JPH1055403A - Information reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always keep a value optimum for binarization without being affected by a change or the like in the intensity of disturbance light by fixing an inputted signal at the clamp voltage of a prescribed fixed value and relatively moving the following signals with the clamp voltage as a reference. SOLUTION: This device is provided with a clamp circuit 6 composed of an operational amplifier OP 3, resistor R11, capacitors C1 and C4 and analog switch SW1. The SW1 is controlled by an output signal CLP from the IO port of a microcomputer, at the level of 'H', the SW1 is turned to a conducted state and a waveform at a point (e) is clamped (fixed) to Vb at one terminal of the C4. In a bar code reading state, the output of the clamp circuit 6 is near the middle of 1st scan and when CLP is turned to 'H', the waveform is clamped (fixed) to Vb during 'H' and changed later so that a bar code signal component can be amplified almost with Vb as a center in the 2nd scan late.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information reading apparatus for reading a bar code or the like.

[0002]

2. Description of the Related Art Hereinafter, among information reading apparatuses, particularly, a bar code reader will be described. It is needless to say that the present invention is not limited to a barcode reader, but can be applied to a portable information terminal such as a handheld terminal that can read information.

As a conventional bar code reader generally used connected to a POS or the like, a linear CCD (Charge Coupled D) is used as an image sensor.
FIG. 5 shows the configuration of a barcode reader using the device (device). 11 is a bar code label, 12 is a plurality of LED light sources arranged in a direction perpendicular to the paper surface, 13 is a reflection mirror, 1
4 is an imaging lens, 15 is a linear CCD, 16 is a circuit unit,
Reference numeral 17 denotes a communication cable to a terminal device such as a POS, and reference numeral 18 denotes a case.

FIG. 6 shows a block diagram of the circuit section 16. The circuit unit 16 includes a waveform processing unit 19, a storage unit 20, and a decoding unit 21. Normally, the waveform processing means 19 is constituted by an analog circuit such as an operational amplifier, the storage means 20 is constituted by a semiconductor memory, and the decoding means 21 is constituted by a microcomputer.

FIG. 7 shows details of the conventional waveform processing means 16. The signal output (OS) and the compensation output (DS) output from the linear CCD 15 are impedance-converted by the emitter follower circuits 1a and 1b including the transistors Tr1 and Tr2 and the resistors R1 to R6, and the operational amplifier OP1 and the resistor The signal is amplified by the differential amplifier circuit 2 composed of R7 to R10. Here, the compensation output (DS) is the original output signal (O
The output is almost the same as the reset pulse noise in S), and the noise is reduced by the differential amplifier circuit 2. Here, the amplification degree of the differential amplifier circuit 2 is determined by R8 / R7 (= R10 / R9).

The DC cut circuit 3 is composed of a capacitor C1 and a resistor R11. The DC component is removed, and only the AC component is input to the next-stage amplifier circuit 4. The amplifier circuit 4 is an operational amplifier O
This is an inverting amplifier circuit composed of P2, resistors R12 to R15 and a capacitor C2. R14 and R15 are used to determine the operating voltage of OP2, and C2 is used to reduce noise. The amplification degree is R13 / R
Decided at 12. 5 is a binarization circuit and a comparator CO
M1 is binarized by the antiparallel diodes D1 and D2, the capacitor C3, and the resistors R16 to R19.

FIG. 8A shows the output of the differential amplifier circuit 2 (point a in the circuit diagram) and FIG. 8A shows the output of the DC cut circuit 3 (b in the circuit diagram).
FIG. 8B). Here, FIG. 8B shows a state where the DC (direct current) component is cut from the output signal of the differential amplifier circuit 2 and the center of gravity Vd of the waveform becomes Vb.
FIG. 8C shows the output of the amplifier circuit 4 (point c in the circuit diagram), which inverts and amplifies the signal from which the DC component has been cut (point b in the circuit diagram). FIG. 8D shows the output of the binarization circuit (point d in the circuit diagram), "H", "H" according to the black and white of the barcode.
L ”is output.

