U.S. patent application number 09/742094 was filed with the patent office on 2001-07-05 for perforating machining method with laser beam.
Invention is credited to Isogai, Kazuo, Okumura, Tokuji, Otake, Tsuneo, Takekuma, Hideshi, Wakabayashi, Kazushiro.
Application Number | 20010006168 09/742094 |
Document ID | / |
Family ID | 26581672 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006168 |
Kind Code |
A1 |
Okumura, Tokuji ; et
al. |
July 5, 2001 |
Perforating machining method with laser beam
Abstract
Assuming that t1 represents a period of time until a detection
signal is outputted after a sensor senses a laser beam passed
through a through-hole of a workpiece, t2 represents a period of
time until the detection signal derived from the sensor exceeds a
preset threshold value, and t3 represents a period of time until
radiation of the laser beam is actually stopped after the threshold
value is exceeded, a total period of time (t1+t2+t3) of the periods
of time t1 to t3 is set to be shorter than a time difference
(T2-T3) between a pulse width (T3) and one cycle (T2) of a pulse
signal for constructing a laser output command signal.
Inventors: |
Okumura, Tokuji;
(Hasuda-shi, JP) ; Wakabayashi, Kazushiro;
(Utsunomiya-shi, JP) ; Isogai, Kazuo; (Sayama-shi,
JP) ; Takekuma, Hideshi; (Utsunomiya-shi, JP)
; Otake, Tsuneo; (Sakado-shi, JP) |
Correspondence
Address: |
BIRCH, STEWART, KOLASCH & BIRCH, LLP
P.O. Box 747
Falls Church
VA
22040-0747
US
|
Family ID: |
26581672 |
Appl. No.: |
09/742094 |
Filed: |
December 22, 2000 |
Current U.S.
Class: |
219/121.7 ;
219/121.71 |
Current CPC
Class: |
B23K 26/382 20151001;
G05B 2219/37583 20130101; B60R 21/2171 20130101; G05B 2219/45139
20130101; B23K 26/0861 20130101; B23K 26/03 20130101 |
Class at
Publication: |
219/121.7 ;
219/121.71 |
International
Class: |
B23K 026/38; G06F
019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 1999 |
JP |
11-365484 |
Dec 22, 1999 |
JP |
11-365485 |
Claims
What is claimed is:
1. A perforating machining method based on the use of a laser beam,
comprising the steps of: forming a through-hole through a workpiece
by radiating said laser beam toward said workpiece; and sensing
said laser beam passed through said through-hole by means of a
sensor to stop radiation of said laser beam on the basis of a
detection signal derived from said sensor, wherein: a pulse signal
for controlling said laser beam is set so that a period of time
until said radiation of said laser beam is stopped after said laser
beam passed through said through-hole is sensed by said sensor is
shorter than a period of time until the next pulse signal to be
continued is in an ON state.
2. The perforating machining method based on the use of said laser
beam according to claim 1, wherein said laser beam is controlled by
a plurality of pulse-shaped laser output command signals, and a
total period of time (t1+t2+t3) of periods of time t1 to t3 is set
to be shorter than a time difference (T2-T3) between a pulse width
(T3) and one cycle (T2) of said pulse signal for constructing said
laser output command signal, assuming that t1 represents a period
of time until said detection signal is outputted after said sensor
senses said laser beam passed through said through-hole of said
workpiece, t2 represents a period of time until said detection
signal derived from said sensor exceeds a preset threshold value,
and t3 represents a period of time until said radiation of said
laser beam is actually stopped after said threshold value is
exceeded.
3. The perforating machining method based on the use of said laser
beam according to claim 2, wherein said plurality of pulse-shaped
laser output command signals are composed of ON/OFF signals.
4. The perforating machining method based on the use of said laser
beam according to claim 2, wherein said plurality of pulse-shaped
laser output command signals are composed of ON/OFF signals each of
which is level-shifted by a predetermined value.
5. A perforating machining method based on the use of a laser beam
for forming a weak portion for an air bag by boring a plurality of
minute through-holes through a cover installed to an opening for
said air bag as an automobile part, said method comprising the
steps of: applying through-hole machining to said cover by
radiating said laser beam toward a back surface of said cover;
sensing said laser beam passed through said through-hole of said
cover by means of a sensor to stop radiation of said laser beam on
the basis of a detection signal derived from said sensor; and
relatively displacing a laser beam-oscillating unit and said cover
by a predetermined pitch to form said weak portion including said
plurality of through-holes in accordance with a predetermined
machining pattern, wherein: a part of said weak portion, which is
disposed on a side of said back surface of said cover, is formed as
a substantially linear groove, while a part of said weak portion,
which is disposed on a side of a front surface of said cover, is
formed by said plurality of through-holes separated from each other
by a predetermined pitch.
