JP2013098145A - Short arc type high-pressure discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure for preventing a cylindrical part from being deformed by making a hollow effect sure in a slit in a short arc type high-pressure discharge lamp in which a pair of electrodes respectively comprising an electrode head part and an electrode shaft part are located oppositely, at least an electrode performing a cathode operation in the pair of electrodes has an annular slit having depth in an axial direction at a rear end of the head part, and the cylindrical part is formed at a rear end side of the head part by the slit.SOLUTION: An outer circumferential surface of the annular slit is gradually reduced in diameter toward a head tip, and the width of the slit is reduced as it goes toward the head tip.

Description

  The present invention relates to a short arc type high pressure discharge lamp that is used as a backlight of a projector apparatus, and more particularly to a short arc type high pressure discharge lamp having a tubular slit at the rear end of an electrode head.

  For example, in a projector apparatus such as DLP (Digital Light Processing: registered trademark) using DMD (digital micromirror device: registered trademark), an image is illuminated uniformly and sufficiently with color rendering on a rectangular screen. Therefore, a short arc type high-pressure discharge lamp enclosing mercury is used as a light source. Recently, such high-pressure mercury lamps have been further reduced in size and made into point light sources, and those with extremely small distances between electrodes have been put into practical use.

For example, Japanese Patent Laying-Open No. 2010-165661 (Patent Document 1) describes a short arc type high-pressure discharge lamp used as a light source of a liquid crystal projector apparatus. FIG. 3 is an overall view thereof, and FIG. 4 is an enlarged view of an electrode.
In FIG. 3, the high-pressure discharge lamp 10 includes a light-emitting tube 11 including a light-emitting portion 12 having a discharge space S therein, sealing portions 13 and 13 provided on both sides of the light-emitting portion 12, and a discharge space S. The electrodes 20 are arranged so as to face each other.
The discharge space S is filled with a predetermined amount of mercury as a luminescent substance, other noble gases for starting assistance, and the like. The base ends of the electrodes 20 and 20 are connected to the metal foils 14 and 14 in the sealing portions 13 and 13 by welding or the like, and the metal foils 14 and 14 are connected to the external leads 15 and 15 protruding to the outside of the sealing portion 13. They are connected by welding or the like, and are supplied with power from the external leads 15 and 15.

The electrode structure in the high-pressure discharge lamp 10 is shown in FIG. 4, and the electrode 20 includes an electrode head 21 and an electrode shaft portion 22. A relatively small-diameter frustoconical protrusion 21a is disposed at the distal end of the electrode head 21, and the diameter of the protrusion 21a greatly increases toward the rear from the large-diameter end. The entire head 21 has a substantially conical shape.
The size of the head 21 needs to have a certain heat capacity so that melting and evaporation are not easily generated even by a thermal load caused by a discharge arc, and it is necessary to secure a volume for that purpose. On the other hand, it is necessary to prevent the light generated by the arc of the discharge lamp from being blocked by the electrodes.

The electrode 20 is formed with an annular slit 23 having a certain width and opened in the rear end surface 21b with a depth in the axial direction at the rear end 21b of the head portion 21. An annular cylindrical portion 24 is formed at the rear portion of the.
Since the cylindrical portion 24 has an integral structure with the electrode head portion 21 made of tungsten, even if the electrode 20 is worn out due to long-term use, the cylindrical portion 24 has a self-holding force and can be dropped. This structure is less likely to cause defects.
For example, as a comparison object, a coil wound around the electrode head has the same cylindrical appearance, but is discontinuous in the axial direction, and may fall if the coil strand is cut However, according to this prior art, the cylindrical portion 24 is composed of an integral cylindrical tungsten, and thus has such a structure that it can withstand long-term use without causing such problems. .

By the electrode structure having such an annular slit, the heat of the cylindrical portion of the electrode head heated at the time of starting the lamp is not directly transmitted to the electrode shaft portion due to the presence of the slit, and thus the heating of the shaft portion is prevented. It is expected that the sealing portion is not overheated by the shaft portion, the quality of the quartz glass constituting the arc tube is prevented from being changed, and deformation of the electrode shaft portion can be prevented.
By the way, although there is no positive or explicit description in Patent Document 1, it is also expected that the slit will exhibit a hollow effect at the time of start-up. It can reduce and can suppress the blackening of an arc_tube | light_emitting_tube.

