JPS6230672B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a barcode reader reading signal conversion circuit that converts an analog signal output from a barcode reader into a pulse signal corresponding to a barcode pattern to be read.

In product shipping departments of factories, supermarkets, department stores, etc., stickers with a barcode symbol as shown in Figure 1 are affixed or printed directly on packaging boxes to identify large quantities of products. A system is used that optically reads the information to manage product entry/exit or inventory management. In this type of entry/exit control or inventory management system, barcodes are read with a barcode reader such as a pen-type barcode reader, and the read analog signal of the barcode reader is converted into a pulse that corresponds to the barcode pattern to be read. The converted pulse signal is then processed by a computer. Therefore, the converted pulse signal obtained from the analog signal of the barcode reader must faithfully correspond to the barcode pattern to be read.

When the barcode shown in Figure 1 is scanned from point O to point P at a constant speed with a barcode reader such as a pen-type barcode reader, the output signal of the ideal barcode reader is as shown by the solid line in Figure 2. As shown by Ea, the maximum value Emax and minimum value Emin of the output signal waveform are approximately constant. however,
The maximum value Emax and minimum value Emin may change as shown by the broken line in FIG. 2 due to the influence of overall dirt on the barcode, uneven printing, the gap or angle between the barcode and the reader, etc. Therefore, it is necessary to convert the output signal into pulses corresponding to the barcode pattern without being affected by the overall dirt on the barcode, uneven printing, the gap between the barcode and the reader, and the angle.

As shown in Figure 2, the maximum value Emax and minimum value Emin of the read signal of a barcode reader are generally affected by dirt on the barcode, the gap between the barcode and the reader, the angle, etc., but the period of the read signal, That is, the time width of the read signal faithfully reflects the barcode pattern without being affected by the overall dirt on the barcode, the gap between the barcode and the reader, or the angle. Therefore, the first method for obtaining a pulse signal that faithfully corresponds to the barcode pattern from the analog signal of the barcode reader is as follows.
As shown in Figure 2, from the maximum value Emax to the minimum value
When the average value Emean of the output signal Ea that changes up to Emin is found and the average value Emean is used as a reference voltage, the analog signal Ea is converted into a digital signal by a conversion circuit, resulting in a conversion pulse that is faithful to the barcode pattern as shown by the solid line Ec in Figure 4. can be obtained. However, in this method, the minimum value Emin is unknown until at least time t ₂ as shown in FIG. 3, or until _time t ₃ for the output signal shown by the broken line in FIG. Since the average value Emean cannot be determined until t ₃ , the reference voltage cannot be obtained and the conversion pulse faithful to the barcode pattern cannot be obtained until these times. That is, the first
This method has the disadvantage that the conversion pulse of at least the first bar B1 of the barcode as shown in FIG. ₁ will be inaccurate or not obtained at all.

As a second method to deal with the shortcomings of the first method, as shown by the broken line in FIG.
A voltage that varies according to the period of the signal Ea, and whose maximum value and minimum value are smaller than each maximum value of the signal Ea by an arbitrary constant voltage e, and larger than each minimum value by a voltage e.
There is a method of creating a voltage Ed and using the voltage Ed as a reference voltage, a conversion circuit converts the analog signal Ea into a pulse signal corresponding to a barcode pattern as shown by the dotted line Ee in FIG. According to this second method, it is possible to convert the initial scanning signal of the barcode reader without missing it; however, as described above, the method of using the voltage Ed, which changes as the analog signal Ea fluctuates, as the reference voltage, If the maximum value Emax or minimum value Emin of the analog signal is affected by overall dirt on the barcode, the gap between the barcode and the reader, or the angle, the amplitude V centered on the average value Emean will not be constant. It is not possible to obtain a conversion pulse that is faithful to the barcode pattern.

