JP2738108B2 - Barcode reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention reads a bar code by scanning a symbol surface on which a bar code is formed with a laser beam and detects light reflected from the symbol surface. The present invention relates to a bar code reading device that performs the following.

<Prior Art> Conventionally, a bar code reader has been widely used as an information input device for a computer, for example, by reading a bar code attached to a card, a packaging package, or the like with a bar code reader, for example, to input and output goods. Efficiency of data entry work for warehouse management and lending management of books and the like has been improved. In recent years, in order to meet various demands for barcode input, a function for reading a symbol in a non-contact state at least a predetermined distance from a symbol surface on which a barcode is formed has been required. I have. That is, for example, a bar code formed on various objects conveyed on a belt conveyor is read by a bar code reader arranged at a fixed position above the conveyor, or a bar code formed on a printed wiring board on which electronic components are mounted. For example, when reading a bar code with a so-called hand-held type bar code reader, it is necessary to read the bar code in a non-contact state with respect to a symbol surface located at various distances from the bar code reader.

A bar code reader that can read a symbol surface in a non-contact manner is, for example, a laser beam from a semiconductor laser light source via a condenser lens is reflected by a polygon mirror or a galvanometer mirror, and is guided to the symbol surface. The symbol surface is scanned by laser light by driving a galvanomirror. Then, the reflected light from the symbol surface is detected by light receiving means in a bar code reader constituted by a photoelectric conversion element. That is, if the laser beam scans the bar code in a direction intersecting the bar constituting the bar code, the light receiving means detects light of a large intensity for the white bar and the black bar. , Light of small intensity is detected. Therefore, the electric signal output from the light receiving means is subjected to waveform shaping and the like, and is binarized by level discrimination at an appropriate slice level.
The bar code is read.

However, for example, in a bar code reader used at a supermarket cash register or the like, the sign surface on which the bar code is formed is irradiated with disturbance light from a fluorescent lamp or the like.
The S / N ratio is degraded, and a bar code cannot be correctly read.

To solve this problem, the semiconductor laser light source is pulse-driven at a high frequency to extract the high-frequency component from the output of the light receiving means to remove the low-frequency component of disturbance light such as a fluorescent lamp, and then to perform the binarization. Techniques for performing processing have been proposed. A typical prior art is disclosed in
No. 37486, the basic configuration of which is shown in FIG. 5 of the present application. Upon receiving a reference frequency signal from the oscillator 1 which oscillates at an oscillation frequency sufficiently higher than the fluctuation frequency of disturbance light (for example, 120 Hz in the case of a fluorescent lamp),
The laser drive circuit 2 drives the semiconductor laser light source 3 in a pulsed manner. As a result, the laser light from the semiconductor laser light source 3 is intermittently emitted, and this laser light L1 is condensed into almost parallel light by the condenser lens 4, reflected by the galvanometer mirror 5, and formed into a bar code 6 The surface 7 is scanned.

The reflected light L2 from the symbol surface 7 is received by a light receiving element 8 constituted by a photodiode or the like, converted into an electric signal, and further amplified by an amplifier 9. The signal is supplied to a filter circuit 10 that selectively passes a signal in a frequency band. The output of the filter circuit 10 is applied to a waveform shaping circuit 11 and shaped into a signal corresponding to a white bar or a black bar of the barcode 6 by envelope detection or the like, and then the barcode 6 is represented by the decoder 11. Decoded into information.

Disturbance light from a fluorescent lamp (not shown) or the like is provided on the symbol surface 7.
LR is irradiated. The light receiving element 8 corresponding to the disturbance light LR
Since the low-frequency component in the electric signal is removed by the filter circuit 10, as a result, the bar code 6 is accurately read without the influence of disturbance light.

However, the oscillation frequency of the oscillator 1, that is, the laser light L1
Is required to be sufficiently higher than the fluctuation frequency of the disturbance light LR (usually, preferably higher by about two digits), and sufficiently higher than the spatial frequency of the bar code (at least about 10 times). . The former is for effectively removing disturbance light components, and the latter is for accurately reproducing signals corresponding to white bars and black bars to secure reading accuracy.
For such a reason, the modulation frequency of the laser light L1 is generally set to several hundred kHz to several tens MHz.

