JPH09283086A - Discharge lamp projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the stable operation of a lighting system using a high- luminance discharge lamp by providing specific magnetic field generating means in the DC-lighting type discharge lamp lighting system provided with the discharge lamp and a power circuit feeding the DC voltage. SOLUTION: This discharge lamp lighting system is provided with a discharge lamp 10 which is preferably a short arc tube, a power circuit 20 feeding the discharge starting voltage required to start a discharge to the discharge lamp 10 and feeding the DC voltage to continue the discharging state thereafter, and magnetic field generating means 31a, 31b generating the magnetic fields perpendicular in direction to the longitudinal direction of the electrodes 10 of the discharge lamp 10 at the tip sections of the electrodes 12. A pair of magnetic field generating means generating the magnetic fields in the perpendicular directions to each other are preferably provided. When the magnetic fields are generated at the tip portions of the electrodes 12, the phenomenon that the end sections of a cord-like arc are instantaneously and intermittently moved can be suppressed, and the fluctuation of luminance caused by the movement can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp projecting device used as a photographing device for visual inspection of products, a high-brightness illuminating device for a high-speed photographing device, or a light source for a projection television. .

[0002]

2. Description of the Related Art At an industrial product manufacturing site, an automatic appearance inspection is adopted in which the appearance of a product being conveyed is photographed by an image pickup device such as a television camera and processed by an electronic computer to judge its quality. Has been done. In this case, in order to transport the product and speed up the inspection, if you try to shoot while keeping the transport state of the product to be inspected without interrupting the transport of the product to be inspected, high-speed shooting is performed to avoid blurring. You will need it.

Further, in a certain type of appearance inspection apparatus, it may be necessary to repeat a number of times of photography for one product by using illumination of different color components through different patterns or filters. In such a case, it is necessary to further speed up the shooting for each time. In recent years, for the reasons described above, further speeding up of photographing (shortening of exposure time) is required, and accordingly, an extremely high-luminance illuminating device is required in order to secure a necessary minimum exposure amount. It's starting. Also, from the purpose of realizing high resolution,
There is a demand for high-luminance lighting devices.

[0004]

Conventionally, as a high-brightness and high-efficiency lighting device, an AC lighting system for lighting a cold cathode high pressure discharge lamp such as a mercury lamp or a metal halide lamp at a high frequency voltage of several tens KHz is generally used. Has been done. Also,
In a high-brightness lighting device that uses this type of high-pressure discharge lamp,
In order to secure the illuminance and improve the illumination efficiency, a reflector is added (Japanese Patent Laid-Open No. 174902/1992), or a reflector is additionally used with a lens.

However, according to the experimental results of the present inventor, when an AC lighting discharge lamp lighting device is used as a lighting device of a photographing device, horizontal noise appears on the photographing screen or a television camera is displayed on the entire screen. There is a problem in that flicker appears due to the difference between the vertical synchronization frequency and the blinking frequency, and high quality images cannot be obtained.

In order to solve the problems of the AC lighting method, the inventor of the present invention uses a high-voltage igniter to start discharge, and thereafter applies a DC voltage instead of an AC voltage to maintain the lighting state. The known DC lighting method was tried. However, if the well-known DC lighting system is attempted to be realized by an extremely high-brightness (high-power) lighting device required by the present inventor, particularly a lighting device using a short arc tube with high energy density, stable operation is achieved. It turned out that there were some problems that had to be solved in order to achieve this.

By the way, direct current lighting is not often performed in a discharge lamp for an ordinary lighting device. In particular, an extremely high-intensity discharge lamp required by the present inventor (a high-intensity discharge lamp in which the illuminance at a location about 2 meters away from the light source is about 10 times the illuminance of the sun's rays and reaches 1,000,000 lux). It is considered that there is no example of direct current lighting. Therefore, one object of the present invention is to realize a stable operation of a lighting device apparatus of a direct current lighting type using a high-intensity discharge lamp.

[0008]

DISCLOSURE OF THE INVENTION A direct current lighting type discharge lamp floodlighting device according to the present invention supplies a discharge lamp and a discharge starting voltage necessary for starting discharge to the discharge lamp, and thereafter maintains a discharge state. In addition to a power supply circuit for supplying a DC voltage for operating the discharge lamp, magnetic field generating means for generating a magnetic field in a direction orthogonal to the longitudinal direction of the electrode of the discharge lamp is provided at the tip of this electrode.

