EP2502037A1

EP2502037A1 - Method and device for determining a characteristic of a beam, by means of a rotating disc, in particular in a laser processing machine

Info

Publication number: EP2502037A1
Application number: EP10800787A
Authority: EP
Inventors: Andreas Lüdi; Christoph Fahrni
Original assignee: Bystronic Laser AG
Current assignee: Bystronic Laser AG
Priority date: 2009-11-19
Filing date: 2010-11-18
Publication date: 2012-09-26
Also published as: WO2011061706A1; CN102667428A; WO2011061706A4

Abstract

A method is indicated for measuring a characteristic of a beam (A, A1.. A3) by means of a disc (3, 3a..3f ), which is rotatably mounted in a device (1) for determining this characteristic in a beam course of the beam (A, A1.. A3) in front of a sensor (6) for measuring an intensity of the beam (A, A1.. A3). For this, the disc (3, 3a..3f) is impermeable to the beam or at least weakens the beam and comprises at least one elongated region (B1.. B7) which is permeable to the beam or at least has higher permeability to the beam compared with the remainder of the disc (3, 3a..3e). By means of this device, an intensity impulse of the part of the beam (A, A1.. A3) impinging on the sensor (6) on rotation of the disc (3, 3a..3e) is detected. The sought characteristic is then determined by application of reconstruction- or modelling methods suitable for inverse problems on the detected intensity impulse. Furthermore, a device (1) and a disc (3, 3a..3f) are indicated for carrying out the method.

Description

Method and device for determining a characteristic of a beam, by means of a rotating disc, in particular in a laser

processing machine This application claims benefit of priority to prior U.S. provisional application no. 61/263,352 filed on November 21, 2009, and as a non-provisional thereof; this application also claims benefit of priority to prior Swiss national

application no. 1789/2009 filed on November 19, 2009; the entirety of Swiss application no. 1789/2009 and of U.S.

application no. 61/263,352 are expressly incorporated herein by reference in their entirety, for all intents and purposes, as if identically set forth herein.

The invention relates to a method for measuring a

characteristic of a beam by means of a disc, which is

rotatably mounted in a device for determining this

characteristic in a beam course of the beam in front of a sensor for measuring an intensity of the beam,

wherein the disc is impermeable to the beam or at least weakens the beam and

wherein the disc comprises at least one elongated region which is permeable to the beam or at least has a higher permeability to the beam compared with the remainder of the disc .

Furthermore, the invention relates to a disc which is

disposed to be arranged rotatably mounted in a device for determining a characteristic of a beam in a beam course of the beam, in front of a sensor for measuring an intensity of the beam,

wherein the disc is impermeable to the beam or at least weakens the beam, wherein the disc comprises several elongated regions which are permeable to the beam or at least have a higher permeability to the beam compared with the remainder of the disc,

- wherein a first region crosses a first radial vector, originating from the rotation point of the disc, at a radial distance in a first direction in relation to the first radial vector and

wherein a second region crosses a second radial vector, originating from the rotation point of the disc, at the same radial distance in a second direction in relation to the second radial vector, which is different from the first direction . In addition, the invention relates to a device for

determining a characteristic of a beam, with a sensor

arranged in the beam course of the beam for measuring an intensity of a beam characteristic and with a rotatably mounted disc arranged in the beam course in front of the sensor.

Finally, the invention relates to a laser processing machine having such a device, wherein a laser beam is provided as the beam for material processing.

It is frequently necessary to determine a characteristic, for example the intensity distribution, of a beam emitted from a beam source, in order for example to establish its

suitability for particular applications, to adapt the beam to a preferred distribution by means of the measured intensity distribution or in order to simply examine the beam as such. Some possibilities are known from the prior art in this respect . For example, US 4,828,384 A describes in this respect a method for measuring the intensity distribution of a high- energy laser beam. Here, a portion of the beam is coupled out by means of a displaceable slit diaphragm. The remaining portion passes through several spiral-shaped slits, and a rotating chopper disc (also designated a "chopper") , and finally impinges onto a heat-sensitive detector.

Furthermore, DD 249 759 Al discloses a method for measuring the intensity distribution of a light beam, in which the beam passes through a rotating disc with a spiral-shaped slit, and a rotating slit diaphragm. The spiral diaphragm rotates here by a whole-number multiple more quickly than the slit

diaphragm. The beam which is thus obtained is evaluated by two-dimensionally aligned light-sensitive elements.

Moreover, JP 63085319 A discloses a device for measuring the intensity distribution of a beam by means of a slitted disc which has two straight slits at right-angles to each other.

Finally, DE 37 06 217 C2 discloses a method for measuring a laser beam in which a portion thereof is coupled out and directed to a pyroelectric detector. Previously, however, the coupled-out beam passes through openings which are arranged at different heights on a rotating cylinder jacket.

The known devices are in most cases technically complex in structure. For example, in US 4,828,384 A a displaceable slit diaphgram is required. In DD 249 759 Al, on the other hand, several rotating diaphragms are provided, which are each driven by a motor. DE 37 06 271 C2 requires, moreover, a cylinder jacket provided with holes, which is comparatively difficult to produce. In JP 63085319 A, finally, a detection of the beam is necessary before the latter passes through the slitted disc. In addition, the slitted disc for the

measurement method disclosed in JP 63085319 A must be large compared with the beam diameter, which makes the apparatus more complex and also more voluminous.

The problem on which the present invention is based consists in providing an improved or alternative method for

determining a characteristic of a beam, a disc and a device for this, and a laser processing machine having such a device .

According to the invention, this problem is solved by a method of the type named in the introduction comprising the steps:

detecting an intensity impulse by means of the part of the beam impinging onto the sensor through the at least one region on rotation of the disc,

determining the sought characteristic by the application of reconstruction or modelling methods, suitable for inverse problems, on the detected intensity impulse.

According to the invention, this problem is additionally solved by a disc of the type named in the introduction, in which the first region is aligned along a spiral and the second region is aligned along a further spiral or along a straight line.

The problem according to the invention is further solved by a device for determining a characteristic of a beam of the type named in the introduction, in which a disc according to the invention is arranged and rotatably mounted in the beam course in front of the sensor. Furthermore, the problem according to the invention is solved by a laser processing machine with a device according to the invention for determining a characteristic of a beam, wherein a laser beam for material processing is provided as a beam.

Within the framework of the invention, "beam" means any kind of beam, but in particular massless beams or substantially massless beams such as light beams and laser beams.

Basically, however, beams with mass can also be provided as a beam, in so far as the entire construction is equipped for the kinetic energy of the said beam. Therefore, in particular electron beams, proton beams can be provided as beams with mass .

"Intensity distribution" is deemed to be any two- or three- dimensional distribution of the intensity of a beam

characteristic of a beam. In two-dimensional distributions, the invention relates in particular to a set of one- dimensional distributions which are determined in different directions transversely through one and the same beam.

"Characteristic of a beam" is deemed to be any characteristic which can characterize a beam. For example, this is the intensity of the light in a differential or sufficiently small region of a light- or laser beam. In addition to the intensity in the sense of an energy flow, i.e. the energy per time and area, for example, however, the intensity

distribution of one or more colours can also be determined in a light beam.

"Intensity impulse" is understood to mean the path of the intensity of the beam impinging on the sensor, which occurs on rotation of the disc and hence on movement of the

elongated region through the beam. The intensity can be received here for example as a function of a time, of an angle or of a length.

"Sensor" is any element for detecting the desired beam characteristic, for detecting the light intensity, for example a photodiode in the visible wave length range or a pyrodetector in the infrared wave length range.

