機(jī)械振動(dòng)測(cè)試系統(tǒng)的設(shè)計(jì)【含CAD圖紙、說明書】
機(jī)械振動(dòng)測(cè)試系統(tǒng)的設(shè)計(jì)1 開題依據(jù)1.1 選題背景用試驗(yàn)方法測(cè)量機(jī)械的振動(dòng)量(如位移、速度和加速度等)和系統(tǒng)特征參數(shù)(如固有頻率、阻尼、振型等),以及振動(dòng)環(huán)境的模擬等,都屬于振動(dòng)測(cè)試。研究機(jī)械振動(dòng)時(shí)通常采用理論分析和測(cè)試兩種手段。通過測(cè)試可驗(yàn)證理論分析計(jì)算的正確性,提供所需的修正依據(jù)。20世紀(jì)80年代以來,振動(dòng)測(cè)試儀器有了顯著的進(jìn)步,如傳遞函數(shù)分析儀、實(shí)時(shí)頻率分析儀和快速傅里葉分析儀的相繼應(yīng)用,并與電子計(jì)算機(jī)相結(jié)合,為振動(dòng)測(cè)試和測(cè)試結(jié)果的分析處理提供了方便的條件,從而也進(jìn)一步推動(dòng)了振動(dòng)理論的研究和發(fā)展。系統(tǒng)的振動(dòng)特性也可以應(yīng)用激光全息照相法拍下實(shí)物或模型在振動(dòng)時(shí)的全息照片,根據(jù)全息照片中的干涉條紋圖案來分析。1.2 本課題意義 對(duì)于機(jī)械振動(dòng)測(cè)試系統(tǒng)目前大多數(shù)的廠家還不具備先進(jìn)的技術(shù),裝置大多從國(guó)外引進(jìn),從而設(shè)備成本較高。為了滿足生產(chǎn)需要而又不需要投資太多的資金,我們需要不斷學(xué)習(xí)國(guó)外的技術(shù)并不斷地創(chuàng)新,研制出自己的產(chǎn)品。因此,我選擇這個(gè)課題,對(duì)我來講,意義非常深刻,也是一次不錯(cuò)的學(xué)習(xí)及自我能力提高的機(jī)會(huì)。2 文獻(xiàn)綜述2.1調(diào)研針對(duì)這次機(jī)械振動(dòng)測(cè)試的題目,我特別到工廠進(jìn)行調(diào)研。我了解到的機(jī)械振動(dòng)測(cè)試的主要原理,方法和基本的過程,機(jī)械振動(dòng)的研究可歸結(jié)為機(jī)械系統(tǒng)的激勵(lì)、響應(yīng)和振動(dòng)特性三個(gè)方面的問題。統(tǒng)稱為機(jī)械阻抗曲線。在已知其中兩個(gè)方面的情況下可求第三方面的問題。測(cè)得的機(jī)械阻抗數(shù)據(jù)通常以幅頻特性曲線和相頻特性曲線、實(shí)部和虛部頻率特性曲線或幅相頻率特性曲線(Nyquist圖)3種形式表達(dá),與之相對(duì)應(yīng),振動(dòng)測(cè)試的基本內(nèi)容包括:已知激勵(lì)和系統(tǒng)的振動(dòng)特性情況下求響應(yīng),即振動(dòng)量的測(cè)量;已知激勵(lì)和響應(yīng)的情況下求系統(tǒng)的振動(dòng)特性,即系統(tǒng)特征參數(shù)的測(cè)定,也稱參數(shù)識(shí)別;已知系統(tǒng)的振動(dòng)特性和響應(yīng)的情況下求激勵(lì),即環(huán)境預(yù)測(cè),即用時(shí)域描述的振動(dòng)量時(shí),這種測(cè)試稱為振動(dòng)環(huán)境模擬試驗(yàn)。 3.振動(dòng)測(cè)試方案3.1 振動(dòng)測(cè)試方案1的提出和組成原理圖振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試儀器的設(shè)計(jì)過程是:首先按圖1所示的流程圖布置好振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試儀器的硬件系統(tǒng);然后,在個(gè)人計(jì)算機(jī)上開發(fā)相應(yīng)的應(yīng)用軟件;最后,振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試與模態(tài)識(shí)別的全過程,都是在個(gè)人計(jì)算機(jī)上通過軟面板對(duì)話框和適當(dāng)?shù)目刂瓢粹o來完成。信號(hào)發(fā)生器被測(cè)機(jī)械振動(dòng)系統(tǒng)輸入輸出個(gè)人計(jì)算機(jī)系統(tǒng)及動(dòng)態(tài)特性測(cè)試分析軟 件X(n)振動(dòng)傳感器及信號(hào)調(diào)理電路Y1(n)被測(cè)振動(dòng)系統(tǒng)的模態(tài)參數(shù)和數(shù)學(xué)模型的輸出激振器振動(dòng)傳感器及信號(hào)調(diào)理電路數(shù)據(jù)采集卡DAQ,包含: 多路開關(guān) 放大器 采樣保持器S/H A/D轉(zhuǎn)換器YN(n) 圖1 振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試儀器原理圖3.2 激振方式、激振器和振動(dòng)傳感器的布置激振方式可分為正弦穩(wěn)態(tài)掃頻和寬頻帶激振兩大類。通常采用“正弦穩(wěn)態(tài)掃頻激振”,其優(yōu)點(diǎn)是激振能量集中,信噪比高,對(duì)于線性系統(tǒng)的動(dòng)態(tài)特性測(cè)試具有很高的測(cè)量精度。首先,根據(jù)測(cè)試分析要求及振動(dòng)系統(tǒng)的機(jī)械結(jié)構(gòu)特點(diǎn),確定激振點(diǎn)的位置和測(cè)量點(diǎn)的數(shù)量N及各測(cè)量點(diǎn)的位置。對(duì)于空間結(jié)構(gòu)系統(tǒng),往往需要測(cè)量1個(gè)點(diǎn)的3個(gè)方向,這時(shí)應(yīng)選用三軸振動(dòng)傳感器。安裝激振器時(shí),必須注意激振力的正確施加。在安裝測(cè)振傳感器時(shí),應(yīng)保證傳感器能正確感受被測(cè)體的振動(dòng)。小型振動(dòng)系統(tǒng)必須選用微型傳感器,以避免傳感器附加質(zhì)量影響振動(dòng)系統(tǒng)動(dòng)態(tài)特性。3.3 振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試應(yīng)用軟件的總體研究 根據(jù)對(duì)前面振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器原理圖的分析可知,振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試應(yīng)用軟件的設(shè)計(jì)流程分為如下步驟: (1)計(jì)算機(jī)發(fā)出指令控制“信號(hào)發(fā)生器”產(chǎn)生激勵(lì)信號(hào),再通過“激振器”施加于被測(cè)振動(dòng)系統(tǒng)。激勵(lì)信號(hào)的數(shù)字序列為X(n)。 (2) 等待被測(cè)振動(dòng)系統(tǒng)穩(wěn)定一定時(shí)間,然后計(jì)算機(jī)再發(fā)出指令同步采集數(shù)據(jù)序列X(n)和Y1(n),Y2(n), ,YN(n) 。采樣時(shí)間間隔或采樣頻率應(yīng)符合采樣定理及頻率分辨率的要求。 (3)利用按本原理設(shè)計(jì)的專用軟件分析處理X(n)和Y1(n),Y2(n),YN(n), 就可得出被測(cè)振動(dòng)系統(tǒng)的模態(tài)參數(shù)和相應(yīng)數(shù)學(xué)模型。顯然,整套應(yīng)用軟件應(yīng)包括兩大部分,即操作控制部分和數(shù)據(jù)處理部分。由于目前計(jì)算機(jī)控制技術(shù)和虛擬儀器技術(shù)的發(fā)展,已足以解決此應(yīng)用軟件中的操作控制部分,且鑒于篇幅有限,所以筆者對(duì)應(yīng)用軟件的操作控制部分不再作進(jìn)一步討論,下面重點(diǎn)研究應(yīng)用軟件的數(shù)據(jù)處理部分。3.4 數(shù)據(jù)處理專用軟件的設(shè)計(jì)原理3.4.1 濾波方法 由于數(shù)據(jù)序列在采集過程中難免會(huì)受到各種干擾, 所以必須采取有效的濾波算法對(duì)采集得到的數(shù)據(jù)序列Y1(n),Y2(n),YN(n)進(jìn)行修正。通常應(yīng)采用相關(guān)濾波算法,因?yàn)橄嚓P(guān)濾波可以有效地把真正由X(n)通過振動(dòng)系統(tǒng)產(chǎn)生的信號(hào)從Y1(n),Y2(n),YN(n)中分離出來。將經(jīng)過濾波算法處理后的數(shù)據(jù)序列記為YN1(n),YN2(n),YNN(n) ,n=1,2, ,D 。D為采樣點(diǎn)數(shù)量。3.4.2 頻率響應(yīng)函數(shù)的確定 將確定性信號(hào)看成隨機(jī)信號(hào),采用離散數(shù)字隨機(jī)信號(hào)的相關(guān)譜分析原理。 XK(k) = FFT X(n) YK(k) = FFT YN(n) SX(k) = XK(k)2 /D SY(k) = YK(k)2 /D SXY(k) = XK*(k)YK(k) /D XK*(K)為XK(k)的共軛復(fù)數(shù)。 為減少數(shù)據(jù)處理誤差,要對(duì)SX(k),SY(k),SXY(k)采取平滑處理算法。分段時(shí),相鄰兩段重疊50的效果最佳,即將記錄段X(n),YN(n)分成多個(gè)樣本,分別進(jìn)行上述運(yùn)算后再求平均值。VXY2(k) = SXY(k)2 / SX(k) SY(k), 相干系數(shù)VXY越接近1效果越好。H(k) =SXY(k) / SX(k), 由變量代換關(guān)系“k/(DTS) =f(TS為采樣時(shí)間間隔)”可得到測(cè)試出的頻率響應(yīng)函數(shù)H(f) 。 對(duì)每一個(gè)數(shù)據(jù)序列Y1(n),Y2(n),YN(n)均用上述方法處理,就可以得到測(cè)試出來的N個(gè)頻率響應(yīng)函數(shù)H1(f),H2(f),HN(f) 。