Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1997-10-22
2002-10-22
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S040600, C428S343000, C428S900000, C428S143000, C428S149000, C428S156000, C428S325000, C428S690000, C428S690000, C428S690000, C428S690000, C252S062540, C264S108000, C264SDIG005, C180S167000, C180S168000, C340S901000, C340S905000, C404S006000, C404S009000, C404S016000, C404S014000, C701S205000
Reexamination Certificate
active
06468678
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of magnetic articles, in particular, to articles which may be applied to a roadway, warehouse floor, and the like, to guide a vehicle or other mobile object thereon.
2. Related Art
Safer, more efficient and more accessible transit for citizens is a high priority for many governments. Public service workers, public transit vehicles and emergency vehicles must have the capability to move more rapidly and safely on roadways in a variety of weather conditions.
Inclement weather and even blinding sunlight or oncoming traffic light present special problems both for existing travel systems and for guidance systems that offer lateral vehicle control. An unfortunate number of tragic accidents have occurred due to people driving under the influence of alcohol and over-the-counter medicines. A magnetic, lateral guidance system addresses the special needs of drivers who cannot, for whatever reason, see the road.
Snowy conditions, fog, heavy rain, blowing dust and smoke are examples of challenges to vehicle drivers. Snowy weather presents particularly challenging driving conditions to snowplow drivers trying to clear lanes in blowing snow or when lane markers are obstructed by snow. Furthermore, reduced visibility brought by blowing snow has caused numerous tragic accidents when automobile drivers have rear-ended snowplows traveling slower than surrounding traffic. Winter weather will continue to challenge any intelligent transportation system (ITS) in which vehicles move at faster speeds and closer together on more crowded roadways.
A magnetic system offers several advantages:
it is not adversely affected by weather conditions;
it does not require expensive video or other radio frequency equipment;
the system's operating costs remain low since the marker is passive—no power is required to make a magnetic marker function;
the system's durability means that, once installed, a magnetic marker will likely last beyond the life of the roadway (typical roadways have lifespans of six to eight years) and may even be reprogrammed while still on the roadway; and
removable magnetic markers offer the convenience of being able to remove the marker from the road and “reprogram” it.
Several alternative methods for sensing the lateral position of a vehicle on a roadway have been suggested. One option involves the use of visible signs or markings and optical sensors. A system that relies on optical sensors can be expected to have reliability problems. The signs or markings can be obscured by dirt, ice, or snow, and visibility can be impaired by fog, blowing snow, blowing dust, and the like. Furthermore, for night usage, a considerable amount of energy must be expended, either to illuminate the signs or to send out a beam from the sensor.
Another approach is the use of radar reflective markers with a radar ranging system on the vehicle. Both the markers and the radar detection systems are expensive in comparison with the magnetic system proposed herein. Metallic radar reflective markers embedded in the roadway are likely to have durability and corrosion problems.
Two known magnetic marking systems deserve attention. One proposal is to use a series of magnetic “nails” embedded in the roadway. Because the field strength decreases as the cube of the distance from such a dipolar magnetic, field source, the “nails” would have to be fairly closely spaced to produce a useful signal. Installation costs would be high since this requires boring holes in the roadway, and materials costs would be very high if the most powerful rare earth magnets were used to minimize the size and maximize the spacing. Boring holes in the roadway may also lead to stress concentration and premature pavement failure, which may be exacerbated by corrosion of nails. The use of simple ferrous metal spikes would not provide the alternating signal desirable for effectively separating the position signal from noise.
Another magnetic marking system employs a magnetic paint to produce magnetic stripes on the roadway. With the typical thickness of paint layers, it would be difficult to obtain a good magnetic signal. If the thickness of the paint were built up to obtain a good magnetic signal, its durability would be poor. The paint stripe could be magnetized only after it had dried. A specially designed magnetizing fixture would have to be driven along the strip. Because of limitations in the magnetic field produced by such a fixture, the coercivity of the magnetic material would have to be limited to about 1000 oersteds, making it susceptible to erasure, and it would be difficult to produce anything other than a longitudinal magnetization pattern.
Conventional conformable non-magnetic pavement marking sheet materials typically comprise a polymeric material, such as one that could be crosslinked to form an elastomer, but which is not crosslinked in the sheet material and thereby provides desired viscoelastic properties. A blend of this material with other polymeric materials and non-magnetic inorganic fillers has been found to provide properties that give long-lasting pavement markings having good conformability to a roadway surface, abrasion resistance, tensile and tear strength. The composition may have glass beads embedded in its upper surface for retroreflective purposes. An example of this type of pavement marking is disclosed in U.S. Pat. No. 4,490,432. Briefly, these advantages can be obtained with a composition that comprises 100 parts of non-crosslinked elastomer precursor; at least 5 parts of a thermoplastic reinforcing polymer (such as a polyolefin) which is dispersed in the elastomer as a separate phase (i.e., because of insolubility or immiscibility with the other polymeric ingredients) and softens at a temperature between about 75° C. and 200° C.; a particulate inorganic filler dispersed in the composition; and preferably an extender resin, such as a halogenated paraffin. This composition is processable on calendering rolls into a thin sheet material, generally between about ¼and 3 millimeters in thickness. The separate-phase nature of the reinforcing polymer is considered desirable, in that it is believed that the polymer becomes oriented during the calendering operation and reinforces the sheet material. Such a reinforcement is indicated by the fact that the tensile strength of the sheet material is significantly stronger in the downweb direction (i.e. in the direction of calendering) than in the crossweb, or transverse, direction.
U.S. Pat. No. 5,316,406 discloses a roadway marker rubber-like strip in which the upper layer is deformed into protuberances such as wedges or ridges, preferably provided with a coating of exposed retro-reflective beads, that have been cross-link-vulcanized to provide the same with memory that permits shape restoration following depression by vehicle traffic, and a cold-flow un-vulcanized bottom layer adhered to the roadway and conforming without memory to the same under vehicle traffic.
Other conformable non-magnetic pavement markings are disclosed in U.S. Pat. No. 4,069,281 (Eigenmann), Italian Patent Application No.MI 003213/91A (which discloses a conformable layer comprising a saturated acrylonitrilel butadiene elastomer grafted with a zinc salt of methacrylic acid), and U.S. Ser. No. 08/056,420 (filed May 3, 1993), which discloses a conformable butadiene layer and at least one resin selected from the group consisting of hydrogenated polycyclodiene resins and aliphatic hydrocarbon resins.
Another approach to pavement markings has recognized that conformability of the pavement marking to the pavement may be enhanced by utilizing a conformable base layer onto which is placed retroreflective elements, either by embedding or by use of a binder layer. In one article, described in U.S. Pat. No. 5,194,113, the conformance layer comprises a ductile thermoplastic polymer (preferably a polyolefin) and a non-reinforcing mineral particulate. Another article, described in U.S. Pat. No. 5,120,154, emp
Dahlin Thomas J.
Fayling Richard E.
Gonzalez Bernard A.
Hopstock David M.
Jacobs Gregory F.
3M Innovative Properties Company
Watkins III William P.
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