Roadway Sensor Systems

In my above-identified application Ser. No. 406,345, I disclose roadway sensors in which a piezoelectric sensor is carried within an envelope and a linear weighting member is substantially coextensive with the sensor to maintain the sensor on the roadway despite being traversed by heavily loaded trailer trucks traveling at high speeds generating trailing air turbulences having the effect of sweeping the roadway. The weight member is uniformly distributed along the roadway portions of the sensor strip to maintain the sensor on the roadway and substantially immune to air effects generated by vehicular traffic on the roadway, such as a loaded truck trailer traveling at high speeds. Preferably the weight is a flat malleable metal such as a lead strip having a weight of about one pound per linear foot. For lower speed roadways and/or roadways restricted to smaller or lighter vehicles (which cause less air flow effects) a lower distributed weight can be used, for example, one-half pound per linear foot of sensor.

Since the weight member, in a preferred embodiment, is a strip of lead, preferably flat for low vertical profile purposes, and since roadways are not flat, e.g., road surfaces wear and wide grooves develop over time and create a cavity or groove where the wheels travel, the flat malleable lead strip adapts to such cavities and undulations and curvatures in the roadway and hugs the surface so that the sensor does not bounce and oscillate for a long period of time as would be the case if the sensor were mounted on a rigid member, such as a rigid steel strip. During the period of time when the rigid steel strip is vibrating, the sensor output signal would mask legitimate pulses from a tire of a closely spaced axle, for example.

The weighted sensor systems disclosed in my above-identified applications monitors a variable number of lanes simultaneously, preferably from one to six lanes or more. In a worst case situation, six lanes, this would require 12 feet times 6 equals 72 feet, plus 8 feet for the shoulder or an 80 foot length. With a rigid steel base member, this would be difficult to install in the field. In my above-identified applications, I teach that the sensor is maintained essentially motionless when a vehicle is traversing the sensor if the linear weight is sufficient to avoid movement effects due to air flow generated by the moving vehicle. Large trucks with wide square backs are one of the worst. As discussed above, experience has demonstrated that a weight of one pound per foot is good for traffic up to speeds of about 85 mph. In order to achieve this weight, a 2" wide piece of lead 3/32" thick is glued to a five ounce per foot elastomeric or rubber carrier. The completed assembly is approximately one pound per foot. In contrast, because the specific gravity of steel is approximately 7.89, and that of lead is 11.35, the steel would need to be thirty percent thicker than lead (0.093" vs. 0.121"). This thicker steel would make the handling of a long sensor very difficult and cause the strip to vibrate as discussed above and, therefore, an integral steel strip is not able to perform according to the invention.

The present invention adapts this distributed weight concept of my earlier above-identified applications and, in addition, provides a unique sensor carrier which is both coilable and reusable and refurbishable and adaptable to wide varieties of roadway conditions and is easily adaptable to multiple lane roadways.

According to one embodiment of the invention, a carrier made of an extruded or molded roadway rubber (such as Neoprene, etc.) is provided with one or more sensor carrying grooves and, depending on the number of lanes of roadway traffic to be sensed, a plurality of parallel signal conductor carrying grooves. In a preferred embodiment, the sensor carrier has an upper surface which is ramped and a lower surface in which are formed a cavity or recess for receiving the weight and has a cross-section corresponding to the cross-section of the weight. In this embodiment, the top surface of the cavity is provided with sensor receiving grooves and coaxial signal conductor receiving grooves. In a preferred embodiment, the sensor receiving grooves are lipped whereas the coaxial signal conductor receiving grooves are deeper and U-shaped. A flat weight member is secured in the cavity or recess to the lower surface of the carrier (the top surface of the cavity), preferably by an adhesive such as a double-faced tape. The weight is lead, it is preferably provided with a protective overcoat, such as a flexible polymer coating. A layer of nylon reinforced tape is adhered to the bottom surface of the lead strip which makes contact with the road. An important feature of this assembly is that it is able to adapt to curvature and undulations in the roadway and hug the roadway surface in such a way as to eliminate or minimize extraneous signals caused by the sensor being bounced up and down on the roadway by traffic and/or by aerodynamic effects caused by high speed heavy vehicular traffic thereover.