The "beam course" comprises the entire path on which the beam exists, irrespective of whether it is deflected, focussed or otherwise influenced by suitable measures. An "elongated region" is a region, the length of which is greater than its width. Therefore, an elongated region in the sense of the invention also has a central axis which crosses a radial vector, in a particular direction, originating from the rotation point of the disc. For these purposes, the central axis can also be regarded as a vector, in particular as a vector directing from the centre of the disc, or respectively a vector which has at least one such directing portion . "Impermeable to the beam" means a degree of transmission of zero, irrespective of whether the beam is absorbed or reflected. "Weakening the beam" accordingly designates a degree of transmission greater than zero, "permeable to the beam" designates a degree of transmission of one.

Preferably, the regions permeable to the beam or regions having a permeability to the beam which is greater than in the case of the remainder of the disc, are formed by holes in the disc. Alternatively, it is conceivable that the disc is constructed from materials having a different degree of transmission. In the case of light, differently transparent plastics come into consideration for this. It is also

conceivable that a layer which is impermeable to the beam or which weakens the beam is applied onto a carrier which is permeable to the beam.

For light- and laser beams, therefore, in particular metal discs with holes, transparent plastic discs with an opaque overprint and discs which are constructed from differently transparent materials, come into consideration. The named examples are in no way restrictive and are intended merely to illustrate the invention. The specialist in the art will readily discover the appropriate structure for a particular type of beam here.

Depending on the embodiment, the disc can accordingly also be regarded as a "slitted disc", "perforated disc", "diaphragm" or the special case of a "filter".

Moreover, it is to be stated at this point that the disc according to the invention in no way has to be circular or (comparatively) thin, although this is a preferred

embodiment. In the sense of the invention, the term "disc" is to be understood to be any type of body which on rotation allows a beam, directed onto the body, to pass through in differing intensity, which also includes the complete cutting off of a beam. In particular, therefore, irregular and angular bodies are also to be understood in the sense of the invention, and "thick" bodies, i.e. bodies, the extent of which is relatively great in the rotation axis. At this point it is further noted that the equipment known from the prior art operates according to the travelling hole measurement principle. The device according to the invention does not operate according to this principle and is therefore only comparable to the known devices to a limited extent. The advantages of the invention compared with the travelling hole method are the simpler mechanical construction and, along with this, lower manufacturing costs and a higher possible chronological resolution.

Advantageous embodiments and further developments of the invention will be apparent from the sub-claims and also from the description, viewed together with the figures of the drawings .

It is advantageous if, as reconstruction- or modelling methods, one or more of the group: regression analysis, polynomial function, neuronal networks is/are provided. These methods have proved to be particularly advantageous for the solving of inverse problems, for which reason the inverse problem occurring in the determining of a characteristic of a beam can be converted into practice with comparatively low technical and financial expenditure. It is particularly advantageous if the method according to the invention comprises:

at least one regression step, in which function

parameters of a function are determined by means of at least one intensity impulse of a beam with a known characteristic as independent variable and with the said characteristic as dependent variable, and

a determining step, in which the function with

determined function parameters contains an intensity impulse of a beam with an unknown characteristic as independent variable .

In this variant of the invention, attempts are made by means of a regression method to deduce the sought beam

characteristic from a measured intensity impulse or from several measured intensity impulses. Basically, in the case of a regression, a possible correlation is examined between data points with an assumed inner correlation. Here, the data points have no uncertainties or measurement errors. They are assumed to be constant and fixed. With an assumed continuous function, an examination is made as to how much the data points can be described with the assumed function.

It is particularly advantageous if the method according to the invention comprises

at least one analysis step in which coefficients of a Taylor polynomial are determined by means of at least one intensity impulse of a beam with a known characteristic as independent variable and with the said characteristic as dependent variable and

a determining step in which the Taylor polynomial with determined coefficients receives an intensity impulse of a beam with an unknown characteristic as independent variable. In this variant of the invention, it is therefore attempted to deduce the sought beam characteristic by means of an approximation polynomial from a measured intensity impulse or from several measured intensity impulses. Basically, in a function adaptation ("fit") , a function is adapted to a predetermined course, wherein measurement errors or

uncertainties of the measurement points are taken into consideration. The resulting function parameters are then, like the measurement values, afflicted with an uncertainty. A frequently applied fit is the smallest square method, wherein a Gauss-distributed measurement value uncertainty is assumed. The result of a fit is an array of curves in which the actual functional correlation lies with a certain probability. It is particularly advantageous if the method according to the invention comprises

at least one training step, in which the neuronal network receives at least one intensity impulse of a beam with a known characteristic as input and the said

characteristic as output and

a determining step, in which the trained neuronal network receives an intensity impulse of a beam with an unknown characteristic as input.

In a neuronal network, it is attempted to model a function correlation by means of cross-linked cells. Originally, the cross-links of the cells are of equal value; the connections are only weighted differently during a "training" of the neuronal network. After completion of the training, the neuronal network behaves similarly to a predetermined, trained correlation, owing to the different weightings. For example, at the output of the neuronal network, an intensity distribution of a beam can be picked up, when at the input an intensity impulse, received from the sensor, is fed in and the neuronal network has previously been trained with this correlation.

It is particularly advantageous if the regression step, analysis step or training step takes place within the

framework of a computer simulation. In this way, the sought correlations between a characteristic of a beam and of an intensity impulse received by the sensor can be modelled particularly accurately, because in a simulation environment, no unknown interfering factors affect the result. However, it is also particularly advantageous if the

regression step, analysis step or training step takes place on a real device. In this way, the sought correlations between a characteristic of a beam and of an intensity impulse received by the sensor can be modelled in a manner which is particularly close to reality.

In a further particularly advantageous variant of the

invention, the regression step, analysis step or training step is carried out both on a real device and also within the framework of a computer simulation. The results are then compared or brought together. In this way, a good compromise can be achieved between accuracy and closeness to reality of the regression or respectively modelling.

It is advantageous if, as sought characteristic of the beam, one or more of the group: intensity distribution of the beam, average diameter of the beam, position of the mid-point of the beam, position of the focal point of the beam, symmetry of the beam, proportion of a colour in the beam and/or proportion of a laser mode is/are provided. These are

frequently required parameters of a beam, for example for laser cutting or laser welding (except a colour proportion of a beam, because the laser beam is monochrome) .

It is advantageous in this connection if as the sought characteristic a portion at least of one laser mode of the group: Gauss, donut or top hat is provided. When the portions of the said (or else further) modes of the laser beam are known, then the intensity distribution of the sum beam can also be reconstructed or at least approximated. It is particularly advantageous in this connection in

addition if as the sought characteristic a portion at least of one laser mode is provided and the steps:

detecting a first width of the intensity impulse at a first intensity level,

detecting a second width of the intensity impulse at a second intensity level

determining the portion of the at least one laser mode by means of the determined first and second width

are comprised.

In this variant of the invention, the determining of the sought portions is reduced to the determining of the width of the intensity impulse, which occurs on travelling through the elongated region by the beam. The width is measured here at two different intensity levels. The determining of mode portions is therefore particularly simple.

A particularly advantageous method is provided, when the disc comprises several elongated regions,

- wherein a first region crosses a first radial vector, originating from the rotation point of the disc, at a radial distance, in a first direction in relation to the first radial vector and

a second region crosses a second radial vector,

originating from the rotation point of the disc, at the same radial distance in a second direction in relation to the second radial vector, which is different from the first direction .

By the regions arranged in different directions on the rotatably mounted disc, it is possible to scan a beam by means of a single disc in different directions. Despite the simplicity of the construction, a beam can therefore be scanned in different directions. It is also particularly advantageous in this connection if several different intensity impulses resulting from the regions are drawn upon to determine the sought

characteristic. In this way, the sought characteristic of a beam can be determined more precisely when the latter is, for example, unsymmetrical . For example, in this way a spatial intensity distribution can be determined, for example the unsymmetrical (elliptical) intensity distribution of a diode laser.

A method is advantageous, comprising the steps:

a) Detecting two intensity impulses by means of the first and second region on rotation of the disc,

b) Determining a width of the intensity impulse based on the detection through the first and/or second region,

c) Determining a distance between the intensity impulse based on the detection through the first region and the intensity impulse based on the detection through the second region and d) Calculating the radius of the beam and the distance of this beam from the rotation point of the disc by means of the determined width and the distance.

