Patent Publication Number: US-2009223083-A1

Title: Bearing including sensor and drying drum including same

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This patent application claims the benefit of U.S. Provisional Patent Application No. 61/034,526, filed Mar. 7, 2008, the entire teachings and disclosure of which are incorporated herein by reference thereto. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to bearings and more particularly to devices and methods for indicating and measuring the remaining useful life of bearings. 
     BACKGROUND OF THE INVENTION 
     In some implementations, bearings are used to support devices that rotate such as mounting or drive shafts. Over time, the bearing will wear due to the interaction between the bearing and the rotating shaft. In some implementations, bearing failure can result in additional, substantial at times catastrophic damage to the shaft or device that is supported by the bearing. 
     In the past, devices measured characteristics of the system relating to failure of the bearing to determine when the bearing required maintenance. Such characteristics include temperature, vibration, lubrication pressure, debris in lubrication, lubrication restrictions, etc. However, by measuring failure characteristics, the bearing has failed or almost at failure and therefore potential damage can occur to the supported shaft or devices connected to the shaft. 
     Further, in many systems, once failure occurs, the system needs to be shut down, which if damage occurs to other components can result in increased down time. As such, waiting for failure to determine when to repair the bearing can be costly and result in un-necessarily long down time. Further, if failure occurs when the system is full of materials, in some implementations, the stoppage of the line can result in spoilage of the materials in the system such that all materials that are not finished must be discarded. 
     These previous devices or methods for analyzing bearing failure and life thus do not provide much predictability of remaining bearing life. 
     In one particular implementation, namely in supporting a journal of a paper drying drum, the bearing may be subjected to very high pressure and velocity due to the large loading. 
     There exists, therefore, a need in the art for a device or bearing that provides the user feedback as to remaining useful life of the bearing and to indicate when a bearing needs to be replaced prior to failure of the bearing. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has several aspects that may be claimed and stand as patentable independently and individually or in combination with other aspects, including but not limited to the following. 
     In one embodiment, a bearing for supporting a rotating shaft including a sensor for measuring the amount of wear of the bearing is provided. The bearing includes a wearable portion and at least one sensor. The wearable portion decreases in thickness as the wearable portion progressively wears due to aggregate use. The wearable portion includes a shaft support surface. The at least one sensor is positioned within the wearable portion at a predetermined position along the thickness of the wearable portion and offset from the shaft support surface. 
     In one implementation of the bearing, the bearing is a bushing. 
     In another implementation, a plurality of sensors are provided in the form of a plurality of wires embedded in the wearable portion. In other implementations, the sensor is a continuous sheet of electrically conductive material that changes electrical properties as the cross-section of the sheet decreases. 
     In another embodiment, a rotatable drying drum for drying moist articles comprising a drum, a journal, a bearing and a sensor is provided. The drum can be used to house moist articles that are dried. The journal is operably coupled to the drum. The bearing supports the journal for rotation on a wearable portion. The wearable portion is configured to wear a predetermined amount before needing replacement. The sensor is disposed within the wearable portion a predetermined distance from a bearing surface of the wearable portion. Interaction of the journal and the sensor after a predetermined amount of wear in the wearable portion allows determination that said amount of wear of the wearable portion has occurred. 
     In a further implementation of the invention, a method of monitoring wear of a wearable portion of a bearing is provided. The method includes sensing an electrical property of a first sensor mounted in the wearable portion of the bearing that decreases in thickness as the wearable portion progressively wears, the wearable portion including a support surface, the first sensor being mounted a first predetermined distance from the support surface. The method further includes sensing a change in the electrical property of the first sensor. Additionally, the method includes determining a first degree of wear of the wearable portion upon the sensed change in the electrical property of the first sensor. 
     In a preferred implementation, the step of sensing a change in the electrical property of the first sensor includes sensing that an electrical circuit established by the first sensor is broken. 
