Method of collecting and adjusting bar code data from a laser bar code reader

• US 5,608,200 A
• Filed: 11/28/1994
• Issued: 03/04/1997
• Est. Priority Date: 09/28/1990
• Status: Expired due to Fees

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Rosa, Ralph, Le Goff, Stephen H.
• Primary Examiner(s): Shepperd, John
• Assistant Examiner(s): Le, Thien Minh
• Application Number:
  US08/345,661
• Time in Patent Office: 827 Days
• Field of Search: 235/462, 235/454, 235/472, 235/463, 356/445, 356/448
• US Class Current: 235/462.02
• CPC Class Codes: G06K 19/06028 using bar codes
• CPC Class Codes: G06K 5/00 Methods or arrangements for verifying the correctness of markings on a record carrier; Column detection devices
• CPC Class Codes: G06K 7/10584 Source control
• CPC Class Codes: G06K 7/10594 Beam path
• CPC Class Codes: G06K 7/10623 Constructional details
• CPC Class Codes: G06K 7/10801 Multidistance reading
• 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 7/10881 constructional details of hand-held scanners
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence

Abstract

A method is disclosed for processing bar code data obtained from a bar code label including large and small bars. A light source such as a laser beam scans across the symbol on a bar code label. Light reflected from the bar code label is collected as the light source scans across the label. The collected light varies in intensity as the light source scans across the label. An electrical signal is generated which is indicative of the amplitude of the light collected in the collecting step. The electrical signal is sampled at a predetermined data rate to produce a sequence of samples representative of the electrical signal. A sequence of samples is stored in a memory. These stored samples include label space values (LSA'"'"'s). The samples also include label bar values (LBA'"'"'s) which include large bar values and small bar values. The sequence of samples is decoded. The label space reflectance (LSR) is determined by dividing the product of the calibration space reflectance (CSR) and a label space value (LSA) by the calibration space average (CSA). The disclosed method also provides for the normalization of label bar values (LBA'"'"'s).

Claims

1. A method of processing bar code data obtained from an unknown bar code label including large and small bars, the method comprising the steps of:

establishing standard values of calibration space reflectance (CSR) and calibration space average (CSA) from a standard, ideal bar code label;

scanning a light source across the unknown bar code label;

collecting light which is reflected from the unknown bar code label as the light source scans across the label thus producing collected light, the light thus collected varying in intensity as the light source scans across the label;

generating an electrical signal indicative of the amplitude of the light collected in the collecting step;

sampling the electrical signal at a predetermined data rate to produce a sequence of samples representative of the electrical signal;

storing the sequence of samples in a memory, the samples including label space values (LSA'"'"'s) and label bar values (LBA'"'"'s) which include large bar values and small bar values;

decoding the sequence of samples; and

determining a label space reflectance (LSR) value of the unknown bar code label by dividing the product of the calibration space reflectance (CSR) and a label space value (LSA) by the calibration space average (CSA).

2. The method of claim 1 wherein the large bar values comprise tall bar values and the small bar values comprise short bar values.

3. The method of claim 1 wherein the large bar values comprise wide bar values and the small bar values comprise narrow bar values.

4. The method of claim 1 further comprising the steps of:

retrieving a calibration space average (CSA) from a first memory;

retrieving a label space value (LSA) from a second memory;

determining a multiplier, MULTIPLR, by dividing the calibration space average (CSA) by the label space value (LSA).

5. The method of claim 4 further comprising the step of:

retrieving a label bar value (LBA) from the second memory to provide a retrieved label bar value (LBA);

modifying the retrieved label bar value (LBA) by multiplying the retrieved label bar value (LBA) by the multiplier, MULTIPLR, to produce a modified label bar value (LBA'"'"').

6. The method of claim 5 further comprising the step of:

normalizing the modified label bar value (LBA'"'"') by performing the following operation on the modified label bar value (LBA'"'"') ##EQU4## thus producing a normalized modified label bar value, NLBA.

7. The method of claim 6 further comprising the step of converting the normalized modified label bar value, NLBA, to reflectance.

8. A method for calibrating a laser bar code scanner for reading bar code labels comprising the steps of:

scanning a calibration standard label with a laser scanner and recording reflectivity characteristics of spaces end bars of the scanned label over a scanned range in a first memory;

dividing the scanned range into a plurality of equal time increments and associating the recorded reflectivity characteristics with a corresponding time increment;

scanning a label to be read with the scanner and storing reflectivity characteristics of the read label in a second memory;

associating the reflectivity characteristics of the read label with corresponding time increments obtained by dividing a range of scanning of the scanner into the plurality of equal time increments; and

comparing each reflectivity characteristic of the read label on a time increment basis to each recorded reflectivity characteristic of the calibration label for interpreting the read label.