JPH08153157A - Optical information reader - Google Patents

Abstract

PURPOSE: To provide an optical information reader which shortens the charging time of a coupling capacitor and improves the read speed. CONSTITUTION: An operational amplifier 46 is connected to a line sensor 30 at its inverted input terminal through a resistance 44 and the coupling capacitor 41. An analog switch 47 is connected to between the common terminal of the coupling capacitor 41 and the resistance 44 of the operational amplifier 46 and the output terminal of the operational amplifier 46. Consequently, the analog switch 47 is turned on to short-circuit the resistances 44 and 45 of the operational amplifier 46, thereby shortening the charging time of the coupling capacitor 41.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reading device for reading optical information from a reading object on which optical information such as a bar code is written.

[0002]

2. Description of the Related Art Conventionally, for example, in a bar code reader, an output of a line sensor composed of a CCD is amplified by an amplifier circuit, and then the amplified result is binarized by a binarizing circuit and decoded. In this case, the offset voltage of the line sensor output varies from sensor to sensor. For this reason, a coupling capacitor is connected between the line sensor and the amplifier circuit to perform AC coupling to balance the offset voltage of the line sensor output and the offset voltage of the amplifier circuit for direct amplification by the amplifier circuit. I try to make effective use of the dynamic range.

[0003]

By the way, in such a bar code reader, when the reading is stopped,
In order to reduce the power consumption, power supply to the line sensor, the amplification circuit and the binarization circuit is cut off. Therefore, the charging voltage of the coupling capacitor is zero immediately after the power is supplied to the line sensor and the amplifier circuit when the reading is started.

The output of the line sensor also needs some rise time in order to reset to the internal charge, during which the output of the line sensor cannot be defined. Therefore, the charging voltage of the coupling capacitor during that time also becomes unstable. Also, after the line sensor rise time has elapsed, the normal charging of the coupling capacitor starts only after the line sensor output is output normally. At this time, the line sensor output impedance is Ro,
If the series resistances constituting the gain of the amplifier circuit are R1 and R2, the impedance R to be charged is Ro, R1 and R2.
It is the sum of two.

Here, when the charging time Tq is obtained, Tq is approximately 4 where C is the capacitance of the coupling capacitor.
Equal to CR. Therefore, the charging time Tq increases in proportion to the impedance R. This means that the larger the difference between the offset voltage of the line sensor output and the offset voltage of the amplifier circuit, the longer the charging time of the coupling capacitor.

Therefore, the rising of the amplified waveform of the output of the amplifier circuit is delayed, and as a result, the output of the amplifier circuit is delayed and the reading speed is lowered. Note that R1 and R2 are
It is necessary to take a large value with respect to Ro, which is on the order of several KΩ to 10 KΩ. Also, when the difference between the offset voltage of the output of the line sensor and the offset voltage of the amplifier circuit is large,
When the light reflectance of the barcode is low, the amplitude portion corresponding to the barcode of the amplitude of the line sensor output becomes relatively small. Therefore, the waveform portion corresponding to the bar code in the waveform amplified by the amplifier circuit also becomes small.

On the other hand, if the gain of the amplifier circuit is increased or the exposure time of the line sensor is increased, the waveform portion corresponding to the bar code in the amplified waveform will be saturated. Therefore, an object of the present invention is to provide an optical information reading device that shortens the charging time of the coupling capacitor and improves the reading speed in order to deal with the above problems.

Further, the present invention provides an optical information reading device which improves the amplified waveform and improves the reading performance by adjusting the DC balance of the coupling capacitor to the amplitude portion corresponding to the optical information to be read. The purpose is to

[0009]

In order to achieve the above object, in the invention described in claim 1, an optical system for optically detecting a reading object (B) having optical information and generating a detection output. Sensor (30), amplification means (40) for amplifying the detection output, coupling capacitor (41) for AC coupling the optical sensor (30) and amplification means (40), and amplification means (40). Reading means (50, 70) for reading the optical information based on the amplified output of
In the optical information reading device including the above, the amplifying means (40) is an initial charging means (47) for initially charging the coupling capacitor (41) before the reading means (50, 70) starts reading. An optical information reading device is provided.

According to a second aspect of the invention, in the optical information reading apparatus according to the first aspect, the amplifying means (40) and the coupling capacitor (41) form an impedance circuit ( 44, 45)
And short-circuiting means (47) for short-circuiting the impedance circuits (44, 45) during the time required for charging the coupling capacitor (41) after the detection of the optical sensor (30) is started. After the short circuit is released by, the detection output is amplified by the gain determined by the impedance circuit (44, 45).

