电竞比分网-中国电竞赛事及体育赛事平台

分享

五軸加工的RTCP技術(shù)[原創(chuàng)+整理

 zfl130 2011-03-24

五軸加工的RTCP技術(shù)【原創(chuàng)+整理】 
    
一點兒背景

      十數(shù)年前,一汽為模具加工招標五軸機床,據(jù)說當時去了不少國際大牌廠商,招標現(xiàn)場有外商提出他們的產(chǎn)品好,有RTCP功能,在坐的國內(nèi)廠商和業(yè)內(nèi)專家一時語塞,幾乎無人知曉RTCP為何方神圣,最后還是國內(nèi)最早從事數(shù)控研究的某高校知名教授現(xiàn)場指點迷津,才為國內(nèi)業(yè)界挽回局面。但一直到十幾年之后的“十一五”數(shù)控重大專項出臺前后,RTCP概念才開始得到國內(nèi)數(shù)控業(yè)界和學界的廣泛關(guān)注。
      差不多兩年,一業(yè)內(nèi)企業(yè)在媒體上高調(diào)宣稱其具有自主知識產(chǎn)權(quán)的高端數(shù)控系統(tǒng)具有RTCP和極高段數(shù)的前瞻功能,問及RTCP和前瞻的精髓是什么時,也就噤聲不語了,不知是不愿說,還是沒法說。
      今年年底“十一五”數(shù)控重大專項的高端數(shù)控系統(tǒng)的五家中標企業(yè):華中、廣數(shù)、高精(藍天)、航天、光洋都將進行項目驗收,屆時RTCP將不可避免地稱為驗收的焦點之一,八仙過海,各顯神通,驗收原則上不會不過,但實效如何,國產(chǎn)的RTCP能否穩(wěn)健走向市場,并為用戶創(chuàng)造價值,大家仍需拭目以待。 
 
個人對RTCP的理解

      一臺數(shù)控機床有五個聯(lián)動軸并不能就此簡單地稱之為五軸機床,同樣,一套數(shù)控系統(tǒng)能控五個軸,也不能就此聲稱為五軸數(shù)控系統(tǒng),判斷一臺數(shù)控機床是不是五軸機床,一套數(shù)控系統(tǒng)是不是真正的五軸系統(tǒng),首先必須看其是否具備RTCP功能,F(xiàn)idia的RTCP是“Rotational Tool Center Point”的縮寫,字面意思是“旋轉(zhuǎn)刀具中心”,業(yè)內(nèi)往往會稍加轉(zhuǎn)義為“圍繞刀具中心轉(zhuǎn)”,也有一些人直譯為“旋轉(zhuǎn)刀具中心編程”,其實這只是RTCP的結(jié)果。PA的RTCP則是“Real-time Tool Center Point rotation”前幾個單詞的縮寫。海德漢則將類似的所謂升級技術(shù)稱為TCPM,即“Tool Centre Point Management”的縮寫,刀具中心點管理。還有的廠家則稱類似技術(shù)為TCPC,即“Tool Center Point Control”的縮寫,刀具中心點控制。
      從Fidia的RTCP的字面含義看,假設(shè)以手動方式定點執(zhí)行RTCP功能,刀具中心點和刀具與工件表面的實際接觸點將維持不變,此時刀具中心點落在刀具與工件表面實際接觸點處的法線上,而刀柄將圍繞刀具中心點旋轉(zhuǎn),對于球頭刀而言,刀具中心點就是數(shù)控代碼的目標軌跡點。為了達到讓刀柄在執(zhí)行RTCP功能時能夠單純地圍繞目標軌跡點(即刀具中心點)旋轉(zhuǎn)的目的,就必須實時補償由于刀柄轉(zhuǎn)動所造成的刀具中心點各直線坐標的偏移,這樣才能夠在保持刀具中心點以及刀具和工件表面實際實際接觸點不變的情況,改變刀柄與刀具和工件表面實際接觸點處的法線之間的夾角,起到發(fā)揮球頭刀的最佳切削效率,并有效避讓干涉等作用。因而RTCP似乎更多的是站在刀具中心點(即數(shù)控代碼的目標軌跡點)上,處理旋轉(zhuǎn)坐標的變化。
      不具備RTCP的五軸機床和數(shù)控系統(tǒng)必須依靠CAM編程和后處理,事先規(guī)劃好刀路,同樣一個零件,機床換了,或者刀具換了,就必須重新進行CAM編程和后處理,因而只能被稱作假五軸,國內(nèi)很多五軸數(shù)控機床和系統(tǒng)都屬于這類假五軸。當然了,人家硬撐著把自己稱作是五軸聯(lián)動也無可厚非,但此(假)五軸并非彼(真)五軸! 
      
