JP2655301B2 - Optical information reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The invention of this application relates to bar codes,
Optical information readers for reading optical information such as characters in general, especially when reading bar codes etc. printed on labels etc., achieve a high reading rate even if there is a transient instantaneous change of disturbance light. Optical information reading device capable of
Wide dynamic range to be used in coded information readers
The present invention relates to a clean slice circuit .

[0002]

2. Description of the Related Art An optical information reading apparatus reads optical information such as bar codes and characters recorded on a recording medium such as a label. A typical and typical example of the optical information reading device is a bar code reader. A bar code reader generally includes a light source, a mirror, an imaging optical system, a line image sensor, an arithmetic circuit, and the like, as shown in FIGS. A slice circuit is used as the arithmetic circuit. 2. Description of the Related Art Conventionally, a slice circuit has a diode tracking slice type and a center slice type.

FIG. 9 shows a diode-following slice type.
The following circuit configuration is conceivable. In the circuit of FIG.
A pair of diodes (d ₁ , d ₂ ) and a smoothing circuit (C, R) connected in anti-parallel form a slice signal generation circuit. The output voltage of this circuit is the charge / discharge voltage of the peak hold capacitor C. Discharge voltage of the peak hold capacitor C in the steady state, at the time of charging, than the analog signal voltage, the forward threshold voltage of the diode d ₂ (hereinafter referred to as "VF value".) As low, at the time of discharge, the diode d ₁ VF value . Therefore, in the steady state, the tracking performance is good even for analog signals from high-resolution barcode symbols (barcode symbols having a small minimum bar width).

A circuit configuration as shown in FIG. 10 is conceivable as a center slice type. In the circuit of FIG. 10 , the circuit elements A ₁ , C, R, A ₂ , C, R ₁ , R ₂ constitute a slice signal generation circuit. In a steady state, the output voltage of the slice signal generating circuit has a substantially center value between the peak voltage value corresponding to the white line bar and the peak voltage value corresponding to the black line bar. Therefore, there is no influence of cracked bar noise or paper surface noise.

[0005]

2. Description of the Related Art The diode-following slice circuit has the following problems or disadvantages. (A) The bandwidth of the slicable signal is determined by the smoothing circuit ( C ,
R ) depends on and is limited by the time constant CR . Therefore, the circuit characteristics are narrow. (B) Since the time constant CR is fixed, when there is a sudden change of disturbance light or the like, it is impossible to accurately follow a sudden change in signal amplitude and frequency caused by the sudden change. . For this reason, the output TTL signal becomes inaccurate, and there is a high possibility that erroneous reading will occur.

(C) In order to increase the rate of change of the output voltage of the smoothing circuit (C, R), not only the time constant CR of itself but also the VF value of the diodes d ₁ and d ₂ need to be reduced. Must be small. Therefore, in order to slice an analog signal from a high-resolution bar code, the value of the peak hold capacitor C must be reduced, and the VF value must be reduced. However, this makes the slicing operation more susceptible to the cracked bar noise and paper surface noise. (D) Conversely, when both the VF value and the time constant CR are increased, a bar code signal including a narrow and small amplitude signal pulse is obtained.
For example, a slice operation is performed on an analog signal from a bar code having a low resolution ratio (a small analog signal having an amplitude of an analog signal from a bar having a minimum bar width / an amplitude of an analog signal from a bar having a maximum bar width × 100 (%)). Becomes inaccurate. (E) Since the rising slope of the slice signal is gentle, the black bar at the end of the bar code cannot be identified. Therefore, the electrically readable barcode length is shorter than the optically readable barcode length. (F) PCS (print contrast sig)
When the nal) value is low, the barcode length that can be electrically read becomes even shorter. (Here, the PCS value is a value indicating the degree of relative density between the printed figure and the paper.)

