GB2144873A

GB2144873A - Apparatus for scanning a laser beam

Info

Publication number: GB2144873A
Application number: GB08321708A
Authority: GB
Inventors: Brian Raymond Moody
Original assignee: Fairey Engineering Ltd
Current assignee: WFEL Ltd
Priority date: 1983-08-12
Filing date: 1983-08-12
Publication date: 1985-03-13

Abstract

Apparatus for scanning a laser beam over a surface includes a focussing element e.g. a single lens 2, a laser 16 positioned to direct a beam of radiation directly onto the lens optionally parallel to the optical axis 4 of the lens but offset from it and a motor 14 connected to rotate the lens about an axis 8 which is offset from the optical axis 4 of the lens. <IMAGE>

Description

SPECIFICATION Apparatus for scanning a laser beam The present invention relates to apparatus for scanning, that is to say progressively moving, a laser beam over a surface and is particularly concerned with such apparatus for heat treating the surface of a workpiece or the like but is applicable also to such apparatus for use in welding, surface alloying and other metallurgical applications.

Lasers produce a substantially parallel beam of radiation which can be focussed down to a very small area and the focussed beam may thus have a very high energy density suitable for use in metallurigical applications when focussed on the surface of a workpiece. However, due to the very small size of the focussed beam it is desirable to be able to scan or progressively move the focus beam over the surface of the workpiece in order to be able to treat an appreciable area.

This could be achieved with the aid of a focussing lens or mirror in conjunction with one or more tilting mirrors but such mirrors are relatively expensive and mechanically complex and thus prone to failure.

According to the present invention an apparatus for scanning a laser beam over a surface includes an optical focussing element, a laser positioned to direct a beam of radiation onto the focussing element and means to rotate the focussing element about an axis which is offset from the optical centre of the focussing element. The laser is preferably positioned to direct the bearm of radiation with its axis substanatially parallel to but offset from the axis of rotation of the focussing element and the axis of rotation is also preferably substantially parallel to, but offset from, the optical axis of the focussing element and in the most preferred construction the axis of rotation is councident with the axis of the beam of radiation.

Thus the present invention makes use of the known principle that a beam of light incident on a focussing lens or mirror parallel to or not significantly inclined to the optical axis of the lens or mirror is focussed on the optical axis of the lens or mirror. Lasers produce a substantially parallel beam of radiation and in the preferred construction of the present invention the axis of the laser beam is parallel to the optical axis of the focussing element and is thus focussed substantially at the focal point.By virtue of the fact that the focussing element is, in use, rotated about an axis which is offset from the optical centre of the focussing element and is preferably paral lel to but offset from the optical axis of the focussing element the focal point of the focussing element is rotated in space and thus the focussed laser beam describes a circle whose radius is equal to that of the offset of the axis of rotation from the optical axis.

The focussing element may be a focussing mirror but it will be appreciated that this will result in the beam being reflected back in the general direction of the laser. For practical reasons, such a construction will in general necessitate the laser beam being inclined at an angle to the optical axis of the focussing mirror and it is more convenient when the focussing element comprises a lens since this inherently results in the laser beam being focussed at a point remote from the laser.

Further features and details of the present invention will be apparent from the following description of one specific embodiment which is given by way of example only with reference to the accompanying diagrammatic drawing which shows an apparatus for heat treating the surface of a workpiece.

The apparatus includes a focussing lens 2 which has an optical axis 4 and which for ease of mounting is asymmetrically shaped or broken away on one side. The lens is retained in an eccentrically disposed aperture in a circular section mounting 6 which is mounted to rotate about an axis 8 and is provided on its outer periphery with a toothed gear ring 10. The gear ring 10 meshes with a gear wheel 12 which is coupled to a motor 14.

A laser 1 6 is arranged to shine a parallel beam of radiation whose axis is coincident with the axis of rotation 8 of the mounting 6 and thus does not pass through the optical centre 9 of the lens. The axis 8 is offset from the optical axis 4 of the lens by a distance X.

When the lens is in the position shown in the drawing, the beam of laser radiation is focussed at the focal point 1 8. However, by virtue of the fact that the axes 4 and 8 are offset the focal point of the lens rotates in space as the lens is rotated and when the lens has rotated through 180 from the position shown in the drawing the focal point of the lens is at the position indicated at 18'. In use, the focussed laser beam thus describes a circle whose diameter is 2X. A workpiece whose surface is to be heat treated is positioned with its surface lying in the plane of the circle described by the focussed laser beam and the workpiece is then progressively moved at such a speed that the laser beam scans over the entire surface or at least a predetermined area of that surface whose width is equal to 2X.

If it is desired to alter the diameter of the circle described by the focussed laser beam, the value of the offset X may be adjusted by arranging the mounting 6 in an eccentric (not shown) which is rotated to the desired position or by arranging the mounting 6 on a slide (not shown) which is movable in a direction transverse to the optical axis 4 of the lens.

