Automatic Region of Interest Focusing for an Imaging-Based Bar Code Reader

• US 20090108071A1
• Filed: 10/31/2007
• Published: 04/30/2009
• Est. Priority Date: 10/31/2007
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Carlson, Bradley S.
• Granted Patent: US 7,854,385 B2
• Time in Patent Office: Days
• US Class Current: 235/462.320
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10811 Focalisation

Abstract

A variable focus imaging lens assembly for an imaging system of an imaging-based bar code reader for imaging and decoding a target bar code. The lens assembly includes an automatic focusing system for energizing a drive mechanism and imaging system to move a movable lens from the predetermined position along its path of travel and generate a series of image frames; analyzing one or more image frames of the series of image frames to determine a region of interest, the region of interest including an image of a target bar code; analyzing the region of interest in subsequent image frames of the series of image frames to determine an amount of blurring; selecting an image frame from the series of image frames having blurring less than a threshold amount of blurring; and utilizing a decoder to decode the image of the target bar code in the selected image frame.

Claims

1. A variable focus imaging lens assembly for an imaging system of an imaging-based bar code reader for imaging and decoding a target bar code, the imaging system generating image frames of a field of view of the imaging system and including an imaging sensor array and a decoder for decoding an image of the target bar code, the variable focus imaging lens assembly comprising:

a lens assembly focusing light from the field of view onto the sensor array, the lens assembly including a lens movable along a path of travel;

a drive mechanism driving the movable lens from a predetermined position along the path of travel;

an automatic focusing system;

energizing the drive mechanism and imaging system to move the movable lens from the predetermined position along its path of travel and generate a series of image frames;

analyzing one or more image frames of the series of image frames to determine a region of interest, the region of interest including an image of a target bar code;

analyzing the region of interest in subsequent image frames of the series of image frames to determine an amount of blurring in each image frame;

selecting an image frame from the subsequent image frames of the series of image frames having an amount of blurring less than a predetermined threshold; and

utilizing the decoder to decode the image of the target bar code in the selected image frame.

2. The variable focus imaging lens assembly of claim 1 wherein the movable lens path of travel is coincident with an optical axis of the lens assembly.

3. The variable focus imaging lens assembly of claim 1 wherein the predetermined position of the movable lens corresponds to a best focus position of the imaging system at a far working range of the imaging system.

4. The variable focus imaging lens assembly of claim 1 wherein the movable lens is moved along a path a travel corresponding to moving a best focus position of the imaging system from a far working range to a near working range of the imaging system.

5. The variable focus imaging lens assembly of claim 1 wherein determination of the region of interest includes contrast and edge detection analysis.

6. An imaging-based bar code reader for imaging and decoding a target bar code, the bar code reader comprising:

an imaging system generating image frames of a field of view of the imaging system and including an imaging sensor array and a decoder; and

a variable focus imaging lens assembly for focusing light from the field of view onto the sensor array, the variable focus imaging lens assembly including;

a lens assembly focusing light from the field of view onto the sensor array, the lens assembly including a lens movable along a path of travel;

a drive mechanism driving the movable lens along the path of travel;

an automatic focusing system;

energizing the drive mechanism and imaging system to move the movable lens from the predetermined position along its path of travel and generate a series of image frames;

analyzing one or more image frames of the series of image frames to determine a region of interest, the region of interest including an image of a target bar code;

analyzing the region of interest in subsequent image frames of the series of image frames to determine an amount of blurring in each image frame;

selecting an image frame from the subsequent image frames of the series of image frames having an amount of blurring less than a predetermined threshold; and

utilizing the decoder to decode the image of the target bar code in the selected image frame.

7. The bar code reader of claim 6 wherein the movable lens path of travel is coincident with an optical axis of the lens assembly.

8. The bar code reader of claim 6 wherein the predetermined position of the movable lens corresponds to a best focus position of the imaging system at a far working range of the imaging system.

9. The bar code reader of claim 6 wherein the movable lens is moved along a path a travel corresponding to moving a best focus position of the imaging system from a far working range to a near working range of the imaging system.

10. The bar code reader of claim 6 wherein determination of the region of interest includes contrast and edge detection analysis.