Fidia C20數(shù)控系統(tǒng)宣傳樣本關(guān)于RTCP的描述

(以下文字面由本人參照英文樣本翻譯,不夠貼切之處請不吝指正) 
 
      RTCP功能可以直接在機床上針對雙擺銑頭和雙轉(zhuǎn)臺管理刀具的空間長度補償。
      這樣一來,五軸刀路的編程就可以不必在數(shù)控代碼生成之前就考慮該如何在刀路中體現(xiàn)數(shù)控機床的刀具或者工作臺的軸心及其偏差。 
 
      RTCP具有一下特點:
      1.針對刀具的實際切削點執(zhí)行進給控制;
      2.針對五個軸的前瞻控制;
      3.可處理垂直、傾斜和存在偏心的銑頭;
      4.“虛擬主軸”:將某個軸定向到刀具軸線上執(zhí)行鉆削和回退操作;
      5.針對五軸的坐標旋轉(zhuǎn)和(或)坐標變換;
      6.參考坐標系(G194)的旋轉(zhuǎn):應用于加工程序以及那些來自JOG或手輪的運動; 

       RTCP功能也可以用于三軸加工程序:在保持刀具與工件的實際接觸點不變的前提下,以手動方式改變銑頭或工作臺的姿態(tài)角。
 
      RTCP和HMS
      RTCP功能和HMS銑頭標定系統(tǒng)相結(jié)合是五軸銑削領(lǐng)域獨一無二的成果技術(shù),非常有助于提高刀尖運動精度。 
  
      HMS(節(jié)選)
      HMS銑頭量測系統(tǒng)用于量測和校驗雙擺銑頭和雙轉(zhuǎn)臺的連續(xù)運動和定位數(shù)據(jù),配備有連接到數(shù)控系統(tǒng)的三只傳感器和專門的測量管理軟件。軟件實時處理輸入數(shù)據(jù),并功能校驗和修正幾何誤差、位置精度,以及銑頭和轉(zhuǎn)臺的RTCP參數(shù)。
HMS是一款高精度量儀,可替代采用標準刻度盤的傳統(tǒng)校驗方法。其優(yōu)點包括:
      1.極大地降低校驗時間(僅半個小時而不是一整天)
      2.量測銑頭和轉(zhuǎn)臺的全部位置(而不僅僅是正交位置)
      3.量測RTCP參數(shù)
      4.自動在數(shù)控系統(tǒng)中插入修正值 
   
摘自“金屬加工世界”《五坐標高速銑削加工與編程的關(guān)鍵技術(shù)》

文中“四、五坐標高速銑削后處理程序開發(fā)”之“1.五軸機床旋轉(zhuǎn)刀具中心編程RTCP(Rotation Tool Centre Point)”一小節(jié)內(nèi)容如下: 
   

