Bar code scanner with simplified auto-focus capablilty

• US 5,920,060 A
• Filed: 08/18/1998
• Issued: 07/06/1999
• Est. Priority Date: 09/21/1995
• Status: Expired due to Fees

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Marom, Emanuel
• Primary Examiner(s): LE, THIEN MINH
• Application Number:
  US09/135,739
• Time in Patent Office: 322 Days
• Field of Search: 235/472.01, 235/462.01, 235/462.1, 235/462.2, 235/462.22, 235/462.23, 235/462.24, 235/462.32, 235/462.36, 235/454, 235/466, 235/470, 250/234, 250/235, 250/236
• US Class Current: 235/462.2
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10811 Focalisation
• CPC Class Codes: G06K 7/1417 2D bar codes

Abstract

A bar code scanner for reading a bar code tag includes a collection optical system, a two dimensional array of detectors, rotating means for imparting rotational movement to the array and displacement means for varying the position of one of the collection optical system and the array along an optical axis of the collection optical system.

Claims

1. A focusing system for focusing an image illuminated with a flood illumination source, said system including:

(a) a focusing lens;

(b) a two-dimensional array of transducers arranged in rows for receiving the image intended to be placed in focus in combination with said focusing lens;

(c) a translation mechanism for changing a translation distance between said focusing lens and said two-dimensional array of transducers along an optical axis of said focusing system; and

(d) a rotation mechanism for rotating said array about a rotational axis perpendicular to the optical axis and parallel to a row orientation, said rotation mechanism operating in conjunction with said translation mechanism and independent of the flood illumination source.

2. The system claimed in claim 1, wherein said transducers comprise CCD elements.

3. The system claimed in claim 1, further including a circuit for receiving a number of groups of electrical signals with each group generated by a corresponding row of said transducers and for examining a frequency content of each of said groups of said received electrical signals.

4. The system of claim 3, wherein said circuit performs Fourier transformations of each of said groups of said received electrical.

5. The system of claim 4, wherein said circuit simultaneously performs said Fourier transformations for each of said groups of said received electrical signals.

6. The system of claim 3, wherein said circuit provides an output signal indicative of the location in said array of the row of transducers whose corresponding group of electrical signals have highest frequency content among said rows of said array.

7. The system of claim 6, further including a processor for receiving said output signal of said circuit, and controlling operation of said translation mechanism and said rotation mechanism.

8. The system of claim 1, wherein said translation mechanism changes the translation distance between said focusing lens and said two-dimensional array of transducers by moving said lens.

9. The system of claim 1, wherein said translation mechanism changes the translation distance between said focusing lens and said two-dimensional array of transducers by moving said array.

10. A method of focusing an image of a target illuminated by a flood illuminating light source on a two-dimensional array of transducers arranged in rows using a focusing lens, said lens separated from said array by a variable translation distance along an optical axis, said method comprising the steps of:

(a) positioning the array at a first angular orientation relative to said optical axis;

(b) locating a row of detectors within said array having a high focus;

(c) changing the translation distance until a predetermined row of detectors exhibits the high focus;

(d) comparing a focus of all other detector rows of said array with the high focus;

(e) rotating said array by a predetermined angle around a rotation axis based on the result of the comparing step; and

(f) repeating steps b through e until all of the rows of detectors exhibit the high focus;

wherein steps (b) through (f) are performed independently of said flood illuminating light source.

11. The method of claim 10, wherein said predetermined row of detectors is a center row.

12. The method of claim 10, wherein the locating step further comprises the steps of:

(a) obtaining a number of groups of electrical signals with each group generated by a corresponding row of said transducers;

(b) performing Fourier transformation on each of said groups of electrical signal;

(c) comparing all of the Fourier transformations; and

(d) determining a group corresponding to the highest focus condition.

13. The method of claim 10, wherein the change in translation distance is accomplished by translating said array.

14. The method of claim 10, wherein the change in translation distance is accomplished by translating said lens.

15. The method of claim 10, wherein the rotating step is performed only if all of the detector rows do not have the same focus.