Laser monitor apparatus and a laser apparatus

In a laser beam processing apparatus, a laser monitor comprises a photo sensor, a laser power measuring circuit, an A-D converter, a monitor control unit, a comparison decision unit, a display control unit, a display, an alarm generating circuit and a buzzer. A measured laser power signal (analog voltage signal) representative of an instantaneous value of laser power of a pulsed laser beam is produced by the photo sensor and the laser power measuring circuit, and the digital measured laser power signal from the A-D converter is supplied to the comparison decision unit and to the monitor control unit. The monitor control unit sets or determines a monitor reference waveform corresponding to a laser control reference waveform used for waveform control in the processing apparatus and controls the comparison decision unit. The comparison decision unit provides a monitoring decision on the power of the pulsed laser beam, which is displayed by a visual presentation or by display lamps on the display.

BACKGROUND OF THE INVENTION 
The present invention relates to a laser apparatus of the waveform control 
type and a laser monitor apparatus for use therewith. 
A pulsed laser beam processing apparatus employs a method to variably 
control a laser power waveform of a pulsed laser beam in order to meet 
various processing requirements. In accordance with the waveform control 
method, a desired reference waveform of laser power is preset into the 
laser beam processing apparatus. In the laser beam processing apparatus, a 
laser electric power supply which supplies electric power to a laser 
oscillator is controlled by an open-loop control or a closed-loop control 
so that the power of the laser beam oscillated from the laser oscillator 
can follow the reference waveform. 
A laser monitor apparatus for monitoring laser power, which is incorporated 
in a laser beam processing apparatus or has the form of an independent 
unit electrically connected thereto, has been used for the sake of quality 
control in a laser beam processing site. 
In the prior art laser monitor apparatus, a part of a laser beam is 
projected on a photo detector such as photo-diode which produces an 
electric signal (a laser detection signal) corresponding to the laser 
power or intensity of light of the laser beam. The signal is integrated to 
obtain a measured value of laser energy (Joule) per unit time or one 
pulse. Judging how far apart the measured laser energy value is from a 
predetermined reference value or whether the measured value is within the 
limit of a predetermined monitoring value or not, the laser monitor 
apparatus outputs decision on whether the laser beam processing has been 
performed normally or not, or whether the resulting quality of processing 
is good or not. 
However, such laser monitor apparatus has not worked effectively in the 
above type of laser apparatus using waveform control method. In the 
waveform control method, it is important how closely an actual laser power 
waveform follows a reference waveform. The prior art laser monitor 
apparatus makes a decision of good or bad on the quality of processing on 
the basis of a measured value (mean value) of laser energy per unit time 
or one pulse. Therefore, even if the actual laser power waveform deviates 
so far apart from the reference waveform as to influence the quality of 
processing, the laser monitor apparatus may determine the processing to be 
normal, failing to determine it to be defective, as long as the total 
laser energy or the average laser energy of the whole pulse is within the 
allowable range. 
SUMMARY OF THE INVENTION 
With the above problems in mind, an object of the invention is to provide a 
laser monitor apparatus capable of being adaptive to any type of reference 
waveform used in a laser power waveform control method and providing 
monitor information useful for quality control. 
Another object of the invention is to provide a laser apparatus capable of 
performing laser power waveform controlling by using any type of reference 
waveform and of providing monitor information useful for quality control. 
In accordance with an aspect of the invention, a laser monitor apparatus 
comprises: 
reference waveform setting means for setting a monitor reference waveform 
corresponding to a reference waveform for waveform control used in a laser 
apparatus; 
first monitoring condition setting means for setting one or more of 
monitoring sections or points in any desired periods or at any desired 
points of time in said monitor reference waveform; 
second monitoring condition setting means for setting a monitoring waveform 
or monitoring value as an upper and/or lower limit being offset by a 
desired allowable value from said monitor reference waveform in each of 
said monitoring sections or points; 
measuring means for measuring the laser power of said laser beam or a 
corresponding predetermined electric parameter; 
comparing means for comparing a measured value provided by said measuring 
means with said monitoring waveform or value at each of said monitoring 
sections or points; and 
decision means for providing a monitor decision result based on the 
comparison result from said comparing means. 
