Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
1999-05-24
2001-10-23
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C445S043000, C445S027000
Reexamination Certificate
active
06306002
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lamp and a manufacturing method of that lamp that has a special structure of electrode sealing and whose internal pressure become one atmosphere or more when operated to light it.
2. Description of the Prior Art
Conventionally, high intensity discharge lamps have been widely used for ordinary illumination in homes, facilities and stores. In recent years, these lamps are being used as light sources for overhead projectors, projection televisions and motion picture projectors. The reason for this is because high intensity discharge lamps emit an extremely bright light.
In particular, in recent years, research has been active on ways to bring lamps closer to a point light source by shortening the length of the discharge arc. However, reductions in lamp voltage occur following efforts to shorten the length of the discharge arc. Therefore, when an attempt is made to operate a lamp using an identical voltage, increases in lamp current generate. These increases in lamp current are linked to large increases in electrode loss, actively vaporize electrode materials worsening the early stages of electrodes. Namely, the increases in lamp current cause the lifecycles of the lamps to shorten. From this type of reason, when shortening the arc length, it is normal to increase the mercury vapor pressure when operating the lamp is made to protect against reductions in lamp voltage (increases in lamp current).
When the mercury vapor pressure and other similar parameters are made to increase when operating the lamp, the lamp must be constructed such that it will not be cracked due to that high operating pressure.
FIG. 11
shows the structure of a conventional discharge lamp. In the figure,
100
is a light emission portion wherein exists a discharge arc and
101
is a side tube portion that extends from light emission portion
100
. Light emission portion
100
and side tube portion
101
are both comprised by quartz glass.
A gas that becomes a high pressure when the lamp is operated is sealed in light emission portion
100
. Further,
102
is an electrode that functions to supply electrical current into light emission portion
100
. The electrode material is normally tungsten. In comparison to the thermal expansion coefficient of tungsten of 5.2×10
−6
, the thermal expansion coefficient of quartz glass is 5.5×10
−7
that is almost one decimal place different. Technology for sealing methods of two types which differ greatly in this way is difficult.
For a sealing method for this case a foil sealing structure is known wherein a metal foil
104
connects between electrode
102
and an external electrical current supply line
103
and glass being sealed airtight in this metal foil. By carrying out plastic deformation on an extremely thin metal foil, the difference in the thermal expansion coefficient between the glass and the metal is absorbed making it possible to obtain a seal.
Conventionally, pinch sealing is a manufacturing method of this foil sealing structure lamp. In the following, conventional pinch sealing will be described referring to FIG.
12
. Glass tube
110
is formed by a separate process in which a quartz glass tube is heated and allowed to expand forming light emission portion
100
in a specified shape. A quartz glass tube that is not deformed is connected to both end portions of light emission portion
100
as side tube portion
101
. Glass tube
110
is retained by a chuck
113
. The end portion of electrode
102
is disposed on light emission portion
100
to maintain a discharge arc. And also, electrode
102
, metal foil
104
(connected to the other end portion of electrode
102
) and electrical current supply line
103
are disposed on side tube portion
101
.
Further, in order to prevent electrode oxidation during the sealing process, side tube portion
101
maintains in a rare gas environment. The glass of this side tube portion
101
is thermally fused by a burner
111
and then pressure formed by a forming die
112
from two directions perpendicular to the surface of metal foil
104
.
Problems to be Solved
The following two problems exist when using this type of sealed lamp.
Electrode
102
and the glass of side tube portion
101
have different thermal expansion coefficients and there is no airtight seal. Thereupon, a gap can be opened between electrode
102
and the glass of side tube portion
101
.
FIG. 13
shows the cross sectional shape of the side tube portion along line
105
shown in FIG.
11
. In the figure,
120
is a side tube portion glass. Further,
121
is a gap between electrode
102
and side tube portion glass
120
. The shape of gap
121
has a sharp notch
122
due to squeezing from two directions of the glass. There was a problem of a concentration of stress acting on sharp notch
122
and the lamp being damaged due to a pressure lower than the pressure strength actually possessed by the glass.
The second problem is a crack
106
shown in FIG.
11
. This crack
106
occurs in the side tube portion glass at the position of electrode
102
. The percentage of cracks which occur during sealing is larger than cracks which occur due to differences in the thermal expansion coefficients of the electrode and the glass. However, this crack has an action that is said to lessen the stress occurring between the electrode and the glass when lighting and extinguishing the lamp. Because of this, cracks which occur due to differences in the thermal expansion coefficients do not interfere with the lamp.
Cracks which occur because of differences in the thermal expansion coefficients however, occur due to another mechanism. The electrode does not cause plastic deformation as with a metal foil. Because of this, if the electrode is struck by the side tube portion glass with a strong force, the glass will crack due to that impact. A concentration of stress will generate at the tip of this crack which will further lower the pressure strength of the lamp. In other words, there is a problem of cracks occurring due to factors other than differences in the thermal expansion coefficients of the glass and the electrode.
Thereupon, a shrink seal method is used to solve the above-mentioned two problems. An example of a shrink seal method is shown in FIG.
14
. Glass tube
110
is retained by chuck
126
. The end portion of electrode
102
is disposed on light emission portion
100
to maintain a discharge arc. And also, electrode
102
, metal foil
104
(connected to the other end portion of electrode
102
) and electrical current supply line
103
are disposed on side tube portion
101
. A reduced pressure state is maintained inside glass tube
110
. While this glass tube
110
is rotated in the circumferential direction of the tube (approximately indicated by arrow
128
), side tube portion
101
is thermally fused uniformly by burner
127
. Side tube portion
101
glass undergoes diameter reduction by means of a pressure difference between the inside and outside of glass tube
110
and then metal foil
104
and side tube portion
101
glass positioned where the metal foil is located are sealed airtight.
According to this method, because the glass undergoes diameter reduction towards the electrode, the shape of the gap between the glass and the electrode becomes almost circular eliminating the notch portion that generates a concentration of stress. Further, because the sealing pressure does not exceed the atmospheric pressure, the glass does not receive any impact when sealed.
However, because the sealing pressure of the metal foil portion does not exceed one atmosphere in this shrink seal method, there are still remaining problems of an insufficient amount of plastic deformation of the metal foil and a weak seal between the metal foil and the glass tube.
Thereupon, a method has been attempted that uses a die to evenly squeeze the glass (for example, a polygon shaped die or a circular die) in order that the shape of the gap between the electrode and the glass does not
Horiuchi Makoto
Kaneko Yuriko
Kurimoto Yoshitaka
Takeda Mamoru
Yoshida Masato
Matsushita Electric - Industrial Co., Ltd.
Ramsey Kenneth J.
Wenderoth , Lind & Ponack, L.L.P.
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