The present invention relates to bearing control and more specifically to bearing wear detection.
In many applications, bearing failure can lead to costly damage to the machines in which the bearings are operating and provides a potential for breakdown at unknown and often inconvenient intervals. Therefore, devices for monitoring bearing wear have shown themselves to be indispensable. Bearings for moving machinery parts and shafts are usually securely covered and sealed for reasons of safety, to prevent foreign material from contaminating the bearing surfaces, and to contain lubricating fluids used in operation of the bearings. In general, shaft bearings are protected by oil or watertight seals and in some cases these seals cannot be removed while the shafts are still in operation or the seals are under high pressure fluid. Under such conditions, if the bearing clearances have to be measured to assure the operation of the machinery, the operation of the shaft has to be shut down, and the high fluid pressure behind the seals, if any, has to be brought down to a workable level before the bearing clearance measurements can be performed. It is known that bearing clearances of submarine control surfaces are measured by means of hydraulic jacks, lift from cranes, and dial gauges. However there were cases, utilizing the prior art measuring procedures, in which the bearings were opened up unnecessarily for repair since the bearings were subsequently found to be in good condition. To obviate the need for such time consuming and involved procedures various systems have been devised to remotely ascertain bearing clearances.
Prior art apparatus used to remotely monitor bearing wear operate in accordance with the principle of galvanic currents passing through the shaft and bearing whereby the illumination of a small lamp on metallic contact taking place between bearing and shaft serves as an indication of the critical condition. Variations on this system include the use of sets of wires annularly disposed around the bearing shaft so that any eccentricities in the rotation of the shaft induced by bearing wear lead to electrical contact which in turn triggers an alarm indicative of excessive bearing wear. However, in all of these systems, the input of electric current to the shaft requries contact points with the latter, e.g. brushes made of speical copper-graphite in contact with a needle mounted centrally on the shaft. This device has shown itself to be inadequate in view of the unavoidable material wear and in the inconsistancy of contact resistances.
An attempt has also been made to determine the magnitude of change in the lubrication gap between shaft and bearing with capacitive measuring devices. This system can only be used in special cases as a contact indicator, namely only in the case where the measuring device is situated at the same height as the load surface of the bearing and the if shaft touches the bearing at this point. Further, arrangements have been proposed whereby capacitive measurements or the clearance of a rotating body take place with the aid of fixed electrodes. With this arrangement, two electrodes are screened off from one another and an alternating voltage of constant amplitude and frequency is fed to one of the electrodes and the voltage arising at the second electrode due to capacitive coupling regulated by the rotating body is amplified and led to an indicating instrument. This system generally works well except that it does not allow the position or degree of the bearing wear to be remotely determined, it requires expensive equipment, and is subject to malfunction if impurities exist in the lubricating fluid.