The reference waveform setting means may comprise a setting means for 
setting said monitor reference waveform based on the measured value 
provided by said measuring means. 
The first monitoring condition setting means may comprise a setting means 
for individually setting allowable values in said monitoring sections or 
points. 
The decision means may comprise means for analyzing and integrating a 
comparison result from said comparison means to provide a monitor decision 
on whether the laser beam processing has been normal or defective. 
In accordance with another aspect of the invention, a laser apparatus 
comprises: 
laser oscillation means supplied with electric power for oscillating a 
laser beam; 
laser electric power supply means for supplying electric power to said 
laser oscillation means; 
first reference waveform setting means for setting a desired reference 
waveform for waveform control with respect to the laser power of said 
laser beam or a corresponding predetermined electric parameter; 
laser control means for controlling said laser electric power supply means 
so that the laser power of said laser beam or said predetermined electric 
parameter can follow said reference waveform for waveform control; 
second reference waveform setting means for setting a monitor reference 
waveform corresponding to said reference waveform for waveform control; 
first monitoring condition setting means for setting one or more of 
monitoring sections or points in any desired periods or at any desired 
points of time in said monitor reference waveform; 
second monitoring condition setting means for setting a monitoring waveform 
or monitoring value as an upper and/or lower limit being offset by a 
desired allowable value from said monitor reference waveform in each of 
said monitoring sections or points; 
measuring means for measuring the laser power of said laser beam or the 
corresponding predetermined electric parameter; 
comparing means for comparing a measured value provided by said measuring 
means with said monitoring waveform or value at each of said monitoring 
sections or points; and 
decision means for providing a monitor decision result based on the 
comparison result from said comparing means. 
The predetermined parameter may be at least one of an electric power, a 
current and a voltage supplied from said laser electric power supply means 
to said laser oscillation means. 
In accordance with the laser monitor apparatus and the laser apparatus of 
the present invention, with respect to a laser power waveform of a pulsed 
laser beam to be variably controlled by a waveform control method, one or 
more desired monitoring sections or points and upper and/or lower 
monitoring waveforms or monitoring points defining desired allowable 
ranges in the monitoring sections or points are set to make a monitoring 
decision, thereby being adaptive to any type of laser power waveform of 
pulsed laser beam for providing useful information for quality control.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The invention will be now described in detail with respect to preferred 
embodiments by reference to the drawings. 
Referring to FIG. 1, a pulsed laser beam processing apparatus according to 
an embodiment of the invention comprises a laser oscillator 10, a laser 
electric power supply 12, a laser control unit 14, a laser projection unit 
16, a laser monitor 18 and so on. 
The laser oscillator 10 comprises a solid-state laser medium 20 made of YAG 
(Yttrium-Aluminum-Garnet) for instance, a laser excitation source 22 to 
project (supply) a laser excitation beam EB to the solid-state laser 
medium 20 and a pair of optical resonance mirrors 24 and 26 to amplify a 
laser beam produced from the solid-state laser medium 20 and to output a 
pulsed laser beam LB. 
The pulsed laser beam LB oscillated and output from the laser oscillator 10 
is sent via a mirror 28 to the laser projection unit 16, from which the 
pulsed laser beam LB is projected onto a workpiece, for instance 
workpieces to be welded (W.sub.1, W.sub.2). 
The laser electric power supply 12 for supplying electric power for laser 
oscillation to the laser excitation source 22 of the laser oscillator 10 
converts a commercial AC power from a commercial AC power supply 30 under 
the control of the laser control 14 into a suitable electric power, 
current and voltage, to drive the laser excitation source 22. 
The laser control unit 14 serves to control the laser electric power supply 
12 so that a desired laser beam LB is produced from the laser oscillator 
10. Especially, in the waveform control function of the embodiment, the 
laser control unit 14 controls the laser electric power supply 12 by an 
open-loop or a closed-loop (feedback) control method so that the power of 
the pulsed laser beam LB or a corresponding predetermined electric 
parameter can follow a preset laser control reference waveform. 
