Extended working range dataform reader including fuzzy logic image control circuitry

• US 5,702,059 A
• Filed: 10/18/1995
• Issued: 12/30/1997
• Est. Priority Date: 07/26/1994
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Meta Holding Corporation
• Inventors: Wang, Ynjiun P., Ju, Paul P., Chu, John B.
• Primary Examiner(s): Hajec, Donald T.
• Assistant Examiner(s): Le, Thien Minh
• Application Number:
  US08/544,618
• Time in Patent Office: 804 Days
• Field of Search: 235/462, 235/472, 235/465, 235/468, 235/470, 395/980, 395/3
• US Class Current: 235/472.01
• CPC Class Codes: G01J 3/0272 Handheld
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/2803 using photoelectric array detector
• CPC Class Codes: G01J 3/51 using colour filters
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: G06K 2007/10524 Hand-held scanners
• CPC Class Codes: G06K 2207/1011 Aiming
• CPC Class Codes: G06K 7/10564 Light sources
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10732 Light sources
• CPC Class Codes: G06K 7/10752 Exposure time control
• CPC Class Codes: G06K 7/10792 Special measures in relation to the object to be scanned
• CPC Class Codes: G06K 7/10851 Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device basic electronic circuitry H03
• CPC Class Codes: G06K 7/10881 constructional details of hand-held scanners
• CPC Class Codes: G06K 7/10891 the scanner to be worn on a finger or on a wrist
• CPC Class Codes: G06K 7/1092 sensing by means of TV-scanning

Abstract

A portable data collection system is disclosed. The system includes a dataform reader module having a board camera electrically coupled to a control and decoder board in an open loop feedback configuration. The control and decoder board includes fuzzy logic image control circuitry which analyzes a captured frame of a video image including a dataform produced by the board camera. Based on the analysis of the captured frame, the fuzzy logic image control circuitry generates control signals to adjust operating parameters of the board camera such that an image suitable for decoding is produced.

Claims

1. A dataform reader comprising:

a) a board camera including a two dimensional photosensor array comprising a set of pixels and control circuitry for generating a video signal representative of an illumination content on each pixel in the set of pixels over an exposure period;

b) the board camera control circuitry including a gain control signal input and an exposure period control signal input;

c) an analog to digital converter coupled to the board camera, the analog to digital converter receiving the video signal and generating gray scale values; and

d) a control unit coupled to the board camera and the analog to digital converter to receive the gray scale values and analyze a portion of the gray scale values, generate at the least one of a gain control signal input to the board camera control circuitry gain control signal input and an exposure period control signal input to the board camera control circuitry exposure period control signal input.

2. The two dimensional dataform reader of claim 1, wherein the control unit accesses one or more membership function charts stored in memory to analyze the portion of the gray scale values, each of the one or more membership function charts including a plurality of overlying functions wherein one function of the plurality of functions represents a normal condition for a magnitude of a gray scale value and at least one function represents a non-normal condition for the magnitude of a gray scale value.

20. The dataform reader of claim 1 wherein the control unit further generates a reference signal input to the analog to digital converter, the reference signal being utilized by the analog to digital converter to generate gray scale values.

3. A dataform reader comprising:

a) a board camera including a two dimensional photosensor array comprising a set of pixels and control circuitry for generating a video signal representative of an illumination content on each pixel in the set of pixels over an exposure period;

b) the board camera control circuitry including a gain control signal input and an exposure period control signal input;

c) a fuzzy logic control unit coupled to the board camera to receive the video signal, capture and analyze a portion of the video signal and, based on the analysis of the captured portion of the video signal, generate at the least one of the gain control signal and the exposure period control signal; and

d) the fuzzy logic control unit accessing one or more membership function charts stored in memory to analyze the video signal, each of the one or more membership function charts including a plurality of overlying functions wherein one function of the plurality of functions represents a normal condition for the captured portion of the video signal and at least one function representing a non-normal condition for the captured portion of the video signal;

e) an A/D converter receiving the video signal and generating a series of gray scale values representative of illumination incident on each pixel in accordance with a reference signal; and

f) the fuzzy logic control unit further generating a reference signal in response to the membership functions inputs.

4. The two dimensional dataform reader of claim 3, wherein the membership function charts include a histogram membership function chart representative of the quantity of pixels in an image area having a corresponding gray scale value in excess of a predetermined number.

5. The two dimensional dataform reader of claim 4, wherein the membership function charts further include at least one of:

a) a dynamic range membership function chart representative of local maximum values in the video signal; and

b) a dynamic range membership function chart representative of local minimum values in the video signal.

6. The two dimensional dataform reader of claim 5, further including an digital to analog converter circuitry convening digital gain control, exposure period control and reference voltage control signals from the fuzzy logic circuitry to analog voltage signals usable by the photosensor array and the A/D converter.

