Led-based planar light illumination beam generation module employing a focal lens for reducing the image size of the light emmiting surface of the led prior to beam collimation and planarization

• US 6,732,929 B2
• Filed: 02/01/2002
• Issued: 05/11/2004
• Est. Priority Date: 09/10/1990
• Status: Expired due to Fees

• Current Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Original Assignee: Metrologic Instruments Incorporated (Honeywell International Inc.)
• Inventors: Good, Timothy A., Knowles, C. Harry, Amundsen, Thomas
• Primary Examiner(s): Lee, Michael G.
• Assistant Examiner(s): Kim, Ahshik
• Application Number:
  US10/066,547
• Publication Number:
  US 20020153422A1
• Time in Patent Office: 830 Days
• Field of Search: 235/462.01, 235/462.11, 235/462.22, 235/462.24, 235/462.32, 235/472.01, 235/462.14, 235/462.17, 235/462.18
• US Class Current: 235/462.01
• CPC Class Codes: G06K 7/10742 including a diffuser for diffusing the light from the light source to create substantially uniform illumination of the target record carrier

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. Advanced high-resolution wavefront control methods and devices are disclosed for use with the PLIIM-based systems in order to reduce the power of speckle-noise patterns observed at the image detections thereof. 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 imaging 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. An LED-based planar light illumination module (PLIM) for use in a planar light illumination and imaging (PLIIM)-based system, comprising:

a linear-type LED array having a light emitting surface from which light rays are emitted,

a focusing lens for focusing said light rays and forming a reduced size image of the light emitting source at a predetermined focal point,

a collimating lens located at about the focal point of said focusing lens, for collimating the light rays associated with said reduced size image, and

a cylindrical lens element for expanding said light rays from said collimating lens so as to produce a spatially-incoherent planar light illumination beam,

wherein said predetermined focal point is located between said focusing lens and said collimating lens; and

wherein each said optical element is mounted within a compact barrel structure, for the purpose of generating said spatially-incoherent planar light illumination beam from said compact barrel structure for use in illuminating objects to be imaged by said PLIIM-based system.

2. An optical process carried out within an LED-based PLIM having a light emitting diode (LED) with a light emitting source, a focusing lens, collimating lens, and a beam expanding element each contained within a barrel structure, said optical process comprising:

using said focusing lens to focus a reduced size image of the light emitting source of the LED towards a focal point within the barrel structure;

using said collimating lens to collimates the light rays associated with the reduced size image of the light emitting source to produce a collimated light beam; and

using said beam expanding element to expand said collimated light beam so as to produce a spatially-incoherent planar light illumination beam.

3. A LED-based planar light illumination module (PLIM) for use in a PLIIM-based system having relatively short working distances, wherein a linear-type LED array, a focusing lens element, a collimating lens element and a cylindrical lens element are each mounted within a compact barrel structure, for the purpose of producing a spatially-incoherent planar light illumination beam therefrom;

wherein said linear-type LED array has a light emitting surface from which light rays are emitted;

wherein said focusing lens element focuses said light rays and forms a reduced size image of the light emitting source at a predetermined focal point;

wherein said collimating lens element is located at about the focal point of said focusing lens element, and collimates the light rays associated with said reduced size image,

wherein said predetermined focal point is located between said focusing lens element and said collimating lens element; and

wherein said cylindrical lens element expands said light rays from said collimating lens element so as to produce said spatially-incoherent planar light illumination beam.

4. A planar light illumination module (PLIM) comprising:

a light emitting diode (LED) having a small and narrow light emitting source realized on a semiconductor substrate;

a focusing lens having a relatively short focal distance for focusing a reduced size image of the light emitting source to a predetermined focal point;

a collimating lens located at about said predetermined focal point, for collimating the light rays associated with said reduced size image;

a cylindrical lens element located closely beyond said collimating lens, for diverging the collimated light rays associated with said reduced size image substantially within a planar extent to produce a spatially-incoherent planar light illumination beam; and

a compact housing for containing and maintaining the above described optical components in optical alignment, as an integrated optical assembly;

wherein said predetermined focal point is located between said focusing lens and said collimating lens.

5. The PLIM of claim 4, wherein said focusing lens is characterized by a large numerical aperture (i.e. a large lens having a small F #), and the distance between said light emitting source and the focusing lens is maintained as large as possible to maximize the collection of the largest percentage of light rays emitted therefrom, within the spatial constraints allowed by the optical system in which said LED-based PLIM is installed.

6. The PLIM of claim 4, wherein flat-top LEDs are used to construct the PLIM.

7. The PLIM of claim 4, wherein the spectral composition of the LED is associated with any or all of the colors in the visible spectrum, including white-type light.

8. The PLIM of claim 4, wherein the focusing lens focuses a reduced size image of the light emitting source of the LED towards a focal point at about which said collimating lens is located.

9. The PLIM of claim 4, wherein the light rays associated with the reduced sized image are collimated by said collimating lens and then transmitted through said cylindrical lens element to produce said spatially-incoherent planar light illumination beam.