JP2752551B2 - Barcode scanner sensitivity adjustment circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensitivity adjusting circuit for a bar code scanner, and more particularly to a CCD adjusting method for a relatively short time.
(Charge storage device) The present invention relates to a sensitivity adjustment circuit of a bar code scanner for performing adjustment setting so that the light receiving sensitivity of a line sensor becomes an optimum value.

[0002]

2. Description of the Related Art Generally, C used for a bar code scanner is used.
The CD line sensor includes a photoelectric conversion unit including a large number of photodiodes, a charge storage unit including a capacitance of a PN junction of each of the photodiodes, and a charge transfer unit including a number of CCDs corresponding to each of the photodiodes. And The photoelectric conversion unit functions to convert light incident from the outside into a charge amount corresponding to the amount,
The charge storage unit temporarily stores the charge obtained by the photoelectric conversion unit, and acts to transfer the charge to the charge transfer unit all at once by applying a start pulse, and the charge transfer unit The charge transferred from the charge accumulating section is transferred one by one every time a clock pulse is applied, and is output from the CCD line sensor as a temporal serial signal.

In this case, the amplitude value of the output serial signal obtained from the CCD line sensor, that is, the light receiving sensitivity of the CCD line sensor depends on the amount of charge obtained by the photoelectric conversion unit and stored in the charge storage unit. And the charge amount is 1
It depends on the time from the application of one start pulse to the application of the next start pulse, that is, the so-called accumulation time.

[0004] Even if the light receiving sensitivity of the CCD line sensor is constant, the amplitude of the output serial signal depends on the operating environment of the CCD line sensor, specifically, the color of the printed bar code, the bar code, and the like. Is changed in accordance with the light reflectance of the paper surface on which is formed, the degree of ambient light intensity, the barcode reading distance, and the like.

On the other hand, the output serial signal of the CCD line sensor is binarized after being amplified. If the amplitude of the output serial signal is too large, the output serial signal saturates at the time of the amplification and is correctly binarized. If the processing cannot be performed and the amplitude of the output serial signal is too small, an appropriate threshold level cannot be obtained at the time of binarization, and similarly, the correct binarization processing cannot be performed. .

Therefore, in order to perform a correct binarization process on the output serial signal, the output serial signal must be adjusted according to its amplitude value.
In practice, it is necessary to appropriately adjust the light receiving sensitivity of the CCD line sensor in accordance with the usage environment of the CCD line sensor. In consideration of this, the sensitivity is adjusted appropriately.

FIG. 3 is a block diagram showing an example of a sensitivity adjustment circuit of a known bar code scanner.

In FIG. 3, 1 is an LED (light emitting diode) array, 2 is an LED drive circuit, 3 is a bar code,
Is a CCD line sensor, 5 is a startup circuit, 6 is an amplification circuit,
7 is a binarization circuit, 8 is a clock signal oscillation circuit, 9 is a decoding number counter, 10 is an accumulation time memory, 11 is an accumulation time comparison circuit, 12 is an accumulation time counter, 13 is a timing signal generation circuit, and 14 is the number of decodes. Comparison circuit, 15
Is a set value memory A, 16 is an address decoder, 17 is a decode circuit, 18 is a microcomputer (microcomputer), and 19 is an OR gate.

The LED array 1 has a configuration in which LEDs are arranged in a straight line, and projects red light onto the bar code 3. The LED drive circuit 2 drives the LED array 1 at a constant current, and the CCD line sensor 4 scans and detects reflected light from the bar code 3 and converts it into a serial electric signal. The starter circuit 5 activates each unit by a start signal, and stops each unit by a reset signal. The amplification circuit 6 amplifies the output serial signal from the CCD line sensor 4, and the binarization circuit 7 functions to convert the amplified serial signal into a digital binary signal. The clock signal oscillating circuit 8 supplies an operation clock signal to each section, and a frequency-divided sensor clock signal to the CCD line sensor 4, respectively.
Counts the number of times a decode NG signal occurs when decoding is impossible.

