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外文資料翻譯 1 護(hù)理床動力學(xué)優(yōu)化 5 1 引言 動 力 學(xué) 是 理 論 力 學(xué) 的 一 個 分 支 學(xué) 科 它 主 要 研 究 作 用 于 物 體 的 力 與 物 體 運(yùn) 動 的 關(guān) 系 動 力 學(xué) 的 研 究 對 象 是 運(yùn) 動 速 度 遠(yuǎn) 小 于 光 速 的 宏 觀 物 體 動 力 學(xué) 是 物 理 學(xué) 和 天 文 學(xué) 的 基 礎(chǔ) 也 是 許 多 工 程 學(xué) 科 的 基 礎(chǔ) 動力學(xué)以牛頓第二定律為核心 這個定律指出了力 加速度 質(zhì)量三者間 的關(guān)系 牛頓首先引入了質(zhì)量的概念 而把它和物體的重力區(qū)分開來 說明物 體的重力只是地球?qū)ξ矬w的引力 多功能醫(yī)用護(hù)理床的運(yùn)動學(xué)分析是基于 ADAMS 建立于在運(yùn)動學(xué)分析的基 礎(chǔ)之上的 根據(jù)先前的運(yùn)動學(xué)分析 以運(yùn)動學(xué)分析結(jié)果作為動力學(xué)分析的初始 值 綜合考慮線性推桿的推 拉力的限制以及機(jī)架各支點的受力狀況 主要對 線性推桿的受力狀況及各床架支點的受力狀況進(jìn)行動力學(xué)分析 5 2 側(cè)翻機(jī)構(gòu)動力學(xué)分析 5 2 1 為機(jī)構(gòu)添加外力 側(cè)翻機(jī)構(gòu)在運(yùn)行的過程中 會有以下幾個方面對機(jī)構(gòu)運(yùn)動產(chǎn)生影響 它們 是機(jī)構(gòu)自身質(zhì)量 患者體重以及各個運(yùn)動副之間的摩擦力 由于摩擦力很小 在此忽略不計 只考慮機(jī)構(gòu)的重量及患者的體重 通過 solidworks 軟件對虛擬樣機(jī)進(jìn)行質(zhì)量測量 測得背板質(zhì)量為 20kg 通 過設(shè)計手冊查得我國身高 1 85m 的成年人平均體重為 83kg 左右 為了真實的模 擬虛擬樣機(jī)的性能 本文采用背板質(zhì)量為 20kg 人體背部重量為 50kg 對機(jī)構(gòu) 添加力之后 運(yùn)行一次動力學(xué)仿真 測量各個點的受力以及電機(jī)的受力 仿真 時間為 25s 步數(shù)為 500 步 添加力測量 測得的各點受力曲線如圖 5 1 所示 圖 5 1 各點受力曲線 外文資料翻譯 2 5 2 MARKER 5 點優(yōu)化前后受力曲線 5 3 MARKER 1 點優(yōu)化前后受力曲線 5 4 MARKER 21 點優(yōu)化前后受力曲線 5 5 各參數(shù)下的翻轉(zhuǎn)角度值 5 2 2 側(cè)翻機(jī)構(gòu)動力學(xué)優(yōu)化仿真 從圖 5 1 中 得知 MAKER 5 點的受力最大 機(jī)構(gòu)的受力優(yōu)化就從 MARKER 5 著入 首先 測試各個設(shè)計變量對 MARKER 5 的受力變化的敏感 度 運(yùn)行一次動力學(xué)仿真 時間為 25s 步數(shù)為 500 步 線性推桿移動速度為 5 5mm s 背板質(zhì)心處加力 500N 背板自重 20kg 運(yùn)行優(yōu)化設(shè)計 優(yōu)化的目標(biāo) 為將 MARLKER 5 點的受力的最大值進(jìn)行最小化 仿真后優(yōu)化數(shù)據(jù)如下 Model Name model 1 Date Run 2009 04 14 17 13 51 Objectives O1 Maximum of MARKER 5 MEA 1 Units newton Initial Value 1444 34 Final Value 1130 2 21 7 Iter O1 DV 1 DV 2 DV 8 0 1444 3 150 00 295 00 136 30 1 1133 7 165 00 265 50 135 83 2 1130 2 165 00 265 50 134 94 3 1130 2 165 00 265 50 134 94 從圖 5 2 至 5 4 中 可以發(fā)現(xiàn)經(jīng)過動力學(xué)優(yōu)化之后 各支點受力均有明顯的改 善 其中圖 5 2 中 MARKER 5 點受力從 1443N 減至 1133N 從圖 5 5 中 背 板的轉(zhuǎn)動角度在角度約束的范圍之內(nèi) 外文資料翻譯 3 5 2 3 樣機(jī)的實際結(jié)構(gòu) 通過以上的分析 在實際設(shè)計中 各關(guān)鍵點的坐標(biāo)取值為如表 5 1 所示 表 5 1 各關(guān)鍵點實際取值 DV L1 mm DV L2 mm DV L4 mm DV L7 mm DV L8 mm 初始值 250 245 330 400 370 優(yōu)化值 265 215 346 1 390 28 359 94 此時 樣機(jī)的背板轉(zhuǎn)動角加速度最小且各支點的受力也達(dá)到了最小化 滿足了 機(jī)構(gòu)的設(shè)計要求 動力學(xué)優(yōu)化前后機(jī)構(gòu)構(gòu)件尺寸表如表 5 2 所示 表 5 2 優(yōu)化前后桿件尺寸對比 A B 水平距離 mm A B 豎直距離 mm BD mm 初始值 50 65 98 4 優(yōu)化值 35 19 118 5 3 抬背機(jī)構(gòu)動力學(xué)分析 5 3 1 為機(jī)構(gòu)添加力 為了較為真實的模擬人體的質(zhì)量 以及考慮背板的推 拉力的限制 在抬 背機(jī)構(gòu)的背部添加豎直向下的均布力 大小為 400N 在臀部床板添加 400N 的 力 運(yùn)行一次動力學(xué)優(yōu)化仿真 5 3 2 抬背機(jī)構(gòu)動力學(xué)優(yōu)化仿真 為了進(jìn)一步研究線性推桿的受力狀況 以及機(jī)架上各支點的受力狀況 使 得機(jī)構(gòu)工作得更安全及更可靠 以抬背機(jī)構(gòu)運(yùn)動學(xué)優(yōu)化數(shù)據(jù)為動力學(xué)優(yōu)化的初 始數(shù)據(jù) 優(yōu)化目標(biāo)函數(shù)為抬背過程中線性推桿受力的最大值最小化 進(jìn)行動力 