3.4.3 擬合求解模態(tài)參數(shù)機(jī)械振動(dòng)系統(tǒng)模態(tài)參數(shù)識(shí)別,又稱為曲線擬合,即采用最小二乘法將測(cè)試所得的頻率響應(yīng)值與系統(tǒng)模型值進(jìn)行曲線擬合。優(yōu)化準(zhǔn)則就是使實(shí)測(cè)的頻率響應(yīng)值與理論數(shù)學(xué)模型對(duì)應(yīng)值的總均方誤差E極小。最小二乘曲線擬合過程中存在的有關(guān)問題,如方程組的病態(tài)問題,可根據(jù)數(shù)值分析理論,采用正交多項(xiàng)式的方法加以解決。通常機(jī)械振動(dòng)系統(tǒng)的“理論數(shù)學(xué)模型”可用有理分式形式的傳遞函數(shù)來表示,即 H(s) = N(s)/D(s) = a0sm+a1sm-1+am-1s+am/ sn+b1sn-1+bn-1s+bn上式中,mn,n=2q,q為系統(tǒng)的自由度數(shù)。一般選定一個(gè)具體q值,令m=2q-1,然后循環(huán)擬合,直到滿足E控制精度Eg。 對(duì)于每一個(gè)頻率響應(yīng)函數(shù),設(shè)由D個(gè)采樣點(diǎn)得到的D個(gè)測(cè)試頻率響應(yīng)值記為HC(f),對(duì)應(yīng)的D個(gè)理論模型值記為HL(f),則總方差為E=(k=1,D)| HC(f)HL(f)|2。這是非線性優(yōu)化問題,為使用方便和保證精度,可轉(zhuǎn)化為線性優(yōu)化問題。令s=jw=j2f,誤差e=N(f) D(f)HC(f),則總方差轉(zhuǎn)化為E=|N(f) D(f)HC(f)|2。此時(shí),總方差函數(shù)為待求系數(shù)的線性函數(shù),最小二乘解已變成線性優(yōu)化問題。首先通過最小二乘擬合識(shí)別出有理分式的系數(shù)ai(i=1,2,m)和bi(i=1,2,n),然后由特征方程D(s)0解得極點(diǎn)sr及sr*(r=1,2,q),由留數(shù)公式ArH(s)(s-sr)| S=Sr”求出留數(shù)Ar及Ar* 。則傳遞函數(shù)可表示為H(s)r=1 , N Ar/(s-sr) + Ar*/(s-sr*)最后以sr= -r wr +j wr (1- r2)1/2,sr為共軛復(fù)數(shù),求得各階模態(tài)固有頻率wr和阻尼比r 。對(duì)于線性系統(tǒng),模態(tài)固有頻率和阻尼比是系統(tǒng)的總體固有參數(shù),理論上應(yīng)該不隨測(cè)量點(diǎn)而改變。依次對(duì)N個(gè)測(cè)量點(diǎn)的頻率響應(yīng)函數(shù)進(jìn)行曲線擬合,可得到N組模態(tài)固有頻率和阻尼比,再求出平均值作為系統(tǒng)的模態(tài)固有頻率和阻尼比,進(jìn)而,再求出各階振型r 。3.4.4 其它輸出振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試所得的系統(tǒng)固有的各階模態(tài)參數(shù)和用模態(tài)參數(shù)表示的各測(cè)量點(diǎn),對(duì)應(yīng)于輸入點(diǎn)的數(shù)學(xué)模型。振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試數(shù)據(jù)處理的全過程,可以用目前流行的程序設(shè)計(jì)語言VC+或Java2開發(fā)成專用的數(shù)據(jù)處理程序軟件包,然后通過相關(guān)程序語言接口方法嵌入到用LabVIEW或LabWindows平臺(tái)開發(fā)的振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器中。采用本虛擬儀器,可以很容易通過計(jì)算機(jī)多次重復(fù)振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試的整個(gè)過程,進(jìn)一步提高振動(dòng)系統(tǒng)動(dòng)態(tài)特性的測(cè)試精度。利用動(dòng)態(tài)測(cè)試得到的數(shù)學(xué)模型,通過Matlab6.1仿真環(huán)境(或自己編制程序)可求出激振點(diǎn)處各種輸入信號(hào)各測(cè)量點(diǎn)處的輸出響應(yīng)信號(hào)。3.5振動(dòng)測(cè)試方案2的組成根據(jù)課題的需要,以及對(duì)實(shí)際情況的考察和比較,我們?cè)O(shè)計(jì)出系統(tǒng)的方案,如下圖所示: 91073掃頻信號(hào)源數(shù)采分析儀計(jì)算機(jī)系統(tǒng)及分析軟件打印機(jī)或繪圖儀電機(jī)調(diào)壓器124568111213141516 系統(tǒng)方案設(shè)計(jì)圖 振動(dòng)測(cè)試與控制實(shí)驗(yàn)臺(tái)由彈性體系統(tǒng)(包括簡(jiǎn)支梁、懸臂梁、薄壁圓板、單自由度系統(tǒng)、二自由度系統(tǒng)、多自由度系統(tǒng)模型)配以主動(dòng)隔振、被動(dòng)隔振用的空氣阻尼減震器、單式動(dòng)力吸振器、復(fù)式動(dòng)力吸振器等組成。是完成振動(dòng)與振動(dòng)控制等近30個(gè)實(shí)驗(yàn)的試驗(yàn)平臺(tái) 1、激振系統(tǒng) 激振系統(tǒng)包括: DH1301正弦掃頻信號(hào)源 JZ-1型接觸式激振器 JZF-1型非接觸式激振器 偏心電動(dòng)機(jī)、調(diào)壓器 力錘(包括測(cè)力傳感器) 2、測(cè)振系統(tǒng)DH5922動(dòng)態(tài)采集分析儀 MT-3T型磁電式振動(dòng)速度傳感器 DH103壓電式加速度傳感器 WD302電渦流位移傳感器 測(cè)力傳感器3、動(dòng)態(tài)采集分析系統(tǒng) 信號(hào)調(diào)理器 數(shù)據(jù)采集儀 計(jì)算機(jī)系統(tǒng)(或筆記本電腦) 控制與基本分析軟件 模態(tài)分析軟件系統(tǒng)軟硬件配置合理、完善,能完成幾乎全部與振動(dòng)相關(guān)的試驗(yàn),可完成各種模態(tài)試驗(yàn)(小到梁、板、構(gòu)件,大到房屋、橋梁等),可完成頻率耦合、結(jié)構(gòu)修改、靈敏度分析等動(dòng)力學(xué)試驗(yàn);4 研究路線和技術(shù)方法振動(dòng)量的測(cè)量測(cè)量機(jī)械系統(tǒng)某些選定點(diǎn)上的振幅(位移、速度和加速度)、頻率、相位、振動(dòng)的時(shí)間歷程和頻譜等。這種測(cè)量通常在機(jī)械系統(tǒng)的工作狀態(tài)下進(jìn)行,以了解其實(shí)際振動(dòng)狀況。也可將其轉(zhuǎn)換為數(shù)字量后分析處理。對(duì)某些精密和大型機(jī)械設(shè)備的振動(dòng)監(jiān)控和診斷所作的測(cè)量也屬這種性質(zhì)。 對(duì)模擬量可直接分析處理,振動(dòng)量測(cè)量按振動(dòng)信號(hào)和轉(zhuǎn)換方式可分為電測(cè)法、光測(cè)法和機(jī)械測(cè)振法,其中以電測(cè)法應(yīng)用最為廣泛。圖1為一個(gè)較完整的振動(dòng)量電測(cè)系統(tǒng)。測(cè)振傳感器(拾振器)將機(jī)械振動(dòng)量轉(zhuǎn)換為與它成比例的電量。 測(cè)試結(jié)果的分析和數(shù)據(jù)處理 測(cè)試結(jié)果所獲得的原始數(shù)據(jù)有兩種表現(xiàn)形式:一種是模擬量,常用的測(cè)振傳感器有發(fā)電型(如壓電式、電動(dòng)式和磁電式等)和電參數(shù)變化型(如電感式、電容式、電阻式和渦流式等)兩類。以保證輸出電信號(hào)的幅值和相位均不失真。不同類型的傳感器需要配接不同類型的中間測(cè)量變換裝置(圖2)。最基本的要求是:在其工作頻率范圍內(nèi)的幅頻特性平坦、相頻特性呈線性關(guān)系,中間測(cè)量變換裝置對(duì)傳感器輸出的電信號(hào)進(jìn)行前置變換(電阻抗變換)、微積分運(yùn)算、放大、調(diào)制和解調(diào)等,以便驅(qū)動(dòng)后接的分析或顯示、記錄設(shè)備。分析設(shè)備完成對(duì)信號(hào)的頻率分析。顯示、記錄設(shè)備給出振動(dòng)信號(hào)(經(jīng)過分析的或未經(jīng)過分析的)的波形,并用數(shù)字或模擬方式指示出測(cè)量結(jié)果,應(yīng)校準(zhǔn)溫度的影響等。以便于儲(chǔ)存、分析信號(hào)和進(jìn)行數(shù)據(jù)處理。 系統(tǒng)特征參數(shù)的測(cè)定主要是應(yīng)用機(jī)械阻抗測(cè)試技術(shù),以獲得機(jī)械阻抗數(shù)據(jù)(有時(shí)亦稱頻率響應(yīng)數(shù)據(jù)),從而得到系統(tǒng)的特征參數(shù)如固有頻率、阻尼、剛度、質(zhì)量和振型等;還可通過模態(tài)分析求取系統(tǒng)在各階模態(tài)下的特征參數(shù),既模態(tài)參數(shù)。這一測(cè)試過程稱為模態(tài)參數(shù)識(shí)別。這種測(cè)定通常在機(jī)械系統(tǒng)的非工作狀態(tài)或模型試驗(yàn)情況下進(jìn)行,以求全面了解其動(dòng)態(tài)響應(yīng)特性。尤其是測(cè)振傳感器必須進(jìn)行定期校準(zhǔn)和定度。若在工作狀態(tài)下進(jìn)行,則常稱為在線識(shí)別。在機(jī)械阻抗測(cè)試技術(shù)中,施加的激勵(lì)有簡(jiǎn)諧、瞬態(tài)和隨機(jī)3種類型,試驗(yàn)根據(jù)不同試驗(yàn)對(duì)象按相應(yīng)的試驗(yàn)規(guī)范進(jìn)行,故機(jī)械阻抗測(cè)試也相應(yīng)地分3類。 振動(dòng)環(huán)境模擬試驗(yàn)研究或考核試驗(yàn)對(duì)象在強(qiáng)度、壽命和功能方面的抗振性。簡(jiǎn)諧激勵(lì)又有單點(diǎn)激勵(lì)和多點(diǎn)激勵(lì)兩種形式。這種模擬試驗(yàn)分為周期性振動(dòng)試驗(yàn)、隨機(jī)振動(dòng)試驗(yàn)和沖擊試驗(yàn) 3種。