Next, FIG. 9 shows a conventional example using an area CCD as an image sensor. The configuration diagram is the linear CC of FIG.
If D15 is replaced with an area CCD, it is almost the same, and therefore will not be described. The VIDEO signal compliant with the NTSC standard output from the area CCD is 1 Vp by the terminating resistor R20.
−p. The DC component of the VIDEO signal is reduced by a DC cut circuit 7 including a capacitor C5 and a resistor R21.

The amplifier circuit 8 includes an operational amplifier OP4 and a resistor R2.
2 and R23. In the binarization circuit 9 composed of the resistors R24 and R25 and the comparator COM2, the comparator COM2 compares the reference voltage Va set by R24 and R25 with the VIDEO signal amplified by the amplifier circuit 8. Note that the reference voltage V
In some cases, a was changed.

FIG. 10 shows waveforms. FIG. 10A shows the output (point f in the circuit diagram) of the area CCD terminated by the resistor R20.
Shown in Here, waveforms for two horizontal scanning lines (also called horizontal lines) are shown. DC cut circuit 7
The signal amplified by the amplifying circuit 8 through FIG.
(B). FIG. 10C shows the output of COM2 comparing the reference voltage Va determined by the resistors R24 and R25 with the output of the amplifier circuit 8. As described above, “H” and “L” are output according to the black and white of the barcode.

[0011]

However, in the case where a linear CCD is used as an image sensor, when a thin bar code or strong disturbance light is generated, the signal output from the linear CCD 15 as shown in FIG. Since the DC component increases, the center of gravity Vd of the waveform becomes larger than the center Ve of the amplitude by the barcode, and in the DC cut circuit 3, the center of gravity Vd of the waveform becomes the pull-up voltage Vb of R11. As shown in b), the DC component cannot be sufficiently removed. For this reason, there is a problem that the output of the amplifier circuit 4 is saturated as shown in FIG. 11C, and a binarized output corresponding to the black and white of the bar code cannot be obtained as shown in FIG. 11D ( In the example shown in FIG.
H ”becomes longer.) Here, VL of FIG.
VH is the minimum output voltage and the maximum output voltage of the operational amplifier, respectively.

In the case of using an area CCD as an image sensor, as shown in FIGS. 12 (a) and 12 (b), the waveform becomes non-uniform due to the influence of disturbance light and a decrease in the amount of peripheral light caused by the lens. It cannot be binarized.

The binarization circuit 5 shown in FIG. 7 is a system in which when binarization is performed, the state before the point of interest is held in the capacitor C3 and binarization is performed based on the voltage difference. CCD
Can be binarized if the information has information only in the horizontal direction (horizontal direction = vertical direction to the bar code), such as a one-dimensional bar code. Although there is information in two directions, binarization cannot be performed.

An object of the present invention is to solve such a problem and to provide a bar code reader having good reading performance.

[0015]

To achieve the above object, a first information reading apparatus according to the present invention comprises: a light projecting means for irradiating light onto a bar code label; and a reflecting means for reflecting light from the bar code label. Imaging means for receiving and forming an image; an image sensor for converting the barcode image into an electric signal; a waveform processing means for performing a predetermined process on the output signal of the image sensor; and image data output from the waveform processing means Decoding means for decoding a barcode symbol based on the waveform data, wherein the waveform processing means fixes a part of the input signal to a clamp voltage which is a predetermined constant value and converts the subsequent signals to the clamp voltage. It is provided with clamping means for relatively moving with respect to the reference.

Further, the second information reading apparatus of the present invention is provided with a means for the clamping means to perform the clamping at a timing once for a predetermined number of scans.

Further, the third information reading apparatus of the present invention is provided with a unit that does not decode data obtained by scanning when the clamping unit performs clamping.

