JPH0344353B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a barcode reading device, and in particular to setting a threshold value, which is a standard for determining the bar width of a read barcode, to an appropriate value. The present invention relates to a barcode demodulation method that improves the reading rate of barcodes.

Recently, due to the mechanization of retail banks, product name code numbers, prices, etc. are expressed in barcodes, and food,
Printed on miscellaneous goods, etc. In industries such as supermarkets that want to handle a large number of shoppers in a short period of time, barcode reading devices are installed.
This barcode is read and the information recorded in the barcode is used for point of sale information management.

Normally, barcodes are read by scanning a surface on which a barcode is printed with light and demodulating coded data from reflected light modulated by the barcode. In other words, there are usually two types of bars: black bars (colors other than black are also available) and white bars (colors other than white are also available), and these black bars and white bars also have two types of width, large and small. A code is then composed of the combination of the black and white bar widths.

Therefore, detecting this bar width is an important matter in demodulating a bar code, and it is necessary to be unaffected by fluctuations in scanning speed when scanning a bar code.

[Conventional technology]

FIG. 3 is a block diagram of a circuit showing an example of a conventional bar code reading device.

For example, when a barcode 1 is scanned with a line pen 2, the reflected light projected from the line pen 2 is
The reflected light that enters the line pen 2 and is modulated by the barcode is sent to the photoelectric conversion circuit 3 where it is converted into an electrical signal and sent to the waveform shaping circuit 4.

The waveform of the electrical signal shaped by the waveform shaping circuit 4 becomes a pulse waveform with a width approximately corresponding to the black and white bar widths, and the bar width is detected by the conversion point detection circuit 6, and the wide width of the black bar (hereinafter referred to as (represented by W), narrow width (hereinafter referred to as N), and W and N of the white bar are sent to the bar width counter 7 in the order in which they are read from barcode 1, and are also sent to the black and white storage register 5. .

W and N of the black bar sent to the bar width counter 7
The white bar W and N data are clock oscillation circuit 8.
The count values counted by this sampling indicate the respective widths. The black bar width register 9 stores the black bar count value, and the white bar width register 10 stores the white bar count value.

The bar width determination circuit 11 compares the count value read from the black bar width register 9 and the count value read from the white bar width register 10 using a threshold value.
Determine whether it is W or N. The result determined by the bar width determination circuit 11 is sent to the bit determination circuit 12, and is determined based on the information from the black and white storage register 5 for one character (in code 39, the total number of black bars and white bars is 9). The corresponding bit pattern is determined from the combination data of W and N of the black bar and white bar.

Then, the bit pattern judged by the bit judgment circuit 12 is checked against a bit pattern table, and the bit pattern with a matching result is judged to have been read correctly and is displayed on the display section 14, as well as being processed. sent to section 13, barcode 1
is processed as read data.

FIG. 4 is a diagram illustrating threshold values used in the bar width determination circuit 11.

Black bar width register 9 and white bar width register 10
The count value entered from is the value counted by the bar width counter 7 as described above. And since this count value is sampled at a constant frequency,
It changes depending on the scanning speed of the line pen 2.

By the way, since the light pen 2 is moved manually, the scanning speed varies. Therefore, for example, if the scanning speed when scanning barcode 1 gradually increases, the bar width count value gradually decreases.

FIG. 4a shows a case where the count value is plotted on the vertical axis and the count value is compared with a constant level threshold value shown by a dotted line to determine the widths N and W of the bar.

The speed at which the barcode 1 is scanned changes each time one bar is read because it is done manually as described above. Therefore, the threshold value shown by the dotted line is determined by the start code read first, and is used when reading multiple bars indicating subsequent data.If this threshold speed becomes faster than the start point, the count value of the W bar will change. decreases and becomes lower than the threshold value, and the bar width of W is determined to be N.

As shown by the dotted line in Fig. 4b, adjacent bars are multiplied by a certain coefficient and compared by setting a range of threshold values, and those determined to be within the range of this threshold value are:
In comparison with the previously determined bar width, there is no change, so they are considered to be the same. However, as described above, if the scanning speed becomes faster than the starting point, W will be determined to be N.

The above description has been made of the case where the scanning speed becomes slower than the starting point, but if it becomes slower, N will be erroneously determined to be W.