學(xué)優(yōu)化仿真 已得到滿足機(jī)構(gòu)設(shè)計要求的最優(yōu)化參數(shù) 通過設(shè)計研究對各個設(shè) 計變量進(jìn)行敏感度測試 根據(jù)設(shè)計研究對各設(shè)計變量的測試 得到的數(shù)據(jù)報表 如下 Trial O1 DV 1 Sensitivity 1 1914 3 369 00 10 740 2 2134 5 389 50 0 021580 3 1913 4 410 00 2 5693 4 2029 1 430 50 0 019588 5 1912 6 451 00 5 6838 Trial O1 DV 2 Sensitivity 1 1913 3 18 000 0 0037970 2 1913 3 27 000 0 0031447 外文資料翻譯 4 3 1913 4 36 000 11 532 4 2120 9 45 000 0 0029932 5 1913 5 54 000 23 048 Trial O1 DV 3 Sensitivity 1 1925 6 90 000 22 755 2 2039 4 95 000 1 2229 3 1913 4 100 00 12 825 4 1911 2 105 00 0 42287 5 1909 2 110 00 0 39627 Trial O1 DV 4 Sensitivity 1 1912 8 50 800 0 079290 2 1913 3 57 150 0 044021 3 1913 4 63 500 0 042952 4 1913 9 69 850 0 069998 5 1914 3 76 200 0 062845 Trial O1 DV 5 Sensitivity 1 1913 5 3 9200 0 011536 2 1913 4 0 00000 0 0081747 3 1913 4 3 9200 0 012181 4 1913 5 7 8400 3 5109 5 1940 9 11 760 6 9926 Trial O1 DV 6 Sensitivity 1 2163 3 111 15 40 476 2 1913 4 117 32 20 238 3 1913 4 123 50 15 895 4 2109 7 129 68 0 0067767 5 1913 5 135 85 31 777 Trial O1 DV 7 Sensitivity 1 1985 6 306 74 4 2359 2 1913 4 323 78 2 1180 3 1913 4 340 82 6 3905 4 2131 2 357 86 0 0011642 5 1913 4 374 90 12 779 Trial O1 DV 8 Sensitivity 1 2163 3 111 15 40 476 外文資料翻譯 5 2 1913 4 117 32 20 238 3 1913 4 123 50 15 895 4 2109 7 129 68 0 0067767 5 1913 5 135 85 31 777 通過設(shè)計研究 觀察計算結(jié)果 可以發(fā)現(xiàn)實際變量 DV 3 DV 4 DV 6 DV 8 的敏感度最大 所以在優(yōu)化設(shè)計的時候著重考慮 上述幾個設(shè)計變量 對它們進(jìn)行優(yōu)化設(shè)計 以期望得到滿足設(shè)計要求的機(jī)構(gòu)最 優(yōu)化參數(shù) 5 3 3 樣機(jī)的實際結(jié)構(gòu) 通過以上的分析 在實際設(shè)計中 各關(guān)鍵點的坐標(biāo)取值為如表 5 3 所示 表 5 3 各關(guān)鍵點實際取值 DV 2 mm DV 5 mm DV 6 mm DV 8 mm 初始值 390 458 330 275 優(yōu)化值 381 452 603 32317 278 8 優(yōu)化前后桿件尺寸變化如表 5 4 所示 表 5 4 優(yōu)化前后桿件尺寸變化表 A C 豎直距 離 mm BC mm CD mm DE mm 初始值 60 236 256 667 優(yōu)化值 62 228 248 659 圖 5 6 抬背機(jī)構(gòu)動力學(xué)優(yōu)化前后電機(jī)受力曲線 觀察圖 5 6 可以得知在機(jī)構(gòu)動力學(xué)仿真之后 機(jī)構(gòu)表現(xiàn)出了良好的動力學(xué) 性能 機(jī)構(gòu)的受力狀況得到了有效的改善 達(dá)到了預(yù)期的效果 即電機(jī)受力的 最大值最小化 5 4 曲腿機(jī)構(gòu)動力學(xué)分析 為了真實的模擬曲腿機(jī)構(gòu)在運(yùn)行過程中的受力性能 以及線性推桿的受力 外文資料翻譯 6 狀況 所以對曲腿機(jī)構(gòu)在運(yùn)動學(xué)仿真的基礎(chǔ)之上進(jìn)行一次動力學(xué)仿真 為了得 到較為真實的機(jī)構(gòu)運(yùn)行狀況 并進(jìn)行優(yōu)化仿真 得到理想機(jī)構(gòu)設(shè)計參數(shù) 5 4 1 為機(jī)構(gòu)添加外力 綜合考慮人體的自身重量以及床板的重量 在小腿板的質(zhì)心處及腳板的質(zhì) 心處各添加豎直向下的力 大小為 500N 5 4 2 曲腿機(jī)構(gòu)動力學(xué)仿真 以運(yùn)動學(xué)優(yōu)化的數(shù)據(jù)作為動力學(xué)優(yōu)化的初始數(shù)據(jù) 進(jìn)行動力學(xué)優(yōu)化 優(yōu)化 的目標(biāo)函數(shù)為電機(jī)受力最大值的最小化 首先 對各個設(shè)計變量進(jìn)行設(shè)計研究 設(shè)計研究的報表如下 Trial O1 DV 1 Sensitivity 1 4229 0 270 00 10 633 2 4548 0 300 00 10 659 3 4868 5 330 00 10 686 Trial O1 DV 2 Sensitivity 1 4435 8 56 700 17 645 2 4519 2 61 425 18 141 3 4607 2 66 150 18 637 Trial O1 DV 3 Sensitivity 1 4833 0 156 75 32 756 2 4427 7 169 12 28 017 3 4139 6 181 50 23 278 Trial O1 DV 4 Sensitivity 1 3850 1 243 00 