NC laser system

An NC laser system turns on and off a laser oscillator at a desired timing. A machining program is decoded to deliver a move command for movement along axes, and an ON-OFF command for turning on and off an laser oscillator. In response to the move command, interpolation processing is effected to deliver interpolation pulses. The interpolation pulses are controlled for acceleration and deceleration to generate a deceleration-starting signal and a deceleration-terminating signal. On the other hand, in response to the ON-OFF command, an ON-OFF signal is delivered. For example, the ON-OFF signal is delivered at any of timings of the start of deceleration, the end of deceleration, etc. Further, the ON-OFF signal can be delivered when an actual position of a machining head becomes closest to a directed end point.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to an NC laser system comprising a laser beam 
machine and a numerical control system associated therewith, and more 
particularly to a numerical control (NC) laser system of this kind adapted 
to deliver an ON-OFF signal for ON-OFF control of a laser oscillator 
thereof. 
(2) Description of the Related Art 
When an NC laser system is operated to cut a workpiece of metal or the like 
by a laser beam generated thereby, the positioning of a machining head is 
first completed, and then a laser oscillator is turned on in a cutting 
mode of the system to thereby start machining of the workpiece. However, 
machining started after completion of positioning of the machining head 
takes time to cut the workpiece. Therefore, there is conventionally 
employed a machining method of sending a command to turn on or off the 
laser oscillator while holding the NC laser system in the cutting mode. 
According to such a laser beam machining method, the machining head is 
moved without waiting for completion of positioning of the machining head, 
which makes it possible to reduce machining time. In laser beam cutting 
performed by the method, an ON-OFF signal for turning on or off the laser 
oscillator is generated by the same block of a machining program as that 
containing a move command for moving the machining head, whereby the laser 
oscillator is turned on or off according to the ON-OFF signal. 
However, in the cutting mode, acceleration/deceleration control is 
performed for control of the speed of servomotors, which makes an actual 
machining path different from a path directed by the program due to delay 
of movement for machining caused by the acceleration/deceleration control. 
Therefore, even if an ON signal is delivered together with a move command 
for moving the machining head, the ON signal is not necessarily delivered 
at an end point of movement of the machining head directed by the move 
command. If interpolation of a subsequent command for moving the machining 
head written in the following block has already been started, the ON 
signal is delivered at a point different from the directed end point. 
Particularly, in cutting a small circle, there are cases in which in spite 
of directions for holding the laser oscillator in an ON state only within 
or on the circle, the laser oscillator continues to be in the ON state 
even after the machining head is outside the circle. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of these circumstances, and the 
object thereof is to provide an NC laser system which is capable of 
turning on and off a laser oscillator at a desired timing. 
To solve the above-described problems, the invention provides an NC laser 
system having a laser beam machine and a numerical control system 
associated therewith, comprising a preprocessing operation unit for 
decoding a machining program to deliver a move command for movements along 
axes, and an ON-OFF command for turning on or off a laser oscillator, an 
interpolating unit responsive to the move command for executing 
interpolation processing to deliver interpolation pulses, an 
acceleration/deceleration control unit for controlling the interpolation 
pulses for acceleration and deceleration, to deliver a 
deceleration-starting signal and a deceleration-terminating signal, and a 
timing control unit for delivering an ON-OFF signal for turning on or off 
the laser oscillator according to the ON-OFF command. 
The preprocessing operation unit decodes the machining program, and 
delivers the move command for movements along axes, and the ON-OFF command 
for turning on or off the laser oscillator. The interpolating unit 
responsive to the move command executes interpolation processing and 
delivers the interpolation pulses. The acceleration/deceleration control 
unit controls the interpolation pulses for acceleration and deceleration, 
and delivers the deceleration-starting signal and the 
deceleration-terminating signal. 
On the other hand, the timing control unit delivers the ON-OFF signal 
according to the ON-OFF command. For example, the ON-OFF signal is 
delivered at any times, such as the start of deceleration, the end of 
deceleration, etc. 
The above and other objects, features and advantages of the present 
invention will become apparent from the following description when taken 
in conjunction with the accompanying drawings which illustrates a 
preferred embodiment of the present invention by way of example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will be described with reference to 
the drawings. 
FIG. 2 is a block diagram showing hardware of an NC laser system according 
to the present invention. A processor (CPU) 1 reads out machining programs 
stored in a memory (RAM) 3, based on a control program stored in a ROM 2, 
to thereby control the overall operation of the NC laser system. A 
machining program for execution of the present invention and other 
parameters are also stored in this memory 3. An I/O unit 4 sends an ON-OFF 
signal from the processor 1 to a laser oscillator 5. The laser oscillator 
5 is controlled for the ON-OFF state thereof by the ON-OFF signal. When 
the laser oscillator 5 is in an ON state, it generates a laser beam 6. The 
laser beam 6 is reflected from a bending mirror 7, and transmitted to a 
laser beam machine 8. 
