Method for inspecting the optical elements of a laser processing device for contaminants.

Abstract

The present invention relates to a method for inspecting an optical element (4) of a laser processing apparatus (10) with respect to contaminants (7), wherein a laser beam (1) passes through the optical element (4), which is specifically directed to emit light through the optical element (4), and scattered light emitted from the optical element (4) is measured by a photosensor (6), and N individual measurements are performed, N≧3, during each individual measurement i, the laser beam (1) passes through the optical element (4), the scattered light emitted from the optical element (4) is measured by the photosensor (6), the signal intensity Si is determined by the photosensor (6), for each individual measurement i, different diameters Di of the laser beam (1) at the location of the optical element (4) are set, and information about location-dependent contaminants of the optical element (4) is confirmed from the signal intensity Si of the N individual measurements, i=1, ..., N, where i is a measurement subscript. The present invention, in particular, enables more information about contaminants on optical elements to be obtained in a simple manner, in order to make the laser processing apparatus more usable.

Description

[Technical Field]

[0001] The present invention relates to a method for inspecting the optical elements of a laser processing apparatus for contaminants, and more particularly, to a method in which a laser beam passes through an optical element directed to emit light through the optical element, and the scattered light emitted from the optical element is measured using a photosensor.

[0002] Laser processing is a frequently used and efficient method for processing workpieces. Laser cutting allows for the simple and efficient cutting of workpieces from metal sheets and other materials, for example, without the need for specialized cutting tools. Laser welding, for instance, can be used to quickly and reliably join partial workpieces together to form a single workpiece.

[0003] When laser processing a workpiece, the laser beam from the laser source is typically directed onto the workpiece using a laser processing head. The laser beam is typically focused onto the surface of the workpiece or into a specific plane near the surface. The laser processing head includes optical elements, particularly lenses and protective glass through which the laser beam passes.

[0004] Laser processing or other processes on the workpiece itself can result in contamination of optical elements. For example, molten workpiece material may splatter onto the optical elements, or dust particles may be introduced into the laser processing head during maintenance. When the laser beam passes through a contaminated optical element, particularly one directed to radiate through it, the contaminants can locally block the laser beam, which can impair the processing results on the workpiece. In addition, the optical element heats up more rapidly at the site of contamination. Such localized heating can, due to thermal expansion, alter the optical imaging characteristics of the optical element, at least locally. The focal point and shape of the laser beam may change or become distorted. Contamination can also occur more widespread on the optical element, for example, due to crude oil components contained in the cooling gas, which can be introduced into the cooling gas by pressure. Such widespread contamination results in overall attenuation of the passing laser beam and widespread heating of the optical element in operation. For example, it is known from DE202010006047U1 that increased absorption of protective glass caused by contaminants can be determined by measuring the temperature.

[0005] To determine the degree of contamination of optical elements within a laser processing device, an optical sensor can be directed towards the optical element to measure the scattered light emitted from it. This scattered light is caused by the passing laser beam. The greater the contamination of the optical element, the more scattered light is generated, and the higher the signal recorded on the sensor. If the signal on the sensor becomes too high, processing of the workpiece can be stopped, and the optical element can be cleaned or replaced.

[0006] This procedure provides essential information about the degree of contamination of the optical element within the cross-section occupied by the laser beam. For example, if localized contaminants are located in the radial edge region of the optical element, laser processing, particularly laser cutting, can often still be continued without having to accept a significant loss of quality in the laser processing of the workpiece. For example, by using a narrower laser beam that does not illuminate the detected contaminants, it may be possible to modify the laser processing of the workpiece into a process that is acceptable due to the location of the detected contaminants. Therefore, in many cases, laser processing using a laser processing device is stopped even if further laser processing of the workpiece is still possible. [Background technology]

[0007] The object of the present invention is to provide a method for inspecting the optical elements of a laser processing apparatus, which allows for obtaining more information about contaminants on the optical elements in a simple manner, and in particular enables greater usability of the laser processing apparatus.

[0008] Summary of the Invention This objective is achieved based on the present invention by the first type of method described, in which N individual measurements are performed, N≧3, and during each individual measurement i, a laser beam passes through an optical element, and the scattered light emitted from the optical element is measured by a photosensor, and the signal intensity S i However, the determination is made by the optical sensor, and for each individual measurement i, the different diameters D of the laser beam at the location of the optical element i However, information about location-dependent contaminants of the optical element is set, and the signal intensity S of N individual measurements is obtained. i It is characterized by the fact that it can be confirmed from the above, and that i = 1, ..., N, and i is a measurement subscript.

[0009] Within the scope of the present invention, it is provided that when measuring scattered light, at least three separate measurements are performed, and these measurements are performed using different diameters of the laser beam at the location of the optical element (the location of the optical element is related to the beam propagation direction). Preferably, to change the diameter at the location of the optical element, the beam divergence of the laser beam is changed, and typically, the focal diameter of the laser beam is changed. For a given beam parameter product, a smaller focal diameter is associated with a larger divergence, and vice versa.

[0010] Depending on the location and size of the localized contamination (localized contaminant), the optical element is illuminated by the laser beam for all or part of the individual measurements, in which case it may be fully illuminated, partially illuminated, or not illuminated at all, thus contributing to the generation of scattered light measured by the sensor. Therefore, the signal intensity S of N individual measurements i This provides information about location-dependent contaminants in optical elements.

[0011] During individual measurements, the laser beam typically remains aligned and centered along the optical axis. This facilitates obtaining information about the radial distribution of contaminants on the optical element, centered on the optical axis. In addition, the laser power typically remains constant across individual measurements. The latter is particularly easy to control and improve the comparability of individual measurements.