The storage time memory A10 stores a plurality of sensor clock numbers corresponding to the storage time of the CCD line sensor 4 in correspondence with addresses.
The accumulation time comparison circuit 11 compares the sensor clock value of the accumulation time memory 10 with the count value of the accumulation time counter 12, and outputs a pulse when the former value matches or exceeds the latter value, and simultaneously outputs a reset signal. Storage time counter 1
2 to act to reset its counter value. The accumulation time counter 12 includes a clock signal oscillation circuit 8
, The timing signal generation circuit 13 generates a start pulse in response to the pulse signal from the accumulation time comparison circuit 11, and the decoding number comparison circuit 14 The value is compared with the value in the set value memory A15, and when they match, an end signal is generated. Set value memory A15
Stores a fixed value corresponding to the number of decodes.
The address decoder 16 operates to select one of the stored values of the accumulation time memory A10 based on the count value of the decoding number counter 9. The decoding circuit 17
When the pulse width of the digital signal binarized by the binarization circuit 7 is measured and converted into character or numeric data corresponding to the combination of the pulse widths and supplied to the microcomputer 18, when the decoding process fails, It outputs a decode NG signal. The microcomputer 18 operates to control the operation of each unit, and the OR gate 19 supplies a reset signal to the start-up circuit 5.

The operation of the sensitivity adjusting circuit of the bar code scanner having the above configuration will be described with reference to the signal waveform diagrams of FIGS.

FIGS. 4A and 4B are signal waveform diagrams showing an example of the state of the signal of each section within one accumulation time. FIG. 4A shows a start pulse, FIG. 4B shows a clock signal, and FIG. An output serial signal, (d) is a sample and hold output of the output serial signal, and (e) is a clamp amplified output signal.

FIG. 5 is a signal waveform diagram showing an example of a signal state of each section when sensitivity adjustment is performed.
(A) is a start pulse, (b) is an output serial signal of the CCD line sensor 4, (c) is a clamp amplified output signal,
(D) is a binarized output signal.

At time t ₀ shown in FIG. 5, when the power is turned on to the bar code scanner, the microcomputer 18 supplies a start signal to the starting circuit 5, and the starting circuit 5 sends out a set signal to initialize each section. To the operating state. In this state, the clock signal oscillating circuit 8 sends out the operation clock signal to each part and outputs the sensor clock signal to C
It is supplied to the CD line sensor 4 and the accumulation time counter 12. The number-of-decodes counter 9 supplies an initial value (for example, 0) to the address decoder 16, and the address decoder 16 stores the accumulation time memory 10 corresponding to the initial value (for example, 0).
The storage time memory 10 supplies a value (for example, 100) corresponding to the set address to the storage time comparison circuit 11. Accumulation time counter 12
Counts the input sensor clock signal and supplies the count value to the accumulation time comparison circuit 11. When detecting that the count value of the accumulation time counter 12 exceeds the value (for example, 100) corresponding to the address, the accumulation time comparison circuit 11 sends a pulse signal to the timing signal generation circuit 13 and sends a reset signal to the accumulation time counter. 12 respectively. At this time, the timing signal generation circuit 13 supplies the first start pulse to the CCD line sensor 4 in response to the pulse signal. At the same time, the accumulation time counter 12 has its count value reset by the reset signal, and starts counting the sensor clock signal again.

At time t ₁ shown in FIG. 5, when the first start pulse is applied to the CCD line sensor 4, the CCD line sensor 4 reads the bar code 3 and outputs a serial signal. The serial signal is amplified by the amplifier circuit 6, converted into a digital signal by the binarizing circuit 7, and decoded by the decoding circuit 17.
However, the serial signal obtained by reading the bar code 3 is a signal when the charge accumulating portion of the CCD line sensor 4 is not charged between the time t ₀ and the time t _1. Therefore, its amplitude is extremely small and completely meaningless.
The decoding circuit 17 cannot generate regular character or numeric data in the output, and generates only a decoding NG signal. Next, the decode NG signal is supplied to the decode number counter 9, and the count value of the decode number counter 9 is increased by one (for example, 1).

When the decoding counter 9 outputs the increment value (for example, 1), the address decoder 16 sets the address of the storage time memory 10 corresponding to the increment value (for example, 1) in the same manner as described above. Then, the accumulation time memory 10 supplies a value (for example, 2500) corresponding to the set address to the accumulation time comparison circuit 11. Next, when the accumulation time comparison circuit 11 detects that the count value of the sensor clock signal in the accumulation time counter 12 exceeds a value (for example, 2500) corresponding to the address, the accumulation signal comparison circuit 11 outputs the pulse signal to the timing signal generation circuit 13. , A reset signal is supplied to the accumulation time counter 12. Also in this case, the timing signal generation circuit 13 supplies the second start pulse to the CCD line sensor 4 in response to the pulse signal, and the accumulation time counter 12 resets its count value by the reset signal, and Start counting the sensor clock signal.