1. Apparatus for scanning a laser beam

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Apparatus for scanning a laser beam The present invention relates to apparatus for scanning, that is to say progressively moving, a laser beam over a surface and is particularly concerned with such apparatus for heat treating the surface of a workpiece or the like but is applicable also to such apparatus for use in welding, surface alloying and other metallurgical applications. Lasers produce a substantially parallel beam of radiation which can be focussed down to a very small area and the focussed beam may thus have a very high energy density suitable for use in metallurigical applications when focussed on the surface of a workpiece. However, due to the very small size of the focussed beam it is desirable to be able to scan or progressively move the focus beam over the surface of the workpiece in order to be able to treat an appreciable area. This could be achieved with the aid of a focussing lens or mirror in conjunction with one or more tilting mirrors but such mirrors are relatively expensive and mechanically complex and thus prone to failure. According to the present invention an apparatus for scanning a laser beam over a surface includes an optical focussing element, a laser positioned to direct a beam of radiation onto the focussing element and means to rotate the focussing element about an axis which is offset from the optical centre of the focussing element. The laser is preferably positioned to direct the bearm of radiation with its axis substanatially parallel to but offset from the axis of rotation of the focussing element and the axis of rotation is also preferably substantially parallel to, but offset from, the optical axis of the focussing element and in the most preferred construction the axis of rotation is councident with the axis of the beam of radiation. Thus the present invention makes use of the known principle that a beam of light incident on a focussing lens or mirror parallel to or not significantly inclined to the optical axis of the lens or mirror is focussed on the optical axis of the lens or mirror. Lasers produce a substantially parallel beam of radiation and in the preferred construction of the present invention the axis of the laser beam is parallel to the optical axis of the focussing element and is thus focussed substantially at the focal point.By virtue of the fact that the focussing element is, in use, rotated about an axis which is offset from the optical centre of the focussing element and is preferably paral lel to but offset from the optical axis of the focussing element the focal point of the focussing element is rotated in space and thus the focussed laser beam describes a circle whose radius is equal to that of the offset of the axis of rotation from the optical axis. The focussing element may be a focussing mirror but it will be appreciated that this will result in the beam being reflected back in the general direction of the laser. For practical reasons, such a construction will in general necessitate the laser beam being inclined at an angle to the optical axis of the focussing mirror and it is more convenient when the focussing element comprises a lens since this inherently results in the laser beam being focussed at a point remote from the laser. Further features and details of the present invention will be apparent from the following description of one specific embodiment which is given by way of example only with reference to the accompanying diagrammatic drawing which shows an apparatus for heat treating the surface of a workpiece. The apparatus includes a focussing lens 2 which has an optical axis 4 and which for ease of mounting is asymmetrically shaped or broken away on one side. The lens is retained in an eccentrically disposed aperture in a circular section mounting 6 which is mounted to rotate about an axis 8 and is provided on its outer periphery with a toothed gear ring 10. The gear ring 10 meshes with a gear wheel 12 which is coupled to a motor 14. A laser 1 6 is arranged to shine a parallel beam of radiation whose axis is coincident with the axis of rotation 8 of the mounting 6 and thus does not pass through the optical centre 9 of the lens. The axis 8 is offset from the optical axis 4 of the lens by a distance X. When the lens is in the position shown in the drawing, the beam of laser radiation is focussed at the focal point 1 8. However, by virtue of the fact that the axes 4 and 8 are offset the focal point of the lens rotates in space as the lens is rotated and when the lens has rotated through 180 from the position shown in the drawing the focal point of the lens is at the position indicated at 18'. In use, the focussed laser beam thus describes a circle whose diameter is 2X. A workpiece whose surface is to be heat treated is positioned with its surface lying in the plane of the circle described by the focussed laser beam and the workpiece is then progressively moved at such a speed that the laser beam scans over the entire surface or at least a predetermined area of that surface whose width is equal to 2X. If it is desired to alter the diameter of the circle described by the focussed laser beam, the value of the offset X may be adjusted by arranging the mounting 6 in an eccentric (not shown) which is rotated to the desired position or by arranging the mounting 6 on a slide (not shown) which is movable in a direction transverse to the optical axis 4 of the lens. CLAIMS

1. Apparatus for scanning a laser beam over a surface including an optical focussing element, a laser positioned to direct a beam of radiation onto the focussing element and means to rotate the focussing element about an axis which is offset from the optical centre of the focussing element.

2. Apparatus as claimed in Claim 1 in which the focussing element is a lens.

3. Apparatus as claimed in Claim 1 or Claim 2 in which the axis of rotation is substantially parallel to but offset from the optical axis of the focussing element.

4. Apparatus as claimed in any one of Claims 1 to 3 in which the laser is positioned to direct the beam of radiation with its axis substantially parallel to the axis of rotation.

5. Apparatus as claimed in Claim 3 and Claim 4 in which the axis of the beam of radiation and the axis of rotation are substantially coincident.

6. Apparatus as claimed in any one of the preceding claims in which the focussing element is eccentrically connected to a gear wheel which is coupled to a motor to be rotated thereby.

7. Apparatus as claimed in any one of the preceding claims in which the focussing element is mounted to be movable in a plane transverse to its optical axis.

8. Apparatus for scanning a laser beam over a surface substantially as specifically herein described with reference to the accompanying drawings.