JPS61203421A - Laser scanning device - Google Patents

Abstract

PURPOSE:To improve magnetic characteristics without flawing the insulating film of a grain oriented electrical steel sheet by providing a cylindrical mirror or lens at the entrance side of a rotary polygon mirror so that its axial direction is parallel to the axis of rotation of said polygon mirror. CONSTITUTION:A laser beam 1 is reflected by the rotary polygon mirror 2 and converted as a fine circular beam by a parabolic mirror 3 on the surface 4 of the grain oriented electrical steel sheet at a distance of focal length (f). In this case, when the cylindrical mirror 10 is arranged at the entrance side of the polygon mirror 2 so that its axial direction 10-1 is parallel to the axis 2-1 of rotation of the polygon mirror 2, the mirror 10 only reflects the laser beam 1 by its yz plane and converges it by its zx plane. Therefore, the laser beam 1 have different convergence positions in its scanning direction and a direction perpendicular to it and has a cross section shape shown in 12 in a figure on the copper plate surface 4 and a shape shown by 12 at a position 5 close to the copper plate surface 4. Therefore, an elliptic beam having its long axis in the scanning direction is formed on the steel sheet surface 4, so that a magnetic domain is fractionized without flawing the steel sheet 4.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a laser scanning device that uses a laser beam to improve the magnetic properties of a grain-oriented electrical steel sheet without damaging its insulation coating.

(Prior art) Lasers such as YAG lasers and C02 lasers are applied to improve magnetic properties by irradiating the surface of grain-oriented electrical steel sheets (hereinafter referred to as steel sheets) to subdivide the magnetic domains of the steel sheets. This is known, for example, from Japanese Patent Publication No. 57-2252. Furthermore, recently, research has been conducted on laser irradiation to improve magnetic properties without damaging the insulation coating on the steel plate surface by controlling the laser beam to an appropriate size and shape on the steel plate. Kaisho 59-358
In No. 93, a steel plate is irradiated with a laser beam having an elliptical cross-sectional shape to avoid damage to an insulating coating and improve iron loss characteristics. The feature of the device used here is that it scans using a rotating polygon mirror, and a cylindrical lens is placed between the rotating polygon mirror and the steel plate, and the cylindrical lens focuses the laser beam only in the direction perpendicular to the scanning direction. An elliptical beam with a long axis in the scanning direction is created to irradiate the steel plate. According to this, the laser beam has the effect of irradiating the steel plate in an elliptical shape. However, this requires a cylindrical lens with the same length as the scanning width.

On the other hand, as an optical material that can be used in high-power lasers,
For example, there are cylindrical lenses made of Zn5e, but large ones are expensive and can currently only be manufactured with a length of about 100 ms. Therefore, in order to scan a wide steel plate, the laser irradiation device must be wide It is necessary to arrange a large number of devices in one direction, which causes disadvantages such as an increase in the size of the device.

In addition, an apparatus for irradiating a steel plate with an elliptical laser beam has been proposed in Japanese Patent Laid-Open No. 59-92191. In this method, the laser reflected by a fixed mirror is input to a rotating device consisting of a diagonal mirror and a cylindrical lens (cylindrical lens), and the laser is deflected by the diagonal mirror and focused on only one side of the laser through the cylindrical lens. The beam is irradiated onto the steel plate surface in an elliptical shape with its long axis in the scanning direction. In this case, the cylindrical lens is small and the scanning width can be widened. However, there is a difference in the optical path length from the cylindrical lens to the steel plate surface between the center and both edges of the scanning section, and the wider the scanning section, the larger this difference becomes.

(Problem to be solved by the invention) In other words, the shape of the focused laser beam on the steel plate surface differs in the width direction of the steel plate, and the beam cannot be focused into a uniform elliptical shape over the entire scanning section. It has a large negative impact on the magnetic improvement effect of grain-oriented electrical steel sheets.
As a countermeasure to this problem, the device curves the steel plate in the scanning direction to eliminate this optical path length difference. Therefore, this requires a device for bending the steel plate, which requires extra equipment.

(Means for Solving the Problems) The object of the present invention is to provide a device that irradiates a laser beam as an elliptical beam over a wide range with a simple equipment configuration. The technical gist is that in a device that scans and irradiates a laser beam using an optical system equipped with a rotating polygonal mirror and a parabolic mirror, a cylindrical mirror or cylindrical lens is provided on the entrance side of the rotating polygonal mirror. It is characterized by

Next, the present invention will be described based on one embodiment with reference to the drawings.

In the drawings, the X axis indicates the scanning direction, the y axis indicates the steel plate conveying direction, and the z axis indicates the laser irradiation direction.

First, an overview of laser scanning will be described with reference to FIGS. 3(a), 3(b), and 3(c).

The laser beam 1 is reflected by a rotating polygon mirror 2, and is reflected by a parabolic mirror 3.
When the 0-rotation polygon mirror 2 is rotated clockwise as shown in the figure, the beam is focused as a minute circular beam on the steel plate surface 4 which is separated by the focal length f of the parabolic mirror 3. The condensed beam scans from left to right, and the system provided with the above-mentioned rotating polygonal mirror and parabolic mirror is called an f/θ scanning system.

The feature of this optical system is that when the distance 1IllfL between the reflecting surfaces of the rotating polygonal mirror 2 and the parabolic mirror 3 is set as shown in the equation 0, the shape of the condensed beam and the beam scanning linear velocity are determined in the scanning section shown in the equation (2). It remains almost constant.

