Regarding the fault diagnosis methods of rolling bearings, traditionally, people mainly classify them according to the state quantities used in monitoring and diagnosis, that is, according to the nature of the measured signals. According to this classification method, rolling bearing working condition monitoring and fault diagnosis methods include temperature method, oil sample analysis method and vibration (noise) method.

The temperature method judges whether the bearing is working normally by monitoring the temperature at the bearing seat (or box). Temperature monitoring is more sensitive to changes in bearing load, speed and lubrication conditions, especially to bearing overheating caused by poor lubrication. Therefore; it is more effective for this kind of occasion. However, when the bearing has relatively minor faults such as early pitting, spalling, and slight wear, the temperature monitoring basically does not reflect it. Only when the fault reaches a certain degree of severity, can it be monitored by this method. Therefore, temperature monitoring is not suitable for so-called local damage such as pitting and local spalling.

The oil sample analysis method is a method of taking an oil sample from the lubricating oil used in the bearing, and judging the working condition and failure of the bearing by collecting and analyzing the size and shape of the metal particles in the oil sample. This method is only suitable for oil-lubricated bearings, not for grease-lubricated bearings. In addition, this method is susceptible to particles dropped from other non-bearing damage. Therefore, this method has great limitations.

The vibration method monitors the bearing vibration signal through a vibration sensor installed in the bearing seat or the appropriate position of the box, and analyzes and processes the signal to determine the bearing condition and fault. Because the vibration method has:

1.It is suitable for various types of bearings under various working conditions;

2.It can effectively diagnose early minor faults;

3. The signal test and processing are simple and intuitive;

4. The diagnosis results are reliable. It has been extremely widely used in practice.

At present, all kinds of rolling bearing testing and diagnostic instruments and system towels developed and produced at home and abroad are mostly made according to the principle of vibration method. More than 80% of the literature on bearing monitoring and diagnosis discusses vibration method. From the point of view of applicability, practicality and effectiveness, there is no better monitoring and diagnosis method for rolling bearings than the vibration method. Closely related to the vibration method is the noise method, which judges the failure of the rolling bearing through the noise during operation. Since the monitored noise signal is mixed with a large amount of non-bearing noise, it is very difficult to separate the bearing noise from other noises, so this method is used less.

With the continuous development of science and technology, some new monitoring technologies continue to appear and are used in the monitoring and diagnosis of rolling bearings, such as acoustic emission technology, optical fiber technology, and so on. However, due to various reasons and limitations, there is still a long way to go before these technologies are truly popularized and applied to actual rolling bearing diagnosis.