Method for determining at least one offset parameter of a laser processing machine

Abstract

The present invention relates to a method for determining at least one offset parameter of a laser processing machine by means of a reference device, wherein the reference device is ground circumferentially and is set up to receive an interchangeable marking element that can be processed by the laser device, and wherein the method comprises steps in which a wear parameter of a measuring probe of a measuring system of the laser processing machine is determined and in which offsets of this measuring probe, an optical measuring device of the measuring system and a laser device are determined, depending on which at least one offset parameter of the laser processing machine is determined.

Description

Technical field

[0001] The present invention relates to a method for determining at least one offset parameter of a laser processing machine by means of a reference device, an adjustment method for a laser processing machine and a laser processing machine which is configured to carry out this method. Background of the invention

[0002] The production of precision components requires adherence to increasingly tighter tolerances. To achieve high precision in material removal, laser processing machines are often used today, whose lasers can be controlled very precisely to remove even the smallest amounts of material with pinpoint accuracy.

[0003] Besides the amount of material to be removed, it is crucial that the position from which material is to be removed can be precisely determined. This requires precise adjustment of the laser processing machine. In particular, the relative positions of the various components of the laser processing machine required for processing a workpiece must be known with the smallest possible measurement tolerances.

[0004] Calibration and adjustment methods are known from the prior art for calibrating and / or adjusting different devices of a laser processing machine.

[0005] Patent EP 3 251 784 A1 proposes a calibration method using a ring-shaped calibration device, which is initially approached by a contact probe. In subsequent steps, a machine operator first calibrates the alignment of a laser on the machine, before creating a reference mark on the reference device based on this calibration and approaching the reference device with a measuring probe.

[0006] However, this and other prior art methods have disadvantages that negatively affect the accuracy of the calibration.

[0007] The aforementioned procedure requires the interaction of a machine operator and is therefore dependent on the operator's accuracy and presence. This can lead to problems in quality assurance if, for example, different machine operators work with varying degrees of accuracy, resulting in the production of defective parts. Furthermore, machines requiring calibration cannot be operated at maximum efficiency, as calibration can only be performed when a machine operator is present and actively involved.

[0008] Furthermore, this method lacks verification mechanisms to monitor the quality of the calibration. For example, there is no information about the condition of the contact probe. Consequently, the calibration depends on an unknown wear state of the contact probe, and this introduces a further source of inaccuracy into the calibration. Summary of the invention

[0009] One objective of the invention is to provide a way to adjust a laser processing machine more accurately and efficiently than is possible with previously known methods.

[0010] To solve this problem, a method for determining at least one offset parameter of a laser processing machine according to claim 1, an adjustment method according to claims 10 to 12, laser processing machines according to claims 13 and 14 and a method for laser processing according to claim 15 are proposed.

[0011] The respective dependent patent claims relate to preferred, particularly advantageous embodiments.

[0012] According to a first aspect of the invention, a method for determining at least one offset parameter of a laser processing machine is proposed. The laser processing machine comprises at least one laser device and a measuring system with a probe and an optical measuring device.

[0013] An offset parameter is any parameter suitable for describing the offset of devices within a laser processing machine. An offset parameter can, for example, be a position specification, particularly with respect to a reference coordinate system. Furthermore, it can be a parameter that specifies a change in position, especially within a reference coordinate system. Such a parameter can, for example, describe a rotation or translation. In particular, such a parameter can also specify a coordinate transformation, such as a zero-point shift. Finally, such a parameter can refer to the laser device, the optical measuring device, or individual devices comprised of these. An offset parameter can also describe the positional relationship between devices within the laser machine.Furthermore, an offset parameter can also refer to different devices or specify offset information, such as that listed above, for multiple devices. For example, an offset parameter could describe a displacement of the probe and a displacement of the laser device, as well as a position of the optical measuring device.

[0014] The laser device of the laser processing machine comprises, in particular, a laser configured to remove material from a workpiece to be processed by the laser processing machine. In particular, the laser device can be machine-controlled for movement. Such movement of the laser device can, for example, be controlled as a function of an offset parameter that specifies a position of the laser device in a reference coordinate system of the laser processing machine or the measuring system of the laser processing machine. An offset parameter of the laser device can, for example, also specify the deviation from an assumed or previously determined position of the laser device in such a reference coordinate system.

[0015] The optical measuring device can be a camera device, or the optical measuring device can include a camera device. The camera device can be configured to acquire image data, for example, of a workpiece to be processed and / or the processing area of ​​the laser processing machine. Furthermore, the camera device can be configured to acquire the image data depending on camera parameters.

[0016] Furthermore, the optical measuring device can also be configured as an optical position detector device, or the optical measuring device can include an optical position detector device. The optical position detector device is configured to detect a focal point of the laser of the laser device. Furthermore, the optical position detector device can be configured to be moved by machine control.

[0017] The optical measuring device can also be machine-controlled. In particular, the measuring device can be machine-controlled in such a way that it maintains or changes its position relative to the laser device. The movement of the optical measuring device can also be controlled depending on an offset parameter.

[0018] According to the invention, the aforementioned method employs a reference device that is ground on all sides. In particular, the edges of the reference device can be unbroken. Furthermore, the reference device is configured to accommodate an interchangeable marking element that can be processed by the laser device of the laser processing machine.

[0019] The following section describes in more detail the steps included in the procedure.

[0020] In a single step, the reference device is provided at the laser processing machine. The reference device can, for example, be clamped into a fixture of the laser processing machine or be permanently mounted or installed on the laser processing machine.

[0021] The reference device is advantageously provided in such a way that it can be rotated and / or moved relative to the laser device and / or relative to the measurement system and / or relative to devices encompassed by the measurement system, such as the probe or the optical measuring device. Generally speaking, the reference device is advantageously provided in such a way that its position can be changed within a reference coordinate system of the laser processing machine and / or a measurement system of the laser processing machine. In particular, changes to the position of the reference device relative to other devices of the laser processing machine, such as the optical measuring device, the laser device, or the probe, may also be possible.It is particularly irrelevant whether the position of the reference device itself is changed, or whether the positions of the respective devices are changed relative to the reference device.

