WO1994012730A1

WO1994012730A1 - A surface mounted sensor

Info

Publication number: WO1994012730A1
Application number: PCT/AU1993/000611
Authority: WO
Inventors: Andre Soussa
Original assignee: Awa Limited
Priority date: 1992-12-02
Filing date: 1993-11-30
Publication date: 1994-06-09

Abstract

A generally rectangular road mounted sensor (1) includes a sensor element in the form of a plurality of loops of a conductor (2) enveloped within top and bottom flexible laminar sheets (3, 4). The bottom sheet (4) includes an integral homogeneous pressure sensitive surface conforming adhesive for securing the sensor (1) to a road surface.

Description

Title: A SURFACE MOUNTED SENSOR

Technical Field

The present invention relates to a sensor and in particular to a surface mounted sensor.

The invention has been developed primarily for use as a road mounted sensor for determining the presence or passage of vehicles at a predetermined location and will be described hereinafter with reference to that application. However, it will be appreciated that the invention is not limited to this particular field of use. Background Art

Hitherto, attempts have been made to improve the regulation of traffic flow by installing inductive loop sensors within a road surface adjacent the stop lines associated with a particular intersection. The use of such sensors allows suitable programming of the traffic lights at the intersection in response to the presence of vehicles at respective stop lines.

The installation of such inductive loop sensors has involved the cutting or severing of the road surface to produce a number of narrow interlinked channels into which one or more turns of conductor are placed. Thereafter, some form of sealant is inserted into the channels both to prevent water disrupting the sensor and to compensate for the loss of road surface integrity created by the channels.

The installation of such sensors takes a considerable amount of time given that the channels must be produced, the conductor and sealant inserted into the channels, and the sealant cure before the road is again suitable for use. Furthermore, the dynamic nature of road surfaces often results in the sealant being damaged which makes the sensors susceptible to water damage and interference. Such movement may also break one or more of the conductors and thereby render the sensor inoperative.

Once such damage has occurred it is necessary to cut or destroy the road surface further in order to carry out repairs or to install a replacement sensor. Disclosure of the Invention

It is an object of the present invention, at least in its preferred embodiment, to overcome or substantially ameliorate at least some of these deficiencies of the prior art. According to a first aspect of the invention there is provided a surface mounted sensor including a sensor element enveloped within top and bottom flexible laminar sheets, the bottom sheet including a surface conforming adhesive for securing the sensor to a support surface.

Preferably, the sensor includes first and second adhesive laminar sheets which are interleaved with the sensor element and respective top and bottom sheets for encapsulating the element. More preferably, the first and second adhesive sheets abut and coextend with opposing sides of respective top and bottom sheets.

Preferably also, the periphery of all the sheets are fused together and the top and bottom sheets are penetration resistant.

According to a second aspect of the invention there is provided a sensing system including a plurality of interlinked sensors as described above, wherein respective sensor elements are interconnected to form a composite element.

Preferably, each sensor includes a sensor element defined by at least one or more strands of conductor which are able to be electrically connected to respective conductors in at least one adjacent sensor. Preferably also, the sensors are arranged to form a square or rectangular configuration wherein ends of adjacent sensors abut or overlap. Brief Description of the Drawings

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a partly cut away top view of a surface mounted sensor according to a first aspect of the invention;

Figure 2 is a cross-section taken along line 2-2 of Figure 1;

Figure 3 is a sensing system according to a second aspect of the invention; and

Figure 4 is a cross-sectional view of a sensor element support means. Modes For Carrying Out The Invention

Referring to Figures 1 and 2, a generally rectangular road mounted sensor 1 includes a sensor element in the form of a plurality of loops of a conductor 2 enveloped within top and bottom flexible laminar sheets 3 and 4. The bottom sheet 4 includes an integral homogenous pressure sensitive surface conforming adhesive for securing the sensor 1 to a road surface.

The sensor also includes first and second adhesive laminar sheets 5 and 6 which are interleaved with the sensor element 2 and respective top and bottom sheets 3 and 4 for encapsulating the conductor. Both sheets 5 and 6 abut and co-extend with respective sheets 3 and 4. Sensor 1 extends from a first end 11 to a second end 12 and has a length and width of about 90 cm and 20 cm respectively. The sensor is able to be manufactured in many other configurations to produce inductive loops of different areas or shapes.

