JPS60157676A - Device for detecting mark - Google Patents

Abstract

PURPOSE:To detect accurately a mark without requiring adjustment by differentiating a sensor output signal, identifying the level of a differentiated signal, and removing noise components. CONSTITUTION:A differentiator 5 differentiates a sensor output signal a', then a differential signal b' is obtained. A peak detector 6 obtains a peak detection signal d' from a comparator 8. While comparators 9 and 10 slices a signal b' with slice levels (+TH) and (-TH), and generates output signals e' and f'. These signals e' and f' are fed to an NOR circuit 15 in a shaping circuit 7 to form a set signal g'. While a signal d' is fed to a latch circuit 14 and sets the circuit 14 to a condition in correspondence with the level of the signal d' when the signal g' is turned on. The circuit 14 holds the condition directly before an off period when the signal g' is in the off period, which makes noise fail to actuate the circuit 14 ignoring the noise, thus a correctly shaped signal h' is obtained from the circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a detection device for a mark such as a bar code, and more particularly to a device for detecting a mark signal with high precision from a mark sensor output signal containing noise and offset.

[Technology background]

A general barcode reader is configured so that reflected light obtained by optically scanning a barcode surface is converted into an electrical signal using an optical sensor. The all-at-once signal output from this optical sensor is amplified and then waveform-shaped by slicing or the like. this is.

To remove shadows 11 such as noise components contained in a signal, offset components due to bias, etc., and make it possible to correctly extract barcode information.

Next, the amplification method and slice method in the barcode reader will be explained.

There are two types of amplification methods: DC coupled amplifier type and AC coupled amplifier type. Although the DC-coupled amplifier type can completely reproduce the C component, it has a small margin against characteristic changes such as deterioration or bias changes in the light source or optical sensor of the barcode reader.

Regular level adjustments are required. In addition, although the AC coupled amplifier type does not require adjustment for changes over time, it has the disadvantage that the amplitude center varies between one signal and subsequent signals, and the margin for the first signal is small. Ta. Figure 1 shows a comparison of the signals of the two types of amplifiers mentioned above. Figure (α) is an example of a barcode. Figure (b) is a D
Output Signal of C-Coupled Amplifier 1 Figure (C) shows the output signal of an AC-coupled amplifier.

On the other hand, the main slicing methods include fixed slicing and floating slicing.

FIG. 2 shows an example of waveform shaping using the fixed slice method. A fixed slice level ES for the input signal
is set, and the signal portion applied to this slice level is output as a pulse.

The disadvantage of this method is that when the spatial frequency of the barcode (barcode density) increases, the level of the sensor output signal, that is, the input signal in the figure, decreases as shown in Pi and P2, and the output pulse width becomes narrower. In some cases, P6. P? If the slice level is below E3, it will not be detected and an error will occur. Furthermore, this situation is also affected by changes in the amount of offset in the signal due to aging of the barcode league or changes in the environment in which it is used.

The floating slice method improves on the drawbacks of the fixed slice method described above, and an example thereof is shown in FIG. As shown in the figure, the slice level is changed according to the level of the input signal (2), and as the slice signal S, a signal obtained by integrating the input signal with a time constant circuit is used. 9. The disadvantage of this method is that when the spatial frequency of the barcode is low, the level difference between the input signal and the slice signal is small. As the S/N margin decreases and the slice point changes depending on the spatial frequency, in a signal with a high spatial frequency, the slice level passes near the amplitude center as shown in Figure 4 (α), and the spatial frequency increases. For low signal, Fig. 4 (h
), the slice level is close to the upper and lower limits of the amplitude, and as a result, the signal at the boundary where the spatial frequency changes,
As shown in FIG. 4(C), the pulse width Tw becomes narrower than in the case of <h>, and the margin in the 9-width direction decreases.