[0022] Advantageously, in a further step, the deviation of the position of the provided reference device from a predetermined position is determined using the measuring probe. Particularly advantageous is the determination of the rotation angle of the provided reference device. This angle can be determined with respect to a reference direction of rotation. For example, the rotation angle is determined by probing at least two points on a circumferential side of the reference device with the measuring probe of the laser processing machine. The rotation angle of the reference device can then be calculated from the coordinates of the probed points. The rotation angle can also be determined, for example, using an angle sensor on the laser processing machine's mounting.

[0023] In a further advantageous step, a position correction parameter is determined based on the measured deviation in the position of the reference device. Such a position correction parameter can, in particular, be an offset parameter, as described above. This parameter can be advantageously used to account for the measured deviation in the position of the reference device in all operations of the laser processing machine. For example, the position of the reference device can be changed directly by rotating or moving the reference device, or by rotating or moving the devices of the laser processing machine relative to the reference device, depending on the determined position correction parameter. In an advantageous alternative to this approach, the position correction parameter has only a mathematical effect.In this process, process steps on the laser processing machine are advantageously performed depending on the position correction parameter. In particular, the steps of measuring the reference device, determining at least one wear parameter, determining the offset of the measuring probe, determining the offset of the optical measuring device, and determining the offset of the laser device can be performed depending on the position correction parameter. Specifically, calculations of positions, absolute or relative, or movements of devices on the laser processing machine, also absolute or relative, can be performed depending on the position correction parameter. Advantageously, transformations of coordinate systems can be performed depending on the position correction parameter. The position correction parameter can also be used particularly advantageously in a termination condition.If the reference device is positioned in such a way that it cannot be moved or rotated, the process can be terminated early if a position correction parameter is determined that deviates too much from a reference parameter. This approach is particularly advantageous for laser processing machines that only have three numerically controlled axes.

[0024] In a further advantageous step, the provided reference device is moved according to the determined position correction parameter to achieve a measurement position. The movement of the reference device according to the position correction parameter can include any relative rotation and / or displacement of the clamped reference device. For example, a physical rotation of the reference device can occur according to the determined position correction parameter. Another possibility for rotation according to the position correction parameter is a coordinate transformation. In this case, a relative rotation would occur because subsequent controls of the laser processing machine would be based on a correspondingly rotated coordinate system. The aforementioned rotation possibilities are merely examples; other rotation and displacement possibilities are conceivable and encompassed by the invention.In particular, combinations of physical rotations of the reference device and transformations of coordinate systems or displacements of devices of the laser processing machine are also included, each depending on the determined position correction parameter.

[0025] The measurement position is defined as a position in which the reference device can be located for subsequent steps of the process. Advantageously, this position is chosen such that specific points of the reference device are aligned with specific points of a coordinate system of the laser processing machine and / or a coordinate system of the laser processing machine's measuring system. Particularly advantageous is the measurement position chosen such that edges of the reference device are aligned along coordinate axes of a coordinate system of the laser processing machine and / or along coordinate axes of a coordinate system of the laser processing machine's measuring system. In these advantageous configurations, subsequent calculations are simplified, as irrelevant coordinates can be disregarded.

[0026] In the next step of the process, target values ​​for at least one first and one second dimension of the reference device are provided. These target values ​​can be values ​​previously determined for the corresponding dimensions of the reference device. Alternatively, they can also be manufacturing parameters for the corresponding dimensions. In any case, the target values ​​are pre-known values ​​for the corresponding dimensions of the reference device. Advantageously, these target values ​​specify the corresponding dimensions as accurately as possible; that is, the measurement deviations in determining the target values ​​should be as small as possible.

[0027] The clamped reference device is then measured. This is done by determining the coordinates of points on the circumferential surface of the reference device using a measuring probe. At least two dimensions of the reference device are determined from these coordinates.

[0028] Advantageously, at least four points on the circumferential surface of the reference device are approached with the measuring probe of the laser processing machine, and coordinates are thus determined for each of these points. Particularly advantageous is the determination of coordinates for more than four points by approaching them with the measuring probe, and these coordinates are then calculated to determine the coordinates used to determine the dimensions of the reference device. This makes it possible to statistically monitor the results of the coordinate determination using the measuring probe.

[0029] In a subsequent step of the procedure, a wear parameter of the measuring probe is determined based on the measurement results from the step of measuring a first and a second dimension of the reference device, as well as on the basis of the provided target values ​​of the first and second dimension of the reference device.

[0030] A wear parameter is any parameter suitable for describing the wear state of a measuring probe. In particular, a wear parameter can be a vector that describes the deviation of a probe dimension from a standard dimension in different coordinate directions. Furthermore, a wear parameter can also specify a direction-dependent correction offset required to correct the probe measurements in the respective direction in order to compensate for wear in that direction.

[0031] A wear parameter of the measuring probe can advantageously be determined by calculating the difference between the determined dimensions of the reference device and the respective predetermined dimensions of the reference device. Since the directions of the corresponding dimensions are known, particularly depending on the measuring position, the calculation can be performed in such a way that the wear of the measuring probe is calculated in a specific direction.

[0032] In a further step of the process, two non-parallel edges of the reference device are defined as alignment edges. These alignment edges serve as reference edges for subsequent steps. The definition can be achieved in various ways. For example, the alignment edges can be defined by corresponding control parameters, or the definition can be implicit, such as through a relation of the alignment edges to coordinate axes of a coordinate system of the laser processing machine's measuring system.

[0033] In the next step, the intersection point of the defined alignment edges is calculated. This calculation is based on the coordinates determined during the wear analysis of the measuring probe. Additional information can also be incorporated into this calculation. In particular, the predetermined dimensions of the reference device can be included.

[0034] The offset of the measuring probe is determined based on the calculated intersection point of the alignment edges. Advantageously, the coordinates of the calculated intersection point of the alignment edges are defined as the offset of the measuring probe.

[0035] In a subsequent step of the procedure, the offset of the optical measuring device of the laser processing machine's measuring system is determined. For this purpose, the optical measuring device is moved iteratively such that a reference point of the optical measuring device, for example, the center point of an image captured by the optical measuring device, is positioned at least at two measuring points on the previously determined alignment edges of the reference device. Each alignment edge contains one measuring point. The intersection point of the alignment edges is then calculated from the coordinates at which the reference point of the optical measuring device lies on the measuring points.

[0036] The offset of the optical measuring device is determined based on this intersection point. Advantageously, the coordinates of the calculated intersection point of the alignment edges are defined as the offset of the optical measuring device.

