Reading device for bar codes

• US 4,746,789 A
• Filed: 10/28/1985
• Issued: 05/24/1988
• Est. Priority Date: 11/02/1984
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Sterken, Hendrikus P. M., Venema, Willem J., Gieles, Antonius C. M.
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US06/791,857
• Time in Patent Office: 939 Days
• Field of Search: 235/462, 235/463
• US Class Current: 235/462.18
• CPC Class Codes: G06K 7/0166 by means of clock-signals derived from the code marks, e.g. self-clocking code
• 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

The code is scanned along at least four non-coincident parallel lines in a bar code reading device. The actual processing is started when a margin of sufficient width is detected. The width of the bar is counted and the width found is used to address a table memory. This results in a width indication for a valid bar and a reset signal for an invalid bar. There is provided an bar counter which counts the bars and which addresses a bar memory in order to store the bar identification therein. When the reset signal is received, the series of bar identification received thus far for the relevant line is invalidated, unless all bars of a complete code have already been received. During validation a check is performed as regards correct contents and possibly correspondence between two potentially correct bar codes found.

Claims

1. A reading device for a bar code provided in/on a carrier, which reading device includes:

a scanning device for line-wise scanning the bar code,

a decision element which is connected to the scanning device in order to form a bivalent signal from the signal of the scanning device,

a code regenerator which is connected to the decision element in order to form a code sequence consisting of valid bar widths from the lengths of successive intervals of the bivalent signal,

a bar counter which is connected to an output of the code regenerator in order to count the number of valid bars, and

an output element which is connected to the code regenerator in order to validate a code sequence and to present a validated code on a user output,

characterized in that the code regenerator includes an address counter for a table memory which counts down the lengths of the intervals, the table memory identifying a valid bar width in the location thus addressed or indicating an invalid bar width, the table thus addressed having a validity range of at least two successive address counter positions for each nominal bar width, the address range of the table memory covering at least two different sequences of consecutively successive invalid counter positions which are separated from one another by at least one sequence of valid counter positions, the table memory containing a sequence of at least two tables of increasing scale, for each table there being provided for each nominal bar width a tolerance range between a largest permissible actual bar width and a smallest permissible actual bar width, said tolerance range amounting to at least a factor 11/2.

2. A reading device as claimed in claim 1, characterized in that bar widths are continuously detected, the bar counter being reset to a starting position per line under the control of an invalid bar width, said resetting being deactivated as soon as a predetermined bar counter position is reached.

3. A reading device as claimed in claim 1 or 2, characterized in that the scanning device is formed by a television camera for the pseudo-simultaneous scanning of of said at least four lines, the validation being activated under the control of a predetermined minimum number of valid scanning lines which is larger than one.

4. A reading device as claimed in claim 3, characterized in that the output element is suitable to present at least two corresponding codes which are correct as regards contents as validated information on the user output.

5. Apparatus for reading a bar code comprising:

a. means (20) for line-wise scanning the bar code;

b. threshold means (44) fed by the scanning means for producing a binarized scanning signal, the binarized scanning signal comprising a plurality of transitions;

c. means (46) for counting a clock signal, said counting means being resettable by said transitions, whereby an output signal of said counting means indicates a length of a time interval between successive transitions in said binarized signal;

d. a bar width table memory (50) for storing a plurality of tables of bar width indications, comprising;

i. location selection means comprising;

A. means for reversibly selecting among said plurality of tables;

B. means for addressing locations within respective tables, said addressing means being coupled to receive the output signal of said counting means as an address;

ii. an output at which said bar width indications are provided from said tables under control of said transitions;

iii. said bar width indications each being one of;

A. a first acceptable bar width indication;

B. a second acceptable bar width indication; and

C. an unacceptable bar width indication;

iv. each table having;

