Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/03—Observing, e.g. monitoring, the workpiece
  • B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/03—Observing, e.g. monitoring, the workpiece
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/14—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor
  • B23K26/1462—Nozzles; Features related to nozzles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/36—Removing material
  • B23K26/38—Removing material by boring or cutting
  • B23K26/382—Removing material by boring or cutting by boring

Definitions

• the present invention relates to the technical field of laser devices. More particularly, the present invention relates to methods for monitoring and control of single pulse laser micro drilling processes, and micro-drilling machines capable of effecting micro-drilling on workpieces with monitorization thereof.
• Micro-drilling a workpiece i.e. formation of holes or through holes on a workpiece when the diameter of the holes is less than 1 ,0 mm, for example between 40 pm and 200 pm, also referred to in the present disclosure as micro-holes- can be a complex task because, usually, the holes have to be drilled very accurately.
• the holes formed shall have a diameter equal or very close to the nominal diameter, and that the holes are formed throughout the part or the entirety of the processed surface of the workpiece in the correct locations, that is to say, they are formed at nominal coordinates so that the placement thereof and the separation with respect to other holes fulfills the intended micro-hole arrangement.
• a large number of holes may need to be formed in a single workpiece, even in the order of 10 s , 10 6 , and/or 10 7 holes; it can be appreciated that the formation of many holes with good precision in both the positioning and the geometry of the holes is complex.
• a laser head delivers a laser beam pulse of a determined energy that impinges on the workpiece to be processed, thereby forming a hole.
• the characteristics of the hole in terms of diameter, depth, shape, aspect ratio, circularity, etc. depend upon the laser guiding optics, the laser parameters like the beam quality, pulse length, power level, etc., the processing and shielding gas parameters, and the distance from the output end of the laser head to the surface of the workpiece. Variations in distance in the order of units or tens of micrometers change the characteristics of the holes formed, in which case it may occur that a workpiece has been incorrectly processed.
• the fulfillment of the characteristics of the holes formed on the workpiece is essential, for example in the aeronautic industry, space industry, naval industry, etc.
• the diameter of the hole on the side where the laser has not impinged is also important and it shall fulfill certain characteristics as well.
• the micro-drilling shall be monitored in order to detect possible erroneous processing.
• a first aspect of the invention relates to a method for single pulse micro-drilling process with a laser head, comprising: micro-drilling a workpiece by intermittently outputting a laser beam while moving the laser head and while a nozzle is spaced apart from the workpiece, the nozzle being for outputting a laser beam through a first end of an opening of the nozzle, the first end being a laser output end -and opposite a second end which is a laser input end through which a laser source provides the laser radiation;- arranging a first plurality of optical fibers on the laser head or a support thereof such that an end of each optical fiber of the first plurality is to face a first surface of the workpiece, the first surface being the surface onto which laser beams impinge, and all optical fibers of the first plurality being coupled with a single photodiode (in the following, also referred to as first photodiode), that is, all optical fibers of the first plurality are coupled with the same photodiode.
• the present method makes possible to monitor a micro-drilling process whereby laser pulses form holes on a workpiece. Whenever the laser beam impinges on the surface of the workpiece, the laser beam forms a hole on the workpiece.
• the optical fibers coupled with the first photodiode capture the light of the laser process, e.g. the light produced during the formation of the holes; to that end, second ends of each optical fiber, that is, the end opposite the end to face the workpiece, are coupled with the photodiode.
• the measurements of the photodiode are indicative of the formation of the micro-holes as well as of their non-formation, that is, of the existence of clogged holes, and may also be indicative of the diameters of the micro-holes formed on the surface of the workpiece onto which the laser beam impinges. This is so because the light produced in the micro-drilling process is correlated with the formation of the hole and the characteristics thereof.
• the optical fibers can be arranged on the laser head by way of e.g. supporting means that may be produced with rapid prototyping.
• the supporting means comprise one or more supporting devices that are attached to the laser head or the nozzle thereof and which have slots for supporting the ends of the optical fibers oriented towards the workpiece; this means that the ends of the optical fibers are oriented along the direction of the opening or oriented such that they are facing a position onto which the laser beam is expected to impinge when the workpiece is arranged; in some cases, the ends of the optical fibers are aligned substantially parallel to a direction along which the laser beams are outputted towards the workpiece.