In some cases, coaxial cable can have a piezoelectric effect, and enlarged coaxial cable grooves disclosed herein mitigate this effect.

In further embodiments, to protect the lead strip the cavity is formed as a totally enclosed passage or aperture in the elastomeric carrier and the lead weight, with a protective polymer plastic overcoat and lubricated with a solid lubricant such as Teflon.TM. is inserted into the cavity. As a further embodiment, the underside of the elastomeric carrier can be slit to enable easy insertion of the lead strip in the enclosed cavity.

The carrier/sensor of the present invention has the following benefits over road tubes and other prior art systems:

(a) Conforms to and hugs roadway surface;

(b) Simultaneous multiple individual lane sensing;

(c) Adjustable, ideal for driveway and turning movement studies;

(d) Excellent for speed, volume and classification sensing;

(e) Eliminates the need for a mechanical air switch;

(f) Eliminates recording failures due to pin hole air leaks in road tube;

(g) Eliminates recording failures due to water in the road tube;

(h) Eliminates recording failures due to nails coming loose due to high tension stretch on the road tube;

(i) Greater accuracy;

(j) Safe, quick installation; and

(k) Rugged, long lasting and reusable.

Traffic engineers throughout the world have been seriously hampered in their efforts to perform volume, speed and classification studies when road tubes are utilized for input to their traffic recorders. The portable over the pavement piezoelectric polymer sensor and method disclosed herein offers the traffic engineer a means of generating electrical impulses when the vehicle's axle traverses the sensor assembly. This invention provides the traffic engineer volume, speed and classification data which would be virtually impossible to record with existing road tubes. Using this method also enables the traffic engineer to field install the piezoelectric sensor assembly in inclement weather on the roadway and to adjust its active detection area to the requirements of the data capture application. An important advantage of this coilable, removable and reusable sensor is its safety and ease of installation. There is no need to dart in and out of traffic attaching clamps or adhesive tape at different points in order to stabilize the sensor. Its rugged construction and wide temperature operating range make it ideal for slow and fast moving traffic in extremely wet or dry weather conditions.

The above and other objects, advantages and features of the invention will become more apparent when considered with the following specification and accompanying drawings wherein:

FIG. 1a is a sectional and isometric view of a roadway sensor disclosed in my above-identified application Ser. No. 07/880,410,

FIG. 1b is an enlarged view of a sensor carrying groove portion of FIG. 1a,

FIG. 1c shows the assembly of FIG. 1a, coiled on a form for transportation,

FIG. 2 illustrates a preferred embodiment of the present invention,

FIG. 3 is an isometric view of the embodiment shown in FIG. 2 on a multi-lane roadway,

FIG. 4 is a cross-sectional view of a further modification of the invention,

FIG. 5 is an isometric view of the lead carrier and sensor, coaxial cable groove pattern in the lead weight shown in FIG. 4, and

FIG. 6 illustrates a further embodiment of the invention.

FIGS. 7-10 illustrate further embodiments of the invention.

A basic construction from application Ser. No. 07/880,410 is illustrated in FIG. 1a wherein a roadway sensor assembly 10 is comprised of an extruded flat elastomeric carrier 11 having an upper surface 12 which may be ramped to better accommodate tire forces and a flat planar lower surface 13. Lower surface 13 is provided with sensor groove 14 which has a narrow mouth 15 and an enlarged sensor carrying portion 16. Mouth 15 has sidewalls which can be spread apart sufficiently to allow the sensor cable to be snugly seated in the enlarged base 16 and then spring back to snugly enclose the sensor in retention position. A piezoelectric sensor cable assembly 17 is carried in sensor groove 14. Piezoelectric sensing cable assembly 17 can be of the type manufactured by Atochem Corporation of Norristown, Pa. In such cables, a piezoelectric plastic polymer such as KYNAR.TM., is provided with sensing electrodes (not shown) which are connected to a flexible coaxial cable 18, which can be encased in a protective envelope. Other forms of sensor cables are shown in my above-identified application Ser. No. 07/880,410.

