Automatic vehicle identification (AVI) system employing planar laser illumination and imaging (PLIIM) based subsystems

• US 6,959,869 B2
• Filed: 05/31/2002
• Issued: 11/01/2005
• Est. Priority Date: 06/07/1999
• Status: Expired due to Fees

• Current Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Original Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Inventors: Zhu, Xiaoxun, Knowles, C. Harry, Schnee, Michael D., Tsikos, Constantine J.
• Primary Examiner(s): LE, THIEN MINH
• Application Number:
  US10/161,091
• Publication Number:
  US 20030042303A1
• Time in Patent Office: 1,250 Days
• Field of Search: 23546201-46248, 235/472.01, 235/472.02, 235/472.03, 235/454, 235/494, 235/375, 235/384, 235/381, 235/380
• US Class Current: 235/462.01
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G06K 7/10594 Beam path
• CPC Class Codes: G06V 20/62 Text, e.g. of license plates, overlay texts or captions on TV images
• CPC Class Codes: G06V 30/144 using a slot moved over the image; using discrete sensing elements at predetermined points; using automatic curve following means
• CPC Class Codes: G07B 15/06 Arrangements for road pricing or congestion charging of vehicles or vehicle users, e.g. automatic toll systems
• CPC Class Codes: H01S 5/005 Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping H01S5/026, H01S5/18388 take precedence
• CPC Class Codes: H01S 5/02325 Mechanically integrated components on mount members or optical micro-benches
• CPC Class Codes: H01S 5/4025 Array arrangements, e.g. constituted by discrete laser diodes or laser bar H01S5/42 takes precedence

Abstract

An automatic vehicle identification (AVI) system for installation along a roadway, comprising one or more a planar laser illumination and imaging (PLIIM) based linear imaging subsystems mounted above the roadway in a spaced apart manner. The PLIIM based subsystems are arranged for capturing digital linear images of both the front and rear license plates mounted on each moving vehicle travelling under the PLIIM based linear imaging subsystem, and generating digital image data representative of each captured digital linear image. An image processing subsystem is provided for receiving and processing the digital image data generated by the PLIIM-based imaging systems, so as to automatically read the alphanumeric strings on the front and/or rear license plates of each the vehicle. These recognized strings are then compared against vehicle registration information stored in a database in order to identify each vehicle travelling under along the roadway. By virtual of the present invention, it is now possible to capture and buffer high-resolution linear images of the license plates on moving vehicles using planar laser illumination beams and coplanar fields of view, so that these linear images can be sequentially assembled to construct 2-D images for OCR processing so that such vehicles can be automatically identified, while avoiding the need for large and expensive high-intensity lighting equipment required by conventional digital cameras employing 2-D electronic image detectors.

Claims

1. An automatic vehicle identification (AVI) system for installation along a roadway, comprising:

a pair of PLIIM-Based linear imaging subsystems mounted above said roadway in a spaced apart manner, and arranged for capturing digital linear images of both the front and rear license plates mounted on each moving vehicle traveling under said PLIIM-based linear imaging subsystems, and generating digital image data representative of each captured digital linear image; and

an image processing subsystem for receiving and processing digital image data generated by said PLIIM-based linear imaging systems, so as to automatically read the alphanumeric strings on the front and/or rear license plates of each said moving vehicle, for subsequent comparison against vehicle registration information stored in a database for identification of moving vehicles traveling along said roadway.

2. The AVI system of claim 1, wherein each said PLIIM-based linear imaging subsystem comprises:

a system housing having first, second and third light transmission apertures linearly aligned with and optically isolated from each other, and said third light transmission aperture being disposed between said first and second light transmission apertures.

3. The AVI system of claim 2, wherein each said PLIIM-based linear imaging subsystem comprises:

a linear image formation and detection (IFD) module disposed in said system housing, and having image formation optics with a field of view projectable through said third light transmission aperture and onto said vehicle moving relative to said first, second and third light transmission apertures during vehicle illumination and imaging operations; and

a pair of planar laser illumination arrays (PLIAs) disposed in said system housing, each said planar laser array (PLIA) including a plurality of laser diodes arranged together in a linear manner and said planar laser illumination arrays being arranged in relation to said linear image formation and detection module, for producing a pair of planar laser illumination beams (PLIBs), and projecting said pair of planar laser illumination beams through said first and second light transmission apertures and oriented such that the plane of said planar laser illumination beams is coplanar with the field of view of said linear image formation and detection module so that the vehicle can be simultaneously illuminated by said planar laser illumination beams and imaged within said field of view of said linear image formation and detection module,

whereby a series of linear images of said vehicle are sequentially detected by said linear image formation and detection module as said vehicle moves past first, second and third light transmission apertures, so that said series of linear images can be grabbed and buffered for subsequent use in constructing two-dimensional images of said vehicle.

