JPH11347771A - Control method for condensing lens height for laser beam machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set simply, accurately and automatically the position of a focal point and that of a machining torch as a preliminary operation of laser machining with respect to a laser beam machine. SOLUTION: Relating to a laser beam machine provided with a condensing lens 4, a machining torch 18, a servo motor 9a for varying an interval between the condensing lens 4 and an object 7 to be machined, a numerical control device 21 for controlling the servo motor 9a, a machining table 10b and a laser generator 1, and a profiling device which is installed in the machining torch 18 and which detects a distance between the condensing lens 4 and the object 7; a profiling sensor part 19, having a tapered hole along a laser beam 1a converged by the condensing lens 4 and thereby passing a laser beam and an auxiliary gas, is provided with guide bearings, which are installed between the profiling sensor part 19 and the machining torch 18, and which are for moving the sensor part 19 along the machining torch 18 and coaxially with the optical axis of the laser beam 1a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing apparatus such as a carbon dioxide laser for processing such as welding, cutting, and drilling of a steel plate or the like. The present invention relates to an improved laser processing apparatus which has been improved and a method of controlling the height of a condensing lens thereof.

[0002]

2. Description of the Related Art FIG. 6 shows a configuration of a conventional laser processing apparatus for cutting a steel plate or the like. In FIG. 6, reference numeral 1 denotes a laser oscillator, 1a denotes a laser beam, 2 denotes a laser light guide, 3 denotes a bending mirror, 4 denotes a condensing lens, 5 denotes a lens guide, and 6 denotes a converging length combined with the lens guide 5. A processing torch having a length substantially coincident with the focal length of the lens 4, a workpiece 7;
Is an auxiliary gas pipe, 8b is an auxiliary gas cylinder, 9a is a servomotor for lifting and lowering the processing torch 6 with the condenser lens 4, 9b is a worm, 9c is a rack, and the worm 9b and the rack 9c are servomotors 9a and the processing torch 6. Is engaged. 10a is a machining table base, 10b is a machining table, 10c is a sword mountain for supporting a workpiece, 10d is a servomotor for driving the operation of the machining table 10b, 11 is a numerical controller, 12 is a scanning sensor unit, and 12a is a scanning sensor. A support rod, 13 is a signal converter, 14 is a laser output command signal, 15 is a servo command signal for determining a processing shape and a processing speed, 16 is a servo command signal for setting a lens height, 1
Reference numeral 7 denotes an output from the copying apparatus.

[0005] Next, the operation of the conventional laser processing apparatus having the above-described configuration and preparation work up to the processing before starting the processing will be described. The laser oscillator 1 excites a laser medium and outputs a laser beam 1a. The laser light 1a passing through the laser light guide 2 is reflected by a bending mirror 3 provided in the middle of the optical path, the optical axis is bent in the direction of the condenser lens 4, and is incident on the condenser lens 4, where The workpiece 7 is focused by the focusing lens 4 and placed near the focal point of the focusing lens 4.
The workpiece 7 is placed on a sword mountain 10c for supporting the workpiece on the processing table 10b, and the servomotor 10d drives the processing table 10b to move the workpiece 7. Between the condenser lens 4 and the workpiece 7, a processing torch 6 whose inner diameter is tapered as approaching the workpiece 7.
Is provided, and the auxiliary gas supplied by the gas cylinder 8b through the gas pipe 8a is sprayed onto the laser-irradiated portion of the workpiece 7 so as to be coaxial with the focused laser beam 1a. The numerical controller 11 to which the processing conditions, such as the processing shape and the moving speed of the workpiece 7 and the laser output, are input, outputs a laser output command signal 14 to the laser oscillator 1 to obtain a predetermined laser output. The servo command signal 15 is sent to the servomotor 10d according to the shape and the required moving speed, and the workpiece 7 on the processing table 10b is moved to be processed into a predetermined shape.

In performing the above-mentioned processing, first, the lens guide 5 is moved in advance, and an interval 0 at which the tip of the processing torch 6 contacts the surface of the workpiece 7 is set between the condenser lens 4 and the workpiece 7. The origin is set in the numerical controller 11 as the coordinate origin of the distance. Then, the distance between the tip of the processing torch 6 and the workpiece 7 is adjusted while setting the distance between the tip of the processing torch 6 and the workpiece 7 to several mm and performing a processing test. Set the distance on the copying device.

