Electric heating – Metal heating – By arc
Patent
1996-12-20
1999-01-05
Mills, Gregory L.
Electric heating
Metal heating
By arc
21912168, 21912176, B23K 2608
Patent
active
058566481
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method and an apparatus for producing wells in the surface of a rotogravure cylinder.
Such a method and such an apparatus are known, for example, from WO-A-92/09399. There the rotogravure cylinder is rotated by a rotational drive at a constant rotational speed and is processed by a laser light source so that wells are produced in its surface. The laser beam emitted as a continuous wave is pulsed by a laser control and is controlled in its power. A processing head, comprising a mirror, an optoacoustic modulator and an optical lens, is moved along the rotogravure cylinder. The pulsed laser beam is deflected by the mirror and adjusted by the optoacoustic modulator to correspond to the rotational speed, and directed in a specific processing mode onto the surface of the rotogravure cylinder. The optoacoustic modulator is likewise controlled by the laser control. It is pointed out specifically that it is hardly possible to carry out processing of adjacently located wells since breaches to the adjacent well can occur due to the intense local heating of the cylinder surface. For this reason, a processing mode is proposed, in which the laser beam is deflected by the optoacoustic modulator in such a way that, for example, starting from a hollowed-out well, firstly two intended wells are missed out forwards and the following well is hollowed out, and then two intended wells are missed out backwards and the following well is hollowed out. The hollowed-out wells have thus cooled down sufficiently to produce an adjacent well without breaches in the wall. In the event of the energy being insufficient to hollow out a relatively large well, the laser beam is directed onto it again subsequently after cooling. The person skilled in the art can assume from all these tasks that the rotational speed of the rotogravure cylinder must be relatively slow and the processing time for an individual well must be relatively long.
The present invention is based on the object of specifying a method and a device for producing wells in the surface of a rotogravure cylinder, which allow far more rapid processing of directly adjacent wells.
SUMMARY OF THE INVENTION
The above and other objects and advantages of the present invention are achieved by a method and apparatus wherein a pulsed laser beam is directed into an optoacoustic modulator, which deflects the laser beam by diffraction into the optical axis of a lens via an optical waveguide. From the lens, the beam is directed onto the surface of a rotating rotogravure cylinder to produce wells in the surface.
The invention is based on the knowledge that the power of the laser light source may be adjusted in such a way that the maximum volume needed for a well can be removed using a single laser beam pulse with a short pulse length. To remove a lesser volume of a well, the energy required to do so is adjusted by an optoacoustic modulator, i.e. the intensity of the laser beam pulse is defined on the basis of the electrical RF power applied to the modulator. This type of power control is far faster than the conventional type with an electromechanical or optoelectrical device which has a delayed response time and functions less precisely at higher speeds.
BRIEF DESCRIPTION OF THE DRAWINGS
Some of the objects and advantages of the present invention having been stated, others will appear when the following description is considered together with the accompanying drawings, in which:
FIG. 1 shows a laser engraving machine with a rotogravure cylinder to be processed with a laser light source;
FIG. 2 shows a laser engraving machine with a rotogravure cylinder to be processed with two laser light sources;
FIG. 3 shows a perspective illustration of an optoacoustic modulator;
FIG. 4 shows a diagrammatic illustration to explain the functioning of the optoacoustic modulator;
FIG. 5 shows an illustration of a travelling sound field and a laser beam pulse over time; and
FIG. 6 shows an illustration of the laser pulses of the two laser light source
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Brockelt Andreas C.
Frauchiger Jakob
Hennig Guido
MDC Max Datwyler Bleienbach AG
Mills Gregory L.
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