)稱性,選其一側(cè)設(shè)計(jì)即可。其機(jī)構(gòu)簡(jiǎn)圖如圖 3b所示,搖桿在運(yùn)動(dòng)時(shí),到達(dá)1和2兩個(gè)極限位置,1和2的延長(zhǎng)線1和2所掃射的角度即裝置拍打板栗的范圍。曲柄1與2的極限位置夾角為0°,此時(shí)2、1、2、、1點(diǎn)在一條線上,能夠保證兩側(cè)搖桿同時(shí)到達(dá)最上和最下2個(gè)極限位置,同時(shí)這條直線與箱體側(cè)面平行,以此滿足拍打條以相同的角度沿上下方向運(yùn)動(dòng)。

1.曲柄 2.機(jī)架 3.連桿 4.搖桿

1. Crank 2. Frame 3. Connecting rod 4. Rocker

a. 搖桿上下極限位置運(yùn)動(dòng)簡(jiǎn)圖

a. Rocker upper and lower limit position motion diagram

注:、、、為曲柄搖桿機(jī)構(gòu)連接點(diǎn);為搖桿延伸點(diǎn);為機(jī)架水平投影方向與豎直投影方向的交點(diǎn);1、2為曲柄的極限位置點(diǎn);1、2為搖桿的極限位置點(diǎn);1、2為搖桿延伸方向的極限位置點(diǎn);1為曲柄長(zhǎng)度,mm;2為連桿長(zhǎng)度,mm;3為搖桿長(zhǎng)度,mm;4為機(jī)架長(zhǎng)度,mm;為機(jī)架水平方向投影長(zhǎng)度,mm;為曲柄角速度,rad·s-1;為搖桿擺角,(°);為傳動(dòng)角,(°)。 Note:、、、are the connecting points of the crank-rocker mechanism;is the extension point of the rocker;is the intersection of the horizontal projection and vertical projection directions for the frame;1、2are the limit positions of the crank;1、2are the limit positions of the rocker;1、2are the limit positions of the extension direction of the rocker;1is the length of the crank, mm;2is the length of the connecting rod, mm;3is the length of the rocker, mm;4is the length of the frame, mm.is a projection length of the rack horizontal direction, mm;is the angular velocity of the crank, rad·s-1;is the swing angle of rocker, (°);is the transmission angle, (°).

b. 無(wú)急回特性曲柄搖桿機(jī)構(gòu)結(jié)構(gòu)簡(jiǎn)圖

b. Structural diagram of crank rocker mechanism without quick return characteristics

圖3 搖桿極限位置和無(wú)急回特性曲柄搖桿機(jī)構(gòu)示意圖

Fig.3 Limit positions of the rocker and schematic diagram of crank rocker mechanism without quick return characteristics

根據(jù)無(wú)急回特性曲柄搖桿機(jī)構(gòu)特性[23]可得:

2.2.1 曲柄長(zhǎng)度1和搖桿長(zhǎng)度3的確定

由于機(jī)架上鉸接孔是在箱體外側(cè),考慮到加工箱體結(jié)構(gòu)的壁厚以及鉸接孔與箱體側(cè)面的預(yù)留間隙,取鉸接孔到箱體內(nèi)側(cè)的長(zhǎng)度為,mm;為避免曲柄1在運(yùn)動(dòng)過(guò)程中干涉箱體內(nèi)側(cè),應(yīng)有:

為了使裝置在工作中有較好的拍打效果,需在保證結(jié)構(gòu)強(qiáng)度以及裝置在移動(dòng)過(guò)程中的靈活性,同時(shí)保證結(jié)構(gòu)的輕量化,本文取1=11 mm,=8 mm,由此可得擺角為

由式(3)解得<60.1°,取=60°,由式(1)得搖桿長(zhǎng)度3= 22 mm。

2.2.2 連桿長(zhǎng)度2和機(jī)架長(zhǎng)度4的確定

在曲柄搖桿機(jī)構(gòu)中,傳動(dòng)角用來(lái)衡量機(jī)構(gòu)的傳力性能,許用傳動(dòng)角[]一般為40°~50°[24],而最小傳動(dòng)角要大于許用傳動(dòng)角[]才能發(fā)揮機(jī)器的傳動(dòng)性能,值越大,代表傳力性能越好。在無(wú)急回運(yùn)動(dòng)的情況下,最小傳動(dòng)角min出現(xiàn)在曲柄與機(jī)架連線重合的2個(gè)位置上,且2位置傳動(dòng)角相等,結(jié)合公式(1)有如下關(guān)系式[25]:

