外文翻譯--數(shù)控機床開環(huán)控制伺服系統(tǒng)與數(shù)控生產設備-14頁[中英word] -中文：4512字【中英文文獻譯文】
外文翻譯--數(shù)控機床開環(huán)控制伺服系統(tǒng)與數(shù)控生產設備-14頁[中英word] -中文：4512字【中英文文獻譯文】,中英word,中英文文獻譯文,外文翻譯,數(shù)控機床開環(huán)控制伺服系統(tǒng)與數(shù)控生產設備-14頁[中英word],-中文：4512字【中英文文獻譯文】,外文,翻譯,數(shù)控機床,開環(huán),控制,節(jié)制,伺服系統(tǒng),數(shù)控,生產
譯文：
數(shù)控機床開環(huán)控制伺服系統(tǒng)與數(shù)控生產設備
摘要
開環(huán)系統(tǒng)的優(yōu)點是系統(tǒng)簡單、成本低，但缺點是精度低。反向間隙、絲杠螺距誤差、起停誤差等都會影響定位精度。下面幾種改進措施可以使定位精度明顯改善。
關鍵字：數(shù)控系統(tǒng)、開環(huán)系統(tǒng)
1） 反向間隙誤差補償
數(shù)控機床加工刀具與工件的相對運動是依靠驅動裝置帶動齒輪、絲杠轉動，從而推動工作臺面等移動部件產生位移來實現(xiàn)的。作為傳統(tǒng)元件的齒輪、絲杠盡管制造精度很高，但總免不了存在間隙。由于這種間隙存在，當運動的方向改變時，開始段時間必然會引起驅動元件的空走，出現(xiàn)指令脈沖推不動執(zhí)行元件的局面。這就影響了機床的加工精度，即指令脈沖與實際進給步數(shù)不相符合，產生加工誤差 因此，開環(huán)數(shù)控系統(tǒng)一般都設置有反向間隙誤差補償功能，用以補足空走的步數(shù)反向間隙差補償就是首先實測反向進給的誤差，把它折算成脈沖當量數(shù)，作為間隙補償子程序的輸出量，當計算機判斷出現(xiàn)的指令為反向運動時，隨即調用間隙補償子程序，通過輸出補償脈沖消除反向間隙后再進行正常的插補運行。
2） 常值系統(tǒng)性定位誤差補償
類庫以供設計者調用。這樣在零件的設計階段，設計者只需輸入特征的參數(shù)，系統(tǒng)直接生成特征的實例模型：在數(shù)據(jù)庫中我們必須存儲相關的特征類的結構信息，數(shù)據(jù)庫表集就是用于存儲這一部分的相關信息。根據(jù)特征類型定義的需要，我們定義了特征類編碼表、特征類版本信息表表示特征類型；定義了特征類構造表表達特征類的結構；并通過零件特征配置表與零件的特征層信息聯(lián)系起來。特征層數(shù)據(jù)表集是本零件模型數(shù)據(jù)庫設計的核心，記錄了特征實例模型的設計、工藝等信息。特征構造表記錄了特征的幾何結構；特征尺寸表、特征形位公差表、特征表面粗糙度表記錄了特征的工程語義引用；尺寸表、形位公差表、表面粗糙度表存儲了所有零件特征的數(shù)據(jù)信息。在特征層，利用特征ID、幾何要素ID、尺寸ID、公差ID、粗糙度ID等主鍵進行數(shù)據(jù)檢索。我們將該零件信息模型的數(shù)據(jù)庫應用于工廠環(huán)境下某型組件的CAD AM 集成系統(tǒng)中，較好地實現(xiàn)了CAD與CAPP的特征信息共享。在該系統(tǒng)中主要使用現(xiàn)成的CAD／CAM 軟件(Unigra—phics 1I)進行產品設計和NC編程，并通過對該軟件進行二次開發(fā)獲取零件的尺寸信息；同時利用自行開發(fā)的對話窗體，讓設計人員交互輸入其它特征信息，實現(xiàn)該軟件與系統(tǒng)的共享數(shù)據(jù)庫的連接。在輔助工藝設計時，工藝設計人員通過程序的查詢功能，從共享數(shù)據(jù)庫中查詢所需的零件信息，進行交互工藝設計。從而方便了CAPP的零件信息獲取，提高了工藝設計的效率。在利用UG進行NC編程時，可以從共享數(shù)據(jù)庫中獲取所需的工藝及制造信息，進行各工序的刀軌設計與加工仿真在數(shù)控機床上建立一個絕對零點，實測出各坐標軸相對點的全部定位誤差，做出曲線以便確定補償點。圖l所示是一個實測的定位誤差曲線，把這個曲線的縱坐標(誤差)以脈沖當量為單位進行分割，作出橫線，每個橫線與曲線的交點即為目標補償點。圖1中的1到6點處的定位誤差為正，需要作減脈沖補償；而6至9處需要進行加脈沖補償圖中陰影部分為補償區(qū)。把這些補償點列成誤差.