Generally, when welding, cutting, or drilling a mild steel plate or the like with a laser processing apparatus of this kind, when the workpiece 7 is placed near the focal position focused by the condenser lens 4, The cutting speed can be increased and the cut surface roughness can be reduced. Further, the tip of the processing torch 6 and the workpiece 7
Is several mm, the removal of the workpiece 7 melted by the laser beam 1a is promoted by the auxiliary gas, and the processing speed is increased. Since the distance between the focus position and the workpiece 7 is determined by the thickness and material of the workpiece, it is necessary to set the position of the processing torch 6 every time the workpiece 7 or the condenser lens 4 is replaced. there were.

[0006]

In the above-described conventional laser processing apparatus, the distance between the focal position and the workpiece 7 and the distance between the processing torch 6 and the workpiece 7 are different from each other. Since the setting must be made every time the lens 4 is exchanged, it takes a lot of time to prepare for the start of processing, and the work efficiency is extremely low. Further, since the length of the processing torch 6 is fixed with respect to the variation of the focal length of the condenser lens 4, if the processing is performed with the distance between the processing torch 6 and the workpiece 7 fixed, the focal position and the workpiece are not fixed. The relative position of the laser beam 7 deviates from the optimum position, the irradiation condition of the laser beam 1a irradiating the workpiece 7 changes, and there is a problem that the processing quality varies and the yield decreases.

The present invention solves such a conventional problem, and simplifies setting of a focus position and a position of a processing torch as preparation work for laser processing, thereby improving work efficiency and improving processing yield. It is an object of the present invention to provide a method of controlling the height of a converging lens of a laser processing apparatus capable of realizing stable processing quality.

[0008]

In order to achieve the above object, a method for controlling the height of a converging lens of a laser processing apparatus according to the present invention comprises the steps of: holding a laser oscillator, a converging lens, a processing torch, and a workpiece; A moving table, a servomotor for changing the distance between the condenser lens and the workpiece, a numerical controller for controlling the servomotor, the processing table and the laser oscillator, and a laser beam irradiation on the surface of the workpiece An optical sensor for detecting light emitted from the unit, wherein the numerical control device is provided with a storage device for storing the interval between the condenser lens and the workpiece in accordance with a change in the output of the optical sensor. Irradiates the workpiece with laser light while changing the distance between the focusing lens and the workpiece within the range including the focal length of the focusing lens, and changes the laser beam irradiation position while moving the workpiece The maximum distance and the minimum distance between the condenser lens and the workpiece are stored in the storage device, and the center of the stored maximum distance and the minimum distance between the condenser lens and the workpiece is stored. The position is the coordinate origin of the servomotor.

[0009]

According to the above-mentioned method, for example, when the workpiece is mild steel or stainless steel, if the laser beam intensity exceeds a limit intensity of 10 ⁶ W or more per 1 cm ² , the surface of the workpiece is removed. Using the color change light from orange to blue, the emission color from the surface of the workpiece is monitored by an optical sensor with a blue filter, and the processing torch is moved up and down while changing the position of the workpiece. Blue light emission is detected in the upper and lower ranges including the focal point of the condenser lens. This operation is performed several times while changing the position of the workpiece, and the center of the upper limit and the lower limit of the range in which blue light emission is detected is set as the focal point of the condenser lens in the numerical controller, thereby automatically setting the focal position. Can be done

(Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of an example of a laser processing apparatus used in the method of the present invention. In FIG. 1, the same parts as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, 18 is a processing torch, 19 is a scanning sensor with a nozzle, 20 is a scanning sensor support rod, 21
Is a numerical controller, 22 is an optical sensor, and 22a is an optical sensor output. FIG. 2 is a cross-sectional view showing the details of the structure of the nozzle tip. In FIG.
9b is a tapered hole, 19c is an opening for looking into a laser beam irradiation part, 22b is a blue filter, 23 is a guide bearing, 24 is an assist gas packing, 25a and 25b are nozzles for preventing the copying sensor 19 with a nozzle from dropping. It is a stopper.

In the laser processing apparatus shown in FIGS. 1 and 2, one end of a laser light guide 2 is connected to an output port of a laser oscillator 1, and a bending mirror 3 is provided in the middle of the laser light guide 2.
The other end of the laser light guide 2 has a cylindrical shape having a circular cross section, and a lens guide 5 to which a condenser lens 4 is attached is inserted. An elevating rack 9c is attached to a side surface of the lens guide 5, and the elevating worm 9b coupled to the servomotor 9a is moved to the elevating rack 9c.
c, and the lens guide 5 is driven by the servo motor 9a.
Up and down. Further, a signal converter 13 is attached to a side surface of the processing torch 18 connected to the lens guide 5, and a side surface of the processing torch 18 is connected to an auxiliary gas cylinder 8b by an auxiliary gas pipe 8a.

