0065-叉形件工藝及車床夾具設(shè)計(jì)

0065-叉形件工藝及車床夾具設(shè)計(jì),叉形,工藝,車床,夾具,設(shè)計(jì) 叉形件加工工藝規(guī)程 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 設(shè)備 定位 夾緊 共 頁(yè) 第 頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 序 目 錄 產(chǎn)品型號(hào) ZL——10 共2頁(yè) 零件組號(hào) ZA10——10——13 第1 頁(yè) 工序號(hào) 工 序 名 稱 設(shè) 備 工序卡片數(shù) 附注 5 毛坯（棒料） 鋁床 1 10 下料 C620 1 15 車端面打中心孔 C620 1 20 粗車外圓,車錐度 C620 1 25 粗銑平面，銑槽 X60 1 30 打毛刺 鉗工臺(tái) 11 35 打中心孔 C620 1 40 打毛刺 鉗工臺(tái) 45 細(xì)車外圓 C620 1 50 鉆孔 Z518 1 55 打毛刺 鉗工臺(tái) 60 銑外圓 X52k 1 65 打毛刺 鉗工臺(tái) 70 銑平面 X52k 1 75 打毛刺 鉗工臺(tái) 80 打標(biāo)記 鉗工臺(tái) 1 85 中檢 檢驗(yàn)臺(tái) 1 90 熱處理 電爐 工 序 目 錄 產(chǎn)品型號(hào) ZL——10 共2頁(yè) 零件組號(hào) ZA10——10——13 第2頁(yè) 工序號(hào) 工 序 名 稱 設(shè) 備 工序卡片數(shù) 附注 95 修復(fù)基準(zhǔn) C620 1 100 精車外圓 C620 1 105 磨外圓 M114 1 110 磨平面及槽 MT120A 1 115 鏜孔 C620 1 120 磁粉探傷 探傷機(jī) 125 車螺紋 C620 1 130 鉆小孔 Z518 1 135 磨小臺(tái) MT475A 1 140 表面處理 槽 1 145 終檢 檢驗(yàn)臺(tái) 1 150 防銹，油封 槽 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 毛坯 （棒料） 5 設(shè)備 鋁床 定位 夾緊 共1頁(yè) 第1頁(yè) 注：每個(gè)毛坯可生產(chǎn)20個(gè)。 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 毛坯由熱軋圓鋼經(jīng)退火處理 米尺 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 下料 10 設(shè)備 C620 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 按上述要求下料，切斷刀寬不 三爪卡盤(pán) 切斷刀 游標(biāo)卡尺 得大于5，切斷面與軸線垂直 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 車端面 打中心孔 15 設(shè)備 鋁床 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 車端面 三爪卡盤(pán) 游標(biāo)卡尺 2 打中心孔，孔深不得大于2.5 三爪卡盤(pán) f1中心孔 塞規(guī) 3 調(diào)頭，重復(fù)上述步驟 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 粗車外圓 車錐度 20 設(shè)備 C620 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 加工外圓表面 頂尖 Y714車刀 卡尺 2 粗車細(xì)外圓 頂尖 Y714車刀 卡尺 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 粗銑平面 銑槽 25 設(shè)備 X60 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 銑槽 專用夾具 （三面刃銑刀）組合刀具 卡尺 尺規(guī) 下接NO.30,打毛刺 什錦銼 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 打中心孔 35 設(shè)備 C620 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 中心鉆f1 下接NO.40,打毛刺 什錦銼 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 細(xì)車外圓 45 設(shè)備 C620 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 細(xì)車外圓 專用頂尖 車刀 千分尺 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 鉆孔 50 設(shè)備 Z518 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 鉆孔 鉆孔 專用夾具 麻花轉(zhuǎn) 塞規(guī) 2 要求孔軸線對(duì)外圓軸線的垂 直度為0.1 標(biāo)準(zhǔn)芯棒 3 鉆孔后打孔 下接NO.55,打毛刺 什錦銼 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 銑外形 60 設(shè)備 X52K 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 銑外形 銑床夾具 f20指狀銑刀 卡尺 尺規(guī) 下接NO.65,去除毛刺 什錦銼 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 銑平面 70 設(shè)備 X52K 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 銑外形 銑床夾具 指狀銑刀 深度尺 尺規(guī) 下接NO.75,打毛刺 什錦銼 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA 打標(biāo)記 80 設(shè)備 鉗工臺(tái) 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 按圖示要求打標(biāo)記 虎銼 振動(dòng)筆 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 中檢 85 設(shè)備 檢驗(yàn)臺(tái) 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 檢驗(yàn)尺寸16.5-0.2 100% 千分尺 檢驗(yàn)尺寸8.50.1 100% 下接NO.90，熱處理 硬度儀 后硬度為HRC36_41，進(jìn)行 調(diào)質(zhì)處理 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 HRC36~41 修復(fù)基準(zhǔn) 95 設(shè)備 C620 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 研磨中心孔，以去除熱處理 三爪卡盤(pán) f1中心孔 塞規(guī) 后的氧化皮等 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 HRC36~41 精車外圓 100 備設(shè) C620 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 精車外圓f9.5-0.1 