Sheets 4, 5 and 6 are self healing and sheets 3 and 4 are penetration resistant. This combination prevents damage to the conductor either by projections in the road surface or any loads applied to sheet 3. Additional penetration resistant sheets are included in high load applications. For example, a pair of such opposed sheets sandwiching the sensor element provides added protection against damage.

As illustrated, all the sheets are coextensive and fused together along their peripheries to provide further cohesion between these sheets. Additionally, such fusing prevents the ingress of water or moisture between the sheets to maintain the conductor 2 in a substantially waterproof environment. Depending upon the materials used, the fusing is achieved by either passing hot air along the periphery, or alternatively by heat welding.

Conductor 2 includes two ends 15 and 16 which extend inwardly to provide a convenient connection with a dual feed cable 17. Cable 17 extends between inner and outer ends 18 and 19 to allow any signals carried by conductor 2 to be communicated to a suitable remote sensing device. Cable 17 is electrically connected to ends 15 and 16 by soldering of the like, as well as being securely anchored between sheets 3 and 4 to prevent inadvertent disconnection of the sensor from the ends of conductor 2.

The length of cable 17 is varied to the particular circumstances. However, it is preferred that adjacent end 18 the cable is surrounded by insulation 20 to provide further reinforcement. Both cable 17 and insulation 30 are secured by a mechanical anchor 21 which transversely extends across sensor 1. The anchor 21 ensures a secure retention of cable 17 between sheets 3 and 4 by spreading any forces on the cable over a large area of the sensor. Anchor 21 also facilitates the isolation of the connection between ends 15, 16 and 18 from any force acting on the end 19 of cable 17.

Sheet 4 preferably includes a non-polymerising organic adhesive which is pressure sensitive. The adhesive is also surface conforming and additionally contains some form of fibre reinforcing. This adhesive sheet would initially be covered with a backing sheet which is removed immediately prior to application of sensor 1 to the road surface.

Sheet 3 is preferably durable, pliable and flexible and in one particular embodiment is constructed from a halogenated aromatic thermoplastic polymer. More preferably, the polymer includes a fibre reinforcement. This material is also puncture and tear resistant which furthers the protection offered to the conductor 2.

In alternative embodiments sheet 3 is constructed from one or a combination of the following materials: polyester; rubber; copolymer thermoplastic; polyoelofins; and other flexible polymer sheets.

Internal adhesive sheets 5 and 6 are required to remain highly flexible while maintaining the separate sensor components together. In this embodiment use is made of a non-polymerising organic adhesive in both layers, however, other similar adhesives are available.

If required, sensor 1 includes a plate 22 disposed between sheets 5 and 6 and which contains information about the sensor.

In use, the preferred sensor 1 is simply placed on an appropriate portion of a road surface with sheet 4 being brought into abutment with that surface. The distribution of the preferred adhesive on layer 4 in combination with its surface conforming properties result in the sensor being immediately available for trafficking. That is, the road traffic need be only briefly interrupted. This interruption time to the normal traffic flow is also reduced due to the sensor not requiring any destruction of the road surface.

The ease of placement involves minimal installation cost and the durable, flexible and self healing nature of the sheets also provides for maintenance cost savings by a substantial reduction in water, puncture or tearing damage.

The preferred sensor is fully constructed before installation and as such can be tested for compliance to performance specifications before the unit is installed.

Although the invention has been described in relation to inductive loop sensors, other sensor elements are able to be used. For example, the sensor elements can include one or a combination of the following: switches; weigh-in-motion devices; proximity switches; microwave transducers; ultrasonic transducers; infrared transducers; and antennas.

The illustrated sensor 1 is suitable for use on all sealed road surfaces and is particularly suitable for surfaces which experience a large degree of movement. This may be due to relatively unstable foundations, a large amount of heavy traffic or the like. The flexible nature of the sheets 3, 4, 5 and 6 allows the sensor to conform to the adjacent road surface although the contour of that surface is being continually deformed in response to the load to which it is subjected.

On less dynamic road surfaces, such as prestressed concrete, the problem of puncturing is more relevant. However, the self healing and flexible properties of the sheets 4, 5 and 6 ensure that any protrusions are less detrimental to the operation and lifespan of the sensor.