In this variant of the invention, the determining of the radius of the beam (or its diameter) and of the distance of this beam from the rotation point of the disc is reduced to the determining of the width of the intensity impulse which occurs on travelling through the elongated region by the beam. For this, the width at least of one impulse and the distance to a further impulse is measured. The determining of beam radius (beam diameter) and beam position is therefore particularly simple. Of course, the method is not restricted to the utilization of two intensity impulses, but rather it can also be expanded to the processing of more than two impulses .

It is advantageous if the first and the second direction enclose a right-angle, when the second direction together with the second radial vector is rotated about the mid-point so that the first and the second radial vector are congruent. In this embodiment, the beam is travelled through from the first and second region in directions which are substantially orthogonal to each other, whereby a spatial intensity

distribution of a beam can be readily detected.

It is also advantageous if the first and the second direction are different in relation to the respective radial vector in each radial distance. According to this variant, curved regions are provided. By corresponding arrangement, an improved detection of the intensity distribution can be achieved . It is, furthermore, advantageous if a region is aligned along a straight line. Straight regions can generally be produced particularly easily, for which reason the production of the disc as a whole is simplified. Moreover, it is advantageous if n regions are aligned along n straight lines and cross associated radial vectors,

originating from the rotation point of the disc, at the same radial distance in n different directions. In this variant of the invention, a plurality of regions (namely n regions) is aligned along a plurality of differently oriented straight lines. In this way, the beam is travelled through by each straight line in a different direction. A beam characteristic, e.g. a spatial intensity distribution of the beam, can therefore be measured particularly efficiently.

In an advantageous variant of the disc according to the invention, a region is aligned along a spiral. When the spiral is sufficiently flat, the beam can be travelled through in a more or less radial direction.

It is also advantageous if n regions are aligned along n spirals and cross associated radial vectors, originating from the rotation point of the disc, at the same radial distance in n different directions. In this variant of the invention a plurality of regions (namely n regions) are aligned along a plurality of differently oriented spirals. In this way, the beam is travelled through by each spiral in a different direction. A beam characteristic, e.g. a spatial intensity distribution of the beam, can therefore be measured

particularly efficiently. It is advantageous in addition if at least one region is aligned along a spiral and at least one region is aligned along a straight line. In this way, the beam can be travelled through once in a more or less radial direction and by means of the straight region once in a more or less tangential direction - respectively in relation to the mid-point of the disc .

It is, moreover, advantageous if the spiral is Archimedic. The radius of Archimedic spirals increases proportionally to its rotation angle. In this way, the spiral-shaped region travels uniformly through the beam with uniform rotation of the disc. It is particularly advantageous if the spiral is logarithmic. A logarithmic spiral is a spiral which on each revolution increases the distance from its mid-point (its pole) by the same factor. Each straight line through the pole always intersects the logarithmic spiral at the same angle. The direction in which a logarithmic spiral travels through the mid-point of a beam is therefore always identical,

irrespective of where the beam is positioned and how large it is .

It is particularly advantageous here if the pitch of a logarithmic spiral for the first region is k=l and the pitch of a logarithmic spiral for the second region is k=-l.

Therefore, the two regions intersect a radial vector through the centre of the beam between + 45° and - 45°. The two regions therefore travel through the beam at least in its centre in orthogonal directions. This applies to any

positions and sizes of the beam. It is particularly advantageous in addition if the disc has a straight third region which is radially aligned. In this variant of the invention, the disc therefore has two spiral- shaped regions aligned with respect to each other, and a radially aligned straight region. Advantageously, the spiral- shaped regions are aligned along logarithmic spirals with the pitches k=l and k=-l, but other pitches and spiral forms (e.g. Archimedic) are also possible.

If sensors are used which detect beam flow changes (in the infrared range e.g. pyrodetectors) , then it is advantageous if a chopper disc is additionally arranged in the beam course, which periodically interrupts the beam. It is advantageous if a shared drive is provided for the disc and the chopper disc. Usually, a fixed rotation rate ratio is provided between the disc according to the invention and the chopper disc, for which reason it is also advantageous to provide a shared drive, for example an electric motor with a corresponding gear.

If the laser beam which is to be measured has a wave length in the infrared wave length range, such as for example the CO₂ laser, often used in material processing, at 10.6 μιτι, then advantageously a pyrodetector, likewise operating in the infrared wave length range, can be drawn upon for measuring the laser beam. Depending on the intensity distribution of the laser beam, different suitabilities result for different purposes, for which reason the knowledge of the said

intensity distribution is significant.

An advantageous type of construction of a laser processing machine according to the invention is present if a beam- splitting element is provided in the beam course of the laser, and a first part of the laser beam is guided onto the processing site and a second part is guided to the sensor, wherein the disc is arranged between beam-splitting element and sensor. In this way, a portion of the laser beams can be "branched off" for measurement purposes. The pure analysis of the laser beam and also the active influencing of the laser beam on the basis of the measurement result, i.e. the

regulating of the laser beam, are both possible. For this, the laser beam can be influenced with elements known per se, for example with optical lenses, mirrors, diaphragms, optical grids etc. Partially permeable mirrors and prisms come into consideration in particular as beam-splitting elements. Finally, it is particularly advantageous if the disc is equally far away from the beam-splitting element as the site at which the sought characteristic of the beam is to be determined, from the beam-splitting element. In so far as no beam-distorting elements are incorporated into the beam course, in this way it can be ensured that the intensity distribution which is of interest is measured. A processing site can be provided for example as the "site at which the sought characteristic, e.g. an intensity distribution of the beam, is to be known".

At this point it is noted that the invention is suited in principle not only for laser processing machines, but for all kinds of beam processing machines, for example also for electron beam processing machines.

Finally, it is pointed out that the variants named for the disc according to the invention, for the device according to the invention and for the laser processing machine according to the invention, and advantages resulting therefrom, relate equally to the method according to the invention and vice versa .

The above embodiments and further developments of the

invention can be combined in any desired manner.

The present invention is explained in further detail below with the aid of the example embodiments indicated in the diagrammatic figures of the drawings, in which are shown:

Fig. 1 a diagrammatically illustrated device according to the invention for determining an intensity distribution of a beam; Fig. 2 a top view onto a disc according to the invention with two regions, permeable to the beam, each aligned along a straight line;

Fig. 3 a diagrammatic illustration of how the regions which are permeable to the beam travel through the beam; Fig. 4a an intensity impulse of the beam received in a first direction;

Fig. 4b an intensity impulse of the beam received in a second direction;

Fig. 5 a diagrammatically illustrated chopper disc;

Fig. 6 a disc according to the invention with regions permeable to the beam, which are aligned along several differently oriented straight lines;

Fig. 7 a disc according to the invention, with a

straight and a spiral-shaped region permeable to the beam;

Fig. 8 a diagrammatic illustration in which direction a logarithmic spiral crosses differently sized and differently positioned beams; Fig. 9 a disc according to the invention with two

regions permeable to the beam, which are aligned along two logarithmic spirals which are

orthogonal to each other; Fig. 10 a disc as illustrated in Fig. 9, only with an additional straight, radially-running region;

Fig. 11 a cut-out from a laser processing machine with a device according to the invention;

Fig. 12 two intensity impulses received by a device

according to the invention with two regions permeable to the beam according to Fig. 9;

Fig. 13 a flow diagram by way of example, which

illustrates a possible process flow and

Fig. 14 a code segment, which shows a section of an

example process flow appropriate to Fig. 9 and 12.

In the figures of the drawings, identical and similar parts are given the same reference numbers, and elements and features which are similar in function - in so far as is not otherwise stated - are given the same reference numbers, but different indications.

