JPH05101211A - Binarizing device for bar code signal - Google Patents

Abstract

PURPOSE:To prevent the influences of noise and to output a binary signal. CONSTITUTION:A primary differentiation circuit 13 is provided to apply the primary differentiation to the analog signal received from a sensor 11 together with a +VR generating circuit 14 which generates a plus slice level based on the envelope waveform of the primary differential signal sent from the circuit 13, an offset adder means 16 which adds an offset level to the slice level obtained by the circuit 14, a -VR generating circuit 15 which generates a minus slice level, a secondary differentiation circuit 19 which applies the secondary differentiation to the primary differential signal, a 1st comparator 17 which outputs 8 pulse signal after comparing the plus slice level with the primary differential signal, a 2nd comparator 18 which outputs a pulse signal after comparing the minus slice level with the primary differential signal, 8 3rd comparator 20 which detects a zero cross point out of the secondary differential signal, and a J-K flip-flop 22 which receives the output of each comparator and outputs a binary signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bar code signal binarizing device incorporated in a bar code reader.

[0002]

2. Description of the Related Art A bar code reader scans a bar code label on which a bar code having a bar having a difference in reflectance is printed by, for example, a laser beam to scan the bar code from the label surface. The bar code is read by condensing the reflected light, but the analog signal obtained by the movement of the label, the reflected light is weak, or the beam diameter of the reading beam changes.
The frequency changes and includes distortion. Then, it is required to binarize such an analog signal into a logic level while accurately holding the bar width information. As a binarizing device that meets such a demand, there is a conventional one disclosed in Japanese Patent Laid-Open No. 63-
The one disclosed in Japanese Patent No. 165979 is known.

As shown in FIG. 4, a sensor 1 for receiving the reflected light from the bar code label surface and outputting an analog signal according to the amount of the received light is provided, and the analog signal from the sensor 1 is supplied to an amplifier 2. After the amplification, the signals are supplied to the primary differentiating circuit 3 and the secondary differentiating circuit 4, respectively.
To the first comparator 5 for comparing with the positive slice level + VR and the second comparator 6 for comparing with the negative slice level -VR, and from the secondary differentiating circuit 4. Third to detect the zero-cross point in the second derivative signal
Is supplied to the comparator 7. The output of the first comparator 5 is supplied to the J input terminal of the JK flip-flop 8 and the output of the second comparator 6 is supplied to the K input terminal of the JK flip-flop 8, and the third comparator 5 is supplied. The output of the comparator is passed through the exclusive OR circuit 9 to the T of the JK flip-flop 8.
Supplying to the (trigger) input terminal. The / Q output terminal output of the JK flip-flop 8 is supplied to the T input terminal of the JK flip-flop 8 via the exclusive OR circuit 9.
A binary signal is output from the Q output terminal.

In this conventional device, the waveform of the analog signal from the amplifier 2 for the bar code shown in FIG.
The waveform shown in (b) of FIG. 5 is differentiated by the primary differentiating circuit 3, and the waveform shown in (c) of FIG. 5 is supplied to the first and second comparators 5 and 6, respectively. And the first comparator 5
Outputs the pulse signal shown in FIG. 5 (d) in comparison with the slice level + VR, and the second comparator 6 outputs the slice level −
The pulse signal shown in FIG. 5 (e) is output in comparison with VR. These pulse signals are sent to the JK flip-flop 8 through the J
It is supplied to the input terminal and the K input terminal, respectively.

The analog signal waveform from the amplifier 2 is 2
The waveform is shown as (f) in FIG. 5 by being secondarily differentiated by the second differentiating circuit 4 and supplied to the third comparator 7. The third comparator 7 compares the input voltage waveform with the zero potential to detect the zero cross point, and outputs the zero cross detection signal shown in FIG. 5 (g). This zero-cross detection signal is input to one input terminal of the exclusive OR circuit 9, and the output from the / Q output terminal of the JK flip-flop 8 is input to the other input terminal of the exclusive OR circuit 9. Since it is input, the exclusive OR circuit 9 outputs a trigger signal corresponding to the rising edge and the falling edge of the zero-cross detection signal as shown in FIG.
It is input to the T input terminal of the K flip-flop 8. Thus, from the Q output terminal of the J-K flip-flop 8 shown in FIG.
A binary signal corresponding to the change of the white and black of the bar code is output as shown in (i).

