Automotive vehicle classification and identification by inductive signature

• US 6,342,845 B1
• Filed: 10/10/2000
• Issued: 01/29/2002
• Est. Priority Date: 12/03/1996
• Status: Expired due to Fees

• Current Assignee: Inductive Signature Technologies Incorporated
• Original Assignee: Inductive Signature Technologies Incorporated
• Inventors: Hilliard, Steven R., Hilliard, Geoffrey W.
• Primary Examiner(s): POPE, DARYL C
• Application Number:
  US09/686,920
• Time in Patent Office: 476 Days
• Field of Search: 340/933, 340/941, 340/934
• US Class Current: 340/941
• CPC Class Codes: G08G 1/015 with provision for distinguishing between two or more types of vehicles, e.g. between motor-cars and cycles
• CPC Class Codes: G08G 1/042 using inductive or magnetic detectors

Abstract

A system and method for measuring a plurality of successive induction measurements, collectively known as the “inductive signature” of a vehicle, and classifying the vehicle described by the measured inductive signature. The system includes a blade-type wire-loop configuration, or blade sensor and a corresponding measurement circuit employing a discrete measurement technique, as opposed to the frequency counting technique of the prior art. The system and method produce repeatable inductive signatures at a high resolution that allows for accurate identification and classification of a vehicle.

Claims

1. A blade sensor for detecting a vehicle, said blade sensor comprising:

a loop forming member; and

a conductor defining at least one loop carried by said loop forming member, said at least one loop defining at least a first leg substantially parallel to a second leg, each of said first leg and said second leg being substantially parallel to a roadway surface, said first leg being closer to the roadway surface than said second leg, said loop having a horizontal dimension and a vertical dimension, said horizontal dimension being substantially greater than said vertical dimension;

whereby said blade sensor has sufficient resolution to detect a plurality of features of the vehicle.

2. The blade sensor of claim 1 wherein said blade sensor presents a uniform geometry to the vehicle regardless of the vehicle'"'"'s lateral position with respect to said blade sensor.

3. The blade sensor of claim 1 further comprising a capacitor in electrical communication with said conductor thereby forming an inductance-capacitance-resistance oscillator circuit.

4. A blade sensor for detecting a vehicle on a driving surface, said sensor comprising:

a first conductor defining a primary loop, said primary loop defining at least a first leg substantially parallel to a second leg, each of said primary loop first leg and said primary loop second leg being substantially parallel to the driving surface;

a second conductor defining a secondary loop, said secondary loop defining a first leg substantially parallel to a second leg, each of said secondary loop first leg and said secondary loop second leg being substantially parallel to the driving surface;

said secondary loop being substantially coplanar with said primary loop;

said primary loop second leg abuts said secondary loop first leg;

said primary loop first leg being closer to the driving surface than said secondary loop second leg.

5. The blade sensor of claim 4 wherein said primary loop and said secondary loop are thermally coupled.

6. The blade sensor of claim 4 further comprising a first capacitor in electrical communication with said primary loop thereby forming a first inductance-capacitance-resistance oscillator circuit and a second capacitor in electrical communication with said secondary loop thereby forming a second inductance-capacitance-resistance oscillator circuit.

7. An apparatus for recording an inductive signature of a vehicle on a driving surface, said apparatus comprising:

at least one sensor for detecting variations in an inductive field due to the presence of a vehicle, said at least one sensor disposed substantially perpendicular to the driving surface, said at least one sensor producing a plurality of inductive measurements;

a measurement circuit in electrical communication with said at least one sensor, said measurement circuit producing a output corresponding to said plurality of inductive measurements; and

a processing circuit producing an inductive signature by normalizing said output based on a characteristic of said output.

8. The apparatus of claim 7 further comprising an analog-to-digital converter in electrical communication with said measurement circuit for sampling said output.

9. The apparatus of claim 7 wherein said measurement circuit includes a charging circuit in electrical communication with each said at least one sensor.

10. The apparatus of claim 9 wherein said charging circuit comprises:

a voltage source;

a switch coupling said voltage source and one of each said at least one sensor;

a timing signal generator in electrical communication with said switch for opening and closing said switch based on a timing signal.

11. The apparatus of claim 7 wherein each of said measurement circuit includes an operation amplifier in electrical communication with each said first sensor and said second sensor, respectively.

12. The apparatus of claim 11 wherein each said operational amplifier is configured as an instrumentation amplifier.

13. The apparatus of claim 7 wherein said at least one sensor includes a first sensor for detecting variations in an inductive field due to the presence of a vehicle, said first sensor disposed substantially perpendicular to the driving surface, said first sensor producing a first plurality of inductive measurements and a second sensor for detecting variations in an inductive field due to the presence of a vehicle, said second sensor disposed substantially parallel to said first sensor at a known fixed distance from said first sensor, said second sensor disposed in a substantially vertical orientation with respect to the driving surface, said second sensor producing a second plurality of inductive measurements.

14. The apparatus of claim 13 wherein a first measurement circuit is in electrical communication with said first sensor and a second measurement circuit is in electrical communication with said second sensor, said first measurement circuit producing a first output corresponding to said first plurality of inductive measurements;

said second measurement circuit producing a second output corresponding to said second plurality of inductive measurements.

15. The apparatus of claim 14 wherein said processing circuit compares said first output to said second output to calculate a time delay between said first output and said second output and normalizes at least one of said first output and said second output with respect to the time delay.

16. A method for measuring an inductive signature of a vehicle, said method comprising the steps of:

(a) charging at least one sensor for a first time period;

(b) discharging said at least one sensor for a second time period;

(c) measuring an output from said at least one sensor at a given frequency as a plurality of discrete measurements during said second time period; and

(d) combining said plurality of discrete measurements to form an inductive signature.

17. A method for identifying a vehicle based upon an inductive signature, said method comprising the steps of:

(a) measuring at least one plurality of data points for a vehicle as a function of time;

(b) normalizing one of said at least one plurality of data points with respect to time to produce an inductive length signature;

(c) comparing said inductive length signature to a reference signature; and

(d) identifying the vehicle when said inductive length signature and said reference signature correlate to a predetermined level of certainty.

18. The method of claim 17 wherein at least two said plurality of data points are contemporaneously measured using at least two sensors, said step of normalizing one of said plurality of data points further comprising the steps of:

(a) calculating an acceleration profile using a pair of said at least two plurality of data points;

(b) separating said plurality of data points into a number of data segments containing a number of said plurality of data points based upon said acceleration profile;

(c) interpolating each said data segment to produce an equal number of said plurality of data points within each said data segment; and

(d) combining each said data segment sequentially to produce an inductive length signature.