DE102010026164B4 - Short arc discharge lamp with insert body in the tip end surface of the anode - Google Patents

Abstract

Short-arc discharge lamp in which an anode (3) and a cathode in a light tube are arranged opposite to each other, characterized in that
a recess (4) is formed in a tip end surface (3A) of the anode (3), an insert body made of the same material as that of the anode (3) is inserted into this recess (4), and between the rear end of the insert body and the recess (4) a free space (6) is formed,
wherein a tip end surface (3A) of the insert body (5) lies in the same plane as the tip end surface (3A) of the anode (3).

Description

The present invention relates to a short-arc discharge lamp, and more particularly to a short-arc discharge lamp used as a light source for exposure in the field of semiconductor or liquid crystal fabrication or as a light source for backlighting projectors.

Short-arc discharge lamps are used as a light source for an exposure apparatus or for backlighting projectors due to a short distance between the tip ends of a pair of electrodes disposed opposite to each other in a luminous tube by a combination with an optical system.

JP-A-10-188890 (1998) discloses a conventional short-arc discharge lamp. This conventional short-arc discharge lamp is in 4 shown. A luminous tube 10 of the short-arc discharge lamp 1 includes a central approximately spherical shaped emission portion 11 and sealing portions 12 at both ends thereof. Inside the emission part 10, a cathode 21 and an anode 31 made of tungsten or the like are arranged opposite to each other so as to face each other. In addition, in a luminous space S inside a phosphor such as mercury or xenon is included. Electrode shafts 22, 32 subsequently formed on the cathode 21 and the anode 31 are sealed in the sealing parts 12 via metal foils, not shown.

In recent years, in short-arc discharge lamps used in the manufacturing process of semiconductors or liquid crystal panels, as shown in FIG JP-A-2000-181075 can be seen, for energy saving applied (hereinafter referred to as full-standby lighting operation) lighting method in which the lamp is not always lit with constant energy, but only at the exposure to the rated power lights (normal lighting) and during waiting times such as at the movement of substrates with a minimum power lower than this nominal power is lit (standby lighting). For example, a cycle of a lighting operation for 0.1 to 10 seconds with the rated power in the exposure and a lighting operation for 0.1 to 100 seconds with the standby power lower than the rated power is repeatedly executed during waiting times.

Since there is a change in the heat flow flowing from the arc to the anode when the lamp is switched on and off or when the input power changes during standby lighting operation, the temperature of the anode changes and internal stresses on the anode occur. In this case, the central region 50 of the anode tip end surface facing the arc, as in FIG 5 (a) and (b) shown, the area with the largest temperature change, and therefore the thermal expansion becomes large. In contrast, the temperature change of the annular portion 51 around the circumference of the central portion 50 is smaller than that of the central portion 50, and also its thermal expansion is small. Therefore, by this thermal expansion, the center region 50 experiences compressive stress from the circumferential annular region and, as a result, deforms to protrude from the tip end surface.

Such a projection does not completely return to its original shape even when the temperature of the anode tip end has stabilized in luminous operation at the rated power but remains. Moreover, this shape change repeatedly occurs in the full-standby lighting operation, and the projection increases by accumulation. Then, there is a problem that the discharge concentrates on this enlarged projection portion, the projection portion is abnormally heated, the electrode material evaporates and adheres to the inner wall of the arc tube and the inner wall of the arc tube is blackened, causing a sudden decrease in illuminance.

From the DE 197 29 129 A1 a high-pressure discharge lamp with a cooled electrode is known. In this case, the anode has an anode head with a tip, wherein the tip is thermally separated from the main body of the anode by a gap. The anode head is placed on the body and covers it completely. The anode configuration is thus substantially different from the anode structure of the short arc discharge lamp of the present application.

In view of the problems of the above-mentioned prior art, it is the object of this invention to provide a short arc discharge lamp having an anode structure, thereby alleviating the thermal stress generated at the anode tip end, particularly in short arc discharge lamps employing the full standby lighting method , deformation of the central portion of the anode tip end is prevented, and blackening can be prevented.