In a fourth information reading apparatus according to the present invention, the waveform processing means includes an operational amplifier and a comparator, and the clamp means determines a voltage within an allowable input range of an upper limit and a lower limit of the comparator and the operational amplifier as a clamp voltage. It is provided with means for performing.

According to a fifth information reading apparatus of the present invention, the waveform processing means includes an AD converter, and the clamping means includes means for setting the low-voltage reference voltage or the high-voltage reference voltage of the AD converter to a clamp voltage. It is.

Further, in a sixth information reading apparatus according to the present invention, the clamp means comprises at least a capacitor and a switch means.

In a seventh information reading apparatus according to the present invention, the clamping means includes means for clamping during a horizontal synchronization period, a vertical synchronization period, or a pedestal period.

[0022]

According to the above configuration, in the first information reading apparatus of the present invention, the waveform processing means fixes a part of the input signal to a clamp voltage which is a predetermined constant value, Since the clamp means for relatively moving the signal with reference to the clamp voltage is provided, the clamp voltage is constant, so that it is not affected by a change in the degree of disturbance light or the like, and is always optimal for binarization. You can keep the value.

In the second information reading apparatus of the present invention, since the clamping means is provided with means for clamping at a predetermined timing for a predetermined number of scans, the center of gravity of the waveform is prevented from shifting, and is always kept constant. It is possible to clamp to a value.

Further, the third information reading apparatus of the present invention is provided with a means for preventing the data obtained by the scanning when the clamping is performed from being performed by the clamping means, so that the confusion caused by the data disturbed by the clamping can be prevented. Can be prevented.

In a fourth information reading apparatus according to the present invention, the waveform processing means includes an operational amplifier and a comparator, and the clamp means determines a voltage within an allowable input range of an upper limit and a lower limit of the comparator and the operational amplifier as a clamp voltage. Therefore, the output waveform of the operational amplifier does not saturate even if it is affected by disturbance light or the like.

In the fifth information reading apparatus of the present invention, the waveform processing means includes an AD converter, and the clamp means includes means for setting the low-voltage reference voltage or the high-voltage reference voltage of the AD converter to a clamp voltage. By reproducing the DC component, multi-value digital conversion can be performed in absolute value.

Further, in the sixth information reading apparatus of the present invention, since the clamp means is constituted by at least a capacitor and a switch means, the clamp means can be realized with a simple structure.

In the seventh information reading apparatus of the present invention, the clamping means includes means for clamping during the horizontal synchronizing period, the vertical synchronizing period, or the pedestal period, so that the absolute value contributes to accurate binarization. can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. Here, the same components as those of the conventional example shown in FIGS. 5 and 7 are denoted by the same reference numerals, and description thereof is omitted.

FIG. 1 shows details of the waveform processing means 19. Instead of the DC cut circuit 3 of FIG. 7, an operational amplifier OP3, a resistor R11 and capacitors C1 and C4, and an analog switch S
A clamp circuit 6 composed of W1 is inserted. SW1
Is controlled by the output signal CLP from the IO port of the microcomputer. When "H", SW1 is turned on (ON) and the waveform at point e in the circuit diagram is clamped to Vb of one terminal of C4 ( Fixed). In the present embodiment, the voltage of one terminal of C4 and the pull-up voltage of R11 are set to the same Vb, but may be different.

FIG. 2 shows a waveform in the same bar code reading state as in FIG. FIG. 2A, which is an output from the linear CCD 15, has the same waveform as FIG. 11A. As shown in FIG. 2B, when the CLP is set to “H” near the middle of the first scan, the output of the clamp circuit 6 (point e in the circuit diagram) is clamped (fixed) to Vb during the “H” period. Since the waveform changes by the same amount as the change in FIG. 2A thereafter, the bar code signal component swings around Vb at the second scan at the latest.