The laser beam machine 8 includes a table 10 for fixing a workpiece 9 and a 
machining head 11 for irradiating the laser beam 6 onto the workpiece 9. 
The laser beam 6 introduced into the machining head 11 is restricted in 
diameter by a nozzle 11a and emitted to the workpiece 9. The laser beam 
machine 8 includes servomotors 12, 13 for control of movement of the table 
10 in two directions of an X-axis and a Y-axis, and a servomotor 14 for 
control of movement of the machining head 11 upward and downward. These 
servomotors 12, 13, and 14 are connected to servo-amplifiers 15, 16 and 
17, respectively, and controlled in respect of rotation thereof by axial 
movement control signals from the processor 1. Further, instructions or 
directions to the laser beam machine 8 are given by way of a CRT/MDI unit 
18. 
FIG. 1 is a conceptual representation of the NC laser system according to 
the present invention. For simplicity of illustration, FIG. 1 shows a 
servomotor and unit associated therewith for one axis (X-axis) alone, and 
ones for the other axes are omitted. 
A machining program 21 contains move commands for positioning control of 
the servomotor 12, speed commands for control of speed, and ON-OFF signals 
for turning on and off the laser oscillator. Preprocessing operation unit 
22 reads the machining program 21, decodes same, and delivers a move 
command and a speed command to interpolating unit 23. The interpolating 
unit 23 performs interpolation for each axis in response to the move 
command and the speed command, to deliver interpolation pulses. 
Acceleration/deceleration control unit 24 receives and controls the 
interpolation pulses for acceleration and deceleration, to deliver the 
resulting controlled pulses to the servoamplifier 15. The servoamplifier 
15 drives the servomotor 12 according to the interpolation pulses 
controlled for acceleration and deceleration. 
On the other hand, timing control unit 25 delivers an ON-OFF signal in 
response to an ON-OFF command from the preprocessing operation unit 22 at 
a predetermined timing. The timing for delivering the ON-OFF signal will 
be described later in detail. The laser oscillator 5 is turned on or off 
in response to the ON-OFF signal. When the laser oscillator 5 is turned 
on, it generates the laser beam 6, which is deflected by a bending mirror 
7, and emitted via the machining head 11 onto the workpiece 9 to cut same. 
Delivery timing of the ON-OFF signal will be described. FIG. 3 shows a 
machining path directed by move commands. The move commands here direct 
that the cutting point should be moved from a point Ps through a point P0 
to a point Pe. Actually, the machining head 11 is moved along a path 
indicated by a curve passing through a point Pn, due to delay of movement 
caused by the acceleration/deceleration control. 
FIG. 4 shows speed curves of movement for machining along respective axes. 
In the figure, the abscissa represents time, while the ordinate represents 
speed. Vx represents a speed in the direction of the X-axis and Vy a speed 
in the direction of the Y-axis. More specifically, when the move commands 
for the path shown in FIG. 3 are executed, an interpolation for movement 
control in the direction of the X-axis is terminated and deceleration in 
the direction of the X-axis is started, at a time point ts. 
Simultaneously, an interpolation for movement control in the direction of 
the Y-axis is started, and at a time point tn, the actual position of the 
machining head 11 becomes closest to the directed end point P0 (see FIG. 
3). Then, at a time point re, the deceleration in the direction of the 
X-axis is terminated, and at the same time, the acceleration in the 
direction of the Y-axis is also terminated. 
Here, the delivery timing of the ON-OFF signal can be set to the time point 
ts at which the deceleration is started, the time point te at which the 
deceleration is terminated, or the time point tn at which the machining 
head is closest to the directed end point P0. Signals indicative of the 
time point ts at which the deceleration is started and the time point te 
at which the deceleration is terminated are sent to the timing control 
unit 25 from the acceleration/deceleration control unit 24. The time point 
tn at which the machining head is closest to the directed end point is 
determined in the following manner: 
Assuming that an actual position of the machining head along the X-axis is 
represented by X, an actual position of same along the Y-axis by Y, and 
the directed end point P0 (see FIG. 3) by coordinates (X0, Y0), the time 
point tn is a time point at which of the following equation becomes the 
minimum: 
EQU .alpha.=(X0-X).sup.2 +(Y0-Y).sup.2 
That is, if .alpha. is calculated for time points with a predetermined time 
interval, .alpha. decreases to the minimum at the point Pn, as is clear 
from FIG. 3, and increases thereafter. Therefore, the point Pn closest to 
the directed end point P0 can be obtained by determining a point where a 
change in .alpha. is inverted from one in a decreasing direction to one in 
an increasing direction. At this time point tn corresponding to the point 
Pn, the ON-OFF signal is delivered. 
