Dataform readers and methods

• US 5,646,390 A
• Filed: 03/25/1996
• Issued: 07/08/1997
• 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:
  US08/622,442
• Time in Patent Office: 470 Days
• Field of Search: 239/462, 239/454, 239/472, 239/436, 239/455, 348/294, 348/297, 348/221, 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 charge accumulation by a line of sensor elements 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 at least one of said selected lines, 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, upon initiation of charge accumulation, 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 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.

9. 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, in response to an exposure start signal, charge accumulation by a line of sensor elements set to a reference potential 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 at least one of said selected lines, 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.

10. A dataform reader as in claim 9, 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.

11. A dataform reader as in claim 10, additionally comprising a memory unit storing a look-up table of line exposure periods versus average image signal levels.

12. A dataform reader as in claim 9, 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.

13. 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 charge accumulation by a line of sensor elements 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.

14. A dataform reader as in claim 13, 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.

15. 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) initiating charge accumulation by a first line of sensor elements in response to an exposure start signal initiating a first line exposure period;

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

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

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

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

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

16. A method as in claim 15, wherein step (a) includes turning on illumination of said target area to provide reflected illumination and step (g) includes turning off said illumination after image signals have been read from all lines of sensor elements of said array.

17. A method as in claim 15, additionally including the following steps between steps (d) and (e):

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

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

18. A method as in claim 17, 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.

19. A method as in claim 17, 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).

20. A method as in claim 15, 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.