When noise is generated in the first-order differential signal as shown by a in the figure, the input to the J input terminal and the K input terminal of the JK flip-flop 8 changes, but at this time, the T input terminal Since the trigger signal is not input, the binary signal from the Q output terminal is not affected. Further, even if the width of the pulse signal from the second comparator 6 is widened as shown by B in the figure, the trigger signal is generated only at the zero cross point,
Also in this case, the binary signal from the Q output terminal is not affected.
Thus, in this conventional device, the JK flip-flop 8 is used.
The noise resistance characteristic is improved by using the exclusive OR circuit 9 and.

By the way, the positive slice level + VR and the negative slice level -VR input to the first and second comparators 5 and 6 are not constant and are waveforms based on the envelope waveform of the primary differential signal waveform. ing. This is done to prevent the influence of noise on the first-order differential signal waveform.

That is, when a bar code is read by the sensor 1 as shown in FIG. 6, when an analog signal as shown in the sixth (a) is output from the amplifier 2 and is input to the primary differentiating circuit 3, The primary differentiation circuit 3 outputs a primary differentiation signal as shown in FIG. 6 (b). Then, this first-order differential signal is input to the first and second comparators 5 and 6.

Positive slice level + VR and negative slice level -VR input to the first and second comparators 5 and 6.
Has an envelope waveform as shown in FIG. 6 (c). The slice levels + VR and -VR are level-shifted to a positive slice level + VR 'and a negative slice level -VR' as shown by the dotted line in the figure, and
Comparator 5 compares the positive slice level + VR 'with the primary differential signal level, outputs a pulse signal that is high during the period when the primary differential signal level is high, and the second comparator 6 Negative slice level-VR 'and 1
The secondary differential signal levels are compared with each other, and a pulse signal that is high level is output while the primary differential signal level is low.

In this way, the first comparator 5 outputs the data shown in FIG.
6 is output to the J input terminal of the JK flip-flop 8 and the second comparator 6 outputs the pulse signal shown in FIG.
The pulse signal shown in (e) is output and input to the K input terminal of the JK flip-flop 8.

On the other hand, the secondary differential circuit 4 outputs a secondary differential signal as shown in FIG. 6 (f), and the zero-cross point of this secondary differential signal is detected by the third comparator 7, A trigger signal synchronized with the zero-cross point is input from the exclusive OR circuit 9 to the T input terminal of the JK flip-flop 8. In this way, the binary signal shown in FIG. 6 (g) is output from the Q output terminal of the JK flip-flop 8.

[0012]

Using such a conventional apparatus, a bar code label 10 as shown in FIG. 7 is provided with a background portion 10a, a bar code portion 10b, and a bar code portion 10b as shown by arrows in the figure.
If the background portion 10a is scanned and read in this order, the following problems occur.

That is, when scanning is performed in this manner and read by the sensor 1, the analog signal waveform from the amplifier 2 becomes as shown in FIG. 8 (a). That is, since the background portion 10a is a space, is a character printed on a product, or is a part of a member for packaging the product, the background portion 10a is
The level of the analog signal waveform obtained by reading is approximately the center level.

When this analog signal waveform is subjected to primary differentiation by the primary differentiating circuit 3, a primary differential signal shown by waveform A in FIG. 8B is obtained. This first-order differential signal is then compared by the first comparator 5 with the positive slice level + VR 'and by the second comparator 6 with the negative slice level -VR'. Then, the first comparator 5 outputs a pulse signal as shown in FIG. 8 (c), and the second comparator 6 outputs the pulse signal shown in FIG.
Although a pulse signal as shown in (d) is output, the first-order differential signal contains a noise signal near the center level, and this noise signal has a certain noise width as shown in (b) of FIG. Therefore, positive and negative slice levels + VR ′, −
If VR 'is within this noise width, an erroneous signal may occur due to noise. Positive and negative slice level + V
The fact that R'and -VR 'fall within this noise width is shown in Fig. 8 (b).
As can be seen from the background part 10a to the bar code part 10
It occurs when the scan transitions to b. However, the background portion 10a
Since the signal obtained by scanning is not read as a bar code, there is no problem even if there is a change in the meshed parts in (c) and (d) of FIG. The shaded area in c) is inside the barcode part 10b, so if noise is placed in this area, the binary signal finally output will change to a black bar even though the actual festival is in the middle of a white bar.
There was a problem that the accurate barcode could not be reproduced.

Therefore, the present invention is intended to provide a bar code signal binarizing device which can reliably prevent the influence of noise and can always output an accurate binary signal corresponding to a bar code.