[0012] For example, if there is localized contamination (such as dust particles) within the radial edge region of an optical element, this will only enter the cross-section of the laser beam at its larger diameter, resulting in scattered light. Conversely, localized contaminants near the beam axis of the laser beam will illuminate the entire diameter of the laser beam, and therefore will result in scattered light in all individual measurements.

[0013] When information regarding contamination of optical elements is spatially resolved, it is possible to determine, based on improved criteria, whether a planned laser processing process using a laser processing apparatus (also called a laser processing machine) is still feasible in the current contamination state. Similarly, based on improved criteria for spatially resolved information of optical elements, it is possible to select a process for further laser processing of a workpiece that is still feasible using a laser processing apparatus in the current contamination state. As a result, the measurement method according to the present invention can provide the necessary information for the improved usability (improved utilization) of the laser processing apparatus.

[0014] Typical optical elements that can be inspected for contaminants using the method according to the present invention are lenses and protective glass, and optionally also mirrors, apertures, beam splitters, diffractive optical elements, or filters, including curved mirrors and translucent mirrors. Typical optical sensors for measuring scattered light are photodetectors, in particular zero-dimensional photodetectors, which are substantially oriented laterally on the optical element. During the measurement of scattered light, the laser beam typically passes through the optical element by being directed to radiate through it, although it is also possible for the laser beam to be reflected by the optical element and thus pass through the optical element.

[0015] Preferred Modifications of the Invention A preferred variation of the method according to the present invention involves a larger diameter D i Smaller diameter D i The increasing signal strength S i Therefore, a smaller diameter D iAn increased contamination level of the optical element within is presumed. In this way, initial qualitative information about location-dependent contaminants can be readily obtained. If local contamination is (solely or mainly) present within a region of smaller diameter, reducing the diameter of the laser beam from a larger diameter to a smaller diameter (having a constant total laser power) results in a higher radiation density within the contaminated region and thus more scattered light. An (relative or absolute) increase in signal intensity can also be used to roughly quantitatively estimate the contamination level within the smaller diameter compared to the larger diameter (which will be further explained hereinafter).

[0016] Similarly, in a preferred variant, an increasing signal intensity S from a smaller diameter Di to a larger diameter D i up to i from which, an increased contamination level of the optical element outside the smaller diameter D i is presumed. In this way, initial qualitative information about location-dependent contaminants can be readily obtained. If local contamination is (solely or mainly) present within a region of larger diameter, the contamination does not enter the cross-section of the laser beam at the smaller diameter of the laser beam but only enters the cross-section of the laser beam at the larger diameter of the laser beam, at which time the contamination solely results in scattered light. This effect is usually more important than the local reduction in radiation density due to an increase in beam diameter (at a constant total laser power). An (relative or absolute) increase in signal intensity can be used to roughly quantitatively estimate the contamination level within the larger diameter (and outside the smaller diameter) compared to the contamination level within the smaller diameter (which will be further explained hereinafter).

[0017] The variant is preferably in that the contamination level G1 of the optical element within the minimum diameter D1 and the respective contamination levels G of the optical element within the region between diameter D i from signal intensity S j and diameter D j-1 and diameter D j are determined, where j = 2,..., N and j is the number of the remaining larger diameter indices. The minimum diameter D1 and each surrounding Dj-1 ~D j Contamination levels G1 and G within the inner ring. j Using this, an intuitively interpretable assessment of location-dependent contaminants can be performed, and the use of laser processing machines can be optimized in a simple and target manner as needed. Alternatively, each diameter D i Please note that the level of essential contamination within the facility can also be determined.

[0018] Further developments of this variant include contamination levels G1 and G j From minimum diameter D1 to maximum diameter D N It is particularly preferable that the determination is repeated up to the point of contamination level G1, G j This makes it easier to determine the contamination G1. Contamination G1 can be determined directly from S1. Then, contamination G in the outer ring j For example, value S j and G1~G j-1 (Diameter D j S for the entire inner region j Unprocessed contaminated G determined from j roh Using (which can be subtracted from), it is possible to determine from the inside to the outside. Alternatively, contamination level G j Also, the value S j and S j-1 Use, or alternatively, values ​​S1~S j-1 You can also use this method to make a determination, and see below for more information.

[0019] Further development of the above modified example is that in step 1), the degree of contamination G1 of the optical element within the minimum diameter D1 is estimated from the signal intensity S1 for the minimum diameter D1, and the expected signal contribution C2 in the signal S2 for the next larger diameter D2 is determined from the signal intensity S1 by the contamination of the optical element within the minimum diameter D1, and in a further step j), diameter D j Each corrected signal strength KS j =S j -C j From, diameter D j and diameter D j-1The degree of contamination G of the optical element within the region between j It is estimated that the signal strength S j From, or alternatively, signal intensity S1~S j Therefore, the next larger diameter D j+1 Signal S j+1 Expected signal contribution C within j+1 However, diameter D j It is also preferable that the determination is made by the contaminants of the optical elements. This procedure is for contamination levels G1 to G N To determine this, it is simple and efficient. In the final step N), C N+1 It is understood that the determination is no longer necessary.

[0020] A favorable sub-modification for this further development is the signal contribution C j However, this provides that it can be determined at least approximately according to the following formula. C j =S j-1 *[D j-1 / D j ] 2

[0021] This simple estimation can contribute to a very accurate estimation of location-dependent pollutants. This estimation is based on the following smaller diameter D j-1 Larger diameter D due to contaminants inside j Internal signal contribution C j However, the next smaller diameter signal intensity S j-1 It is substantially proportional to, and also to a smaller diameter D j-1 Area and larger diameter D j This is based on the assumption that it is also proportional to the area. The latter considers the redistribution of the total beam power of the laser beam (assuming it is constant) when the diameter is changed, and this is assumed to be the main factor for the scattering intensity caused by contaminants in smaller diameters. If necessary, C j The accuracy of the determination is determined by the specific correction coefficient F for j in the above formula. j It can be increased by the signal contribution C. jFor a more precise determination, these can be calculated as the sum of m augends, each of which is G m The region assigned to it is specifically determined, where m = 1, ..., j-1, and m is the subscript of the smaller diameter.

