Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-04-10
2002-11-26
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C384S448000, C384S535000
Reexamination Certificate
active
06484582
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to rolling bearings with a sensing unit which can be remotely interrogated for sensing rolling bearing data. The sensing unit in this case includes at least one acoustoelectronic component which operates on the SAW principle or BAW principle.
DESCRIPTION OF RELATED ART
Bearing with Sensors
Known rolling bearings may include units for sensing rolling bearing data, such as forces acting on the bearing or structure-borne sound occurring in the operating state.
Among devices suitable for the early detection of damage or for monitoring the operating state of a machine are sensing units arranged directly on the rolling bearings. For example, the structure-borne sound which occurs at the rolling bearing and which is important for the early detection of damage or the forces supported by the rolling bearing can be determined by sensing units arranged on the rolling bearing.
In what are known as force-measuring bearings, for example, in U.S. Pat. No. 5,952,587, the rolling bearings are provided with strain gages to measure forces acting on the bearing. The strain gages are usually arranged in recesses on the outer side of the outer race and/or in the bore of the inner race. The force-measuring bearing works on the principle that the forces supported in the bearing cause deformations in the bearing races. These deformations are transferred to the strain gages that are fastened on the outer or inner race and produce changes in electrical resistance which can be measured. The low sensitivity and resolution of the strain gages with respect to the deformations which can be sensed are disadvantageous. Further, on account of the susceptibility of the strain gages to shock, it is necessary for such rolling bearings that are provided with strain gages to be handled with corresponding care. Furthermore, the strain gages cannot sense any structure-borne sound that occurs in the bearings, since the strains caused by the structure-borne sound waves are too small. Furthermore, the high temperature dependence of the strain gages can cause great errors when measuring small strains, as described in the “Handbuch für experimentelle Spannungsanalyse” [handbook for experimental stress analysis], published by Professor Christof Rohrbach, VDI-Verlag, Düsseldörf, 1989.
The VDI Progress Report, Series 8, No. 729, Section 1.2, mentions the fitting of shafts with strain-gage-based torque pickups. The shafts are in this case reduced in diameter to the extent that the stresses or strains occurring due to the loading fully utilize the elastic range of the material used. This is because it is the only way in which adequately accurate sensing of the strains and stresses is possible with the strain gages. In an application of these strain-gage-based torque pickups in rolling bearings, the necessary reduction in the cross sections of the rolling bearing components would greatly reduce the operational reliability and service life of the rolling bearings. Conversely, dimensioning appropriate for rolling bearings leads to inadequate accuracy when strain-gage torque pickups are used.
Saw Sensor and Identification Systems
Components which operate on the SAW principle are known. They are used in particular in the form of frequency filters in the area of telecommunications and in audio equipment. Likewise known are SAW arrangements with sensor and/or identification functions which can be interrogated by wire-bound or radio links.
A sensor including a SAW device which can be interrogated by radio is described in DE 42 00 076-A1, published Aug. 6, 1993.
SAW sensors can be used for measuring stress, temperature, pressure and acceleration and also as chemical and biological sensors. See the document Sensorik [sensor technology), Vol. 8, published by Karl Walter Bonfig, Expert Verlag, “Möglichkeiten und Grenzen der Oberflächenwellen-Sensorik” [possibilities and limitations of surface-wave sensor technology], from page 25.
A passive sensor operating on the SAW principle which can be wirelessly interrogated is described in EP 619 906 B1. The sensor contains first SAW structures as sensor elements and second SAW structures as reference elements. The measured values which can be interrogated are formed from a comparison of the response signals of the sensor and reference elements resulting from the interrogation signals.
A sensor system for monitoring the grip of vehicle tires on the roadway is specified in DE 198 07 004 A1. In this case, sensors which can be remotely interrogated by radio are integrated with SAW elements in the vehicle tire close to the tire carcass. The sensors can in this case supply the monitoring system with measured values concerning various tire operating variables, such as pressure, vibration, wear and identification. That patent application likewise refers to the possibility of coupling the SAW element with other classic sensor elements, for example, capacitive acceleration pickups. In this case, the SAW element serves not only as a signal transmitter but also as an energy supply means for the capacitive sensor.
Fitting of SAW elements into a shaft, for example for measuring torque, is described in the literature (Sensorik, Vol 8, Karl Walter Bonfig, Expert Verlag). No mention is made, however, of the integration of SAW elements in rolling bearings for sensing rolling bearing data or structure-borne sound.
Furthermore, it is known to provide SAW elements with an identification function, although the storing of further parameters, such as characteristic variables, in the SAW elements is not described. The characteristic variables stored according to the present invention may be used in the interrogation units in combination with the values measured by the sensors, in order to ascertain corresponding descriptions of states appropriately devised for the rolling bearings respectively in use.
The combination of the aforementioned identification and sensor functions in a sensing unit with a SAW element is mentioned in various publications. Examples of such combined identification and sensor systems are described in DE 42 17 049 A1, U.S. Pat. No. 5,872,520 and DE 198 54 606 A1.
Apart from the SAW elements described above and their possible applications, bulk acoustic wave (BAW) elements are also known. For instance, the document “Remote Sensing using Quartz Sensors”, written by Sachs, Thomas et al., appearing in SPIE Vol. 2718, page 47 et seq., mentions not only SAW elements but also the use of BAW elements for sensing mechanical stresses in a shaft.
The full disclosure of each reference, patent or publication mentioned herein is incorporated by reference in the present patent application.
SUMMARY OF THE INVENTION
In order to address these problems of the prior art, the invention provides a rolling bearing with a sensing unit which can be remotely interrogated and that has adequate sensitivity and resolution with respect to the rolling bearing data to be sensed.
Sensing units which can be remotely interrogated, with at least one acoustoelectronic component operating on the SAW principle or BAW principle, can sense rolling bearing data, such as measured variables and/or rolling bearing parameters. The sensing units may be arranged on the rolling bearing components, such as the outer race, inner race, cage, seal, rolling elements and/or conversion parts integrated in the bearing. The sensing units may be fitted in machined recesses on the rolling bearing components, for example in groove-shaped depressions that extend circumferentially along or transversely across the races.
SAW components are acoustoelectronic elements in which at least a partial region of a substrate surface is provided with piezoelectric properties. Finger-shaped or interdigital electrode structures in various shapes may be applied on or in the piezoelectric region of the substrate surface. Electric signals can be transformed by means of these electrode structures in the piezoelectric surface region into surface waves on the substrate surface, usually known as surface acous
Ehrfeld Wolfgang
Gempper Sven
Graeff Volker
Hassiotis Vasilis
Heim Jens
FAG OEM und Handel AG
Larkin Daniel S.
Miller Rose M.
Ostrolenk Faber Gerb & Soffen, LLP
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