JPH11267871A - Method and device for yag laser processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve stability, accuracy, and working efficiency of laser processing by simply and accurately deciding the moving position in a height direction of a nozzle. SOLUTION: A work processing position WP against a laser beam axial center position on a surface of a work W is detected by an image pick-up means 13 provided to a laser processing head 9. The work processing position WP against a laser beam focal position in a height direction is detected by a focal position detecting device 21 or a contact type sensor 23. Since the focal position is displayed by a display means 19 based on the detected signals detected at the image pick-up means 13 and the focal position detecting device 21 or the contact type sensor 23, any operator can simply and accurately match the laser beam focal position with the work processing position WP.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a YAG laser processing method and apparatus, and more particularly to a YAG laser processing for quantitatively detecting a distance between a nozzle and a work and positioning a laser beam focal position at the work processing position during teaching. A method and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, a YAG laser robot uses an image pickup means such as a CCD camera provided inside a YAG laser processing head to perform an image (monitoring) from a CCD camera by a worker before laser processing a work. ), A teaching operation for adjusting the laser beam focal position to the work processing position on the XY plane (on the surface of the work) is performed.

[0003] Since the cross target on the monitor and the focal position of the laser beam are adjusted in advance to match,
The teaching point is determined by aligning the cross target on the monitor with the work processing position, for example, the butted portion of the work, and a teaching program is created based on the teaching point. With the above operation, the work can be positioned on the XY plane.

In order to position the focal point of the laser beam at the workpiece processing position in the height direction of the nozzle and the workpiece,
At the position where the XY plane is focused by the CCD camera as described above, the operator looks at the laser beam while watching the YAG
The teaching point is searched and matched by raising and lowering the laser processing head.

[0005]

By the way, in the conventional teaching work, it is not possible to judge the position of the laser beam in the height direction to the work processing position by the monitor alone. The YAG laser processing head is moved up and down while looking through the camera. Therefore, there is a problem that it is difficult to perform quantitative positioning, and there is a possibility that danger is involved because an operation of looking into the vicinity of the nozzle occurs.

In addition, the position (focus) where the laser beam focal position matches the work processing position is determined by the operator's feeling, so that the focus range is 2-3 mm, and there is a problem that individual differences appear.

Further, the operator repeatedly raises and lowers the YAG laser processing head many times in order to search for the center of a certain range of focus, so that there is a problem that workability is poor.

In addition, since the focus range is 2 to 3 mm, there is a problem that the positioning accuracy is at the same level.

[0009] Since the allowable range of the depth of focus in the welding processing of the YAG laser is about 1 mm, there is a problem that if the allowable depth is out of the allowable range, processing defects (for example, insufficient penetration or penetration) may occur. there were.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to quantitatively detect a distance between a nozzle and a work to improve the positioning accuracy at the time of teaching, thereby improving processing defects. It is an object of the present invention to provide a YAG laser processing method and an apparatus therefor, which reduce the cost and simplify the operation.

[0011]

According to a first aspect of the present invention, there is provided a laser processing method comprising the steps of:
In a YAG laser processing method, a laser beam is condensed by a condensing lens provided in a YAG laser processing head and irradiated on a work from a nozzle provided at the tip of the laser processing head to perform laser processing. The work means for detecting the work position of the YAG laser beam on the surface of the work is detected by the imaging means provided in the apparatus, and the work position of the laser beam in the height direction is detected by the focus position detection device. The display means displays based on the detected detection signal and the detection signal detected by the focal position detecting device, and based on the display, the laser processing head is three-dimensionally adjusted to adjust the laser beam focal position to the work processing position. The movement is adjusted.

Therefore, the axial position of the YAG laser beam and the work processing position on the surface of the work detected by the imaging means are displayed on the screen of the display device.
The operator moves and adjusts the YAG laser processing head while viewing the image to easily adjust the axis position of the YAG laser beam to the work processing position. In addition, since the focal position detecting device indicates whether or not the distance between the nozzle and the workpiece is at the focal position of the laser beam, the YAG laser processing head can be easily moved and positioned also in the height direction. There is no individual difference between the workers, and the laser beam focal position is quantitatively and accurately positioned at the work processing position.

As described above, since there is no defocus, stable laser processing with high accuracy can be performed. The working efficiency of laser processing is improved.

