GB2098133A

GB2098133A - A device for marking surfaces by laser radiation

Info

Publication number: GB2098133A
Application number: GB8211156A
Authority: GB
Original assignee: Datograf Apparatebau GmbH and Co
Current assignee: Datograf Apparatebau GmbH and Co
Priority date: 1981-05-13
Filing date: 1982-04-16
Publication date: 1982-11-17
Also published as: JPS57206591A; DE3118938A1

Abstract

In a device for marking surfaces by laser radiation from a laser light source (1), the radiation is shaped by beam- shaping means (5, 6, 8) and illuminates a mask (7). Objective means (9) forms an image of the illuminated mask (7) on the surface (10) to be marked. The laser light source (1), the beam-shaping means (5, 6, 8), the mask (7) and the objective means (9) are mounted on a common frame (4) and the beam path is deflected round the outside of the laser light source so that the available space is used to best advantage. <IMAGE>

Description

SPECIFICATION A device for marking surfaces by laser radiation The invention relates to a device for marking surfaces by laser radiation in which radiation issuing from a laser light source and shaped by beamshaping means illuminates a mask and in which objective means forms an image of the illuminated mask on a surface to be marked.

Using known devices of this type it is possible to employ the action of intense laser pulses for marking the surfaces of articles such as packaged goods, for example, to apply packaging or "sell-by" dates. The data can consist of letters, numbers or other symbols. Metallic masks are used which have apertures in the form of the data to be applied and are illuminated uniformly by laser radiation. An image of the part of the radiation which passes through the mask is formed on the surface to be marked by an optical system which is similar to the objective lens in a slide projector. Preferably a reducing image is used, so that the mask needs to be exposed onto to a relatively low power density, but sufficient intensity is nevertheless available at the marking location.

In known devices and beam-shaping means, mask, objective means, and any deflecting mirrors which are necessary, are designed as a separate unit which is attached to a suitable commercially available laser. The stability of such an arrangement as a whole is a problem, especially stability of the optical beam path. It is possible to seal off the beam-guiding system from environmental influences such as dust and moisture only by making the components of the device less easily accessible. Afurther problem with known marking devices of this kind is that it is complicated and time-consuming to replace the mask when different marking data is to be applied, and the required number of different marking data are frequently not available at all.

A main object of the invention is to provide a marking device whose design is stableperse and space-saving, and which has a mask which can be varied in a simple way to permit a wide variety of marking data to be used.

According to the invention there is provided a device for marking surfaces by laser radiation, in which radiation issuing from a laser light source and shaped by beam-shaping means illuminates a mask and in which objective means form an image of the illuminated mask on a surface to be marked, wherein the laser light source, the beam-shaping means, the mask and the objective means are arranged on a common frame, and beam deflecting means is mounted on the frame for guiding the beam around the outside of the laser light source for effective utilisation of the available space.

Preferably the mask comprises several metal strips which are arranged adjacent one another and behind a mask window and are displaceable relative to one another.

Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates diagrammatically a device for marking by means of laser radiation, Figure 2 is a sectional view along the line 2-2 of Figure 1, Figure 3 illustrates one embodiment of a variable mask, Figure 4 illustrates a second embodiment of a variable mask, Figure 5 is a sectional view of a mask, and Figure 6 is a sectional view of another embodi mentofa mask.

The broken lines in Figure 1 represent a light source 1. The actual laser light source can be a conventional pulsed CO2 laser, which is sealed in a housing 2. The laser 1 is illustrated simply by dot-and-dash lines in Figure 2. The laser 1 and housing 2 are fixed firmly to a frame 4 formed by profiled metal strips 3. Also mounted firmly on the frame 4 are a deflecting mirror 5, a further deflecting mirror 6 which is, for example, a three-dimensionally ground mirror which acts as beam-shaping means, a mask 7, another deflecting mirror 8 and an objective lens 9 which may comprise several lenses.The radiation emitted by the laser 1 and emergentfrom the housing 2 is incident on the first deflecting mirror 5, is deflected round the outside of the laser 1 and the housing 2 as illustrated, and emerges from the objective 9 to strike an article 10 to be marked, which can be, for example, a packaged article, especially the crown cork of a bottle. The arrangement illustrated is a very compact construction which permits exact, non-varying and mutual adjustment of the individual components. The guiding of the beam path round the outside of the laser is especially space-saving.

A hood 12 is sealed on to the frame 4, with interposed sealing means 11 for example, elastomer strips. The hood is firmly connected to the frame, so that all the components of the device are enclosed and are hermetically sealed. As shown in Figures 1 and 2, the objective 9 can be mounted in the hood 12 so as to be removable with the hood. In another embodiment, the objective 9, as already mentioned, is fixed firmly to the frame 4, and the radiation emerges through a window in the hood 12 towards the article 10.