[0037] In a particularly advantageous embodiment of the method, the optical measuring device is moved iteratively such that a reference point of the optical measuring device is positioned at up to 10 different measuring points per alignment edge. This enables quality control of the results of the optical measuring device using statistical methods. Advantageously, the method is terminated and / or a warning signal is issued if a statistical value, determined as a function of the approach to the measuring points with the optical measuring device, exceeds or falls below a corresponding limit value.

[0038] In a further step, the offset of the laser device is determined. For this purpose, a reference mark is created at a predetermined position on a marking element mounted in the reference device using the laser of the laser device. Following the creation of this reference mark, the optical measuring device of the laser processing machine's measuring system is moved such that a reference point of the optical measuring device, for example, the center point of an image captured by the optical measuring device, is positioned on a reference point of the created reference mark, for example, a center point or intersection of the reference mark or sections thereof.The offset of the laser device is then determined depending on the coordinates of the predetermined position where the reference mark was formed and depending on the coordinates of the position where the reference point of the optical measuring device is positioned on the reference point of the reference mark.

[0039] In a particularly advantageous embodiment of the method, the reference device has a polygonal, and in particular rectangular, horizontal cross-section. Particularly preferably, the reference device further has only rectangular vertical cross-sections. "Horizontal" is to be understood as running parallel to a top or bottom surface of the reference device. "Vertical" cross-sections are to be understood as running perpendicular to a horizontal cross-section.

[0040] This significantly simplifies the corresponding coordinate calculations, as only x and y coordinates need to be included. If the alignment edges are also advantageously aligned parallel to the x and y coordinates, the calculations can be simplified even further.

[0041] Furthermore, the polygonal cross-section and the resulting elimination of complex curves on the perimeter walls of the reference device advantageously simplify its precise manufacturing. This allows for cost savings and further improvements in the accuracy of the process.

[0042] In a further advantageous embodiment of the method, the reference device is provided by clamping. Preferably, the reference device is clamped in the laser processing machine in such a way that it can be rotated about a rotational axis C, and this rotational axis is perpendicular to a surface of the reference device.

[0043] This makes it advantageously easier to correct a rotational deviation in the position of the reference device, since only the rotational axis C needs to be controlled.

[0044] In a further advantageous embodiment of the method, the reference marking is formed in a cross shape at a predetermined position on a marking element mounted in the reference device. Furthermore, the position of the reference marking is determined by the optical measuring device by positioning a reference point of the optical measuring device on points on the edges of the legs of the reference marking. For each leg of the reference marking, at least two points on opposite edges of the leg are approached to position the reference point of the optical measuring device. The coordinates of the approached points determined by this positioning are calculated for each leg. Subsequently, these points calculated for each leg are further combined to determine the coordinates of a reference point of the reference marking.Depending on the coordinates of the predetermined position where the reference mark was formed and the calculated coordinates of the reference point of the reference mark, an offset of the laser device of the laser processing machine is determined.

[0045] Advantageously, a difference is calculated between this reference point and the predetermined position where the reference mark was formed, which is then determined as the offset of the laser device.

[0046] In this advantageous embodiment of the method, the quality of the reference marking is additionally determined. This quality determination is carried out by measuring the thickness, for example, of each leg of a cross-shaped reference marking. The thickness is determined at predetermined points. For a cross-shaped reference marking, the thickness is measured, for example, on each leg at a predetermined distance from the reference point of the marking. To determine the thickness, the camera device determines the coordinates of points on the edges of the reference marking at the predetermined points, from which the thickness of the respective reference marking at the predetermined points is calculated.For example, with a cross-shaped reference mark, points on the arms of the cross are determined at a predetermined distance from the reference point of the mark, and a thickness is measured at these points. Advantageously, the camera device does not need to be physically moved to determine the coordinates of points, as these can also be calculated from the images captured by the camera device. A particularly advantageous method is to map distances in pixels in the images captured by the camera device to distances in a metric within a reference coordinate system of the laser processing machine or the optical measuring device of the laser processing machine.

[0047] This approach offers a particular advantage: the possibility of additional quality assurance to achieve the highest precision in determining offsets. The process can be terminated if a characteristic value calculated from several thicknesses of the reference mark, such as a quotient, deviates too significantly from certain target quality limits and their associated parameters.

[0048] Such deviations indicate problems with the laser processing machine that go beyond mere temperature drift and the associated coordinate deviations or changing misalignments of the machine's components. Stopping the process, and in particular warning the machine operator or indicating the need for comprehensive maintenance, makes it possible to reduce the production of defective parts and increase the efficiency of the laser processing machine through appropriate maintenance intervals.

[0049] The process can also be advantageously aborted if the difference between the calculated reference point of the reference mark and the predetermined position at which the reference mark was formed is too large. In such a case, there is an offset of the laser device that is significantly larger than expected. It is particularly difficult to determine the cause of such an unexpectedly large offset. In such a case, aborting the process and possibly warning the machine operator can advantageously prevent damage to the laser processing machine caused by its use in an undefined state.

[0050] In a further advantageous embodiment of the method, the reference marking is formed by at least two laser engravings that at least partially overlap, each of which is formed depending on laser parameters. In particular, the laser parameters for different engravings can remain unchanged or be changed. For example, according to this advantageous embodiment of the method, the edges of the reference marking could be post-processed with the laser of the laser device by forming a second laser engraving in the edge region of the reference marking, which again removes material to form a particularly clean edge. For example, an angle, laser power, frequency, engraving speed, or laser focus could be changed to remove more or less material and thus further improve the edge of the reference marking.

[0051] Because each laser engraving can be re-parameterized according to this method, the process is particularly flexible and advantageously allows the use of different materials or different coatings for the marking element included in the reference device.

[0052] This design of the method also advantageously allows for the creation of particularly high-contrast reference markings. Additionally, reference markings with exceptionally smooth edges can be created; that is, the transition area from the reference marking to surrounding unmarked areas of the marking element is particularly uniform across the entire circumference of the reference marking. This is especially advantageous when the reference markings are to be detected automatically, particularly by machine control. The greater the contrast of the reference markings in this case, and the smoother the edges of the reference markings, the easier and more accurate the identification of the reference markings using automatic image recognition.Furthermore, other image processing, such as that which can be used for automated determination of the quality of the reference markings, is also facilitated by this advantageous design of the method.