3 拍打機(jī)構(gòu)仿真分析

落果裝置在采收過(guò)程中拍打機(jī)構(gòu)穩(wěn)定運(yùn)動(dòng)能減小采收機(jī)振動(dòng),提高機(jī)械整體性能;故本文還需進(jìn)一步分析拍打機(jī)構(gòu)曲柄搖桿機(jī)構(gòu)的運(yùn)動(dòng)規(guī)律,并對(duì)搖桿進(jìn)行運(yùn)動(dòng)學(xué)仿真,分析其在不同轉(zhuǎn)速下的性能。

3.1 運(yùn)動(dòng)規(guī)律分析

注:1為曲柄角位移,rad;2為連桿角位移,rad;3為搖桿角位移,rad。

Note:1is the angular displacement of the crank, rad;2is the angular displacement of the connecting rod, rad;3is the angular displacement of the rocker, rad.

圖5 曲柄搖桿機(jī)構(gòu)矢量圖

Fig.5 Vector diagram of crank-rocker mechanism

根據(jù)式(5)在軸和軸上的投影可得:

角位移分析:

由式(6)可得:

將三角函數(shù)式:

由此解得:

角速度分析:

將式(5)對(duì)時(shí)間求導(dǎo),得到:

式中1為曲柄角速度,rad/s;3為搖桿角速度,rad/s;類似求得:

式中2為連桿角速度,rad/s。

角加速度分析

將式(12)對(duì)時(shí)間再次求導(dǎo)得:

式中3為搖桿運(yùn)動(dòng)角加速度,rad/s2;類似求得2為:

式中2為連桿運(yùn)動(dòng)角加速度,rad/s2。

3.2 運(yùn)動(dòng)學(xué)仿真分析

為得到搖桿運(yùn)動(dòng)過(guò)程中的規(guī)律,使用ADAMS仿真軟件對(duì)其進(jìn)行仿真分析。由于三對(duì)曲柄搖桿機(jī)構(gòu)運(yùn)動(dòng)的一致性,選擇其中一對(duì)分析即可,本文為了分析簡(jiǎn)便,建模時(shí)將軸承座與箱體簡(jiǎn)化為一個(gè)整體。箱體添加固定副,偏心塊與箱體連接使用旋轉(zhuǎn)副,偏心塊與軸使用恒速副,連桿與軸使用旋轉(zhuǎn)副,連桿與搖桿、搖桿與箱體鉸接孔分別添加旋轉(zhuǎn)副,在偏心塊輸出軸上添加旋轉(zhuǎn)驅(qū)動(dòng)。

由于在實(shí)際板栗采收中,300 r/min以下拍打效果不佳,而大于600 r/min拍打機(jī)構(gòu)振動(dòng)效果較為明顯,故在300~600 r/min的轉(zhuǎn)速內(nèi)分析搖桿運(yùn)動(dòng)較為合適;設(shè)定分析時(shí)間為0.5 s,仿真步數(shù)為500步,通過(guò)改變偏心塊的輸出軸轉(zhuǎn)速,在300、450、600 r/min的條件下分析搖桿的運(yùn)動(dòng)曲線。

表2 仿真分析主要結(jié)果

通過(guò)圖6a搖桿角速度和圖6b搖桿加速度曲線圖分析可得,搖桿在運(yùn)動(dòng)過(guò)程中角速度和角加速度的最大值隨轉(zhuǎn)速的增大不斷增大;結(jié)合表2數(shù)據(jù),在同一轉(zhuǎn)速下,左右兩側(cè)搖桿所能達(dá)到的角速度和角加速度最大值基本一致,且在不同轉(zhuǎn)速下,運(yùn)動(dòng)規(guī)律對(duì)稱,說(shuō)明兩側(cè)搖桿運(yùn)動(dòng)的一致性,表明設(shè)計(jì)合理,滿足落果裝置工作過(guò)程中的穩(wěn)定性要求。因?yàn)閾u桿在不同轉(zhuǎn)速下的上下極限位置角位移基本不變,通過(guò)圖6c分析可得兩側(cè)搖桿擺角分別為60.1°和60.2°,且上下極限角度與30°偏差很小,表明在實(shí)際板栗收獲中拍打條上下拍打角度為60°。