6. The perforating machining method based on the use of said laser
beam according to claim 5, wherein a diameter of said through-hole
on said side of said front surface of said cover is formed to be
not more than about 50 .mu.m.
7. The perforating machining method based on the use of said laser
beam according to claim 5, wherein said laser beam, which is
radiated from said laser beam-oscillating unit, is controlled on
the basis of a laser output command signal composed of a plurality
of pulse-shaped ON/OFF signals.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a perforating machining
method based on the use of a laser beam, which makes it possible to
form invisible minute through-holes through a workpiece by
radiating the laser beam onto the workpiece. In particular, the
present invention relates to a perforating machining method based
on the use of a laser beam, which makes it possible to form, for
example, a weak portion for an air bag of an air bag system to be
installed to an automobile.
[0003] 2. Description of the Related Art
[0004] In recent years, the air bag system has been widespread, for
example, for vehicles such as automobiles. The air bag system is
provided with an air bag which functions as an air-expandable bag
to be used for an apparatus for absorbing the shock. The air bag is
folded, and it is accommodated in an accommodating air bag module.
When the collision of the vehicle is detected by a sensor, the air
bag is instantaneously expanded by the gas supplied from a gas
generator. Thus, the air bag functions as a cushion to absorb the
shock applied to a driver or a passenger.
[0005] The air bag is installed in a state of being hidden in an
interior part such as a steering wheel cover and an instrument
panel. When the air bag is expanded, then a door panel for
developing the air bag is opened by force, and the air bag is
exposed to the outside of the accommodating air bag module.
[0006] In this arrangement, in order to reliably open the door
panel, for example, a weak portion for the air bag is formed with a
predetermined machining pattern composed of grooves, holes and the
like.
[0007] As a method for forming the weak portion for the air bag,
for example, Japanese Laid-Open Patent Publication No. 58-16784
discloses a method for perforating and machining a workpiece by
providing a photodetector on the side of a surface opposite to a
machining surface of the workpiece, and sensing, with the
photodetector, a laser beam passed through a through-hole of the
workpiece.
[0008] Japanese Laid-Open Patent Publication No. 8-282420 discloses
a method for forming a weak portion by partially forming grooves
with a laser beam for a door panel of an automobile interior cover
at an opening for developing an air bag.
[0009] Japanese Laid-Open Patent Publication No. 10-85966 discloses
a method for forming a linear weak portion based on the use of
radiation of a controllable pulse-shaped laser beam.
[0010] However, in the case of the technical concept disclosed in
Japanese Laid-Open Patent Publication No. 58-16784 concerning the
conventional technique described above, the following inconvenience
arises. That is, the diameter of the through-hole formed by the
perforating machining is increased due to the influence of the
delay time until the radiation of the laser beam is actually
stopped after the laser beam is detected with the photodetector.
The bored through-hole is visible, and hence the appearance quality
is inferior. Further, the strength and rigidity are decreased, and
hence the durability is deteriorated concerning the function of the
weak portion for the air bag.
[0011] In the case of the technical concept disclosed in Japanese
Laid-Open Patent Publication No. 8-282420 concerning the
conventional technique described above, the following inconvenience
arises. That is, a considerable burden is imposed on the investment
for the equipment, because it is necessary to use the expensive
sensor for sensing the laser. Further, the control of the laser
beam is complicated in order to obtain a constant thickness of the
weak portion for the air bag.
[0012] In the case of the technical concept disclosed in Japanese
Laid-Open Patent Publication No. 10-85966 concerning the
conventional technique described above, the following inconvenience
arises. That is, the arrangement of the control unit is
complicated, and the production cost is expensive, because a method
is adopted, in which the comparison is made for the correlative
reference value concerning the residual strength and the integral
value obtained with a detection signal.
SUMMARY OF THE INVENTION
[0013] A general object of the present invention is to provide a
perforating machining method based on a laser beam, which makes it
possible to reduce the diameter of a through-hole bored by means of
a convenient method without requiring any excessive equipment
investment.
