Autofocus barcode scanner and the like employing micro-fluidic lens

• US 20050218231A1
• Filed: 01/20/2005
• Published: 10/06/2005
• Est. Priority Date: 01/23/2004
• Status: Active Grant

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Inventors: Massieu, Jean-Louis
• Granted Patent: US 7,296,749 B2
• Time in Patent Office: Days
• US Class Current: 235/472.10
• CPC Class Codes: G02B 26/005 based on electrowetting
• CPC Class Codes: G02B 3/14 of variable focal length
• CPC Class Codes: G06K 2007/10485 Arrangement of optical elements
• CPC Class Codes: G06K 7/10702 Particularities of propagating elements, e.g. lenses, mirrors G06K7/10831 takes precedence
• CPC Class Codes: G06K 7/10801 Multidistance reading

Abstract

A machine-readable symbol reader includes a microfluidic lens assembly providing responsive, reliable auto-focus functionality. A range finder may provide distance to a planar target (e.g., barcode symbol) information for use in auto-focusing, with or without localization. Illumination system, if included, is selectively controlled based on the distance to target and auto-focusing functionality to substantially reduce power consumption. The localization may color optical sensors.

Claims

1. A machine-readable symbol reader to read machine-readable symbols carried by targets, the machine-readable symbol reader comprising:

a microfluidic lens assembly having at least one fluid and a number of electrodes selectively operable to modify a shape of the at least one fluid;

an optical sensor positioned along an optical axis of the microfluidic lens assembly relatively behind the microfluidic lens assembly with respect to the target; and

at least one controller, the controller coupled to cause a selected potential to be applied to at least some of the electrodes of the microfluidic lens assembly to focus images of the target on the optical sensor.

2. The machine-readable symbol reader of claim 1, further comprising:

a range finder system positioned to assess a distance between the microfluidic lens assembly and the target.

3. The machine-readable symbol reader of claim 1, further comprising:

a range finder system positioned to assess a distance between the microfluidic lens assembly and the target, wherein the at least one controller is coupled to receive range finding information from the range finder system and configured adjust a focal length of the microfluidic lens assembly based on the range finding information.

4. The machine-readable symbol reader of claim 1, further comprising:

a range finder system positioned to assess a distance between the microfluidic lens assembly and the target, wherein the at least one controller is coupled to receive range finding information from the range finder system and configured to determine a focal length for the microfluidic lens assembly based on the determined focal range.

5. The machine-readable symbol reader of claim 1, further comprising:

a range finder system positioned to assess a distance between the microfluidic lens assembly and the target, the range finder system comprising a range finder output device selectively operable to produce an output in a defined frequency range in an electromagnetic spectrum and a range finder input device sensitive in the defined frequency range of the electromagnetic spectrum.

6. The machine-readable symbol reader of claim 1, further comprising:

a range finder system positioned to assess a distance between the microfluidic lens assembly and the target, the range finder system comprising a range finder output device selectively operable to produce an output pressure pulse in a defined frequency range and a range finder input device sensitive to pressure pulses in the defined frequency range.

7. The machine-readable symbol reader of claim 1, wherein the focal characteristics of the microfluidic lens assembly are controlled by application of pre-selected electrical fields to a second fluid surrounding the first fluid, where the first and the second fluids are immiscible with respect to one another, the second fluid is a conductor and the first fluid is an insulator.

8. The machine-readable symbol reader of claim 1, wherein the microfluidic lens assembly comprises a single optical interface element.

9. The machine-readable symbol reader of claim 1, wherein at least one optical interface element of the lens comprises a second fluid, the first and the second fluids being non-miscible fluids of different optical indexes and of substantially same density with second fluid being substantially electrically-conductive and the first fluid being substantially electrically-non-conductive.

10. The machine-readable symbol reader of claim 1, further comprising:

an illumination system, the illumination sources selectively actuatable to produce different intensities of illumination.

11. The machine-readable symbol reader of claim 1, further comprising:

an illumination system comprising a number of illumination sources, where the controller is configured to determine a desired intensity of illumination and coupled to selectively activated a number of the illumination sources to produce desired intensity of illumination.

12. The machine-readable symbol reader of claim 1, further comprising:

a color filter assembly positioned between the target and the optical sensor.

13. The machine-readable symbol reader of claim 1, further comprising:

a Bayer color filter assembly positioned between the target and the optical sensor.