At time t ₂ shown in FIG. 5, when the second start pulse is applied to the CCD line sensor 4,
As in the case described above, the CCD line sensor 4 reads the barcode 3 and outputs a serial signal. This serial signal is amplified by an amplifier circuit 6 and then binarized by a binarizing circuit 7.
Is converted into a digital signal, and is decoded by the decoding circuit 17. Meanwhile, the serial signals obtained by the reading of this barcode 3 is is in the storage time A shown in Figure 5 between the time t ₁ to time t _2, the storage time A is CCD until then Line sensor 4
The electric charge accumulated in the electric charge accumulating portion is swept out, the amplitude is extremely large, and
Since it is completely meaningless, the decoding circuit 17
Cannot generate regular character or numeric data in the output, and generates only the decoded NG signal. Next, the decoded NG signal is supplied to the decoding number counter 9 again, and the count value of the decoding number counter 9 is further increased by one (for example, 2).

In the following, the same as in the above case, the output of the increment value (for example, 2) in the decoding counter 9 and the address of the accumulation time memory 10 corresponding to the increment value (for example, 2) in the address decoder 16 are described. A value corresponding to the set address in the setting / accumulation time memory 10 (for example, 2500) is supplied to the accumulation time comparison circuit 11, and the count value of the sensor clock signal of the accumulation time counter 12 in the accumulation time comparison circuit 11 is equal to the address. (E.g., 2500) corresponding to the pulse signal and the reset signal generated from the accumulation time comparison circuit 11, and the timing signal generation circuit 13 generates a third start pulse based on the pulse signal. Generation and the accumulation time counter 12 based on the reset signal. Reset count value is performed, respectively.

At time t ₃ shown in FIG. 5, when the third start pulse is applied to the CCD line sensor 4,
As in the case described above, the CCD line sensor 4 reads the barcode 3 and outputs a serial signal. This serial signal is amplified by an amplifier circuit 6 and then binarized by a binarizing circuit 7.
Is converted into a digital signal, and is decoded by the decoding circuit 17. In this case, the serial signal obtained by reading the bar code 3 at this time is the one during the accumulation time B shown in FIG. 5 between the time t _{2 and the} time t ₃ , and the bar code 3 is read normally. However, since the setting of the light receiving sensitivity of the CCD line sensor 4 is still inadequate and the amplitude thereof is considerably small, the decoding circuit 17 outputs the regular character and numeral data again in the output. Cannot be generated, and only the decoded NG signal is generated as before. Next, the decoded NG signal obtained here is supplied again to the decoding number counter 9, and the count value of the decoding number counter 9 is further increased by one (for example, 3).

Similarly, every time a decode NG signal is generated from the decode circuit 17, the count value of the decode counter 9 is incremented by one. The count value of the sensor clock signal in the counter 12 is changed,
The storage time of the CD line sensor 4 is changed to a storage time C and a storage time D shown in FIG.

When a proper (optimal) decode signal is obtained at the output of the decode circuit 17, no decode NG signal is generated from the decode circuit 17, so that the count value of the decode counter 9 is set to the immediately preceding count value. Thereafter, the accumulation time of the CCD line sensor 4 is maintained at the accumulation time corresponding to the count value, and the CCD line sensor 4 is adjusted to the light receiving sensitivity corresponding to the accumulation time.

The decode N from the decode circuit 17
The count value of the decoding number counter 9 based on the G signal can be changed by a number determined by the set number (eg, 20) in the set value memory, for example, 20 times. When the adjustment of the light receiving sensitivity of the sensor 4 is not completed, the decoding number comparison circuit 14 generates an end signal, and this end signal is supplied as a reset signal to the starting circuit via the OR gate 19, so that the starting circuit 5 The operation of each section is stopped, and the apparatus enters a state of waiting for the next start signal from the microcomputer 18.