     The method may also include the additional steps of 1) sensing an electrical property of a second sensor mounted in the wearable portion of the bearing a second predetermined distance from the support surface, the second predetermined distance being further from the support surface than the first predetermined distance; 2) sensing a change in the electrical property of the second sensor; and 3) determining a second degree of wear of the wearable portion upon the sensed change in the electrical property of the second sensor. In this form of the method, the first degree of wear identifies an acceptable amount of wear and the second degree of wear identifies a replacement required degree of wear such that the bearing, or at least the wearable portion, needs to be replaced. Further yet, the second degree of wear may be established at a non-complete failure predetermined distance from the support surface such that the bearing has not yet failed but that it will fail in a short period of time, thereby eliminating damage prior to indicating a need to replace the bearing. 
     Other embodiments of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a top perspective illustration of a saddle bushing according to the teachings of the present invention; 
         FIG. 2  is a top plan view of the saddle bushing of  FIG. 1 ; 
         FIG. 3  is a schematic implementation of the saddle bushing of  FIG. 1  used in a drying drum; 
         FIG. 4  is a simplified end view of the saddle bushing of  FIG. 1  coupled to an indicator module; 
         FIG. 5  is a further simplified end view of the saddle bushing of  FIG. 4  illustrating the inclusion of numerous sensor wires; 
         FIG. 6  is simplified cross-section of a bushing liner illustrating sensor wires imbedded in the bushing liner; 
         FIG. 7  is a simplified cross-section of another bushing liner illustrating sensor wires mounted in channels formed in the bushing liner; 
         FIG. 8  illustrates another embodiment of a bushing liner using normally off technology; and 
         FIG. 9  is a further simplified cross-section of another bushing liner illustrating a sensor using a continuous sheet extending along the thickness of the bushing liner. 
     
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  illustrate a first bearing device (as used herein, bushing and bearing can be used interchangeably) according to the teachings of the present invention in the form of a saddle bushing  100 . The saddle bushing  100  includes a support  102  supporting a wearable portion in the form of bushing liner  104 . As the illustrated bearing is a saddle bushing, the support  102  is in the form of an arcuate U-shaped or trough-shaped shell that is preferably formed from a rigid metal. The bushing liner  104  is preferably formed from polytetrafluoroethylene or other fluoropolymer. However, other materials may be used for the support shell and the bushing liner. 
     With reference to  FIG. 3 , the saddle bushing  100  is used to support a rotating body  110  which typically includes a journal  111  or shaft of a rotating load. One particular implementation is the use of the saddle bushing  100  for supporting a journal coupled to a paper drying drum  112  for drying paper in a paper mill. Typically, a film of oil is present between the bushing liner  104  and the supported shaft of the rotating drying drum. The film of oil provides hydrodynamic lifting to help support the shaft or journal to reduce the rate of wear on the bushing liner  104 . 
     The bearing surface  106  of the bushing liner  104  will include oil distribution grooves  105  (see for example  FIG. 2 ) for permitting oil to be distributed between the bushing liner  104  and the shaft or journal. 
     Over time, as the shaft rotates within the saddle bushing  100 , the bushing liner  104  will wear reducing its thickness t (see also  FIGS. 6-9 ), including a reduction in the depth of the grooves  105 . At a given percentage of wear, the bushing liner  104  is sufficiently worn that the bushing liner  104  is spent and needs to be replaced to prevent the shaft or journal from riding on or contacting the support  102  and to prevent the grooves  105  from being worn away which would prevent the proper amount of oil to pass between the bearing  100  and the shaft. 
     The present saddle bushing  100  includes a wear detection system  120  (illustrated in simplified form in  FIGS. 4 and 5 ) for determining the amount of the bushing liner  104  that has been worn away. The system allows for measurable and predictable bearing life, rather than relying on bearing failure or symptoms of bearing failure for determining the need to replace the bushing  100 . The system  120  permits for predictably scheduling downtime for maintenance activities prior to failure of the bushing  100 . 
     The wear detection system  120  of the illustrated embodiment is an electronic system that includes a plurality of sensors imbedded or otherwise mounted into the bushing liner  104  of the saddle bearing  100  connected to an indicator module  122 . The sensors of the illustrated embodiment are in the form of wires  124 - 127  (shown schematically in  FIGS. 5 and 6 ). The wires  124 - 127  are positioned at various predetermined depths relative to the bearing surface  106  to sense the bushing&#39;s remaining useful life. 