In this case, in the fixed slice method, a frequency AGC method can be considered in which the gain of the amplifier is increased in the high frequency range of one frequency, the amplitude of the input signal is equalized with respect to the spatial frequency, and then the fixed slice is performed. In the floating slice method, in order to correct the excessive fluctuation of the DC component of the slice level, the diodes DI and Da are connected to the time constant circuit including the slice level holding capacitor C, as shown in FIG. A conceivable method is to insert it on the input side so that the slice level is suppressed within the upper and lower limits of the input signal image width by the forward voltage vDf, as shown in FIG. 5<b). However, in the case of the circuit shown in Figure 5(a), the stable DC level must be fixed at + or -, and extreme AC coupling is not possible. Even by improvement.

There is a problem in that pulse width fluctuations based on the height of the spatial frequency of the barcode are unavoidable, and the margin in the width direction is reduced.

In the first place, considering the slice method with a large margin in the width direction, the input signal waveform has a sine wave shape as shown in Fig. 6, and the rate of change is large near the center level, and the rate of change is slow near the upper limit. slow. Therefore, as shown in the figure, when a constant amplitude change value △V1 is set between the center and upper limit of the waveform, the respective time widths ΔTx and △
The relationship ΔTl'CΔT2 holds between TlI and TlI.

Therefore, it is desirable to slice near the center of the waveform where the amplitude change is maximum in order to minimize the pulse width change. FIG. 7(α) shows an example of a slice in which the slice level is set to be located at the center of the positive peak and negative peak of the input signal, and FIG. It is. 1 in the figure is a positive peak detector,
2 is a negative peak detector, and 3 is a comparator, which connects the peak outputs of the positive peak detector 1 and the negative peak detector 20 with resistance, determines the midpoint level, and supplies this to the comparator 3 as a slice level. It has become.

However, this center slice method does not respond very quickly to changes in barcode scanning speed.

Another disadvantage is that the cost increases due to strict requirements for circuit components.

[Object and structure of the invention]

The purpose of the present invention is to enable a mark detector such as a barcode league to accurately extract mark information from the start of reading without being affected by the height of the spatial frequency or the magnitude of the offset amount. 9. The purpose of this invention is to provide a peak detection method that differentiates the sensor output signal and detects the edge portion of the mark from its peak value. At that time, to remove the effects of noise and offset fluctuations.

Means for limiting the peak detection period is provided.

Accordingly, the configuration of the present invention includes a mark sensor, a means for differentiating an output signal of the mark sensor, a means for detecting each peak in the differentiated signal, and a means for detecting each peak in the differentiated signal. means for slicing each at a predetermined level; and a latch means that is activated according to the output of the slicing means and whose state is controlled to be inverted each time the peak detection means detects a peak during the activated period. The entire feature is that the output of the latch means is used as a mark detection signal.

[Embodiments of the invention]

The details of the present invention will be explained below based on examples.

FIG. 8 is a block diagram showing the overall configuration of a barcode league, which is an embodiment of the present invention.

4 is a sensor, 5 is a differentiator, 6 is a peak detector, and 7 is a shaping circuit.

FIG. 9 is a signal waveform diagram for explaining the function of each block element in FIG. 8. @ to ■ in the figure are the signals @ to ■ in FIG. 8, respectively.

FIG. 9 (■) is an example of a bar code, and the figure shows an output signal of the sensor 4. As shown, as the spatial frequency increases, the amplitude of the sensor output signal decreases.

3 in the figure is a signal waveform differentiated by the differentiator 5. 3 shows a signal waveform whose peak has been detected by the peak detector 6. In FIG. As shown in the figure, the signal waveform (2) includes noise. 3 in the figure is a shaped output signal waveform from which noise has been removed by the shaping circuit 7.

The peak detector 6 has two slice levels +
It has TH, -TH. A slice output signal based on these two slice levels is supplied to a shaping circuit 7. The shaping circuit 7 uses these signals to prohibit signal changes outside the peak detection section.

FIG. 10 shows the differentiator 5 in the embodiment shown in FIG. Peak detector 6. 7 is a detailed circuit diagram of the shaping circuit 7. FIG. In the figure,
8 to 10 are comparators, 11 is an integration circuit, and 12 is 10'FH.
Level setting circuit, 13 -TH level setting circuit, 14
is a latch circuit, 15 is a NOR circuit, 16 is an AND circuit,
17 indicates a monostable multivibrator.

