Automatic exposure single frame imaging systems

• US 5,572,006 A
• Filed: 07/26/1994
• Issued: 11/05/1996
• 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:
  US08/280,489
• Time in Patent Office: 833 Days
• Field of Search: 235/462, 235/472, 235/454, 235/455, 235/467, 348/229, 348/362
• 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

An automatic exposure imaging system operating on a single frame image capture basis is adapted for single chip CMOS type construction. For reading dataforms, such as two-dimensional bar codes and matrix codes, the system can provide automatic gain control, automatic exposure control, automatic focus sensing and single frame imaging and decoding, with reduced power consumption. A fixed focus distance sensor element array assembly and optical distance sensing enable automatic initiation of exposure when the image is in-focus. Exposure provided by image illuminators is automatically controlled by sensing of the cumulative level of reflected light during the exposure period. Alternatively, exposure time is determined from a look-up table, based upon the level of light reflected during an initial illumination period of fixed duration. Automatic system turn-off or re-reading can be provided, depending upon whether a dataform is successfully decoded. Power use is reduced by terminating the reading of sensor elements upon successful decoding. A complete, light-weight, hand-held reader is described, including provision for transmission of decoded dataform information and a wide range of additional capabilities via plug-in cards. Related methods are also described.

Claims

1. An automatic exposure imaging system, usable as a dataform reader to read a dataform in a target area at a distance from said reader, comprising:

a plurality of sensor elements which are readable to provide image signals and at least some of which are positioned in a two-dimensional array;

at least one focus illuminator arranged to illuminate said target area with an area of illumination characterized by at least one of a size, a brightness and a location which varies with the distance between the array and the target area;

a user trigger device arranged to activate said at least one focus illuminator and initiate reading of selected sensor elements;

an in-focus sensing device responsive to image signals from at least one of said sensor elements and arranged to provide an in-focus signal when said area of illumination is characterized by at least one of a size within a predetermined size range, a brightness within a predetermined brightness range and a location within a predetermined location range;

a gain control device responsive, in a period after said in-focus signal, to the level of reflected light as represented by image signals from at least one of said sensor elements and arranged to control image signal amplification;

an exposure control device, responsive to image signals from at least one of said sensor elements, and arranged to provide a start signal in response to said in-focus signal and a stop signal in response to reflection of a predetermined level of illumination from said target area;

at least one exposure illuminator responsive to said start signal and to said stop signal, and arranged to illuminate said target area during an exposure period determined by said start and stop signals;

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

a processing unit coupled to said memory unit and arranged to process stored image data to decode said dataform, and to provide an end-cycle signal effective to terminate reading of selected sensor elements and operation of the dataform reader, upon successful decoding of the dataform; and

an output device coupled to said processing unit and arranged to provide output signals representative of decoded dataform information.

2. An imaging system as in claim 1, additionally comprising an optical filter positioned in front of said array, transmissive to illumination from said exposure illuminator and effective to reduce transmission in other portions of the ambient light spectrum.

3. An imaging system as in claim 1, wherein said gain control device provides a signal used to control the gain of image signals provided from sensor elements included in said two-dimensional array.

4. An imaging system as in claim 1, wherein said at least one focus illuminator comprises two focus illuminators providing respective beams of light which intersect in front of the array at a focus distance representative of a fixed focus plane of said array.

5. An imaging system as in claim 4, additionally comprising a central focusing lens positioned in front of said array and arranged to provide a plane of focus at said focus distance, with a depth of focus range extending about said focus distance.

6. An imaging system as in claim 4, wherein said in-focus sensing device is arranged to sense at least a predetermined degree of convergence of the illumination areas provided on said target area by said beams of light.

7. An imaging system as in claim 1, wherein said at least one exposure illuminator comprises an array of illuminator devices arranged to provide a predetermined level of illumination across the target area when said array and said image are separated by a predetermined distance.

8. An imaging system as in claim 7, additionally comprising a lens array assembly for providing predetermined focusing of light from said array of illuminating devices.

9. An imaging system as in claim 7, wherein said illuminator devices are light emitting diodes.

10. An imaging system as in claim 1, wherein said exposure control device develops a voltage representative of the cumulative value of image signals over a period of time and provides said stop signal when said voltage reaches a predetermined threshold voltage.