周期性振動(dòng)試驗(yàn)一般采用耐共振、耐掃頻和耐預(yù)定頻率試驗(yàn) 3種形式。在進(jìn)行振動(dòng)壽命試驗(yàn)時(shí),為了縮短試驗(yàn)時(shí)間常采用提高振動(dòng)量級(jí)的辦法,即幅頻特性;測(cè)定振動(dòng)響應(yīng)與激勵(lì)間的相位差隨激勵(lì)頻率變化的關(guān)系,即強(qiáng)化試驗(yàn)。提高的程度,即強(qiáng)化系數(shù), 簡(jiǎn)諧激勵(lì)機(jī)械阻抗的測(cè)試 以簡(jiǎn)諧力作為激勵(lì)并保持其幅值恒定,應(yīng)根據(jù)試件的振動(dòng)響應(yīng)特性和疲勞強(qiáng)度分析來考慮。試驗(yàn)根據(jù)不同試驗(yàn)對(duì)象按相應(yīng)的試驗(yàn)規(guī)范進(jìn)行,并用模擬振動(dòng)試驗(yàn)機(jī)來實(shí)現(xiàn)。 測(cè)試系統(tǒng)的校準(zhǔn)和定度為了保證測(cè)試結(jié)果的可靠性和測(cè)試精度,對(duì)所使用的儀器,尤其是測(cè)振傳感器必須進(jìn)行定期校準(zhǔn)和定度。以求全面了解其動(dòng)態(tài)響應(yīng)特性。在進(jìn)行重要的或特殊的試驗(yàn)前,這種測(cè)定通常在機(jī)械系統(tǒng)的非工作狀態(tài)或模型試驗(yàn)情況下進(jìn)行,常直接對(duì)整套測(cè)試系統(tǒng)進(jìn)行現(xiàn)場(chǎng)校準(zhǔn)和定度。測(cè)試系統(tǒng)最基本的校準(zhǔn)項(xiàng)目包括靈敏度、頻率響應(yīng)和線性度。既模態(tài)參數(shù)。此外,從而得到系統(tǒng)的特征參數(shù)如固有頻率、阻尼、剛度、質(zhì)量和振型等;還可通過模態(tài)分析求取系統(tǒng)在各階模態(tài)下的特征參數(shù),根據(jù)需要還可進(jìn)行某些特殊的校準(zhǔn),如所測(cè)振級(jí)變化范圍大時(shí),應(yīng)校準(zhǔn)動(dòng)態(tài)線性范圍;高溫下測(cè)試時(shí),以便于儲(chǔ)存、分析信號(hào)和進(jìn)行數(shù)據(jù)處理。應(yīng)校準(zhǔn)溫度的影響等。測(cè)振傳感器的校準(zhǔn)在測(cè)試系統(tǒng)的校準(zhǔn)中具有特別重要的意義。校準(zhǔn)方法主要有兩種:一是絕對(duì)校準(zhǔn)法,分析設(shè)備完成對(duì)信號(hào)的頻率分析。二是比較校準(zhǔn)法。無論是對(duì)測(cè)振傳感器或?qū)M成測(cè)試系統(tǒng)的儀器和對(duì)整個(gè)測(cè)試系統(tǒng)的校準(zhǔn),最基本的要求是:在其工作頻率范圍內(nèi)的幅頻特性平坦、相頻特性呈線性關(guān)系,不同類型的傳感器需要配接不同類型的中間測(cè)量變換裝置(圖2)。以保證輸出電信號(hào)的幅值和相位均不失真。 測(cè)試結(jié)果的分析和數(shù)據(jù)處理測(cè)試結(jié)果所獲得的原始數(shù)據(jù)有兩種表現(xiàn)形式:一種是模擬量,如電壓和電流等;一種是數(shù)字量。對(duì)不同的數(shù)據(jù)形式,其中以電測(cè)法應(yīng)用最為廣泛。分析處理方法也不相同。 對(duì)模擬量可直接分析處理,也可將其轉(zhuǎn)換為數(shù)字量后分析處理。前者設(shè)備較簡(jiǎn)單,后者精度和速度較高。 當(dāng)模擬量是振動(dòng)的時(shí)間歷程,即用時(shí)域描述的振動(dòng)量時(shí),即環(huán)境預(yù)測(cè),分析處理的主要內(nèi)容就是進(jìn)行各種頻譜分析,以了解測(cè)試對(duì)象在頻率域內(nèi)的振動(dòng)特性。即系統(tǒng)特征參數(shù)的測(cè)定,常用的頻譜分析儀有恒定百分比帶寬式、恒定帶寬式、采用壓縮時(shí)間歷程的實(shí)時(shí)分析儀和具有并聯(lián)濾波器的實(shí)時(shí)分析儀等。當(dāng)模擬量是頻率響應(yīng)時(shí),可歸結(jié)為對(duì)機(jī)械阻抗數(shù)據(jù)的分析處理。測(cè)得的機(jī)械阻抗數(shù)據(jù)通常以幅頻特性曲線和相頻特性曲線、實(shí)部和虛部頻率特性曲線或幅相頻率特性曲線(Nyquist圖)3種形式表達(dá),統(tǒng)稱為機(jī)械阻抗曲線。因此分析處理的主要內(nèi)容是:根據(jù)機(jī)械阻抗曲線,通過模態(tài)分析,系統(tǒng)的振動(dòng)特性也可以應(yīng)用激光全息照相法拍下實(shí)物或模型在振動(dòng)時(shí)的全息照片,識(shí)別測(cè)試對(duì)象在選定頻率范圍內(nèi)的各階模態(tài)參數(shù)和建立它的數(shù)字模型。 模擬量的數(shù)字分析處理是將測(cè)得的振動(dòng)模擬量信號(hào),經(jīng)過模-數(shù)轉(zhuǎn)換器變?yōu)橄鄳?yīng)的數(shù)字量,并與電子計(jì)算機(jī)相結(jié)合,然后輸入數(shù)據(jù)處理機(jī)進(jìn)行各種必要的分析。當(dāng)測(cè)試結(jié)果直接以數(shù)字量表示時(shí),則可利用軟件在電子計(jì)算機(jī)上分析處理。20世紀(jì)80年代以來,4 畢業(yè)設(shè)計(jì)內(nèi)容4.1 原理圖的設(shè)計(jì) 測(cè)振傳感器(拾振器)將機(jī)械振動(dòng)量轉(zhuǎn)換為與它成比例的電量。常用的測(cè)振傳感器有發(fā)電型(如壓電式、電動(dòng)式和磁電式等)和電參數(shù)變化型(如電感式、電容式、電阻式和渦流式等)兩類。不同類型的傳感器需要配接不同類型的中間測(cè)量變換裝置中間測(cè)量變換裝置對(duì)傳感器輸出的電信號(hào)進(jìn)行前置變換(電阻抗變換)、微積分運(yùn)算、放大、調(diào)制和解調(diào)等,以便驅(qū)動(dòng)后接的分析或顯示、記錄設(shè)備。分析設(shè)備完成對(duì)信號(hào)的頻率分析。顯示、記錄設(shè)備給出振動(dòng)信號(hào)(經(jīng)過分析的或未經(jīng)過分析的)的波形,并用數(shù)字或模擬方式指示出測(cè)量結(jié)果,以便于儲(chǔ)存、分析信號(hào)和進(jìn)行數(shù)據(jù)處理。4.2 機(jī)械結(jié)構(gòu)設(shè)計(jì)4.3 控制設(shè)計(jì)硬件實(shí)現(xiàn)硬件實(shí)現(xiàn)的關(guān)鍵是要設(shè)計(jì)一個(gè)能夠快速跟蹤信號(hào)頻率變化的倍頻電路。利用鎖相環(huán)的輸出信號(hào)動(dòng)態(tài)跟蹤輸入信號(hào)頻率的這一特點(diǎn),將VCO的輸出信號(hào)經(jīng)一分頻器后送入相位比較器,則鎖定時(shí)VCO輸出信號(hào)的頻率將等于K倍的輸入信號(hào)的頻率,即Kfi,適當(dāng)?shù)剡x擇分頻系數(shù)K就可以得到所需要的倍頻信號(hào)的輸出。本文所選的鎖相環(huán)芯片為CD4046,使用中無需解調(diào)信號(hào)輸出。比較器PC2用于比較兩輸入波形前沿或后沿相位的上跳或下跳(本電路采用上跳邊沿觸發(fā)方式)。如圖所示,該電路主要由輸入信號(hào)、隔直電容、平移、整形、鎖相環(huán)組成。首先取鍵相位信號(hào)CIR作為測(cè)頻輸入,通過10F電容濾去太高的直流電壓,送入MAX903比較放大器調(diào)節(jié)平移,輸出的脈沖由74HCT14進(jìn)一步整形后作為鎖相環(huán)的輸入信號(hào);由鎖相環(huán)電路實(shí)現(xiàn)倍頻。為了實(shí)現(xiàn)FFT分析,在一個(gè)周期內(nèi)采集2 n個(gè)數(shù)據(jù),本設(shè)計(jì)中n取為6,也即是在一個(gè)周期內(nèi)采集64個(gè)數(shù)據(jù)。分頻器的輸出信號(hào)CLK_64由CPLD產(chǎn)生。鎖相環(huán)的輸出信號(hào)CLK64實(shí)現(xiàn)AD的采樣控制。本電路可以保證在有鍵相位的情況下,信號(hào)采集的第一起點(diǎn)在以鍵相位為基準(zhǔn),旋轉(zhuǎn)36064點(diǎn)的位置上(因系統(tǒng)每周期采樣64點(diǎn))。軟件實(shí)現(xiàn)圖是本系統(tǒng)通過CPLD實(shí)現(xiàn)整周期采樣的波形仿真圖。實(shí)驗(yàn)中AD選用MAX1292,F(xiàn)IF0選用IDT7202。根據(jù)MAX1292的采樣時(shí)序和FIFO的寫時(shí)序,在CPLD中采用MOORE有限狀態(tài)機(jī)來實(shí)現(xiàn)對(duì)時(shí)序的控制。RESET為系統(tǒng)的復(fù)位信號(hào),CLK64為轉(zhuǎn)速信號(hào)的64倍頻;GLOBAL_CLK為CPLD的時(shí)鐘信號(hào);FF為FIFO的滿標(biāo)志位;AD_DATA為寫入AD中的控制字節(jié);AD INT、AD_WR、AD_RD、AD_HBEN、AD_CS為AD的相關(guān)控制信號(hào):AD_START為啟動(dòng)AD采集信號(hào),由MCU發(fā)出。AD_CHANNEL為AD的通道選擇控制字,硬件電路上用兩位開關(guān)來實(shí)現(xiàn)單通道、雙通道及四通道的采集。圖中為四通道采集。EF、HF、FIFOINT為FIF0單元控制模塊。CLK 64、CLK 1000為分頻器模塊,用來實(shí)現(xiàn)整周期采樣和自適應(yīng)抗混疊濾波。實(shí)現(xiàn)AD整周期采樣的過程描述如下:首先,CPLD在接收到CLK64信號(hào)的上升沿后,開始進(jìn)行轉(zhuǎn)換。MAX1292按照時(shí)序依次將四個(gè)通道的模擬量轉(zhuǎn)換為數(shù)字量。其中,在每個(gè)通道的數(shù)據(jù)轉(zhuǎn)換過程中,都要判斷AD INT信號(hào)是否為低,若為低則表示轉(zhuǎn)換完成,可以進(jìn)行讀操作。