According to a second aspect of the present invention, there is provided a YAG laser processing method according to the first aspect, wherein the focus position detecting device is disposed at a position offset with respect to the YAG laser beam. The present invention is characterized in that feedback control is performed in real time based on a detection signal detected by the device.

Therefore, since the focal position detecting device is arranged at the offset position, the positional relationship between the laser beam focal point and the work processing position is fed back in real time even during laser processing, so that it is automatically performed. Stable high-precision laser processing is performed.

According to a third aspect of the present invention, there is provided a YAG laser processing apparatus, wherein a YAG laser beam is condensed by a condensing lens provided in a YAG laser processing head, and is irradiated onto a work from a nozzle provided at a tip of the laser processing head. A YAG laser processing apparatus for performing laser processing by using an image pickup means for detecting a work processing position relative to a position of a YAG laser beam on a surface of a work in a three-dimensionally movable YAG laser processing head; A focus position detection device is provided for detecting a workpiece processing position with respect to the laser beam focus position in the height direction, based on a detection signal detected by the imaging unit and a detection signal detected by the focus position detection device. A display means for displaying a workpiece processing position with respect to a laser beam focal position is provided. The one in which the features.

Therefore, the operation is the same as that of the first aspect, and the axial position of the YAG laser beam and the work processing position on the surface of the work detected by the imaging means are:
Displayed on the screen of the display device, the operator can move and adjust the YAG laser processing head while viewing the image to easily adjust the YAG laser processing head.
The axis position of the AG laser beam is adjusted to the work processing position. In addition, since the focal position detecting device indicates whether or not the distance between the nozzle and the workpiece is at the focal position of the laser beam, the YAG laser processing head can be easily moved and positioned also in the height direction. There is no individual difference between the workers, and the laser beam focal position is quantitatively and accurately positioned at the work processing position.

As described above, since there is no defocus, stable laser processing with high accuracy can be performed. The working efficiency of laser processing is improved.

According to a fifth aspect of the present invention, there is provided a YAG laser processing apparatus according to the fourth aspect, wherein:
The contact can be moved to a retracted position.

Therefore, when the laser processing is not performed, the contact is moved to the retracted position and does not become an obstacle.

According to a fifth aspect of the present invention, in the YAG laser processing apparatus according to the third aspect, the focus position detecting device includes a contact member which comes into contact with the surface of the workpiece on a side surface of the YAG laser processing head. And a biasing means for constantly biasing the contact in a direction approaching the work is provided, and a tip of the contact is located at a laser beam focal position in a height direction. Is a contact-type actuator provided with a contact position detector for detecting the contact position.

Therefore, when the YAG laser processing head approaches the work, the contact is pressed by the work in a direction approaching the nozzle, and the contact position is set when the tip of the contact is located at the laser beam focal position in the height direction. The detector detects.

According to a sixth aspect of the present invention, in the laser processing apparatus of the third aspect, the focus position detecting device is a laser displacement sensor disposed at a position offset from a work processing position. It is a feature.

Therefore, since the laser displacement sensor is arranged at the offset position, the positional relationship between the laser beam focal point and the workpiece processing position is fed back in real time even during laser processing, so that the laser automatically becomes stable. High-precision laser processing is performed.

According to a seventh aspect of the present invention, in the laser processing apparatus according to the third aspect, the focal position detecting device is a capacitance sensor for detecting a gap between the nozzle and the work. Is what you do.

Therefore, the capacitance sensor becomes very compact, and even during laser processing, the positional relationship between the laser beam focal point and the workpiece processing position is fed back in real time, so that automatically stable high precision is achieved. Laser processing is performed.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the laser processing method and apparatus according to the present invention will be described below with reference to the drawings.

Referring to FIG. 1, a YAG laser beam LB output from a YAG laser oscillator 1 according to the present embodiment can move in a three-dimensional direction, for example, in the X, Y, and Z directions via an optical fiber 3. It is sent to the YAG laser processing head 5 provided at the tip of the robot arm. This YA
The G laser beam LB is condensed by a focusing lens 7 provided inside the laser processing head 5. A nozzle 9 is provided at the tip of the laser processing head 5 as shown in FIG.
Is emitted toward the workpiece W from the nozzle hole 11 at the tip of
Laser processing such as cutting or welding is performed to a desired shape.

