Electric heating – Metal heating – By arc
Reexamination Certificate
2003-05-01
2004-11-16
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C700S166000
Reexamination Certificate
active
06818856
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser machining apparatus for machining a workpiece by a laser beam, and in particular to a laser machining apparatus equipped with a high power laser for performing laser machining by frequently changing and precisely controlling a laser output.
2. Description of Related Art
It has been carried out to utilize a successively measured value of a laser output of a laser oscillator provided in a laser machining apparatus for stabilizing laser machining by the laser machining apparatus. In general, a part of the laser beam transmitted through a rear mirror arranged opposite to an output mirror of the laser oscillator is inputted into a power sensor for measurement of the laser output. In a case of a laser oscillator having a reflecting mirror for reflecting the laser beam emitted from a laser resonator, there can be adopted an arrangement for taking out the part of the laser beam by transmission through the reflecting mirror for the measurement.
Thus, the laser output power is measured on the real-time basis in the laser machining. The laser output measured on the real-time basis is utilized in the following applications.
(1) Utilization of the measured value as data representing a present value of the laser output in a feedback control of the laser output for stabilizing the laser output.
(2) Detection of an abnormal status of laser machining by an prominent increase of a laser beam reflected on a workpiece made of material having high reflectance with respect to the laser beam and returned to the laser oscillator.
(3) Diagnose of malfunction of the laser oscillator by abnormal decrease of the laser output.
There is an nonnegligible delay of response in the power sensor for measuring the laser output. Particularly for measurement of high-power laser, it is generally adopted a type of a power sensor in which the laser beam is converted into heat and heat flow rate is measured. The time required for response to a change of the laser output is considerably late in comparison with the time from issuance of a laser output command to an actual output of the laser beam.
In an ordinary laser machining apparatus, time required for an actual output of the laser beam to reach 95% of the laser output command from an issuance of the laser output command is approximately 0.0002 sec, whereas the time required for the measured value to reach 95% of the laser output command is approximately 3 sec. Thus, it takes a long time for the measured value of the power sensor to reflect the actual output, whereas a time period from issuance of the output command to the actual output of the laser beam is instantaneous, no to be satisfactory for the foregoing applications (1)-(3).
In order to explain the above circumstance using an example,
FIG. 1
shows an example of a system configuration of a conventional laser machining apparatus in which the above applications (1)-(3) can be performed. As shown in
FIG. 1
, a laser oscillator
5
for outputting a laser beam LB to be irradiated on a workpiece W through a mirror
7
and a condenser lens
8
may comprise a YAG laser which is pumped by a pumping source
4
such as a pumping lamp and a pumping LED to which electric power is supplied from a laser pumping power supply
3
.
A laser output command for controlling the laser output is issued from a laser output commanding section
1
to the laser pumping power supply
3
through a feedback control section
2
to supply an electric power to the laser pumping power supply
3
. The laser output command is designated by a machining program or a manual operation on a control panel (not shown).
A laser power sensor
6
provided outside of a rear mirror
5
a
of the laser oscillator
5
regularly monitors the laser output (laser power). An output signal of the laser power sensor
6
is amplified by an amplifier
7
and compared with the laser output command, and a difference therebetween is inputted into the feedback control section
3
. The laser power sensor
6
and the amplifier
7
constitutes laser output measuring means.
As a result of the comparison, if the measured value of the laser output is lower than the laser output command value, a signal indicating a positive difference is outputted to the feedback control section
2
, and if the measured value is greater than the laser output command value, a signal indicating a negative difference is outputted to the feedback control section
2
. The feedback control section
2
compensates the laser output command in accordance with the signal indicating the difference by a feedback control. The feedback control of the laser output to control the laser output to coincide with the command value is performed.
Further to the above feedback control, the output of the amplifier
7
indicating the measured value of the laser power is compared with the laser output command and a difference therebetween is inputted into an output abnormality detecting section
10
. As a result of the comparison, if the measured value of the laser power is lower than the laser output command value, a signal indicating a positive difference is outputted to the laser power abnormality detecting section
10
, and if the measured value is greater than the command value, a signal indicating a negative difference is outputted to the laser power abnormality detector
10
.
The output power abnormality detector
10
determines whether or not the difference is within an allowable range and if the difference deviates from the allowable range, it is determined that an abnormality has occurred and a stop signal is issued to the laser output command means to stop the operation of the laser oscillator
5
.
It is determined that an abnormality occurs in a case where a laser beam reflected on a workpiece and returned to the laser oscillator greatly increases by an abnormality of the laser machining on the workpiece which is made of a material having high reflectance of the laser beam (in the application of (2)), and in a case where the laser output abnormally decreases by a malfunction of the laser oscillator (in the application (3)).
The delay of response of the laser power sensor
6
will be described on a case where a laser output command as shown in
FIG. 2
a
is issued from the laser output commanding section
1
. In
FIG. 2
a
, a pattern of a laser output command
101
is shown with an axis of abscissa representing time (sec.) and an axis of ordinate representing an output power (W). In this example, the laser output command
107
is designated by a machining program. The command value is 4 kW in an early section for 3.5 sec., and is 1 kW in a later section for 4 sec.
FIG. 2
b
shows a transition of the measured value
107
of the laser output power, a laser output command value
104
after subjected to the feedback control and a difference
110
between the laser output command and the measured value
107
in a case where the laser output command
101
is issued to the laser machining system with the feedback control of the laser output power, as shown in FIG.
1
. In
FIG. 2
b
, an axis of abscissa indicates time (sec.) and an axis of ordinate indicates output power (W).
As shown in
FIG. 2
b
, a status where the measured value
107
is lower than the command value
101
continues for a considerable rise period (from 0 kW to 4 kW) immediately after an issuance of the laser output command
101
due to a delay of response of the power sensor
6
. Accordingly, a signal indicating a luck of output power is issued to the feedback control section
2
, so that the laser output command
104
increases to an upper limit of the laser oscillator
5
under the feedback control, as indicated by a reference numeral
51
. Then, the measured value
107
approaches the command value
101
of 4 kW to terminate the above status and enters a state where the command value
101
, the laser output command
104
subjected to the feedback control and the measured value
107
coincide with one another. Thus, there exists a time period in wh
Mori Atsushi
Sato Motohiko
Yamazaki Etsuo
Fanuc LTD
Heinrich Samuel M.
Staas & Halsey , LLP
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