Fiber optic load sensing device

Abstract

A transverse load sensitive optical treadle switch. The switch includes a deformable longitudinal housing and a fiber optic assembly positioned within the housing The fiber optic assembly includes an optical fiber having a first end and a second end, the optical fiber being subject to bending upon application of a transverse load to said housing. Means for mounting the optical fiber in the housing so as to permit bending of the fiber in response to application of a transverse load to said housing are provided, the degree of bending sufficient to cause a significant decrease in passage of light through said fiber when said fiber is bent. Means permitting introduction of light into said optical fiber at the first end of the optical fiber and means for permitting the exit of light from the second end are also provided.

What is claimed is: 
     
       1. A treadle sensing device for vehicular traffic adapted to be mounted transversely on a roadway and to receive and sense a downward load of the type imparted by a vehicle wheel comprising a longitudinal elastomeric envelope having spaced apart longitudinal walls in a lengthwise region of said envelope adapted to receive said load;   a portion of foam rubber embedded within said envelope; a fiber optic cable supported by said foam rubber within said region of said elastomeric envelope and running generally perpendicular to the direction of the load to be applied substantially the length of said region, said fiber optic cable having a first end adapted to be connected to a signal source of light and a second end adapted to be connected to a receiver;   means permitting deformation of said fiber optic cable within said envelope when a transverse load of the type applied by a vehicle wheel is applied to said envelope sufficient to significantly alter the amount of light transmitted through said fiber optic cable; and   means for preventing complete compression of said foam rubber where said fiber optic cable rests against said foam rubber during application of said load when said device is mounted on a roadway.   
     
     
       2. A load sensing device adapted to be mounted transversely on a roadway and to receive downwardly applied loads of the type imparted by an automotive vehicle wheel comprising a longitudinal envelope having spaced apart peripheral walls defining an interior space therebetween in a region of said envelope adapted to receive said load, said walls remaining substantially longitudinally parallel to one another substantially throughout the region of said envelope adapted to receive said load, at least one of said walls in said region having an elastically deformable portion having a first interior surface deflectable into said interior space towards an opposing second interior surface of one of said peripheral walls upon the application of said load to said envelope;   a relatively soft compressible elastomeric insert embedded in said interior space of said envelope;   a fiber optic cable longitudinally positioned within said interior space of said envelope and resting against said insert, said fiber optic cable comprising an optical fiber having a first end adapted to receive light and a second end adapted to permit the exit of said light, said fiber optic cable being subject to sufficient deformation into said insert upon deflection of said first interior surface caused by application of said load so as to permit localized bending of said optical fiber sufficient to substantially alter the light transmitted through the optical fiber; and   means for preventing complete compression of said elastomeric insert where said fiber optic cable rests against said elastomeric insert during application of said load when said device is mounted on the surface of the roadway.   
     
     
       3. The load sensing device defined in claim 2, wherein said insert is a foam elastomeric. 
     
     
       4. The load sensing device defined in claim 2, wherein said fiber optic cable is bonded to said insert. 
     
     
       5. The load sensing device defined in claim 2, wherein said optical fiber has an inner core of a first refractive index and an outer layer of a second refractive index which is lower than said first refractive index, and wherein said tint end adapted to receive light and said second end adapted to permit the exit of said light permits introduction and exit of light from said core of said optical fiber. 
     
     
       6. The load sensing device defined in claim 5, wherein said fiber optic cable is a self contained sleeved fiber optic cable assembly comprising a sleeve surrounding said optical fiber;   fulcrum means between said sleeve and said optical fiber spaced apart along the length of said optical fiber a predetermined average distance sufficient to facilitate said sufficient bending of said optical fiber between said fulcrum means in response to a load applied to said deflectable wall portion of said envelope to substantially alter the light transmitted through the optical fiber.   
     
     
       7. The load sensing device defined in claim 6, wherein said fulcrum means comprise a spiral fiber wound around said optical fiber and disposed within said sleeve. 
     
     
       8. The load sensing device defined in claim 7, wherein said spiral fiber is wound with a distance between winds in the range of at least twice the diameter of said optical fiber. 
     
     
       9. The load sensing device defined in claim 6, wherein said envelope is made of an elastomeric material and said sleeve is made of a material which is deformable but relatively stiffer than said elastomeric material of said envelope to facilitate said sufficient bending of said optical fiber between said fulcrum means when a load is applied to said envelope. 
     
     
       10. The load sensing device defined in claim 2, wherein said substantial alteration of said light passing through said optical fiber is an attenuation which is substantially linear in response to the magnitude of the applied load. 
     
     
       11. The load sensing device defined in claim 2, wherein said substantial alteration of said light is substantially complete attenuation of the amount of light passing through said optical fiber in response to the applied load. 
     
     
       12. The load sensing device defined in claim 2, wherein said interior surface of said deflectable wall portion is substantially fiat when undeformed. 
     