修正表存入計算機，當工作臺由零點位置移動時，安裝在絕對原點處的微動開關發(fā)出絕對原點定位信號，以后計算機將隨時發(fā)出目標補償點的補償信號，對機床進行定位誤差補償。余弦發(fā)生器給定的滑尺激磁信號a電與由步進電。
3） 反饋補償開環(huán)控制
該系統(tǒng)由開環(huán)控制和感應同步器直接位置測量兩個部分組成。這里的位置檢測不用作位置的反饋，而是作為位置誤差的補償反饋。其基本的原理是：由機床數(shù)控裝置CNC發(fā)出的指令脈沖，一方面供給開環(huán)系統(tǒng)，控制步進電機按指令運轉，并直接驅動機床工作臺移動，構成開環(huán)控制；另一方面該指令脈沖又供給感應同步器的測量系統(tǒng)(即數(shù)字式正、余弦發(fā)生器)，作為位置給定信號a由。工作在鑒幅方式的感應同步器此時既是位置檢測器，又是比較器，它把由正、余弦發(fā)生器給定的滑尺激磁信號a電與由步進電。
4） 結 論
CIMS環(huán)境下基于特征的零件信息建模還是一門不斷發(fā)展的技術，怎樣提高特征設計所能完成的零件復雜度；如何使特征設計適應特征識別、特征語義轉換的要求等問題還有待人們去解決。本文介紹了特征技術在零件信息建模中的應用，重點描述該零件數(shù)據(jù)模型的數(shù)據(jù)庫實現(xiàn)；所建立的零件信息數(shù)據(jù)庫系統(tǒng)可以較好地滿足CIMS系統(tǒng)對信。
數(shù)字控制是用數(shù)字、字母和其他控制字符進行編程，來實現(xiàn)機械設備自動化的一種形式。號碼，字母和符號是為特定的工作環(huán)境或工作而設定的一種適當?shù)膬染幋a。根據(jù)程序指示的改變，機械的加工也隨之改變方式。更易改寫程序的優(yōu)越性使NC系統(tǒng)更適合加工微小體積的產品。與更換生產設備相比，通過編輯新的程序來實現(xiàn)產品的加工要容易得多。
NC的基本零部件
一個數(shù)控系統(tǒng)包括以下3個基本零部件：
①指示程序
②機器控制單元
③機床
機床根據(jù)輸入計算機的程序來執(zhí)行相應的動作。詳細的指示程序直接控制機床一步一步的執(zhí)行命令。在通常情況下，刀具參考點的指令與工作臺的機床原點位置有關。更先進的指令系統(tǒng)包括機床進給速度的選擇，切削工具和其他功能。在過去幾十年里最常用的信息載體是1英寸寬的穿孔紙帶。因為穿孔紙帶的廣泛使用，NC系統(tǒng)有時也叫“帶子控制”，不過，這是現(xiàn)代用法過程中對數(shù)字控制的誤稱。近年來，卡型盒式磁帶和軟磁盤開始廣泛使用。機器控制單元（MCU）由讀取并理解程序說明，進而將程序轉變成機床或另外生產設備可執(zhí)行的機械動作所需的硬件和電子元件組成。機床是NC系統(tǒng)中的第3個基本零部件。它是有用的執(zhí)行部件，在數(shù)字控制的最普通的例子里，進行機器加工操作就是其中之一，機床由工作臺、主軸和控制主軸所必須的驅動電機組成。
控制系統(tǒng)的類型
在數(shù)字控制過程中有兩類基本的控制系統(tǒng)：點位控制和輪廓控制。點位控制也被稱作為位置控制，通過電機以不同的速度分別驅動機器的各軸，這取決于操作的方式。為了減少空操作的時間，機器在最初是以最大速度移動，但在刀具到達設定的位置時，要降低速度，這樣，在進行過程中，如鉆孔或打洞的操作是在準確的位置進行持續(xù)切削。在鉆孔或打洞后，刀具退回并迅速移動到另一個位置進行重復操作。從一點大另一點的路徑是一個重要的方面：為提高效率，要求移動時間降到最小。點位控制系統(tǒng)主要用于鉆孔、打洞及直線磨削等方面。
在輪廓控制，也就是所謂的連續(xù)路徑運行系統(tǒng)中，位置的確定和切削操作同時沿著設定的路徑以不同的速度運行。因為當?shù)毒哐刂?guī)定的路徑切削進給時，準確控制速度和運動的同步性是相當重要的，連續(xù)切削控制用于車床、銑床、磨床、焊接機器和機械加工中心。
沿路徑運動或位置插補是幾種基本的方法之一。在整個插補過程中，路徑控制以刀具的轉動為中心。對于不同的刀具補償，不同的刀具，及在機器加工過程中刀具的磨損，都能通過NC程序進行調節(jié)。
有許多插補程序被開發(fā)用于處理連續(xù)切削控制系統(tǒng)中形成光滑、連續(xù)的軌跡所遇到的各種各樣的問題，他們包括：
· 直線插補
· 圓弧插補
· 螺旋線插補
· 拋物線插補
