EP4680426A1

EP4680426A1 - Closed-loop control of an optical system of a laser cutting machine in order to compensate for thermal drift

Info

Publication number: EP4680426A1
Application number: EP24745937.3A
Authority: EP
Inventors: Christoph Fahrni
Original assignee: Bystronic Laser AG
Current assignee: Bystronic Laser AG
Priority date: 2023-07-19
Filing date: 2024-07-17
Publication date: 2026-01-21
Also published as: WO2025017079A1; EP4494801A1; CN121712609A

Abstract

The present invention relates to a method, a device (100) and a system, a laser cutting head and a computer program for the closed- loop control of an optical system of a laser cutting machine (L). The system comprises a controller (105), which is provided for determining at least one control variable for re-setting the optical system on the basis of the change in the focal position estimated by a drift estimator (104) in order to return the changed focal position to the respectively set target focal position if the drift estimator (104) has estimated a change in the focal position exceeding a predetermined threshold value. The estimation is based on first and second optical signals.

Description

Title: Closed-loop control of an optical system of a laser cutting machine in order to compensate for thermal drift

DESCRIPTION

The present invention relates to a method for the closed-loop control of an optical system of a laser cutting machine to compensate for thermal drift, a corresponding device, a laser cutting head having the device and a system as well as a computer program.

The processing of workpieces, in particular cutting, by means of a laser processing machine requires the precise setting or closed-loop control of the optical system, comprising lenses, mirrors and/or other optical components, in order to focus the laser beam at the desired position, usually within the workpiece. If the focal position is not set correctly, this may lead to a loss of quality or faults. However, the optical system itself is heated by absorption during material processing using laser light, which may also change the optical properties of the system, for example the lens system used. This may also lead to a change in the focal position of the beam path of the laser light. As mentioned, a change in this focal position relative to the position of the materials to be processed may lead to the desired processing result not being achieved.

Sensors that provide reliable signals regarding the state of the optics or optical system are not available. This measurement of the temperature of the lens, for example, is not a simple matter as the material of the lens is a poor conductor of heat and the laser radiation may skew the actual value.

From DE 10 2018 119 900 B4, a method is known for measuring a focal point shift caused by the contamination of components of the optical system, in particular the lens. The amount of energy from the laser light is measured using thermal sensors, for example.

It is known from DE 10 2012 001 609 DE to measure a change in the focal position by means of photodiodes in order to compensate for the changed focal position with little equipment expense.

In the prior art, it is also known from DE 10 2019 122 064 A1 to counteract a change in the focal position caused by thermal influences by means of suitable cooling measures. Based on the prior art, it is the object of the present disclosure to provide a method, a device, a laser cutting head and a system as well as a computer program which make it possible to improve the quality of the cutting process and, in particular, to detect and reduce the risk of a loss of cut as early as possible. Furthermore, it should be possible to use existing laser cutting machines, in particular without any constructive enhancements.

This object is achieved by the enclosed independent patent claims, namely by a method according to claim 1 , a device according to claim 12, a laser cutting head according to claim 13, a system according to claim 14 and a computer program according to claim 15.

In a first aspect, the invention relates to a method for the closed-loop control of an optical system of a laser cutting machine. The method may comprise the following method steps:

- Generating or reading reference data; the reference data may be calculated from first optical signals, which represent a process light during a reference cutting process in a first state of the optical system, wherein the first optical signals can each be assigned a set focal position and/or a setting value of the optical system; the reference data may, in particular, comprise a first feature vector, which is extracted from the first optical signals;

- Setting the optical system to a target focal position and initiating a cutting process;

- Reading of second optical signals, which represent a process light during the initiated cutting process in a second state of the optical system;

- Evaluating the read second optical signals, if applicable in pre-processed form, in particular in the form of a second feature vector calculated therefrom with a drift estimator, by comparison with the generated or read reference data in order to estimate a change in the focal position;

- Determining at least one control variable for re-setting or controlling the optical system on the basis of the estimated change in the focal position in order to return the changed focal position to the target focal position that was set in the “Setting” step if the drift estimator has estimated a change in the focal position exceeding a predetermined threshold value.

The laser cutting machine comprises a laser. The laser is a high-power laser, in particular for metal processing, which is operated in the power range of more than 1 kW and preferably in the range of 1 - 100 kW, in particular 4 - 100 kW. The laser cutting machine may preferably be part of a laser cutting system with a loading and unloading system, an automation system and/or an automatic sorting system. The laser cutting machine may be designed for cutting flat workpieces, in particular those made of metal (such as metal or sheet metal plates), and/or tubular workpieces, in particular in the context of industrial production.

The laser cutting system may comprise an optical sensor arrangement. Preferably, the optical sensor arrangement is arranged on the laser cutting machine, in particular on, in particular in, a cutting head of the laser. The optical sensor arrangement is used to acquire the first and second optical signals. The optical sensor arrangement comprises at least one (optical) sensor. The optical sensor arrangement may be or comprise a camera, in particular a CMOS and/or a CCD camera. The optical sensor may be an in-process camera, for example. The optical sensor may alternatively or cumulatively be a 2D camera. Alternatively or in addition, the optical sensor may be a 3D camera, such as a stereo vision camera, light field camera, etc. Alternatively or cumulatively, the optical sensor arrangement may comprise at least one neuromorphic sensor (neuromorphic camera). The neuromorphic sensor is an event sensor that is designed to display the differences in light intensity acquired by the sensor over time. The neuromorphic sensor has a very high temporal resolution (in the microsecond range). The neuromorphic sensor may be designed as a retinomorphic sensor. Alternatively or cumulatively, the optical sensor may be or comprise at least one photodiode and particularly preferably a photodiode and preferably spatially resolved a 2D sensor, for example a CMOS camera. Alternatively or cumulatively, the optical sensor arrangement may be activated or deactivated as required. The optical sensor arrangement is used to acquire images. The optical sensor arrangement is used in particular to acquire the process light during cutting. Alternatively or cumulatively, the optical sensor arrangement may be part of a more comprehensive sensory system consisting of optical and/or acoustic and/or sound-based sensor systems and optionally electronic components (semiconductor, circuit board, etc.). The electronic components are preferably also arranged in the cutting head. The components may comprise at least one light source. The light source may optionally be activated when the optical sensor is activated in order to, in other words, acquire illuminated or non-illuminated images.

