Method of and system for automatically producing digital images of moving objects, with pixels having a substantially uniform white level independent of the velocities of the moving objects

• US 6,978,936 B2
• Filed: 04/23/2002
• Issued: 12/27/2005
• 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, Good, Timothy A., Knowles, C. Harry, Au, Ka Man, Ghosh, Sankar, Kolis, George, Colavito, Stephen J., Amundsen, Thomas, Vatan, Pirooz, Naylor, Charles A., Defoney, Shawn, Skypala, Edward, Schwartz, Barry E., Jankevics, Andrew, Schnee, Michael D., Wilz, David W. Sr., Blake, Robert, Tsikos, Constantine J., Giordano, Patrick A., Yorsz, Jeffery, Wirth, Allan, Kim, Steven Y., Dobbs, Russell Joseph, Svedas, William, Fisher, Dale, Schmidt, Mark C., Tassell, Jon Van
• Primary Examiner(s): LE, THIEN MINH
• Application Number:
  US10/131,796
• Publication Number:
  US 20030052175A1
• Time in Patent Office: 1,344 Days
• Field of Search: 23546201-46247, 235/472.01, 235/472.02, 235/472.03, 235/375, 235/454, 235/455, 235/494, 235/470
• US Class Current: 235/462.01
• CPC Class Codes: G02B 19/0014 at least one surface having optical power
• CPC Class Codes: G02B 19/0052 the light source comprising a laser diode coupling into light guides using intermediate optical elements G02B6/4204; semiconductor lasers having optical devices external to the laser cavity H01S5/005
• CPC Class Codes: G02B 19/0085 for use with both a detector and a source , e.g. in a transceiver, G02B19/009, G02B19/0095 take precedence
• CPC Class Codes: G02B 19/009 for use with infrared radiation
• CPC Class Codes: G02B 19/0095 for use with ultraviolet radiation
• CPC Class Codes: G02B 26/10 Scanning systems
• CPC Class Codes: G02B 27/095 Refractive optical elements
• CPC Class Codes: G02B 27/48 Laser speckle optics
• CPC Class Codes: G06K 7/10 by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
• CPC Class Codes: G06K 7/10594 Beam path
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10732 Light sources
• CPC Class Codes: G06K 7/146 the method including quality enhancement steps
• CPC Class Codes: G06Q 10/00 Administration; Management
• CPC Class Codes: G06Q 30/00 Commerce
• 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: 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

Methods of and systems for illuminating objects using planar laser illumination beams having substantially-planar spatial distribution characteristics that extend through the field of view (FOV) of image formation and detection modules employed in such systems. Each planar laser illumination beam is produced from a planar laser illumination beam array (PLIA) comprising an plurality of planar laser illumination modules (PLIMs). Each PLIM comprises a visible laser diode (VLD, a focusing lens, and a cylindrical optical element arranged therewith. The individual planar laser illumination beam components produced from each PLIM are optically combined to produce a composite substantially planar laser illumination beam having substantially uniform power density characteristics over the entire spatial extend thereof and thus the working range of the system. Preferably, each planar laser illumination beam component is focused so that the minimum beam width thereof occurs at a point or plane which is the farthest or maximum object distance at which the system is designed to acquire images, thereby compensating for decreases in the power density of the incident planar laser illumination beam due to the fact that the width of the planar laser illumination beam increases in length for increasing object distances away from the imaging optics. By virtue of the present invention, it is now possible to use both VLDs and high-speed CCD-type image detectors in conveyor, hand-held and hold-under type scanning applications alike, enjoying the advantages and benefits that each such technology has to offer, while avoiding the shortcomings and drawbacks hitherto associated therewith.