The coaxial cable 18 has a conventional signal cable connector 19 for secure electrical connection or coupling of analog signals generated by vehicular traffic to recorder and counter circuit 20 of the type disclosed in U.S. Pat. No. 4,258,430 for example, owned by the assignee hereof.

The carrier 11 with piezoelectric sensor cable assembly 17 installed and snugly seated in groove portion 16 has a linear weight 21 secured, preferably by a flexible adhesive 21A, to the lower surface 13 of flat carrier 11. Weight 21 can be of a type disclosed in my above-identified applications, and preferably is a flat malleable metal strip made of lead, for example. The weight and the carrier have a weight per unit length of at least about one pound per foot for heavily traveled high speed highways. For three twelve foot roadways, this amounts to about 36 pounds. For lower speed roadway uses, the weight can be less as disclosed above and in my above-identified applications.

As shown in FIG. 1c, the sensor assembly 10 is coilable on a form 23 so that it can be easily unrolled upon a roadway. The weight will cause the sensor assembly to hug the roadway and because the lead is malleable, roadway traffic will cause the assembly to closely conform to the roadway surface including roadway undulations.

Referring now to FIG. 2, sensor carrier 30 includes an extruded, flexible member 31 having a ramped or sloped leading (up road) edge 32 which is engaged first by the vehicle tires and a slightly chamfered or beveled trailing edge 33. Member 31 is made of a conventional roadway grade elastomeric material such as tough Neoprene rubber, or the like. The dimensions are exemplary and FIG. 2 is slightly enlarged. The lower surface of member 31 has a rectangular cavity or recess 34 which has leading, up-road or upstream wall 35 and trailing down-road or downstream wall 36 and an upper surface 37'.

Sensor groove 38 has a mouth 39 defined by lips 40 and 41, which, in conjunction with the dimension of the piezoelectric sensor 42, is adapted to snugly retain the sensor in position on the up-road or leading edge of linear weighting member 45. A layer of nylon reinforced tape 45N is adhered to the bottom surface of the lead strip which makes contact with the roadway surface.

It has been found that when the piezoelectric sensor is on the leading edge or within 1/2 inch of the leading or upstream edge of the lead weight 45 in the unit, impact measurements of the tire are most accurate and least susceptible to being masked by subsequent effects of the vehicle suspension and/or rebound as the tire moves over the unit. The piezoelectric sensor cable can be so sensitive that even with the extremely low vertical profile (0.375 inch), effects of the vehicle suspension can be detected and ambiguities can be eliminated or minimized by placement of the sensor cable as close to the leading edge of the unit as is practicable.

As shown in FIG. 3, the unit is designed for a multiple lane roadway. In this case, sensor groove 38 contains four sensors aligned in groove 38 and spanning the individual lanes: piezoelectric sensor 42-1 for lane number #1, piezoelectric sensor 42-2 for lane number #2, piezoelectric sensor 42-3 for lane number #3, and piezoelectric sensor cable 42-4 for lane number #4. Each piezoelectric sensor cable may have a connector (not shown) for connection to a coaxial cable leading to an electronic counter and/or analyzer of the type referred to above in connection with FIG. 1. Piezoelectric sensor 42-2 is connected to coaxial cable 46-2 which is carried in U-shaped coaxial cable groove 38-2, piezoelectric sensor 42-3 is connected to coaxial cable 46-3 in U-shaped groove 38-3 and piezoelectric sensor 42-4 is connected to coaxial cable 42-4 in groove 38-4, cross-over cut-outs 47, 48 and 49 enable the coaxial cable to be fitted into their respective grooves.

Some coaxial cables have insulator portions which may have significant piezoelectric properties, and to mitigate or minimize inducing piezoelectric potentials in the coaxial signal carrying cables or wires, the grooves 38-2, 38-3 and 38-4 are made "U" shaped and slightly deeper so that significantly less of pressure on the elastomeric member is transmitted to these coaxial cables. In contrast, it will be noted that the piezoelectric sensor cables 42-1, 42-2, 42-3 and 42-4 are relatively snug in groove 38 so that the effect of the pressure on the upper surfaces US of member 31 are effectively transmitted to the piezoelectric sensors while in contrast, in regards to the coaxial signal carrying cables, the U-shaped grooves 38 provide a small air space above the cable to prevent or mitigate piezoelectric voltages being induced in the coaxial cables.