[0022] Sub-variations of the above further developments also include contamination levels G1-G N However, it is preferable that the determination is made at least approximately according to the following formula. G1 = F * S1 * [D1] 2 and G j =F*KS j *[(D j ) 2 -(D j-1 ) 2 ]

[0023] In the equation, F is the proportionality constant. Using this simple estimation, the degree of contamination can be easily compared. The area of ​​the ring region located further out is considerably larger than the area of ​​the ring region located further in (assuming the same ring width). Therefore, in that case, the laser power is distributed over a larger area, and the signal intensity due to the resulting scattered light is weaker (for local contaminants of similar size and nature). In that case, G j In [(D j ) 2 -(D j-1 ) 2 By multiplying by a coefficient proportional to the area of ​​each ring, the signal intensity attenuation related to area can be equalized. Alternatively, pollution levels G1 and G j Also, G1 = F'*S1 and G j =F'*KS j It is also possible to make a determination via (without weighting by area), where F' is an alternative proportionality constant.

[0024] Furthermore, a preferred further development of the above modified examples is the contamination level G1, G j However, within the minimum diameter D1 for V1, or each V jRegarding D j and D j-1 The remaining usability V1, V within the region between j is to be provided to be converted to

[0025] In particular, the contamination levels G1, G j are the respective assigned maximum values M1, M j and when the maximum value is reached, laser processing becomes no longer usable, and the remaining usability V1, V j is calculated as follows V1 = 1 - G1 / M1 and V j = 1 - G j / M j

[0026] In particular, the remaining usability V1, V j is displayed on the laser processing apparatus. In particular, M1, M j , and the determination of the remaining usability via V1, V j enables the user of the laser processing apparatus to have an intuitive and application - relevant understanding of the contamination level, facilitating further planning of the production of the workpiece or the selection of the further processing process to be executed on the workpiece

[0027] Another preferred variant provides that before further evaluation of the signal strength S i the signal strength S i is adjusted only by the bias after measurement of the signal strength by subtracting the basic signal strength B i obtained using an optical element in a contamination - free state with a corresponding laser beam having a diameter D i from each respective signal strength S i This makes the determination of location - dependent contaminants more accurate. For example, when significant scattered light occurs within the laser processing head even though the contamination of the optical element is being inspected due to the surface roughness of the optical element or scattering at a location away from the optical element, bias correction taking into account the offset is particularly recommended

[0028] Alternatively or additionally, the signal strength Si For further evaluation of signal intensity S, i This is set with respect to the bias after measuring the signal intensity to determine the degree of contamination, which corresponds to the contamination state relative to the clean state. This makes the determination of location-dependent contaminants more accurate. For example, if significant scattered light occurs within the laser processing head despite the contamination of the optical element being inspected, due to surface roughness of the optical element or scattering at a location away from the optical element, a bias correction that takes a coefficient into account is particularly recommended.

[0029] Operating method according to the present invention The scope of the present invention also includes methods for operating a laser processing apparatus. The optical elements of the laser processing equipment are inspected for contaminants. This delicious, Inspecting the optical elements of a laser processing apparatus for contaminants is performed based on the method according to the present invention described above. A decision will be made, based on the inspection results, regarding whether the scheduled process of laser processing for workpieces can be executed using the laser processing equipment. The determination of whether a scheduled process can be executed is characterized by considering at least determined location-dependent information about contaminants on the optical element and information about the diameter of the laser beam on the optical element used within the scope of the scheduled process. When the current location-dependent contaminants on the optical element and the diameter of the laser beam used for the scheduled process at the location of the optical element are considered when determining whether the scheduled process can still be executed, unnecessary downtime of the laser processing equipment can be minimized.

[0030] The scope of the present invention also includes a method for operating a laser processing apparatus, wherein the optical elements of the laser processing apparatus are inspected for contaminants. This delicious, Inspecting the optical elements of a laser processing apparatus for contaminants is performed based on the method according to the present invention described above. If the determined information regarding location-dependent contaminants of an optical element indicates that the relevant contaminants are present only in the radial edge region of the optical element but not in the central region, the laser processing apparatus remains ready for operation, provided that the process for the laser processing the workpiece is performed within the range that the diameter of the laser beam in the optical element remains within the central region, until the optical element is cleaned or replaced. This procedure means that, with respect to the relevant contaminants (excluding further operation), the laser processing apparatus remains available only in the radial edge region for at least certain processes that require only a laser beam directed within the central region of the optical element. With appropriate planning or rescheduling of processes, the downtime of the laser processing apparatus can be minimized. In the advantageous modifications of the two methods described above for operating the laser processing device, the optical elements of the laser processing device are, with respect to contaminants, -After each maintenance and repair of the laser processing head of the laser processing equipment, and / or, -After each predetermined operating time of the laser processing device, and / or, -At each startup of the laser processing machine, and / or - Before each start of a new process for the laser processing equipment for the workpiece, and / or - It is checked during manual startup.

[0031] This ensures high processing quality of the workpiece. At the same time, it enables good usability of the laser processing equipment.