The center slice type circuit has the following problems or disadvantages. (W) At the start of each scanning, the paper surface is scanned first, but the slice signal at that time is almost the same as the analog signal, so that the TTL signal corresponding to the first bar is distorted. That is, the pulse width is larger than the correct value. (F) When disturbance light is strong or when PCS (print
When contras ts ignal) value is low, because the whole bar code signal approaches the extreme white level slice signal follows the bar code signal hesitation. (G) a bar code signal including a narrow and small amplitude signal pulse,
For example, for an analog signal from a bar code having a low resolution ratio, the slice operation becomes inaccurate. (T) The electrically readable barcode length is shorter than the optically readable barcode length. (V) When the PCS value is low, the electrically readable barcode length becomes even shorter.

[0008]

SUMMARY OF THE INVENTION It is, therefore, a first object of the present invention to provide an optical information reading apparatus which solves the above-mentioned drawbacks and has a simple structure and a high reading rate. A second object of the invention of this application, even for transient MatoMadoka time variation of the analog signals derived from the sudden instantaneous change of disturbance light such as, while maintaining a predetermined differential voltage, follow the wide dynamic Can,
An object of the present invention is to provide a wide dynamic range slice circuit. A third object of the invention of this application is to reduce the leakage current of the peak rectification hold circuit in the slice signal generation circuit to zero, improve the holding capacity of the peak value, and reduce the time constant of the peak hold capacitor to zero. An object of the present invention is to achieve a wide band of a slice signal generating circuit.

[0009]

In order to achieve the above object, in the optical information reading apparatus according to the present invention, a transient instantaneous change of an analog signal resulting from a sudden instantaneous change of disturbance light or the like is suppressed. Even if it occurs, a new and unique wide dynamic range slicing circuit that can follow a wide dynamic while maintaining a predetermined difference voltage is used.
In the above wide dynamic range slice circuit,
A new and unique slice signal generation circuit in which a forward peak rectification hold circuit, a reverse peak rectification hold circuit, and a series-connected diode pair are connected in a loop, and the middle point of the series-connected diode pair is set as an output point. Is used. A diode having a significant forward rising voltage value VF is used as the series-connected diode pair. No resistance component is connected to the peak hold capacitors in the forward and reverse peak rectification hold circuits.

[0010]

In the optical information reading apparatus according to the present invention, when the amplitude value of the analog signal (bar code signal) from the optical sensor changes, the amplitude value of the slice signal automatically follows the change. Change. Moreover, this change has no time delay. That is, if the analog signal (barcode signal) from the optical sensor changes from the black level peak value to the white level peak value, the slice signal automatically follows the new signal without delay, and the new peak signal is generated. Transition to a value (Relation 1). After the end of the transition operation, the new peak value of the slice signal is a predetermined value (a voltage value corresponding to the forward rising voltage value of the used diode element = VF value) higher than the white level peak value of the analog signal.
(Relationship 2).

Conversely, if the analog signal (bar code signal) from the optical sensor transitions from the peak value of the white level to the peak value of the black level, the slice signal automatically follows the slice signal without delay. , Transition to a new peak value (relation 1 '). After the end of the transition operation, the new peak value of the slice signal becomes a value larger than the black level peak value of the analog signal by a predetermined value (a voltage value corresponding to the forward rising voltage value of the used diode element = VF value). (Relation 2 '). The analog signal and the slice signal intersect once during the transition of the analog signal from the white level peak value to the black level peak value, and again intersect during the transition from the black level peak value to the white level peak value. Then, the same process is repeated.

