JPH08147402A - Signal processor of optical information reader - Google Patents

Abstract

PURPOSE: To provide the signal processor of the optical information reader which is short in process time and high in precision. CONSTITUTION: This processor is equipped with a differentiating means (step 404) which differentiates respective digital values of a digital signal converted by an analog/digital converting means, a peak point detecting means (step 412) which detects the peak point of the differentiated values obtained by the differentiating means (step 404), a temporary bar width calculating means (step 414) which calculates temporary bar width from the peak value detected by the peak detecting means (step 412), and a correcting means (steps 416-422) which corrects the temporary bar width calculated by the temporary bar width calculating means (step 414); and the temporary bar width calculated by the temporary bar width calculating means (step 414) is corrected by the correcting means (step 424) to detect the bar width included in optical information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reader, and more particularly to a signal processor for an optical information reader such as a bar code reader.

[0002]

2. Description of the Related Art Conventionally, in an optical information reading device such as a bar code reader, an analog signal output from a reading sensor is subjected to analog / digital conversion (A / D conversion).
After being converted into a digital signal and quantized by the means,
It is known to perform a differential process (differential process) to detect the bar boundaries (black and white boundaries) of a barcode. In this case, since one pixel of the reading sensor element (generally a CCD element) performs sampling processing for A / D conversion,
There is a problem in accuracy that the reading accuracy of one pixel (1 bit) or more of the reading sensor element cannot be obtained.
Therefore, for example, in Japanese Unexamined Patent Publication No. 5-290201, difference processing between quantized digital values is performed,
A method has been proposed in which a predetermined calculation is performed from the obtained difference value to correct the bar boundaries (black and white boundaries) of the barcode.

[0003]

However, in the above correction, since the peak point of the differential waveform is detected based on the previous difference, an accurate inflection point (black / white boundary) is detected. No, not at most 1 as shown in Figure 7.
There is a problem that an error of one pixel (1 bit) occurs. On the other hand, in order to detect an accurate inflection point, various interpolation methods are known in which some data are interpolated between data of digital signals to approximate an analog waveform, but these interpolation methods are not accurate. Although it is good, it has a drawback that the processing time becomes long, and therefore it is not suitable for an optical information reading device or the like which requires a processing speed.

Here, taking the Lagrange's interpolation method as an example, it will be explained that this interpolation method takes a long processing time. For example, (n + 1) independent variables x _i (i = 0,
1, ..., N), the unknown function f (x) is y
_It is assumed that the value _i (i = 0, 1, ..., N) is taken.
At this time, (n + 1) points (x _i , y _i ) (i = 0,
An n-th order polynomial Pn (x) passing through all of 1, ..., N) is given by the following equation 1.

[0005]

## EQU1 ## Pn (x) = a ₀ x ⁿ + a ₁ x ^n-1 + ... a _n-1 x + a _n Here, the value of f (x) other than discretely given points x _i is The Lagrange interpolation method is to be approximated.

Pn (x) is given by the Lagrange's interpolation polynomial Pn (x) of the following equation 2.

[0007]

[Equation 2]

As is clear from the equation (2), when one point is interpolated between certain data, the difference from all data is taken and these differences are multiplied, so that the amount of calculation becomes enormous. For example, if there are 2,000 total data and 100 peak points, and 5 points are interpolated before and after the peak point,
× 2 × 100 = 1,000 times, the difference from 2,000 pieces of data is calculated, the equation 2 is calculated, the peak point is found again, and this processing is repeated. Even if other interpolation methods or sampling theorems are used, it is necessary to repeatedly calculate all data, and a huge processing time is required.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a signal processing device of an optical information reading device having a short processing time and high accuracy.

[0010]

SUMMARY OF THE INVENTION The present invention provides a signal for an optical information reading device having an optical information reading means and an analog / digital converting means for converting an analog signal output from the optical information reading means into a digital signal. A processing device, the first structural feature of the present invention is
Differentiating means for differentiating each digital value of the digital signal converted by the analog / digital converting means, peak point detecting means for detecting the peak point of the differential value differentiated by the differentiating means, and detection by the peak point detecting means The provisional bar width calculation means includes a provisional bar width calculation means for calculating the provisional bar width from the calculated peak value and a correction means for correcting the provisional bar width calculated by the provisional bar width calculation means. The provision is made to correct the temporary bar width calculated by the correction means to detect the bar width included in the optical information.