Lead weight member 45 is provided with a protective flexible polymer coating 45C to prevent spalling and oxidation of lead strip 45. Weight 45 is adhesively secured in the recess or cavity 34 by adhesive, preferably a double-faced adhesive tape 50.

Another use for this sensor assembly of this invention is the utilization of the sensor's ability to generate different amplitude pulses based on the weight of the vehicle's axle(s). using the weight information in conjunction with axle spacings results in obtaining a more refined selection of vehicles when vehicles exhibit similar axle spacing characteristics, e.g. truck with a trailer versus a car with a boat. Electronic circuitry in the recorder would quantify the energy (e.g. weight and speed) in the pulse in order to distinguish between a car and a truck which normally has a weight difference of 2-6 times. This resultant data would become part of the classification software algorithm used within the recorder to separate vehicle types for accumulation and storage in memory.

The sensor assembly could be assembled using a polled sensor cable as opposed to a separate sensor and a separate coax cable. The use of a polled sensor cable has the advantage of eliminating the need of making a mechanical connection between the sensor and the coax cable. The polled sensor cable is a single piece of cable with an active area of approximately 8 feet and an inactive area to carry the signal to the recorder of approximately 100 to 200 feet. Another advantage in using the polled sensor cable would be quicker assembly due to the sensor and cable being in their own groove. In such case, in FIGS. 2 and 3 the grooves 382, 38-3 and 38-4 are made similar to sensor groove 38.

Although the preferred embodiment of the invention refers to a piezoelectric cable as the sensor element, piezoelectric film, as disclosed in my application Ser. No. 346,685, could be used as the sensor element. The advantages of construction on a single substrate would be a much lower profile and shorter assembly time. The disadvantage would be the pre-designated fixed active sensing area of the assembly. In this case, individual wafers of film could be utilized to preserve the lower profile at the expense of making the assembly wider.

The invention can also be used to make speed measurements. A pair of spaced sensor grooves, aligned in a given lane can be used to measure speed of a vehicle in the manner disclosed in Dixon application Ser. No. 07/880,638 entitled "VEHICLE SPEED MEASUREMENT APPARATUS", and assigned to the assignee hereof.

Traffic engineers throughout the world have been seriously hampered in the efforts to perform volume, speed and classification studies when road tubes are utilized for input to their traffic recorders. The piezoelectric sensor disclosed herein offers the traffic engineer a means of generating electrical impulses when the vehicle's axle traverses the sensor assembly. This invention provides the traffic engineer volume, speed and classification data which would be virtually impossible to record with existing road tubes. Using this method also enables the traffic engineer to field install the piezoelectric sensor assembly in inclement weather on the roadway and to adjust its active detection area to the requirements of the data capture application.

There are definite advantages in not having to glue, tape or nail the sensor to the roadway. As noted above, experience has shown that tape and glue do not stick to moist or wet roads. Nailing the assembly in place is time consuming, therefore, for safety purposes, vehicles would need to be redirected for a short period. This redirection of traffic is usually done only for serious road repair work, not sensor placement work.

In the embodiment illustrated in FIGS. 4 and 5, the sensor positioning grooves and coaxial cable grooves are formed in the upper surface 60 of the lead weight member 61. Flexible protective polymer coating 45C' prevents erosion and spalling of the lead. Sensor groove 62 has a first portion 62-1 for receiving a polled sensor cable 63-1 having an integrally connected coaxial cable 64-1 which is connected to electronic recording and analyzing circuitry shown in FIG. 1. Similarly, sensor groove 62 has a second portion 62-2 and third portion 62-3 for receiving piezoelectric sensors 63-2 and 63-3, respectively, which may be polled and have integrally connected coaxial cables 64-2 and 64-3 in grooves 65 and 66, respectively. Groove 65 has an off-set portion 65-0 in which the coaxial cable 64-2 is seated and, likewise, groove 66 has an off-set portion 66-0 in which is seated coaxial cable 64-3. Grooves 65 and 66 may be slightly deeper than groove 62 to minimize piezoelectric voltages being induced in the coaxial cable portions of the assembly. A foam cushion (not shown) may be positioned and adhered over the coaxial cable portions to further minimize inducing voltages as in the coaxial signal carrying cables. Because the lead metal is relatively soft and malleable, the grooves for sensors and coaxial signal cables can be easily embossed or formed into the upper surface.

