Patent Description:
A conventional apparatus for machining a workpiece with a laser beam is known. Also a conventional apparatus for machining a workpiece with a laser beam coupled into a fluid jet, wherein the fluid jet impinges onto the workpiece, is generally known.

A problem typically encountered during the laser beam machining process of a conventional apparatus is that, due to the lack of mechanical interactions of the apparatus with the workpiece, it is difficult to determine characteristic states of the process of machining the workpiece. This difficulty often leads to a significant increase of the machining process time. For example, when a conventional apparatus is used to cut a workpiece with the laser beam, it is problematic to accurately determine, if and when the laser beam has broken through the workpiece material. Thus, the cutting process cannot be finished in a time-optimized manner. Additionally, it would also be beneficial to have the possibility to accurately determine other states of machining the workpiece, for example, states that indicate an instability of the machining process.

Since the laser beam may be scattered back from the workpiece in an uncontrolled manner, a determination of the process state by visual inspection of the workpiece is difficult or even dangerous. Further, if the conventional apparatus uses a laser beam guided in a fluid jet, additional difficulties arise due to the wet workpiece environment. For instance, since the fluid jet may splatter back from the workpiece in an uncontrolled manner, the fluid may accumulate on surface regions of the workpiece, thereby making it even more difficult to determine states of the machining process.

Conventional solutions are largely based on visual inspection by means of a camera, for instance, disposed next to the apparatus and/or the workpiece. However, the conventional visual inspection is not very precise, due to the above-mentioned environmental difficulties, especially in wet environments. Further, there is a high risk that the inspection equipment, e.g. the camera, is damaged by splattering fluids. Moreover, the apparatus according to this conventional solution is relatively large, and is inconveniently distributed into multiple separate components.

In view of these problems and disadvantages, the present invention aims at improving the conventional apparatus and solutions. It is accordingly an object of the present invention to provide an apparatus and a method for machining a workpiece with a laser beam coupled into a fluid jet, which allow reducing the machining process time. In particular, the invention should allow determining more precisely a state of the machining process. The higher the accuracy of determining the state of machining the workpiece is, the better the machining process can be time-optimized. In particular, the invention desires a reliable determination of whether the laser beam has broken through the workpiece material or not. The present invention thereby aims particularly for a compact apparatus and a solution, which is not disturbed by the wet environment caused by the fluid jet. Accordingly, damages to the apparatus and equipment should be avoided.

<CIT> describes an apparatus for determining a spatial position of a liquid jet, in particular a liquid jet for optically guiding a laser beam, through the modification of an orientation.

<CIT> discloses a machine tool that performs machining while ejecting a pressurized liquid toward a workpiece.

<CIT> describes a method for determining hole completion in laser drilling of an article of manufacture with a laser beam that is directed inside a fluid column.

<CIT> discloses a method and system for confined laser drilling with a laser beam within a liquid column.

<CIT> (forming the basis for the preamble of the independent claims) discloses high power lasers systems, apparatus and methods for performing laser operations, in particular, in environments where an optically obstructive medium is present in the laser beam path, such as within a borehole of an oil, gas, or geothermal well.

Advantageous implementations of the present invention are defined in the dependent claims.

In particular, the present invention proposes detecting a state of machining the workpiece based on a process emission, i.e. based on a laser-induced electromagnetic radiation that results from the machining of the workpiece with the laser beam.

A first aspect of the present invention provides an apparatus for machining a workpiece according to claim <NUM>.

In the machining unit the laser beam is coupled into the pressurized fluid jet, which acts like a waveguide for the laser beam and guides the laser beam onto the workpiece by means of total internal reflection. The pressurized fluid jet is preferably provided by a fluid nozzle, and the laser beam may be directed by the at least one optical element through the fluid nozzle into the fluid jet and towards the workpiece. The fluid nozzle and the at least one optical element may be separated, for instance by an optical window, in order to prevent contact of the optical element and the fluid.

The spectral separation unit is arranged and configured to receive the laser-induced electromagnetic radiation propagating away from the workpiece, and separates the electromagnetic radiation of interest from the received radiation, and may provide the radiation of interest including the at least part of said secondary radiation to the sensing unit. The spectral separation unit has the effect that the state of machining the workpiece can be determined even more accurately and more reliably. The spectral separation unit prevents that unwanted radiation reaches the sensing unit. The sensing unit can therefore more sensitively and accurately detect the radiation of interest. The radiation of interest may be the secondary radiation with unwanted other radiation removed, or may be a part of the secondary radiation. It may, for instance, be that the laser beam induces different kinds of electromagnetic radiation caused by different mechanisms. In this case, the radiation of interest may be only secondary radiation caused by one specific mechanism.

The secondary radiation is specifically caused by the processing of the workpiece with the laser beam, for instance, because the machined surface region of the workpiece is transformed into a plasma. This plasma emits a characteristic radiation, which can be easily isolated on the sensing unit by means of the spectral separation unit, in order to allow a particularly accurate determination of the state of machining the workpiece, especially of whether the laser beam broke through the workpiece.