[0053] According to a further advantageous embodiment of the method, the determination of the offset of the laser device is iteratively repeated in a machine-controlled manner such that a new reference marking is formed depending on the offset of the laser device determined in the previous iteration, and the reference marking is formed at a different predetermined position than in the previous iteration.

[0054] For example, the offset of the laser device determined in one iteration step is used to correct the positioning of the laser device in the next iteration step. This can be done, for instance, by storing the offset of the laser device from the previous iteration in the machine control. The determined offset of the laser device can be stored as a zero-point shift in the machine control, or in a memory location of the control device within the machine control.

[0055] This advantageous embodiment of the method enables the offset of the laser device to be determined with significantly increased accuracy. For example, the determination of the laser device's offset can be repeated a predetermined number of times. Alternatively, machine-controlled iteration can be performed until the difference between the determined offset and the offset determined in the previous iteration falls below a certain threshold.

[0056] The size of the reference mark and the dimensions of the marking element are advantageously coordinated, allowing 500 reference marks to be formed at different positions on a single marking element. This makes it possible to iteratively apply a large number of marks to the marking element using machine control, without the need for manual replacement of the marking element.

[0057] This opens up advantageous possibilities for automating the adjustment of the laser processing machine, especially without interaction by a machine operator, and with high accuracy.

[0058] In particular, the amount of data collected to determine the offset can be increased by iteratively repeating the machine-controlled calculation. This allows, for example, the use of statistical methods that can observe and evaluate the determination of the laser device's offset across different iteration steps. This could, among other things, determine whether a shift in the laser device's offset exhibits a directional dependency.

[0059] According to a further preferred embodiment of the method, the determination of the rotation angle of the reference device and the rotation of the reference device as a function of the determined rotation angle are alternately repeated iteratively by machine control. These iterations are performed until a rotation angle of the reference device is determined that falls below a predetermined reference angle.

[0060] Similar to the machine-controlled iterative repetition of determining the laser device's offset, this advantageous embodiment of the method allows for particularly precise correction of the reference device's rotation angle, meaning that the reference device can be positioned with exceptional accuracy in a measurement position. This advantageous embodiment also enables statistical evaluation across various iteration steps of determining and correcting the rotation angle. This advantageously allows the angle of the reference device to be set with exceptional precision to a predetermined angle, thus aligning the reference device very accurately. This, in turn, advantageously increases the accuracy for all subsequent steps and therefore improves the achievable accuracy in determining the offsets.

[0061] In a further advantageous embodiment of the method, the determined wear parameter of the measuring probe is compared with a predetermined wear limit. If the determined wear exceeds the limit, the method is terminated, i.e., no offsets are determined.

[0062] This advantageous design allows for a self-test before further process steps are carried out. Since the determination of the probe offset takes place at the beginning, and any error in determining the probe offset consequently affects the subsequent steps—meaning a measurement error in this step propagates through the further process—the accuracy of all offsets determined after the probe offset can be advantageously improved if the process is only started with a probe whose wear is below a predetermined wear limit. Advantageously, this wear limit is chosen such that wear of the probe below this limit can be disregarded. Analogous to a wear parameter, the wear limit is understood to be any value that is suitable for describing a wear state of the probe.As an example, but not exhaustive, a maximum wear limit for the measuring probe in a specific direction may be mentioned. If the measuring probe were worn more in this specific direction than the wear limit indicates, the process would be terminated in this advantageous configuration. In particular, a warning can also be issued to a machine operator if the process is terminated due to excessive wear of the measuring probe. This facilitates necessary maintenance of the machine.

[0063] Furthermore, this design of the procedure allows for better automation of the process, since the execution of the procedure can be aborted in a machine-controlled manner, especially without interaction of a machine operator, if inaccurate results are to be expected due to wear of the measuring probe.

[0064] In a further advantageous embodiment of the method, the offset of the laser device is not determined by means of a reference mark. Instead, the optical measuring device is moved by machine control until it detects the focal point of the laser. In this case, the offset of the laser device is determined as a function of the distances by which the optical measuring device was moved until it detected the focal point of the laser.

[0065] This design advantageously increases the efficiency of the process and reduces material usage. For example, no marking element needs to be inserted into the reference device, as the formation of a reference mark is unnecessary with this design. Furthermore, since this design eliminates the need for optical detection of a reference mark using the optical measuring device, and the offset of the laser device is instead determined directly by the distances traveled by the optical measuring device, another source of inaccuracies is removed. The process can therefore deliver more accurate results with this design. In particular, determining the offset of the laser device in this design is also independent of the quality of the reference mark produced.

[0066] According to a further aspect of the invention, an adjustment method for a laser processing machine is proposed. This method comprises detecting a time-dependent change in the value of a measured quantity in the environment of the laser processing machine and the current processing status of the laser processing machine.

[0067] The processing status of a laser processing machine refers to one or more values ​​indicating whether and which devices of the laser processing machine are currently active. Furthermore, the processing status also indicates whether a workpiece is currently being processed in the laser processing machine or not.

[0068] An example of a measured parameter in the environment of a laser processing machine is the ambient temperature. A change in the ambient temperature can affect the offsets of the laser processing machine's devices, as these are dependent, among other things, on the temperature of the laser processing machine itself, which in turn depends on the ambient temperature and its changes.

[0069] Furthermore, the proposed adjustment method comprises a machine-controlled iterative determination of at least one offset parameter of the laser processing machine by means of a method according to one of claims 1 to 9 depending on the detected time-dependent change in the value of the measured variable of the environment of the laser processing machine and depending on the detected current processing status of the laser processing machine.

[0070] Advantageously, the machine-controlled iterative determination of at least one offset parameter is only initiated when the current processing status indicates that the laser processing machine's fixtures are inactive and / or no workpiece is currently being processed on the machine. This prevents the adjustment process from interrupting workpiece processing, thus increasing the efficiency of the laser processing machine.

[0071] This process also includes an adjustment step in which the laser processing machine is adjusted as a function of at least one offset parameter. Adjustment encompasses any setting or changing of settings, control parameters, zero-point shifts, or coordinate systems of the laser processing machine and / or devices encompassed by the laser processing machine. In particular, it also includes persisting offset parameters so that they can be used for motion calculations of the laser processing machine.

