抽屜式換煤機(jī)設(shè)計(jì)【含CAD圖紙、PROE三維】
抽屜式換煤機(jī)設(shè)計(jì)【含CAD圖紙、PROE三維】,含CAD圖紙、PROE三維,抽屜,式換煤機(jī),設(shè)計(jì),CAD,圖紙,PROE,三維
并聯(lián)機(jī)床中工件安裝定位系統(tǒng)的開發(fā)
趙曉明,邵 華,服部和也,堤正臣
1. 上海交通大學(xué)機(jī)械與動(dòng)力工程學(xué)院, 上海200030;
2. 日本豐田工機(jī)公司技術(shù)研究所, 刈谷市44828652;
3. 日本東京農(nóng)工大學(xué)生物系統(tǒng)應(yīng)用科學(xué)研究科, 東京18428858
顧曉華 譯
摘 要: 并聯(lián)機(jī)床由于結(jié)構(gòu)和工作空間極其復(fù)雜, 在加工工件時(shí)經(jīng)常出現(xiàn)各種干涉. 以日本豐田工機(jī)公司的HexaM 并聯(lián)機(jī)床為模型, 討論了并聯(lián)機(jī)床的自己干涉、機(jī)床與工件的干涉、機(jī)床與周邊器械的干涉的檢查方法和回避方法. 提出了在不修改刀具軌跡的情況下, 通過(guò)調(diào)整工件的安裝位置來(lái)回避以上干涉的計(jì)算方法. 最后通過(guò)實(shí)驗(yàn), 證明了算法對(duì)于在實(shí)際加工前檢查可能出現(xiàn)的干涉,以及確定出無(wú)干涉的工件安裝位置是非常有用的.
關(guān)鍵詞: 并聯(lián)機(jī)床; 干涉檢查; 回避; 刀具軌跡; 安裝位置
近年來(lái), 并聯(lián)機(jī)床的開發(fā)和應(yīng)用日益增多, 但由于其結(jié)構(gòu)及工作空間非常復(fù)雜, 在使用它加工工件時(shí), 極有可能發(fā)生機(jī)床零件間的自己干涉及機(jī)床與工件的干涉. 另外, 如果像并聯(lián)機(jī)床HexaM 那樣,在工作臺(tái)上還安裝有自動(dòng)換刀裝置等周邊器械, 在安裝工件時(shí), 它可能會(huì)限制工件的安裝位置, 即出現(xiàn)工件與周邊器械的干涉, 加工時(shí)還可能出現(xiàn)機(jī)床與周邊器械的干涉.
關(guān)于并聯(lián)機(jī)床自己干涉的檢查方法和機(jī)床工作空間已有諸多研究. 其中, 筆者等以日本豐田工機(jī)公司的并聯(lián)機(jī)床HexaM 為模型, 探討了并聯(lián)機(jī)床自己干涉的檢查方法, 提出了工作空間的近似表達(dá)式. 另一方面, 在5 坐標(biāo)數(shù)控加工時(shí), 刀具系統(tǒng)(刀具、夾頭和主軸) 與工件系統(tǒng)(工件和夾具) 干涉的檢查方法也有多種. 其中, 竹內(nèi)等從刀具系統(tǒng)表面上取若干個(gè)點(diǎn)作為干涉檢查點(diǎn), 而工件表面均由較簡(jiǎn)單的函數(shù)構(gòu)成, 當(dāng)干涉檢查點(diǎn)位于函數(shù)內(nèi)部時(shí),可以判斷為機(jī)床與工件發(fā)生干涉; 筆者等提出的方法與此正好相反, 即是從工件系統(tǒng)表面上選取干涉檢查點(diǎn), 看是否進(jìn)入刀具系統(tǒng)來(lái)進(jìn)行干涉檢查. 由于數(shù)控機(jī)床的周邊器械一般都不是放置在工作臺(tái)面上, 所以, 在這兩種檢查方法中, 都沒(méi)有考慮加工過(guò)程中機(jī)床與周邊器械的干涉問(wèn)題.
以上這些研究詳細(xì)討論了并聯(lián)機(jī)床的自己干涉及機(jī)床與工件的干涉檢查和回避方法, 但在使用并聯(lián)機(jī)床前, 還存在如下幾個(gè)問(wèn)題:
① 對(duì)于工作臺(tái)上有周邊器械等障礙物的機(jī)床, 應(yīng)考慮機(jī)床與周邊器械可能發(fā)生的干涉;
② 在檢查機(jī)床與工件的干涉時(shí), 還應(yīng)考慮主軸夾板、夾板鉸鏈及連桿與工件可能發(fā)生的干涉, 但現(xiàn)有的CAM 軟件中并不包含這樣的干涉檢查;
③ 當(dāng)機(jī)床與工件存在干涉時(shí), 一般總是通過(guò)調(diào)整刀具姿勢(shì)來(lái)回避干涉的. 事實(shí)上, 對(duì)于并聯(lián)機(jī)床, 除調(diào)整刀具姿勢(shì)外, 還可以通過(guò)調(diào)整工件的安裝位置來(lái)回避各種干涉. 而且, 這種回避方法的最大優(yōu)點(diǎn)是可以不改變現(xiàn)有的CAM 軟件.
本文以通用CAM 軟件輸出的刀具軌跡為基礎(chǔ), 提出了縮短檢查干涉時(shí)間的檢查點(diǎn)文件的組成方式, 并通過(guò)調(diào)整工件的安裝位置來(lái)回避可能發(fā)生的各種干涉, 提出了檢驗(yàn)該工件能否進(jìn)行加工以及可加工時(shí)工件最佳安裝位置的計(jì)算方法.
