Omnidirectional reading of two-dimensional symbols

• US 6,672,511 B1
• Filed: 07/25/2000
• Issued: 01/06/2004
• Est. Priority Date: 06/03/1996
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Shellhammer, Stephen J.
• Primary Examiner(s): Lee, Michael G.
• Assistant Examiner(s): WALSH, DANIEL I
• Application Number:
  US09/625,374
• Time in Patent Office: 1,260 Days
• Field of Search: 235/462.08, 235/462.09, 235/462.1, 235/462.2, 235/462.12, 235/462.14, 235/472.01, 235/462.25, 235/462.32, 235/462.45
• US Class Current: 235/462.08
• CPC Class Codes: G06V 10/245 by locating a pattern; Special marks for positioning

Abstract

A method and apparatus for aligning a scan pattern to a two dimensional bar code having parallel rows of codewords. The two dimensional bar code is scanned with a scanning pattern oriented such that a plurality of lines thereof cross the bar code rows. A determination if there is a non-zero angle between at least one of the plurality of lines and the rows by decoding codewords in rows intersected by the at least one line is made and the orientation of the scanning pattern is adjusted to reduce the absolute value of the angle.

Claims

1. A method for aligning a scan pattern to a two dimensional bar code having parallel rows of codewords, comprising the steps of:

scanning the two dimensional bar code with a scanning pattern oriented such that a plurality of lines thereof cross the bar code rows;

determining if there is a non-zero angle between at least one of the plurality of lines and the rows by decoding codewords in rows intersected by the at least one line; and

adjusting the orientation of the scanning pattern to reduce the absolute value of the angle;

wherein the bar code has row indicator code words in each row and wherein the step of determining comprises decoding the row indicator codewords read by the at least one line and determining the slope of the angle therefrom.

2. The method according to claim 1, wherein the bar code has a fixed number of module widths in each codeword and a row height which is a function of the module width and the number of codewords per row encoded therein and wherein the step of determining further comprises determining a magnitude of the angle from the number of codewords per row and the aspect ratio of the row height to the module width.

3. The method according to claim 1, wherein the step of adjusting comprises repeating the step of determining after a delay following the step of adjusting.

4. A method for aligning a scan pattern to a two dimensional bar code having parallel rows of codewords, comprising the steps of:

scanning the two dimensional bar code with a scanning pattern oriented such that a plurality of lines thereof cross the bar code rows;

determining if there is a non-zero angle between at least one of the plurality of lines and the rows by decoding codewords in rows intersected by the at least one line; and

adjusting the orientation of the scanning pattern to reduce the absolute value of the angle;

wherein the bar code has codewords that are divided into a plurality of clusters and wherein each row uses codewords of only one cluster and where the step of determining comprises decoding the codewords read by the at least one line to determine the cluster of each codeword and determining the slope of the angle therefrom.

5. The method according to claim 4, wherein the bar code has a fixed number of module widths in each codeword and a row height which is a function of the module width and the number of codewords per row encoded therein and wherein the step of determining further comprises determining a magnitude of the angle from the number of codewords per row and the aspect ratio of the row height to the module width.

6. The method according to claim 4, wherein the step of adjusting comprises repeating the step of determining after a delay following the step of adjusting.

7. A method for aligning a scan pattern to a two dimensional bar code having parallel rows of codewords, comprising the steps of:

scanning the two dimensional bar code with a scanning pattern oriented such that a plurality of lines thereof cross the bar code rows;

determining if there is a non-zero angle between at least one of the plurality of lines and the rows by decoding codewords in rows intersected by the at least one line; and

adjusting the orientation of the scanning pattern to reduce the absolute value of the angle;

wherein the step of scanning comprises scanning the bar code with a locating pattern to determine the position of the bar code to initially orient the scanning pattern with respect thereto.

8. A system for aligning a scan pattern to a two dimensional bar code having parallel rows of codewords, comprising:

a pattern generator for generating a scanning pattern oriented to scan the two dimensional bar code such that a plurality of scan lines cross the bar code rows;

a processor for determining if there is a non-zero angle between at least one of the plurality of lines and the rows by decoding codewords in rows intersected by the at least one line; and

an alignment mechanism based upon the determined angle for adjusting the orientation of the scanning pattern generated by the pattern generator to reduce the absolute value of the angle;

wherein the bar code has row indicator code words in each row and wherein the processor has a decoder for decoding the row indicator codewords read by the at least one line to determine the slope of the angle therefrom.

9. The system according to claim 8, wherein the bar code has a fixed number of module widths in each codeword and a row height which is a function of the module width and the number of codewords per row encoded therein and wherein the processor determines a magnitude of the angle from the number of codewords per row and the aspect ratio of the row height to the module width.

10. The system according to claim 8, wherein the processor repeats the determination after a delay following the adjustment by the alignment mechanism.

11. A system for aligning a scan pattern to a two dimensional bar code having parallel rows of codewords, comprising:

a pattern generator for generating a scanning pattern oriented to scan the two dimensional bar code such that a plurality of scan lines cross the bar code rows;

a processor for determining if there is a non-zero angle between at least one of the plurality of lines and the rows by decoding codewords in rows intersected by the at least one line, and an alignment mechanism based upon the determined angle for adjusting the orientation of the scanning pattern generated by the pattern generator to reduce the absolute value of the angle;

wherein the bar code has codewords that are divided into a plurality of clusters and wherein each row uses codewords of only one cluster and where the processor has a decoder for decoding the codewords read by the at least one line to determine the cluster of each codeword and to determine the slope of the angle therefrom.

12. The system according to claim 11, wherein the bar code has a fixed number of module widths in each codeword and a row height which is a function of the module width and the number of codewords per row encoded therein and wherein the processor determines a magnitude of the angle from the number of codewords per row and the aspect ratio of the row height to the module width.

13. The system according to claim 11, wherein the processor repeats the determination after a delay following the adjustment by the alignment mechanism.

14. A system for aligning a scan pattern to a two dimensional bar code having parallel rows of codewords, comprising:

a pattern generator for generating a scanning pattern oriented to scan the two dimensional bar code such that a plurality of scan lines cross the bar code rows;

a processor for determining if there is a non-zero angle between at least one of the plurality of lines and the rows by decoding codewords in rows intersected by the at least one line; and

an alignment mechanism based upon the determined angle for adjusting the orientation of the scanning pattern generated by the pattern generator to reduce the absolute value of the angle;

wherein the system is incorporated in a hand held scanner which is initially manually oriented the to the bar code.

15. A system for aligning a scan pattern to a two dimensional bar code having parallel rows of codewords, comprising:

a pattern generator for generating a scanning pattern oriented to scan the two dimensional bar code such that a plurality of scan lines cross the bar code rows;

a processor for determining if there is a non-zero angle between at least one of the plurality of lines and the rows by decoding codewords in rows intersected by the at least one line; and

an alignment mechanism based upon the determined angle for adjusting the orientation of the scanning pattern generated by the pattern generator to reduce the absolute value of the

further comprising a locating pattern for generating a locating pattern and a bar code position calculator for determining the position of the bar code to initially orient the scanning pattern with respect thereto.