     With primary reference to  FIG. 5 , the indicator module  122  senses changes in the wires  124 - 127  to determine the status of the bushing liner  104 . In a first embodiment, each of wires  124 - 127 , in an undisturbed state, completes an independent electrical circuit which is monitored by indicator module  122 . In the undisturbed state, each wire represents that more useful life is available than the amount of useful life for which the wire represents, as will be more fully explained below. 
     The indicator module  122  can continuously pass an electrical current through wires  124 - 127 . Alternatively, the indicator module  122  may pulse the sensors so as to reduce the energy consumption of the system  120 . 
     Once the bushing liner  104  has worn sufficiently along its thickness t that wire  124  is worn through, i.e. switching the sensor wire  124 , the wire enters a disturbed state and the circuit that includes the wire is broken such that electricity is prevented from passing through the circuit. The indicator module  122  can determine that the circuit is broken and then activate a warning signal, such as indicator light  134 . At this point, in the illustrated example, the user is aware that at least twenty-five percent of the useful life of the bushing liner  104  has been spent and between seventy-five percent and fifty percent of the useful life of the bushing liner  104  remains. At this point, none of the other wires  125 - 127  have become disturbed indicating that at least as much useful life for which they represent still remains. 
     The same process occurs for the subsequent sensors, i.e. wires  125 - 127  having indicator lights  135 - 137 , respectively. Thus, once wire  125  is worn through, a reduced level of remaining life is indicated, such as approximately between fifty percent and twenty-five percent of the remaining useful life. Once wire  126  is worn through, the user is informed that seventy-five percent of the useful life has been used and between about twenty-five percent and zero useful life remains. Finally, once wire  127  is worn through, the user is informed that the saddle bushing  100  needs to be replaced as the useful life of the bushing liner  104  has run. Typically, wire  127  will be set so as to a position such that the bearing does not reach absolute failure at the time it is worn through, but that the user needs to address the issue immediately. 
     The breaking of the circuits that includes wire  124 - 127  can be sensed using standard sensing technology such as by measuring a change in current flow or a change in potential difference across the circuit or wires  124 - 127 . 
     In a preferred embodiment, such as illustrated in  FIG. 6 , the sensor wires  124 - 127  are directly molded into the bushing liner  104  as the bushing liner  104  is formed. Then, the bushing liner  104  is subsequently secured to support  102 . 
     In an alternative embodiment illustrated in  FIG. 7 , the sensor wires  124 - 127  may be subsequently added to the bushing liner  104 . As such, the bushing liner  104  may first be formed. Then, grooves  141 - 144 , having different depths corresponding to different percentages of wear, are formed, preferably but not necessarily, in a back side  140  (i.e. a side that is mounted against support  102  and is opposite bearing surface  106 ). Finally, the wires  124 - 127  are inserted into the grooves  141 - 144 . The grooves  141 - 144  may then be filled with a filler, such as an adhesive or a plug of the material forming bushing liner  104  to maintain the wires  124 - 127  at the desired depth of the grooves. 
     In some embodiments, the sensor wires  124 - 127  may include an insulator in the event that bushing liner  104  is formed of a conductive material. 
     In another alternative embodiment, a wear detection system  220  may be configured as a “normally open” system where the circuits are normally broken and then once the shaft wears through a busing liner  204  sufficiently to complete the circuit by connecting wires  224 - 227 . In such an embodiment, current only flows through the circuit once the circuit is completed. Thus, indicator module  122  can sense when a given circuit at a predetermined depth is completed and thus activate a corresponding warning signal  234 - 237 . 
     In yet a further embodiment illustrated in  FIG. 9 , the sensor is in the form of a continuous sheet  324  extending along the thickness t of the bushing liner  304 . The sheet conducts electricity much like the wires  124 - 127 . However, the sheet  324  is configured such that it need not be worn completely through to trigger a warning, i.e. switch the sensor. Instead, the sheet  324  is configured such that as the sheet is continuously worn along the thickness t, the electrical properties of the sheet  324  alter. For example, as the sheet is continuously worn, the resistance of the sheet  324  may increase, due to a reduction in cross-sectional area. This change in electrical property can then be sensed by the indicator module  122 . In such an arrangement, the configuration permits continuous monitoring or estimation of the remaining useful life of the bushing liner  304  as there are not gaps of non-sensing, such as with the wire arrangements discussed previously. 
     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.