此時(shí),再去判斷FIFO的FF標(biāo)志,若為1則表明FIFO未滿,可以將數(shù)據(jù)寫入FIFO中。當(dāng)四個(gè)通道都完成如上操作后,再繼續(xù)判斷CLK64信號(hào),循環(huán)執(zhí)行,完成在一個(gè)轉(zhuǎn)速信號(hào)周期內(nèi)對(duì)各路信號(hào)采集64次。本裝置中,被測(cè)的最大轉(zhuǎn)速信號(hào)為1kHz,GLOBAL_CLK的信號(hào)頻率為7MHz。畢業(yè)設(shè)計(jì)進(jìn)度二月份:開題報(bào)告三月份:英文翻譯1萬字(10頁(yè))1-2個(gè)星期 完成緒論,第一章 拿出一個(gè)方案四月份:(理論設(shè)計(jì)) 第二章 方案比較 具體設(shè)計(jì) 建立數(shù)學(xué)模型五月份:第三章 理論 實(shí)驗(yàn)仿真 設(shè)計(jì)圖紙六月初:中英文摘要 打印圖紙,整理論文參考文獻(xiàn)1 黃文虎,等設(shè)備故障診斷原理、技術(shù)及應(yīng)用M北京:科學(xué)出版社,1994 2 趙俊超集成電路設(shè)計(jì)VHDL教程M北京:希望電子出版社,20023 李方澤,劉馥清,王正工程振動(dòng)測(cè)試與分析M北京:高等教育出版社,19924 胡時(shí)岳、朱繼梅:機(jī)械振動(dòng)與沖擊測(cè)試技術(shù),科學(xué)出版社,北京,19835 聞邦椿 顧家柳 等.高等轉(zhuǎn)子動(dòng)力學(xué)理論、技術(shù)與應(yīng)用M.北京:機(jī)械工業(yè)出版社,2000.1-76.6 陳德新 徐嵐.灰度相關(guān)法在流動(dòng)可視化圖像解析中的應(yīng)用J.華北水利水電學(xué)院學(xué)報(bào),2000,21(1):47-50,55.7 萬軍,蔣世祥,蔡智勇; 旋轉(zhuǎn)機(jī)械振動(dòng)信號(hào)的小波包分解及故障檢測(cè) J;汽輪機(jī)技術(shù); 2002年02期8 江志農(nóng),李艷妮; 旋轉(zhuǎn)機(jī)械軸心軌跡特征提取技術(shù)研究 J;振動(dòng)、測(cè)試與診斷; 2007年02期; 7-10+779 郭月強(qiáng); 振動(dòng)信號(hào)的測(cè)試與分析及其軟件系統(tǒng)的開發(fā) D;北京工業(yè)大學(xué); 2002年10 張令彌. 振動(dòng)測(cè)試與動(dòng)態(tài)分析. 航空工業(yè)出版社,1992. 11 黃長(zhǎng)藝, 嚴(yán)普強(qiáng). 機(jī)械工程測(cè)試技術(shù)基礎(chǔ), 機(jī)械工業(yè)出版社, 1999. 12 姚天任, 江太輝. 數(shù)字信號(hào)處理. 華中科技大學(xué)出版社,2000. 目 錄1 概述2 系統(tǒng)方案設(shè)計(jì) 2.1振動(dòng)測(cè)試?yán)碚?2.2 振動(dòng)測(cè)試技術(shù) 2.3 測(cè)試問題的提出 2.4 問題的解決和研究?jī)?nèi)容 2.5 方案1的設(shè)計(jì) 2.6 方案2的設(shè)計(jì)3 振動(dòng)測(cè)試系統(tǒng)設(shè)計(jì) 3.1 機(jī)械系統(tǒng)設(shè)計(jì) 3.2 實(shí)驗(yàn)裝置的選型 3.3 振動(dòng)測(cè)試的激勵(lì)4 實(shí)驗(yàn)結(jié)果及其分析 4.1 實(shí)驗(yàn)操作步驟 4.2 實(shí)驗(yàn)結(jié)果參考文獻(xiàn)振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器的研究摘要:通過把振動(dòng)系統(tǒng)動(dòng)態(tài)分析理論與數(shù)字信號(hào)處理方法相結(jié)合,提出并系統(tǒng)地論述了振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器的開發(fā)原理。1 引言 隨著數(shù)字計(jì)算機(jī)仿真技術(shù)的發(fā)展,虛擬儀器技術(shù)的應(yīng)用越來越廣泛,所謂虛擬儀器就是在通用計(jì)算機(jī)上增加一組軟件和相關(guān)硬件,使使用者在操縱這臺(tái)計(jì)算機(jī)時(shí),就像是在操作一臺(tái)他自己設(shè)計(jì)的專用傳統(tǒng)電子儀器。在虛擬儀器系統(tǒng)中,硬件僅僅是為了解決信號(hào)的輸入輸出,而軟件才是整個(gè)儀器系統(tǒng)的關(guān)鍵。任何一個(gè)使用者都可以通過修改軟件的方法,很方便地調(diào)整儀器系統(tǒng)的功能與規(guī)模。虛擬儀器技術(shù)給用戶一個(gè)充分發(fā)揮自己才能及想象力的空間,用戶(而不是儀器廠家)可以根據(jù)自己的需求隨心所欲地設(shè)計(jì)自己的儀器系統(tǒng)。因此有軟件就是儀器的說法。 本文正是根據(jù)數(shù)字計(jì)算機(jī)仿真技術(shù)和虛擬儀器技術(shù)的思想,從簡(jiǎn)單實(shí)用的角度出發(fā),把振動(dòng)系統(tǒng)的動(dòng)態(tài)測(cè)試?yán)碚摵蛿?shù)字信號(hào)處理方法相結(jié)合,提出并系統(tǒng)地論述了振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器的開發(fā)原理。2 動(dòng)態(tài)測(cè)試的基本概念 工程中大多數(shù)實(shí)際系統(tǒng)均用線性系統(tǒng)來描述,而線性系統(tǒng)的輸入輸出之間存在著簡(jiǎn)單的因果關(guān)系。因此,可以通過對(duì)被測(cè)系統(tǒng)輸入輸出物理量的測(cè)量和分析來確定系統(tǒng)的動(dòng)態(tài)特性,這就是動(dòng)態(tài)測(cè)試。動(dòng)態(tài)特性的數(shù)學(xué)模型有多種形式:時(shí)域中常用的有微分方程、差分方程和狀態(tài)方程;復(fù)數(shù)域中有傳遞函數(shù)、結(jié)構(gòu)圖;頻域中有頻率響應(yīng)函數(shù)等。對(duì)機(jī)械振動(dòng)系統(tǒng)進(jìn)行動(dòng)態(tài)特性辨識(shí)的主要目的是得到系統(tǒng)的頻域特性或傳遞函數(shù),并進(jìn)一步獲得機(jī)械振動(dòng)力學(xué)系統(tǒng)的模態(tài)參數(shù)。頻率響應(yīng)函數(shù)用頻率響應(yīng)數(shù)據(jù)和曲線來表示,可以把頻率響應(yīng)函數(shù)看成是描述線性系統(tǒng)的非參數(shù)模型。對(duì)于機(jī)械振動(dòng)系統(tǒng),其動(dòng)態(tài)特性常用“固有頻率、阻尼比和振型”等所謂的模態(tài)參數(shù)來描述。在頻率響應(yīng)函數(shù)測(cè)試的基礎(chǔ)上,可以通過參數(shù)識(shí)別的方法,即試驗(yàn)?zāi)B(tài)分析來建立機(jī)械振動(dòng)系統(tǒng)的模態(tài)參數(shù)。 動(dòng)態(tài)測(cè)試技術(shù)的主要內(nèi)容就是對(duì)被測(cè)振動(dòng)系統(tǒng)進(jìn)行激勵(lì),通過振動(dòng)測(cè)試、數(shù)據(jù)采集和信號(hào)分析,由輸入和輸出確定機(jī)械振動(dòng)系統(tǒng)的動(dòng)態(tài)特性。可見,動(dòng)態(tài)測(cè)試分為兩大部分:頻率響應(yīng)函數(shù)的測(cè)繪和模態(tài)參數(shù)的識(shí)別。機(jī)械振動(dòng)系統(tǒng)動(dòng)態(tài)特性測(cè)試與分析的重點(diǎn)是,如何利用測(cè)試分析所得的頻率響應(yīng)函數(shù)曲線,通過模態(tài)識(shí)別的方法,求解出表征機(jī)械振動(dòng)系統(tǒng)動(dòng)態(tài)特性的模態(tài)參數(shù)。模態(tài)識(shí)別可分為單模態(tài)識(shí)別和多模態(tài)識(shí)別,單模態(tài)識(shí)別是建立在小阻尼、弱耦合假設(shè)的基礎(chǔ)上。對(duì)于模態(tài)密集的復(fù)雜結(jié)構(gòu)或大阻尼情況,則需采用多模態(tài)分析。隨著數(shù)字計(jì)算機(jī)技術(shù)的深入發(fā)展,現(xiàn)代模態(tài)參數(shù)識(shí)別大都采用多模態(tài)識(shí)別。3 振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器的設(shè)計(jì)3.1 虛擬儀器的提出和組成原理圖虛擬儀器的優(yōu)點(diǎn)在于能夠共享計(jì)算機(jī)輔助測(cè)試系統(tǒng)的硬件資源和輸入輸出接口軟件,用戶只需設(shè)計(jì)有關(guān)的應(yīng)用軟件便可以實(shí)現(xiàn)相應(yīng)的測(cè)試分析功能。這樣不僅節(jié)約成本,而且還具有“實(shí)用性強(qiáng),準(zhǔn)確度高,效價(jià)比良,靈活性好,全自動(dòng)化”的特點(diǎn)?;跀?shù)字計(jì)算機(jī)仿真技術(shù)和虛擬儀器技術(shù)的快速發(fā)展,通過把機(jī)械振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試技術(shù)和數(shù)字信號(hào)處理方法相結(jié)合,提出了一種構(gòu)建“振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器”的原理和方法。