[0032] Laser processing apparatus according to the present invention The scope of the present invention also includes laser processing apparatus, which is a laser processing apparatus. A laser source for providing a laser beam, An optical element through which a laser beam passes, and in particular an optical element that is designed to emit light through the optical element, An adjustment device for adjusting the diameter of the laser beam at the location of the optical element, It comprises an optical sensor for measuring scattered light emitted from an optical element, and an electronic control unit, The electronic control unit is configured to perform, in an automated sequence, a method for inspecting the optical elements of a laser processing apparatus for contaminants, based on the method according to the present invention described above. The electronic control unit, using an adjustment device, adjusts the different diameters D of the laser beam at the location of the optical element for N individual measurements. i Set the diameter D continuously for each of the following: i Using this, the associated signal intensity S in the light sensor i It is characterized by being configured to determine [something]. By using this laser processing apparatus, contaminants on optical elements can be detected locally, and a high degree of usability for processing workpieces can be achieved.

[0033] A preferred embodiment of the laser processing apparatus according to the present invention is that the laser processing apparatus is a laser cutting apparatus. In laser cutting, the cutting process can often be modified with little effort and without any significant impairment of the quality of the diameter of the laser beam at the location of the optical element, which can achieve a particularly high level of usability when contaminants are located only within the radial edge region of the optical element.

[0034] Further advantages of the present invention will become apparent from the specification and drawings. Similarly, the features described above, and the features further described, can be used, on their own, or together in any desired combination according to the present invention. The illustrated and described embodiments should not be understood as an exhaustive list, but rather as typical in nature for illustrating the present invention. [Brief explanation of the drawing]

[0035] [Figure 1a] A typical modification of the method according to the present invention for inspecting contamination of optical elements in a laser processing apparatus is schematically illustrated, specifically a first individual measurement having a minimum laser beam diameter D1 at the location of the optical element in the longitudinal direction along the beam propagation direction. [Figure 1b] Regarding the modified example of Figure 1a, a second individual measurement having an intermediate diameter D2 is illustrated. [Figure 1c] Regarding the modified example of Figure 1a, a third individual measurement having a maximum diameter D3 is illustrated. [Figure 2a] A schematic example of the first individual measurement for the modified version of Figure 1a is provided, along with a cross-section at the location of the optical element. [Figure 2b] A second individual measurement for the modified version of Figure 2a is illustrated as an example. [Figure 2c] A third individual measurement for the modified version of Figure 2a is illustrated as an example. [Figure 3] Figure 1a shows a simplified example of the measurement conditions for three individual measurements, accompanied by a cross-sectional view of the optical element location (left), contamination in the region between D2 and D3, and a schematic diagram of the measured signal intensity in relation to it (right). [Figure 4] Figure 1a illustrates the measurement conditions for three individual measurements similar to the modified example shown, with a cross-section of the optical element location (left side), accompanied by a schematic diagram of contamination in the region between D1 and D2, and the associated measured signal intensity (right side). [Figure 5] Figure 1a illustrates the measurement conditions for three individual measurements similar to the modified example shown, with a cross-section of the optical element location (left), accompanied by a schematic diagram of contamination within the region D1 and the measured signal intensity (right). [Figure 6] Figure 1a illustrates the measurement conditions for three individual measurements similar to the modified example shown, and includes cross-sections of the optical element locations in the case of a bias measurement without contamination. [Figure 7a] A typical embodiment of the laser processing apparatus according to the present invention is schematically illustrated, and the minimum diameter D1 of the laser beam is set on the optical element using an adjustment device. [Figure 7b] The embodiment shown in Figure 7a illustrates how the intermediate diameter D2 of the laser beam is set on the optical element using an adjustment device. [Figure 7c] The embodiment shown in Figure 7a illustrates how the maximum diameter D3 of the laser beam is set on the optical element using an adjustment device. [Figure 8] A typical design of the laser processing head of a laser processing apparatus for the present invention is schematically illustrated, in which protective glass is monitored using a sensor as an optical element. [Figure 9] A typical design of the laser processing head of a laser processing apparatus for the present invention is schematically illustrated, in which the beam splitter is monitored using a sensor as an optical element. [Figure 10] A typical design of the laser processing head of a laser processing apparatus for the present invention is schematically illustrated, in which the lens is monitored using a sensor as an optical element.

[0036] Figures 1a-1c and 2a-2c illustrate exemplary modifications of the method according to the present invention for inspecting contamination of optical elements in a laser processing apparatus using three separate measurements. Figures 1a-1c each show longitudinal sections along the beam propagation direction through the laser processing head of the laser processing apparatus, close to the workpiece being processed, while Figures 2a-2c each show cross-sections at the location of the optical elements.

[0037] As shown in Figure 1a, the laser processing apparatus directs a laser beam 1 onto a workpiece (not shown, but for this purpose, see Figure 7a), where the focal point of the laser beam 1 is typically located on the surface of the workpiece. In the illustrated modification, the laser beam 1 is focused by a lens 3, and the laser beam 1 passes through an optical element 4, in this case a protective glass 5, located between the lens 3 and the focal point 2. The protective glass 5 can be contaminated, for example, as a result of splashes of molten workpiece material or simple dust particles. As an example, localized contamination 7 in the form of dust particles is illustrated here. A light sensor 6 is directed onto the optical element 4 from the side and measures the scattered light emitted from the optical element 4. Scattered light is mainly generated by contaminants 7 on the optical element 4 when the laser beam 1 is scattered by contaminants 7.

[0038] Within the scope of the invention, several individual measurements of scattered light were performed, and different diameters D of the laser beam 1 were measured. i However, at the location of optical element 4, it is always used. In all cases, the laser beam 1 remains centered on the common optical axis OA, and the laser power is kept constant. However, the beam divergence changes, and the diameter D at the location of the optical element changes. i This changes (this will be explained further in Figures 7a-7c).

[0039] In the first individual measurements in Figures 1a and 2a, the minimum diameter D1 is used. Since the contamination 7 is outside the diameter D1 of the laser beam 1, it does not contribute to the generation of scattered light.