The above relations indicate that the white level signal duration and the black level signal duration are very short, that is, the frequency is high, and that the amplitude of the white level signal and / or the black level signal suddenly increases and decreases greatly. In this case, even when the disturbance light suddenly increases or decreases greatly, it is completely preserved. Therefore,
The slice circuit according to the invention of this application can correctly convert an incoming analog signal (bar code signal) into a TTL signal (logic high signal or logic low signal) regardless of the frequency. In addition, it can be correctly converted to a TTL signal regardless of a sudden change in the amplitude level. Further, small-amplitude paper noise (negative-polarity small-amplitude noise caused by spots, stains, poor paper quality, etc.) superimposed on the white level signal, and spike-shaped cracked bar noise superimposed on the black level signal (dot printer) even small amplitude minute duration noise) or the like of the positive polarity due to void portion in cracks bars derived from equal, it is possible to sufficiently follow. Therefore, even if there is a noise component as described above, there is no possibility of erroneous conversion.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a bar code reader as a typical example of the invention of this application will be described in detail. FIG. 7 is an overall configuration diagram of a bar code reader according to an embodiment of the present invention, and FIG. 8 is an optical path diagram thereof. 7 and 8, 1 is a housing, 2 is a plurality of light sources, 3 is a mirror, 4
Is an image forming optical system, 5 is a line image sensor (one-dimensional light receiving element), and 6 is an arithmetic circuit unit. Multiple light sources 2
Is as shown in FIG. 8, are arranged in a horizontal clear distinction shape and is disposed inside the housing 1. The plurality of light sources 2 irradiate the barcode label L with illumination light. The illumination light 21 and disturbance light (environmental light) are reflected by the barcode label L,
It becomes reflected light. A part 22 of the reflected light is re-reflected by the mirror 3 and changes the reflection direction. An imaging optical system 4 is provided in the traveling direction of the re-reflected light 23 from the mirror 3.
A line image sensor (one-dimensional light receiving element) 5 is provided downstream of the imaging optical system 4. The line image sensor (one-dimensional light receiving element) 5 is, as is well known to those skilled in the art, a charge coupled device (CCD).
device). The output terminal of the line image sensor (one-dimensional light receiving element) 5 includes an arithmetic circuit unit 6
Is connected.

In general, a front amplifier circuit, a slice circuit and the like are connected inside the arithmetic circuit section 6. The front amplification circuit receives an electric analog signal (bar code signal) output from the line image sensor (one-dimensional light receiving element) 5 and amplifies the signal. The slice circuit
In response to the incoming electric analog signal (bar code signal), the electric analog signal derived from the black bar symbol is converted to a “logic 1” level, and the electric analog signal derived from the white bar symbol is converted to “logic 0”. To a level. According to the invention of this application, a new and unique wide dynamic range slice circuit is adopted as the slice circuit. The wide dynamic range slicing circuit according to the invention of the present application causes the instantaneous change of disturbance light or the like while preserving the relations 1 and 1 'and the relations 2 and 2' (see the section of "Function of the Invention"). It is possible to dynamically follow a transient change of an analog signal (bar code signal).

FIG. 1 is an electrical connection diagram showing a first embodiment of a slice circuit according to the present invention. In FIG. 1, ID ₁ and ID ₂ are ideal diodes, 61 and 61 are peak hold capacitors, and 62 and 62 are diodes. These elements cooperate to form a slice signal generation circuit. The forward ideal diode ID ₁ includes an operational amplifier A ₁ and a forward FET pseudo diode 64. Forward ideal diode ID ₁ and peak holding capacitor 61 and the forward peak rectifier hold circuit (I
D ₁ , 61). FET pseudo diode 64
Is an FET connected as a diode,
To reduce leakage current, the peak hold capacitor 6
1 enables a more accurate hold of the peak value.

The reverse ideal diode ID ₂ comprises an operational amplifier A ₂ and a reverse FET pseudo diode 64. The reverse ideal diode rectifier hold circuit (I) includes the reverse ideal diode ID ₂ and the peak hold capacitor 61.
D ₂ , 61). A pair of diodes 62 and 6
2 are connected in series. Ideal diode ID ₂ , I
D ₂ via a series connected diodes 62 and 62 are connected in a loop. The input terminal of the slice signal generation circuit is a common connection point of the + terminals of the operational amplifiers A ₁ and A ₂ , and the output terminal is the middle point of the diodes 62 and 62.
The DC power supply VCC can be omitted.

