JPH0727773B2 - Discharge lamp - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention illuminates a document in a slit shape in document illumination of a copying machine or the like, and exposes the document surface illuminated in the slit shape through a lens system. The present invention relates to a discharge lamp used when projecting onto paper, a photosensitive drum, or the like, and further to a discharge lamp arranged directly in the vicinity of a document surface or an illuminated surface.

[Prior Art and Problems Thereof] In the above industrial field, when a linear discharge lamp is used as an illumination light source for a copying machine or the like, the amount of light at both ends of the discharge lamp decreases, so that the lamp surface of the lamp is illuminated. The irradiance distribution on the surface was large in the central part and small in the parts near both ends. When such an illuminated surface is imaged by the SELFOC lens array (trade name), the illuminance of the imaged surface near both ends is naturally low, and the image is projected on the illuminated surface with a normal optical lens system. In that case, there is a problem that the peripheral portion becomes darker on the irradiated surface according to the “cosine fourth law”.

As a solution to this problem, a dimming means having an aperture with a narrow central opening and wide opening at both ends is provided along the longitudinal direction of the discharge lamp between the illuminated surface light source and the illuminated surface. The light quantity on the surface to be illuminated is adjusted by the light means. Further, in some cases, a discharge lamp whose discharge path length is considerably larger than the width of the original is used to suppress the decrease in illuminance at the edge of the original.

However, in these methods, the amount of light emitted from the illumination surface light source is not effectively used, and there is a problem that the volume occupied by the dimming means is necessary or that a discharge lamp longer than necessary is used. When such a light source is incorporated in a small and lightweight device, the functionality of the device is significantly impaired.

On the other hand, various researches have been made on a linear discharge lamp for a copying machine in which the amount of light emitted from the central portion is suppressed by the discharge lamp alone, for example, Japanese Utility Model Laid-Open No. Sho 47-6847 and Japanese Patent Laid-Open No. Sho 48-48.
Although disclosed in Japanese Patent No. 11879 and Japanese Utility Model Laid-Open No. Sho 49-136085, it has been difficult to manufacture a discharge lamp and it has not been put into practical use.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and an object thereof is a discharge lamp having a long effective light emission length even if the total lamp length is short, suitable for being incorporated in a small and lightweight device, It is an object of the present invention to provide a novel discharge lamp that can make the illuminance on the surface to be illuminated uniform or have a predetermined distribution.

[Structure of Invention and Its Action]

In order to achieve the above object, the discharge lamp of the present invention has a pair of electrodes connected to a high frequency power source arranged at both ends inside a tubular bulb having a linear discharge path and connected to a high frequency power source. The third electrode (barrier electrode) is provided at a predetermined position on the outer surface of the tubular bulb surrounding the discharge path.

That is, when the third electrode connected to the high frequency power source is arranged on the outer surface of the tubular bulb, the glass forming the tubular bulb acts as a capacitor because it is a dielectric, and plasma is generated near the inside where the third electrode is arranged. Accumulation and divergence of ions and electrons inside occur depending on the frequency. That is, since barrier discharge occurs, the density of ions and electrons becomes high, and the brightness of that portion becomes relatively high. At this time, the degree of increase in brightness can be adjusted by the voltage and frequency of the applied high frequency power supply, and other conditions, so if the discharge lamp is designed by combining the position of the third electrode and the conditions of the high frequency power supply, It is possible to obtain a distribution and obtain a discharge lamp having a brightness distribution according to the purpose of use.

〔Example〕

FIG. 1 is an explanatory diagram showing a discharge lamp for image reading and its luminance distribution. A tube bulb in which a discharge path 3 is linearly formed in a pair of electrodes 2a and 2b connected to a high frequency power source 1 is shown. Four
Place on both ends inside. Then, the third electrodes 6a, 6b are arranged on the outer surface of the linear portion 5 surrounding the discharge path 3 of the tubular bulb 4 and near the electrodes 2a, 2b, which are also connected to the high frequency power supply 1. Note that 7a, 7b, 7c, 7d are capacitors, and in the illustrated example, the electrodes 2a, 2b and the third electrodes 6a, 6b are connected to the same high frequency power source 1, but they are connected to different high frequency power sources respectively. May be.

