JP7617426B2 - Laser Processing Equipment - Google Patents

Description

The present invention relates to a laser processing device.

A so-called magnetic domain control process has been put into practical use in which an electromagnetic steel sheet, a type of steel sheet, is passed at high speed along a conveyor line and a high-power laser beam is irradiated onto the surface of the electromagnetic steel sheet and scanned in a straight line in a direction nearly perpendicular to the sheet passing direction, forming linear grooves and distortions at regular intervals and reducing the iron loss of the electromagnetic steel sheet.
Magnetic steel sheets that have undergone the magnetic domain control process are used as materials for transformer cores, etc., and contribute to improving power loss. In particular, magnetic domain control materials in which linear grooves have been formed by a laser have the characteristic that the magnetic domain control effect is maintained even after heat treatment in the wound core manufacturing process.
However, since the electromagnetic steel sheet is bent during the manufacturing process of the wound iron core, if the direction of the bend line during bending coincides with the direction of the linear groove, stress will be concentrated in the linear groove, and the electromagnetic steel sheet may break.
Since the direction of the bend lines during bending of the electromagnetic steel sheet, i.e., the bending direction, is generally the sheet width direction of the electromagnetic steel sheet, it is desirable to adjust the direction of the linear grooves so that they are not parallel to the sheet width direction. For example, it is considered desirable to tilt the direction of the linear grooves by about 10° from the sheet width direction.

For example, the following Patent Documents 1, 3, and 4 disclose a technique in which a steel sheet is transported along the peripheral surface of a steel sheet support roll and a laser beam is irradiated, with the laser beam being irradiated in a range separated from this reference point by 3 to 7° in the sheet passing direction along the outer peripheral surface of the steel sheet support roll, using the laser beam irradiation position at the apex of the steel sheet support roll in contact with the steel sheet as a reference point. Furthermore, the techniques described in these Patent Documents employ a method in which the scanning direction of the laser beam is tilted by about 4° from the sheet width direction at a position moved 3 to 7° in the rotational direction from the apex of the steel sheet support roll.
Furthermore, Patent Document 2 discloses a technology in which a steel plate is transported along the peripheral surface of a steel plate support roll, a laser beam is irradiated along the width direction of the steel plate, and the inclination of the steel plate support roll is changed in accordance with a change in the focal length of the laser beam along the width direction of the steel plate.

Patent No. 6826603 Patent No. 6826604 Patent No. 6826605 Patent No. 6826606

When the steel plate support rolls are tilted as described in Patent Document 2, the balance of tension in the plate width direction is lost, making the steel plate more likely to meander and, in the worst case, causing the steel plate to break. In addition, the steel plate support rolls are heavy, and there is a problem that a large, high-precision actuator is required to precisely control the tilt of the steel plate support rolls.

However, in order to perform high-speed groove processing on the surface of a steel plate using a laser beam, a high laser power density is required, so that a high-power laser beam of 1 kW or more must be focused to a minute beam spot diameter of 100 mμ or less and irradiated and scanned on the surface of the steel plate. Generally, an fθ lens or a parabolic mirror is used as a focusing element for a laser, but when a high-power laser is applied to a lens, which is a transmitting element, there is a problem that a slight heat generation due to absorption or dirt in the lens causes a change in refractive index or thermal expansion, resulting in deterioration of the focusing performance. It is said that the deterioration of the focusing performance of the lens is due to the thermal lens effect, but because of the occurrence of such a thermal lens effect, there is a problem that it is practically difficult to use a high-power laser for the above-mentioned purpose.
On the other hand, the focusing mirror can be easily cooled by a metal element, and the deterioration of the focusing ability is small, which is convenient for the above-mentioned purpose. In addition, the requirement of focusing to a minute beam spot diameter requires the use of a focusing element with a short focal length, but the short focal depth may result in the allowable fluctuation width against vibrations, etc., being ±0.5 mm or less in order to perform stable groove processing.

In the steel sheet manufacturing process, the steel sheet is passed at high speed over multiple rotating support rolls. During this process, the steel sheet vibrates between the support rolls due to factors such as tension fluctuations and strength changes in the steel sheet. If the vibration amplitude of the steel sheet becomes larger than the focal depth of the laser beam, the laser beam becomes out of focus, which causes a problem of degraded workability.
Methods for suppressing vibration of steel sheets include, for example, adjusting the parallelism, interval, inter-roll tension, etc. of support rolls, and it is possible to suppress vibration to a certain extent by using such methods. However, it is difficult to adjust all of these sufficiently, and there is a limit to the suppression of vibration.

Another method for suppressing vibration is to force the steel sheet against the support rolls (i.e., by applying tension to the steel sheet, the steel sheet is pressed against the support rolls so that it is in close contact with them and passes along the apex of the support rolls), and to irradiate the laser beam at the position where the steel sheet passes over the support rolls. In this method, the steel sheet follows the curved surface of the apex of the roll surface, so there is almost no vibration of the steel sheet. However, since the direction of the rotation axis of the support rolls coincides with the width direction of the steel sheet, as described above, it is necessary to set a certain angle between the scanning direction of the laser beam and the width direction of the sheet. In this case, due to the influence of the curved surface of the support rolls, the distance from the focusing element to the steel sheet changes from the center position on the scanning path to the end position on the scanning path, and even if the laser beam is focused at the center position of the laser beam scanning line, there is a problem that the laser beam becomes significantly out of focus at the end side of the laser beam scanning line, and the workability deteriorates.

The present invention has been made in consideration of the above-mentioned problems, and aims to provide a laser processing device that can form linear grooves or linear distortions with stable widths and depths in a steel plate while minimizing defocusing over the entire scanning area of the laser beam, using a simple device configuration, when a laser beam is irradiated onto a steel plate that is being passed through while being forced by support rolls.

In order to solve the above problem, according to one aspect of the present invention, a laser processing device is provided that scans the surface of a steel sheet that is passed through a support roll with a laser beam having a circular or elliptical beam spot diameter to form a linear groove or linear distortion in the steel sheet, the device comprising: a laser beam emitting unit that emits a laser beam; a scanning mirror that reflects the laser beam; a short-axis focusing mirror that reflects the laser beam reflected by the scanning mirror and focuses the laser beam in the direction of a first axis corresponding to the short axis of the beam spot diameter; and a focus position adjustment mirror that reflects the laser beam reflected by the short-axis focusing mirror and irradiates the surface of the steel sheet. The scanning mirror changes the direction in which the laser beam is reflected, and changes the position at which the laser beam is irradiated on the surface of the steel plate, thereby scanning the surface of the steel plate with the laser beam, and the focus position adjustment mirror has a curvature that focuses the laser beam at a point on the surface of the steel plate where the focusing focal length, which is the distance obtained by subtracting the distance between the point at which the laser beam is reflected by the short axis focusing mirror and the point at which the laser beam is reflected by the focus position adjustment mirror, from the focal length of the short axis focusing mirror, is equal to the distance from the point at which the laser beam is reflected by the focus position adjustment mirror.