[0014] A principal object of the present invention is to provide a
perforating machining method based on a laser beam, which makes it
possible to reduce the diameter of a through-hole bored through a
weak portion for an air bag by means of a convenient method without
requiring any excessive equipment investment.
[0015] Another object of the present invention is to provide a
perforating machining method based on a laser beam, which makes it
possible to form a weak portion for an air bag having such an
appearance quality that a through-hole bored by the laser beam is
invisible, in which the durability is realized for the
function.
[0016] The above and other objects, features, and advantages of the
present invention will become more apparent from the following
description when taken in conjunction with the accompanying
drawings in which a preferred embodiment of the present invention
is shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows a schematic arrangement illustrating a
workpiece-machining system for carrying out a method for forming a
weak portion for an air bag according to an embodiment of the
present invention;
[0018] FIG. 2 shows a flow chart illustrating machining steps for
forming the weak portion for the air bag at an instrument panel by
using a laser beam;
[0019] FIG. 3 shows a time chart illustrating the timing for
radiating the laser beam onto the instrument panel;
[0020] FIG. 4 shows a plan view illustrating the instrument panel
in which the weak portion for the air bag is formed in accordance
with a predetermined machining pattern;
[0021] FIG. 5 shows a time chart illustrating another method for
radiating the laser beam onto the instrument panel;
[0022] FIG. 6 shows, with partial omission, plan views as viewed
from the front surface side and the back surface side respectively
depicting through-holes formed through the instrument panel by
means of the method for forming the weak portion for the air bag
according to the embodiment of the present invention;
[0023] FIG. 7 shows a time chart illustrating still another method
for radiating the laser beam onto the instrument panel;
[0024] FIG. 8 shows, with partial omission, plan views as viewed
from the front surface side and the back surface side respectively
depicting through-holes formed through the instrument panel by
means of the method shown in FIG. 7; and
[0025] FIG. 9 shows a time chart illustrating the timing for
radiating a laser beam concerning Comparative Example.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] In FIG. 1, reference numeral 10 indicates a
workpiece-machining system for carrying out a method for forming a
weak portion for an air bag according to an embodiment of the
present invention.
[0027] The workpiece-machining system 10 comprises a six-axis robot
16 which has an arm 14 for holding an instrument panel 12 as a
workpiece and which causes displacement or rotational movement of
the instrument panel 12 about multiple axes including three axes of
X, Y, and Z, and a robot controller 18 for controlling the six-axis
robot 16. The instrument panel 12 functions as a cover to be
installed to an unillustrated opening for an air bag (not
shown).
[0028] A sensor 20 for sensing a laser beam passed through a
through-hole bored through the instrument panel 12 is placed on a
support base 22 under the instrument panel 12. The instrument panel
12 is held so that the side on which the laser beam is radiated is
a back surface 24, and the side opposed to the sensor 20 is a front
surface 26.
[0029] The workpiece-machining system 10 further comprises a laser
beam-oscillating unit 32 for forming a plurality of penetrating
small holes in accordance with a predetermined machining pattern by
radiating the laser beam onto the instrument panel 12 via a bend
mirror 28 and a light-collecting lens 30, a laser controller 34 for
controlling the laser beam-oscillating unit 32, and a feedback
circuit 36 connected to the laser controller 34, for controlling
the output of the laser beam on the basis of a detection signal
from the sensor 20.
[0030] Those preferably used as the laser beam-oscillating unit 32
include, for example, laser oscillators based on, for example,
CO.sub.2, excimer, semiconductor, argon gas, and diode. An assist
gas supply unit 38 for supplying gas to the focus lens 30 is
arranged.
[0031] The feedback circuit 36 includes a digital/analog converter
40 for deriving a laser output command signal for the laser
controller 34, a timer controller 42 for deriving a pulse command
signal, and an analog/digital converter 44 for converting the
analog signal into the digital signal for the detection signal
outputted from the sensor 20.
[0032] The feedback circuit 36 comprises ROM 46, RAM 48, a
pulse-setting unit 50 in which one cycle T1 of the pulse command
signal, one cycle T2 of the laser output command signal, and a
pulse width T3 of the laser output command signal are previously
set, for holding the preset data as memory as described later on,
and a laser power-setting unit 52 in which the output (power) of
the laser beam is previously set, for holding the preset data as
memory.
[0033] In this arrangement, the digital/analog converter 40, the
timer controller 42, the analog/digital converter 44, ROM 46, RAM
48, the pulse-setting unit 50, and the laser power-setting unit 52
are connected to CPU 56 via a bus line 54 respectively. It is
assumed that the pitch threshold preset value data, which is the
distance of separation between the small holes penetrating through
the instrument panel 12, is stored in ROM 46.