這些插補程序是程序員（或操作員）用來生成直線或曲線路徑的機器指令，以相對減少輸入餓參數(shù)。在MCU方面的插補模式進行計算并按指定的路徑執(zhí)行。
直線插補是最基本的方法，在NC系統(tǒng)中生成連續(xù)軌跡時經常用到。在實踐中，兩軸和三軸直線插補有時有所區(qū)別，但他們的原理是相同的。程序被要求指定直線的起點和終點，及沿著直線跟隨的進給量，為了取得被指定的進給量，插補器為兩軸（或三軸）中的每個軸計算插補量。
因為程序員要求指定的直線部分和將用來接近圓的各自的終點有差別，用直線插補生成圓弧軌跡不適合。圓弧插補程序被開發(fā)用于圓弧插補，通過指定組成圓弧軌跡的下列參數(shù)：終點、中心、半徑。刀具沿著圓弧的指示坐標進給，被生成的刀具軌跡由一系列直線部分組成。只是這部分是用插補模塊來計算，而不是由程序員預先給定。為了生成光滑的圓弧軌跡，切削刀具被指定沿著每段直線一步一步的進給。圓弧插補的局限性在用兩軸NC系統(tǒng)加工飛機部件時有所體現(xiàn)。
螺旋線插補是結合應用第三軸的直線運動和圓弧插補的兩軸運動，這就定義了三維空間的螺旋軌跡。
拋物線插補是使用高命令方程式得到的近似值所生成的自由形式的曲線，他一般需要相當多的計算功能，并且與普通的直線和圓弧插補不同。他們應用于汽車制造業(yè)，適合建立因內應力集中而導致車體損壞，對那些不能準確計算用以生成自由形式的小汽車的設計，這樣可以方便地通過結合直線和圓弧的插補來接近設計要求。
NC編程
數(shù)控程序由指導一臺NC機器進行某種操作的一連串命令組成。機械加工是最常見的方式，NC編程可以由內部的編程部門完成，或者從外面購買。此外，編程可以是手工或計算機輔助完成。
程序包括命令和說明。幾何學說明刀具和工件之間的有關運動；設備說明有關主軸的速度，進給，刀具等；行程說明屬于哪類型的插補及刀具和工作臺移動的快慢，接通命令說明開/關冷卻劑的非工作狀態(tài)，旋轉及其方向，刀具的更換，工件的進給，夾具等方面。
①人工編程?? 人工零件編程由先計算刀具、工件和工作臺之間的相對位置，基于零件的工程圖，以及執(zhí)行生產操作的順序等組成。然后準備的圖表包含執(zhí)行操作的各種必要信息。比如切削刀具，主軸速度、進給，切削深度，切屑，驅動及刀具和工件間的相對位置和運動。有了這些基本的信息，零件程序準備就緒。通常先準備一盤紙帶用來調試程序。帶子可能用更耐用的Mylar材料做成，這取決于它被使用的頻率。
人工程序由那些專門的編程員鐘對特別的生產而編輯，以變化零件加工過程，因為熟悉機床功能和工序，熟練的機械師能在編程過程中得到某些訓練，不過，工作是乏味、費時和不經濟的，而且主要是簡單的點對點應用。
② 計算機輔助編程?? 計算機輔助零件涉及確定刀具落點，刀具切削刃，零件表面等有特別象征的程序語言，程序語言是與計算機進行信息交流的一種方法，其中包含標志符號的使用。程序員用這種語言對生產加以描述，而計算機把這種語言轉化成NC機器能識別的指令，在市場上有各種各樣象征和應用的幾種語言可買，使用英語那樣陳述的第一種語言在20世紀50年代末被發(fā)展成為APT（自動編程工具）。這種語言發(fā)展成了各種形體，仍被廣泛應用于點位和連續(xù)切削。
計算機輔助零件編程與手工方法相比有以下優(yōu)點：
· 使用相對易于使用的符號語言；
· 減少編程時間。程序能提供大量關于機器特性的數(shù)據(jù)和處理變量，例如驅動，速度，進給，刀具形狀，對工具形狀的補償，刀具磨損，撓度及冷卻劑的使用；
· 降低在人工編程中可能發(fā)生的人為錯誤的可能性；
· 從機器順序的簡單切換加工能力；
· 因減少編程時間而降低成本。
一種特別的NC程序語言的選擇取決于下列因素：
①生產過程中人員的專門技能水平；
②零件的復雜程度；
③可提供的計算機和設備型號；
④編程涉及的時間和費用。
因為NC系統(tǒng)與工件材料和過程參數(shù)的插入有關，程序必須由懂得生產設備使用相關方面知識的專門人員編輯，在投入使用前，程序應進行調試，通過CRT屏幕觀看用一種廉價材料加工零件的模擬過程，例如鋁，木頭或者塑料，而不是適合成品生產的指定素材。
參考文獻：
[1]. 張華書．并行環(huán)境下基于特征的零件定義模型 [J]．機械科學與技術，1999，18(1)：14l 144．
[2]. 林曉星，杜全文，許建新．特征與(',M)／CAPP／CAM 集成系統(tǒng) [J]．計算機輔助設計與制造，1998，28(5)：51 55．
