System and method for acquiring an optical target

• US 5,291,564 A
• Filed: 08/20/1993
• Issued: 03/01/1994
• Est. Priority Date: 07/11/1991
• Status: Expired due to Term

• Current Assignee: United Parcel Service of America (United Parcel Service Incorporated)
• Original Assignee: United Parcel Service of America (United Parcel Service Incorporated)
• Inventors: Shaw, David G., Chandler, Donald G., Shah, Govind
• Primary Examiner(s): Couso, Jose L.
• Application Number:
  US08/109,692
• Time in Patent Office: 193 Days
• Field of Search: 382/1, 382/8, 382/10, 382/17, 382/30, 382/34, 382/48
• US Class Current: 382/291
• 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 7/10861 sensing of data fields affixed to objects or articles, e.g. coded labels postal sorting B07C3/14, conveying articles B65G47/48

Abstract

An optical target is acquired by an optical scanning system according to an in-band target frequency in an input signal from an optical scanning device. Both the in-band energy level and the out-of-band energy level of the input signal from the optical scanning device are determined. These two energy levels are compared and a possible detection of the target is determined according to this comparison. A minimum threshold of in-band energy is required in order for the possible detection to be confirmed.

Claims

1. A method for detecting a package label positioned within the field of view of an optical scanning device and acquiring encoded information from said label, said label being comprised of an optical acquisition target having an associated predetermined target frequency which is detectable when said optical acquisition target is scanned by said optical scanning device, said label being further comprised of encoded data, comprising the steps of:

(a) optically scanning said field of view with said optical scanning device to determine a detector input signal;

(b) filtering said detector input signal with a band-pass filter to determine the level of energy inside a target frequency band of said detector input signal, said target frequency band having been determined in accordance with said associated predetermined target frequency;

(c) filtering said detector input signal with a band-reject filter to determine the level of energy outside said target frequency band of said detector input signal;

(d) comparing said determined level of energy inside said target frequency band with said determined level of energy outside of said target frequency band;

(e) comparing said determined level of energy within said target frequency band to a predetermined set point; and

(f) detecting a target frequency signal if said determined level of energy within said target frequency band exceeds said determined level of energy outside of said target frequency energy band and said determined level of energy within said target frequency band exceeds said predetermined set point.

2. The method of claim 1, comprising the further step of varying said predetermined set point.

3. The method of claim 1, comprising the further step of providing a detection signal in accordance with the detecting of step (f).

4. The method of claim 1, comprising the further step of acquiring said encoded data from said label in response to said detected target frequency signal.

5. The method of claim 1, wherein the frequency of said detector input signal varies, comprising the further step of frequency shifting prior to determining said energy level within said target frequency band and prior to determining said energy level outside said target frequency band.

6. The method of claim 5, wherein said target frequency signal is representative of said optical acquisition target disposed at a scanning distance from said optical scanning device, further comprising the step of frequency shifting in accordance with said scanning distance between said optical scanning device and said optical acquisition target.

7. The method of claim 6, wherein the step of frequency shifting in accordance said scanning distance comprises the step of compensating for varying magnification of said optical acquisition target due to varying scanning distance

8. The method of claim 7, wherein steps (b) and (c) comprise applying said detector input signal to filter means having singularities and said frequency shifting comprises shifting said singularities.

9. The method of claim 7, wherein the step of frequency shifting comprises frequency shifting said varying frequencies of said detector input signal to a single fundamental frequency.

10. The method of claim 9, wherein said fundamental frequency corresponds to a predetermined scanning distance.

11. A system for detecting a package label positioned within the field of view of an optical scanning device and acquiring encoded information from said label, said label being comprised of an optical acquisition target having an associated predetermined target frequency which is detectable when said optical acquisition target is scanned by said optical scanning device, said label being further comprised of encoded data, comprising:

means for optically scanning said field of view with said optical scanning device to determine a detector input signal;

means for filtering said detector input signal with a band-pass filter to determine the level of energy inside a target frequency band of said detector input signal, said target frequency band having been determined in accordance with said associated predetermined target frequency;

means for filtering said detector input signal with a band-reject filter to determine the level of energy outside said target frequency band of said detector input signal;

means for comparing said determined level of energy inside said target frequency band with said determined level of energy outside of said target frequency band;

means for comparing said determined level of energy within said target frequency band to a predetermined set point; and

means for detecting a target frequency signal if said determined level of energy inside said target frequency band exceeds said determined level of energy outside of said target frequency energy band and said determined level of energy within said target frequency band exceeds said predetermined set point to provide a detection determination.

12. The system of claim 11, further comprising means for varying said predetermined set point.

13. The system of claim 11, further comprising means for providing a detection signal in accordance with said detection determination.

14. The system of claim 11, further comprising means for acquiring said encoded data from said label in response to said detection determination.

15. The system of claim 11, wherein the frequency of said detector input signal varies, further comprises means for frequency shifting prior to determining said energy level within said target frequency band and prior to determining said energy level outside said target frequency band.

16. The system of claim 15, wherein said target frequency signal is representative of said optical acquisition target disposed at a scanning distance from said optical scanning device, further comprising means for frequency shifting in accordance with said scanning distance between said optical scanning device and said optical acquisition target.

17. The system of claim 16, wherein said means for frequency shifting in accordance with said scanning distance comprises means for compensating for varying magnification of said optical acquisition target due to varying scanning distance.

18. The system of claim 17, wherein said means for filtering said detector input signal with a band-pass filter and said means for filtering said detector input signal with a band-reject filter comprise filter means having singularities, further comprising means for frequency shifting said singularities.

19. The system of claim 17, wherein said means for frequency shifting is adapted to frequency shift said varying frequencies of said detector input signal to a single fundamental frequency.

20. The system of claim 19, wherein said fundamental frequency corresponds to a predetermined scanning distance.