扁頂尖 頂尖 Y714車刀 千分尺 2 倒角0.3×30o 卡板 3 精車外圓f6.5-0.1 4 精車外圓f5-0.012 測(cè)量外圓時(shí)應(yīng)卡在圓孔最低點(diǎn) 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 HRC36~41 磨外圓 105 備設(shè) M114 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 磨外圓f9.03h6 扁頂尖 頂尖 砂輪 千分卡尺 2 磨外圓f6h6 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 HRC36~41 磨平面 及槽 110 備設(shè) MT120A 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 磨床夾具 砂輪 千分尺 測(cè)量心軸 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 HRC36~41 鏜孔 115 備設(shè) C620 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 粗鏜孔f9.3+0.09 車床夾具 f9.3鏜刀 塞規(guī) 2 精鏜孔f9.8+0.036 f9.8鏜刀 3 鉸孔f10+0.015 f10鏜刀 4 倒角0.3×45o 锪鉆 下接NO.30,打毛刺 注：磁粉探傷前后均須清洗磁粉探傷要求表面無(wú)明顯裂紋，允許表面留有磁粉 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 HRC36~41 車螺紋 125 備設(shè) C620 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 車螺紋 軟三爪 螺紋車刀 螺紋量規(guī) 2 車端面 卡規(guī) 3 倒角0.5×45o 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 HRC36~41 鉆小孔 130 備設(shè) Z518 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 鉆床夾具 f1.5鉆頭 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA YB674--73 HRC36~41 磨小臺(tái) 135 備設(shè) M7475A 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 磨小臺(tái) 磨小臺(tái) 夾具 砂輪 游標(biāo)卡尺 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA HRC36~41 表面熱處理 140 備設(shè) 槽 定位 夾緊 共1頁(yè) 第1頁(yè) 注：L段和表面C鍍鎘，發(fā)蘭，其余表面鍍鎘8~12u，鈍化。 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 工序卡片 零件名稱 材 料 硬度 工序名稱 工序號(hào) 叉形件 30CrMnSiA HRC36~41 終檢 145 備設(shè) 檢驗(yàn)臺(tái) 定位 夾緊 共1頁(yè) 第1頁(yè) 序號(hào) 加 工 要 求 說(shuō) 明 夾具 刀具 量具 1 按圖示尺寸檢驗(yàn) 卡尺 2 檢驗(yàn)粗糙度 千分尺 尺規(guī) 終檢前后須清洗，最后須接 螺紋量規(guī) NO.150，防銹油封，按冶金 垂度直測(cè)具 說(shuō)明書(shū)進(jìn)行 比較樣板 叉形件工藝及其車床夾具設(shè)計(jì),,設(shè)計(jì)思路：分析零件的特點(diǎn)、擬訂合理的工藝規(guī)程，選擇適當(dāng)?shù)臋C(jī)床、設(shè)計(jì)合理的夾具。在機(jī)械加工零件中如果能夠廣泛地使用夾具，就能極大的節(jié)省加工時(shí)所用的時(shí)間，以減輕工人的勞動(dòng)量，提高勞動(dòng)生產(chǎn)率和產(chǎn)品的質(zhì)量。 設(shè)計(jì)夾具一般先對(duì)原始材料進(jìn)行分析，明確設(shè)計(jì)的要求和意圖，然后提出具體的定位和夾緊方案及車床夾具設(shè)計(jì)。本文采用5號(hào)莫氏錐體（錐柄式心軸）和彈簧片式自動(dòng)定心裝置，來(lái)保證設(shè)計(jì)的可靠。,論文的結(jié)構(gòu)和主要內(nèi)容,第一章 零件的分析 第二章 工藝規(guī)程設(shè)計(jì) 第三章 車床夾具設(shè)計(jì) 第四章 全文總結(jié),第一章 零件的分析,1.1 零件的作用 叉形件零件是飛機(jī)液壓助力器執(zhí)行機(jī)構(gòu)中的主要部之一。從整體上來(lái)看，飛機(jī)液壓助力器是安裝在飛機(jī)副翼縱機(jī)構(gòu)中或方向舵操縱系統(tǒng)中，用于不可逆的液壓助力器縱。當(dāng)飛機(jī)液壓系統(tǒng)損壞或壓力下降時(shí)，液壓助力器外筒左右兩腔溝通，即助力器當(dāng)一拉桿使用，以實(shí)現(xiàn)人力應(yīng)急操縱。每架飛機(jī)上裝有兩臺(tái)液壓助力器。分別操縱左右副翼或方向舵。如下圖所示 1.2 零件的結(jié)構(gòu)與工藝分析 從叉形件的結(jié)構(gòu)特征來(lái)看，它是長(zhǎng)度大于直徑的回轉(zhuǎn)體零件，其被加工表面有外圓柱面、外圓錐面、螺紋、溝槽、孔等。根據(jù)它的結(jié)構(gòu)特點(diǎn)和精度要求，應(yīng)選擇合理的定位基準(zhǔn)和加工方法。,,叉形件,設(shè)計(jì)基準(zhǔn)是φ9的中心線；配合表面是外圓φ9，內(nèi)孔φ10，叉形件在裝配過(guò)程中，內(nèi)孔φ10H7 和外圓φ9h6在叉形組件中是配合表面，因此配合部分的尺寸公差、形位公差要求比較高，表面粗糙度要求較高，外圓φ10H7是設(shè)計(jì)基準(zhǔn)表面；M5-6h螺紋上有一個(gè)φ1.5的小孔起漏氣漏油作用，因此這部分的精度要求不高。,第二章 工藝規(guī)程設(shè)計(jì),2.1確定毛坯的制造形式 零件材料30CrMnSiA，為高級(jí)優(yōu)質(zhì)合金結(jié)構(gòu)鋼，并要求進(jìn)行淬火后回火，保持硬度為HRC=36-41, 考慮到零件受力情況，批量的大小等因素，因此應(yīng)該選用棒料。以使金屬纖維盡量不被切斷，保證零件工作可靠。由于零件屬于大批量生產(chǎn)，應(yīng)保證尺寸的精確。這對(duì)提高生產(chǎn)率、保證加工質(zhì)量也是有利的。 2.2 基準(zhǔn)的選擇 粗基準(zhǔn)選擇毛坯的外圓表面徑向基準(zhǔn)，以端面作為軸向基準(zhǔn)下料，這樣選擇可以保證在粗加工時(shí)零件精度。 零件圖紙的要求，又因?yàn)樵摿慵に嚮鶞?zhǔn)與設(shè)計(jì)基準(zhǔn)重合，故而我們以設(shè)計(jì)基準(zhǔn)φ9的中心線為零件的徑向精基準(zhǔn)，這樣定位不僅滿足上述原則，同時(shí)也是多次裝夾和定位中精度最高的。,,方 案,叉形件工藝,第三章 車床夾具設(shè)計(jì),3.2工件自由度分析 主要定位元件限制五個(gè)自由度：Y和Z方向的移動(dòng)和轉(zhuǎn)動(dòng)，圓柱面支撐限制了X軸的旋轉(zhuǎn)，保證鏜孔的深度。 3.3定位基準(zhǔn)的選擇 本夾具主要是用來(lái)在叉形件上鏜孔.