7. The two dimensional dataform reader of claim 5, wherein the fuzzy logic control unit includes a processor for calculating an index value as a function of values derived from the captured video signal and the membership function charts and a memory including a look-up table for selecting a gain control value, exposure period and reference voltage setting in accordance with the index value.

8. The two dimensional dataform reader of claim 7, wherein the index value is further a function of a previous index value calculated during a previous dataform reading session.

9. A method of imaging a dataform in a target area using a dataform reader including a two dimensional photosensor array, a control unit and an A/D converter, said method including:

a) imaging said target area including said dataform onto a two dimensional photosensor array comprising a set of pixels;

b) generating a video signal representative of an illumination content on each pixel in the set of pixels of the two dimensional photosensor array over an exposure period in accordance with a gain control input and an exposure period input;

c) converting a portion of the video signal to a set of gray scale values utilizing the A/D converter;

d) inputting the set of gray scale values to the control unit which utilizes a portion of the set of gray scale values to generate at least two membership function input values representing characteristics of said video signal; and

e) applying a fuzzy logic control function to said membership function values utilizing the control unit to generate at least one of said gain control input and said exposure period input.

10. The method of claim 9, wherein said membership function input values include a dynamic range maximum value and a dynamic range minimum value and step (d) includes:

a) generating a dynamic range maximum value representative of local maximum values in the video signal; and

b) generating a dynamic range minimum value representative of local minimum values in the video signal.

11. A method of reading a dataform in a target area, said method including:

a) imaging said target area including said dataform onto a two dimensional photosensor array;

b) generating a video signal representative of said image in accordance with a gain control input and an exposure period input;

c) generating a digital video signal from the video signal, the digital video signal including a sequence of gray scale values representative of said bar code in accordance with the difference between said video signal and a reference voltage;

d) generating at least two membership function input values representing characteristics of said video signal; and

e) applying a fuzzy logic control function to said membership function values to generate at least one of said gain control input and said exposure period input.

12. The method of claim 11, wherein said membership functions input values include a histogram value and step (d) includes:

a) generating a histogram value representative of the quantity of pixels in the image area with a gray scale value in excess of a predetermined number.

13. The method of claim 12, wherein said membership function inputs further include a dynamic range maximum value and a dynamic range minimum value and step (d) further includes:

a) generating a dynamic range maximum value representative of local maximum values in the video signal; and

b) generating a dynamic range minimum value representative of local minimum values in the video signal.

14. The method of claim 11, wherein step (e) includes the following substeps:

a) generating an index number as a function of said membership function values; and

b) applying the index number to a look-up table to determine said gain control input, the exposure period input and the reference voltage in accordance with the index number.

15. The method of claim 14, wherein the index number is further a function of a previous index number generated during a previous dataform reading session and step (e) of the method further includes:

a) storing said index value in a memory for use in a future dataform reading session.

16. A method of imaging a dataform in a target area, said method including:

a) imaging said target area including said dataform onto a two dimensional photosensor array;

b) selecting at least one of an exposure period value and gain control value in accordance with values selected during a previous dataform reading session;

c) generating a video signal representative of said dataform and in accordance with at least one of the exposure period value and gain control value;

d) generating a set of gray scale values corresponding to the video signal;

e) utilizing the set of gray scale values to generate at least two membership function input values representative of characteristics of said video signal;

f) applying a fuzzy logic control function to said membership function input values to determine at least one of an updated exposure period value and an updated gain control value; and

g) storing a value representative of said updated exposure period and gain control values in memory for use in a subsequent dataform reading session.

17. The method of claim 16, wherein said membership function values include at least one of a dynamic range minimum value and step (e) includes:

a) generating a dynamic range maximum value representative of local maximum values in the video signal; and

b) generating a dynamic range minimum value representative of local minimum values in the video signal.

18. The method of claim 16, wherein step (e) includes the sub-steps of:

a) generating an index number as a function of the membership function values and a previous index number generated during a previous imaging session; and

b) applying the index number to a look-up table to determine the at least one of the updated exposure period value and the updated gain control value.

19. A low power consumption dataform reader for reading a dataform in a target area, the reader comprising:

a) an illumination source directing illumination towards the target area;

b) a board camera including a two dimensional photosensor array comprising a set of pixels which receive reflected illumination from the target area, the board camera further including camera control circuitry for generating a signal representative of accumulated illumination incident on each of said pixels during an exposure period; and

c) illuminator control circuitry providing operating power to the illumination source during the exposure period when the exposure period is in excess of a predetermined duration and not providing operating power to the illumination source when the exposure period is less than or equal to the predetermined duration.