The sensing unit may be a photo-detecting device or light sensor, and is configured to detect the secondary radiation included in the laser-induced radiation that travels along the fluid jet in the direction opposite to the primary laser beam, i.e. propagates away from the workpiece. Notably, some electromagnetic radiation induced by the laser beam machining the workpiece may not back-propagate through the fluid jet, but may travel elsewhere.

The secondary radiation received by the sensing unit provides a very accurate fingerprint of different states of machining the workpiece. In particular, the signal, which is accordingly output by the sensing unit, shows characteristic behaviors depending on the different states of machining the workpiece. Therefore, the signal processing unit is able to accurately and efficiently determine states of machining the workpiece based on the signal. As a consequence, it may trigger according actions of the apparatus based on the determined state, in order to significantly improve the machining process time.

The fact that the laser-induced electromagnetic radiation is received via the fluid jet allows arranging the sensing unit safe from the wet environment of the machining process. Advantageously, the fluid jet acts as a waveguide also for back-propagating laser-induced radiation, and thus allows a more accurate detection of the secondary radiation included in this laser-induced radiation, and consequently an analysis or post-processing of the signal that the sensing unit supplies when sensing this secondary radiation. Preferably, the sensing unit is housed in the apparatus, more preferably such that it is separated from any fluid circuitry and the fluid nozzle, in order to be protected from fluid contact and thus enjoy an increased lifetime. The apparatus of the first aspect can be built in a very compact manner, and all components of the apparatus may advantageously be integrated.

Integrating the signal over time improves further the reliability of determining the state of machining the workpiece. In particular, patterns that occur in a single (non-integrated) signal can be enhanced in the integrated signal. Furthermore, additional patterns that appear only in the integrated signal may allow determining further states, or determining the states more precisely. Also the sensitivity of the determination is generally enhanced, since the signal noise impact is reduced.

In a preferred implementation form of the apparatus, the signal processing unit is configured to determine, as the state of machining the workpiece, whether the laser beam has broken through the workpiece.

The apparatus of the invention can particularly determine very accurately and quickly, whether the laser beam has broken through the workpiece. Accordingly, the machining process time can be significantly reduced, particularly when the apparatus is used for cutting a workpiece with the laser beam. This is due to the fact that the machining process can be stopped immediately, once the state that the laser beam has broken through the workpiece is determined. The signal processing unit may be configured to automatically provide such an instruction.

In a further preferred implementation form of the apparatus, the spectral separation unit is arranged to receive the laser-induced electromagnetic radiation propagating through the fluid jet through the at least one optical element, which is configured to couple the laser beam into the fluid jet.

In this specific way, the apparatus can be built particularly compact. Furthermore, the least amount of optical components are required.

The apparatus may comprises an optical head including the machining unit and the sensing unit. Accordingly, in the optical head the laser beam can be coupled by the machining unit into the fluid jet, and the sensing unit may sense the secondary radiation included in the laser-induced radiation back-propagating from the workpiece. The signal processing unit may in this case be arranged in the apparatus, e.g. in a housing thereof, but outside the optical head. A laser unit comprising laser source and/or laser controller may be part of the apparatus or not, but is at least separate from the optical head.

In a further preferred implementation form of the apparatus, the apparatus comprises an optical head including the machining unit, and a laser unit including the spectral separation unit and the sensing unit.

The laser unit may comprise laser source and/or laser controller. In this implementation form, the laser beam may be provided by the laser unit to the optical head, where it is coupled into the fluid jet by the machining unit. Laser-induced radiation back-propagating from the workpiece may be guided through the optical head to the laser unit, where it is received by the spectral separation unit. The optical head can be optically connected to the laser unit, for instance, by an optical fiber.

It was surprisingly found that the state of machining the workpiece can be determined precisely by the signal processing unit based on the signal, which is provided by the sensing unit based on the received secondary radiation, even when the sensing unit is arranged in the laser unit, i.e. distanced from the optical head. An advantage of having the spectral separation unit and the sensing unit, and optionally associated optical elements like a beam splitter and/or focusing optics etc., provided in the laser unit is that the handling of these elements, and e.g. their maintenance or replacement, becomes easier. A further advantage is that the optical head can be exchanged without having to exchange the sensing unit and associated optical elements. The optical head can also be built smaller, and the sensing unit and associated optical elements can be built larger, due to more space available in the laser unit.

In a further preferred implementation form of the apparatus, the apparatus further comprises an optical connection element, particularly an optical fiber, for optically connecting the optical head and the laser unit, wherein the machining unit in the optical head is configured to receive the laser beam via the optical connection element, and the spectral separation unit in the laser unit is configured to receive the laser-induced electromagnetic radiation via the optical connection element.

Accordingly, the same optical connection element, e.g. optical fiber, is used to transport the laser light for the laser beam and the laser-induced radiation, respectively, within the apparatus, i.e. between the optical head and the laser unit. Nevertheless, the state of machining the workpiece can be accurately determined by the processing unit based on the signal produced accordingly by the sensing unit.

In a further preferred implementation form of the apparatus, the at least one optical element includes a lens for coupling the laser beam into the fluid jet, and the spectral separation unit is arranged to receive the back-propagating laser-induced electromagnetic radiation through said lens.

This specific implementation form therefore allows using the lens in a double manner and allows positioning the sensing unit such that it is protected from fluid contact. Further, the apparatus can be built in a compact manner.

It may be the case that in addition to the secondary radiation emitted from a portion of the workpiece that is machined with the laser beam, also primary laser radiation that is reflected from the workpiece, and/or another secondary radiation generated by scattering of the laser beam in the fluid jet, propagates away from the workpiece through the fluid jet and through the at least one optical element. In this case, the spectral separation unit is used to filter out any unwanted laser-induced electromagnetic radiation, and to focus only the secondary radiation emitted from a portion of the workpiece that is machined with the laser beam, onto the sensing unit.

In a further preferred implementation form of the apparatus, the signal processing unit is configured to process the signal with a temporal resolution of below <NUM>, preferably of below <NUM>.

For instance, the temporal resolution of the signal processing unit may be between <NUM>-<NUM>, or between <NUM>-<NUM>, or between <NUM>-<NUM>, or even between <NUM>-<NUM>. These preferred temporal resolutions provided by the signal processing unit allow an accurate detection of the state of machining the workpiece, and thus a particularly stable control of the machining process. In particular, the machining process time can be reduced even further with such a signal processing unit.

In a further preferred implementation form of the apparatus, the apparatus further comprises at least one peripheral device, preferably a laser controller, fluid supply controller, gas supply controller, and/or movement axes controller, wherein the signal processing unit is configured to provide the at least one peripheral device with an instruction signal based on the determined state of machining the workpiece, in order to start, break, stop and/or restart an action of the peripheral device. Accordingly, the machining process time can be optimized. In particular, based on the determined state of machining the workpiece, the apparatus can react quickly to take the necessary actions. For instance, if the laser beam broke through the workpiece, the apparatus can stop the machining process. As a further advantage, the machining process quality can be improved.

A second aspect of the present invention provides a method of machining a workpiece according to claim <NUM>.

With the method of the second aspect, the same advantages and effects can be achieved as with the apparatus of the first aspect.

In a preferred implementation form of the method, the method further comprises, for determining the state of machining the workpiece, recording a plurality of signals, comparing the recorded signals with predetermined reference signals, and determining the state of machining the workpiece based on similar or matching reference signals.

By providing reference signals and carrying out the comparison with these reference signals, an easy implementation with very accurate results can be provided.

In a further preferred implementation form of the method, the method comprises determining, as the state of machining the workpiece, that the laser beam has broken through the workpiece, when a value of a single signal or the integrated signal, which increased after a start of machining the workpiece, decreases again below a determined threshold value.

The above-mentioned characteristic fingerprints in the single signal or integrated signal, i.e. the patterns followed by the signal or integrated signal, have been found to provide very accurate determination results. Moreover, the processing load is low, so that the method can be carried out very quickly.

The above-described aspects and preferred implementation forms of the present invention are explained in the following description of specific embodiments in relation to the enclosed drawings, in which.

<FIG> shows an apparatus <NUM> according to an example. In particular, the apparatus <NUM> is configured to machine a workpiece <NUM> with a laser beam <NUM>. The workpiece <NUM> may be a made of a material including, for example, metals, ceramics, diamonds, semiconductors, carbides, alloys, superalloys, or ultra-hard materials. The workpiece <NUM> is notably not a part of the apparatus <NUM>. However, the workpiece <NUM> can be positioned on a machining surface, which may or may not be part of the apparatus <NUM>. In either case, the apparatus <NUM> can be arranged such that it can machine the workpiece <NUM> disposed on the machining surface. The apparatus <NUM> may also control movements of the machining surface in up to three dimensions.

The apparatus <NUM> comprises a machining unit <NUM>, a sensing unit <NUM>, and a signal processing unit <NUM>. These units <NUM>, <NUM> and <NUM> of the apparatus <NUM> are preferably all integrated into the apparatus <NUM>, i.e. they are preferably disposed within a housing or enclosure of the apparatus <NUM>. The apparatus <NUM> may also comprise further units also disposed within the same housing or enclosure.

The machining unit <NUM> is configured to provide a pressurized fluid jet <NUM> onto the workpiece <NUM>, and to couple the laser beam <NUM> into the fluid jet <NUM>. In particular, the laser beam <NUM> is coupled into the fluid jet <NUM> by means of at least one optical element <NUM>. This at least one optical element <NUM> may include, for example, one or more lenses, lens assemblies, light guiding optics, beam splitters, mirrors, filters, or polarizers. The laser beam <NUM> is guided by the preferably thin (i.e. having a diameter in the µm range) fluid jet <NUM>, in principle like it would be guided in an optical fiber. The laser beam <NUM> is a pulsed laser beam <NUM> and is directed towards and onto the workpiece <NUM>, and can thus be used to precisely machine the workpiece <NUM>, while the fluid jet <NUM> continually cools the workpiece <NUM> and potentially removes debris. For instance, the apparatus <NUM> may specifically be configured to accurately cut or shape the workpiece <NUM>.

The laser beam <NUM> is provided by a laser, which may be a part of the apparatus or which may be external but couple the laser beam <NUM> into a laser supply port of the apparatus <NUM>. The laser beam <NUM> may be visible, and is preferably from the green spectrum. For instance, the laser beam <NUM> may have a wavelength of <NUM>.

The sensing unit <NUM> is arranged to receive laser-induced electromagnetic radiation <NUM>, i.e. an electromagnetic emission that occurs when the workpiece <NUM> is machined with the laser beam <NUM>. Thus, the laser-induced electromagnetic radiation <NUM> may also be referred to as "process emission". The sensing unit <NUM> is arranged such that it can receive, and thus sense, the laser-induced electromagnetic radiation <NUM> propagating away from the workpiece <NUM> through the fluid jet <NUM> and through at least one optical element. Accordingly, the back-propagating process emission <NUM> can reach the sensing unit <NUM> guided in and by the fluid jet <NUM>. The at least one optical element, through which the sensing unit <NUM> can receive the process emission <NUM> can be the at least one optical element <NUM>, which is used to couple the laser beam <NUM> into the fluid jet <NUM>. This is exemplarily shown in <FIG>.

The sensing unit <NUM> is further configured to convert the received laser-induced electromagnetic radiation <NUM> into a signal <NUM>, for instance, it provides a photo current as output signal. The sensing unit <NUM> may thus, for example, be a photodetector, but it can also be any other device or light sensor that is able to convert at least the electromagnetic radiation of interest into an electrical signal. The signal <NUM> is provided to the signal processing unit <NUM> for further analysis and/or processing.

The signal processing unit <NUM> is, for example, realized by a microprocessor or computer, and is specifically configured to determine a state of machining the workpiece <NUM> based on the signal <NUM>, which it receives from the sensing unit <NUM>. In particular, the signal processing unit <NUM> is configured to determine, as the state of machine the workpiece <NUM>, whether the laser beam <NUM> has broken through the workpiece <NUM>. In other words, it can determine that and when the laser beam <NUM> breaks through the workpiece <NUM>. To this end, the signal processing unit <NUM> may apply signal processing on the signal <NUM>. Signal processing may include, for example, scaling, averaging, recording over time, integrating over time, or converting the signal <NUM>, and may include comparing the signal <NUM> or an integrated signal with one or more reference signals. For instance, the signal processing unit <NUM> may be configured to record a plurality of signals <NUM>, and to compare the recorded signals <NUM> with pre-stored reference signals. The signal processing unit <NUM> is configured to integrate a plurality of signals <NUM> over time to produce an integrated signal, and to evaluate a pattern or a change of a pattern in the integrated signal. The plurality of signals <NUM> arise from laser-pulse induced electromagnetic radiation <NUM> sensed by the sensing unit <NUM>, as the laser beam <NUM> is a pulsed laser beam.

The signal processing unit <NUM> may then be configured to determine the state of machining the workpiece <NUM> based on similar or matching reference signals (in the first case) or based on the pattern or the change of the pattern (in the second case). Preferably, the signal processing unit <NUM> provides a temporal resolution of below <NUM>, preferably of below <NUM>, more preferably of below <NUM>, since preferably the sensing unit <NUM> is operated with at least <NUM>, more preferably with at least <NUM>.

<FIG> shows an apparatus <NUM> according to an embodiment of the present invention, which builds on the apparatus <NUM> shown in <FIG>. Identical elements in <FIG> and <FIG> are labeled with the same reference signs and function likewise. Accordingly, the apparatus <NUM> of <FIG> includes the machining unit <NUM>, which is configured to provide the pressurized fluid jet <NUM> onto the workpiece <NUM>, and to couple the laser beam <NUM> into the fluid jet <NUM>. It also includes the sensing unit <NUM>, which is configured to receive secondary radiation that is included in a back-propagating laser-induced electromagnetic radiation <NUM> via the fluid jet <NUM> and through the machining unit <NUM>, preferably through the at least one optical element <NUM>, and to convert the secondary radiation into the signal <NUM>. The signal processing unit <NUM> (here referred to as "Digital signal processing unit + IPC", i.e. the signal processing unit <NUM> may also provide inter-process communications (IPC)) is again configured to determine a state of machine the workpiece <NUM> based on the signal <NUM>. <FIG> additionally shows further details about the preferred overall layout of the apparatus <NUM>. The apparatus <NUM> of <FIG> especially includes several peripheral devices.

The apparatus <NUM> may include a laser source <NUM> and a laser controller <NUM> for controlling the laser source <NUM>. The laser source <NUM> is configured to supply <NUM> the laser light for the laser beam <NUM>. The laser source <NUM> may also be an external device not included in the apparatus <NUM> but for supplying <NUM> the laser light to a laser supply port of the apparatus <NUM>. In the apparatus <NUM> the laser beam <NUM> is preferably directed by an optical unit <NUM> of the apparatus <NUM>, which is preferably a beam splitter and preferably arranged in the optical path between the machining unit <NUM> and the sensing unit <NUM>, towards the machining unit <NUM>. In the machining unit <NUM>, the laser beam <NUM> is coupled into the fluid jet <NUM>. Notably, also the back-propagating laser-induced electromagnetic radiation <NUM> passes preferably through this optical unit <NUM>, but is directed towards the sensing unit <NUM>.

The apparatus <NUM> includes also a spectral separation unit <NUM>, which is configured to isolate only electromagnetic radiation of interest <NUM> including the secondary radiation 206a on the sensing unit <NUM>. The spectral separation unit <NUM> is arranged in the optical path between the machining unit <NUM> and the sensing unit <NUM>, such that it can receive the laser-induced electromagnetic radiation <NUM> travelling away from the workpiece <NUM> through the fluid jet <NUM> and through the at least one optical element <NUM>, and can output the radiation of interest <NUM>, which includes at least a part of secondary radiation 206a included in the received laser-induced electromagnetic radiation <NUM>, onto the sensing unit <NUM>. The spectral separation unit <NUM> may be an optical filter unit, which may consist of one or more optical filters and is configured to filter out unwanted electromagnetic radiation, i.e. to prevent electromagnetic radiation of certain (unwanted) wavelengths from reaching the sensing unit <NUM>. The electromagnetic radiation of interest <NUM> may particularly be only the secondary radiation206a, wherein other electromagnetic radiation that accidently reaches the spectral separation unit <NUM> (and would reach the sensing unit <NUM> without the spectral separation unit <NUM>) is filtered out. The electromagnetic radiation of interest <NUM> is also be a part of the laser-induced electromagnetic radiation <NUM> that reaches the spectral separation unit <NUM> (and would reach the sensing unit <NUM> without the spectral separation unit <NUM>), wherein laser-induced electromagnetic radiation that is not of interest is filtered out. In the embodiment of <FIG>, the laser-induced electromagnetic radiation includes secondary radiation, and the spectral separation unit <NUM> is configured to prevent laser light reaching the sensing unit <NUM>. That is, the spectral separation unit <NUM> is configured to filter out light of the same wavelength than provided by the laser source <NUM>. There are specifically three mechanisms envisaged by this disclosure, which produce laser-induced electromagnetic radiation <NUM> that can provide an accurate fingerprint of the state of machining the workpiece <NUM>.

In the embodiment of <FIG>, the laser-induced electromagnetic radiation <NUM> includes the secondary radiation 206a that is emitted from the portion of the workpiece <NUM> that is machined with the laser beam <NUM>. The machined surface portion of the workpiece <NUM> may, for instance, be transformed into a plasma by the laser beam <NUM>, which plasma is the source of the secondary radiation 206a. Typically, this secondary radiation 206a is from the yellow and/or orange spectrum. Accordingly, the spectral separation unit <NUM> may in this case be configured to allow light from the yellow and/or orange spectrum to reach the sensing unit <NUM>, while it blocks light from other parts of the spectrum, especially blocks the laser light e.g. from the green spectrum. Thus, the radiation of interest <NUM> includes only the secondary radiation 206a. The sensing unit <NUM> can in this case be configured to be particularly sensitive to the yellow and/or orange spectrum.

In an example, the laser-induced electromagnetic radiation <NUM> could also be or include primary laser radiation 206b reflected from the workpiece <NUM>, especially from the workpiece surface. Since the laser light is preferably from the green spectrum, the spectral separation unit <NUM> may in this case be configured to allow light from the green spectrum to reach the sensing unit <NUM>, while it blocks light from other parts of the spectrum. Thus, the radiation of interest <NUM> may include only the secondary radiation 206b. The sensing unit <NUM> can in this case be configured to be particularly sensitive to the green spectrum.

In another example, the laser-induced electromagnetic radiation <NUM> could also be or include secondary radiation 206c generated by scattering of the laser beam <NUM> in the fluid jet <NUM>. Particularly, this secondary radiation 206c can be caused by Raman scattering of the laser beam <NUM>. Typically, this secondary radiation 206c is from the red spectrum. Accordingly, the spectral separation unit <NUM> may in this case be configured to allow light from the red spectrum to reach the sensing unit <NUM>, while it blocks light from other parts of the spectrum, especially the laser light e.g. from the green spectrum. Thus, the radiation of interest <NUM> may include only the secondary radiation 206c. The sensing unit <NUM> can in this case be configured to be particularly sensitive to the red spectrum.

Notably, both the secondary radiation 206a and the laser reflection 206b originate from the workpiece <NUM>, particularly from the machined workpiece surface portion, while the secondary radiation 206c originates from the fluid jet <NUM>, particularly from one or several different locations along the fluid jet <NUM>.

The apparatus <NUM> can further include several peripheral devices, and the signal processing unit <NUM> is preferably configured to provide one or more of the peripheral devices with instruction signals based on the determined state of machining the workpiece <NUM>. In this manner, the signal processing unit <NUM> can control the peripheral devices in dependence of the determined state, and can for example instruct these peripheral devices to start, break, stop and/or restart their respective actions.

For example, the apparatus <NUM> shown in <FIG> includes as peripheral devices a laser controller <NUM>, a fluid supply controller (here optionally integrated with a fluid pump) <NUM>, a gas supply controller <NUM> (here a "Protection gas controller", since the gas is preferably used to protectively surround the fluid jet <NUM>), and a movement axes controller <NUM> (here a "Computer Numerical Control (CNC)"), which may be configured to move in perpendicular X, Y and Z directions and/or rotational a, b, c directions a machining surface, onto which the workpiece <NUM> is put, or alternatively the workpiece <NUM> itself.

The signal processing unit <NUM> is configured to provide respective instruction signals to the different peripheral devices. Preferably, the signal processing unit <NUM> can control the laser controller <NUM> via a signal <NUM>, the fluid supply controller <NUM> via a signal <NUM>, the gas supply controller <NUM> via a signal <NUM>, and the movement axes controller <NUM> via a signal <NUM>. The signal processing unit <NUM> preferably controls the peripheral devices independently from another, and without any outside input, but only based on the signal <NUM> and the determined state of machining the workpiece <NUM>. Nevertheless, it is additionally possible that the apparatus <NUM> includes a human machine interface <NUM>, which can receive human/script input <NUM>, in order to provide additional instructions to the signal processing unit <NUM> via a signal <NUM>.

According to the instructions provided by the signal processing unit <NUM> based on the determined state of machining the workpiece <NUM>, the peripheral devices can take instructed actions. For instance, the laser controller <NUM> may start, pause or stop the supply of laser light for the laser beam <NUM>. The fluid supply controller <NUM> may control a fluid pressure control valve <NUM>, in order to start, break or stop a supply <NUM> of fluid, which is preferably water, to the machining unit <NUM>. The gas supply controller <NUM> can control a protection gas control valve <NUM>, in order to start, break or stop a supply <NUM> of gas, which is preferably helium, to the machining unit <NUM>. The movement axes controller <NUM> may provide specific movement of the workpiece <NUM>, i.e. it can control a machining surface, onto which the workpiece <NUM> is disposed.

<FIG> shows an apparatus <NUM> according to an embodiment of the present invention, which builds on the apparatus <NUM> shown in <FIG> and the apparatus <NUM> shown in <FIG>. Identical elements in <FIG> and in <FIG> and/or <FIG> are labeled with the same reference signs and function likewise. In particular, <FIG> illustrates more details about the optical arrangement and fluid circuitry of the apparatus <NUM>, particularly as provided in the machining unit <NUM>. The machining unit <NUM> may particularly include a lens <NUM> for coupling the laser beam <NUM> into the fluid jet <NUM>. Also back-propagating laser-induced electromagnetic radiation <NUM>, which includes the secondary radiation 206a, is preferably transferred through the fluid jet <NUM> via this lens <NUM>, and then further towards the sensing unit <NUM>. Thereby, the radiation <NUM> preferably travels from the lens <NUM> through the optical unit <NUM> to the spectral separation unit <NUM>, and further as radiation of interest <NUM> including at least a part of the secondary radiation 206a to the sensing unit <NUM>.

The machining unit <NUM> may also include an optically transparent protection window <NUM>, in order to separate the optical arrangement, here exemplarily the lens <NUM>, from the fluid circuitry and the region of the machining unit <NUM> where the fluid jet <NUM> is produced. For producing the fluid jet <NUM>, the machining unit <NUM> preferably includes a fluid nozzle <NUM>. This fluid nozzle <NUM> is provided with the fluid via the fluid supply <NUM>, which may be implemented as a channel through the housing or enclosure of the apparatus <NUM>. To this end, the fluid nozzle <NUM> includes a fluid aperture, which defines the width of the fluid jet <NUM>. The aperture has preferably a diameter of <NUM>-<NUM>, and the fluid jet <NUM> has preferably a diameter of about <NUM>-<NUM> times the fluid aperture. The pressure for the pressurized fluid jet <NUM> is provided via the fluid supply <NUM>. Preferably, the pressure is between <NUM>-<NUM> bar.

It can also be seen in <FIG> that a protection gas, preferably helium, can be supplied via gas supply <NUM> into the machining unit <NUM>, particularly into a space provided within the machining unit <NUM>, through which the generated fluid jet <NUM> passes after leaving the fluid nozzle <NUM>. Here, the protection gas can protectively envelop the fluid jet <NUM>, before the fluid jet <NUM> exits the machining unit <NUM> through a lower exit aperture, and then travels further towards and onto the workpiece <NUM>.

The apparatus <NUM> shown in <FIG> also includes focusing optics <NUM> preferably arranged in the optical path between the spectral separation unit <NUM> and the sensing unit <NUM> and for directing light on the sensing unit <NUM>. In particular, the laser-induced electromagnetic radiation <NUM>, which back-propagates through the fluid jet <NUM> through the lens <NUM>, preferably passes the optical unit <NUM>, then the optical separation unit <NUM>, and the remaining filtered electromagnetic radiation of interest <NUM> is focused by the focusing optics <NUM> onto the sensing unit <NUM>, particularly onto a light-sensitive area of the sensing unit <NUM>. The focusing optics <NUM> preferably includes or is at least one lens, but may also include or be another optical element like a parabolic mirror. The sensing unit <NUM> is configured to convert the received filtered radiation of interest <NUM> into the signal <NUM> for further analysis and/or processing by the signal processing unit <NUM> (which is not shown here).

<FIG> also shows that the above-described elements of the apparatus <NUM> may be provided within an enclosure, particularly within an optical head <NUM>. That is, the apparatus <NUM> may further comprises the optical head <NUM>, which may include the machining unit <NUM> and the sensing unit <NUM>. The optical head <NUM> may also include the optical unit <NUM>, the spectral separation unit <NUM>, and/or the focusing optics <NUM>.

<FIG> shows a method <NUM> according to an example. The method <NUM> includes a step <NUM> of providing a pressurized fluid jet <NUM> onto a workpiece <NUM> and coupling a laser beam <NUM> through at least one optical element <NUM> into the fluid jet <NUM> towards the workpiece <NUM>. Further, the method <NUM> includes a step <NUM> of receiving a laser-induced electromagnetic radiation <NUM> propagating away from the workpiece <NUM> through the fluid jet <NUM> and through at least one optical element, preferably the at least one optical element <NUM> used for coupling the laser beam <NUM> into the fluid jet <NUM>. Further, the method <NUM> includes a step <NUM> of converting the received radiation into a signal <NUM>. Finally, the method <NUM> includes a step <NUM> of determining a state of machining the workpiece based on the signal <NUM>.

The method <NUM> may be carried out by the apparatus <NUM>, <NUM> or <NUM> shown in the <FIG>, <FIG> and <FIG>, respectively. In particular, step <NUM> may be carried out by the machining unit <NUM>, the steps <NUM> and <NUM> by the sensing unit <NUM>, and step <NUM> by the signal processing unit <NUM>.

The method <NUM> particularly includes an automated time-recording of multiple signals <NUM>, wherein each signal <NUM> is caused by one of a plurality of laser pulses. That is, the laser beam <NUM> is a pulsed laser beam. The laser pulses may be provided regularly and may be in the order of ns. Each signal <NUM> may be represented by a single numeric value or by a sequence of values as a function of time. Multiple obtained signals <NUM> are integrated over time to produce an integrated signal. The method <NUM> may further include an automated comparison of the obtained signals <NUM> with reference signals, which are read out from a reference storage e.g. from a memory of the signal processing unit <NUM>. The method <NUM> then includes evaluating a pattern or a change of a pattern in the obtained signals <NUM> or integrated signal, and determines the state of machining the workpiece <NUM> based on said pattern or change of the pattern. Optionally, the method <NUM> may include the automated generation of instruction signals or instruction codes and subsequent transmission to one or more peripheral devices, so that these peripheral devices start, break, stop or restart their respective actions.

<FIG> schematically shows two specific signal patterns 500a and 500b, which are preferably used in the method <NUM> (or by the signal processing unit <NUM> of the apparatus <NUM>, <NUM>, <NUM>), in order to determine the state of machining the workpiece <NUM>.

In particular, the left-hand side signal pattern 500a is preferably used, if the laser-induced electromagnetic radiation <NUM> is or includes the above-mentioned secondary radiation 206a emitted from a portion of the workpiece <NUM> that is machined with the laser beam <NUM>. The signal pattern 500a indicates that the laser beam has broken through the workpiece <NUM>, when the signal <NUM> or the integrated signal first increases after the "Start" of machining the workpiece <NUM> towards an "In-Process" time section, and then decreases again after the "In-Process" time section. When the signal <NUM> or integrated signal falls below a determined threshold value, the "Finish" of the process is reached, i.e. it can be determined that the laser beam broke through the workpiece <NUM>.

Likewise, the right-hand signal pattern 500b is preferably used, if the laser-induced electromagnetic radiation <NUM> is or includes primary laser radiation 206b reflected from the workpiece <NUM>. The signal pattern 500b indicates that the laser beam has broken through the workpiece <NUM>, when the signal <NUM> or the integrated signal first decreases after the "Start" of machining the workpiece <NUM> towards an "In-Process" time section, and then increases again from the "In-Process" time section. When the signal <NUM> or integrated signal rises above a determined threshold value, the "Finish" is reached, i.e. the laser beam broke through the workpiece <NUM>.

<FIG> shows an apparatus <NUM> according to an embodiment of the present invention, which builds on the apparatus <NUM> shown in <FIG>. Identical elements in <FIG> and <FIG> are labeled with the same reference signs and function likewise.

<FIG> shows in particular that the apparatus <NUM> may further include an enclosure, particularly and optical head <NUM>, which may include the machining unit <NUM> and the sensing unit <NUM>. The optical head <NUM> also includes the spectral separation unit <NUM> and may include also the optical unit <NUM>. As described already with respect to <FIG>, the laser light for the laser beam <NUM> may be provided <NUM> by a laser unit <NUM> (comprising laser source <NUM> and/or laser controller <NUM>), for instance via an optical fiber and to a laser supply port of the apparatus <NUM> (if the laser unit <NUM> is not part of the apparatus <NUM>) or to the optical head <NUM>, e.g. to a laser supply port of the optical head <NUM> (if the laser unit <NUM> is part of the apparatus <NUM>).

<FIG> shows an apparatus <NUM> according to an embodiment of the invention, which builds on the apparatus <NUM> shown in <FIG> and has elements in common with the apparatus <NUM> of <FIG> and <FIG>. Identical elements in <FIG> and in <FIG>, <FIG> and/or <NUM> are labeled with the same reference signs and function likewise.

The apparatus <NUM> of <FIG> has a different configuration than the apparatus <NUM> shown in <FIG>. In particular, the apparatus <NUM> comprises an optical head <NUM>, which includes the machining unit <NUM>. However, the optical head <NUM> does not comprise the sensing unit <NUM>. The sensing unit <NUM> is provided in a laser unit <NUM> (including laser source <NUM> and/or laser controller <NUM>). Notably, the laser unit <NUM> may be formed by the laser controller <NUM> being provided in the laser source <NUM> or vice versa. The laser unit <NUM> is part of the apparatus <NUM>. The machining unit <NUM> in the optical head <NUM> is configured to couple the laser beam <NUM> into the fluid jet <NUM>. The sensing unit <NUM> in the laser unit <NUM> is configured to receive secondary radiation 206a emitted from a portion of the workpiece <NUM> that is machined with the laser beam <NUM>.

The apparatus <NUM> comprises also an optical connection element <NUM>, particularly an optical fiber <NUM>, optically connecting the optical head <NUM> and the laser unit <NUM>. The laser unit <NUM> is configured to provide the laser light for the laser beam <NUM>, which is transported through the optical connection element <NUM> to the optical head <NUM>, e.g. to a supply port of the optical head <NUM>, where it is further provided to the machining unit <NUM>, which couples it into the fluid jet <NUM>. Laser-induced electromagnetic radiation <NUM> is received via the fluid jet <NUM> by the machining unit <NUM>, and is further provided through the optical head <NUM> and through the optical connection element <NUM> to the laser unit <NUM>, e.g. to a supply port of the laser unit <NUM>, where it is further provided towards the sensing unit <NUM>, which converts the secondary radiation 206a, which is included in the laser-induced electromagnetic radiation <NUM>, into the signal <NUM>.

The laser unit <NUM> may accordingly comprise also the optical unit <NUM>, which is preferably a beam splitter and is preferably arranged in the optical path between laser source <NUM> and optical connection element <NUM>, in order to provide the laser light for the laser beam <NUM> from the laser source <NUM> to the optical connection element <NUM>. Also the back-propagating laser-induced electromagnetic radiation <NUM> may pass through this optical unit <NUM>, but is then directed towards the sensing unit <NUM>. The laser unit <NUM> also includes the spectral separation unit <NUM>, which is configured to isolate only electromagnetic radiation of interest <NUM> including secondary radiation 206a on the sensing unit <NUM>. The spectral separation unit <NUM> is arranged in the optical path between the optical unit <NUM> and the sensing unit <NUM>, such that it receives the laser-induced electromagnetic radiation <NUM> including the secondary radiation 206a from the optical unit <NUM> and provides the radiation of interest <NUM> onto the sensing unit <NUM>.

In summary, the present invention provides an apparatus <NUM>, <NUM>, <NUM> and <NUM>, and a method <NUM>, that enable machining a workpiece <NUM> with a laser beam <NUM> coupled into a fluid jet <NUM>, wherein due to accurate determination of a state of the machining process, the machining process time can significantly be reduced.

Claim 1:
Apparatus (<NUM>, <NUM>, <NUM>, <NUM>) for machining a workpiece (<NUM>) with a pulsed laser beam (<NUM>), the apparatus (<NUM>, <NUM>, <NUM>, <NUM>) comprising
a machining unit (<NUM>) configured to provide a pressurized fluid jet (<NUM>) onto the workpiece (<NUM>) and to couple the laser beam (<NUM>) through at least one optical element (<NUM>) into the fluid jet (<NUM>) towards the workpiece (<NUM>),
a sensing unit (<NUM>),
a spectral separation unit (<NUM>) arranged to receive, during the machining of the workpiece (<NUM>) with the laser beam (<NUM>), a laser-induced electromagnetic radiation (<NUM>) including secondary radiation (206a) emitted from a portion of the workpiece (<NUM>) that is machined with the laser beam (<NUM>) and propagating away from the workpiece (<NUM>) through the fluid jet (<NUM>) and through the at least one optical element, and configured to isolate only electromagnetic radiation of interest (<NUM>) including at least a part of the secondary radiation (206a) on the sensing unit (<NUM>) and to prevent initial laser light (<NUM>) to reach the sensing unit (<NUM>), characterized by,
the sensing unit being configured to convert the secondary radiation (206a) into a signal (<NUM>) for each laser pulse, and
a signal processing unit (<NUM>) configured to integrate a plurality of signals (<NUM>) over time to produce an integrated signal, and to determine, during the machining of the workpiece (<NUM>) with the laser beam (<NUM>), a state of machining the workpiece (<NUM>) based on a pattern (500a, 500b) or a change of a pattern (500a, 500b) in the integrated signal (<NUM>).