JP2000163504A - Symbol information reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize both of a function to correct the irregularity of a detected signal and a high-speed read function without making a device complicated and large-sized as the whole. SOLUTION: An amplification means is included which amplifies the electric signal which is detected by scanning a symbol expressed with codes different in reflection factor while irradiating it with beam light. This amplification means includes a fixed gain amplification circuit (amplification circuit 13) which amplifies the detected electric signal with a fixed gain, an automatic gain control circuit (a gain control amplification circuit 11 and an amplification circuit 13) which amplifies the detected electric signal with a gain varied in accordance with its magnitude, and an operation switching means 32 which switches the operation so that the signal may be amplified by the fixed gain amplification circuit when reading the symbol at high speed and may be amplified by the automatic gain control circuit when the symbol is usually read.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a symbol information reading device.

[0002]

2. Description of the Related Art A bar code information reading device has been conventionally known as one of symbol information reading devices.
Various proposals have been made for such a barcode information reading device in order to improve barcode reading accuracy. For example, US Pat. No. 5,557,093 discloses that a light beam from a light source is sequentially emitted as a plurality of scanning beams having different scanning directions by an optical scanning means, so that an operator does not need to be aware of the sticking direction of the bar code. Discloses a bar code information reading device that can be read in any direction.

[0003] As this type of bar code information reading device, a relatively large stationary bar code information reading device and a relatively small hand-held bar code information reading device that can be held and moved by an operator are included. is there. The stationary barcode information reader can read a barcode by transferring articles manually or automatically. For example,
Barcodes cannot be read for relatively large or heavy articles that cannot be held by the operator or that can be installed for automatic conveyance of articles, so they may be used in combination with a handheld barcode information reader. is there.

As a mode of use using only a hand-held bar code information reading apparatus, for example, with a scanner main body held in a predetermined holder, an operator holds an article in his / her hand and applies the bar code to the surface. The bar code is read by allowing the scanner to face the reading window of the scanner body.For relatively large items that cannot be held by the operator, the operator removes the scanner body from the holder and puts it in the hand. The bar code can be read by moving it and making the reading window face the bar-coded surface of the article.

[0005] At a site where a barcode is read, a barcode list is created separately from the articles in order to recognize the item codes of the articles to which the barcodes cannot be pasted, and the barcodes are read from the barcode list according to the articles. Often, the code is selected and read by the operator.

In this case, when a desired bar code in the bar code list is read by the above-described hand-held bar code information reading device, a plurality of scanning beams having different operation directions are sequentially emitted from the scanner. In this case, another bar code is read.

As a method for solving such a problem, for example, as described in Japanese Patent Application Laid-Open No. 9-91368, a stationary reading device and a hand-held reading device are used in common, a scanning range is widened and a plurality of scanning operations are performed. A reading device has been proposed which has a first scanning pattern from which lines are emitted and a second scanning pattern from which a single scanning line is emitted only for a very narrow range.

Japanese Patent Application No. 9-181122 discloses a bar having scanning beam switching means for selectively switching to a smaller number of scanning beams than a plurality of scanning beams that can be emitted without using a plurality of optical systems. A code information reading device has been proposed.

FIGS. 4A to 4D are diagrams showing signal flows in a conventional bar code information reading apparatus.
FIG. 5 is a diagram showing a configuration of the barcode information reading device 1 for reading barcode information. A bar code information reading device 1 shown in FIG. 5 includes a photo sensor 2 for receiving reflected light of light obtained by scanning a bar code symbol 10, a current-to-voltage converter 3 for converting an output current of the photo sensor 2 into a voltage, It comprises an amplifying means 4, a binarizing means 5, a decoding means 6, a mirror 7 driven by a mirror scanning drive circuit 8, and a light source 9, and reads a bar code symbol 10 which is present at a distance from the apparatus. .