25 573 2 4367 9 263 25 26 353 3 4917 4 283 50 27 134 Trial O1 DV 5 Sensitivity 1 4792 4 81 498 55 604 2 4434 7 87 932 51 809 3 4125 8 94 366 48 013 Trial O1 DV 6 Sensitivity 1 4541 0 597 60 0 10561 2 4548 0 664 00 0 098506 3 4554 0 730 40 0 091406 根據(jù)上述的設(shè)計研究的結(jié)果對 外文資料翻譯 7 DV 1 DV 2 DV 3 DV 4 DV 5 DV 7 DV 9 七變量 作為優(yōu)化設(shè)計時 的設(shè)計變量 進(jìn)行動力學(xué)優(yōu)化仿真 圖 5 7 曲腿機(jī)構(gòu)動力學(xué)優(yōu)化前后電機(jī)受力曲線圖 觀察圖 5 7 可以得知 經(jīng)過動力學(xué)優(yōu)化后的電機(jī)受力的最大值由原來的 4550N 減小為優(yōu)化后的 2850N 電機(jī)的受力大大的減小 從而保證了機(jī)構(gòu)運(yùn)行 的安全性及運(yùn)行的穩(wěn)定性 5 4 3 樣機(jī)的實際結(jié)構(gòu) 通過以上的分析 在優(yōu)化設(shè)計時選取上述設(shè)計變量作為優(yōu)化設(shè)計時的設(shè)計變 量 進(jìn)行動力學(xué)優(yōu)化 經(jīng)過動力學(xué)優(yōu)化之后 各關(guān)鍵點的坐標(biāo)取值為如表 5 5 所示 表 5 5 各關(guān)鍵點實際取值 DV 1 mm DV 2 mm DV 3 mm DV 4 mm DV 5 mm 初始值 300 63 165 270 85 788 優(yōu)化值 270 56 7 181 5 243 94 36 此時 樣機(jī)的線性推桿的受力最小且各支點的受力也達(dá)到了最小化 滿足 了機(jī)構(gòu)的設(shè)計要求 優(yōu)化前后機(jī)構(gòu)桿件尺寸變化見表 5 6 表 5 6 優(yōu)化前后構(gòu)件尺寸變化表 AB mm BC mm CD mm DE mm BE mm 初始值 380 144 6 85 207 5 185 6 優(yōu)化值 350 136 7 83 6 209 35 192 8 5 5 本章小結(jié) 本章在運(yùn)動學(xué)分析的基礎(chǔ)之上的 利用運(yùn)動學(xué)分析的數(shù)據(jù)作為動力學(xué)分析 的初始數(shù)據(jù) 對機(jī)構(gòu)進(jìn)行動力學(xué)分析 在滿足機(jī)構(gòu)運(yùn)動學(xué)要求的基礎(chǔ)上改善機(jī) 構(gòu)的動力學(xué)性能及機(jī)架的受力性能 使得樣機(jī)的運(yùn)動性能及受力性能達(dá)到最好 滿足人體工學(xué)以及機(jī)構(gòu)在工作過程中的穩(wěn)定性及安全性 本章是進(jìn)行樣機(jī)物理 設(shè)計的依據(jù) 外文資料翻譯 8 6 護(hù)理床的力學(xué)分析 6 1 引言 多功能醫(yī)用護(hù)理床在滿足運(yùn)動學(xué)及動力學(xué)性能要求的基礎(chǔ)上 需要對其中 的一些主要零件進(jìn)行強(qiáng)度校核 以便在設(shè)計的時候合理的選材 在保證多功能 醫(yī)用護(hù)理床安全性和穩(wěn)定型以及盡可能的降低生產(chǎn)成本 6 2 力學(xué)計算 護(hù)理床各主要部件及連桿材料均選用 Q235A 鋼 6 2 1 床底架桿校核 考慮到由于多功能醫(yī)用護(hù)理床內(nèi)的機(jī)構(gòu)角度 不可避免的會使床的質(zhì)量增 加 由于整床的重量將全部壓在床底架長桿上 所以底架長桿將會是受力最大 的桿件 根據(jù)設(shè)計尺寸 底架長桿的長度為 1440mm 床底架長桿上有兩個支 撐點 假設(shè)床身的質(zhì)量為 400kg 人體的質(zhì)量為 150kg 總重為 550kg 具體計 算如下所示 圖 6 1 床底架受力示意圖 根據(jù) solidworks 的稱重功能 測得床的質(zhì)量為 365kg 假設(shè)床身的質(zhì)量為 400kg 人體的質(zhì)量為 150kg 總重為 550kg 所以 F2 F3 2750N 1440mm 1020mm 70mm ADlBClCDl 根據(jù)力矩平衡公式 F1 F2 F3 ADlBlCl 得 F1 2215 3N27501927504 F1 F4 F2 F3F 外文資料翻譯 9 得 F4 3284 7N 通過上述已知條件 計算桿各段所受的剪力及彎矩 以 A 為原點 在 AB 端內(nèi) 剪力 F F1 2215 3N 方向向下 彎矩 M F1 x 得 M 0 775 355N M 方向為逆時針方向 在 BC 段內(nèi) 剪力 F F2 F1 534 7N 方向向上 彎矩 M F1 x F2 x 0 35 得 M 229 9 775 355N M 方向為逆時針方 向 在 CD 段內(nèi) 剪力 F F4 3284 7N 方向向上 彎矩 M F4 x 得 M 0 229 9N M 方向為逆時針方向 所以 根據(jù)計算分析 得出的結(jié)果為 B 點的受力最大且彎矩也最大 所以 B 點所在在截面為危險截面 計算后的剪力圖及彎矩圖如圖 6 2 所示 圖 6 2 床底架剪力及彎矩圖 根據(jù)剪力及彎矩圖說明了床底架桿在整體上的受力并沒有發(fā)生突變 同時 也不存在在某段的力值特別大的現(xiàn)象 所以從整體上而言 床框架的力學(xué)性能 良好 受力情況滿足了機(jī)構(gòu)的設(shè)計要求 6 2 2 抬背桿校核 多功能醫(yī)用護(hù)理床在抬背的時候 其抬背擺桿將是受力較大的桿件 由于 人的背部質(zhì)量較大 所以其將會時比較危險的桿件 對其的力學(xué)計算如下 外文資料翻譯 10 圖 6 3 抬背桿受力示意圖 按照人體的質(zhì)量及床板的質(zhì)量均分 則圓整后的數(shù)據(jù)為 F1 500N 方向向 上 F3x 950N F3y 2039N 830mm 680mm 54mm AClABlBDl F2x F3x 950N F2y F1 F3y 500 2039 2539N 在 AB 段 剪力 F