11. An automatic exposure system, comprising:

a plurality of sensor elements which are readable to provide image signals representative of reflected illumination and at least some of which are positioned in a two-dimensional array;

at least one exposure illuminator including an array of illuminator devices arranged to provide a predetermined level of illumination across a selected target area when said array and said target area are separated by a predetermined distance; and

an exposure control device responsive to image signals from at least one of said sensor elements and arranged to provide an exposure stop signal in response to a predetermined level of reflected illumination, said exposure stop signal being utilized to turn off said at least one exposure illuminator, which provides illumination resulting in said reflected illumination.

12. An automatic exposure system as in claim 11, wherein said exposure stop signal is utilized to trigger reading of image data from one of the following:

at least one sensor element, and all sensor elements.

13. An automatic exposure system as in claim 11, additionally comprising an optical filter positioned in front of said array, transmissive to illumination from said exposure illuminator and effective to reduce transmission in other portions of the ambient light spectrum.

14. An automatic exposure system as in claim 11, wherein said sensor elements are arranged to accumulate charge representative of said reflected illumination and said exposure stop signal is provided by said exposure control device when said charge is accumulated to a predetermined level by said at least one of the sensor elements.

15. An automatic exposure system as in claim 14, wherein said at least one of the sensor elements is arranged to have a predetermined initial charge accumulation at the start of an exposure period.

16. An automatic exposure system as in claim 11, wherein said exposure control device develops a voltage representative of the cumulative value of image signals over a period of time and provides said exposure stop signal when said voltage reaches a predetermined threshold voltage.

17. An automatic exposure imaging system, comprising:

a plurality of sensor elements which are readable to provide image signals and at least some of which are positioned in a two-dimensional array;

at least one focus illuminator arranged to illuminate a target area with an area of illumination characterized by at least one of a size, a brightness and a location which varies with the distance between the array and the target area;

an in-focus sensing device responsive to image signals from at least one of said sensor elements and arranged to provide an in-focus signal when said area of illumination is characterized by at least one of a size within a predetermined size range, a brightness within a predetermined brightness range and a location within a predetermined location range;

an exposure control device, responsive to image signals from at least one of said sensor elements, and arranged to provide a start signal in response to said in-focus signal and a stop signal in response to reflection of a predetermined level of illumination from said target area; and

at least one exposure illuminator responsive to said start signal and to said stop signal, and arranged to illuminate said target area during an exposure period determined by said start and stop signals.

18. An imaging system as in claim 17, additionally comprising an optical filter positioned in front of said array, transmissive to illumination from said exposure illuminator and effective to reduce transmission in other portions of the ambient light spectrum.

19. An imaging system as in claim 17, wherein said at least one focus illuminator comprises two focus illuminators providing respective beams of light which intersect in front of the array at a focus distance representative of a fixed focus plane of said array.

20. An imaging system as in claim 19, additionally comprising a central focusing lens positioned in front of said array and arranged to provide a plane of focus at said focus distance, with a depth of focus range extending about said focus distance.

21. An imaging system as in claim 19, wherein said in-focus sensing device is arranged to sense at least a predetermined degree of convergence of the illumination areas provided on said target area by said beams of light.

22. An imaging system as in claim 17, wherein said at least one exposure illuminator comprises an array of illuminator devices arranged to provide a predetermined level of illumination across the target area when said array and said image are separated by a predetermined distance.

23. An imaging system as in claim 17, additionally comprising a lens array assembly for providing predetermined focusing of light from said array of illuminating devices.

24. An imaging system as in claim 17, wherein said illuminator devices are light emitting diodes.

25. An imaging system as in claim 17, wherein said exposure control device develops a voltage representative of the cumulative value of image signals over a period of time and provides said stop signal when said voltage reaches a predetermined threshold voltage.

26. An imaging system, comprising:

a plurality of sensor elements which are readable to provide image signals and at least some of which are positioned in a two-dimensional array;

at least one focus illuminator arranged to illuminate a target area with an area of illumination characterized by at least one of a size, a brightness and a location which varies with the distance between the array and the target area; and

an in-focus sensing device responsive to image signals from at least one of said sensor elements and arranged to provide an in-focus signal when said area of illumination is characterized by at least one of a size within a predetermined size range, a brightness within a predetermined brightness range and a location within a predetermined location range.