1 干涉檢查與干涉回避
本文使用的并聯(lián)機(jī)床HexaM、周邊器械(刀庫(kù))和工件的安裝簡(jiǎn)圖如圖1 所示. 因此, 對(duì)于本機(jī)床來(lái)說(shuō), 在加工過(guò)程中和安裝工件時(shí)可能發(fā)生的干涉有自己干涉、機(jī)床與工件的干涉、機(jī)床與周邊器械的干涉以及工件與周邊器械的干涉.
如果所用并聯(lián)機(jī)床的工作臺(tái)上沒(méi)有周邊器械或周邊器械放置的比較遠(yuǎn), 不會(huì)影響工件的安裝位置或加工過(guò)程中也不會(huì)出現(xiàn)機(jī)床與周邊器械干涉現(xiàn)象時(shí), 則可省略機(jī)床及工件與周邊器械的干涉檢查.
圖1 并聯(lián)機(jī)床HexaM 簡(jiǎn)圖
1. 1 自己干涉
1. 1. 1 檢查點(diǎn)的組成 在加工過(guò)程中, 所有刀具位置可以應(yīng)用文獻(xiàn)中所述方法檢查是否會(huì)發(fā)生自己干涉. 如果發(fā)生干涉, 則用調(diào)整工件的安裝位置來(lái)回避干涉. 工件的安裝位置改變后, 加工過(guò)程中的刀具位置自然也就改變了. 因此, 還須再次進(jìn)行檢查,直到不發(fā)生自己干涉為止. 由于在每一個(gè)安裝位置上要對(duì)所有的刀具位置進(jìn)行檢查, 計(jì)算時(shí)間必定很長(zhǎng). 為了縮短計(jì)算時(shí)間, 本文并非對(duì)所有刀具位置,而只是抽出少量的刀具位置(以下稱為檢查點(diǎn)) 進(jìn)行干涉檢查. 因此, 抽出檢查點(diǎn)時(shí)必須要作到: 在檢查點(diǎn)如果不發(fā)生自己干涉, 則在其他的刀具位置也不會(huì)發(fā)生自己干涉. 設(shè)置檢查點(diǎn)的優(yōu)點(diǎn)是可以大量減少檢查次數(shù).
刀具距z 軸越遠(yuǎn)、位置越高、傾斜程度越大, 就越容易發(fā)生自己干涉. 因此, 對(duì)于待加工的工件,從刀具軌跡中抽出最外測(cè)的點(diǎn)、刀具位置較高的點(diǎn)、刀具傾斜角較大的點(diǎn)作為判斷是否發(fā)生自己干涉的檢查點(diǎn).
1. 1. 2 檢查干涉的方法 刀具位置和姿勢(shì)分別在直進(jìn)空間圓和回轉(zhuǎn)空間圓內(nèi)時(shí), 一定不會(huì)發(fā)生自己干涉. 所以, 自己干涉的檢查方法為: ① 讀取所有檢查點(diǎn), 求出每一個(gè)檢查點(diǎn)所對(duì)應(yīng)的直進(jìn)空間圓和回轉(zhuǎn)空間圓. ② 刀具位置和姿勢(shì)分別在對(duì)應(yīng)的直進(jìn)空間圓和回轉(zhuǎn)空間圓內(nèi)時(shí), 判定為在該檢查點(diǎn)不會(huì)發(fā)生自己干涉; 在所有的檢查點(diǎn)都不發(fā)生干涉時(shí),則判定為在該安裝位置不會(huì)發(fā)生自己干涉. ③ 如果在某檢查點(diǎn)的位置或姿勢(shì)超出了直進(jìn)空間圓或回轉(zhuǎn)空間圓, 則用文獻(xiàn)中所述的檢查干涉的方法進(jìn)行復(fù)檢. 由于空間圓比一般的檢查干涉的計(jì)算量要小的多, 所以, 這樣的檢查方法可以縮短每次檢查的計(jì)算時(shí)間.
1. 1. 3 回避干涉的方法 由于在同一水平面內(nèi), 刀具位置在z 軸上時(shí)最不容易出現(xiàn)自己干涉. 所以, 如果在某個(gè)檢查點(diǎn)出現(xiàn)了自己干涉, 則將該檢查點(diǎn)與z 軸的連線作為回避方向. 然后, 將工件的安裝位置沿回避方向移動(dòng)10 mm. 如果連續(xù)兩次回避方向的夾角大于150°, 可以認(rèn)為回避方向已經(jīng)翻轉(zhuǎn), 在該水平面內(nèi)不存在能夠安裝的位置, 所以, 只能將工件的安裝位置向上提高. 本文中, 每次提高10 mm. 如果自己干涉是主電機(jī)與回轉(zhuǎn)絲杠下端的干涉,則說(shuō)明工件過(guò)高或工件的安裝位置過(guò)高, 不能采用本機(jī)床加工.
1. 2 機(jī)床與工件的干涉
1. 2. 1 檢查點(diǎn)的組成 如圖2 所示, 機(jī)床與工件之間可能發(fā)生干涉的零部件有刀具、夾頭、主軸頭、主軸夾板、夾板鉸鏈和連桿. 工件可以認(rèn)為是由加工表面和非加工表面構(gòu)成. 其中, 加工表面由加工點(diǎn)、與機(jī)床可能會(huì)發(fā)生干涉的非加工表面由非加工點(diǎn)構(gòu)成, 在此, 將加工點(diǎn)和非加工點(diǎn)統(tǒng)稱為查詢點(diǎn).
圖2 并聯(lián)機(jī)床與工件干涉的檢查方法
查詢點(diǎn)與刀具、夾頭、主軸頭和主軸夾板發(fā)生的干涉稱為第1 類干涉.這類干涉只與刀具的姿勢(shì)有關(guān), 與工件的安裝位置無(wú)關(guān). 所以, 如果檢查到這類干涉, 只能通過(guò)調(diào)整刀具姿勢(shì)進(jìn)行回避, 這就要修改CAM 軟件, 超出了本文討論的范圍.