[0072] For example, if an increase in the ambient temperature of the laser processing machine is detected that exceeds a certain temperature difference, it can be expected that, due to the influence of the ambient temperature on the temperature of the laser processing machine, the offsets of the laser processing machine's fixtures will also have changed accordingly and will need to be recalculated. In this case, the iterative, machine-controlled determination of the offsets as a function of a detected temperature increase allows for an automated response to the changed environment and ensures consistent manufacturing quality. In particular, no interaction from a machine operator is required.

[0073] Furthermore, this method also allows appropriately configured laser processing machines to be used in locations where, for example, temperature control of the installation site is not feasible without major modifications or financial expenditure. The proposed adjustment method thus increases the operational flexibility of appropriately configured laser processing machines.

[0074] Another adjustment method for a laser processing machine is proposed, which includes capturing a value of a measured quantity of the environment of the laser processing machine and capturing a current processing status of the laser processing machine.

[0075] This method further comprises a machine-controlled iterative determination of at least one offset parameter of the laser processing machine by means of a method according to any one of claims 1 to 9, depending on the measured value of the parameter of the environment of the laser processing machine and depending on the measured current processing status of the laser processing machine. As described above, the machine-controlled iterative determination of at least one offset parameter is advantageously carried out only when no workpiece is currently being processed on the laser processing machine.

[0076] This adjustment method allows for automated readjustment even in the case of slow temperature changes at specific absolute temperatures. For example, if the ambient temperature is 15 °C in the morning, it can reach significantly higher values ​​by midday, despite a slow increase over several hours, without any large temperature jump occurring in between. This method allows for a response to specific temperature thresholds, independent of any changes. For example, readjustment could occur at 10 °C, 20 °C, 30 °C, or 40 °C.

[0077] If the laser processing machine is readjusted using absolute temperatures according to this method, its operational efficiency can be further increased. In particular, machine accuracy can be automatically maintained or restored even in locations subject to large periodic temperature fluctuations, but where large temperature jumps do not occur.

[0078] A further adjustment method for a laser processing machine is proposed, which includes recording a first time, recording a second time, and recording the current processing status of the laser processing machine. The first time can be, in particular, a start time, for example, of the machine or a current production run. The second time can be, for example, the time at which the production of a specific part begins, or it can be a current time. This list is not exhaustive, and it is apparent to those skilled in the art that any time can be recorded.

[0079] Furthermore, the machine-controlled iterative determination of at least one offset parameter of the laser processing machine is included, using a method according to any one of claims 1 to 9, depending on the recorded first time, the recorded second time, and the recorded current processing status of the laser processing machine. As described above, the machine-controlled iterative determination of at least one offset parameter is advantageously performed only when no workpiece is currently being processed on the laser processing machine.

[0080] This adjustment method enables time-dependent, automated adjustment of a laser processing machine. On the one hand, this guarantees the accuracy of the laser machine over a long period, as the offsets of the machine's components are recalculated at fixed intervals and incorporated into the machine's adjustment. On the other hand, this method allows for readjustment at varying intervals depending on the machine's operating time. For example, this makes it possible to guarantee high manufacturing accuracy even during the initial period after commissioning the laser processing machine.Especially during this initial phase after commissioning, the misalignments of the laser processing machine's fixtures change more rapidly because the machine is not yet in thermal equilibrium and its temperature is constantly fluctuating. This temperature drift also causes the fixture misalignments to change. The proposed method allows for adjustments to be made every 15 minutes during this initial phase, for example, within the first three hours after commissioning, thus ensuring high manufacturing accuracy even during this initial period.

[0081] This process consequently reduces the number of defective parts produced and thus increases the efficiency of the laser processing machine being adjusted.

[0082] A further adjustment method for a laser processing machine is proposed, which includes recording a counter value and the current processing status of the laser processing machine. The counter value could, for example, indicate how many workpieces have already been processed on the laser processing machine. Alternatively, it could indicate how often a specific control program of the laser processing machine has been executed, or the distance traveled by certain devices of the laser processing machine. This list is not exhaustive, and it is apparent to those skilled in the art that other counter values ​​can also be recorded.

[0083] Furthermore, the machine-controlled iterative determination of at least one offset parameter of the laser processing machine is included, using a method according to any one of claims 1 to 9, depending on the recorded counter value and the recorded current processing status of the laser processing machine. As described above, the machine-controlled iterative determination of at least one offset parameter is advantageously performed only when no workpiece is currently being processed on the laser processing machine.

[0084] This adjustment method enables the automated adjustment of a laser processing machine based on countable machine characteristics. Particularly advantageous is automated adjustment of the laser processing machine after a predetermined number of processed workpieces. This provides significant automated support for quality assurance, as the laser processing machine is adjusted regularly and automatically. For example, an adjustment can be performed automatically after every 50 processed workpieces. The adjustment frequency can also be advantageously linked to the number of specific, countable control operations using this method. For instance, an adjustment could be performed after every 50 meters a laser processing machine device has traveled.This ensures regular, automated adjustment of the laser processing machine, regardless of the specific workpieces being processed. This further increases the operational flexibility of the presented method and the laser processing machine.

[0085] According to a further aspect of the invention, a laser processing machine is proposed comprising a laser device, a measuring system with a measuring probe and an optical measuring device, and a control device configured to iteratively perform a method according to one of claims 1 to 9 in a machine-controlled manner in order to determine at least one offset parameter of the laser processing machine.

[0086] According to the invention, such a laser processing machine allows for machine-controlled determination of at least one offset parameter relevant to laser processing. This offers the advantage that no interaction by a machine operator is necessary to determine the offset parameter. In particular, machine-controlled determination of the offset parameter can be performed faster than determination by a machine operator. Consequently, the laser processing machine according to the invention can be used more efficiently.

[0087] The faster, machine-controlled determination of the offset parameter also offers the advantage that a laser processing operation can be (re)commenced more quickly after the offset parameter determination begins. This reduces the time between determining the offset parameter and (re)commencing laser processing, during which the offset parameter can change. This can occur, for example, due to thermal drift, which can lead to changes in the offsets of the laser processing machine's fixtures. Determining an offset parameter in close temporal proximity to laser processing with the laser processing machine therefore results in more precise laser processing.

[0088] Furthermore, inaccuracies that can arise from different determination of the offset parameters by different machine operators can be avoided. The offset parameters of the proposed laser processing machine can therefore be determined more accurately and with smaller deviations across different determination iterations by machine control, which has a direct positive impact on the achievable processing accuracy.