The laser processing device may also have a long axis focusing mirror (Mc) that reflects the laser beam emitted from the laser beam emitting unit and focuses the laser beam in the direction of a second axis corresponding to the long axis of the beam spot, and the scanning mirror (Mp) may be configured to reflect the laser beam reflected by the long axis focusing mirror (Mc).

In addition, in the laser processing apparatus, the curvature α2 of the focus position adjustment mirror (Ms), which is defined by the angle of incidence of the laser beam when seen from the direction of the first axis onto the focus position adjustment mirror (Ms), can be configured as shown in the following equations (1) to (3).
In addition, (S ₂ , Z ₂ ) are the coordinates on a plane (SZ plane) perpendicular to the first axis of the point (A2′) at which the laser beam is reflected by the focal position adjustment mirror (Ms),
(S ₄ , Z ₄ ) are coordinates on a plane perpendicular to the first axis of a point on the surface of the steel plate where the focusing focal length (G3′) is equal to the distance from the point (A2′) where the laser beam is reflected by the focus position adjustment mirror (Ms);
α1 is the angle of incidence of the laser beam on the focal position adjustment mirror (Ms) in a plane perpendicular to the first axis,
β is the angle of incidence of the laser beam on the focal position adjustment mirror (Ms) in a plane perpendicular to the second axis,
θso is the reflection angle when the laser beam is reflected by a plane mirror (M0) having no curvature at the position of the focus position adjustment mirror (Ms) in a plane perpendicular to the first axis, and θ's is the reflection angle when the laser beam is reflected by the focus position adjustment mirror (Ms) in a plane perpendicular to the first axis.

In the laser processing device, it is preferable that the reflecting surface of the short axis focusing mirror (ML) is a linear paraboloid.
In the laser processing apparatus, the scanning mirror (Mp) is preferably a rotating polygon mirror or a galvanometer mirror.

According to the present invention, a laser beam is focused and scanned on a steel sheet that is being passed through a support roll, forming linear grooves or linear distortions, so that linear grooves or linear distortions can be formed stably.

1 is a schematic diagram of a processing system including a laser processing apparatus according to an embodiment of the present invention. FIG. 2 shows the relationship between the support roll and the laser beam irradiation position provided in the processing system shown in FIG. 1, where FIG. 2(A) is a plan view showing the relationship between the top surface of the support roll and the irradiation position, FIG. 2(B) is a side view showing the relationship between the side surface of the support roll and the irradiation position, and FIG. 2(C) is an enlarged view of the laser beam irradiation area near the apex of the support roll. FIG. 3 shows the relationship between the steel plate surface position and the laser beam irradiation position in the processing system of the reference example, where FIG. 3(A) is a side view showing the positional relationship from the laser beam irradiation part for the steel plate near the apex of the support roll to the polygon mirror, and FIG. 3(B) is an enlarged view of the laser beam irradiation part for the steel plate near the apex of the support roll. FIG. 4 shows the relationship between the steel plate surface position and the laser beam irradiation position in the processing system according to the first embodiment of the present invention, where FIG. 4(A) is a side view showing the positional relationship from the laser beam irradiation unit for the steel plate near the apex of the support roll to the polygon mirror, and FIG. 4(B) is an enlarged view of the laser beam irradiation unit for the steel plate near the apex of the support roll. 1 is a graph showing the results of determining the coordinates of the intersection between the focal position of the laser beam and the steel plate surface on a coordinate plane including the scanning direction of the laser beam when the reflection angle (θs) of the laser beam irradiated by the polygon mirror of the first embodiment is 10°. FIG. 6A shows the reflection angle at the second mirror, and is an explanatory diagram showing a case where the virtual reflection angle _θs0 at the special reflection curved surface of the second mirror is changed to an effective reflection angle θs'. FIG. 6B is an explanatory diagram showing a case where the virtual reflection angle _θs0 is changed to an effective reflection angle θs' in the optical path of the laser beam from the second mirror to the steel sheet surface on the support roll. This is a graph showing the relationship between the inclination angle _α1 of the normal to the special reflective surface of the second mirror with respect to the Z axis and the position along the scanning direction when the virtual reflection angle _θs0 at the special reflective surface of the second mirror is changed from 0 to 20° under the conditions shown in Table 1. 10 is an explanatory diagram showing the reflection angle of a laser beam reflected from a second mirror when a laser beam is incident from a first mirror to the second mirror at an incident angle β. FIG. FIG. 1 is a perspective view showing an example of a galvanometer mirror that can be used as a scanning mirror.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
In the drawings used in the following description, characteristic parts may be enlarged or otherwise emphasized for ease of understanding.

First, an overview of the grain-oriented electrical steel sheet, which is the object to be processed in this embodiment, will be described.
<Outline of Grain-Oriented Electrical Steel Sheets>
A typical grain-oriented electrical steel sheet is an electrical steel sheet in which the magnetization easy axis (body-centered cubic <100> direction) of the crystal grains of the steel sheet is approximately aligned in the rolling direction of the steel sheet. Grain-oriented electrical steel sheets have a structure in which multiple magnetic domains, each with a magnetic pole facing the rolling direction, are arranged with a magnetic domain wall between them. Since such grain-oriented electrical steel sheets are easily magnetized in the rolling direction, they are suitable as materials for the iron core of transformers in which the magnetic lines of force flow in an approximately constant direction.

Transformers are generally classified into stacked transformers and wound transformers. Grain-oriented electrical steel sheets are preferably used as materials for the iron core of wound transformers, which are manufactured by winding steel sheets in multiple layers and then forming them into the shape of an iron core (for example, a rectangular column shape having a hollow portion).
The grain-oriented electrical steel sheet has, for example, a steel sheet body (base steel), glass coatings formed on both sides of the steel sheet body, and an insulating coating formed on the glass coating. The steel sheet body is made of, for example, an iron alloy containing Si.

In order to reduce iron loss (i.e., for magnetic domain control), a laser beam is irradiated onto the surface of the steel sheet and scanned in a direction intersecting the rolling direction of the steel sheet (i.e., the conveying direction during production, the sheet length direction of the steel sheet), thereby forming linear grooves or linear distortions extending in a direction intersecting the rolling direction of the steel sheet. A plurality of these grooves or distortions are formed at predetermined intervals in the rolling direction on the surface of the grain-oriented electrical steel sheet.
In this embodiment, a laser beam is linearly scanned and irradiated onto the surface of the grain-oriented electrical steel sheet to form linear grooves or linear distortion portions at regular intervals in order to control the magnetic domains of the grain-oriented electrical steel sheet. In the following description, the grain-oriented electrical steel sheet may be referred to simply as steel sheet.