For instance, a driving current, driving voltage or driving electric power 
supplied to the laser excitation source 22 from the laser electric power 
supply 12 may be selected as such electric parameter corresponding to the 
power of the laser beam LB. The laser control unit 14 may comprise a 
microcomputer. Selected values or data of laser control reference waveform 
are input to the laser control unit 14 from an input device 32 such as 
keyboard, mouse and so on. 
The laser monitor 18 comprises a photo sensor 34, a laser power measuring 
circuit 36, an analog-to-digital (A-D) converter 38, a monitor control 
unit 40, a comparison decision unit 42, a display control unit 44, a 
display 46, an alarm generating circuit 48 and a buzzer 50. 
The photo sensor 34 comprising a photo-diode for instance, receives a laser 
beam LB' that is a part (e.g. 0.1%) of the laser beam LB and that has 
transmitted a mirror 28 to produce an electric current (photo-current) 
I.sub.B corresponding to the laser power or intensity of light of the 
pulsed laser beam LB. The laser power measuring circuit 36, which includes 
a current-to-voltage converting circuit to convert the photo-current from 
the photo sensor 34 into a corresponding voltage, generates a measured 
laser power signal (analog voltage signal) S.sub.B representing the 
instantaneous value of power of a pulsed laser beam LB. The measured laser 
power signal S.sub.B from the laser power measuring circuit 36 is 
converted into a corresponding digital signal at a predetermined sampling 
frequency, and the digital measured laser power signal D.sub.B is supplied 
to the comparison decision unit 42 and to the monitor control unit 40. 
When the power of a pulsed laser beam LB is to be fedback for waveform 
control, the measured laser power signal D.sub.B output from the A-D 
converter 38 may be supplied to the laser control unit 14, too. 
The monitor control unit 40 and the comparison decision unit 42 may be 
constituted by a microcomputer. FIG. 2 shows a functional configuration of 
the monitor control unit 40 and the comparison decision unit 42 in the 
embodiment. 
Referring to FIG. 2, the monitor control unit 40 comprises a memory 52, a 
calculator 54, a timing generator 56 and a control logic 58. The memory 52 
stores various selected data of monitoring conditions input from the input 
device 32, for instance a monitoring section, a monitoring point, a 
monitor reference waveform, an allowable value and a monitoring value. In 
the embodiment, a monitor reference waveform can be also used that 
corresponds to a laser power waveform of a pulsed laser beam LB oscillated 
and output from the laser oscillator 10, which has been normal or good. 
Such a monitor reference waveform corresponding to an actual normal laser 
power waveform is also stored in the memory 52. 
The calculator 54 executes various computations necessary for monitor 
control, including a computation for determining a monitor reference 
waveform corresponding to an actual normal laser power waveform and a 
computation for determining a monitoring waveform or monitoring value as 
described later. The timing generator 56 operates in synchronization with 
the laser oscillation operation of the laser oscillator 10 under control 
of the laser control unit 14 to provide various timing signals or clock 
signals for monitoring to respective components such as the control logic 
58 in the monitor control 40 and a decision logic 64 in the comparison 
decision unit 42. 
The control logic 58 serves to manage and execute the entirely of setting 
operation of monitoring conditions and control operation of monitoring. In 
setting operation of monitoring conditions, the control logic 58 receives 
not only various selected values of monitoring conditions from the input 
device 32 in the above manner but also a digital measured laser power 
signal D.sub.B from the A-D converter 38 in order to set a monitor 
reference waveform corresponding to an actual normal laser power waveform. 
In monitoring control operation, the control logic 58 responds to a clock 
signal from the timing generator 56 during emission of a pulsed laser beam 
LB to provide upper and lower limits LM.sub.H and LM.sub.L to upper and 
lower limit comparators 60 and 62, respectively, in the comparison 
decision unit 42 and to provide a monitor timing signal K.sub.T 
representing the timing of each monitoring section or point to a decision 
logic 64 in the comparison decision unit 42. 
The comparison decision unit 42 includes the upper limit comparator 60, the 
lower limit comparator 62 and the decision logic 64. As a pulsed laser 
beam LB is produced from the laser oscillator 10, a digital measured laser 
power signal D.sub.B from the A-D converter 38 is supplied to the upper 
and lower limit comparators 60 and 62. 
