Patent Grant
7057346
1. Field of the Invention
The invention relates to a short arc ultra-high pressure mercury lamp. The invention relates especially to a discharge lamp used as a light source for a liquid crystal display device in which the light source is an ultra-high pressure mercury lamp filled with at least 0.15 mg/mm3 of mercury, and in which the mercury vapor pressure during operation is greater than or equal to 110 atm. The discharge lamp can also be used in a projector device such as a digital light processor (DLP) or the like having a digital micro mirror device (DMD).
2. Description of the Related Art
In a projector device of the projection type, there is a demand for illumination onto an image device in a uniform manner and with adequate color rendering. The light source is therefore often a metal halide lamp which is filled with mercury and a metal halide. Furthermore, recently smaller and smaller metal halide lamps and point light sources are being produced for such use and these lamps have extremely small distances between the electrodes.
Instead of metal halide lamps, discharge lamps with an extremely high mercury vapor pressure, for example with 150 atm, have been recently proposed. In these lamps, the broadening of the arc is suppressed (the arc is compressed) by the increase of the mercury vapor pressure and a substantial increase of light intensity is realized. Lamps of these ultra-high pressure discharge type are disclosed, for example, in Japanese Patent document HEI 2-148561 (see the English equivalent—U.S. Pat. No. 5,109,181) and Japanese Patent document HEI 6-52830 (see the English equivalent—U.S. Pat. No. 5,497,049).
When an ultra-high pressure mercury lamp is used, a pair of opposed electrodes are positioned with a spacing distance of at most 2 mm in a silica glass arc tube filled with at least 0.15 mg/mm3 of mercury and halogen in the range of 1×10−6 μmole/mm3 to 1×10−2 μmole/mm3. The main purpose of adding the halogen is to prevent devitrification of the arc tube. However, when constructed in this manner a so-called “halogen cycle” arises.
In the above described ultra-high pressure mercury lamp (hereinafter also called only a “discharge lamp”), the phenomenon occurs that, in the course of operation, projections are produced on the electrode tips. This phenomenon is not entirely clear, but the following can be reliably determined.
The tungsten which is vaporized from the high temperature area in the vicinity of the electrode tip during lamp operation combines with the halogen and residual oxygen which are present in the arc tube. When bromine (Br) is added as the halogen, it is present in the form of a tungsten compound such as WBr, WBr2, WO, WO2, WO2Br, WO2Br2 or the like. These compounds decompose in the gaseous phase in the high temperature area in the vicinity of the electrode tip and yield tungsten atoms or cations. Due to thermal diffusion (i.e., diffusion of the tungsten atoms which are moving from the high temperature area in the gaseous phase (=arc center) in the direction of the low temperature area (=vicinity of the electrode tip)) and due to the fact that in the arc the tungsten atoms are ionized, i.e., as cations, the tungsten cations are pulled during operation of the electrode as a cathode by the electrical field in the direction to the cathode. The tungsten vapor density in the gaseous phase in the vicinity of the electrode tip therefore becomes high, which results in precipitation on the electrode tip to form the tungsten projections. The formation of the above described projections is disclosed, for example, in Japanese Patent document 2001-312997 (see the English equivalent—U.S. Pat. No. 6,545,430).
a) and 7(b) each schematically show the electrode tips and projections. In the
However, the formation and growth of the above described projections have some disadvantages.
Fluctuation of the Lamp Voltage—The above described projections are not present in the lamp when it is manufactured, but the projections are produced and grow in the course of subsequent operation. The formation of projections also depends on the types of lamps and the like, but after for example 80 to 100 minutes have passed, the growth is essentially ended. During formation of these projections and after usage is ceased for the first time, the distance between the electrodes in the course of operation has been shortened. Additionally, the operating voltage of the discharge lamp is reduced.
Reduction of the Light Utilization Efficiency—The above described projections do not always form on the electrode axis. If, for example, as in
A primary object of the invention is to devise an ultra-high pressure mercury lamp in which the above described disadvantages, caused by projections formed on the electrode tips, can be eliminated.
The above described object is achieved according to a first embodiment of the invention in which a short arc ultra-high pressure mercury lamp, which includes a silica glass arc tube having positioned therein a pair of opposed electrodes spaced apart a distance of less than or equal to 2 mm and filled with greater than or equal to 0.15 mg/mm3 mercury, rare gas and halogen in the range from 1×10−6 μmole/mm3 to 1×10−2 μmole/mm3, has at least one electrode of the electrode pair which includes a part with a greater diameter formed on the shaft by melting. A projection is formed by using the tip of the electrode shaft, and there is a decreasing diameter part which extends from the part with the greater diameter in the direction to the projection and which is formed by melting.