According to the invention described in claim 3, in the optical information reading device according to claim 2, the amplifying means (40) is an optical sensor (30) and an amplifying means (40).
And a setting means (48) which is connected between and and sets the DC balance of the coupling capacitor (41) to a level corresponding to the reading timing of the optical information of the optical sensor (30). .

The reference numerals in parentheses of the above means indicate the correspondence with the concrete means described in the embodiments described later.

[0013]

According to the invention described in claim 1, the initial charging means of the amplifying means initially charges the coupling capacitor before the reading by the reading means is started. Thus, even if there is a large difference in offset balance between the output of the optical sensor and the output of the amplifying means, the output waveform of the amplifying means can be quickly raised by the initial charging. As a result, the reading timing of the reading means for the stable amplified output of the amplifying means can be accelerated.

According to the second aspect of the invention, the short-circuiting means short-circuits the impedance circuit during the time required to charge the coupling capacitor after the optical sensor starts to detect. Therefore, while achieving the same effect as that of the first aspect of the invention, it is possible to perform rapid amplification and reading with a stable detection output after the short circuit is released by the short circuit means.

According to the third aspect of the invention, the setting means of the amplifying means sets the DC balance of the coupling capacitor to a level corresponding to the reading timing of the optical information from the optical sensor. As a result, the DC balance of the coupling capacitor can be adjusted to the level of the output portion corresponding to the optical information in the output of the optical sensor. As a result, an appropriate amplified waveform can be obtained even if the reading target is a low reflectance bar code and the amplitude during sensor output is small. As a result, it is possible to achieve the same effect as that of the second aspect of the invention.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 3 and FIG. 2 show the entire configuration of the bar code reader having the amplifier circuit configuration shown in FIG. This bar code reader has a casing 1 as shown in FIG.
0, the casing 10 includes a head portion 11
The grip portion 12 and the grip portion 12 are formed in a bent shape.
A rectangular reading port 11a is provided at the tip of the head unit 11.
Is formed, and a trigger switch SW (see FIG. 2) is attached to the outer peripheral wall of the head portion 11. In addition, the power supply to each circuit element of the bar code reader described later is supplied to the power source connector PC (see FIG. 2) of the bar code reader.
Is connected to a commercial power source.

The optical system 20 is disposed in the head portion 11, and the optical system 20 is composed of a light source 21, a mirror 22, a diaphragm 23 and a condenser lens 24. Light source 2
1 is a semi-cylindrical lens 21a and this semi-cylindrical lens 21a
A plurality of light emitting diodes (not shown) arranged along the longitudinal direction on the incident surface of. Then, in the light source 21, the light emitted from each of the light emitting diodes is condensed into a bar shape by the semi-cylindrical lens 21a and emitted toward the bar code B through the reading port 11a.

The mirror 22 receives the reflected light from the bar code B and reflects it toward the diaphragm 23. The diaphragm 23 narrows the amount of light reflected by the mirror 22 and condenses the lens 24.
Incident on. The condenser lens 24 causes the diffracted light from the diaphragm 23 to enter the line sensor 30. In this case, the diaphragm 23
Is within the object-side focal length of the condenser lens 24, so that the light from the condenser lens 24 enters the line sensor 30 while spreading in the length direction of the line sensor 30.

The line sensor 30 is disposed in the grip portion 12 of the casing 10 behind the condenser lens 24. As the line sensor 30, the optical information Ba of the bar code B is read. An image sensor is used in which a plurality of vertically long pixels (corresponding to photodiodes) are arranged in correspondence with the length direction of the barcode B.

As a result, the line sensor 30 is controlled by the microcomputer 70 which will be described later.
The light from the condenser lens 24 is received, and charges corresponding to the photoelectric effect of each pixel are generated and generated as a light reception signal. In this case, the charge generation amount is proportional to the incident time of light (corresponding to the exposure time) to the line sensor 30. Next, the electronic circuit configuration of the barcode reader will be described with reference to FIG.