FIG. 1 is a schematic diagram of a processing system including a laser processing device 1 according to an embodiment of the present invention.
In this embodiment, the laser processing apparatus 1 has a laser beam emitting section LL, a long axis collecting mirror Mc, a plane mirror MF, a scanning mirror Mp, a short axis collecting mirror ML, and a focal position adjustment mirror Ms.
The laser processing apparatus 1 is an apparatus that forms linear grooves or linear distortions in the steel sheet ES by scanning the surface of the steel sheet ES, which is forced against a support roll and passed through, with a laser beam LB having a circular or elliptical beam spot diameter.
That is, the laser processing apparatus 1 can, for example, form linear grooves on the surface of the electromagnetic steel sheet or form linear distorted portions on the surface of the electromagnetic steel sheet by irradiating the surface of the electromagnetic steel sheet with a laser beam LB and scanning the laser beam LB in a direction intersecting the rolling direction of the electromagnetic steel sheet in order to control the magnetic domains of the electromagnetic steel sheet.
The laser beam emitting unit LL has a known laser light source LM, a transmission fiber 4, and an emitter 7, and the laser light source LM oscillates and outputs a laser beam LB, which is transmitted via the transmission fiber 4 made of an optical fiber or the like and irradiated into the atmosphere from the emitter 7. The laser beam LB emitted from the laser emitting unit LL is irradiated toward a long axis focusing mirror Mc, which will be described later.

The laser light source LM is preferably a fiber laser or disk laser with excellent micro-focusing characteristics, from the viewpoint of being able to form narrow grooves, but various known laser light sources can be selected instead of a fiber laser or disk laser, for example, a continuous wave laser or a pulsed laser can be used. The wavelength of a fiber laser or disk laser is in the near ultraviolet to near infrared range (e.g., 1 μm band), and the laser beam LB can be transmitted with high efficiency by optical fiber. Therefore, by transmitting the laser beam using a transmission fiber 4 made of optical fiber, the laser processing device 1 can be realized with a relatively compact configuration.

The laser beam LB has high energy, and when it is irradiated to a steel sheet, it can scatter the steel sheet to form grooves or apply thermal distortion to the steel sheet to form distorted parts. The laser beam LB already has a circular or elliptical beam spot when it is emitted from the emitter 7 into the atmosphere, and is reflected by various mirrors (long axis focusing mirror Mc, flat mirror MF, scanning mirror Mp, short axis focusing mirror ML, focal position adjustment mirror Ms, etc.) described later and then irradiated to the steel sheet ES. Even just before hitting the steel sheet ES, the laser beam LB has a circular or elliptical beam spot (although the size and shape are often different from when it was emitted from the emitter 7).
Therefore, when the shape of the beam spot immediately before it hits the steel sheet ES is elliptical, the directions of the minor and major axes that pass through the center and intersect at right angles can be specified. Then, the laser processing device 1 in this embodiment scans the laser beam LB in the direction of the major axis of the shape of the beam spot immediately before it hits the steel sheet ES.

On the other hand, if the shape of the beam spot immediately before it hits the steel plate ES is a perfect circle, there is no distinction between short and long axes, so any two axes that pass through the center and intersect at right angles can be considered as the short axis and long axis. In this embodiment, the laser processing device 1 scans the laser beam LB in the direction of the long axis of the shape of the beam spot immediately before it hits the steel plate ES.

In this way, the direction in which the laser processing apparatus 1 scans the laser beam LB is the direction corresponding to the long axis direction of the beam spot (regardless of whether the beam spot is circular or elliptical), so in the following, the direction corresponding to the long axis direction of the beam spot will be referred to as the second axis, and the direction corresponding to the short axis direction of the beam spot perpendicular to the second axis will be referred to as the first axis.
The direction parallel to the second axis is referred to as the S direction, and the straight line that passes through the surface of the steel sheet ES at the apex of the support roll SR and is parallel to the second axis (i.e., parallel to the S direction) is referred to as the S axis.
The laser processing device 1 is configured so that the scanning direction of the laser beam LB can be set to the S direction by a rotation adjustment device (not shown).

The steel sheet ES is an electromagnetic steel sheet that is the subject of axial control; it is cold-rolled into a strip shape and forced through the support roll SR, which constitutes part of the conveying device. That is, the steel sheet ES is subjected to tension from the conveying device, and is pressed against the upper side of the support roll SR near the apex of the curved surface of the support roll SR so that it is in close contact with the upper side of the support roll SR, and is curved into an upwardly convex mountain shape and passed along the support roll SR. As a result, the steel sheet ES is restrained near the apex of the support roll SR, making it less likely to vibrate.

FIG. 1 illustrates, as an example, a state in which a steel sheet ES is being passed along the upper surface side of a support roll SR while being curved into a gently inclined mountain shape.
In this embodiment, a laser beam LB is irradiated onto the surface of the steel sheet ES near the apex of the support roll SR while being narrowed down to a minute elliptical beam spot BS of several tens of μm level via various mirrors, and the laser beam LB is scanned in the direction of the second axis to form a linear groove portion or a linear distortion portion on the surface of the steel sheet ES. The beam spot diameter is about several tens of μm, but in FIG. 1, the beam spot BS is enlarged for illustrative purposes.

In the embodiment shown in Fig. 1, the support rolls SR are installed so that their rotation axes are horizontal, and the strip-shaped steel sheet ES is passed through with its rolling direction perpendicular to the direction of the rotation axes of the support rolls SR. The steel sheet ES is passed through with its width direction aligned with the direction of the rotation axes of the support rolls SR.
As shown in Fig. 1, in the present invention, for the sake of convenience, the width direction of the steel sheet ES located at the apex of the support roll SR is defined as the X direction, and the direction perpendicular to the X direction and along the length direction of the electromagnetic steel sheet ES is defined as the Y direction. In addition, the direction of a straight line perpendicular to the X direction and connecting the center of the reflection position of the focus position adjustment mirror Ms described later and the steel sheet ES located at the apex of the support roll SR is defined as the Z direction. Therefore, when the support roll SR is arranged so that the rotation axis is horizontal and the laser beam LB is irradiated vertically from the focus position adjustment mirror Ms toward the steel sheet ES, the Z direction means the height direction (vertical direction).

The long axis focusing mirror Mc is a mirror that reflects the laser beam LB emitted from the laser beam emission part LL and focuses the laser beam in the direction of the second axis, which corresponds to the long axis of the beam spot immediately before it is irradiated onto the steel sheet ES. Therefore, the component of the laser beam LB in the direction of the second axis is focused at a point equidistant from the long axis focusing mirror Mc (regardless of the presence of a mirror on the optical path). The laser beam LB reflected by the long axis focusing mirror Mc travels to the plane mirror MF, which will be described later.
The plane mirror MF reflects the laser beam LB reflected by the long axis focusing mirror Mc and changes the traveling direction. The plane mirror MF does not have to have the function of focusing the laser beam LB. The laser beam LB reflected by the plane mirror MF travels to a scanning mirror Mp, which will be described later.