查詢點(diǎn)與夾板鉸鏈或連桿發(fā)生的干涉稱為第2類干涉.這類干涉是能夠通過(guò)調(diào)整工件安裝位置回避的.下面介紹這兩類干涉的檢查點(diǎn)的組成方法.
設(shè)有一圓錐體, 其頂點(diǎn)為刀具中心、圓錐角H0為包含刀具、夾頭、主軸頭和主軸夾板的最小角度;刀具中心到夾板鉸鏈的最小距離為d 0; 在刀具軸方向上的最小距離為h0, 則H0、d 0 和h0 可以根據(jù)機(jī)床零部件的結(jié)構(gòu)尺寸和夾板鉸鏈的最大回轉(zhuǎn)角等參數(shù)求出.
對(duì)于任一加工點(diǎn)P , 計(jì)算P 與所有查詢點(diǎn)Q 的連線PQ 和刀具軸的夾角H、線段的長(zhǎng)度d 以及線段PQ 在刀具軸線方向上投影的長(zhǎng)度h. 因此, 滿足條件H< H0 的查詢點(diǎn)作為第1 類干涉的檢查點(diǎn); 滿足條件d < d 0 且h< h0 的查詢點(diǎn)作為第2 類干涉的檢查點(diǎn).對(duì)于所有的加工點(diǎn),均求出這兩類檢查點(diǎn),并存入檢查點(diǎn)文件.
1. 2. 2 檢查干涉的方法 在檢查是否出現(xiàn)第1 類干涉時(shí), 首先將刀具、夾頭、主軸頭和主軸夾板(簡(jiǎn)稱為刀具系統(tǒng)) 以及第1 類干涉的檢查點(diǎn)向x z 平面投影, 然后, 檢查落入刀具系統(tǒng)投影內(nèi)的檢查點(diǎn)是否與刀具系統(tǒng)發(fā)生干涉. 由于第1 類干涉與工件的安裝位置無(wú)關(guān), 所以, 在計(jì)算工件的安裝位置之前, 只需進(jìn)行1 次這樣的檢查計(jì)算.
由于工件安裝位置的不同, 必將導(dǎo)致夾板鉸鏈和連桿的位置與姿勢(shì)的變化. 所以, 工件的安裝位置每次調(diào)整后, 都必須檢查是否會(huì)發(fā)生第2 類干涉. 因此, 如何減少第2 類干涉的檢查點(diǎn)是縮短檢查時(shí)間的關(guān)鍵. 本文中, 判斷第2 類干涉檢查點(diǎn)的條件是滿足d < d 0 且h < h0, 這對(duì)于較小的工件或者較平坦的工件, 可以大幅度地削減檢查點(diǎn)數(shù).
1. 2. 3 回避干涉的方法 當(dāng)出現(xiàn)干涉時(shí), 其回避方法與出現(xiàn)自己干涉時(shí)的回避方法相同.
1. 3 機(jī)床與周邊器械的干涉
1. 3. 1 檢查點(diǎn)的組成 圖3 為并聯(lián)機(jī)床HexaM中的周邊器械、工件以及加工時(shí)刀具軌跡的俯視圖.從圖3 可以看出, 周邊器械設(shè)置在工作臺(tái)的第1 象限, 所以, 將刀具軌跡中心的第1 象限的外測(cè)點(diǎn)(·)作為干涉的檢查點(diǎn).
圖3 機(jī)床與周邊器械干涉的檢查點(diǎn)與回避方向
1. 3. 2檢查干涉的方法 可能與周邊器械發(fā)生干涉的機(jī)床零件有刀具、夾頭、主軸頭、夾板鉸鏈、連桿和主軸夾板, 它們的形狀為圓柱體和有界平面構(gòu)成的多面體, 而周邊器械的外形為多面體.所以,周邊器械與機(jī)床零件之間可以沿用“有界平面與圓柱體”及“有界平面與有界平面”的干涉檢查方法.即在所有的檢查點(diǎn)上, 計(jì)算構(gòu)成周邊器械的有界平面與機(jī)床零件的圓柱體或有界平面之間是否有交點(diǎn).如有交點(diǎn), 說(shuō)明發(fā)生干涉; 如無(wú)交點(diǎn), 則說(shuō)明不發(fā)生干涉. 如上所述, 工件安裝位置的不同必將帶來(lái)機(jī)床零件位置和姿勢(shì)的變化, 所以, 每次設(shè)定新的工件安裝位置之后, 必須再次檢查是否發(fā)生機(jī)床與周邊器械的干涉.
1. 3. 3 回避干涉的方法,如果機(jī)床與周邊器械發(fā)生干涉, 則將周邊器械前表面的法線方向作為回避方向, 回避方法與發(fā)生自己干涉時(shí)的回避方法相同.
1. 4 工件與周邊器械的干涉
為了能快速地檢查出在安裝時(shí)工件與周邊器械是否存在干涉, 首先將工件向xy 平面投影,并用有界多邊形包絡(luò)工件的投影.然后,使用“有界平面與有界平面”來(lái)檢查工件與周邊器械的干涉. 每次給出工件安裝位置以后, 都必須進(jìn)行這種干涉檢查.如果工件與周邊器械發(fā)生干涉, 則將周邊器械前表面的法線方向作為回避方向, 回避方法與發(fā)生自己干涉時(shí)的回避方法相同.
1. 5 檢查點(diǎn)的插補(bǔ)
從上述內(nèi)容知道, 除工件與周邊器械的干涉檢查外, 其他的干涉檢查都是在檢查點(diǎn)處計(jì)算是否存在干涉. 因此, 如果檢查點(diǎn)之間的距離過(guò)大, 則存在著在檢查點(diǎn)沒(méi)有干涉, 而在檢查點(diǎn)之間會(huì)發(fā)生干涉,而這樣的干涉又沒(méi)有被發(fā)現(xiàn)的可能. 這在實(shí)際加工時(shí)是絕對(duì)不允許的.