[0023]

However, in the impression adjusting circuit of the known bar code scanner, each time a decode NG signal is supplied, an accumulation time memory A is used.
Are sequentially selected, and the accumulation time of the CCD line sensor 4 is sequentially determined based on the value corresponding to the selected address (for example, accumulation time A, accumulation time B, accumulation time C,
Since the bar code scanner is changed little by little (as in the accumulation time D) and the bar code scanner is adjusted to the optimum sensitivity, the bar code 3 is scanned many times until the optimum sensitivity is adjusted. Usually, the reading time of the barcode 3 increases with an increase in the number of scans, and the operator feels uneasy or uneasy during the reading operation of the barcode 3. There's a problem.

An object of the present invention is to eliminate the above-mentioned problem, and an object of the present invention is to reduce the number of barcode scans when adjusting the sensitivity to an optimum value and reduce the time required for barcode reading. An object of the present invention is to provide a scanner sensitivity adjustment circuit.

[0025]

To SUMMARY OF THE INVENTION To achieve the above object, the present invention is, by changing the accumulation time of the line sensor, while rows that have the adjustment of the light-receiving sensitivity, be subject
In a sensitivity adjustment circuit of a bar code scanner for repeatedly reading a bar code, a peak detecting means for obtaining a white level peak value read by a line sensor ;
Analog-digital conversion means for converting a bell peak value into a digital value, wherein the target value of the white level peak and the storage value are stored.
The multiplication value with the product time is divided by the digital value, and the division is performed.
Means for determining the next accumulation time of the line sensor based on the calculated value .

[0026]

[0027]

According to the above means, a line sensor, for example, C
After amplifying the serial signal output from the CD line sensor, the peak level circuit holds the white level peak value in the peak hold circuit, and then converts the hold signal into a digital signal in the analog-to-digital conversion circuit.
A predetermined operation is performed on this digital signal, and the next accumulation time of the CCD line sensor is set based on the operation result.

By the way, the predetermined operation is to multiply the previously set accumulation time of the CCD line sensor by the target value of the white level peak value by using a target value memory, a multiplier, a divider and the like. The multiplication value is calculated by dividing the multiplication value by the digital signal indicating the measured white level peak value. If the accumulation time of the next CCD line sensor is set based on the value obtained by the calculation, the peak value is calculated. The white level peak value obtained in the hold circuit can be immediately converged to the vicinity of the target value.

As described above, according to the above means, the minimum number of barcode scans by the CCD line sensor is
The optimal accumulation time of the CCD line sensor, that is, the optimal adjustment sensitivity of the barcode scanner can be obtained.

If the time required for scanning and reading the barcode is reduced, the accumulation time of one scan can be increased, so that the light receiving sensitivity of the CCD line sensor is improved and the LED drive current is accordingly reduced. The value can be reduced.

[0031]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a sensitivity adjustment circuit of a bar code scanner according to the present invention.

In FIG. 1, reference numeral 20 denotes a peak hold circuit, 21 denotes an analog-digital (A / D) conversion circuit,
2 is a temporary storage circuit, 23 is a divider, 24 is an accumulation time memory B, 25 is a multiplier, 26 is a target value memory, 27 is a previous accumulation time memory, 28 is a switcher, 29 is a decoding number comparison circuit B, 30 Is the set value memory B , 31 is the storage time determination
The same components as those shown in FIG. 3 are denoted by the same reference numerals.

The configuration of the sensitivity adjustment circuit of this embodiment shown in FIG. 1, the configuration and the ratio of the known sensitivity adjustment circuit shown in FIG. 3
In other words, the storage time determining means indicated by a dotted line in FIG.
31 is a newly added storage time determining means.
31 is a peak hold circuit 20, analog-digital
(A / D) conversion circuit 21, temporary storage circuit 22, divider 2
3. Storage time memory B24, multiplier 25, target value memory
26, previous storage time memory 27, switch 28, decode
A number comparison circuit B29 and a set value memory B30 are provided.
You .