        五坐標機床及其加工編程,常用RTCP功能對機床的運動精度和數(shù)控編程進行簡化,下面對RTCP(Rotation Tool Centre Point 旋轉(zhuǎn)刀具中心)編程進行簡要說明。
      非RTCP模式編程:為了編程五坐標的曲面加工,必須知道刀具中心與旋轉(zhuǎn)主軸頭中心的距離:這個距離我們稱為轉(zhuǎn)軸中心(pivot)。根據(jù)轉(zhuǎn)軸中心和坐標轉(zhuǎn)動值計算出X、Y、Z 的直線補償,以保證刀具中心處于所期望的位置。運行一個這樣得出的程序必須要求機床的轉(zhuǎn)軸中心長度正好等于在書寫程序時所考慮的數(shù)值。任何修改都要求重新書寫程序。對于FIDIA C20數(shù)控系統(tǒng)G96 激活RTCP,G97 禁止RTCP
      RTCP模式編程:選件RTCP 的運行原理是當存在此選項時,控制系統(tǒng)會保持刀具中心始終在被編程的XYZ位置上。為了保持住這個位置,轉(zhuǎn)動坐標的每一個運動都會被XYZ 坐標的一個直線位移所補償。因此,對于其它傳統(tǒng)的數(shù)控系統(tǒng)而言,一個或多個轉(zhuǎn)動坐標的運動會引起刀具中心的位移;而對于FIDIA 數(shù)控系統(tǒng)(當RTCP 選件起作用時),是坐標旋轉(zhuǎn)中心的位移,保持刀具中心始終處于同一個位置上。在這種情況下,可以直接編程刀具中心的軌跡,而不需考慮轉(zhuǎn)軸中心,這個轉(zhuǎn)軸中心是獨立于編程的,是在執(zhí)行程序前由顯示終端輸入的,與程序無關(guān)。通過計算機編程或通過PLP 選件被記錄的三坐標程序,可以通過RTCP 邏輯,以五坐標方式被執(zhí)行。對于這種特殊的應用方法,必須要求使用球形刀具。這些轉(zhuǎn)動坐標的運動,可以通過JOG 方式或通過手輪來完成,所以在某些加工條件下,允許所使用的刀具,其長度值小于用于三坐標加工的刀具。 
   
國外關(guān)于RTCP的實際應用價值的兩則討論和觀點

以下文字由本人親自翻譯(不夠貼切之處請不吝指正):
  
【1】很多數(shù)控系統(tǒng)具備一種叫做“刀具中心管理”的實用功能,該功能可以被稱作 RTCP, TCPC或者TCPM,具體稱呼往往因數(shù)控系統(tǒng)的制造商而異,無論是哪個牌子的數(shù)控系統(tǒng),該功能都會起到一些大致相同的作用,“刀具中心管理”最關(guān)鍵的功能就是允許數(shù)控系統(tǒng)在五軸加工模式下按照裝夾偏差在線調(diào)整數(shù)控代碼的執(zhí)行,因而可以把同一個后處理代碼應用于整批零件。
      好處是操作工不必把工件精確地和轉(zhuǎn)臺的軸心線對齊,工件安裝后用探頭進行測量,將軸心偏差存入數(shù)控系統(tǒng)的指定寄存器并在加工過程中隨數(shù)控代碼一起應用。該功能可以降低銑床因工件裝卡造成的空閑時間,使機床有更多的時間用于金屬切削。與購置第二套托盤和工作臺,在加工第一個托盤上的工件時,同期裝卡后續(xù)工件的方法相比,該方法更為經(jīng)濟。
      更有甚者,“刀具中心管理”功能還允許降低同一系列零件的裝夾精度,既不必精確實現(xiàn)與機床的定位關(guān)系,也不必精確實現(xiàn)與同批次的其它零件的相對定位關(guān)系。這樣一來,我們不僅能夠減少裝夾工件的勞動量和機床空閑時間,而且該控制功能還可以降低夾具成本和準備時間,甚至可以免除工

原帖中幾段翻譯內(nèi)容所對應原文如下:

【Fidia C10-C20】

RTCP
Applied to bi-rotary heads and roto-tilting tables, the RTCP function manages tool length compensation in space, directly from the machine tool.
A 5-axis tool path can therefore be programmed without having to consider the pivot that will be inserted in the NC tool table before the program is executed.

RTCP characteristics:
■ controlled feed at the tool tip
■ look ahead on 5 axes
■ management of orthogonal, angular and eccentric heads
■ “virtual quill”: manages an axis oriented in the tool direction for executing drilling and release movements
■ rotation and/or translation on 5 axes
■ rotation of the reference system (G194): applied to programmed movements and to those executed by jog or by means of the handwheel

The RTCP function can also be used for 3-axis programs: by orientating the head or table manually, the tool tip is maintained in contact with the part.