振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器的設(shè)計(jì)過程是:首先按流程圖布置好振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器的硬件系統(tǒng);然后,在個(gè)人計(jì)算機(jī)上開發(fā)相應(yīng)的應(yīng)用軟件;最后,振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試與模態(tài)識(shí)別的全過程,都是在個(gè)人計(jì)算機(jī)上通過軟面板對(duì)話框和適當(dāng)?shù)目刂瓢粹o來完成。3.2 激振方式、激振器和振動(dòng)傳感器的布置激振方式可分為正弦穩(wěn)態(tài)掃頻和寬頻帶激振兩大類。通常采用“正弦穩(wěn)態(tài)掃頻激振”,其優(yōu)點(diǎn)是激振能量集中,信噪比高,對(duì)于線性系統(tǒng)的動(dòng)態(tài)特性測(cè)試具有很高的測(cè)量精度。首先,根據(jù)測(cè)試分析要求及振動(dòng)系統(tǒng)的機(jī)械結(jié)構(gòu)特點(diǎn),確定激振點(diǎn)的位置和測(cè)量點(diǎn)的數(shù)量N及各測(cè)量點(diǎn)的位置。對(duì)于空間結(jié)構(gòu)系統(tǒng),往往需要測(cè)量1個(gè)點(diǎn)的3個(gè)方向,這時(shí)應(yīng)選用三軸振動(dòng)傳感器。安裝激振器時(shí),必須注意激振力的正確施加。在安裝測(cè)振傳感器時(shí),應(yīng)保證傳感器能正確感受被測(cè)體的振動(dòng)。小型振動(dòng)系統(tǒng)必須選用微型傳感器,以避免傳感器附加質(zhì)量影響振動(dòng)系統(tǒng)動(dòng)態(tài)特性。3.3 振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試應(yīng)用軟件的總體研究 根據(jù)對(duì)前面振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器原理圖的分析可知,振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試應(yīng)用軟件的設(shè)計(jì)流程分為如下步驟: (1)計(jì)算機(jī)發(fā)出指令控制“信號(hào)發(fā)生器”產(chǎn)生激勵(lì)信號(hào),再通過“激振器”施加于被測(cè)振動(dòng)系統(tǒng)。激勵(lì)信號(hào)的數(shù)字序列為X(n)。 (2) 等待被測(cè)振動(dòng)系統(tǒng)穩(wěn)定一定時(shí)間,然后計(jì)算機(jī)再發(fā)出指令同步采集數(shù)據(jù)序列X(n)和Y1(n),Y2(n), ,YN(n) 。采樣時(shí)間間隔或采樣頻率應(yīng)符合采樣定理及頻率分辨率的要求。 (3)利用按本原理設(shè)計(jì)的專用軟件分析處理X(n)和Y1(n),Y2(n),YN(n), 就可得出被測(cè)振動(dòng)系統(tǒng)的模態(tài)參數(shù)和相應(yīng)數(shù)學(xué)模型。顯然,整套應(yīng)用軟件應(yīng)包括兩大部分,即操作控制部分和數(shù)據(jù)處理部分。由于目前計(jì)算機(jī)控制技術(shù)和虛擬儀器技術(shù)的發(fā)展,已足以解決此應(yīng)用軟件中的操作控制部分,且鑒于篇幅有限,所以筆者對(duì)應(yīng)用軟件的操作控制部分不再作進(jìn)一步討論,下面重點(diǎn)研究應(yīng)用軟件的數(shù)據(jù)處理部分。3.4 數(shù)據(jù)處理專用軟件的設(shè)計(jì)原理3.4.1 濾波方法 由于數(shù)據(jù)序列在采集過程中難免會(huì)受到各種干擾, 所以必須采取有效的濾波算法對(duì)采集得到的數(shù)據(jù)序列Y1(n),Y2(n),YN(n)進(jìn)行修正。通常應(yīng)采用相關(guān)濾波算法,因?yàn)橄嚓P(guān)濾波可以有效地把真正由X(n)通過振動(dòng)系統(tǒng)產(chǎn)生的信號(hào)從Y1(n),Y2(n),YN(n)中分離出來。將經(jīng)過濾波算法處理后的數(shù)據(jù)序列記為YN1(n),YN2(n),YNN(n) ,n=1,2, ,D 。D為采樣點(diǎn)數(shù)量。3.4.2 頻率響應(yīng)函數(shù)的確定 將確定性信號(hào)看成隨機(jī)信號(hào),采用離散數(shù)字隨機(jī)信號(hào)的相關(guān)譜分析原理。 XK(k) = FFT X(n) YK(k) = FFT YN(n) SX(k) = XK(k)2 /D SY(k) = YK(k)2 /D SXY(k) = XK*(k)YK(k) /D XK*(K)為XK(k)的共軛復(fù)數(shù)。 為減少數(shù)據(jù)處理誤差,要對(duì)SX(k),SY(k),SXY(k)采取平滑處理算法。分段時(shí),相鄰兩段重疊50的效果最佳,即將記錄段X(n),YN(n)分成多個(gè)樣本,分別進(jìn)行上述運(yùn)算后再求平均值。VXY2(k) = SXY(k)2 / SX(k) SY(k), 相干系數(shù)VXY越接近1效果越好。H(k) =SXY(k) / SX(k), 由變量代換關(guān)系“k/(DTS) =f(TS為采樣時(shí)間間隔)”可得到測(cè)試出的頻率響應(yīng)函數(shù)H(f) 。 對(duì)每一個(gè)數(shù)據(jù)序列Y1(n),Y2(n),YN(n)均用上述方法處理,就可以得到測(cè)試出來的N個(gè)頻率響應(yīng)函數(shù)H1(f),H2(f),HN(f) 。3.4.3 擬合求解模態(tài)參數(shù)機(jī)械振動(dòng)系統(tǒng)模態(tài)參數(shù)識(shí)別,又稱為曲線擬合,即采用最小二乘法將測(cè)試所得的頻率響應(yīng)值與系統(tǒng)模型值進(jìn)行曲線擬合。優(yōu)化準(zhǔn)則就是使實(shí)測(cè)的頻率響應(yīng)值與理論數(shù)學(xué)模型對(duì)應(yīng)值的總均方誤差E極小。最小二乘曲線擬合過程中存在的有關(guān)問題,如方程組的病態(tài)問題,可根據(jù)數(shù)值分析理論,采用正交多項(xiàng)式的方法加以解決。通常機(jī)械振動(dòng)系統(tǒng)的“理論數(shù)學(xué)模型”可用有理分式形式的傳遞函數(shù)來表示,即 H(s) = N(s)/D(s) = a0sm+a1sm-1+am-1s+am/ sn+b1sn-1+bn-1s+bn上式中,mn,n=2q,q為系統(tǒng)的自由度數(shù)。一般選定一個(gè)具體q值,令m=2q-1,然后循環(huán)擬合,直到滿足E控制精度Eg。 對(duì)于每一個(gè)頻率響應(yīng)函數(shù),設(shè)由D個(gè)采樣點(diǎn)得到的D個(gè)測(cè)試頻率響應(yīng)值記為HC(f),對(duì)應(yīng)的D個(gè)理論模型值記為HL(f),則總方差為E=(k=1,D)| HC(f)HL(f)|2。這是非線性優(yōu)化問題,為使用方便和保證精度,可轉(zhuǎn)化為線性優(yōu)化問題。令s=jw=j2f,誤差e=N(f) D(f)HC(f),則總方差轉(zhuǎn)化為E=|N(f) D(f)HC(f)|2。此時(shí),總方差函數(shù)為待求系數(shù)的線性函數(shù),最小二乘解已變成線性優(yōu)化問題。首先通過最小二乘擬合識(shí)別出有理分式的系數(shù)ai(i=1,2,m)和bi(i=1,2,n),然后由特征方程D(s)0解得極點(diǎn)sr及sr*(r=1,2,q),由留數(shù)公式ArH(s)(s-sr)| S=Sr”求出留數(shù)Ar及Ar* 。則傳遞函數(shù)可表示為H(s)r=1 , N Ar/(s-sr) + Ar*/(s-sr*)最后以sr= -r wr +j wr (1- r2)1/2,sr為共軛復(fù)數(shù),求得各階模態(tài)固有頻率wr和阻尼比r 。對(duì)于線性系統(tǒng),模態(tài)固有頻率和阻尼比是系統(tǒng)的總體固有參數(shù),理論上應(yīng)該不隨測(cè)量點(diǎn)而改變。依次對(duì)N個(gè)測(cè)量點(diǎn)的頻率響應(yīng)函數(shù)進(jìn)行曲線擬合,可得到N組模態(tài)固有頻率和阻尼比,再求出平均值作為系統(tǒng)的模態(tài)固有頻率和阻尼比,進(jìn)而,再求出各階振型r 。3.4.4 其它輸出振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試所得的系統(tǒng)固有的各階模態(tài)參數(shù)和用模態(tài)參數(shù)表示的各測(cè)量點(diǎn),對(duì)應(yīng)于輸入點(diǎn)的數(shù)學(xué)模型。振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試數(shù)據(jù)處理的全過程,可以用目前流行的程序設(shè)計(jì)語言VC+或Java2開發(fā)成專用的數(shù)據(jù)處理程序軟件包,然后通過相關(guān)程序語言接口方法嵌入到用LabVIEW或LabWindows平臺(tái)開發(fā)的振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器中。采用本虛擬儀器,可以很容易通過計(jì)算機(jī)多次重復(fù)振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試的整個(gè)過程,進(jìn)一步提高振動(dòng)系統(tǒng)動(dòng)態(tài)特性的測(cè)試精度。利用動(dòng)態(tài)測(cè)試得到的數(shù)學(xué)模型,通過Matlab6.1仿真環(huán)境(或自己編制程序)可求出激振點(diǎn)處各種輸入信號(hào)各測(cè)量點(diǎn)處的輸出響應(yīng)信號(hào)。4 結(jié)論經(jīng)過實(shí)踐檢驗(yàn),振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器在具體運(yùn)用中具有“實(shí)用性強(qiáng)、準(zhǔn)確度高、效價(jià)比良、重復(fù)性好及全自動(dòng)化等優(yōu)點(diǎn)??