<Problem to be Solved by the Invention> FIG. 6 is a diagram showing a change in the diameter of the laser beam L1 from the semiconductor laser light source 3. Since the laser light generated from the semiconductor laser light source 3 spreads, it is narrowed down to almost parallel light by the condenser lens 4, but it cannot be made completely parallel light.
Normally, a focus is set at a focus position F1 at a certain distance from a housing (not shown) of the barcode reader, and the light is focused, so that a beam waist BW is formed near the focus position F1. ing.

In order to accurately read a barcode, it is necessary that the beam diameter of the laser beam L1 is generally smaller than the width of the bar constituting the barcode, but the laser beam having the beam waist BW as described above is required. In L1, this beam waist
When the barcode is arranged near the focal position F1 where the BW is formed, the barcode with the highest resolution and the minimum width can be read.

However, at a position apart from the focal position F1, for example, at a position where the distance from the barcode reader 15 is large, the beam diameter becomes large, so that the width of each bar constituting the barcode needs to be somewhat large. Normally, as the distance from the barcode reader 15 to the barcode (hereinafter, referred to as “reading distance”) increases, the laser beam becomes more proportional to the reading distance.
Since the beam diameter of L1 increases, after all, when the reading distance is increased, only a bar code having a wider bar than the increased reading distance can be read.

On the other hand, when the maximum reading distance expected in the apparatus is set, in order to obtain sufficient sensitivity in the light receiving element 8, the light receiving area of the light receiving element 8 is set so that a sufficient amount of received light is obtained. It must be determined corresponding to the maximum reading distance. If a condenser lens is interposed between the light receiving element 8 and the symbol surface 7, a decrease in the amount of received light can be prevented. However, in order to completely prevent a decrease in the amount of received light, a condenser lens having a large diameter is required. If a large condenser lens is used, the size of the entire apparatus will be increased. Such an increase in the size of the device is not allowed in a hand-held type bar code reader, and therefore the light receiving area of the light receiving element 8 must be increased to some extent.

However, for a light receiving element such as a photodiode, for example, if the light receiving area is increased, the junction capacitance increases,
As a result, the response characteristic is deteriorated, and the reflected light L2 having a high modulation frequency is not properly detected, so that the barcode identification accuracy is deteriorated. That is, for example, when reading a bar code at the maximum reading distance, the response of the light receiving element 8 is poor even if the diameter of the laser beam L1 is smaller than the bar width. Since the detection of L2 cannot be performed satisfactorily, the barcode cannot be read satisfactorily when the reading distance is long.

Therefore, the present invention provides a bar code reading device that solves the above-described technical problem, can eliminate the influence of disturbance light, and can read a bar code satisfactorily even when the reading distance is long. The purpose is to:

<Means for Solving the Problems> In order to achieve the above object, a bar code reader according to the present invention scans a symbol surface on which a bar code is formed with modulated light from a pulsed laser light source. The reflected light from the surface is received by the light receiving means and converted into an electric signal, and the modulated light component is extracted from the electric signal to remove the influence of disturbance light on the symbol surface to read the bar code. In a bar code reading device, a laser driving unit that performs pulse driving of the laser light source at one driving frequency selected from a plurality of types of driving frequencies, and the driving frequency of the laser driving unit is changed every predetermined scanning. Switching means for switching.

<Operation> According to the above configuration, the laser driving unit pulse-drives the laser light source at one driving frequency selected from a plurality of driving frequencies, and the driving frequency is switched by the switching unit every predetermined number of scans. Thus, the modulation frequency of the modulated light from the laser light source is automatically set to a plurality of types.

When the reading distance is long, the decrease in the amount of light received by the light receiving means becomes a problem. However, if the light receiving area of the light receiving means is set in accordance with the maximum reading distance, the response characteristics are poor. Even if this happens, the detection of the changed light with a low modulation frequency can be performed well. Therefore, even if the reading distance is long, if the reading is performed based on the output of the light receiving means corresponding to the reflected light when the modulation frequency of the laser beam is low, this modulation frequency becomes equal to the spatial frequency of the bar code. When the barcode is sufficiently high (that is, when a sufficient margin is provided), the barcode can be read accurately.