[0040] The second individual measurements in Figures 1b and 2b are performed at the location of the optical element 4 using the midpoint diameter D2 of the laser beam 1. In this case, the contamination 7 is also outside D2 and therefore does not contribute to the generation of scattered light in the second individual measurement.

[0041] The third individual measurement in Figures 1c and 2c is performed at the location of the optical element 4 using the maximum diameter D3 of the laser beam 1. Here, the contamination 7 is located within D3 and therefore contributes to the generation of scattered light.

[0042] In the contamination scenarios shown in Figures 2a-2c, the significant signal intensity due to scattered light is therefore achieved only in the third separate measurement involving D3. This makes it easy to infer that significant contamination exists only in the region between D2 and D3.

[0043] It is understood that the individual measurements illustrated in Figures 1a-1c and 2a-2c can be performed in any order. According to the present invention, four, five, or even more individual measurements (with additional diameters D4, D5, etc.) can be performed.

[0044] In the following, typical contamination conditions on optical elements will be examined using the method according to the present invention and discussed qualitatively and quantitatively with examples. Three separate measurements, as shown in Figures 1a-1c and 2a-2c, are assumed to be performed using the laser beam diameters D1, D2, and D3 at the location of the optical element, where D1 = 1.0 mm, D2 = 1.5 mm, and D3 = 2.0 mm were selected. The laser beam diameter can be determined using the 86% criterion (86% of the laser power is found within a circle having a specified diameter). In these measurements, the signal intensities S1, S2, and S3 are measured, for example, using photocurrent (unit: milliamperes, mA).

[0045] Figure 3 shows the contamination situation already discussed in Figures 1a-1c and 2a-2c. As can be seen in the left cross-section of Figure 3, a single localized contaminant 7 is located within the region between D2 and D3. Corresponding diameters D and D i Regarding the signal strength S and S i Typical corresponding measurements are shown in the schematic diagram on the right side of Figure 3, and in Table 1 below (along with other values). [Table 1]

[0046] As shown in Figure 3, (in this example only) because the localized contamination 7 is located outside D2, only a clear signal intensity S3 is acquired by the sensor for scattered light in the third individual measurement, which occurs with a diameter D3. Signal intensities S1 and S2 are, in contrast, much smaller.

[0047] In the situation shown in Figure 4, only the localized contamination 7 is located within the innermost diameter D1; please refer to the cross-section on the left side of Figure 4. As can be seen in the schematic diagram on the right side of Figure 4 and in Table 2, a high signal intensity S1 is obtained in the first individual measurement i=1. Since this localized contamination 7 is also located within D2 and D3, significant signal intensities S2 and S3 are also measured. Because the beam power of laser beam 1 is distributed over a larger area in individual measurements i=2 and i=3, the scattered light intensity (and therefore the measured signal intensity S) decreases as the diameter D of laser beam 1 increases. [Table 2]

[0048] In the situation shown in Figure 5, only localized contamination 7 is located within the region between D1 and D2; please refer to the cross-section on the left side of Figure 5. Therefore, the sensor signal intensity S2 for scattered light is maximum in the second individual measurement. Contamination 7 also affects the third individual measurement i=3, and a significant signal intensity S3 is obtained, but it is lower than S2 because the laser power is distributed over a larger area from D2 to D3. In the first individual measurement for D1, only the minimum signal intensity S1 is obtained because contamination 7 is not within D1. All of this can be seen and understood in the schematic on the right side of Figure 5 or in Table 3. [Table 3]

[0049] Here, contamination level G1 should be determined for the region within D1, contamination level G2 should be determined for the ring region between D1 and D2, and contamination level G3 should be determined for the ring region between D2 and D3.

[0050] According to the present invention, this can be done "from the inside out". Assuming nearly uniform illumination of the cross-section of the laser beam for all beam diameters D1, D2, and D3, the inner diameter D j-1 Signal intensity S for (subscript j-1) j-1 Using the following equation, the next larger beam diameter D j Signal intensity S for (subscript j) j Regarding this, the expected signal contribution C due to contaminants within this inner diameter. j It is possible to determine this. C j =S j-1 *[D j-1 / D j ] 2

[0051] In the formula, j is a subscript for the (larger) diameter, starting from j=2 and progressing up to a maximum of N=3. Here, [D1 / D2] 2 =0.4444 and [D2 / D3] 2 Note that this is = 0.5625. Next, this expected signal contribution C j The corrected signal strength can be determined using the following formula. KS j =S j -C j

[0052] Note that for the outermost (ring-shaped) region, the innermost region (within D1) does not require such correction. Therefore, the corrected signal strength KS j D j-1 ~D j This is due to scattered light from contaminants in each ring region, i.e., diameter D j-1Each signal intensity is represented without the respective signal intensity due to scattered light from pollutants inside. Figures 3, 4, and 5 show C for different situations. j and KS j The corresponding values ​​are entered in Tables 1, 2, and 3, respectively.

[0053] To obtain comparable levels of contamination for each region, the contamination levels G1 and G in a specific region are used. j Here, this can be determined according to the following formula. G1 = F * S1 * [D1] 2 and G j =F*KS j *[(D j ) 2 -(D j-1 ) 2 ]

[0054] In the formula, F is the proportionality constant simply selected as 1 / mA in Tables 1, 2, and 3 above. This coefficient [(D j ) 2 -(D j-1 ) 2 ] compensates for the low power density of the laser beam when the beam diameter increases. Here, [(D2) 2 -(D1) 2 ]=1.25 and [(D3) 2 -(D2) 2 Note that ] = 1.75. Next, the respective values ​​G1, G j This roughly corresponds to the absolute amount (size / area) of scattered contaminants within each associated region. These values ​​are also entered in Tables 1, 2, and 3.

