On-line identification and monitoring method for external grinding flutter based on BP neural network
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摘要: 为提高机床磨削加工过程中对颤振现象识别的能力,提出一种基于BP(back propagation)神经网络模型的颤振识别方法。通过对加工过程中传感器采集到的高频声发射信号以及振动信号相关特征值的提取,获得关于颤振的多特征参数样本库,并用其对BP神经网络模型进行学习和训练,建立BP神经网络在线识别颤振的算法模型,实现对机床加工过程中是否发生颤振的在线监测和识别。试验结果表明:这种基于BP神经网络模型的颤振识别测试结果与磨削加工试验中的磨削颤振现象结果相符合。该方法能够有效地识别磨削加工过程中的颤振,并起到在线监测识别的作用。Abstract: To improve the ability of the machine tool to identify chatter during the grinding process, a chatter recognition method is proposed based on the BP (back propagation) neural network model. By extracting the relevant feature values of the high-frequency acoustic emission signals and vibration signals in the processing process, multi-feature signal samples library about flutter are obtained. The multi-feature signal sample library is used to learn and train the BP neural network to establish recognition model. The model realizes on-line monitoring and accurate identification of whether chattering occurring during machine tool processing. The experimental results show that the flutter recognition based on the BP neural network model verifies that the measured test results are consistent with the actual flutter and network recognition results. Therefore, this method can effectively identify the flutter phenomenon in the processing process and play the role of online intelligent monitoring.
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表 1 时域特征参数计算公式
Table 1. Calculation formula of time domain characteristic parameter
参数 计算公式 参数 计算公式 标准差 $\sigma {\text{ = }}\sqrt {\dfrac{1}{n}\displaystyle\sum\limits_{i = 1}^n {{{({x_i} - \bar x)}^2}} } $ 方差 ${\sigma^2} = \dfrac{1}{{n - 1}}\displaystyle\sum\limits_{i = 1}^n {{{({x_i} - \bar x)}^2}} $ 极差 $R = {x_{\max }} - {x_{\min }}$ 均方根 ${X_{RMS}} = \sqrt {\left(\dfrac{1}{n}\displaystyle\sum\limits_{i = 1}^n {x_i^2} \right)} $ 均值 $\bar x = \dfrac{1}{n}\displaystyle\sum\limits_{i = 1}^n {{x_i}} $ 偏态系数 $C_{\rm s} = \dfrac{{\dfrac{1}{n}\displaystyle\sum\limits_{i = 1}^n {{{({x_i} - \bar x)}^3}} }}{{{{\left(\dfrac{1}{n}\displaystyle\sum\limits_{i = 1}^n {{{({x_i} - \bar x)}^2}} \right)}^{\textstyle\frac{3}{2}}}}}$ 峰值 ${X_{\text{p}}} = \max \left| {x(n)} \right|$ 峰值
因子$C = \dfrac{{{X_P}}}{{\sqrt {\left(\dfrac{1}{n}\displaystyle\sum\limits_{i = 1}^n {x_i^2} \right)} }}$ 表 2 工件磨削AE频谱能量分布占比
Table 2. AE spectrum energy distribution occupation of workpiece grinding
节点 低速时能量占比 η1 / % 高速时能量占比 η2 / % 1 77.127 7 36.612 5 2 2.842 3 27.440 2 3 5.690 3 9.365 1 4 1.766 0 4.963 5 5 2.751 3 4.787 6 6 2.292 2 3.981 8 7 5.201 5 8.793 2 8 2.328 7 4.056 1 表 3 高频声发射小波包能量占比(高速)
Table 3. High frequency acoustic emission wavelet packet energy ratio (high speed)
序号能量占比 η3 / %
现象节点1 节点2 节点3 1 36.6 22.0 10.5 有颤振 2 34.3 21.9 11.1 有颤振 3 30.9 13.8 14.7 有颤振 ··· ··· ··· ··· ··· 78 36.1 21.9 10.3 有颤振 79 35.3 21.8 10.5 有颤振 80 29.7 14.3 14.3 有颤振 表 4 高频声发射小波包能量占比(低速)
Table 4. High frequency acoustic emission wavelet packet energy ratio (high speed)
序号能量占比 η4 / %
现象节点1 节点2 节点3 1 78.5 1.78 5.33 无颤振 2 78.0 2.00 5.40 无颤振 3 78.5 1.81 5.30 无颤振 ··· ··· ··· ··· ··· 78 78.2 1.57 5.47 无颤振 79 78.0 1.65 5.55 无颤振 80 77.7 1.87 5.56 无颤振 表 5 三向振动信号特征值提取
Table 5. Eigenvalue extraction of three-way vibration signal
序号 x轴振动信号
均方根XRMSy轴振动信号
偏态系数$Cs$z轴振动信号
标准差$\sigma $现象 1 0.022 8 0.005 6 0.021 6 有颤振 2 0.021 4 0.030 5 0.017 3 有颤振 3 0.019 6 −0.082 7 0.014 9 有颤振 ··· ··· ··· ··· ··· 158 0.141 8 0.035 9 0.012 1 无颤振 159 0.141 7 0.087 0 0.011 7 无颤振 160 0.141 8 −0.011 0 0.011 8 无颤振 表 6 预测结果数据
Table 6. Forecast result data
序号 真实值 预测值 算法误差 现象 预测结果 1 2.000 0 1.991 5 0.42% 无颤振 正确 2 1.000 0 1.001 2 0.12% 有颤振 正确 3 2.000 0 1.992 8 0.36% 无颤振 正确 4 1.000 0 1.008 0 0.80% 有颤振 正确 5 2.000 0 1.992 3 0.39% 无颤振 正确 6 1.000 0 0.994 6 0.54% 有颤振 正确 7 1.000 0 1.005 4 0.54% 有颤振 正确 8 2.000 0 1.992 6 0.37% 无颤振 正确 9 2.000 0 1.982 9 0.85% 无颤振 正确 10 2.000 0 1.990 5 0.47% 无颤振 正确 -
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