[0016]

SUMMARY OF THE INVENTION According to the present invention, a first-order differentiating circuit for first-order differentiating an analog signal obtained by reading a bar code and a first-order differentiating signal output from the first-order differentiating circuit are positive and negative. First and second comparators for comparing the slice level with the first and second slice levels, and slice level generating means for generating positive and negative slice levels based on the envelope waveform of the primary differential signal output from the primary differential circuit, Offset addition means for adding an offset level to the positive slice level of the positive and negative slice levels generated by the slice level generation means, and a secondary differential for differentially differentiation the primary differential signal output from the primary differential circuit. A circuit and a change point signal output means for detecting a zero cross point of the secondary differential signal from the second differentiating circuit and outputting a change point signal having the zero cross point as a change point. A binary signal output for outputting a binary signal corresponding to a bar code by inverting the output level according to the output level state of the first and second comparators at the input timing of the change point signal from the change point signal output means. Means are provided.

[0017]

In the present invention having such a structure, the analog signal obtained by reading the bar code is 1
After the second differentiation, the first and second comparators compare the positive and negative slice levels with each other and the second differentiation circuit performs the second differentiation.

The positive and negative slice levels are generated by the slice level generating means based on the envelope waveform of the first-order differential signal, and the offset level is further added to the positive slice level by the offset adding means.
That is, the barcode shown in (a) of FIG.
Positive and negative slice levels + VR and -VR shown in (b) are generated from the slice level generating means. That is, the positive slice level + VR does not fall within the noise width even at the minimum value due to the addition of the offset level.

As a result, the pulse signal is reliably output from the first comparator only at the changing point where the bar code changes from the white bar to the black bar, and the bar code from the black bar to the white bar is output from the second comparator. The pulse signal is reliably output only at the changing point that changes to. Thus, the binary signal output means always outputs an accurate binary signal corresponding to the bar code.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 2, a sensor 11 for receiving the reflected light from the bar code label surface and outputting an analog signal according to the amount of received light is provided, and the analog signal from the sensor 11 is amplified by an amplifier 12. After that, the primary differentiating circuit 13
Is being supplied to. 1 from the first-order differentiation circuit 13
The next differential signal is supplied to the + VR generating circuit 14 and the -VR generating circuit 15 as the slice level generating means. The + VR generating circuit 14 is also supplied with an offset level (voltage) from the offset adding means 16.

The + VR generating circuit 14 generates a slice level + VR by adding an offset level to a positive slice level based on the envelope waveform of the primary differential signal, and the -VR generating circuit 15 generates an envelope of the primary differential signal. A negative slice level -VR based on the waveform is generated.

The + VR generating circuit 14 is specifically shown in FIG.
As shown in, a parallel circuit of a capacitor C1 and a series circuit of resistors R1 and R2 is provided, and an input terminal Vin is connected to a diode D.
1 is connected in the forward direction to the connection point between the capacitor C1 and the resistor R1 of the parallel circuit. The connection point between the capacitor C1 and the resistor R2 of the parallel circuit is connected via the resistor R3.
It is connected to the V terminal, grounded via a capacitor C2, and connected to the positive terminal of the offset adding means 16 via a diode D2 in the reverse direction. The offset level from the offset adding means 16 can be variably adjusted. And the resistors R1 and R
The connection point with 2 is connected to the output terminal Vout.

The primary differential signal from the primary differential circuit 13 is supplied to the non-inverting input terminal (+) of the first comparator 17 and the inverting input terminal (-) of the second comparator 18. is doing. A positive slice level + V from the + VR generation circuit 14 is applied to the inverting input terminal (-) of the first comparator 17.
R is input, and a negative slice level -VR is input from the -VR generating circuit 15 to the non-inverting input terminal (+) of the second comparator 18.

Further, the primary differential signal from the primary differential circuit 13 is supplied to the secondary differential circuit 19. The secondary differential signal from the secondary differential circuit 19 is supplied to the third comparator 2
It is supplied to the 0 non-inverting input terminal (+). The inverting input terminal (-) of the third comparator 20 is grounded.

The third comparator 20 constitutes a changing point signal output means together with the exclusive OR circuit 21 in the subsequent stage, and supplies its output to one input terminal of the exclusive OR circuit 21. There is. The output of the exclusive OR circuit 21 is supplied to the CK (clock) input terminal of the JK flip-flop 22 which constitutes the binary signal output means. The J input terminal of the JK flip-flop 22 has the first
The output of the comparator 17 is input, and the output of the second comparator 18 is input to the K input terminal.

The JK flip-flop 22 is
The output from the Q output terminal is supplied to the other input terminal of the exclusive OR circuit 21, and a binary signal is output from the Q output terminal.

In the embodiment having such a structure, the sensor 11 receives the reflected light from the bar code label surface, and the sensor 11 outputs an analog signal according to the amount of received light. After this analog signal is amplified by the amplifier 12,
The first-order differentiation circuit 13 performs first-order differentiation.