要解決檢查點(diǎn)之間可能存在的干涉問(wèn)題, 主要有兩種方法: 一是簡(jiǎn)單函數(shù)與多面體求交的方法;二是將檢查點(diǎn)之間的距離縮小. 第1 種方法對(duì)于檢查機(jī)床與工件的干涉特別有效, 但不能用來(lái)解決自己干涉; 第2 種方法對(duì)于各種干涉的檢查都適用, 但如果檢查點(diǎn)之間的距離過(guò)小, 則檢查點(diǎn)的數(shù)量巨大,檢查干涉的計(jì)算時(shí)間會(huì)很長(zhǎng). 所以, 本文中設(shè)定一個(gè)安全距離, 根據(jù)這個(gè)安全距離來(lái)縮短檢查點(diǎn)之間的距離,以便達(dá)到檢查結(jié)果既要可靠, 檢查時(shí)間又要短的目的. 具體方法如下.
在進(jìn)行判斷兩個(gè)物體是否干涉時(shí),首先將其中一個(gè)物體擴(kuò)大5 mm. 如果擴(kuò)大后兩個(gè)物體有交點(diǎn),則判定為兩個(gè)物體有干涉. 如果交點(diǎn)在距物體表面5 mm 以內(nèi),實(shí)際上還是沒(méi)有發(fā)生干涉.即如果判定兩個(gè)物體不存在干涉, 那么, 兩個(gè)物體的距離應(yīng)在5mm以上.在此,將這5mm稱為安全距離.
對(duì)于由CAM 系統(tǒng)輸出的查詢點(diǎn)和刀具軌跡,如果相鄰的查詢點(diǎn)的距離或刀具軌跡的距離大于安全距離, 則在查詢點(diǎn)之間或刀具軌跡間插補(bǔ)一些點(diǎn).即經(jīng)過(guò)插補(bǔ)后的查詢點(diǎn)間及刀具軌跡間的距離均小于安全距離. 所以, 當(dāng)在兩個(gè)檢查點(diǎn)上不發(fā)生干涉時(shí), 則在它們之間也不會(huì)發(fā)生干涉. 因此,用安全距離判斷是否需要插補(bǔ), 既可以防止漏檢干涉, 又不過(guò)多地增加計(jì)算時(shí)間.
2 工件安裝位置的計(jì)算方法
2. 1 工件的最佳安裝位置
本文將“墊塊高度最低; 距工作臺(tái)中心距離最短”作為衡量工件最佳安裝位置的標(biāo)準(zhǔn).具體地說(shuō),就是首先以工件底面放置在工作臺(tái)上(此時(shí), 墊塊的高度為0)、刀具軌跡在xy 平面上的投影中心與工作臺(tái)中心重合時(shí)(距工作臺(tái)中心距離為0),作為工件的最佳安裝位置. 如果在該位置存在干涉不能安裝時(shí), 為保證墊塊高度最低, 則將工件在同一水平內(nèi)由內(nèi)向外移動(dòng), 尋找不會(huì)出現(xiàn)干涉的安裝位置. 如果在同一水平面內(nèi)找不到不發(fā)生干涉的安裝位置,則將工件逐漸向上(加大墊塊高度) 移動(dòng)后,再在同一水平面內(nèi)繼續(xù)尋找,直到找到安裝位置或者得出在本機(jī)床上不能加工的結(jié)論為止.
2. 2 最佳安裝位置的計(jì)算方法
基于工件最佳安裝位置的概念,本文提出了加工時(shí)工件安裝位置計(jì)算步驟如下:
(1) 讀取基本數(shù)據(jù). 包括有:刀具夾頭的半徑和伸出長(zhǎng)度;查詢點(diǎn);刀具軌跡;周邊器械的位置和在xy 平面上的投影等.
(2) 判斷能否在本機(jī)床上進(jìn)行加工.根據(jù)工件的查詢點(diǎn)和刀具軌跡,計(jì)算工件在xyz方向的外形尺寸和刀具的移動(dòng)距離.當(dāng)工件的外形尺寸或刀具的移動(dòng)距離過(guò)大,給出該工件在機(jī)床上不能加工的警告后,結(jié)束系統(tǒng)的運(yùn)行.
(3) 生成檢查各類干涉的檢查點(diǎn)文件.其中有:檢查自己干涉、機(jī)床與工件的第1 類和第2 類干涉、機(jī)床與周邊器械干涉的檢查點(diǎn)文件.
(4) 檢查是否存在機(jī)床與工件的第1 類干涉.如果存在, 由于該干涉無(wú)法通過(guò)移動(dòng)工件安裝位置來(lái)回避, 所以, 在給出“存在無(wú)法回避的第1 類干涉”的警告后, 結(jié)束系統(tǒng)運(yùn)行.
(5) 設(shè)定刀具軌跡中心C (x , y , z ) 的初始位置為了滿足工件最佳安裝位置的定義, C (x , y , z ) 的初始置設(shè)定為: x = 0; y = 0; z = s. 其中, s 為刀具軌跡中心到工件底面的距離.
(6) 計(jì)算刀具軌跡中心C 的位置. 根據(jù)干涉的檢查方法和回避方法, 不斷移動(dòng)刀具軌跡中心的安裝位置, 直到找到不會(huì)出現(xiàn)干涉的安裝位置或給出該工件不能在本機(jī)床上加工的警告為止.
(7) 輸出工件的安裝位置. 在(6) 中如果求得了不會(huì)出現(xiàn)干涉的刀具軌跡中心的位置, 則根據(jù)該值和工件的結(jié)構(gòu)尺寸, 計(jì)算并輸出工件的安裝位置.