In the slice circuit of FIG. 1, the slice signal voltage at the input terminal of the comparator can automatically follow the analog signal voltage (solid line) without time delay as shown in FIG. . The difference voltage b between the two signals is maintained at a constant value VF without a time delay. The details are as described below. When a large amplitude analog signal corresponding to the paper itself or the white line bar arrives, the ideal diode ID
₁ conducts, and through this, the peak hold capacitor 61 connected thereto, that is, the upper capacitor 61 in the drawing is instantaneously charged without time delay. The terminal voltage of the upper capacitor 61 becomes the same as the analog signal voltage. When the analog signal voltage reaches the peak value, ideal diode ID ₁ becomes non conduction subsequent peak value is held in the upper capacitor 61 (relationship 1). During this time, ideal diode ID ₂ is a non-conductive, the terminal voltage of the upper capacitor 61 Ya exceeds {(2 times the VF value) + (holding voltage lower capacitor 61)} whether or lower capacitor 61 is also charged via diodes 62,62. The terminal voltage of the lower capacitor 61 is naturally lower than the terminal voltage of the upper capacitor 61 by twice the VF value.
Until the analog signal voltage reaches the peak value, the potential at the midpoint of the diodes 62, that is, the output voltage of the slice signal generating circuit, is lower than the holding voltage of the upper capacitor by the VF value of the diode 62. Therefore, referring to FIG. 3, the difference voltage b between the analog signal voltage (solid line) and the slice signal voltage (dashed line) at the comparator input terminal is maintained at a substantially constant value VF (relation 2). ).

Next, the analog signal is arrived corresponding to the black line bar, its voltage becomes smaller than the holding voltage of the lower capacitor 61, it becomes conductive ideal diode ID _2, through which the lower Is discharged instantaneously without time delay. The terminal voltage of the lower capacitor 61 becomes the same as the analog signal voltage corresponding to the black line bar. Analog signal voltage is the minimum value reaches the (peak value), the ideal diode ID ₂ becomes nonconductive subsequent, the minimum value will be retained in the lower capacitor 61 (relationship 1 '). During this time, ideal diode ID ₁ is the terminal voltage of the lower capacitor 61 is non-conductive - dividing Ya not <br/> and a {(voltage held by the upper capacitor 61) (2 times the VF value)}, The upper capacitor 61 also discharges via the diodes 62,62. The holding voltage of the upper capacitor 61 is naturally higher than the terminal voltage of the lower capacitor 61 by twice the VF value. Until the analog signal voltage reaches a minimum value (peak value), the potential at the midpoint of the diodes 62, that is, the output voltage of the slice signal generating circuit, is higher than the holding voltage of the lower capacitor by the VF value of the diode 62. Naturally high by the minute. Therefore, the voltage of the difference between the analog signal voltage at the comparator input terminal and the slice signal voltage is maintained at a substantially constant value VF (relation 2 '). Then, the same process is repeated until the scanning is completed.

The signal waveform diagrams of FIGS. 3 to 6 will be described. FIG. 3 is a signal waveform diagram when the amplitude of the analog signal is large. In this case, the slice signal waveform maintains the peak hold value a and the difference between the slice signal waveform and the analog signal voltage.
This is a waveform approaching a diode-following type while keeping the voltage constant . FIG. 4 is a signal waveform diagram when the amplitude of the analog signal is small. The signal waveform in this case is a waveform approaching the center slice shape while maintaining the peak hold value a.

FIG. 5 is a signal waveform diagram when the analog signal changes transiently due to an instantaneous change such as disturbance light. This indicates that the slice signal follows the analog signal in a wide dynamic manner while holding the peak hold value a and keeping the voltage of the difference from the analog signal voltage constant. FIG. 6 is a signal waveform diagram in the case where paper noise and cracked bar noise are superimposed on the analog signal. This shows that the slice signal follows these noises as a result of widening the band.

FIG. 2 is an electrical connection diagram showing a second embodiment of the slice circuit according to the present invention. This circuit, the circuit in FIG. 1, and the offset signal generating means,
An exclusive NOR circuit ExNOR is added, and the series-connected diodes 62, 62 also operate as diode switches. The offset signal generating means includes:
As shown, an offset signal voltage source, a knot circuit,
And a resistor 63. Off from the offset signal voltage source
The offset signal generation terminal is led out, and the anti-knot of the resistor 63 is
The inverted offset signal generation terminal is derived from the circuit side terminal.
It is. The exclusive NOR circuit ExNOR outputs an H level (logic 1) only when both inputs are at H level or when both inputs are at L level (logic 0). When the offset signal voltage is at H level (logic 1), the output of the exclusive NOR circuit ExNOR is also at H level if the output of the comparator is at H level, and the exclusive NOR circuit Ex is output if the output of the comparator is at L level.
Since the output of NOR also becomes L level, the corresponding relationship between the white level, black level and logic symbols does not change. However, when the offset signal voltage is at L level (logic 0 ), the exclusive NOR circuit ExNOR is output when the output of the comparator is at L level.
Is at the H level, and when the output of the comparator is at the H level, the output of the exclusive NOR circuit ExNOR is at the L level. Therefore, the correspondence between the white level and the black level and the logic symbol is inverted.