In the YAG laser processing head 5, there is provided a nozzle hole 11, in other words, for example, a CCD camera 13 as an example of an image pickup means for acquiring an image for detecting the position of the YAG laser beam LB on the XY plane, and an illuminance. A light source (not shown) for securing is provided. The CCD camera 13 is electrically connected to an image processing device 15 that processes an image acquired by the CCD camera 13, and the image processing device 15 is connected to a sensor controller 17.

An image acquired by the CCD camera 13 is configured to be displayed on a monitor 19 as a display device, for example.
The laser beam LB is adjusted to coincide with the axis.

Further, the YAG laser processing head 5 has a focus position detecting device for detecting a matching state between the distance in the height direction from the tip of the nozzle 9 to the work processing position WP and the laser beam focal position LF from the nozzle 9. 21 are provided.

In the present embodiment, when the distance between the nozzle 9 and the work W is detected by the above-described focal position detecting device 21, the following specifications must be satisfied. That is, (1) ±
(2) Since the laser processing of the three-dimensional work W is performed by the laser robot, the accuracy is about 0.1 mm.
It is necessary to measure the actual machining point, (3) C
Since the imaging means of the CD camera 13 looks coaxially, the focus position detecting device 21 cannot be coaxially arranged, so that the measurement can be performed at an angle from the outside of the laser processing head 5; And that the detection characteristics do not change even if different materials such as stainless steel and aluminum are used.

Sensors for measuring the distance between the nozzle 9 and the work W include a proximity switch (such as an eddy current type), a laser type displacement sensor, an ultrasonic sensor, and a contact type sensor. As the focal position detecting device 21 according to the embodiment of the present invention, a contact type actuator, a laser displacement sensor, a capacitance sensor, and the like are particularly preferable.

Incidentally, the proximity switch has difficulty in accuracy, and also has difficulty in dissimilar materials, and is affected by the angle.

Since the laser type displacement sensor is usually a PSD element (analog), it detects the center value of the average value of the received laser light, so that the state of reflection changes depending on the material of the work W. An error occurs in the measurement.

The ultrasonic sensor hardly changes due to the difference in the material of the work W, but has a weak angle characteristic because the allowable angle range is ± 1 to 3 °.

Hereinafter, a contact sensor 23 as a representative example of the focal position detecting device 21 will be described with reference to FIGS.

Referring to FIGS. 1 to 3, a fixing bracket 25 is fixed to the side of the YAG laser processing head 5. A substantially rectangular contact bracket 27 is provided on the side surface of the fixed bracket 25 so as to be rotatable up and down in a substantially vertical plane with a support pin 29 fixed at one end thereof to the fixed bracket 25 as a support axis. ing.

The side face of the contact bracket 27 is provided with a penetrating position detecting hole 31. The contact detecting hole 31 is detected to detect whether the contact bracket 27 is at a predetermined position. For example, a proximity switch 33 as a type position detector is fixed to the fixing bracket 25 by a set. The proximity switch 33 is Y
It is electrically connected to the sensor controller 17 via a proximity switch relay amplifier 35 such as a confirmation LED as an example of a display device provided on the side of the AG laser processing head 5. The sensor controller 17 is connected to a robot controller 37 that controls the three-dimensional operation of the robot arm.

At the end of the contact bracket 27, a contact 39 for contacting the work W is provided so as to protrude. Therefore, when the tip of the contact 39 comes into contact with the work W and is pressed, the contact 39 can rotate together with the contact bracket 27. Since the contact 39 is attached to the tip of the contact bracket 27 in a detachable joint shape, the contact 39 can be replaced with a contact 39 having various shapes.

When the contact bracket 27 is rotated to the lower position, the contact 39 at the tip is constantly urged in a direction away from the nozzle 9 by a spring plunger 41 fixed to the fixed bracket 25.

A ball plunger 43 is provided above the fixed bracket 25 for holding the contact bracket 27 rotated upward to hold the contact bracket 27 in a semi-fixed state from both sides so as to retract the contact bracket 27. It is provided on the upper part of the fixing bracket 25.