Note that, in order to be able to read a barcode, it is necessary that the diameter of the laser beam is generally smaller than the width of the bar constituting the barcode. On the other hand, the laser light from the laser light source is generally condensed so as to have a focal position near the main body of the bar code reader, and the diameter of the laser light is proportional to the reading distance as the reading distance increases. growing. Therefore, at a long reading distance, reading is possible only when the width of the bar of the barcode is wider than the reading distance. However, in this case, since the spatial frequency of the bar code is lower than that in the case where the reading distance is short, the bar code can be accurately recognized even if the modulation frequency of the laser beam is lowered.

When the reading distance is short, the laser beam is sufficiently narrowed, so that it is necessary to be able to read a bar code with a narrow bar width. However, when the reading distance is short, even if the spatial frequency of the bar code is high and the modulation frequency of the laser beam needs to be high, the light receiving amount of the light receiving unit is large, so that the responsiveness of the light receiving unit is a problem. Therefore, the reflected light from the symbol surface can be detected satisfactorily. In other words, in this case, since the signal strength is large, even when the detection signal becomes dull, the noise component in the detection signal is surely distinguished from the signal corresponding to the barcode having a large amplitude to accurately read the barcode. Can be done.

<Example> Hereinafter, an example will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a basic configuration of a bar code reader according to one embodiment of the present invention. Laser drive circuit 21
The modulated laser light l1 from the semiconductor laser light source 22 that is pulse-driven by the laser beam is condensed by a condenser lens 40 into substantially parallel light.
The light is reflected by the polygon mirror 23 set as a. The reflected laser beam 11 enters the symbol surface 24 on which the bar code 24a is formed. The polygon mirror 23 is driven to rotate at a constant angular velocity around its axis by a motor 25, so that the traveling direction of the laser beam l1 from the deflecting / reflecting surface 23a changes with time. Scanning is performed at almost the same speed in 26 directions. Polycon mirror 23
Along with the rotation of the laser light l1 from the semiconductor laser light source 22
Are successively incident on different deflecting / reflecting surfaces 23a, so that the bar code 24a is repeatedly scanned in the direction of the arrow 26.

The laser drive circuit 21 drives the laser light source 22 in a pulse at one drive frequency selected from a plurality of different drive frequencies. If the drive frequency changes, the modulation frequency of the laser light 11 changes. The driving frequency is switched in response to a control signal from the switching circuit 20. For example, the switching circuit 20 has a laser beam
A control signal for changing the drive frequency is generated each time the scanning of the symbol surface 24 is started.

The reflected light l2 from the symbol surface 24 is received by the light receiving element 27 formed of, for example, a photodiode and converted into an electric signal. The light receiving area of the light receiving element 27 is determined so that a sufficient amount of received light can be obtained when a maximum reading distance within a reading range expected in the apparatus is set. The electric signal from the light receiving element 27 is supplied to a filter circuit 29 after being amplified by an amplifier 28. Filter circuit
29 selectively passes an electric signal in a frequency band near the modulation frequency of the modulated laser light l1, and the passing frequency band is changed to the modulation frequency of the laser light l1 by the control signal from the switching circuit 20 via the line 30. Changed accordingly.

The output signal of the filter circuit 29 is provided to the waveform shaping circuit 31, where the waveform is shaped into signals corresponding to the white and black bars of the barcode 24a. The output signal of the waveform shaping circuit 31 is discriminated at an appropriate slice level in the decoder circuit 32, thereby generating a binary signal of "0" or "1" corresponding to a white bar and a black bar. The information is decoded into information represented by the barcode 24a.

As the waveform shaping circuit 31, for example, as shown in FIG. 2, an envelope circuit configured by using a diode D1, a resistor R1, a capacitor C1, and the like is applied. The resistance or the capacitance of at least one of the resistor R1 and the capacitor C1 is variable. In this envelope circuit, a time constant determined by the resistance value of the resistor R1 and the capacitance of the capacitor C1 is a line 30 and a line 30a (see FIG. 1). The signal corresponding to the bar code 24a is accurately reproduced by changing the time constant according to the modulation frequency of the laser light 11 by changing the control signal through the control signal.