A processing torch 18 is provided at the tip of the lens guide 5.
Is attached. As the processing torch 18 moves away from the condenser lens 4, the inner diameter becomes smaller to about half the diameter of the condenser lens 4, and then becomes cylindrical to the tip. Processing torch 18
A guide bearing 23 is attached to the inner surface at the tip of the nozzle, and the copying sensor with nozzle 19 is inserted into the guide bearing 23. On the inner surface of the processing torch 18, a gas packing 24 for keeping the auxiliary gas airtight between the processing torch 18 and the processing torch 18 and a nozzle stopper 25b for preventing the falling off of the scanning sensor 19 with the nozzle are attached. On the 19 side, a nozzle stopper 25a for preventing the copying sensor with nozzle 19 from dropping is opposed to the nozzle stopper 25b for preventing the copying sensor with nozzle 19 from falling off. Further, an optical sensor 22 is attached to an outer wall of the processing torch 18, and an optical sensor output 22 a is connected to the numerical controller 21.

The scanning sensor 19 with a nozzle is provided with a tapered hole 19b along the laser beam condensed inside. The center axis of the tapered hole 19b is aligned with the laser optical axis so that the center of the auxiliary gas flow is substantially aligned. Match. A guide roller 19a for keeping a constant distance from the workpiece 7 is embedded on the lower surface of the scanning sensor 19 with the nozzle, and a processing torch 18 is provided.
An opening 19c is provided so as not to block between the optical sensor 22 attached to the side surface of the laser beam and the laser beam irradiation unit.

The numerical control device 21 receives processing conditions such as a processing shape, a moving speed, and a laser output of the workpiece 7, outputs a laser output command signal 14 to the laser oscillator 1, and outputs a laser output command signal 14 according to the processing shape and the moving speed. The servo command signal 15 is sent to the servomotor 10d, and the workpiece 7 is moved by the processing table 10b.

Next, the operation will be described. In the example shown in FIG. 1, the laser oscillator 1 excites the laser medium and outputs a laser beam 1a in response to a command from the numerical controller 21. The laser light 1a passing through the laser light guide 2 is bent by the bending mirror 3 so that the optical axis is bent toward the condenser lens 4 and is incident on the condenser lens 4 to be condensed. The placed workpiece 7 is irradiated. The workpiece 7 is placed on the workpiece supporting blade 10c on the processing table, and the servo motor 10d drives the processing table 10b to move the workpiece 7. The auxiliary gas is supplied from the gas cylinder 8b to the processing torch 18 through the gas pipe 8a, and the processing torch 18 and the scanning sensor 19 with the nozzle blow the auxiliary gas onto the laser light irradiation part of the workpiece 7 coaxially with the focused laser light. . As described above, laser processing is performed on the workpiece 7 placed on the processing table 10b.

The laser beam 1a for performing the laser processing as described above
FIG. 4A shows the relationship between the beam diameter of the laser light 1a and the distance from the lens 4 when the light is condensed by the condenser lens 4.
FIG. 4B shows the relationship between the laser intensity and the distance from the lens 4.
FIG. 4C shows a relationship between a change in emission color observed on the surface of the workpiece 7 and a distance from the lens 4 when the workpiece 7 is further irradiated with the condensed laser light 1a. FIG.
As shown in (A), the beam diameter changes in proportion to the distance between the lens position and the focal position. On the other hand, the beam intensity increases in inverse proportion to the beam cross section. That is, the beam intensity changes in inverse proportion to the square of the distance between the lens position and the focal position. When the beam intensity gradually increases and exceeds a limit intensity _Io of about 10 6 W / cm 2 or more in the case of mild steel or stainless steel, the emission color changes from orange to blue. In FIG. 4B, in the case of the output a, the limit intensity I at the distance Za from the lens is shown.
_The blue light emission is obtained in a range from the distance Za to the focal position Zf and a range from the focal position Zf to a position symmetrical with respect to the focal position Zf of the Za point. In the case of the output b, blue light emission is obtained in a range from the distance Zb from the lens to the focal position Zf and a range from the focal position Zf to a position symmetrical with respect to the focal position Zf of the Zb point.
The output c emits blue light only at one point of the focal position.