With the above structure, when the nozzle 9 is separated from the work W, the contact bracket 27 together with the contact 39 is urged by the spring plunger 41 in a direction away from the nozzle 9, and the lower two-dot chain line in FIG. It is tilted as shown. At this time, since the position detection hole 31 of the contact bracket 27 is displaced from the detection unit 45 of the proximity switch 33, the proximity switch 33 detects the metal member of the contact bracket 27 and is turned on. Lights up.

When the nozzle 9 approaches the work W, the contact bracket 27 is pressed together with the contact 39 in a direction approaching the nozzle 9, and the position detecting hole 31 of the contact bracket 27 is moved to a detecting portion of the proximity switch 33 at a predetermined position. As a result, the proximity switch 33 is turned off, and the proximity switch relay amplifier 35 is turned off.

When the contact bracket 27 moves closer to the nozzle 9 together with the contact 39, the position detection hole 31 is again shifted from the proximity switch 33, so that the proximity switch 33 is turned on and the proximity switch relay amplifier 35 is turned on.

Therefore, by setting the position where the proximity switch 33 is turned off and the laser beam focal position LF in advance, it is detected that the distance between the nozzle 9 and the work W is located at the laser beam focal position LF in the height direction. Is done.

During the actual laser processing, the contact 39 becomes an obstacle, and in this case, the contact bracket 27 moves upward by one.
After being rotated by 80 °, it is semi-fixed in the retracted state by the ball plunger 43.

The contact 39 may be in the form of a plate. Considering the effect on the CCD camera 13 viewed concentrically, for example, as shown in FIGS. The contact 39A is provided with a hole at the tip,
The contact 39B shown in FIGS. 5 (A) and 5 (B) is not limited since the tip is formed in a semicircular shape or other various shapes are effective.

As a contact type position detector for detecting the contact bracket 27, a proximity switch 33 is used.
However, the present invention is not limited to this, and can be implemented with a high-precision limit switch, photoelectric sensor, or the like.

The mechanism of the contact 39 is as follows.
The invention is not limited to the rotation using the link mechanism, but may be implemented as, for example, an actuator that slides vertically.

From the above, the CCD as the image pickup means
The position of the YAG laser beam LB on the surface of the workpiece W (XY plane) by the camera 13 and the workpiece processing position W
The position of P is detected, and this detection signal is sent to the sensor controller 17 electrically. The image is displayed on a screen of, for example, a monitor 19 as a display device based on a detection signal from the CCD camera 13. The operator moves the robot arm while watching the displayed image, and moves the laser processing head 5 in the XY plane direction to adjust the position of the laser beam LB on the XY plane to the work processing position WP. adjust. Further, the YAG laser processing head 5 is also moved and adjusted in the height direction so as to match the position where the proximity switch relay amplifier 35 is turned off.

For example, when the position of the nozzle 9 is farther from the surface of the work W, it is located at the position of the contact 39 indicated by the two-dot chain line in FIG.
Is further approached toward the work W. The tip of the contact 39 is pushed by the work W to reach the position of the contact 39 indicated by the solid line in FIG. 1, and at this time, the proximity switch relay amplifier 35 is turned off. When the YAG laser processing head 5 comes too close to the work W, the tip of the contact 39 is pushed by the work W to the position of the contact 39 indicated by a two-dot chain line in FIG. 35 lights up.

Thus, the laser beam focal position LF is easily and accurately three-dimensionally moved and adjusted so as to match the desired position of the workpiece processing position WP, so that an appropriate teaching point is determined. Since an accurate teaching program is created based on the teaching points, highly accurate laser processing is performed in accordance with the teaching program.

In the example described above, the nozzle 9 and the work W
Switch relay amplifier 35 after detecting the height (distance) of
However, as another example, the contact type sensor 23 quantitatively detects the distance in the height direction between the laser beam focal position LF and the work processing position WP, and monitors this detection signal. 19, and the worker
The distance between the nozzle 9 and the work W can be displayed on the screen from the CCD camera 13 of the monitor 19, which is viewed when teaching the Y plane. Thereby, the operator can efficiently adjust the laser beam focal position LF to the work processing position WP.

In the above-described example, the tip of the contact 39 is configured to be located at the workpiece processing position WP (a position below the center of the nozzle). However, as another example, the tip of the contact 39 is located at the workpiece processing position. By being arranged offset from the WP, the contact 39 can always detect the workpiece processing position WP with respect to the laser beam focal position LF in the height direction without the contact 39 even during laser processing. Therefore, the position of the nozzle 9 in the height direction can be detected in real time during laser processing, and the laser processing can be controlled by feedback to the sensor controller 17.