Hereinafter, reading of the bar code symbol 10 will be described with reference to FIGS. 4 (a) to 4 (d) and FIG.
The light generated by the light source 9, the mirror 7, and the mirror scanning drive circuit 8 of the bar code information reading device 1
As shown in (a), scanning is performed so as to be orthogonal to the bar code symbol 10. As shown in FIG. 4B, the reflected light obtained by scanning the bar code symbol 10 with light is small in the dark (black) portion of the print and large in the light (white) portion. When light is detected by the photo sensor 2, FIG.
The shading of the bar pattern shown in (c) is replaced by the magnitude of the electric signal. The obtained current signal is applied to the binarizing means 5 via the current-voltage converting means 3 and the amplifying means 4, converted into a digital signal, and read out as a code by the decoding means 6.

Here, when the bar code information reading device 1 reads a bar code symbol 10 arranged at a position distant from the device 1, the distance between the device and the bar code is incident on the bar code (scanning). The magnitude of the signal detected by the photosensor 2 and the noise component included in the signal greatly change due to the ratio of the light to the ambient light and the difference in the density of the bar code signal. As described above, when a signal greatly different depending on the condition is directly added to the binarizing unit 5 and the decoding unit 6 restores the code, a noise component included in the signal to be binarized and an error caused by distortion of the signal are restored. And the read accuracy is reduced.

As a technique for solving these problems, Japanese Patent Application Laid-Open No. 7-302299 discloses an automatic gain control (Automatic gain control).
A technique related to Gain Control (AGC) is disclosed. That is, in this Japanese Unexamined Patent Publication No. 7-302299, the amplifying means 4 inserted between the photosensor 2 and the binarizing means 5 is an AGC circuit, and if the detection signal from the photosensor 2 is small, the gain of the amplifying means 4 is increased. By controlling the gain of the amplifying means 4 to be small when the detection signal from the photosensor 2 is large, it is possible to suppress a decrease in the accuracy of the decoded code data.

FIG. 6 is a diagram showing an example of the configuration of the AGC circuit. The AGC circuit comprises a gain control amplifier circuit 11, an amplifier circuit 13 having a gain of A, and an amplitude detection circuit 14. The output is input to the input of the amplification circuit 13 and the amplification circuit 1
3 to the input of the amplitude detection circuit 14, and the output of the amplitude detection circuit 14 to the gain control terminal V of the gain control amplification circuit 11.
By connecting to cnt, a negative feedback circuit that controls so that the amplitude of the output of the amplifier circuit 13 becomes constant is configured. Here, reference numeral 30 is an input terminal, and 31 is an output terminal. The normal state of the AGC circuit is determined by the amplification factor, and its transient characteristics mainly depend on the amplitude detection circuit 1.
4 is determined by the frequency characteristics.

FIG. 7A is a diagram showing a gain characteristic of the gain control amplifier circuit 11, and FIG. 7B is a diagram showing a characteristic of the amplitude detection circuit 14.

Here, the gain Gv of the gain control amplification circuit 11
Gv = Gm-k * Vcnt is represented by the following equation 1, where Gm is the maximum gain of the gain control amplifier circuit 11, k is the gain control coefficient, and Vcnt is the gain control voltage.

The characteristic of the amplitude detection circuit 14 is expressed by DET (Vo) = Amplitude (Vo), where DET (Vo) is the output of the amplitude detection circuit 14, and Amplitude (x) is the amplitude of the signal x. , Vo:
Output of the AGC circuit.

FIG. 8 is a diagram showing characteristics of the AGC circuit in a steady state, in which the input Vi, the gain G of the gain control amplifier circuit 11 are shown.
v, output Vo, output DET (Vo) of the amplitude detection circuit 14
3 shows the waveforms of FIG.

Further, the output of the amplifier circuit 13 can be expressed by the above-described equations 1 and 2 and the following equations 3 and 4 to equation 5.

Det (Vo) = Vcnt Equation 3 Vo = (Gv + A) * Vi Equation 4 Vo = (Gm + A) / ((1 / Vi) + k) Equation 5 Equation 5 is a general equation showing the characteristics of the AGC circuit. Input Vi
And the gain control coefficient k (this boundary is shown in FIG. 8).