In this example, the numerical controller 21
First, a position approximately 10% higher than the focal length of the condenser lens 4 and a position approximately 10% lower than the focal length are determined, and then the laser oscillator 1 is instructed to output the laser beam 1a. While moving the workpiece and gradually shifting the laser irradiation position, the servo motor 9a moves the condenser lens 4 to ± 1 of the focal length with respect to the focal position.
Lower or raise in the range of 0%. The laser output at this time is a value such that the distance from the lens exceeding the limit intensity _Io has a width as in the output a or b shown in FIG. 4B.

As the condenser lens 4 moves up or down and approaches the focal position, the laser light is condensed, and the intensity of the laser light applied to the surface of the workpiece 7 is inversely proportional to the beam cross-sectional area. The color of the light emitted from the laser light irradiation point changes from orange to blue. Further, when the condenser lens 4 is moved up or down after passing through the focal position, the laser light is diffused and the laser light intensity is reduced after the condenser lens 4 has passed the focal position, and the laser light irradiation point is reduced. The color of the light coming out of it changes from blue to orange.

Optical sensor 22 mounted on processing torch 18
, The orange color is blocked by the blue filter 22b of the light receiving unit, and the orange color is not sensed. When the color of light emitted from the laser light irradiation point changes from orange to blue at the time of laser light irradiation, the blue light passes through the blue filter 22b of the light receiving section, and the optical sensor 22 senses the light transmitted through the blue filter 22b. And outputs an output signal 22a. Numerical controller 2
1 stores the height of the condenser lens 4 at which the optical sensor 22 starts outputting the output signal 22a and the height of the condenser lens 4 at which the output signal 22a is no longer output, and stores the central value of the two heights. , And controls the servo motor 9a to control the light receiving lens 4
Is moved up and down, and the height of the central value of the two heights is set as the reference height of the light receiving lens 4, and the light receiving lens 4 is set at that height. Since the focal position of the condenser lens 4 is located at the center of the range where the emission color is blue, the work 7
The focal point of the condenser lens 4 is set on the surface of. The position of the condenser lens 4 is used as the coordinate origin of the servo motor 9a that moves the processing torch 18 up and down.

FIG. 3 shows an optical sensor 2 used in the second embodiment.
2 shows a processing circuit for the output signal 22a. In the signal processing circuit in FIG. 3, the output signal 22a of the optical sensor 22
Is input to the pulse counter 26, the number of pulses of the output signal 22a is counted while the elevation signal of the servo motor 9a is being output, and the output side of the pulse counter 26 is used as the signal register 27 and one of the inputs of the comparator 28. To the side. The signal register 27 stores and outputs the output of the pulse counter 26 at the beginning of the output of the elevation signal 16. Signal register 27
Is connected to the other input of the comparator 28. In this embodiment, the output 29 of the comparator 28 is connected to the numerical controller 21 instead of the optical sensor output 22a.

The operation of the second embodiment will be described below. Since the beam intensity is proportional to the laser output, FIG.
As shown in (B), as the output a decreases from the output a to the output b and c, the range in which the color of the light emitted from the laser beam irradiation point becomes blue decreases, and the beam intensity at the focal position Zf, which is the maximum intensity, becomes the limit intensity. Focus position Zf of output c that matches _Io
Only from the surface of the workpiece. Irradiating the workpiece with pulsed laser light while increasing or decreasing the average output, and increasing or decreasing the distance between the condenser lens and the workpiece, the pulsed laser light having a beam intensity exceeding the limit intensity _Io Is emitted only when the workpiece is irradiated, and the pulse counter 26 counts. Therefore, as the lens position moves and the focal position approaches the workpiece, the pulse count gradually increases, and the focal position increases. As the distance from the workpiece increases, the pulse count decreases.