并且對(duì)孔φ10.0mm也有一定的技術(shù)要求（垂直度的偏移不能大于0.05mm，圓柱度的偏移不能大于0.1mm），由于孔還沒(méi)有加工，所以在本道工序加工時(shí)，主要應(yīng)考慮如何保證加工質(zhì)量、提高勞動(dòng)生產(chǎn)率和降低勞動(dòng)強(qiáng)度，故定位基準(zhǔn)應(yīng)選擇A和端面如圖,115工序 鏜孔 車床夾具 如圖,,,夾車床具設(shè)計(jì),參考了一些車床類專用夾具的設(shè)計(jì)，最終確定下圖所示的車床夾具：,,,3.5夾具精度分析 在夾具結(jié)構(gòu)方案確定及總圖設(shè)計(jì)完成之后，還應(yīng)該對(duì)夾具精度進(jìn)行分析和計(jì)算，以確保設(shè)計(jì)的夾具能滿足工件的加工要求。 1.影響精度的因素（造成誤差的原因） 在加工工序所規(guī)定的精度要求中，與夾具密切相關(guān)的是被加工表面的位置精度——位置尺寸和相互位置關(guān)系的要求。影響該位置精度的因素可分為δ定基δ安 裝，δ加工三部分，夾具設(shè)計(jì)者應(yīng)充分考慮估算各部分的誤差，使其綜合影響不致超過(guò)工序所允許的限度。 2． 精度的分析 δ≥δ定基+δ定位+δ夾安+δ加工+δ夾緊 即0.05≥0+0.02+0+0+0.015 所以該夾具可以確保工件所要求的技術(shù)要求。,第四章 全文總結(jié),本次畢業(yè)設(shè)計(jì)，到此為止基本完成了叉形件工藝及車床夾具設(shè)計(jì)。在工藝規(guī)程的編制中，首先通過(guò)分析零件圖，著重討論了各表面的加工余量、工序余量和工序平均尺寸等問(wèn)題，繪制出毛坯圖。然后以第115號(hào)工序?yàn)槔龑?duì)切削余量及基本工時(shí)進(jìn)行了計(jì)算。接著繪制出工藝卡片，在填寫(xiě)、繪制工藝卡片的同時(shí)對(duì)每道工序的定位與夾緊方式順便做了分析和選擇。 在夾具設(shè)計(jì)方面，采用機(jī)床夾具手冊(cè)的相關(guān)知識(shí)和計(jì)算研究方法，首先對(duì)夾具結(jié)構(gòu)類型、定位方案、加緊方案做出選擇，再對(duì)定位元件、夾緊裝置等各個(gè)部分進(jìn)行具體設(shè)計(jì)，然后對(duì)夾具精度等做出分析，最終繪制出夾具裝配圖和圓盤(pán)等非標(biāo)準(zhǔn)件的零件圖。,謝 謝, 機(jī)械專業(yè)外語(yǔ)文獻(xiàn)翻譯 系 別 機(jī)電工程系 專 業(yè) 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 班 級(jí) 161001 學(xué)生姓名 劉立 學(xué) 號(hào) 103298 日 期 2014、6 2.2.5 Vector fields A vector-field is essentially a 2-Dimentional field with vectors. A vector consists of magnitude and angle, which represent importance or speed and demanded heading angle respectively. The magnitude interpretation as a an importance is useful when vector fields are combined by addition of each vector. The more important vector is longer, and therefore the resulting heading angle will be more into the direction of the more important vector. Some vector field generators, such as basic potential field methods, are not concerned about the magnitude. In this case the magnitude is often normalized. 2.2.5.1 Potential fields The theory of potential fields as trajectories is derived from an electrical field of a sphere in physics. The ormulae for an attractive field is as follows: where is a vector from the origin to the target position is a vector from the origin to the robot is the resultant vector with normalized length, indicating the direction of the field at the robots current position. The resultant is pointing towards the target. The attractive potential field is therefore related to line of sight guidance. A repulsive field is generating vectors pointing away from T. The formulae is Fig 6: attractive potential field Figure 6 shows a attractive potential field with a target point at T(0,0) . In an application usually only the vector at the current position of the robot is calculated, for demonstration graphs such as Figure 6 the robot is assumed to be in every possible position in the field, and therefore generating the vectors at each point. 2.2.5.2 Limit cycle based vector fields Limit cycles are part of nonlinear control theory. However the properties of a graph representing a limit cycle, Figure 7, can be adopted for path generation. For further reading see D-H Kim (2000). The limit-cycle characteristics of the 2nd order nonlinear function can be represented as a vector field containing a unit circle. Vectors outside the circle will be directed tangentially onto the circle. It can be seen as an arc/circle trajectory generator that lines up the robot coming in from any direction automatically. The resulting vector-field can be used like a arc trajectory generator or for obstacle avoidance. The disadvantage of the limit cycle method is that once the robot crosses the unit circle, the