Tacholess Speed Estimation in Order Tracking: A Review With Application to Rotating Machine Fault Diagnosis

Order tracking (OT), which is realized by signal sampling in equal-angle increment according to the measured rotating speed, is a powerful technique for rotating machine fault diagnosis under variable-speed condition. However, if the tachometer cannot be installed on the rotating machine or the speed signal is not available for some reasons, OT is difficult to be realized. This review summarizes recent advances in the development of tacholess speed estimation methods for OT with its applications to fault diagnosis. First, the basis of rotating speed estimation and OT is revisited. Then, the methods are categorized into three groups including vibration or sound signal, electrical motor current signal, and video stream according to the signal source from which the speed is estimated. The principle, implementation procedures, key techniques, along with the merits, and shortcuts of these methods are summarized and discussed in detail. Afterward, a contrastive case study using three kinds of methods is provided to intuitively illustrate the performances of OT along with the applications in motor bearing fault diagnosis. A bibliography of the recent publications related to this topic is also provided to facilitate the selection and improvement of the tacholess OT methods in fault diagnosis applications. Finally, the research prospects are discussed.