The instantaneous speed fluctuation is the most direct manifestation of system dynamics behavior, which reflects the running status of the hydraulic system. It is crucial to mine the information contained in instantaneous speed fluctuation and extract them accurately. This paper first introduces the instantaneous speed measurement of the hydraulic system, and it is found that the instantaneous speed signal with an equal angle sampling is a harmonic signal. Next, causes of instantaneous speed fluctuation for hydraulic system are derived by kinetics analysis, where the working mechanism of the axial piston motor and the inevitable misalignment of the shafts are concerned. Then the normal time–frequency transform and the inaction method are introduced, and its high accuracy for harmonic signal extraction in additive noise is verified by comparing with the wavelet packet method with simulation analysis. Finally, the validity of the cause analysis and the extraction method are verified by experiments under different working conditions. The experimental results show that the frequencies of the instantaneous speed fluctuation components can be displayed automatically by normal time–frequency transform spectrum and their waveforms can be extracted accurately by the inaction method. It is also found that the change of the rotating speed and torque can be presented by the variety of the magnitude of the instantaneous speed fluctuation components at the 7th order and the 14th order, respectively. Cause analysis and accurate extraction of the instantaneous speed fluctuation will provide theoretical support and data support for the performance evaluation, state monitoring, and fault diagnosis of the hydraulic system.

中文翻译：

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基于常态时频变换的液压系统瞬时速度波动提取

瞬时速度波动是系统动力学行为最直接的表现，它反映了液压系统的运行状态。挖掘瞬时速度波动中包含的信息并准确提取它们是至关重要的。本文首先介绍了液压系统的瞬时速度测量，发现等角采样的瞬时速度信号为谐波信号。其次，通过动力学分析推导出液压系统瞬时速度波动的原因，其中涉及轴向柱塞马达的工作机制和轴的不可避免的错位。然后引入正常时频变换和inaction方法，并通过与小波包法的比较和仿真分析，验证了其在加性噪声中提取谐波信号的高精度。最后通过不同工况下的实验验证了原因分析和提取方法的有效性。实验结果表明，瞬时速度波动分量的频率可以通过正常的时频变换频谱自动显示出来，其波形可以通过静止方法准确提取。还发现转速和转矩的变化可以分别表现为7阶和14阶瞬时速度波动分量的大小变化。