According to the experimental results of the present inventor, the tip of the cord-shaped arc extending from the surface of the electrode instantaneously and intermittently moves from one place to another on the surface of the electrode, Along with this, a phenomenon occurs in which the brightness of the arc, and thus the illuminance of the lighting device fluctuates instantaneously and intermittently. This phenomenon occurred frequently on the cathode side where the temperature increased due to the collision of ions. The frequency of the instantaneous and intermittent movement of the tip of the cord-shaped arc could be reduced by applying a magnetic field to the tip of the electrode and in a direction orthogonal to the longitudinal direction of the electrode.

Conventionally, in the AC lighting system, a structure is known in which a magnetic field is applied to the central portion of the arc to generate Lorentz force to suppress the deformation (change in shape) of the arc and stabilize the discharge. (JP-A-60-235392). However, in the direct current lighting method, not only the fluctuation of the brightness due to the deformation of the string-shaped arc but also the fluctuation of the brightness generated due to the intermittent movement of the end portion is more problematic. This is because in AC lighting, since the generation and extinction of the arc are repeated at a frequency higher than the frequency of movement of the ends of the arc generated under the DC lighting state, It is considered that the probability that the tip portion will move within a short time is smaller than that in the case of DC lighting.

Therefore, the fluctuation of the brightness due to the intermittent movement of the end of the arc is a conspicuous phenomenon mainly in the DC lighting system, particularly in the short arc tube of high energy density, and it can be suppressed by the Lorentz force. It is effective to generate a magnetic field not at the central portion of the arc but at the end portion thereof, that is, near the electrode.

[0012]

According to an embodiment of the present invention, the magnetic field generating means includes a pair of magnetic field generating means for generating a magnetic field only in the cathode or in a direction orthogonal to the longitudinal directions of both the cathode and the anode.

[0013]

1 is a block diagram showing the overall construction of a discharge lamp illuminating device according to an embodiment of the present invention, in which 10 is a metal halide discharge lamp, 20 is a power supply circuit, and 31a and 31b are magnets. In this figure, in order to avoid complication, optical systems such as a reflecting mirror and a lens are not shown. The discharge lamp illuminating device of this embodiment is used as an illuminating device for photographing of an automatic inspection device for photographing the appearance of an industrial product to judge acceptability.

The metal halide discharge lamp 10 opposes an elliptical quartz tube 11 in which a metal halide, mercury, and a rare gas for starting are enclosed, and along the long axis direction of the elliptical quartz tube. It is composed of a cathode 12 and an anode 13 which are arranged in a line. This metal halide discharge lamp is generally called a short arc tube because the distance between the electrodes is relatively short. The power circuit 20 is an igniter 2
1, DC stabilized power supply 22, ammeter 23, controller 2
4, a DC blocking capacitor 25 and a choke coil 26.

At the start of lighting of the discharge lamp 10, the controller 24 of the power supply circuit 20 first activates the DC stabilized power supply 22 to cause the discharge lamp 10 to start the discharge once it has not reached the discharge start voltage. A DC voltage of several hundreds V which can be maintained is supplied. Next, the controller 24 activates the igniter 21 to generate a pulsed discharge starting voltage of several tens of KV, and supplies this to the metal halide discharge lamp 10.

When the controller 24 detects that the discharge has started inside the metal halide discharge lamp 10 from the increase in the value of the current flowing through the ammeter 23, the controller 24 stops the operation of the igniter 21 and the direct current generated by the stabilized direct current power supply 22 is generated. The discharge is sustained by supplying only the voltage to the metal halide discharge lamp 10.

Under an extremely high-intensity direct current lighting condition in the apparatus of this embodiment, the temperature of the tube wall at the central portion of the quartz tube 11 becomes as high as 1000 ^° C., and the cathode 12 and the anode 13 are heated.
The temperature of each of the external electrode terminals connected to each is as high as 300 ^o C. And since each external electrode terminal is connected to the power supply circuit through a thin electric wire,
The amount of heat dissipated to the outside of the discharge lamp by conduction mode in such a thin wire is negligibly small.