[Problem that the invention seeks to solve]

As mentioned above, conventional barcode reading errors tend to occur due to fluctuations in the scanning speed at which the light pen is run, resulting in a poor reading rate.

[Means for solving problems]

The above problem is caused by barcode reading devices that use thresholds to classify the count values obtained by sampling the waveform of the read barcode and determine the bar width. Extract the count value N of the narrow bar and the count value W of the wide bar that are first read from the start code or stop code whose combination status is predetermined and calculate (N+W)/2. is set as a threshold value SH, the bar width of the bar to be subsequently read is determined using the threshold value SH, and the bar width count value N' or W' of the subsequently read bar is determined, and the count value is determined as follows: Using N or W, (N′+W)/2
Or, calculate (N+W')/2 and set it as the threshold value SH', use the threshold value SH' to calculate (SH+SH')/2 and set it as the threshold value SH'', and use the threshold value SH'' to set the threshold value SH'. Determine the bar width of the bar read next to the bar read subsequently, and for the bars read thereafter, consider the SH′ as SH, the SH″ as SH′, and calculate (SH+SH′). )/2 to create a new threshold
Repeat the operation of determining the bar width as "SH" for the black bar and white bar, and if an error occurs, calculate the total count value of all the bar widths of the black bar for one character. 1st
The bar width of the black bar is determined as a new threshold by dividing by a specific number, and the sum of the count values of all the bar widths of the white bar for one character is divided by a second specific number. This problem is solved by the barcode demodulation method according to the present invention, which performs an operation to determine the bar width of the white bar as a new threshold value.

[Effect]

In other words, in order to be able to divide the bar width count value, which changes in response to fluctuations in the scanning speed of the light pen, by using appropriate threshold values, a threshold value is calculated for each bar, and the judgment is made by calculating the threshold value for each bar. This is to accommodate variations when the scanning speed increases or decreases sequentially. However, if the scanning speed of the light pen changes from fast to slow while reading a barcode, or from slow to fast, the threshold value may follow the change in scanning speed too much. If a reading error occurs,
Divide the total count value of the black bar for each character by a first specific number and use it as a threshold for determining the bar width of the black bar,
Retry by dividing the total count value of the white bar by a second specific number and using it as the threshold for determining the bar width of the white bar,
We are trying to improve the reading rate.

〔Example〕

FIG. 1 is a block diagram of a circuit showing one embodiment of the present invention.

In this embodiment, the bar width determination circuit 11 shown in FIG. 3 is modified as shown in the bar width determination circuit 15 shown in FIG. 1, and the other circuits are the same as in FIG. 3. Then, the count values of the black bar and the white bar are separated and processed separately.

FIG. 5 is a diagram explaining the start code.

This start code is determined by code 39 and forms one character, the black bar indicated by and is N, and the black bar indicated by and is W. And the white bar indicated by is W,
The white bar indicated by ~ is N. This start code is recorded at the beginning of barcode 1 shown in FIG.

The count value of each black bar that enters the size judgment circuit 17 from the black bar width register 9 via the multiplexer 16 is ignored because the black bar shown here has a large variation in bar width, and the bar width of the black bar shown in The count value is stored in the N data register 21, and the count value of the bar width of the black bar that is read next is W.
The data is stored in the data register 18.

The (N+W)/2 arithmetic circuit 19 adds the count value of the N data register 21 and the count value of the W data register 18, divides the result by 2, and sends the result to the threshold determination circuit 20 as SH. The threshold determining circuit 20 sends this SH to the threshold register 22 via the multiplexer 16. Size judgment circuit 17
is the threshold value SH stored in this threshold value register 22
determine the width of the next black bar.

For example, if the width of the next black bar is determined to be N and stored in the N data register 21, then (N+
The W)/2 arithmetic circuit 19 adds the count value left in the W data register 18 and the count value newly stored in the N data register 21, divides the result by 2, and sets the result as SH'. It is sent to the threshold value determination circuit 20.

If the width of the next black bar is not determined to be N as described above, but is determined to be W, the width of the next black bar is determined to be W and the width is stored in the W data register 18
(N+W)/2 arithmetic circuit 19
adds the count value left in the N data register 21 and the count value newly stored in the W data register 18, divides the result by 2, and sends the result to the threshold determination circuit 20 as SH'. .