However, in order to obtain the hollow effect, it is necessary that the relationship between the ion density (≈pressure) in the discharge space and the width of the slit is appropriate. However, if the pressure increases as the temperature rises during lighting, there is a problem that the hollow effect cannot be expected until the relationship with the width becomes appropriate.
Moreover, if the temperature of the boundary region between the cylindrical part and the head rises excessively due to the inflow of heat from the arc during steady lighting, the boundary part is deformed, and the cylindrical part is tilted, bent, and eventually broken. As a result, there was a problem that the lamp function was lowered.
Such deformation or breakage of the electrode cannot satisfy the function required for the video apparatus, and becomes a serious defect event as a product.
In order to avoid this problem, simply increasing the thickness of the cylindrical part or the boundary region to obtain strength results in an increase in the volume of the cylindrical part and impedes the original function of this electrode. Become.

JP 2010-165661 A

  In view of the above-described problems of the prior art, a pair of electrodes each having an electrode head portion and an electrode shaft portion are opposed to each other, and at least a cathode-operating electrode of the pair of electrodes In a short arc type high-pressure discharge lamp having an annular slit having an axial depth at the rear end and a cylindrical portion formed by the slit on the rear end side of the head, the cylindrical portion is formed by the slit. While maintaining the effect that heat transfer from the electrode shaft to the electrode shaft is prevented, the hollow effect by the slit is sufficiently obtained, and the temperature of the boundary region between the cylindrical portion and the head is not excessively increased. It is intended to provide a structure that can ensure the heat capacity.

In order to solve the above problems, a short arc type high-pressure discharge lamp according to the present invention comprises:
The annular slit formed in the electrode head is characterized in that the outer circumferential surface thereof is gradually reduced in diameter toward the head tip side, and the width of the slit decreases as it goes toward the head tip side. To do.
Further, the annular slit has a V-shaped cross section.
The angle between the outer circumferential surface of the slit and the axis of the electrode is 5 ° to 45 °.

According to the present invention, since the width of the slit formed at the rear end of the electrode head changes so as to decrease toward the head tip side, the pressure in the discharge space varies due to lighting, and the hollow effect Even if the proper separation distance for obtaining the distance is changed, the appropriate separation distance is provided at any position in the width where the separation distance changes, and an accurate hollow effect can be obtained.
In other words, the range of pressure at which the hollow effect occurs is widened, and the time for waiting for a pressure change due to a temperature rise to cause the hollow effect at the start of lighting is shortened. That is, the hollow effect is generated more quickly at the time of lighting, and the wear of the cathode at the start of lighting is reduced.
In addition, the outer circumferential surface of the slit is gradually reduced in diameter toward the tip of the head, and the width of the slit decreases as it goes toward the tip of the head, so that the boundary region between the cylindrical portion and the head As a result, the heat capacity is sufficiently secured, and thermal deformation at the portion is less likely to occur.

Sectional drawing of the electrode of the short arc type high pressure discharge lamp which concerns on this invention. The table | surface which shows the effect of this invention. FIG. 6 is an overall cross-sectional view of a conventional short arc type high pressure discharge lamp. Sectional drawing of the electrode of FIG.

In FIG. 1, an electrode 1 comprises an electrode head portion 2 and an electrode shaft portion 3. The head portion 2 opens at the rear end face 2a at the rear end of the head portion 2, and has an axial depth. An annular slit 4 having a thickness is formed, and a cylindrical portion 5 is formed on the rear end side of the head 2 by the slit 4.
The annular slit 3 is reduced in diameter so that its outer circumferential surface 3a is closer to the tip side of the head 2, while the inner circumferential surface 4b of the slit 4 is parallel to the electrode axis O. Thereby, the cross section of the slit 3 is V-shaped, and its width is gradually smaller toward the head end side. Due to the tapered shape of the slit 3, the cylindrical portion 5 gradually increases from the thickness Xb at the rear end 5 b (head 2 rear end side) toward the thickness Xa at the tip 5 a (head 2 tip side). The wall thickness Xa at the tip 5a is maximized.
In the above, the inner circumferential surface 4b of the slit 4 does not necessarily have to be parallel to the axis O, and the diameter may be increased toward the head tip side. It only needs to be smaller toward the tip side.
Such a gap can be easily formed by, for example, laser processing.

