Yarn twist variations may cause stripes in the direction of weft yarns or local defects on a fabric surface. Since fast Fourier transform and time analysis cannot directly detect local frequency variations of yarn signal and defect sensors are designed to detect the diameter decreases without considering frequency analysis, no data associated with twist-related frequency changes can be obtained when inspecting Chenille yarn (Cy) defects. This study proposes the prediction of twist level (T) and twist variations (ΔT) of Cy whose twist changes in accordance with the spatial period of pile density by using wavelet analysis, allowing localized frequency variations to be obtained. Complex-valued Paul wavelet was used to determine the ΔT of signals with small frequency fluctuations, while Morlet wavelet was addressed for signals with high frequency change. The relation of the signal frequency to the pile yarn density and, correspondingly, twist was modeled by equations. To prevent discontinuities in wavelet cross-spectrum (WCS), the twist simulation signal was generated by equalizing twist oscillation amplitudes without changing their phase. To compare ideal twist to the local twist, another simulation signal demonstrating the ideal twist at sample-specific frequency was generated. The WCS of the simulation signals allowing the segmentation of variation intervals was used for determining ΔT and yarn portions, where the twist is compatible with ideal twist, by establishing correlation between scales and twists. For yarn samples with various T and ΔT types, the T and ΔT results obtained by the proposed wavelet-based algorithm showed the mean absolute relative percentage errors of 1.617% and 37.062%, respectively.

中文翻译：

---

使用传感器信号的小波分析表征花式纱线的捻度

纱线捻度变化可能会导致纬纱方向出现条纹或织物表面的局部缺陷。由于快速傅立叶变换和时间分析无法直接检测纱线信号的局部频率变化，并且缺陷传感器旨在检测直径减小而不考虑频率分析，因此在检查雪尼尔纱线 (Cy) 时无法获得与捻度相关的频率变化相关的数据缺陷。本研究提出通过使用小波分析预测 Cy 的扭曲水平 (T) 和扭曲变化 (ΔT)，其扭曲根据桩密度的空间周期而变化，从而获得局部频率变化。复值Paul小波用于确定频率波动小的信号的ΔT，而 Morlet 小波则针对高频变化的信号。信号频率与绒头纱线密度以及相应的捻度的关系由方程建模。为了防止小波交叉谱 (WCS) 中的不连续性，通过在不改变相位的情况下均衡扭曲振荡幅度来生成扭曲模拟信号。为了将理想扭曲与局部扭曲进行比较，生成了另一个模拟信号，演示了样本特定频率下的理想扭曲。通过建立尺度和捻度之间的相关性，允许分割变化间隔的模拟信号的 WCS 用于确定 ΔT 和纱线部分，其中捻度与理想捻度兼容。对于各种 T 和 ΔT 类型的纱线样品，