JPS62165282A - Bar code reader - Google Patents

Abstract

PURPOSE:To increase a light scan speed, and to reduce a read time by assembling a synchronizing rectifier circuit operated synchronizing with the light emitting cycle of a light source at a light reception circuit which receives reflecting light from a bar code, and performing the synchronizing rectification of a light receiving signal at the circuit. CONSTITUTION:The luminescent spot of a scan light source 11 is image-formed in the neighborhood of almost the origin of X-Z axes with a lens 13 arranged on a light path from the scan light source 11 to a scan mirror 12. At a position near a bar code travel A, a pair of light receivers 31 and 32 in order to receive the reflecting light from the bar code travel is arranged, for example, at an X-Y plane, and the receiving light outputs from the light receivers 31 and 32 are supplied to the light reception circuit. The light reception circuit consists of a photoelectric conversion circuit 30, a high-pass amplifier 40, a high-pass buffer circuit 50, a synchronizing rectifier circuit 60, and a binarization circuit 90, etc. The light receiving signal on which noise is overlapped is inputted as it is to the synchronizing rectifier circuit 60, however, it is restored to its original signal waveform from which a noise component is eliminated by applying the synchronizing rectification. In such a way, a device resistant to the noise even when feeble light is used, and also, the light scan speed can be increased, thereby the read time being reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an apparatus for reading barcodes printed on the surfaces of packaging boxes and cans in order to indicate the classification of the products contained therein.

The Jubei Hikigi blood barcode reading device includes a scanning light source for optically scanning the barcode, and receives reflected light from the barcode.
It consists of a light receiving circuit that performs the necessary processing for reading the received light signal. Conventionally, as scanning light sources, there are those that use weak light intensity such as LEDs, and those that use He-N
There are also those that use a laser with a strong light intensity, such as an e-laser.

I try to solve it. By the way, in scanning light sources that use weak light such as LEDs, the level of external noise from fluorescent lights cannot be ignored, making them vulnerable to noise, and on top of that, the light intensity is weak, making it difficult to scan. The speed has to be slow (normally 55can/5ee) and it takes time to read (approximately 0
．． 5 sec) If the data cannot be read, there is a problem that the display becomes slow as a result.

On the other hand, a He-Ne laser that uses a He-Ne laser as a scanning light source has a high light emission amount, so it is resistant to noise and can increase the scanning speed. Since the -Ne laser itself is large and expensive, there are problems in that a part of the hand scanner is large and difficult to handle, and the cost of the device is high.

Purpose of the Invention Therefore, the present invention is highly resistant to noise even when using a light source with a weak light intensity, can speed up the optical scanning speed and shorten the reading time, and has a hand scanner that is small in size and inexpensive, making it very useful. The purpose is to provide a highly efficient barcode reading device.

Means for Achieving the Object The above object is to emit pulses repeatedly from a scanning light source that optically scans a barcode, modulates the intensity of the light emission, and sends the scanning light to a light receiving circuit that receives reflected light from the barcode. This is achieved by incorporating a synchronous rectifier circuit that operates in synchronization with the light emission period of the light source and demodulating the received light signal through the synchronous rectifier circuit.

Embodiment FIG. 1 shows a layout diagram of an optical system of a barcode reading device as an embodiment of the present invention. As shown in the figure, when the label A on which the reading barcode B is printed is positioned in the XZ plane near the origin of the x, y, and z axes, the scanning light source 11 is positioned on the Yz plane. The light from the scanning light source 11 is projected toward the scanning mirror 12 located on the same plane, is reflected there, and is irradiated onto the barcode label A.

An imaging lens 13 is arranged on the optical path from the scan light source 11 to the scan mirror 12, and the bright spot of the scan light source 11 is imaged approximately near the origin of the XYZ axes by this lens 13. The scan mirror 12 is attached to the rotating shaft of the scan motor 14, and is swung by the drive of the scan motor 14 to move the bright spot of the scan light source 11 projected onto the label surface onto the X axis centered around the origin of the XYZ axes. +, scan alternately in one direction. Near the barcode label A, there is a pair of light receivers 31.3 on the XY plane, for example, to efficiently receive reflected light from the barcode label.
2 is placed. The light receiving outputs of the light receivers 31 and 32 are supplied to the light receiving circuit shown in FIG. 2 and subjected to necessary processing. Incidentally, when the scanning light source 11 projects the light emitted by it onto a barcode label, it is advantageous in terms of light intensity that it is narrow in the barcode width direction and long in the height direction, and also provides high readability. This is desirable because it provides good resolution.