Vo = (Gm + A) / k Equation 6 k >> (1 / Vi) Vo = 0 Equation 7 k << (1 / Vi) In the range where the input Vi is small, the gain control terminal Vcnt of the gain control amplifier circuit 11 Is zero (DET)
(0)), and the gain becomes the maximum value Gm. However, when the output of the gain control amplifier circuit 11 is zero and Vi increases, the output of the gain control amplifier circuit 11 becomes the input Vi as shown in Expression 8. It is constant regardless of.

Vo2 / Vo1 ≒ 1 << Vi2 / Vi1 Equation 8 (k >> (1 / Vi1), (1 / Vi2)) Next, AGC determined by the frequency characteristic of the amplitude detection circuit 14
The transient characteristics of the circuit will be described.

FIG. 9 shows the characteristics of the AGC circuit when the input changes from small to large (across the boundary between Equations 6 and 7). The time indicated by dt in FIG. 9 is the time required for the output Vo to change from the value represented by Expression 7 to the value represented by Expression 6, and represents the delay time that occurs when the AGC circuit rises.

The relationship between dt and the frequency characteristics of the amplitude detection circuit 14 will be described below with reference to FIG. 10 using an example of amplitude detection.

The circuit shown in FIG. 10 is called a peak hold circuit. The non-inverting terminal is the input terminal of the input Vi, the inverting terminal is the output terminal of the output Vo, and the output terminal is the cathode terminal of the output Vo. It comprises a comparator 15 connected to the anode terminal of a diode 16 connected to the output terminal, a hold capacitor 17 and a discharge resistor 18 connected between the output terminal of the output Vo and GND, and a reference voltage (GND) ) And the peak difference D of the input signal
It has a function as an amplitude detection circuit for detecting ET (Vi).

If the input signal Vi of the present peak hold circuit is symmetric with respect to the reference (GND), the output will be １ ／ of the amplitude of the input signal. Assuming that the output impedance when the comparator constituting the peak hold circuit charges the hold capacitor 17 is Ro, the band fc of the amplitude detection circuit (peak hold circuit) is expressed by Expression 9. The magnitude of this value is a negative feedback circuit.
Determine the stability of the AGC circuit, and if the value is small, AGC
The circuit works more stably. On the other hand, this value has the relationship of the equation 10 with the delay time dt described above (the time dt is inversely proportional to the band of the amplitude detection circuit 14).

Fc = k * Ro * Cp Equation 9 (k1: proportional constant) dt = k2 * (1 / fc) Equation 10 (k2: proportional constant) FIG. 11 shows the amplification means of the bar code information reading apparatus according to the prior art. It shows the signals actually obtained.

[0027]

As described above, according to the omnidirectional reading of a barcode by using a plurality of scanning beams, a scanner can be used without being aware of the sticking direction of the barcode.
It can be read easily and instantly. When a plurality of barcodes are present in the same direction as the scanning beam direction and an arbitrary barcode is read from the barcodes, it is very effective to selectively switch to a smaller number than the plurality of scanning beams for reading. It is a selection method.

A more preferable use of the hand-held bar code reader is that the bar code reading distance is wide from a short distance side to a long distance side. However, in a bar code information reading apparatus having a function of switching a scanning pattern, for example, a mode of switching between omnidirectional reading (omni scanning) and bidirectional reading (single scanning), optimal setting of a reading circuit in accordance with the form of the scanning mode. Is required.

In the omnidirectional reading, since the scanning area is read by enlarging the scanning area by a plurality of scanning patterns, the gain of the fixed gain section is set large in consideration of the responsiveness of the circuit. Therefore, the AGC control is normally used as a non-operation.

On the other hand, in the bidirectional reading, contrary to the omnidirectional reading, the setting gain of the fixed gain section of the circuit is reduced to meet the demand for increasing the reading distance (depth), and the AGC circuit is mainly used. By making the operation work effectively, the dynamic range of the circuit is obtained. Therefore, the characteristics of the circuit are different depending on each application.