4 板栗果實(shí)與樹枝的分離力測(cè)量

4.1 試驗(yàn)設(shè)備與方法

為獲取板栗樹果實(shí)與樹枝的分離力,2020年9月份在湖北省孝感安陸市孛畈鎮(zhèn)板栗園對(duì)板栗果實(shí)與樹枝的分離力進(jìn)行了測(cè)量。測(cè)力設(shè)備采用數(shù)顯拉力計(jì)(型號(hào):ELK-300,量程:0~300 N,精度±0.5%),測(cè)量位置為果實(shí)與果柄連接處,選擇果實(shí)數(shù)量較多的板栗樹,由于落果裝置拍打時(shí)板栗果實(shí)主要沿著果實(shí)生長(zhǎng)方向0°~90°脫落,故選擇沿著板栗果實(shí)生長(zhǎng)0°、45°和90°三個(gè)拉力角方向進(jìn)行測(cè)量[26],每個(gè)測(cè)量角度的試驗(yàn)樣本數(shù)量為40個(gè)。所測(cè)樣本在果實(shí)與果柄位置處的分離力如圖7所示。

4.2 試驗(yàn)結(jié)果分析

由圖7a可知,在0°方向上,最大分離力為65.24 N,最小分離力為14.81 N,平均分離力為39.38 N,分離力范圍主要集中在20~60 N之間。由圖7b可知,在45°方向上,最大分離力為45.64 N,最小分離力為13.56 N,平均分離力為28.94 N,大部分果實(shí)分離力集中在15~40 N之間。由圖7c可知,在90°方向上,最大分離力為46.13 N,最小平均力4.56 N,平均分離力為19.31 N,分離力范圍主要集中5~30 N之間,大部分果實(shí)分離力小于30 N。

a. 0°b. 45°c. 90°

根據(jù)測(cè)量數(shù)據(jù)分析可得,平均分離力的大小與作用在果實(shí)生長(zhǎng)方向的拉力角有關(guān),在不同的角度上其平均分離力也不同。隨著拉力角的增大,分離力主要分布范圍和平均分離力逐漸減小[27],在0°時(shí)的平均分離力比90°時(shí)大20.09 N,說(shuō)明在板栗采摘過(guò)程中垂直果柄方向比沿果柄方向更易脫落。為了保證收獲效率,拍打機(jī)構(gòu)所提供的最大拍打力應(yīng)不低于最大分離力65.24 N。

5 拍打力試驗(yàn)

5.1 板栗采摘過(guò)程碰撞力分析

拍打機(jī)構(gòu)在板栗收獲過(guò)程中,會(huì)與樹枝和果柄產(chǎn)生碰撞,碰撞模型如圖8所示,為減小碰撞過(guò)程中拍打條對(duì)板栗樹的損傷,擬采用表面光滑、具備彈性變形能力的材料。根據(jù)所選材料性質(zhì),忽略碰撞過(guò)程中的切向摩擦力和能量損失,在Hertz理論接觸力模型[28]中以純彈性接觸力模型進(jìn)行試驗(yàn),其法向接觸力為

式中R(=)為接觸體、的曲率半徑,mm;β(=)與接觸體材料屬性有關(guān),表達(dá)式為

注:ω' 為拍打條角速度,rad·s-1;O為碰撞接觸點(diǎn);ατ為碰撞點(diǎn)切向加速度rad·s-2;αn為碰撞點(diǎn)法向加速度rad·s-2;Fτ為碰撞點(diǎn)切向摩擦力N;Fn為碰撞點(diǎn)法向接觸力N。

通過(guò)圖8模型可知拍,打條與板栗樹枝的碰撞力大小與接觸變形量、接觸位置曲率半徑、材料彈性模量和泊松比有關(guān)。由于材料屬性系數(shù)是常數(shù),因此碰撞時(shí)接觸位置處的變形量和曲率半徑是影響接觸力的2個(gè)主要參數(shù)。拍打機(jī)構(gòu)在工作過(guò)程中,在接觸位置處,電機(jī)轉(zhuǎn)速和拍打條拍打部位是影響變形量和曲率半徑的關(guān)鍵因素,因此可通過(guò)改變電機(jī)轉(zhuǎn)速、拍打條長(zhǎng)度和拍打角度使拍打條達(dá)到不同的拍打力。