The peak hold circuit 20 holds the white level peak value of the serial signal obtained at the output of the amplifier circuit 6, and the A / D conversion circuit 21 outputs the white level peak value held by the peak hold circuit 20. The peak value is converted into a digital value, for example, a digital value D ₂₁ having a resolution of 8 bits, and the temporary storage circuit 22 temporarily stores the digital value D ₂₁ of the white level peak obtained in the A / D conversion circuit 21. Let it. The target value memory 26 stores the target value at the white level peak value as a digital value D ₂₆ , and the previous accumulation time memory 27 stores the previous accumulation time in association with the count value D ₂₇ of the sensor clock signal. ing. The multiplier 25 stores the digital value D ₂₆ stored in the target value memory ₂₆ and the previous accumulation time memory 27
Wherein multiplying the count value D _27, which is held, and outputs a digital value D ₂₅ obtained as a result of the multiplication. Divider 23, the output digital value D ₂₅ of the multiplier 25 is divided by the digital value D ₂₁ stored in the temporary storage circuit 22, and outputs a digital value D ₂₃ obtained as a result of the division. Accumulation time memory 24 stores the output digital value D ₂₃ of the divider 23. The switch 28 is switched to the terminal A in the initial state, but is switched to the terminal B by the supply of a switching signal from the decoding number comparison circuit B29. When the count value D ₉ of the decode number counter 9 becomes larger than the set value D ₃₀ of the set value memory B 30, the decode number comparison circuit B 29 supplies a switch signal to the switch 28.

Hereinafter, the operation of the sensitivity adjustment circuit of this embodiment will be described with reference to the signal waveform diagram of FIG.

FIG. 2 is a signal waveform diagram showing an example of a signal state of each section when sensitivity adjustment is performed.
(A) is a start pulse, (b) is an output serial signal of the CCD line sensor 4, (c) is a clamp amplified output signal,
(D) is a peak hold output signal of the peak hold circuit 20.

The configuration of the sensitivity adjustment circuit excluding the portion within the dotted line in FIG. 1 is the same as the configuration of the known sensitivity adjustment circuit in FIG. 3, and the sensitivity adjustment circuit excluding the portion within the dotted line in FIG. Is also partially the same as the operation of the known sensitivity adjustment circuit of FIG.

Here, in order to facilitate understanding of the operation of the sensitivity adjustment circuit of the present embodiment, the entire operation including the operation already described in the known sensitivity adjustment circuit of FIG. 3 will be described.

At time t ₀ , when the power is turned on to the bar code scanner, the microcomputer 18 supplies a start signal to the starting circuit 5, and the starting circuit 5 sends out a set signal to initialize each part to the operating state. I do. In this state,
The clock signal oscillating circuit 8 sends an operation clock signal to each section and supplies a sensor clock signal to the CCD line sensor 4 and the accumulation time counter 12. The decoding number counter 9 sets an initial value (for example, 0) to the address decoder 1.
6, the address decoder 16 sets the address of the storage time memory 10 corresponding to the initial value (for example, 0), and the storage time memory 10 stores the value (for example, 100) corresponding to the set address for the storage time. Comparison circuit 11
To supply. The accumulation time counter 12 counts the input sensor clock signal, and supplies this count value to the accumulation time comparison circuit 11. The accumulation time comparison circuit 11
When detecting that the count value of the accumulation time counter 12 exceeds a value (for example, 100) corresponding to the address, the pulse signal is supplied to the timing signal generation circuit 13 and the reset signal is supplied to the accumulation time counter 12, respectively.
At this time, the timing signal generation circuit 13 supplies the first start pulse to the CCD line sensor 4 in response to the pulse signal. At the same time, the accumulation time counter 12
The count value is reset by the reset signal, and the counting of the sensor clock signal is started again.

At time t ₂ , the CCD line sensor 4
When the second start pulse is applied to the CCD line sensor 4, the CCD line sensor 4 reads the bar code 3 and outputs a serial signal as in the case described above. The serial signal is amplified by the amplifier circuit 6, converted into a digital signal by the binarizing circuit 7, and decoded by the decoding circuit 17. By the way, the serial signal obtained by reading the bar code 3 at this time is equal to the time t _{1 to the} time t _2.
The accumulation time A is obtained by sweeping out the electric charges accumulated in the electric charge accumulating portion of the CCD line sensor 4 and has an extremely large amplitude. The decoding circuit 17 is unable to generate regular character or numeric data in the output again this time, and
Generates only G signal. Next, the decoded NG signal is supplied to the decoding number counter 9 again, and the count value of the decoding number counter 9 is further increased by one (for example, 2).

