Abstract:
A seal for preventing leakage of fluid from between a first member and a second member has a seal body and a seal wear indicator. The second member is capable of moving toward and away from the first member. The seal body is adapted for engaged contact with the first and second members so as to prevent leakage of fluid as long as the seal has not worn beyond a specified depth. A seal wear indicator is positioned within the seal body at approximately the specified depth, such that when the seal has worn to the specified depth, a change in the optical conductor is detected, indicating that the seal needs replacement.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This continuation-in-part application of my application Ser. Nos. 09/090,056 entitled “SELF MONITORING STATIC SEAL”, now U.S. Pat. No. 6,615,639, and 09/089,580 entitled “SELF MONITORING MECHANICAL SEAL”, now U.S. Pat. No. 6,595,523, both filed Jun. 3, 1998. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to seals which are positioned against a moving surface, and more particularly to seals which prevent fluid, e.g. lubricant, leakage or passage between two surfaces. More particularly, the present invention relates to a self-monitoring seal employing an optical device for indicating when the body of a seal has undergone excessive wear or deterioration. 
   Machinery often includes members which move with respect to each other. Bearings have long been used to facilitate such movement, particularly for members that move rotationally with respect to each other. Brass rings or sleeves have long been used to facilitate such movement where the members are reciprocating with respect to each other. Bearings and brass rings are used to aid in transmitting forces from one member to another and to reduce friction. Rolling elements are often used in bearings to reduce friction, such as in ball bearings. Bearings often contain lubricant to reduce the friction created within the bearing. 
   Leakage of fluid from between mechanical parts has long been a problem. Contamination of the bearings or seals with foreign material such as dirt has also long been a problem. Both loss of fluid and contamination lead to increased friction and wear within the structure, damaging the structure and perhaps damaging the machinery. 
   Seals composed of a soft polymeric material are used with bearings to prevent lubricant leakage and contamination. The polymeric material contacts a moving surface in the bearing and provides a seal. Friction between the polymeric material and the moving surface gradually wears the surface of the polymeric material away. If the polymeric material becomes too worn, it will no longer form a tight seal against the moving surface, and fluid leakage from the bearing and contamination of the bearing again become problems. 
   In other instances metal or polymeric seals are placed between the moving parts. This arrangement is particularly useful when the movement is a reciprocal movement. Non-limiting illustrations of a reciprocating seal include a piston and cylinder structure, hatches, air locks, doors, covers, lids and caps. With regard to such seals as found in hatches, air locks, doors, covers, lids and caps, the interfitting members can reciprocate with respect to each other, in the sense of opening and closing with regard to each other. However, when a seal is in fluid tight sealing relationship between such interfitting members, the seal may more properly be termed a static or stationary seal, since the interfitting members and the interposed seal are all stationary with regard to each other while the integrity of the sealing relationship is maintained. Sealing integrity or effectiveness can also be compromised by cracking, breaking, loss of flexibility or deterioration due to such conditions as repeated flexing, bending and/or compression, or length of contact with various fluids or container contents. 
   Various methods have been developed to prevent or detect leakage past a seal. As shown in U.S. Pat. No. 4,761,023, one method involves monitoring the pressure of the fluid on the high pressure side of the seal, with a loss of pressure indicating leakage past the seal. Alternatively, as shown in U.S. Pat. No. 4,290,611, the fluid pressure on the low pressure side of the seal may be monitored, with an increase in pressure indicating fluid leakage. A third method, such as that shown in U.S. Pat. No. 4,178,133, uses colored fluid and visual monitoring of leakage past a seal. Still other methods involve manual maintenance procedures, wherein seals are inspected or replaced on a regular basis. 
   These various methods to prevent or detect leakage past a seal have not proven satisfactory due to a number of problems. A problem with monitoring fluid pressure is that it is only effective to detect leakage of the fluid. Often this is too late to prevent damage. It is desired that the seal be replaced before leakage has begun. Similarly, visual monitoring of fluid leakage can only indicate that leakage has begun, not that leakage is about to begin. A problem with manual inspection of a seal is that it requires an inspector who is not only trained but also diligent. Often seals are not inspected merely due to neglect or lack of diligence. Another problem with manual inspection is that it may require the machinery to be stopped during the inspection, which can be inconvenient. Scheduled seal replacement also has problems. Seals may wear more or less quickly depending on operating conditions, and scheduled seal replacement may occur too early (before the seal needs to be replaced) or too late (after the seal starts leaking). 
