JPH02290681A - Focusing method for laser beam machine - Google Patents

Abstract

PURPOSE:To relatively accurately execute focusing of laser beam by changing distance between a condenser lens and a high reflection metal plate while scanning along a slit having the same width as width of laser beam waist arranged to the high reflection metal plate and deciding the position where the intensity of reflecting returned beam is minimum to the focus. CONSTITUTION:The laser beam is made to scan onto the high reflection metal plate 11 in the arrow mark direction shown as the figure (a) to measure 3 the reflecting beam. Then, the laser beam comes to the above slit position and at the time when the intensity of the reflecting returned beam is rapidly reduced shown as the figure (b), the scanning direction is changed 90 deg. angle and the beam is made to scan along the slit shown as the figure (c). Together with this, the distance L between the condenser lens 7 and the metal plate 11 is continuously changed, and at the time of becoming L = focus length L of the lens 7, i.e., the position where the intensity of the reflecting returned beam is minimum is decided to the focus. Therefore, the focusing having much more accuracy than that of the ordinary method without any consumption of material for testing can be executed.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a focusing method for a laser processing machine.

(Prior Art) When cutting a material with laser light, the full width of the cut between the incident surface and the exit surface varies greatly depending on the focal position of the laser light. Generally, when the distance between the laser condensing lens and the surface of the material matches the focal length of the condensing lens, the most parallel cutting groove can be obtained.

Conventionally, in order to determine the focal position of a laser beam, for example, a slit was cut by irradiating a plywood board with a laser beam while changing the focus, and the position where the slit width was the smallest was determined as the focal position. Also, as shown in Figure 3, on an acrylic resin plate,
A hole is made by irradiating a laser beam, and the cross-sectional shape of the hole is, for example,
In the case of figure (a), the focal point is below the surface F, in the case of figure (b) it is above the surface, and in the case of figure (C) it is just above the surface F. I had determined that there was.

(Problem to be Solved by the Invention) As described in +ilff, the method of cutting slits in a plywood board to determine the focal position of the laser beam requires cutting slits many times, and each time the slits are cut, the cost of cutting the plywood board is increased. Another problem was that it was not clear which side of the thickness of the plywood the focal point was located on. In addition, the method of making holes in the acrylic resin plate requires
Generally, it is necessary to make many holes, which causes wear and tear on the acrylic plate and is time-consuming.

The present invention was devised in view of these problems, and an object of the present invention is to provide a method for focusing laser light that is relatively accurate and does not consume test material.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above-mentioned object, the focusing method of the laser processing machine of the present invention calculates the diameter of the beam waist of the laser beam from a calculation formula, and A slit with the same width as the above-mentioned diameter is provided in the reflective metal plate, this highly reflective metal plate is placed in a laser processing machine, laser light is scanned from a direction perpendicular to the slit, and the reflected light is measured. From the slit position where the intensity suddenly decreases, the scanning direction is changed to the direction along the slit and the reflected light is measured, and the distance between the condenser lens and the highly reflective metal plate is changed to minimize the intensity of the reflected light. seek a position,
This position is taken as the focal position.

Here, the formula for calculating the diameter of the beam waist of laser light is T
In the case of EMoo mode, it is as follows. However, the spherical aberration of the condenser lens is ignored.

d・-4λf/(πD) In this formula, λ is the wavelength of the laser beam, [ is the focal length of the condensing lens, and D is the diameter of the laser beam (6-2
beam diameter).

(Function) When the laser beam is focused by a condensing lens, the diameter of the laser beam becomes the narrowest beam at the focal point, that is, the beam waist.
The area before and after the focal point is more crowded than the beam waist. The width of the slit provided in the highly reflective metal plate is the same as the diameter of the beam waist, so while scanning the laser beam along this slit, the distance 11iL between the condenser lens and the highly reflective metal plate is changed. When the reflected return light is measured, when L matches the focal length of the condenser lens, most of the laser beam enters the slit, and the intensity of the reflected return light becomes minimum.In other words, this position can be found. For example, the focal position of the condenser lens can be determined.