27. An imaging system as in claim 26, wherein said at least one focus illuminator comprises two focus illuminators providing respective beams of light which intersect in front of the array at a focus distance representative of a fixed focus plane of said array.

28. An imaging system as in claim 26, additionally comprising a central focusing lens positioned in front of said array and arranged to provide a plane of focus at said focus distance, with a depth of focus range extending about said focus distance.

29. An imaging system as in claim 26, wherein said in-focus sensing device is arranged to sense at least a predetermined degree of convergence of the illumination areas provided on said target area by said beams of light.

30. An automatic exposure imaging system comprising:

a plurality of sensor elements which are readable to provide image signals and at least some of which are positioned in a two-dimensional array;

at least one exposure illuminator arranged to illuminate a target area during a preset initial period and during an adjustable exposure period; and

an exposure control device responsive to image signals, from at least one of said sensor elements, which are representative of the level of illumination reflected from said target area during said preset initial period, said exposure control device arranged to provide an exposure control signal representative of the duration of said adjustable exposure period.

32. An automatic exposure imaging system as in claim 30, wherein said at least one exposure illuminator includes a plurality of illuminators at least one of which is turned on during said preset initial period and at least one of which is turned on during said adjustable exposure period.

38. An automatic exposure imaging system as in claim 30, additionally comprising a gain control device responsive to the level of reflected light as represented by image signals from at least one of said sensor elements and arranged to control image signal amplification.

31. An automatic exposure imaging system comprising:

a plurality of sensor elements which are readable to provide image signals and at least some of which are positioned in a two-dimensional array;

at least one exposure illuminator arranged to illuminate a target area during a preset initial period and during an adjustable exposure period;

an exposure control device responsive to image signals, from at least one of said sensor elements, which are representative of the level of illumination reflected from said target area during said preset initial period, said exposure control device arranged to provide an exposure control signal representative of the duration of said adjustable exposure period;

a memory unit arranged to store a look-up table of exposure periods correlated to exposure control signal value; and

a processing unit coupled to said exposure control device and said memory unit and responsive to said exposure control signal to utilize said look-up table to determine the duration of said adjustable exposure period.

34. An automatic exposure imaging system as in claim 31, wherein said sensor elements include charge storage devices which, under the control of said processing unit, are discharged prior to the start of said adjustable exposure period.

35. An automatic exposure imaging system as in claim 34, wherein, under the control of said processing unit, said at least one exposure illuminator is first turned on for said preset initial period and subsequently turned on for said adjustable exposure period after said charge storage devices are discharged.

36. An automatic exposure imaging system as in claim 35, wherein image data representative of image signals sensed by said sensor elements during said adjustable exposure period is coupled to said memory unit in preparation for further processing.

33. An automatic exposure imaging system comprising:

a plurality of sensor elements which are readable to provide image signals and at least some of which are positioned in a two-dimensional array;

at least one exposure illuminator arranged to illuminate a target area during a preset initial period and during an adjustable exposure period; and

an exposure control device responsive to image signals, from two rows of said sensor elements positioned in said two-dimensional array, which are representative of the level of illumination reflected from said target area during said preset initial period, said exposure control device arranged to provide an exposure control signal representative of the duration of said adjustable exposure period;

said exposure control device arranged to determine said level of illumination by summing the pixel values represented by image signals from all sensors included in said two rows of sensor elements.

37. An automatic exposure imaging system comprising:

a plurality of sensor elements which are readable to provide image signals and at least some of which are positioned in a two-dimensional array;

at least one exposure illuminator arranged to illuminate a target area during a preset initial period and during an adjustable exposure period;

an exposure control device responsive to image signals, from at least one of said sensor elements, which are representative of the level of illumination reflected from said target area during said preset initial period, said exposure control device arranged to provide an exposure control signal representative of the duration of said adjustable exposure period;

at least one focus illuminator arranged to illuminate a target area with an area of illumination characterized by at least one of a size, a brightness and location which varies with the distance between the array and the target area; and

an in-focus sensing device responsive to image signals from at least one of said sensor elements and arranged to provide an in-focus signal effective to initiate said preset initial period of illumination by said exposure illuminator when said area of illumination is characterized by at least one of a size within a predetermined size range, a brightness with a predetermined brightness range and a location within a predetermined location range.