   An excellent solution to these problems has been provided by the inventions disclosed in my U.S. Pat. No. 5,540,448, issued Jul. 30, 1996, entitled SEAL WITH ELECTRICAL CONDUCTOR WEAR INDICATOR and in my U.S. Pat. No. 5,246,235, issued Sep. 21, 1993, entitled SEAL WITH EMBEDDED WIRE. The present invention is an improvement on my earlier disclosed seals and is particularly adapted to work with reciprocating surfaces which require a seal there between. Illustrative of such reciprocating surfaces are the piston and cylinder, hatches, air locks, doors, covers, lids, caps, etc. 
   SUMMARY OF THE INVENTION 
   A seal for preventing leakage between two members has a seal member and an optical indicator. The seal member is positioned to prevent fluid leakage from between two members and is more readily abraded than either of the two members. The seal member is adapted to maintain a fluid tight seal with the two members until it is abraded beyond a specified depth. The optical indicator is positioned within the seal member at or slightly above the specified depth to provide an indication that the seal needs replacing before the fluid tight seal is breached. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a cross-sectional side view of the seal in place, adjacent a bearing and around a rotating shaft. 
       FIG. 2  shows a cross-sectional side view of the seal in place, adjacent a brass ring and around a reciprocating shaft. 
       FIG. 3  is an enlarged top view of the seal of  FIG. 1 . 
       FIG. 4  is a cross-sectional view taken along the line  4 - 4  in  FIG. 3 . 
       FIG. 5  is an enlarged top view of the seal of  FIG. 1 , after the seal body has worn to the specified depth (d). 
       FIG. 6  is a cross-sectional view taken along the line  6 - 6  in  FIG. 5 , after the seal body has worn to the specified depth (d). 
       FIG. 7  shows a cross-sectional side view of an alternate embodiment of the seal in place around a shaft. 
       FIG. 8  is an enlarged top view of the embodiment of the seal shown in  FIG. 7 . 
       FIG. 9  is a top view of an alternate embodiment of the signaling circuit. 
       FIG. 10  is a top view of an alternate embodiment of the seal with an embedded optical indicator connected to a sensor 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a seal  10  of the present invention in place, against a bearing  12  and around a shaft  14 . The shaft  14  rotates as indicated by arrow  16 . The bearing  12  has an inside race  18 , an outside race  20 , and a plurality of rolling elements, e.g. balls  22 . The inside race  18  is connected with the shaft  14  and rotates with the shaft  14 . The outside race  20  is connected to the housing  24  and may remain stationary The rolling elements  22  may be spherical balls (or bearings) as shown, or may be other cylindrical or needle rolling elements. 
   The seal  10  of the present invention includes a seal body  26  and an embedded optical indicator  28 . Leads or posts  30  and  32  connect with the optical indicator  28  and extend out from the seal body  26 . 
   As shown, the optical indicator  28  may be a standard fiber optic cable or an optical cable formed from a material that glows or fluoresces when exposed or worn. Depending on the specific implementation, an optical sensor may be coupled with the optical indicator  28  to generate a signal when the optical indicator  28  is exposed or worn or when the optical indicator  28  is exposed to ambient conditions. 
   As shown in  FIG. 1 , the seal body  26  presses against the shaft  14 , forming a tight seal between the seal body  26  and the shaft  14 . Alternatively, the seal body  26  may press against the inside race  18 , forming a tight seal between the seal body  26  and the inside race  18 . The seal body  26  functions to prevent fluid leakage from the bearing  12 . 
   The seal body  26  has a contact surface  34  defined as the surface which contacts the adjacent moving surface of the shaft  14  to form a tight seal. The seal body  26  may be composed of a polymeric material or other suitable substance. The material of the seal body  26  is generally softer than the shaft  14 , so that friction preferentially wears the seal body  26  rather than the shaft  14 . The contact surface  34  of the seal body  26  gradually wears away due to friction between the outer surface of the shaft  14  and the seal body  26 . 
     FIG. 2  shows a seal  10  of the present invention in place, against a brass ring  36  and around a shaft  14 . In this embodiment, the shaft  14  reciprocates as indicated by arrow  38 . The brass ring  36  has an inside bearing surface  40  and an outside surface  42 . The inside bearing surface  40  is in contact with the shaft  14  and slides along the surface of the shaft  14 . The outside surface  42  may be connected to the housing  24 . 
   The seal  10  has a seal body  26  and an embedded optical indicator  28 . As in  FIG. 1 , the seal body  26  presses against the shaft  14 , forming a tight seal between the seal body  26  and the shaft  14 . The seal body  26  functions to prevent fluid leakage or to prevent exposure of a sealed portion  44  of the shaft  14  to the outside environment. 