A retaining sheath 70 can be applied either as a shrink fitted plastic member or as a conformal coating, to retain the sensors and coaxial cables in their respective grooves and serve as a further protective layer for the lead strip. Finally, a road-grade elastomeric envelope 71 such as Neoprene rubber is applied. Envelope 71 can be extruded on the assembly shown in FIG. 5 after application of retaining conformal member or protective layer or coating 70, or be one or two strips of road-grade elastomer, such as Neoprene, glued together along one edge to form the envelope (one strip) or glued along two edges (for two strips). One important advantage of this embodiment is that it has a very low vertical profile.

The assembly can be coiled on a coil form such as shown in FIG. 1, for rapid dispensing onto a roadway and rapid retrieval from a roadway.

In the embodiment shown in FIG. 6, the grooves are partially in the elastomeric member and partially in the lead weight member 83, which has a protective polymer plastic covercoat 45C". Note that the sensor groove 80 in the elastomeric member 81 and, sensor groove 82 in the weight member 83 retain sensor 84 in very precise fixed positions on the lead weight. Coaxial cable grooves 85 and 86 in lead weight 83 are deep and cooperating grooves 87 and 88 in elastomeric member 81 coact to minimize the generation of voltages in coaxial cables 89 and 90. An adhesive 91 retains the lead weight 83 in recess 34'.

In the embodiments of FIGS. 7-10 (shown in section) a totally enclosed cavity passage or space is provided in the elastomeric strip and the lead weight with or without a protective polymer over-coat, with or without a lubricant, is inserted into the cavity passage or aperture. Referring to FIG. 7, extruded elastomeric carrier strip 80 has a ramped leading or up-road edge 81 which is first engaged by the vehicle wheels, a chamfered trailing or down-road edge 82 and elongated sensor bore 83 with a slit 84 allowing sensor cables 85 (if desired, one for each lane of the multi-lane roadway) to be inserted in bore 83. Bore 83 closely conforms to the outside diameter of the sensor cable 85. Coaxial signal cable bores or passages 86, 87 and 88 are connected to their respective piezoelectric sensors via short cross-over cut-outs (47, 48 and 49) in the elastomeric material between bores in the manner discussed above in connection with FIG. 3. Coaxial signal carrying cables 89, 90 and 91 are fitted into bores 86, 87 and 88, respectively. The dimensions are exemplary in FIG. 7. Note that bores 86, 87 and 88 are significantly larger than the coaxial signal cables 89, 90 and 91, respectively, to minimize inducing ambiguous voltages in these coaxial cables. Weight cavity, passage or aperture 89 is adapted to retain lead weight strip 90 which may have a protective polymer coating or a solid lubricant coating such as Teflon.TM., optional slots 92, 93 and 94 facilitate fitting the coaxial signal cables in the respective grooves.

In the embodiments shown in FIGS. 8-10, like parts are provided with primed numerals.

In FIG. 8, the weight cavity 89' is provided with very shallow ribs 96 to reduce friction lengthwise and to facilitate introduction of the weight axially or lengthwise of the cavity 89. Note that ribs 96 are spaced a distance from the sensor bore 83 so that they do not interfere with the inducing of signals in sensor cable 85. In the embodiment shown in FIG. 9, the bottom portion 97 is slit as at 98 so that weight 90" can more easily be introduced into weight cavity 89". A reinforced nylon tape 101 is adhered to the roadside engaging surface of elastomeric carrier member 80". In the embodiment of FIG. 10, the sides 9 and 99' to each side of slit 98' are strengthened with Kevlar.TM. strands 100.

While preferred and exemplary embodiments of the invention have been illustrated and described, it will be appreciated that various other modifications and adaptations of the invention will be apparent to those skilled in the art and it is intended that such modifications and adaptations be encompassed by the claims appended hereto.