Because of this sealed arrangement, it is possible to introduce a clean, dry scavenging gas, for example N2, under a slight excess pressure into the inner space between the hood 12 and the housing 2 enclosing the laser light source, so as to prevent contamination of the device. If the laser light source 1 is a pulsed CO2 laser, it is advantageous to use spent CO2 gas from the laser as the scavenging gas.

On top of the frame 4 there is mounted a base plate 13 which is fixed firmly to the frame and carries the components of the device, that is the laser light source 1 and the parts 5,6,7,8 and 9 which are provided if appropriate with holders.

Figures 3 to 6 show preferred embodiments of variable masks according to the invention.

Figure 3 shows a mask window 14 behind which several adjacent metal strips 15, 16, 17 and 18 arranged side-by-side, which are displaceable relative to each other. The markings to be transferred are introduced above one another by known photo etching techniques into the individual strips in the manner of a stencil. The individual strips, which may be of metal foil can be wound next to one another onto two rolls, or can be unwound from those rolls.

The top rolls 19 in Figure 3 are driven manually or by a motor, and tubular drive shafts 21 located concentrically in one another serve for individual drives to the rolls. The bottom rolls 22 can be pretensioned by springs in a way known for blinds, so that automatic rewinding of the individual metal strips is possible. It is possible, in this way, to introduce a wide variety of combinations of symbols into the mask window, for example manufacturing dates of packaged goods, and to transfer these combinations permanently to the article to be marked.

Figure 4 shows a modified embodiment of an interchangeable mask. The adjacent metal strips of Figure 1 extending in a straight line are replaced by concentric rings 23, 24, 25, 26, 27 and 28. A mask window 14 is provided in front of the rings. A window is preferably located at the rear of the rings, so that the rings are guided between the two windows. Each ring has stencil-like perforations representing the marking data to be transferred. For adjustment each ring has perforations 29 into which the pins or teeth of pinwheels or gear wheels 31 engage. If these wheels 31 are rotated by means of drive shafts 32, manually or by means of drive motors, the individual rings 23 to 28 can be adjusted so that the desired complete marking appears in the mask window 14.

As seen in Figure 5, the metal bands 15 to 18 or the metal rings 23 to 28 can be designed so that they overlap one another. This prevents harmful light from escaping between the individual members. The same effect can also be achieved by the arrangement shown in Figure 6, in which the gaps between the individual metal members are each covered, at least in the region of the mask window (Figures 3 and 4) by masking webs 33.

The interchangeable masks described above have the advantage that a large store of symbols can be represented and applied to articles in the form of marking data. The masks are especially suitable for identifying foodstuffs or drinks with their "sell-by" date. The consecutive numbering of work pieces or the like is also possible.

Claims

1. A device for marking surfaces by laser radiation, in which radiation issuing from a laser light source and shaped by beam-shaping means illuminates a mask and in which objective means form an image of the illuminated mask on a surface to be marked, wherein the laser light source, the beamshaping means, the mask and the objective means are arranged on a common frame, and beam deflecting means is mounted on the frame for guiding the beam around the outside of the laser light source for effective utilisation of the available space.

2. A device according to Claim 1, comprising a hood which encloses all the components and is fixed to the frame, and sealing means for sealing the hood to the frame.

3. A device according to Claim 2, wherein the objective means is carried by the hood.

4. A device according to Claim 3, wherein the objective means is an objective lens.

5. A device according to Claim 2, wherein the hood has a beam-transmitting window.

6. A device according to any one of Claims 2 to 5, comprising means for introducing a dry scavenging gas under slight excess pressure into the interspace between the hood and a housing enclosing the laser light source.

7. A device according to Claim 5, wherein the laser light source is a pulsed CO2 laser, and spent CO2 gas is introduced from the laser into the interspace.

8. A device according to any one of Claims 1 to 7, wherein the mask comprises several metal strips which are arranged adjacent one another and behind a mask window and are displaceable relative to one another.

9. A device according to Claim 8, wherein the metal strips are located side-by-side to constitute a band which extends between winding devices.

10. A device according to Claim 8, wherein the metal strips are concentric rings.

11. A device according to Claim 10, wherein the concentric rings are guided between two mask windows and are driven by pinwheels or gear wheels which engage in performations in the rings.

12. A device according to any one of Claims 8 to 11, wherein the metal strips overlap one another.

13. A device according to any one of Claims 8 to 11, wherein separation gaps between the metal strips are covered, at least in the region of the mask window, by masking webs.