14. A method of operating a machine-readable symbol reader to read machine-readable symbols carried by targets, the method comprising:

determining a distance between a microfluidic lens assembly of the machine readable symbol reader and the target;

adjusting a focal length of the microfluidic lens assembly based on the determined distance to the target;

capturing an image of a machine-readable symbol carried by the target; and

decoding the machine-readable symbol carried by the target.

15. The method of claim 14 wherein adjusting a focal length of the microfluidic lens assembly includes applying a potential to at least one of a number of electrodes.

16. The method of claim 14 wherein adjusting a focal length of the microfluidic lens assembly includes applying a first potential to at least one of a number of electrodes spaced from a substantially non-conducting fluid by a dielectric, and applying a second potential to a substantially conducting fluid surrounding the first fluid, where the non-conducting fluid and the conducting fluid are immiscible with respect to one another.

17. The method of claim 14 wherein capturing an image of a machine-readable symbol carried by the target includes electronically scanning an optical sensor positioned along an optical axis of the microfluidic lens assembly relatively behind the microfluidic lens assembly with respect to the target.

18. The method of claim 14 wherein determining a distance between a microfluidic lens assembly of the machine readable symbol reader and the target includes emitting energy in a defined range of an electromagnetic spectrum toward the target, and receiving energy in the defined range of the electromagnetic spectrum reflected from the target.

19. The method of claim 14 wherein determining a distance between a microfluidic lens assembly of the machine readable symbol reader and the target includes emitting pressure pulses a defined range of frequencies toward the target, and receiving pressure pulses in the defined range of frequencies reflected from the target.

20. The method of claim 14, further comprising:

adjusting an output intensity of an illumination system of the machine-readable symbol reader based on at least one of the determined distance between the microfluidic lens assembly and the target and the focal length of the microfluidic lens assembly.

21. The method of claim 14, further comprising:

minimizing an output intensity of an illumination system of the machine-readable symbol reader based on at least one of the determined distance between the microfluidic lens assembly and the target and the focal length of the microfluidic lens assembly.

22. The method of claim 14, further comprising:

identifying the target in an image before determining the distance between a microfluidic lens assembly of the machine readable symbol reader and the target.

23. The method of claim 22 wherein identifying the target in an image before determining the distance between a microfluidic lens assembly of the machine readable symbol reader and the target comprises:

determining a plurality of sub-windows of the image on which to operate;

determining a subtraction-modulus-difference value for each of a number pixels in horizontally adjacent ones of the sub-windows and for each of a number pixels in vertically adjacent ones of the sub-windows;

aggregating adjacent sub-windows having determined subtraction-modulus-difference values below a defined threshold into a meta window of the image on which to operate;

determining a focus value corresponding to a focus condition at an initial focal length of the microfluidic lens assembly;

adjusting the microfluidic lens assembly to a second focal length;

determining a focus value corresponding to a focus condition at the second focal length of the microfluidic lens assembly;

determining a direction of change in the determined focus values;

repeatedly, adjusting the microfluidic lens assembly at different incremental focal lengths in a space of the image along the same direction in the space, and determining a focus value corresponding to a focus condition at the different incremental focal lengths until the focus value drops by more than a defined threshold; and

interpolating a best focus length from at least three of the focal lengths.

24. The method of claim 23, further comprising:

accumulating the subtraction-modulus-difference value for at least three different colors.

25. A method of operating a machine-readable symbol reader to read color encoded machine-readable symbols carried by targets, the method comprising:

acquiring an image through a three color filter at a single optical sensor;

determining a plurality of sub-windows of the image on which to operate;

for each of the colors, determining a subtraction-modulus-difference value for each of a number pixels in horizontally adjacent ones of the sub-windows and for each of a number pixels in vertically adjacent ones of the sub-windows;

accumulating the subtraction-modulus-difference value for each of at least three different colors;

aggregating adjacent sub-windows having accumulated subtraction-modulus-difference values below a defined threshold into a meta window of the image on which to operate;

determining a focus value corresponding to a focus condition at an initial focal length of the microfluidic lens assembly;

adjusting the microfluidic lens assembly to a second focal length;

determining a focus value corresponding to a focus condition at the second focal length of the microfluidic lens assembly;

determining a direction of change in the determined focus values;

repeatedly, adjusting the microfluidic lens assembly at different incremental focal lengths in a space of the image along the same direction in the space, and

determining a focus value corresponding to a focus condition at the different incremental focal lengths until the focus value drops by more than a defined threshold; and

interpolating a best focus length from at least three of the focal lengths.

26. The method of claim 25 wherein interpolating a best focus length from at least three of the focal lengths comprises a quadratic or a Gaussian interpolation.