[0055] In Figures 3, 4, and 5, and Tables 1, 2, and 3, it can be seen that similarly large pollutants are present within their respective regions in each example. In Figure 3 / Table 1, within the region between D2 and D3, G3 = 7.212, and G1 and G2 are each < 0.1. In Figure 4 / Table 2, within the region of D1, G1 = 7.134, and G2 and G3 are each < 0.1. In Figure 5 / Table 3, within the region D1 to D2, G2 = 7.005, and G1 and G3 are each < 0.1. This is because G i This means that by using measurements and evaluations, it is possible to track the exact location of each contamination.

[0056] In reality, a great many individual, smaller contaminants (e.g., dust particles, splashes of workpiece material) contribute to the overall contamination of the optical element 4, typically distributed across various regions of the optical element 4. The highest degree of contamination can be experimentally determined for each region, and here, M i This is called a [specific term], where laser processing of the workpiece (with sufficient quality) is no longer possible. In this case, the values ​​M1=7.5, M2=15, and M3=30 were determined or specified for the laser processing apparatus. In other words, more contaminants may be accepted in the outer region than in the inner region, which can generally be considered a preferred specification according to the present invention and is suitable for many laser cutting processes.

[0057] Formula V i = 1-G i / M i Using this, the remaining usability V of the optical element in each range to be assigned to the subscript value i i It is possible to determine G i >M i In the case of V i = 0 V i It can also be expressed as a percentage.

[0058] As can be seen from Tables 1, 2, and 3, the contaminants in Figures 3, 4, and 5 are comparable in size. This means that in the case of contamination 7 in the innermost region of Figure 4, the region within D1 is already almost completely depleted, with remaining usability of only V1 = 0.049 or 4.9%. In contrast, in the case of Figure 3 with contamination 7 in the radially outermost region between D2 and D3, the remaining usability is V3 = 0.760 or 76%, and this region is only slightly depleted. In the case of Figure 5 with contamination 7 in the intermediate ring region between D1 and D2, the remaining usability V2 is 0.533 or 53.3%.

[0059] Contamination level G in a specific area i Or the remaining usability of a specific area V i This represents representative information about location-dependent pollutants (also called spatially decomposed pollutant information) via an optical element for the present invention.

[0060] Remaining usability of the specific area V i Based on this, the electronic control unit can estimate whether the laser processing device is still largely operational. In the case of such an inspection, for example, the minimum remaining usability (here, MIN) i A check (also known as) can be specified for individual areas. A simple and common operational check is, for example, in each area, before the next process with respect to the workpiece begins, at least 10% of the remaining usability V i It must be usable (i.e., for all i, i=1 to N, MIN i It may be required that the minimum value be ≥10%. If the quality requirements are higher, a higher minimum value MIN may be required. i For example, we can offer at least 50%.

[0061] Preferably, the present invention relates to a specific minimum value (MIN(p)) of remaining availability for process execution. iAlso known as, in the formula, p is a process indicator and i is a subscript of an individual measurement or measured diameter) which provides that a particular minimum value of these individual specific minimum values ​​of the remaining available MIN(p) i This includes information about the diameter of the laser beam to be used in the planned process (specified by p). The electronic control unit then determines a specific minimum value MIN(p) i The remaining usability V i Using the comparison, we can estimate whether a particular scheduled process (corresponding to p) can still be started. For all i, MIN(p) i ≥V i If that is the case, then it is possible to start.

[0062] For example, a scheduled process for p=X that uses only a laser beam with a diameter of D2 or smaller (in the "central region") might specify, for example, MIN(X)1=25%, MIN(X)2=25%, and MIN(X)3==0%. The availability in the third region D2-D3 is irrelevant to this process because it does not use any laser power in the region larger than D2 (in the "radial edge region"). In this example, if the remaining availability, for example, V1=77%, V2=88%, and V3=0%, is experimentally determined for the laser processing equipment, then this process X may be acceptable without any problems, as can be seen from V3=0%, even if the optical elements are completely contaminated in the third region D2-D3 (in the "radial edge region").

[0063] In a similar manner, the electronic control unit determines the remaining usability V experimentally determined from the workpiece machining process that is suitable for the upcoming machining task, as shown above. i The minimum value MIN(p) is achieved by iEach set can be selected. The process that is currently suitable for the machining task, and the remaining available options V i Depending on the case, the minimum value MIN(p) may no longer be achieved. i Each set is blocked unless the optical element is cleaned or replaced. One or more processes currently have remaining usability V i The minimum value MIN(p) is still being performed by i As long as the set remains intact, the laser processing equipment remains usable for processing workpieces. In principle, the latter is the case where the relevant contaminants detected substantially affect only the radial edge region of the optical element, and not the central region of the optical element. In that case, a narrow laser beam (radially) at the location of the optical element can still be used effectively.

[0064] Bias correction can be performed to enable a more accurate estimation of contamination levels in individual areas. Figure 6 shows a schematic cross-section of the optical element 4, which is measured in a contaminant-free state in three individual measurements i=1, 2, and 3 with laser beam diameters D1, D2, and D3 (at the location of the optical element) by a sensor for scattered light. Basic signal intensity B i However, please refer to the items listed in Table 4 for details. Each basic signal intensity may be based, for example, on scattering from the surface roughness of the optical element free of contaminants, or scattering in front of or behind the optical element, and, if necessary, on multiple scattering.