Fig. 1 shows a device 1 for determining an intensity

distribution of a beam A, which is emitted from a beam source 2. A rotatably mounted disc 3 is arranged in the beam course. By means of a lens 4, the beam A is concentrated after passing through the disc 3, and after passing through a chopper disc 5 it impinges onto a sensor 6 for measuring an intensity of a beam characteristic. In this example, the disc 3 and the chopper disc 5 are driven by a shared drive 7. Fig. 2 shows an example disc 3a, now in top view. The disc 3a itself is impermeable to the beam or at least weakens the beam and has a first elongated region Bl and a second

elongated region B2, which are permeable to the beam or at least have a higher beam permeability compared with the remainder of the disc 3a. The first region Bl crosses a first beam si, originating from the rotation point M, at a radial distance r in a first direction in relation to the first radial vector si. In this example, the first region Bl crosses the first radial vector si from interior left to exterior right.

In addition, the second region B2 crosses a second radial vector s2, originating from the rotation point M of the disc 3a, at the same radial distance r in a second direction in relation to the second radial vector s2, which is different from the first direction, namely from interior right to exterior left. The function of the arrangement illustrated in Figures 1 and 2 is now as follows:

By rotating the disc 3, 3a, the light beam A passes once through the first region Bl, once through the second region B2. With regard to the light beam A, it can also be stated that the first region Bl is moved once, and the second region B2 is moved once therethrough. Fig. 3 shows in this respect the beam A in cross-section and the two regions Bl and B2 together with their movement direction. The following

explanations are based on this viewpoint or respectively this reference system. On passing through the first region Bl, a first intensity impulse of the beam A is now received. Fig. 4a shows the result, namely a relatively narrow distribution, similar to Gauss (Fig. 4a and also Fig. 4b show the intensity I over the rotation angle Φ of the disc 3, 3a) . On passing through the second region B2, a second intensity impulse of the beam A is now received. Fig. 4b shows the result, namely a relatively wide intensity distribution. From the two results, first simple conclusions can be drawn, namely that the beam A has a rather elongatedly formed intensity distribution. In simple approximation, an intensity impulse namely conveys a first impression of a one-dimensional section through the (spatial) intensity distribution. Nevertheless, it must be taken into account that owing to the length of the regions Bl and B2, the beam A is integrated over its width on detecting of an intensity impulse, whereas a one-dimensional intensity distribution represents a cross-section through the beam A.

At this point, it is noted that a one-dimensional profile of the beam A is not obtained directly when a region Bl, B2 travels over the beam A. This is because in the detected signal of the regions Bl, B2, information of the beam extent is also contained orthogonally to the movement direction of the regions Bl, B2 (this is different in measurement methods known from the prior art by means of a travelling hole) .

However, a one-dimensional profile can be recovered, assuming for example that the beam A is circularly symmetrical. The signals of both regions Bl, B2 can also be used, in order to recover the one-dimensional beam profile.

The obtained result can now be used for example to influence the beam A at the source 2 itself or by means of elements, not illustrated, in the beam course (e.g. lenses, mirrors, diaphragms, and other adaptive elements) until the measured intensity distributions correspond to the desired intensity distributions. In particular, in this way a rotationally symmetrical intensity distribution can be set.

The quantitative knowledge of the intensity distribution or individual characteristics of the intensity distribution (e.g. beam radius, site of the beam focal point etc.) of the beam A are generally not able to be read directly from the measured signals. The two-dimensional intensity distribution of the beam A is indeed projected through the movement of the region Bl, B2 onto one-dimensional intensity impulses. With this projection, information which relates to the second dimension of the intensity distribution is largely lost.

Several characteristics of a beam A can nevertheless be determined relatively precisely, in particular when the beam A is symmetrical. Regression analyses known per se from the literature, neuronal networks and other mathematical and numerical recovery algorithms are suitable to recover the sought beam characteristic ( s ) . This does indeed mean

additional software-technical and mathematical expenditure compared with, for example, a travelling hole measurement system, but this is more than compensated for by the simple mechanical structure of the device according to the

invention. A simple example of a recovery algorithm is presented further below in the course of the description of Fig. 12.

Viewed mathematically, the task of reconstruction corresponds to an inverse problem, because the causes forming the basis of the effect (here of the sought beam characteristic) can be deduced from the observed effect of the system (here of intensity impulses) . Contrary to the forward problem (the effect results from the cause) , inverse problems are often very difficult to solve or are even not able to be solved. Nevertheless, in the present invention this route, which at first sight appears to be difficult, is taken. Alongside this is the surprisingly simple structure and, connected

therewith, the lower production costs of the measurement device 1 compared with devices for direct measurement (e.g. travelling hole method) . However, a model representation is also necessary for the method according to the invention, i.e. the mathematical correlation of cause to effect should be known at least in a rough outline. In actual terms, this means that the forms of the regions Bl, B2 should be known mathematically. An

exception to this exists in the case of neuronal networks which acquire the said correlation during a training step as it were "automatically".

Generally, artificial neuronal networks (ANN) are frequently used when in the case of inverse problems a reconstruction by means of regression analysis is difficult. Neuronal networks are able to also acquire complicated non-linear functions via a training step. Here, by iterative or recursive procedures, it is attempted to determine from existing input- and desired output values all the correlation between input- and output values. In the actual case, for example, a plurality of beams A with variations in diameter, beam position, symmetry, mode mixtures etc. is calculated and represented via discs 3 on intensity impulses, whereby the neuronal network can be trained. This can either take place in a pure simulation environment or else also on the real device 1. Advantageously a functional correlation, with the application of a neuronal network, as already mentioned neither has to be known or assumed .

To increase the accuracy, in particular in the case of unsymmetrical beams A, by means of the regions Bl, B2

different intensity impulses are established from different directions of the beam A. Subsequently, different

characteristics of the beam A can be determined from these intensity impulses, for example the surface structure of the intensity distribution of the beam A, which is not directly detected, can be reconstructed.

The lens 4, the chopper disc 5 and the drive 7 constitute - although also advantageous - only optional elements of the device 1. The lens 4 serves in a manner known per se to concentrate the beam A onto the sensor 6. The chopper disc 5 serves to chop the beam A. This is advantageous particularly when a detector, e.g. pyrodetector, is provided as sensor 6, which detects a beam flow alteration. In the case of sensors 6 which can detect the beam flow directly (e.g. a

photodiode) , the chopper disc 5 can also be dispensed with.

The chopper disc 5 rotates at a rotation rate which is a whole-number multiple of the rotation rate of the disc 3, 3a. For example, with a chopper disc which has 30 holes and rotates 40 times faster than the disc 3, 3a, 720 measurement points can be received per revolution of the disc 3, 3a.

Therefore, a measurement point is received every 0.5°. Owing to the fixed rotation rate ratio between disc 3, 3a and chopper disc 5, it is also advantageous to provide a shared drive 7, for example an electric motor with corresponding gear. Of course, the rotation rates can, however, also be realized with separate drives and with a corresponding rotation rate regulation.

Fig. 5 shows an example chopper disc 5. Here, the internally arranged regions, permeable to the beam, for interrupting the beam A, and the externally arranged, optional markings or respectively holes for determining the position of the chopper disc 5 are provided by means of a light barrier. The regions Bl and B2 of the disc 3a illustrated in Fig. 2 intersect at an acute angle. This is in no way compulsory for the invention. Flat crossing angles are also conceivable. Moreover, it is particularly advantageous if the two regions Bl and B2 intersect at right-angles, because then also intensity distributions of the beam A are detected on two axes arranged at right-angles to each other.