(Example) Next, a case of focusing a carbon dioxide laser processing machine embodying the present invention will be described. As shown in FIG. 2, this carbon dioxide laser processing machine is comprised of a carbon dioxide laser oscillator 1, a reflected return light detector 3, a pendor mirror 5, a condenser lens 7, a processing table 9, and the like. The highly reflective metal plate 11 placed on the processing table 9 is made of a thin aluminum or copper plate, and has a slit with a groove width d as shown in FIG. 1(a). This groove width d is J3 in the above formula, and f=2
．． If it is 5 inches, λ-10.6 μs, and D=10 am, then d=0.086+no+.

This highly reflective metal plate 11 is scanned with a laser beam in the direction of the arrow as shown in FIG. 1(a), and the reflected light is measured by the reflected return light detector 3. When the laser beam reaches the slit, the reflected return light suddenly decreases as shown in the figure <b), indicating that the laser head has come directly above the slit. Although the laser light of the carbon dioxide laser is far infrared rays and cannot be seen with the naked eye, it is possible to confirm that the laser head is positioned above the slit using this method.

When the laser head is above the slit, the scanning direction is
0 degrees and move it along the slit as shown in Figure 1 (C).
In the direction of the arrow in the figure), the distance L between the condenser lens 7 and the eight reflective metal plates 11 is continuously changed. Figure 1 (
d), if L<f, the intensity of the reflected return light increases when the condensing lens 7 is brought closer to the highly reflective metal plate 11, and gradually decreases when it is moved away from it, and when L=r becomes the minimum.

Moreover, in the case of L>f, if the condensing lens 7 is moved away,
The intensity of the reflected return light increases and gradually decreases as you approach L.
It becomes minimum when = f. Therefore, in any case, if the condenser lens 7 is moved in the direction where the intensity of the reflected return light decreases and the position where the intensity of the reflected return light is the minimum is found, then
The focus of the condensing lens 7 will be on the surface of the highly reflective metal plate 11. At this time, by measuring the distance between the tip of the laser head and the surface of the highly reflective metal plate, the focal position can be determined based on the tip position of the laser head.

The reflected return light detector 3 rotates a thin wire with a cross section perpendicular to the beam, receives the reflected light with an infrared sensor, and measures its intensity. Anything that can be used to measure is fine.

[Effect of the invention 1] As understood from the above explanation, this application has the structure described in the claims, so it is much more accurate than the conventional method, and it can be used to decolorize materials for testing, etc. It is possible to provide a method for focusing a laser beam without using a laser beam.

[Brief explanation of the drawing]

Figure 1 (a) is a plan view of a highly reflective metal plate with slits, and Figure 1 (b) shows the scanning distance and reflected return light when the highly reflective metal plate is scanned with a laser beam from a direction perpendicular to the slits. (C) is an explanatory diagram of the scanning direction of the laser beam along the slit of the highly reflective metal plate (arrow), and (d) is an explanatory diagram of the direction of scanning of the laser beam as shown in (C). FIG. 3 is a diagram showing the relationship between the distance between the condenser lens and the highly reflective metal plate and the intensity of reflected return light. FIG. 2 is an explanatory diagram of a carbon dioxide laser processing machine embodying the present invention. FIG. 3 is an explanatory diagram of a conventional focusing method using an acrylic resin plate. Explanation of the symbols representing the main parts of the drawing 1... Carbon dioxide laser oscillator 3... Reflected return light detector 7... Condensing lens 11... Highly reflective metal plate agent Patent attorney Hidekazu Miyoshi

Claims (1)

[Claims] Calculate the diameter of the beam waist of the laser beam in advance, make a slit with the same width as the diameter in a highly reflective metal plate, attach this highly reflective metal plate to a laser processing machine, and insert the laser beam from a direction perpendicular to the slit. From the slit position where the intensity suddenly decreases, change the scanning direction to the direction along the slit, measure the reflected light, and adjust the distance between the condenser lens and the highly reflective metal plate. A method of focusing a laser processing machine by changing the position to find the position where the intensity of the reflected light is minimum and using this position as the focal position.