Communications: electrical – Vehicle detectors – Inductive
Reexamination Certificate
1993-04-30
2001-03-27
Tong, Nina (Department: 2736)
Communications: electrical
Vehicle detectors
Inductive
C340S940000, C340S933000, C324S247000, C324S207260, C324S174000, C324S179000, 36, 36
Reexamination Certificate
active
06208268
ABSTRACT:
ORIGIN OF THE INVENTION
The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon.
FIELD OF THE INVENTION
The invention relates generally to highway vehicle sensing systems, and more particularly to a magnetic roadway installed detector and system capable of detecting the presence of a motor vehicle and accurately determining the vehicle's speed and length.
BACKGROUND OF THE INVENTION
Vehicle detectors are key components in all street and freeway traffic control and surveillance systems. An ideal detector for these applications should be low in cost, provide accurate detection, require minimum installation time and cost, be reliable under all environmental conditions, have low maintenance and calibration requirements, and be able to detect all vehicles on any standard roadway surface.
The United States Navy has developed and patented (U.S. Pat. No. 4,302,746) a self-powered vehicle detection (SPVD) system for the Federal Highway Administration. The SPVD system detector includes a two-axis magnetometer that measures a motor vehicle's magnetic signature. The signature is processed to determine vehicle presence and is then transmitted to a road-side receiver system. The operating principle of the SPVD is to sense the magnetic field of the vehicle and transmit a leading and trailing edge signals corresponding to magnetic signature threshold levels. Since the magnetic field signature amplitudes vary with respect to the size and shape of motor vehicles, the speed of a motor vehicle must be determined using two precisely spaced SPVD detectors or other current state of the art speed sensors (eg., loop detectors). Unfortunately, the process of burying a plurality of SPVD detectors and/or loop detectors in a roadway is time consuming and costly.
In addition, the amount of magnetic material used in motor vehicles has decreased over the last ten years. A recently built motor vehicle's magnetic field signature amplitude is less than that of a comparably sized motor vehicle built a decade ago. Therefore, today's highway vehicle sensing system based on magnetic field signatures requires a greater sensitivity to detect smaller amplitude magnetic signatures.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a highway vehicle sensing system for detecting the presence and speed of a passing vehicle.
Another object of the present invention is to provide a highway vehicle sensing system that minimizes roadway surface disturbances in order to install the system's roadway detector.
Yet another object of the present invention is to provide a magnetic highway sensing system for sensing vehicle magnetic signatures with an improved sensitivity to magnetic field strength.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, an improved detector is provided for installation in a roadway surface. The detector finds utility in a highway vehicle detection system for determining vehicle presence, vehicle speed and vehicle length. First and second matched induction coil magnetic sensors are maintained at or near the roadway surface. Each of the sensors has a longitudinal axis aligned normal to the roadway surface. The first and second sensors are separated from one another by a known distance in a direction substantially aligned with a direction of traffic flow. Each of the sensors generate a differential magnetic field signature with respect to time to indicate a passing vehicle's leading and trailing edge magnetic signatures. First, second and third time intervals associated with the leading and trailing edge magnetic signatures are used in conjunction with the known distance to determine vehicle speed and vehicle length. Specifically, the first time interval occurs between the passing vehicle's leading edge magnetic signatures detected by the first and second sensors, the second time interval occurs between the passing vehicle's trailing edge magnetic signatures detected by the first and second sensors, and the third time interval occurs between the passing vehicle's leading and trailing edge magnetic signatures detected by one of the first and second sensors. Vehicle speed is determined by a time-distance relationship using at least one of the first and second time intervals and the known distance. Vehicle length is determined by a time-speed relationship using the third time interval and the determined vehicle speed.
A triaxial magnetometer maintained at a location in close proximity to the first and second sensors measures a DC magnetic field. The DC magnetic field has vertical and horizontal magnetic field components with the horizontal components including a component substantially aligned with the direction of traffic flow and a component substantially perpendicular to the direction of traffic flow. The vertical and horizontal components caused by the passing vehicle are used to determine vehicle presence.
In addition, third and fourth matched induction coil magnetic sensors may be provided and maintained at or near the roadway surface in close proximity to the first and second sensors. Each third and fourth sensor lies in a unique horizontal plane and has a longitudinal axis aligned substantially parallel to the roadway surface. The third and fourth sensors form an orthogonal crossing pattern when viewed with respect to a direction normal to the roadway surface. The orthogonal crossing pattern is arranged so that each of the third and fourth sensor's longitudinal axis bisects the direction of traffic flow by an angle of approximately 45°. The third and fourth sensors may be used to transmit and/or receive extremely low frequency (ELF) (generally 30-300 Hz) signals to/from the passing vehicle or a remotely located roadside control unit.
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Feaga Adam C.
Lenko Daniel S.
Scarzello John F
Forrest John
Shuster Jacob
The United States of America as represented by the Secretary of
Tong Nina
LandOfFree
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