梢詫?shù)據(jù)采集功能和數(shù)據(jù)處理功能的軟硬件集成在一起,生產(chǎn)出智能化振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試虛擬儀器,也可以把數(shù)據(jù)處理軟件單獨(dú)形成專用的振動(dòng)系統(tǒng)動(dòng)態(tài)測(cè)試數(shù)據(jù)處理軟件包,無論采取何種方式都具有廣闊的應(yīng)用前景。Virtual Instrument Research for Dynamic Testing of Vibration SystemAbstract: Through combining dynamic analyzing theory of vibration system with digital singles process method, developing principle of virtual instrument for dynamic test of vibration system is proposed and discussed.1. INTRODUCTIONWith the development of digital computer simulation technology, virtual instrument technology applications become wider, and the so-called virtual instrument is on the increase in the general computer a group of related hardware and software, so that users in the manipulation of this computer, as in the operation of a his design for the traditional electronic devices. In the virtual instrument system, the hardware simply to solve the input and output signals, and software is the key to the whole instrument. Any user can modify the software through the method, it is very easy to adjust the function of the system and apparatus scale. Virtual instrument technology to users a fully display their talent and imagination of space, users (rather than equipment manufacturers) can be arbitrary in accordance with their own needs and design their own instrument system. It is software is the apparatus argument. In this paper, in accordance with the digital computer simulation and virtual instrument technology ideas, from simple practical point of view, the vibration theory of the dynamic test and digital signal processing method, and proposed a systematic exposition vibration system dynamic testing Virtual Instrument development principle.2. The basic concept of dynamic testingMost of the actual system works were used to describe the linear system, the input-output linear system exists between the simple causal relationship. Therefore, it can be measured by the input-output system physical measurement and analysis to determine the dynamic characteristics, and this is dynamic testing. Dynamic characteristics of the mathematical model takes many forms: the time domain is commonly used differential equations, differential equations and equation of state; a complex domain transfer function, structure diagram; frequency domain, such as a frequency response function. Mechanical vibration system of the dynamic characteristics is the main purpose of identification by the system or frequency domain characteristics of the transfer function, and further mechanical vibration mechanical system modal parameters. Frequency response function with data and the frequency response curve, frequency response function can be described as a non-linear system parameter model. The mechanical vibration system, the dynamic characteristics of common natural frequency, damping and mode shape than the so-called modal parameters to describe. In the frequency response function test on the basis of parameters can be identified, that is, experimental modal analysis to establish the mechanical vibration system modal parameters. Dynamic testing technology is the main content of the measured vibration of the incentive system, through vibration testing, data acquisition and signal analysis, input and output determined by the mechanical vibration system dynamic characteristics. Thus, dynamic test is divided into two parts: the frequency response function mapping and identification of the modal parameters. Dynamic mechanical vibration system of testing and analysis of the key is how to use the proceeds of testing frequency response function curves through modal identification method for the characterization of mechanical vibration system dynamic characteristics of modal parameters. Modal Recognition state recognition can be divided into single-mode and multi-modal identification, identification of single-mode state is built on small damping loose on the basis of assumptions. The modal-intensive complex structure or damping, required a multi-modal analysis. With the in-depth development of the digital computer technology, the modern modal parameters to identify most of a multi-modal identification.3 Virtual Instrument Desire for Dynamic Testing of Vibration System3.1 Virtual Instrument made and composed schematicVirtual instrument has the advantage of being able to share computer-aided test the systems hardware resources and input-output interface software, users design of the application software will be able to achieve the corresponding test analysis functions. This