[3]. 曾慧娥，周慶忠．基于特征的機械產品造型研究 [J]．機械設計與制造 [程，1999，28(2)：1 2～l4．
附錄
譯文：
The open system merit of Computer Numerical Control and Numerical control of production equipments
Abstract
The open system merit is the system simple, the cost low, but the shortcoming is the precision is low. The reverse gap, the guide screw pitch error, stop inferiorly can affect the pointing accuracy by mistake. Following several kind of improvements measure may cause the pointing accuracy distinct improvement.
The key word:numerical control 、NC 、the open systerm
1）reverse gap error compensates
?? The numerical control engine bed processing cutting tool and the work piece relative motion is depends upon the drive impetus gear,the guide screw rotation, thus the impetus work floor and so on moves the part to produce moves realizes. As traditional part gear, guide screw although the manufacture precision is very high, but always unavoidably has the gap. As a result of this kind of gap existence, when movement direction change, starts the section time to be able to
cause inevitably actuates the part wasting time, appears the instruction pulse to push the motionless functional element the aspect. This has affected the engine bed processing precision, namely the instruction pulse and actual enters for the step does not tally,has the processing error therefore, the split-ring numerical control system all establishes generally has the reverse gap error
compensatory function, with by makes up which wastes time the step reverse gap difference compensates is first actual reverse enters for the error, converts the pulse equivalent number it, compensates the subroutine as the gap the output, when the computer judgment appears
when instruction for counter motion, transfers the gap to compensate the subroutine immediately, compensates the pulse after the output to eliminate the reverse gap to carry on again normally inserts makes up the movement.