F1 500N 方向向上 彎矩 M F x 得 M 0 340N M 方向為順時針方向 在 BC 段 剪力 F F3y 2039N 方向向下 彎矩 M F2y x 0 68 F1 x 0 68 x 0 734 得 M 229 9 340N M 方向逆時針方向 M F2y x 0 68 F2x F1 x 0 734 x 0 83 0 734 得 M 18 5 229 9 N M 方向逆時針方向 所以 根據(jù)上述計算結(jié)果 得知 B 點的剪力最大且所受的彎矩也是最大 綜上所述 B 點所在的截面為危險截面 根據(jù)計算結(jié)果畫出的剪力圖及彎矩圖 如圖 6 4 所示 外文資料翻譯 1 NC and CNC The History of NC and CNC Development Numerical Control NC is any machining process in which the operations are executed automatically in sequences as specified by the program that contains the information for the tool movements The NC concept was proposed in the late 1940s by John Parsons of Traverse City Michigan Parsons recommended a method of automatic machine control that would guide a milling cutter to produce a thru axis curve in order to generate smooth profiles on work pieces In 1949 The U S Air Force awarded Parsons a contract to develop a new type of machine tool that would be able to speed up production methods Parsons commissioned the Massachusetts Institute of Technology M I T to develop a practical implementation of his concept Scientists and engineers at M I T built a control system for a two axis milling machine that used a perforated paper tape as the input media In a short period of time all major machine tool manufacturers were producing some machines with NC but it was not until the late 1970s that computer based NC became widely used NC matured as an automation technology when inexpensive and powerful microprocessors replaced hard wire logic making computer based NC systems When Numerical Control is performed under computer supervision it is called Computer Numerical Control CNC Computers are the control units of CNC machines they are built in or linked to the machines via communications channels When a programmer input some information in the program by tape and so on the computer calculates all necessary data to get the job done On the first Numerically Controlled NC machines were controlled by tape and because of that the NC systems were known as tape controlled machines They were able to control a single operation entered into the machine by punched or magnetic tape There was no possibility of editing the program on the machine To change the program a new tape had to be made Today s systems have computers to control data they are called Computer Numerically Controlled CNC machines For both NC and CNC systems work principles are the same Only the way in which the execution is controlled is different 外文資料翻譯 2 Normally new systems are faster more powerful and more versatile The Applications of NC CNC Since its introduction NC technology has found many applications including lathes and turning Centers milling machines and machining centers punches electrical discharg machines EDM Flame cutters grinders and inspection equipment the most complex CNC machine tools are the