3 解析、實(shí)驗(yàn)結(jié)果
對(duì)于圖4 所示的外形尺寸為350mm ×350mm×150 mm 工件, 當(dāng)采用垂直加工時(shí), 使用通用的CAM 軟件CAMAND 生成加工時(shí)的刀具位置和刀具姿勢(shì)(與加工點(diǎn)的法線相同). 圖中, 刀具軌跡中的位置點(diǎn)數(shù)為123 201 點(diǎn). 刀具為球頭銑刀、直徑10mm、從夾頭中伸出長(zhǎng)度50 mm , 夾頭直徑60 mm、從主軸中伸出45 mm.
圖4 工件及刀具軌跡
根據(jù)上述算法, 本文開發(fā)出并聯(lián)機(jī)床切削加工時(shí)工件安裝位置計(jì)算系統(tǒng). 計(jì)算了加工圖4 所示工件時(shí)的安裝位置, 計(jì)算時(shí)間(計(jì)算機(jī)的CPU: AMD A THLON 850MHz) 約15 min.
3. 1 檢查點(diǎn)數(shù)
在CAMAND 軟件生成的刀具軌跡中,由于不存在相鄰刀具軌跡大于安全距離, 所以, 不需要插補(bǔ)輔助點(diǎn). 還有, 圖4 所示的工件上, 除加工面之外,其余表面均不可能與機(jī)床發(fā)生干涉,所以,查詢點(diǎn)全部由刀具軌跡點(diǎn)構(gòu)成. 從查詢點(diǎn)中抽出的自己干涉檢查點(diǎn)數(shù)為2382點(diǎn);機(jī)床與周邊器械干涉的檢查點(diǎn)數(shù)為248 點(diǎn);機(jī)床與工件的第1種、第2種干涉的檢
查點(diǎn)數(shù)均為0 點(diǎn).工件與周邊器械的干涉檢查則成為2個(gè)四邊形求交點(diǎn)的問(wèn)題.
3. 2 安裝位置的解析、實(shí)驗(yàn)結(jié)果
工件安裝位置的變化過(guò)程如圖5 所示. 從計(jì)算過(guò)程知道,當(dāng)工件安裝位置較低且靠近工作臺(tái)中心時(shí),容易發(fā)生機(jī)床與周邊器械的干涉;如果工件的安裝位置距中心較遠(yuǎn), 則容易發(fā)生機(jī)床的自己干涉.最后,當(dāng)工件的安裝高度達(dá)到70 mm 時(shí),才找到了不發(fā)生干涉的可安裝位置.
圖5 工件安裝位置的變化過(guò)程
圖6 為將工件安裝在圖5 中位置★時(shí)的安裝簡(jiǎn)圖.從圖6 可以看出, 工件底面中心并不在工作臺(tái)的中心上, 而是從工作臺(tái)中心偏離(- 42.05,- 42.05,70)mm.這是因?yàn)?要回避機(jī)床與放置在工作臺(tái)第1象限的周邊器械發(fā)生的干涉, 就必須將工件向工作臺(tái)第3 象限移動(dòng), 同時(shí)還要向上移動(dòng), 安裝時(shí)必須給工件下放置70 mm 高的墊塊.
圖6 工件的最終安裝位置
為了檢查圖6 所示安裝位置以及將該位置做適當(dāng)取整后是否會(huì)出現(xiàn)干涉, 本文使用機(jī)床HexaM進(jìn)行實(shí)驗(yàn), 安裝位置和實(shí)驗(yàn)結(jié)果如表1 所示. 其中,最小間隙是采用目測(cè)方法得到的.
表1中,除在第3 行位置(x = - 35, y = - 35, z= 70)mm 之外安裝工件時(shí), 解析結(jié)果和實(shí)驗(yàn)結(jié)果相同,即不會(huì)出現(xiàn)干涉.而在第3行所示位置安裝工件時(shí), 由實(shí)驗(yàn)知, 機(jī)床與周邊器械的最小間隙是3mm ,這比本解析系統(tǒng)設(shè)定的安全距離5 mm小,在解析時(shí)自然被判定為出現(xiàn)干涉. 雖然解析結(jié)果與實(shí)驗(yàn)結(jié)果不同,但仍然可以認(rèn)為解析結(jié)果是合理的、正
確的. 因此, 可以說(shuō)本文中提出的計(jì)算方法和開發(fā)的工件安裝位置計(jì)算系統(tǒng)是有效的,在實(shí)際加工中是可用的.
4 結(jié) 論
本文以日本豐田工機(jī)公司的并聯(lián)機(jī)床HexaM為模型, 探討了在使用并聯(lián)機(jī)床加工時(shí),機(jī)床的自己干涉、機(jī)床與工件、機(jī)床與周邊器械以及工件與周邊器械的干涉的檢查方法, 以及通過(guò)調(diào)整工件的安裝位置來(lái)回避干涉的方法.最后,通過(guò)一系列的解析結(jié)果和實(shí)驗(yàn)結(jié)果的對(duì)比, 證明了本研究提出的計(jì)算工件安裝位置的算法和開發(fā)的軟件是正確的. 從以上的論述過(guò)程中還可得到如下結(jié)論:
(1) 所開發(fā)的系統(tǒng)能夠自動(dòng)算出在本機(jī)床上能否按照給定的加工軌跡加工給定的工件.
(2) 在判斷可以加工的情況下,能算出不會(huì)發(fā)生干涉的工件安裝位置.
本文提出的干涉檢查方法和回避方法是有效的,能解決實(shí)際問(wèn)題.