Accordingly, in the second embodiment, the numerical controller 21 determines that the position of the condenser lens 4 is 10% higher than the focal length of the condenser lens 4 and that the position of the condenser lens 4 is higher than the focal length. The servo motor 9a is moved up and down between the position 10% lower. Next, the laser oscillator 1 outputs a pulse output while increasing or decreasing the pulse peak output by a certain width. If blue light is emitted on the surface of the workpiece 7 while the pulse peak output is increasing or decreasing in one round trip, the optical sensor 22 outputs a pulse-like output signal 22a, and the number of pulses of the output signal 22a is pulsed. It is measured by the counter 26. When the pulse increase / decrease is completed, the condenser lens 4 is lowered or raised. At this time, at the first moment when the elevation signal 16 of the servo motor 9a is output, the signal register 27 stores the pulse counter 2
6 holds the counted pulse number. Next, the laser oscillator 1
And the pulse signal is counted in the same manner. As the condenser lens continues to descend or rise,
The laser beam is condensed as the workpiece approaches the focal position of the condenser lens 4, and the intensity of the irradiated laser beam increases even with the same output. Therefore, the limit beam accompanied by blue light emission during one cycle of increase and decrease of the pulse peak output. The number of pulses exceeding the intensity _Io increases. As a result, the output of the pulse counter 26 continues to increase and becomes maximum when the focal position comes on the workpiece. The output of the pulse counter 26 and the output of the signal register 27 are compared by a comparison calculator 28. Whenever the number of pulses is increased by the pulse counter every time the focusing lens 4 is moved, the focal position is shifted to the workpiece 7. When the pulse counter starts approaching and the pulse counter starts to decrease, the focal position is shifted to the workpiece 7.
Will be on top. Therefore, the position of the condenser lens 4 with respect to the workpiece 7 when the sign of the output of the comparison calculator 28 is reversed is set as the coordinate origin of the servomotor 9a that moves up and down the processing torch 18.

FIG. 5 shows the beam intensity and the sensor pulse output at each position as the pulse peak output increases and decreases. That is, FIG. 5A is a pattern diagram for increasing / decreasing the laser beam output override, FIG. 5B is a graph showing a change in beam intensity at three types of work positions with an increase / decrease in the pulse peak output, and FIG. ) Are graphs showing sensor pulse outputs at three types of work positions as the pulse peak output increases and decreases, and Za, Zb and Z in the figure.
f corresponds to Za, Zb and Zf in FIGS. 4B and 4C.

In the above two embodiments, the focus position is searched by detecting the blue light emission on the surface of the workpiece 7 by irradiating the workpiece 7 with the laser beam by the optical sensor 22. The focus position can be searched for by using the method of emitting a popping sound when the workpiece 7 is irradiated with laser light and emitting blue light on the surface of the workpiece 7, and the origin of the servo motor 9 a can be set. it can. That is, a sound collecting sensor is used in place of the optical sensor 22 to detect a plosive sound generated when emitting blue light on the surface of the workpiece 7,
By using the output of the sound collecting sensor instead of the output of the optical sensor 22, it is possible to realize the above two embodiments in the same manner.

The procedure of adjusting the focal position on the workpiece 7 while changing the position of the condenser lens 4 shown in the above embodiment is stored and fixed in a storage device in the numerical controller 21.
The origin is set by the numerical controller 21.

With the above configuration and method, it is possible to automate the operation of setting the focal position of the condenser lens on the surface of the workpiece, and to set the focal position based on individual differences of the operators who operate the apparatus. The distance between the processing torch and the workpiece, and the relative position between the focal point of the focusing lens and the workpiece can always be kept optimal regardless of the variation and the variation of the focal length of the condenser lens itself. .

[0028]

As is apparent from the above description, according to the method of controlling the height of the condenser lens of the present invention, the dispersion of the focal position setting due to the individual difference of the worker and the dispersion of the focal length of the condenser lens itself. Irrespective of the distance between the processing torch and the workpiece, and the relative position between the focal position of the condenser lens and the workpiece can always be kept optimal, so that the laser beam irradiation conditions do not change, Variations in processing quality and a decrease in yield due to variations in irradiation conditions can be prevented beforehand.
Further, since the operation of setting the focal position on the surface of the workpiece is automated, the work preparation time is greatly reduced, and
No skill is required to set the focus position on the workpiece surface.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an example of a laser processing apparatus used in the present invention.

FIG. 2 is an enlarged sectional view of a nozzle portion of the same example.

FIG. 3 is a processing circuit diagram of an output signal of an optical sensor used in a second embodiment.

