JPS6159573A - Noise removing circuit of bar signal in bar code reader - Google Patents

Abstract

PURPOSE:To prevent a passing of a noise contained in a bar signal by generating another pulse signal from a photo-electric converting signal and its detecting output when a bar signal is formed and executing an on and off control of an output gate of the bar signal by using the signal. CONSTITUTION:A photo-electric converting signal of a bar code is inputted together with a noise ripple to detecting circuits 15 and 16. From the circuit 15, a + polarity signal of the lowest level 0 level or above appears and from the circuit 16, a - polarity signal of the highest level 0 or below appears and both signals are synthesized and inputted to a comparator 17. When reference voltage is added to the comparator 17, a pulse-shaped bar signal and an unneces sary noise signal, which are corresponding to a bar code pattern, also appear. On the other hand, in a photo-electric converting signal, a - polarity peak value is preserved at a peak holding circuit 36 and a 1/k voltage dividing volt age - K is formed. To a comparator 37, the - polarity signal and a voltage dividing voltage -K from the circuit 16 are added and a - polarity pulse signal voltage appears. In a gate circuit 40, the - polarity pulse signal voltage is set to a + polarity at an inverting circuit 47, and a noise signal is removed at a NAND circuit 42.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a bar signal noise removal circuit in a bar code reader, and more specifically, to a photoelectric conversion signal of a bar or code pattern obtained via a photo sensor. When forming a pulsed bar signal from.

The present invention relates to a noise removal circuit for removing unnecessary signal components such as noise contained in a bar signal.

[Prior Art] In barcode labels whose display contents are read by the reflected light of the irradiated light, for example, a color with a relatively high reflectance is set as the base color of the label in consideration of the wavelength of the irradiated light, and then Barcodes and other items are printed using colors that have a high light absorption rate. Also.

Detection of display contents requires a light emitting element and a light receiving element.71
An example of this barcode label is shown in Figure 4. The thick fiA and thin line B are converted into electrical signals via a photosensor, and then subjected to waveform shaping, etc. in the subsequent stage, and time widths corresponding to the widths of the thick, aA, and thin lines B are determined by a comparator or the like. A pulse-like signal voltage, a so-called bar signal, can be obtained.

A conventional example of a bar signal forming circuit that converts the output signal of this photosensor into a pulsed signal voltage is shown in FIG.

According to the figure, a barcode label l is irradiated with light from a light emitting element (not shown) in a photosensor 2.

The reflected light is made to enter a light receiving element (not shown) within the photosensor 2. This incident light is.

Here, after being converted into an electrical signal, it is applied to one input terminal of a comparator 5 via a buffer amplifier 4 provided at the first stage of the bar signal forming circuit 3, for example, and is also applied to another buffer amplifier 6. . The voltage level of the output signal of the buffer amplifier 6 is adjusted to a predetermined value by, for example, a slice circuit 7, and then its phase is shifted by a delay circuit 8 and applied to the other input terminal of the comparator 5. This signal is used as a reference voltage for determining the threshold level of the signal voltage input from the buffer amplifier 11. As a result, a pulsed signal voltage is output from the comparator 5, and is sent to, for example, a display circuit (not shown) via the amplifier 9, output terminal 10, etc. In this display circuit, logic signals of "1" and rOJ are formed from the pulsed signal voltages corresponding to the thick line A and thin line B of the barcode, respectively, and are displayed on a numeric display etc. via a decoder etc. It looks like this.

In this case, ripple voltage is likely to be superimposed on the photoelectric conversion signal output from the sensor 2 due to dust adhering to the surface of the barcode label 1 or uneven printing of the barcode pattern. An example is shown in FIG. 6, in which the photo sensor 2 is connected to the barcode label 1
For example, if there is dust r,... adhering to the movement path, the photosensor moves as shown in Figure (b). Ripple voltage R1 . . . is superimposed on the photoelectric conversion signal No. 2.

Since these ripple voltages R are unnecessary signal components that tend to cause noise, in the conventional bar signal forming circuit 3 shown in FIG.
The signal above level E and below level E are cut by a slice circuit 7 or the like.

However, if the amount of cut above the D level is reduced, there is a risk that a relatively large ripple voltage will be sent to a display circuit, etc. in the same way as a bar signal. Contrary to the above, if the amount of cut above the D level is increased and the brightness happens to decrease due to changes in the characteristics of the light emitting element, the output level of the photoelectric conversion signal will also decrease as shown in (c). Therefore, the signal level that can be effectively used becomes even smaller, which is not preferable for the subsequent signal processing circuit.

[Purpose of the Invention] This invention has been made in view of the above points, and its purpose is to form a pulsed bar signal from a photoelectric conversion signal obtained through a photo sensor. By forming another pulse-like signal whose timing matches the bar signal from the detection output and controlling the output gate of the bar signal on and off using this pulse-like signal, the effective usage level of the photoelectric conversion signal can be increased. An object of the present invention is to provide a bar signal noise removal circuit which prevents unnecessary signal components such as noise contained in a bar signal from passing through without causing any damage.