It is possible to scan with a uniform beam over a wide area.

The laser beam is focused to the smallest extent on the steel plate surface 4 which is away from the paraboloid fi3 and its focal layer 1111f.

Before and after that, the laser beam is poked. The diameter of the condensed beam at the focal position is shown in equation 0.

do: Condensed beam diameter entered: Laser wavelength f: Focal length of parabolic mirror D: Diameter of laser beam incident on parabolic mirror Also, position 5 separated by α in two axial directions from the focal position, respectively. The laser beam diameter at .6 is shown in equation 0.

FIG. 3(c) shows the beam shape 7 on the steel plate surface 4 corresponding to the focal position and a position 5.6 separated by α from the steel plate surface 4.
The beam shape at 8.9 is shown.

Next, an example will be described in which the present invention is applied to transform this circular focused beam into an elliptical shape with long sleeves in the scanning direction.

As shown in FIGS. 1(a) and 1(b), a cylindrical mirror IO is placed on the entrance side of the rotating polygon mirror 2. This cylindrical mirror 10 has its axial direction 10-1 rotated by a polygon mirror 2.
The polygon mirror 2 is parallel to the rotation axis 2-1 of the polygon mirror 2, and is provided opposite to the polygon mirror 2 so that the laser beam reflected by the mirror surface is incident on the polygon mirror 2. Therefore, the cylindrical mirror IO merely reflects the laser beam within the yz plane, and the laser beam enters the rotating polygon mirror 2 without changing the size of the laser beam in the plane direction. Therefore, in the laser beam irradiated via the rotating polygonal mirror 2 and the parabolic mirror 3, the direction perpendicular to the scanning direction is the same as when the cylindrical mirror 10 is not used.
The light is focused to a minute size at a position separated by the focal length f of the parabolic mirror. On the other hand, since the cylindrical mirror 10 has a condensing effect as a concave mirror within the ZX plane, the laser beam is focused within that plane and is incident on the rotating polygon mirror 2. Therefore, from the rotating polygon mirror to the parabolic mirror 3
The scanning direction of the laser beam irradiated through the parabolic mirror 3 is focused to a minimum at a position 5 closer than the focal length f of the parabolic mirror 3. Therefore, the laser beam focuses at different positions in the scanning direction and in the direction orthogonal thereto, and the cross-sectional shape of the laser beam at the steel plate surface 4 (focal length f of the parabolic mirror 3) is shown in Fig. 1 (C). The cross-sectional shape at the position 5 has the shape shown at 12 in FIG. 1(c).

As is clear from the above, by disposing the cylindrical mirror 10 on the inlet side of the rotating polygon mirror 2 with its axial direction 10-1 parallel to the rotation axis 2-1 of the rotating polygon mirror 2, the steel plate An elliptical laser beam having a long sleeve in the scanning direction is formed on the surface 4, and scanning can be performed, and the magnetic domains can be subdivided without causing any flaws to the steel plate.

Another method of making the condensed beam into an elliptical shape with long sleeves in the scanning direction is shown in Figure 2 (a), (b), and (c), which is similar to the concave cylindrical shape in Figures 1 (a) and (b). It is a similar device except that the mirror IO is replaced with a convex cylindrical lens IOA. However, in this case ZX
Since the convex mirror has a diverging effect within the plane, the light is focused at a position 6 farther than the focal length f of the parabolic mirror 3. Steel plate surface (
The beam shape at the focal path fa) 4 is shown at 13.6 and the beam shape at 14 is shown.Also, the same effect can be obtained even if the cylindrical mirror in the above embodiment is replaced by a cylindrical lens.

(Example) Next, examples will be shown.

Using the apparatus shown in FIGS. 1(a) and 1(b), a laser beam was directed onto the surface of a steel plate using a parabolic mirror 3 with a focal length f = 380 m and a concave cylindrical mirror 10 with a radius of curvature of 2,500 to 1,000 layers. Scanning was carried out using an elliptical beam with a length of 8 to 20 m2, and an effect of reducing iron loss of more than 10% was obtained, and no damage to the insulating coating was observed.

It was verified that the effective scanning section at this time was irradiated with a predetermined elliptical beam over a wide range of 240 layers.

(Effects of the Invention) As described above, the present invention is a laser scanning device which has a simple device configuration and whose shape is uniform over the entire wide scanning section using an elliptical laser beam with a long sleeve in the scanning direction. By irradiating a grain-oriented electrical steel sheet, it is possible to improve the magnetic properties without damaging the insulation coating.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the invention, FIG. 2 is a diagram showing another embodiment of the invention, and FIG. 3 is a diagram for explaining the outline of a laser scanning device. 1... Laser beam, 2... Rotating polygon mirror, 3...
Parabolic mirror, 4... Steel plate surface, 10.1OA... Cylindrical mirror, 11, 12, 13.14... Cross-sectional shape of laser beam.

Claims (1)

[Scope of Claims] A device that scans and irradiates a laser beam with an optical system provided with a rotating polygonal mirror or a parabolic mirror, wherein a cylindrical mirror or a cylindrical lens is provided on the entrance side of the rotating polygonal mirror, and its axial direction is A laser scanning device characterized in that the laser scanning device is installed parallel to the rotation axis of the rotating polygon mirror.