[0089] According to a further aspect of the invention, a laser processing machine is proposed comprising a laser device, a measuring system with a measuring probe and an optical measuring device, a measuring device configured to record values ​​of a measured quantity of the environment of the laser processing machine and its time-dependent changes, a time recording device, a counting device and a control device, and which is configured to perform a machine-controlled adjustment method according to one of claims 10 to 12.

[0090] According to the invention, this laser processing machine allows for particularly high manufacturing accuracy because it can be adjusted by machine control. In particular, no interaction by a machine operator is necessary. Adjustment of the laser processing machine can therefore be carried out more quickly and accurately by machine control.

[0091] Since the machine-controlled adjustment is based on measured values ​​of parameters in the laser processing machine's environment or their changes over time, an efficiency advantage is achieved compared to conventional laser processing machines, as adjustments are made on an ad-hoc basis. If, based on measured values ​​of parameters in the laser processing machine's environment or their time-dependent changes, a high level of manufacturing accuracy can be maintained, no adjustment is performed. This allows the laser machine to be used for the production and / or processing of workpieces with high accuracy, and adjustment is only necessary when a loss of accuracy is anticipated.

[0092] According to a further aspect of the invention, a method for laser processing is proposed. The processing is carried out using a laser processing machine according to claim 13 or 14, and the laser processing takes place depending on at least one determined offset parameter.

[0093] The at least one determined offset parameter can be incorporated into the laser processing in various ways. This method makes it possible to perform particularly precise laser processing. Fig. Figure 1 shows a model of one embodiment of the reference device. Fig. Figure 2 shows a view of the top of the model of the reference device with the marker element in place. Fig. Figure 3 shows a sketch of a reference marker with measuring points and reference point. Fig. Figure 4 shows a flowchart of an advantageous method for determining at least one offset parameter of a laser processing machine according to claim 1 with the additional optional steps S2 and S3. Fig. Figure 5 shows a flowchart of the adjustment procedure for a laser processing machine according to claims 10 to 12. Fig. Figure 6 shows a flowchart of the laser processing method according to claim 15. Detailed description of the characters

[0094] Fig. Figure 1 shows a model of an embodiment of the reference device (100). Two non-parallel edges are marked as alignment edges (1, 2). The intersection of these alignment edges (3) serves to determine offsets of fixtures on the laser processing machine. Furthermore, the intersection of the alignment edges (3) can also be defined as the reference point of the reference device, advantageously forming a zero point for a coordinate system referenced to the reference device. The reference device can then be positioned via this point in a machine coordinate system or in a coordinate system of the laser processing machine's measuring system.

[0095] A marking element (10) is mounted in the reference device (100). This marking element (10) is configured to be processed by the laser of the laser processing machine. In particular, the laser is configured to form reference markings on the marking element (10). The marking element can be mounted in the reference device in various ways. By way of example, and without limitation, the marking element can be magnetically mounted or glued in place. In an alternative embodiment, the marking element can be integrally connected to the reference device, for example, by milling a marking surface out of the reference device.

[0096] Advantageously, the reference device is mounted in a holder (6), which in turn can be clamped into a receptacle (not shown) of the laser processing machine. Particularly advantageously, the reference device can also be clamped directly into a receptacle of the laser processing machine without a holder (6). Advantageously, the reference device is oriented such that the underside of the device points towards the clamping point, or towards the receptacle. Advantageously, the top side of the reference device is the side opposite the underside of the reference device, where the marking element is mounted.

[0097] The edges of the reference device are ground all around. This reduces manufacturing costs and enables high accuracy despite the cost-effective production. The fact that the upper edges, such as the alignment edges (1, 2), are not chamfered is particularly advantageous. This facilitates automated edge detection using an optical measuring device, as a higher-contrast image of the edges can be generated. The optical measuring device can advantageously generate images depending on the acquisition parameters, which allows for further improvement of automated edge detection, as the acquisition parameters can be adjusted iteratively. Image processing techniques such as edge detection filters or subpixel interpolation can be used for automated edge detection with the optical measuring device.The use of these techniques is facilitated by the advantageously unbroken edges of the reference device, or rather, its results are improved.

[0098] According to the invention, at least two dimensions of the reference device (4, 5) are known beforehand, or they are measured before the target values ​​of the dimensions are provided in the method for determining at least one offset parameter.

[0099] Fig. Figure 2 shows a view of the top of the reference device (100) with a marker element (10) attached. Various measuring points (20-27) are also indicated. These measuring points (20-27) are examples of measuring points that can be accessed either by the measuring probe of the laser processing machine or by the optical measuring device. In particular, the measuring points (20-23), for example, are measuring points on non-parallel edges (1, 2) of the reference device. These edges are defined as alignment edges (1, 2) by way of example. This configuration is merely an example. Other edges could also be defined as alignment edges without affecting the invention.

[0100] Furthermore, a dimension of the reference device can be determined from each pair of opposing measurement points on edges (20, 25), (21, 24), (22, 27), (23, 26). Advantageously, the reference device is positioned in a measurement position that allows irrelevant coordinates to be disregarded, for example, by aligning the reference device along a corresponding reference coordinate system.

[0101] Fig. Figure 3 shows a sketch of a reference marker (30) with potential measurement points (31 - 40) and a reference point (41) of the reference marker (30).

[0102] A cross-shaped reference marking is shown as an example. This form of reference marking is merely an advantageous embodiment; in particular, the reference marking can also be shaped differently. For example, the reference marking can be star-shaped, square, rectangular, or polygonal in another way. The marked measuring points (31–40) are also to be understood merely as exemplary embodiments. In particular, the measuring points (31–40) can also be positioned at other locations or at a different distance from a reference point (41) of the reference marking (30). Furthermore, it is advantageously possible for more than one pair of measuring points to be located on each leg (42, 43, 44, 45) of a cross-shaped reference marking (30). This enables a particularly precise measurement of the reference marking (30), which allows for a particularly accurate determination of any offset of the laser device.

