Design and implementation of ultrasound based lubrication film measurement in a fluid power motor
Authors
Rendbæk, Jens ; Jensen, Lasse Almind
Term
4. term
Education
Publication year
2017
Submitted on
2017-06-08
Pages
107
Abstract
Dette speciale undersøger, hvordan en ultralydstransducer kan monteres i en Calzoni hydraulikmotor for at måle tykkelsen af den tynde smørefilm (olielag) mellem bevægelige dele. For at finde egnede monteringssteder blev der opbygget en komplet 3D-CAD-model af motoren. Med udgangspunkt i modellen blev krav til transducerens fysiske mål og akustiske egenskaber fastlagt ved hjælp af akustisk bølgeudbredelsesteori og de geometriske begrænsninger i motoren. Flere monteringsløsninger blev udviklet og vurderet, og den mest egnede viste sig at være at lime transduceren til overfladen og indkapsle den i en epoxy-støbning. Specialet undersøger desuden efterbehandlingsmetoder til at estimere smørefilmtykkelse ud fra ultralydssignaler, herunder fjeder-metoden, den direkte metode, resonansmetoden og krydskorrelationsmetoden. For hver metode bestemmes det måleområde, hvor tykkelsen kan estimeres pålideligt. Til at estimere refleksionskoefficienten (hvor stor en del af lyden der reflekteres) for et indlejret lag fra forsøgsdata anvendes Empirical Transfer Function Estimate (ETFE). Analysen viser, at resonans kan medføre fejlagtige estimater. Metodernes støjrobusthed undersøges også, og de forbliver anvendelige ned til et signal-støj-forhold på 40 dB. En lineær regressionsmodel med mindste kvadraters estimering (LSE) anvendes til at estimere den indfaldende bølge ud fra reflekterede bølger, men nøjagtigheden forringes, når resonans bliver tydelig i de reflekterede signaler. Til sidst monteres en transducer i Calzoni-motoren efter den valgte løsning, en testopstilling bygges, og der indsamles målinger af smørefilmen ved en fast omdrejningshastighed for at observere dens opførsel.
This thesis examines how to mount an ultrasonic transducer inside a Calzoni hydraulic motor to measure the thickness of the thin lubrication film (oil layer) between moving parts. A complete 3D CAD model of the motor was built to identify feasible mounting locations. Using the model, requirements for the transducer’s size and acoustic performance were derived based on acoustic wave propagation theory and the motor’s geometric constraints. Several mounting concepts were designed and evaluated, and the best solution was to glue the transducer to the surface and encapsulate it with an epoxy cast. The thesis also investigates signal post-processing methods to estimate lubrication film thickness from ultrasonic echoes, including the spring method, the direct method, the resonance method, and the cross-correlation method. For each method, the range of film thicknesses that can be measured reliably is determined. To estimate the reflection coefficient (how much sound is reflected) of an embedded layer from experimental data, the Empirical Transfer Function Estimate (ETFE) is used. The analysis shows that resonance can lead to incorrect estimates. Noise robustness is also assessed, and the methods remain usable down to a signal-to-noise ratio of 40 dB. A linear regression model with Least Squares Estimation (LSE) is used to estimate the incident wave from reflections, but accuracy degrades when resonance becomes visible in the reflected waves. Finally, a transducer is mounted in the Calzoni motor using the chosen solution, a test bench is built, and fluid film measurements are collected at a fixed rotational speed to observe the film’s behavior.
[This abstract was generated with the help of AI]
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