JPH0566235B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for detecting the inclination and focus of a laser beam in a laser processing apparatus.

[Technical background of the invention and its problems] To date, more than 70% of the uses of CO ₂ laser processing equipment have been in the field of cutting, and this is also precision processing of metal plates mainly for prototyping. Therefore, the scope of use is limited. However, there is a strong desire to use this laser processing apparatus for processing three-dimensional parts, and for this purpose, it is necessary to always focus the laser beam at right angles to the processing surface and perform cutting while irradiating the laser beam. On the other hand, it is extremely difficult to control the processing of such three-dimensional parts while irradiating the laser beam at right angles, and the development of such a method is strongly desired.

Conventionally, in order to keep the laser beam always perpendicular to the machined surface of the three-dimensional workpiece and its focus in a constant positional relationship, the intensity of the laser beam was detected, and the focus of the laser beam on the workpiece was detected. A method has been proposed to do this. This conventional method of detecting the focus of laser light is shown in FIG.

This conventional method uses a semiconductor laser as a light source.
The laser beam LB from the semiconductor laser 1 is
is first corrected into a circular aberration-free light source by the intensity correction lens 3, then converted into parallel light by the coupling lens 5, and is made to enter the pinhole slit 7. The pinhole slit 7 is provided with four pinholes symmetrically in the XY2 direction, and through the pinholes 9a, b, c, and d, four beams LF that are symmetrical with the XY axes are obtained, and these beams are sent to the first beam beam. 1/4 wavelength plate 1 through the printer 11
3, converted into circularly polarized light, and irradiated onto the three-dimensional workpiece W.

The laser beam LF reflected by the three-dimensional workpiece W is returned to linearly polarized light through the quarter-wave plate 13, and is reflected in the right angle direction by the first beam splitter 11 to be used as back light for the detection system. Filter 15
guided by. Then, the second beam splitter 17 separates the reflected light and the transmitted light at right angles.
The four-focal point signal detection sensor 19 is configured to detect the intensity of the reflected light from the second beam splitter 17.

However, in this conventional method of detecting the focus of laser light, the deviation from the focus is detected based on the intensity of the received light, so the amount of reflected light may change due to changes in the surface condition of the workpiece W. If the intensity of the received light changes, the overall intensity of the received light also changes, making it impossible to detect a shift in the focal position.

Furthermore, there is no known method for continuously optically monitoring the inclination of a laser beam in a laser processing device.

[Object of the Invention] The present invention has been made in view of such conventional problems, and provides a laser processing device that can continuously monitor the inclination and focus of a laser beam by an optical method. The present invention provides a method for detecting the inclination and focus of a laser beam.

[Summary of the Invention] This invention guides the reflected light of a laser beam irradiated onto a workpiece to a plurality of divided photo sensors via a critical angle prism or a cylindrical lens, and detects the workpiece based on the output signal of each photo sensor. The first invention is a method for detecting a focal position, in which the reflected light of a laser beam irradiated onto a workpiece is divided into a plurality of beams by a slit, the intensity of each beam is individually detected, and the detected value is obtained. In comparison, the second invention is a method of detecting the inclination of the laser beam with respect to the surface of the workpiece, and continuously monitors the direction of incidence of the laser beam on the workpiece and the focal position.

[Embodiments of the Invention] FIG. 1 shows the configuration of an apparatus used in an embodiment of the method for detecting a focal point position of the present invention, in which a semiconductor laser 21 for a tracer separate from a laser cutting head is used as a light source; An intensity correction lens 23 for turning the laser beam LB from this semiconductor laser into an aberration-free light source, a collimator lens 25 for converting the laser beam LB into a parallel beam, and a collimator lens 25 installed at a position to condense the light onto the workpiece W. objective lens 2
7. A polarizing beam splitter 29 that reflects the reflected light from the workpiece W in the direction of the detection system and separates it from the laser beam LB of the incident system, and a quarter-wave plate 31 that converts linearly polarized light into circularly polarized light arranged in a straight line on the axis.