[0065] These basic signal strengths B i The S values ​​in Table 4 are specified from the "raw" (directly measured, yet unbiased) signal intensity of the sensor for scattered light, and from the individual measurements of the contaminant inspection. i roh It is possible to subtract. For example, the signal intensity S from Table 3 i This was adopted as the unadjusted signal strength in Table 4. The signal strength S thus adjusted i =S iroh -B i When using this method, the calculations shown above can be performed with improved accuracy (further explanation is omitted). [Table 4]

[0066] In the example shown here, the basic signal intensity is extremely low compared to the signal intensity accompanied by scattered light from contaminants, which is actually a common occurrence. In this case, bias correction results in only a minor change in the calculation of contamination or the spatially resolved determination of contamination. However, when scattered light independent of contamination (e.g., due to surface roughness) plays a significant role, bias correction can significantly improve the accuracy of the spatially resolved determination of contamination.

[0067] Figure 7a shows a typical embodiment of the laser processing apparatus 10 according to the present invention, in the region of the laser processing head, generally in the longitudinal direction.

[0068] The laser beam 1 diverges out from a laser source 11, for example, the end of an optical fiber (not shown in detail) connected to a laser oscillator. The laser beam 1 is collimated by two lenses 14 and 15 of a collimation system, where lens 14 images the exit pupil of the laser source 11 to an intermediate focal point 16, which is located in front of lens 15 at a focal length distance. The laser beam 1 is then focused onto the surface of the workpiece 12 using lens 3. The laser beam 1 passes through an optical element 4, which is designed here as protective glass 5. A light sensor 6 is directed onto the optical element 4 and records the scattered light from the optical element 4.

[0069] At the location of the optical element 4, the laser beam 1 in Figure 7a has a diameter D1 for the first individual measurement. To adjust this diameter for further individual measurements of the scattered light from the optical element 4, the laser processing apparatus 10 has an adjustment device 13. Using this adjustment device 13, the locations of lens 14 and lens 15 can be changed along the beam propagation direction. The sensor 6 and the adjustment device 13 are connected to an electronic control unit 17 that can automatically perform individual measurements of the scattered light.

[0070] Here, the laser processing device 10 is a laser cutting device capable of cutting the workpiece 12. The workpiece 12 may be, for example, a metal plate.

[0071] In Figure 7b, lens 14 is moved slightly away from the laser source 11 using an adjustment device (which is not shown in further detail for simplicity), and lens 15 is moved slightly away from lens 14 depending on the imaging requirements. This results in a slightly larger diameter D2 at the location of the optical element 4.

[0072] In Figure 7c, lens 14 is moved slightly away from the laser source 11 using an adjustment device (which is not shown in further detail for simplicity), and lens 15 is moved slightly away from lens 14 depending on the imaging requirements. This results in a larger diameter D3 at the location of the optical element 4.

[0073] Figures 8, 9, and 10 illustrate typical optical elements and their locations within the laser processing apparatus 10 that can be tested for contaminants within the scope of the present invention. The laser processing apparatus 10 largely corresponds to the laser processing apparatus shown in Figure 7a (see there).

[0074] In the design shown in Figure 8, the optical sensor 6 monitors the protective glass 5 as an optical element 4 for contaminants and measures the scattered light emitted from the protective glass 5 at different laser beam diameters.

[0075] In the design shown in Figure 9, the sensor 6 monitors a beam splitter 20 or a translucent mirror as an optical element 4 for contaminants. For example, the translucent mirror can analyze the process by blocking thermal radiation emitted from the workpiece surface for process monitoring.

[0076] In the design shown in Figure 10, the optical element 4 monitored by the sensor 6 is a lens 3 that focuses the laser beam 1 onto the workpiece (not shown). [Explanation of symbols]

[0077] 1. Laser beam 2 focus 3. Lens (Concentrating Lens) 4 Optical elements 5. Protective Glass 6. Light sensor 7. (Local) contamination 10 Laser processing equipment 11 Laser Source 12 Workpiece 13 Adjustment device 14. Lenses (Collimation type) 15 lenses (collimation type) 16 intermediate focus 17 Electronic control unit 20 Beam Splitter / Semi-Transparent Mirror D. Diameter of the laser beam (general) Diameter of D1, D2, and D3 laser beams OA optical axis S Signal strength (general)

Claims

1. A method for inspecting an optical element (4) of a laser processing apparatus (10) with respect to contaminants (7), wherein a laser beam (1) passes through the optical element (4), which is directed to emit light through the optical element (4), and the scattered light emitted from the optical element (4) is measured by a light sensor (6), N individual measurements are performed, N ≥ 3, and during each individual measurement i, the laser beam (1) passes through the optical element (4), and the scattered light emitted from the optical element (4) is measured by the photosensor (6), and the signal intensity S ｉ However, this is determined by the light sensor (6), For each of the individual measurements i, the different diameters D of the laser beam (1) at the location of the optical element (4) ｉ However, it is set and Information about the location-dependent contaminants of the optical element (4) is obtained from the signal intensity S of the N individual measurements. ｉ Confirmed from, A method characterized in that i = 1, ..., N, where i is a measurement subscript.

2. Larger diameter D ｉ Smaller diameter D ｉ The signal intensity S increases up to ｉ Therefore, a smaller diameter D than the above ｉ The method according to claim 1, characterized in that it is presumed that the degree of contamination of the optical element (4) inside is increasing.

3. A smaller diameter D ｉ to a larger diameter D ｉ The signal intensity S that increases up to ｉ from the smaller diameter D ｉ outside of which it is presumed that the contamination degree of the optical element (4) is increasing, characterized in that it is the method according to claim 1 or 2.

4. The signal intensity S ｉ Therefore, minimum diameter D １ The degree of contamination G of the optical element (4) inside １ , and diameter D ｊ and diameter D ｊ－１ The degree of contamination G of each optical element (4) in the region between ｊ The method according to any one of claims 1 to 3, characterized in that it is determined that j = 2, ..., N, where j is the number of the remaining larger diameter subscripts.