vector pointing towards a singularity in the centre. Therefore, a practical implementation is not easy, since is likely to overshoot the circle border slightly when arriving at the circle. A modification of the field within the circle is a proposed solution to the problem. Fig 7: limit cycle 2.2.5.3 Vector field fusion All discussed vector field methods can be applied at the same time. The author developed a way of combining (fusing) vector fields, which is published in Robinson P. (2004). Constraints and requirements: -Two or more vector fields are given -These vector fields contain normalized vectors The method is best described in an example. A typical combination of vector-field shall be analyzed where a Robot R avoids and obstacle Robot O on the way to a target point T. See figure 8 below. A weighting function is required to fuse the vector fields together. Experiments have shown that the Gaussian normal distribution function is an acceptable method of combining these fields. (A cylinder or cone would create a sudden change in heading angle and excites instability.) The angle Δ is the difference between the instant heading angle of the robot and the vector ro which points from robot to obstacle. Fig 8: avoidance scenario ThusΔ is an indication of how much the robot is on collision course with the obstacle. The smaller the angle, the more it is on collision course and the importance to avoid the obstacle is high. The mission of the robot is to go to T. In order to take into account the obstacle on its way towards the target it must consider how close the obstacle is. The distance to the obstacle is defined as ro . A smaller distance to an obstacle means that is more important to avoid it. An avoidance vector field VOshall be defined which is normal tot he mission vector field rt .The normalized target vector is VT. Suppose two vectors VTand VOare added together – ‘fused’ -with a Gaussian weighting function m*G(d). Where: is the resultant modified target vector Mis a additional constant weighting factor G() is the Gaussian distribution function. μ is the offset of the Gaussian hat is the distribution of the Gaussian hat We just learned that there are essentially two factors that define how important it is to avoid the obstacle. Δ and ro . The author will base the principle of vector field fusion by relating the length of each vector to importance towards the mission at a particular point in the field. Thus Δ and ro can be modelled as follows to influence the length of VO. -r1 is the maximum offset that Δ can cause. θ is steepness of the slope ( relationship of μ and Δ ) A larger θ will result in higher angles already to be considered as important. And the distance of the robot to the obstacle ro is modelled as the position parameter in the Gaussian function. Finally, the resultant vector field VMTindicates the new instant heading angle for the robot. Test results at different speeds with a robot football robot. The maximum speed is 100% corresponding to 3.0 m/sec. The coordinate system is in inches. Fig 9: avoidance path at 0.36 m/sec Fig 10: avoidance path at 0.51 m/sec Fig 11: avoidance path at 0.84 m/sec 2.2.6 Matching the trajectories to the dynamic model of mobile robots A current attempt of the author is to compare a path through a potential field with the robots dynamics model in order to determine if the robot can follow it. This can be done in frequency domain, by comparing the bandwidth of the robot plus controller model to the bandwidth of the input signal when trying to follow the path. This approach can be taken further. This could provide a basis of matching a vector-field by design to the robot’s bandwidth. 