Source: http://www.google.com/patents/US5466979?dq=6078894
Timestamp: 2014-03-10 00:11:20
Document Index: 287619603

Matched Legal Cases: ['art 2', 'art 1', 'art 3', 'art 2', 'art 1', 'art 3']

Patent US5466979 - Methods and apparatus to reduce wear on sliding surfaces - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsMethods and apparatus to reduce wear on surfaces in sliding contact by inducing vibratory movement in one or more of the surfaces. The movement is substantially perpendicular to a plane of contact between the surfaces and substantially nonuniform across the area of contact. The nonuniform vibratory motion...http://www.google.com/patents/US5466979?utm_source=gb-gplus-sharePatent US5466979 - Methods and apparatus to reduce wear on sliding surfacesAdvanced Patent SearchPublication numberUS5466979 APublication typeGrantApplication numberUS 08/026,676Publication dateNov 14, 1995Filing dateMar 3, 1993Priority dateMar 3, 1993Fee statusLapsedPublication number026676, 08026676, US 5466979 A, US 5466979A, US-A-5466979, US5466979 A, US5466979AInventorsMichael D. Bryant, Jau-Wen LinOriginal AssigneeBoard Of Regents, The University OfExport CitationBiBTeX, EndNote, RefManPatent Citations (12), Non-Patent Citations (38), Referenced by (2), Classifications (8), Legal Events (6) External Links: USPTO, USPTO Assignment, EspacenetMethods and apparatus to reduce wear on sliding surfacesUS 5466979 AAbstract Methods and apparatus to reduce wear on surfaces in sliding contact by inducing vibratory movement in one or more of the surfaces. The movement is substantially perpendicular to a plane of contact between the surfaces and substantially nonuniform across the area of contact. The nonuniform vibratory motion of one surface with respect to another results in small rotational vibration of one surface with respect to another even as contact is maintained between the surfaces. Rotational motions tend to decrease surface wear due to thermal mounding by moving the zone of actual contact with time; rotational motions also open temporary gaps between the surfaces which allow the escape of wear particles, thus decreasing subsequent abrasive wear. The invention may be applied to sliding electrical contacts, either linear or rotating, and to sliding frictional contacts, as in brakes and clutches. Application of the invention reduces wear on electrical contacts while maintaining electrical continuity, and reduces wear on brake system components without substantially reducing effective braking force.
What is claimed: 1. Apparatus for reducing wear on first and second surfaces in substantially sliding contact at a zone of contact, the zone comprising a reference plane of contact, and relative movement between the surfaces having a direction of movement, the apparatus comprisinga vibration force actuator coupled to the first surface to impart a vibratory movement to the first surface, said vibratory movement being substantially perpendicular to the reference plane of contact and substantially nonuniform across the zone of contact, wherein the nonuniform movement across the zone of contact being a greater movement of one surface with respect to the other in some portion of the zone, relative to the analogous movement in another portion of the zone. 2. The apparatus of claim 1 wherein said vibration force actuator is additionally coupled to said second surface to impart a vibratory movement to said first surface, said vibratory movement being substantially perpendicular to said reference plane of contact and substantially nonuniform across said zone of contact.
9. A method for reducing wear on first and second surfaces having first and second resonant frequencies respectively, wherein the first surface moves at a movement velocity with respect to and in substantial sliding contact with the second surface at a zone of contact, the zone comprising a reference plane of contact, comprisingforming spaced surface height variations in said first surface for causing vibratory motion of the second surface substantially perpendicular to the reference plane and substantially nonuniform across the zone of contact, wherein the nonuniform motion across the zone of contact being a greater motion of one surface with respect to the other in some portion of the zone, relative to the analogous motion in another portion of the zone, thereby reducing surface wear. 10. The method of claim 9 wherein spaced surface height variations are additionally formed in said second surface for causing vibratory motion of said first surface with respect to said second surface substantially perpendicular to said reference plane of contact and substantially nonuniform across said zone of contact, thereby reducing surface wear.
15. A method for reducing wear in electric machinery brushes, the brushes having at least one resonant frequency and contacting an electrically conductive surface at a zone of contact with a surface speed, comprisingestimating a resonant frequency of the brushes; and forming spaced surface height variations in the conductive surface, said surface height variations causing vibratory motion of the brushes substantially perpendicular to said conductive surface and substantially nonuniform across the zone of contact at said resonant frequency, thereby reducing surface wear. 16. The method of claim 15 wherein the brushes have a plurality of resonant frequencies, and spaced surface height variations are formed on the conductive surface spaced to cause vibratory motion of the brushes substantially perpendicular to the conductive surface and substantially nonuniform across the zone of contact at a plurality of frequencies substantially equal to the resonant frequencies, thereby reducing brush wear.