11. A method of imaging and decoding a target bar code reading, the steps of the method comprising:

providing an imaging system generating image frames of a field of view of the imaging system and including an imaging sensor array and a decoder;

a variable focus imaging lens assembly for focusing light from the field of view onto the sensor array, the variable focus imaging lens assembly including a lens assembly focusing light from the field of view onto the sensor array, the lens assembly including a lens movable along a path of travel;

a drive mechanism driving the movable lens along the path of travel; and

an automatic focusing system;

energizing the drive mechanism and imaging system to move the movable lens from the predetermined position along its path of travel and generate a series of image frames;

analyzing one or more image frames of the series of image frames to determine a region of interest, the region of interest including an image of a target bar code;

analyzing the region of interest in subsequent image frames of the series of image frames to determine an amount of blurring in each image frame;

selecting an image frame from the series of image frames having an amount of blurring less than a predetermined threshold value; and

utilizing the decoder to decode the image of the target bar code in the selected image frame.

12. The method of imaging and decoding a target bar code of claim 11 wherein the movable lens path of travel is coincident with an optical axis of the lens assembly.

13. The method of imaging and decoding a target bar code of claim 11 wherein the predetermined position of the movable lens corresponds to a best focus position of the imaging system at a far working range of the imaging system.

14. The method of imaging and decoding a target bar code of claim 11 wherein the movable lens is moved along a path a travel corresponding to moving a best focus position of the imaging system from a far working range to a near working range of the imaging system.

15. The method of imaging and decoding a target bar code of claim 11 wherein determination of the region of interest includes contrast and edge detection analysis.

16. A method of imaging and decoding a target bar code reading, the steps of the method comprising:

providing an imaging system generating image frames of a field of view of the imaging system and including an imaging sensor array and a decoder;

a variable focus imaging lens assembly for focusing light from the field of view onto the sensor array, the variable focus imaging lens assembly including a lens assembly focusing light from the field of view onto the sensor array, the lens assembly including a movable lens movable along a path of travel; and

an automatic focusing system;

energizing the imaging system to generate an image frame with the lens in a predetermined, stationary position;

analyzing the image frame to determine a region of interest, the region of interest including an image of a target bar code;

analyzing the region of interest to determine an amount of blurring;

if the amount of blurring is less than a predetermined threshold value, utilizing the decoder to decode the image of the target bar code in the image frame;

if the amount of blurring is greater than or equal to the predetermined threshold value, determining a new position along the movable lens path of travel PT wherein the region of interest RI in a captured image frame would be more in-focus; and

moving the movable lens to one or more new positions and generating one or more image frames until an amount of blurring is less than the predetermined threshold value.

17. A variable focus imaging lens assembly for an imaging system of an imaging-based bar code reader for imaging and decoding a target bar code, the imaging system generating image frames of a field of view of the imaging system and including an imaging sensor array and a decoder for decoding an image of the target bar code, the variable focus imaging lens assembly comprising:

a lens assembly focusing light from the field of view onto the sensor array, the lens assembly providing for a best focus position that is movable between a far working range and a near working range of the imaging system;

an automatic focusing system;

energizing the imaging system and the lens assembly to move the best focus position of the lens assembly from a predetermined focus position between the near working range and the far working range and generate a series of image frames;

analyzing one or more image frames of the series of image frames to determine a region of interest, the region of interest including an image of a target bar code;

analyzing the region of interest in subsequent image frames of the series of image frames to determine an amount of blurring in each image frame;

selecting an image frame from the subsequent image frames of the series of image frames having an amount of blurring less than a predetermined threshold; and

utilizing the decoder to decode the image of the target bar code in the selected image frame.

18. The variable focus imaging lens assembly of claim 17 wherein the lens assembly includes a movable lens and the lens moves along a path of travel, one end of the path of travel corresponds a best focus position at a far working range of the imaging system and an opposite end of the path of travel corresponding to a best focus position at a near working range of the imaging system.

19. The variable focus imaging lens assembly of claim 17 wherein the predetermined focus position corresponds to the far working range of the imaging system.

20. The variable focus imaging lens assembly of claim 17 wherein determination of the region of interest includes contrast and edge detection analysis.