11
JOURNAL OF SHANG HAI JIAO TONG UNIVERSITY1994-2007 ChinaAcademicJournal Electronic PublishingHouse.Allrights reserved.http:/DevelopmentDevelopmentDevelopmentDevelopmentofofofofa a aaWorkpieceWorkpieceWorkpieceWorkpieceLocationLocationLocationLocationDetermDetermDetermDeterminationinationinationinationSystemSystemSystemSystemininininParallelParallelParallelParallelMechanismMechanismMechanismMechanismTypeTypeTypeTypeMachineMachineMachineMachineToolsToolsToolsToolsZHAO Xiao ming,SHAO Hua,HATTORIKazuya,TSUTSUMIM asaom i1.School ofMechanical Eng, Shanghai Jiao tong Univ, Shanghai 200030,China;2.Technical Research Dept,ToyodaMachineWorks, Kariya 44828652,Japan;3.Bio Applications and Systems Eng,TokyoUniv of Agriculture and Technology,Tokyo18428858, Japan.Abstract:This paper uses HexaM made by ToyodaMachine Works Co.as an analyticalmodel of parallelmechanism type machine tools. Much collision may be generated foritscomplicatedstructure and working space, when a workpieceismach inedusing this machine. Forexample, those collisions are generated.between the moving components of the parallelmechanism ,between the moving components and a workpiece and between themovingcomponents and the tool storage for autom atic changing.In thispaper,an algorithmfor detecting and avoiding those collision swasproposed. The method for avoiding thecollisions was conducted by readjusting the location of the workpiece without am endingthe toolpath.Itisconfirmed through experim ent that the proposed algorithmisuseful for detecting the collisions and determining the location of the workp iecepriortothe actual machining.Keywords: parallel machine tools;ollision check; avoidance; toolpath; in stallation siteIn recent years, the PMT development and application of the growing, but because ofitsstructure andworking spaceisvery complicated, use it for processing the workpiece, itisvery possible the machinecomponents themselves interfere with the workpiece and the machine interference.Also, if like PMT HexaM1, work on stage in the installation of automatic tool change devices and other peripheral equipment, theinstallation of the workpiece. It may limit the installation of the workpiece location, that is, peripheral equipmentand workpiece interference that may arise when processing machines and peripheral equipmenttointerfere.PMT on their waytocheck interference and machine work space has been much research 2 5.Among them, This writer and other Japanese companies Toyota Machine Works of PMT HexaM 1asa model.Discussion ofPMTstheir interference in the inspection, the work space approximate expression 5. the otherhand, 5-axis NC machining, cutting tool (knife, Chuck and Spindle) and the workpiece (workpiece and fixture)interference methods also have many. Among them, Takeuchi, etc. 6 tool system from the surface for anumber of pointsasinterference checking, and the workpiece surface are relatively simple function, wheninterference check point at the internal functions, be abletojudge for the machine and workpiece occurredinterference; The author, etc. 7 and the method proposed here just the opposite. that is, from the workpiecesurface, system selection interference checking, whether the system access tool for interference checking. AsCNC machine peripheral devices are not generally placed in the work tops , So, in these two methods, they didnot consider processing machines and peripheral equipmenttointerfere in the issue.These studies are discussed in detail PMT their interference in the machine tool and workpiece and theinterference checking and evasive methods, However, the use of PMT ago, but there are several problems:JOURNAL OF SHANG HAI JIAO TONG UNIVERSITY1994-2007 ChinaAcademicJournal Electronic PublishingHouse.Allrights reserved.http:/ working platform for peripheral devices suchasa barrier Machine 1 should consider the machines andperipheral equipment possible interference; the inspection machine and the interference of the workpiece. Consideration should also be given spindleplywood, plywood hinge link with the workpiece and the possibility of interference, However, the existing CAMsoftware does not include such interference detection; machine when thereisinterference with the workpiece. GeneralToolalways postural adjustmentstoavoidinterference. In fact, PMT, in additiontopostural adjustment tool,Youcan also adjust the location of theworkpiecetoavoid all interference. Moreover, This approach avoided the biggest advantageisnottochangethe existing CAM software.Based on common CAM software tool path of the output-based, shorten the timetointerfere in theinspection checkpoints document composition, By adjusting the location of the installation of the workpiecetoavoid the possibility of all kinds of interference, of the workpiece can test for processing at the workpiece andmachinability best installation location calculation.1.Interference1.Interference1.Interference1.InterferencecheckingcheckingcheckingcheckingandandandandavoidavoidavoidavoidinterferenceinterferenceinterferenceinterferenceUsing the PMT HexaM, peripheral equipment (the knife) and the workpiece installation diagram shownin Figure 1. Therefore, For the machine, during processing and installation of the workpiece at the possibility ofinterference with his interference, machine tool and workpiece interference machines and the peripheralequipment, and interference with the surrounding devices workpiece interference.If you are using a parallel machine table without peripheral devices or devices placed around the farmore, will not affect the location of the workpiece machining process or there will not be machines andperipheral equipment interference, can be omitted from the workpiece and the machine and equipment aroundthe interference checking.F ig. 1Schemat ic of the parallelmechanism HexaM1.11.11.11.1TheirTheirTheirTheirinterferenceinterferenceinterferenceinterference1.1.11.1.11.1.11.1.1TheTheTheThecompositioncompositioncompositioncompositioncheckpointscheckpointscheckpointscheckpointsDuring processing, All tools can be appliedtoposition literature 5described methodtocheck whether their intervention will happen. if thereisinterference, can be used in theadjustment of the workpiece locationtoavoid interference. Parts of the installation location changes,ProcessingToolposition will naturally be changed. Therefore, the needtoconduct another inspection, notoccur until the date their interference. As an installation at each locationtolocation of all the tools for inspectionJOURNAL OF SHANG HAI JIAO TONG UNIVERSITY1994-2007 ChinaAcademicJournal Electronic PublishingHouse.Allrights reserved.http:/computing time will be very long.Toshorten