The threshold determining circuit 20 performs an operation of adding SH' and SH and dividing by 2, and stores the result as SH'' in the threshold register 22 via the multiplexer 16. The magnitude determining circuit 17 calculates the threshold SH''. to determine the width of the next black bar.

From now on, each time a new black bar is determined, the above
SH'' is regarded as SH', the above SH' is regarded as SH, and the result of performing the same calculation as above is repeated as SH'', and the magnitude judgment circuit 17 always uses the newly obtained SH'' as a threshold. The width of the next black bar is determined from the count value of the width register 9.

The data determined by the magnitude determination circuit 17 is sent to the bit determination circuit 12, where it is converted into a bit pattern as described above. Then, as described above, the bit pattern is compared with the bit pattern table, and if a match is found, it is determined that the bit pattern has been read correctly.

FIG. 2 is a diagram illustrating the relationship between the bar width and the threshold value in this embodiment, and FIG. 2a is a diagram illustrating the relationship between the threshold value SH'' and the count value of the bar width.

The threshold value indicated by the dotted line is that when the count value of the black bar decreases in proportion to the increase in the scanning speed of the light pen 2, the threshold value also decreases, and the threshold value changes according to the change in the scanning speed of the light pen 5. are doing.

In the case of FIG. 2 a, if the scanning speed of the light pen 2 increases or decreases sequentially, it is possible to follow the change in scanning speed and obtain the optimal threshold value. If the scanning speed changes from fast to slow while reading a barcode, or from slow to fast, the threshold may follow the change too much and reading may not be possible. .

FIG. 2b is a diagram illustrating a case where the scanning speed of the light pen 2 changes from a tendency to become slower to faster while scanning a bar code.

Based on the scanning speed of light pen 2 up to the black bar shown in , the light pen 2 when reading the black bar shown in
When the scanning speed suddenly increases, the count value of the black bar of W shown by and the count value of the black bar of W shown by change greatly, and the count value of the black bar shown by decreases, but the threshold value is slow. This indicates that the width of the black bar indicated by cannot be read as W because it follows the scanning speed.

In this case, as described above, if the results checked by the bit determination circuit 12 do not match and a read error is determined, a switching signal is sent to the multiplexer 16 from a control circuit (not shown).

When the multiplexer 16 is switched, the count value of the black bar width register 9 is sent to the timer value calculation circuit 23. The timer value calculation circuit 23 sums up all the black bar count values for one character from the black bar count values stored in the black bar width register 9, and calculates all the black bar count values for one character by Then, X/A is calculated using A obtained from X'/A=(N+W)/2, which is determined in advance from the bar code standard.

That is, as described above, the start code forms one character, the black bar indicated by and is N, and the black bar indicated by and is W. and,
The white bar indicated by is W, and the white bar indicated by .about. is N. Further, it is determined that W=2N or W=3N.

Therefore, when W = 2N, X' = +++
+=N+N+2N+2N+N=7N, and W
If = 3N, then X' = +++++ = N+
N+3N+3N+N=9N.

Therefore, when W=2N, X'/A=(N+W)/
When finding A from 2, 7N/A=3N/2,
A=14/3=4.66.

Also, if W = 3N, X'/A = (N+W)/2
Find A from 9N/A=2N, and A=9/
2=4.5.

Therefore, A=4.5 to 4.66.

The timer value calculation circuit 23 uses A obtained in advance in this manner to calculate X/A and sends it to the threshold register 22 via the multiplexer 16. Therefore, the magnitude determination circuit 17 uses X/A to determine the count value of the black bar width register 9 again. That is, based on this new threshold value, the black bar shown in FIG. 2b is determined to be W.

Although the value of A was calculated using the start code, in the case of other codes as well, most codes are composed of a combination of three N black bars and two W black bars. Therefore, the error can be ignored.

Processing of the count value of the white bar width register 10 is as follows.
Since this process is the same as the process of the count value of the black bar width register 9, detailed explanation will be omitted. However, the calculation contents of the timer value calculation circuit 24 are as follows: From the white bar count value stored in the white bar width register 10, all the white bar count values for one character are totaled, and the total white bar count value for one character is calculated. Assuming that the count value for each is Y, Y'/B = (N
+W)/2 is used to calculate Y/B.