The discharge lamp of the invention is characterized specifically in that the projections do not form and grow in the course of operation, but that they are formed beforehand during the production step for the electrodes. This arrangement makes it possible to keep the lamp voltage constant from the start of lamp operation and furthermore to produce an arc discharge between the projections which constitute the desired arc formation positions. Thus, the disadvantage of arc spot deviations from the optical system is eliminated. Since the projections are formed by the shafts of the electrodes, the production process is simplified, and, furthermore, the discharge arc can be positioned at the correct point, i.e., from a starting point which is located on the projection.
One embodiment of the invention is characterized in that the ratio L1/D1 of the value of the maximum outside diameter D1 of the above described part with the decreasing diameter to the distance L1 between the tip of the above described projection and the maximum outside diameter of this part with a decreasing diameter in the axial direction is 0.5 to 1.5, and more preferably the above described ratio L1/D1 is 0.8 to 1.2.
Still another embodiment of the invention is characterized in that the width of the above described part with a decreasing diameter or of the above described part with a larger diameter at a distance of 0.5 mm from the tip of the projection is 0.5 mm to 1.0 mm. In the above described embodiment, the electrode shape is established with specific numerical values.
Still another embodiment of the invention is characterized in that the above described part with a decreasing diameter is formed by melting through irradiation with laser light or electron beams. That is, the above described cannon ball-shaped electrodes can be advantageously formed by irradiation with laser light or electron beams. Specifically, the electrode surface is melted and shaped with high precision by irradiation with laser light from a small diameter light beam.
Still another embodiment of the invention is characterized in that the side of the above described part with the decreasing diameter is provided with a corrugated shape. While, in another embodiment of the invention, the above described part with the larger diameter is provided with a coil-like shape. Further, another embodiment of the invention is characterized by the area in which the part with the decreasing diameter is connected to the part with a larger diameter is formed in fillet-like shape.
The invention is further described below with reference to the accompanying drawings.
a) and 2(b) each schematically show the arrangement of the electrodes of an ultra-high pressure mercury lamp of the invention;
a) to 3(d) each schematically show the arrangement of one electrode of an ultra-high pressure mercury lamp of the invention;
a) to 4(d) each schematically show the arrangement of one electrode of an ultra-high pressure mercury lamp of the invention;
a) to 5(c) each schematically show the arrangement of one electrode of an ultra-high pressure mercury lamp of the invention;
a) and (b) each schematically show the arrangement of the electrodes of a conventional ultra-high pressure mercury lamp.
The light emitting part 11 is filled with mercury, a rare gas and a halogen gas. The mercury is used to obtain the required wavelength of visible radiation, for example, to obtain radiant light with wavelengths from 360 nm to 780 nm, and is added in an amount of at least 0.15 mg/mm3. The added amount of mercury differs depending on the temperature condition, but during operation, an extremely high vapor pressure, i.e., at least 150 atm, is achieved. By adding a larger amount of mercury, a discharge lamp with a high mercury vapor pressure during operation of at least 200 atm or at least 300 atm can be produced. That is, the higher the mercury vapor pressure, the more suitable the light source for use in a projector device. The rare gas can be argon, at roughly 13 kPa, which enables the starting property to be improved.
The halogens can be iodine, bromine, chlorine and the like in the form of a compound with mercury or another metal. The halogen is added in an amount which ranges from 10−6 μmol/mm3 to 10−2 μmol/mm3 which enables a prolonged service life. For an extremely small discharge lamp with a high internal pressure, such as in the discharge lamp of the invention, the main purpose of adding the halogen is to prevent devitrification of the discharge vessel.
Normally, the lamp is operated using an alternating current. While the numerical values of the discharge lamp are shown by way of example below:
Such a discharge lamp can be located in a small projector device that is as small as possible. Since the overall dimension of the projector device is extremely small and since there is a demand for high light intensity, the thermal influence within the arc tube portion is therefore extremely limited, i.e., the value of the wall load of the lamp is 0.8 W/mm2 to 2.0 W/mm2, specifically 1.5 W/mm2.
The lamp of the invention, which has such a high mercury vapor pressure and a high value of the wall load, leads to the ability of the discharge lamp to produce radiant light with good color rendering when installed in a projector device or a presentation apparatus, such as an overhead projector or the like.
a) and 2(b) each schematically show the electrodes 1 in an enlargement.
The electrode 1 includes a projection 2, a part with a decreasing diameter 3, a part with a larger diameter 4 and a shaft 1b. The spherical part 1a in
For example, for the part of the electrode with the greater diameter 4, filamentary tungsten can be wound in the manner of a coil. The greater diameter part 4 acts as a starting material through the concave-convex effect of the surface when the lamp operation begins (start position). Moreover, greater diameter part 4 makes the breakdown easy through the concave effect of the surface when the lamp is ignited. Since the coil is thin, it is easily heated which simplifies the transition from a glow discharge to an arc discharge. Further, the part with a decreasing diameter 3 is located between the part with a larger diameter 4 and the tip projection 2 and is formed, as is described below, by the melting of the tungsten.
a) to 3(d) schematically show the process for producing the electrode 1. That is,
The numerical values are shown by way of example below.