A second feature of the configuration of the present invention is that the above-mentioned correction means includes a difference (V) between a peak value obtained by the peak point detection means and a data value before the peak value, A determination means for determining the difference (W) between the peak value and the data value after the peak value, and a correction value for calculating the correction value by a predetermined arithmetic expression based on the determination by the determination means. And a calculation means.

Further, the third structural feature of the present invention is that
The calculation formula of the correction value calculation means described above is S = 0.5 (V−W) when it is determined that the difference (V) is greater than or equal to the difference (W) based on each determination by the determination means. When it is determined that the difference (V) is smaller than the difference (W) by using the arithmetic expression of / V, the difference (V) or the difference (V) is calculated by using the arithmetic expression of S = −0.5 (W−V) / W. If the difference (W) is determined to be 0,
It is to use an arithmetic expression of S = -0.5. However, S
Represents a correction value.

[0013]

In the present invention configured as described above, the difference between before and after the peak point is calculated by the number of peak points, and the interpolation is performed only by applying a simple mathematical expression based on the comparison of the magnitudes. Therefore, it is possible to shorten the processing time (for example, 1/5000 or less of the processing time of the Lagrange's interpolation method), and it is possible to perform a highly accurate signal processing, which is a particular effect.

[0014]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of a bar code reading apparatus which is an optical information reading apparatus according to an embodiment of the present invention. In FIG. 1, in a casing 10, an LED module 100 in which a plurality of LEDs for irradiating light to the barcode label 1 are arranged side by side, and light emitted from the LED module 100 is condensed on the barcode label 1. An irradiation lens 20, an image forming lens 40 for forming an image of the light reflected by the barcode label 1 on an image sensor 200 via a mirror 30, and an optical signal formed by the image forming lens 40 into an electric signal. Image sensor 200 for conversion
A control device 300 for reading the information content of the barcode label 1 based on an electric signal from the image sensor 200 (for example, 2048 CCD sensors).
And are arranged.

In the casing 10, an LED lamp 60 and a buzzer 70 for indicating the completion of reading the barcode, and a connector 80 for connecting the information content of the barcode label 1 to an external device (not shown). The cable 90 is arranged. Further, the control device 300 for reading the information content is arranged on the substrate 50.

FIG. 2 is a diagram showing a block circuit of the control device 300 described above. In FIG. 2, the control device 300
Is a noise removal and amplification circuit 310 that removes noise generated in the output signal from the image sensor 200 to shape the waveform, and amplifies the waveform-shaped signal, and the amplified analog output signal to a digital signal sequentially. Analog / digital conversion (A / D conversion) circuit 32 for conversion
0, a drive circuit 330 that drives the CCD sensor of the image sensor 200 based on a command from the microcomputer 350, and an L that drives each LED of the LED module 100 based on a command from the microcomputer 350.
The microcomputer 350 that performs various kinds of arithmetic processing based on the digital signal output from the ED drive circuit 340 and the A / D conversion circuit 320, and sends out the arithmetic result to the output circuit 360, and the microcomputer 3
The output circuit 360 sends the data sent from the external device 50 to an external device.

Next, the operation of the bar code reading apparatus of this embodiment will be described with reference to FIGS. When light is emitted from the LED module 100 toward the barcode of the barcode label 1 via the irradiation lens 20, the reflected light from the barcode label 1 reaches the mirror 30 while diffusing. At this time, the mirror 30 changes the optical path of the reflected light from the barcode label 1 in the direction of the image forming lens 40 so that the reflected light reaches the image forming lens 40. The reflected light reaching the image forming lens 40 passes through the image forming lens 40 and forms an image on the light receiving surface of the image sensor 200.

The reflected light formed on the light receiving surface of the image sensor 200 is reflected by each light receiving element (C
The image sensor 200 outputs the electric signal sequence according to the light intensity received by the CD sensor element. That is, the bar code on the bar code label 1 is formed of a bar portion (A) and a space portion (B) as shown in FIG. 4A, and the bar portion (A) and the space portion ( Since the reflectance of the irradiated light is different from that in B), the light receiving intensity (signal level) is low in the bar portion (A), and the light receiving intensity (signal level) is high in the space portion (B).
Therefore, each light receiving element (CC
The image sensor 200 outputs the electric signal sequence corresponding to the light intensity (signal level) received by the D sensor element).