the time of calculation, thisisnot the right tool for all locations andtoextract only a small number of knives location (hereinafter referredto ascheck points) interference checking.Therefore, point out checks must be done:at checkpoints if no interference initsown. in the other cutterlocation would not interfere in their occurrence. setting up check-points advantage of a significant reduction inthe frequency of inspections.From the z-axis cutter farther, the higher the position, the greater the degree of tilt, the more prone theyinterfere in 5. Therefore, wait for the processing of the workpiece, the tool path from the outsidetoshare themeasurement point, the higher the cutter location, tool tilt angle larger pointas todetermine whether theyinterfere in the check points.1.1.21.1.21.1.21.1.2InterfereInterfereInterfereInterferewithwithwithwiththethethetheinspectioninspectioninspectioninspectionmethodsmethodsmethodsmethodsToolposition and posture straight at the moon and the spacerotary disk space, it would be interference initsown 5. Therefore, they interfere with the inspection methods: read all checkpoints, obtained a checkpoint each correspondingtothe straight and rotating space YuanYuan space 5. cutter position and posture in response The straight round space and space Rotary Circle,convicted of the checkpoint will not interfere in their occurrence;Inall the check points are not interfered, werejudgedtobe installed in the position nottointerfere in their occurrence. If a check point in the location orposition of the straight excess space Yuan Yuan, or rotating space, can be used in the literature 5 mentionedin the inspection methodstointerfere in the review. As space than the average round of inspectionsinterference 5 calculationtobe much smaller, so this kind of method can shorten each inspection, thecomputation time.1.1.31.1.31.1.31.1.3AvoidAvoidAvoidAvoidinterferenceinterferenceinterferenceinterferencemethodmethodmethodmethodAs in the same horizontal plane, the cutter in the z-axis location at the leastpronetohis interference. Therefore, If a checkpoint in a self-interference then we check points and the z-axisdirection connectivityasevasive. Then, Parts of the installation location along the direction of movement ofevading 10 mm. If two consecutive evade direction of the angleisgreater than 150 . that could have beenavoided reversed direction in the horizontal plane does not exist in the locationtoinstall, soThe workpiece canbe installedtoenhance upward position.Inthis paper, each increase by 10 mm. If they interfere with the mainmotorisa rotary screw lower interference Note workpieceistoo high or the location of the workpiece too high,not with the machine tool.1.21.21.21.2MachineMachineMachineMachineinterfereinterfereinterfereinterferewithwithwithwiththethethetheworkpieceworkpieceworkpieceworkpiece1.2.11.2.11.2.11.2.1TheTheTheThecompositioncompositioncompositioncompositioncheckpointscheckpointscheckpointscheckpointsAs shown in figure2,machine and workpiece possible interferencebetween parts of a knife, chuck, spindle head, spindle splint, Hinges and plywood link. workpiece can be seenfrom the surface and surface composition. Among them, Surface processing from the point with machine mighthappentothe non-interference by non-machined surface processing point is, here, processing and point andnon-point processing collectively referred inquiriestothe point.JOURNAL OF SHANG HAI JIAO TONG UNIVERSITY1994-2007 ChinaAcademicJournal Electronic PublishingHouse.Allrights reserved.http:/F ig. 2Check method of the collision betw een the parallelmechanism and wo rkp ieceInquiries point with knives, and Chuck, The first spindle axis and the splint interference knownasacategory interference. Such interference only with knives, the posture, and workpiece position unrelatedtotheinstallation. Therefore, if the screening of such interference, and only postural adjustment tool for evasive, Thisrequires changes CAM software, beyond the scope of this discussion.Inquiries point splint hinge connecting rod or interfere in the resolutionasinterference in two categories.Such interference can be adjusted through the installation of the workpiece - Purchase avoided. Below thesetwo types of intervention onthe check points formed.With a cone,itscenter point for the tool, cone angle of H0 included knives, and Chuck, The first spindleaxis and the minimum angle of plywood;Toolcenter hinge splinttothe minimum distance of d002;Toolaxis inthe direction of the minimum distance of h0, H0, d002 and h0 machine parts accordingtothe size and structureof plywood hinge back corner of the largest such parameters obtained.For the processing of a pointP,P calculated with all inquiries Q-point connectivity PQ and the tool axisangle H, d line segment and the length of the segment PQ tool axis direction on the length of the projection h.Therefore, satisfy conditions H H 0 inquiries pointasa kind of interference in check; satisfy conditions d h andd 0 h0 inquiries pointsasClass 2 interfere in the check points. As with all the processing points have obtainedtwo checkpoints, and deposited checkpoints document.1.1.21.1.21.1.21.1.2InterfereInterfereInterfereInterferewithwithwithwiththethethetheinspectioninspectioninspectioninspectionmethodsmethodsmethodsmethodsChecking whether there was interference in Category1,thefirst knife, Chuck, The first spindle axis and splint (referredto asToolSystem), and a type of interventioncheckpoints x z planetothe projection, then,Toolchecks into the projection system checks whether the pointsystem and tool interference 7. As the No. 1 category interfere with the workpiece unrelatedtothe installationlocation, in the calculation of the workpiece location, only for a meeting of this kind of checking calculations.Duetothe location of the installation of the workpiece, which will definitely leadtosplint hinge and linkthe position and posture change. Therefore, Parts of each installation location adjustments, we must checkwhether there will be interference in the first two categories. Therefore, Howtoreduce interference in the firsttwo categories of the inspectionistoshorten the clearance time of the key.Inthis paper, judgment Category 2interference check pointistosatisfy the conditions d h and d 0 h0, This small workpiece or relatively flatworkpiece can be significantly reduced check points.JOURNAL OF SHANG HAI JIAO TONG UNIVERSITY1994-2007 ChinaAcademicJournal Electronic PublishingHouse.Allrights reserved.http:/1.2.31.2.31.2.31.2.3AvoidAvoidAvoidAvoidinterferenceinterferenceinterferenceinterferencemethodmethodmethodmethodWhen interference, anditsmethod of avoiding interference