[Configuration of the Invention] The present invention will now be described in detail with reference to embodiments shown in the accompanying drawings.

According to FIG. 1, this bar signal noise removal circuit includes a bar signal forming circuit 13 that forms a pulsed signal corresponding to a barcode pattern from a photoelectric conversion signal obtained via, for example, a photosensor 2, and a control pulse generation circuit 35 that generates a pulse signal for removing a noise signal superimposed on the bar signal; and this control pulse generation circuit 3.
It is controlled by the pulse from No. 5 (No. 1) and is composed of a circuit 40 to the gate 1 which is configured to prevent the output of the noise signal superimposed on the bar signal.

Next, to explain step by step, the barcode label 1 is irradiated with light from the photosensor 2 as in the conventional example, and the reflected light is made to enter the photosensor 2 again. This incident light is converted into a voltage signal via the photosensor 2 and applied to the bar signal forming circuit 13. In the bar signal forming circuit 13, a pulsed signal voltage corresponding to the bar code pattern is formed from this applied signal, that is, a bar (No. The signal is then sent to a display circuit (not shown).

The bar signal forming circuit 13 includes a buffer amplifier 111, first and second detection circuits 15, 16, a comparator I7, a reference voltage generation circuit 18, and the like.

In this embodiment, the buffer amplifier 14 uses an operational amplifier, a transistor, etc., like the buffer amplifier 4 of the conventional example described above. The photoelectric conversion signal from the photosensor 2 is added to this buffer amplifier 14,
The output is branched into a first detection circuit 15 and a second detection circuit 1.
It can be added to 6. The output sides of these two detection circuits 15 and 16 are connected by a common wiring, and are connected to one input terminal of a comparator 17 configured using an operational amplifier, and the other input terminal is connected to, for example, a potentiometer, etc. A reference voltage generating circuit 18 whose output level can be adjusted is connected thereto.

The first detection circuit 15 is an operational amplifier, for example.

It is composed of a diode, a capacitor, a resistor, etc., and detects the input photoelectric conversion signal and outputs a (+) polarity detection signal whose lowest level is equal to or higher than zero level. The second detection circuit 16 has the same configuration as the first detection circuit 15 except that the direction of the diode is reversed, and detects the photoelectric conversion signal so that its highest level is below the zero level. (−
) outputs a polarity detection signal.

The control pulse generation circuit 35 is composed of, for example, a peak hold circuit 3G and a comparator 37, and the photoelectric conversion signal from the photosensor 2 is inputted to the peak hold circuit 36 via the buffer amplifier 14. It has become.

- In this embodiment, the peak hold circuit 36 is a general circuit composed of, for example, an operational amplifier, a diode, a capacitor, and a resistor, and rectifies the input photoelectric conversion signal to (-) polarity. The peak value is held in a capacitor, and the held voltage is divided into 1/k and output via a resistor. In this case, the value of the voltage division ratio is set so that the 1-divided voltage is greater than the noise signal level. The comparator 37 is composed of an operational amplifier, etc., like the comparator 37 of the bar signal forming circuit 13, and one input terminal receives a (-) polarity detection signal from the second detection circuit, and the other A divided voltage of negative polarity is applied as a reference voltage from the peak hold circuit 36 to the other input terminal.

The goo 1-circuit 40 is, for example, an inverting circuit 41 and a NAND circuit 4.
It is composed of 2 etc. The output of the comparator 37 is applied to this inverting circuit 41, and the inverted signal is applied to one input terminal of a NAND circuit 42. The other input terminal of the NAND circuit 42 is adapted to receive the bar signal output from the comparator 17 of the bar signal/formation circuit 13. The output signal of the NAND circuit 42 is sent from the output terminal 10 to a display circuit (not shown) via the amplifier 9, as in the conventional example.

[Operation of the invention] First, with reference to FIG.
3 will be explained, and then the operations of the control pulse forming circuit 35 and the Goo 1-circuit 40 will be described with reference to FIG. In addition, the first
In the figures, (B) or (N) in Figures 2 and 3 above.
In the 3-bar signal forming circuit 13, where the signal waveform shown in is indicated by the same reference numeral, the second
As shown in (a) of the figure, the movement of E 1 and sensor 2! I!
If there is dust r,... on the II path, the photoelectric conversion signal will be a regular photoelectric conversion signal corresponding to the line widths A and B of the barcode pattern, as shown in the same figure (b). In addition to the noise ripple voltage R2, which is an unnecessary signal...
As mentioned above, ... appears. When this signal is input to the first detection circuit 15 and the second detection circuit 16, the output side of the first detection circuit 15 has a (+) polarity whose lowest level is higher than zero level as shown in (c). A detection signal of (-) polarity appears on the output side of the second detection circuit 16, and the maximum level is below the zero level, as shown in (d). These two detected signals are combined on the output side to form a signal voltage with a waveform as shown in (e), which is applied to the comparator 17. When the reference voltage of this comparator 17 is set to Ov, for example, unnecessary noise No. 48 is also generated on the output side of the pulsed bar signal corresponding to the bar code pattern, as shown in (f). appear.

