Dataform readers having controlled and overlapped exposure integration periods

• US 5,521,366 A
• Filed: 10/31/1994
• Issued: 05/28/1996
• Est. Priority Date: 07/26/1994
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Metanetics Corporation
• Inventors: Wang, Ynjiun P., Ju, Paul P.
• Primary Examiner(s): Hajec, Donald T.
• Assistant Examiner(s): Le, Thien Minh
• Application Number:
  US08/332,592
• Time in Patent Office: 575 Days
• Field of Search: 348/294, 348/297, 348/221, 348/296, 348/362, 348/231, 235/436, 235/454, 235/455, 235/472, 250/208.1
• US Class Current: 235/454
• CPC Class Codes: G06K 7/10564 Light sources
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10752 Exposure time control
• 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 7/1092 sensing by means of TV-scanning

Abstract

Dataform readers and methods provide operation with a sequence of overlapping exposure periods for successive lines of sensor elements of an array. Also, the exposure periods for successive lines of sensor elements, or successive subsets of lines, can be independently determined. In operation of a dataform reader illumination of a target area is turned on before exposure of the first line of sensor elements, each line of sensor elements is exposed by reflected illumination in an exposure period which overlaps with the exposure period of one or more other lines, and illumination is then turned off. Using a CMOS construction, for example, the level of image signals read from one line of sensor elements is referred to a look-up table to determine an appropriate exposure period for a subsequent line or lines of elements of an array. This process is repeated to achieve exposure periods adjusted for localized exposure conditions for each successive line or subset of lines of sensor elements.

Claims

1. A dataform reader comprising:

an array of sensor elements readable to provide image signals, including a plurality of lines of sensor elements;

an array control assembly coupled to said array and arranged to initiate exposure of a line of sensor elements by causing sensor elements of said line to be set to a reference potential in response to an exposure start signal, and to cause image signals to be read from sensor elements of said line in response to an exposure stop signal and coupled to an output point; and

an exposure control system coupled to said output point and successively responsive to the level of image signals read from selected lines of sensor elements to determine an exposure period for at least one subsequent line of sensor elements based on the level of image signals from each said selected line, and arranged to provide said exposure start and stop signals to said array control assembly to implement said exposure periods in a sequence causing the exposure period for one line of sensor elements to overlap the exposure period for at least one subsequent line of sensor elements.

2. A dataform reader as in claim 1, wherein said array control assembly is arranged to cause individual image signals from complete lines of sensor elements to be sequentially read and coupled to said output point in response to an exposure stop signal.

3. A dataform reader as in claim 1, wherein said exposure control system is arranged to utilize the image signals from a plurality of sensor elements of a selected line of said array to develop an average image signal level which is usable for determining an exposure period for one of the following:

a single subsequent line of sensor elements, a plurality of successive lines of sensor elements.

4. A dataform reader as in claim 3, additionally comprising a memory unit storing a look-up table of line exposure periods versus average image signal levels.

5. A dataform reader as in claim 1, wherein said array control assembly causes a line of sensor elements to be set to a reference potential by being coupled to a ground reference potential.

6. A dataform reader as in claim 1, wherein said exposure control system provides said start signals to said array control unit for successive lines of sensor elements at predetermined uniform time intervals.

7. A dataform reader as in claim 1, wherein said array control assembly comprises a line control shift register unit enabling individual element sensor lines of said array to be selected for one of reading and coupling to said reference potential, and a readout shift register unit enabling individual element sensors to be selected for coupling of image values to said output point.

8. A dataform reader as in claim 7, additionally comprising a plurality of sample and hold amplifiers, each usable between one column of sensor elements of said array and said output point.

9. A dataform reader as in claim 8, additionally comprising a plurality of output switches controlled by said readout shift register, one coupled between each of said sample and hold amplifiers and said output point.

10. A dataform reader as in claim 1, wherein each of said sensor elements is a light sensitive diode element formed on a CMOS chip.

11. A dataform reader as in claim 1, additionally comprising:

a memory unit coupled to said output point and arranged to store image data representative of said image signals; and

a processing unit coupled to said memory unit and arranged to process said stored image data to decode a dataform represented by said image signals.

12. A dataform reader comprising:

an array of sensor elements readable to provide image signals, including a plurality of lines of sensor elements;

an array control assembly arranged to initiate exposure of a line of sensor elements by causing sensor elements of said line to be set to a reference potential in response to an exposure start signal and to cause image signals to be read from sensor elements of said line in response to an exposure stop signal and coupled to an output point; and

an exposure control system coupled to said output point and successively responsive to the level of image signals read from selected lines of sensor elements to determine an exposure period for at least one subsequent line of sensor elements based on the level of image signals from each said selected line, and arranged to provide said exposure start and stop signals to said array control assembly to implement said exposure periods for lines of sensor elements.

13. A dataform reader as in claim 12, wherein said exposure control system is arranged to utilize the image signals from a plurality of sensor elements of a selected line of said array to develop an average image signal level which is usable for determining an exposure period for one of the following:

a single subsequent line of sensor elements, a plurality of successive lines of sensor elements.

14. A dataform reader as in claim 13, additionally comprising a memory unit storing a look-up table of line exposure periods versus average image signal levels.

15. A dataform reader as in claim 12, wherein said exposure control system provides said start signals to said array control unit for successive lines of sensor elements at predetermined uniform time intervals.

16. A dataform reader as in claim 12, wherein each of said sensor elements is a light sensitive diode element formed on a CMOS chip.