[0103] In addition to determining the reference point (41) of the reference marking (30) and the offset of the laser device as a function of the coordinates of this reference point (41), the quality of the reference marking (30) can also be determined using the measurement points. For this purpose, the thickness of each leg (42, 43, 44, 45) of the cross-shaped reference marking (30) is determined as a function of the coordinates of pairs of measurement points (31, 40), (32, 35), (33, 34), (36, 37), (38, 39) located on opposite sides of the legs. It is particularly advantageous to determine the thickness of each leg using more than two measurement points. This is illustrated by way of example for leg (43). The measuring points (32 - 35) located on this leg are advantageously used to determine two thicknesses of the leg at different distances from the reference point (41) of the reference mark (30).This advantageously allows the thickness of leg (43) to be statistically evaluated. Advantageously, the thickness of a single leg is determined based on up to 20 measurement points, i.e., up to 10 determined thicknesses, at varying distances from a reference point of the reference mark. This procedure allows the quality of the formed reference mark to be monitored and statistically evaluated with particular precision. This monitoring is advantageous because the quality of a reference mark affects its automated detection by the optical measuring device, and this detection, in turn, affects the determination of the laser device's offset. High-quality reference marks therefore allow for a more accurate determination of the laser device's offset.

[0104] The reference point (41) of the reference marker shown is merely a preferred embodiment of a reference point. In particular, a reference point of a reference marker can be positioned arbitrarily relative to it. For example, in the case of a cross-shaped marker, a reference point could also be positioned at the ends of any leg. If a polygonal reference marker is formed, for example, a geometric centroid of the polygon could serve as the reference point.

[0105] Fig. Figure 4 shows a flowchart of the method for determining at least one offset parameter of a laser processing machine according to claim 1, also showing the optional steps S2 and S3 as claimed in claim 3.

[0106] In step S1, the reference device is provided at the laser processing machine.

[0107] In the optional step S2, a deviation of the position of the reference device provided at the laser processing machine from a predetermined position is determined using the measuring probe.

[0108] In the optional step S3, a position correction parameter is determined depending on the position deviation determined in step S2.

[0109] In step S4, target values ​​for at least one first dimension and one second dimension of the reference device are provided.

[0110] In step S5, the clamped reference device is measured by determining the coordinates of points on the circumferential surface of the clamped reference device using the measuring probe.

[0111] In step S6, at least one wear parameter of the measuring probe is determined based on the measurement results from step S5 and on the basis of the target values ​​provided in step S4.

[0112] In step S7, two non-parallel edges of the reference device are determined as alignment edges.

[0113] In step S8, the offset of the measuring probe is determined. This determination is based on the intersection point of the alignment edges of the reference device, which is calculated using the coordinates determined in step S6.

[0114] In step S9, the offset of the optical measuring device of the laser processing machine's measuring system is determined. This determination is carried out using an iterative procedure for the optical measuring device, such that a reference point of the optical measuring device is positioned on at least two measuring points on the alignment edges of the reference device, with at least one measuring point located on each of the alignment edges. From the coordinates at which the reference point of the optical measuring device lies on the measuring points, an intersection point of the alignment edges is calculated, and the offset of the optical measuring device is determined based on this intersection point.

[0115] In step S10, the offset of the laser device is determined. This is done by creating a reference mark at a predetermined position on a marking element held in the reference device using the laser device, and subsequently moving the optical measuring device such that a reference point of the optical measuring device is positioned on a reference point of the created reference mark. The offset of the laser device is then determined as a function of the coordinates of the predetermined position at which the reference mark was created and the coordinates of the position at which the reference point of the optical measuring device is positioned on the reference point of the reference mark.

[0116] In step S11, at least one offset parameter is determined depending on the offset of the measuring probe and / or the offset of the optical measuring device and / or the offset of the laser device.

[0117] If the optional steps S2 and S3 have been performed, steps S5, S6, S8, S9 and S10 can additionally be performed depending on the specific position correction parameter.

[0118] Fig. Figure 5 shows a flowchart for an adjustment procedure for a laser processing machine according to claims 10 to 12.

[0119] In step S1, at least one value is recorded, depending on which an adjustment of the laser processing machine is to be made.

[0120] In the method according to claim 10, in step S1 a time-dependent change in the value of a measured quantity from the environment of the laser processing machine is detected, or a value of a measured quantity from the environment of the laser processing machine is detected. In a method according to claim 11, two times are detected. Between the detection of the first time and between the detection of the second time, other, non-inherent parameters can be detected. Fig. The steps shown in Figure 5 take place; in particular, manufacturing or processing steps can take place after the first time has been recorded and before the second time is recorded. Alternatively, processing steps can also be carried out before the first time is recorded or after the second time has been recorded. In a method according to claim 12, a count value, for example a value indicating the number of workpieces being processed in the laser processing machine, is recorded in step S1.

[0121] In step S2, the current processing status of the laser processing machine is recorded. This processing status indicates, for example, whether a workpiece is being processed in the laser processing machine at a given time and / or whether, and if so, which devices of the laser processing machine are active at a given time.

[0122] In step S3, at least one offset parameter of the laser processing machine is determined machine-controlled and iteratively by means of a method according to one of claims 1 to 9 as a function of the at least one recorded value from step S1 and as a function of the current processing status recorded in step S2.

[0123] In step S4, the laser processing machine is adjusted depending on the offset parameter determined in step S3.

[0124] Fig. Figure 6 shows a flowchart for a laser processing method according to claim 15.

[0125] In step S1, at least one offset parameter of the laser processing machine is determined by means of a method according to one of claims 1 to 9.

[0126] In step S2, laser processing takes place depending on at least one offset parameter of the laser processing machine determined in step S1. List of reference symbols 100 Reference device 1, 2 alignment edges 3 Intersection of the alignment edges 4, 5 Dimensions of the reference device 6 brackets 10 marking element 20 - 27 measuring points 30 Reference marking 31 - 40 measuring points 41 Reference point of the reference marker 42 - 45 Legs of the reference marking QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 3 251 784 A1

[0005]

