US 4,799,381 AGranted

Vehicle road sensor

AssigneeCMI International, Inc.

InventorCorwin M. Tromp

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Abstract

A sensor used for detecting the passage of vehicles over a roadway is formed of a force sensing variable resistor which is embedded in a resilient, rubber-like strip that is molded around the resistor within an elongated sheet metal channel. The channel is sized to fit within a narrow saw-cut groove across the roadway, so that the strip exposed surface at the open top of the channel is exposed at the road surface for contact by the tires of passing vehicles. The resistor is formed of a printed circuit having a pair of separated conductive stripes with a repetitive pattern of gap areas between them, and a sheet of variable resistance material overlying each of the gap areas to form conductive shunts between the printed conductive stripes. The material forming each of the sheets normally resists the flow of electrical current, but its resistance decreases in response to physical pressure so as to become a conductor over its respective gap area in response to the direct pressure from a vehicle tire compressing the resilient strip above the sheet. A detector is used to sense the flow of current through the printed circuit for sensing the vehicle.

Claims18

Dependent claims

A vehicle road sensor for signaling the passage of a vehicle over a predetermined location on a roadway, comprising:

a force sensing resistor formed of a pair of overlapped non-conductive substrates, each having a controllable conductive coating, with the coatings being overlapped in adjacent surface to surface relationship;
at least one of said coatings being formed of a force responsive material characterized by normally resisting the passage of electrical current therethrough, but whose resistance decreases upon the application of pressure upon the coating;
and the second of said coatings having at least one area which precludes the passage of electrical current therethrough, and with said area being overlapped by a portion of the one coating so that said portion functions to shunt current across said area upon the application of pressure to said portion;
said substrates being completely embedded within a block formed of a resilient, rubber-like material;
said block having an upper, contact surface, with the substrates being embedded within the block beneath the contact surface so that vehicle pressure upon the contact surface is transmitted to the substrates;
means for normally applying an electrical potential to the second coating sufficient to induce the flow of current therethrough when the applied pressure reduces the electrical resistance of said portion;
means for detecting the flow of current through the second coating;
and the block forming material between the block contact surface and the substrates being resiliently compressible under the weight of a vehicle for temporarily applying enough pressure to the portion of the one coating so that it temporarily functions as a shunt across the area which it overlaps so that electrical current temporarily flows through the second coating for indicating the temporary presence of a vehicle upon the block contact surface.

5 more elements

A vehicle road sensor for signaling the passage of a vehicle over a predetermined location on a roadway, comprising:

a force sensing resistor formed of an elongated circuit pattern printed upon a substrate, with the pattern including a pair of separated, conductive printed strips and a series of gap areas formed between the strips, with the strips being arranged for normal connection to a source of electrical power;
said force sensing resistor including a pressure responsive sheet portion overlapping each gap area, and the sheet being formed of a material characterized by being normally electrically resistant so that it is substantially non-conductive, but whose resistance to electrical flow reduces, in general proportion to pressure applied to the material, with each sheet portion forming an electrical shunt over its overlapping gap area upon the application of sufficient pressure upon the sheet portion;
said force sensing resistor being embedded within an elongated, relatively narrow block made of a resilient, rubber-like material;
the block being of a cross-sectional size to closely fit within a saw-cut made in a roadway surface so that the wheels of a vehicle running over the block apply sufficient pressure upon the block to compress it and thereby, apply sufficient pressure to those sheet portions which are located beneath the tires, to reduce their resistance and permit electrical current to flow across the gap areas which they overlap and through the strips for detection by a detection means.

1 more element

Dependencies are inferred from the claim text.