5. The aforementioned degree of contamination G １ G ｊ However, the minimum diameter D １ From the maximum diameter D Ｎ The method according to claim 4, characterized in that the determination is repeated until the condition is met.

6. In step 1), the minimum diameter D １ Signal strength S １ Therefore, the minimum diameter D １ The degree of contamination G of the optical element (4) inside １ It is presumed that the signal intensity S １ Therefore, the next larger diameter D ２ Signal S ２ Expected signal contribution C within ２ However, the minimum diameter D １ The determination is made by the contaminants (7) of the optical element (4) inside, Furthermore, in step j), the diameter D ｊ Each corrected signal strength KS ｊ = S ｊ -C ｊ Therefore, the diameter D ｊ and the diameter D ｊ－１ The degree of contamination G of the optical element (4) in the region between ｊ It is estimated that the signal intensity S ｊ From, or alternatively, the signal intensity S １ ~S ｊ Therefore, the next larger diameter D ｊ＋１ Signal S ｊ＋１ Expected signal contribution C within ｊ＋１ However, the diameter D ｊ The method according to claim 4 or 5, characterized in that the determination is made by the contaminant (7) of the optical element (4) inside.

7. The signal contribution C ｊ The method according to claim 6, characterized in that it is determined at least approximately according to the following formula. C ｊ =S ｊ－１ *[D ｊ－１ / D ｊ ] ２

8. The aforementioned degree of contamination G １ ~G Ｎ However, it can be determined at least approximately according to the following formula, G １ = F * S １ *[D １ ] ２ and G ｊ =F*KS ｊ *[(D ｊ ) ２ -(D ｊ－１ ) ２ ] The method according to claim 6 or 7, characterized in that, in the formula, F is a proportionality constant.

9. The aforementioned degree of contamination G １ G ｊ However, V １ The minimum diameter D １ within, or each V ｊ Regarding D ｊ and D ｊ－１ The remaining usability V within the region between １ , V ｊ It is converted to, In particular, the aforementioned pollution level G １ G ｊ Each of these has a maximum value M. １ M ｊ A point has been assigned, and at that point, laser processing is no longer usable, and the remaining usability V １ , V ｊ However, it is calculated as follows: V １ = 1 - G １ / M １ and V ｊ =1-G ｊ / M ｊ 、 In particular, the remaining usability V １ , V ｊ The method according to any one of claims 4 to 8, characterized in that the information is displayed on the laser processing apparatus (10).

10. the signal strength S ｉ Before further evaluation of the signal strength S ｉ the signal strength S ｉ is subtracted from the respective signal strength S ｉ to obtain a basic signal strength B acquired using the optical element (4) in a non-contaminated state, accompanied by a corresponding laser beam (1) having the diameter D ｉ and the method according to any one of claims 1 to 9, characterized in that the bias after measurement of the signal strength is adjusted by this subtraction.

11. A method for operating a laser processing apparatus (10), wherein the optical element (4) of the laser processing apparatus (10) is inspected for contaminants (7), The inspection of the optical element (4) of the laser processing apparatus (10) with respect to contaminants (7) is performed by the method according to any one of claims 1 to 10. Based on the results of the inspection, a decision is made as to whether or not the scheduled process of laser processing the workpiece (12) can be executed using the laser processing apparatus (10), and A method characterized in that, in determining whether the scheduled process can be executed, at least the determined location-dependent information regarding the contaminants of the optical element (4) and information regarding the diameter (D) of the laser beam (1) on the optical element (4) used within the scope of the scheduled process are taken into consideration.

12. The optical element (4) of the laser processing apparatus (10) is inspected for contaminants (7), The inspection of the optical element (4) of the laser processing apparatus (10) with respect to contaminants is performed by the method described in any one of claims 1 to 10, and A method for operating a laser processing apparatus (10), characterized in that, if the determined information regarding the location-dependent contaminants of the optical element (4) indicates that the relevant contaminants (7) are present only in the radial edge region of the optical element (4) but not in the central region of the optical element (4), the laser processing apparatus (10) remains ready for operation, under the condition that only a process for laser processing a workpiece (12) is performed, such that the diameter (D) of the laser beam (1) in the optical element (4) remains within the central region, until the optical element (4) is cleaned or replaced.

13. The optical element (4) of the laser processing apparatus (10) is, with respect to the contaminant (7), - After each maintenance or repair of the laser processing head of the laser processing apparatus (10), and / or - After each predetermined operating time of the laser processing apparatus (10), and / or, - At each startup of the laser processing apparatus (10), and / or - Before the start of each new process for laser processing (10) of the workpiece (10), and / or - The method according to claim 11 or 12, characterized in that it is inspected when manually started.

14. A laser processing apparatus (10), A laser source (11) for providing a laser beam (1), An optical element (4) through which the laser beam (1) passes, and in particular an optical element (4) which is directed to radiate through the optical element (4), An adjustment device (13) for adjusting the diameter (D) of the laser beam (1) at the location of the optical element (4), The system comprises a light sensor (6) for measuring scattered light emitted from the optical element (4), and an electronic control unit (17), The electronic control device (17) is configured to perform, in an automated sequence, a method for inspecting the optical element (4) of the laser processing apparatus (10) with respect to contaminants (7) according to any one of claims 1 to 10, The electronic control device (17), using the adjustment device (13), adjusts the different diameters D of the laser beam (1) at the location of the optical element (4) for each of the N individual measurements. ｉ Set the diameter D continuously for each of the following: ｉ Using this, the associated signal intensity S in the light sensor (6) ｉ A laser processing apparatus (10) characterized by being configured to determine [something].

15. The laser processing apparatus (10) according to claim 14, characterized in that the laser processing apparatus (10) is a laser cutting apparatus.

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