The upper limit comparator 60 compares the measured laser power signal 
D.sub.B with an upper limit monitoring waveform or value LM.sub.H provided 
from the control logic 58 to generate a comparison result signal CP.sub.H 
representative of the comparison in magnitude between D.sub.B and 
LM.sub.H. The lower limit comparator 62 compares the measured laser power 
signal D.sub.B with a lower limit monitoring waveform or value LM.sub.L 
from the control logic 58 to generate a comparison result signal CP.sub.L 
representative of the comparison in magnitude between D.sub.B and 
LM.sub.L. 
The comparison result signals CP.sub.H and CP.sub.L from the upper and 
lower limit comparators 60 and 62 are supplied to the decision logic 64 at 
the timing of each monitoring section or point given by the monitor timing 
signal K.sub.T from the control logic 58. The decision logic 64 makes a 
monitoring decision based on CP.sub.H and CP.sub.L to produce a decision 
result signal which is then supplied to the laser control unit 14, the 
display control unit 44 and an alarm generating circuit 48. 
Turning to FIG. 1, the display control unit 44 displays the result of 
monitoring decision provided from the decision unit 42 by a visual 
presentation or by display lamps on the display 46. The display 46 may 
comprise a liquid crystals display, a CRT display or a photo diode 
display. The alarm generating circuit 48 drives the buzzer 50 to generate 
a predetermined sound of alarm when the result of monitoring decision is 
to be notified, particularly when the decision logic 64 has provided a 
decision result of "defective" or "bad". The display control unit 44 is 
connected to the monitor control unit 40 and to the laser control unit 14 
so that various settings of monitoring conditions and laser control 
conditions can be displayed on the display 46. 
Next, examples of methods to set or determine a laser control reference 
waveform, a monitor reference waveform, a monitoring waveform and a 
monitoring value in the laser beam processing apparatus of the embodiment 
will be described with reference to FIGS. 3 to 10. 
FIG. 3 shows an example of reference waveform for laser control. The 
reference waveform shown PW is for controlling the laser power of a pulsed 
laser beam LB to be produced from the laser oscillator 10 and has a pulse 
duration or pulse width consisting of three split periods--a first period 
[t.sub.0 .about.t.sub.1 ], a second period [t.sub.1 .about.t.sub.2 ] and a 
third period [t.sub.2 .about.t.sub.3 ]. The reference waveform PW rises 
lineally from zero to a peak value P.sub.S in the first period [t.sub.0 
.about.t.sub.1 ] and keeps the peak value P.sub.S in the second period 
[t.sub.1 .about.t.sub.2 ] and falls lineally from the peak value P.sub.S 
to zero in the third period [t.sub.2 .about.t.sub.3 ]. On the whole, the 
reference waveform PW takes the shape of a trapezoidal. Selected values 
for defining the reference waveform for laser control PW are input to the 
laser control unit 14 from the input device 32 and then stored in the form 
of a digital waveform data in the storage of the laser control unit 14. 
FIGS. 4 to 9 show some examples of monitor reference waveforms and 
monitoring waveforms adaptable to the laser control reference waveform PW 
of FIG. 3. 
Referring to FIG. 4, upper and lower limit monitoring waveforms LM.sub.H 
and LM.sub.L are set in a monitoring section extending over the whole 
pulse time of a monitor reference waveform MW corresponding to the 
reference waveform for laser control PW, wherein LM.sub.H and LM.sub.L are 
offset by an allowable value K.sub.C upward and downward, respectively, 
from every part of the monitor reference waveform MW. 
The lower limit monitoring waveform LM.sub.L is omitted in the range of 
negative value of laser power around the start time t.sub.0 and the 
terminal time t.sub.3 because a laser beam can not have a negative value 
of laser power. In this method, data of the monitoring reference waveform 
MW as well as the allowable value K.sub.C are input by the input device 32 
to the monitor control unit 40, which in turn produces data of the upper 
and lower monitoring waveforms LM.sub.H and LM.sub.L depending on MW and 
K.sub.C. The allowable value K.sub.C may be input as a value of laser 
power (W) or as a value of .+-.%. 