In the bar code symbol reading device, data reading is started by operating the light beam on the bar code symbol. However, when an AGC circuit is used for amplifying the signal detected by the photo sensor, the reading starts. During the delay time dt described above, since the input of the binarizing means includes noise and distortion and the data restored by the decoding means includes an error, in order to perform accurate reading, the time dt from the start of reading is required. You have to start reading the data later.

One of the methods for shortening the delay time dt is to increase the band of the amplitude detection circuit 14 based on Equation 10, but if the band is increased, the operation of the AGC circuit becomes unstable. There is an upper limit. As described above, the AGC circuit used in the amplifying means of the bar code information reading apparatus is capable of both correcting the variation of the signal detected by the photo sensor caused by the distance between the apparatus and the bar code, the difference between the bar code symbol and the shading, and performing high-speed reading. It does not fulfill the function.

The present invention has been made in view of such a problem, and an object thereof is to function as a fixed gain amplifying circuit which does not cause a reading delay at the time of high-speed reading and to improve the stability at the time of normal reading. A symbol information reading device that realizes both the function of correcting variations in detected signals and the function of high-speed reading without complicating and enlarging the entire device by providing an amplifying unit that functions as an AGC circuit with a reduced delay without any loss. Is to provide.

[0034]

In order to achieve the above object, a symbol information reading apparatus according to a first aspect of the present invention comprises:
A symbol information reading device for reading information contained in a symbol represented by a code having a different reflectance, wherein the symbol is scanned while irradiating the symbol with a light beam, and the intensity of the reflected light is detected as an electric signal. Means, amplification means for amplifying the electric signal detected by the detection means, and restoration means for restoring the code based on the electric signal amplified by the amplification means, wherein the amplification means A fixed gain amplifier circuit that amplifies the detected electric signal with a fixed gain, an automatic gain control circuit that amplifies the detected electric signal with a gain that can be varied according to the magnitude thereof, and a high-speed reading of symbols. Amplification is performed by the fixed gain amplifying circuit, and during normal reading of a symbol, the operation is stopped so that amplification is performed by the automatic gain control circuit. And an operation switching means to change.

The symbol information reading device according to a second aspect of the present invention is the symbol information reading device according to the first aspect, wherein the automatic gain control circuit includes the fixed gain amplifying circuit as a component thereof, The amplifying circuit has a first gain used when amplifying the detected electric signal with a fixed gain and a second gain used when amplifying the detected electric signal with a variable gain. The first gain is larger than the second gain.

The symbol information reading device according to a third invention is the symbol information reading device according to the first or second invention, wherein the fixed gain control circuit is constituted by an amplification circuit using an operational amplification circuit. I have.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the outline of an embodiment of the present invention will be described. A bar code information reading apparatus to which the present invention is applied scans a bar code expressing arbitrary information with a code having a different reflectance while irradiating the bar light with a light beam, and detects the intensity of the reflected light with a photo sensor. And read the information. Here, amplifying means for amplifying the electric signal detected by the photo sensor is constituted by a gain control amplifying circuit, a switch circuit, and a fixed gain amplifying circuit. And switch. That is, at the time of high-speed reading of a barcode, the switch circuit is controlled by a control signal from the operation switching means to operate only the fixed gain amplifier circuit having a gain of A1 to eliminate the reading delay, and at the time of normal reading, to switch the operation. The switch circuit is controlled by a control signal from the means to increase the gain to A2 (A2
By operating the fixed gain amplifier circuit set in <A1) and the gain control amplifier circuit, an amplification unit that functions as an AGC circuit with reduced delay without losing stability is provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First Embodiment) FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention. The amplifying means of the first embodiment includes a gain control amplifier circuit 11 and a switch (SW) circuit 1.
2, an amplification circuit 13, an amplitude detection circuit 14, and an operation switching means 32.