     
       13. The load sensing device defined in claim 2, wherein said envelope is formed of an elastomeric material. 
     
     
       14. The load sensing device defined in claim 2, wherein said fiber optic cable is U-shaped within said envelope. 
     
     
       15. The load sensing device defined in claim 2, wherein said region of said envelope adapted to receive a load includes an upper wall having an exterior side, said exterior side including a generally central portion adapted to receive the load to be applied so that the load to be applied will tend to be concentrated in the generally central portion of the exterior side of said upper wall. 
     
     
       16. The load sensing device defined in claim 15, wherein said generally central portion includes a convex exterior bump. 
     
     
       17. The load sensing device defined in claim 16, wherein said exterior side of said upper wall includes substantially horizontally fiat exterior portions to the sides of said convex exterior bump. 
     
     
       18. The load sensing device defined in claim 2, wherein said envelope includes exterior retention surfaces adapted to cooperate with and be retained by a frame assembly. 
     
     
       19. The load sensing device defined in claim 18, wherein at least one of said exterior retention surfaces includes an inwardly sloped exterior side surface. 
     
     
       20. The load sensing device defined in claim 2, wherein said preventing means comprises a frame assembly, said frame assembly including frame members adjacent said envelope, said frame members having a vertical height sufficient to prevent said complete compression of said elastomeric insert where said fiber optic cable rests against said elastomeric insert during application of said load. 
     
     
       21. The load sensing device defined in claim 20, wherein said frame assembly includes a member partially extending over at least a portion of said envelope, said member leaving a sufficient portion of envelope exposed to the load to be sensed to permit said sufficient bending of said optical fiber. .Iadd. 
     
     
       22.  A treadle sensing device for vehicular traffic adapted to be mounted transversely on a roadway and to receive and sense a downward load of the type imparted by a vehicle wheel comprising a longitudinal elastomeric envelope having spaced apart longitudinal walls in a lengthwise region of said envelope adapted to receive said load;   a substantially deformable inner member embedded within said envelope;   a fiber optic cable supported by said substantially deformable inner member within said region of said elastomeric envelope and running generally perpendicular to the direction of the load to be applied substantially the length of said region, said fiber optic cable having a first end adapted to be connected to a signal source of light and a second end adapted to be connected to a receiver;   means permitting deformation of said fiber optic cable within said envelope when a transverse load of the type applied by a vehicle wheel is applied to said envelope sufficient to significantly alter the amount of light transmitted through said fiber optic cable; and   means for preventing complete compression of said substantially deformable inner member where said fiber optic cable rests against said substantially deformable inner member during application of said load when said device is mounted on a roadway. .Iaddend. .Iadd.23. The device defined in claim 22, wherein said substantially deformable inner member includes a relatively compressible portion. .Iaddend. .Iadd.24. The device defined in claim 22, wherein said substantially deformable inner member is adapted to deflect downwardly to a substantial degree where it supports said fiber optic cable in response to application of said applied load. .Iaddend. .Iadd.25. The device defined in claim 22, wherein said substantially deformable inner member is a portion of air-conditioning elastomeric material. .Iaddend. .Iadd.26. The device defined in claim 22, wherein said envelope is mounted with respect to said roadway in such a manner that said deformation of said envelope during application of said load is limited to a predetermined amount. .Iaddend. .Iadd.27. The device defined in claim 26, wherein said predetermined amount is a deformation to a position substantially flush with an upper surface of said roadway proximate to said envelope. .Iaddend. .Iadd.28. The device defined in claim 22, wherein said envelope is mounted with respect to said roadway such that at least most of said envelope lies below an upper surface of said roadway and at least a portion of said envelope is uncovered by roadway material. .Iaddend. .Iadd.29. The device defined in claim 28, wherein a small portion of said envelope protrudes above said surface of said roadway. .Iaddend. .Iadd.30. The device defined in claim 22, wherein said load sensing device is configured as a vehicle axle counter and further comprises:   means operatively connected to said optical fiber for introducing light into said optical fiber;   means operatively connected to said optical fiber for receiving said light after it has been transmitted through said optical fiber and for sending said detectable alteration of said light caused by deformation of said optical fiber;   means operatively connected to said means for receiving and sensing said light for determining whether a predetermined threshold value of alteration of said light exists; and   means operatively connected to said threshhold determining means for causing a count when said threshhold value of alteration of said light exists due to the passage of said vehicle wheel over said device.   
     