Next, a laser displacement sensor 47 as a focal position detecting device 21 according to an embodiment of the present invention will be described with reference to the drawings.

Referring to FIG. 6, the laser displacement sensor 47
Is mounted outside the laser processing head 5, and the laser displacement sensor 47 is electrically connected to the sensor controller 49.
Is connected to, for example, a monitor 51 as an example of a display device, and measures the distance between the nozzle 9 and the work W at an angle to the YAG laser beam LB.

The laser displacement sensor 47 can detect an allowable angle range of about ± 30 °. Moreover, recently, the peak position of the received laser beam LB is output by using a CCD element (digital) as the detection element of the laser displacement sensor 47, so that errors generated due to the work W being made of a different kind of material hardly occur. Absent. Laser beam focal position LF
To preset the monitor 51 and raise / lower the laser processing head 5 so that the monitor 51 is adjusted to a position where the monitor 51 becomes 0 (zero).

Therefore, similar to the contact type sensor 23 described above, the information is displayed on the monitor 51 based on the detection signals from the laser displacement sensor 47 and the CCD camera 13.
The laser beam focal position LF can be easily and accurately adjusted to the work processing position WP. Since an appropriate teaching point is determined and an accurate teaching program is created, highly accurate laser processing is performed.

The laser displacement sensor 47 is disposed at a position offset from the workpiece processing position WP, so that feedback control can be performed in real time based on a detection signal detected by the laser displacement sensor 47.

Next, a capacitance sensor as a focus position detecting device 21 according to an embodiment of the present invention will be described with reference to the drawings.

Referring to FIG. 7, the capacitance sensor 53 is incorporated in the nozzle 9 at the tip of the YAG laser processing head 5, and the gap between the nozzle 9 and the work W is detected by the capacitance.

By using this capacitance sensor 53, it is possible to make it very compact. The capacitance sensor 53 is connected to, for example, a monitor 57 as an example of a display device from the sensor controller 55 in the same manner as the laser displacement sensor 47 described above, and is used at the time of teaching. The capacitance sensor 53 is electrically connected from the sensor controller 55 to the robot controller 59, and can perform feedback control in real time based on a detection signal detected by the capacitance sensor 53 during laser processing.

The present invention is not limited to the above-described embodiment, but can be embodied in other forms by making appropriate changes.

[0065]

As can be understood from the above embodiments of the present invention, according to the first aspect of the present invention, the position of the axis of the YAG laser beam on the surface of the work detected by the imaging means and the work processing. The position can be displayed on the screen of the display device, and the focus position detection device can display whether or not the distance between the nozzle and the work is at the laser beam focus position. By moving and adjusting, the focal position of the laser beam can be quantitatively and easily and accurately positioned at the work processing position. Since there is no individual difference between workers and no focus shift, high-precision laser processing can be stably performed. The working efficiency of laser processing can be improved.

According to the second aspect of the present invention, since the focal position detecting device is disposed at the offset position, the positional relationship between the laser beam focal point and the work processing position can be fed back in real time during laser processing. Automatic and stable high-precision laser processing can be performed.

According to the third aspect of the present invention, the same effect as in the first aspect is achieved, and the center position of the YAG laser beam and the work processing position on the surface of the work detected by the imaging means are displayed on the screen of the display device. The operator can adjust the YAG laser processing head while looking at the display to see if the distance between the nozzle and the workpiece is at the laser beam focal position. The focus position can be quantitatively, easily and accurately positioned at the work processing position. Since there is no individual difference between workers and no focus shift, high-precision laser processing can be stably performed. The working efficiency of laser processing can be improved.

According to the fourth aspect of the present invention, when the YAG laser processing head approaches the work, the contact is pressed by the work in the direction approaching the nozzle and moves. It can be detected when the tip is located at the laser beam focal position in the height direction.

According to the fifth aspect of the present invention, when the laser processing is not performed, the contact is moved to the retracted position, so that it does not interfere with other devices or the like and does not interfere.

According to the sixth aspect of the present invention, since the laser displacement sensor is arranged at the offset position, the positional relationship between the laser beam focal point and the workpiece processing position can be fed back in real time, so that the automatically stable high position can be obtained. Laser processing with high precision can be performed.