This setting method has an advantage that the monitor control unit 40 can 
easily execute the computation to determine the upper and lower monitoring 
waveforms LM.sub.H and LM.sub.L. In this method, however, the sharper the 
slope of the reference waveform is, the narrower the margin of the 
allowable range in the direction of time axis is. In FIG. 4, for instance, 
the downslope of the reference waveform MW (PW) is rather sharp in the 
falling period [t.sub.2 .about.t.sub.3 ], whereby the time margin of the 
allowable range is considerably narrow in the period. When the time margin 
of the allowable range is too narrow, a slight deviation of time at which 
the laser power is measured can cause an actual laser power (measured 
value) to be out of the allowable range, namely leading to excessively 
high sensitivity of decision of "defective." 
Referring to FIG. 5, upper and lower limit monitoring waveforns LM.sub.H 
and LM.sub.L defined in a monitoring section covering over the whole pulse 
time of a monitor reference waveform MW corresponding to the laser control 
reference waveform PW are offset by an allowable value K.sub.C in the 
normal direction from every part of the monitor reference waveform MW. 
In the same manner as the method of FIG. 4, the monitor control unit 40 
determines the upper and lower monitoring waveforms LM.sub.H and LM.sub.L 
as shown in FIG. 5 on the basis of the selected values of the monitoring 
reference waveform MW and the allowable value K.sub.C, which are input by 
the input device 32. 
According to the method of FIG. 5, the time margin of the allowable range 
is permitted to keep a suitable width with respect to any given slope of 
the reference waveform. However the allowable range in the upward and 
downward direction varies depending on the degree of slope of the 
waveform. That is, the gentler the slope is, the smaller the upward and 
downward allowable range is, and the sharper the slope is, the larger the 
upward and downward allowable range is. 
FIG. 6 shows a modification of the setting method of FIG. 5, in which there 
is provided a difference between the upper and lower allowable values 
K.sub.CH and K.sub.CL by which the upper and lower monitoring waveforms 
LM.sub.H and LM.sub.L are offset respectively in the normal direction from 
every part of the reference waveform MW. As occasion demands, only one of 
the monitoring waveforms LM.sub.H and LM.sub.L can be selected. 
With reference to FIG. 7, monitoring sections [t.sub.a .about.t.sub.b ] and 
[t.sub.c .about.t.sub.d ] are provided in the rising period and the peak 
keeping period of the monitoring reference waveform MW, respectively, and 
upper and lower limit monitoring waveforms (LM.sub.H1, LM.sub.L1) and 
(LM.sub.H2, LM.sub.L2) are offset by an allowable value K.sub.C upward and 
downward, respectively, from the reference waveform MW in each of the 
monitoring sections [t.sub.a .about.t.sub.b ] and [t.sub.c .about.t.sub.d 
]. 
The method of FIG. 7 defines a monitoring section or point not in the whole 
period of the monitor reference waveform MW but in a selected part 
(usually, an important part) to be monitored selectively or 
preponderantly, while excluding or neglecting the remaining part 
(unimportant part) from the object of monitoring. According to this 
method, the monitor decision function is prevented from being disturbed by 
a distortion of a laser power waveform which may be produced due to the 
properties of the laser electric power supply 12 and the laser oscillator 
10, thereby permitting a more complicated monitor reference waveform to be 
selected. 
FIG. 10 shows an example of the setting method of FIG. 7 applied to a more 
complicated monitor reference waveform MU. The reference waveform MU 
provides three important conditions. The first condition is to keep the 
laser power constant at a relatively low level P.sub.A in the period of 
the front part of the reference waveform NMU. The second is to raise the 
laser power to a considerably high level P.sub.B in the period of the 
central part of MU. The third is to keep the laser power constant at 
another relatively low level P.sub.C in the period of the rear part of MU. 
The transitional portions of the waveform MU (the rising and falling 
periods) preceding and succeeding the above three intermediate portions 
are not so important. Thus, monitoring sections [t.sub.a .about.t.sub.b ] 
and [t.sub.d .about.t.sub.e ] are set in the front and rear selected level 
portions of MU having a relatively long period, respectively, and a 
monitoring point [t.sub.c ] is set in the central selected level portion 
of MU having a relatively short period. Moreover, upper and lower 
monitoring waveforms (LM.sub.H1, LM.sub.L1) and (LM.sub.H3, LM.sub.L3) and 
upper and lower monitoring points (LM.sub.H2, LM.sub.L2) are set with 
different allowable ranges in the monitoring sections [t.sub.a 
.about.t.sub.b ] and [t.sub.d .about.t.sub.e ] and in the monitoring point 
[t.sub.c ], respectively. 