     
        .Iaddend. .Iadd.31.  A sensing device for vehicular traffic adapted to be mounted transversely on a roadway and to receive and sense a downward load of the type imparted by a vehicle wheel as the wheel passes over the device comprising a longitudinal deformable envelope having a lengthwise region adapted to receive said load, said envelope being mounted with respect to said roadway at least partially exposed such that application of said load will cause deformation of said envelope; and   a fiber optic cable disposed within said region of said envelope and running generally perpendicular to the direction of the load to be applied substantially the length of said region, said fiber optic cable including an optical fiber adapted to be connected to a signal source of light and to a receiver, said fiber optic cable being disposed within said envelope such that deformation of said envelope in response to said load will cause deformation of said fiber optic cable and its included optical fiber sufficient to detectably alter the light transmitted through said optical fiber without overstressing said optical fiber upon a multiplicity of repeated applications of said load. .Iaddend. .Iadd.32. A sensing device for vehicular traffic adapted to be mounted transversely on a roadway and to receive and sense a downward load of the type imparted by a vehicle wheel as the wheel passes over the device comprising   a longitudinal elastomeric envelope having a lengthwise region adapted to receive said load, said envelope being adapted to be mounted with respect to said roadway such that application of said load will cause deformation of said envelope; and   a fiber optic cable disposed within said region of said elastomeric envelope and running generally perpendicular to the direction of the load to be applied substantially the length of said region, said fiber optic cable including an optical fiber adapted to be connected to a signal source of light and to a receiver, said fiber optic cable being disposed within said envelope such that deformation of said envelope in response to said load will cause deformation of said fiber optic cable and its included optical fiber sufficient to detectably alter the light transmitted through said optical fiber, said envelope being mounted with respect to said roadway in such a manner that said deformation of said envelope during application of said load is limited to a predetermined amount to prevent overstressing said optical fiber upon a multiplicity of repeated applications of said load. .Iaddend. .Iadd.33. The device defined in claim 32, wherein said predetermined amount is a deformation to a position substantially flush with an upper surface of said roadway proximate to said envelope. .Iaddend. .Iadd.34. The device defined in claim 32, wherein said envelope is mounted with respect to said roadway such that at least most of said envelope lies below an upper surface of said roadway and at least a portion of said envelope is uncovered by roadway material. .Iaddend. .Iadd.35. The device defined in claim 34, wherein a small portion of said envelope protrudes above said surface of said roadway. .Iaddend. .Iadd.36. A sensing device for vehicular traffic adapted to be mounted transversely on a roadway and to receive and sense a downward load of the type imparted by a vehicle wheel as the wheel passes over the device comprising   a longitudinal elastomeric envelope having at least one deformable side in a lengthwise region of said envelope adapted to receive said load and means defining a longitudinal cavity in said lengthwise region, said envelope being adapted to be mounted with respect to said roadway such that application of said load to cause deformation of said deformable side will cause deformation of said longitudinal cavity;   a compressible cushion within said envelope in a portion of said envelope disposed below said longitudinal cavity;   a fiber optic cable disposed within said means defining a longitudinal cavity in said region of said envelope and running generally perpendicular to the direction of the load to be applied substantially the length of said region, said fiber optic cable including an optical fiber adapted to be connected to a signal source of light and to a receiver,   said fiber optic cable being disposed within said envelope such that deformation of said cavity in response to said load will cause deformation of said fiber optic cable and its included optical fiber sufficient to detectable alter the light transmitted through said optical fiber,   said envelope being adapted to be mounted with respect to said roadway as to prevent complete compression of said cushion during application of said   
     
     
        load. .Iaddend. .Iadd.37.  A sensing device for vehicular traffic mounted transversely on a roadway and adapted to receive and sense a downward load of the type imparted by a vehicle wheel as the wheel passes over the device comprising a longitudinal envelope having at least one deformable wall and means defining a longitudinal cavity in a lengthwise region of said envelope adapted to receive said load, said longitudinal cavity being subject to deformation upon deformation of said deformable wall;   a compressible cushion disposed in said envelope below said longitudinal cavity;   a fiber optic cable disposed within said cavity in said region of said elastomeric envelope and running generally perpendicular to the direction of the load to be applied substantially the length of said region, said fiber optic cable including an optical fiber adapted to be connected to a signal source of light and to a receiver;   means permitting deformation of said fiber optic cable and said included optical fiber within said longitudinal cavity of said envelope when a transverse load of the type applied by a vehicle wheel is applied to said envelope sufficient to detectably alter the light transmitted through said optical fiber.   said envelope being mounted with respect to said roadway in such a manner as to prevent complete compression of said cushion. .Iaddend. .Iadd.38. The device defined in claim 37, wherein said envelope is formed of elastomeric material. .Iadd.39. The device defined in claim 37, wherein said load sensing device is configured as a vehicle axle counter and further comprises:   means operatively connected to said optical fiber for introducing light into said optical fiber;   means operatively connected to said optical fiber for receiving said light after it has been transmitted through said optical fiber and for sensing said detectable alteration of said light caused by deformation of said optical fiber;   means operatively connected to said means for receiving and sensing said light for determining whether a predetermined threshhold value of alteration of said light exists; and   means operatively connected to said threshhold determining means for causing a count when said threshhold value of alteration of said light exists due to the passage of said vehicle wheel over said device.