The following is the same as the above case, and the increment value (for example, 2) of the decoding number counter 9 is
To the address setting of the storage time memory 10 corresponding to the increase value (for example, 2) of the address decoder 16 and to the storage time comparison circuit 11 of the value (for example, 2500) corresponding to the set address of the storage time memory 10. The count value of the sensor clock signal of the supply and accumulation time counter 12 is a value (for example, 2500) corresponding to the address.
The generation of a pulse signal and a reset signal in the accumulation time comparison circuit 11 based on the fact that the accumulation time has been exceeded by the accumulation time comparison circuit 11, and the generation of a third start pulse from the timing signal generation circuit 13 based on the pulse signal , The count value of the accumulation time counter 12 is reset based on the reset signal.

At time t ₃ , the CCD line sensor 4
When the third start pulse is applied, the CCD line sensor 4 reads the bar code 3 and outputs a serial signal as in the case described above. The serial signal is amplified by the amplifier circuit 6, converted into a digital signal by the binarizing circuit 7, and decoded by the decoding circuit 17. In this case, the serial signal obtained by reading the bar code 3 at this time is the time t _{2 to the} time t _3.
, And even if the bar code 3 is normally read, the setting of the light receiving sensitivity of the CCD line sensor 4 is still insufficient, and the amplitude thereof is considerably small. Therefore, the decoding circuit 17 cannot generate regular character or numeric data in the output again this time, and generates only the decoded NG signal as before. Next, the decoded NG signal obtained here is supplied to the decoding number counter 9 again, and the count value of the decoding number counter 9 is further increased by one (for example, 3).

Similarly, every time a decode NG signal is generated from the decode circuit 17, the count value of the number-of-decodes counter 9 is incremented by one, and as the count value increases, the accumulation time increases. The count value of the sensor clock signal in the counter 12 is changed,
The storage time of the CD line sensor 4 is changed to a storage time C and a storage time D.

The operation up to this point is the same as the operation of the above-described known sensitivity adjustment circuit, but the operation described below is an operation specific to the sensitivity adjustment circuit of this embodiment.

Each time a serial signal obtained by reading the bar code 3 is output from the CCD line sensor 4, the serial signal amplified by the amplifier circuit 6 is supplied to the peak hold circuit 20, and the peak hold circuit 2
A white level peak value corresponding to the amplitude of the serial signal is obtained at an output of 0. Next, the white level peak value is A
The digital value D ₂₁ is converted into a digital value D ₂₁ indicating the white level peak in the / D conversion circuit 21, and the digital value D ₂₁ is temporarily stored in the temporary storage circuit 22.

Meanwhile, white the last storage memory 27 are stored output digital value D ₁₀ of the accumulation time memory A10, obtained immediately before at all times, in the multiplier 25, which is read from the target value memory 26 Level peak target value D ₂₆
If, with the digital value D ₁₀ read out from the storage time memory A10 are multiplied, the multiplication digital output D ₂₅ is obtained. Further, in the divider 23, the multiplication digital output D 25 from the multiplier ₂₅ is divided by the digital value D ₂₁ read from the temporary storage circuit 22, and the division digital output D ₂₃ obtained here is stored. It is temporarily stored in the time memory B24.

In addition, the decoding number comparison circuit B29
Includes a supply count D ₉ decode NG signal in the decoding counter 9, set value memory set value of B30 is compared with the D _30, the decode NG signal supplied count D ₉ is the set value memory B30 of exceeds the set value D _30, it supplies a switching signal to the switching unit 28. The switch 28 switches the previously connected contact from the terminal A side to the terminal B side by the supply of the switching signal, and the digital value D stored in the storage time memory B24 corresponding to the switching. ₂₃ is supplied to the accumulation time comparison circuit 11 and the previous accumulation time memory 27, and the stored contents thereof are updated.

[0049] In this case, in the accumulation time comparison circuit 11, the count value D ₁₂ of the sensor clock signal accumulation time counter 12 detects that exceeds a value corresponding to the digital value D _23, the accumulation time comparison circuit 11 Generate a pulse signal and a reset signal. Among them, the pulse signal is
The timing signal generating circuit 13 is energized to supply a start pulse to the CCD line sensor 4, and at the same time, a hold reset signal is supplied to the peak hold circuit 20 to release the hold state, and the set signal is sent to the temporary storage circuit 22. Supply and discard the stored contents. The reset signal is supplied to the accumulation time counter 12 to reset the count value.