2.3 Modelling mobile robots This chapter is concerned with developing and understanding models of mobile robot kinematics and the control of each individual motor actuating the links within the kinematic model. Further reading is available in McKerrow P J (1991) chapter 8.1 which references to Muir P F and Neuman C P (1986). Muir and Neuman introduced a way of model ling wheeled mobile robots. It is related to model ling the kinematics of robot arms (manipulator kinematics). Differential driven Robot Differential driving is one of the simplest methods of model ling a mobile robot. This is probably why it is so common. The robot consists of 2 diagonally opposing wheels, see Fig. 12. If both wheels have the same velocity, the robot will go straight. If one wheel goes faster than the other the robot will follow a circular trajectory. If one wheel turns in the opposite direction of the other but with the same magnitude in speed, the robot will turn around its cent re, “on the spot”. The wheel Jacobian matrix is given and can be used as follows: Where v is the velocity forward of the centre of the robot and . is the angular velocity around the centre of the robot, see Fig 12. p& wheel Jacobian. p is the posture of the robot. The posture gives information about how the robot moves with respect to the floor. indicates the instant heading angle of the robot. Assuming no slip, the direction the vehicle is facing towards, is the same as the direction of the velocity vector (at and instant in time). An advantage of this fact, it simplifies calculations. A disadvantage however is that it can not move side wards. Fig 12: Differential driven Robot 3 DESIGN AND IMPLEMENTATION 3.1 Specification for fast autonomous mobile platform: faster than 1m/sec large enough for real world application, such as picking up goods space for a onboard laptop enough sensors for autonomous movements battery life for several hours inexpensive ( < ￡1000) 3.2 Mechanical Design Every part of the mechanical design is build from basic materials, only the caster wheels are a ready made construction. One focus of the project was to build the mechanical construction rather than buy a ready made gearbox and frame. As a benefit the authors machining skills has improved. 3.2.1 Frame The robot body consists of a steel frame that is welded together forming a box. Initially the frame was screwed together until the design was fully developed. Then the screws and brackets have been replaced by welded joints. The top rectangle can be taken of in order to do repair work. A large orange plastic sheet is mounted on top as a base for the circuit boards and the notebook. The battery is placed on top of the bottom frame. The key point is here that the bottom frame is lower than the wheel axis. It is placed just 2 cm above ground to prevent the robot from toppling at high speed. 