Therefore, if it is assumed that a normal bar code of a black bar can be read on a white background when the offset signal voltage is at H level (logic 1), the offset signal voltage is at L level (logic 0). , It is possible to read an inverted bar code of a white bar on a black background. Further, when the offset signal voltage is continuously supplied to the exclusive NOR circuit ExNOR in an alternating manner, automatic reading of both the normal bar code and the inverted bar code becomes possible. Inverted voltage of the offset signal voltage (from the offset signal voltage source, the knot circuit (inverter) and the resistor 63
And the signal voltage applied to the intermediate connection point of the series-connected diode pair (62, 62). The series-connected diodes (62, 62) are operated as diode switches by the cooperation of this voltage and ground or the DC power supply VCC. If the hold voltage of the forward peak rectification hold circuit (ID ₁ , 61) does not exceed this voltage + VF value, the upper diode 61
Does not conduct, and the reverse peak rectification hold circuit (I
D _2, 61) hold voltage is the voltage of - if to break the VF value, lower side of the diode 61 does not conduct. As a result, the increase in the time constant of the peak hold capacitor 61 and the fixation thereof are avoided irrespective of the connection of the resistor 63. The inverted signal of the offset signal supplied to the intermediate connection point between the diode switches (62, 62) determines the spatial level logic (H, L).

[0023]

The main effects of the invention of this application are as follows. Eliminates leakage current (a) a peak rectifier hold circuit almost becomes constant substantially zero when the peak-hold capacitor 61, whereby is achieved broadband, the peak value despite the constant depleted when the peak holding capacitor 61 Holding capacity is increased. (B) The slice signal voltage (broken line) is an analog signal voltage (solid line) caused by an instantaneous change of disturbance light or the like as shown in FIG.
Can be followed in a wide dynamic manner while maintaining the peak hold value a. (C) As shown in FIG. 3, the slice signal voltage (broken line) is a constant voltage b (= V
F), it changes automatically following the amplitude change. Therefore, unlike the diode-following type, as shown in FIGS.

(D) Accurate slicing of the first pulse was made possible by reducing the fixed time constant. Therefore, for all bars within the optical angle of view (optical field of view), the PCS
Complete reading was possible even with small values. (E) As a result of the above (a) , for analog signals of various amplitudes and frequencies generated from barcodes from high resolution to low resolution (for example, 0.07 mm to 1.00 mm),
Slicing is now possible. (F) Since the slice signal (broken line) has a wide band, as shown in FIG. 6, it is possible to follow a paper noise with a small amplitude and a crack bar noise. (G) It is possible to cope over a wide range of scanning speeds (for example, 33 scans / sec to 100 scans / sec) without changing the constant of the peak hold capacitor 61.

[Brief description of the drawings]

FIG. 1 is an electrical connection diagram showing a first embodiment of a slice circuit according to the present invention.

FIG. 2 is an electrical connection diagram showing a second embodiment of the slice circuit according to the present invention.

FIG. 3 is a signal waveform diagram when the amplitude of an incoming analog signal is large in the embodiment of FIG.

4 is a signal waveform diagram when the amplitude of an incoming analog signal is small in the embodiment of FIG.

FIG. 5 is a signal waveform diagram when the amplitude of an incoming analog signal changes drastically due to disturbance light in the embodiment of FIG.

FIG. 6 is a signal waveform diagram when an incoming analog signal includes a page noise and a broken bar noise in the embodiment of FIG. 1;

FIG. 7 is an overall configuration diagram showing an embodiment of an optical information reading device according to the invention of this application.

8 is an optical path diagram of the embodiment of FIG 7.