The optical system of the laser cutting machine is used to guide the laser beam onto the workpiece. The optical system may comprise multiple components, in particular at least one optical and/or adaptive lens (for example an adaptive polymer lens for variable focal lengths), at least one mirror, in particular a deflecting mirror and/or an adaptive mirror, at least one protective glass, at least one optical filter, a variable telescope, a housing for enclosing the optical system and/or further electronic, mechanical and/or optical elements, such as an illuminating means. The optical filters may be used in particular to attenuate the intensity of the emitted laser radiation and/or limit the wavelength spectrum and/or change the polarization. The optical system and/or its components may be electronically controlled in an open- or closed-loop - in particular separately - in particular by instructing corresponding actuators. The individual components may each have a different temperature behaviour and/or be cooled. Therefore, the components may each be individually controlled in a closed-loop via corresponding commands, in particular with regard to their position (for example a lens) and/or function (for example curvature of an adaptive lens). Positioning and/or other forms of closed- loop control may be achieved by means of actuators, for example piezo actuators, which may be controlled in an open loop or closed loop.

The laser cutting system may be operated in two phases:

1. in a reference phase, as the reference cutting process, which is used to generate reference data and/or which may also be referred to as a teach-in run and/or which precedes a productive cutting process in time - in the reference phase, the cutting process is referred to as the reference cutting process - and

2. in a productive phase in which a workpiece is cut according to the cutting plan. The process carried out in the productive phase may be referred to as the productive cutting process (in the following, abbreviated simply as: cutting process, in contrast to the reference cutting process).

Preferably, the first optical signals may be acquired in the (first phase) reference phase and/or the second optical signals may be acquired in the (second phase) productive phase. The term productive phase therefore refers to a (productive) cutting process.

The workpiece to be cut may be flat (2-dimensional) or 3-dimensional (for example in the form of a hollow body, in particular a tube). The workpieces may be made of metal or an alloy or of plastics or combinations thereof. The workpieces may be sheet metal parts or sheet metal tubes, for example.

The cut or cutting process is used to sever and in particular to completely sever or cut the workpiece and is carried out in accordance with commands from a control system. Cutting is carried out according to a cutting plan, which may, for example, specify certain contours on a metal sheet. After cutting a sheet metal plate, for example, the differently contoured, finished cut parts may be separated from the remaining metal sheet. The cutting plan defines in which sequence, on which trajectory and/or with which cutting parameters parts are to be cut from the workpiece. This means that several contours may be cut from the workpiece, wherein the laser is activated for cutting, in each case, and may be deactivated for the movement between the parts to be cut. The cutting parameters specify the telescope, focal position, gas pressure, laser power, etc.

The term “setting value” should be understood here in the plural and as a set of setting values. The setting value thus combines different component setting values in order to set and/or reset the different components of the optical system (cf. above: lens, filter, housing, etc.) separately, individually and/or independently of one another in each case.

In other words, each component of the optical system (for example the mirror, lens, etc.) has a dedicated component setting value. All component setting values of all components may be combined in the setting value. For example, a first component setting value may be provided for setting and/or re-setting the optical lens and/or a second component setting value may be provided for setting and/or re-setting another component of the optical system. This makes it possible to control the optical system very flexibly and/or with very fine granularity even in different states (in particular thermal states) of the optical system. The setting value may, for example, be a position specification for an optical lens or a radius specification for setting an adaptive mirror.

The reference cutting process does not necessarily have to be carried out immediately prior to the productive cutting process, but may, for example, have been carried out in the past, so that only the reference data from the previously carried out reference cutting process is read immediately before the initiation of the (productive) cutting process. Preferably, it may be configured when, at which trigger events (for example trigger conditions fulfilled) and/or how often the reference cutting process is carried out. For example, it may be set that the reference cutting process is carried out for each new workpiece, in particular after it has been placed on the cutting table, or after a predeterminable time interval (every 2 hours) or once a day or once per batch and/or machine in each case. The trigger conditions may be configured in advance via a human-machine interface (HMI). Alternatively, the reference cutting process may also be carried out immediately prior to the productive cutting process. It is used to acquire reference data, based on first optical signals from the respective laser cutting machine, for the workpiece currently to be cut in a first, in particular cold, state of the laser cutting machine.

Generally speaking, the reference cutting process is used to generate reference data based on first optical signals. The reference data is to be understood as an electronic or digital data set. The reference data may contain or correspond to the image data from the reference cutting process. The reference data may preferably be subjected to pre-processing, for example by calculating a feature vector from the first optical signals. The reference data may therefore also be present in the form of at least one (extracted) first feature vector.

The reference data may be stored, for example, in the form of a first data structure, such as a look-up table. The first data structure may comprise: the first optical signals (images) from the reference cutting process in the first (in particular cold) state of the optical system, and, optionally, the respectively set focal position, and, optionally: the respective setting value for the optical system (preferably comprising: multiple component setting values for the respective components of the optical system).

In the first data structure (with the reference data), the first optical signals and optionally, but preferably, the associated set focal position and optionally the respective setting value (comprising the respective component setting values) are stored in a manner assigned to one another, for example as a relational database. For example, a first of the first optical signals, for example a first image, is assigned a first set focal position and optionally a first setting value, and a second of the first optical signals, for example a second image, is assigned a second set focal position and optionally a second setting value, etc. This has the advantage that, during a comparison, in particular an indirect image comparison, namely, for example, of the pre-processed first and/or second optical signals, in the form of a first and/or second feature vector in each case, based on the first and second optical signals, the corresponding further data sections of the first data structure, which are assigned to the first optical signals, may be determined by a simple read access to the stored data structure. The control variable can thus be easily determined from the setting value determined in this way.

Alternatively or cumulatively, the second optical signals may be stored in a second data structure, wherein a target focal position set during the cutting process and optionally a setting value for the optical system are assigned to the second optical signals in the second data structure.

The reference cutting process or the cutting process carried out in the teach-in phase is used to generate the reference data for the optical system. Alternatively or cumulatively, the reference data may be generated using the teach-in cutting process within a time window of 1 second to max. 1.5 seconds after the start of the reference cutting process. In order for the first optical signals used as a reference to be acquired, the laser cutting machine must be in the reference cutting process for a time of 200 ms, for example. This may be achieved, for example, when cutting the first part of a new cutting plan. Whether this condition is fulfilled, however, depends heavily on the respective cutting plan and/or the cutting parameters, but typically takes place during the first second to max. 1 .5 seconds after the start of a reference cutting process.

