Xenon lamp for projector

Abstract

The xenon lamp for a projector, the xenon lamp comprises a light-emitting tube and an anode and a cathode that are arranged inside the light-emitting tube so as to face each other through a gap in a first direction, the anode including: a body part and a chip part whose cross-sectional area cut along a first plane orthogonal to the first direction is smaller than the cross-sectional area of the body part, the chip part including: a first part joined to the body part, the first part protruding toward the cathode and having a tapered shape; and a second part joined to the first part, the second part protruding toward the cathode and having a shape such that an angle of inclination of an outer profile of the second part differs from an angle of inclination of an outer profile of the first part.

Claims

1. A xenon lamp for a projector, the xenon lamp comprising: a light-emitting tube; and an anode and a cathode that are arranged inside the light-emitting tube so as to face each other through a gap in a first direction, the anode including: a body part whose cross-sectional area cut along a first plane orthogonal to the first direction is substantially uniform; and a chip part whose cross-sectional area cut along the first plane is smaller than the cross-sectional area of the body part, the chip part protruding in a direction that extends from an end face of the body part adjacent to the cathode toward the cathode, the chip part including: a first part joined to the body part, the first part protruding toward the cathode and having a tapered shape such that a cross-sectional area of the first part cut along the first plane shrinks with a decrease in distance to the cathode in the first direction; and a second part joined to the first part, the second part protruding toward the cathode and having a shape such that an angle of inclination of an outer profile of the second part differs from an angle of inclination of an outer profile of the first part when viewed in a second direction that is parallel to the first plane and orthogonal to the first direction, wherein the shape of the second part satisfies the following relationships (1) and (2):
0.5D2/D11.5(1)
0.3H1/D11.0(2) where H1 represents a length of the second part in the first direction; D1 represents a length of a distal end of the second part adjacent to the cathode in a third direction orthogonal to the first direction and the second direction; and D2 represents a length between places at which the first part and the second part are joined together in the third direction, when viewed in the second direction.

2. The xenon lamp for a projector, according to claim 1, wherein the shape of the second part further satisfies the following relationships (3) and (4):
1.2D2/D11.5(3)
0.31H1/D10.36(4) where H1 represents a length of the second part in the first direction; D1 represents a length of a distal end of the second part adjacent to the cathode in a third direction orthogonal to the first direction and the second direction; and D2 represents a length between places at which the first part and the second part are joined together in the third direction, when viewed in the second direction.

3. The xenon lamp for a projector according to claim 1, wherein the xenon lamp is disposed so that the first direction matches a horizontal direction during lighting up.

4. The xenon lamp for a projector according to claim 2, wherein the xenon lamp is disposed so that the first direction matches a horizontal direction during lighting up.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a conceptual diagram showing an overview of a xenon lamp according to an embodiment of the present invention;

(2) FIG. 2 is an enlarged cross-sectional view of a cathode;

(3) FIG. 3 is an enlarged cross-sectional view of an anode;

(4) FIG. 4A is a conceptual diagram of equipotential surfaces formed in a neighborhood of a conventional anode;

(5) FIG. 4B is a conceptual diagram of equipotential surfaces formed in a neighborhood of an anode according to an embodiment of the present invention;

(6) FIG. 5 is a drawing showing parameters of an anode;

(7) FIG. 6A is a conceptual diagram of an arc generated when a xenon lamp is lit;

(8) FIG. 6B is a conceptual diagram of an arc that is changed in position by convection of a gas; and

(9) FIG. 6C is a conceptual diagram showing a change in shape of a cathode of a lamp that has undergone a lighting operation for a long time.

MODE FOR CARRYING OUT THE INVENTION

(10) [Overview of Lamp]

(11) A short-arc xenon lamp according to an embodiment of the present invention will be described with reference to the drawings. Note that the drawings are all schematic illustrations and dimensional ratios and numbers of parts on the drawings do not necessarily match the actual dimensional ratios and numbers of parts.

(12) FIG. 1 is a conceptual diagram showing an overview of a lamp. In the following drawings, an X-Y-Z coordinate system is also appropriately shown as needed. In the coordinate system, a direction in which a cathode 2 and an anode 3 face each other is defined as an X direction, and other directions that are orthogonal to the X direction and orthogonal to each other are defined as a Y direction and a Z direction. Under this definition, FIG. 1 is a schematic view of a lamp 10, viewed in a Y direction.