The disc 3a illustrated in Fig. 2 now only permits deductions as to be intensity distribution in two axes, however the principle according to the invention can also be expanded to several axes if the disc 3a is equipped for this with

additional, but respectively differently aligned regions. In this way, a very precise statement can be made as to the intensity distribution of the beam A. Fig. 6 shows a possible example for this with a total of 7 regions B1..B7, which cross a radial vector, originating from the mid-point M and respectively associated, at the same radial distance in different directions. Furthermore, the disc 3b of Fig. 6 has in the outer region an optional marking for a light barrier for determining position. In this way, not only can the distance of the beam A from the rotation point M of the disc 3b be determined, but - as in fact in this special variant the position of the disc 3b in the space is now also known - the position of the beam A is able to be determined absolutely in 2 dimensions on the measurement plane. Of course, the disc 3a of Fig. 2, the disc 3c of Fig. 7 and the disc 3e of Fig. 9 and other conceivable variants can have such a marking for determining position. Finally, it is also pointed out that the regions B1..B7 are not necessarily straight, but may also be curved or may have curved sections.

In the above observations, it was not taken into

consideration that the regions Bl and B2 actually do not move on straight lines through the beam A, i.e. are not moved in a translatory manner, but rather, owing to the rotation of the disc 3, 3a, in fact rotate through the beam A. For very small beam diameters or very large distances from the mid-point M, this can, however, be disregarded. If these conditions do not apply or very high demands are made of the beam measurement, then the rotation of the regions Bl and B2 can be taken into consideration in the evaluation. In particular, the method according to the invention makes possible the use of very small discs 3, 3a, the radius of which can lie in the region of the diameter of the beam A which is to be measured. Owing to the compact overall size, the device 1 can therefore for example also be arranged directly in the processing head of a laser processing machine.

It is also a problem that the beam A can be travelled through by the regions Bl and B2 only in a more or less tangential direction, but not in a more or less radial direction. A possibility for solving this problem consists in selecting a different form for the regions Bl and B2, namely regions Bl and B2 aligned along spirals. By the provision of

sufficiently flat spirals, the respective region travels more or less radially through the beam A. Archimedic spirals have proved to be particularly suitable for this, the radius of which increases proportionally to the rotation angle. In this way, the spiral-shaped region Bl, B2 travels with uniform rotation of the disc 3 uniformly through the beam A.

Fig. 7 shows a particularly advantageous variant of the invention, in which the first region Bl is arranged along a spiral (in particular an Archimedic spiral) and the second region B2 is arranged along a radially-running straight line. On rotation of the disc 3c, the first region Bl travels in a more or less radial direction, the second region B2 travels in a direction more or less at right-angles thereto, through the beam A. The second region B2 can also be deviated

somewhat with respect to a radial vector, in order to better approximate the said right angle. In the example shown, the second region B2 would therefore have to be inclined from interior right to exterior left. Finally, Fig. 7 also shows the radius rs of the beam A and its position, i.e. its distance rp from the mid-point M of the disc 3c.

In a further advantageous variant, the first region Bl is not arranged along an Archimedic spiral, but rather along a logarithmic spiral. A logarithmic spiral is a spiral which with each revolution increases by the same factor the

distance from its mid-point M, the pole. In the reverse rotation direction, the curve winds itself with a decreasing radius ever closer around the pole. Each straight line through the pole always intersects the logarithmic spiral at the same angle. Owing to this characteristic, one also speaks in terms of an equiangular spiral.

Therefore, the first region Bl always travels in more or less the same direction through the beam A, irrespective of how large the latter is and where the latter is positioned, because, as mentioned, a straight line through the pole (e.g. a radial vector through the centre of the beam A) always intersects a logarithmic spiral - differently from an

Archimedic spiral - at the same angle. Fig. 8 shows a disc 3d with several beams A1..A3 of differing size and in differing position. It can readily be seen that a logarithmic spiral always directs at the same angle through the centre of the beams A1..A3. In Fig. 7 the first region Bl could therefore advantageously also be arranged along a logarithmic spiral.

Fig. 9 now shows a further advantageous variant of the invention, in which for the pitch of the logarithmic spiral for the first region Bl k=l is selected and for the pitch of the logarithmic spiral for the second region B2 k=-l is selected. Thereby, the two regions Bl and B2 intersect a radial vector through the centre of the beam A at +45° and - 45°. The two regions Bl and B2 travel through the beam A therefore - at least in its centre - in orthogonal

directions. This applies for any positions and sizes of the beam A. In addition, the regions Bl and B2 - differently from in the case of the arrangement according to Fig. 7 - need approximately the same time (in the case of symmetrical beam A even exactly the same time) to travel through the beam A.

Fig. 10 shows an extension of the disc 3e shown in Fig. 9. In addition to the two regions Bl and B2 which are arranged along logarithmic spirals, the disc 3f comprises a straight and radially aligned region B3. As tests have shown,

characteristics of a highly asymmetrical beam A can be determined particularly well with such a disc 3f . Compared with the disc 3e of Fig. 9, which provides two intensity impulses, the disc 3f of Fig. 10 produces three intensity impulses. Consequently, three pulse widths and two distances between the pulses can now be determined (see also in this respect Fig. 12) . This results in an equation system with three equations, wherein the values of mean radius, ellipticity (ratio of the main axes) and beam position are determined from 5 measurement values by means of the least- square-fit method (which of course can also be applied in all the discs 3e..3f illustrated in the Figures) . Conventional mathematics software (e.g. Scilab, Matlab) can be used for this. It has been found that quadratic equations provide very precise results. An additional expansion of the algorithm is possible by the widths of the pulses being determined at at least two

heights, i.e. at at least two intensity levels. Thereby the pulse form enters into the evaluation, whereby it is made possible to make statements as to the mode composition of the beam A. Experimentally, the pulse width was determined at two intensity levels and as a result the percentage proportions of the Gauss, donut and top hat modes in the beam A were determined. In an analogous manner, further/other modes can also be taken into consideration.

Fig. 11, finally, shows a cut-out from a laser processing machine, in actual terms a beam-splitting element 8 in the beam course of the laser. A partially permeable mirror or a prism can be provided for example as beam-splitting element 8. A first part C of the laser beam A is guided onto the processing site and a second part D is guided to the device 1 according to the invention. The beam division takes place here so that the second part D is much smaller than the first part C (e.g. division of the beam A into 0.1% / 99.9%) . In this way it is achieved that the main part of the beam A is guided to the processing site. The second part D is scarcely of any consequence energetically and should also be selected so that the arrangement 1 according to the invention can not be adversely affected by the energy of the second partial beam D. In Fig. 11 the distance covered by the first part C is substantially equal in length and without beam-forming elements as the distance covered by the second part D between beam-splitting element 8 and disc 3 (not illustrated

explicitly here) . Preferably, the partial beams C and D do not pass through any further beam-forming elements, or respectively these are preferably taken into consideration arithmetically. One can therefore assume that the sought beam characteristic, e.g. the (relative) intensity distribution, is identical in the first part C and in the second part D. Of course, it is also conceivable that further beam-forming elements are additionally provided in the beam course. Important criteria of a laser cutting machine are cutting speed, cutting quality and reliability. The first two

criteria can be fulfilled as well as possible when the laser beam A can be adapted optimally to the material which is to be processed. This requires adaptive elements in the beam course (variable beam diameter) and if applicable adaptive elements in the resonator (intracavitary mode adaptation) . However, the more adaptive elements are used, the more likely also are possible misadj ustments thereof. The beam A alters over time solely though material ageing and the material- and adjustment tolerances of the elements. Contamination effects are a factor in addition. In addition to the known beam alterations due to ageing, beam alterations dependent on output are also a problem, in particular in the case of C02 high energy lasers. As the laser beam A e.g. with half output has a different

characteristic than with maximum output, normally a

"universal beam" is selected, i.e. a compromise between everything which would actually be possible, which, for example, prevents a maximizing of the cutting output. Also after the starting and heating up of the laser, the laser beam A alters approximately in the first minute, which can likewise lead to problems in the cutting operation.

So that the laser beam A of a laser cutting machine can always be adapted optimally to the workpiece which is to be processed, a measuring of the intensity distribution of the laser beam A, a so-called "beam monitoring" is helpful.