The (first and/or second) optical signals are used in particular to estimate a change in the focal position as caused by temperature changes. The optical signals are acquired during the cutting process or while the laser is activated (for example with a pulsed laser). Preferably, the optical signals are only acquired when the laser is activated in order to acquire the process light.

The first optical signals are acquired in a reference phase or teach-in phase. This reference phase may precede the cutting process. The reference phase may also be carried out immediately prior to the cutting process.

The terms “first/second optical signal” are also to be understood as being used in the plural. An image may be generated from an optical signal. Therefore, for the purposes of this disclosure, the term “optical signal” corresponds to an image generated therefrom. If the term “optical signal(s)” is used without the adjective “first”/”second,” it refers to the first and/or second optical signals. Otherwise, a distinction is made between the first and second optical signals. Generally, multiple first and second optical signals are generated and/or read, namely to represent the different states of the optical system, its settings and/or the focal positions caused by them.

Usually, multiple optical signals or multiple images are generated in the reference phase, in particular multiple images for different states of the optical system, in particular for differently set focal positions in each case, including the target focal position as well as focal positions deviating positively and negatively therefrom.

In the (productive) cutting phase, the second optical signals (also to be understood as images) are read. The second optical signals may be acquired continuously during the (productive) cutting process. Alternatively, it is possible to configure when the second optical signals are acquired, for example only when the laser is activated or, for example, when certain acquisition conditions are met, such as certain contours being cut or after a certain period of time.

The setting of the optical system should be understood as the initial setting of the optical system to the target focal position, i.e. , to the focal position with which the (productive) cutting process is to be carried out. Due to thermal influences, the current focal position may not match the intended and initially set target focal position. The determined control variable is then to be used to automatically readjust or control the focal position. This is what is meant by the term “re-setting.”

As re-setting is based on the estimated change of the focal position by means of the drift estimator, which in turn in based on first and second optical signals, the term “re-setting” may be understood as controlling and in particular closed loop controlling of the optical system, in particular a target focal position. The re-setting may be applied continuously. Alternatively or in addition, the re-setting may be applied according to a predefined activation scheme (e.g. event-based and/or time-based). Alternatively or in addition, the re-setting may be applied on instruction, e.g. once. In simple forms, the re-setting may be a open-loop control.

The first state is to be understood as a cold or non-heated state of the laser cutting machine and in particular of the optical system. The reference phase corresponds in an identical or approximately the same manner to the first state of the optical system.

The second state of the optical system is to be understood as a state that is temporally after the first state and/or that designates a heated or no longer cold state of the optical system. The (productive) cutting process may be carried out in the first state and in the second state. Usually, the cutting process begins in the first (cold) state and is then successively transferred to the second state as the optical system is successively heated during the cutting process.

The term “focal position” is used in three variations in this disclosure: as a set focal position, as a target focal position, and as a current (and possibly deviating from the target focal position or changed with respect thereto) focal position.

The target focal position is to be understood as a predetermined or intended focal position as a target or goal during a productive cutting process. The target focal position is set in the “Setting the optical system” step. It may therefore also be referred to as the target focal position set for the productive cutting process. The target focal position may be understood as a command variable. The target focal position may also be understood as the nominal focal position. The target focal position may represent an initial value that is to be maintained by applying the method for the closed-loop control of the optical system.

The current focal position is the focal position that is actually active during a productive cutting process and may deviate from the target focal position and is therefore also referred to as the “changed focal position,” in particular “changed” with respect to the target focal position. The current focal position is an estimated value (estimated focal position) that is determined by the drift estimator on the basis of the first and second optical signals. The term “current focal position” should therefore be understood as the current estimated focal position.

The set focal position is the focal position that was set in the reference phase or when performing a teach-in run or during the reference cutting process in order to generate the reference data in each case. Usually, multiple different focal positions are set during the reference cutting process in order to obtain many data points in the first (cold) state.

The drift estimator is used to carry out a drift estimation method. The drift estimation method is used to estimate an unintentional change (drift) in the focal position over time. The drift/change in focal position may be caused or contributed to by, for example, thermal influences from components of the optical system. The drift estimator may be implemented by means of software and/or hardware. The drift estimator may be designed as an electronic component, for example as a computing unit, computer, microcontroller, DSP, FPGA and/or PLC.

The at least one control variable is used for the closed-loop control (re-setting) of at least one actuator for adjusting, for example positioning, a component of the optical system. Preferably, more than one control variable is calculated for more than one actuator for each component of the optical system. In the simplest case, the control variable may be an offset, in particular for positioning the lens. The control variable may comprise the following commands, for example: a positioning command for an electronically controllable lens, in particular for an actuator for vertically changing the position of the lens; a curvature command for setting the curvature of a liquid lens and/or a radius command for an actuator for setting a radius for an adaptive mirror.

Advantageous embodiments of the invention, which may also be used in combination, are explained below.

The reading of the reference data may be performed by reading from an internal or external memory. The internal memory may be arranged in the device, which will be described later and which is used to carry out the method. Alternatively, the reference data may also be read from an external memory via an interface.

Reference data that has already been generated may be used (in which case it is read) or the reference data may also be generated by carrying out a reference cutting process, particularly at the start of a productive cutting process. As already explained above, the optical system may have or comprise at least one component, preferably multiple components. Alternatively or cumulatively, each of the components may be individually controllable, in particular by means of the multiple different control variables.

Alternatively or cumulatively, the read second optical signals are evaluated on-line and/or continuously and/or intermittently by means of the drift estimator while the (productive) laser cutting process is being carried out.

Alternatively or cumulatively, the drift estimation method is used to estimate the drift of the optical system. The drift estimation method may use a thermal model which may be characterized by the following exponential function: wherein different time constants tauj have different degrees of influence cj on the drift, and/or wherein the laser power Pi_aser has a direct, in particular proportional, influence on the drift. Doubling the laser power, for example, results in double the absorption.

The thermal model acts as a digital twin for the drift. The thermal model may be designed to calculate an offset for the focal position in relation to the current laser power so that the target focal position may be maintained. The thermal model may be refined using a neural network to avoid over- or undercompensation. The thermal model does not require any optical signals to predict or estimate the drift and may therefore also be used with the laser switched off or with a pulsed laser.