Various electronic circuit elements (see FIG. 2) of the bar code reader are provided in the casing 1 behind the line sensor 30.
It is mounted on a printed circuit board P (see FIG. 3) arranged in the grip portion of No. 0. The amplifier circuit 40 constitutes an essential part of the present invention. As shown in FIG. 1, the amplifier circuit 40 includes a coupling capacitor 41 connected to the line sensor 30.
Serves to AC-couple the line sensor 30 and an operational amplifier 46 described later.

The operational amplifier 46 functions as a phase inverting amplifier, and the operational amplifier 46 receives a DC voltage of 5 (V) from the DC power supply through the resistor 42 at its non-inverting input terminal. Has become. The non-inverting input terminal of the operational amplifier 46 is grounded via the resistor 43. As a result, the offset voltage V _O (reference voltage V _O ) is generated at the non-inverting input terminal of the operational amplifier 46.

The operational amplifier 46 has its inverting input terminal connected via the resistor 44 to the coupling capacitor 41.
A resistor 45 is connected between the non-inverting input terminal and the output terminal of the operational amplifier 46. As a result, the gain G of the operational amplifier 46 is specified by the resistance value R ₁ of the resistor 45 / the resistance value R ₂ of the resistor 44. Then, the operational amplifier 46 is connected to the coupling capacitor 4
The light reception signal from the line sensor 30 via 1 is amplified by the gain G with the offset voltage V _O as a reference to generate an amplified signal. The offset voltage V _O is set to ½ of the amplified signal level of the operational amplifier 46.

Further, an analog switch 47 is connected between the common terminal of the coupling capacitor 41 and the resistor 44 and the output terminal of the operational amplifier 46. As a result, the analog switch 47 is turned on under the control of the microcomputer 70, which will be described later, to short-circuit both the resistors 44 and 45. The binarization circuit 50
The amplified signal from the amplifier circuit 40 is binarized to generate a binarized signal. The analog switch 60 is turned on under the control of the microcomputer 70, and the power connector PC
A commercial voltage from a commercial power source is applied to each electronic circuit element except the microcomputer 70.

The microcomputer 70 executes the computer program according to the flow chart shown in FIG. 4, and during the execution, the line sensor 30, the light source drive circuit 80, based on the outputs of the trigger switch SW and the binarization circuit 50, Calculation processing such as driving processing and reading processing of the analog switch 47 and the buzzer BZ is performed. The microcomputer 70 is put into operation by connecting the power supply connector PC to the power supply on the host computer side.

The operation of the first embodiment constructed as above will be described. When the power supply connector is connected to the power supply on the host computer side, the microcomputer 70 is put into operation, and according to the flowchart of FIG. 4, the computer program starts to be executed in step 100 and the initial setting is made in the next step 101. .

At this stage, the trigger switch SW
Is turned on, it is determined to be YES in step 110, and in the next step 111, the counter value S is S.
= 0 is cleared. At the same time, the analog switch 60 is turned on under the control of the microcomputer 70 to apply the voltage of the circuit power supply to other electronic circuit elements. Then, the light source drive circuit 80 drives each light emitting diode of the light source 21 to emit light. Therefore, the light source 21 causes the light from each light emitting diode to enter the barcode B through the reading port 11a. Further, the line sensor 30 is also activated.

After that, in step 112, the exposure time of the line sensor 30 is set and a shift pulse is generated and output to the line sensor 30. As a result, the line sensor 30 is driven. At this time, the starting point of the exposure time of the line sensor 30 is specified by the shift pulse. In this state, when the light incident on the barcode B is reflected as described above, the reflected light is incident on the line sensor 30 by the optical system 20. For this reason,
The line sensor 30 generates an electric charge and a light reception signal during the exposure time.

Next, at step 120, the counter value S is compared with the predetermined charging time value n of the coupling capacitor 41 and judged. Here, the predetermined charging time value n is the amplification circuit 4 when the analog switch 47 is turned on.
It corresponds to a value representing the time for which the coupling capacitor 41 is charged by the impedance of 0, that is, the sum of the internal impedance of the analog switch 47 and the impedance of the coupling capacitor 41.

At the present stage, since S = 0, the determination in step 120 is NO, and in the next step 121, the counter value S is added and updated to S = S + 1. Then, in step 122, the analog switch 47 is turned on, and thereafter, in step 123, an interruption waiting is made until the exposure time elapses. When the wait for interrupt in step 123 ends, the exposure time interrupt is permitted in step 140 and the computer program proceeds to step 112. Hereafter, steps 112, 120, 12
The processing from 0 to 123 and 140 is repeated,
The addition and update of the counter value S and the ON process of the analog switch 47 are repeated.

