JPH02184108A - Binarizing device - Google Patents

Abstract

PURPOSE:To obtain an accurate binarizing signal without effect of noise by monitoring a difference of signal levels of upper and lower limit envelopes of a photoelectric conversion signal from a paper front with a bar code printed thereupon and adjusting a storage time of the upper limit envelope so that the difference does not reach a specified value or below. CONSTITUTION:Output levels from upper and lower limit envelope circuits 3, 4 are monitored by a differential amplifier 8 and a control means 10. When the level reaches a specified value or below, a switch of the upper limit envelope circuit 3 is turned off to make a storage time of the upper limit envelope close to infinite. Thus, a level of a threshold level signal from a midpoint detection circuit 5 even at a blank of a bar code is set sufficiently higher than a level of a noise signal included in the analog signal. Then an accurate binarized signal not affected by noise is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a binarization device that binarizes an analog signal using a floating threshold, and in particular, is capable of accurately separating the analog signal and noise. The present invention relates to a binarization device.

[Conventional technology]

Traditionally, devices that read barcode information printed on products scan the bars that form the barcode using a beam spot, and then photoelectrically convert the reflected light to read the barcode information using electrical signals obtained. is being read. For this reading process, the electric signal obtained by the above-mentioned photoelectric conversion is binarized.

Figure 4 shows an example of the configuration of a conventional binarization circuit that performs this binarization process. It is a photodetector such as a sensor.

2 is an amplifier that amplifies the output of the photodetector l to an appropriate signal level. 3 is an upper limit envelope circuit for obtaining the upper limit envelope of the amplified analog signal; 4
is a lower bound envelope circuit that obtains the lower bound envelope of the amplified analog signal. 5 is envelope circuit 3
．． 4 is a midpoint detection circuit that calculates the midpoint of the output; 6 is a comparator that binarizes the output of the amplifier 2 using the output of the midpoint detection circuit as a threshold; and 7 is an output terminal of the comparator 6.

The envelope circuit is also well known as a peak hold circuit, and an example of its upper limit is shown in Figure 5. In the figure, 31.32 is a buffer amplifier for removing the influence from other circuits on the envelope operation, and 33 .34
is a diode that determines the direction of the envelope, and 36 is a capacitor that stores the level of the envelope. Also,
35° and 37 are resistors for adjusting the envelope level storage (tracking) time. Note that if the directions of the diodes 33 and 34 in the figure are reversed, they correspond to the lower limit side.

Next, the operation of each part will be explained using FIG.

The output of the photodetector 1 is the signal A (sixth
(See Figure (a)) is an analog signal containing a mixture of barcode shading information, small irregularities on the paper surface, electrical noise, and the like. This signal is converted into upper and lower limit envelope signals C and B (see FIG. 6(a)) by two envelope circuits 3.4. The midpoint detection circuit 5 simultaneously receives the envelope signals C and B, calculates the midpoint of the levels of the two envelope signals, and outputs this midpoint signal D (see Figure 6(a) 1()) to the comparator 6. The signal A, which is the amplified output of the photodetector l, is input to the other terminal of the comparator 6. As a result, the output terminal 7 of the comparator 6 receives the signal A. Binarized signal E with the output of the midpoint detection circuit 5 as a threshold
(see FIG. 6(b)) appears, and a decoder (not shown) analyzes the information of the barcode based on this signal E.

[Problem to be solved by the invention]

However, in such conventional binarization circuits, the output of the midpoint detection circuit 5 hardly changes in the margins before and after the barcode (unprinted paper surface), so small irregularities on the paper surface (background ) or the noise signal N shown in FIG. 6(a), which is generated due to the influence of electrical noise generated in a circuit such as an amplifier, may be mistakenly converted to 2 as shown in the pulse signal M shown in FIG. 6(b). Value.

Therefore, if you measure the number of pulses and the width of each pulse of a binarized bar and try to identify those values based on a predetermined format, the barcode may not be decipherable or may be misread, and the decoding time will be longer. A serious problem arises as the length increases.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a binarization device that can accurately separate signals from barcodes and noise signals and binarize only barcode information.

[Means to solve the problem]

a first detecting means having a switching means capable of obtaining an upper limit envelope signal of the analog signal and adjusting a storage time of the envelope signal; and a first detecting means for obtaining a lower limit envelope signal of the analog signal. a third detection means for detecting a midpoint level from the signal level of the upper limit envelope obtained by the first detection means and the signal level of the lower limit envelope obtained from the second detection means; a calculation means for calculating the difference between the signal level of the upper limit envelope obtained from the first detection means and the signal level of the lower limit envelope obtained from the second detection means; and a comparison determination of the output of the calculation means with a predetermined reference level. A control means for controlling opening and closing of the switch means is provided to set the output of the third detection means to a threshold level and to prevent this level from approaching the analog signal level beyond a certain level.

[Effect]

The output level from the two envelope circuits (first and second detection means) is monitored by the differential circuit (calculation means) and the control means, and if the output level falls below the specified value, the output level from the upper limit envelope circuit (first detection means) is monitored. means), turn the switch on
By using FF and making the storage time of the upper limit envelope approach infinity, the level of the threshold signal from the midpoint detection circuit (third detection means) can be maintained at the same level as described above even in the margin area of the barcode (on the unprinted paper surface). Since the level can be set sufficiently higher than the level of the noise signal contained in the analog signal, it is possible to obtain an accurate binary signal free from the influence of noise.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific example of the upper limit envelope circuit used in FIG. 1, and FIG. 3 is a waveform showing operating waveforms of each part of FIG. 1. It is a diagram.