Alternatively or cumulatively, the drift estimation method may execute a processing algorithm, in particular an indirect image comparison algorithm. “Indirect” in the sense that the image comparison is not carried out directly on the images, but on the basis of the images. The image comparison may, for example, be carried out on the basis of features, in particular feature vectors, which have been calculated from the images as part of a pre-processing. In particular, a second feature vector may be calculated on the basis of the second optical signals, in particular images from a productive cutting process, which have been acquired in a second state of the laser cutting machine, in particular in a second time interval and/or at an actual temperature. Cumulatively on the basis of reference data (also: reference cutting data), in particular the first optical signals, in particular images, which have been acquired in the first state, in particular in a first time interval and/or at a target temperature and/or in a non-heated state of the optical system, a first feature vector may be calculated. The processing algorithm, in particular the indirect image comparison algorithm, may be designed to compare the first feature vector with the second feature vector in order to estimate the drift.

Alternatively or cumulatively, the drift estimation method may be or comprise a trained neural network which in particular estimates (classification) or quantifies (regression) a thermal change in the optical system and the change in the focal position caused or at least contributed to by the thermal change.

The input data for the neural network comprises the first and second optical signals. Cumulatively, another architecture may be provided in which other input data is also taken into account, such as cutting parameters, for example the laser power, the target focal position, feed rate, nozzle distance, nozzle type and/or other variables, such as information about the workpiece (for example material and/or thickness).

The training data for the neural network may comprise the first and second optical signals in labelled form, wherein a change in the focal position is used to label the first and second optical signals. Cumulatively, the set focal position of the first optical signals, the current focal position of the second optical signals and/or the target focal position of the second optical signals and optionally the setting values for the optical system may also be used optionally. From the difference between the current focal position (= estimated by the drift estimator) and the target focal position, the change in the focal position or its drift may be determined by simple subtraction.

The drift estimator on which the drift estimation method is executed may alternatively or cumulatively be implemented in the cutting head and/or in a separate control system for the laser cutting machine.

The drift estimation method may also be executed in a distributed manner and/or on different computing units.

The method may additionally comprise applying the calculated control variable during the (productive) cutting process in order to counteract the - in particular unintentional - change in the focal position in advance. This may advantageously provide a control loop for the closed- loop control of the cutting process. For this purpose, a return channel is established between the device that calculates the at least one control variable and the laser cutting machine or its control system. In particular, the return channel exhibits a fast cycle time so that the target focal position may still be maintained even during prolonged cutting, which is accompanied by heating of the components of the optical system.

Alternatively or cumulatively, the estimated change in the focal position and/or the calculated control variable may be displayed in a human-machine interface.

In an advantageous embodiment, the method and in particular the drift estimator may estimate the current focal position from the following data and calculate at least one control variable therefrom: set of first optical signals as reference data in the reference state (cold state of the optical system) with respectively assigned set focal position and/or optionally respectively assigned setting values for the optical system; second optical signals that represent the current (productive) cutting process with process light; and target focal position for the current (productive) cutting process.

In an advantageous embodiment, a second feature vector may be calculated from the read second optical signals (images) and/or a first feature vector may be calculated from the read first optical signals (images). The two calculated feature vectors may be compared for (approximate) correspondence using an indirect image comparison algorithm. The feature vector calculated in each case may be assigned to the underlying image. As soon as the first image (first feature vector) that corresponds to the second image (second feature vector) has been determined, the set focal position assigned to the first image may be determined in a first data structure. A change in the focal position may be estimated by subtraction of the determined set focal position with the set target focal position.

The achievement of the object has been described above in terms of the method. Features, advantages, or alternative embodiments mentioned in this way may also be applied to the other claimed subjects and vice versa. In other words, the present claims (which are directed, for example, to a device, a laser cutting head or a system) may also be further developed with the features described and/or claimed in connection with the method, and vice versa. The corresponding functional features of the method are thereby provided by corresponding modules, in particular by hardware modules or microprocessor modules of the device, and vice versa. The preferred embodiments of the invention described above in connection with the method are not explicitly repeated for the device. In principle, the claimed device is designed to carry out the claimed method. In a further aspect, the invention relates to a device. In particular, the device is electronic and/or is used for the closed-loop control of an optical system of a laser cutting machine, wherein the device is designed to carry out the method described above in the various embodiments. The device may comprise the following:

- a first reading interface for reading reference data, calculated from first optical signals, which represent a process light during a reference cutting process in a first state of the optical system, wherein the first optical signals are each assigned a set focal position and/or a setting value of the optical system; wherein a first feature vector may be calculated from the first optical signals, which may be a component of the reference data;

- a second reading interface for reading second optical signals, which represent a process light during a cutting process initiated by a processor in a second state of the optical system;

- the processor, which is designed to set the optical system to a target focal position and to initiate a cutting process;

- a drift estimator, which is designed to evaluate the read second optical signals, if applicable in pre-processed form, in particular in the form of a second feature vector calculated therefrom, by comparison with the generated or read reference data in order to estimate a change in the focal position;

- a controller, which is provided for determining at least one control variable for resetting the optical system on the basis of the change in the focal position estimated by the drift estimator in order to return the changed focal position to the target focal position respectively set by the processor for the initiated cutting process if the drift estimator has estimated a change in the focal position exceeding a predetermined threshold value.

The first and second reading interfaces may be implemented in a common data interface. The device may advantageously also comprise a further closed-loop control interface for transmitting the determined at least one control variable to the laser cutting machine or its control system. The closed-loop control interface may also be combined with one or both of the reading interfaces or integrated into them.

The object is also achieved by a laser cutting head having a device, as described above, in order to control the optical system with the determined control variable in such a manner that the current focal position corresponds to the respectively set target focal position. The object is also achieved by a system for the closed-loop control of a laser cutting process with the following units:

- a device as described above,

- a laser cutting machine,

- a sensor arrangement, in particular for acquiring the first and second optical signals, and

- data interfaces between the units mentioned above or implemented in the system, which may be implemented in addition to the units mentioned.

The sensor arrangement is usually provided in the laser cutting machine, in particular in or on the cutting head. Alternatively, the device may also comprise the optical sensor arrangement. Alternatively, the (first and second) optical signals acquired by the optical sensor arrangement may also be read via a (for example first) reading interface, in particular if the sensor arrangement is provided as a separate unit.

The object is also achieved by a computer program or a computer program product having such a computer program, wherein the computer program may be loaded into a memory unit of a computing unit and contains program code segments for causing the computing unit to carry out the method for position control of an optical system according to any one of the preceding method claims when the computer program is executed in the computing unit.