turning center shown in Fig 4 1 Amodern turning center with a ten station turret that accepts quick chang tools Each tool can be positioned in Seconds with the press of a button And the machine center shown in Fig 4 2 Vertical machining center the tool magazine is on the machine the control panel on the right can be swiveled by the operator and Fig 4 3 horizontal machining center equipped with an automatic tool changer tool magazines can store 200 ctting tools When preparing a progam for a particular operation the prommer must select all cutting data using recommendations for conventional machining this includes proper Selection of cutting speeds feedrate tools and tool geometry and so on when the programmer has chosen all of the necessary information properly the operator loads the programme into the machine and presses a button to start the cutting crycle the CNC machine moves automatically from one maching operation to another changing the cutting tols and applying the coolent in a surprisingly short time the workpiece is Machined according to the highest quality stangards But that is not all no matter how big the work series is all of the parts will be almost identical in size and surface finishing At this time of advanced technology with its high demands for surface finishing and tolerances of components in for example aerospace nuclear and medical equipment manufacturing only CNC machines provide successful results Numerical control NC is a form of programmable automation in which the processing equipment is controlled by means of numbers letters and other symbols The numbers letters and symbols are coded in an appropriate format to define a program of instructions for a particular workpart or job The instructions are provided by either of the two binary coded decimal systems the Electronic Industries Association EIA code or the American Standard Code for Information Interchange ASCII ASCII coded machine control units will not accept EIA coded instructions 外文資料翻譯 3 and vice versa Increasingly however control units are being made to accept instructions in either code 121Automation operation by NC is readily adaptable to the operation of all metalworking machines Lathes milling machines drill presses boring machines grinding machines turret punches flame or wire cutting and welding machines and even pipe benders are available with numerical controls Basic Components of NC A numerical control system consists of the following three basic components 1 Program instructions 2 Machine control unit 3 Processing equipment The program instructions are the detailed step by step commands that direct the processing equipment 31In its most common form the commands refer to positions of a machine tool spindle with respect to the worktable on which the part is fixtured More advanced instructions include