The solution to this problem is achieved with the short-arc discharge lamp according to claim 1. Preferred developments are described in the subclaims.

To achieve the above object, the short-arc discharge lamp according to this invention is characterized in that a recess is formed in the tip end surface of the anode, an insert body made of the same material as that of the anode is inserted into this recess, and between the rear end of the insert body and a clearance is formed in the recess, wherein a tip end surface of the insert body is in the same plane as the tip end surface of the anode.

A development consists in that at least part of the free space is present within the range of the heat diffusion length from the anode tip end.

In addition, a further development is that the clearance at a distance L from the anode tip end surface to the free space and a largest cross-sectional area S of the free space in a vertical sectional plane with respect to the electrode axis is in a range of S ≦ πL ² .

Since, according to the short-arc discharge lamp of the present invention, an insert body made of the same material as that of the anode is inserted into a recess formed in the tip end of the anode and a clearance is formed between the rear end of the insert body and the recess, the temperature will change even if the temperature changes Anoden tip end, especially about the full-standby lighting operation, this temperature change by the presence of the free space is not as it is transmitted straight to the rear. In addition, the clearance acts as a distortion relief area allowing thermal expansion and contraction of the insert body. This prevents the anode tip end, i. H. the insert body, so deformed that it comes to a projection. As a result, blackening of the arc tube associated with the evaporation of the electrode is prevented, and a decrease in the degree of maintenance of the illuminance can be prevented.

• 1 ist eine teilweise geschnittene Ansicht des Spitzenendes der Anode einer Kurzbogen-Entladungslampe nach der vorliegenden Erfindung.
• 2 ist eine teilweise geschnittene Ansicht einer anderen Ausführungsform.
• 3 ist eine teilweise geschnittene Ansicht noch einer anderen Ausführungsform.
• 4 ist eine Gesamtansicht des Stands der Technik.
• 5 ist eine erklärende Ansicht des wichtigsten Teils von 4.

The invention will be explained in more detail with reference to drawings. The drawings are schematic, and like reference numerals denote like parts.

• 1 Fig. 10 is a partially cutaway view of the tip end of the anode of a short arc discharge lamp according to the present invention.
• 2 is a partially sectional view of another embodiment.
• 3 is a partially sectional view of yet another embodiment.
• 4 is an overall view of the prior art.
• 5 is an explanatory view of the most important part of 4 ,

1 shows a first embodiment, wherein 1 (a) is a partially sectioned view in the assembled state, and 1 (b) is an explanatory view of the composition process.

In the figures, at the tip end of an anode 3 that z. B. tungsten, a depression 4 formed, located in the top end surface 3A opens. An insert body 5 of the same material as that of the anode 3 is by pressing o. Ä. In this depression 4 and its tip end surface is in the same plane as the tip end surface 3A the anode 3 , Between the rear end of the inserted insert 5 and the depression 4 is a free space 6 educated.

• L: Wärmediffusionslänge (m)
• α: Wärmediffusionsrate (m²/s)
• f: Wiederholungsfrequenz (Hz)

In 1 (a) is the position L of the free space 6 who is in the depression 4 is formed so that at least a part thereof is within the range of the heat diffusion length from the tip end surface 3A located. The heat diffusion length is an index that indicates how far its wavelength reaches in the diffusion of AC-induced heat (a temperature) in a material, and is given by the following formula. $$\text{L}=\surd \left(\mathrm{\alpha }/\text{f}\right)$$

• L: heat diffusion length (m)
• α: heat diffusion rate (m ² / s)
• f: repetition frequency (Hz)

k: Wärmeleitfähigkeit 120 (J/s·m·K) *für Wolfram W ρ: Dichte 19,1 × 10³ (kg/m³) *für W Cp: spezifische Wärme 134,4 (J/kg·K) *für W The heat diffusion rate α is defined as follows: $$\mathrm{\alpha \; =}\text{k}/\left(\mathrm{\rho }\times \text{C}\mathrm{\rho }\right)$$

k: thermal conductivity 120 (J / s · m · K) * for Wolfram W. ρ: density 19.1 × 10 ³ (kg / m ³ ) * for W Cp: specific heat 134.4 (J / kg · K) * for W

To give an example, L is at an anode 3 of tungsten (W) and a repetition frequency f of 1 (Hz) 6.84 mm. At f = 1000 (Hz), L = 0.216 mm.