5.2 材料與方法

剛?cè)岵?jì)的材料能避免拍打機(jī)構(gòu)工作時(shí)在鉸接處因受力過(guò)大而產(chǎn)生結(jié)構(gòu)破壞[29],同時(shí)也能減少剛性碰撞對(duì)板栗樹枝的傷害,選用彎曲能力不同的PU(聚氨酯,Poly-urethane)、LDPE(低密度聚乙烯,Low Density Polyethylene)、鐵片(鍍鋅鐵皮)和玻璃纖維4種常見材料進(jìn)行試驗(yàn),材料屬性如表3所示。所選材料PU最易彎曲,其次是LDPE,鐵片和玻璃纖維較難彎曲。

針對(duì)公式(18)分析出的2個(gè)主要影響參數(shù),進(jìn)行如圖9所示試驗(yàn),拍打機(jī)構(gòu)固定,壓力采集設(shè)備采用JN-CJ型采集卡和平面膜盒式壓力傳感器(型號(hào)JHBM-H1,量程200 N,精度0.1%)。試驗(yàn)過(guò)程中,拍打條拍打壓力傳感器,采集卡將采集數(shù)據(jù)上傳到上位機(jī),實(shí)時(shí)記錄傳感器測(cè)量數(shù)據(jù)。絲杠升降臺(tái)調(diào)節(jié)拍打條的測(cè)力角度,以得到不同拍打角度的拍打力;在拍打條不同長(zhǎng)度處標(biāo)記測(cè)試點(diǎn),測(cè)試不同拍打長(zhǎng)度的拍打力;驅(qū)動(dòng)器改變電機(jī)的轉(zhuǎn)速,使拍打條達(dá)到不同的拍打頻率,從而得到不同頻率下的拍打力。采集卡采樣頻率選擇200 Hz,采樣時(shí)間10 s,拍打力取采樣平均值;上位機(jī)測(cè)試界面結(jié)果顯示如圖10。

表3 材料屬性

1.臺(tái)架 2.采集卡 3.可調(diào)電源 4.上位機(jī) 5.升降臺(tái) 6.傳感器 7.拍打機(jī)構(gòu) 8.電機(jī)驅(qū)動(dòng)器

5.3 正交試驗(yàn)

5.3.1 試驗(yàn)方案

5.3.2 試驗(yàn)方案與結(jié)果

通過(guò)表5數(shù)據(jù)分析可得,4種材料中,影響PU材料拍打力大小的主次因素為、、,較優(yōu)組合為332,在該因素組合下進(jìn)行試驗(yàn),得出拍打力大小為 44.31 N;影響LDPE材料拍打力大小的主次因素為、、,較優(yōu)組合為321,在該組合下進(jìn)行試驗(yàn),得出拍打力大小為70.71 N;影響鐵片材料拍打力大小的主次因素為、、,較優(yōu)組合為321,在該因素組合下進(jìn)行試驗(yàn),得出拍打力大小為87.46 N;影響玻璃纖維材料拍打力大小的主次因素為、、,較優(yōu)組合為311,在該因素組合下進(jìn)行試驗(yàn),得出拍打力大小為94.03 N。

表4 因素水平

表5 試驗(yàn)結(jié)果與分析

分析可知,采用PU材料進(jìn)行拍打力試驗(yàn),最大拍打力44.31 N小于板栗與樹枝的最大分離力65.24 N,因此在實(shí)際采摘中最大分離力超過(guò)44.31 N會(huì)導(dǎo)致板栗果實(shí)落果困難。其他3種材料在最優(yōu)條件下最大拍打力均大于65.24 N,故滿足板栗果實(shí)落果要求,結(jié)合公式(18)可知,拍打接觸力與材料屬性有關(guān),通過(guò)對(duì)比,鐵片和玻璃纖維拍打力雖然較大,但其彎曲能力較LDPE弱,易損傷樹枝,且對(duì)機(jī)械裝置沖擊較大,因此拍打條材料選擇LDPE較為合適,電機(jī)轉(zhuǎn)速600 r/min,拍打條長(zhǎng)度350 mm以及拍打角度+20°時(shí)拍打條能提供最大拍打力70.71 N。

6 田間試驗(yàn)

每年8月下旬是板栗收獲時(shí)期。如圖11所示,2020年9月份在湖北省孝感市安陸市孛畈鎮(zhèn)板栗種植林區(qū)進(jìn)行田間試驗(yàn)。為了驗(yàn)證實(shí)際工作中拍打機(jī)構(gòu)能否有效拍落板栗果實(shí),根據(jù)臺(tái)架測(cè)力試驗(yàn)最優(yōu)組合,選擇拍打條材料LDPE,長(zhǎng)度350 mm,電機(jī)轉(zhuǎn)速600 r/min。