Even when the laser control unit 14, the laser electric power supply 12 and 
the laser oscillator 10 normally operate with respect to the laser control 
reference waveform PW and the obtained weld quality in the workpieces 
(W.sub.1, W.sub.2) is good, the measured laser power values (S.sub.B, 
D.sub.B) provided from the laser power measuring units (34, 36, 38) do not 
always approximate to the laser control reference waveform PW. Actually, 
it is common that the laser control reference waveform PW is influenced by 
the properties of the laser electric power supply 12 and the laser 
oscillator 10 so that errors of various patterns and degrees occur between 
the measured laser power values (S.sub.B, D.sub.B) and the laser control 
reference waveform PW. Such errors can be compensated or masked by the 
above method of setting a monitoring section and point in a selected part 
or period of the monitor reference waveform. 
Alternatively, such errors can be effectively compensated by a method of 
determining a monitor reference waveform corresponding to the reference 
waveform for laser control on the basis of data of the measured value 
(emprical value). In this method, an actual laser power waveform by which 
a good weld quality has been obtained in the workpieces (W.sub.1, W.sub.2) 
is calculated based on the measured laser power value (D.sub.B) and the 
data of the actual laser power waveform is registered as a monitor 
reference waveform in the memory 52. Using the average value of measured 
values of more than one good laser power waveforms can improve the 
reliability of the determined monitor reference waveform, thus assuring a 
still better result of processing. 
FIG. 8 shows an example of a monitor reference waveform MW' determined 
based on the data of measured values (emprical values) with respect to the 
laser control reference waveform PW of FIG. 3. 
FIG. 9 shows upper and lower limit monitoring waveforms LM.sub.H' and 
LM.sub.L' determined by the same method as that of FIG. 5 with respect to 
the monitor reference waveform MW' of FIG. 8. The other methods of the 
embodiment, for example the methods of FIG. 4 and FIG. 7 can be employed 
to determine a monitoring waveform or monitoring point for such monitor 
reference waveform MW'. In either method of those, since the monitor 
reference waveform MW' based on the actual laser power waveform (measured 
value) is highly precise, a small (strict) value for an allowable range 
can be selected to improve the precision of monitoring decision and 
thereby to raise the level of quality control. 
Next, operation of the pulsed laser beam processing apparatus, especially 
the laser monitor 18 in the embodiment, will be described. 
The laser control unit 14 makes the laser electric power supply 12 start to 
operate after sending a start signal ST for notifying the start timing to 
the monitor control unit 40. The laser electric power supply 12 supplies a 
driving electric power, driving current or driving voltage corresponding 
to the laser control reference waveform PW to the laser excitation source 
22. The excitation beam EB emitted from the laser excitation source 22 
excites the solid-state laser medium 20 so that a pulsed laser beam LB is 
produced from the output mirror 26. The output pulsed laser beam LB is 
sent via the mirror 28 to the laser projection unit 16, from which the 
pulsed laser beam is projected onto the workpieces (W.sub.1, W.sub.2). The 
laser control unit 14 controls the laser electric power supply 12 by an 
open-loop control method or a feedback control method for waveform control 
so that the laser power of the pulsed laser beam LB can follow the laser 
control reference waveform PW. 
When the pulsed laser beam LB is oscillated and output from the laser 
oscillator 10, a laser beam LB' which is a part (e.g. 0.1%) of the laser 
beam LB and which has transmitted the mirror 28 is received (detected) by 
the photo censor 34. Then, the laser power measuring circuit 36 generates 
a measured laser power signal S.sub.B representing an instantaneous value 
of power of the pulsed laser beam LB. The A-D converter 38 supplies to the 
comparison decision unit 42 a digital measured laser power signal D.sub.B 
corresponding to the analog voltage signal S.sub.B. 