(13) In FIG. 1, the X direction corresponds to a first direction, the Y direction corresponds to a second direction, and the Z direction corresponds to a third direction.

(14) In the following description, in the case of distinguishing whether the direction is positive or negative, the positive or negative symbol is added, such as the +X direction or the X direction. In the case where there is no need to distinguish between positive and negative directions, the direction is simply described as the X direction. Namely, in the present specification, in the case where the direction is simply described as the X direction, both +X direction and X direction are included. The same applies to the Y direction and the Z direction.

(15) The lamp 10 is a short-arc discharge lamp. More specifically, as shown in FIG. 1, the lamp 10 includes the cathode 2 and the anode 3 that are disposed inside a light-emitting tube 1. The cathode 2 and the anode 3 are supported by lead rods (4a, 4b), respectively, inside the light-emitting tube 1. Shapes of the cathode 2 and the anode 3 will be described later.

(16) The short-arc discharge lamp is a lamp in which the cathode 2 and the anode 3 are arranged so as to face each other through a gap of 10 mm or less (a value when the lamp is turned off without thermal expansion). The gap between the electrodes is, for example, 4 mm. The lamp 10 is primarily mounted on a projector. The lamp is typically disposed, when being lit, such that the Z direction matches a vertical direction.

(17) The light-emitting tube 1 is, for example, shaped from a quartz glass tube and may be in the shape of a sphere or an ellipsoid. In an internal space of the light-emitting tube 1, xenon gas is sealed as a light-emitting substance at a predetermined pressure.

(18) Sealed tubes (not shown) are disposed on both ends of the light-emitting tube 1 in the X direction. In addition, bases are attached to the sealed tubes and are electrically connected to the lead rods (4a, 4b). The lead rods (4a, 4b) are made of a material containing a high melting point metal such as tungsten.

(19) [Cathode Structure]

(20) With reference to FIG. 2, a structure of the cathode 2 will be described. FIG. 2 is an enlarged cross-sectional view of the cathode in the lamp 10. The cathode 2 is in the shape of a rotating body centered around a central axis R1. FIG. 2 shows a cross section of the cathode 2 on an X-Z plane that includes the central axis R1.

(21) As shown in FIG. 2, the cathode 2 includes a conical trapezoidal part and a cylindrical part located on a +X direction side of the conical trapezoidal part, for example. A width of the conical trapezoidal part in the Z direction gets narrower with a decrease in distance to the anode 3 in the X direction, whereas a width of the cylindrical part in the Z direction is substantially uniform. The +X direction side of the cylindrical part is connected to the lead rod 4a. A maximum outer diameter of the cathode 2 is, for example, 6 mm. The cathode 2 is made of a material containing a high melting point metal such as thoriated tungsten.

(22) [Anode Structure]

(23) With reference to FIG. 3, a structure of the anode 3 will be described. FIG. 3 is an enlarged cross-sectional view of the anode in the lamp 10. The anode 3 is in the shape of a rotating body centered around the central axis R1. FIG. 3 shows a cross section of the anode 3 on the X-Z plane that includes the central axis R1.

(24) As shown in FIG. 3, the anode 3 includes a body part 21 and a chip part 22 that are each described later. A side of the body part 21 opposite the chip part 22 in the X direction is connected to the lead rod 4b. The body part 21 includes a cylindrical part whose width in the Z direction is substantially uniform. An outer diameter of the body part 21 is, for example, 15 mm.

(25) The chip part 22 is located nearer to the cathode 2 in comparison with the body part 21 in the X direction and includes a first part 22a and a second part 22b. A width of the chip part 22 in the Z direction is narrower than the body part 21.

(26) The first part 22a has a tapered shape such that a width of the first part in the Z direction gets narrower with a decrease in distance to the cathode 2 in the X direction. In other words, a cross-sectional area of the first part 22a cut along a Y-Z plane shrinks with progress in the +X direction.

(27) The second part 22b is joined to the first part 22a and protrudes in the +X direction. When viewed in the Y direction, an outer profile 23 of the chip part 22 includes an outer profile 23a of the first part and an outer profile 23b of the second part, and these outer profiles have different shapes. In an example shown in FIG. 3, the second part 22b has a tapered shape such that a width of the second part in the Z direction gets narrower with a decrease in distance to the cathode 2 in the X direction. However, the shape may be such that the width of the second part in the Z direction gets greater with a decrease in distance to the cathode 2 in the X direction.