RTCP and HMS
Combining the RTCP function with the HMS head calibration system is a winning and unique formula in 5-axis milling technology, with clear benefits for accuracy of movement at the tool tip.

HMS
The HMS system is a device designed for measuring and checking continuous and indexed bi-rotary heads and roto-tilting tables. Equipped with 3 sensors connected to the CNC, the HMS system is managed by a specific measurement software. By processing incoming data in real time, the software is able to check and correct geometric error, positioning accuracy and the RTCP parameters for the heads and tables.

HMS is a high-precision instrument and provides an alternative to the traditional checking method using dial gauges. It has many advantages:
■ a drastic reduction in checking time (half an hour rather than an entire day)
■ measurement of all head and/or table positions (not just orthogonal positions)
■ measurement of RTCP parameters
■ automatic insertion of correction values in the CNC.

【1】http://www./articles/010704.html

Most CNC controls have a utility function called tool center point management. Depending on the control manufacturer, this function may be named RTCP, TCPC or TCPM. The utility performs many functions with similar behavior no matter the controller. The key function performed by tool center point management systems is to allow the CNC control to accept fixture offsets and adjust NC data—on the fly—while working in five-axis mode; thereby, allowing one set of post-processed data to work for an entire batch of parts.

The benefit is that an operator need not align a workpiece precisely to the rotary table centerline. A part can be mounted and probed, and the offsets from center can be loaded into the control registers and processed with the NC data during operation. This function can reduce idle time on a milling machine while mounting a part and have the machine tool focus on chip removal. This is a more economical approach than purchasing a secondary pallet and table to allow part mounting while the part on the first pallet is being machined.

Taken one step further, the tool center point management allows a series of parts to be mounted without being precisely located on the machine or without being precisely mounted relative to the remainder of the production lot. So not only can we reduce the labor for mounting parts and the machine idle time, this control function can reduce the cost and preparation time for mounting fixtures and otherwise non-critical mounting surfaces on the workpiece.

【2】http://www./forums/showthread.php?t=82998

Generically speaking they are the same. But the actual performance of these functions is not in a manual, but inside the software/firmware of the control manufacturers. And they don‘t seem to tell you exactly how they accomplish the mathematics for tool center point control.

There are a few different functions that may be included in the "tool center point" technology concepts.

1. Kinematic transformations (multi-axis) are performed inside the CNC control. A benefit of this is that the CAM software postprocessor need not perform this math. The second benefit is that pivot offsets are held within the machine control register tables. The big benefit of this function is that one NC program can be applied to different machines in your shop that may have different pivot offsets. In the old days (not so long ago), you would have to include the pivot offsets in the CAM postprocessor, and then need different NC code to run the same part on machineA and machineB (same maker and kinematics).

Together with this, feedrate is controlled at the tool tip using math inside the control. This latter point is in contrast to historical "inverse time" modes where the CAM software had to calculate a time (feedrate) for each block.

2. Tool center point management often includes fixture offsets. A part is placed on the machine tool. The local is determined by on-board probes. The position offsets are added to the above-mentioned pivot offsets.

The benefit again is that serial parts can be put on the same machine, located by probe, and one set of NC instructions can cut all parts. The end-user need not spend extra hours "tapping" in a part so that it is located on center within an acceptably small tolerance.

    本站是提供個人知識管理的網(wǎng)絡(luò)存儲空間,所有內(nèi)容均由用戶發(fā)布,不代表本站觀點。請注意甄別內(nèi)容中的聯(lián)系方式、誘導購買等信息,謹防詐騙。如發(fā)現(xiàn)有害或侵權(quán)內(nèi)容,請點擊一鍵舉報。
    轉(zhuǎn)藏 分享 獻花(0

    0條評論

    發(fā)表

    請遵守用戶 評論公約

    類似文章 更多