When the determination in step 120 is YES in such a state, the analog switch 47 is turned off in step 124. This means that the charging of the coupling capacitor 41 is performed by the analog switch 47.
It means completed under the off condition. As described above, after the driving of the line sensor 30 is started, the resistors 44 and 45 of the operational amplifier 46 are short-circuited by the analog switch 47 until the predetermined charging time value n elapses.
The impedance of the operational amplifier 46 from the output stage of the line sensor 30 to the output terminal of the operational amplifier 46 becomes small.

Therefore, the charging time of the coupling capacitor 41 due to the output of the line sensor 30 immediately after the start of activation of the line sensor 30 is shortened. Therefore, even if there is a large difference between the offset voltage of the line sensor 30 and the offset voltage of the operational amplifier 46, the waveform of the amplified signal of the operational amplifier 46 rises quickly, so that the amplifier circuit 40 output to the binarization circuit 50. The waveform stabilization period of the amplified signal from is faster. As a result, the microcomputer 70-2
Decoding for the output of the binarization circuit 50 can be done quickly and properly.

In the subsequent read processing routine 130, the information of the bar code B is decoded based on the binarized signal from the binarization circuit 50, and then the buzzer BZ is sounded. Regarding the effect of the presence or absence of the analog switch 47 when the difference between the offset voltage of the line sensor 30 and the offset voltage of the operational amplifier 46 is large,
When the result of the experiment was compared by comparing the case of the first embodiment and the case of the conventional amplifier circuit (see FIG. 6), the results shown in FIGS. 5 and 7 were obtained.

However, charging impedance Ro = 250
Ω, internal resistance Rsw of analog switch 47 is 100
Ω, R1 and R2 are 7.5 KΩ and 51 KΩ, respectively. According to this, in the conventional amplifier circuit of FIG. 6, since there is no analog switch 47, the output terminal of the amplifier circuit 46 (for the signal waveform generated at the common terminal T ₁ between the coupling capacitor 41 and the resistor 44) Code T ₂
The rising edge of the amplified signal waveform, which is shown in FIG. 7, is significantly delayed as shown in FIG.

On the other hand, in the amplifier circuit according to the first embodiment, since the analog switch 47 is provided, the amplifier circuit follows the signal waveform generated at the common terminal N ₁ between the coupling capacitor 41 and the resistor 44. The rising edge of the amplified signal waveform generated at the output terminal of 46 (represented by symbol N ₂ ) is remarkably fast, as shown in FIG. The value of (Ro + R1 + R2) / (Ro + Rsw) is 1
It becomes 67.8, which is about 1/170 of the conventional value.

Next, a second embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to 0. In the second embodiment, the analog switch 48 is connected between the line sensor 30 and the coupling capacitor 48 in the amplifier circuit 40 described in the first embodiment, and the read processing routine 130 is executed in the flowchart of FIG. Instead of the above, the reading processing routine 200 shown in FIGS. 9 and 10 is adopted, which is a characteristic of the configuration.

The analog switch 48 is controlled by the microcomputer 70 to turn on / off to disconnect the connection between the line sensor 30 and the coupling capacitor 41. The other structure is similar to that of the first embodiment. In the second embodiment thus configured, when the analog switch 47 is turned off in step 124 (see FIG. 4) with the completion of charging of the coupling capacitor 41, as described in the first embodiment, The computer program proceeds to the read processing routine 200 of FIGS.

If decoding is not in progress at the present stage, NO is determined in step 210, and step 211
Will reset the interrupt. This prohibits the return to the interrupt processing. If the binary signal has not yet been taken in, it is determined as NO in step 220. Then, the flag C is set to step 101 (see FIG.
If it is assumed that C = 0 has been initialized in step 231), NO is determined in step 230, and step 231
At, the analog switch 47 is turned off, while the analog switch 48 is turned on (see FIG. 11). This allows
The short circuit between the resistors 44 and 45 is released by the analog switch 47, while the line sensor 30 is connected to the coupling capacitor 41 by the analog switch 48.

After that, in step 232, the binary signal from the binary circuit 50 is taken into the microcomputer 70 (see FIG. 11), and in step 240, the waiting time for the exposure time of the line sensor 30 is waited. Interrupt waiting processing is performed. Then, when the exposure time elapses, the computer program executes step 140 (see FIG.
Refer to) to proceed to step 112 and thereafter. As a result, similar to the case described in the first embodiment, processing such as setting and driving the exposure time of the line sensor 30 and updating the counter value is performed.