According to the invention of claim 7, the capacitance sensor can be made very compact. During laser processing, the positional relationship between the laser beam focus and the workpiece processing position can be fed back in real time, so that stable and high-precision laser processing can be automatically performed.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention and is a side view of a contact-type sensor as a focal position detecting device provided in a YAG laser processing head.

FIG. 2 is a front view of a contact sensor as a focal position detecting device in FIG.

FIG. 3 is a rear view of a contact-type sensor as the focus position detecting device in FIG. 1;

FIG. 4 shows another embodiment of the present invention, in which (A)
FIG. 2 is a side view of the contact, and FIG. 2B is a plan view of the contact.

FIG. 5 shows another embodiment of the present invention, in which (A)
FIG. 2 is a side view of the contact, and FIG. 2B is a plan view of the contact.

FIG. 6 shows another embodiment of the present invention, in which YAG
FIG. 3 is a front view of a laser displacement sensor as a focal position detection device provided in the laser processing head.

FIG. 7 shows another embodiment of the present invention, in which YAG
FIG. 3 is a front view of a capacitance sensor as a focal position detection device provided in the laser processing head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 YAG laser oscillator 5 YAG laser processing head 7 Focal lens 9 Nozzle 13 CCD camera (imaging means) 17 Sensor controller 19 Monitor (display device) 21 Focus position detecting device 23 Contact type sensor (focal position detecting device) 31 Position detecting hole 33 proximity switch (contact position detector) 35 proximity switch relay amplifier (display device) 37 robot controller 41 spring plunger 47 laser displacement sensor (focal position detection device) 49 sensor controller 51 monitor (display device) 53 capacitance sensor (focus) Position detecting device) 55 Sensor controller 57 Monitor (display device) 59 Robot controller

Claims (7)

[Claims] 1. A YAG laser beam is condensed by a condensing lens provided in a YAG laser processing head, and the YAG laser beam is condensed.
From the nozzle provided at the tip of the AG laser processing head
YA that performs laser processing by irradiating a laser beam to a work
In the G laser processing method, an imaging means provided in the YAG laser processing head detects a work position of the laser beam on the surface of the work with respect to the position of the laser beam, and a focus position detection device detects the work position of the laser beam in the height direction. The processing position is detected, and displayed by the display means based on the detection signal detected by the imaging means and the detection signal detected by the focus position detection device, and the laser beam focal position is set to the workpiece processing position based on the display. Said YA to match
A YAG laser processing method comprising: moving and adjusting a G laser processing head in three dimensions. 2. A real-time feedback control based on a detection signal detected by the focal position detecting device by arranging the focal position detecting device at a position offset with respect to the YAG laser beam. 2. The laser processing method according to 1. 3. A YAG laser beam is condensed by a converging lens provided in a YAG laser processing head, and the YAG laser beam is condensed.
From the nozzle provided at the tip of the AG laser processing head
YA that performs laser processing by irradiating a laser beam to a work
In a G laser processing apparatus, an imaging means for detecting a work processing position with respect to a position of a YAG laser beam on a surface of a work is provided in a YAG laser processing head movable in three dimensions. A focus position detecting device for detecting a work position of the laser beam with respect to the focal position of the laser beam in the direction, and detecting the workpiece with respect to the laser beam focal position based on a detection signal detected by the imaging means and a detection signal detected by the focus position detecting device. A YAG laser processing apparatus comprising display means for displaying a processing position. 4. The apparatus according to claim 1, wherein said focus position detecting device is provided on a side surface of said YAG laser processing head so as to be movable toward and away from said workpiece, and to contact said workpiece with said workpiece. A contact-type actuator which is provided with a biasing means for constantly biasing the contact, and a contact position detector for detecting that the tip of the contact is located at the laser beam focal position in the height direction. The laser processing apparatus according to claim 3. 5. The laser processing apparatus according to claim 4, wherein said contact is movable to a retracted position. 6. The laser processing apparatus according to claim 3, wherein said focus position detecting device is a laser displacement sensor arranged at a position offset from a work processing position. 7. The laser processing apparatus according to claim 3, wherein the focus position detection device is a capacitance sensor that detects a gap between a nozzle and a work.