Claims

1. A method of automatically producing digital images of a moving object, with pixels having a substantially uniform white level independent of the velocity of the moving object, said method comprising the steps of:

(a) determining the velocity of an object moving relative to a planar laser illumination and imaging (PLIIM) based imaging system having

a linear image detection array with a field of view (FOV) projectable onto the moving object,

a planar laser illumination array (PLIA) with a plurality of laser diodes arranged in a linear array, for producing a planar laser illumination beam (PLIB) coplanar with the FOV of said linear image detection array, and

a micro-controller for controlling the operation of the PLIIM-based imaging system;

(b) using the detected velocity determined in step (a) to computed the optical power which each said laser diode must produce in order that each digital image of the object, formed by illuminating said object with said computed optical power, will have pixels with a substantially uniform white level independent of the velocity of said object moving relative to said PLIIM-based imaging system;

(c) transmitting the computed optical power value(s) to said micro-controller; and

(d) said micro-controller using said computed optical power value to drive each said laser diode so that said laser diode produces a planar laser illumination beam (PLIB) having the computed optical power level within said FOV, whereby the PLIB illuminates said object as said object moves through said FOV, and said PLIIM-based imaging system automatically produces a digital image of the moving object, with pixels having a substantially uniform white level, independent of the velocity of the moving object.

2. The method of claim 1, wherein step (a) comprises illuminating said object with a pair of amplitude-modulated (AM) laser beams, capturing a pair of images of said moving object, and processing said pair of images so as to compute the velocity of said object.

3. The method of claim 2, wherein step (b) comprises computing said optical power of said laser diodes by:

(1) computing the line rate of said linear image detection array based on the computed object velocity and the constant image resolution desired;

(2) computing the photo-integration time period of said linear image detection array based on the computed line rate; and

(3) computing the optical power of each laser diode based on the computed photo-integration time period.

4. The method of claim 1, wherein step (a) comprises detecting the velocity of the object transported relative to said PLIIM-based imaging system supported above a conveyor belt structure, along which the object is being transported.

5. The method of claim 1, wherein step (a) comprises detecting the velocity of the object transported relative to said PLIIM-based imaging system embodied within a hand-supportable housing, past which the object is being transported.

6. A planar laser illumination and imaging (PLIIM) based system for producing digital images of a moving object, with pixels having a substantially uniform white level, said PLIIM-based system comprising:

a system housing of unitary construction having a first light transmission aperture and a second light transmission aperture, wherein said first and second light transmission apertures are spatially aligned with each other;

a linear PLIIM-based imaging subsystem mounted within said system housing and having

a planar laser illumination array (PLIA) including a plurality of laser diodes for producing and projecting a planar laser illumination beam (PLIB) through said first light transmission aperture, so as to illuminate an object as it is moving past said PLIM-based system, and

an image formation and detection (IFD) module having a linear image detection array and image forming optics for providing said linear image detection array with a field of view (FOV) which is projected through said second light transmission aperture, and along which images of illuminated portions of said object can be detected,

wherein said PLIB and said FOV are arranged in a coplanar relationship along the working range of said PLIIM-based system so that the PLIB illuminates primarily within said FOV of said IFD module;

an object velocity measurement subsystem for projecting and scanning a light beam along the surface of said object, receiving light reflected from said object generating electrical signals representative to a characteristics of said received light, processing said electrical signals to determine the velocity thereof and generating object velocity data indicative of the determined velocity of the object;

a camera control computer, mounted within said system housing, for controlling the operation of said linear PLIIM-based imaging subsystem, in response to control data generated by said object velocity measurement subsystem and transmitted to said camera control computer,

wherein said camera control computer

(1) uses said object velocity data to compute the optical power which each laser diode in said linear PLIIM-based imaging system must produce in order that each digital image captured by said PLIIM-based system will have pixels with a substantially uniform white level, independent of object velocity; and

(2) generates and transmits control signals to said laser diodes in order to control the operation thereof so that said PLIIM-based imaging subsystem produces digital images of said object, wherein the pixels in each said digital image have a substantially uniform white level independent of the measurement object velocity.

7. The PLIIM based system of claim 6, wherein said PLIIM-based system is supported above a conveyor belt structure, along which the object is being transported.

8. The PLIIM based system of claim 6, wherein said PLIIM-based system is embodied within a hand-supportable housing, past which the object is being transported.