In the vicinity of the polygon mirror 23, this polygon mirror 23
There is provided a reflection type photo sensor 33 for detecting the start of scanning of the symbol surface 24 due to the rotation of. The reflection-type photo sensor 33 includes a polygon mirror 23 facing the sensor 33.
When the deflecting / reflecting surface 23b faces a predetermined direction,
The light la from 3a is received by the light receiving element 33b, and the predetermined direction is, for example, a polygon mirror 23.
The laser beam l1 reflected at the position of one end of the scanning range
When irradiating 35, the deflecting / reflecting surface 23b faces in the direction.

The output of the reflection type photosensor 33 is supplied to a scanning start detection circuit 36, and the detection output of the scanning start detection circuit 36 is supplied to the switching circuit 20. The switching circuit 20 changes the drive frequency of the laser drive circuit 21 in response to the detection output from the scan start detection circuit 36.

That is, the scanning start detection circuit 36 receives a signal from the photo sensor 33 and generates a detection pulse indicated by reference numeral P1 in FIG. 3A every time scanning starts. With the detection pulse as a trigger, the switching circuit 20 changes its control signal. As a result, as shown in FIG. 3 (b), the driving frequency of the laser driving circuit 21 becomes, for example, 3 every time the scanning starts.
The frequency is cyclically switched between different types of frequencies f1, f2, f3 (where f1 <f2 <f3).

As a result, the modulated laser light 11 from the laser light source 22 becomes light modulated at a different frequency every time the symbol surface 8 is scanned. When the drive frequency of the laser drive circuit 21 changes, the pass frequency band in the filter circuit 29 is changed to a band near the drive frequency in response to the control signals from the lines 30 and 30a, and The constant is changed to a value corresponding to the drive frequency.

FIG. 4 is a waveform diagram for explaining the bar code reading operation. A curve S1 shows a modulated wave signal output from the amplifier 28, and curves S2a and S2b show carrier components corresponding to the black and white of the bar code 35. The curve S3 indicates the disturbance light IR (first
See figure. 4) shows the disturbance light component corresponding to ()). The signal detected by the light receiving element 27 and amplified by the amplifier 28 is a signal obtained by subjecting the modulated laser light l1 to amplitude modulation corresponding to the black and white of a bar code, and further superimposing a disturbance light component. In the filter circuit 29, the disturbance light component (curve S3) is removed.
In the waveform shaping circuit, the carrier component (curve S2a or S2a
2b, that is, the upper envelope or the lower envelope of the modulated wave signal) is detected. Further, if the carrier component is discriminated at an appropriate threshold level, a binary signal corresponding to the bar code 24a can be obtained.

In this way, in the filter circuit 29, only the component corresponding to the modulated laser light 11 out of the reflected light l2 from the symbol surface 24 is extracted, whereby the disturbance light from a fluorescent lamp or the like is obtained.
The barcode 24a can be accurately recognized by removing the component corresponding to lR.

As described above, the light receiving area of the light receiving element 27 is relatively large corresponding to the maximum reading distance expected in the apparatus, so that even when the reading distance is long, a sufficient amount of light is received. Can be incident. When the reading distance is long, the diameter of the laser beam l1 becomes large in the same manner as in the conventional case, and therefore, when the reading distance is long, the barcode can be read only when the barcode is read. Is the case where the width of the bar constituting is larger than proportional to the reading distance. In this case, after all, it can be said that the spatial frequency of the barcode is low.

Therefore, in this case, the bar code can be read accurately even if the modulation frequency of the laser beam 11 is lowered. That is, the barcode 24a can be identified based on the output signal of the light receiving element 27 corresponding to the laser beam 11 when the modulation frequency is relatively low. Since the light receiving area of the light receiving element 27 is large, its response characteristics are not very good, but if the modulation frequency of the laser beam l1 is lowered as described above,
Barcodes can be read accurately without considering the response characteristics. As described above, since the modulation frequency of the laser beam l1 is changed every time the symbol surface 24 is scanned by the laser beam l1, even if the modulation frequency is high, the response of the light receiving element 27 is limited due to the limitation. Even if a reading error occurs, the bar code 24a can be read well by scanning when the modulation frequency is lowered.