An alternative solution therefore provides for a storage medium, in particular a computer- readable storage medium, which is intended for storing the method according to the disclosure (as program code) and may be read by a computer or a processor of the computer. The program code, when executed by a processor circuit of a computer or computer network, causes an embodiment of the method according to the disclosure to be executed. The storage medium may, for example, be provided at least in part as a non-volatile data memory (for example as a flash memory and/or as a solid state drive, SSD) and/or at least in part as a volatile data memory (for example as a random access memory, RAM). The storage medium may be arranged in the processor circuit in its data memory. However, the storage medium may also be operated as a so-called appstore server on the Internet, for example. A processor circuit with at least one microprocessor may be provided by the computer or computer network.

The program code may be provided as binary code or assembler and/or as source code of a programming language (for example C) and/or as a program script (for example Python). Brief description of the figures

The features, characteristics and advantages of the present invention described above and the manner in which they are achieved will become more clear and more clearly understandable in connection with the following description of the exemplary embodiments, which will be explained in more detail in connection with the figures. To this end, the figures show the following in a schematic representation:

Fig. 1 shows a flow chart of a method according to one embodiment of the invention and in one variant;

Fig. 2 shows a schematic block diagram of a system according to one embodiment of the invention;

Fig. 3 shows a further schematic block diagram of a system according to another embodiment of the invention;

Fig. 4 also shows a schematic block diagram of a system according to a further embodiment of the invention;

Fig. 5 shows an overview of the determination of the thermal drift;

Fig. 6 shows an overview of components of the laser cutting machine that influence the thermal drift; and

Fig. 7 shows a representation of a drift estimator according to an exemplary embodiment of the invention.

Detailed description of the figures

The invention is used to detect thermal drift. The term “thermal drift” should be understood as an undesired or unintentional deviation of the target focal position caused or contributed to by thermal influences on the optical system of the laser cutting machine.

The above-described may be summarized in other words and with reference to a possible more specific embodiment of the disclosure as described below, wherein the following description is to be construed as not limiting the disclosure. As optical components (transmissive and reflective) heat up due to absorption in applications with high laser power despite the best possible cooling, this may lead to the cutting process no longer being optimal as the focal position has changed unintentionally. This influence is referred to as “drift.”

The method presented here and the other claimed objects are intended to detect and compensate for this drift by means of sensors and in the way of evaluation. By detecting and compensating for the drift, the desired process is continued for hours at the desired optimum setting - and the probability of drift occurring may be continuously kept very low.

The drift is continuously corrected or controlled, in particular when using a thermal model as a dynamic function of the laser power.

By using a cutting head camera as an optical sensor together with artificial intelligence, the probability of drift can be minimized by adjusting the coefficients of the dynamic function.

Since the correction occurs instantaneously, the probability of a critical drift is excluded.

The “cutting process” uses high laser power to cut the workpiece, for example sheet metal, according to the cutting plan. The parameters control the laser power, the speed/feed, the nozzle, the nozzle distance and the gas to be blown out. A very important parameter is the position of the focal point - normally inside the material. The drift has a direct effect on the focal position. Since thermal processes usually follow a combination of exponential functions, the drift can be estimated using this formula: wherein c is a constant and t is the time and TauJ is a further time constant.

If the formula is adjusted to follow dynamic thermal changes (cooling, positioning between parts or modulation of the laser when cutting corners), the actual drift may be estimated. The thermal model acts akin to a “digital twin” of the optical drift.

In a next step, the actual optical drift may be automatically compensated for by the closed-loop control of an actuator for changing the focal position.

The thermal stability may change from machine to machine - and also over time. These differences may be taken into account with the proposal according to the invention. Therefore, the time constants T_(i ) are constant, but the coefficients c_i must be updated by measuring the actual drift.

The optical signals or images read are processed in order to determine the drift factor. After calculating the difference to the reference of 0 drift, the coefficients c_i of the thermal model may be updated in order to refine the thermal model. In addition, the coefficients cj also describe the thermal robustness of an optical system. This information may be used for important predictions as part of a “predictive maintenance.”

The sensors for acquiring the first and second optical signals may be part of an optical sensor arrangement. A possible image processing system may consist of a CMOS area image sensor. Other alternatives are also conceivable to achieve similar results, such as a polarization image sensor, UV image sensor, SWIR image sensor, ToF image sensor and/or an event-based image sensor.

Fig. 1 shows the method for the closed-loop control of an optical system of a laser cutting machine L in a preferred embodiment. In a first step S1 , reference data may be generated. This may be done by running a reference cutting process on the laser cutting machine L. In particular, first optical signals, in particular a series of different images, are acquired which represent a process light during a reference cutting process in a first state of the optical system, in particular in a cold state of the optical system or at the beginning of cutting.

The reference data is generated from these first optical signals (image data). In the simplest case, the reference data may match the first optical signals. Preferably, at least a first feature vector is extracted from the first optical signals, which serves as reference data. A data structure, namely the first data structure, may be created from the reference data by assigning to the first optical signals a respective set focal position and a respective setting value of the optical system (for example a position value of an optical lens), which were applied in order to acquire the first optical signals.

As an alternative to generating the reference data, as described above, in step S1 , reference data that has already been generated may also be read in step S2. In this case, the reference data may already be available in generated form and stored in a memory, for example, from which it can be read. Alternatively or cumulatively, it is possible to read the first data structure.

In a step S3, the optical system may be set to a target focal position. The target focal position defines the desired focal position with which the subsequent productive cutting process is to be carried out. After this setting, the cutting process may be initiated or triggered in step S4. This may be done using a corresponding command, for example.

During the execution of the (productive) cutting process, second optical signals, in particular a series of different images, are read continuously or at certain points in time or after certain events in step S5.

In a subsequent step S6, the read second optical signals are evaluated. This is done by a drift estimator 104, which may be provided as an electronic component. In particular, the drift estimator 104 is designed to evaluate the read second optical signals by comparing them, in particular in pre-processed form (for example in the form of a second feature vector calculated from the second optical signals), with the reference data generated in step S1 or read in step S2 (with the first feature vector) in order to estimate a change in the focal position. In particular, an indirect image comparison algorithm may be used for feature comparison. Once a set of matching features (calculated from the images, in particular from a pair of first and second optical signals) has been found, the respective entries may be read from the first and/or second data structure in order to estimate a drift based on the acquired optical signals and determine a corresponding control variable, in the simplest case an offset for the re-setting of the optical system, in particular the lens.