20. An electric machine comprising at least one brush having at least one resonant frequency, the at least one brush being in sliding contact with an electrically conductive surface at a zone of contact, the zone comprising a reference plane of contact, and relative movement between the at least one brush and surface being in a direction of movement, the machine comprisinga vibration force actuator coupled to the at least one brush to impart vibratory movement to the at least one brush, said vibratory movement being substantially perpendicular to the reference plane of contact, substantially nonuniform across the zone of contact, wherein the nonuniform movement across the zone of contact being a greater movement of the at least one brush with respect to the electrically conductive surface in some portion of the zone, relative to the analogous movement in another portion of the zone, and at a frequency substantially equal to the resonant frequency. 21. The electric machine of claim 20 wherein the at least one rush has a plurality of resonant frequencies, and wherein said conductive surface comprises surface height variations spaced to induce substantially nonuniform vibratory motion across each of the at least one brush in a direction substantially perpendicular to the conductive surface at frequencies substantially equal to a plurality of the resonant frequencies.
DETAILED DESCRIPTION Preferred Embodiments A first embodiment of the invention relates to apparatus for reducing wear on first and second surfaces in substantial sliding contact at a zone of contact, the zone comprising a reference plane of contact, and relative movement between the surfaces having a direction of movement. The apparatus comprises a vibration force actuator coupled to the first and/or second surfaces to impart a vibratory movement to the first and/or second surfaces, said vibratory movement being substantially perpendicular to the reference plane of contact and substantially nonuniform across the zone of contact.
Tm is related to the minimum frequency of required rotational vibration by the relationship f=1/Tm. For Tm of 4 to 35 ms, the minimum vibration frequency range would be ≈29 to 250 Hz. Although any rotational vibration frequency higher than the minimum thus established could be used (including ultrasonic vibrations), preferred embodiments of the present invention have at least one resonant frequency of at least one of the contacting surfaces which substantially exceeds 1/Tm for those surfaces.
Application of the Invention to an Electrical Machine One embodiment of the present invention may be applied to a rotating electrical machine (i.e., a motor or generator), wherein the first surface (e.g., the surface of an electrical commutator or slip ring, hereinafter rotor) is wavy (i.e., having ridges or surface height variations), and the second surface (e.g., an electrical brush in contact with the rotor) is substantially smooth.
Calculation of the Brush/Rotor Resonant Frequency Often, system differential equations are formulated and solved and resonant frequencies are derived from eigenvalues. In the present case, nonlinearities in the conforce spring and the contact stiffness render this approach difficult. An alternative method based on energy conservation during a vibration cycle may be used. Simplifying assumptions commonly known by those skilled in the art, such as absence of energy gain or loss during operation, are applied. Hence, during longitudinal vibration of the brush-spring/rotor system, potential energy stored in conforce spring extension is converted into motional energy of the brush mass, which is then converted to potential energy of compression of the brush/rotor contact surface. Energy then reverts from the contact back to the spring via the brush mass. The system vibration energy is constant; energy losses (e.g., brush rubs against the holder) are replenished by the source driving the rotor. As a consequence, the maximum kinetic energy of the brush mass motions, which occurs at the instant between the end of the spring extension and the start of the contact compression, must equal the maximum potential energy which occurs either during the maximum extension of the spring or compression of the contact.
Excitations occur as the brush rides over the surface height variations (waves) of the rotor. The frequency of excitation for a certain waviness mode is the product of the rotational speed N (in rpm) and the wave number m of the waviness mode divided by a factor 60 which converts minutes to seconds. At resonance, the period T is the inverse of the excitation frequency, giving the resonant condition:
A(M/2Fx).sup.1/10 +2(2Mx/F).sup.1/2 =60/Nm
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a pattern of surface height variations which may induce vibrational motion in surfaces in sliding contact.
BACKGROUND Field of the Invention The invention relates to the reduction of wear on surfaces maintaining sliding contact.
Friction and Wear of Sliding Surfaces All real surfaces are rough, possessing topographies on a macro- or microscopic scale that consist of surface height variations (hills and valleys) with respect to an idealized reference plane which lies within or substantially parallel to the surface. The reference plane shape corresponds to that of the surface without roughness.
Methods of Reducing Contact Wear The high wear rates associated with thermal mounding have been alleviated by several techniques. For example, making one of the contact surfaces more compliant to deforming forces applied substantially perpendicular to the plane of contact tends to quench thermal mounds because the compliant surface remains more substantially in contact and load concentration at thermal mounds is thereby reduced. Compliant surfaces, however, require special materials and/or manufacturing techniques which tend to raise their cost.
