【摘要】：作為機械設備的關鍵零部件,凸輪的磨削精度直接影響著發(fā)動機等機構(gòu)的整體性能。近年來隨著數(shù)控磨削技術(shù)的不斷發(fā)展,凸輪磨削精度得到了大幅度提高。不同于傳統(tǒng)靠模仿形的加工方式,目前多采用兩軸聯(lián)動系統(tǒng)精密加工。通過控制工件旋轉(zhuǎn)軸與砂輪進給軸的協(xié)同運動,完成凸輪磨削。由于凸輪的磨削精度最終反映在凸輪的輪廓誤差上,可以將磨削過程的精度問題看作是對輪廓誤差的控制問題,因此相比于通過減小各單軸跟蹤誤差以間接減小輪廓誤差的方法,直接減小輪廓誤差的方法效果更佳。本文引入切向-輪廓控制算法,以減小凸輪輪廓誤差、提高系統(tǒng)磨削精度為目標,對該控制算法提出一系列的改進,從而實現(xiàn)對輪廓誤差直接有效的控制。主要研究內(nèi)容如下:1、磨削前的準備工作。為了維持凸輪輪廓的原有特性,消除升程數(shù)據(jù)可能帶有的誤差,對廠家提供的原始升程數(shù)據(jù)進行光順處理和三次樣條插值。在此基礎上通過反轉(zhuǎn)法和聯(lián)動數(shù)學模型,求得系統(tǒng)的輸入序列值。2、引入切向-輪廓控制算法。為了促進切向-輪廓控制算法在凸輪磨削系統(tǒng)中的應用,選取合適的轉(zhuǎn)換矩陣,實現(xiàn)坐標系間的轉(zhuǎn)換。并提出了位置跟蹤補償算法,與切向-輪廓控制器、位置環(huán)控制器共同構(gòu)成整體輪廓誤差控制算法,實現(xiàn)輪廓誤差的進一步減小。并由仿真實驗驗證上述算法的有效性。3、設計切向-輪廓控制器的參數(shù)優(yōu)化算法。在整體輪廓誤差控制算法中,切向-輪廓控制器的參數(shù)選取直接影響凸輪的磨削精度。為了能夠有效減小輪廓誤差,采用差分進化算法,對切向控制器與輪廓控制器的增益系數(shù)進行優(yōu)化。以當前磨削過程中凸輪輪廓誤差的最大絕對值為適應度函數(shù),由增益系數(shù)構(gòu)成的二維矢量作為進化的種群個體,經(jīng)迭代計算得出個體最優(yōu)解。仿真實驗表明,具有最優(yōu)解的系統(tǒng)其磨削精度得到了提高。4、設計切向-輪廓控制器的參數(shù)自適應控制算法。由于凸輪的輪廓曲率復雜多變,若要減小凸輪的輪廓誤差,還可以從參數(shù)自適應控制方面展開研究。采用BP(Back Propagation)神經(jīng)網(wǎng)絡算法,令網(wǎng)絡輸出層的輸出分別對應切向控制器與輪廓控制器的增益系數(shù),通過實時修正各層權(quán)系數(shù),實現(xiàn)控制器增益系數(shù)根據(jù)不同磨削點和輪廓誤差的自適應變化,并由仿真實驗驗證了其有效性。另外,對比分析參數(shù)優(yōu)化算法與參數(shù)自適應控制算法的優(yōu)缺點,在時效性方面參數(shù)優(yōu)化算法更省時,在輪廓誤差控制方面參數(shù)自適應控制算法更具優(yōu)勢。
[Abstract]:As the key parts of mechanical equipment, the grinding accuracy of cam has a direct impact on the overall performance of the engine and other mechanisms. In recent years, with the development of NC grinding technology, the precision of cam grinding has been greatly improved. Different from the traditional way of machining by imitation, two-axis linkage system is widely used in precision machining at present. The cam grinding is accomplished by controlling the coordinated movement between the workpiece rotary shaft and the grinding wheel feed shaft. Because the precision of cam grinding is reflected in the profile error of cam, the precision of grinding process can be regarded as the control problem of contour error. Therefore, the method of direct reduction of contour error is better than the method of reducing the error of contour indirectly by reducing the tracking error of each single axis. In this paper, a tangential contour control algorithm is introduced to reduce cam profile error and improve grinding accuracy of the system. A series of improvements are put forward to realize direct and effective control of contour error. The main research contents are as follows: 1. Preparation work before grinding. In order to maintain the original characteristics of the cam profile and eliminate the possible errors in the lift data, the original lift data provided by the manufacturer are faired and cubic spline interpolation is carried out. On this basis, the input sequence value of the system is obtained by inversion method and linkage mathematical model. 2, and the tangential contour control algorithm is introduced. In order to promote the application of tangential contour control algorithm in cam grinding system, a suitable transformation matrix is selected to realize the transformation between coordinates. A position tracking compensation algorithm is proposed, which, together with the tangent-contour controller and the position loop controller, constitutes the overall contour error control algorithm, which can further reduce the contour error. The effectiveness of the above algorithm is verified by simulation experiments. 3. The parameter optimization algorithm of tangential-contour controller is designed. In the overall contour error control algorithm, the selection of the parameters of the tangential contour controller directly affects the grinding accuracy of the cam. In order to reduce the contour error effectively, the gain coefficients of tangential controller and contour controller are optimized by differential evolution algorithm. The maximum absolute value of cam profile error in the current grinding process is taken as fitness function, and the two-dimensional vector composed of gain coefficients is used as the evolutionary population individual, and the individual optimal solution is obtained by iterative calculation. The simulation results show that the grinding accuracy of the system with optimal solution is improved. 4. A parameter adaptive control algorithm for tangent-contour controller is designed. Because the contour curvature of the cam is complex and changeable, if we want to reduce the contour error of the cam, we can also study the parameter adaptive control. Using the BP (Back Propagation) neural network algorithm, the output of the network output layer corresponds to the gain coefficients of the tangential controller and the contour controller respectively, and the weight coefficients of each layer are corrected in real time. The gain coefficient of the controller is adaptively changed according to different grinding points and contour errors, and its effectiveness is verified by simulation experiments. In addition, by comparing the advantages and disadvantages of parameter optimization algorithm and parameter adaptive control algorithm, parameter optimization algorithm is more time-saving in terms of timeliness, and parameter adaptive control algorithm has more advantages in contour error control.
【學位授予單位】：吉林大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG580.6;TP273

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