Ultrafast laser damaging of ball bearings for the condition monitoring of a fleet of linear motors

Abstract

Machine learning-based condition monitoring of mechanical systems, such as bearings, employs two primary approaches: unsupervised and supervised methods. Unsupervised approaches aim to characterize the healthy state of the machine and monitor deviations from this state. The advantage lies in requiring only the health condition of the component without the need for historical data until breakdown. However, the disadvantage is the lack of information regarding the root cause of any potential malfunction.
On the other hand, supervised methods consider both healthy and faulty cases, aiming to maximize the difference between them through post-processing, as well as among different fault types. The advantage is the ability to analyze the specific signature of a particular fault type. Nonetheless, the disadvantage is that available data usually do not cover all possible faults that may occur.
Typically, obtaining a faulty bearing involves either a time-consuming run-to-failure test or the artificial induction of faults using drills, electro-discharge pens, etc. While artificial faults offer a quicker procedure, they often fail to replicate real faults faithfully. This paper suggests using picosecond laser technology to engrave the surface of the bearing and create artificial faults. Modern laser technology allows for precise control over the dimensions of injected faults, enhancing the understanding of fault progression at various stages in the life of bearings. These measurements are crucial parameters for evaluating the robustness of diagnostic algorithms. This paper focuses on artificially damaging a ball bearing used in an independent cart systems application, which comprises a fleet of linear motors moving on the same rail. These systems have recently been proposed by different manufacturers and adopted in the field of packaging machines for their flexibility. For such systems, no prior instances of faulted bearings are available, and the size of a real fault is also unknown. Hand-made faults with drills did not produce discernible faults appreciable in post-processing of the data. Therefore, a picosecond laser with a pulse duration of 10 ps and a maximum energy per pulse of approximately 100 µJ is utilized to create a set of test bearings with increasing fault sizes on the outer race. Post-processing of the data enables the qualification of the minimum fault severity detectable in this specific application.