The gain control amplifier circuit 11 has two input terminals, a terminal connected to the input terminal 30 of the amplification means and a gain control terminal Vcnt. One input terminal of the switch circuit 12 is connected to the output terminal of the gain control amplifier circuit 11, and the other input terminal is connected to the input terminal 30.
The output terminal of the switch circuit 11 has two different gains A1,
It is connected to the input of the amplifier circuit 13 having A2. The operation of the switch circuit 12 is controlled by a control signal from the operation switching means 32. The gain of the amplifier circuit 13 is switched to A1 or A2 by a control signal from the operation switching unit 32.

Further, an amplification amplitude circuit 14 is connected to an output terminal of the amplification circuit 13, and the output is connected to the gain control amplification circuit 1.
1, the connection point between the output terminal of the amplifier circuit 13 and the input terminal of the amplitude detection circuit 14 is defined as the output terminal 31 of the amplification means.

The operation of the amplifying means having the above configuration will be described below.

(High-speed reading) In this case, the SW circuit 12 is switched and connected to the input terminal 30 of the amplifying means by the control signal from the operation switching means 32, and the gain is set to A1 by the control signal. 13. With such a configuration, the amplifying unit of the present embodiment operates as a fixed gain amplifying circuit having a gain of A1.

(Normal reading) In this case, the SW circuit 12 is switched by the control signal from the operation switching means 32 to be connected to the output of the gain control amplifier circuit 11, and the gain is set to A2 by the control signal. Circuit 1
Connect to 3. With such a configuration, the amplifying unit of the present embodiment operates as an AGC circuit whose characteristics are expressed by Expressions 6 and 7. Although the delay generated in the AGC circuit is determined by the amplitude detection circuit 14 in Expression 10, it can be expressed by Expression 12 derived from the characteristics shown in FIG.

Dt = k * DET (Vo) = k * DET ((Gm + A2) / k) Equation 13 Equation 13 sets the gain A2 of the amplifier circuit 13 small in order to reduce the output signal obtained by the AGC circuit. This indicates that the delay time dt is reduced, and an AGC circuit with a reduced delay time dt can be realized by setting the gain A2 of the amplifier circuit 13 as in Expression 14 during normal reading.

A1> A2 Equation 14 The method of switching the gain of the amplifier circuit 13 between high-speed reading and normal reading differs from the means for increasing the bandwidth of the amplitude detection circuit 14 shown in Equation 10 without deteriorating the stability of the AGC circuit. The delay time dt can be reduced.

FIG. 2 shows how the delay of the automatic gain control circuit changes by setting the gain of the amplifier circuit 13. The difference between the delay time dt when the gain of the amplifier circuit 13 is 25 and 8 is shown in FIG. Is shown.

(Second Embodiment) FIG. 3 is a diagram showing a configuration of a second embodiment of the present invention. This is one in which the amplifier circuit 13 of the first embodiment is configured by an inverting amplifier circuit using an operational amplifier circuit. In FIG. 3, the amplifier circuit 1
Reference numeral 3 denotes capacitors 20, 23, 30, resistors 19, 21, 24, and an operational amplifier 22. The amplitude detection circuit 14 includes a comparator 15, a diode 16, a holding capacitor 17, and a discharge resistor 18.

In the above configuration, the following settings can be made by the control signal from the operation switching means 32.

(High-speed reading) In this case, the circuit operates as the fixed amplifier circuit described in the first embodiment. The gain is R24 / R19.

(Normal Reading) In this case, the circuit operates as an automatic gain control circuit. At this time, the gain of the inverting amplifier circuit composed of the amplifier circuit 13 is R24 / R21 (R21> R1
9).

In the circuit of the second embodiment, the amplifier circuit whose gain can be switched is constituted by one operational amplifier circuit. However, this part can be realized by combining a plurality of operational amplifier circuits. is there. Also, as in the second embodiment, the resistance 2
If the capacitor 23 is connected in parallel with the capacitor 4, the amplifier circuit 13 will have both an amplification function and a filter function.

