System and method to automatically focus an image reader

• US 20060202038A1
• Filed: 03/11/2005
• Published: 09/14/2006
• Est. Priority Date: 03/11/2005
• Status: Active Grant

• Current Assignee: Hand Held Products Incorporated (Honeywell International Inc.)
• Original Assignee: Hand Held Products Incorporated (Honeywell International Inc.)
• Inventors: Havens, William H., Wang, Ynjiun
• Granted Patent: US 7,611,060 B2
• Time in Patent Office: Days
• US Class Current: 235/462.240
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10732 Light sources
• CPC Class Codes: G06K 7/10811 Focalisation
• CPC Class Codes: G06K 7/10831 Arrangement of optical elements, e.g. lenses, mirrors, prisms optical elements per se G02B
• CPC Class Codes: H04N 23/689 Motion occurring during a rolling shutter mode

Abstract

The invention features a system and method to automatically focus an image reader using a single frame of image data. The method comprises exposing sequentially a plurality of rows of pixels in the image sensor. The method further comprising varying in incremental steps the focus of the image reader'"'"'s optical system from a first setting where a distinct image of objects located at a first distance from the image reader is formed on the image sensor to a second setting where a distinct image of objects located at a second distance from the image reader is formed on the image sensor. As part of the method, the varying of the focus of the optical system occurs during the exposure of the plurality of rows of pixels.

Claims

1. A method for automatically focusing a hand held bar code reading device, said hand held bar code reading device having an imaging lens and a focus setting, said method comprising the steps of:

generating a trigger signal to drive said hand held bar code reading device from an idle state to an active reading state;

directing with said imaging lens light energy reflected from a target onto an image sensor having a plurality of rows of pixels;

exposing sequentially a plurality of rows of pixels in the image sensor during a frame exposure period, the frame exposure period being defined as a time duration extending from the beginning of the exposure of the first of the plurality of rows to the end of the exposure of the last of the plurality of rows;

controlling said focus setting of said hand held bar code reading device so that said focus setting changes one of continuously or stepwise continuously between first setting where a distinct image of objects located at a first distance from the image reader is formed on the image sensor to a second setting where a distinct image of objects located at a second distance from the image reader is formed on the image sensor; and

reading out a plurality of rows of image data from the plurality of rows of pixels in the image sensor,

wherein controlling step includes the step of changing said focus setting one of continuously or stepwise continuously between said first focus setting and said second focus setting during at least a portion of said frame exposure period.

2. The method according to claim 1 further comprising processing the plurality of rows of image data to determine an in-focus setting for said hand held bar code reading device corresponding to a distinct image of the target being formed on the image sensor.

3. The method according to claim 1 further comprising simultaneously exposing the plurality of rows in the image sensor to generate an image of the target.

5. The method according to claim 1 further comprising processing the plurality of rows of image data to determine an in-focus setting for said hand held bar code reading device corresponding to a distinct image of the target being formed on the image sensor, simultaneously exposing said plurality of rows to collect image data after said in-focus setting is determined, and transferring collected image data corresponding to pixels exposed during said simultaneous exposing step to a bar code decode module.

6. The method according to claim 1 wherein said controlling step includes the step of moving said imaging lens.

7. The method according to claim 5 wherein said generating step includes the step of depressing a manual trigger of said hand held bar code reading device.

4. The method according to claim I wherein the exposure period for adjacent rows of pixels in said image reader overlap.

8. A bar code decoding device with an automatic focusing capability, the bar code decoding device comprising:

an integrated circuit including at least an image sensor array, said image sensor array having a plurality of rows of pixels, each pixel of the plurality of rows of pixels having an associated pixel amplifier;

a hand held housing encapsulating said image sensor array;

an imaging lens capable of directing light reflected from a target onto the image sensor array, the imaging lens having a focus setting;

a rolling shutter control module configured to sequentially expose a plurality of rows of pixels in the image sensor array to collect focusing image data;

an automatic focusing module configured to analyze the focusing image data to determine an in-focus setting for the target corresponding to a distinct image of the target being formed on the image sensor; and

a bar code symbol processing module configured to identify the presence of a bar code symbol representation within collected image data,

wherein said focus setting of said imaging lens is controlled to be changed one of continuously and stepwise continuously between a first focus setting corresponding to distinct images of objects located at a first distance from the image reader being formed on the image sensor array and a second focus setting corresponding to distinct images of objects located at a second distance from the image reader being formed on the image sensor array during at least a portion of a time period during which the rolling shutter control module is sequentially exposing the plurality of rows of pixels.

9. The image reader according to claim 8 further comprising a global electronic shutter control module configured to simultaneously expose the plurality of lines of pixels in the image sensor array to collect a frame of image data once the in-focus setting for the target has been determined.

10. The image reader according to claim 9 wherein the rolling shutter control module and the global electronic shutter control module are integrated on the same integrated circuit containing the image sensor array.

11. The image reader according to claim 9 wherein said bar code reading device is configured so that said global electronic shutter control module is activated when said automatic focusing module determines said in-focus setting.

12. The image reader according to claim 8 wherein the rolling shutter control module is capable of causing exposure periods for adjacent rows of pixels to overlap.

13. A bar code reading device for minimizing ambient light image degradation, the bar code reading device comprising:

an integrated circuit including at least an image sensor array, the image sensor array providing a signal suitable for light intensity determination;

a hand held housing encapsulating said image sensor array;

a rolling shutter control module configured to sequentially expose a plurality lines of pixels in the image sensor array;

a global electronic shutter control module configured to simultaneously expose the plurality of lines of pixels in the image sensor array,

a bar code processing module configured to identify the presence of a bar code symbol represented in collected image data;

wherein said bar code reading device is programmable to operate in a mode in which said bar code reading device selects one of the rolling shutter control module and the global electronic shutter control module in response to the signal suitable for light intensity determination.

14. The bar code reading device according to claim 13 wherein the signal suitable for light intensity determination includes information related to an intensity of a light source of the image reader.

15. The bar code reading device according to claim 13 wherein the signal suitable for light intensity determination is useful for determining whether a minimum integration time is satisfied.

16. The bar code reading device according to claim 13 wherein the signal suitable for light intensity determination is useful for determining whether an integration time for the current environmental condition is less than a calculated minimum integration time.

17. The bar code reading device according to claim 13 wherein the rolling shutter control module and the global electronic shutter control module are integrated on the same integrated circuit containing the image sensor array.

18. A method for operating a portable bar code reading device, the method comprising:

determining at least one parameter related to an ambient light intensity;

analyzing the at least one parameter;

switching control of an image sensor array in the portable bar code reading device from a global electronic shutter control module to a rolling shutter control module in response to the analysis of the at least one parameter;

collecting image data while said image sensor array is being controlled by said rolling shutter control module; and

transferring collected image data collected while said image sensor array is controlled by said rolling shutter control module to a bar code decode module.

19. The method according to claim 18 wherein the at least one parameter includes an exposure time for current environmental conditions.

20. The method according to claim 19 wherein the analyzing the at least one parameter includes calculating a ratio of the exposure time for current environmental conditions to a predetermined exposure time.

21. The method according to claim 20 wherein the predetermined exposure time is based on illumination supplied by light sources of the image reader.

22. The method according to claim 18 wherein the analyzing the at least one parameter includes determining whether a ratio of the ambient light intensity to an intensity of a light source of the image reader exceeds a specified threshold.