If the drift estimator 104 has estimated a change in the focal position exceeding a predetermined threshold value, at least one control variable for controlling or re-setting the optical system is determined in step S7 on the basis of the estimated change in the focal position in order to return the changed focal position to the respectively set target focal position. The method may then end or be applied continuously during the productive cutting process.

Optionally, which is why this step is shown dashed in Fig. 1 , in step S8, the determined at least one control variable may be transmitted to the control system of the laser cutting machine L for use.

Fig. 2 shows a schematic representation of a device 100 which is designed to carry out the method described above. The device 100 may be provided in different variants, which are described in more detail below in Fig. 3 and Fig. 4. In the variant shown in Fig. 2, the device 100 is designed with two reading interfaces 101 , 102, which are used to read the first and second optical signals, which are acquired by one or more optical sensors of an optical sensor arrangement S, which may be arranged on the laser cutting machine L, in particular on the cutting head SK.

The result that is provided after the device 100 has carried out the method, namely the determined at least one control variable, may be fed back to the laser cutting machine L or its control system in the form of a control loop in order to control the laser cutting process accordingly, in particular in such a way that the current focal position, which may have changed due to heating, is returned to the target focal position. This is indicated in Fig. 2 (and Fig. 3) with the arrow pointing from the device 100 towards the laser cutting machine L, which is representative of the transmission of the at least one control variable.

The device further comprises a processor 103, the drift estimator 104 and the controller 105. The processor 103 is designed to set the optical system to a target focal position and to initiate a cutting process, which may also be referred to as a productive cutting process. The controller 105 is provided for determining at least one control variable for re-setting or controlling the optical system on the basis of the change in the focal position estimated by the drift estimator 104 in order to return the changed focal position to the respectively set target focal position if the drift estimator 104 has estimated a change in the focal position exceeding a predetermined threshold value. In particular, as explained above, the drift estimator 104 may be provided for comparing a first feature vector (from the reference data) with a second feature vector from the current cutting process data.

Optionally, the device 100 may have a memory MEM for storing the read data, in particular the first and second optical signals, the set focal position from the reference cutting process, the target focal position from the (productive) cutting process and/or the estimated change in the focal position and/or the determined control variable.

As mentioned above, a different architecture may also be chosen, so that the drift estimator 104 and the controller 105 may be provided in the processor 103, as shown in Fig. 3.

Alternatively, as shown in Fig. 4, it is possible for the device 100 to be implemented directly on the laser cutting machine.

Fig. 5 shows an overview illustrating the integration of the device 100 according to the invention for the closed-loop control of the focal position in order to avoid drift due to thermal influences in advance.

Based on the images acquired during the cutting process (second optical signals), referred to as “optical signals” in Fig. 5, in particular the first feature vector calculated therefrom, the drift estimator 104 estimates the actual or current focal position - which may have changed compared to the set target focal position.

The read second optical signals may therefore be subjected to pre-processing, in particular in order to extract or calculate a second feature vector.

If the intermediate result of the drift estimator 104 indicates that the estimated current focal position does not match the target focal position, the controller 105 determines the control variable in order to re-set or control the optical system and in particular its individual components via at least one actuator, so that the current focal position may be returned to the target focal position.

The drift estimator 104 carries out a preferably computer-implemented drift estimation method.

The drift estimator 104 may execute a processing algorithm, in particular an indirect image comparison algorithm, in order to determine a control variable by means of a comparison between feature vectors calculated from the first and second optical signals and/or by means of referencing with respect to assigned focal positions and/or setting values, which is fed to a controller 105 in order to return the possibly changed focal position to the target focal position that was set in step S3.

In particular, in the indirect image comparison algorithm, the calculated features from the first optical signals (from the reference cutting process) or the first feature vector may be compared with the features from the second optical signals from the current cutting process or the second feature vector in order to then determine the assigned further data sections in the first data structure, which comprise at least the respectively set focal position and may optionally also comprise the setting values for the actuators for setting the components of the optical system.

Cumulatively or alternatively, the drift estimator 104 may utilize a thermal model in order to determine the control variable. The control variable may then be used to control at least one actuator in such a manner that the possibly changed focal position is returned to the target focal position that was set in step S3.

The term “optical system” covers multiple components with differing thermal cooling: One possible topology is shown in Fig. 6. Each component has its own thermal properties - some of them are cooled. All have an effect on the focal position. Therefore, according to the invention, multiple control variables are determined, in particular in order to be able to re-set or control the individual components of the optical system separately and/or individually. The components may comprise a fibre with an end cap lens, a mirror, one or more optical lenses, protective glasses, a telescope and a housing for the optical system.

The drift estimator 104 estimates the current focal position and a deviation from the target focal position. If a deviation has been determined, a control variable is determined by the controller 105 in order to control the actuators accordingly in such a manner that the current focal position may be returned to the target focal position that was set in step S3.

Basically, a control system, for example a programmable logic controller (PLC), calculates the paths for the next milliseconds. Up to this point in the prior art, the feedback from the cutting process could only be read out using a light sensor that measures the process emission. With the proposal of this disclosure, it is also possible to control the cutting process in a closed- loop, i.e. , to re-set the components of the optical system based in particular on the results of the drift estimator 104. This enables a dynamic interaction.

With the method according to the invention or an intelligent control system, ICP or “Intelligent Cutting Process,” a modular frame is provided as an extension of the laser cutting machine L, which is connected to the PLC, the cutting head SK with the optical sensor of the optical sensor arrangement S (such as a camera) and the human-machine interface HMI (HMI shown in Fig. 2). The HMI may be displayed in a browser and/or in a machine operating software. The acquired optical signals (camera images) and/or status information may be displayed in the HMI of the control system, e.g., the device 100. Status information may be output as a traffic light signal, for example: green - for current focal position in the cutting process still within the tolerance range around the target focal position, orange - for current focal position in the cutting process has slightly exceeded a configurable threshold value and red - for current focal position in the cutting process has significantly exceeded a configurable threshold value.

The data exchange between the components of the system may be carried out via a suitable network connection, for example: EtherCAT, Ethernet (ADS, http, GigE Vision).

The system acts as a process controller or closed-loop control and has multiple interfaces to devices or equipment on the laser cutting machine L. As such, it collects or acquires sensor data, such as first and second optical sensor data (photodiode for measuring the process light), nozzle distance signal, position of sensors on the axis and/or many other signals. The camera images (first and second optical signals) and optionally other machine data, such as the cutting parameters, are available. The system processes the data in real time. The image processor (may be implemented as part of the processor 103) extracts features using image algorithms and/or artificial intelligence (Al) methods.