In Fig. 5, when W = 2N, Y' = +
++=2N+N+N+N=5N, and W=
In the case of 3N, Y'=+++=3N+N+N
+N=6N.

Therefore, when W=2N, Y'/B=(N+W)/
When finding B from 2, 5N/B=3N/2,
A=10/3=3.33.

Also, if W=3N, Y'/B=(N+W)/2
Find B from 6N/B=2N, and A=6/
2=3.

Therefore, B=3 to 3.33.

As described above, the timer value calculation circuit 24
Y/B is calculated using . The other multiplexers 25 are connected to the multiplexer 16, the magnitude judgment circuit 28 is connected to the magnitude judgment circuit 17, and the W data register 2
9 to W data register 18, N data register 27 to N data register 21, (N+W)/2
The arithmetic circuit 30 is (N+W)/2 arithmetic circuit 19,
The threshold value determination circuits 31 correspond to the threshold value determination circuits 20, respectively.

The above explanation was based on the start code that is read first when barcode 1 is scanned in the forward direction, but when barcode 1 is scanned in the reverse direction, the first code that is read is the stop code. The same applies to this case as above.

〔Effect of the invention〕

As explained above, the present invention is resistant to fluctuations in the scanning speed of the light pen, and can achieve a better reading rate than other methods.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a circuit showing an embodiment of the present invention, FIG. 2 is a diagram explaining the relationship between the bar width and the threshold value of this embodiment, and FIG. 3 is an example of a conventional barcode reading device. A block diagram of the circuit shown in FIG.
FIG. 5 is a diagram explaining the start code. In the figure, 1 is a barcode, 2 is a light pen, 3 is a photoelectric conversion circuit, 4 is a waveform shaping circuit, 5 is a black and white storage register, 6 is a conversion point detection circuit, 7 is a bar width counter, 8 is a clock oscillation circuit, 9 is a black bar width register, 10 is a white bar width register, 11,
15 is a bar width judgment circuit, 12 is a bit judgment circuit,
13 is a processing section, 14 is a display section, 16 and 25 are multiplexers, 17 and 28 are size determination circuits, 18,
29 is a W data register, 19 and 30 are (N+
W)/2 arithmetic circuit, 20 and 31 are threshold value determination circuits,
21 and 27 are N data registers, 22 and 26 are threshold registers, and 23 and 24 are timer value calculation circuits.

Claims (1)

[Claims] 1. In a barcode reading device that divides the count value obtained by sampling the waveform of a read barcode using a threshold value and determines the bar width, there is a barcode reading device that determines the bar width according to the standard of the barcode. Extract the count value N of the narrow bar and the count value W of the wide bar that are first read from the start code or stop code in which the combination of bars is predetermined (N+W)/ 2 is calculated as a threshold value SH, and using the threshold value SH, determine the bar width of the next successively read bar, and determine the bar width count value N' or W' of the subsequently read bar,
Using the count value N or W, (N′+W)/
2 or (N+W')/2 and set it as a threshold value SH', using the threshold value SH', calculate (SH+SH')/2 and set it as a threshold value SH'', and using the threshold value SH'',
Determine the bar width of the bar read next to the subsequently read bar, and for the bars read thereafter, consider the SH′ as SH, the SH″ as SH′, and calculate (SH+SH). ′)/2 to create a new threshold
Repeat the operation of determining the bar width as "SH" for the black bar and white bar, and if an error occurs, calculate the total count value of all the bar widths of the black bar for one character. 1st
The bar width of the black bar is determined as a new threshold by dividing by a specific number, and the sum of the count values of all the bar widths of the white bar for one character is divided by a second specific number. A barcode demodulation method characterized by performing an operation of determining the bar width of a white bar as a new threshold value. 2 The first specific number above is A, which is determined by X'/A=(N+W)/2, where X' is the sum of all the count values of the black bars for one character determined from the bar code standard. , the above-mentioned second specific number is determined from the bar code standard, where Y' is the total count value of all the white bars for one character, Y'/B' = (N+W)/2
2. The barcode demodulation method according to claim 1, wherein B is determined by .