The incremental motion encoder: a sensor for the integrated condition monitoring of rotating machinery

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Ayandokun, O.K., 1997. The incremental motion encoder: a sensor for the integrated condition monitoring of rotating machinery. PhD, Nottingham Trent University.

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Abstract

In highly automated modern process and manufacturing industries predictive maintenance has become the prime method of avoiding costly unscheduled stoppages due to machine breakdown. A successful predictive maintenance strategy is based on the condition monitoring of equipment through the selection, measurement, and trending of critical machine parameters. Monitoring these parameters allows detection of the gradual deterioration of key components without physical examination. This ensures that only necessary repairs and replacements are conducted. Maintenance resources are optimally employed, downtime of equipment is reduced and maximum economic use is gained from components with a certain wear lifetime.

The key components in many rotating machines, from large turbines to small scale machine tools, are the rolling element bearings that support shafts and spindles. As a bearing begins to fail the frequency at which its rotation excites its supporting structure changes. The machine vibration caused by this excitation is currently the main parameter used to monitor bearing condition. An investigation of the conventional techniques for vibration based bearing monitoring using analogue electromechanical sensors showed that despite good performance in ideal conditions there were many common circumstances where the vibration at the machine surface might not reflect the state of a machine's bearings accurately. The vibration signal from a bearing commonly suffers attenuation in transmission through the machine structure to the machine casing. As the bearing may be only one of several vibration sources, adequate diagnosis of an individual fault can be difficult, particularly in the early stages of bearing failure. The most commonly used vibration sensor, the accelerometer, has a limited ability to measure the low level, low frequency vibrations from bearings in machines operating at low rpm.

Proximity measurement of shaft relative displacement has been suggested to overcome the problems inherent in monitoring bearing condition via transmitted vibration. Previous attempts to use this technique were limited by the lack of a sensor capable of measuring the extremely small clearances between a shaft and its supporting bearing. It was suggested that the principle of a new sensor concept, the Incremental Motion Encoder, offered the ability to sense the mechanical motion of a shaft due to defects in its supporting bearings.

The hardware and software of a novel bearing condition monitoring system were successfully developed around a prototype Incremental Motion Encoder sensor. Signal processing algorithms were developed which enabled the experimental system to detect a variety of induced bearing defect conditions. The system was able to identify individual defects on bearing elements and pre-defect bearing conditions of lubricant contamination and corrosion. The principal claim to novelty made is the method by which an IME signal is interpreted to yield an accurate indication of bearing condition. The successful application of the IME principle to rolling element bearing condition monitoring represents the first completely new technique for a decade in this area.

On the basis of the results of experimentation with this system a completely new method of monitoring bearings is proposed in which an Incremental Motion Encoder sensor is integrated with the bearing as a single unit.

Item Type:

Thesis

Creators:

Ayandokun, O.K.

Date:

1997

ISBN:

9781369313048

Identifiers: