WO2018029259A1 - Method for observing and/or monitoring a laser processing process and observation device - Google Patents

Abstract

The invention relates to a method for observing and/or monitoring a laser processing process for a workpiece (3) by means of a camera (10), wherein the transmission of an adjustable filter (11) arranged in an observation beam path (5) of the camera (10) is set. According to the invention, the transmission of the filter (11) is set to different transmittances (a, b, c, a' b' c') in a controlled manner in at least two different regions (I, II, III) of the filter (11) and/or the transmission is set to different transmittances (a, b, c, a' b' c') at least in one region of the filter (11) in a manner synchronized temporally with recording times (a1, a2, a3, a'1, a'2, a'3) of the camera (10) and/or with times of changes in the brightness of at least one additional illumination source (25, 26). The invention furthermore relates to an observation device (4) and to a laser processing device (1).

Description

 Method for monitoring and / or monitoring a

The invention is based on a method for observing and / or monitoring a laser processing process of a workpiece by means of a camera, wherein the transmission of a in a

Observation beam path of the camera arranged, adjustable filter is set.

It is known to observe a laser processing process, for example a laser welding or laser cutting process, for camera-based monitoring. For this purpose, the amount of light must be limited during image acquisition of a processed by a laser process zone of a workpiece during the laser processing process, so that even at very high radiation intensities in the process zone overexposures or

Saturation in the recorded image can be avoided. Such a limitation is generally determined by an appropriate choice of Aperture, a narrow-band bandpass filter and / or a neutral density filter in the observation beam path of a process zone observing camera tries. Due to the insufficient

Dynamics of the image sensors of the cameras available in the prior art, however, under these conditions, processing areas that are outside the actual process zone can not be observed, since these are then too dark. By choosing the camera exposure time, this can be counteracted to some extent,

However, arbitrarily short exposure times are not possible or the cameras required for it very expensive. Therefore, it requires one or

several additional illumination source (s) for illuminating dark workpiece areas, if different measuring tasks are to be variably combined.

From DE 10 2009 050 784 B4 and EP 2 061 621 Bl two arrangements are known which control the amount of light falling on the image sensor over the exposure time and / or the illumination intensity. These parameters are varied between individual images.

From DE 10 2009 016 125 AI it is known in a

Laser processing method to evaluate back reflections of a laser beam with a sensor. There is also an electrically adjustable or

variable attenuator described. The attenuator may comprise a motorized gray wedge, an electrochromic element or an LCD screen.

It is also known from JPS 58157596 A to arrange an adjustable filter in front of a camera with which radiation from a welding zone is detected. In these known devices, the amount of light falling on the camera or the sensor can only be set or changed to a limited extent as a function of the observation task. For example, to obtain information from different areas of the workpiece (eg, the process zone and the environment), a repetition with different settings is required.

The present invention has for its object to provide a method and an apparatus by which an image-based observation of different bright areas of a workpiece during a

Laser processing process is improved.

This object is achieved according to the invention by a method for observing and / or monitoring a laser processing process of a workpiece by means of a camera, the transmission of which is arranged in an observation beam path of the camera,

adjustable filter is set, wherein the transmission of the filter is controlled in at least two different regions of the filter controlled to different degrees of transmission and / or the

Transmission at least in a region of the filter with time

Recording times of the camera and / or with times of

Brightness changes of an additional illumination source

synchronized to different transmission levels is set. Thus, according to the invention, a controlled, flexibly adjustable or switchable filter is used in the observation beam path of the camera. A

controlled adjustment of the filter means that the setting of the filter can be changed depending on the application, in particular that the filter can be controlled by a control unit. The transmittances of the filter are variably selectable (eg by a control),

in particular dependent on a measuring task. The term "switching" of the filter should be understood as meaning a setting of the filter to a new state or a change in the state of the filter within a relatively short period of time, in particular shorter than 20% of the duration between two successive recording times.

If the transmission of the filter is synchronized with recording times of the camera, the amount of light incident on the camera can be individually adapted to an image acquisition as needed during the processing process. By synchronization with times of brightness changes of an additional

Lighting source can also meet the needs of the

Brightness contrast range of the image to be recorded in addition

be limited. In particular, additional lighting may be provided to illuminate areas outside of a process zone. The illumination source can with the transmission of the filter or with the amount of light falling on the camera

be controlled synchronously.

In particular, in contrast to, for example, an aperture stop, the adjustable filter can almost arbitrarily along the

Observation beam to be positioned. Also, by using the tunable filter, changes in depth of field from one shot to another can be avoided. As a result, the image recording can be done with a fixed, predefinable aperture, whereby the recorded image can be easily evaluated automated. An adjustable or switchable filter also allows, in contrast to, for example, iris diaphragms, very fast setting changes. So can changes in transmittance in the range of milliseconds and sometimes in the range of microseconds. An adjustable or switchable filter can also work very long-term stable, so that a continuous operation is possible.

The transmittance of the filter can be adjusted by changing the spectral range of the radiation transmitted through the filter. For this purpose, the filter may be formed, for example, as a bandpass filter whose center wavelength and / or its bandwidth is set. If, for example, the central wavelength of a wavelength which is visible within the wavelength range is in the range, for example, in the ultraviolet or in the infrared range

Wavelength changed or switched so it can be the

Transmittance in the wavelength range of visible light set, in particular reduced.

It can also be provided, especially if the filter as

Bandpass filter is designed to select or switch the observed wavelength range, for example, between visible and infrared radiation. Advantageously, it can be provided that also other elements along the observation beam path, in particular the camera, on each observed

Wavelength range are set and / or formed for observation in all observed wavelength ranges.

Alternatively or additionally, it may also be provided to set the transmittance of the filter only within a predetermined wavelength range. It is particularly advantageous if the transmission of the filter with a predefined time offset, in particular a time lead, at the recording times and / or the times of the

Brightness changes the illumination source is changed. As a result, switching times or setting speeds of the filter can be taken into account in a simple manner, so that an image with high reliability can be recorded with the desired transmission of the adjustable filter.

The transmittance of the filter can vary depending on a

Measuring task, such as a recording of radiation of the

Machining process, a recording under incident illumination of a workpiece, the seam position control and / or seam quality control set. Thus, the amount of light arriving on the camera during the recording can be adjusted as needed in accordance with the

respective measuring task to be controlled. It can also be provided to set or select the observed wavelength range depending on the measurement task.

Preferably, the brightness of the illumination source, the

Exposure time and / or the recording sensitivity of the camera depending on the set transmission of the filter can be selected. Thus, other recording parameters, the on the

Camera incident light quantity and / or additionally control the image quality, tuned to the transmission of the filter set or

be switched.

In particular, it can be provided that first the transmission of the filter is adjusted, then or at the same time

Lighting source set, in particular on or off, is and then a picture is taken by the camera. Thus, different adjustment speeds of the filter and / or the illumination source can be taken into account in a simple manner.

In an alternative variant of the method, the transmission of the filter in at least two different regions (pixels) of the filter is set to be controlled to different degrees of transmission. Thus, the adjustable filter can be used as an optical mask. For example, relatively dark zones of the observation area of a workpiece to be observed or processed can be filtered little and, at the same time, very bright zones of the observation area can be very heavily filtered. The settings of the filter areas can remain unchanged during the observed laser processing process.

In this variant of the method according to the invention, the filter can be subdivided into at least two, in particular into many areas (pixels). Physically, this can be an area (pixel) with respect to its

Transmission behave like a standalone, fast switched filter. It can be set in the areas of different degrees of transmission in a certain contrast ratio. This setting can be spatially resolved before a measurement is started.

Within the image recorded by the camera, several measurement areas or measurement windows can be provided, wherein the evaluation of the acquired image data can be limited to these measurement windows.

For each desired measuring range or measuring window,

for example, leading and trailing to the processing location and at the processing location, a suitable transmittance can be preset in the filter, which is suitable for the respective measuring task, for example, depending on the workpiece material and / or the laser power.

To set the areas, a control unit can be provided which allows the transmission levels of the individual areas (pixels) to be adjusted in a controlled manner and, for example, to be communicated to an image processing unit via a corresponding digital interface. Changing the transmittance can also be done independently of a measurement or recording in this process variant. As a result, a communication interface between the control unit of the filter and the image processing unit can also be lower

 Transmission speed can be used. In addition, a higher contrast of the filter between minimum and maximum transmission can be achieved, as longer setting or switching times are possible.

The controlled adjustable spatial transmission profile of the filter can depend on a respective desired application or a Messbzw. Image processing task to be selected. The transmission profile for a specific measurement task can be described, for example, as

Configuration data set may be provided in the control unit and be selectable for example by an operator, by a machine program of a laser processing machine via a corresponding interface and / or by the image processing unit itself.

In this variant of the method, the image acquisition for different measurement windows at the same time over a large image area with the same

Exposure time, whereby the measurement speed can be increased. The setting of the transmittance in front of the measuring windows can remain unchanged in the course of the measurement in this process variant.

Adapted to the measuring or observation task and to the parameters of the process to be observed, however, the transmittances can also be controlled and flexibly changed between two measurements.

The image acquisition can be done simultaneously in this process variant for all measurement windows. Alternatively, image recordings for the individual measurement windows can take place one after the other in order, for example, to be able to use different exposure times of the camera.

In addition, it may be useful to change the position of the measurement window and / or the position of individual transmission ranges during a measurement run, for example to compensate for the influence of heating of the optical components in the laser beam path. The tracking of the positions can take place from picture to picture; however, it can also slow down tracking over multiple camera images

be provided.

Possible applications of this process variant may be, for example:

- Switching the transmittance in a leading

 Measuring window between e.g. 80%, if an incident light measurement for seam position control during laser welding is to be used, and 10% when using a light section measurement.

 - Controlled adjustment of the spatial position and / or

Extension of a measuring window containing the laser focal spot to a shift (drift) of the laser focal spot position in

 Camera image.

 - Adjustment of the distance of the leading and / or trailing measurement window from the position of the laser focal spot in dependence on process parameters.

 Changing the transmittance of the adjustable filter at the

 Position of the laser focal spot between setup mode and

 Process mode:

 • Setup: e.g. 80% transmission for incident light measurement

 Reference mark on a test workpiece.

 • process operation: e.g. 10% transmission for the measurement of

 Laser focal spot.

The scope of the invention further includes a

Observation device, in particular for carrying out the method according to the invention, with a camera, at least one additional illumination source and an adjustable filter arranged in an observation beam path of the camera, wherein the

Observation device comprises a control unit which is adapted to the transmission of the filter in at least two different

Areas of the filter to different transmittances

adjust, and / or wherein the observation device a

Synchronization unit, which is set up, the transmission at least in an area of the filter with recording times of the camera and / or with times of brightness changes of the additional illumination source (s) synchronized to different

Adjust transmission levels.

It can be provided that the filter is designed as a neutral density filter. Thus, the transmission of the filter can be largely neutral in color be set. A neutral density filter also provides a simple

Possibility to adjust the transmission without changing the depth of field of the image to be recorded.

The camera can be designed as a surface detector. The camera may for example comprise a CCD element and / or a CMOS element.

It is particularly advantageous if the transmission of the filter is electrically switched to different degrees of transmission is adjustable. For this purpose, the filter may comprise at least one liquid crystal element. The filter may be formed, for example, as an LCD element.

It may be particularly preferred that the

Liquid crystal element with an AC voltage, preferably with a square-wave AC voltage is driven. In particular, when the filter is formed as an LCD element, so unwanted

DC creepage currents are avoided, the one

Liquid crystal layer of the LCD element could destroy in the medium term due to unwanted ion migration.

It can be provided that the filter has a liquid crystal retarder. In particular, it may be provided to combine individual variable liquid crystal retarders. Also, several can

Liquid crystal cells are combined. Adjustable transmission can also be achieved by using a liquid crystal module, e.g. monolithic in an optical element combined with polarizers. For adjustment, the polarizers can then be specified

Angle and be rotated in predetermined directions of rotation. It is particularly advantageous if the filter is a

Transmission setting of at least 2: 1. Transmission ratio is understood to be the ratio of the maximum transmittance that can be set to a minimum. Already a transmission setting ratio of the adjustable filter of 2: 1 already gives clear advantages over a system without adjustable or switchable filter. In particular, particularly high measurement rates can be achieved during monitoring or observation. A transmission setting ratio of 2: 1 already allows approximately a doubling of the achievable measuring rate over one

conventional observation without adjustable filter. Thus, the laser processing process can be observed with improved accuracy.

It is particularly preferred if the filter has a switching time of at most 5 ms, preferably between 1 s and 5 ms. It is under

Switching time to understand the length of time from a setting of a transmittance to a next setting. In this way, a required synchronization of the adjustment process with the image acquisition by the camera is reliably possible.

When the filter is in a spectral range of 400 to 950 nm

transmits, the transmission can be largely changed in the wavelength range of visible light.

It can preferably be provided that the filter has a free aperture of at least 1 mm, preferably between 1 mm and 20 mm. This ensures that there are no unwanted filters on the filter

Diffraction effects occur. At the same time, the space requirement of the filter can be kept sufficiently small. It can be provided that the observation beam path runs at least in a section coaxial with a processing beam. Alternatively it can be provided that the observation beam path off-axial to the processing beam, in other words obliquely to

Processing beam, runs.

When the synchronization unit is designed, it is particularly advantageous for at least a first control signal to be synchronized with respect to time

To generate control of the transmission of the filter and / or the recording times of the camera and / or the times of brightness changes of the additional illumination source. It can be provided in particular that the synchronization unit generates a plurality of control signals, in particular in each case at least one element to be controlled. The control signals can in particular for temporal

Synchronization or control of the filter, the camera and / or the additional illumination source serve. The control signals can also be used to control other settings, for example to vary the power of the additional illumination source, for

Brightness control or sensitivity control of the camera and the like.

For this purpose, the synchronization unit can be designed as a computer unit or a part of a computer unit, in particular the

Image processing unit, form.

It can be provided that the observation device a

Real-time computer program component for generating at least one synchronization control signal. Advantageously, the real-time computer program component in a memory area of the Computing unit executable stored. This makes it possible to have the real-time computer program component on the computer unit

perform.

In particular, the real-time computer program component

be configured to generate the at least one synchronization control signal and to deliver to the synchronization unit. Thus, in a simple way required for synchronized control

Control tasks are realized.

The real-time computer program component can be designed as an independent real-time program component. It can also be provided that the computer unit with a real-time operating system

equipped real-time computer program component under real-time conditions. The configuration as a real-time computer program component can advantageously ensure that the control signals formed by the synchronization unit can be provided not only correctly but also on time in accordance with the respective control task.

The synchronization unit can be designed as a trigger board. In particularly advantageous embodiments, the trigger board can be controlled by a frame grabber processing the images recorded or by a coded process implemented in the latter. The frame grabber can also be part of the computer unit. Also may be provided in alternative embodiments, the synchronization unit on an independent control board and / or in the camera

train. The monitoring device, preferably the synchronization unit and / or the real-time computer program component, can be

Have delay element for delaying a control signal. The delay element can be formed, for example, as a program element of the real-time computer program component. Also, the delay element may be formed as an electronic circuit, preferably as part of the synchronization unit. Is that for example

Control signal pulse-based, so the delay element can

Delay pulses of the control signal by a predefined period of time.

In particular, one of the

Control signals of the synchronization unit with respect to one of the other control signals of the synchronization unit delayed or offset. In particular, the control signal that controls the camera may be delayed from a control signal that controls the adjustable filter and / or the additional illumination source by at least the amount of time that the adjustable filter sets for setting a next transmittance and / or the additional illumination source for adjustment a next brightness needed. Thus, the predefined delay, the individual components to each other even better timed. In particular, other delays caused by the components and / or a possible jitter can also be compensated.

The control unit can be designed as a separate module. It can in particular on a machining head of a

Laser processing machine, in a control cabinet or in the

Be arranged image processing computer unit. Alternatively, the control unit can also be integrated into the computer unit or the synchronization unit or the trigger board and / or into the real-time computer. Computer program component integrated or as more on the

Computer unit executable installable real-time computer program component be formed.

The control unit can interface with others

Have image processing units, to further sensor and / or other machine controls. This interface can be used to parameterize and control the filter. The

Parameterization can be done very easily. Furthermore, it can be provided that the parameterization can be adjusted manually by an operator, automated, via software algorithms and / or external interfaces.

Furthermore, it can be provided that the observation device has a spectral filter arranged in the observation beam path. Thus, for example, cooler and usually darker zones with low color temperature can be filtered weaker and at the same time hotter and therefore generally lighter zones with higher color temperature. Also, the spectral filter, for example, the adjustable filter and / or the camera against damage from one to

machining or observing workpiece outgoing

Protect back reflection or radiation from heat radiation.

Furthermore, provision may be made for the observation device to have an observation objective arranged in the observation beam path, wherein the spectral filter is arranged between the workpiece and the object

Observation lens and the adjustable filter between the

Observation lens and the camera can be arranged.

In particular, the adjustable filter can be placed close to the camera. Furthermore, it is within the scope of the invention

 Laser processing device for processing a workpiece with an observation device according to the invention. The

 Laser processing device can be designed as a laser welding device, as a laser cutting device and / or as a laser scanning device.

Further advantages of the invention will become apparent from the following

Description of variants of the method according to the invention and of exemplary embodiments of the devices according to the invention, with reference to the figures of the drawing, which show details essential to the invention, as well as from the claims. The features shown there are not necessarily to scale and presented in such a way that the features of the invention can be made clearly visible. The various features may be implemented individually for themselves or for a plurality of combinations in variants of the invention. Show it :

Fig. 1 shows a laser processing apparatus with a

 Observation device according to the invention;

FIG. 2a shows a schematic representation of the control of a camera, an adjustable filter and an illumination source synchronized according to FIGS. 2c to 2c

 resulting time courses and

Fig. 3 is a schematic representation of an adjustable filter with three areas set to different degrees of transmission. 1 shows in a first embodiment of the invention, a laser processing apparatus 1. In this embodiment, the laser processing apparatus 1 is a laser welding apparatus. The

Laser processing apparatus 1 comprises a laser 2, the one

Workpiece 3 is processed by means of a machining beam 6, i.

laser welded.

The laser welding process, generally the laser processing process, is monitored by an observation device 4. The observation device 4 has a camera 10 for this purpose. The camera 10 is designed as a surface detector with a CMOS-based photosensor element.

Along its observation beam path 5 is a controllable adjustable or switchable between different degrees of transmission filter 11 is arranged. The adjustable or switchable filter 11 is as

partially transparent LCD element formed. It has a spectral range of 400 to 950 nm and a free aperture of 20mm. In this spectral range, the filter 11 acts as a neutral density filter or is designed as such in this spectral range. Light passing through the filter 11 thus becomes corresponding to one, respectively

adjusted transmittance largely neutral color neutral.

Designed as an LCD element, the filter 11 allows pixel-wise to be controlled by suitable electrical control signals and thus different areas of its filter surface to different

Adjust transmission levels. Thus, an adjustable pattern with different degrees of transmission can be produced on the filter 11 become. The transmission setting ratio of the filter 11 is at least 2: 1, for example 100: 1.

With its filter surface of the adjustable filter 11 covers the

Photosensor element of the camera 10.

Along the observation beam path 5, an objective 13 is disposed upstream of the adjustable filter 11.

In front of the objective 13 along the observation beam path 5, a spectral filter 14 is disposed in front of it. The spectral filter 14 serves for pre-filtering the light incident on the camera 10. Also, the spectral filter 14 serves to protect the adjustable filter 11 and the camera 10 against excessive heat radiation.

Starting from the laser 2 passes emitted laser light 6 a

Collimating lens 21 and a beam splitter 22 to be subsequently focused by a focusing lens 23 to a focal point 24 on the workpiece 3.

From the workpiece 3 and the focal point 24 and from one to the

Focusing 24 adjacent process zone outgoing radiation in turn passes through the focusing lens 23. At the beam splitter 22, the incident on this coaxial radiation is deflected into the observation beam 5 of the observation device 4. Thus, the radiation passes through the spectral filter 14, the objective 13 and the adjustable filter 11 and impinges on the camera 10.

In order to additionally illuminate the workpiece 3 outside of the focal point 24 and also to be able to observe there, is also a additional illumination source 25 in the form of a light-section illumination off-axially, ie obliquely to the processing beam 6, respectively. In addition, a further additional illumination source 26 is arranged as a reflected-light illumination annularly around the processing beam 6 around.

For switching the filter 11 between different degrees of transmission is a synchronization unit 15 via control lines 16a, 16b, 16c, 16d with the additional illumination sources 25 and 26, a

Control electronics 12 and the camera 10 connected. The

Control electronics 12 is connected via a control line 16e with the

adjustable filter 11 connected.

The synchronization unit 15 is formed by means of the

Control line 16a, 16b, 16c and 16d transmitted control signals the camera 10, the control electronics 12 and the additional

Lighting sources 25 and 26 synchronized to control.

The synchronization unit 15 is a triggerboard one

Image processing computer unit 17 is formed. In a storage area of the image processing computer unit 17 is a

Computer program component 18, which is designed as a real-time computer program component executable

stored. The computer program component 18 is configured to generate synchronization control signals and to the

Synchronization unit 15 to deliver. For this purpose, the

Computer program component 18 as a program element

trained delay element 19. Delay element 19 delays pulses of a pulse train

Synchronization control signal for the filter 11 by predefined

Time intervals and forms from this synchronization control signals or Pulse trains for the additional illumination sources 25, 26 and the camera 10.

The synchronization unit 15 converts these

Synchronization control signals in on the camera 10, the

Control electronics 12 and the additional illumination sources 25 and 26 adapted electrical control signals and transmits them via the control lines 16a, 16b, 16c, 16d.

The control electronics 12 are designed to transmit a control signal via the control line 16e to the adjustable filter 11 as a function of the control signal received via the control line 16b. The drive signal is expediently designed as a rectangular alternating voltage and is used to generate a desired

Transmittance transmitted to the switchable or adjustable filter 11.

With the control electronics 12 of the adjustable filter 11 designed as an LCD element, a control unit 20 is also connected via a

Control line 16f connected, which generates the necessary for driving a pixel-by-pixel transmission pattern of the filter 11 control signals. Various spatial transmission profiles of the filter 11 are each stored as a configuration data set in the control unit 20 and are processed by the image processing computer unit 17 via a control line 16 g, via which the control unit 20 to the image processing unit 17

connected, selected. In an alternative embodiment, the configuration data sets may also be stored by an operator (e.g.

Control computer of the overall system) or be selected by a control program of the laser processing apparatus 1 via a corresponding interface. Depending on a predefined measurement task sets a configuration record the position and extent of individual transmission areas of the filter 11 and the there to be adjusted

Transmittance fixed. In addition, a configuration data set may also contain data on the illumination intensity and time of the illumination sources 25, 26 and on exposure times of the camera 10.

With reference to Figures 2a to 2c and Figure 3, the method according to the invention and resulting temporal sequences are now explained in more detail.

FIG. 2a shows a time profile of the transmission of the

adjustable filter 11 of Figure 1. Figure 2a recording times ai, a ₂ , a3 of the camera 10 (Figure 1) can be seen. Before the

Recording time ai starts with a time lead Afi

Transmittance b of the filter 11 is set or switched, b is 50% in this embodiment.

With a time advance Af ₂ to the subsequent recording time a ₂ , the transmission of the filter 11 is set or switched to a transmittance a, in this embodiment 10%. With a further time advance Af ₃ for the subsequent recording time 33, the transmission of the filter 11 is then set or switched to a transmittance c, in this case 90%. The lead times Afi, Af ₂ , Af ₃ are selected to be slightly longer than the switching time of the filter 11, which in this embodiment is at most 5 ms. Thus, the filter 11 can be safely switched to the desired following transmission before the next image is taken.

FIG. 2b shows corresponding exposure times of the camera 10. For this purpose, each phases 33, 34, 35 are marked, in which the Camera 10 takes an image or the photosensor element of the camera 10 is exposed.

It can be seen that starting with recording time ai the camera 10 with an exposure time Aki, at the recording time a ₂ with an exposure time Ak ₂ and at the recording time 33 with a

Exposure time Ak _{3 is} exposed. In this embodiment, the shortest exposure time is given by Ak ₂ and the longest

Exposure time by Aki.

The figure 2c are brightness changes of the additional

Illumination sources 25 and 26 (Figure 1) can be seen. It can be seen that at the time of recording ai the additional illumination source 25 with the brightness e and at the time of recording 33 the additional

Illumination source 26 is switched on with the brightness d. To the

Recording time a ₂ , the additional illumination sources 25, 26 are turned off. The brightness changes or adjustments take place with a time lead Abi at the time of recording ai, Ab ₂ for

Recording time a ₂ or from ₃ to the recording time 33. These time lapses Abi, Ab ₂ , Ab ₃ are tuned and selected a little longer than the respective setting times of the additional

Illumination sources 25, 26.

It can also be seen that, at the time of recording ai, the brightness of the additional illumination source 25 (laser line for light section) is set to a maximum value e, whereas the brightness of the illumination source 26 (incident illumination) is set to a lower brightness value d at the time of recording a ₃ . Thus, the settings of the transmission of the filter 11 and the brightness changes of the illumination sources 25, 26 are synchronized to recording times ai, a ₂ , a _{3 of} the camera 10. For example, based on the recording time 33 can also be seen that initially the

Transmission of the filter 11 is set, then the illumination sources 25, 26 are turned on or off and then an image is taken by the camera 10.

Incidentally, in this embodiment, the time intervals between the recording times ai, a ₂ , 33 correspond to the reciprocal of the frame rate or the frame change duration of the camera 10.

The timing of the filter 11 and the timing of the additional illumination sources 25, 26 are the respective

Reception task designed adapted. The admission to

Recording time ai is used, for example, for seam quality control with the aid of a light section measurement. The recording at the time of recording a ₂ serves to monitor the laser focal point 24 (FIG. 1). The

Recording at recording time 33 is used for example for

Seam position control by detecting the joint with the help of a

Incident illumination.

Therefore, it can be seen from FIGS. 2 a to 2 c that the

Recording time ai the workpiece 3 (Figure 1) with a high

Intensity is additionally illuminated, the filter 11 is set to the average transmittance b.

At the time of recording a ₂ , a recording of the radiation takes place at the position of the focal point 24, which must be greatly attenuated. For seam position control, the workpiece 3 is illuminated at incident time 33 with incident light from the additional illumination source 26. For safe detection, for example, a joint is a high

Light intensity on the photosensor element of the camera 10 is required. Therefore, the image through the filter 1 1 with the comparatively high

Transmittance c only slightly attenuated and recorded by the camera 10.

The image recordings at the times ai, a ₂ and 33 are repeated consecutively during the laser welding process.

FIG. 3 shows a further variant of the method according to the invention. For this purpose, a schematic front view of the camera 10 and of the camera 10 upstream filter 1 1 are shown in the figure.

It can be seen that in this variant, the transmission of the filter 1 1 in the areas I, II and III is set to different transmittances b \ a \ c '. Also in this process variant, the smallest transmittance is given by a 'and the highest transmittance by c'.

To recognize are measuring windows 30, 31 and 32, d. H . Areas of the

Camera image of the camera 10, which are evaluated for process monitoring. In front of the measuring windows 30, 31, 32 different transmittances in the different regions I, II and III of the filter 1 1 are set. The measuring window 30 of state I is for seam quality control

educated. The transmittance b 'of the filter 11 is set to a value of 50%, for example.

The measuring window 31 of the area II is for monitoring the

Laser focal point 24 is formed. The transmittance a 'of the filter 11 is set to a value of 10%, for example. ,

The measuring window 32 of the area III is designed for seam position control. The transmittance c 'of the filter 11 is set to a value of 90%, for example.

The image acquisition takes place in this process variant for all measurement windows at the same time. Adapted to the measuring or observation task and to the parameters of the process to be observed, the

Transmittances a b c 'controlled as needed and flexibly changed between two measurements.

Claims

claims 1. Method for monitoring and / or monitoring a  Laser processing process of a workpiece (3) by means of a  Camera (10), the transmission of a in a  Observation beam (5) of the camera (10) arranged adjustable filter (11) is set, characterized in that the transmission of the filter (11) in at least two controlled in different regions (I, II, III) of the filter (11) to different transmittances (a, b, c, ab) is set and / or the transmission at least in a region of the filter (11) in time with recording times (ai, a ₂ , a3, a \, a ' ₂ , a ^) of the camera (10) and / or with times of brightness changes of at least one additional illumination source (25, 26) synchronized to different transmittances (a, b, c, ab) is set , 2. The method according to claim 1, characterized in that the  Transmittance of the filter is adjusted by the  Spectral range of the transmitted through the filter (11) radiation is changed. 3. The method according to any one of the preceding claims, characterized characterized in that the transmission of the filter (11) with a predefined time offset, in particular a time lead (Afi, Af ₂ , Af ₃ ), at the recording times (ai, a ₂ , 33, a, a ' ₂ , a ^) and / or the times of the brightness changes of the additional illumination source (25, 26) is changed. 4. The method according to any one of the preceding claims, characterized characterized in that the brightness of the additional Illumination source (25, 26), the exposure time (Aki, Ak ₂ , Ak ₃ ) of the camera (10) and / or the recording sensitivity of the camera (10) in dependence on the set transmission of the filter (11) is selected. 5. The method according to any one of the preceding claims, characterized  characterized in that first the transmission of the filter (11) is adjusted, then or at the same time the additional  Illumination source (25, 26) is set, in particular switched on or off, and then an image is taken by the camera (10). 6. observation device (4), in particular for carrying out the method according to one of the preceding claims, with a camera (10), at least one additional illumination source (25, 26) and one in an observation beam path (5) of the camera (10) arranged adjustable filter (11), characterized in that the observation device (4) has a control unit (20) which is set up, the transmission of the filter (11) in at least two different regions of the filter (11) to different transmittances (a, b, c , ab), and / or that the observation device (4) a  Synchronization unit (15) which is arranged, the  Transmission at least in a region of the filter (11) with Recording times (ai, a ₂ , a3, a, a, a ^) of the camera (10) and / or with times of changes in brightness one  additional illumination source (25, 26) synchronized on to set different transmittances (a, b, c, ab). 7. Observation device according to claim 6, characterized in that the filter (11) is designed as a neutral density filter. 8. Monitoring device according to one of claims 6 or 7, characterized in that the transmission of the filter (11) is electrically adjustable to different degrees of transmission. 9. Observation device according to one of claims 6 to 8, characterized in that the filter (11) has at least one liquid crystal element, wherein the liquid crystal element is preferably driven with a rectangular AC voltage. 10. Observation device according to one of claims 6 to 9, characterized in that the filter (11) comprises a liquid crystal retarder. 11. Observation device according to one of claims 6 to 10, characterized in that the filter (11) a  Transmission setting of at least 2: 1. 12. Monitoring device according to one of claims 6 to 11, characterized in that the filter (11) has a switching time of at most 5 ms, preferably between 1 s and 5 ms. 13. Monitoring device according to one of claims 6 to 12, characterized in that the filter (11) transmits in a spectral range of 400-950 nm. 14. Monitoring device according to one of claims 6 to 13, characterized in that the filter (11) has a free aperture of at least 1 mm, preferably between 1 mm and 20 mm. 15. Monitoring device according to one of claims 6 to 4, characterized in that the synchronization unit (15) is formed, at least a first control signal for time-synchronized  Control of the transmission of the filter (11) and / or the Recording times (ai, a ₂ , a ₃ , a \, a ' ₂ , a ^) of the camera (10) and / or the times of brightness changes of the additional  Generate illumination source (25, 26). 16. Observation device according to one of claims 6 to 15, characterized in that the observation device (4), preferably the synchronization unit (15) and / or a real-time computer program component (18) for generating at least one synchronization control signal, a delay element (19) for delay a control signal. 17. Laser processing device (1) for processing a workpiece (3) with an observation device (4) according to one of claims 6 to 16, characterized in that the  Laser processing device (1) as a laser welding device, as a laser cutting device and / or as a laser scanning device  is trained.