10. The PLIIM-based system of claim 6, wherein said PLIIM-based system is supported above a conveyor belt structure, along which the object is being transported.

11. The PLIIM-based system of claim 6, wherein said PLIIM-based imaging system is embodied within a band-supportable housing, past which the object is being transported.

9. A planar laser illumination and imaging (PLIIM) based system for producing digital images of a moving object, with pixels having a substantially uniform white level, said PLIIM-based system comprising:

a system housing of unitary construction having a first light transmission aperture, a second light transmission aperture, and a third light transmission aperture, wherein said first and second light transmission apertures are spatially aligned with each other, and said third light transmission aperture is disposed at a predetermined distance away from said first and second light transmission apertures;

a linear PLIIM-based imaging subsystem mounted within said system housing and having

a planar laser illumination array (PLIA) including a plurality of laser diodes for producing and projecting a planar laser illumination beam (PLIB) through said first light transmission aperture, so as to illuminate an object as the object is moving past said linear PLIIM-based imaging system, and

an image formation and detection (IFD) module having a linear image detection array and image forming optics for providing said linear image detection array with a field of view (FOV) which is projected through said second light transmission aperture, and along which images of illuminated portions of said object can be detected,

wherein said PLIB and said FOV are arranged in a coplanar relationship along the working range of said PLIIM system so that the PLIB illuminates primarily within said FOV of said IFD module;

a laser scanning object velocity measurement subsystem mounted within said system housing, for producing a pair of amplitude modulated (AM) laser scanning beams which are projected through said third light transmission aperture so as to scan the surface of said transported object and determine the velocity thereof and generate object velocity data indicative of the determined velocity of the object;

a camera control computer, mounted within said system housing, for controlling the operation of said linear PLIIM-based imaging subsystem, in response to control data generated by said laser scanning object velocity measurement subsystem and transmitted to said camera control computer,

wherein said camera control computer

(1) uses said object velocity data to compute the optical power which each laser diode in said linear PLIIM-based imaging subsystem must produce in order that the pixels in each digital image captured by said linear PLIIM-based imaging subsystem will have substantially the same white level, independent of object velocity; and

(2) generates and transmits control signals to said laser diodes in order to control the operation thereof so that said linear PLIIM-based imaging subsystem produces digital images of said object, wherein the pixels in each said digital image have a substantially uniform white level independent of the measured object velocity.

12. A planar laser illumination and imaging (PLIIM) based imaging system for automatically producing digital images of a moving object with pixels having a substantially uniform white level independent of the velocity of the moving object, said PLIIM-based imaging system comprising:

a linear image detection array with a field of view (FOV) projectable onto the moving object;

a planar laser illumination array (PLIA) with a plurality of laser diodes arranged in a linear array, for producing a planar laser illumination beam (PLIB) coplanar with the FOV of said linear image detection array;

an object velocity measurement subsystem for automatically measuring the velocity of the moving object;

a micro-controller for controlling the operation of the linear image detection array and said PLIA, and carrying out the following control operations;

(1) using the velocity of the object measured by said object velocity measurement subsystem, to compute the optical power which each said laser diode must produce in order that each digital image of the object, formed by illuminating said object with said computed optical power, will have pixels with a substantially uniform white level independent of the velocity of said object moving relative to said PLIIM-based imaging system; and

(2) using said computed optical power value to drive each said laser diode so that it produces a planar laser illumination beam (PLIB) having the computed optical power level within said FOV,

whereby the PLIB illuminates said object as said object moves through said FOV, and said PLIIM-based imaging system automatically produces a digital image of the moving object, with pixels having a substantially uniform white level, independent of the velocity of the moving object.

13. The PLIIM-based imaging system of claim 12, wherein said PLIIM-based imaging system is supported above a conveyor belt structure, along which the object is being transported.

14. The PLIIM-based imaging system of claim 12, wherein said PLIIM-based imaging system is embodied within a hand-supportable housing, past which the object is being transported.