In the comparison decision unit 42, upper and lower limit comparators 60 
and 62 compare the digital measured laser power signal D.sub.B input from 
the A-D converter 38 with the digital data of the upper monitoring 
waveform or value LM.sub.H and the lower monitoring waveform or value 
LM.sub.L which are provided from the monitor control unit 40 in 
synchronization with (at the same data rate as) the signal D.sub.B. Then, 
the upper and lower comparators 60 and 62 generate comparison result 
signals CP.sub.H and CP.sub.L representing the comparisons in magnitude 
between D.sub.B and [LM.sub.H, LM.sub.L ], respectively. The comparison 
result signals CP.sub.H and CP.sub.L from the comparison decision unit 42 
are supplied to the decision unit 64 which in turn analyzes and integrates 
the signals CP.sub.H and CP.sub.L to generate a monitoring decision result 
after the pulse time or duration of the pulsed laser beam LB terminates. 
There are various modes in the monitoring decision result provided from the 
comparison decision unit 42. A basic mode is to inform whether or not the 
actual laser power waveform of the pulsed laser beam LB has deviated from 
the allowable range defined by the monitoring waveform or value. Computing 
out a point at which the actual laser power waveform has deviated, if any, 
is advantageous. 
For example, in the case of setting the monitor reference waveform MW and 
the upper and lower limit monitoring waveforms LM.sub.H and LM.sub.L as 
shown in FIG. 4, when a pulsed laser beam LB having a laser power waveform 
as shown in FIG. 11 is produced, the laser power waveform is within the 
allowable range over the whole of the monitoring section. Therefore, a 
monitoring decision result notifying that the pulsed laser beam LB is 
"normal" would be provided. 
In an example of FIG. 12, however, the actual or measured laser power 
waveform of the pulsed laser beam LB deviates from the allowable range in 
the middle of the pulse time. In that case, another monitoring decision 
result notifying that the pulsed laser beam LB is "defective" would be 
provided. 
As occasion demands, the deviation positions [t.sub.A .about.t.sub.B ], 
[t.sub.C .about.t.sub.D ] may be indicated on display, too. Moreover, a 
predetermined sound of alarm may be generated from the buzzer 50 that is 
energized by the alarm generating circuit 48. 
In a pulsed laser processing apparatus such as in the embodiment, it is 
also advantageous to provide a monitoring decision regarding a quality of 
weld obtained in the workpieces (W.sub.1, W.sub.2). Generally, a decision 
of "good" or "bad" may be given on the obtained weld quality in accordance 
with a decision of "normal" or "defective" on the pulsed laser beam LB. 
However, different decision criteria can apply between "good" or "bad" of 
weld quality and "normal" and "defective" of pulsed laser beam. For 
instance, in a case of setting plurality of monitoring sections or points 
as shown in FIG. 7 and FIG. 10, when the measured laser power value is out 
of the allowable range in at least one of the monitoring sections or 
points, a decision of "defective" may be made on the pulsed laser beam LB 
in the above manner while a decision of "good" may be made on the 
resulting weld quality depending on the position of the deviation. 
In the illustrated embodiment, the laser monitor 18 is incorporated in the 
pulsed laser beam processing apparatus. However the laser monitor 18 can 
be in the form of an independent unit which is electrically connected to 
the main unit or laser control unit of the processing apparatus by an 
electric cable. In the case of an independent unit, the laser monitor 18 
may be provided with necessary peripheral equipments such as an input 
device, a display and so on separately from the main unit or laser control 
unit in the processing apparatus. 
In the illustrated embodiment, a monitor reference waveform is set with 
respect to the laser power waveform of a pulsed laser beam LB. However, in 
the same manner as the laser control reference waveform in the laser 
control unit 14, a monitor reference waveform can be set to a waveform of 
an electric parameter corresponding to the power of a pulsed laser beam 
LB, for example, a driving current, driving voltage or driving electric 
power. In that case, the measuring means of the laser monitor apparatus 
may be composed to measure the instantaneous value of such electric 
parameter. 
Although the illustrated embodiment relates to a pulsed laser processing 
apparatus, the present invention can be also adapted to a laser beam 
processing apparatus of the continuous wave type and to other laser 
apparatuses than a laser beam processing apparatus.