To give a concrete numerical example, the outer diameter of the tubular valve 4 is 3.1 mm, the length of the discharge path 3, that is, the distance between the electrodes 2a and 2b is 90 mm.
20 kPa (25 torr) of krypton gas inside the valve.
(° C) gas pressure, and the inner surface of the valve is Zn ₂ Si.
OO ₄ : Mn phosphor is applied. High frequency power with a frequency of 50 KHz is applied between the electrodes 2a and 2b, but the voltage is 495V,
The discharge current is 10mA and the power consumption is about 5W. on the other hand,
The third electrodes 6a, 6b are made by adhering aluminum foil with a width of 15 mm over the outer circumference of the valve over a half circumference, and have a capacity of
It is connected to the high frequency power source 1 through the 25pF capacitors 7b and 7d. The capacitors 7a, which are connected to the electrodes 2a, 2b,
The capacitance of all 7c is 110pF. Then, the third electrode 6a,
The amount of electricity supplied to 6b is about 2.2 W, and thus the total power consumption is about 7.2 W in this embodiment, but the third electrodes 6a, 6
Electricity of less than 30% of the total is input to b. The amount of electricity supplied to the third electrodes 6a, 6b can be changed by changing the output of the high frequency power supply 1.

The brightness distribution of the discharge lamp is as shown by the solid line A, and the brightness of the portion where the third electrodes 6a and 6b are arranged is higher than that of the central portion of the bulb. The dotted line B shows the luminance distribution in the case where the third electrodes 6a and 6b are not arranged. As can be understood from this, the radiation intensity from the portion in which the third electrodes 6a and 6b are arranged is more than that in the case where the third electrodes 6a and 6b are not arranged. large. Third electrode 6a, 6
Since the brightness of the portion where b is arranged can be adjusted by changing the size of the third electrodes 6a, 6b and the capacitance of the capacitors 7b, 7d, in addition to this, the position of the third electrodes 6a, 6b can be changed. If so, a predetermined brightness distribution can be obtained, and a discharge lamp having a brightness distribution according to the purpose of use can be obtained.

FIG. 2 is an explanatory view of the method for measuring the luminance distribution, and is shown in a cross section perpendicular to the longitudinal direction of the discharge lamp. A round rod-shaped lens 8 is arranged in parallel with the tube bulb 4, and the emitted light from the discharge lamp is focused on the surface of the photodiode 9 via the lens 8. The photodiode 9 is arranged in the longitudinal direction of the discharge lamp. When the vehicle is driven along the line, its output is read and a graph is drawn, the luminance distribution shown in FIG. 1 is obtained.

FIG. 3 is an explanatory view of another embodiment, in which the third electrode 6c is made of a strip-shaped metal foil, and the outer surface of the bulb has a section (a),
They are in contact with each other at (b) and (c), and are separated at other areas (d) and (e). Therefore, the area of the tubular valve 4 (a),
The radiant intensity of the light in (b) and (c) is relatively higher than that in other areas.

〔The invention's effect〕

As explained above, in a linearly long discharge lamp,
Since the radiation intensity of light can be changed along the longitudinal direction, it is convenient to obtain a predetermined irradiation intensity distribution required in the longitudinal direction of the discharge lamp on the surface to be illuminated.

In particular, since the radiant intensity at both ends of the discharge lamp can be relatively increased, the illuminance distribution on the illuminated surface, which is the photoelectric conversion surface, can be made uniform without using a dimmer. Therefore, the utilization rate of synchrotron radiation is high, and as the irradiated area, the length of the discharge path can be used to the full extent.
It is no longer necessary to use a discharge lamp longer than necessary as in the conventional case. Therefore, it is possible to provide not only a convenient discharge lamp to be incorporated in a small and lightweight device, but also an excellent discharge lamp for an optical machine adopting a slit exposure illumination system such as a copying machine.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of a data collection method, and FIG. 3 is an explanatory diagram of another embodiment. 1 ... High frequency power source, 2a, 2b ... Electrode 3 ... Discharge path, 4 ... Tube type valve 6a, 6b, 6c ... Third electrode, 8 ... Lens 9 ... Photodiode

Claims (1)

[Claims] 1. A tube in which a pair of electrodes connected to a high frequency power source are arranged at both ends inside a tubular bulb having a linear discharge path, and a third electrode connected to the high frequency power source surrounds the discharge path. A discharge lamp, which is provided at a predetermined position on the outer surface of a bulb and has a radiance distribution of a linear discharge path according to the purpose of use.