[0034] The workpiece-machining system 10 for carrying out the
method for forming the weak portion for the air bag according to
the embodiment of the present invention is basically constructed as
described above. Next, its operation, function, and effect will be
explained on the basis of a flow chart shown in FIG. 2.
[0035] CPU 56 reads the data previously set in the pulsesetting
unit 50 and the laser power-setting unit 52 to set the frequency
(1/T2) and the duty ratio (T3/T2) in the timer controller 42 and
set the laser output in the digital/analog converter 40 (step S1).
Subsequently, CPU 56 derives the pulse start signal to the timer
controller 42. The pulse command signal is changed from the OFF
state to the ON state on the basis of the pulse start signal.
Accordingly, the pulse start state is established from the pulse
stop state (step S2).
[0036] When the pulse start state is established for the pulse
command signal, the laser output command signal, which is composed
of the pulse waveform set in the step S1, is outputted to the laser
controller 34 via the digital/analog converter 40 (see FIG. 3). The
laser beam is radiated from the laser beam-oscillating unit 32. The
laser beam is reflected by the bend mirror 28, and then it is
transmitted through the light-collecting lens 30. After that, the
laser beam is radiated toward the back surface 24 of the instrument
panel 12 as the workpiece. Accordingly, the laser machining is
applied to the instrument panel 12.
[0037] As indicated by the "laser beam arrival position" shown in
FIG. 3, the boring operation is started, and it is gradually
effected from the side of the back surface 24 of the instrument
panel 12 by means of the laser beam. Consequently, the penetration
is achieved between the back surface 24 and the front surface 26 of
the instrument panel 12. During this process, the laser beam, which
has passed through the through-hole of the instrument panel 12, is
sensed by the sensor 20 (see the step S3). The detection signal
(feedback signal), which is derived from the sensor 20, is
converted into the digital signal by the analog/digital converter
44, and then it is introduced into CPU 56. CPU 56 derives the pulse
stop signal to the timer controller 42 to establish the stop state
for the pulse command signal (step S4). As a result, the laser
power output command signal is in the OFF state, and the radiation
of the laser beam onto the instrument panel 12 is stopped. Thus,
the boring machining for one through-hole is completed for the
instrument panel 12.
[0038] Subsequently, the arm 14 of the six-axis robot 16 is
operated in accordance with the control operation of the robot
controller 18. The instrument panel 12 is displaced by a
predetermined pitch, and it is positioned at a position at which
the boring operation is to be performed next time in accordance
with the machining pattern for the weak portion for the air bag
(step S5).
[0039] When the time corresponding to one cycle T1 of the pulse
command signal has elapsed (step S6), then the laser beam is
radiated onto the instrument panel 12 in accordance with the steps
S2 to S4, and a new through-hole is bored. When a plurality of
through-holes are bored in accordance with the predetermined
machining pattern, the weak portion 58 is formed as shown in FIG.
4. The machining steps for the instrument panel 12 come to an end
(step S7).
[0040] In this case, as shown in FIG. 3, it is assumed that tl (not
shown) represents a period of time until the detection signal is
outputted after the sensor 20 senses the laser beam passed through
the through-hole of the instrument panel 12, t2 represents a period
of time until the threshold value previously set in ROM 46 is
exceeded after the detection signal from the sensor 20 is inputted
into the analog/digital converter 44, and t3 represents a period of
time until the radiation of the laser beam is actually stopped
after the threshold value is exceeded. In the embodiment of the
present invention, the total period of time of the periods of time
t1 to t3 is set to be shorter than a period of time (T2-T3).
Therefore, it is possible to stop the radiation of the laser beam
before the next pulse signal P6 for constructing the laser output
command signal is outputted.
[0041] In other words, the total time (t1+t2+t3) of the periods of
time t1 to t3 is set to be shorter than the difference in time
between the pulse width T3 and one cycle T2 of the laser output
command signal, i.e., the period of time between the previous pulse
signal P5 and the next pulse signal P6 (see the hatched portion).
Accordingly, the pulse command signal is in the OFF state before
the next pulse signal P6 rises, and the output of the laser beam is
stopped as the pulse signal P5 outputted just before the next pulse
signal P6 falls. Therefore, the radiation of the laser beam can be
quickly stopped after the sensor 20 senses the laser beam.