The objective lens 27 consists of a condensing lens part 27a at the center and a transparent part 27b at the outer periphery, and separates the laser beam LB into a convergent beam LC and a parallel beam _LL .

A back light filter 33 is placed on the reflection optical axis horizontal to the polarizing beam splitter 29, and a beam splitter 35 separates the incident reflected light into 50% of the reflected light and 50% of the transmitted light. ,
Furthermore, an aperture 37 for narrowing down the reflected light, a collimator lens 39, and a critical angle prism 41 are arranged on the reflected optical axis of the beam splitter 35. A four-focus signal detection sensor 43 is arranged on the critical angle prism 41 so as to be centered on the output optical axis of the critical angle prism 41.

This four-focal point signal detection sensor 43 consists of four divided photo sensors 43a, b, c, and d, and the photo sensors 43a, b, and photo sensors 43c, d are connected to amplifiers 45a and 45b, respectively, and their combined inputs are sent to a comparator 47. It is connected to the. Therefore, the focal position shift is detected in the form (a+b)-(c+d).

In FIG. 1, the transmitted light of the beam splitter 35 is guided to a pinhole slit 49 for splitting into four beams.
The light beams pass through pinholes 49a, b, c, and d on the top of the light beam 9, are divided into four beams 51a, b, c, and d, and are input to the four normal detection sensors 53, where the intensities of each beam are compared. ing. The pinhole slit 49 and the four normal detection sensors 53 constitute a device used in an embodiment of a method for detecting the inclination of a laser beam according to the second invention, which will be described later.

To further explain the method of detecting the focus of laser light using the device having the above configuration, first, the laser light LB from the semiconductor laser 21 is transmitted to the intensity correction lens 2.
3, the light is corrected as aberration-free light, and the collimator lens 25 converts the light into parallel light, which is then incident on the objective lens 27.

The objective lens 27 uses a central condensing lens part 27a to condense a part of the central part of the laser beam LB onto the workpiece W as convergent light L _C , and at the same time, the peripheral transparent part 27
At b, most of the laser beam LB is guided as a parallel beam L _L to the polarizing beam splitter 29 and the quarter-wave plate 31,
Therefore, it is converted into circularly polarized light and irradiated onto the workpiece W.

The reflected light from the workpiece W is returned to linearly polarized light by the 1/4 wavelength plate 31, becomes linearly polarized light rotated by 90 degrees, is totally reflected by the polarizing beam splitter 29, and is reflected by the backlight filter 33. It is reflected in the direction. The back light filter 33 passes only reflected light, excluding natural light, and the beam splitter 35
lead to.

At the beam splitter 35, approximately half of the reflected light is reflected again toward the aperture 37, and only the central portion of the light is passed from the aperture 37 to the collimator lens 39, where it is returned to the critical angle prism 41 as parallel light. lead

By allowing only the central part of the reflected light to pass through the aperture 37, it is possible to select only the light beam focused on the workpiece W by the objective lens 27 and guide it to the critical angle prism 41. It can be done.

The function of the critical angle prism 41 will be explained based on FIG. 2. When the workpiece W is located at the focal position (B) of the objective lens 27, the reflected light that has passed through the objective lens 27 becomes a parallel beam of light and enters the critical angle prism 41. If the angle between the prism 41 and the reflecting surface is set to be a critical angle, the entire incident luminous flux will be reflected. On the other hand, when the workpiece W is on the objective lens 27 side (A), the reflected light passing through the objective lens 27 becomes diverging light, and conversely, when the workpiece W is at a position far from the focal point (c), it is convergent. Become light.

Therefore, when the focal point is at the focal position (B), the light emitted from the critical angle prism 41 is transmitted to each photo sensor 43.
The light is equally incident on a, b, c, and d to give equal electrical outputs, and the comparator 47 gives zero output.