The scanning mirror Mp is a mirror that reflects the laser beam LB reflected by the plane mirror MF, in other words, it is also a mirror that reflects the laser beam LB reflected by the long axis focusing mirror Mc (and further reflected by the plane mirror MF). The scanning mirror Mp has a function of changing the direction in which the laser beam LB is reflected and changing the position at which the laser beam LB is irradiated on the surface of the steel sheet ES, thereby scanning the surface of the steel sheet ES with the laser beam LB.
Therefore, more specifically, the scanning mirror Mp is realized by a polygon mirror, a galvanometer mirror, or the like, and the direction in which the laser beam LB is irradiated is changed by rotating the polygon mirror or changing the angle of the galvanometer mirror from time to time in accordance with the irradiation of the laser beam LB. The laser beam LB reflected by the scanning mirror Mp travels toward a short-axis focusing mirror ML, which will be described later.

The short-axis focusing mirror ML is a mirror that reflects the laser beam LB reflected by the scanning mirror Mp and focuses the laser beam in the direction of the first axis, which corresponds to the short axis of the beam spot immediately before it is irradiated onto the steel sheet ES. Therefore, the component of the laser beam LB in the direction of the first axis is focused at a point equidistant from the short-axis focusing mirror ML (regardless of the presence of a mirror on the optical path). The laser beam LB reflected by the short-axis focusing mirror ML travels toward the focus position adjustment mirror Ms, which will be described later.
The focal position adjustment mirror Ms is a mirror that reflects the laser beam LB reflected by the short axis focusing mirror ML and irradiates the surface of the steel sheet ES. The direction in which the laser beam LB is reflected by the scanning mirror Mp changes over time, and the focal position adjustment mirror Ms reflects the laser beam LB, whose incident position has changed, toward the steel sheet ES, so that the position on the surface of the steel sheet ES where the laser beam LB is irradiated changes over time. As a result, the surface of the steel sheet ES can be scanned with the laser beam LB.

The focal position adjustment mirror Ms has a curvature that focuses the laser beam LB at a point on the surface of the steel plate where the focusing focal length (G3') obtained by subtracting the distance between the point (A1') where the laser beam LB is reflected by the short axis focusing mirror ML and the point (A2') where the laser beam LB is reflected by the focus position adjustment mirror Ms from the focal length F_0 of the short axis focusing mirror ML is equal to the distance from the point (A2') where the laser beam LB is reflected by the focus position adjustment mirror Ms (see Figure 4).

When forming a linear groove or a linear distortion portion using the laser beam LB, it is necessary to focus the laser beam LB in order to increase the energy density of the laser beam LB. In particular, focusing the laser beam in the first axial direction affects the processability of the linear groove or linear distortion portion.
Therefore, it is necessary to focus the light in the first axial direction on the surface of the steel plate ES, but if a flat mirror M0 without curvature is used instead of the focus adjustment mirror Ms, the light in the first axis will be focused at a point on the projection line of the linear groove portion or linear distortion portion onto a plane perpendicular to the Z direction passing through the surface of the steel plate ES located at the apex of the support roll SR (a point on the S axis passing through the surface of the steel plate ES located at the apex of the support roll SR), which will deviate from the surface of the steel plate ES which is curved as it is transported, and the light cannot be focused on the surface of the steel plate ES.
Therefore, by using the focal position adjustment mirror Ms, the direction of the laser beam LB can be changed so that the focal point, which would otherwise deviate from the surface of the steel sheet ES, can be aligned with a position on the steel sheet ES. As a result, linear grooves or linear distortions can be stably formed.

Next, the relationship between the components of the laser processing device 1 in this embodiment, the movement of the laser beam LB, and the like will be described with reference to FIG.
In the embodiment shown in Figure 1, a polygon mirror is used as an example of the scanning mirror Mp, and a rotating polygon mirror with its rotation axis 2 oriented horizontally is disposed above the center of the support roll SR in the direction of the rotation axis.
1, the polygon mirror has a flattened regular polygonal prism shape when viewed from the side from the direction of a rotation axis 2. The polygon mirror has a rotation axis 2 extending in the horizontal direction and rotates around the rotation axis 2.
The outer peripheral surface of the polygon mirror is formed by a plurality of rectangular reflective surfaces 3 (which form each face of the regular polygonal shape of the polygon mirror) and corners 5 formed by these reflective surfaces 3. Each reflective surface 3 is a flat surface to which a mirror is attached. If the number of reflective surfaces 3 (the number of corners 5) is N, then the polygon mirror has a regular N-sided polygonal prism shape. In the embodiment shown in FIG. 1, the polygon mirror has a regular dodecagonal prism shape, and N (the number of reflective surfaces 3) is 12.
By rotating the polygon mirror around the rotation axis 2, specific reflecting surfaces 3 out of the 12 reflecting surfaces 3 can be made to face the plane mirror MF and the short-axis collector mirror ML in sequence.

In this embodiment, the long axis focusing mirror Mc and the plane mirror MF are installed on the front left side (-X direction side) of the polygon mirror shown in Figure 1, one above the other. The long axis focusing mirror Mc is placed with its reflective surface 6 facing diagonally downward so as to face the polygon mirror, and the plane mirror MF is placed with its reflective surface 8 facing diagonally upward, toward the side of the polygon mirror.

As shown in FIG. 1, the emitter 7 of the laser beam emission unit LL is arranged horizontally in front of the reflecting surface 6 of the long axis focusing mirror Mc.

The laser beam LB is emitted from an emitter 7 of the laser beam emission unit LL and is reflected by the reflecting surface 6 of the long axis collecting mirror Mc. The laser beam LB reflected downward by the reflecting surface 6 of the long axis collecting mirror Mc is incident on the reflecting surface 8 of the plane mirror MF below. The laser beam LB incident on the reflecting surface 8 of the plane mirror MF is reflected again and incident on one of the twelve reflecting surfaces 3 of the polygon mirror Mp.
The arrangement of the long axis collector mirror Mc and the plane mirror MF is not limited to the example in Fig. 1, and any arrangement may be adopted as long as the laser beam LB can be incident on the reflection surface 3 of the polygon mirror. For example, the long axis collector mirror Mc and the plane mirror MF may be arranged in the left-right direction, or in the diagonal up-down direction or diagonal left-right direction.

When the reflecting surface 3 of the polygon mirror receives the laser beam LB, it reflects the laser beam LB toward a reflecting surface 9 of a minor axis collector mirror ML disposed obliquely below the polygon mirror.
As shown in Fig. 1, the focal position adjustment mirror Ms is installed near the short axis collector mirror ML on the left side, and the reflection surface 9 of the short axis collector mirror ML reflects the laser beam LB toward the special reflection curved surface 10 of the focal position adjustment mirror Ms located on the left side of Fig. 1. When the special reflection curved surface 10 of the focal position adjustment mirror Ms receives the laser beam LB, it reflects the laser beam LB toward the surface of the steel sheet ES located at the apex portion of the support roll SR.