FIG. 9 is a diagram illustrating the operation of the diode-following slice circuit.

FIG. 10 is a diagram illustrating the operation of the center slice circuit.

[Explanation of symbols]

The first housing 2 light sources 21 illuminating light 22 reflected light 23 re-reflected light 3 mirror 4 the image-forming optical system 5 optical sensor (e.g., a line image sensor) 6 arithmetic circuit unit 61 Peak holding capacitor 62 diode 63 resistor 64 FET emulated diode L Reading member ID ₁ Ideal diode ID ₂ Ideal diode ExNOR Exclusive NOR circuit GND Ground VCC DC power supply

Claims (3)

(57) [Claims] A member to be read (L) on which information to be read is recorded.
A member-to-be-reader irradiating means (2) for irradiating light; an image-forming optical system (4) for forming a light image reflected from the member-to-be-read (L) at a predetermined position; An optical sensor (5) disposed downstream of the system (4) for converting the optical image into an electrical analog signal; and an arithmetic circuit unit (6) connected to an output terminal of the optical sensor (5) The arithmetic circuit section (6) includes a wide band wide dynamic range slice circuit, and the wide band wide dynamic range slice circuit includes
A chair signal generation circuit and a comparator, wherein the slice signal generation circuit includes an analog signal input point;
Forward peak rectification hold circuit (ID ₁ , 61) and reverse
Direction peak rectification hold circuit (ID ₂ , 61), in series
Connection diode pair (62, 62) and slice signal output
And the series-connected diode pair (62, 6
2) is the forward peak rectification hold circuit (ID ₁ ,
61) and the above reverse peak rectification hold circuit
(ID ₂ , 61), and the slice signal output point is connected to the series-connected diode pair.
One of the input terminals of the comparator is integrated with the intermediate connection point of (62, 62).
The other input terminal is connected to the slice signal output
An optical information reader connected to the point of force . 2. A slice signal generation circuit comprising: an analog signal input terminal; a slice signal generation circuit; a comparator; and a TTL signal output terminal.
It comprises a forward peak rectification hold circuit (ID ₁ , 61), a reverse peak rectification hold circuit (ID ₂ , 61), a series-connected diode pair (62, 62), and a slice signal output point. Peak rectification hold circuit (I
D ₁ , 61) comprises only a forward ideal diode (ID ₁ ) and a peak hold capacitor (61), and includes the reverse peak rectifier hold circuit (ID ₂ , 61).
Consists of only a reverse ideal diode (ID ₂ ) and a peak hold capacitor (61), and the two diodes (62) and (62) constituting the series-connected diode pair (62, 62) are both in the forward direction. The anode at one end of the series-connected diode pair (62, 62) is connected to a forward peak rectification hold circuit (I
D ₁ , 61) is directly connected to the peak hold capacitor (61), and the other end of the cathode is directly connected to the peak hold capacitor (61) of the reverse peak rectifier hold circuit (ID ₂ , 61), An input terminal of the peak rectification hold circuit (ID ₁ , 61) and the reverse peak rectification hold circuit (ID
₂ , 61) are connected to the analog signal input point, and an intermediate connection point between the series-connected diode pair (62, 62) is integrated with the slice signal output point; one input terminal of which is connected to the analog signal input terminal, the other input terminal is connected to the slice signal output point, an output terminal, that is integrated with the TTL signal output terminal, coding Wideband wide dynamic range slice circuit for information reader. 3. An exclusive logical NOR circuit ( ExNOR ) and an offset signal generating means are added to the wide band wide dynamic range slice circuit for an encoded information reading device according to claim 2 , wherein the exclusive logical NOR circuit is provided. One input terminal of the circuit ( ExNOR ) is connected to the output terminal of the comparator, the other input terminal is connected to the offset signal generation terminal of the offset signal generation means, and the output terminal is a TTL signal output terminal. At the intermediate connection point of the diode pair (62, 62),
A wide-band wide dynamic range slicing circuit for an encoded information reading device, wherein an inverted voltage of an offset signal voltage is supplied from an inverted offset signal generating terminal of an offset signal generating means, and the diode pair (62, 62) operates also as a diode switch. .