In FIG. 1, 8 is a differential circuit that calculates the difference in level between the output signals from the two envelope circuits 3.4, 9 is a reference 'lta that generates a predetermined reference level, and 10 is this reference level and 2 The value of the difference between the levels of the two envelope signals is determined, and the switch circuit 38 shown in FIG.
This is a comparator controlled by FFi#I. That is, the switch circuit 38 in FIG. 2 is for adjusting the envelope storage time under the control of the above-mentioned comparator, and is a switch circuit using a typical FET or the like. Note that the photodetector 1. Since the operation of the amplifier 2 and the lower limit envelope circuit 4 is similar to that described in the conventional example shown in FIG. 4, detailed explanation thereof will be omitted.

From the differential circuit 8, a difference signal F (see FIG. 3(b)) between the upper and lower envelope levels of the analog signal is always transmitted to one terminal of the comparator IO. A reference level G (see FIG. 3(b)) which is at least twice the level of the noise signal contained in the analog signal from the reference power source 9 is input to the other terminal of the comparator 10. The output signal H (third
(see figure (C)), the switch circuit 38 is turned on in the barcode area and turned off in the margins before and after the barcode.

As a result, the upper limit envelope circuit 3 converts the envelope of the analog signal into an optimized time in the barcode part.
The threshold signal D(
The level (see FIG. 3(a)) does not fall below the specified value at any time. Therefore, the comparator 6 always has a threshold higher than the level of the noise signal, and the binarized signal E (see FIG. 3(d)) appearing at its output terminal 7 has a bar code. Only this information appears, eliminating the influence of small irregularities on the paper (background) or electrical noise generated in circuits such as amplifiers.

Note that the threshold signal is as shown in Figure 3 (a) when the power is turned on.
), as shown by the broken line in Figure 3(d), because the envelope is not stored, the first barcode scan produces a noise signal on top of the binary signal as shown by the broken line in Figure 3(d). This noise signal generation can be prevented if there are things printed before and after the margins of the code, such as letters, patterns, etc. that serve as grayscale signals, and even if there is no such thing, the barcode is Scanning does not generate noise signals. Therefore, there is no problem in use.

According to this embodiment, as shown in FIG. 3(a), the photoelectrically converted signal in the margins before and after the barcode has a predetermined minimum value that is sufficiently higher than the noise signal level. On the other hand, the signals photoelectrically converted in the barcode section are compared using the optimized threshold as in the past, so there is no influence of noise as shown in Figure 3(d). As a result, the barcode portion and the margin portion are accurately binarized, and the barcode can be identified more reliably and accurately.

〔Effect of the invention〕

As explained above, according to the present invention, the difference in the signal level of the upper and lower limit envelopes of the photoelectric conversion signal from the printed barcode paper is monitored, and the upper limit envelope example is By adjusting the storage time, the threshold level of the binarization processing, which is the midpoint of the calculated upper and lower limit envelope, will be adjusted to the margin of the barcode (
Since the level can be set sufficiently higher than the level of the noise signal included in the above-mentioned analog signal even on a non-printed paper surface, it is possible to obtain an accurate binarized signal without the influence of noise.

Therefore, in the process of reading barcode information, it is possible to obtain a binary signal in which the start and end of a bar, the number and width of pulses corresponding to the bar, etc. match the planned format, and the barcode identification efficiency is improved. This results in remarkable effects such as a reduction in the misreading rate.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing a specific example of the upper limit envelope circuit used in Fig. 1, and Fig. 3 is a waveform for explaining the operation of Fig. 1. Figure 4 is a block diagram showing a conventional example of a binarization circuit, Figure 5 is a block diagram showing a conventional example of a binarization circuit.
4 is a circuit diagram showing a specific example of the upper limit envelope circuit used in FIG. 4, and FIG. 6 is a waveform diagram for explaining the operation of FIG. 4. Symbol explanation 1... Photodetector, 2... Amplifier, 3... Upper limit envelope circuit, 4... Lower limit envelope circuit, 5...
- Midpoint detection circuit, 6.10... Comparator, 7... Output terminal, 8... Differential circuit, 9... Reference power supply, 31.3
2...Buffer amplifier, 33.34...Diode, 35.37...Resistor, 36...Capacitor, 3
8...Switch circuit. Agent Patent Attorney Akio Namiki

Claims (1)

[Scope of Claims] 1) A first detection means having a switch means capable of obtaining an upper limit envelope signal of an analog signal and adjusting a storage time of this envelope signal; and the analog signal. The second to obtain the lower bound envelope signal of
a third detection means for detecting a midpoint level between the signal level of the upper limit envelope obtained from the first detection means and the signal level of the lower limit envelope obtained from the second detection means;
a calculating means for calculating the difference between the signal level of the upper limit envelope obtained from the first detecting means and the signal level of the lower limit envelope obtained from the second detecting means; Binarization, characterized in that the analog signal is binarized using the output of the third detection means as a threshold, and a control means for controlling opening/closing of the switch means based on comparison with a reference level. Device. 2) The binarization device according to claim 1, wherein the reference level is set higher than the level of a noise signal included in the analog signal.