selection of spindle speeds cutting tools and other functions The machine control unit MCU consists of the electronics and control hardware that reads and interprets the program of instructions and convert it into mechanical actions of the machine tool or other processing equipment The processing equipment is the component that performs metal process In the most common example of numerical control it is used to perform machining operations The process ing equipment consists of the worktable and spindle as well as the motors and controls needed to drive them Types of NC There are two basic types of numerical control systems point to point and contouring Point to point control system also called positioning is simpler than contouring control system Its primary purpose is to move a tool or workpiece from one programmed point to another Usually the machine function such as a drilling operation is also activated at each point by command from the NC program Point to point systems are suitable for hole machining operations such as drilling countersinking couterbofing reaming boring and tapping Hole punching machines 外文資料翻譯 4 spotwelding machines and assembly machines also use point to point NC systems Contouring system also known as the continuous path system positioning and cutting operations are both along controlled paths but at different velocities Because the tool cuts as it travels along a prescribed path accurate control and synchronization of velocities and movements are important The contouring system is used on lathes milling machines grinders incrementally by one of several basic methods There are a number of interpolation schemes that have been developed to deal with the various problems that are encountered in generating a smooth continuous path with a contouring type NC system They include linear interpolation circular interpolation helical interpolation parabolic interpolation and cubic interpolation In all interpolations the path controlled is that of the center of rotation of the tool Compensation for different tools different diameter tools or tools wear during machining can be made in the NC Programming for NC A program for numerical control consists of a sequence of directions that causes an NC machine to carry out a certain operation machining being the most commonly used process Programming for NC may be done by an internal programming department on the shop floor or purchased from an outside source Also programming may be done manually or with computer assistance The program contains instructions and commands Geometric instructions pertain to relative movements between the tool and the workpiece Processing instructions pertain to spindle speeds feeds tools and so on Travel instructions pertain to the type of interpolation and slow or rapid movements of the tool or worktable Switching