The system may execute a script to process the raw data (in particular the first and second optical signals) and/or the features extracted by the image processor using filters and conditions (if ... then ... else ... end). The script decides whether the cutting process and in particular the optical system should be adjusted and sets the offset/override values for resetting (FeedOverride, LaserpowerOffset, FocalOffsetOptotune, FocalOffset, GasPressureOffset, NozzleDistanceOffset). The behaviour of the laser cutting machine L may be quickly adapted by changing the offsets/overrides.

On the one hand, the system collects the first and second optical signals (images) or reads them, on the other hand, a return channel is also provided, in particular a fast return channel to the control system, for example the PLC, in order to set the offsets/overrides (re- setting/closed-loop control) and/or exchange messages, such as alarm states, for example “Loss of Cut” or “Loss of Nozzle.”

Finally, data showing irregular behaviour may be collected and/or stored in a memory MEM (see Fig. 2). In the event of a file test, the dumps are automatically sent to a cloud storage (not shown). The cloud storage may be accessed via a network connection and implemented as a server, for example.

The system or the framework presented here has a highly extensible architecture. First, the process may be started by reading the cutting plan with the cutting parameters. The operator instructs the laser cutting machine L to start cutting a new metal sheet. The laser process emits process light during the cutting process. Camera images of the emitted process light are acquired by the cutting head camera as first and second optical signals. A common preprocessor may be provided, which rotates, crops, scales and normalizes the respective image. A gamma correction may also be applied. Image processing is used to extract or calculate features 1..n, such as the mean value (image) or the diameter of the nozzle opening. The calculated features may be fed to further algorithms, in particular an indirect image comparison algorithm. The comparison between current data, in particular cutting data from the current cutting process, and reference cutting data from the reference cutting process takes place indirectly after the backbone with the features - either by the head or by applying a subtraction. The same images are processed in neural networks (convolutional neural networks). The models may predict in parallel so that multiple features A..Z are available. A multithreaded implementation allows the simultaneous prediction of the same pre-processed image by different inference execution units running in parallel. These execution units, which are applied in the inference phase, may be provided in the device 100 and in particular in the processor 103. The process controller may act as a high-level arbiter (decision logic) in order to define useful loop-back parameters, in particular the at least one control variable. The signals from time series (features, sensor signals) may be filtered to have more confidence in the process state before a feedback parameter is defined. If the process controller recognizes an ambiguous irregular pattern, the data is collected in the dump controller (for example implemented in the MEM memory). The dumps may be uploaded to a cloud. This may be done either by ingestion (push operation, i.e., an automatic upload) or by manual upload. If possible, the labels are also included as a dump for storage and/or transmission so that the neural network may start supervised learning, and in particular without the need for expensive manual creation of labelled data as training data.

The basic approach of how the Al model, in particular the neural networks, are created and operated is described in the following. Data must be collected during the development phase. The results must be defined and validated in order to obtain a labelled data set (data set provided with labels) of first optical signals (images from the reference process). The data must be converted into tensors, the input format for a training machine for neural networks (e.g., keras/tensorflow, pytorch). The accuracy and sensitivity of the model may be improved by adjusting the network topology and hyperparameters. The model must be saved in a compatible format so that the edge device of the laser cutting machine L can process the images in real time. Once the model is running on the machine L or a control system, the process controller will process the features in real time in order to improve the cutting process. In the event of irregular patterns, poor confidence or out-of-domain detection, new data is collected by compiling dumps. The data is uploaded to the data backbone either manually or automatically. During data preparation, the combination of new and old data is prepared in order to train and validate the neural network. After model validation, the model is used on laser cutting machines L.

A mixed model input (input for the neural network) may be used. Normally, the pre-processed image is fed to the input of the model. Since neural networks may have multiple inputs, scalars such as laser power, focal position, magnification, nozzle distance, gas pressure, speed, nozzle type and/or other cutting parameters may be sent to the model.

Since individual images may not provide stable features, the network receives multiple sensor values or images (aggregation of the history). In the example of the drift estimator 104, a reference for 0 drift was used. The topology may look as follows: If features from the reference (reference cutting process) and the current process are available, a head (also a neural network) compares the two feature vectors and creates a new feature based on the comparison between the reference and the current process.

With reference to Fig. 7, the system with the drift estimator 104 may be described as follows.

Pre-processing: The following functions may be applied to the first and/or second optical signals (camera image): Rotation, scaling, cropping of the ROI (region of interest), gamma correction and/or normalization.

Feature extraction: The neural network, e.g., Mobilenet_V2 as backbone extracts/encodes the 576 features from 3 images. Mobilenet_V2 is a deep and highly optimized neural network that has been pre-trained. The decoder reproduces a synthetic image from the features. Comparing the real input image and the generated output image, the reconstruction error (mean square error, mse) is low if the type of image was included in the training set. If mse is high, new data must be collected.

Processing of features: In order to compare the reference state 0 (cool) with the current state from the current cutting process (heated), the features from the reference (first optical signals) are compared with the runtime features (second optical signals). The fully linked network “Head” predicts with high probability that there will be no change/shift or a shift upwards or a shift downwards (3 classes).

The first and second optical signals are pre-processed, as shown for example in Fig. 7, and converted into first and second features (or first and second feature vectors). In this regard, a feature vector (vector with features) is created with the backbone in the form of a KN N, such as Mobilenet, preferably from 3 images.

For downstream filtering, 3 features are preferably created from 3x3 images.

There are therefore 3 features from the first optical signals. The 3 features from the first optical signals are preferably only calculated once and then written to a memory for later use.

During the current cutting process (runtime), 3 new features are also available cyclically. The head (not a KN N as shown in Fig. 7, but a fully connected network) may determine the drift from each of the 3 features, wherein all combinations of both 3 features are taken into account (3x3=9 results for the focal position drift).

During cutting, 9 results for the focal position drift are thus available cyclically after 3 images. A time series filter in the form of a mean value filter determines a filtered result (dfl_mean) from a sequence of, for example, 6*9=54 results.

Note on features:

- The length of the vector may be 576, the head processes 2 inputs with 576 values each (embeddings).

- The length of the vector may be 1 , the head only performs a subtraction (no NN is used here). The difference indicates whether there is a focal position drift.

Process controller: After filtering, for example, the lens and/or the mirror is checked (or the thermal model is refined in the event of a shift).