Various investigations have shown that the laser beam A alters in position, size and mode during operation, in particular depending on output. Furthermore, the laser beam A also alters over a lengthy period of time owing to ageing and contamination of the optical elements. Such changes can be detected by the beam monitoring according to the invention and can be largely corrected by adaptive elements, i.e. the beam A can be regulated. This leads to a distinct increase in the process stability and the cutting speed.

Frequently the determining of the beam diameter and of the beam mid-point or beam focal point is sufficient, i.e. the precise intensity distribution is not necessary. Thereby, the methods and models which are to be used are simplified. In an experiment the laser beam with a chronological resolution of approximately 1.5 Hz was able to be precisely determined with regard to its position rp and its radius rs to at least 0.2 mm. The width of the regions B1..B7 permeable to the beam should not be selected to be too small here, so that

diffraction effects do not have an appreciable influence. For e.g. 10.6 μιη wave length (CO₂ laser) a slit width of 1 mm is a good choice.

It is described below with the aid of Fig. 12 how the size of the beam A and its position can be determined by means of the received intensity impulses. Fig. 12 shows in this regard the determined distribution of the intensity I over the angle Φ of the disc 3e of Fig. 9. The graphs are represented for a beam A with Gauss distribution (solid lines) and for a beam A with so-called donut distribution (dashed lines) ,

respectively normalized to 1. Different signals clearly result for different beam sizes and positions.

Readily measurable values now are the width of the intensity impulses (pulse width) Ml and the distance between the intensity impulses (pulse distance) M2. Both values are dependent on the two beam parameters beam radius rs and the radial position rp on the disc 3e. The azimuthal angle position Φ of the beam A can be determined by knowledge of the disc position and the azimuthal position of the two pulses. An azimuthal displacement of the beam A does not alter either the pulse width Ml or the pulse distance M2, but rather displaces the two pulses only on the Φ axis. With knowledge of the polar coordinates, the position of the beam A can also be easily converted into Cartesian coordinates in a manner known per se.

It would be expected that the pulse width Ml and the pulse distance M2 also depend on the mode distribution of the laser beam A. However, investigations showed that the Gauss distribution, the donut distribution and a top hat distribution (not illustrated) have an almost common

intersection point with the same beam radius rs (2^nd moment) and the same beam position. For the ranges of the beam diameter of 6 to 11 mm and of the radial position of 26 to 32 mm, these intersection points lie on average at 1=0.158 for the outer side of the normalized pulse and at 1=0.125 for the inner side. Therefore, the beam position rp and beam size rs can be determined absolutely, independently of the mode number or respectively intensity distribution.

Of course, the above information is merely to be regarded as an example instance. Another choice of the disc C with other regions Bl to Bn can lead to different results, the locating of which, however, lies within the scope of the routine of the specialist in the art.

From the named intersection points, the 4 angles l.. 4 are determined .

The width of the pulse is now given by:

Ml = (o(2- oil + 4 - 3) / 2 and the distance of the pulses is given by:

M2 = ( 4 + 3 - 2 - l) / 2

The pulse width Ml and the pulse distance M2 can be

calculated as a function of beam radius rs and its radial position rp on the disc 3e. Therefore, an equation system is produced having two unknowns, which can be solved in a manner known per se. As shown from an investigation, the pulse width Ml depends predominantly on the beam radius rs and only a little on the radial position rp . Vice versa, the pulse distance M2 depends only a little on the beam radius rs and principally on the radial position rp .

With a conventional mathematics software (e.g. Scilab) , the determining of beam radius rs and beam position Rp can also be carried out in a simplified manner with the following approach : rs = pl*M2² + p2*Ml*M2 + p3*Ml + p4*M2 + p5 rp = ql*M2² + q2*Ml*M2 + q3*Ml + q4*M2 + q5 As an investigation showed, the errors caused by the

approximation for a beam diameter of 6 to 11 mm and a radial position of 26 to 32 mm lie at approximately 0.02 mm for the beam radius rs and at approximately 0.05 mm for the beam position rp and can therefore generally be disregarded.

With other disc forms and other regions B1..B7, comparable simple models can be developed, in order to determine the beam radius rs and the beam position rp in an analogous manner. The invention is not, however, restricted to the determining of the beam radius rs and the beam position rp, but rather can be extended to the determining of the mode distribution, the beam quality M², the beam parameter product BPP, etc. For example, the left and/or the right impulse in Fig. 12 can be measured with two different levels of

intensity which, as can readily be seen, leads to two different impulse widths Ml. The proportions of the

individual modes can be deduced in turn from these different widths Ml. To locate the polynomials and their coefficients, the beams A which are to be expected are modelled as already explained and their image is simulated on the detector 6. A

corresponding method, i.e. program, can be implemented in an evaluation microcontroller or in a personal computer (PC) . Fig. 13 shows in this regard an example flow diagram which represents a possible process flow for the above example. The flow diagram, in particular the parameters cited therein, apply/applies to the above-mentioned example. By variation of the parameters, the illustrated flow diagram can, however, also be adapted without difficulty for example to the disc 3f of Fig. 10 and the ellipticity determining or respectively the determining of the modes contained in a laser beam A.

An array of values results for predetermined input parameters rp, rs and resulting output parameters Ml, M2. These values are stored, e.g. in the form of the table below: rsl rpl Mil M21

rs2 rp2 M12 M22

rs3 rp3 M13 M23 etc .

With the (possibly very extensive) table of values and the polynomial equation, then e.g. by means of the least-square- fit method the polynomial coefficients are determined, which constitute as good a correlation as possible between the output parameters Ml, M2 and the associated input parameters rs and rp . This takes place for example by means of the commercially available mathematics tool Matlab, in particular with the "Polyfitn" function contained therein (e.g. described under

http : //www . mathworks . com/matlabcentral/fileexchange/10065- polyfitn) Fig. 14 now shows an actual code segment for calculating the named parameters. Instead of only 2 sought values rs, rp and 2 measurement values Ml and M2, the number of measurement values can of course be increased without appreciable

additional difficulties. Likewise, the number of sought values can also be increased in so far as this is less than the number of measurement values.

Finally, it is noted that the indicated variants represent only a portion of the many possibilities for the disc 3, 3a..3f according to the invention, the device 1 according to the invention and the laser processing machine according to the invention, and must not be drawn upon to limit the range of application of the invention. It should be easy for the specialist in the art to adapt the invention to his

requirements, based on the considerations presented here, without, in so doing, departing from the scope of protection of the invention.

Moreover, it is pointed out that the figures are generally not drawn to scale and that parts of the arrangements

illustrated in the figures can also form the basis for independent inventions.

The following list of reference numbers and the technical teachings of the claims are deemed to be lying within the framework of the disclosure and disclose for the specialist in the art alone or when viewed together with the figures further details of the invention and its example embodiments. List of reference numbers

1 device

2 beam source

3, 3a ..3f disc

4 lens

5 chopper disc

6 sensor

7 drive

8 beam-splitting element

A, Al .. A3 beam

B1..B7 region permeable to the beam

C first partial beam

D second partial beam

I intensity

M rotation point of the disc

Ml width of an intensity impulse

M2 distance between two intensity impulses r radial distance

rp beam position

rs beam radius

si, s2 radial vector

al .. a4 angle position intersection point intensity impulse

Φ angle position disc

Claims

1. Method for measuring a characteristic of a beam (A,

A1..A3) by means of a disc (3, 3a..3f) , which is rotatably mounted in a device (1) for determining this characteristic in a beam course of the beam (A, A1..A3) in front of a sensor (6) for measuring an intensity of the beam (A, A1..A3),

wherein the disc (3, 3a..3f) is impermeable to the beam or at least weakens the beam,

- wherein the disc (3, 3a..3f) comprises at least one elongated region (B1..B7) which is permeable to the beam or at least has a higher permeability to the beam compared with the remainder of the disc (3, 3a..3f) ,

characterized by the steps:

- detecting an intensity impulse by means of the part of the beam (A, A1..A3) impinging onto the sensor (6) on

rotation of the disc (3, 3a..3f) by the at least one region (Bl ..B7) ,

determining the sought characteristic by application of reconstruction- or modelling methods on the detected

intensity impulse suitable for inverse problems.

