JP3548874B2 - Non-adjustable bar code reading circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a circuit for electrically reading a barcode.
[0002]
[Prior art]
In most cases, a conventional bar code reading circuit uses one or two semi-fixed adjusting resistors to correct a large variation in optical characteristics including a light emitting diode and a light receiving element. In addition, the non-adjustable type is selected and uses an optical element with very little variation. Also amplifier circuit each case linear der Luke, have used non-linear amplifier circuit of a voltage input type.
[0003]
[Problems to be solved by the invention]
The above-mentioned conventional adjustment method requires advanced techniques at the time of adjustment in order to correct variations in optical characteristics including aging of the light emitting diode, and is one of the factors that increase the manufacturing cost. In addition, since the adjustment is performed with a small variable resistor that is semi-fixed, there is a problem in reliability against mechanical shock and long-term use. Also, the conventional non-adjustable bar code reading circuit is one of the factors of high cost because an expensive optical element whose characteristic variation is selected is used.
[0004]
[Means for Solving the Problems]
Performs non-linear signal amplification by current input, and provides white peak current holding circuit etc. to perform compression operation on the upper and lower sides of a wide dynamic range, and the part corresponding to bar code signal is decompressed even during compression characteristics Perform high-efficiency signal amplification that is not compressed.
[0005]
[Action]
This is a non-linear amplification operation in which a white peak current holding circuit is provided in the feedback circuit of the operational amplifier, and only the amount of change in the bar code signal is output uncompressed using the white peak current as a reference current.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
The circuit of the present invention is not limited to the pen type bar code scanner, and the circuit of the present invention demodulates the original digital value in the case where the carrier frequency is modulated and transmitted by a digital value by a wired or wireless carrier frequency. It can also be used effectively in circuits.
[0007]
【Example】
The details of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an external view of a bar code reading pen by manual scanning. By tracing (scanning) the tip of the pen 1 on the bar code 3, information on the bar code 3 is read optically / electrically, and the information is read. An electric code is output as a result of the determination. The side push button 2 is a push button normally pressed by an operator's finger to enable reading only when the button is pressed.
[0008]
FIG. 2 shows a non-linear amplifier circuit which is a basic part of the non-adjustable bar code reading circuit according to the present invention. The light emitting diode 6 emits light by the applied current, illuminates the bar code 3, receives the reflected light through the optical lens or a small hole, and the light receiving element 7 flows a current corresponding to the amount of received light to the light receiving element 7 itself. Some light from the light emitting diode 6 reaches the light receiving element 7 without passing through the bar code 3. Therefore, the current flowing through the light receiving element 7 always has a bias current, and the current due to the light reflected from the bar code 3 surface is superimposed on the bias current.
[0009]
The switch 4 is a switch that conducts when the side push button 2 of the pen 1 is pressed, and a current flows through the light emitting diode 6 to emit light only when the switch 4 is turned on. The current supply resistor 5 (for example, 330Ω) is a current supply resistor for allowing a substantially constant current to flow through the light emitting diode 6.
[0010]
The reference voltage source 8 always supplies a constant voltage [+ VR] to the positive input terminal of the operational amplifier 9. The negative input terminal of the operational amplifier 9 is always held at the same voltage as [+ VR] by a feedback circuit denoted by reference numerals 10 to 18 in FIG. Therefore, the voltage applied to the light receiving element 7 is always a constant [+ VR]. The stabilizing capacitor 10 (for example, 10PF) is a small-capacitance capacitor for stabilizing the system including the operational amplifier 9 at a high frequency.
[0011]
A basic amplification factor (a basic coefficient of current-voltage conversion) is determined by the feedback resistor 11 (for example, 1 MΩ). If there is no circuit denoted by reference numerals 12 to 18, it is a normal current-voltage conversion type linear amplification circuit. The circuit shown in FIG. 2 obtains a very wide dynamic range by incorporating non-linear elements denoted by reference numerals 12 to 18 into a feedback loop and performing a special compression operation on both sides of the dynamic range.
[0012]
Here, the non-linear operation of the present circuit will be described in detail. Now, it is assumed that the switch 4 is turned on, the light emitting diode 6 emits light, and the light receiving element 7 starts receiving light. Since the current flowing through the light receiving element 7 increases, the output [non-linear analog output voltage] of the operational amplifier 9 increases. The current flowing through the light receiving element 7 is maximized when light reflected from a white background of the bar code 3 is received. At that time, the diode 14 is turned on and the white peak current holding capacitor 15 (for example, 0.22 μF) is charged. Further, the transistor 16 is also turned on to supply current to the light receiving element 7 via the current supply resistor 17 (for example, 15 kΩ). The current flowing through the light receiving element 7 at this time is the sum of the current flowing through the feedback resistor 11 and the current flowing through the current supply resistor 17.