Then, the determination in step 120 is Y.
When the ES is reached, step 124 is performed as in the first embodiment.
At, the analog switch 124 is turned off, and the computer program proceeds to the reading processing routine 200. At this stage, since the binarized signal has been captured in step 232, YES is determined in step 220, and both analog switches 47 and 48 are turned on in step 221. As a result, the resistors 44 and 45 are short-circuited by the analog switch 47, while the connection between the line sensor 30 and the coupling capacitor 41 is maintained by the analog switch 48.

Next, at step 222, the fetched binarized signal is decoded. If the result of decoding corresponds to the unsuccessful reading, NO is determined in step 250. With this determination, it is determined in step 260 whether or not to execute the coupling control. However, this determination is made based on whether or not all the reading is performed based on the exposure condition of the normal reading control (the product of the exposure time of the line sensor 30 and the gain of the operational amplifier 46). In addition, the coupling control is control in which the binarized signal is taken in along with the change of the analog switch 48 from ON to OFF.

Here, when the reading is performed under the exposure condition of the normal reading control, the determination in step 260 is N.
It becomes O, and the processing from step 240 onward is performed. On the other hand, if the exposure cannot be performed under the exposure conditions of the above-described normal reading control, the determination in step 260 is YES based on the determination that the exposure conditions are outside the normal exposure conditions. Then, in the next step 261, the value of the timer is set to Ct = Ct1 and in step 262 the flag C is set to Ct.
= 1 is set. Here, Ct = Ct1 is set by predicting the timing at which the amplitude portion of the bar code B appears during the output of the line sensor 30. That is, when the amplitude portion of the bar code B appears in the output of the line sensor 30, the time counting with respect to Ct1 of the timer ends. C = 1 indicates that the above-mentioned coupling control is performed.

After that, when the computer program reaches step 230 of the reading processing routine 200, YES is determined based on C = 1 in step 262, and in the next step 231, the analog switch 4 is selected.
Both 7 and 48 are turned on. Then, in step 232, the timer is started to measure the set value Ct = Ct1 in step 261 (see FIG. 11).

When the time measured by the timer is up,
In step 270, YES is determined, and in the next step 271, the analog switch 48 is turned off.
As a result, the DC balance of the coupling capacitor 41 is maintained to substantially match the bar code amplitude portion in the output of the line sensor 30 when the analog switch 48 is off. Since the analog switch 47 is turned on even when the analog switch 48 is turned off, unnecessary oscillation of the operational amplifier 46 can be prevented. Further, C = 0 after the analog switch 48 is turned off.

After waiting for the interrupt in step 240, the processing from step 112 onward is performed through step 140 in FIG. As a result, the coupling capacitor 4
After shortening the charging time of step 1, step 231 of FIG.
At, the analog switch 47 is turned off and the analog switch 48 is turned on, and the processing in step 232 is performed.

In this case, the waveform of the amplified signal of the amplifier circuit 40 is already stable due to the promotion of the charging of the coupling capacitor 41, and moreover, the coupling capacitor 41.
As described above, the DC balance of is maintained so as to substantially match the bar code amplitude portion in the output of the line sensor 30. Therefore, under the direct current balance, the binary signal from the binary circuit 50 is stabilized in step 2
At 32, it is loaded into the microcomputer 70 (see FIG. 11).

As described above, in the second embodiment, by executing the coupling control in response to the determination of YES in step 260, the timer value Ct ₁ of the above timer is measured when C = 1 is satisfied. Analog switch 4 at the end
8 off, the coupling capacitor 41 at this time
The DC balance of the above is adjusted to the amplitude portion corresponding to the barcode B in the output of the line sensor 30.

In other words, by switching the analog switch 48 from ON to OFF as described above, the level of the amplitude portion corresponding to the bar code B and the offset voltage Vo are replaced with the conventional offset voltages Vc and Vo.
I tried to balance DC. Thereby, the waveform of the bar code amplitude portion in the amplified output of the amplifier circuit 40 is
It can be located near the center of the amplified output waveform. Therefore, for example, even when the amplitude during the output of the line sensor 30 is small, like the barcode B having a low reflectance, the barcode B can be properly amplified. As a result, the reading performance of this type of optical reading device can be improved.