In this embodiment, as shown in Fig. 1, the laser beam LB is focused so as to form a circular or elliptical laser spot BS on the surface of the steel sheet ES. Then, the steel sheet ES is linearly scanned with this laser beam LB in the S direction inclined at a scanning angle (θc) of about 10° with respect to the X direction, to form a linear groove or distortion portion along the S direction on the surface of the steel sheet ES.
The reason why grooves or distortions are formed in the steel sheet ES at a scan angle of about 10° is that, as described above, when the steel sheet ES is used to manufacture an iron core for a wound transformer, the grooves improve the magnetic properties of the grain-oriented electromagnetic steel sheet while preventing breakage of the steel sheet ES. Note that the scan angle may be smaller than 10°, but since a scan angle approaching 0° may cause breakage during the manufacture of the iron core, it is desirable to avoid angles approaching 0°.

The diameter of the beam spot immediately before being irradiated onto the steel sheet ES is about several tens of μm, but the beam spot BS is shown enlarged in Fig. 1. The laser beam LB is scanned along the second axis of the beam spot BS (i.e., along the S direction).
Furthermore, when the laser beam LB is scanned in the direction of the second axis of the beam spot BS, the width of the groove or distorted portion to be formed on the surface of the steel plate ES can be accurately processed by accurately focusing the first axis of the laser beam LB.
The laser spot BS can be focused in the first axis direction by the short axis focusing mirror ML, and the laser spot BS can be focused in the second axis direction by the long axis focusing mirror Mc. Even if the focusing of the laser spot BS in the long axis direction varies slightly, it has little effect on the accuracy of the groove or distortion formed in the steel sheet ES.

For example, in the beam spot BS, the focused diameter in the second axis direction is larger than the focused diameter in the first axis direction, and in groove machining of steel plate ES, the diameter of the second axis is generally about 5 to 10 times the diameter of the first axis. Therefore, the focusing focal length of the focus position adjustment mirror Ms is 5 to 10 times that of the short axis focusing mirror ML, and the processable focal depth is also approximately the same. For this reason, even if some defocusing occurs on the long axis side of the laser spot BS, the impact on processability is small.

The short-axis collector mirror ML is formed in a pentahedral body 11 that is elongated in a direction parallel to the S direction, and the body 11 has five side faces 11a and two end faces 11b. The body 11 is disposed so that the length direction is parallel to the S direction and the two end faces 11b are parallel to the S direction.
The reflecting surface 9 is formed of a minor-axis linear paraboloid on one of the five side surfaces 11a of the main body 11. As shown in FIG. 1, the reflecting surface 9 is inclined so as to face both the polygon mirror installed diagonally above the reflecting surface 9 and the focal position adjustment mirror Ms arranged on the left side of the reflecting surface 9. When the cross section of the main body 11 is viewed, the reflecting surface 9 is a reflecting surface whose outline draws a parabola, and the reflecting surface 9 maintains the same outline shape from one end side to the other end side along the length direction of the main body 11. That is, the reflecting surface 9 is formed as a linear paraboloid of the same shape from one end side to the other end side in the length direction of the main body 11.
The reflecting surface 9 is formed of a linear paraboloid that focuses the incident laser beam LB in the direction of the first axis.

The focal position adjustment mirror Ms has a main body 12 in the shape of a rectangular prism elongated in a direction parallel to the S direction, and this main body 12 has four side surfaces 12a and two end surfaces 12b. The main body 12 is arranged so that the length direction is parallel to the S direction and the two end surfaces 12b face one side and the other side in a direction parallel to the S direction. Of the four side surfaces 12a of the main body 12, one side surface 12a has a special reflective curved surface 10 made of a special curved surface formed thereon.
As shown in Figure 1, the special reflective curved surface 10 is a reflective surface that has an inclination that faces both the short-axis focusing mirror ML installed to the right side (Y direction) of the special reflective curved surface 10 and the support roll SR arranged below the special reflective curved surface 10.
As described below, the special reflecting curved surface 10 is a reflecting surface whose curvature gradually changes along the length direction of the main body 12, and the detailed shape of the special reflecting curved surface 10 will be described in detail later.
In addition, the side surfaces 12a, 12a of the main body 12 are arranged on both the top and bottom sides of the special reflective curved surface 10, but the special reflective curved surface 10 is formed in a straight line without curvature from the upper side surface 12a to the lower side surface 12a. That is, the curvature of the special reflective curved surface 10 changes along the length direction of the main body 12 (i.e., the direction corresponding to the second axis), but in the width direction (i.e., the direction corresponding to the first axis), it is a flat reflective surface without curvature.

While the laser beam LB is irradiated onto the reflecting surface 3 of the polygon mirror, the polygon mirror rotates about the rotation axis 2, whereby the laser beam LB reflected by the polygon mirror can be made to scan within a predetermined range.
In FIG. 1, half the reflection angle range in the case where the laser beam LB is reflected by the rotation of the polygon mirror is indicated as a reflection angle (half reflection angle) θs.

As shown by the solid line in FIG. 1, the scanned laser beam LB is incident on the special reflective curved surface 10 of the focal position adjustment mirror Ms from the short axis focusing mirror ML, reflected by the special reflective curved surface 10, and irradiated along the S direction on the surface of the steel sheet ES. By scanning in this state, a linear groove or linear distortion 15 can be formed.

Next, the special reflective curved surface 10 of the focal position adjustment mirror Ms will be described in detail.
As a premise for the explanation, it is assumed that the center of scanning of the laser beam LB is located on the surface of the steel sheet ES at the apex of the support roll SR. Here, the sheet width direction of the steel sheet ES or the rotation axis direction of the support roll SR can be defined as the X direction, the sheet passing direction can be defined as the Y direction, the direction of the straight line connecting the center of the reflection position of the focal position adjustment mirror Ms and the steel sheet ES located at the apex of the support roll SR in the normal direction of the XY plane can be defined as the Z direction, and the scanning direction (i.e., the direction of the second axis) can be defined as the S direction. Each of the XYZ directions is perpendicular to each other, and the angle between the S direction and the X direction can be defined as the scanning angle θc. The reflection angle (half reflection angle) of the laser beam LB scanned by the scanning mirror Mp on a plane perpendicular to the first axis is defined as θs.

In this embodiment, a mirror that does not cause a thermal lens effect even when a high-power laser is used is used as the focusing optical element. The focusing shape of the laser beam LB (shape of the beam spot BS) is a minute perfect circle or ellipse with a second axis in the same direction as the scanning direction and a first axis perpendicular to the second axis. The ellipse shape is used because it is easier to process than a perfect circle. The focus in the minor axis direction of the ellipse particularly affects the processability, and it is desirable to focus the beam so that the minor axis diameter is a minute beam spot BS shape of, for example, 0.05 mm or less over the entire scanning width, and then perform laser processing. However, this embodiment can be implemented even if the shape is a perfect circle rather than an ellipse.