3.2.2 Steering The steering consists of 2 links, i.e. 2 wheels. Fig 13: Explosion picture of one steering link One steering link consists of a medium duty caster wheel that has been welded to a plate. The plate and the underlying caster-wheel have a 12 mm shaft welded on in order to enable steering of the wheel. The wheel is not offset its centre, unlike on a shopping trolley for example. Therefore it must be controlled by active steering to line it up with the direction of movement. Both steering shafts are driven by a motor-gearbox combination (gear-ratio 1:50) over a belt system (ratio 1:2). The motor is a 12 Volt DC Motor. A potentiometer on the top of one shaft is read by a micro con troller to determine the current steering angle. The overall system is a servo system, since it has positional feedback, see section 3.3.5 for a description of the control. The above design, is the finally implemented one, the initial design had a stepper motor with controller circuit. However, the stepper motor was not powerful enough to turn the steering on rough surfaces. The implemented system responds quick and accurate within a fraction of a second to any angle. There are 3 ball bearings per link: one in the axis of the wheel and two in line with the 12mm steering shaft. This two ball-bearings shift the weight of the robot onto the wheel. One steering link is designed to carry a weight of 120Kg. One could argue that axial-ball bearings would have been better, but the axial load of the radial ball-bearings chosen is much higher than the maximum weight that the robot will ever experience. The two ball-bearings are placed in a machined al u minium housing. All the machining for the slot and the place to fit the bearing was done with a lathe and a milling machine. 3.2.3 Gearbox Fig 14: Gearbox in AutoCAD The two gearboxes are constructed out of 4 solid al u minium bars each, which are bolted together. On the bottom bar two slots are milled out, increasing the accuracy of their alignment with the other bars. During construction the bars where clamped together, in order to align the shaft holes of both bars precisely. The surfaces of the bars have been milled straight at the beginning, to have accurate reference during construction. The gearbox has 2 ball bearings on the shaft that is connected to the wheel. The other two shafts are for transmission gears. Each shaft has sleeves to adapt to the different diameters of the gears. The gear ratio is: n.b. Wheel diameter = 125mm Wheel circumference
392.7mm A further ball bearing with housing is mounted onto the frame. Thus the frame is connected to the housing and the housing to the gearbox. The holes marked with stripes in figure 15 are for fixing frame an housing together. Fig 15: Housing with 3 holes for gearbox-mount 3.2.4 Accuracy For the construction of the gearbox, only machine tools such as a lathe and a milling machine can achieve the accuracy. A stand drill is already problematic. The machines should be calibrated with a dial indicator. A dial indicator is a dial gauge that can measure distance in fractions of millime tres. It is mounted onto the lathe or milling machine to align the tool with the work piece. 3.3 Electronic Hardware Design Every circuit in the robot has been designed from basic principles. The design consists of two modular Micro controllers, the power electronics and the ultrasonic sensors. 3.3.1 Power Supply circuit The robot runs of a 12Volt battery. In the cent re of the frame is place to strap on a car battery or motor-cycle battery. With a car battery, the robot runs approximately 3-4 hours in constant action. The power is split up into signal power and motor power from the battery on wards to minimize noise distribution. The motor power goes through an emergency stop button before being fed to the electronics board. All circuits can be switched of through a lever switch added next to the emergency stop. A bipolar capacitor with 4700uF is placed on the power