2）often the value systematic characteristic position error compensates
A kind of storehouse by transfers for the designer. Like this in the components design stage, the designer only must input the characteristic the parameter, the system direct production
characteristic example model: We must save the related characteristic class in the database the structure information, the database table collection are use in saving this part of related information. According to the characteristic type definition need, we defined the characteristic class code table, the characteristic class edition information have outstanding shown the characteristic type; Defined the characteristic class structure outstanding to reach the characteristic class the structure; And relates through the components characteristic disposition table and the components characteristic level information. The characteristic level data sheet collection is
this components model database design core, has recorded characteristic example information and so on model design, craft. The characteristic structure table has recorded the characteristic
geometry structure; The characteristic size table, the characteristic shape position table of limits, the characteristic surface roughness table has recorded the characteristic project semantics quotation; The size table, the shape position table of limits, the surface roughness
table saved all components characteristic data message. In the characteristic level, using characteristic ID, geometry principal linkage and so on essential factor ID, size ID, common difference ID, roughness ID carries on the data retrieval. We apply this components information model database under the factory environment some module CAD in the AM integrative system, has realized CAD and the CAPP characteristic information sharing well. Main use ready-made CAD/the CAM software (Unigra □phics 1I) carries on the product design and the NC programming in this system, and through carries on two times of developments gains components to this software the size information; At the same time uses the dialogue window which develops voluntarily, lets design the personnel to input other characteristic information alternately, realizes this software and the system sharing database connection. When assistance technological design, the technological design personnel through the procedure inquiry function, inquires the components information from the sharing database which needs, carries on the interactive technological design. Thus has facilitated the CAPP components information acquisition, enhanced the technological design efficiency. When carries on the NC programming using UG, may from the sharing database gain the craft and the manufacture information which needs, carries on various working procedures the knife axle design and the processing simulation establishes an absolute zero spot on the numerical control engine bed, the actual various coordinate axes syzygy completely position error, makes the curve in order to determined compensates the spot. Attempts l to show is an actual position error curve, (error) carries on this curve y-coordinate take the pulse equivalent as the unit the division, makes the horizontal line, each horizontal line and the curve point of intersection namely compensates the spot for the goal. Chart 1 the center 1 to 6 o'clock place position errors for, needs to do reduces the pulse to compensate; But needs to carry on 6 to 9 adds the pulse to compensate in the chart the shadow partially for to compensate the area. Compensates the range of points these to become the error
??? The calibration corrections stores the computer, when work table by zero displacement in position, installs sends out the absolute zero point localization signal in the absolute zero point micros witch, later computer as necessary will send out the goal to compensate to compensate the signal, will carry on the position error to the engine bed to compensate. The cosine generator assigns slide guage initiation signal a electricity and by step of transmission.
3） feedbacks compensates the open-loop control
??? Chart 2 has produced this kind of system schematic diagram. This system surveys two parts by the open-loop control and the induction synchromesh direct position to be composed. Here position examination does not serve as the position the feedback, but is compensates the feedback as the position error. Its cardinal principle is: Installs the instruction pulse by the engine bed numerical control which CNC sends out, on the one hand the supplies open system, the
control step-by-steps the electrical machinery according to the instruction revolution, and the direct drive platen moves, constitutes the open-loop control; On the other hand this instruction pulse supplies the induction synchromesh the measurement system (namely digitally, cosine generator), as position demand signal a by. The work in the warning way induction synchromesh this time not only is the position sensor, also is the comparator, it by, The cosine generator assigns slide guage initiation signal a electricity and by step of transmission.
4） conclusions
??? Under the CIMS environment the technology which develops unceasingly based on characteristic components information modeling, how enhances the components order of complexity which the characteristic design can complete; How causes question and so on request which the characteristic design adoption trick recognition, the characteristic semantics transforms also to wait for the people to solve. This article introduced the characteristic technology in the components information modeling application, describes this components data model database realization with emphasis; Establishes the components information database system may satisfy the CIMS system well to the letter.
?? 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. When the job changes, the program of instructions is changed. The capability to change the program is what makes NC suitable for low-and medium-volume production. It is much easier to write new programs than to make major alterations of the processing equipment.
Basic components of NC
A numerical control system consists of the following three basic components:
·Program of instructions
·Machine control unit
·Processing equipment
The general relationship among the three components is illustrated in Fig.2.1. The program is fed into the control unit, which directs the processing equipment accordingly.
The program of instructions is the detailed step-by-step commands that direct the processing equipment. In 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 tool, and other function. The most common medium in use over the last several decades has been 1-in. -wide punched tape. Because of the widespread use of the punched tape, NC is sometimes called “tape control”. However, this is a misnomer in modern usage of numerical control. Coming into use more recently have been magnetic tape cassettes and floppy diskettes.
The machine control unit (MCU) consists of the electronics and control hardware that read and interpret the program of instruction and convert it into mechanical actions of the machine tool or other processing equipment.
The processing equipment is the third basic component of an NC system. It is the component that performs useful work. In the most common example of numerical control, one that performs machining operations, the processing equipment consists of the worktable and spindle as well as the motors and controls needed to drive them.
