Electric heating – Metal heating – By arc
Patent
1981-01-07
1983-03-29
Evans, F. L.
Electric heating
Metal heating
By arc
350 68, 350486, 219121LT, 219121LW, G02B 2717, B23K 2700
Patent
active
043784801
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention concerns a device for optical chopping of a laser beam into discrete light pulses incident sequentially and repeatedly on a number of target points.
With the use of lasers for the treatment or machining of substrates, the problem of a simultaneous or nearly simultaneous incidence on the substrate in several target zones often arises. The application of several lasers as a rule is impossible for reasons of cost and space. A division of the beam by a so-called beam splitter is unfavorable because the resulting partial beams have a correspondingly diminished intensity which is not sufficient for certain machining processes and the split beams furthermore exhibit changing and in any case different intensities.
If laser beams are used, e.g. for the perforation of paper, a certain, relatively high and constant intensity of the laser beam performing the perforation must be assured in order to obtain a uniform size and quality of the perforations. In that case, beam splitting would be unfavorable for the reasons mentioned above.
A device for optical chopping of a laser beam is already known in which a continuous laser beam is introduced into an optical mirror system consisting of several consecutive rotating disks exhibiting reflecting and transmitting segments. The system thus generates a large number of light paths formed by the different combination of reflecting and transmitting segments. The beam introduced into the system is guided into the different light paths in steps according to the respective angular position of the disks and in this process, the beam is successively incident on different target points. Such an arrangement makes it possible to provide a paper web passing through the system at high speed with rows of perforations located transverse to the machine direction. The known device has several disadvantages, however. Since only a limited number of perforation combinations find space on the disks, it is not possible to realize an arbitrarily high perforation frequency. Since the beam paths have different lengths, this gives rise to focusing difficulties on the substrate.
This invention provides improved apparatus of the type described above which will furnish the highest chopping frequency, but at the same time is simple in structure and contains only a minimum of moving parts.
SUMMARY OF THE INVENTION
Thus, according to the invention, the laser beam, focused by a first collecting lens, is incident on the rotating mirror and then intermittently sweeps a first lens system consisting of several collecting lenses of equal focal length. The distance of the first lens system to the rotating mirror corresponds to the focal length of the individual lenses. The first system of lenses is followed by a row of focusing lenses, of which each is assigned to one of the lenses of the first system and which focus the parallel light beam on a substrate, for example, a moving paper web. As long as the beam sweeps a lens of the first system, the intensity remains constant in the focus of the respective focusing lens. At the moment when the beam deflected by the rotating mirror reaches the next lens of the first lens system, it jumps to the focal point of the next focusing lens. The full intensity of the original laser beam is available in each focusing point. If a polygonal mirror with a suitably large number of faces and high speed of rotation is used, it is possible to reach frequencies higher than those attainable with known devices, so that when the device is used to perforate cigarette paper, for example, the speed-determining step is the technically realizable paper feed rather than the perforation frequency. A particularly surprising finding in the invention is that only a single rotating part, i.e. the polygonal mirror, is necessary in order to realize the extremely high chopping frequencies.
Further objects, features and advantages of the present invention will become apparent from a consideration of the following description, the appended claims and the acco
REFERENCES:
patent: 4131782 (1978-12-01), Einstein et al.
patent: 4265254 (1981-05-01), Koch et al.
Grimm; IBM Technical Disclosure Bulletin, vol. 14, No. 9, Feb. 1972, pp. 2641 and 2642.
IBM Technical Disclosure Bulletin, vol. 15, No. 2, Jul., 1972, p. 495-5.
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