electronics board. Each power regulator is surrounded by capacitors as well. The larger electrolytic capacitors are always accompanied by a bipolar 10nF or 100nF ceramic capacitor. The tracks on the power electronics board have a diameter of 6mm. The motor power cables have a diameter of 4.4mm. The cable is originally designed for speakers. The noise amplitude on the 12Volt rail is less than 100mV. 3.3.2 Micro controller Module The modular micro controllers was designed to be an improvement from the popular robot football circuit, which is used by many students at the university. Unfortunately the chip used in the old circuit (90S8515) is discontinued and the new generation, the Atmel Mega series usually comes as surface mount device). At a development stage, surface mount is a problem. Firstly, it is not easy to unsolder asurface mount chip and secondly, a surface mount chip can not be stuck into a breadboard to do a quick design check. The module was designed with the following specification in mind: -similar amount of ports as the 90S8515 -only a bare minimum on components on board -serial and programming connector (Robot football compatible) -Avoid extra features such as test LEDs, I2C connector etc. since they are application dependant -Power LED for quick confirmation -Crystal with build-in capacitors -Plug-in design with a Pin distance usable for bread-boards The specification is appreciated by the technicians and other students of the University. Several other students already applied this design to their final year project, which proves the flexibility of the design. The author is currently writing a guide on how to develop with an At mel Mega and the new g cc 3.X compiler. A draft version of the guide can be found in the Appendix. Fig 16: At mel Mega16 Micro controller board used for designing the motor controllers Technical Details of the Microcontroller Module -Atmel Mega16-AI in TQFP package (Atmel Package Code 44A) -16 MHz Crystal -Atmel ISP Programming connector (IDC10, right angled) -Robot Football 4-Pin Molex Serial Port connector -3x 10Pin Single-in-Line connectors for IO-Ports 3.3.3 Ultra Sonic Sensors design The final design of the sensor is more simple than the original. The flexibility has increased since modulation and signal decoding is part of the software. Faster sensing is made possible through the changes. However, it demands more computing time. Features of the new design include: -frequency can be set by software -signal can be coded -reliable range 1.3 m The transmitter consists of a software running in a timer at 76 to 84 kHz and toggling the transistor Q1. The toggling divides the frequency by two. Unfortunately none of the timer frequency settings match the resonance frequency of the transducers. Therefore, the timer frequency must be programmed to sweep from a few kilohertz under the resonance frequency to a few over the resonance frequency. Fig 17: Ultra sonic distance measurement electronics The receiver end consists of a operational amplifier for signal boosting, a transistor Q2 for level shifting (12V to 5V) and a low pass filter R7,C7. The Op Amp is configured with a only positive rail at 12V. The positive input is clamped to 6V. Feedback resistor RV1 is a 47KOhm potentiometer in the final version, thus creating a variable gain from 1 to 48. Practically gain values over about 30 amplify noise created by the transmitter over the power rail. Even the extensive use of capacitors could not remove this problem. The sensor