TYPES OF CONTROL SYSTEMS
There are two basic types of control systems in numerical control: point-to-point and contouring. In the point-to-point system, also called positioning, each axis of the machine is driven separately by leadscrews and, depending on the type of operation, at different velocities. The machine moves initially at maximum velocity in order to reduce nonproductive time but decelerates as the tool reaches its numerically defined position. Thus in an potation such as drilling or punching, the positioning and cutting take place sequentially. After the hole is drilled or punched, the tool retracts, moves rapidly to another position, and repeats the operation. The path followed from one position to another is important in only one respect: The time required should be minimized for efficiency. Point-to-point systems are used mainly in drilling, punching, and straight milling operations.
In the 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, welding machinery, and machining centers.
Movement along the path, or interpolation, occurs incrementally, by one of several basic methods. In all interpolations, the path controlled is that of the center of rotation of the tool. Compensation for different tools, different diameter tools, or tool wear during machining, can be made in the NC program.
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
·Cubic interpolation
Each of these interpolation procedures permits the programmer (or operator) to generate machine instructions for linear or curvilinear paths, using a relatively few input parameters. The interpolation module in the MCU performs the calculations and directs the tool along the path.
Linear interpolation is the most basic and is used when a straight-line path is to be generated in continuous-path NC. Two-axis and three-axis linear interpolation routines are sometimes distinguished in practice, but conceptually they are the same. The program is required to specify the beginning point and end point of the straight line, and the feed rate that is to be followed along the straight line. The interpolator computes the feed rates for each of the two (or three) axes in order to achieve the specified feed rate.
Linear interpolation for creating a circular path would be quite inappropriate because the programmer would be required to specify the line segments and their respective end points that are to be used to approximate the circle. Circular interpolation schemes have been developed that permit the programming of a path consisting of a circular arc by specifying the following parameters of the arc: the coordinates of its end points, the coordinates of its center, its radius, and the direction of the cutter along the arc. The tool path that is created consists of a series of straight-line segments, but the segments are calculated by the interpolation module rather than the programmer. The cutter is directed to move along each line segment one by one in order to generate the smooth circular path. A limitation of circular interpolation is that the plane in which the circular arc exists must be a plane defined by two axes of the NC system.
Helical interpolation combines the circular interpolation scheme for two axes described above with linear movement of a third axis. This permits the definition of a helical path in three-dimensional space.
Parabolic and cubic interpolation routines are used to provide approximations of free-form curves using higher-order equations. They generally require considerable computational power and are not as common as linear and circular interpolation. Their applications are concentrated in the automobile industry for fabricating dies for car body panels styled with free-form designs that cannot accurately and conveniently be approximated by combining linear and circular interpolations.
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.
① Manual Programming?? Manual part programming consists of first calculating dimensional relationships of the tool, workpiece, and work table, based on the engineering drawings of the part, and manufacturing operations to be performed and their sequence. A program sheet is then prepared, which consists of the necessary information to carry out the operation, such as cutting tools, spindle speeds, feeds, depth of cut, cutting fluids, power, and tool or workpiece ally a paper tape is first prepared for trying out and debugging the program. Depending on how often it is to be used, the tape may be made of more durable Mylar.
Manual programming can be done by someone knowledgeable about the particular process and able to understand, read, and change part programs. Because they are familiar with machine tools and process capabilities, skilled machinists can do manual programming with some training in programming. However, the work is tedious, time consuming, and uneconomical-and is used mostly in simple point-to-point applications.
② Computer-Aided Programming?? Computer-aided part programming involves special symbolic programming languages that determine the coordinate points of corners, edges, and surfaces of the part. Programming language is the means of communicating with the computer and involves the use of symbolic characters. The programmer describes the component to be processed in this language, and the computer converts it to commands for the NC machine. Several languages having various features and applications are commercially available. The first language that used English-like statements was developed in the late 1950s and is called APT (for Automatically Programmed Tools). This language, in its various expanded forms, is still the most widely used for both point-to-point and continuous-path programming.
Computer-aided part programming has the following significant advantages over manual methods:
· Use of relatively easy to use symbolic language
·Reduced programming time. Programming is capable of accommodating a large amount of data concerning machine characteristics and process variables, such as power, speeds, feed, tool shape, compensation for tool shape changes, tool wear, deflections, and coolant use.
· Reduced possibility of human error, which can occur in manual programming
· Capability of simple changeover of machining sequence or from machine to machine.