Next, details of the machining program will be described. FIG. 5 shows an 
example of the machining program. FIG. 6 shows a machining path directed 
by the machining program of FIG. 5. In FIG. 6, the solid line represents 
portions of the path where the laser beam is irradiated (for cutting a 
workpiece), and the broken line represents potions of the path where the 
laser beam is not irradiated. 
A block designated by a sequence number N010 directs that the cutting point 
should be moved from a point Pa to a point P1 (X1, Y1) by cutting feed 
(G01), with the laser output of 0 (SO) and at a feed speed of 50000 mm/min 
(F50000). Further, this block contains a command C5 for turning on the 
laser oscillator at a time point when the machining head becomes closest 
to the directed end point. That is, the laser oscillator is turned on at a 
point closest to the directed end point. 
A block designated by a sequence number N011 directs that the cutting point 
should be moved from the point P1 (X1, Y1) to a point P2 (X2, Y2) by 
cutting feed (G01), with the laser output of 1000 W (S1000) and at a feed 
speed of 8000 mm/min (F8000). 
A block designated by a sequence number N012 directs that the cutting point 
should be moved from the point P2 round a circle 30 back to the point P2 
with the same laser output (1000 W) and at the same feed speed (8000 
mm/min) as by the preceding block N011. In short, this block gives the 
commands for cutting out the circle 30. 
A block designated by a sequence number N013 directs that the cutting point 
should be further moved (cutting should be further effected) from the 
point P2 to a point P3 on the circle 30, by cutting feed. Further, this 
block also contains a command (C2) for turning off the laser oscillator at 
a start of deceleration. Therefore, the laser oscillator is turned off 
before it reaches the point P3. 
A block designated by a sequence number N014 directs that the cutting point 
should be moved from the point P3 to a point P4, by cutting feed, at a 
feed speed of 50000 mm/min (F50000) with the laser output of 0 (SO). 
For example, commands for the ON-OFF signal can be determined as follows: 
C1 ON signal is delivered at the start of deceleration. 
C2 OFF signal is delivered at the start of deceleration. 
C3 ON signal is delivered at the end of deceleration. 
C4 OFF signal is delivered at the end of deceleration. 
C5 ON signal is delivered at a point closest to a directed end point. 
C6 OFF signal is delivered at the point closest to the directed end point. 
Next, an actual machining path will be described. FIG. 7 shows the actual 
machining path. In this figure, similarly to FIG. 6, a portion of the path 
where the laser beam is irradiated is indicated by a solid line, while a 
portion of same where it is not irradiated is indicated by a broken line. 
As shown in the figure, due to delay of movement for machining caused by 
the acceleration/deceleration control, the actual machining path is curved 
inward compared with the directed path (points Pa-P1-P2-P3-P4). Since the 
block (of N010) for moving the cutting point from the point Pa to the 
point P1 contains the command (C5) for turning on the laser oscillator at 
a point closest to the directed end point, an ON signal is delivered at a 
point Pon to turn on the laser oscillator. 
Further, the block (of N013) for moving the cutting point from the point P2 
to the point P3 contains the command (C2) for turning off the laser 
oscillator at the start of deceleration. Accordingly, the laser oscillator 
is turned off at a point Pof. 
If the command C6 (for delivering an OFF signal at a point closest to the 
directed end point) or the command C4 (for delivering an OFF signal at the 
end of deceleration) is contained, the laser oscillator would be in an ON 
state up to a point Pof1, or to a point Pof2, thereby performing an 
excessive cutting operation in cutting a round hole defined by the circle 
30. 
Thus, according to the present embodiment, control can be effected such 
that signals for turning on and off the laser oscillator are delivered at 
desired time points, which makes it possible to perform a high-speed 
precision machining. 
Although in the above embodiment, the invention is described by way of an 
example of application thereof to the NC laser system, this is not 
limitative, but the invention may be applied to a water jet machine, a 
plasma jet machine, a sealant-applying machine, etc. 
As described heretofore, the present invention is constructed such that 
signals for turning on and off the laser oscillator can be delivered at 
any of the start of deceleration, the end of deceleration, and a time 
point that the machining head is closest to a directed end point. 
Therefore, it is possible to perform a high-speed precision machining. 
The foregoing is considered as illustrative only of the principles of the 
present invention. Further, since numerous modifications and changes will 
readily occur to those skilled in the art, it is not desired to limit the 
invention to the exact construction and applications shown and described, 
and accordingly, all suitable modifications and equivalents may be 
regarded as falling within the scope of the invention in the appended 
claims and their equivalents.