commands pertain to on off position for coolant supplies spindle rotation direction of spindle rotation tool changes workpiece feeding clamping and so on The first NC programming language was developed by MIT developmental work on NC programming systems in the late 1950s and called APT Automatically Programmed Tools DNC and CNC The development of numerical control was a significant achievement in batch and job shop manufacturing from both a technological and a commercial viewpoint 外文資料翻譯 5 There have been two enhancements and extensions of NC technology including 1 Direct numerical control 2 Computer numerical control Direct numerical control can be defined as a manufacturing system in which a number of machines are controlled by a computer through direct connection and in real time The tape reader is omitted in DNC thus relieving the system of its least reliable component Instead of using the tape reader the part program is transmitted to the machine tool directly from the computer memory In principle one computer can be used to control more than 100 separate machines One commercial DNC system during the 1970s boasted a control capability of up to 256 machine tools The DNC computer is designed to provide instructions to each machine tool on demand When the machine needs control commands they are communicated to it immediately Since the introduction of DNC there have been dramatic advances in computer technology The physical size and cost of a digital computer has been significantly reduced at the same time that its computational capabilities have been substantially increased In numerical control the result of these advances has been that the large hard wired MCUs of conventional NC have been replaced by control units based on the digital computer Initially minicomputers were utilized in the early 1970s As further miniaturization occurred in computers minicomputers were replaced by today s microcomputers Computer numerical control is an NC system using dedicated microcomputer as the machine control unit Because a digital computer is used in both CNC and DNC it is appropriate to distinguish between the two types of system There are three principal differences 1 DNC computers distribute instructional data to and collect data from a large number of machines CNC computers control only one machine or a small number of machines 2 DNC computers occupy a location that is typically remote from the machines under their control CNC computer are located very near their machine tools 3 DNC software is developed not only to control individual pieces of production 外文資料翻譯 6 equipment but also to serve as part of a management information system in the manufacturing sector of the firm CNC software is developed to augment the capabilities of a particular machine Tool
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