17. A dataform reader, usable to read a dataform in a target area at a distance from said reader comprising:

an array of sensor elements readable to provide image signals, including a plurality of lines of sensor elements;

at least one exposure illuminator arranged to illuminate said target area;

a focusing device positioned in front of said array and arranged to focus on said array illumination reflected from at least a portion of said dataform when said distance is within a focus range;

an array control assembly coupled to said array and arranged to initiate exposure of a line of sensor elements by causing sensor elements of said line to be set to a reference potential in response to an exposure start signal and to cause image signals to be read from sensor elements of said line in response to an exposure stop signal and coupled to an output point;

an exposure control system coupled to said array control assembly and arranged to provide said exposure start and stop signals to said array control assembly to implement said exposure periods in a sequence causing the exposure period for one line of sensor elements to overlap the exposure period for at least one subsequent line of sensor elements; and

a processing unit coupled to said output point and arranged to process said image signals to decode said dataform.

18. A dataform reader as in claim 17, wherein said exposure control system provides said start signals to said array control unit for successive lines of sensor elements at predetermined uniform time intervals.

19. A dataform reader as in claim 17, wherein said array control assembly comprises a line control shift register unit enabling individual element sensor lines of said array to be selected for one of reading and coupling to said reference potential, and a readout shift register unit enabling individual element sensors to be selected for coupling of image values to said output point.

20. A dataform reader as in claim 19, additionally comprising a plurality of sample and hold amplifiers, each usable between one column of sensor elements of said array and said output point.

21. A dataform reader as in claim 17, wherein each of said sensor elements is a light sensitive diode element formed on a CMOS chip.

22. A dataform reader as in claim 17, additionally comprising a memory unit coupled between said output point and said processing unit and arranged to store image data representative of said image signals.

23. A method, for use with a dataform reader including an array of sensor elements, comprising the following steps:

(a) causing illumination of a target area including a dataform image to be reflected onto said array of sensor elements;

(b) coupling a first line of sensor elements to a reference potential in response to an exposure start signal;

(c) accumulating charge on sensor elements of said first line in an exposure period;

(d) terminating said first line exposure period by reading image signals from sensor elements of said first line in response to an exposure stop signal;

(e) coupling said first line image signals to an output point;

(f) repeating steps (b) through (d) for successive lines of sensor elements, with step (b) for each successive line of sensor elements initiated during the step (c) exposure period for the respective preceding line of sensor elements, resulting in partially overlapping exposure periods;

(g) coupling image signals from successive lines of sensor elements to said output point in sequence following image signals from the respective preceding line; and

(h) terminating said reflection of illumination onto said array of sensor elements.

24. A method as in claim 23, wherein step (a) includes turning on illumination of said target area to provide reflected illumination and step (h) includes turning off said illumination after image signals have been read from all lines of sensor elements of said array.

25. A method as in claim 23, additionally including the following steps between steps (e) and (f):

(x) determining an averaged level of first line image signals as coupled to said output point in step (e);

(y) utilizing said averaged image signal level to determine the timing of an exposure stop signal applied in a repetition of step (d) to terminate the exposure period for at least one line of sensor elements subsequent to said first line.

26. A method as in claim 25, wherein step (y) includes using a look-up table to determine the timing of said exposure stop signal based upon said averaged image signal level.

27. A method as in claim 25, wherein in step (y) said averaged image signal is used to determine the timing of an exposure stop signal applied to terminate the exposure period of a subsequent line of sensor elements at least one line removed from the line whose image signal level is averaged in step (x).

28. A method as in claim 23, additionally including the steps of:

(i) coupling said image signals from said output point to a memory unit; and

(j) decoding said dataform in a decoder coupled to said memory unit.

29. A method, for use with a dataform reader including X lines of sensor elements arranged in an array, comprising the following steps:

(a) reading image signals from sensor elements of a selected line of sensor elements, said image signals including image signals representative of at least a portion of a dataform;

(b) utilizing the level of image signals read in step (a) to determine an exposure period;

(c) utilizing said exposure period to control the duration of exposure to illumination reflected from a target area onto a first subset of Y lines of sensor elements, where Y is at least one and less than X; and

(d) repeating steps (a) through (c) substituting in step (a) image signals from a line subsequent to said selected line, and in step (c) utilizing said exposure period to control the duration of exposure of a second subset of Y lines subsequent to said first subset of Y lines.

30. A method as in claim 29, wherein the exposure period determined in step (b) is utilized in step (c) as the exposure period for each of a plurality of lines comprising a subset of Y lines, each line being individually exposed for said exposure period.

31. A method as in claim 30, wherein Y equals three, each line of sensor elements of a subset of three lines being exposed for an exposure period determined on the basis of the level of image signals read from a selected earlier line of sensor elements.

32. A method as in claim 29, wherein Y equals one, each subset of one line of sensor elements being exposed for an exposure period determined on the basis of the level of image signals read from a selected earlier line of sensor elements.

33. A method as in claim 29, wherein step (b) includes using a look-up table to determine said exposure period based upon an averaged value of the level of image signals read in step (a).

34. A method as in claim 29, wherein in step (c) said exposure period is utilized to determine the timing of an exposure stop signal effective to cause image signals to be read from a line of sensor elements, relative to a prior exposure start signal effective to cause said line of sensor elements to be coupled to a reference potential to start the exposure period.

35. A method as in claim 29, additionally comprising the step of utilizing said image signals to decode said dataform.