Furthermore, the position of the filament coil 4′ is in the range from 0.4 mm to 0.6 mm from the tip of the shaft 1b. The filament coil 4′ is wound proceeding from a position which can be 0.5 mm away from the tip of the shaft 1b. Additionally, the position of the filament coil 4′ is in the range from 1.5 mm to 3.0 mm in the axial direction, e.g., the coil 4′ is wound in a length of 1.75 mm.
The wire diameter of the filament coil 4′ is in the range from 0.1 mm to 0.3 mm, e.g., 0.25 mm. The two-layer winding of the shaft 1b in the above described manner easily forms a tapering shape. This wire diameter and this number of layers of the filament coil 4′ can be suitably adjusted according to the particular requirements of the discharge lamp and according to the light beam diameter of the laser light.
b) shows a state in which the coil 4′ is irradiated with laser light. The laser light is radiant light, e.g., from a YAG laser, which irradiates the coil 4′ at a position which is closest to the tip of the shaft 1b and can proceed, if necessary, towards the rear end such that the entirety of the filament coil 4′ is irradiated. The uniform irradiation of a given position of the coil 4′ with laser light, of a small light beam diameter, results in the coil 4′ on the shaft 1b being melted in the manner illustrated. In this way, the shape of the electrode can be matched to the specification of the discharge lamp.
The filament coil 4′ can be irradiated perpendicularly with laser light, or, as illustrated in
As is shown in
Furthermore, it is within the scope of the invention to not limit to irradiation with laser light to only four directions, but that irradiation with laser light from one direction, two directions, three directions, five directions or some other number of directions is possible.
It is preferred that the light beam diameter is roughly equal to the diameter of the electrode axis. The numerical values are shown by way of example below.
c) shows the state of the electrode in which the part with a decreasing diameter 3 has been formed by the above described laser light irradiation process. It is noted that the surface of the part 3 with the decreasing diameter and the surface of the part 4 with a greater diameter 4 have been melted and are now smooth. Further, it is not necessary to melt the interior of the parts 3 and 4 of the electrode. That is, the desired shapes can be produced by merely melting of the surfaces.
The numerical values are shown, by way of example, below.
The electrode arrangement of the discharge lamp of the invention is characterized in that the coil wound on the shaft is irradiated with laser light and that the electrode provided with a projection is shaped by melting. The shape of the electrode can be adjusted by laser irradiation such that a projection having small dimension remains.
A corrugation can be formed in the surface of the part with a decreasing diameter by melting the tungsten filament with laser light irradiation from three to four directions, one direction after the other, such that the decreasing diameter coiled filament is heated and shaped in an interrupted manner followed by cooling and solidification. This is possible due to the thermal effect being limited to an extremely small area in which shaping takes place upon heating for a short duration.
Instead of laser light irradiation, electron beams can also be used for the irradiation. Since an electron beam can have a diameter that is small, the electron beam is also well-suited for melting extremely small areas of tungsten filament in the invention. For example, the electron beam device disclosed in Japanese patent disclosure document 2001-59900 and Japanese patent disclosure document 2001-174596 is especially suited for the practice of the invention due to its small shaped beam.
The production of electrodes using conventional TIG welding, instead of laser light or an electron beam, becomes difficult when the electrode diameter is less than or equal to 1 mm. This is because in TIG welding the entire coil 4′ serves as the electrode (anode) during welding, and, therefore, fine melt control for formation of the projection can be achieved only with great difficulty. However, if forming the desired projection and the desired electrode shape of the invention is successful by TIG welding, the invention is not limited only to laser light irradiation and electron beam irradiation, but can include conventional TIG welding as well.
The electrode arrangement of the discharge lamp of the invention is provided with the projection using the shaft of the electrode prior to construction of the discharge lamp. That is, the projection on the electrode arrangement of the discharge lamp of the invention is not produced in the course of operation of the discharge lamp, i.e. by the natural phenomenon described previously, but that it is produced beforehand in the described production process. In this way, the arc discharge between the projections can be produced with certainty from the start of lamp operation and the lamp voltage maintained at an essentially constant value. This eliminates the disadvantage of a major reduction of lamp voltage due to production of the projections during operation and the disadvantage of reduction of the degree of light utilization as a result of the unwanted occurrence of an arc position.
In the previous discharge lamps, an ultra-high pressure mercury lamp is constructed in which the distance between the electrodes is at most 2 mm and in which the light emitting part is filled with at least 0.15 mg/mm3 of mercury, rare gas and halogen in the range from 10−6 μmole/mm3 to 10−2 μmole/mm3. Further, since the discharge lamp has the above described arrangement, in the course of lamp operation projections are formed on the electrode tips.
