Real-time measurement of dynamic film thickness via ultrasonic technology

When the thickness of the lubricating film between friction pairs is too thin, it leads to severe wear. Ultrasonic technology has the feature of non-destructive and strong penetrability in the field of film thickness measurement. However, real-time systems for measuring film thickness with ultrasonic technology have been little researched. This study proposes a real-time measuring system and performs online measurements of four kinds of dynamically changing film thicknesses. A new method for selecting probe model is proposed, and this method uses effective bandwidth as a “connecting bridge” between target film thickness and probe model. Little is known about the measurement failure zone between the measuring ranges of the spring model and the resonance model, and this study develops an understanding of influence of the material and thickness of the friction pair on the measurement failure zone. When the friction pair thickness exceeds 30 mm, the “vacuum zone” of film thickness measurement begins to appear. To measure the film thickness in the failure zone, a composite model using both the phase and amplitude of the reflection coefficient is proposed. Finally, the present work constructs physical model of ultrasonic measurement experiment. This study provides a method for monitoring the lubrication and friction status of important rotating parts of mechanical equipment in real-time.