will not only save costs, but also had a practical, accurate and high-titer, flexibility, and the fully automated features. Based on digital computer simulation and virtual instrument technology and the rapid development of the mechanical vibration system through dynamic testing technology, and digital signal processing method, the proposed construction of a dynamic vibration test system virtual machines the principles and methods. Dynamic vibration testing virtual instrument design process are as follows: First flow chart layout by good dynamic vibration test system hardware Virtual Instrument System; Then, in the corresponding development of personal computer software applications; Finally, the dynamic vibration testing and modal identification the entire process is in the personal computer through the soft panel dialog and appropriate control button.3.2 Vibration, vibration and vibration sensor layoutSinusoidal excitation mode can be divided into static and broadband excitation Swept two categories. Usually adopts a sine steady Sweep exciting, the merits of excitation energy is concentrated, high signal to noise ratio for linear dynamic characteristics of the test system with high precision. First, in accordance with requirements analysis and testing of mechanical vibration system structure, determine the location and vibration measurement points N and the number of the location of measurement points. The spatial structure system, often requires a measurement point three directions, then should use three-axis vibration sensors. Exciter installed, it should be noted excitation of the right to impose. Vibration sensors in the installation, should ensure that the sensor can accurately measured feelings of the vibration. Small vibration system to select micro-sensors, in order to avoid affecting the quality vibration sensors additional dynamic characteristics of the system.3.3 Dynamic vibration tests on the overall application softwareUnder the previous system dynamic vibration testing Virtual Instrument schematic analysis, we can see the dynamic vibration test application software design process is divided into the following steps: (1) directive issued computer control signal generator, produced encouraging signals, and through the Vibrator imposed on the measured vibration system. Encouraging signals in the digital sequence X (n). (2) the measured vibration system is stable for a certain period of time, and then issued instructions to the computer data acquisition synchronization sequence X (n) and Y1 (n), Y2 (n), YN (n). Sampling frequency or time interval should be consistent with the sampling theorem and frequency resolution requirements. (3) make use of the principle of design analysis software for X (n) and Y1 (n), Y2 (n), YN (n), measured vibration system can arrive at the modal parameters and the corresponding mathematical model . Obviously, application software package should include two parts, namely, operational control and data-processing part of some. As computer control technology and the development of virtual instrument technology has been sufficient to resolve this application in the operational control of light and space is limited, so the author on the application of software is no longer part of the operational control for further discussion below focuses on the application software data-processing part.3.4 Data processing software for the design principle3.4.1 filtering method The sequence data in the acquisition process will inevitably be all kinds of interference, it is necessary to take effective filtering algorithm to the data acquisition sequence Y1 (n), Y2 (n), YN (n) be amended. Usually associated filtering algorithm should be used, because the relevant filter can effectively from the real X (n) through the vibration signal from the system Y1 (n), Y2 (n), YN (n) separated. After filtering algorithm will be dealt with after the sequence data recorded as YN1 (n), YN2 (n), YNN (n), n = 1,2, D. D is the number of sampling points. 