2. Method according to Claim 1, characterized in that one or more of the group: regression analysis, polynomial function, neuronal networks is/are provided as reconstruction- or modelling methods.

3. Method according to Claim 2, characterized by

at least one regression step, in which function

parameters of a function are determined by means of at least one intensity impulse of a beam (A, A1..A3) with a known characteristic as independent variable and of the said characteristic as dependent variable and a determining step, in which the function with determined function parameters receives an intensity impulse of a beam (A, A1..A3) with an unknown characteristic as independent variable.

4. Method according to Claim 2, characterized by

at least one analysis step, in which coefficients of a Taylor polynomial are determined by means of at least one intensity impulse of a beam (A, A1..A3) with a known

characteristic as independent variable and the said

characteristic as dependent variable and

a determining step, in which the Taylor polynomial with determined coefficients receives an intensity impulse of a beam (A, A1..A3) with an unknown characteristic as

independent variable.

5. Method according to Claim 2, characterized by

at least one training step, in which the neuronal network receives at least one intensity impulse of a beam (A, A1..A3) with a known characteristic as input and the said characteristic as output and

a determining step in which the trained neuronal network receives an intensity impulse of a beam (A, A1..A3) with an unknown characteristic as input.

6. Method according to one of Claims 2 to 5, characterized in that the regression step, analysis step or training step takes place within the framework of a computer simulation.

7. Method according to one of Claims 2 to 5, characterized in that the regression step, analysis step or training step takes place on a real device.

8. Method according to one of Claims 1 to 7, characterized in that as sought characteristic of the beam (A, A1..A3) one or more of the group: intensity distribution of the beam (A, A1..A3), mean diameter of the beam (A, A1..A3), position of the mid-point of the beam (A, A1..A3), position of the focal point of the beam (A, A1..A3), symmetry of the beam (A, A1..A3), proportion of a colour in the beam (A, A1..A3) and/or proportion of a laser mode is/are provided.

9. Method according to Claim 8, characterized in that as sought characteristic a portion is provided at least of one laser mode of the group: Gauss, donut, or top hat.

10. Method according to Claim 8 or 9, characterized in that as sought characteristic a portion at least of one laser mode is provided and the steps:

detecting a first width of the intensity impulse at a first intensity level,

detecting a second width of the intensity impulse at a second intensity level

are comprised.

11. Method according to one of Claims 1 to 10, characterized in that the disc (3, 3a..3e) comprises several elongated regions (Bl .. B7 ) ,

wherein a first region (Bl) crosses a first radial vector (si) originating from the rotation point (M) of the disc (3, 3a..3e) at a radial distance (r) in a first

direction in relation to the first radial vector (si) and

a second region (B2) crosses a second radial vector (s2) originating from the rotation point (M) of the disc (3, 3a..3e) at the same radial distance (r) in a second direction in relation to the second radial vector (s2), which is different from the first direction.

12. Method according to Claim 11, characterized in that

several different intensity impulses resulting from the regions (B1..B7) are drawn upon for determining the sought characteristic .

13. Method according to one of Claims 11 to 12, characterized by the steps:

a) detecting two intensity impulses by means of the first and second regions (Bl, B2) on rotation of the disc (3, 3a..3e), b) determining a width (Ml) of the intensity impulse based on the detection by the first and/or second region (Bl, B2), c) determining an angle distance (M2) between the intensity impulse based on the detection by the first region (Bl) and the intensity impulse based on the detection by the second region (B2) and

d) calculating the radius (rs) of the beam (A, A1..A3) and of the distance (rp) of this beam (A, A1..A3) from the rotation point (M) of the disc (3, 3a..3e) by means of the determined width (Ml) and of the distance (M2) .

14. Method according to one of Claims 11 to 13, characterized in that the first and the second direction enclose a right- angle when the second direction together with the second radial vector (s2) is rotated about the mid-point (M) so that the first and the second radial vectors (si, s2) are

congruent.

15. Method according to one of Claims 11 to 14, characterized in that the first and the second directions are different in relation to the respective radial vector (si, s2) at every radial distance (r) .

16. Method according to one of Claims 11 to 14, characterized in that a region (Bl, B2) is aligned along a straight line.

17. Method according to Claim 16, characterized in that n regions (B1..B7) are aligned along n straight lines and cross associated radial vectors (si, s2) originating from the rotation point (M) of the disc (3, 3a..3f) at the same radial distance (r) in n different directions.

18. Method according to one of Claims 11 to 15, characterized in that a region (Bl, B2) is aligned along a spiral.

19. Method according to Claim 18, characterized in that n regions (Bl, B2) are aligned along n spirals and cross associated radial vectors (si, s2) originating from the rotation point (M) of the disc (3, 3a..3f) at the same radial distance (r) in n different directions.

20. Method according to one of Claims 16 to 19, characterized in that at least one region (Bl) is aligned along a spiral and at least one region (B2) is aligned along a straight line.

21. Method according to one of Claims 18 to 20, characterized in that the spiral is Archimedic.

22. Method according to one of Claims 18 to 20, characterized in that the spiral is logarithmic.

23. Method according to Claim 19 to 22, characterized in that the pitch of the spiral for the first region (Bl) is k=l and the pitch of the spiral for the second region (B2) is k=-l.

24. Method according to Claim 23, characterized in that the disc (3, 3a..3f) has a straight third region (B3) which is radially aligned.

25. Disc (3, 3a..3f) which is disposed to be arranged

rotatably mounted in a device (1) for determining a

characteristic of a beam (A, A1..A3) in a beam course of the beam (A, A1..A3) in front of a sensor (6) for measuring an intensity of the beam (A, A1..A3),

wherein the disc (3, 3a..3f) comprises several elongated regions (B1,,B7) which are permeable to the beam or at least have a higher permeability to the beam compared with the remainder of the disc (3, 3a..3f) ,

- wherein a first region (Bl) crosses a first radial vector (si) originating from the rotation point (M) of the disc (3, 3a..3f) at a radial distance (r) in a first

direction in relation to the first radial vector (si) and

wherein a second region (B2) crosses a second radial vector (s2) originating from the rotation point (M) of the disc (3, 3a..3f) at the same radial distance (r) in a second direction in relation to the second radial vector (s2), which is different from the first direction,

characterized in that

the first region (Bl) is aligned along a spiral and the second region (B2) is aligned along a further spiral or along a straight line.

26. Disc (3, 3a..3f) according to Claim 25, characterized in that the first and the second direction enclose a right-angle when the second direction together with the second radial vector (s2) is rotated about the mid-point (M) so that the first and the second radial vectors (si, s2) are congruent.

27. Disc (3, 3a..3f) according to Claim 25 or 26,

characterized in that n regions (B1..B7) are aligned along n straight lines and cross associated radial vectors (si, s2) originating from the rotation point (M) of the disc (3,

3a..3e) at the same radial distance (r) in n different directions .

28. Disc (3, 3a..3f) according to one of Claims 25 to 27, characterized in that n regions (Bl, B2) are aligned along n spirals and cross associated radial vectors (si, s2)

originating from the rotation point (M) of the disc (3,

3a..3f) at the same radial distance (r) in n different directions .

29. Disc (3, 3a..3e) according to one of Claims 25 to 28, characterized in that the spiral is Archimedic.

30. Disc (3, 3a..3e) according to one of Claims 25 to 28, characterized in that the spiral is logarithmic.

31. Disc (3, 3a..3f) according to Claim 28 and 30,

characterized in that the pitch of the spiral for the first region (Bl) is k=l and the pitch of the spiral for the second region (B2) is k=-l.

