條碼的識讀原理

MechanismofBarCodeRecognition&Reading條碼識讀原理2.2BarCodeTechnologyanditsapplicationCONTENTS目

錄02條碼技術(shù)識讀原理Barcodetechnologyrecognition&readingmechanism03條碼識讀系統(tǒng)的基本概念Basicconceptsofbarcoderecognition&readingsystem01條碼識讀系統(tǒng)的組成Compositionofbarcoderecognition&readingsystems條碼識讀系統(tǒng)的組成Compositionofbarcoderecognition&readingsystems01Thebarcodereadingsystemiscomposedofthreeparts:scanningsystem,signalshapinganddecoding.條碼識讀系統(tǒng)是由掃描系統(tǒng)、信號整形、譯碼三部分組成。1、條碼識讀系統(tǒng)的組成Compositionofbarcoderecognition&readingsystemsopticalsystemdetectorAmplifyingthesignalfilteringshapingScanningsystemSignalshapingTothecomputerInterfacecircuitDecoderDecodingThereadingofbarcodesymbolsinvolvesmultipletechnologiessuchasoptics,electronics,andmicroprocessors.Tocompletethecorrectreading,thefollowingconditionsmustbemet:條碼符號的識讀涉及光學(xué)、電子學(xué)和微處理器等多種技術(shù)。要完成正確識讀，必須滿足以下幾個(gè)條件：1、條碼識讀系統(tǒng)的組成Compositionofbarcoderecognition&readingsystems建立一個(gè)光學(xué)系統(tǒng)并產(chǎn)生一個(gè)光點(diǎn)，使該光點(diǎn)在人工或自動控制下能沿某一軌跡作直線運(yùn)動且通過一個(gè)條碼符號的左側(cè)空白區(qū)、起始符、數(shù)據(jù)符、終止符及右側(cè)空白區(qū)。1Anopticalsystemisestablishedandalightspotgenerated,sothatthelightspotcanmoveinastraightlinealongacertaintrackundermanualorautomaticcontrolandpassthroughtheleftblankarea,startsymbol,datasymbol,terminatorandtheblankareaontherightofabarcode.建立一個(gè)反射光接收系統(tǒng)，使它能夠接收到光點(diǎn)從條碼符號上反射回來的光。同時(shí)要求接受系統(tǒng)的探測器的敏感面盡量與光點(diǎn)經(jīng)過光學(xué)系統(tǒng)成像的尺寸相吻合。2Areflectedlightreceivingsystemisestablishedsothatitcanreceivethelightreflectedbythelightspotfromthebarcodesymbol.Atthesametime,thesensitivesurfaceofthedetectorofthereceivingsystemisrequiredtomatchthesizeofthelightspotimagedbytheopticalsystemasmuchaspossible.要求光電轉(zhuǎn)換器將接收到的光信號不失真地轉(zhuǎn)換成電信號。3Thephotoelectricconverterisrequiredtoconvertthereceivedopticalsignalintoanelectricalsignalwithoutdistortion.要求電子電路將電信號放大、濾波、整形，并轉(zhuǎn)換成電脈沖信號。4Theelectroniccircuitisrequiredtoamplify,filter,andreshapetheelectricalsignal,andconvertitintoanelectricalpulsesignal.建立某種譯碼算法，將所獲得的電脈沖信號進(jìn)行分析和處理，從而得到條碼符號所表示的信息。5Establishacertaindecodingalgorithm,analyzeandprocesstheobtainedelectricpulsesignal,andobtaintheinformationrepresentedbythebarcodesymbol.將所得到的信息轉(zhuǎn)儲到指定的地方。6Dumptheobtainedinformationtoadesignatedplace.上述的前四步一般由掃描器完成，后兩步一般由譯碼器完成。Thefirstfourstepsmentionedabovearegenerallycompletedbythescanner,andthelasttwostepsaregenerallycompletedbythedecoder.1、條碼識讀系統(tǒng)的組成Compositionofbarcoderecognition&readingsystems光源。主要有半導(dǎo)體光源和激光光源，也有選用白熾燈、閃光燈等光源的。1lightsource.Therearemainlysemiconductorlightsourcesandlaserlightsources,aswellaslightsourcessuchasincandescentlampsandflashlamps.光電轉(zhuǎn)換接收器。接收到的光信號需要經(jīng)光電轉(zhuǎn)換器轉(zhuǎn)換成電信號。2Photoelectricconversionreceiver.Thereceivedopticalsignalneedstobeconvertedintoanelectricalsignalbyaphotoelectricconverter.放大、整形與計(jì)數(shù)。3Amplify,reshapeandcount.譯碼。包括硬件譯碼和軟件譯碼。硬件譯碼通過譯碼器的硬件邏輯來完成，軟件譯碼通過固化在ROM中的譯碼程序來完成。實(shí)際上每種譯碼器的譯碼都是通過硬件邏輯與軟件共同完成的。4Decoding.Includinghardwaredecodingandsoftwaredecoding.Thehardwaredecodingiscompletedbythehardwarelogicofthedecoder,andthesoftwaredecodingiscompletedbythedecodingprogramsolidifiedintheROM.Infact,thedecodingofeachkindofdecoderiscompletedbyhardwarelogicandsoftware.通信接口。主要有鍵盤接口和串行接口（RS232）。