Next, in the control pulse generation circuit 35, when the photoelectric conversion signal shown in FIG. Along with being retained.

As shown in (1-) in FIG. 3, a voltage (-K) divided by l/k of the peak value is formed. This voltage (-K
) can easily be changed in proportion to the magnitude of the peak value of the input photoelectric conversion signal level. This divided voltage (-K) is applied as a reference voltage to the comparator 37 as shown by the dotted line in (d).
Since a detection signal as shown by the solid line in the same figure is also applied from , a pulse-like signal voltage of (-) polarity, for example, as shown in (h) appears on the output side.

In circuits 1 to 40, as shown in (S), the pulsed signal voltage of (-) polarity is changed to the signal voltage of (+) polarity via the inverting circuit 41. In the NAND circuit 42, (N) is generated by the input signal from the comparator 17 shown in (F) and the signal voltage shown in (S) above.
As shown in , the noise signal voltage is removed and an L level signal voltage corresponding to the bar code pattern is formed. This signal voltage is sent to a display circuit or the like from the output terminal IO via the amplification W9 at a temperature of 71°C.

Although this embodiment describes a case where a logic element is used in the gate circuit 40, it may be replaced with a switching transistor or the like.

[Effects of the Invention] As explained above, the bar signal noise removal circuit 1 according to the present invention detects the photoelectrically converted signal through the sensor 2 and generates detected signals of (+) polarity and ( -)I
It has two detection circuits that output f-characteristic detection signals, and a first comparator that compares a composite signal of both signals with a reference voltage to form a pulse-like bar signal. Furthermore, in order to remove the noise signal 0 superimposed on this bar signal,
A peak hold circuit that detects a photoelectric conversion signal and outputs the DC peak value as a divided voltage at a predetermined voltage division ratio, and a control pulse that uses this divided voltage output as a reference voltage to remove noise signals from the (-) polarity detection signal. The bar signal includes a second comparator that forms a gate circuit.
Its passage is prevented by a control pulse inputted from the second comparator in the path.

As a result, even if a noise signal is superimposed on the photoelectric conversion signal due to dust attached to the barcode label, the noise signal is reliably removed, and the subsequent display circuit receives a regular bar signal corresponding to the barcode pattern. is sent, so
Misreading of barcodes can be prevented. In addition,
The DC divided voltage formed in the peak hold circuit is proportional to the level of the photoelectric conversion signal, so it is effective for signal processing even when the level of the photoelectric conversion signal is small. It can be used for.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1 to 3 all relate to a sound removal circuit for the bar signal 111 according to the present invention, FIG. 1 is a block diagram thereof, and FIG. 2 is a bar signal in FIG. FIG. 3 is an explanatory diagram of the signal waveforms of the signal forming circuit. FIG. 3 is an explanatory diagram of the signal waveforms of the control pulse generation circuit and gate circuit in FIG. 1. FIG. 1 is a plan view showing an example of a barcode label. FIG. 6 is a block diagram of a conventional bar signal forming circuit, and is an explanatory diagram of input signal waveforms in the conventional bar signal forming circuit. In the figure, 1 is a barcode label, 2 is a photo sensor, I3 is a bar signal forming circuit, 15 is a first detection circuit, 16 is a second detection circuit, and 17 is a first comparator. 35 is a control pulse generation circuit, 36 is a peak hold circuit, 37 is a second comparator, 40 is a gate circuit, and 41 is an inverter circuit.

Claims (1)

[Claims] first and second detection circuits that detect a photoelectric conversion signal of a barcode pattern obtained through a photo sensor and output a positive detection signal and a negative detection signal, respectively; and the first and second detection circuits. A first comparator that compares a composite signal of the two detection signals of positive polarity and negative polarity output from the circuit with a reference voltage and outputs a pulsed bar signal, and detects the DC peak value of the photoelectric conversion signal. At the same time, a peak hold circuit divides the DC peak value at a predetermined voltage division ratio to form a negative polarity DC voltage, and the DC voltage outputted from the peak hold circuit is used as a reference voltage, and the reference voltage and the second detection are a second comparator that generates a pulse-like signal by comparing the detection signal from the circuit; the pulse-like signal sent from the second comparator is used as a control signal; 1. A bar signal noise removal circuit in a bar code reader, comprising a gate circuit that allows a signal to pass through and blocks a noise signal included in the bar signal from passing through.