However, when the workpiece W is on the objective lens 27 side, the reflected light from the workpiece becomes stronger on the photo sensor 43d, c side, and conversely
3a and 3b become weaker, and the negative side of the output of the comparator 47 becomes stronger, resulting in a negative output.

Conversely, when the workpiece W is far from the focal point, when the reflected light passing through the objective lens 27 is reflected by the critical angle prism 41, the photo sensor 4
The sides 3a and 3b receive strong light, and the output of the comparator 47 becomes positive, allowing us to know that the workpiece W is out of focus. In this way, the positional relationship between the workpiece W and the objective lens 27 can be known from the positive, 0, and negative values of the output of the comparator 47.

In this way, it is possible to detect a shift in the focal position of the objective lens 27 with respect to the workpiece W, and to maintain an appropriate focal position even for a three-dimensional workpiece by controlling according to the output of the comparator 47. It becomes possible.

FIG. 3 shows a diagram of a device used in another embodiment of this method of detecting the focal point, and shows the incident and reflection paths of the laser light from the semiconductor laser 21 to the beam splitter 35 in the device shown in FIG. have the same configuration, and show the configuration of a processing system for reflected light to the beam splitter 35 as a characteristic part. An aperture 37 for passing only the central part of the reflected light to the beam splitter 35, a cylindrical lens 55 for converging the light from the aperture 37, and a four-part photodiode 57 for receiving the transmitted light from the cylindrical lens 55. It also includes amplifiers 59a, b and a comparator 61 for arithmetic processing of the light reception signal of the photodiode 57.

The operation of this second embodiment will be explained next. As shown in FIG. 4, the image formation position of the surface intersection of the workpiece W imaged by the objective lens 27 is assumed to be Q. When a cylindrical lens 55 is placed behind the objective lens 27 to provide astigmatism, the image formation position by the cylindrical lens 55 is assumed to be P. Between PQ, the cross section of the ray bundle changes from an ellipse with a vertical major axis to an ellipse with a horizontal major axis as it goes from point P to point Q. At point S during this period, the cross-sectional shape becomes a circle. Therefore, the cross-sectional shape of the light beam at the point S changes depending on the position of the surface of the workpiece W, as shown in the figure. In other words, when the workpiece W is at the focal point of the objective lens, a circular beam of light is given at point S, but when it is closer to the objective lens 27 than the focal point (A), it becomes a vertically elongated ellipse; If it is located outside position B (C), it has a horizontally elongated cross-sectional shape.

Therefore, the light is photoelectrically converted by the four-division photodiode 57, and the amplifier 59a,
b. By calculating with the comparator 61, the suitability of the position of the workpiece W with respect to the objective lens 27 can be constantly monitored.

Returning to FIG. 1, an embodiment of the second invention will be specifically described based on the apparatus shown in FIG. The laser beam LB from the semiconductor laser 21 is transmitted through the intensity correction lens 2.
3. Passing through the collimator lens 25 and the outer circumferential transparent portion 27b of the objective lens 27, the parallel light beams L _L enter the quarter-wave plate 31, where they are converted into circularly polarized light and irradiated onto the surface of the workpiece W. The reflected light from the workpiece is returned to linearly polarized light by the 1/4 wavelength plate 31,
It is reflected by the polarizing beam splitter 29, passes through the filter 33, passes through the beam splitter 35, and is guided to the pinhole slit 49. Each pinhole 49a, b of this pinhole slit 49,
A light beam 51 divided into four parts passes through c and d and comes out.
a, b, c, d are each four normal detection sensors 53
The light enters each light intensity sensor 53a, b, c, d and is output as an electrical signal proportional to the light intensity. The output from each light intensity sensor 53a, b, c, d is sent to an X-axis comparator 63a and a Y-axis comparator 63.
b, and the respective outputs positive, 0,
Inclinations in the X-axis and Y-axis directions are detected using negative signals.

