Triggerless optical reader with signal enhancement features

• US 6,695,209 B1
• Filed: 10/04/1999
• Issued: 02/24/2004
• Est. Priority Date: 10/04/1999
• Status: Expired due to Term

• Current Assignee: PSC Scanning, Inc. (Datalogic ADC Incorporated)
• Original Assignee: PSC Scanning, Inc. (Datalogic ADC Incorporated)
• Inventors: La, Chay K.
• Primary Examiner(s): St. Cyr, Daniel
• Application Number:
  US09/412,015
• Time in Patent Office: 1,604 Days
• Field of Search: 235/462.1, 235/462.2, 235/462.08, 235/462.25, 235/462.31, 235/494, 356/237.2, 356/237.4, 356/235.5
• US Class Current: 235/462.2
• CPC Class Codes: G06K 2207/1011 Aiming
• CPC Class Codes: G06K 2207/1012 Special detection of object
• 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

Abstract

An optical reader includes targeting illuminators (e.g., LEDs) which generate a predetermined illumination pattern upon a target. The optical reader captures an image of the target and processes the captured image to determine whether the target is off-pitch or skewed, by analyzing the appearance and characteristics of the predetermined illumination pattern. The illumination pattern may consist of two identical triangles adjacently located but slightly separated so as to cause the pattern to be symmetrical when the target is at perfect alignment, but having shifting characteristics when the target is off-pitch or skewed. The optical reader may use the knowledge of pitch and skew to adjust the captured image. Triggerless operation of the optical reader is provided by placing the optical reader in a cradle and stand having a base with a known target printed on or affixed thereto, within the viewpath of the optical reader. So long as the known target is in the view of the optical reader, it remains in a standby mode, and leaves the standby mode and begins reading when a target is interposed or the optical reader is removed from the cradle. Automatic gain control circuitry is provided having a gain control level which is continuously adjusted when the optical reader is in a standby mode. When the optical reader leaves the standby mode and begins reading, the gain level is pre-adjusted, resulting in a faster read of good data.

Claims

1. A method for optically reading a target using a data reading system, comprising the steps of:

generating a predetermined targeting pattern and projecting said predetermined targeting pattern onto the target;

capturing an image of the target and capturing a return image of said predetermined targeting pattern;

the data reading system measuring distortion in shape of said return image of said predetermined targeting pattern;

the data reading system determining a characteristic of target orientation based upon said distortion;

the data reading system compensating for said characteristic of target orientation.

2. The method of claim 1, further comprising the steps of:

enhancing the contrast of said captured image, thereby generating a contrast-enhanced image; and

generating a binarized image from said contrast-enhanced image.

3. The method of claim 1, further comprising the step of storing said captured image as a two-dimensional array of gray-scale pixel values.

4. The method of claim 1, wherein said predetermined targeting pattern comprises a pair of symmetrical triangles, and wherein said step of measuring distortion comprises comparing shape of the triangles in said return image being captured to an expected non-distorted return image.

5. The method of claim 1, wherein said characteristic is an angle of pitch of said target.

6. The method of claim 1, wherein said characteristic is an angle of skew of said target.

7. The method of claim 1, wherein said step of measuring distortion of said return image of said predetermined targeting pattern is carried out over a window region within the captured image.

8. The method of claim 1 wherein said targeting pattern comprises a plurality of two-dimensional geometric shapes offset from each other.

9. A method for optically reading a target using a data reading system, comprising the steps of:

generating a predetermined illumination pattern;

capturing an image of the target and capturing a return image of said predetermined illumination pattern;

the data reading system measuring distortion of said return image of said predetermined illumination pattern;

the data reading system determining a characteristic of target orientation based upon said distortion;

the data reading system compensating for said characteristic of target orientation,

wherein said predetermined illumination pattern comprises a pair of symmetrical triangles,

wherein said symmetrical triangles are adjacent, are separated by a narrow contrasting margin, and point outwardly in opposite directions.

10. A method for optically reading a target, comprising the steps of:

generating a predetermined illumination pattern, wherein said predetermined illumination pattern comprises a pair of symmetrical triangles, wherein said symmetrical triangles are adjacent, are separated by a narrow contrasting margin, and point outwardly in opposite directions;

capturing an image of the target, said captured image including a return image of said predetermined illumination pattern;

measuring distortion of said return image of said predetermined illumination pattern, wherein said step of measuring distortion of said return image of said predetermined illumination pattern comprises the steps of identifying a pair of triangles in said return image and measuring a width of each of said triangles; and

determining a characteristic of target orientation based upon said distortion, wherein said step of determining said characteristic of target orientation based upon said distortion comprises the step of calculating an angle of skew of said target based upon the relative measured widths of each of said triangles in said return image.