Claims

[1] Method for determining at least one offset parameter of a laser processing machine comprising a laser device and a measuring system with a measuring probe and an optical measuring device, by means of a reference device, wherein the reference device is ground circumferentially and is set up to receive an interchangeable marking element that can be processed by the laser device, wherein the method comprises the following steps: a) Providing reference device at a predetermined position of the laser processing machine; b) Providing target values ​​for at least one first dimension and one second dimension of the reference device; c) Measuring the clamped reference device by determining coordinates of points on the circumferential surface of the clamped reference device using the measuring probe, in a reference coordinate system of the measuring system; d) Determining at least one wear parameter of the measuring probe based on the measurement results from the step of measuring a first and a second dimension of the reference device and on the basis of the provided target values ​​of the first and second dimension of the reference device; e) Determining two non-parallel edges of the reference device as alignment edges; f) Determining an offset of the measuring probe as a function of an intersection point of the alignment edges of the reference device, which is calculated based on the coordinates determined during the determination of the wear of the measuring probe; g) Determining an offset of the optical measuring device of the measuring system of the laser processing machine by iteratively using the optical measuring device such that a reference point of the optical measuring device is positioned on at least two measuring points on the alignment edges of the reference device, wherein at least one measuring point lies on each of the alignment edges and wherein an intersection point of the alignment edges is calculated from the coordinates at which the reference point of the optical measuring device lies on the measuring points, and the offset of the optical measuring device is determined as a function of this intersection point; h) Determining an offset of the laser device by forming a reference mark at a predetermined position on a marking element received in the reference device using the laser device and subsequently moving the optical measuring device such that a reference point of the optical measuring device is positioned on a reference point of the formed reference mark, whereby the offset of the laser device is determined depending on the coordinates of the predetermined position at which the reference mark was formed and the coordinates of the position at which the reference point of the optical measuring device is positioned on the reference point of the reference mark; i) Determine at least one offset parameter as a function of the offset of the measuring probe and / or the offset of the optical measuring device and / or the offset of the laser device. [2] Method according to claim 1, wherein the reference device has a polygonal, in particular rectangular, cross-section parallel to a top side of the reference device. [3] Method according to one of the preceding claims, wherein the provision of the reference device on the laser processing machine is preferably carried out by clamping the reference device in such a way that the clamped reference device can be rotated about an axis of rotation C and the axis of rotation C is perpendicular to a surface of the reference device and the method after the provision of the reference device comprises the following additional steps: a) Determining a deviation of the position of the reference device provided on the laser processing machine from a predetermined position using the measuring probe; b) Determining a position correction parameter as a function of the determined position deviation; and wherein the steps of measuring the reference device, determining at least one wear parameter, determining an offset of the measuring probe, determining an offset of the optical measuring device and determining an offset of the laser device are additionally carried out as a function of the position correction parameter and / or the position of the provided reference device is changed as a function of the position correction parameter. [4] Method according to any one of the preceding claims, wherein: - the reference mark is cross-shaped and formed at a predetermined position on a marking element received in the reference device; and - a position of the reference mark is determined by measuring points on the edges of the legs of the reference mark using the optical measuring device, wherein at least two points on opposite edges are measured on each leg and the coordinates of the measured points per leg are calculated to determine the coordinates of a reference point of the reference mark; and - an offset of the laser device depending on the coordinates of the predetermined position at which the reference mark was formed and is determined depending on the calculated coordinates of the reference point of the reference mark; and - the quality of the reference marking is determined by means of at least one measurement of the thickness of each arm of the cross at at least a predetermined distance from the reference point, wherein the optical measuring device is used to determine the coordinates on the edges of the cross from which the thickness of the respective arm of the cross is calculated; and - the procedure is aborted if the determined offset of the laser device or a characteristic value calculated from the thicknesses of the legs is above or below the respective predetermined limit values. [5] Method according to one of the preceding claims, wherein the reference marking is formed by the laser of the laser device by at least two laser engravings that at least partially overlap each other and wherein each of the at least two engravings is formed depending on laser parameters. [6] Method according to one of the preceding claims, wherein the determination of the offset of the laser device is iteratively repeated in a machine-controlled manner such that a new reference marking is formed depending on the offset of the laser device determined in the previous iteration and the reference marking is formed at a different predetermined position than in the previous iteration. [7] Method according to one of the preceding claims, wherein the determination of the rotation angle and the rotation of the reference device are alternately repeated iteratively by machine control depending on the determined rotation angle, until a rotation angle of the reference device is determined which is less than a predetermined reference angle. [8] Method according to one of the preceding claims, wherein the method is terminated if the determined at least one wear parameter of the measuring probe is above a predetermined wear limit value. [9] Method according to claim 1, wherein determining the offset of the laser device comprises: - Measuring the position of a focused laser beam of the laser device using the optical measuring device, wherein the optical measuring device is moved in a machine-controlled manner until it detects the focus point of the laser and wherein the offset of the laser device is determined as a function of the distances by which the optical measuring device was moved until it detected the focus point of the laser. [10] Adjustment procedure for a laser processing machine, comprising the following steps: a) Recording a value of a measured quantity in the environment of the laser processing machine and / or a time-dependent change in a value of a measured quantity in the environment of the laser processing machine; b) Recording the current processing status of the laser processing machine; c) Machine-controlled, iterative determination of at least one offset parameter of the laser processing machine by means of a method according to one of claims 1 to 9 depending on the current processing status of the laser processing machine and the detected value of the measured quantity and / or the detected time-dependent change of the value of the measured quantity; d) Adjusting the laser processing machine depending on at least one specific offset parameter. [11] Adjustment procedure for a laser processing machine, comprising the following steps: a) Capturing an initial time; b) Capturing a second time; c) Recording the current processing status of the laser processing machine; d) Machine-controlled, iterative determination of at least one offset parameter of the laser processing machine by means of a method according to one of claims 1 to 9 depending on the current processing status of the laser processing machine and the recorded first time and the recorded second time; e) Adjusting the laser processing machine depending on at least one specific offset parameter. [12] Adjustment procedure for a laser processing machine, comprising the following steps: a) Recording a counter value; b) Recording the current processing status of the laser processing machine c) Machine-controlled, iterative determination of at least one offset parameter of the laser processing machine by means of a method according to one of claims 1 to 9 depending on the current processing status of the laser processing machine and the recorded counter value; d) Adjusting the laser processing machine depending on at least one specific offset parameter. [13] Laser processing machine comprising a laser device, a measuring system with a measuring probe and an optical measuring device and a control device which is configured to carry out a method according to one of claims 1 to 9 in a machine-controlled iterative manner in order to determine at least one offset parameter of a laser processing machine. [14] Laser processing machine comprising a laser device, a measuring system with a measuring probe and an optical measuring device, a measuring device which is configured to record values ​​of a measured quantity of the environment of the laser processing machine and its time-dependent changes, a time recording device, a counting device and a control device, wherein the laser processing machine is configured to perform a machine-controlled adjustment method according to one of claims 10 to 12. [15] Method for laser processing using a laser processing machine according to claim 13 or claim 14, wherein the laser processing takes place depending on at least one offset parameter determined according to a method according to one of claims 1 to 9.

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