If left in the same state, gradually as shown in FIG.
Since the center of gravity Vd of the waveform approaches Vb as shown in FIG.
It is useful to set the CLP to "H" once every two or three scans. In addition, since the waveform in the scan in which the CLP is set to “H” is disturbed as shown in the first scan in FIG. 2C, the decoding process is not performed.

(Embodiment 2) Next, a second embodiment of the present invention will be described with reference to FIGS.
In the second embodiment, an area CC is used as an image sensor.
D was used. Here, the same components as those of the conventional example shown in FIG. 9 are denoted by the same reference numerals, and description thereof is omitted.

FIG. 3 shows the waveform processing means 19. IC1 is an IC for a synchronization signal separation circuit and outputs a clamp pulse CLP.

The clamp circuit 10 includes an operational amplifier OP5, capacitors C6 and C7, a resistor R26, an analog switch S
W2. The IC 2 converts an analog signal into an 8-bit digital signal by an AD converter.

FIG. 4 shows a waveform in a bar code reading state. FIG. 4 showing the output of the area CCD (point f in the circuit diagram)
(A) shows waveforms for two horizontal scanning lines (also called horizontal lines). t1 is a horizontal synchronization signal, t
The period of 2 is a period called a pedestal and is a black reference. “H” is output by the IC 1 only during the period of t2, and the AD converter IC is output by the clamp circuit 10 of FIG.
2 is clamped at the low voltage side reference voltage Vref. As a result, the black reference voltage does not change even under the influence of disturbance light or the like, so that the digital conversion can be accurately performed using the absolute value. Note that the clamp may be performed during the vertical synchronization period.

As described above, according to the embodiment of the present invention,
Even in the case where a direct current component cannot be changed due to the influence of disturbance light or the like as in the related art and cannot be accurately binarized, the output waveform of the operational amplifier is not saturated and the binarization can be performed correctly.

Further, by reproducing the DC component, multi-value digital conversion can be performed in absolute value, and an accurate value can be obtained without being affected by a decrease in ambient light due to a lens.

[0039]

According to the above arrangement, in the first information reading apparatus of the present invention, the waveform processing means fixes a part of the input signal to a clamp voltage which is a predetermined constant value and outputs the subsequent signals. Since the clamp means for relatively moving the clamp voltage as a reference is provided, the clamp voltage is a constant value, so that the clamp voltage is not affected by a change in the degree of disturbance light or the like. Can be kept.

In the second information reading apparatus of the present invention, since the clamping means is provided with means for clamping at a predetermined timing for a predetermined number of scans, it is possible to prevent the center of gravity of the waveform from being shifted, and to always keep the constant. It is possible to clamp to a value.

Further, the third information reading apparatus of the present invention is provided with a means for preventing the data obtained by scanning when the clamping is performed from being performed by the clamping means. Can be prevented.

In a fourth information reading apparatus according to the present invention, the waveform processing means includes an operational amplifier and a comparator, and the clamp means determines a voltage within an allowable input range of the upper limit and the lower limit of the comparator and the operational amplifier as a clamp voltage. Therefore, the output waveform of the operational amplifier does not saturate even if it is affected by disturbance light or the like.

Also, in the fifth information reading apparatus of the present invention, the waveform processing means includes an AD converter, and the clamp means includes means for using the low-side reference voltage or the high-side reference voltage of the AD converter as a clamp voltage. By reproducing the DC component, multi-value digital conversion can be performed in absolute value.

Further, in the sixth information reading apparatus of the present invention, since the clamping means comprises at least a capacitor and a switch means, the clamping means can be realized with a simple configuration.

In the seventh information reading apparatus of the present invention, the clamping means includes means for clamping during the horizontal synchronizing period, the vertical synchronizing period, or the pedestal period, so that the absolute value contributes to accurate binarization. can do.

[Brief description of the drawings]

FIG. 1 is a diagram showing a waveform processing unit in a barcode reader according to a first embodiment of the present invention.