     FIG. 3  shows an optical indicator  28  embedded within the seal body  26  at a specified depth (d). The optical indicator  18  may be composed of any material which conducts light, such as a fiber optic cable. The specified depth (d) at which the optical indicator  18  is embedded within the seal body  26  may be slightly less than the depth (d) of seal wear which will cause the seal  10  to leak. 
   The conductor  18  has a first post  30  and a second post  32  which extend outside the seal body  26 . The first post  30  and the second post  32  are for connection to an exterior signaling circuit  46  (shown in  FIGS. 4 ,  6 ,  8  and  9 ) or a light sensor (shown in  FIGS. 9 and 10 , and shown as a bar code reader in  FIG. 11 ). The signaling circuit  46  may transmit an optical signal through the embedded indicator  18 . If the optical indicator  18  is a fiber optic cable, discontinuity or a change in the optical signal can be detected, indicating a wear point in the optical indicator  18  such that the total internal reflectance of the fiber optic cable is disrupted. A discontinuity (or absence of optical continuity) or a change in the optical signal is an instance when the optical signal is either totally interrupted or when the optical signal is disrupted enough that a sensor in the signaling circuit  46  can detect a change in the received optical signal. Additionally, the signaling circuit  46  can generate a warning signal to an operator that the seal  10  requires replacement either based on the discontinuity or change in the optical signal. 
     FIGS. 5 and 6  show the seal  10  immediately after friction between the shaft  14  and the seal body  26  has worn the seal body  26  to the specified depth (d). The original contact surface  34  is shown in phantom, while the current contact surface  34 ′ of the seal body  26  is shown as a continuous line. As shown, the optical indicator  28  has worn completely through at point  48 , causing a disruption or optical discontinuity between the first post  30  and the second post  32 . A suitable mechanism (such as an optical sensor) may be provided in the signal-type circuit  46  to detect a change or a discontinuity in the optical signal, which may then trigger an alarm signal (such as a warning light) indicating the need for seal replacement. 
     FIGS. 7 and 8  show an alternate embodiment of the seal  10  wherein the optical indicator  28  has only a first post  30 . In this embodiment, the optical indicator  28  does not encircle the shaft  14 , but merely ends at the specified depth. When wear of the seal body  26  reaches the specified depth (d), the shaft  14  becomes visible to the end of the optical indicator  28 , causing an optical change. For example, if the optical indicator  28  is a fiber optic cable and the post  30  is connected to a signaling circuit  46  that transmits a pulsed optical signal, it is possible to detect the pulsed optical signal that is reflected back from the end of the fiber optic cable after each pulse. If the shaft  14  has a bar code  50  printed on one side and in line with the embedded optical indicator  28 , when the seal body  26  is worn sufficiently to expose the end of the embedded optical indicator  28 , the pulsed signal can be used like a bar code reader to detect a change in the reflected optical signal. 
   As shown in this alternate embodiment, the shaft  14  reciprocates as indicated by arrow  26 . The shaft  14  alternatively rotates or oscillates (i.e. changes a direction of rotation), or otherwise moves with respect to the seal  10 . If the shaft  14  rotates, the bar code  50  may be oriented differently on the shaft  14 . 
   Alternatively, instead of a bar code reader, the signaling circuit  46  may simply transmit light through the embedded optical indicator  28 . If the embedded optical indicator  28  becomes worn, light escapes from the optical indicator  28  at the worn location  48  and becomes visible to an operator or to an optical sensor, thereby indicating the need for a seal replacement. 
   As shown in  FIG. 9 , the seal  10  has an embedded optical indicator  28  extending around the entire seal body  26 . The first post  30  and second post  32  extend from the seal body  26  and are connected to the signaling circuit  46 . The first post  30  is connected to a light source  52 . The light source  52  may be any light generating source or optical signal generating source. The second post  32  is connected to a light sensor  54 , which can be any device capable of detecting an optical signal. 
   In this embodiment, the signaling circuit  46  includes a light source  52  and a light sensor  54 . The light source  52  transmits an optical signal through the embedded optical indicator  28 . The light sensor  54  detects the transmitted optical signal. The light sensor  54  generates an alarm signal if it detects a change in the transmitted signal. 