4. The AVI system claim 3, wherein each said PLIIM-based linear imaging subsystem further comprises:

an image frame grabber for grabbing digital linear images formed and detected by said image formation and detection module,

an image data buffer for buffering said grabbed digital linear images for subsequent processing by said image processing computer; and

a camera control computer for controlling said linear image formation and said detection module and said pair of planar laser illumination arrays.

5. The AVI system of claim 3, wherein said image forming optics have a fixed focal distance and a fixed focal length providing a fixed field of view.

6. The AVI system of claim 3, wherein said image forming optics have a variable focal distance and a fixed focal length providing a fixed field of view.

7. The AVI system of claim 3, wherein said image forming optics have a variable focal distance and a fixed focal length providing a fixed field of view.

8. The AVI system of claim 3, wherein said image forming optics have a variable focal distance and a variable focal length providing a variable field of view.

9. An automatic vehicle identification (AVI) system for installation along a roadway, comprising:

a planar laser illumination and imaging (PLIIM) based vehicle detection and imaging subsystem mounted above said roadway, for (1) detecting the presence of each moving vehicle traveling under said PLIIM based vehicle detection and imaging subsystem, and generating vehicle detection data for each vehicle detected by said PLIIM based vehicle detection and imaging subsystem, also for (2) capturing digital linear images of both the front and rear license plates mounted on each said moving vehicle traveling under said PLIIM-based vehicle detection and imaging subsystem and generating digital image data representative of each captured digital linear image; and

an image processing subsystem for receiving and processing digital image data generated by said PLIIM based vehicle detection and imaging subsystem, so as to automatically read the alphanumeric strings on the front and/or rear license plates of each said moving vehicle for subsequent comparison against vehicle registration information stored in a database and identification of each moving vehicle traveling under along said roadway.

10. The AVI system of claim 9, wherein said PLIIM based vehicle detection and imaging subsystem comprises:

a system housing having first, second and third light transmission apertures linearly aligned with and optically isolated from each other, and said third light transmission aperture being disposed between said first and second light transmission apertures.

11. The AVI system of claim 10, wherein said PLIIM based vehicle detection and imaging subsystem comprises:

a linear image formation and detection (IFD) module disposed in said system housing, and having image formation optics with a field of view projectable through said third light transmission aperture and onto said vehicle moving relative to said first, second and third light transmission apertures during vehicle illumination and imaging operations; and

a pair of planar laser illumination arrays (PLIAs) disposed in said system housing, each said planar laser array (PLIA) including a plurality of laser diodes arranged together in a linear manner and said planar laser illumination arrays being arranged in relation to said linear image formation and detection module, for producing a pair of planar laser illumination beams (PLIBs), and projecting said pair of planar laser illumination beams through said first and second light transmission apertures and oriented such that the plane of said planar laser illumination beams is coplanar with the field of view of said linear image formation and detection module so that the vehicle can be simultaneously illuminated by said planar laser illumination beams and imaged within said field of view of said linear image formation and detection module,

whereby a series of linear images of said vehicle are sequentially detected by said linear image formation and detection module as said vehicle moves past first, second and third light transmission apertures, so that said series of linear images can be grabbed and buffered for subsequent use in constructing two-dimensional images of said vehicle.

12. The AVI system of claim 11, which further comprises an electronically-controlled module, operably connected to said PLIIM based vehicle detection and imaging subsystem, for switching the direction of the coplanar PLIB and FOV in response to the detection of each said vehicle under each said PLIIM based vehicle detection and imaging subsystem.

13. The AVI system of claim 9, wherein said PLIIM based vehicle detection and imaging subsystem further comprises:

an image frame grabber for grabbing digital linear images formed and detected by said image formation and detection module,

an image data buffer for buffering said grabbed digital linear images for subsequent processing by said image processing computer; and

a camera control computer for controlling said linear image formation and said detection module said pair of planar laser illumination arrays.

14. The AVI system of claim 11, wherein said image forming optics have a fixed focal distance and a fixed focal length providing a fixed field of view.

15. The AVI system of claim 11, wherein said image forming optics have a variable focal distance and a fixed focal length providing a fixed field of view.

16. The AVI system of claim 11, wherein said image forming optics have a variable focal distance and a fixed focal length providing a fixed field of view.

17. The AVI system of claim 11, wherein said image forming optics have a variable focal distance and a variable focal length providing a fixed field of view.