為評(píng)估所設(shè)計(jì)落果裝置的拍打落果性能,將落果裝置移動(dòng)后進(jìn)行定點(diǎn)采收,選擇多塊相互獨(dú)立、果實(shí)數(shù)量較多、面積相差不大且拍打條能覆蓋到的樹枝作為采收區(qū)域。在采收過(guò)程中,拍打后存在少數(shù)板栗果實(shí)難以脫落,但長(zhǎng)時(shí)間在同一區(qū)域拍打會(huì)對(duì)樹枝產(chǎn)生損傷;經(jīng)試驗(yàn)采摘時(shí)間超過(guò)10 s后,果實(shí)雖能完全采收,但板栗樹大量樹葉被打落,樹枝出現(xiàn)磨損情況,對(duì)枝芽產(chǎn)生一定程度損傷,如圖12所示,而采摘時(shí)間在10 s內(nèi)能完成大部分果實(shí)采收,打落樹葉較少且對(duì)樹枝無(wú)明顯損傷,故每次試驗(yàn)時(shí)間選擇10 s較合適。試驗(yàn)前,先統(tǒng)計(jì)所選各區(qū)域樹枝板栗果實(shí)總數(shù),拍打采收后,記錄各區(qū)域未被采收板栗果實(shí)數(shù),以落果率評(píng)價(jià)落果裝置的工作性能:

田間試驗(yàn)結(jié)果表明,所設(shè)計(jì)的落果裝置的平均落果率達(dá)到90.5%(表6),且拍打力滿足板栗采收要求。由于該機(jī)器仍處于試驗(yàn)階段,目前鮮有板栗樹標(biāo)準(zhǔn)化果園種植模式(湖北地區(qū)板栗多種植于山坡及梯田),離真正的機(jī)械化采摘還存在一定的差距,因此后期需要農(nóng)機(jī)與農(nóng)藝深度融合,種植出宜機(jī)化板栗樹形,研制出適合國(guó)內(nèi)丘陵山地種植模式的板栗收獲機(jī)械。

表6 收獲試驗(yàn)結(jié)果

7 結(jié) 論

1)針對(duì)國(guó)內(nèi)丘陵山地板栗人工收獲效率低、勞動(dòng)強(qiáng)度大、高空落果易傷人等問(wèn)題,本文設(shè)計(jì)了一種板栗收獲拍打式落果裝置,可實(shí)現(xiàn)丘陵山地等地形條件下板栗機(jī)械化采收。

2)闡述了整機(jī)結(jié)構(gòu)和工作原理,落果裝置拍打機(jī)構(gòu)兩側(cè)根據(jù)無(wú)急回特性曲柄搖桿機(jī)構(gòu)進(jìn)行設(shè)計(jì);得出拍打機(jī)構(gòu)運(yùn)動(dòng)規(guī)律方程,對(duì)其進(jìn)行運(yùn)動(dòng)學(xué)仿真分析,通過(guò)結(jié)果可得:拍打機(jī)構(gòu)兩側(cè)搖桿隨曲柄轉(zhuǎn)速增大而不斷增大,且運(yùn)動(dòng)過(guò)程基本能保持一致性,兩側(cè)搖桿擺角分別為60.1°和60.2°,滿足運(yùn)動(dòng)穩(wěn)定性要求。

3)通過(guò)板栗果實(shí)與樹枝的分離力試驗(yàn),得出在0~90°上,隨著拉力角的增大分離力逐漸減小,在0°拉力角上存在最大分離力為65.24 N;對(duì)4種材料的拍打條進(jìn)行三因素三水平正交試驗(yàn),結(jié)果表明:最佳拍打條材料為L(zhǎng)DPE,當(dāng)電機(jī)轉(zhuǎn)速600 r/min,拍打條長(zhǎng)度350 mm,拍打角度20°時(shí),拍打力大小為70.71 N。通過(guò)田間試驗(yàn)結(jié)果表明:落果裝置的平均落果率達(dá)到90.5%,且對(duì)樹枝損傷較小。所設(shè)計(jì)落果裝置基本滿足板栗采收要求。

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Design and experiment of the fruit-beating dropping device for chestnut harvesters

Zong Wangyuan1,2, Huang Muchang1, Xiao Yangyi1,2, Li Mao1, Deng Dinglin1

(1.,,430070,;2.,,430070,)

