Glass manufacturing – Processes – With measuring – sensing – inspecting – indicating – or testing
Reexamination Certificate
2000-10-30
2003-05-06
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
With measuring, sensing, inspecting, indicating, or testing
C065S057000, C065S109000, C065S110000
Reexamination Certificate
active
06557379
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing an arc tube which is used as a light source of a vehicle headlamp or the like, and more particularly to a method of forming a light emitting tube portion in an intermediate portion of a cylindrical glass tube blank.
2. Description of the Related Art
Since an arc tube can perform bright irradiation, it has recently been used as a light source for a vehicle headlamp or the like.
FIG. 5
shows a typical arc tube as used in, for example, a vehicle headlamp. The arc tube includes an arc tube body
4
made of quartz glass, and a pair of electrode assemblies
6
A and
6
B. In the arc tube body
4
, pinch seals
4
b
1
and
4
b
2
are formed on opposite sides of a light emitting tube portion
4
a
having a substantially elliptical spherical shape, wherein the light emitting tube portion
4
a
forms a discharge space
2
. The electrode assemblies
6
A,
6
B are pinch-sealed to the pinch seals
4
b
1
and
4
b
2
so that their tip ends are protruded into the discharge space
2
.
In a process of producing such an arc tube, first, the light emitting tube portion
4
a
is formed in an intermediate portion of a cylindrical glass tube blank. The formation of the light emitting tube portion
4
a
is conducted by the steps shown in
FIG. 6
, and is described below.
As shown in FIGS.
6
(
a
) and (
b
), a cylindrical glass tube blank G is rotated about its axis Ax while end portions of the cylindrical glass tube blank G are gripped by chucks
12
A and
12
B. As the cylindrical glass tube blank G is rotated, an intermediate portion A thereof is heated by burners
14
so as to be softened. As the cylindrical glass tube blank G is rotated, and heated, the chucks
12
A and
12
B are moved a predetermined distance toward each other, thereby gathering softened glass in the intermediate portion A so as to form an intermediate portion B. Thereafter, as shown in FIG.
6
(
c
), a split mold
16
is pressed against opposite sides of the intermediate portion B of the cylindrical glass tube blank G. Under this state, blow molding is conducted by blowing a gas into the cylindrical glass tube blank G, thereby forming the intermediate portion B into a substantially elliptical spherical shape.
Conventionally, as shown in
FIG. 7
, a chuck moving mechanism is used to cause the chucks
12
A and
12
B to approach one another in the process of forming a light emitting tube portion.
As illustrated, the chuck moving mechanism
120
includes a chuck supporting mechanism
122
and a chuck pressing mechanism
124
.
In the chuck supporting mechanism
122
, the chucks
12
A and
12
B are supported by a guide rod
126
so as to be slidable in the direction of the cylindrical glass tube blank's axis Ax, and the chucks
12
A and
12
B can be moved in opposite directions by an interlocking mechanism which is not shown.
On the other hand, the chuck pressing mechanism
124
includes a stepping motor
128
, a screw feeding mechanism
130
, and a pressing block
132
. The pressing block
132
is fixed to a movable portion
130
a
of the screw feeding mechanism
130
, and is driven by the stepping motor
128
to be moved in the direction of the axis Ax.
A roller
136
is attached via a bracket
134
to one of the chucks
12
A and
12
B, for example chuck
12
A. The pressing block
132
abuts against the roller
136
to press the roller
136
. This pressing operation causes the chuck
12
A to be moved toward the other chuck
12
B along the axis Ax. At this time, the chuck
12
B also is moved, by the interlocking mechanism, toward the chuck
12
A in an interlocked manner with the movement of chuck
12
A.
In the process of forming a light emitting tube portion, the shape of the intermediate portion B is a factor which largely determines the thickness and the inner face shape of the light emitting tube portion
4
a
—i.e., the size and the shape of the discharge space
2
—that is to be formed in the subsequent blow molding. In order to accurately form the light emitting tube portion
4
a
to enhance the optical quality of the arc tube, therefore, it is very important for the chuck moving mechanism
120
to correctly control the approach movement, including distance, of the chucks
12
A and
12
B.
In the conventional process of forming a light emitting tube portion, the approaching movement of the chucks
12
A and
12
B in the gathering operation is controlled in accordance with the number of pulses which are sent from a controller to the stepping motor
128
in the chuck pressing mechanism
124
. Consequently, a problem arises in that the approaching movement of the chucks
12
A and
12
B is deviated from that desired by, for example, variation in the positional relationship between the pressing block
132
of the chuck pressing mechanism
124
and the roller
136
of the chuck
12
A, deformation of the bracket
134
, deformation of the roller
136
, or backlash of the screw feeding mechanism
130
, and the like.
To account for variation in the approaching movement, a method may be employed in which the position of the pressing block
132
is detected during the gathering operation and a result of the detection is fed back to the controller for the stepping motor
128
. Even when this method is employed, however, it is impossible to eliminate error caused by variation in the positional relationship between the pressing block
132
and the roller
136
, or deformation of the bracket
134
, deformation of the roller
136
, and the like.
SUMMARY OF THE INVENTION
The present invention has been conceived in view of the above-described circumstances. It is an object of the invention to provide a method of producing an arc tube in which, in a process of forming a light emitting tube portion in an intermediate portion of a cylindrical glass tube blank, the light emitting tube portion can be accurately formed.
In the present invention, a method of controlling the approach movement of a chuck in a gathering operation is improved so as to attain the above and other objects and advantages.
The method of the present invention is a method of producing an arc tube in which, in a process of producing an arc tube including a light emitting tube portion having a substantially elliptical spherical shape, the light emitting tube portion is formed in an intermediate portion of a cylindrical glass tube blank, and the method includes:
rotating the cylindrical glass tube blank while gripping end portions of the cylindrical glass tube blank with chucks;
heating a vicinity of the intermediate portion of the cylindrical glass tube blank to soften the intermediate portion;
moving the chucks, by a chuck moving mechanism, a predetermined distance toward each other, thereby gathering softened glass in the intermediate portion; and
expanding the intermediate portion by blow molding into a substantially elliptical spherical shape,
wherein the step of moving the chucks further includes detecting a position of at least one of the chucks by using a position detector, and the method further includes feeding a result of the detection back to the chuck moving mechanism to control an approach distance of the chucks.
The specific configuration of the above-mentioned “position detector” is not particularly restricted as long as it can detect the position of at least one of the chucks. In order to enhance the detection accuracy, however, it is preferable to use a non-contact position detector such as a laser position detector, an electrostatic capacitance type position detector, an image sensor, or a linear encoder.
As described above, according to the invention, in the process of forming a light emitting tube portion in an intermediate portion of a cylindrical glass tube blank, the pair of chucks gripping the end portions of the cylindrical glass tube blank are moved—by the chuck moving mechanism—so as to approach each other, thereby performing the gathering operation. In this case, the position of at least one of the chucks is detected by using the position detec
Goto Hiroshi
Nagasawa Masakazu
Umehara Masayuki
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