SUMMARY OF THE INVENTION The invention relates to methods and apparatus to reduce wear of one or both of first and second surfaces in sliding contact substantially within a zone of contact. The zone lies within or substantially conforms to a reference plane of contact, which may be curved or flat. Wear reduction is achieved by inducing vibratory motion in one or both surfaces with a vibration force actuator, the vibratory motion comprising motion substantially perpendicular to the reference plane of contact and also substantially nonuniform across the zone of contact. Substantially nonuniform motion across the zone of contact implies a greater motion of one surface with respect to the other in some portion of the zone, relative to the analogous motion in another portion of the zone. Such nonuniform movement is associated with rotation of one surface with respect to the other surface about an axis nonperpendicular to the reference plane of contact, i.e., the movement results in rotational vibration. Three preferred embodiments of the invention are distinguished by the form of the vibration force actuator used to induce the nonuniform motion.
A First Invention Embodiment A first embodiment has a vibration force actuator comprising a series of spaced, surface ridges (surface height variations comprising hills separated by valleys) in one or both surfaces, which are oriented with the ridge lines (longitudinal axes) substantially nonparallel and nonperpendicular to the direction of relative motion between the surfaces. The ridges may induce vibrations in the surfaces during such relative motion of the surfaces. The frequencies of induced vibrations are functions of the spacing of the ridges in the direction of relative motion and the velocity of the relative motion (surface velocity).
Nonuniform vibration may be induced across an area of contact between first and second surfaces, in a direction substantially perpendicular to the reference plane of contact between surfaces, by several means. One means would be to induce a mechanical response to applied vibration force which would vary across the area of contact (as by changing the damping of surface movement substantially perpendicular to the reference plane of contact across the area of contact). Alternatively and preferably, one may apply vibratory forces nonuniformly (i.e., where surface ridges corresponding to a particular vibration frequency are oriented to apply out-of-phase forces between contacting surfaces across a contact area, the phase shift across the area of contact being an angle Θ where 0 invention having spaced surface ridges, this is accomplished by having the ridge lines (longitudinal axes) of the surfaces ridges oriented substantially at an angle α to the direction of relative surface movement (ridge lines are not necessarily either straight or parallel), where 0 value of α is that which results in a phase shift across the zone of contact of about 90 180
A Second Invention Embodiment A second embodiment of the invention comprises one or more (separate) vibration force actuators having driving elements coupled to, and capable of imparting vibratory motion to, first and/or second surfaces. The surfaces are substantially smooth and are in sliding contact. As in the first embodiment, vibratory movement is induced substantially nonuniformly across the zone of first and second surface contact. Such vibratory movement is associated with small rotations of one surface with respect to the other about an axis nonperpendicular to the reference plane of contact. Inventions of the second embodiment include actuators comprising hydraulic, pneumatic, mechanical, electromagnetic, and piezoelectric or magnetostrictive driving elements, e.g., a hydraulic cylinder coupled to a time-varying source of hydraulic pressure (as in a hydraulic brake system or hydraulically operated clutch), or an electrical solenoid coupled to a time-varying source of electric current (as a vibrating solenoid coupled to a sliding contact carrying power to an electric train).
A Third Invention Embodiment A third embodiment of the invention includes an actuator comprising a plurality of component vibration force actuators (including separate actuators) analogous to those found in the first and second embodiments. Each component actuator may be coupled to first and/or second surfaces in sliding contact. As in the first and second embodiments, vibratory motions induced by each component actuator may be characterized by a plurality of frequencies, and are induced substantially nonuniformly across the zone of first and second surface contact.
Work on the invention was supported in part by National Science Foundation grant MSM-8818337. The government has certain rights in the invention.
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Shamoto, 1991, Ultrapreciation Diamond Turning of Stainless Steel by Applying Ultrasonic Vibration, Annals of the CIRP, vol. 40, No. 1, pp. 559 562.* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS5969857 *Sep 4, 1998Oct 19, 1999Samsung Electronics Co., Ltd.Stage assembly of microscope which prevents its particles of wear from being dispersedUS6264467Apr 14, 1999Jul 24, 2001Applied Materials, Inc.Micro grooved support surface for reducing substrate wear and slip formation* Cited by examinerClassifications U.S. Classification310/248, 310/251International ClassificationH01R39/56, H01R39/46Cooperative ClassificationH01R39/56, H01R39/46European ClassificationH01R39/46, H01R39/56Legal EventsDateCodeEventDescriptionJan 13, 2004FPExpired due to failure to pay maintenance feeEffective date: 20031114Nov 14, 2003LAPSLapse for failure to pay maintenance feesJun 21, 1999SULPSurcharge for late paymentJun 21, 1999FPAYFee paymentYear of fee payment: 4Jun 8, 1999REMIMaintenance fee reminder mailedMay 17, 1993ASAssignmentOwner name: BOARD OF REGENTS, THE UNIVERSITY OF TEXAS SYSTEM,Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BRYANT, MICHAEL D.;LIN, JAU-WEN;REEL/FRAME:006540/0320;SIGNING DATES FROM 19930429 TO 19930504RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google