Therefore, the heat dissipated from the discharge lamp 10 is
It consists of a convection component radiated from the tube wall of the quartz tube 11 by natural convection, and an infrared radiation component that does not contribute to illumination and is radiated from a high temperature portion such as the arc or the tube wall of the quartz tube. Unlike the conduction mode in which the amount of heat released is proportional to the temperature difference, the amount of heat released by radiation or convection increases or decreases with the power of the discharge gas or tube wall temperature, and the ionization coefficient determines the ease of discharge. Also changes exponentially with respect to the gas temperature, so that the discharge state tends to be quite unstable.

As described above, as a problem peculiar to the direct current lighting, the tip of the string-shaped arc is instantaneously and intermittently moved from one place to another place on the surface of the electrode, and the arc is accompanied by this. The brightness of fluctuates. In order to prevent this phenomenon, in the present embodiment, a pair of magnets 31a and 31b, which are composed of electromagnets and permanent magnets and have opposite polarities, are arranged to face each other. As a result, a magnetic field is generated at the tip of the cathode 12 in a direction orthogonal to the longitudinal direction of the cathode 12. As a result, a Lorentz force is generated at the tip of the cathode 12 in a direction orthogonal to both the arc and the magnetic flux orthogonal thereto.

As a result, the tip of the arc tends to move in the same direction as the Lorentz force, but hard to move in the opposite direction. That is, as a result of the directionality of the movement, the instantaneous and intermittent movement of the tip of the string-shaped arc, which is repeated in a certain direction at the electrode tip and then in the opposite direction, is effectively suppressed. To be done.

FIG. 2 is a block diagram showing the structure of a discharge lamp lighting device according to another embodiment of the present invention. Also in this figure, in order to avoid complication, the illustration of the reflecting mirror is omitted. In this embodiment, a pair of magnets 32a and 32b for generating a magnetic field is added not only to the cathode 12 side but also to the anode 13 side, whereby a magnetic field in a direction orthogonal to the longitudinal direction of the anode 13 is added. Is generated at the tip of the. As a result,
Intermittent movement of the tip of the string-shaped arc at the tip of the anode 13 is also suppressed.

The structure in which the magnetic field is generated only in one direction orthogonal to the longitudinal direction of the electrode has been described above. However,
With the configuration in which the magnetic field is generated in each of two directions orthogonal to the longitudinal direction of the electrode and orthogonal to each other, the movement of the tip portion of the arc can be suppressed more effectively.

Further, the present invention has been described by taking as an example the case of being used as an illuminating device for a photographing device for visual inspection of products. However, the application of the present invention is not limited to such an application, and the present invention can be used as various light sources and light sources that require high brightness, such as light sources for projection televisions, OHPs, and the like, and illumination devices for high-speed imaging devices.

[0024]

As described above in detail, in the discharge lamp lighting device according to the present invention, the end of the string-shaped arc moves instantaneously and intermittently by generating a magnetic field at the tip of the electrode. With the configuration that suppresses the phenomenon described above, the fluctuation of the brightness due to such movement is suppressed, and a high-quality lighting device is realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a discharge lamp lighting device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a discharge lamp lighting device according to another embodiment of the present invention.

[Explanation of symbols]

 10 Metal halide discharge lamp 11 Quartz tube 12 Cathode 13 Anode 20 Power circuit 21 Igniter 22 DC stabilized power supply 23 Controller 31a, 31b, 32a, 32b Magnet

Front page continuation (72) Inventor Koichi Ishida 1-19-12 Umesato, Suginami-ku, Tokyo Nichikan Kogyo Co., Ltd.

Claims (3)

[Claims] 1. A DC lighting type discharge lamp comprising: a discharge lamp; and a power supply circuit which supplies the discharge lamp with a discharge starting voltage necessary for starting discharge and thereafter supplies a DC voltage for maintaining a discharge state. A discharge lamp lighting device, comprising: a magnetic field generation unit that generates a magnetic field in a direction orthogonal to a longitudinal direction of an electrode of the discharge lamp at a tip portion of the electrode. 2. The discharge lamp floodlighting device according to claim 1, wherein the magnetic field generating means includes a pair of magnetic field generating means for generating magnetic fields in directions orthogonal to each other. 3. The discharge lamp floodlighting device according to claim 1, wherein the discharge lamp is a short arc tube.