Further, when the intended maximum resolution is required in the apparatus, that is, when the bar width is small and the reading distance is relatively long (that is, the scanning speed is high), the spatial frequency of the bar code becomes large. The bar code 24a can be read based on the output signal of the light receiving element 27 corresponding to the laser light 11 with the increased frequency. That is, since the modulation frequency of the laser beam l1 changes every scanning, even if the modulation frequency is low, a reading error occurs because the modulation frequency is not sufficiently high with respect to the spatial frequency of the bar code. Even if this is done, if the barcode is read based on the output signal of the light receiving element 27 corresponding to the laser beam l1 with the increased modulation frequency, the barcode can be read accurately.

Since the light receiving area of the light receiving element 27 is relatively large as described above, the response characteristics of the light receiving element 27 are not so good. However, when the reading distance is short, the amount of received light is large, A good signal corresponding to the change in the intensity can be output from the light receiving element 27, so that the bar code 24a can be read accurately. That is, even if the detection signal is dull due to the large amount of received light, the amplitude of the signal corresponding to the bar code 24a is large, so that it can be distinguished from the noise component in the output signal of the light receiving element 27 well. By doing so, a signal corresponding to the barcode 24a can be reliably extracted, thereby enabling accurate reading of the barcode.

In this way, according to the present embodiment, the influence of the disturbance light lR is prevented, and the barcode is accurately read in a wide reading range. As a result, the barcode can be read easily and reliably, and for example, data can be more efficiently input to a computer. Particularly, in the case of a hand-held type, it is important to secure a wide reading range in order to ensure complete reading. According to the present embodiment, such a demand can be sufficiently satisfied.

Note that the present invention is not limited to the above-described embodiment. That is, for example, instead of the film circuit 29 and the waveform shaping circuit 31, the disturbance light component (curve S3) is obtained by taking the difference between the upper envelope (curve S2a) and the lower envelope (curve S2b) in FIG. A demodulation circuit which removes the difference signal and performs level discrimination of the difference signal to obtain a binary signal corresponding to the bar code may be applied.

Further, in the above-described embodiment, the time constant of the waveform shaping circuit 31 constituted by the envelope circuit is changed based on the control signal from the switching circuit 20. However, even when a constant time constant is set, the laser driving is performed. If it is possible to detect the envelope in a manner that corresponds to the modulation frequency in the range set by the circuit 21, it is not necessary to change the time constant as described above.

Further, in the above-described embodiment, the laser light
Although the modulation frequency is changed, the modulation frequency may be changed every two scans, for example. To the extent that the gist of the present invention is not changed,
Various design changes can be made.

<Effect of the Invention> As described above, according to the barcode reader of the present invention,
Since the influence of disturbance light is eliminated and the bar code can be read well when the reading distance is long, the bar code can be read accurately over a wide reading range. As a result, the barcode can be read easily and reliably, so that the efficiency of the data input operation can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a bar code reader according to an embodiment of the present invention. FIG. 2 is an electric circuit diagram showing a configuration example of a waveform shaping circuit. FIG. 3 is a switching operation of a modulation frequency. FIG. 4 is a waveform diagram for explaining an operation for extracting a signal corresponding to a bar code, FIG. 5 is a block diagram showing a basic configuration of the prior art, FIG. The figure shows a change in the diameter of the laser beam with respect to the reading distance. 20 switching circuit, 21 laser driving circuit, 22 laser light source, 24 symbol surface, 24a barcode, 27 light receiving element, 29 filter circuit, 31 waveform shaping circuit

Claims (1)

(57) [Claims] 1. A symbol surface on which a barcode is formed is scanned with modulated light from a pulsed laser light source, and reflected light from the symbol surface is received by a light receiving means and converted into an electric signal. A bar code reading device configured to extract the modulated light component from the data to remove the influence of disturbance light on the symbol surface and to read a bar code, wherein the laser light source is selected from a plurality of types of driving frequencies. A bar code reader comprising: a laser driving unit that performs pulse driving at one driving frequency; and a switching unit that switches the driving frequency of the laser driving unit every predetermined number of scans.