It may be possible that there is a discharge lamp with projections or the like formed inherently beforehand among those discharge lamps which do not have the above described inventive arrangement and which have completely different applications and the like. However, since in such discharge lamps there is no technical problem and object associated with respect to production and growth of projections, it can be stated that any such discharge lamps relate to a completely different field than the invention described above.
The invention of the currently described discharge lamp, used under the conditions in which in the course of lamp operation projections are normally formed and grow, substantially eliminates the formation and growth of the projections during operation of the discharge lamp and thus eliminates the disadvantages associated with this phenomenon.
It is of particular note that the projection growth disclosed in Japanese patent disclosure document 2001-312997 (see the English equivalent—U.S. Pat. 6,545,430) described previously is characterized in that the conditions for projection growth are determined for each lamp, e.g., the properties of the individual discharge lamp, the operating conditions and the like, and the projections form as a natural phenomenon proceeding from the zero state prior to use of the discharge lamp. On the other hand, in the discharge lamp of the invention, based on the operating specification conditions determined beforehand and the properties of the discharge lamp (distance between the electrodes, the amount of gas added and the like), the size of the projection can be estimated and artificially produced using the tip of the shaft as discussed above. In this respect, the two technical approaches differ considerably from one another.
The various shapes of the electrodes of the invention are described with reference to
a) illustrates the embodiment in which the part with the decreasing diameter in the direction toward the projection of the tip is hemispherical while
When the part with the decreasing diameter decreases its diameter from the part with the larger diameter in the direction toward the projection during melt formation process described above, the shapes are not limited to those described above, but other variation can also be constructed. For each variation, however, the projection is formed at the tip area of the electrode shaft. These shapes can be produced with high precision by the above described laser light irradiation process.
a) to 5(c) each schematically show the bullet tip-shaped electrode shown in
In
By fixing the numerical values in this way, the surface of the part with the decreasing diameter assumes a shape which is vigorously subjected to the radiant heat from the arc discharge. Specifically, the tip surface of the electrode is massively subjected to radiant heat from the arc by which melt vaporization forms on the tip surface of the electrode. This melt vaporization of the electrode material not only makes the shape of the electrode unstable, but causes the disadvantage of contamination of the inside of the arc tube by the vaporized material and similar disadvantages. Furthermore, by vaporizing the tungsten as the electrode material the amount of tungsten which floats within the light emitting part is increased, by which the growth of the projection can be intensified. In the current invention, the overall shape can be made cannon ball-shaped by the above described fixing of the numerical values, especially by the measure that L1/D1 is fixed at 0.8 to 1.2. In this way, the absorbed amount of radiant heat from the arc can be reduced and the melt vaporization of the electrode surface can be prevented.
As was described above, this fine formation of the electrode shape of the invention is made possible by the melt shaping with laser light irradiation.
The numerical values of the discharge lamp are shown by way of example below.
The discharge lamp is operated with a rated wattage of 200 W and a rectangular waveform of 150 Hz.
The discharge lamp 10 is held through an upper opening of the concave reflector 20. A feed device (not shown) is attached to the terminals T1 and T2 of the discharge lamp 10. For a concave reflector 20, an oval reflector or a parabolic reflector is used. The reflection surface is provided with a film which has been formed by vacuum evaporation and which reflects light with given wavelengths. The focal position of the concave reflector 20 lies in the arc position of the discharge lamp 10. The light of the arc spot can emerge with high efficiency from the reflector. Furthermore, the concave reflector 20 can also be provided with a translucent glass which closes the front opening.
While it is desirable for the above described electrode arrangement to be used for the both electrodes of the discharge lamp, the above described electrode arrangement can also be used only for one of the electrodes. Further, while an ultra-high pressure mercury lamp of the AC operating type was described above, the above described electrode arrangement can also be used for an ultra-high pressure mercury lamp of the DC operating type.
As was described above, the electrode arrangement of the discharge lamp of the invention is characterized by a projection that is formed at the tip of the shaft prior to the production of the discharge lamp. Therefore, an arc discharge can be reliably produced at the projections from the start of lamp operation, and the lamp voltage can be maintained at an essentially constant value. Furthermore, the arc can also be formed at a given point and when employed in conjunction with the optical system the degree of light utilization can be increased.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-033811 | Feb 2003 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5109181 | Fischer et al. | Apr 1992 | A |
| 5497049 | Fischer | Mar 1996 | A |
| 6545430 | Ono et al. | Apr 2003 | B1 |
| Number | Date | Country |
|---|---|---|
| 2001-059900 | Mar 2001 | JP |
| 2001-174596 | Jun 2001 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20040155588 A1 | Aug 2004 | US |