According to the above-described embodiment, by appropriately switching the switch circuit 12 according to the control signal from the operation switching unit 32, the amplifying unit of the present embodiment can be used as a fixed gain amplifying circuit that does not cause a reading delay during high-speed reading. An AGC which makes the amplifying means of this embodiment function at the time of normal reading and has a small delay without losing stability.
Since it is made to function as a circuit, both the function of correcting the variation of the detected signal and the function of high-speed reading can be realized without making the whole apparatus complicated and large.

[0054]

According to the present invention, it functions as a fixed gain amplifying circuit which does not cause a reading delay at the time of high-speed reading,
Equipped with an amplifying means that functions as an AGC circuit with a small delay without losing stability during normal reading, so that both the function of correcting variations in detected signals and the function of high-speed reading are not complicated and the whole apparatus is not enlarged. Can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of an amplification unit of a barcode information reading device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing that a delay of an automatic gain control circuit changes by setting a gain of an amplifier circuit 13;

FIG. 3 is a diagram illustrating a configuration example of an amplification unit of a barcode information reading device according to a second embodiment of the present invention.

FIG. 4 is a diagram for explaining a basic operation of a conventional barcode information reading apparatus.

FIG. 5 is a view showing the structure of a conventional bar code information reading apparatus.

FIG. 6 is a diagram illustrating a configuration example of an amplification unit of a barcode information reading device according to a conventional technique.

7A is a diagram illustrating a gain characteristic of the gain control amplifier circuit, and FIG. 7B is a diagram illustrating a characteristic of the amplitude detection circuit 14. FIG.

FIG. 8 is a diagram showing an ideal operation of an amplifying unit of a bar code information reading apparatus according to the related art.

FIG. 9 is a diagram showing an operation of an amplitude detection circuit constituting an amplifying means of a bar code information reading apparatus according to a conventional technique.

FIG. 10 is a diagram illustrating a configuration of a peak hold circuit.

FIG. 11 is a diagram showing a signal actually obtained by an amplifying unit of a bar code information reading apparatus according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Bar code information reading device, 2 ... Photosensor, 3 ... Current-voltage conversion means, 4 ... Amplification means, 5 ... Binarization means, 6 ... Decoding means, 7 ... Mirror, 8 ... Mirror scanning drive circuit, 9 ... Light source, 10 bar code symbol, 11 gain control amplifier circuit, 12 switch circuit, 13 amplifier circuit, 14 amplitude detector circuit, 15 comparator, 16 diode, 17 capacitance for holding, 18 discharge resistance, 19, 21, 24 ... resistance, 20, 23, 30 ... capacity, 22 ... operational amplifier circuit, 32 ... operation switching means.

Claims (3)

[Claims] 1. A symbol information reading device for reading information included in a symbol represented by a code having a different reflectance, wherein the symbol information is scanned while irradiating with light beam,
Detecting means for detecting the intensity of the reflected light as an electric signal; amplifying means for amplifying the electric signal detected by the detecting means; and restoring means for restoring a code based on the electric signal amplified by the amplifying means Wherein the amplifying means comprises: a fixed gain amplifying circuit for amplifying the detected electric signal with a fixed gain; and an automatic amplifying circuit for amplifying the detected electric signal with a gain variable according to the magnitude thereof. A gain control circuit, and operation switching means for performing amplification by the fixed gain amplifier circuit at the time of high-speed reading of a symbol and switching the operation so that amplification is performed by the automatic gain control circuit at the time of normal reading of a symbol. A symbol information reading device comprising: 2. The automatic gain control circuit includes the fixed gain amplifying circuit as a component thereof, wherein the fixed gain amplifying circuit is used for amplifying a detected electric signal with a fixed gain. 2. The method according to claim 1, further comprising a gain and a second gain used when amplifying the detected electric signal with a variable gain, wherein the first gain is larger than the second gain. Symbol information reading device according to the description. 3. The symbol information reading device according to claim 1, wherein the fixed gain control circuit is constituted by an amplifier circuit using an operational amplifier circuit.