Therefore, the present invention makes use of the advantages of the first method and the second method, and uses the second method at the initial stage of scanning by the barcode reader to obtain the bar B ₁ or B ₂ at the initial stage of scanning. The conversion pulse is also reliably obtained from the read analog signal of B ₃ , and after that, the first
To provide a barcode reader reading signal conversion circuit capable of obtaining a conversion pulse faithful to a barcode pattern from an analog signal regardless of dirt on the barcode, gap between the barcode and the reader, angle, etc. purpose.

Next, the present invention will be explained in detail using the drawings.

FIG. 5 is a circuit diagram showing one embodiment of the barcode reader reading signal conversion circuit according to the present invention;
The figure is a diagram showing the relationship between the amplified analog signal Ea' of the barcode reader and the reference voltage Er of the comparator to explain its operation. In FIG. 5, 1 is an input terminal, and the output signal Ea of the barcode reader is input to the input terminal. 2 is an operational amplifier which amplifies the output signal Ea of the barcode reader. D ₁ , D ₂ , D ₃ , and D ₄ are diodes, D ₁ and D ₂ have the function of regulating the charging and discharging of capacitors C ₁ and C _{2 ,} and D ₃ and D ₄ are reference voltages as described later. It has the effect of selectively applying Er and bias voltage Eb to the comparator 4. C ₁ , C ₂ , C ₃ are capacitors, and capacitors C ₁ and C ₂ are equal;
Use with capacitor C larger than ₃ . _R1 ,
R ₂ and R ₃ are resistors, and the resistors R ₁ , R ₂ , and R ₃ are selected so that their time constants with the corresponding capacitors are equal to each other, and when the time constants are sufficiently larger than the maximum period of the barcode output waveform. Set it so that it becomes a constant. The diodes D ₁ , D ₂ , the capacitor C ₁ ,
A circuit composed of C ₂ , C ₃ and resistors R ₁ , R ₂ , and R ₃ is a reference voltage circuit 3 that receives the output signal of the amplifier 2 and generates a reference voltage Er. A comparator 4 has the function of converting the analog signal Ea' from the amplifier 2 into pulses corresponding to the bar code pattern based on the reference voltage generated from the reference voltage circuit 3.
5 is an output terminal, and the pulses emitted from the output terminal 5 are processed by a computer. In FIG. 6, Ea' is a signal obtained by amplifying the barcode reader reading signal and indicates the voltage at point X of the circuit of FIG. 5, and Er is a reference voltage at the output terminal of the reference voltage circuit 3 of FIG. Indicates the voltage at point Y.

Next, the operation of the circuit shown in FIG. 5 will be explained. As the voltage Ea' increases from time _t1 in FIG. 6, the capacitors _C1 and _C3 are charged through the diode _D1 until the voltage Ea' reaches its maximum value, and the respective voltages become _E1 and _E2 . Next, when the voltage Ea' starts to decrease and becomes less than the voltage _E2 of the capacitor _C3 , the capacitor _C3 is discharged through the diode _D2 until the voltage Ea' reaches the minimum value, and the capacitor _C2 is charged.
The voltages become E ₄ and E ₃ respectively, and the capacitor C ₁ maintains the voltage E ₁ . Next, the voltage Ea′ increases again and the voltage E ₁ +
When E ₄ or higher, capacitors C ₁ and C ₃ are charged again through diode D ₁ until voltage Ea' reaches its maximum value, and the voltage of capacitor C ₁ further increases to voltage E ₅ . The voltage across capacitor C ₃ becomes E ₆ , and capacitor C ₂ maintains voltage E ₃ . Next, when the voltage Ea′ decreases again and becomes less than the voltage E ₆ −E ₃ , the capacitor C ₃ is discharged through the diode D ₂ until the voltage Ea′ reaches its minimum value, and the capacitor C ₂ is charged again and the voltage increases further. The voltage becomes E ₇ and the voltage across capacitor C ₃ becomes E ₈ . In this way, the voltages of capacitors C ₁ and C ₂ increase sequentially, and the voltage fluctuation of capacitor C ₃ becomes small, and the voltages E ₂ and E ₄ set corresponding to the maximum and minimum values of the analog signal are increased. converges to the average value of In other words, the voltage at point Y has the waveform of voltage Er shown by the broken line in FIG. Therefore, using the voltage Er as the reference voltage, the voltage
If Ea' is applied to the comparator 4, the barcode reader's scanning initial stage is converted to the second conversion method, that is, the analog signal Ea is converted using the voltage Ed shown in FIG. 3 as a reference voltage, and then the average value Emean The method switches to converting the voltage as a reference voltage. Also, in Figure 6, the voltage
Eb is the bias voltage to keep the comparator output at a low potential (bar code black level) when there is no signal, and diodes _D3 and _D4 are the reference voltage Er.
and bias voltage Eb and comparator 4
It has the effect of applying

