Patent Grant
7719193
This application claims priority from Japanese Patent Application Ser. No. 2006-023675 filed on Feb. 2, 2007, the contents of which are incorporated herein by reference in its entirety.
Described herein is a xenon lamp used as a light source in a projector in which, for example, DLP® technology (Digital Light Processing) may be used.
This discharge lamp 1 comprises a bulb which is made of quartz glass, and has an arc tube 2 and sealed tube portions 3, and a cathode 4 and an anode 5. The cathode 4 and the anode 5 are provided so as to face each other in an arc tube 2 and are supported by respective electrode rods 6 made from tungsten. Moreover, support tube bodies 7 are fixed in the sealed tubes 3, respectively. Each of the support tube bodies 7 is cylindrical and is made from quartz glass and has a through hole therein, extending in the axis direction. While the electrode rods 6 are inserted in the respective support tube bodies 7 so that the rods are supported by the respective support tube bodies, the rods are attached in a way of sealing to the sealed tubes 3 by connection glass members 8. These electrode rods 6 extend outward from outer ends of the bulb, respectively, and serve as external lead rods from which electric power is supplied to the cathode 4 and the anode 5.
However, since elements of a digital projector are smaller in size, than those of the conventional film projector, the use efficiency of light decreases. Therefore, the discharge lamp 1 having high intensity is demanded as a light source. If an electric power input is increased to raise the intensity of the discharge lamp 1, expansion and contraction of the arc will occur. The intensity is related to the temperature of the tip of the cathode, in that the temperature of the tip portion 22 becomes high, as the intensity becomes high. Since the speed of evaporation of thorium will become high when the temperature of the tip portion 22 becomes high, the balance of demand and supply of thorium is disrupted. Therefore, the thorium is excessively consumed, so that thorium becomes insufficient, whereby expansion and contraction of an arc occurs. If expansion and contraction of an arc occurs, since an arc shakes, the luminescent spot moves. Since the position of the luminescent spot is not settled at a focal point within a condensing mirror if the luminescent spot moves so that an optical output fluctuates, flickering is generated when light is irradiated on a screen. Moreover, in order that expansion and contraction of an arc may not occur, it is conceivable that the cathode 4 and the anode 5 are arranged so that the distance therebetween may become long, thereby decreasing the temperature of the tip portion 22, or that the diameter at the tip of the tip portion 22 is enlarged, so that heat is dispersed, thereby making temperature per unit area low. However, if the distance of the cathode 4 and the anode 5 becomes long or the diameter at the tip of the tip portion 22 is enlarged, although expansion and contraction of an arc does not occur, since the light intensity decreases greatly, the light intensity of a light source may not be increased.
Described herein is a discharge lamp having high intensity in which the luminescent spot of an arc is stabilized.
The present discharge lamp, comprising a cathode and an anode which face each other in an arc tube, wherein the cathode is made of tungsten in which thorium oxide is doped, wherein the cathode has a cylindrical body portion, a tip portion having a cone shape, and a middle portion formed between the body portion and the tip portion, and wherein an angle of the tip portion is 55 degrees or more and 65 degrees or less, and an angle formed by the meddle portion is smaller than that of the tip portion.
Also, in the discharge lamp, an axial direction length of the tip portion may be 3 mm or more but 4 mm or less, and an angle formed by side faces (ridge lines) of the middle portion may be 30 degrees or more but 40 degrees or less.
In such a discharge lamp according to an embodiment, the angle of a tip portion may be 55 degrees or more and 65 degrees or less. Thus, since the angle formed by the side faces of a middle portion is smaller than the angle of a tip portion, the luminescent spot of an arc can be stabilized in the high-intensity discharge lamp.
Other features and advantages of the present discharge lamp will be apparent from the ensuing description, taken in conjunction with the accompanying drawings, in which:
A first embodiment is explained below.
Thus, connection glass members 8 are arranged in the respective sealed tubes 3. One end of each connection glass member 8 is made of glass whose expansion coefficient is matched to that of quartz glass which forms the sealed tubes 3, and is welded with an end portion of the sealed tube 3. Another end of each connection glass member 8 is made of glass whose expansion coefficient is matched to that of tungsten which forms the electrode rod 6, and is attached to the electrode rod 6 by sealing. Moreover, a pair of electrode rods 6 is projected from the respective connection glass members 8 to the exterior of the respective sealed tubes 3, and the electric supply mechanism which is not illustrated is connected to these projected portions.