     FIG. 10  illustrates an embodiment wherein the embedded optical indicator  28  has only one post  30 , which is connected to a light sensor  54 . In this embodiment, the light sensor  54  detects an optical change coming from the embedded optical indicator  28 . This optical change may be from ambient light. Alternatively, the embedded optical indicator  28  may be coated with or formed from a substance that fluoresces when worn or when exposed to whatever substance is contained by the seal  10 . In this instance, when the seal body  26  is worn sufficiently to expose the coating, the coating would glow or otherwise generate a light signal that can be detected by the light sensor  54 . An appropriate coating is a fluorescent paint, a reflective paint, or any coating capable of causing a optical change when exposed or worn. 
   One such coating is be a polymer thin film carrying embedded indicators sensitive to the presence of a certain chemical of interest or sensitive to wear. In this instance, the polymer thin film can be coated on the optical indicator to indicate exposure of the indicator to that chemical. When the seal body  26  wears to the specified depth (d) as described above, the coating on the embedded indicator  28  changes to a distinct identifying color upon contact with the chemical of interest or upon experiencing wear from the relative motion of the shaft  14 . Such a coating of indicator-embedded polymer thin films on the embedded optical indicator of this invention may be used to indicate not only exposure of the seal  10  to a certain chemical, but also any possible deterioration or weakening of the seal  10  due to such exposure. Suitable embedded indicators for this application are Polymer thin films with chemical sensitive embedded indicators admixed therein are available from Geo-Centers Inc., Newton Centre, Mass. 
   Alternatively, by shining an appropriate querying light on the seal  10  with a polymer thin film coated and embedded indicator  28 , the color of the indicator  28  can indicate exposure of the seal  10  to the chemical, leaking of the chemical and wear or deterioration of the seal  10  due to the action of the chemical. In a suitable querying light, when the embedded indicator  28  is exposed by wear, the color of the indicator  28  due to the thin film coating is transmitted by an optical fiber back to a light sensor  54 . Such a querying light may use at least two light sources, one where the indicator shows the most change and one where it shows the least. Such a querying light is available from Geo-Centers Inc., Newton Centre, Mass., under the trade name “Optrode.”. Another suitable querying light may be a flashlight which illuminates using a light-emitting diode (LED) of a proper wave length, rather than an incandescent bulb. Such LED flashlights are available from LEDtronics, Inc., 4009 Pacific Coast Hwy., Torrance, Calif. 90505. 
   Operation of the Invention 
   Although operation of the present invention is apparent from the preceding description, it will be detailed hereinafter to provide a more complete understanding of the present invention. As the contact surface  34  of the seal body  26  wears away, the optical indicator  28  gradually moves closer and closer to the shaft  14 . As seal wear continues, the optical indicator  28  contacts the shaft  14  and wears away along with the seal body  26 . The optical indicator  28  is embedded at a specified depth (d) relative to the shaft  14  such that the optical indicator  28  can wear entirely through before the seal  10  begins to leak. When the optical indicator  28  is worn entirely through, as shown in  FIGS. 4 and 5  at point  48 , there is no longer optical continuity between the first post  30  and the second post  32 . Because further wear of the seal body  26  may cause the seal  10  to leak, the absence or change in the optical signal between the first post  30  and the second post  32  indicates to an operator that the seal body  26  has worn to a point such that the seal  10  requires replacement. 
   Alternatively, the optical indicator  28  may be placed at a specified depth such that exposure of the optical indicator  28  to the moving surface of the shaft  14  occurs at the time when the seal body  26  has worn such that the seal  10  requires replacement. In this case, when the seal body  26  wears to the specified depth (d), an optical change is detected by the signaling circuit  46  or by a light sensor  54 , which causes an alarm signal to be sent, indicating to an operator that the seal  10  should be replaced. 
   The optical optical indicator  28  may be composed of any material which conducts light waves, such as glass, plastic, or fibers of these, also included are glues, resin, lenses, and mirrors. The light may be in the visible spectrum or the invisible spectrum. A source of components of this nature is Edmund Industrial Optics, 101 East Gloucester Pike, Barrington, N.J. 08007-1380. 
   While it is possible to attach the optical indicator  28  to the outside of the seal body  26 , it is preferable to insulate the optical indicator  28  by the seal body  26  or by an insulation layer of a optically opaque material. The opaque layer helps to prevent accidental or premature changes in the optical signal of the optical indicator  28 . The insulation layer may be provided by a material which is applied in a liquid or paste form, which dries or cures into a solid material. An example of a material suitable for use as the insulation layer is LIQUID ELECTRICAL TAPE manufactured by Starbright of Fort Lauderdale, Fla. 
   Although the present invention has been described with reference to a preferred embodiment, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.