5CommunicationInterface.Therearemainlykeyboardinterfaceandserialinterface(RS232).Onewayforthebarcodereadertocommunicatewiththecomputeriskeyboardemulation,thatis,thebarcodereadersendsinformationtothecomputerthroughthecomputerkeyboardinterface.Thebarcodereaderisconnectedtothecomputerkeyboardportthroughafour-corecable,andthescaninformationisseriallytransmittedthroughthedataline.Theadvantageofthismethodis:nodriverisrequired,ithasnothingtodowiththeoperatingsystem,anditcanbeuseddirectlyonvariousoperatingsystemswithoutanexternalpowersupply.鍵盤接口方式（Keyboardinterfacemode）1、條碼識讀系統(tǒng)的組成Compositionofbarcoderecognition&readingsystems通信接口CommunicationInterface條碼識讀器與計(jì)算機(jī)通信的一種方式是鍵盤仿真，即條碼閱讀器通過計(jì)算機(jī)鍵盤接口給計(jì)算機(jī)發(fā)送信息。條碼識讀器與計(jì)算機(jī)鍵盤口通過一個(gè)四芯電纜連接，通過數(shù)據(jù)線串行傳遞掃描信息。這種方式的優(yōu)點(diǎn)是：無需驅(qū)動程序，與操作系統(tǒng)無關(guān)，可以在各種操作系統(tǒng)上直接使用，不需要外接電源。Thedataobtainedbyscanningthebarcodeisinputbytheserialport,whichneedstobedrivenordirectlyreadtheserialportdata,andanexternalpowersupplyisrequired.串口方式（Serialportmode）1、條碼識讀系統(tǒng)的組成Compositionofbarcoderecognition&readingsystems通信接口CommunicationInterface掃描條碼得到的數(shù)據(jù)由串口輸入，需要驅(qū)動或直接讀取串口數(shù)據(jù)，需要外接電源。receivingdevicetransmittingdevice條碼技術(shù)識讀原理Barcodetechnologyrecognition&readingmechanism02Thelightemittedbythelightsourceilluminatesthebarcodesymbolthroughtheopticalsystem,andthereflectedlightisimagedonthephotoelectricconverterthroughtheopticalsystemtogenerateelectricalsignals.Thesignalisamplifiedbythecircuittogenerateananalogvoltage,whichisproportionaltothereflectedlightonthebarcodesymbol.Afterfilteringandshaping,asquarewavesignalcorrespondingtotheanalogsignalisformed.Thedecodercanbeinterpretedasacomputerdirectlyacceptabledigitalsignal.條碼識讀的基本工作原理（Thebasicworkingmechanismofbarcoderecogntion&reading）由光源發(fā)出的光線經(jīng)過光學(xué)系統(tǒng)照射到條碼符號上面，被反射回來的光經(jīng)過光學(xué)系統(tǒng)成像在光電轉(zhuǎn)換器上，使之產(chǎn)生電信號。信號經(jīng)過電路放大后產(chǎn)生一模擬電壓，它與照射到條碼符號上被反射回來的光成正比，再經(jīng)過濾波和整形，形成與模擬信號對應(yīng)的方波信號，經(jīng)譯碼器解釋為計(jì)算機(jī)可以直接接受的數(shù)字信號。2、條碼技術(shù)識讀原理Barcodetechnologyrecognition&readingmechanism2、條碼技術(shù)識讀原理Barcodetechnologyrecognition&readingmechanism圖6.3條碼的掃描信號Fig.6.3ScanningsignalofbarcodeLightspotScanlightLightintensitysignalElectricalsignalsPost-shapingsignal條碼識讀系統(tǒng)的基本概念Basicconceptsofbarcoderecognition&readingsystem033、條碼識讀系統(tǒng)的基本概念Basicconceptsofbarcoderecognition&readingsystem首讀率、誤碼率、拒識率（Firstreadingrate,biterrorrate,rejectionrate）1a.首讀率（firstreadrate）是指首次讀出條碼符號的數(shù)量與識讀條碼符號總數(shù)量的比值。Thefirstreadratereferstotheratioofthenumberofbarcodesymbolsreadforthefirsttimetothetotalnumberofbarcodesymbolsread.b.誤碼率（misreadrate）是指錯誤識別次數(shù)與識別總次數(shù)的比值。Themisreadratereferstotheratioofthenumberofincorrectidentificationstothetotalnumberofidentifications.c.拒識率（non-readrate）是指不能識別的條碼符號數(shù)量與條碼符號總數(shù)量的比值。Thenon-readratereferstotheratioofthenumberofunrecognizedbarcodesymbolstothetotalnumberofbarcodesymbols.掃描器的分辨率（Scannerresolution）2掃描器在識讀條碼符號時(shí)能夠分辨出的條(空)寬度的最小值。Theminimumvalueofthebar(space)widththatthescannercandistinguishwhenreadingbarcodesymbols.工作距離和工作景深（Workingdistanceandworkingdepthoffield）3掃描器可分為接觸式和非接觸式兩種。掃描時(shí)掃描器與被掃描的條碼符號之間可保持一定距離范圍，這一范圍就叫做掃描景深。Scannerscanbedividedintocontacttypeandnon-contacttype.Whenscanning,acertaindistancerangecanbemaintainedbetweenthescannerandthebarcodesymbolbeingscanned.Thisrangeiscalledthescanningdepthoffield.掃描頻率（scanningfrequency）4是指條碼掃描器進(jìn)行多重掃描時(shí)每秒的掃描次數(shù)。Referstothenumberofscanspersecondwhenthebarcodescannerperformsmultiplescans.抗鏡向反射能力（Anti-reflectionability）5最好選擇那些有較強(qiáng)抗鏡向反射能力的掃描器。Itisbesttochoosethose