The primary differential signal from the primary differentiating circuit 13 is supplied to the + VR generating circuit 14, the -VR generating circuit 15, the first and second comparators 17 and 18, and the secondary differentiating circuit 19, respectively.

The + VR generation circuit 14 produces a positive slice level based on the envelope waveform of the primary differential signal,
The offset level from the offset adding means 16 is added to it to generate a positive slice level + VR. The offset level at this time is the positive slice level + VR
The minimum value of is above the noise width. -V
The R generation circuit 15 generates a negative slice level -VR based on the envelope waveform of the primary differential signal. Thus, for the barcode label scanning shown in FIG.
Positive and negative slice levels + VR, -as shown in (b)
VR starts to occur.

The first comparator 17 compares the level of the input first-order differential signal with the positive slice level + VR and outputs a pulse signal having a width equal to or greater than the slice level + VR. The second comparator 18 compares the level of the first-order differential signal with the negative slice level -VR and outputs a pulse signal having a width of a period equal to or less than the slice level -VR. The pulse signal from the first comparator 17 is input to the J input terminal of the JK flip-flop 22, and the pulse signal from the second comparator 18 is input to the JK flip-flop 2.
2 is input to the K input terminal.

On the other hand, the primary differential signal is further secondary differentiated in the secondary differential circuit 19 and supplied to the third comparator 20. Then, the third comparator 20 detects the zero-cross point from the secondary differential signal, and the CK input terminal of the JK flip-flop 22 corresponds to the change point of the bar code through the exclusive OR circuit 21. The trigger signal is input.

The JK flip-flop 22 corresponds to the bar code by inverting the output level from the Q output terminal according to the level input to the J and K input terminals at the timing when the trigger signal is input to the CK input terminal. It outputs a binary signal.

As described above, since the positive slice level + VR generated from the + VR generation circuit 14 is added with the offset level so that the minimum value thereof exceeds the noise width, the bar code is scanned from the background portion in the scanning of the bar code label. There is no possibility that noise will exceed the positive slice level + VR even when shifting to the code section, and the first comparator 17
There is no false pulse signal generated from. Therefore J
The binary signal output from the Q output terminal of the -K flip-flop 22 is always an accurate binary signal corresponding to the bar code.

Therefore, if the bar code is reproduced based on this binary signal, the accurate bar code can be reproduced. If this binarizing device is used in a bar code reading device, erroneous reading can be greatly reduced and reliability can be improved.

[0036]

As described above in detail, according to the present invention, it is possible to provide a bar code signal binarizing device which can reliably prevent the influence of noise and can always output an accurate binary signal corresponding to a bar code. It is a thing.

[Brief description of drawings]

FIG. 1 is a waveform diagram for explaining an essential part of the present invention.

FIG. 2 is a circuit block diagram showing an embodiment of the present invention.

FIG. 3 is a specific circuit diagram of a + VR generation circuit of the same embodiment.

FIG. 4 is a circuit block diagram showing a conventional example.

FIG. 5 is an output waveform diagram of each unit of the conventional example.

FIG. 6 is a diagram for explaining the relationship between a conventional slice level and binarization processing.

FIG. 7 is a diagram showing an example of scanning a barcode label.

FIG. 8 is a diagram for explaining a conventional problem.

[Explanation of symbols]

11 ... Sensor, 13 ... Primary differentiation circuit, 14 ... + VR generation circuit, 15 ... -VR generation circuit, 16 ... Offset addition means, 17 ... First comparator, 18 ... Second comparator, 19 ...
Second-order differentiating circuit, 20 ... Third comparator, 22 ... JK flip-flop.

Claims (1)

[Claims] 1. A first-order differentiating circuit for first-order differentiating an analog signal obtained by reading a bar code, and a first-order comparing the first-order differentiating signal output from the first-order differentiating circuit with positive and negative slices. A second comparator, a slice level generating means for generating the positive and negative slice levels based on the envelope waveform of the primary differential signal output from the primary differentiating circuit, and the slice level generating means. Offset adding means for adding an offset level to the positive slice level of the positive and negative slice levels, a secondary differentiating circuit for second-order differentiating the first-order differential signal output from the first-order differentiating circuit, and this secondary Change point signal output means for detecting a zero cross point of the secondary differential signal from the differentiating circuit and outputting a change point signal having the zero cross point as a change point;
A binary signal for outputting a binary signal corresponding to a bar code by inverting the output level according to the output level state of the first and second comparators at the input timing of the changing point signal from the changing point signal output means. A bar code signal binarizing device comprising an output means.