11. The method of claim 10, wherein said angle of skew is determined according to a formula

12. A method for optically reading a target, comprising the steps of:

generating a predetermined illumination pattern, wherein said predetermined illumination pattern comprises a pair of symmetrical triangles, wherein said symmetrical triangles are adjacent, are separated by a narrow contrasting margin, and point outwardly in opposite directions;

capturing an image of the target, said captured image including a return image of said predetermined illumination pattern;

measuring distortion of said return image of said predetermined illumination pattern, wherein said step of measuring distortion of said return image of said predetermined illumination pattern comprises the steps of identifying a pair of triangles in said return image, measuring a separation of said pair of triangles at a top point and at a bottom point of said pair of triangles, and measuring a height of at least one of said triangles; and

determining a characteristic of target orientation based upon said distortion, wherein said step of determining said characteristic of target orientation based upon said distortion comprises the step of calculating an angle of pitch of said target based upon the relative separations of said triangles at said cop point and at said bottom point and upon said measured height of at least one of said triangles in said return image.

13. The method of claim 12, wherein said angle of pitch is determined according to a formula

14. A method for optically reading a target using a data reading system, comprising the steps of:

generating a predetermined targeting pattern and projecting the targeting pattern onto the target;

capturing an image of the target and capturing a return image of said predetermined targeting pattern;

the data reading system determining a characteristic of orientation of the target based upon differences between said return image of said predetermined targeting pattern and an expected return image of said predetermined illumination targeting pattern;

the data reading system compensating for said characteristic of orientation of the target.

15. The method of claim 14, wherein said predetermined targeting pattern comprises a pair of identical two-dimensional geometric shapes symmetrically disposed about a center axis.

16. The method of claim 14, wherein said step of determining said characteristic of orientation of the target based upon differences between said return image of said predetermined targeting pattern and an expected return image of said predetermined targeting pattern comprises the step of determining an angle of skew of the target.

17. The method of claim 14, wherein said step of determining said characteristic of orientation of the target based upon differences between said return image of said predetermined targeting pattern and an expected return image of said predetermined targeting pattern comprises the step of determining an angle of pitch of the target.

18. A method for optically reading a target using a data reading system, comprising the steps of:

generating a predetermined illumination pattern;

capturing an image of the target and capturing a return image of said predetermined illumination pattern;

the data reading system determining a characteristic of orientation of the target based upon differences between said return image of said predetermined illumination pattern and an expected return image of said predetermined illumination pattern;

the data reading system compensating for said characteristic of orientation of the target,

wherein said predetermined illumination pattern comprises a pair of identical two-dimensional geometric shapes symmetrically disposed about a center axis,

wherein said identical shapes comprise isosceles triangles, said isosceles triangles separated by a narrow band.

19. A method for optically reading a target, comprising the steps of;

generating a predetermined illumination pattern, wherein said predetermined illumination pattern comprises a pair of identical shapes symmetrically disposed about a center axis, wherein said identical shapes comprise isosceles triangles, said isosceles triangles separated by a narrow band;

capturing an image of the target, said captured image including a return image of said predetermined illumination pattern; and

determining a characteristic of orientation of the target based upon differences between said return image of said predetermined illumination pattern and an expected return image of said predetermined illumination pattern, wherein said step of determining said characteristic of orientation of the target based upon differences between said return image of said predetermined illumination pattern and an expected return image of said predetermined illumination pattern comprises the step of determining an angle of skew of the target based upon relative measured widths of triangles in said return image.

20. The method of claim 19, further comprising the step of determining a second characteristic of orientation of said target based upon differences between said return image of said predetermined illumination pattern and the expected return image of said predetermined illumination pattern.

21. The method of claim 20, wherein said step of determining a second characteristic of orientation of said target based upon differences between said return image of said predetermined illumination pattern and the expected return image of said predetermined illumination pattern comprises the step of determining an angle of pitch of the target based upon relative separations of said triangles in said return image at a top and bottom of said narrow band and upon a measured height of at least one of said triangles in said return image.

22. A method for data reading using a data reading system, comprising the steps of:

projecting a targeting pattern onto a surface of an item to be read;

capturing an image of the surface of the item and capturing a return image of said targeting pattern; and

the data reading system determining an orientation characteristic of the surface of the item based upon differences between shape of said return image of said targeting pattern being captured and shape of an expected return image of said targeting pattern.

23. A method of data reading according to claim 22 wherein said step of determining an orientation characteristic comprises the step of determining an angle of skew of the surface of the item based upon relative measured widths of triangles in said return image.

24. An optical reading system comprising

means for generating a predetermined targeting pattern;

means for capturing an image of the target and capturing a return image of said predetermined targeting pattern;

means for measuring distortion in shape of said return image of said predetermined targeting pattern;

means for determining a characteristic of target orientation based upon said distortion;

means for compensating for said characteristic of target orientation.