32. Device (1) for determining a characteristic of a beam (A, A1..A3) characterized by: a sensor (6) arranged in the beam course of the beam (A, A1..A3) for measuring an intensity of a beam characteristic and

a rotatably mounted disc (3, 3a..3f) arranged in the beam course in front of the sensor (6), according to one of Claims 25 to 31.

33. Device (1) according to Claim 32, characterized in that a shared drive (7) is provided for the disc (3, 3a..3f) and a chopper disc (5) arranged in the beam course.

34. Laser processing machine comprising a device (1)

according to one of Claims 32 to 33, characterized in that a laser beam for material processing is provided as beam (A, Al ..A3) .

35. Laser processing machine according to Claim 34,

characterized in that in the beam course of the laser a beam- splitting element (8) is provided and a first part (C) of the laser beam (A, A1..A3) is directed onto the processing site and a second part (D) is directed to the sensor (6), wherein the disc (3, 3a..3f) is arranged between beam-splitting element (8) and sensor (6) .

36. Laser processing machine according to Claim 35,

characterized in that the disc (3, 3a..3f) is equally far away from the beam-splitting element (8) as the site at which the sought characteristic of the beam (A, A1..A3) is to be determined, from the beam-splitting element (8).

37. A method for measuring a beam characteristic,

comprising,

providing a rotary disc in a beam path, providing a sensor configured to measure beam intensity behind said rotary disc,

providing a plurality of elongated regions permeable to the beam in said disc;

crossing a first one of said plurality of elongated regions on a first radial vector originating from a rotation axis of the disc, at a radial distance in a first direction in relation to the first radial vector, and crossing a second one of said plurality of elongated regions on a second radial vector originating from a rotation axis of the disc, at the same radial distance in a second direction in relation to the second radial vector, different from the first direction; rotating said disc in the beam path;

sensing intensity impulses from the beam as it passes the elongated regions;

processing said intensity impulses by at least one technique selected from the group consisting of: regression analysis, polynomial function fitting, and neural network; and,

determining the beam characteristic by said processing of said intensity impulses.

38. A method as claimed in claim 37, further comprising, determining function parameters of a function for regression, by employing at least one intensity impulse having a known characteristic as independent variable, and by having the determinable beam characteristic as dependent variable; and,

providing the function for regression with at least one intensity impulse of a beam with an unknown beam

characteristic as independent variable.

39. A method as claimed in claim 37, further comprising, determining coefficient of a Taylor polynomial by employing at least one intensity impulse having a known characteristic as independent variable, and by having the determinable beam characteristic as dependent variable; and, providing the Taylor polynomial with at least one intensity impulse of a beam with an unknown beam

characteristic as independent variable.

40. A method as claimed in claim 37, further comprising, providing a neural network with at least one intensity impulse having a known characteristic as input and the determinable beam characteristic as output, for training; and,

providing the trained neural network with at least one intensity impulse of a beam with an unknown beam

characteristic as input.

41. The method for measuring a beam characteristic as claimed in claim 37, wherein,

said step of determining the beam characteristic

includes determining at least one of the group comprising: intensity distribution of the beam, mean diameter of the beam, position of the mid-point of the beam, position of the focal point of the beam, symmetry of the beam, proportion of a color in the beam, and proportion of a laser mode.

42. The method as claimed in claim 41, wherein, said step of determining the beam characteristic includes determining at least one laser mode of the group comprising: Gauss, donut, and top hat.

43. A method as claimed in claim 42, further comprising, detecting a first width of an intensity impulse at a first intensity level;

detecting a second width of an intensity impulse at a second intensity level; and,

determining a portion of the at least one laser mode by the determined first and second widths.

44. A method as claimed in claim 37, further comprising,

utilizing plural different intensity impulses resulting from the plurality of elongated regions for determining the beam characteristic.

45. A method as claimed in claim 37, further comprising,

detecting two intensity impulses by using the first and second of the plurality of elongated regions upon rotation of the discdetermining respective widths of the two intensity impulses ;

determining an angle distance between the intensity impulses based on the detection by the first region and the intensity impulse based on the detection by the second region; and,

calculating the radius of the beam and the distance of this beam from the rotation axis of the disc by employing the determined widths and the angle distance.

46. A method as claimed in claim 37, further comprising,

choosing the first and the second directions to enclose a right-angle when the second direction together with the second radial vector is rotated about the rotation axis so that the first and the second radial vectors are congruent.

47. A method as claimed in claim 37, further comprising, configuring the first one and the second one of said plurality of elongated regions so that the first and the second directions are different in relation to the respective radial vector at every radial distance.

48. A method as claimed in claim 37, further comprising, aligning a region along a straight line.

49. A method as claimed in claim 37, further comprising, aligning a number n of elongated regions along a

respective number n of straight lines, and cross associating respective radial vectors originating from the rotation axis of the disc at the same radial distance in n respective different directions.

50. A method as claimed in claim 37, further comprising, aligning an elongated region along a spiral.

51. A method as claimed in claim 37, further comprising, aligning a number n of elongated regions along a

respective number n of spirals, and cross associating

respective radial vectors originating from the rotation axis of the disc at the same radial distance in n respective different directions.

52. A method as claimed in claim 51, further comprising, selecting the pitch of the spiral for the first region as k=l; and,

selecting the pitch of the spiral for the second region as k=-l.

53. A method as claimed in claim 50, further comprising, aligning at least one region along a straight line.

54. A method as claimed in claim 50, further comprising, choosing the spiral as Archimedic.

55. A method as claimed in claim 50, further comprising, choosing the spiral as logarithmic.

56. A method as claimed in claim 55, further comprising, radially aligning a straight third elongated region of the disc.

57. Device for determining a beam characteristic,

comprising,

a rotatably mounted disc configured to rotate in a beam path;

a sensor for beam intensity disposed behind said beam; a plurality of elongated regions in said disc, said regions permeable to the beam;

a first elongated region crosses a first radial vector originating from a disc rotation axis at a radial distance r in a first direction in relation to the first radial vector, and a second elongated region crosses a second radial vector originating from the disc rotation axis at the same radial distance r in a second direction in relation to the second radial vector, said second direction being different from said first direction;

said first elongated region is aligned along a spiral; said second elongated region is aligned along one of either (a) a further spiral, or (b) a straight line.

58. A device for determining a beam characteristic as claimed in claim 57, further comprising,

said first and second directions enclose a right-angle when the second direction together with the second radial vector is rotated about the disc axis so that the first and the second radial vectors are congruent.

59. A device for determining a beam characteristic as claimed in claim 57, further comprising,

a number n of elongated regions being aligned along respective n straight lines, and cross associated radial vectors originating from the rotation axis of the disc at the same radial distance in respective n different directions.

60. A device for determining a beam characteristic as claimed in claim 57, further comprising,

a number n of elongated regions being aligned along respective n spirals, and cross associated radial vectors originating from the rotation axis of the disc at the same radial distance in respective n different directions.

61. The device for determining a beam characteristic as claimed in claim 57, wherein,

said first elongated region spiral is Archimedic.

62. The device for determining a beam characteristic as claimed in claim 57, wherein,

said first elongated region spiral is logarithmic.

63. The device for determining a beam characteristic as claimed in claim 57, wherein,

the pitch of said spiral for said first elongated region is k=l and the pitch of said further spiral for said second elongated region is k=-l.

64. A device for determining a beam characteristic as claimed in claim 57, further comprising,

a chopper disc arranged in the beam course; and,

a shared drive configured to drive said rotatably mounted disc and said chopper disc.

65. A device for determining a beam characteristic as claimed in claim 57, further comprising,

a beam splitter provided in the beam course, said beam splitter configured to direct a first part of the beam onto a processing site and a second part of the beam to said sensor, said rotary disc being arranged between said beam splitter and said sensor; said disc being equally far away from said beam splitter as said processing site at which the beam characteristic is to be determined, from the beam-splitting element .