[0013]
FIG. 3 shows this operating characteristic. The horizontal axis represents the value of the current flowing through the light receiving element 7, the vertical axis represents the output voltage, and the vertical and horizontal axes are linear scales. As shown in the figure, in the vicinity of the [white bar portion], even if the [non-linear analog output voltage] slightly increases, the current flowing through the current supply resistor 17 sharply increases.
[0014]
When the tip of the barcode reading pen 1 moves from the white bar portion to the black bar portion of the barcode 3, the amount of light entering the light receiving element 7 decreases, and the current flowing through the light receiving element 7 decreases. At this time, the voltage of the white peak current holding capacitor 15 is held for a long time, and the current at the time of the white peak continues to flow for a long time by the transistor 16 and the current supply resistor 17, so that the current flowing through the feedback resistor 11 is reduced or reversed. In this case, a part of the white peak holding current flowing through the transistor 16 and the current supply resistor 17 is canceled, and the current is reduced in accordance with the decrease in the current of the light receiving element 7. As a result, the [non-linear analog output voltage] decreases due to non-compression. .
[0015]
Therefore, even if the current variation with respect to the white bar portion of the optical system is about 10 times (900%), it is in the compression characteristic of this circuit, and when it becomes an important signal change portion, the output voltage changes largely without compression. And an efficient amplification operation.
[0016]
When the current of the light receiving element 7 further decreases, the diode 13 turns on and a large current flows through the resistor 12 (for example, 15 kΩ), so that the [non-linear analog output voltage] also shows a compression characteristic (see FIG. 3). ).
[0017]
When the tip of the barcode reading pen 1 scans the white and black bar portions of the barcode 3 alternately, the characteristic curve between the point of [white bar portion] and the point of [black bar portion] shown in FIG. It is an operation of reciprocating above. When the tip of the barcode reading pen 1 floats away from the surface of the barcode 3 and rises in the air, the amplification characteristic of the circuit in FIG. 2 passes through the point [floating in the air] in FIG. 15 gradually discharges due to the base current of the transistor 16, the white peak holding current flowing through the transistor 16 and the current supply resistor 17 also gradually decreases to zero, and the characteristic curve of FIG. Return to point.
[0018]
The resistor 18 in FIG. 2 is for preventing an excessive current and is not related to a normal operation. As described above, the circuit shown in FIG. 2 performs the current input type nonlinear operation, but the operational amplifier 9 does not saturate. Since the current flowing through the light receiving element 7 is at most about 10 μA, the forward voltage of VBE of each of the diodes 13 and 14 and the transistor 16 is about 0.35 V, and the voltage between the two non-linear analog output voltages is shown in FIG. As shown in FIG.
[0019]
The circuit diagram shown in FIG. 4 also includes a white / black discriminating circuit, and is slightly modified from that of FIG. The left half of the circuit diagram of FIG. 4 is a non-linear amplifier circuit, which is different from that of FIG. 2 in that a transistor 20 is connected in place of the resistor 12 as shown in FIG. 21 and the point that [+ VR] is set using the anode voltage of the light emitting diode 6 instead of the reference voltage source 8.
[0020]
The operation relating to the white bar portion of the barcode 3 is exactly the same as the operation in FIG. When the tip of the barcode reading pen 1 moves to the black bar portion of the barcode 3, the operation in FIG. 2 is slightly different from the operation in FIG. 99% or more flows through the collector of the transistor 20, discharges the white peak current holding capacitor 15, and the white peak holding current flowing through the transistor 16 and the current supply resistor 17 decreases.
[0021]
When the value obtained by subtracting the value of the current flowing through the feedback resistor 11 from the value of the current flowing through the current supply resistor 17 becomes equal to the value of the current flowing through the light receiving element 7, the voltage of the output voltage [non-linear analog output voltage] of the operational amplifier 9 falls. Stops, the current flowing through the diode 13 also becomes zero, and the discharge current of the white peak current holding capacitor 15 flowing through the transistor 20 also stops. This point corresponds to the point of [black bar] in FIG. 5 (amplification characteristic diagram of the circuit of FIG. 4).
[0022]
At this time, the current flowing through the transistor 16 and the current supply resistor 17 is maintained at the corrected value. Here, if the output voltage of the operational amplifier 9 drops even a little, the current flowing through the current supply resistor 17 changes greatly. Therefore, the point of [black bar] is a compressed amplification operation as shown in FIG. .
[0023]
Here, when the tip of the bar code reading pen 1 moves from the black bar to the white bar of the bar code 3, the current flowing through the light receiving element 7 increases again, and the output of the operational amplifier 9 rises. At this time, only the current flowing through the feedback resistor 11 changes until the diode 14 is turned on, resulting in an incompressible amplification characteristic (see FIG. 5). When the diode 14 is turned on, the compression characteristic starts from there, and the white peak current holding capacitor 15 holds a new peak voltage.