can detect flat objects, such as walls and boxes up to 3 meters away. Reliable detection of humans can only be achieved within 1.3 meters. Fig 18: design of a ultra sonic distance sensor with 8-bit bus connector (original design) Low pass Filter The micro controller recognizes a logical high at 3.5V and above, Atmel (2003), on an digital IO pin. The filter must be matched to give this voltage at the maximum acceptable frequency. Experiments show that, the a design with the 3dB point at 42KHz (Transducer frequency) has not enough safety margin and the micro controller does not always recognise the signal as high when it should be. Therefore the 3dB point is set to 49KHz. The question is which R and C values to choose in order to have 3.5 Volt at the output at 49 kHz. Fig 19: low pass filter (used in ultra sonic circuit) Initial formulae (15) rearranged for R. (16) n.b. the output impedance of the transistor circuit has been neglected, since it is lower than the low-pass circuit. The input impedance of the micro controller is much higher than the one of the low-pass circuit, and the impedance can be neglected in the calculation again. Fig 20: Ultrasonic sensor electronics (final design) 快速自動(dòng)機(jī)器人人平臺(tái)-2 2.2.5向量場(chǎng) 一個(gè)向量場(chǎng)實(shí)質(zhì)是由一個(gè)2-維向量組成的區(qū)域。一個(gè)向量由大小和方向組成，向量對(duì)于速度和航向角而言相當(dāng)重要。 大小被認(rèn)為是向量場(chǎng)中很重要的問(wèn)題，大小對(duì)于通過(guò)每個(gè)向量組合成為向量場(chǎng)是很有用的。越重要的向量越長(zhǎng)，航向角貼近的是更加重要的向量。 一些向量場(chǎng)產(chǎn)生器，像是基礎(chǔ)的勢(shì)場(chǎng)產(chǎn)生法，是不考慮大小的。這種情況下大小經(jīng)常被忽略。 2.2.5.1勢(shì)場(chǎng) 勢(shì)場(chǎng)的一些理論像是軌跡的概念是從物理領(lǐng)域中的電學(xué)部分中分化而出的。 引力場(chǎng)公式如下： 這里 是一個(gè)沖起始到目標(biāo)位置的向量 是一個(gè)從起始指向機(jī)器人的向量 是一個(gè)表征機(jī)器人當(dāng)前位置的單位化的長(zhǎng)度和預(yù)計(jì)的角度。結(jié)果是指向目標(biāo)的。引力場(chǎng)是關(guān)聯(lián)其中的可視的指引。斥力場(chǎng)產(chǎn)生背向目標(biāo)的向量。等式是 表格6展示了一個(gè)引力場(chǎng)指向目標(biāo)點(diǎn)（0.0）。在當(dāng)前應(yīng)用的機(jī)器人僅有當(dāng)前位置的向量才加入計(jì)算 ，對(duì)于多為圖表像表格6這樣，機(jī)器人可以在場(chǎng)中任何可能的地方，同時(shí)也可以在任何點(diǎn)長(zhǎng)生向量。 表格6：引力場(chǎng) 2.2.5.2基于極限環(huán)的向量場(chǎng) 極限環(huán)是非線性控制理論的一部分。但是一個(gè)表格能夠表現(xiàn)極限環(huán)的屬性，像是表格7，那么這個(gè)表格便可以適應(yīng)路徑生成。此問(wèn)題更深入的解讀請(qǐng)閱讀D-H Kim（2000）。極限環(huán)的非線性功能的第二位表現(xiàn)為一個(gè)向量場(chǎng)包含一個(gè)單位環(huán)。單位環(huán)外的向量將產(chǎn)生于單位環(huán)相切的方向。這可以看成是一個(gè)圓弧/圓軌跡生成率可以引導(dǎo)機(jī)器人自動(dòng)從任何方向進(jìn)入該圓。最終生成的向量場(chǎng)可以用來(lái)產(chǎn)生圓弧軌跡或者是用于避障。 極限環(huán)的缺點(diǎn)在于一旦機(jī)器恩跨過(guò)了單位元，向量場(chǎng)將指向中心。所以，具體實(shí)現(xiàn)極限環(huán)控制并不容易，因?yàn)闄C(jī)器人在接近單位圓時(shí)可能會(huì)稍稍的越過(guò)邊界。 這種場(chǎng)在單位環(huán)內(nèi)進(jìn)行修改時(shí)一個(gè)解決此種問(wèn)題的可行的措施。 對(duì)圖表7：極限環(huán) 2.2.5.3矢量場(chǎng)的融合 所有的可提供向量場(chǎng)都可以在同一時(shí)間進(jìn)行討論。作者開(kāi)發(fā)了一種可供合并向量場(chǎng)合并的方法，該方法在Robinson P(2004)中論述。 約束和要求： -兩個(gè)或者更多的向量場(chǎng)。 -這些向量場(chǎng)包含標(biāo)準(zhǔn)化的向量。 這種方法最好用一個(gè)例子來(lái)描述。一個(gè)典型的需要向量場(chǎng)合并的地方在于當(dāng)一個(gè)機(jī)器人R需要避免和機(jī)器人O在路上相遇去目標(biāo)T時(shí)?？聪旅鎴D表8。 在融合向量場(chǎng)過(guò)程中，需要一個(gè)加權(quán)函數(shù)。經(jīng)驗(yàn)已經(jīng)證明，高斯正態(tài)分布函數(shù)在合并兩個(gè)場(chǎng)域是很合適的方式。（一個(gè)圓柱體或是一個(gè)椎體都可能產(chǎn)生一個(gè)突然的沖擊以使航向角發(fā)生變化并產(chǎn)生激發(fā)不穩(wěn)定現(xiàn)象。） 圖表8：回避方案 角和當(dāng)前的機(jī)器人航向角q是不同的，ro向量是指向機(jī)器人回避方向。 那個(gè)角是表征機(jī)器人和障礙物碰撞程度的量。這個(gè)角度越小，碰撞事件發(fā)生的情況就越小，同時(shí)避開(kāi)障礙物的可能性越高。 這個(gè)機(jī)器人的任務(wù)是走到T點(diǎn)。為了將攔在它和目標(biāo)點(diǎn)之間的障礙物也納入考慮，那個(gè)機(jī)器人就必須計(jì)算障礙物和自己的距離。這個(gè)距離在式子中是以矢量ro定義的。和障礙物的距離越短就意味著避開(kāi)障礙物的重要性越大。 一個(gè)回避向量場(chǎng)應(yīng)該被定義的和任務(wù)向量場(chǎng)rt場(chǎng)一樣。標(biāo)準(zhǔn)化后的目標(biāo)向量是。 提供的兩個(gè)向量和是用高斯加權(quán)方程加在一起的-融合