To achieve this type of focusing, a long axis focusing mirror Mc and a short axis focusing mirror ML are used, and the second axis and first axis, which correspond to the long axis and short axis directions of the elliptical focusing, are focused by independent linear parabolic mirrors.
A linear parabolic mirror is a mirror that has a parabolic surface in one direction, reflects and focuses a laser beam in a direction determined by the parabolic surface shape, and has a flat surface with no curvature in the perpendicular direction, reflects a laser beam at an incident reflection angle symmetrical to the normal to the flat surface, and has no focusing function. A linear curved mirror can also be described as a mirror that has a specific curved surface in one direction, reflects and focuses a laser beam in a direction determined by the mirror curved surface at the incident position, and has a flat surface in the perpendicular direction, reflects a laser beam at an incident reflection angle symmetrical to the normal to the flat surface, and has no focusing function.

Next, the focal position at which light is focused by the laser processing device will be described with reference to FIG.
FIG. 3 shows a reference example laser processing apparatus 20 in which, instead of the focal position adjustment mirror Ms in the laser processing apparatus 1 shown in FIG. 1, a plane mirror M0 is provided in which the special reflective curved surface 10 is replaced with a general planar reflective surface 18.
In the laser processing apparatus 20 shown in Figure 3, the plane mirror M0 is located at the position of the focal position adjustment mirror Ms in Figure 1, and the positional relationship between the support roll SR and the steel sheet ES, the arrangement of the laser beam emission section LL, long axis focusing mirror Mc, plane mirror MF, scanning mirror Mp, and short axis focusing mirror ML, and the relative positional relationships between these are the same as in Figure 1.

3 shows an SZ plan view of the trajectory of the laser beam LB scanned by the scanning mirror Mp. The steel sheet ES follows the curved surface of the top portion of the support roll SR, and in FIG. 3, for simplicity, the surface of the support roll SR is illustrated as the surface of the steel sheet.
This S-Z plane view is a plane formed by the S-direction axis and the Z-direction axis passing through the surface of the steel sheet ES located at the apex of the support roll SR, i.e., a plane perpendicular to the first axis passing through the surface of the steel sheet ES located at the apex of the support roll SR. In addition, the point on the surface of the steel sheet ES located at the apex of the support roll SR is set as the origin, and the origin is located at the center of the scanning direction of the laser beam LB.

Although the laser beam LB actually undergoes reflection in three-dimensional directions as shown in Fig. 1, for the sake of simplicity, the reflection from the scanning mirror Mp, the short-axis collecting mirror ML, the plane mirror M0, and the steel plate ES is shown in a linear arrangement in Fig. 3(A). Therefore, Fig. 3 can be said to be a projection onto the SZ plane of the trajectory of the laser beam LB passing through the scanning mirror Mp, the short-axis collecting mirror ML, and the plane mirror M0.
The reflection point on the reflecting surface 3 of the scanning mirror Mp is designated as A0, the reflection point of the laser beam LB on the short-axis focusing mirror ML on the scanning central optical axis (θs=0) is designated as A1, and the virtual reflection point on the plane mirror M0 is designated as A2. The point where the laser beam LB is focused on the surface of the steel sheet ES is designated as A3, the distance between the reflection point A0 and the reflection point A1 is designated as G1, the distance between the reflection point A1 and the virtual reflection point A2 is designated as G2, and the distance between the virtual reflection point A2 and the arrival point A3 is designated as G3.
In this case, if the focal length of the short axis collector mirror ML is F_0, the relationship of distance G2+distance G3=F_0 holds.

On the optical axis reflected from reflection point A0 at an arbitrary reflection angle (virtual reflection angle) _θs0 , an arbitrary reflection point of the laser beam LB on the short-axis focusing mirror ML is designated as A1', and a virtual reflection point on the plane mirror M0 is designated as A2'. Also, a point where the laser beam LB is focused on the way to the surface of the steel sheet ES is designated as A3', and the distances between reflection point A0 and reflection point A1', reflection point A1' and virtual reflection point A2', and virtual reflection point A2' and focal position A3' of the laser beam LB are designated as G1', G2', and G3', respectively.
In this case, the focal position A3' is the focal point of the short-axis collector mirror ML at the reflection angle (virtual reflection angle) θs ₀ as described above, but the focal point of the short-axis collector mirror ML at any reflection angle θs exists on the S-axis (Z = 0). This is derived from the following calculation.

When the laser beam LB is incident at a predetermined angle of incidence θs in a direction perpendicular to the parabolic curve of the short-axis focusing mirror ML (a plane perpendicular to the first axis), the focusing focal length F(θs) of the short-axis focusing mirror ML can be expressed by the following equation (4).

In formula (4), _F0 indicates the focal length of the short axis collector mirror ML, and coincides with the focal length at the center of the scan, "θs = 0". Therefore, the focal length of the short axis collector mirror ML becomes longer as the reflection angle θs increases. On the other hand, the propagation distance (G2' + G3') from the short axis collector mirror ML to the steel sheet ES also depends on the reflection angle θs and can be expressed by the following formula (5).

Therefore, since the focal length and the propagation distance change at the same ratio depending on the reflection angle θs, the focal position is located on the S axis (Z = 0) over the entire width of the scanning line. For reference, the diameter d ₀ of the focused beam can be expressed by the following equation (6).

In equation (6), Const is a constant specific to the laser determined by the quality of the laser beam LB, D is the diameter in the first axis direction of the laser beam incident on the short axis focusing mirror ML, and λ is the laser wavelength.
According to equation (6), F(θs) increases with an increase in the reflection angle θs, and therefore the laser beam diameter at the focal point increases as the reflection angle θs increases. However, if the scanning optical system is designed with the maximum reflection angle θs of 20°, the beam diameter expansion rate at the scanning end is about 6% of that at the scanning center, and it is considered that there will be almost no deterioration in processability.

Figure 2(A) is an expanded view of the top side of the support roll SR as viewed from the XY plane, Figure 2(B) is an expanded view of the side side of the support roll SR as viewed from the YZ plane, and Figure 2(C) is an enlarged view of the top region of the support roll SR in Figure 2(B).
In the XY plan view shown in FIG. 2(A), when a laser beam LB is scanned in the S direction at a scanning angle θc with respect to the X direction, the distance Wy in the Y direction from the X-axis (Y=0) forming the ridge line of the top of the support roll SR to the point where the laser beam LB reaches the surface of the steel sheet ES can be expressed as a function of S by the following equation (7).

From the YZ plane diagrams shown in Figures 2(B) and 2(C), the distance h(s) between the tangent at the apex of the support roll SR and the surface of the support roll SR can be derived as a function of S using the following equations (8) to (10).

