Bidirectional road traffic sensor

• US 5,477,217 A
• Filed: 02/18/1994
• Issued: 12/19/1995
• Est. Priority Date: 02/18/1994
• Status: Expired due to Fees

• Current Assignee: International Road Dynamics Incorporated (Quarterhill Inc. (f/k/a Wi-LAN Inc.))
• Original Assignee: International Road Dynamics Incorporated (Quarterhill Inc. (f/k/a Wi-LAN Inc.))
• Inventors: Bergan, Terry
• Primary Examiner(s): Peng, John K.
• Assistant Examiner(s): Lefkowitz, Edward
• Application Number:
  US08/198,634
• Time in Patent Office: 669 Days
• Field of Search: 340/933, 340/665, 340/666, 200/86 A, 310/339, 310/800
• US Class Current: 340/933
• CPC Class Codes: G08G 1/02 using treadles built into the road pads or other sensitive devices responsive to passage of vehicles E01F11/00
• CPC Class Codes: G08G 1/065 by counting the vehicles in a section of the road or in a parking area, i.e. comparing incoming count with outgoing count
• CPC Class Codes: Y10S 310/80 Piezoelectric polymers, e.g. PVDF

Abstract

A bidirectional road traffic sensor include several respective lengths of coaxial piezoelectric cable each having a conductive core, a conductive polymer surrounding the core, a conductive sheath therearound and an electrically non-conductive jacket therearound. The cables are spliced together such that conductive core and conductive sheath of one length of piezoelectric cable is spliced respectively to the conductive sheath and conductive core of another piezoelectric cable. The splices are encapsulated in an electrically non-conductive material so that the spliced lengths of piezoelectric cables respectively constitutes positive, neutral and negative piezoelectric sensors. Pressure changes in the piezoelectric sensors are caused by vehicle passage thereover. In such a manner, electrical pulses are responsively produced by passage of vehicles traversing respective detection zones defined by the sensors and moving in respective particular directions so that such passage of such vehicles may be registered.

Claims

1. A bidirectional road traffic sensor comprising:

(i) a first length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding the core, a conductive sheath therearound and an electrically non-conductive jacket therearound;

(ii) a second length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding the core, a conductive sheath therearound and an electrically non-conductive jacket therearound;

(iii) a first splice between the first length of coaxial piezoelectric cable and the second length of piezoelectric cable in which the conductive core of the first length of piezoelectric cable is spliced to the conductive sheath of the second piezoelectric cable, and in which the conductive sheath of the first piezoelectric cable is spliced to the conductive core of the second piezoelectric cable, the first splice being encapsulated in an electrically non-conductive material, thereby constituting the first length of piezoelectric cable as a positive piezoelectric sensor;

(iv) a third length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding the core, a conductive sheath therearound, and an electrically non-conductive jacket therearound; and

(v) a second splice between the second length of coaxial piezoelectric cable and the third length of piezoelectric cable in which the conductive core of the second length of piezoelectric cable is spliced to the conductive core of the third piezoelectric cable, and in which the conductive sheath is spliced to the conductive sheath of the second piezoelectric cable, the second splice being encapsulated in an electrically non-conductive material;

thereby constituting the second length of piezoelectric cable as a neutral piezoelectric sensor, and further constituting the third length of piezoelectric cable as a negative piezoelectric sensor.

2. The bidirectional road traffic sensor of claim 1 wherein said conductive core is made of copper.

3. The bidirectional road traffic sensor of claim 1 wherein said conductive sheath is formed of braided copper.

4. The bidirectional road traffic sensor of claim 1 wherein said conductive polymer is polyvinylidene chloride.

5. The bidirectional road traffic sensor of claim 1 wherein said non-conductive jacket is formed of polyethylene.

6. The bidirectional road traffic sensor of claim 1 wherein said first and said second splices are encapsulated in polyethylene.

7. The bidirectional road traffic sensor comprising:

(i) a shielded coaxial cable including a conductive core, a conductive sheath and an electrically non-conductive jacket therearound;

(ii) a first length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding the core, a conductive sheath therearound and an electrically non-conductive jacket therearound;

(iii) a splice between the shielded coaxial cable and the first length of coaxial piezoelectric cable in which the conductive core of the coaxial lead cable is spliced to the conductive core of the first length of piezoelectric cable, and in which the conductive sheath of the coaxial lead cable is spliced to the conductive core of the first piezoelectric cable, the third splice being encapsulated in an electrically non-conductive material, thereby constitutes the shielded coaxial cable as a lead cable;

(iv) a second length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding the core, a conductive sheath therearound and an electrically non-conductive jacket therearound;

(v) a first splice between the first length of coaxial piezoelectric cable and the second length of piezoelectric cable in which the conductive core of the first length of piezoelectric cable is spliced to the conductive sheath of the second piezoelectric cable, and in which the conductive sheath of the first piezoelectric cable is spliced to the conductive core of the second piezoelectric cable, the first splice being encapsulated in an electrically non-conductive material, thereby constituting the first length of piezoelectric cable as a positive piezoelectric sensor;

(vi) a third length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding the core, a conductive sheath therearound, and an electrically non-conductive jacket therearound; and

(vii) a second splice between the second length of coaxial piezoelectric cable, and the third length of piezoelectric cable, in which the conductive core of the second length of piezoelectric cable is spliced to the conductive core of the third piezoelectric cable, and in which the conductive sheath is spliced to the conductive sheath of the second piezoelectric cable the second splice being encapsulated in an electrically non-conductive material, thereby constituting the second length of piezoelectric cable as a neutral piezoelectric sensor, and also constituting the third length of piezoelectric cable as a negative piezoelectric sensor.