This is because the parallel rays L _L incident on the workpiece W
If it is incident in the normal direction to the surface of the workpiece W, the reflected light intensity can be uniform around the optical axis, but if it is inclined to the normal line, the reflected light intensity is uniform. By detecting this imbalance in light intensity, it is possible to correct the incident axis of the laser beam LB so that it coincides with the normal direction of the surface of the workpiece W.

In this way, the parallel laser beam is incident on the workpiece, the reflected light is divided into multiple beams, and the relative inclination of the laser beam with respect to the workpiece is determined by comparing the light intensity of each beam. can be detected.

In addition, in the above embodiment, the intensity correction lens 2
3 is used because the semiconductor laser 21 usually has astigmatism, and this is to correct it to a light beam with a circular cross section. Therefore, if a sufficient aberration-free light source can be used, the intensity correction lens 23
There is no need to use Furthermore, if the reflected light from the surface of the workpiece is reflected in the direction of the semiconductor laser 21, the oscillation of the semiconductor laser 21 itself becomes unstable. If the isolator is configured using the /4 wavelength plate 31, it is possible to prevent the reflected light from the workpiece W from being reflected in the direction of the semiconductor laser 21, and stable laser oscillation can be obtained. It is possible.

[Effects of the Invention] This invention guides the reflected light of the laser beam irradiated onto the workpiece to a plurality of divided photo sensors via a critical angle prism or a cylindrical lens, and determines the direction of the workpiece based on the output signal of each photo sensor. This is a method of detecting the focal position. Therefore, unlike the conventional method that compares the intensity of light divided into multiple parts, it is possible to detect the relative position of the laser processing device to the workpiece based on the position of the light. Even if the intensity of reflected light changes depending on the surface condition, the focal position can be detected accurately.

Further, in the second invention, the reflected light of the laser beam irradiated onto the workpiece is divided into a plurality of beams by a slit, the intensity of each beam is individually detected, and the detected values are compared, This method detects the inclination of a laser beam with respect to the surface of a workpiece. Therefore, it is possible to optically detect the inclination of the incident laser beam with respect to the surface of the workpiece using laser light, and it can be used to monitor the incidence of the laser beam from the normal direction on a three-dimensional workpiece. can.

[Brief explanation of the drawing]

FIG. 1 is an optical diagram showing an example of a device for detecting the inclination and focus of a laser beam used in the embodiments of the first and second inventions, and FIG. 2 is an optical diagram showing the principle of an embodiment of the first invention. FIG. 3 is an optical diagram of the laser beam focal position detection unit of the second embodiment of the first invention, FIG. 4 is an optical diagram showing the principle of the second embodiment, and FIG. 5 is a conventional laser beam focal point. FIG. 2 is an optical diagram of a device for detecting . 21...Semiconductor laser, 23...Intensity correction lens, 25...Collimator lens, 27...Objective lens, 29...Polarizing beam splitter, 31...
...1/4 wavelength plate, 33...Backlight filter, 3
5...beam splitter, 37...aperture,
39...Collimator lens, 41...Critical angle prism, 43...4 focal point signal detection sensor, 43a,
b, c, d...Photo sensor, 45a, b...Amplifier, 47...Comparator, 49...Pinhole slit, 53...4 normal detection sensor, 55...
... Cylindrical lens, 57 ... Four-division photodiode, 59a, b ... Amplifier, 61 ... Comparator, 63a, b ... Comparator.

Claims (1)

[Claims] 1. The reflected light of the laser beam irradiated onto the workpiece is guided to a plurality of divided photo sensors via a critical angle prism or a cylindrical lens, and the focal position with respect to the workpiece is determined based on the output signal of each photo sensor. How to detect. 2 The reflected light of the laser beam irradiated onto the workpiece is divided into multiple beams by a slit, the intensity of each beam is individually detected and the detected values are compared, and the laser beam is applied to the surface of the workpiece. How to detect the slope of.