Electricity: circuit makers and breakers – Weight – Treads
Reexamination Certificate
2001-03-09
2002-10-22
Scott, J. R. (Department: 2832)
Electricity: circuit makers and breakers
Weight
Treads
C200S08600A, C264S271100
Reexamination Certificate
active
06469266
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
This invention relates to a sensing device which preferably is flush with the surface of a road, for sensing the passage of vehicles over the device and, if connected with a properly programmed computer, determines the presence of the vehicle passing over the device.
(b) Description of the Prior Art
Government agencies often require the submission of reports concerning truck travel at specific locations on roadways before authorizing funding for the repair and improvement of such roadways. A number of classifying machines are currently used to provide such reports concerning truck travel. Typically, they require two axle detector inputs which are positioned a known distance apart. The classifying machine measures the time interval between axles, calculates the speeds at which the axles are travelling, counts the number of axles travelling at the same rate of speed, and then, depending upon results, records the vehicle type in a predetermined classification bin. Such studies are typically undertaken over a continuous 24 hour period and are broken down into one hour increments. Portable axle detectors which are manufactured and are presently available vary greatly in cost, durability, limitations of operation and set up procedure difficulty.
One common type of such portable axle deflector was a pneumatic road tube which was laid across the roadway. Rubber pneumatic road tubes created an air pulse when impacted by a tire. The air pulse was sensed by a counting machine and treated as an axle actuation.
Such detectors were relatively easily damaged in use. In addition, they were not capable of producing sophisticated indications of location of the vehicle wheel on the road or vehicle speed data. Moreover, when the road tube was placed across multiple lanes, it was not possible for the counting machine to discriminate from which lane the air pulse originated. In order to accomplish such lane discrimination, air tubes were typically tied off so that only tire impacts by traffic in a specific lane created an air pulse to be counted. In order to obtain a count for each of the multiple lanes, it was necessary to use separate air pulse to be counted. In order to obtain a count for each of the multiple lanes, it was necessary to use separate air pulse counting machines for each lane. Excess costs resulted from the duplication of equipment and the lengthy set up time required. In addition, vehicles travelling at low speeds across the road tubes sometimes failed to create an air pulse which was strong enough to be sensed. As a result, human classifiers were often also needed to avoid inaccurate traffic counts.
Electrical contact systems or treadle switches have also been used in counting operations, particularly in multiple lane vehicular traffic counting applications.
Examples of early patents for such sensors include the following:
U.S. Pat. No. 1,125,963, patented Aug. 27, 1929 by H. I. Morris, provided a switch, including a body of material, and electrically-conductive contacts having portions which were embedded in the material. Portions in superposed relation were arranged to contact one with the other when the body was compressed. Means were connected with the contacts to permit connection with an external circuit. Compressible means were interposed between portions of the contacts which normally maintained their contacting portions out of contact.
U.S. Pat. No. 2,067,336, patented Jan. 12, 1937, by Paver, disclosed a deformable strip with flat bottom and an inclined approach to the top. Pressure exerted by traffic deformed the strip by pressing the deformable strip and spacer locks at one or more points so as to bring strips into electrical contact at one or more places. Each of the contact strips was connected to a separate counter or recorder using connector strips which carried a plurality of flexible wires, in order to obtain a separate count for each traffic lane. One problem was that the spaced strips which were made of resilient metal, e.g., phosphor bronze, were held in separated relation by resilient or compressible spaced members in the form of short blocks of sponge rubber. Even through both the rubber and the spaced strips were resilient, the inability of the strips to move within the surrounding sponge rubber caused them to undergo significant stresses which reduced traffic cord life and caused early failures.
U.S. Pat. No. 2,611,049, patented Sep. 16, 1952, by S. S. Ruby, assigned to The Stanley Works, provided a switch including three superposed, generally-parallel imperforate sheet metal plates. The upper two plates were sufficiently flexible and resilient to permit flexing responsive to predetermined operating pressures to effect engagement between at least two of three plates. A plurality of spaced-apart, thin, non-conducting elements which were disposed on each side of the intermediate plate separated the plates in superposed parallel relationship. The elements between the bottom and intermediate plates were disposed in staggered relationship with respect to the elements between the intermediate and top plates. Means were provided for forming a first electrical connection with the intermediate plate and a second electrical connection jointly with the top and bottom plates.
U.S. Pat. No. 2,823,279, patented Feb. 11, 1958 by E. S. Schulenburg disclosed a strip that was adapted to be buried in the road. It had a switch construction in which upper and lower switch contacts were mounted to contact strips so that a contact was moved into engagement with another contact when the wheel of a vehicle depressed the top wall of the tube. The contact strips were supported by resilient fingers which maintained the separation of contacts when vehicle pressure was not present. The lower resilient fingers acted as a strain release to prevent undue pressure from being applied to the contact strips and to the contacts. The tube housing had a hollow interior into which these contacts and contact strips were assembled.
U.S. Pat. No. 2,909,628, patented Oct. 1959 by Cooper, disclosed a treadle switch with a common contact strip affixed to an upper portion of an envelope forming the top wall of a hollow longitudinal pocket in a rubber envelope. A single contact strip was positioned under the common contact strip. Segments were spaced one from the other in aligned relation and were moulded with conductors embedded therein. The conductors were connected to respective contact segments. The angular shape of the contact segments was an important design factor. Cooper relied on the inherent resiliency of the rubber envelope to flex the contact strip sequentially to make contact with each of the contact segments. In addition, a cable-like, piezo-type axle sensor had been used. Generally, this consisted of a central, or inner conductor which was surrounded by a piezo ceramic material which, in turn, was surrounded by an outer tubular conductor. Pressure on the cable-like sensor caused an electrical signal to flow between the conductors, the signal being proportional to the amount of pressure. However, this sensor was prone to false signals because the round cable was susceptible to pressure from any direction, including pressure from pavement movement, heavy weights and poor truck suspension systems. Also, it functioned poorly under light pressure from light vehicles, since piezo material was a rate-of-change, or speed-dependent material.
U.S. Pat. No. 4,782,319, patented Nov. 1, 1988 by R. Dell'Acqua et al, assigned to Marelli Autronics SpA, provided a pressure sensor including a rigid support, a diaphragm having a peripheral portion fixed by a layer of glue to the support, and a central portion spaced from the support. At least one thick-film resistor acted as a piezo-resistive transducer and was carried by the diaphragm on its surface facing the support. The diaphragm was able to deform resiliently towards the support when a pressure was exerted on its other surface. The surface of the support which was connected to the diaphragm w
International Road Dynamics Inc.
Nixon & Vanderhye P.C.
Scott J. R.
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