The electric signal output from the image sensor 200 is a noise removing and amplifying circuit 31 of the control device 300.
Input to 0. In the noise removal / amplification circuit 310, the noise generated in the electric signal including the information of the barcode output from the image sensor 200 is removed and the waveform is shaped, and then the waveform shaped signal is amplified. The analog signal containing the information of this amplified bar code is A / D
The A / D conversion circuit 320 is input to the conversion circuit 320.
At, the analog signal is converted to a digital signal.
(See FIG. 4 (b) and FIG. 5 (c), FIG. 4 (b))
Shows the digital value (each point) of the A / D converted digital signal, and FIG. 5 (c) shows the digital waveform of the A / D converted digital signal. ) In this way, A /
After the analog signal is converted into a digital signal in the D conversion circuit 320, this digital signal is input to the microcomputer 350, the input digital signal is subjected to signal processing described later, and the signal processed bar is applied. The code data will be output to the output circuit 360. When the bar code data is output to the output circuit 360, the bar code data is transmitted to an external device (not shown).

Next, the signal processing of the bar code reading apparatus of this embodiment, that is, the processing for calculating an accurate bar width will be described. The microcomputer 350 is
It is composed of a CPU, a ROM, a RAM, etc., and a signal processing program for calculating an accurate bar width shown in the flowchart of FIG. 3 is stored in the ROM in advance. Therefore, signal processing for calculating an accurate bar width will be described based on the flowchart of FIG. Under the command from the microcomputer 350, the LED drive circuit 340 drives to drive each LE of the LED module 100.
D emits light. Then, the microcomputer 35
The drive circuit 330 of the image sensor 200 is driven under the command from 0, the image sensor 200 receives the reflected light from the barcode label 1, and the A / D conversion circuit 320
The signal processing program is executed in the state where the digital signal sequentially converted in is input to the microcomputer 350.

First, when this signal processing program is executed in step 400, the next step 402
Then, in step 402, median filter processing is performed. This median filtering process arranges the data values of the point, the point before the point, and the point after the point in descending order, and the middle data value of the arranged data values This is a data value, and by this median filter processing, noise remaining after A / D conversion can be removed.

Then, the process proceeds to step 404, in which differential processing (difference processing between data) is performed.
Is made. The reason for performing this differential processing is as follows. That is, the digital signal containing the information of the bar code is formed from a plurality of continuous peaks and valleys as shown in FIG. 4B, and the boundary (inflection point) between the peaks and valleys.
Is the border between black and white. At this black and white boundary, the difference between the data (that is, the slope of the digital signal) becomes large,
The difference between the data is taken (that is, differentiated), and the peak point is estimated to be the boundary between black and white.

Then, in order to detect this peak point,
First, in step 406, the threshold value is calculated. This threshold value is calculated by first calculating 50% of the maximum and minimum differential values obtained in step 404.
(See ± S _{1 in} FIG. 4C). Then, the process proceeds to step 408, and points (P ₁ , P ₂ , P ₃ , P _{4 in} FIG. 4C) that are equal to or greater than the threshold value (+ S ₁ ) or equal to or less than the threshold value (−S ₁ ) obtained in step 406. Is set as the first peak point.

Here, the actual differential waveform is the peak point output as shown in FIG. 4 (c) due to the reflectance of the bar code, the illuminance distribution on the bar code, the cosine fourth law of the optical system, and the like. There are various values of ₁ , P ₂ , P ₃ , and P _4, and some peak points that are not detected also appear. Therefore, the peak point is detected again. First, in step 410, the second threshold detection is performed. That is, the maximum value and the minimum value are obtained for each peak point between the peak points obtained in step 408, and 50% of these values are used as the threshold value for each peak point (FIG. 4). (D) S ₂ , S ₃ ,
S ₄ , S ₅ , S ₆ and S ₇ ). Then, step 4
12, the threshold value for each peak point obtained in step 410 (S ₂ , S ₃ , S ₄ , S ₅ , S _{6 in} FIG. 4D).
And S ₇ ), points above or below these thresholds (Q ₁ , Q ₂ , Q ₃ in FIG. 4D),
Each point of Q ₄ , Q ₅ , and Q ₆ ) is set as the second peak point.