initsown whenthere are evading the same method.1.31.31.31.3MachineMachineMachineMachineandandandandequipmentequipmentequipmentequipmentaroundaroundaroundaroundthethethetheinterferenceinterferenceinterferenceinterference1.3.11.3.11.3.11.3.1TheTheTheThecompositioncompositioncompositioncompositioncheckpointscheckpointscheckpointscheckpointsFigure 3 for PMT HexaMof peripheral equipment, workpiecemachining and tool path when the vertical view. From Figure3,we can see that peripheral equipment installedin the workstationstoa quadrant, soToolpathtothe center of a quadrant of the outer (.),asinterference in thecheck points.Fig. 3Check po ints and avo idance vecto r of thecollisionbetw een the parallelmechanism and magazine1.3.21.3.21.3.21.3.2InterfereInterfereInterfereInterferewithwithwithwiththethethetheinspectioninspectioninspectioninspectionmethodsmethodsmethodsmethodsAnd peripheral equipment may interfere with the parts of amachine tool, chuck, spindle head, plywood hinge connectingrodand spindle splint, Their shape of a cylinderand the plane circles constitute the polyhedron, and peripheral equipment for the many facets of the shape.Therefore, peripheral equipment and machine parts will be used between bounded plane and cylinder andbounded plane and bounded plane interference method 5. That is, in all the checkpoints, causing peripheralequipment bounded plane and the cylindrical machine parts sector plane or whether thereisan intersectionbetween. If Nodal, Information on interference; If no intersection, a statement that no interference. As notedabove, workpiece location of the installation will bringdifferent machine parts location and posture change, soeach set new workpiece location, must re-examine whether there has been peripheral equipment and machineinterference.1.3.31.3.31.3.31.3.3AvoidAvoidAvoidAvoidinterferenceinterferenceinterferenceinterferencemethodmethodmethodmethodIf the machine occurred with the surrounding equipment interference,peripheral equipment will surface before the normal directionas toevade direction, and the occurrence ofevading their own methods of avoiding interference in the same way.1.41.41.41.4WorkpieceWorkpieceWorkpieceWorkpieceandandandandthethethetheinterferenceinterferenceinterferenceinterferenceofofofofneighboringneighboringneighboringneighboringdevicesdevicesdevicesdevicesInordertobe abletoquickly detect when installing the workpiece and the existence of peripheralequipment interference, the first of the workpiecetothe xy plane projection, and bounded by polygonsworkpiece envelope projection. Then, use bounded plane and bounded plane 5tocheck the workpiece andthe interference of neighboring devices. each installation location given workpiece after, the need for suchinterference checking.If the workpiece and interfere with the surrounding equipment, peripheral equipment will surface beforethe normal directionas toevade direction, and the occurrence of evading their own methods of avoidinginterference in the same way.JOURNAL OF SHANG HAI JIAO TONG UNIVERSITY1994-2007 ChinaAcademicJournal Electronic PublishingHouse.Allrights reserved.http:/1.51.51.51.5InterpolationInterpolationInterpolationInterpolationofofofofcheckcheckcheckcheckpointspointspointspointsFrom the above content aware that apart from the workpiece and the interference of neighboringequipment checks, other checks are interfering in the inspection point in terms of interference. Therefore, if thecheck points between the distanceistoo large, There wereatcheckpoints without interference, whileatcheckpoints will happen between interference, But such interference has not been found possible. in actualprocessing timeisabsolutely impermissible.Tosolve checkpoints may exist between the interference problem, there are two major ways:First, asimple function with polyhedron intersection method 8; twoistocheck the distance between the pointnarrowing. No. 1 methods for screening machine and the interference of the workpiece particularly effective,But they can not be usedtosolve interference; 2 methods for the various types of interference in the inspectionappliestoall, But if the checkpoints between the distanceistoo small, check points, a huge amount, Inspectioninterfere in the calculation will be very long. Therefore, we set a safe distance, Under this safe distance fromthe check pointtoshorten the distance between, in ordertoachieve the results we are reliable, also short timeinspection purposes. specific methods areasfollows.Conducting two objects judgment interference, One of the first objectstoexpand 5 mm. If the expandedintersection of two objects. was convicted of two objects thereisinterference. If the intersection from thesurface of objects within 5 mm.Infact, thisisstill no interference. If convicted of two objects thereisnointerference, then the distance between the two objects in more than 5 mm. Here, this 5 mm called safedistance.CAM system for output from the reference point and tool path, If adjacenttothe inquiry or the distancetool pathisgreater than the distance between a safe distance Inquiries points in the tool path between oramong some interpolation points. thatis, after inquiries after the interpolation between the points and tool pathisthe distance between less safe distance. So, when the two checkpoints there are no interference. in betweenthem would not have happened interference. Thus, a safe distance from the needtodetermine whether theinterpolation, can prevent missed interference, without excessive increase in computing time.2.2.2.2.WorkpieceWorkpieceWorkpieceWorkpiecelocationlocationlocationlocationofofofofthethethetheinstallationinstallationinstallationinstallationmethodmethodmethodmethodofofofofcalculationcalculationcalculationcalculation2.12.12.12.1PartsPartsPartsPartsofofofofthethethethebestbestbestbestinstallationinstallationinstallationinstallationlocationlocationlocationlocationInthis paper, Pad of the minimum height; from the shortest distance from the center stage as ameasure of the workpiece best installation location standards. Specifically, Firsttothe workpieceisplaced inthe bottom table (At this point, the height of the pan 0)Tooltracks in the xy plane projection center and thecenter coincides workstations (distance from the center of the worktable 0) Workpieceasthe best installationlocation. If thereisinterference in the locationtobe installed, in ordertoguarantee the minimum height Pad,will be the workpiece within the same level from the inside outward movement Find no interference in theinstallation location. If not found in the same horizontal plane does not interfere with the
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