8. The bidirectional road traffic sensor of claim 7 wherein said conductive core is made of copper.

9. The bidirectional road traffic sensor of claim 7 wherein said conductive sheath is formed of braided copper.

10. The bidirectional road traffic sensor of claim 7 wherein said conductive polymer is polyvinylidene chloride.

11. The bidirectional road traffic sensor of claim 7 wherein said non-conductive jacket is formed of polyethylene.

12. The bidirectional road traffic sensor of claim 7 wherein said first and said second splices are encapsulated in polyethylene.

13. The bidirectional road traffic sensor of claim 7 wherein said third splice is encapsulated in natural or synthetic rubber.

14. A system for selective detection of vehicles passing over at least one lane of a multiple number of lanes said system comprising at least two vehicle detector zones, each zone including a single bidirectional road traffic sensor comprising:

(i) a shielded coaxial cable including a conductive core, a conductive sheath and an electrically non-conductive jacket therearound;

(ii) a first length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding said core, a conductive sheath therearound and an electrically non-conductive jacket therearound;

(iii) a splice between said shielded coaxial cable and said first length of coaxial piezoelectric cable in which said conductive core of said coaxial lead cable is spliced to said conductive core of said first length of said piezoelectric cable, and in which said conductive sheath of the coaxial lead cable is spliced to said conductive core of said first piezoelectric cable, said third splice being encapsulated in an electrically non-conductive material, which thereby constitutes said shielded coaxial cable as a lead cable;

(iv) a second length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding said core, a conductive sheath therearound and an electrically non-conductive jacket therearound;

(v) a first splice between said first length of coaxial piezoelectric cable and said second length of piezoelectric cable in which said conductive core of said first length of piezoelectric cable is spliced to said conductive sheath of said second piezoelectric cable, and in which said conductive sheath of said first piezoelectric cable is spliced to said conductive core of said second piezoelectric cable, said first splice being encapsulated in an electrically non-conductive material, which thereby constitutes said first length of piezoelectric cable as a positive piezoelectric sensor;

(vi) a third length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding said core, a conductive sheath therearound, and an electrically non-conductive jacket therearound; and

(vii) a second splice between said second length of coaxial piezoelectric cable, and said third length of piezoelectric cable, in which said conductive core of said second length of piezoelectric cable is spliced to said conductive core of said third piezoelectric cable, and in which said conductive sheath is spliced to said conductive sheath of said second piezoelectric cable, said second splice being encapsulated in an electrically non-conductive material;

wherein pressure changes in said piezoelectric sensor caused by vehicle passage thereover responsively produce electrical pulses for registering the passage of vehicles moving in respective particular directions and which respectively traverse one and another of said vehicle detection zones.

15. The system of claim 14 includes two spaced-apart bidirectional piezoelectric road traffic sensors for classifying moving traffic.

16. A traffic counter including:

(a) at least two bi-directional road traffic sensors comprising;

(i) a shielded coaxial cable including a conductive core, a conductive sheath and an electrically non-conductive jacket therearound;

(ii) a first length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding the core, a conductive sheath therearound and an electrically non-conductive jacket therearound;

(iii) a splice between said shielded coaxial cable and said first length of coaxial piezoelectric cable in which said conductive core of said coaxial lead cable is spliced to said conductive core of said first length of piezoelectric cable, and in which said conductive sheath of said coaxial lead cable is spliced to said conductive core of said first piezoelectric cable, said third splice being encapsulated in an electrically non-conductive material, which thereby constitutes said shielded coaxial cable as a lead cable;

(iv) a second length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding said core, a conductive sheath therearound and an electrically non-conductive jacket therearound;

(v) a first splice between said first length of coaxial piezoelectric cable and said second length of piezoelectric cable in which said conductive core of said first length of piezoelectric cable is spliced to said conductive sheath of said second piezoelectric cable, and in which said conductive sheath of said first piezoelectric cable is spliced to said conductive core of said second piezoelectric cable, said first splice being encapsulated in an electrically non-conductive material, which thereby constitute said first length of piezoelectric cable as a positive piezoelectric sensor;

(vi) a third length of a coaxial piezoelectric cable having a conductive core, a conductive polymer surrounding said core, a conductive sheath therearound, and an electrically non-conductive jacket therearound; and

(vii) a second splice between said second length of coaxial piezoelectric cable, and said third length of piezoelectric cable, in which said conductive core of said second length of piezoelectric cable is spliced to said conductive core of said third piezoelectric cable, and in which said conductive sheath is spliced to said conductive sheath of said second piezoelectric cable, said second splice being encapsulated in an electrically non-conductive material;

wherein pressure changes in said bi-directional road traffic sensors caused by vehicle passage thereover responsively produce electrical pulses;

(b) means for removably mounting said bi-directional road traffic sensor to a roadway;

(c) signal transmitting means connected to, and actuated by, said bi-directional road traffic sensor for transmitting said electrical pulses; and

(d) tally means triggered by said pulses from said signal transmitting means for tallying said pulses.

17. The traffic counter of claim 16 including two spaced-apart bidirectional piezoelectric road traffic sensors for classifying moving traffic.