[0024]
The characteristic shown in FIG. 5 is different from the characteristic shown in FIG. 3 in that the characteristic shown in FIG. 5 has a hysteresis characteristic that draws a loop for white / black bars, the peak current holding value is updated for each bar, and the white bar And black bars are symmetrical with respect to the reference voltage [+ VR]. Therefore, there is a merit that the characteristic balance between the white and black portions of the barcode 3 is very good, and even when the state of light reflection changes in the middle of the barcode 3, the reference peak holding current value is immediately updated. This makes it possible to read the barcode 3 with very high reliability.
[0025]
The voltage between the two non-linear analog output voltages of the circuit shown in FIG. 4 becomes larger than that of FIG. 2 by the addition of the VBE of the transistor 20, and becomes about 1.5 V as shown in FIG.
[0026]
Here, the white / black discrimination circuit will be described. What is immediately apparent from the characteristic diagram of FIG. 5 is to determine whether the output voltage [non-linear analog output voltage] of the operational amplifier 9 is higher or lower than the voltage value of [+ VR]. In that case, the negative input terminal of the voltage comparator 31 may be connected as shown by a broken line instead of the circuit constituted by reference numerals 22 to 30 in FIG. This is sufficient for reading ordinary barcodes.
[0027]
Here, when reading the gray (small contrast ratio) bar code 3, or when the bar code reading pen 1 is used at an angle to deteriorate the optical focus and reduce the current change of the light receiving element 7, or the light emitting and receiving element It is assumed that the optical system including 6 and 7 has deteriorated over time, or that dust has adhered to the tip of the barcode reading pen 1 and the amount of change in the current of the light receiving element 7 has been reduced. Now, a typical example of reading the gray bar code 3 will be described. The amplification characteristic point linearly reciprocates between the point of [white bar part] and the point of [gray bar part] in the characteristic diagram of FIG. For example, the point of the [gray bar portion] approaches the voltage of [+ VR], which is the determination level, and is likely to be erroneously determined due to the influence of noise, deterioration of the signal duty ratio, and the like. Alternatively, when the point of [gray bar portion] is on the plus side of [+ VR], it cannot be determined.
[0028]
Although a circuit that can discriminate in these cases has been devised, the circuits indicated by reference numerals 22 to 30 are basically an AM envelope detection circuit and an addition circuit. Preferably, the diodes 23 and 24 are Schottky barrier diodes having uniform characteristics. The white level holding capacitor 26 (for example, 0.22 μF) temporarily stores the level of the [white bar portion] as an analog voltage at the point [W], and the black level holding capacitor 25 (for example, 0.22 μF) outputs the [black bar portion] or The level of the [gray bar portion] is temporarily stored as an analog voltage at the point [B].
[0029]
The resistor 27 (for example, 3.3 MΩ) is a pull-up resistor, and the resistor 28 (for example, 2.2 MΩ) is a pull-down resistor. The resistors 29 and 30 (for example, 1 MΩ) are summing resistors for addition, and apply an intermediate value between the voltages at the points [W] and [B] to an intermediate point (a negative input terminal of the voltage comparator 31).
[0030]
Diodes 23 and 24 each cause a forward voltage drop, but when summed by summing resistors 29 and 30, cancel each other. Therefore, the voltage at the intermediate level between the voltage of [white bar portion] and the voltage of [black bar portion] or [gray bar portion] shown in FIG. 5 is applied to the negative input terminal of the voltage comparator 31. The positive-side input terminal of the voltage comparator 31 is connected by two resistors so as to have a hysteresis (Schmitt) characteristic. The resistance 32 (for example, 2.2 MΩ) is a positive feedback resistance, and the resistance 33 (for example, 33 kΩ) is a hysteresis voltage generation resistance, and has a hysteresis voltage level of about 80 mV.
[0031]
As can be understood from the above description, the discrimination circuit in FIG. 4 uses the intermediate level of the signal amplitude level of [non-linear analog output voltage] as the discrimination level. Therefore, even if the bar code 3 has a small contrast ratio, the bar code reading pen is tilted and the optical focus is weakened, and even if the optical system deteriorates due to aging and the signal level drops to about half, the bar code 3 can be reliably used. Can be read.
[0032]
The diode 22 has a function of limiting the discrimination level to a voltage slightly lower than the voltage level of the [white bar portion] in FIG. 5 without increasing the discrimination level. This prevents erroneous determination when scanning a white background.
[0033]
The circuits indicated by reference numerals 21 and 34 to 36 are for fixing the [bar code discrimination output] to the “low” level when the switch 4 is OFF, and the minute current supply resistor 21 (for example, 33 kΩ) The input voltage of the positive input terminal of the operational amplifier 9 is prevented from becoming zero, and the operational amplifier 9 is prevented from being saturated. The voltage comparator 31 can be replaced by an operational amplifier.