4A is a diagram showing the relationship between the distance from the lens position and the laser beam diameter. FIG. 4B is a diagram showing the relationship between the distance from the lens position and the laser beam intensity. FIG. Relationship diagram

FIG. 5A is a graph showing an increase / decrease pattern of laser beam output override. FIG. 5B is a graph showing a change in beam intensity at three types of work positions with an increase / decrease in pulse peak output. FIG. Showing sensor pulse output at three types of work positions accompanying

FIG. 6 is a configuration diagram of a conventional laser processing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser oscillator 1a Laser light 2 Laser light guide 3 Bending mirror 4 Condensing lens 7 Workpiece 8b Auxiliary gas cylinder (auxiliary gas source) 9a Servomotor 10b Processing table 10d Servomotor 13 Signal converter 18 Processing torch 19 Copying with nozzle Sensor (copy sensor part) 19b Tapered hole 21 Numerical control device 22 Optical sensor 23 Guide bearing

Claims (5)

[Claims] 1. A laser oscillator, a condenser lens, a processing torch, a processing table for holding and moving a workpiece, a servomotor for changing a distance between the condenser lens and the workpiece, and a servomotor for the servomotor. A numerical controller that controls a motor, a processing table, and a laser oscillator, and an optical sensor that detects light emitted from a laser light irradiating unit on the surface of the workpiece, and condenses light in relation to changes in the output of the optical sensor. Using a laser processing device provided in the numerical controller with a storage device for storing the distance between the lens and the workpiece a plurality of times, the distance between the focusing lens and the workpiece within a range including the focal length of the focusing lens. By irradiating the workpiece with laser light while changing it, and changing the laser beam irradiation position while moving the workpiece, the distance between the condensing lens and the workpiece when there is output from the optical sensor is obtained. maximum The distance and the minimum distance are stored in a storage device, and the center of the maximum distance and the minimum distance between the stored condenser lens and the workpiece is stored as the coordinate origin of the servomotor. Height control method. 2. A laser oscillator, a condenser lens, a processing torch, a processing table for holding and moving a workpiece, a servomotor for changing a distance between the condenser lens and the workpiece, and a servomotor for the servomotor. A numerical controller that controls a motor, a processing table, and a laser oscillator; an optical sensor that detects light emitted from a laser light irradiation unit on the surface of the workpiece; a pulse counter that inputs an output of the optical sensor; and a numerical controller. A signal register for holding a pulse counter output immediately before the drive signal is output every time the drive signal of the servomotor is output, and inputting the pulse counter output and the signal register output to a comparison arithmetic unit, Using a laser processing device for inputting power, a workpiece is irradiated with pulsed laser light while increasing or decreasing the average output, and the average output is increased or decreased by 1%.
The interval between the condenser lens and the workpiece is increased or decreased in each cycle, and the position of the condenser lens with respect to the workpiece when the sign of the output of the comparator is inverted is the coordinate origin of the servo motor. Concentrating lens height control method for a laser processing apparatus. 3. A laser oscillator, a condenser lens, a processing torch, a processing table for holding and moving a workpiece, a servomotor for changing a distance between the focusing lens and the workpiece, and a servomotor for the servomotor. A numerical control device for controlling a motor, a processing table, and a laser oscillator; and a sound collecting sensor for detecting a sound emitted from a laser light irradiating section on the surface of the workpiece. Using a laser processing device provided with a numerical control device with a storage device for storing the distance between the optical lens and the workpiece a plurality of times, the distance between the focusing lens and the workpiece within a range including the focal length of the focusing lens. By irradiating the workpiece with laser light while changing it, and changing the laser beam irradiation position while moving the workpiece, the distance between the condensing lens and the workpiece when there is an output of the sound collection sensor is obtained. Maximum spacing and maximum The distance is stored in a storage device, and the stored lens height control of the laser processing apparatus is performed using the center position of the maximum distance and the minimum distance between the condensing lens and the workpiece as the coordinate origin of the servomotor. Method. 4. A laser oscillator, a condenser lens, a processing torch, a processing table for holding and moving a workpiece, a servomotor for changing an interval between the condenser lens and the workpiece, and a servomotor for the servomotor. A numerical controller that controls the motor, the processing table, and the laser oscillator, a pulse counter that inputs the sound-collecting sensor output, and a pulse counter that is output immediately before the numerical controller outputs a drive signal for the servo motor. A signal register for holding the output, and using a laser processing device for inputting the pulse counter output and the signal register output to the comparator and inputting the output of the comparator to increase or decrease the average output of the workpiece. While irradiating pulsed laser light, the interval between the condenser lens and the workpiece is increased or decreased every period of increase or decrease of the average output,
A method of controlling the height of a condensing lens of a laser processing apparatus in which the position of the condensing lens, which is the distance between the condensing lens and the workpiece when the sign of the output of the comparator is inverted, is the coordinate origin of the servomotor. 5. The height of a converging lens of a laser processing apparatus according to claim 2, wherein the procedure for setting the coordinate origin of the servomotor is stored in a storage device in the numerical controller and executed. Control method.