JPH04367085A - Lighting device for bar code reader - Google Patents

Abstract

PURPOSE:To use the image sensor approximately at the wavelength area of the maximum sensitivity by using the light emitting diode (LED) of a green light emission for the lighting device of a bar code reader. CONSTITUTION:Plural LEDs are linearly arranged at a constant interval and out of these, some LEDs at both edge sides are green light emitting LEDs and some LEDs2 at a central side are red light emitting LEDs. That is, the sensitivity peak of a general semiconductor image sensor is at the wavelength area of 500nm, the light emitting intensity peak of the orange and red LEDs used conventionally is 600nm and dislocated from the sensitivity peak of the image sensor. For this, for a green LED, the light emitting intensity peak is generally at the wavelength area of 525-605nm and this is approximately coincident to the sensitivity peak of the image sensor. Then, the image sensor can be operated approximately at the wavelength area of the maximum sensitivity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device for a barcode reader.

0002

2. Description of the Related Art A barcode reader includes an illumination device that irradiates a barcode with light, and a semiconductor image sensor that receives an image of light reflected from the barcode and converts it into an electrical signal. Here, as a lighting device, a device in which red light emitting light emitting diodes (LEDs) are arranged in a linear manner has conventionally been used.

0003

[Problem to be Solved by the Invention] Conventionally used red-emitting LEDs have a peak emission wavelength of 660 nm.
It's nearby. However, the peak of the spectral sensitivity of the semiconductor image sensor that receives the reflected light is in a wavelength range about 100 nm shorter than that, so conventional barcode readers are used in wavelength ranges that are not the most sensitive.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an illumination device for a barcode reader that can solve the problems of the conventional techniques described above and operate a semiconductor image sensor for reading barcodes at the highest sensitivity. It is in.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a plurality of light emitting diodes that emit light to irradiate a barcode, and some or all of the light emitting diodes are green light emitting diodes. It is characterized by this.

[0006]

[Operation] The lighting device of the present invention uses a green-emitting LED. The peak of the emission intensity of green LED is approximately 525 ~
The wavelength range is 605 nm, which almost corresponds to the wavelength range of peak sensitivity of general semiconductor image sensors. Therefore, the image sensor can be used at almost the highest sensitivity.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a lighting device for a barcode reader according to the present invention will be described below with reference to FIG.

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

As shown in FIG. 1, the sensitivity peak of a typical semiconductor image sensor is in the wavelength range of 500 nm, but the emission intensity peak of conventionally used orange and red LEDs is in the 600 nm range. However, it is shifted from the image sensor's sensitivity peak. In contrast, the green LED used in the present invention has an emission intensity peak of approximately 525
It is in the wavelength range of ~605 nm, which almost coincides with the sensitivity peak of the image sensor. Therefore, the image sensor can be operated in the wavelength range of approximately the highest sensitivity. It is also known that the shorter the wavelength of the irradiated light, the lower the reflectance of the black bar of the barcode and the stronger the contrast with the white bar. It is advantageous to use green light.

FIGS. 2 to 7 show the L of the illumination device according to the present invention.
Some examples regarding the arrangement of EDs are shown. In addition, Figure 2
- FIG. 6 is a plan view seen from the barcode side, and FIG. 7 is a side sectional view.

All of these arrangements are intended to ensure that the entire barcode image is input to the image sensor with uniform brightness. That is, L.E.
D is arranged along the longitudinal direction of the strip-shaped barcode (direction orthogonal to the bar) as a whole, and illuminates the entire range of the barcode. In this case, the reflected light from both ends of the barcode reaches the image sensor through a longer optical path than that from the center, so the image sensor has brighter light along the longitudinal direction of the barcode. Samurai arises. In order to eliminate this brightness unevenness and obtain uniform brightness, the arrangement 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 these, some LEDs 1 on both ends are green-emitting LEDs, and some LEDs 2 on the center side are green-emitting LEDs. It is a red light emitting LED. As a result, light is received by the image sensor at both ends of the barcode with higher sensitivity than at the center, and as a result, the above-described uneven brightness is eliminated.

In the arrays shown in FIGS. 3 to 5, the illuminance at both ends is increased compared to the center by making the arrangement density or arrangement pattern of the LEDs 3, 4, and 5 different between the ends and the center. be. Further, in the arrangement shown in FIG. 6, a condensing lens 8 is provided on the output side of the LED 6 on both end sides, so that more irradiation light is collected on both end sides of the barcode. In the case of FIG. 7, the distance from the barcode to the mounting position of the LED 9 is set closer at both ends than at the center.

LEDs 3, 4, 5, 6, 7 in FIGS. 3 to 7
9 are all green light emitting LEDs. Alternatively, as shown in Figure 2, both ends are green-emitting LEDs, and the center side is a red-emitting LED.
It may also be D.

[0015] In addition to the method described above, another possible method for eliminating uneven brightness is to change the LED current between both ends and the center, but compared to the method of controlling this current, the method of changing the arrangement described above is This is advantageous in that it does not require a complicated circuit configuration.

[0016]

[Effects of the Invention] As explained above, according to the present invention,
Since a green LED is used for the illumination device of the barcode reader, the image sensor can be used in the wavelength region of almost the highest sensitivity compared to conventional ones.

[Brief explanation of the drawing]

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

FIG. 2 is a plan view showing an embodiment of the LED arrangement of the lighting 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 example of an LED array.

FIG. 6 is a plan view showing a fifth example of an 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 LED8 Lens

Claims (5)

[Claims] 1. A lighting device used in a barcode reader that irradiates light onto a barcode and receives reflected light on a semiconductor image sensor, comprising a plurality of light emitting diodes that emit the light, and a part or all of the light emitting diodes. An illumination device for a barcode reader, characterized in that 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 the longitudinal direction of the barcode, and only some of the light emitting diodes at both ends of the arrangement are green light emitting diodes. An illumination device for a barcode reader, characterized in that: 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 barcode, 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 barcode reader characterized by: 4. The device according to claim 1, wherein the plurality of light emitting diodes are arranged as a whole along the longitudinal direction of the barcode, and the light is focused only on some light emitting diodes at both ends of the arrangement. An illumination device for a barcode reader, characterized in that it is provided with a lens for use in the barcode reader. 5. The device according to claim 1, wherein the plurality of light emitting diodes are arranged as a whole along the longitudinal direction of the barcode, and both ends of the arrangement are closer to the barcode than the center side. A barcode reader illumination device that is characterized by its short distance.