A. a first address range corresponding to locations where said first acceptable bar width indication is stored;

B. a second address range corresponding to locations where said second acceptable bar width indication is stored;

C. at least third and fourth address ranges corresponding to locations where said unacceptable bar width indication is stored, the third and fourth address ranges being separated from each other by at least one of the first and second address ranges; and

said first and second address ranges including respective lowest and highest address values corresponding to respective lowest and highest acceptable bar widths, the ratio of the respective lowest and highest acceptable bar widths being at least 11/2, whereby the apparatus recognizes bar widths within a tolerance factor of 11/2; and

at least one of the tables having at least one of said third and fourth address ranges between said first and second address ranges,

whereby bar widths are verified as soon as the bar widths are recognized;

e. code regenerating means (60), fed by said bar width table, for progressively storing a sequence of valid bar width indications, under control of said transitions;

f. a bar counter (58) for counting said transitions; and

g. an output element (66) fed by said code regenerator for providing a valid output code, under control of a predetermined count value of said bar counter.

6. The apparatus of claim 5 wherein the bar counter is resettable to a line start position under control of the bar width indication, so that the bar counter is reset when the bar width indication indicates an invalid bar width when a predetermined bar count has not been reached.

7. A reading device as claimed in claims 5 or 6, characterized in that the decision element includes a multiplexed input whereto at least two scanning devices can be selectively connected.

8. A reading device as claimed in claims 5 or 6, characterized in that said tables can be separately selected.

9. A reading device as claimed in claim 8, in which the scanning device is formed by a television camera, characterized in that there is provided a selector for the table memory which, in the absence of a validated code on the user output, selects a different table during a repeat scan of the code, but which maintains the selector position when a validated code is output.

10. A reading device as claimed in claim 9, characterized in that in a selector position a sub-set of tables which consists of at least two tables can be selected as a whole.

11. The apparatus of claim 5 wherein the scanning means is a television camera.

12. The apparatus of claim 11 wherein the television camera pseudo-simultaneously scans at least four lines, the apparatus further comprising means for validating said sequence of bar width indications under the control of a plurality of scanning lines.

13. The apparatus of claim 12 wherein the output element presents at least two corresponding sequences of bar width indications.

14. A method for reading bar codes comprising the steps of:

a. scanning the bar code in a direction transverse to the bar code;

b. forming a bivalent signal comprising a plurality of transitions between first and second levels, there being respective time intervals between successive transitions, whereby one of the levels represents black and the other represents white;

c. first counting durations of said intervals to produce an interval duration count;

d. selecting a table within a table memory;

e. addressing the table using the interval duration count to provide a respective bar width validity indication, the table containing a plurality of bar width validity indications, the table including at least two sections for invalid bar width indications and at least two sections for valid bar width indications corresponding to respective valid bar widths, the highest and lowest respective valid bar widths, corresponding to the respective valid bar width sections, having a respective ratio of at least 11/2;

f. storing the bar width indication provided in step e.;

g. repeating steps a. through f. until a predetermined number of valid bars is stored, the table used in at least one repeating of step e being such that one of the sections of invalid bar width indications corresponds to bar widths lying between the valid bar widths; and

h. providing the stored bar width indication signals as an output code.

15. The method of claim 14 comprising the step of restarting if the bar width validity indication provided in step e. indicates an invalid bar width.

16. A bar code reading device comprising:

scanning means for line-wise scanning the bar code;

threshold means fed by the scanning means for producing a binarized scanning signal;

counter means for counting a clock signal and having reset means for being reset by a transition in said binarized scanning signal;

a bar width table memory for storing a plurality of tables, each table being addressable by said counter means for under control of said transition outputting a signal indicating a first acceptable bar width in a first address range thereof, a second acceptable bar width in a second address range thereof, or an unacceptable bar width in each of a third and a fourth address ranges thereof that are separated from each other by at least one of said first and second address ranges, wherein at least one table has at least one of said third and fourth address ranges between said first and second address ranges, wherein said first and second address ranges have a ratio of the least 11/2 between lowest and highest acceptable bar width therein, and wherein furthermore selection means are present for reversibly selecting among said plurality of tables;

code generating means fed by said bar width table for under control of each transition progressively storing a sequence of valid bar width indications;

a bar counter for counting said transitions;

and an output element fed by said code regenerator for under control of a predetermined bar count outputting said sequence of bar width indications.