• the optical fibers are preferably arranged symmetrically around the laser head, namely, evenly distributed around the laser head.
• a controlling device of the micro-drilling machine that includes the laser head is preferably coupled with the photodiode such that it receives the values measured by the photodiode. Based on the measurements, the controlling device may halt the micro-drilling process by stopping or turning off the laser head, for example when the measurements are indicative of holes being or not being formed with a diameter falling within a predetermined accepted diameter range. Additionally or alternatively, the measurements can be provided to a user for information purposes so as to assist the user in the configuration of the laser head for adjusting the micro-drilling process; the measurements can be provided in user presenting means such as e.g. a screen, loudspeakers, etc., like a human machine interface.
• the method further comprises: determining, with a controlling device of a micro-drilling machine comprising the laser head, whether holes formed during the micro-drilling step meet one or more predetermined criteria based on measurements of the photodiode that is coupled with the first plurality of optical fibers; and, when the controlling device determines that one or more holes do not meet the one or more predetermined criteria, at least one of: stopping the micro-drilling; providing the measurements or results of the determination made to user presenting means -that are part of the micro- drilling machine or are communicatively coupled thereto-; and digitally flagging the micro- drilled workpiece, the flag being indicative of erroneous processing. By flagging the workpiece, the workpiece may be later on discarded or its quality reviewed prior to using the workpiece or installing it in a device.
• the method further comprises arranging a second plurality of optical fibers arranged on a support of the laser head such that an end of each optical fiber of the second plurality is to face a second surface of the workpiece, the second surface being opposite the first surface, and the optical fibers of the second plurality being coupled with a single photodiode (in the following, also referred to as second photodiode), that is, all optical fibers of the second plurality are coupled with the same photodiode, but different from the photodiode that the optical fibers of the first plurality are coupled.
• a single photodiode in the following, also referred to as second photodiode
• the arrangement of the second plurality of optical fibers coupled with the second photodiode serves the purpose of informing about and/or adjusting the micro-drilling process, especially when the holes to be formed are through holes.
• An end of each optical fiber of the second plurality is arranged facing a second side of the workpiece, the first side being that on which the laser beam is to impinge. To this end, the optical fibers are on the support which is on the other side of the workpiece.
• the second photodiode measures the light captured by the optical fibers of the second plurality and caused by the laser beam that exits the workpiece through the second side.
• This light and, thus, the measurements thereof are indicative of holes being or not being formed with a diameter on the second side of the workpiece falling within an accepted diameter range.
• the diameter of the hole on the second side -namely second diameter- is smaller than the diameter of the hole on the first side -namely first diameter,- in which case the resulting measurements of the light captured by the first plurality of optical fibers are to indicate whether the first diameter falls within a first predetermined accepted diameter range, and the measurements of the second plurality of optical fibers are to indicate whether the second diameter falls within a second predetermined accepted diameter range.
• the first predetermined accepted diameter range may be from 100 pm to 130 pm
• the second predetermined accepted diameter range may be from 50 pm to 70 pm
• the first and the second predetermined accepted diameter ranges may both be from 70 pm to 100 pm.
• the resulting measurements of the photodiode coupled with the second plurality and/or the resulting measurements of the photodiode coupled with the first plurality can also be used to determine whether a hole is not formed or is not completely formed -e.g. due to a low laser power output, no laser radiation at all, etc -
• the intensity of the light measured by the photodiode coupled with the respective plurality of optical fibers and the comparison between intensities of the light measured by the photodiode of both pluralities are indicative of possible problems in the hole formation.
• the time difference between the measurements of the first photodiode and the second photodiode that is, with how much delay the light is measured at the second photodiode with respect to a light measurement at the first photodiode, is indicative of the drilling time.
• the controlling device is preferably coupled with the photodiode coupled with the second plurality such that it receives the values measured by said photodiode like with the photodiode coupled with the first plurality, and may halt the micro-drilling process based on the measurements of the photodiode coupled with the second plurality as well.
• the measurements may likewise be provided to a user.
