Extraction of the instantaneous speed fluctuation based on normal time–frequency transform for hydraulic system

Abstract

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.