Then, the process proceeds to step 414. In this step 414, each peak point obtained in step 412 (Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q ₅ , Q _{6 in FIG.}
The respective distances between the respective peak points are calculated as the temporary bar width. However, as shown in FIG. 4D, the peak points obtained in step 412 (each point of Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q ₅ , Q ₆ in FIG. 4D)
And the peak point of the actual analog waveform do not match,
The temporary bar width obtained in step 414 is different from the actual bar width, and it is necessary to correct the temporary bar width obtained in step 414. In the following steps, the process of correcting the temporary bar width obtained in step 414 is performed.

First, in step 416, the differential waveform obtained in the differential processing of step 404 (FIG. 5D).
Refer to) to determine the shape. For example, as shown in FIG. 6, the determination of the shape of the differential waveform is performed by determining the peak point Q ₇ obtained in step 412 and the point Q _7a before the peak point Q _7.
When the difference in data between V and W is V, and the difference in data between the peak point Q ₇ and the point Q _7b after this peak point Q ₇ is W, the magnitude relationship between V and W, that is, peak point Q ₇ And this peak point Q _7
Is determined by examining the difference between the slope of the straight line connecting the point Q _7a before the point Q _7a and the slope of the straight line connecting the peak point Q ₇ and the point Q _7b after the peak point Q _7. .

If it is determined in step 416 that V is greater than or equal to W (V ≧ W), the process proceeds to step 418, where S = 0.5, an equation for calculating the inflection point error S obtained by experiment. Inflection point error S based on (V−W) / V
To calculate. In step 416 described above, V
Alternatively, if W is determined to be 0 (V = 0 or W = 0), the process proceeds to step 420, where the inflection point error S is calculated based on S = −0.5 To calculate. Furthermore, if it is determined in step 416 that V is smaller than W (V <W), the process proceeds to step 422, where S =-, the formula for calculating the inflection point error S obtained by experiment.
The inflection point error S is calculated based on 0.5 (W−V) / W. Here, in each calculation formula of the inflection point error S described above,
The reason for multiplying by 0.5 is to suppress the error range within half (0.5 bit) of one pixel of the CCD sensor.

Steps 418, 420 and 4 described above
After the inflection point error S is calculated at 22, the process proceeds to the next step 424, and the temporary bar width obtained at step 414 is corrected based on the inflection point error S to calculate the accurate bar width. Then proceed to step 425 and proceed to step 4 above.
The processing from 16 to step 424 is repeated, and if “YES” is determined in this step 425, that is, the correction of the bar width for one scan (the entire width of the bar portion and the space portion of the barcode) is completed. Then, the process proceeds to the next step 426.

Proceeding to step 426, this step 4
At 26, it is determined whether the bar width data calculated at step 424 is correct data. In this determination, the above-described processing from step 402 to step 426 (e.g., 8 ms) is repeated (e.g., 3 times), and when all of these data match, it is determined as "YES",
In the next step 428, the data obtained in step 426 is output to the output circuit 360 (see FIG. 2). If "NO" is determined in step 426,
The processing from step 402 to step 426 described above is repeated.

As described above, in the present embodiment, the difference between before and after the peak point is calculated by the number of peak points, and the interpolation can be performed by applying a simple mathematical expression based on the comparison of the magnitudes. For example, the signal processing can be performed in a processing time of 1/5000 or less of the Lagrange's interpolation method, the processing time can be remarkably shortened, and a highly accurate signal processing can be performed.

Although the image forming lens 40 is provided between the bar code label 1 and the image sensor 200 in the above embodiment, the image forming lens 40 is provided if the image sensor has an image forming member. Need not be provided. Further, the example in which the CCD sensor is used as the image sensor 200 has been described, but any sensor element such as a contact sensor or a photodiode that can detect the intensity of light may be used in addition to the CCD sensor. good. Then, depending on the sensor element used (for example, a contact sensor), it is not necessary to provide a space between the barcode label 1 and the image sensor 200.