The heat from the tip end of the anode 3 may be expected in the range exceeding the above range only as a direct-current heat effect and ceases to exhibit a periodic temperature change in this range. In other words, in the area where periodic temperature variation occurs due to the full-standby lighting operation, heat distortion tends to accumulate as compared with other areas, and as a result, a non-conductive effect occurs in the electrode. plastic deformation occurs. However, the presence of the clearance formed in the anode hinders the heat transfer from the anode tip end to the rear, and therefore, the heat distortion based on the thermal expansion difference becomes small.

Although thermal expansion occurs at the anode tip end, since the clearance itself acts as a distortion relief region allowing free thermal expansion and contraction inside the electrode, deformation of the electrode is ultimately suppressed. That is, at the electrode tip end, although a compressive strain corresponding to the thermal expansion, but since this compressive stress is relieved on the side of the free space, deformations in the direction of the electrode tip are suppressed.

However, when the clearance is too large, the cross-sectional area of the heat conduction from the electrode tip to the rear end becomes small, and a temperature increase occurs near the electrode tip end, and therefore the evaporation of the electrode material is promoted, resulting in a decrease in the degree of maintenance the illuminance brings with it. The size of the open space 6 can be made to satisfy a relationship of S ≦ πL ² at a transverse sectional area of the clearance, that is, a maximum cross-sectional area S in a vertical sectional plane with respect to the electrode axis.

2 is a partially sectioned view of a second embodiment, wherein 2 (a) is a partially sectioned view in the assembled state and 1 (b) an explanatory view of the composition process.

In this embodiment, the recess exists 4 from two wells 4A . 4B , The first recess 4A has approximately the same diameter as the insert body 5 on, and inside is the second well 4B formed with a small diameter. The insert body 5 is in the first recess 4A pressed in, and its advancing inward is through the second recess 4B established. The second well 4B forms the free space 6 ,

3 is a partially sectioned view of a third embodiment, wherein 3 (a) is a partially sectioned view in the assembled state and 3 (b) an explanatory view of the composition process.

In this embodiment is at the rear end of the insert body 5 an annular rib 5A projecting formed and formed in the rear end face a round recess area 5B. When the insert body 5 into the depression 4 is pressed, meets the annular rib 5A on the bottom surface of the recess 4 and forms the recessed area 5B the free space 6 , If according to the above in 2 and 3 shown two embodiments of the insert body 5 into the depression 4 is used, it hits the bottom of the depression 4 and automatically becomes the free space 6 educated.

For comparison of the present invention and the prior art, a lighting test was performed on the degree of maintenance of illuminance based on the first embodiment. The lamps used in the experiment had an enclosed amount of mercury of 2 mg / cc and about 3.5 atm of argon. As for the dimensions of the anode (tungsten), the diameter was 29 mm, the total length was 50 mm and the diameter of the tip end was 10 mm. The cathode had a diameter of 12 mm, a taper angle of 60 degrees, and a tip end diameter of 1 mm. The electrode distance before the lighting operation was 6.5 mm.

For this experiment, three kinds of anodes were prepared, and in the anode of the present invention, a recess was formed in the tip end surface of the anode 4 was formed with a diameter of 3.5 mm and a depth of 10 mm and into the recess 4 an insert body 5 with a diameter of 3.5 mm and a thickness of 8 mm was pressed. As a result, between the insert body 5 and the bottom of the well 4 a free space 6 formed with a height of 2 mm.