Next, in the CCD line sensor 4, by supplying the start pulse, a serial signal obtained by reading the bar code 3 is again output. The circuit 20 supplies the peak hold circuit 20
, A white level peak value corresponding to the amplitude of the serial signal is obtained. Next, the white level peak value is calculated by A / D
The conversion circuit 21 converts the digital value into a digital value D ₂₁ indicating the white level peak, and the digital value D ₂₁ is temporarily stored in the temporary storage circuit 22 again.

At this time, since the digital value D ₂₃ read from the storage time memory B 24 is stored in the previous storage memory 27, the multiplier 25 sets the target value memory 26
The target value D ₂₆ of the white level peak read from, read from the storage time memory B24 the digital value D ₂₃
To generate a multiplication digital value D ₂₅ , and the divider 23 divides the multiplication digital value D ₂₅ from the multiplier ₂₅ by the digital value D ₂₁ read from the temporary storage circuit 22. updating the digital value D ₂₃ is obtained, the update digital value D ₂₃ is temporarily stored in the accumulation time memory B24.

After reading the updated digital value D ₂₃ stored in the storage time memory B 24, the switch 2
8 are supplied to the accumulation time comparison circuit 11 and the previous accumulation time memory 27, and the stored contents are updated, whereby the above-described operation is repeatedly executed.

During this series of operations, when a normal (optimal) decode signal is obtained as the output of the decode circuit 17, the hold output of the peak hold circuit 20 hardly changes thereafter, and Last storage memory 2
Since the digital value D ₂₃ stored in the 7 also will not be updated, as a result, have never digital value D ₂₃ stored in the storage time memory B24 is also updated. Therefore, the count value D of the sensor clock signal of the accumulation time counter 12
₁₂ also becomes constant, thereafter, the accumulation time of the CCD line sensor 4 is maintained so that the accumulation time corresponding to the count value D _12, the CCD line sensor 4 is adjusted to the light receiving sensitivity commensurate with the accumulation time Will be done.

Next, the reason why the sensitivity can be quickly converged to the target value by the calculation executed in this embodiment will be described using numerical values.

The operation executed in this embodiment is as shown in the following equation (1). In the following equation (1), Tn indicates the next accumulation time, Dt indicates the target value of the white level peak, Tg indicates the current accumulation time, and Dm indicates the measured value of the white level peak.

Tn = (Dt × Tg) / Dm (1) Here, for example, the input range of the white level peak value of the A / D conversion circuit 21 is 0 to 5 V, and the resolution is 8 bits. Assuming that the target value of the white level peak is 2.5 V, the data obtained by the A / D conversion is 128 V.
become. The frequency of the sensor clock signal at this time is 250 KHz (one sensor clock signal corresponds to 4 μsec).

Now, the white level peak value obtained by the latest scanning in the CCD line sensor 4 is 1.25 V
(The data obtained by the A / D conversion is 64), and the accumulation time of the CCD line sensor 4 at that time is 20 msec.
Assuming that c (for a 5K sensor clock signal, where 1 sensor clock signal is 4 μsec), then (128 × 5000) / 64 = 640000/64 = 10000 from equation (1), and the next start pulse is generated After the supply of the 10,000 sensor clock signal.

Then, the white level peak value obtained by the next scan of the CCD line sensor 4 by the supply of the next start pulse is 2.3 V (data obtained by A / D conversion is 117). Yes, CC at that time
Assuming that the accumulation time of the D-line sensor 4 is 40 msec (10 K sensor clock signal, where 1 sensor clock signal is 4 μsec), the expression (128) / 117 = 1280000/117 is obtained from Expression (1) as before. = 10940, and the generation of the next start pulse is 1094
After the supply of the 0 sensor clock signal.

Subsequently, the white level peak value obtained by the next scan of the CCD line sensor 4 by the supply of the next start pulse becomes 2.53 V (A
The data obtained by the / D conversion is 130), and the accumulation time of the CCD line sensor 4 at that time is 43.76 m
sec (1 sensor clock signal is 4 μsec, 1
0940 sensor clock signal), (128 × 10940) / 130 = 1400320/130 = 110771 from Expression (1) as before, and the generation of the next start pulse is 10771.
After the supply of the sensor clock signal.