Here, R is the radius of the support roll SR, and φ is the central angle of the support roll SR at the intersection B of the straight line S=Wy and the surface of the support roll SR (approximation of the surface of the steel sheet ES) (see Figures 2(B) and 2(C)).
Therefore, when the scanning angle θc>0°, h(s) increases with an increase in S, that is, with a distance S from the scanning center. Therefore, when laser scanning and irradiation is performed at the apex of the support roll SR, the focus of the scanning laser beam LB becomes a tangent to the apex of the support roll SR, so that the out-of-focus becomes larger toward the scanning end, and the processability is significantly deteriorated.

In addition, in the focused shape of the laser beam, the focused diameter in the direction of the second axis (C direction) of the beam spot BS is larger than the direction of the first axis (L direction) of the beam spot BS, and when machining grooves in steel plate ES, the second axis diameter dL is 5 to 10 times larger than the first axis diameter dc. Therefore, the focusing focal length of the long axis focusing mirror Mc is 5 to 10 times larger than the short axis focusing mirror ML, and the processable focal depth is also similarly long, so it does not affect processability as much as the defocusing of the first axis.

In this embodiment, a focal position adjustment mirror Ms having a specific special curved reflecting surface 10 that changes the propagation direction of the laser beam LB without changing the focal length in the first axial direction (L direction) is installed between the short axis focusing mirror ML and the surface of the steel sheet ES. This allows the focal position to coincide with the curved surface of the support roll ES.
The function of the focal position adjustment mirror Ms and the method of setting the curved surface will be described in detail below.

FIG. 4 shows an SZ plan view of the trajectory of the laser beam LB scanned by the scanning mirror Mp (a polygon mirror, for example) in the laser processing apparatus 1 of the present embodiment shown in FIGS.
The steel sheet ES follows the curved surface of the top portion of the support roll SR, and for simplicity, the surface of the support roll SR is illustrated as the steel sheet surface. The laser beam LB actually undergoes three-dimensional reflection as shown in Fig. 1, but for simplification, Fig. 4 shows the scanning mirror Mp, the short axis collector mirror ML, the focal position adjustment mirror Ms, and the steel sheet ES as a straight line. Therefore, Fig. 4 can be said to be a diagram in which the trajectory of the laser beam LB passing through the scanning mirror Mp, the short axis collector mirror ML, and the focal position adjustment mirror Ms is projected onto the SZ plane.

The focal position adjustment mirror Ms has a curvature only in the direction parallel to the S direction, and is flat in the direction perpendicular to the direction. Therefore, it does not affect the focusing characteristics of the short axis focusing mirror ML. That is, the focusing focal length G3' from the short axis focusing mirror ML shown in FIG. 3 (the distance obtained by subtracting the distance between the point (A1') where the laser beam LB is reflected by the short axis focusing mirror ML and the point (A2') where the laser beam LB is reflected by the focal position adjustment mirror Ms from the focal length F_0 of the short axis focusing mirror ML) is F(θs)=G3', and does not change in FIG. 4.
Therefore, a curved surface that changes the reflection angle so that the focal point of the laser beam LB reaches a surface point A4 shown in Fig. 4(B) of the support roll SR that is equidistant from an arbitrary virtual reflection point A2' on the focal position adjustment mirror Ms as the focusing focal length G3' is provided on the special reflection curved surface 10 of the focal position adjustment mirror Ms. Note that the arbitrary virtual reflection point A2' shown in Fig. 3 and the arbitrary virtual reflection point A2' shown in Fig. 4 indicate equivalent positions within a rectangular area shown as the outline of the main body 12 in Figs. 3 and 4.

The presence of the special reflecting curved surface 10 makes it possible to make the focal point of the short-axis focusing mirror ML coincide with the surface of the support roll SR along the scanning direction S. The surface point A4 shown in Fig. 4(B) is the intersection point of the function h(S) shown in the above formula (10) and the circle f(S, Z) of radius G3' centered on the virtual reflecting point A2'.
Here, f(S, Z) can be expressed by the following equations (11) and (12) with the coordinates of the virtual reflection point A2' being (S ₂ , Z ₂ ).

From equations (11) and (12), the intersection coordinates A4 (S ₄ , Z ₄ ) on the SZ plane can be found for any virtual reflection angle θs ₀ .
As an example, under the setting conditions shown in Table 1 below, h(s) and f(S, Z) when the virtual reflection angle θs = 10° are plotted on the SZ plane (SZ coordinate plane), and the intersection coordinate A4 is calculated. The result is shown in FIG. 5.
As shown in FIG. 5, the intersection coordinates A4 are determined to be (42.45, -0.27).

Next, the changed effective reflection angle θs′ is calculated. The changed effective reflection angle θs′ can be calculated from the coordinates A2′ (S ₂ , Z ₂ ) and A4 (S ₄ , Z ₄ ) using the following formula (13).

Here, Z ₂ =G3, and S4 and Z4 are determined as the intersection of equations (11) and (12) as described above, so that the changed effective reflection angle θs′ becomes a function of S ₂ from equation (13).
That is, the design value of the curved surface at any position in the S direction of the effective reflection angle θs′ of the focal position adjustment mirror Ms can be obtained.
The curved surface of the special reflecting curved surface 10 provided on the focal position adjustment mirror Ms can be defined by its normal angle.
6, to change the virtual reflection angle at the focal position adjustment mirror Ms from _θs0 to the effective reflection angle θs', if the normal to the special reflection curved surface 10 is tilted by an angle α1 with respect to the Z axis, α1 can be expressed by the following formula (14). That is, α1 is the angle of incidence when the laser beam is incident on the focal position adjustment mirror Ms on a plane perpendicular to the first axis.

As described above, the changed effective reflection angle θs′ is a function of S, so the normal angle at each position in the S direction on the special reflection curved surface 10 of the focal position adjustment mirror Ms can be determined.
Fig. 7 shows the relationship between the position in the S direction and _α1 when the virtual reflection angle _θs0 is changed from 0 to 20° under the conditions in Table 1, which is a specific example. As shown in Fig. 7, the relationship between the position in the S direction and _α1 is almost proportional.

The normal angle distribution _α1 that defines the S-direction curved surface of the special reflecting curved surface 10 of the focus position adjustment mirror Ms, obtained as described above, is the value when the laser beam LB incident on the special reflecting curved surface 10 of the focus position adjustment mirror Ms is specularly reflected in the direction of the short axis focusing mirror ML.

However, in an actual mirror arrangement, as shown in Figure 8, the focal position adjustment mirror Ms reflects the incident laser beam LB from the short axis focusing mirror ML almost vertically downward along the Z axis. Therefore, the incident and reflection angle must be taken into consideration when designing the reflecting surface (curved surface design) of the focal position adjustment mirror Ms to be manufactured.