However, since the tip portion 22 becomes high temperature at the time of lighting when the angle θ1 of the tip portion 22 is too small, crystal grain of the tungsten grows thereby becoming large, and flow paths of the doped thorium oxide are closed, so that the thorium becomes deficient. If the thorium runs short, an arc will shrink and many electrons will be emitted. Since the temperature of the cathode 4 rises if an arc contracts, the amount of supply of the thorium temporarily supplied from the middle portion 25 increases, so that the arc expands. However, since the crystal grain of the tungsten of the tip portion 22 grows again, the thorium becomes insufficient.
Thus, when the angle θ1 of the tip portion 22 is small, expansion and contraction of the arc occurs. On the other hand, when the angle θ1 of the tip portion 22 is too large, since the temperature of the tip portion 22 at the time of lighting drops, expansion and contraction of the arc can be prevented, but there is a problem that the light intensity decreases.
Cathode
Discharge Lamp
The expansion and contraction of an arc repeatedly appears as rises and falls of lamp voltage, in which the voltage change is 0.2 V to 0.5 V. For example, a period of the voltage fall is one to five minutes, and after the voltage fall, the voltage rises and becomes stable for four minutes to 9 minutes, that is, a period of the cycle is five minutes to 10 minutes. A cycle of the voltage fall and the voltage rise is repeated for a couple of hours to several dozen hours. The reference symbol “x” was put down when occurrence of expansion and contraction of an arc was assumed when the cycle of the voltage rise and the voltage fall (the period of the cycle is 5 to 10 minutes) is repeated, and a reference symbol “◯” was put down when the light intensity was 80000 lm or more. This result shows that expansion and contraction of an arc does not occur when the angle θ1 of the tip portion was 55 degrees or more. Moreover, when the angle θ1 of the tip portion was 65 degrees or less, the light intensity was sufficient. As mentioned above, if the angle θ1 of the tip portion was set to a range of 55 degrees to 65 degrees (55 degrees≦θ1≦65 degrees), and the angle θ2 formed by the side faces of the middle portion was set so as to be smaller than the angle θ1 of the tip portion, it turned out that in a discharge lamp with high intensity, the luminescent spot of an arc could be stabilized.
Cathode
Discharge Lamp
Flicker appears as change of the voltage impressed to the discharge lamp. It is assumed that flicker occurred, when the voltage impressed to the discharge lamp changes by 1.2 V or more, and the time from start of lighting to time of occurrence of the flicker was measured. Since it is not practical unless it is lighted with the arc of the stable luminescent spot for at least 500 hours or more, ◯ was put down when lighting time until the flicker occurred was 500 hours or more, and x was put down when it is 500 hours or less. As a result, it turned out that when the axial direction length A of the tip portion was in a range of 3 mm or more but 4 mm or less (3 mm≦A≦4 mm), and the angle θ2 formed by the side faces of the middle portion was 30 degrees or more but 40 degrees or less (30 degrees≦θ2≦40 degrees), a period from the start of lighting to a time when a flicker occurred was 500 hours or more. Accordingly, when the axial direction length A of the tip portion was set to the range of 3 mm or more but 4 mm or less (3 mm≦A≦4 mm), and the angle θ2 formed by the side faces of the middle portion was set to the range of 30 degree or more but 40 degrees or less, the demand of the thorium at the tip portion 22 and supply of the thorium from the middle portion 25 was balanced, so that it was possible to offer a discharge lamp with high intensity in which the arc of the stable luminescent spot can be maintained for 500 hours or more.
A second embodiment of is explained.
The preceding description has been presented only to illustrate and describe exemplary embodiments of the discharge lamp according to the present invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. The invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-023675 | Feb 2007 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20050099121 | Kikuchi et al. | May 2005 | A1 |
| Number | Date | Country |
|---|---|---|
| 02-304857 | Dec 1990 | JP |
| 03-225741 | Oct 1991 | JP |
| 10-283987 | Oct 1998 | JP |
| 2002-50315 | Feb 2002 | JP |
| 2005-142071 | Jun 2005 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20080185965 A1 | Aug 2008 | US |