The preferred sensor is satisfactorily adhered to the road surface due to the combination of the adhesive being distributed over substantially all of sheet 4 and the flexible nature of the sheets. Viscous or fluid ^' adhesives can be advantageously used and contribute to the flexibility of the sheets.

The sensor can be produced in a variety of lengths and widths, as discussed above. Furthermore, a sensing system can be constructed from a plurality of the sensors. For example, if an inductive loop of large area is to be produced two or more like spaced apart sensors can be arranged in series by appropriately connecting respective cables 17. Alternatively, four sensors are arranged in a square configuration as shown in Figure 3. The conductors in each sensor include one or a plurality of separate strands 23 of conductor which are interconnected with respective strands in adjacent sensors to form a composite sensing element. The sensors also include ends which abut or overlap with the ends of adjacent sensors to provide continuous protection to the strands. Collectively the separate strands form a plurality of loops for providing a signal indicative of the inductance in the vicinity of the sensing system. Such a sensing system enjoys all the benefits of sensor 1 and provides a cost effective system especially where sensing systems of large dimensions are required.

Any variety of configurations can be produced as required. For example, differing configuration are preferred for detecting the presence of larger vehicles such as buses or trucks.

In applications where a sensor having a lower profile is required, adhesive sheets 5 and 6 are omitted, and the adhesive nature of sheet 4 ensures that the separate components of the sensor are maintained in a fixed configuration. In this embodiment it is preferred that sheet 3 has a high skid resistance as well as including a textured top surface.

A further preferred embodiment of the invention includes a support element which co-extends with the sensor element. One particular form of support element is illustrated in Figure 4. The element 25 is preferably formed in a continuous length and includes a base 26 for abutting layer 6 and two opposed inwardly inclined sides 27 and 28. These sides terminate in a top 29 which includes a continuous channel 30 for retaining therein the conductor loops 2.

Element 25 is either rigid or semi-rigid and is non-metallic. Preferably, the support element is produced from a polymer or polymer composite. For example, in one particular embodiment fibreglass is used.

Element 25 can comprise a number of separate spaced apart support elements although it is preferred that substantially all the length of loops 2 are retained within a channel 30. In this preferred form element 25 will provide a maximum stabilising effect and more effectively protect loops 2. By ensuring the loops 2 are maintained in a fixed configuration the inductance of the loops can be maintained at a substantially constant value.

Sides 27 and 28 are inclined to provide a ramping effect for vehicles traversing the sensor. Accordingly, the propensity for vehicles to force the sensor in their direction of travel will be reduced.

Although the invention has been described with reference to particular examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

CLAIMS : -

1. A surface mounted sensor including a sensor element enveloped within top and bottom flexible laminar sheets, the bottom sheet including a surface conforming adhesive for securing the sensor to a support surface.

2. A sensor according to claim 1 including first and second adhesive laminar sheets which are interleaved with the sensor element and respective top and bottom sheets for encapsulating the element.

3. A sensor according to claim 2 wherein the first and second adhesive sheets abut and co-extend with opposing sides of respective top and bottom sheets.

4. A sensor according to any one of the preceding claims wherein all of the sheets are fused together along their edges.

5. A sensor according to any one of the preceding claims wherein the top and bottom sheets are penetration resistant.

6. A sensor according to any one of the preceding claims wherein said sensor element is electrically accessible via a cable extending from said sheets, wherein said cable is mechanically anchored within said sensor by anchor means extending substantially perpendicularly to said cable at the point of connection therebetween.

7. A sensor according to any one of the preceding claims wherein said sensor element is retained within a rigid or semi-rigid support means.

8. A sensor according to claim 7 wherein said support means includes a base, a pair of upwardly and inwardly directed sidewalls extending from said base, and a top having a channel for receiving the sensor element.

9. A sensor according to claim 8 wherein said support means forms a continuous body supporting substantially all of said sensor element.

10. A sensing system including a plurality of interlinked sensors as defined in any one of the preceding claims, wherein respective sensor elements are interconnected to form a composite element.

11. A sensing system according to claim 10 wherein each sensor includes a sensor element defined by at least one or more strands of conductor which are able to be electrically connected to respective conductors in at least one adjacent sensor.

12. A sensing system according to claim 11 wherein the sensors are arranged to form a square or rectangular configuration where ends of adjacent sensors abut or overlap.