As the comparative product, an anode was prepared in which the thickness of the insert body was performed the same as the depth of the recess, the insert body was pressed into the recess and no space was available. For the conventional product, an anode was prepared which did not have such a configuration.

For each of these lamps, an accelerated attempt was made to evaluate the degree of illuminance maintenance in a short time ( 100 Hours), wherein a periodic heat load of a violent input power variation width at which the luminous flux was switched every 50 seconds between 50 A and 140 A every other second (0.5 Hz) was applied. Regarding the degree of illuminance maintenance, the degree of illuminance maintenance after 100 hours was calculated with the UV illuminance at a wavelength of 365 nm (i-line) at the start of the lighting operation under the same lighting conditions as a basis.

Freiraum - keiner ∅ 3,5 Höhe: 2 mm Grad der Aufrechterhaltung 52 % (abgebrochen) 65 % 85 % Verformung groß mittel klein The test results are shown in Table 1. Table 1 conventional product Comparative example present invention construction

free space - none ∅ 3,5 Height: 2 mm Degree of maintenance 52% (canceled) 65% 85% deformation large medium small

As can be seen from Table 1, in the conventional product, the center portion of the tip end of the anode deformed so as to protrude violently, and the tip end melted. Since there was a risk of bursting, the lighting test was stopped during its course. At this time, the degree of maintenance of illuminance was 52%. The comparative product deformed so that the pressed-insert body jumped forward. The top end bulged and the degree of illuminance maintenance was 65%. In contrast, in the present invention, the deformation of the insert body constituting the central portion of the tip end was small and the degree of maintenance of the illuminance was good at 85%.

As explained above, in the short-arc discharge lamp of the present invention, an insert body made of the same material as that of the anode is inserted into a recess formed in the tip end of the anode, and a clearance is provided between the rear end of the insert body and the bottom of the recess With a tip end face of the insert body lying in the same plane as the tip end face of the anode, especially in the embodiment of the full standby lighting method with periodic heating of the middle portion of the anode tip end, the heat distortion in the clearance is relieved, thereby giving the effect in that there is no deformation such as local protrusion to the tip end, and a decrease in the illuminance based on blackening by the evaporation of the anode material can be suppressed.

Claims (3)

Short arc discharge lamp in which an anode (3) and a cathode are arranged in a luminous tube opposite each other, characterized in that in a tip end face (3A) of the anode (3) a recess (4) is formed, an insert body of the same Material such as that of the anode (3) is inserted into this recess (4) and between the rear end of the insert body and the recess (4) has a free space (6) is formed, wherein a Spitzendendfläche (3A) of the insert body (5) in the same level as the tip end surface (3A) of the anode (3). Short arc discharge lamp after Claim 1 characterized in that at least a portion of the clearance (6) is present within the range of the heat diffusion length (L) from the anode tip end (3A), the heat diffusion length (L) being an index indicative of the diffusion of AC induced heat in a material indicates how far its wavelength reaches, and wherein the heat diffusion length (L) is given by the following formula: $$\text{L}=\surd \left(\mathrm{\alpha }/\text{f}\right).$$

where α represents the heat diffusion rate of the anode material and f the repetition frequency, wherein the repetition frequency f refers to a cycle in the full standby lighting method in which the lighting operation is carried out first at the rated power and then at the standby power, and further the heat diffusion rate α of the anode material is defined by the following formula: $$\mathrm{\alpha \; =}\text{k}/\left(\mathrm{\rho }\times \text{C}\mathrm{\rho }\right)$$

where k is the thermal conductivity of the anode material, ρ is the density of the anode material, and Cρ is the specific heat of the anode material. Short arc discharge lamp after Claim 1 or 2 characterized in that the clearance (6) at a distance L from the anode tip end face (3A) to the clearance (6) and a largest cross sectional area S of the clearance (6) in a vertical sectional plane with respect to the electrode axis in a range of S ≤ πL ² .

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