(28) A material for the anode 3 is, for example, a high melting point metal such as tungsten. The anode 3 is made by cutting any of these materials through a process such as lathing. Some areas, such as a place at which the body part 21 and the chip part 22 are joined together and a place at which the first part 22a and the second part 22b are joined together, may be chamfered.

(29) As for the anode 3 shaped in this way, a shape of an electric field that is formed in a neighborhood of the anode 3 when a voltage is applied will be described. FIG. 4A is a conceptual diagram of equipotential surfaces formed in a neighborhood of a conventional anode, and FIG. 4B is a corresponding diagram in a case of the anode 3 according to the present embodiment. In FIGS. 4A and 4B, the equipotential surfaces are schematically indicated by solid lines. As shown in FIG. 4B, since the anode 3 has the shape described above, an equipotential surface 30 in the neighborhood of the anode 3 is curved more toward the anode 3 as compared with a case of the conventional anode 83. In this way, the equipotential surface is curved toward the anode 3, and hence lines of the electric field orthogonal to the equipotential surface are directed toward the chip part 22 of the anode 3. Thus, the arc formed between the cathode and the anode is attracted to a neighborhood of the chip part 22, and a change of the arc is lessened. This helps to reduce the tendency of the lamp to go out.

(30) [Experiment 1]

(31) The inventors of the present invention made a detailed study of the anode shape configured as described above and conducted an experiment using a lamp they actually made to observe whether or not the lamp goes out during the start of operation. A description of this experiment 1 will be given below.

(32) Table 1 below shows results obtained through a determination of the studied anode shape of the lamp in terms of lamp going-out and illuminance maintenance. As shown in FIG. 5, H1 represents a length of the second part 22b in the X direction, D1 represents a Z direction length of an end face of the second part 22b adjacent to the cathode 2, and D2 represents a Z direction length between places at which the first part 22a and the second part 22b are joined together, when viewed in the Y direction. In a conventional example, such an anode does not have the second part 22b, and thus a diameter of an end face of the anode in the +X direction is written in the D1 column for convenience.

(33) In tests to determine the tendency of the lamp to go out, in order to reproduce the lamp that has been lit for a long time, the diameter of the end face of the cathode 2 in the X direction was set to 1.9 mm, and the distance between the cathode and the anode was set to 5 mm (refer to FIG. 6C). A starting process for this lamp was performed 10 times to ascertain whether or not the lamp to go out. One that did not go out was evaluated as A, and one that went out was evaluated as B. The lamp was disposed, when being lit, such that the Z direction matched a vertical direction and that the X and the Y directions matched a horizontal direction (refer to FIG. 1).

(34) Tests were also conducted to determine the illuminance maintenance rate. The illuminance maintenance rate referred to herein was a ratio of illuminance the lamp had after being lit for 3,000 hours relative to illuminance the lamp had in a state immediately after being produced. Illuminance was measured in accordance with JIS C 7801 Measuring methods of lamps for general lighting. An illuminance maintenance rate of 50% or more was evaluated as C and an illuminance maintenance rate of less than 50% was evaluated as D. Since the illuminance maintenance rate in the conventional example was around 50%, 50% was used as a standard. Just to be sure, at the time of starting tests to determine the illuminance maintenance, the shape of the cathode was in an initial state (a state immediately after the cathode was produced), unlike in the tests to determine the tendency of the lamp to go out.

(35) TABLE-US-00001 TABLE 1 Determine Determine Rated Lamp Going Illuminance Power D1 D2 H1 D2/D1 H1/D1 Out Maintenance Conventional 2 kW 3.5 B C Example Comparative 3.5 8.3 2 2.36 0.57 B Example 1 Comparative 4 4.4 1 1.11 0.25 B Example 2 Example 1 4.2 6.3 1.5 1.5 0.36 A C Example 2 4.3 6 1.5 1.4 0.35 A Example 3 4.4 5.4 1.5 1.23 0.34 A C Example 4 5.8 7 1.8 1.2 0.31 A C Example 5 5 5.8 1.5 1.16 0.3 A D Example 6 3.5 4.6 2 1.31 0.57 A Example 7 4 4.6 1.5 1.16 0.38 A D Example 8 4.5 5.1 1.5 1.14 0.33 A D Example 9 4.5 3.9 1.5 0.86 0.33 A