Accordingly, it is possible to decrease the diameter of the
through-hole on the side (side of the surface 26 of the instrument
panel 12) which is penetrated by the laser beam (see FIG. 6).
[0042] It is preferable that the diameter of the through-hole on
the side penetrated by the laser beam is within an invisible range,
i.e., it is larger than 0 .mu.m not including 0 .mu.m, and it is
not more than 50 .mu.m. If the diameter of the through-hole on the
side penetrated by the laser beam is larger than 50 .mu.m, the
following inconvenience arises, because the hole itself is visible.
That is, the appearance quality is deteriorated, and the strength
and the rigidity are inferior.
[0043] The most preferred range of the diameter of the through-hole
is not less than 10 .mu.m and not more than 30 .mu.m. In this
range, it is possible to improve the appearance quality of the air
bag cover, and it is possible to increase the durability of the
function of the weak portion 58.
[0044] It is preferable that the distance of separation (pitch)
between the through-holes formed in accordance with the machining
pattern is within a range of not less than 0.5 mm and not more than
1.5 mm.
[0045] As shown in FIG. 5, the following procedure is preferably
adopted. That is, the laser output is controlled by means of a
continuous laser output command signal P1 (laser output command
signal in which the ON state is continued for a predetermined
period of time) when the through-hole machining is started.
Further, the laser output is controlled by means of a plurality of
pulse signals P2 to P4 composed of ON/OFF states just before the
laser beam is sensed by the sensor 20, i.e., just before the
through-hole is formed through the instrument panel 12 by means of
the laser beam. In this procedure, the pulse command signal is in
the OFF state before the next pulse signal P5 is outputted, which
is performed in the same manner as described above.
[0046] As shown in FIG. 7, the laser beam may be radiated onto the
instrument panel 12 by using a laser output command signal composed
of a pulse signal level-shifted by a predetermined value by using a
level shifter (not shown). In this case, as shown in FIG. 8, a
continuous groove is formed on the side of the back surface 24 of
the instrument panel 12 onto which the laser beam is radiated. When
the pulse signal is completely in the OFF state (see FIG. 7), it is
possible to further decrease the diameter of the through-hole
penetrating on the side of the front surface 26 of the instrument
panel 12.
[0047] Next, a case as Comparative Example is shown in FIG. 9, in
which the through-hole machining is performed for one hole by using
a continuous laser output.
[0048] In this case, as shown in FIG. 9, it is assumed that t1 (not
shown) represents a period of time until the detection signal is
outputted after the sensor 20 senses the laser beam passed through
the through-hole of the instrument panel 12, t2 represents a period
of time until the threshold value previously set in ROM 46 is
exceeded after the detection signal from the sensor 20 is inputted
into the analog/digital converter 44, t3 represents a period of
time until the laser output signal is in the OFF state after the
threshold value is exceeded, and t4 represents a period of time
until the radiation of the laser beam from the laser
beam-oscillating unit 32 is actually stopped after the laser output
signal is in the OFF state. In Comparative Example, the total
period of time (t1+t2+t3+t4) of the periods of time t1 to t4
respectively is the delay time. Therefore, it is difficult to
shorten the radiation time of the laser beam after the sensor 20
senses the laser beam. There is a limit to reduce the diameter of
the through-hole formed by the laser beam.
[0049] The "laser beam arrival position" in FIGS. 3, 7, and 9 is
conveniently expresses how far the laser beam radiated in the
thickness direction of the instrument panel 12 as the workpiece
arrives, which is not depicted in a time-dependent manner. In this
case, the wave form, which indicates the arrival position of the
laser beam, expresses the machining state based on the pulse
signal. Actually, the movement speed of the instrument panel 12 is
slow as compared with the pulse frequency. Therefore, the machining
is effected in the groove-shaped configuration, and no indented
wave form is formed on the inner circumferential surface of the
penetrated through-hole.
[0050] In the embodiment of the present invention, the period of
time (t1+t2+t3), which is obtained by adding the periods of time t1
to t3 respectively, is set to be shorter than the period of time
(T2-T3). Accordingly, the delay time can be shortened, and it is
possible to reduce the diameter of the through-hole (through-hole
on the side of the penetrated surface 26) formed by the laser beam,
as compared with Comparative Example. Further, in the embodiment of
the present invention, no complicated control method is used. The
present invention can be carried out by using the simple apparatus.
Therefore, an advantage is obtained such that the production cost
can be reduced.
* * * * *