Further, in the above embodiment, the LED module 100 is used as a light source for irradiating the bar code label 1 with light, but any light source such as a laser diode or a lamp may be used. You may use.
Further, if the bar code label 1 is irradiated with external light, the light source may be omitted. Further, in the above-described embodiment, when the peak point of the differential waveform is detected, the median filter and the threshold value are set twice.
Although the processing steps from step 406 to step 412 in FIG. 3 are performed, step 406 is performed until the peak point is detected.
~ Any process other than step 412 may be performed.

Further, the data processing after A / D conversion is performed by the software processing for calculating the bar width in the microcomputer 350, but all may be performed by a hardware configuration. Further, in the above-mentioned embodiment, the bar code reading device is described as the optical information reading device, but the present invention can be applied to any optical information reading device other than the bar code reading device.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a bar code reading apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a circuit block of the control device of FIG.

FIG. 3 is a flowchart showing a processing operation of bar width calculation of the signal processing device of the present invention.

4A and 4B are diagrams illustrating a processing operation for detecting a peak point, FIG. 4A is a diagram showing a bar code having a bar portion (black) and a space portion (white), and FIG. 2C is a diagram showing digital data after receiving the barcode of FIG. 2 and A / D converting it, FIG. 7C is a diagram showing a differential waveform of FIG. 7B and a first threshold value, and FIG. b) differential waveform and 2
It is a figure which shows the threshold value of the time.

5A and 5B are diagrams illustrating a processing operation for detecting an accurate bar width, FIG. 5A is a diagram showing pixels of a light receiving element (CCD), and FIG. 5B is a bar portion (black) and a space portion ( It is a figure which shows the barcode which has (white), (c) is a figure which shows the digital data waveform after light-receiving the barcode of (b) and A / D-converting it, and (d) of (c). It is a figure which shows a differential waveform, (e) is a figure which shows a temporary bar width, (e)
FIG. 4 is a diagram showing an accurate bar width calculated according to the present invention.

FIG. 6 is a diagram illustrating the determination of the shape of a differential waveform.

FIG. 7 is a diagram illustrating a processing operation for detecting a bar width in a conventional optical information reading device.

[Explanation of symbols]

100 ... LED module, 200 ... Image sensor,
300 ... Control device, 320 ... A / D conversion circuit (analog / digital conversion means), 350 ... Microcomputer (differentiation means, peak point detection means, temporary bar width calculation means, correction means)

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[Procedure amendment]

[Submission date] March 16, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

5A and 5B are diagrams illustrating a processing operation for detecting an accurate bar width, FIG. 5A is a diagram showing pixels of a light receiving element (CCD), and FIG. 5B is a bar portion (black) and a space portion ( It is a figure which shows the barcode which has (white), (c) is a figure which shows the digital data waveform after light-receiving the barcode of (b) and A / D-converting it, and (d) of (c). It is a figure which shows a differential waveform, (e) is a figure which shows a tentative bar width, ( f )
FIG. 4 is a diagram showing an accurate bar width calculated according to the present invention.

Claims (3)

[Claims] 1. An optical information reading device comprising: an optical information reading means; and an analog / digital converting means for converting an analog signal output from the optical information reading means into a digital signal, wherein the analog / digital converting means Differentiating means for differentiating each digital value of the converted digital signal, peak point detecting means for detecting a peak point of the differential value differentiated by the differentiating means, and temporary from the peak value detected by the peak point detecting means. The provisional bar width calculation means for calculating the provisional bar width calculation means, and the correction means for correcting the provisional bar width calculation means calculated by the provisional bar width calculation means. The bar width included in the optical information is detected by correcting the bar width of The signal processing apparatus of the multi-address reading device. 2. The correction means includes a difference (V) between a peak value obtained by the peak point detection means and a data value before the peak value, the peak value and a data value after the peak value. And a correction value calculation means for calculating a correction value by a predetermined arithmetic expression based on the determination made by the determination means. The signal processing device of the optical information reading device according to claim 1. 3. The arithmetic expression of the correction value calculation means is based on each judgment by the judgment means, and the following (1), (2),
The signal processing device of the optical information reading device according to claim 2, wherein the arithmetic expression of (3) is used. (1) When it is determined that the difference (V) is greater than or equal to the difference (W), S = 0.5 (V−W) / V (2) The difference (V) is When it is determined that the difference (W) is smaller than the difference (W), S = −0.5 (W−V) / W (3) When the difference (V) or the difference (W) is 0, S = − 0.5 However, S in each equation represents a correction value.