  The electrode configured as described above is an electrode that operates as a cathode, and is a cathode in a discharge lamp that is lit in direct current, both electrodes in a discharge lamp that is lit in alternating current, and further, In the case of direct current lighting at start-up, the electrode operates as a cathode during direct current lighting.

Hereinafter, experiments were conducted to verify the effects of the present invention. The specific lamp specifications and electrode specifications are as follows.
lamp:
Mercury enclosed amount: 0.15 mg / mm ³ or more Noble gas (argon gas): 10 to 26 kPa
Halogen encapsulation amount: 10 ⁻⁶ to 10 ⁻² mol / mm ³
Arc tube maximum outer diameter: 12mm
Distance between electrodes: 1.2mm
Arc tube inner volume: 120 mm ³
Rated voltage: 85V
Rated power: 300W
Lamp wall load value of the lamp: 2.1 W / mm ³

Electrode dimensions Shaft diameter D2: φ0.5mm
Diameter (maximum) outer diameter part D1: 3mm
Total head length L1: 3mm
Thickness Xb at the rear end of the cylindrical part: 2 mm
Full length L2 of slit: 0.6mm

Various changes were made to the angle α of the outer circumferential surface of the annular slit formed on the electrode of this lamp, and the transition time from the glow discharge to the arc discharge at the start was measured to confirm the startability.
A lamp of each specification was produced, and the lighting / flashing test was repeated 100 times.
The result of this experiment is shown in FIG. In the figure, a lamp 1 is a conventional lamp (FIG. 4) as a comparative control.
In addition, the thickness ratio of the front-end | tip part of a cylindrical part and a rear-end part is calculated and described.

<Startability evaluation>
○: Glow-arc transition occurs quickly, no problem (within 1 second)
Δ: Glow-arc transition takes some time, but no problem (1-3 seconds)
×: Slow glow-arc transition (3 seconds or more)

As a result, it can be seen that an angle α of the outer circumferential surface of the slit of 5 ° to 45 ° is preferable in the evaluation of ◯.

As described above, in the short arc type high-pressure discharge lamp of the present invention, the width of the annular slit provided in the electrode head, that is, the separation distance between the cylindrical portion formed by the slit and the electrode body is on the electrode tip side. Since the appropriate distance for producing the hollow effect corresponding to the pressure in the discharge space is provided by any one of the slit widths, an accurate hollow effect can be obtained.
Further, the cylindrical portion has a large thickness at the tip thereof, a sufficient heat capacity is ensured, and thermal deformation does not occur at the portion.

DESCRIPTION OF SYMBOLS 1 Electrode 2 Electrode head 3 Electrode axial part 4 Slit 4a Outer circumferential surface 4b Inner circumferential surface 5 Cylindrical part 5a Tip 5b Rear end Xa Tip thickness Xb Rear end thickness α Between slit outer circumferential surface and shaft center angle

Claims (3)

A pair of electrodes, each consisting of an electrode head and an electrode shaft, are opposed to each other, and at least a cathode-operating electrode of the pair of electrodes is an annular slit having an axial depth at the rear end of the head In a short arc type high-pressure discharge lamp in which a cylindrical portion is formed by the slit on the rear end side of the head,
A short arc type high-pressure discharge lamp characterized in that the outer circumferential surface of the annular slit is gradually reduced in diameter toward the head tip side, and the width of the slit decreases as it goes toward the head tip side.   2. The short arc type high-pressure discharge lamp according to claim 1, wherein the annular slit has a V-shaped cross section. The short arc type high-pressure discharge lamp according to claim 1 or 2, wherein an angle formed between an outer circumferential surface of the slit and an axis of the electrode is 5 ° to 45 °.

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