FIG. 2 shows an overall circuit diagram of a barcode reading device as an embodiment of the present invention. In the figure, 10 is a scan light source lighting circuit, 20 is a synchronization pulse generation circuit, and 30 to 90 are light receiving circuits. In the illustrated example, the light receiving circuit includes a photoelectric conversion circuit 30, a high-frequency amplifier 40, a high-frequency C/F circuit 50, and a synchronous rectifier circuit 6.
0, sample and hold circuit 70, low band amplifier 80.2
It consists of a value conversion circuit 90.

The scan light source lighting circuit 10 includes a synchronization pulse generation circuit 20
The scanning light source 11 is controlled by a pulse supplied from
is emitted in high-speed pulses. In this embodiment, an LED capable of high-speed intensity modulation is used as the scanning light source 11.

The synchronization pulse generation circuit 20 generates a synchronization pulse of 100 kHz and a duty ratio of 115. A synchronous pulse generated in this circuit is applied to the switching FET Q61 of the synchronous rectifier circuit 60 via the scan light source lighting circuit 10, the sample/hold circuit 70, and the impark 21.

The photoelectric conversion circuit 30 includes the pair of light receivers 31 and 32 described above.
The received light outputs are added together to obtain a voltage output proportional to the received light outputs. Note that photodiodes are used as the light receivers 31 and 32 in this embodiment.

The high-frequency amplifier 40 converts DC and low frequency components (several kilohertz or less) of the voltage signal output from the photoelectric conversion circuit 30.
and cut the high frequency component (emission frequency (100kHz)
(above)). The high band buffer circuit 50 also amplifies a similar band.

The synchronous rectifier circuit 60 includes a switching FETQ61, a coupling capacitor C62, and an operational amplifier A63.
The switching FET Q61 is turned on and off by the pulses generated by the synchronizing pulse generating circuit 20, thereby operating in synchronization with the light emission period of the scanning light source 11.

The sample/hold circuit 70 tracks the signal voltage during the light emission period of the scan light source 11, and holds the signal voltage during the light emission period until the next light emission pulse signal is input during the light emission period of the scan light source 11. Perform the action.

Low-pass amplifier 80 level-converts, smoothes, and slightly amplifies the output signal from sample-and-hold circuit 70.

The binarization circuit 90 binarizes (digitizes) the analog barcode scan waveform obtained by the low-pass amplifier 80 to facilitate input into a microcomputer, etc. The barcode reading operation in the above configuration is shown in FIG. The explanation will be given according to the waveform diagram shown. When the synchronizing pulse generation circuit 20 generates a pulse waveform as shown in the figure (a), the scanning light source 11 emits pulses with the period and duty ratio as shown in the figure (b).At this time, the white bar area of the barcode Assuming that the black bar areas are lined up as shown in Figure (C), the light reception signal of the photoelectric conversion circuit 30 when light is scanned while the scanning light source 11 emits pulse light is arranged in the white bar area as shown in Figure (D). The area has a large amplitude, and the black bar area has a small amplitude, resulting in an amplitude-modulated waveform.

On the other hand, at this time, if external noise such as a fluorescent light is input as shown in Figure (E), this noise signal will be reflected as shown in Figure (D) above.
This will be superimposed on the barcode signal shown in . This superimposed signal is as shown in the figure. It is assumed that the noise signal has a frequency that is about 1/10 or less of the light emission frequency of the scanning light source 11. In practice, it is sufficient to allow for a frequency of this order in the noise signal. Immediately,
While the light emission frequency of the scan light source 11 is 100 kHz, the hum noise is 120 fiz even if the commercial frequency is 60 fiz, and the ratio is much smaller than about 1/10.

The above-described noise-superimposed light reception signal is input as is to the synchronous rectification circuit 60, but by synchronous rectification, it is restored to the original signal waveform from which noise components have been removed, as shown in Figure (H). . The noise removal operation by the synchronous rectifier circuit 60 will be described later.