39. An imaging method, for use with an imaging system including an array of sensor elements, comprising the following steps:

(a) illuminating a target area with an area of illumination characterized by at least one of a size, a brightness and a location which varies with the distance between the array and the target area;

(b) adjusting said distance to cause said area of illumination to be characterized by at least one of a size within a predetermined size range, a brightness within a predetermined brightness range and a location within a predetermined location range;

(c) providing an in-focus signal when an image signal from at least one sensor element indicates that said area of illumination is characterized as described in step (b);

(d) turning on an exposure illuminator in response to said in-focus signal;

(e) providing a stop signal when image signals from at least one sensor element indicate reflection of a predetermined level of illumination from said target area;

(f) turning off said exposure illuminator in response to said stop signal; and

(g) processing image data from sensor elements of said array.

40. An imaging method as in claim 39, wherein step (a) additionally includes initiating reading of selected sensor elements to provide image signals, and additionally including the following step:

(h) terminating reading of selected sensor elements.

41. An imaging method as in claim 40, wherein step (h) comprises terminating reading of selected sensor elements by causing the termination of at least one of the following:

the providing of input power required for such reading, the providing of clock signals required for timing control of such reading.

42. An imaging method as in claim 39, additionally including an initial step as follows:

(x) positioning in front of said array of sensor elements an optical filter transmissive to light from said exposure illuminator and effective to reduce transmission in other portions of the ambient light spectrum.

43. An imaging method as in claim 39, additionally including an additional step between steps (d) and (e) as follows:

(y) utilizing image signals from at least one sensor element, as representative of the level of reflected ambient light, to provide a gain control signal to control amplification of image signals from said array.

44. An imaging method as in claim 39, wherein step (g) includes processing said image data to decode a dataform included in said target area, and said method includes the additional steps of:

(i) providing an end-cycle signal effective to terminate operation of the method upon successful decoding of the dataform; and

(ii) coupling the decoded dataform information to an output device for further utilization.

45. An imaging method as in claim 39, wherein in step (a) said target area is illuminated with an area of illumination comprising spots of illumination provided by two angled light beams which intersect at an in-focus distance in front of the array.

46. An imaging method as in claim 45, wherein step (b) comprises adjusting said distance to cause said two spots of illumination incident on said target area to merge to at least a predetermined degree.

47. An imaging method as in claim 46, wherein step (c) comprises providing said in-focus signal when said image signal indicates that said two spots of illumination are merged to at least said predetermined degree.

48. An imaging method as in claim 39, wherein step (e) comprises providing said stop signal when a voltage developed as representative of the cumulative value of said image signals reaches a threshold value.

49. An imaging method, for use with an imaging system including an array of sensing elements, comprising the following steps:

(a) illuminating a target area with an area of illumination characterized by at least one of a size, a brightness and a location which varies with the distance between the array and the target area;

(b) adjusting said distance to cause said area of illumination to be characterized by at least one of a size within a predetermined size range, a brightness within a predetermined brightness range and a location within a predetermined location range; and

(c) providing an in-focus signal when an image signal from at least one sensing element indicates that said area of illumination is characterized as described in step (b).

50. An imaging method as in claim 49, wherein in step (a) said target area is illuminated with an area of illumination comprising spots of illumination provided by two angled light beams which intersect at an in-focus distance in front of the array.

51. An imaging method as in claim 50, wherein step (b) comprises adjusting said distance to cause said two spots of illumination incident on said target area to merge to at least a predetermined degree.

52. An imaging method as in claim 51, wherein step (c) comprises providing said in-focus signal when said image signal indicates that said two spots of illumination are merged to at least said predetermined degree.

53. An imaging method, for use with an imaging system including an array of sensing elements, comprising the following steps:

(a) turning on an exposure illuminator for a preset initial period;

(b) determining the level of illumination sensed by at least one sensing element in said preset initial period; and

(c) utilizing said level to determine an adjustable exposure period.

54. An imaging method, for use with an imaging system including an array of sensing elements, comprising the following steps:

(a) turning on an exposure illuminator for a preset initial period;

(b) determining the level of illumination sensed by at least one sensing element in said preset initial period; and

(c) utilizing a look-up table of exposure periods to determine an adjustable exposure period on the basis of said level.

55. An imaging method as in claim 54, wherein said look-up table includes a portion usable to provide said adjustable exposure period and a portion usable to provide gain control values for adjusting the gain of image signals provided by said sensing elements.