FIG. 8 illustrates a case where the incident reflection angle from the short axis collector mirror ML to the focus position adjustment mirror Ms is β on a plane perpendicular to the second axis.
8 with respect to a focus position adjustment mirror Ms having a radius of curvature in the S direction, the reflected beam is reflected with a radius of curvature obtained by multiplying the S direction radius of curvature by 1/cos β. Therefore, when the curved surface distribution of _α1 shown in the above formula (14) is realized at an incident/reflection angle β, the actual normal angle design value _α2 of the focus position adjustment mirror Ms can be expressed by the following formula (15).

Since the special reflective curved surface 10 of the focal position adjustment mirror Ms has a curvature distribution in the scanning direction (S direction) of the laser beam, the laser beam LB has a focusing property in the major axis direction of the elliptical focusing shape thereof at the same time as the change in the virtual reflection angle θs _0. However, as shown in FIG. 7, the change in the curvature is very small, so that the effect on the major axis direction of the elliptical focusing shape of the laser beam LB is small.

From the above explanation, the normal angle design value _α2 of the actual focus position adjustment mirror Ms can be obtained. Based on this value, the curvature along the direction parallel to the S direction of the special reflecting curved surface 10 of the focus position adjustment mirror Ms can be obtained. If the special reflecting curved surface 10 is manufactured based on this curvature, the desired focus position adjustment mirror Ms can be manufactured.
1 and 4, a linear groove or linear distortion can be formed with high accuracy along the target scanning direction on the steel sheet ES. That is, since the focal position can be accurately aligned on the surface of the steel sheet ES from one end to the other end in the scanning direction S, a linear groove or linear distortion can be formed without defocusing.

When scanning the surface of the steel sheet ES with the laser beam LB, the laser beam LB may be scanned so as to form a clearly defined groove shape, or the laser beam LB may be scanned so as not to form a clearly defined groove shape but to form a distorted portion. By providing a distorted portion, it is possible to perform the desired magnetic domain control as a grain-oriented electrical steel sheet.
In addition, the above has been explained using an example in which the laser processing apparatus 1 has a long axis focusing mirror Mc and a plane mirror MF, but as described above, since focusing in the first axial direction has little effect on the formation of linear grooves or linear distorted portions, it is also possible for the laser processing apparatus 1 to be configured so as not to have a long axis focusing mirror Mc and a plane mirror MF.

In addition, although the laser beam LB is a fiber laser or a disk laser in the description using Fig. 1, it is not limited to these. For example, it may be a _CO2 laser.
Moreover, the rotary polygon mirror used as the scanning mirror Mp in the previous embodiment may be changed to a galvanometer mirror 30 having a configuration shown in FIG.
A galvanometer mirror 30 shown in Fig. 9 is rotated in the direction of the arrow in Fig. 9 by a drive motor 31. The reflection direction of the laser beam LB can be changed according to the rotation angle of the galvanometer mirror 30, thereby enabling scanning with the laser beam LB.

1...laser processing device, 3...reflective surface, 6...reflective surface, 8...reflective surface, 9...reflective surface, 10...special reflective curved surface, 11...main body, 11a...side surface, 12...main body, 12a...side surface, 30...galvanometer mirror, BS...beam spot, ES...directional electromagnetic steel sheet (steel sheet), LB...laser beam, Mc...long axis focusing mirror, MF...flat mirror, ML...short axis focusing mirror, Mp...scanning mirror, Ms...focus position adjustment mirror, SR...support roll, θc...scanning angle, θs...reflection angle (half reflection angle), _θs0 ...virtual reflection angle, θs'...effective reflection angle, S...scanning direction, G1, G2, G3...distance, G1', G2'...distance, focusing focal length...G3', A0, A1...reflection point, A2...virtual reflection point, A1'...reflection point, A2'...virtual reflection point, A3, A3'...focus position.

Claims (5)

A laser processing apparatus for forming a linear groove portion or a linear distortion portion in a steel sheet by scanning a surface of the steel sheet, which is passed through the steel sheet while being biased by a support roll, with a laser beam having a circular or elliptical beam spot, the laser processing apparatus comprising:
a laser beam emitting unit that emits a laser beam;
a scanning mirror that reflects the laser beam;
a short-axis focusing mirror that reflects the laser beam reflected by the scanning mirror and focuses the laser beam in a direction of a first axis corresponding to a short axis of the beam spot;
a focal position adjustment mirror that reflects the laser beam reflected by the short axis focusing mirror and irradiates the laser beam onto the surface of the steel sheet;
having
the scanning mirror changes a direction in which the laser beam is reflected, and changes a position at which the laser beam is irradiated on the surface of the steel sheet, thereby scanning the surface of the steel sheet with the laser beam;
The focus position adjustment mirror adjusts the laser beam to
A laser processing device having a curvature that focuses light at a point on the surface of a steel plate at which the focusing focal length, which is the distance obtained by subtracting the distance between the point at which the laser beam is reflected by the short axis focusing mirror and the point at which the laser beam is reflected by the focus position adjustment mirror from the focal length of the short axis focusing mirror, is equal to the distance from the point at which the laser beam is reflected by the focus position adjustment mirror. a long-axis focusing mirror that reflects the laser beam emitted from the laser beam emitting portion and focuses the laser beam in a direction of a second axis corresponding to a long axis of the beam spot;
The laser processing device according to claim 1 , wherein the scanning mirror reflects the laser beam reflected by the long axis focusing mirror. 3. The laser processing apparatus according to claim 1, wherein a curvature α2 of the focus position adjustment mirror, which is defined by an incident angle of the laser beam when it is incident on the focus position adjustment mirror as viewed from the direction of the first axis, is expressed by the following formulas (1) to (3).
Here, (S ₂ , Z ₂ ) is the coordinate on a plane perpendicular to the first axis of the point where the laser beam is reflected by the focal position adjustment mirror,
(S ₄ , Z ₄ ) are coordinates on a plane perpendicular to the first axis of a point on the surface of the steel plate where the focusing focal length is equal to the distance from the point where the laser beam is reflected by the focus position adjustment mirror,
α1 is an incident angle of the laser beam on the focal position adjustment mirror in a plane perpendicular to the first axis,
β is an incident angle of the laser beam on the focal position adjustment mirror in a plane perpendicular to a second axis corresponding to the major axis of the beam spot ,
θso is a reflection angle when the laser beam is reflected by a plane mirror having no curvature at the position of the focus position adjustment mirror in a plane perpendicular to the first axis,
θ's is the reflection angle when the laser beam is reflected by the focal position adjustment mirror on a plane perpendicular to the first axis.

The laser processing device according to any one of claims 1 to 3, wherein the reflecting surface of the short-axis focusing mirror is a linear paraboloid. The laser processing device according to any one of claims 1 to 4, wherein the scanning mirror is a rotating polygon mirror or a galvanometer mirror.

Images