(36) As shown in Table 1, it is observed that the lamp does not go out in a range in which D2/D1 is 1.5 or less and H1/D1 is 0.3 or greater. Further, in a range in which D2/D1 is from 1.2 to 1.5 and H1/D1 is from 0.31 to 0.36, results were obtained such that the lamp is prevented from going out and the illuminance maintenance rate is satisfactory. In this way, the results have proven that the shape of the anode configured as described above helps to reduce the tendency of the lamp to go out.

(37) From the viewpoint of guaranteeing mechanical strength of the second part 22b of the anode 3, D2/D1 is preferably 0.5 or greater and more preferably 0.6 or greater. If H1/D1 increases, heat capacity in a tip portion of the anode decreases, and the temperature is likely to rise. As a result, during lighting up, the anode is likely to be melted or deformed. With this in view, H1/D1 is preferably 1.0 or less and more preferably 0.8 or less.

(38) In Experiment 1 above, the results were observed using the lamp with a rated power of 2 kW. Meanwhile, even if the rated power of the lamp changes, dimensions of the cathode 2, the anode 3, and other parts only increase, and the dimensional ratio does not greatly change. Thus, the present invention can be applied to lamps with different rated power levels through the similar logic.

(39) When D1 is taken as an example, the lamp with a rated power of 2 kW is designed with D1 ranging from 3.5 mm to 5.8 mm. D1 ranges from 5.4 mm to 9.0 mm for a rated power of 4 kW, and D1 ranges from 7.4 mm to 10.0 mm for a rated power of 6.5 kW. D1 can be designed according to the following equation (5), which is obtained by approximating a relationship between D1 and rated power (referred to as P1 for convenience).
D1=810.sup.8P1.sup.2+0.0017P1+1.0033(5)

(40) Table 2 shows results obtained by ascertaining whether lamps with rated powers of 4 kW and 6.5 kW configured as described above help to similarly reduce the tendency of the lamps to go out. Methods of determining measurements in lamp going-out and illuminance maintenance corresponded to those in Experiment 1.

(41) TABLE-US-00002 TABLE 2 Determine Determine Rated Lamp Going Illuminance Power D1 D2 H1 D2/D1 H1/D1 Out Maintenance Comparative 4 kW 7 14.2 3 2.02 0.43 B C Example 3 Comparative 7 7.6 1.5 1.09 0.21 B D Example 4 Example 10 6 8.8 2 1.47 0.33 A C Example 11 8.4 11.9 3 1.41 0.36 A C Example 12 9 11.8 3 1.31 0.33 A C Example 13 7 9.1 3 1.3 0.43 A D Example 14 6 7.6 3 1.27 0.5 A D Example 15 6 7.1 2.5 1.18 0.42 A D Comparative 6.5 kW 8.4 17.9 4 2.14 0.48 B C Example 5 Comparative 10 10.9 2 1.09 0.2 B D Example 6 Example 16 7.4 11 2.6 1.49 0.35 A C Example 17 9 12.5 3 1.38 0.33 A C Example 18 8.4 12.1 4 1.44 0.48 A D Example 19 10 12.8 4 1.28 0.4 A D Example 20 9 11.2 4 1.24 0.44 A D Example 21 10 11.3 3 1.13 0.3 A D

(42) As shown in Table 2, the results have confirmed that even the lamps with higher rated powers, if configured as described above, help to reduce the tendency of the lamps to go out.

(43) The present invention is not limited to the embodiment and examples described above in any way. Various improvements and modifications may be made without departing from the scope of the subject matter of the present invention.

DESCRIPTION OF REFERENCE SIGNS

(44) 1 Light-emitting tube 2 Cathode 3 Anode 4a Lead rod 4b Lead rod Xenon lamp 21 Body part 22 Chip part 22a First part 22b Second part 23 Outer profile 23a Outer profile 23b Outer profile 30 Equipotential surface 80 Xenon lamp 81 Light-emitting tube 82 Cathode 82a Diameter 82b Position 82c Position 83 Anode A1 Arc A2 Arc R1 Central axis