When the difference between the offset voltage of the line sensor 30 and the offset voltage of the operational amplifier 46 is large, the effect of the presence / absence of the analog switch 48 when the barcode B has a low reflectance will be described in the second embodiment. When the case and the case of the conventional amplifier circuit (see FIG. 6) were compared and confirmed by experiments, the results shown in FIGS. 12 and 13 were obtained.

According to this, in the conventional amplifier circuit of FIG. 6, since the analog switch 48 is not provided, the line sensor 3
The amplified output waveform of the amplifier circuit 40 with respect to the output waveform of 0 is
As shown in FIG. 13, it becomes saturated. In contrast,
In the amplifier circuit according to the second embodiment, the analog switch 4
8, the analog switch 48 is turned off when the timer value Ct ₁ has elapsed, and as shown in FIG.
By adjusting the offset voltage to the level Vb of the amplitude portion corresponding to the bar code B in the output of the line sensor 30, Vb and Vo are DC-balanced. As a result, even if the barcode B is a low reflectance barcode and the amplitude during the output of the line sensor 30 is small, an appropriate amplified waveform can be obtained.

In implementing the present invention, various switching elements such as semiconductor switching elements may be adopted instead of the analog switches 47 and 48. Further, in implementing the present invention, the binarization circuit 5
The binary processing of 0 may be performed by the microcomputer 70.

Further, in implementing the present invention, a quick charging means may be employed in place of the analog switch 47, whereby the coupling capacitor 41 may be initially charged rapidly. In implementing the present invention, the amplifier circuit 40
As the above, a non-inverting amplifier having a coupling capacitor or other amplifying element may be adopted for implementation.

Further, each step in each flow chart of each of the above-mentioned embodiments may be realized by a hardware logic configuration as a function executing means.

[Brief description of drawings]

FIG. 1 is a detailed circuit diagram of an amplifier circuit shown in FIG.

FIG. 2 is a block circuit diagram showing a first embodiment of a bar code reader according to the present invention.

FIG. 3 is a partially cutaway external view configuration diagram of the barcode reader.

4 is a flowchart showing the operation of the microcomputer of FIG.

FIG. 5 is a waveform diagram for explaining a function and effect in the first embodiment.

FIG. 6 is a conventional amplifier circuit diagram.

FIG. 7 is a waveform diagram for explaining a function and effect when the amplifier circuit of FIG. 6 is used.

FIG. 8 is a detailed circuit diagram of an amplifier circuit constituting a main part of the second embodiment of the bar code reader according to the present invention.

FIG. 9 is a part of a flow chart of a reading routine in the second embodiment.

FIG. 10 is a part of a flow chart of a reading routine in the second embodiment.

FIG. 11 is a waveform diagram showing operating states of both analog switches in the second embodiment.

FIG. 12 is an output waveform diagram of the line sensor and the amplifier circuit for explaining the function and effect in the second embodiment.

FIG. 13 is an output waveform diagram for explaining a function and effect when a conventional amplifier circuit is adopted.

[Explanation of symbols]

B ... Bar code, 30 ... Line sensor, 40 ...
..Amplification circuits, 41 ... Coupling capacitors, 4
4, 45 ... Resistance, 46 ... Operational amplifier, 47, 4
8 ... Analog switch, 70 ... Microcomputer.

Claims (3)

[Claims] 1. An optical sensor for optically detecting a reading target in which optical information is written to generate a detection output, an amplification unit for amplifying the detection output, the optical sensor and the amplification unit. In an optical information reading device including a coupling capacitor for AC coupling and a reading unit that reads the optical information based on an amplified output of the amplifying unit, the amplifying unit includes the cup before starting reading by the reading unit. An optical information reading device comprising an initial charging means for initially charging a ring capacitor. 2. A short circuit in which the amplifying means short-circuits the impedance circuit that forms a charging path together with the coupling capacitor and the impedance circuit during a time required to charge the coupling capacitor after the detection of the optical sensor is started. The optical information reading device according to claim 1, further comprising: means for amplifying the detection output by a gain determined by the impedance circuit after the short circuit is released by the short circuit means. 3. The amplifying means is connected between the optical sensor and the amplifying means, and sets the direct current balance of the coupling capacitor to a level corresponding to a reading timing of the optical sensor for the optical information. The optical information reading device according to claim 2, further comprising setting means for setting.