Optical: systems and elements – Mirror – Including specified control or retention of the shape of a...
Reexamination Certificate
1999-08-06
2001-07-17
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Mirror
Including specified control or retention of the shape of a...
C359S846000, C219S121670, C219S121740
Reexamination Certificate
active
06260976
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a laser beam collimation apparatus (collimator) and a laser processing machine using the same, and more particularly to a collimation apparatus and a laser processing machine using the same which can control a laser beam diameter or a converged position of a laser beam by means of controlling a curvature of a reflecting mirror arranged in a light path of the laser beam.
BACKGROUND OF THE INVENTION
Conventionally, there has been a laser processing machine as one of processing devices for cutting a workpiece having a form like a flat plate. Types of the laser processing machine are divided to one based on the fixed light axis system in which a length of a light path from a laser oscillator to a lens for converging a laser beam inside a processing head is kept constant, and the other one based on the optical scanning system in which a length of a light path from a laser oscillator to a lens for converging a laser beam inside the processing head varies during processing.
In a laser processing machine based on the optical scanning system, as a length of a light path from the laser oscillator to a lens for converging a laser beam is not kept constant, a beam diameter of a laser beam introducing into the lens for converging light changes, and for this reason a beam diameter at a converged position is not kept constant, which may badly affect a cut surface of a workpiece.
So there has been invented a laser processing machine based on the optical scanning system in which, to keep a beam diameter of an incident laser beam into a converging lens constant during processing, a laser beam oscillated from a laser oscillator is converted to a collimated beam which proceeds without diverging or converging the laser beam against the light axis and is introduced into a converging lens. Japanese Patent Laid-Open Publication No. HEI 1-166894 discloses a laser processing machine having a collimation apparatus which converts a laser beam to a collimated beam.
FIG. 14
shows configuration of the laser processing machine disclosed in Japanese Patent Laid-Open Publication No. HEI 1-166894.
The laser processing machine based on the conventional technology comprises a laser oscillator
1
forming an optical resonator by holding an excitation medium
2
for a laser with a full-reflection mirror
3
as well as a partial reflection mirror
4
and outputting a laser beam; a laser beam collimation apparatus
6
B for converting a laser beam
5
a
(indicated by an alternate dot and dash line in the figure) outputted from the laser oscillator
1
to a collimated beam
5
b
(indicated by an alternate dot and dash line in the figure); a flat-surface reflection mirror
7
for reflecting the collimated beam
5
b
converted by the collimation apparatus
6
B to change a direction of the light path by 90 degrees; a processing head
8
into which the collimated beam
5
b
reflected by the flat-surface reflection mirror
7
is introduced; a collimation control unit
15
for controlling a curvature of a collimation mirror
11
in the laser beam collimation apparatus
6
B; a beam diameter detecting mechanism
13
for detecting a beam diameter of the collimated beam
5
b
introduced into a converging lens
9
inside the processing head
8
; and an NC (Numerical Control) device
14
, a driving mechanism (not shown) which is driven and controlled by the NC device
14
.
Provided inside the collimation apparatus
6
B are a collimation mirror
11
which can change a curvature R thereof and a flat-surface mirror
12
for introducing the laser beam
5
a
into the collimation mirror
11
at a small angle for suppressing aberration.
A curvature of the collimation mirror
11
is controlled according to a control signal S
16
which is generated by and outputted from the collimation control unit
15
.
When laser oscillation occurs inside an optical oscillator comprising the full reflection mirror
3
and partial reflection mirror
4
, a portion thereof is oscillated from the partial reflection mirror
4
to outside of the laser oscillator
1
as a laser beam
5
a
. The laser beam
5
a
oscillated to outside of this laser oscillator
1
passes through the collimation apparatus
6
B, is reflected by the flat-surface reflection mirror
7
to change its direction by 90 degrees, is introduced into the converging lens
9
in the processing head
8
, is converged by the converging lens
9
, and is irradiated onto the workpiece
10
. The laser beam converged and irradiated onto the workpiece
10
is freely moved on the workpiece
10
by a driving mechanism (not shown) controlled by the NC device
14
to process the workpiece
10
into a desired form.
A beam diameter of the collimated beam
5
b
introduced into the converging lens
9
is detected by the beam diameter detecting mechanism
13
. And in the NC device
14
, determination is made as to whether the detected beam diameter is a desired one or not, and if it is determined that the detected beam diameter is not a desired one, a control signal S
16
is sent from the collimation control unit
15
to the collimation apparatus
6
B. With this feature, a curvature R of the collimation mirror
11
is changed so that a beam diameter of the collimated beam
5
b
introduced into the converging lens
9
will be a desired one.
FIG. 15
shows the laser beam collimation apparatus
6
B based on the conventional technology. This collimation apparatus
6
B comprises a disk-shaped collimation mirror
11
, an actuator
17
comprising a piezoelectric element for pressurizing a central section of a rear surface of the collimation mirror
11
from the rear side, and a mirror holder
18
A for accommodating the actuator
17
and collimation mirror
11
and also for fixing a periphery of the collimation mirror
11
as fixing means.
When a drive control signal S
16
is sent from the collimation control unit
15
(Refer to
FIG. 14
) through a signal line
16
to the actuator
17
, the actuator
17
presses a rear surface of the collimation mirror
11
with a force corresponding to the drive control signal S
16
. Because of this operation, the collimation mirror with the periphery fixed to the mirror holder
18
A deforms and the curvature changes.
Herein, as shown in
FIG. 15
, a deflection rate W at a given radius r when a periphery of the disk-shaped collimation mirror
11
is fixed and the central portion is pressed with a load P is expressed by the following expression (1) assuming that a indicates a significant radius of the mirror and D indicates a bending component of the plate.
W
=
Pa
2
16
π
D
{
1
-
(
1
+
2
In
a
r
)
r
2
a
2
}
(
1
)
As clearly understood from this expression (1), the deflection rate W at a radius r is not a solution of a two-dimensional function.
It should be noted that, in Japanese Patent Laid-Open Publication No. HEI 1-166894, a curvature of the collimation mirror
11
is changed by changing a pressure of gas (or liquid) applied to a rear surface of the collimation mirror
11
.
However, with the laser beam collimation apparatus based on the conventional technology as described above, it is possible to change a curvature of the collimation mirror
11
, as a periphery of the collimation mirror
11
is fixed to the mirror holder
18
A, a large force is required to change the curvature, or a reflecting surface of the collimation mirror
11
does not become an ideal parabolic surface (Refer to the expression (1) above), and a converging capability of a laser beam becomes lower, which makes it impossible to always process a workpiece
10
under stable conditions.
When a piezoelectric element is used for the actuator
17
, as only a force in a pressing direction can be obtained with the piezoelectric element, it is possible only to simply press a rear surface of the collimation mirror
11
and only to change a reflecting surface of the collimation mirror
11
into a convex mirror, in other words it is impossible to change a reflecting surface of the collimation mirror
11
into a co
Endou Tetsuya
Ikemi Atsushi
Cherry Euncha
Mitsubishi Denki & Kabushiki Kaisha
Spyrou Cassandra
Sughrue Mion Zinn Macpeak & Seas, PLLC
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