The process controller may comprise the thermal model, which counteracts the expected drift during cutting by means of the coefficients cj. The drift is thus minimized with a consistent optical system. However, if something changes in the optical system, a drift could still occur.

The process controller continuously compares the results dfl_mean with an upper and lower threshold value (e.g., +/-0.3 mm). If a drift is detected in spite of the thermal model, the process controller adjusts the coefficients c_i. An adjustment could, for example, mean increasing the coefficients c_i by 5%. The closed-loop control takes place in that the adjusted coefficients of the thermal model lead to a change in the control of the optical actuators and thus to a reduction in drift.

Regarding training of the network:

While the laser cutting machine L cuts any contour, the process controller forces the focal position (actuator for lenses and/or mirrors) to change in a sequence of, for example, 6 steps: [0, 0.166, 0.33, 0, -0.166, -0.33] (mm). For example, 40 images (a total of 6x40=240 images) with the corresponding focal position as a label may be output for each setting. The cutting parameter may also be part of the data set.

Many data sets must be acquired for a single parameter of a machine. The data must be collected following a predetermined design of experiment (DoE). When training the network, images from different steps are combined as pairs of first optical signals and second optical signals so that the head and the backbone can be trained/fine- tuned.

The method or system presented here can be used for quality control through process stabilization. Furthermore, cutting losses and/or a loss of cut are avoided through process stabilization.

Although the invention has been illustrated and described in more detail by the exemplary embodiments, the invention is not limited by the disclosed examples, and other variations may be derived therefrom by a person skilled in the art without departing from the scope of the invention.

Claims

1 . A method for the closed-loop control of an optical system of a laser cutting machine (L), wherein the method comprises the following method steps:

- Generating (S1) or reading (S2) reference data, calculated from first optical signals, which represent a process light during a reference cutting process in a first state of the optical system, wherein the first optical signals are each assigned a set focal position and/or a setting value of the optical system;

- Setting (S3) the optical system to a target focal position and initiating (S4) a cutting process;

- Reading (S5) second optical signals, which represent a process light during the initiated cutting process in a second state of the optical system;

- Evaluating (S6) the read second optical signals, if applicable in pre-processed form, with a drift estimator (104), by comparison with the generated or read reference data in order to estimate a change in the focal position;

- If the drift estimator (104) has estimated a change in the focal position exceeding a predetermined threshold value:

- Determining (S7) at least one control variable for re-setting the optical system on the basis of the estimated change in the focal position in order to return the changed focal position to the respectively set target focal position.

2. The method according to claim 1 , wherein the method additionally comprises:

- Applying (S8) the calculated control variable in order to counteract the - in particular unintentional - change in the focal position in advance.

3. The method according to any one of the preceding claims, wherein the optical system comprises at least one component, in particular multiple components, and/or wherein each of the components is individually controllable with separate control variables.

4. The method according to any one of the preceding claims, wherein the reading of the reference data is performed by reading from an internal or external memory.

5. The method according to any one of the preceding claims, wherein the drift estimation method serves the estimation of a drift of the optical system and uses a thermal model which may be characterized by the following exponential function: drift wherein different time constants tauj have different degrees of influence c_i on the drift, and/or wherein the laser power Pi_aser has a direct influence on the drift.

6. The method according to any one of the preceding claims, wherein the drift estimation method executes a processing algorithm, in which features from the second optical signals, in particular images, from a productive cutting process, which have been acquired in a second state of the laser cutting machine (L), in particular in a second time interval and/or at an actual temperature, are compared with features from reference data, in particular from the first optical signals, in particular images, which have been acquired in the first state, in particular in a first time interval and/or at a target temperature and/or in a non-heated state of the optical system.

7. The method according to any one of the preceding claims, wherein the drift estimation method is or comprises a trained neural network (KNN) which in particular estimates or quantifies a thermal change in the optical system and the change in the focal position caused or at least contributed to by the thermal change.

8. The method according to the immediately preceding claim, wherein input data for the neural network (KNN) comprises the first and second optical signals.

9. The method according to any one of claims 7 or 8, wherein training data for the neural network (KNN) comprises the first and second optical signals in labelled form, wherein a change in the focal position and optionally setting values for the optical system are used to label the first and second optical signals.

10. The method according to any one of the preceding claims, wherein the drift estimator (104) on which a drift estimation method is executed is implemented in the cutting head (SK) and/or in a separate control system.

11. The method according to any one of the preceding claims, wherein the first optical signals or a first feature vector calculated therefrom are stored in a first data structure, wherein a focal position set during the reference cutting process and optionally a setting value for the optical system are assigned to the first optical signals in the first data structure and/or wherein the second optical signals or a second feature vector calculated therefrom are stored in a second data structure, wherein a target focal position set during the cutting process and optionally a setting value for the optical system are assigned to the second optical signals in the second data structure.

12. A device (100) for the closed-loop control of an optical system of a laser cutting machine (L), wherein the device is designed to carry out a method according to any one of the preceding method claims, comprising:

- a first reading interface (101) for reading reference data, calculated from first optical signals, which represent a process light during a reference cutting process in a first state of the optical system, wherein the first optical signals are each assigned a set focal position and/or a setting value of the optical system;

- a second reading interface (102) for reading second optical signals, which represent a process light during a cutting process initiated by a processor (103) in a second state of the optical system;

- the processor (103), which is designed to set the optical system to a target focal position and to initiate a cutting process;

- adrift estimator (104), which is designed to evaluate the read second optical signals, if applicable in pre-processed form, by comparison with the generated or read reference data in order to estimate a change in the focal position;

- a controller (105), which is provided for determining at least one control variable for re-setting the optical system on the basis of the change in the focal position estimated by the drift estimator (104) in order to return the changed focal position to the respectively set target focal position if the drift estimator (104) has estimated a change in the focal position exceeding a predetermined threshold value.

13. A laser cutting head having a device (100) according to claim 12, in order to control the optical system with the determined control variable in such a manner that the current focal position corresponds to the respectively set target focal position.

14. A system for the closed-loop control of an optical system during a laser cutting process with the following units:

- a device (100) according to claim 12,

- a laser cutting machine (L),

- a sensor arrangement and

- data interfaces between the aforementioned units.

15. A computer program, wherein the computer program may be loaded into a memory unit of a computing unit and contains program code segments for causing the computing unit to carry out the method for position control of an optical system according to any one of the preceding method claims when the computer program is executed in the computing unit.