FIG. 11 shows the difference between ω′ and ω′ in the embodiment circuit of FIG. 10.
FIG. 2 is a signal waveform diagram of a portion indicated by . below.

The operation of the circuit shown in FIG. 10 will be explained with reference to the waveforms shown in FIG. 11.

In FIG. 11, Mi and Ma are parts of the barcode mark, and D is a scratch generated in the barcode mark Ml.

As a result, a noise signal d is generated in the output signal @' of the sensor 4. The differentiator 5 differentiates this sensor output signal σ, thereby obtaining a differential signal ■'.

In the differential signal ■′, Pi, P4. pa, p
a is a signal corresponding to the edges of marks Ml and M2, and 9
．． pH.

and P3 are signals corresponding to the flaw D.

In the peak detector 6, one of the two input signals to the comparator 8, I, is a differential signal ■', and the other S, the differential signal ■', is delayed by an integrating circuit 11 for a certain period of time. As a result, as shown by σ, intersection points t] to t6 occur near the peaks of the two signals I and S, and a peak detection signal value is obtained from the comparator 8.

On the other hand, the comparators 9 and 10 produce slice output signals 2' and C at slice levels +TH and -TH, respectively, from the differential signals. These signals σ.

Now, the NOR circuit 15 in the shaping circuit 7 is applied to generate the bill set signal @'.

The peak detection signal @' from the comparator 8 is applied to the input terminal A of the latch circuit 14 of the shaping circuit 7.

When the set signal ■' from the NOR circuit 15 is on.

The latch circuit 14 is set to a state corresponding to the level of the peak detection signal @'. The latch circuit 14 includes, for example, L8
IC such as 157 can be used. The latch circuit 14 does not operate while the set signal ■' is off, and maintains the state immediately before the off period. Therefore, the noise SP appearing in the peak detection signal @' cannot operate the latch circuit and is ignored, resulting in a correctly shaped signal σ.

The monostable multivibrator 17 is triggered by the first rising edge of the 1TH slice output signal ■', and the enable signal ω is activated for a period sufficient for the bar code mark to be read.
', opens the AND circuit 10, and outputs the shaped signal W.

〔Effect of the invention〕

As described above, the present invention eliminates the dependence between amplitude and spatial frequency by differentiating the sensor output signal.
Furthermore, apart from peak detection, the differential signal is subjected to level discrimination to remove noise components, thereby enabling accurate mark detection without adjustment.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the amplification method, FIG. 2 is an explanatory diagram of the fixed slice method, FIG. 3 is an explanatory diagram of the floating slice method, and FIG. 4 is an explanatory diagram showing the relationship between the floating slice method and spatial frequency.
FIG. 5 is an explanatory diagram of the improved floating slicing method, FIG. 6 is an explanatory diagram of the relationship between the slice level and the width direction margin,
Fig. 7 is an explanatory diagram of the center slice method, Fig. 8 is a block diagram of a barcode league according to an embodiment of the present invention, Fig. 9 is a signal waveform diagram thereof, and Fig. 10 is a detailed circuit of the main part of this embodiment. figure,
FIG. 11 is a diagram of the signal waveform. In the figure, 4 is a sensor, 5 is a differentiator, 6 is a peak detector, 7
is a shaping circuit, 8 to 10 are comparators, 11 is an integration circuit, 1
5 is a NOR circuit, and 14 is a latch circuit. Patent applicant: Patent attorney representing Usatsuk Electronic Industry Co., Ltd. Necessity: Fumihiro (and two others) How many times - Yen Ku late

Claims (1)

[Claims] A mark sensor, a means for differentiating an output signal of the mark sensor, a means for detecting each peak in the differentiated signal, and a means for detecting a loss width of the differentiated signal at a predetermined upper and lower level. With a means of slicing each at a level. A latch means is activated by the output of the slicing means and whose state is fully inverted every time the peak detection means detects a peak during the activated period, and the output of the latch means is used as a mark detection signal. A mark detection device with all the features.