[0034]
Although the description so far has been limited to the pen-type barcode scanner, this circuit can also be used as a barcode reading circuit by electronic scanning using a CCD. In that case, the CCD output may be input as a current instead of the light receiving element 7. This circuit can also be used for a circuit that demodulates the original digital value when a wired or wireless carrier frequency is modulated and transmitted with a digital value. In that case, the detection output of the carrier may be input as a current instead of the light receiving element 7.
[0035]
【The invention's effect】
The non-adjustable bar code reading circuit according to the present invention enables non-adjustment, which has been difficult in the past, has a simple configuration, and has reduced manufacturing costs. Also, since there are no adjustment points, the durability is increased, and the aging of the optical system is automatically corrected. Since the black-and-white determination balance under various conditions is excellent, the output duty ratio is less likely to collapse. Overall, the barcode reading reliability is greatly increased at a low cost, and is maintained for a long time.
[Brief description of the drawings]
Fig. 1 Bar code reading pen Fig. 2 Non-linear amplifier circuit (basic part)
[Fig. 3] Non-linear amplification characteristics [Fig. 4] Non-linear barcode reading circuit [Fig. 5] Symmetric non-linear amplification characteristics [Explanation of symbols]
REFERENCE SIGNS LIST 1 bar code reading pen 2 side push button 3 bar code 4 switch 5 current supply resistor 6 light emitting diode 7 light receiving element 8 reference voltage source 9 operational amplifier 10 stabilizing capacitor 11 feedback resistor 12 resistor 13 diode 14 diode 15 white peak current holding capacitor Reference Signs List 16 transistor 17 current supply resistor 18 resistor 19 filter capacitor 20 transistor 21 minute current supply resistor 22 diode 23 diode 24 diode 25 black level holding capacitor 26 white level holding capacitor 27 pull-up resistor 28 pull-down resistor 29 summing resistor 30 summing resistor 31 voltage comparator 32 Positive feedback resistance 33 Resistance 34 Diode 35 Resistance 36 Resistance

Claims (5)

An operational amplifier, a voltage source for applying a reference voltage to a positive input terminal of the operational amplifier, and a light source connected between the negative input terminal of the operational amplifier and the ground for receiving light from a bar code surface and performing light / current conversion A light receiving element, a feedback resistor connected between the output terminal and the negative input terminal of the operational amplifier, and a voltage obtained by adding a constant voltage set by a circuit to the output terminal voltage of the operational amplifier to the reference voltage. A current supply circuit for flowing a current corresponding to the peak value toward the negative input terminal of the operational amplifier when the voltage becomes high, and for maintaining a constant current for a certain period of time; A circuit that causes a current corresponding to the instantaneous value to flow out from the negative input terminal of the operational amplifier when the voltage becomes lower than a voltage obtained by subtracting a constant voltage set by the circuit. No adjustment bar code reading circuit having a current input type non-linear amplifier circuit according to symptoms. An operational amplifier, a voltage source for applying a reference voltage to a positive input terminal of the operational amplifier, and a light source connected between the negative input terminal of the operational amplifier and the ground for receiving light from a bar code surface and performing light / current conversion A light receiving element, a feedback resistor connected between the output terminal and the negative input terminal of the operational amplifier, and an output terminal voltage of the operational amplifier higher than a voltage obtained by adding a constant voltage set by a circuit to the reference voltage. A current supply circuit that supplies a current corresponding to the peak value toward the negative input terminal of the operational amplifier and holds a constant current for a certain period of time; when it becomes lower than the voltage obtained by subtracting a predetermined voltage set by the current, characterized in that comprising a holding current correction circuit for reducing the holding current value of the current supply circuit oN No adjustment bar code reading circuit with type non-linear amplifier circuit. A positive polarity AM envelope detection circuit using a diode and a capacitor for applying the output voltage of the non-linear amplifier circuit, a negative polarity AM envelope detection circuit using a diode and a capacitor for applying the output voltage of the non-linear amplifier circuit, and the positive polarity AM Two resistor circuits connected in series, which add an output voltage of an envelope detection circuit and an output voltage of the negative polarity AM envelope detection circuit and output an intermediate voltage, the intermediate voltage, an output voltage of the non-linear amplifier circuit, 3. A non-adjustable bar code reading circuit according to claim 2, further comprising a voltage level discriminating circuit comprising a voltage comparator for comparing and outputting a bar code. 4. The non-adjustable barcode reading circuit according to claim 3, further comprising a diode limiting circuit for preventing an output voltage of the negative polarity AM envelope detection circuit from being higher than a voltage obtained by adding a constant voltage to the reference voltage. . 3. The non-adjustable bar code reading circuit according to claim 2, wherein the voltage source for applying the reference voltage is a light emitting diode.

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