2A is a diagram showing a waveform at point a in FIG. 1; FIG. 2B is a diagram showing a waveform at point e; FIG. 2C is a diagram showing a waveform at point c; Diagram showing waveform

FIG. 3 is a diagram showing a waveform processing unit in a barcode reader according to a second embodiment of the present invention.

4A is a diagram showing a waveform at point f in FIG. 3; FIG. 4B is a diagram showing a waveform at point h in FIG. 3;

FIG. 5 is a diagram showing a configuration of a conventional barcode reader.

FIG. 6 is a diagram showing a configuration of the circuit unit.

FIG. 7 is a diagram showing first waveform processing means in a conventional barcode reader.

8A is a diagram showing a waveform of an output (point a in the circuit diagram) of the differential amplifier circuit in the conventional first waveform processing means. FIG. 8B is an output of the DC cut circuit (b in the circuit diagram). (C) shows the waveform of the output (point c in the circuit diagram) of the amplifier circuit. (D) shows the waveform of the output (point d in the circuit diagram) of the binarization circuit. Figure

FIG. 9 is a diagram showing a second waveform processing means in a conventional barcode reader.

10A is a diagram showing a waveform of an output (point f in the circuit diagram) of the area CCD in the second conventional waveform processing means. FIG. 10B is a diagram showing the output of the amplifier circuit (point g in the circuit diagram). FIG. 3C shows a waveform of an output (point h in the circuit diagram) of the binarization circuit.

11A is a diagram showing a waveform at point a in FIG. 7 when the conventional bar code reader is affected by disturbance light or the like; FIG. 11B is a diagram showing a waveform at point b in FIG. 7C; The figure which shows the waveform at the same c point (d) The figure which shows the waveform at the same d point

12A is a diagram showing a waveform at point f in FIG. 9 when the conventional bar code reader is affected by disturbance light or the like; FIG. 12B is a diagram showing a waveform at point g in FIG. 9C; Diagram showing waveform at point h

[Explanation of symbols]

 1a, 1b Emitter follower 2 Differential amplifier circuit 3 DC cut circuit 4 Amplifier circuit 5 Binarization circuit 6 Clamp circuit 7 DC cut circuit 8 Amplifier circuit 9 Binarization circuit 10 Clamp circuit 11 Bar code label 12 LED light source 13 Light receiving Reflecting mirror 14 Imaging lens 15 Linear CCD 16 Circuit section 17 Cable 18 Case 19 Waveform processing means 20 Storage means 21 Decoding means

Claims (7)

[Claims] 1. A light projecting means for irradiating light on a bar code label, an image forming means for receiving reflected light from the bar code label to form an image, and an image sensor for converting the bar code image into an electric signal. A waveform processing unit that performs a predetermined process on the image sensor output signal; and a decoding unit that decodes a barcode symbol based on image data output from the waveform processing unit. An information reading apparatus comprising: a clamp unit that fixes a part of the obtained signal to a clamp voltage that is a predetermined constant value, and relatively moves a subsequent signal based on the clamp voltage. 2. An information reading apparatus according to claim 1, wherein said clamping means comprises means for clamping at a timing once in predetermined scanning. 3. An information reading apparatus according to claim 1, wherein said clamping means does not decode data obtained by scanning when the clamping is performed. 4. The information according to claim 1, wherein the waveform processing means includes an operational amplifier and a comparator, and the clamp means includes means for setting a voltage within an allowable input range of an upper limit and a lower limit of the comparator and the operational amplifier as a clamp voltage. Reader. 5. The information reading apparatus according to claim 1, wherein the waveform processing means includes an AD converter, and the clamping means includes means for setting a low-voltage-side reference voltage or a high-voltage-side reference voltage of the AD converter to a clamp voltage. 6. An information reading apparatus according to claim 1, wherein said clamp means comprises at least a capacitor and a switch means. 7. An information reading apparatus according to claim 1, wherein said clamping means includes means for clamping during a horizontal synchronization period, a vertical synchronization period, or a pedestal period.