· Lower cost because less time is required for programming.
Selection of a particular NC programming language depends on the following factors:
①??? Level of expertise of the personnel in the manufacturing facility.
②? Complexity of the part.
③?? Type of equipment and computers available.
④??? Time and costs involved in programming.
Because numerical control involves the insertion of data concerning workpiece materials and processing parameters, programming must be done by operators or programmers who are knowledgeable about the relevant aspects of the manufacturing processes being used. Before production begins, programs should be verified, either by viewing a simulation of the process on a CRT screen or by making the part from an inexpensive material, such as aluminum, wood, or plastic, rather than the material specified for the finished part.
Reference:
[1]? Zhang Huashu under. parallel environment based on characteristic components definition ?????????model [J]. mechanical science with technology, 1,999, 18 (1): 14l 144.
[2] ?forest morning star, Du full text, Xu Jianxin. characteristic and (',M)/CAPP/CAM integrative system [J]. the computer-aided design and makes, 1998, 28 (5): 5155.
[3] ?Zeng Hui E, Zhou Qingzhong. studied J based on the characteristic mechanical product modelling ]. the machinery to suppose Counts with the manufacture [ the regulation, 1,999, 28 (2): 12 ~ l4.
譯文：
數(shù)控機床開環(huán)控制伺服系統(tǒng)與數(shù)控生產設備
摘要
開環(huán)系統(tǒng)的優(yōu)點是系統(tǒng)簡單、成本低，但缺點是精度低。反向間隙、絲杠螺距誤差、起停誤差等都會影響定位精度。下面幾種改進措施可以使定位精度明顯改善。
關鍵字：數(shù)控系統(tǒng)、開環(huán)系統(tǒng)
1） 反向間隙誤差補償
數(shù)控機床加工刀具與工件的相對運動是依靠驅動裝置帶動齒輪、絲杠轉動，從而推動工作臺面等移動部件產生位移來實現(xiàn)的。作為傳統(tǒng)元件的齒輪、絲杠盡管制造精度很高，但總免不了存在間隙。由于這種間隙存在，當運動的方向改變時，開始段時間必然會引起驅動元件的空走，出現(xiàn)指令脈沖推不動執(zhí)行元件的局面。這就影響了機床的加工精度，即指令脈沖與實際進給步數(shù)不相符合，產生加工誤差 因此，開環(huán)數(shù)控系統(tǒng)一般都設置有反向間隙誤差補償功能，用以補足空走的步數(shù)反向間隙差補償就是首先實測反向進給的誤差，把它折算成脈沖當量數(shù)，作為間隙補償子程序的輸出量，當計算機判斷出現(xiàn)的指令為反向運動時，隨即調用間隙補償子程序，通過輸出補償脈沖消除反向間隙后再進行正常的插補運行。
2） 常值系統(tǒng)性定位誤差補償
類庫以供設計者調用。這樣在零件的設計階段，設計者只需輸入特征的參數(shù)，系統(tǒng)直接生成特征的實例模型：在數(shù)據(jù)庫中我們必須存儲相關的特征類的結構信息，數(shù)據(jù)庫表集就是用于存儲這一部分的相關信息。根據(jù)特征類型定義的需要，我們定義了特征類編碼表、特征類版本信息表表示特征類型；定義了特征類構造表表達特征類的結構；并通過零件特征配置表與零件的特征層信息聯(lián)系起來。特征層數(shù)據(jù)表集是本零件模型數(shù)據(jù)庫設計的核心，記錄了特征實例模型的設計、工藝等信息。特征構造表記錄了特征的幾何結構；特征尺寸表、特征形位公差表、特征表面粗糙度表記錄了特征的工程語義引用；尺寸表、形位公差表、表面粗糙度表存儲了所有零件特征的數(shù)據(jù)信息。在特征層，利用特征ID、幾何要素ID、尺寸ID、公差ID、粗糙度ID等主鍵進行數(shù)據(jù)檢索。我們將該零件信息模型的數(shù)據(jù)庫應用于工廠環(huán)境下某型組件的CAD AM 集成系統(tǒng)中，較好地實現(xiàn)了CAD與CAPP的特征信息共享。在該系統(tǒng)中主要使用現(xiàn)成的CAD／CAM 軟件(Unigra—phics 1I)進行產品設計和NC編程，并通過對該軟件進行二次開發(fā)獲取零件的尺寸信息；同時
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