Difficult picking is often found in the harvesting of fresh chestnut, particularly in the low efficiency and high labor cost of manual harvesting, as well as the high risk of high-altitude picking. However, only a few research focused on this field in China. In this study, a beating-type fruit dropping device was proposed for a chestnut harvester, according to the characteristics of chestnut trees and the planting mode of Chinese chestnut. The overall structure and working principle were also introduced into the design of the chestnut harvester. Two situations were included to separate the chestnut fruit from the branch. When the beating bars hit the fruit, the beating force was directly transferred to the fruit. As such, the fruit was separated from the branch, if the beating force was greater than the binding force between the fruit and the branch. When the beating bars hit the branch, an inertia force was transmitted from the branch to the fruit, where the chestnut was separated from the branch to complete the chestnut harvest, if the inertia force was greater than the binding force. A beating mechanism was also designed as a crank-rocker without quick returning, in order to ensure the overall performance of the machine, and the stability of the fruit dropping device in the process of operation. The size of the crank-rocker mechanism was also determined under the optimal conditions. A kinematic model was established for the crank-rocker mechanism, further to obtain the kinematic relationships of angular displacement, angular velocity, and angular acceleration of the rocker. A dynamic simulation was also performed on both sides of the beating device in the crank-rocker mechanism. It was found that the motion of the rocker was symmetrical in terms of the motion curve, where the swing angle of the rocker reached 60° suitable for the stability requirements. Furthermore, the variation of separation force between chestnut fruit and branch was obtained at different tension angles. Specifically, the separation force decreased gradually with the increase of tension angle in the range of 0°-90°, where the maximum separation force was 65.24 N at 0° tension angle. The collision model between the beating bars and the branch was established to determine the main factors affecting the beating force, including the speed of the motor, the length of the beating bars, and the beating angle. A three-factor three-level orthogonal test was conducted, where the materials of beating bars were selected as polyurethane, low-density polyethylene, iron sheet, and glass fiber. The results show that the maximum beating force was only 44.31N for the polyurethane, while the maximum separation force of chestnut fruit and branch was 65.24 N, indicating that the maximum beating force provided by polyurethane was less than that of chestnut fruit and branch, fail to meet the requirements of beating force for fruit picking. The maximum beating forces of iron sheet and glass fiber were 87.46 N and 94.03 N, respectively. Nevertheless, the excessive force was easy to damage chestnut branches. Fortunately, the maximum beating force of low-density polyethylene was 70.71 N, similar to that of chestnut fruit and branch (65.24 N), indicating the best beating material. In this case, the optimal combination was achieved, where the motor speed of 600 r/min, the beating bar length of 350 mm, and the tapping angle of 20°. A field test of the chestnut harvesting machine was carried out to verify each area for harvesting. Several areas were selected on the chestnut tree for the harvest experiment after the positioning structure moved the fruit dropping device. The field test shows that the beating force provided by the fruit dropping device can effectively beat the chestnut fruits within 10s, where the fruit drop rate was 90.1%, while less damage to the chestnut trees. Consequently, the beating-type fruit dropping device can fully meet the harvest requirements of chestnut fruits. The finding can provide a strong reference for further research and development of chestnut harvesting machinery.

agricultural machinery; harvest; chestnut; fruit dropping device; numerical simulation; separation force; beat

10.11975/j.issn.1002-6819.2021.18.001

S23-01

A

1002-6819(2021)-18-0001-10

2021-07-05

2021-08-21

湖北省重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2020BED027)

宗望遠(yuǎn),教授,博士生導(dǎo)師,研究方向?yàn)楝F(xiàn)代農(nóng)業(yè)裝備設(shè)計(jì)與測(cè)控。Email:zwy@mail.hzau.edu.cn

宗望遠(yuǎn),黃木昌,肖洋軼,等. 板栗收獲拍打式落果裝置設(shè)計(jì)與試驗(yàn)[J]. 農(nóng)業(yè)工程學(xué)報(bào),2021,37(18):1-10. doi:10.11975/j.issn.1002-6819.2021.18.001 http://www.tcsae.org

Zong Wangyuan, Huang Muchang, Xiao Yangyi, et al. Design and experiment of the fruit-beating dropping device for chestnut harvesters[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2021, 37(18): 1-10. (in Chinese with English abstract) doi:10.11975/j.issn.1002-6819.2021.18.001 http://www.tcsae.org

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