JP2962495B2 - Illumination device for bar code reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination device for a bar code reader.

[0002]

2. Description of the Related Art A bar code reader has an illuminating device for irradiating a bar code with light, and a semiconductor image sensor for receiving an image by reflected light from the bar code and converting the image into an electric signal. Here, as the illuminating device, a device in which light-emitting diodes (LEDs) emitting red light are arranged in a line is conventionally used.

[0003]

A conventionally used red-emitting LED has a peak emission wavelength of 660 nm.
Nearby. However, since the peak of the spectral sensitivity of the semiconductor image sensor receiving the reflected light is in a wavelength range shorter than that by about 100 nm, the conventional barcode reader is used in a wavelength range that is not the highest sensitivity.

It is an object of the present invention to provide a lighting device for a bar code reader which solves the above-mentioned problems of the prior art and can operate a semiconductor image sensor for reading a bar code with the highest sensitivity. It is in.

[0005]

In order to achieve the above object, the present invention comprises a plurality of light emitting diodes for emitting light to a bar code, and some or all of the light emitting diodes are green light emitting diodes. It is characterized by the following.

[0006]

The illumination device of the present invention uses a green light emitting LED. The peak of the emission intensity of the green light emitting LED is approximately 525 to 525.
It is in the wavelength range of 605 nm, which substantially coincides with the wavelength range of the sensitivity peak of a general semiconductor image sensor. Therefore, the image sensor can be used with almost the highest sensitivity.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an illumination device for a bar code reader according to the present invention will be described below with reference to FIG.

FIG. 1 shows a spectral sensitivity characteristic of a general semiconductor image sensor by a curve a. Also, the relative light emission intensity characteristics of the green, orange and red LEDs are shown by curves b, c and d, respectively.

As shown in FIG. 1, the sensitivity peak of a general semiconductor image sensor is in a wavelength range of the order of 500 nm, whereas the emission intensity peak of a conventionally used orange or red LED is in the order of 600 nm. And deviates from the sensitivity peak of the image sensor. In contrast, the green LED used in the present invention has an emission intensity peak of about 525.
In the wavelength range of ６０605 nm, this almost coincides with the sensitivity peak of the image sensor. Therefore, the image sensor can be operated in the wavelength region having almost the highest sensitivity. It is also known that the shorter the wavelength of the irradiation light, the lower the reflectance of the black bar of the barcode and the stronger the contrast with the white bar, but from this point, the wavelength is shorter than that of the red light. It is advantageous to use green light.

FIGS. 2 to 7 show the L of the illumination device according to the invention.
Several examples relating to the arrangement of the ED are shown. Note that FIG.
6 to 6 are plan views as viewed from the barcode side, and FIG. 7 is a side sectional view.

All of these arrangements are for ensuring that the entire barcode image is input to the image sensor with uniform brightness. That is, LE
D is arranged along the longitudinal direction (the direction perpendicular to the bar) of the band-shaped barcode as a whole, and illuminates the entire range of the barcode. In this case, the reflected light from both end portions of the bar code reaches the image sensor through a longer optical path than that from the central portion, so that the image sensor is bright along the longitudinal direction of the bar code. Unevenness occurs. In order to eliminate the brightness unevenness and obtain a uniform brightness, an arrangement as shown in FIGS. 2 to 7 is adopted.

In the arrangement shown in FIG. 2, a plurality of LEDs are linearly arranged at regular intervals. Among them, some LEDs 1 at both ends are green light-emitting LEDs, and some LEDs 2 at the center are green LEDs. It is a red light emitting LED. As a result, both ends of the barcode are received by the image sensor with higher sensitivity than the center side, and as a result, the above-mentioned uneven brightness is eliminated.

In the arrangements of FIGS. 3 to 5, the illuminance at both ends is higher than that at the center by making the arrangement density or arrangement pattern of the LEDs 3, 4, 5 different at both ends and at the center. is there. In the arrangement shown in FIG. 6, a condenser lens 8 is provided on the output side of the LEDs 6 on both ends, so that more irradiation light is collected on both ends of the bar code. In FIG. 7, the distance from the bar code to the mounting position of the LED 9 is set to be closer at both ends than at the center.

The LEDs 3, 4, 5, 6, 7, and 7 shown in FIGS.
Reference numeral 9 denotes green light-emitting LEDs. Alternatively, as shown in FIG. 2, both ends are made to emit green light, and the center is made to emit red light LE.
D may be used.

As a method for eliminating the uneven brightness, a method of changing the LED current between the both ends and the center side is considered in addition to the method described above. This is advantageous in that a complicated circuit configuration is not required.

[0016]

As described above, according to the present invention,
Since a green light emitting LED is used for the illuminating device of the bar code reader, the image sensor can be used in a wavelength region having almost the highest sensitivity as compared with the conventional one.

[Brief description of the drawings]

FIG. 1 is a diagram showing spectral sensitivity characteristics of a semiconductor image sensor and light emission intensity characteristics of LEDs having various light emission colors.

FIG. 2 is a plan view showing one embodiment of an LED array of the illumination device of the present invention.

FIG. 3 is a plan view showing a second embodiment of the LED array.

FIG. 4 is a plan view showing a third embodiment of the LED array.

FIG. 5 is a plan view showing a fourth embodiment of the LED array.

FIG. 6 is a plan view showing a fifth embodiment of the LED array.

FIG. 7 is a side sectional view showing a sixth embodiment of the LED array.

[Explanation of symbols]

 1,2,3,4,5,6,7,9 LED 8 lens

Claims (5)

(57) [Claims] An illumination device used in a bar code reader for irradiating a bar code with light and receiving reflected light by a semiconductor image sensor, comprising a plurality of light emitting diodes for emitting the light, and part or all of the light emitting diodes. Is a green light emitting diode. 2. The device according to claim 1, wherein the plurality of light emitting diodes are arranged as a whole along a longitudinal direction of the bar code, and only some of the light emitting diodes at both ends of the arrangement are green light emitting diodes. An illumination device for a bar code reader. 3. The device according to claim 1, wherein the plurality of light emitting diodes are arranged as a whole along the longitudinal direction of the bar code, and the arrangement density or arrangement pattern at both ends of the arrangement is different from that at the center. An illumination device for a bar code reader. 4. The device according to claim 1, wherein the plurality of light emitting diodes are arranged along the longitudinal direction of the bar code as a whole, and only a part of the light emitting diodes at both ends of the arrangement are focused. An illumination device for a bar code reader, comprising a lens for use in a bar code reader. 5. The device according to claim 1, wherein the plurality of light emitting diodes are arranged as a whole along a longitudinal direction of the bar code, and both ends of the arrangement are closer to the bar code than a center side. An illumination device for a bar code reader, wherein the distance is short.