As described above, according to the above calculation, after the light receiving sensitivity of the CCD line sensor 4 is converged at a stroke to a value near the target value, the target value is gradually increased until a decode output is obtained from the decode circuit 17. Since it is made to converge, it is possible to converge to the target value within a considerably short time as compared with the conventional sensitivity adjustment of this kind, and usually, it converges to a value near the target value at a stretch. sometimes,
In many cases, a decode output is obtained from the decode circuit 17.

As described above, according to this embodiment, the CCD
The light receiving sensitivity of the line sensor 4, that is, the sensitivity of the barcode scanner can be converged to the optimum value in a very short time, and the number of scans of the CCD line sensor 4 when obtaining the optimum value can be reduced. As a result, the operator does not feel uncomfortable or uneasy.

Further, according to the present embodiment, the number of times of reading and scanning of the bar code 3 can be reduced, so that the accumulation time can be increased and the sensitivity can be improved. Can be reduced.

Further, according to the present embodiment, the peak level of the white level is held, and the hold signal is set to A during the accumulation time.
Since the A / D conversion is performed, a sufficient conversion time can be taken, a low-speed A / D conversion circuit 21 can be used, and a barcode scanner can be configured at low cost. Becomes possible.

In the above embodiment, the case where a CCD line sensor is used as the line sensor 4 has been described. However, the present invention is not limited to the case where a CCD line sensor is used. The same can be applied to the used ones.

[0065]

As described above, according to the present invention,
The light receiving sensitivity of the line sensor 4, that is, the sensitivity of the bar code scanner can be adjusted to converge to the optimum value in a very short time, and the bar code 3 is read and scanned by the line sensor 4 when obtaining the optimum value. Since the number of times can be reduced, there is an effect that the operator does not feel uncomfortable or uneasy.

Further, according to the present invention, the number of times the bar code 3 is read and scanned by the line sensor 4 when obtaining the optimum value can be reduced, so that the accumulation time can be lengthened and the sensitivity can be improved. Therefore, there is an effect that the LED drive current can be reduced by the length of the accumulation time.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a sensitivity adjustment circuit of a barcode scanner according to the present invention.

FIG. 2 is a signal waveform diagram showing an example of a signal state of each unit when sensitivity adjustment is performed in the sensitivity adjustment circuit shown in FIG.

FIG. 3 is a block diagram showing an example of a sensitivity adjustment circuit of a known barcode scanner.

4 is a signal waveform diagram illustrating an example of a state of a signal of each unit within one accumulation time of the sensitivity adjustment circuit illustrated in FIG. 3;

5 is a signal waveform diagram showing an example of a signal state of each unit when sensitivity adjustment is performed in the sensitivity adjustment circuit shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 LED (light emitting diode) array 2 LED drive circuit 3 Barcode 4 CCD line sensor 5 Starting circuit 6 Amplifying circuit 7 Binarization circuit 8 Clock signal oscillation circuit 9 Decoding number counter 10 Storage time memory 11 Storage time comparison circuit 12 Storage time Counter 13 Timing signal generation circuit 14 Decoding count comparison circuit 15 Set value memory A 16 Address decoder 17 Decoding circuit 18 Microcomputer (microcomputer) 19 OR gate 20 Peak hold circuit 21 Analog-digital (A / D) conversion circuit 22 Temporary storage circuit 23 Divider 24 Storage time memory B 25 Multiplier 26 Target value memory 27 Previous storage time memory 28 Switching device 29 Decode times comparison circuit B 30 Set value memory B 31 Storage time setting means

Claims (1)

(57) [Claims] By changing the 1. A storage time of the line sensor, without leaving rows adjustment of the light-receiving sensitivity, be subject
In a sensitivity adjustment circuit of a bar code scanner for repeatedly reading a bar code, a peak detecting means for obtaining a white level peak value read by a line sensor ;
Analog-digital conversion means for converting a bell peak value into a digital value, wherein the target value of the white level peak and the storage value are stored.
The multiplication value with the product time is divided by the digital value, and the division is performed.
A sensitivity adjustment circuit for a bar code scanner, comprising: accumulation time determining means for determining a next accumulation time of the line sensor based on a calculated value .