The output signal from the synchronous rectifier circuit 60 is sampled and held to have a stepped waveform with a series of envelope lines as shown in the figure. This signal is then passed through a low-pass amplifier 80 and shaped as shown in FIG. Only at this point can a signal corresponding to the barcode scan waveform be obtained. This signal is binarized by a binarization circuit 90 as shown in the figure (R), and a reading analysis circuit (
(not shown).

Next, the operation of the synchronous rectifier circuit 60 will be described in detail. The main function in this circuit is the potential holding capacitor C6.
2 and a switching FET Q61 that is repeatedly turned on and off by synchronizing pulses. Now, the input side voltage of the potential holding capacitor C62 is vJ, the output side voltage is v4, and the charging voltage of the capacitor C62 is ■. Then, ■period t during which the scanning light source is turned off. -tμ, (1) The switching FET Q61 is turned on as shown in FIG. 3 (H). Therefore, the score is 4-0.

(2) Vc follows Va (vo
=v,). ■, is t as shown in Figure 3 (f)
0-1. Since there is only the noise component during the period, the capacitor C62 is charged by the noise component during this period.

■ During the period t, ~t2 during which the scan light source is turned on, (1) If the value of V immediately before the scan light source turns on at time t1 is Va-1, then during the period t, ~t2, Since switching FETQ61 is off,
(2) maintains V, -Va-1.

(2) When a signal component of Δji is generated due to the scanning light source emitting light, ■2 changes from ■, -1 to (Va-++ΔVJ).

(3) On the other hand, ■. As stated in (1), 3-1 is still maintained, so the capacitor charging voltage v, = v3-. A voltage is generated by subtracting . 17jJ, V4= VJ V, = (VJ-1+Δv4)
-v3-1 ==Δv3 In other words, the output side of the capacitor C62 has a useful signal component ΔV caused by the scanning light source emitting light! only occurs. This signal component Δv3 becomes an output signal of the synchronous rectifier circuit 60 through a buffer A63 having a high input impedance.

Based on this principle, the synchronous rectifier circuit 60 removes noise components and outputs only useful signal components. Note that noise removal using a synchronous rectifier circuit is possible if there is a frequency difference between the signal and the noise as described above, so it will work effectively if the frequency band of the noise is at least a certain level lower than the emission frequency of the scanning light source. . It goes without saying that the types of noise that can be removed include external light entering the photoreceiver, external electrical noise entering the circuit, and drift occurring within the circuit.

Although the illustrated synchronous rectifier circuit 60 includes a buffer A63 with high input impedance, it can also be replaced with a source-Faroor circuit consisting of one FET and a resistor.

] As described above, in the present invention, the scan light source emits pulse light, and the light receiving circuit works in synchronization with the light emitting cycle of the scanning light source (a synchronous rectifier circuit is incorporated to synchronously rectify the light receiving signal). Even if weak light such as an LED is used as a scanning light source, it is resistant to noise and has excellent effects such as being able to read barcodes with a good signal-to-noise ratio.

In addition, as mentioned above, barcodes can be read even if the light intensity of the scanning light source is small, so the speed at which light scans the barcode can be further increased compared to conventional methods, resulting in a reduction in reading time. However, in the case of unreadability, the results can be displayed quickly, making it possible to respond to high-speed processing of work.

In addition, since a compact light source such as an LED can be used as the scanning light source, a part of the hand scanner can be made smaller and lighter, and the device cost can also be reduced.

[Brief explanation of drawings]

Fig. 1 is a layout diagram showing the optical system of a barcode reading device as an embodiment of the present invention, Fig. 2 is a diagram showing the overall circuit of the reading device, and Fig. 3 is a signal diagram of each part of the device shown in Fig. 2. It is a figure which shows a waveform. 11... Scan light source 60... Synchronous rectifier circuit patent applicant Minolta Camera Co., Ltd. Figure 1

Claims (1)

[Claims] A scanning light source that optically scans the barcode for reading is caused to emit pulses repeatedly, and a synchronous rectifier circuit that operates in synchronization with the light emission cycle of the scanning light source is incorporated into the light receiving circuit that receives reflected light from the barcode. A barcode reading device characterized by performing synchronous rectification of a received light signal.