Time-frequency (TF) analysis (TFA) to nonstationary signals can reveal the nonlinearly changing instantaneous frequencies (IFs) of signals; it is, therefore, widely used for rotating machinery fault diagnosis under time-varying speed conditions. However, the traditional TFA methods may only reveal the outline of IFs due to the extra TF diffusion caused by limited TF resolution, hindering the fault diagnosis of rotating machinery. To enhance the readability of the time-frequency representation (TFR) of the signals with IF trajectories linearly time-varying, linear chirplet transform has been proved effective. To effectively tackle the signal with nonlinearly changing IFs, a string of chirp-rates is preferred, where the final TFR is obtained by superposition of each corresponding sub-TFR at each TF point. However, the extra cross-term interferences resulted from a string of chirp-rates cannot be neglected on TFRs. Aiming at alleviating the cross-terms from the TFR, matching and reassignment based TF enhancement strategy is proposed, where only the appropriate chirp-rate and its corresponding TFR slice is retained at each time instant. The appropriate chirp-rate is adaptively selected by the index—spectral kurtosis. To further increase the readability of the resulting TFR, a reassignment technique synchrosqueezing transform is integrated with the proposed matching strategy. By iteratively employing reassignments, TFR with the enhanced energy and sharp IF ridges can be generated. The effectiveness of the proposed method is validated by both simulated and experimental analyses. It is shown that the proposed method is effective in processing time-varying signals and can provide more accurate IF estimation, which paves the way for rotating machinery fault diagnosis under nonstationary speed conditions.

对非平稳信号的时频 (TF) 分析 (TFA) 可以揭示信号的非线性变化的瞬时频率 (IF)；因此，它被广泛用于时变速度条件下的旋转机械故障诊断。然而，传统的 TFA 方法由于有限的 TF 分辨率导致额外的 TF 扩散，可能只能揭示 IF 的轮廓，阻碍了旋转机械的故障诊断。为了提高具有线性时变中频轨迹的信号的时频表示 (TFR) 的可读性，线性 chirplet 变换已被证明是有效的。为了有效地处理具有非线性变化中频的信号，首选一串线性调频率，其中最终的 TFR 是通过在每个 TF 点叠加每个相应的子 TFR 来获得的。然而，在 TFR 上不能忽略由一串啁啾率引起的额外交叉项干扰。为了减轻TFR的交叉项，提出了基于匹配和重新分配的TF增强策略，在每个时刻只保留适当的chirp-rate及其对应的TFR切片。适当的啁啾率由指数——谱峰度自适应选择。为了进一步提高所得 TFR 的可读性，重新分配技术同步压缩变换与所提出的匹配策略相结合。通过反复使用重新分配，可以生成具有增强能量和尖锐中频脊的 TFR。通过模拟和实验分析验证了所提出方法的有效性。