3.4.2 determine the frequency response function Signal will be uncertainty as random signal, a number of discrete random signals in the spectrum analysis of the relevant principles. XK (k) = FFT X (n) YK (k) = FFT YN (n) SX (k) = | XK (k) | 2 / D SY (k) = | YK (k) | 2 / D SXY (k) = XK * (k) YK (k) / D XK * (K) XK (k) Conjugate complex. In order to reduce data processing error, the SX (k), SY (k), SXY (k) to smoothing algorithm. Subparagraph, the two overlap adjacent 50 best results, the forthcoming record of the X (n), YN (n) is divided into a number of samples, respectively, to carry out such operations after seeking average. VXY2 (k) = | SXY (k) | 2 / SX (k) SY (k), the more coherent coefficient close to 1 VXY better results. H (k) = SXY (k) / SX (k), variable substitution k / (DTS) = f (TS for the sampling time interval) available to test the frequency response function H (f). For each data series Y1 (n), Y2 (n), YN (n) are dealing with the above method, it can be tested by the frequency response function of N H1 (f), H2 (f), HN (f).3.4.3 Fitting Solution modal parameters Mechanical vibration system modal parameter identification, also known as curve fitting, that is, using the least square method will test the frequency response of the system model and the value curve fitting. Optimization criterion is the value of the measured frequency response corresponds with the theoretical mathematical model of the total value of the minimum mean square error E. Least-squares fitting in the course of the relevant issues, such as the sick equations, numerical analysis according to theory, orthogonal polynomials method used to solve the problem. Usually mechanical vibration systems theory mathematical model can be rational fraction of the transfer function to indicate that H (s) = N (s) / D (s) = + a0sm a1sm-1 + + + am-1s am / sn-1 + + b1sn-1s + + bn bn - On, m n, n = 2q, q freedom of the system. Q general selected a specific value of the m = 2q-1, and then cycle fitting, until the E control accuracy Eg. For each frequency response function, a sampling from D-D tests by the frequency response of mind for HC (f), the corresponding value of D-theoretical model in mind for the HL (f), the total variance for E = (k = 1, D) | HC (f)-HL (f) | 2. This is the non-linear optimization problem, as easy to use and guarantee accuracy, and can be transformed to a linear optimization problem. Order s = = j2 f jw error e = N (f) - D (f) HC (f), the total variance into E = | N (f) - D (f) HC (f) | 2. At this time, the total variance function question for coefficient of linear functions, linear least squares solutions have become optimization problem. First identified by the least square fitting rational fraction of the coefficient ai (i = 1, 2, m) and the bi (i = 1, 2, n), and then by the characteristic equation D (s) = 0 Solutions in the pole sr and sr * (r = 1,2, q), by the residue formula Ar = H (s) (s-sr) | S = Sr sought stay of Ar and Ar *. will transfer function can be expressed as H (s) = r = 1, N Ar / (s-sr) + Ar * / (s-sr *) Finally, sr = - r wr + j wr (1 - r2) 1 / 2, sr for complex conjugate, and get the band Modal wr natural frequency and damping ratio r. For linear systems, modal natural frequency and damping ratio is inherent in the overall system parameters, in theory, should not change with the measurement point. N followed by the measurement point to the frequency response curve fitting function, can be inherent in group N modal frequencies and damping ratio, then calculated the average as a modal system natural frequency and damping ratio, in turn, obtained the order again r mode.3.4.4 Other Output System Dynamic vibration test systems inherent in the band modal parameters and the use of modal parameters of the measurement point, corresponding to the input point of the mathematical model. Dynamic vibration test data-processing system in the whole process can be used currently popular programming language VC + + or Java2 developed into a dedicated data processing package, and then through the relevant procedures language interface method using LabVIEW embedded development platform or LabWindows Dynamic vibration testing virtual instruments. Using the virtual instrument, can be easily repeated by the computer system dynamic vibration testing of the whole process, and further enhance the dynamic characteristics of vibration test system accuracy. The use of dynamic testing mathematical model through Matlab6.1 simulation environment (or their own development process) can be derived exciting point of the input signal measurement point response to the output signal. 4 Conclusion After the test of practice, vibration, dynamic testing system in the specific application of virtual instruments in a practical, accurate and high-titer, good repeatability, and the entire automation, etc. can function data acquisition and data processing hardware and software integration together to produce intelligent system dynamic vibration testing virtual instrument, can also form a separate data processing software for the system dynamic vibration test data-processing package, no matter in what ways have broad prospects.
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