FIG. 7 is an example of a modification of the circuit shown in FIG. 5, and a voltage of Ea'-Er appears at point Y as shown in FIG.
Therefore, if this is applied to the comparator 4 at zero level, the desired converted pulse output can be obtained. In FIG. 8, voltage Eb' is a bias voltage for keeping the output of comparator 4 at black level when there is no signal.

As described in detail above, the barcode reader read signal conversion circuit according to the present invention has a voltage setting section that sets a voltage that changes in accordance with the maximum value and minimum value of the analog signal read from the barcode reader. a reference voltage generating circuit that outputs a reference voltage from the voltage generating section that sequentially generates a voltage of a magnitude that causes the set voltage to converge to around the average value of the maximum value and the minimum value of the analog signal; A comparison circuit is provided which generates a pulse signal corresponding to the barcode pattern using the output signal of the circuit as a reference voltage, and from the reference voltage generation circuit, a predetermined level of magnitude corresponding to the maximum value and minimum value is provided at the initial stage of barcode scanning. A reference voltage is obtained at the set voltage of Or, from the voltage signal of the difference between the read analog signal from the barcode reader and the reference voltage, a pulse corresponding to the barcode pattern is obtained using a comparator with the base voltage as a reference, so the barcode pattern at the initial stage of scanning is It is possible to reliably obtain conversion pulses from code bar reading signals, and convert barcode patterns from read analog signals regardless of the overall dirt on the barcode, the gap between the barcode and the reader, the angle, or the scanning speed. This has the excellent effect of making it possible to obtain faithful conversion pulses.

[Brief explanation of the drawing]

Figure 1 shows the barcode, Figure 2 shows the output signal of the barcode reader, Figure 3 shows the relationship between the output signal of the barcode reader and the reference voltage, and Figure 4 shows the conversion pulse. 5 is a circuit diagram showing an embodiment of the barcode reader reading signal conversion circuit according to the present invention, FIG. 6 is an explanatory diagram thereof, and FIG. 7 is a barcode reader reading signal conversion circuit according to the present invention. FIG. 8 is a circuit diagram showing another embodiment of the present invention. 2: operational amplifier, 3: reference voltage circuit, 4: comparator, Ea: barcode reader reading signal, Er: reference voltage, Eb: bias voltage.

Claims (1)

[Claims] 1. In a barcode reader reading signal conversion circuit that converts an analog signal read from a barcode reader into a pulse signal corresponding to a barcode pattern to be read, a voltage that changes in accordance with the maximum and minimum values of the analog signal. a reference voltage generation circuit that outputs a reference voltage from a voltage setting section that sets the set voltage and a voltage generation section that sequentially generates a voltage of a magnitude that converges the set voltage to the average value of the maximum value and the minimum value of the analog signal. and a comparison circuit that generates a pulse signal corresponding to the barcode pattern using the output signal of this reference voltage generation circuit as a reference voltage.The set voltage is used as the reference voltage at the beginning of scanning of the barcode reader, and thereafter, the set voltage is used as the reference voltage. A barcode reader reading signal conversion circuit characterized in that a reference voltage is a voltage that converges to the average value of a maximum value and a minimum value of an analog signal.