• the determining step is further based on measurements of the photodiode coupled with the second plurality.
• each photodiode coupled with a plurality of optical fibers is a photodiode with four quadrants
• each plurality of optical fibers comprises four optical fibers.
• the ends of each optical fiber of each plurality of optical fibers are arranged according to a square arrangement around the laser head, that is, at intervals between 85° and 95°, and preferably at 90° intervals.
• Such configuration enables determination, in a precise manner, of how the micro-drilling is conducted.
• the symmetrical arrangement around the area where the laser impinges and drills enables not only to obtain an integrated measurement of the dispersed laser light in the micro drilling process but also to capture the angular dispersion of the laser light.
• determination of existing deviations in the impingement of the laser beams towards one quadrant or other is possible, which is important for making corrections in the micro-drilling and for the quality of the resulting workpiece because considerable deviations and/or numerous deviations make the micro-drilled workpiece not to fulfill with established specifications or with established quality parameters.
• the determining step comprises calculating: intensity of light based on a sum of the measurements of the respective photodiode in its four respective quadrants; and/or angular dispersion of the light based on one or more differences between: o the sum of the measurements of the respective photodiode in two adjacent quadrants of its respective four quadrants and the sum of the measurements of the respective photodiode in its other four adjacent quadrants of its respective four quadrants; and/or o the measurement of the respective photodiode in a quadrant of its respective four quadrants and the measurement of the respective photodiode in other quadrant of its respective four quadrants.
• the computation of the intensity of the light can be carried out, for instance, by way of the arithmetic sum of the electrical intensity signal in each quadrant of the respective photodiode, which provides a signal that is proportional to a sum of the diffused radiation.
• the computation of the angular dispersion of the diffused laser light can be carried out, for instance, by way of the arithmetic sum of the electrical intensity signal in two adjacent quadrants minus the arithmetic sum of the electrical intensity signal in the other two adjacent quadrants.
• the directionality of the dispersion can be established in the north-south direction. If the result of the subtraction is positive, then the dispersed radiation has more north component, whereas if the result of the subtraction is negative, then the dispersed radiation has more south component; the magnitude of the difference indicates how much difference exists.
• the directionality in the east- west, northeast-southwest, and northwest-southeast directions can also be determined in the same or a similar fashion. Regarding the latter two, the computation can be carried out by means of the difference between the electrical intensity signal of the corresponding quadrants (e.g. difference between the signal in the northeast quadrant and the signal in the southwest quadrant provides the northeast-southwest directionality).
• the disperse light of the process is asymmetrical. That is a sign of misalignment.
• the computation or computations of intensity of light and/or angular dispersion of the light can be carried out with respect to the first photodiode and/or the second photodiode. It is preferably to make the calculations with respect to both photodiodes because, in that way, it can be determined more precisely how the micro-drilling is conducted both from the impinging side and the exit side of the laser beams.
• the method further comprises: arranging an optical device on the laser head such that it is to face the first surface of the workpiece; and taking images of the workpiece during the micro-drilling step.
• the optical device e.g. a camera
• the optical device is preferably arranged on the laser head based on how the laser head will move to process the workpiece. More particularly, the optical device is preferably arranged in such a way that it is facing new holes formed after the laser head has moved, therefore the optical device is capable of capturing the resulting holes as the laser head is moving and micro-drilling the workpiece.
• the images taken by the optical device can be provided to a user for quality monitoring of the resulting workpiece, or to a processing device -e.g. a computer, a graphics processing unit, a digital signal processor, etc - configured to digitally process the images so that it determines characteristics of the holes formed, e.g. the diameter of the holes formed and the separation between each pair of neighboring holes.
• a processing device e.g. a computer, a graphics processing unit, a digital signal processor, etc - configured to digitally process the images so that it determines characteristics of the holes formed, e.g. the diameter of the holes formed and the separation between each pair of neighboring holes.
• the images may also be used for determining other characteristics such as e.g. the number of clogged holes, the area or how circular the holes are, etc.
• the quality of the workpiece Prior to installing and using the workpiece, for example in an airplane, the quality of the workpiece can be established in this manner.
• a warning may be provided to notify that the workpiece does not meet the minimum quality requirements.
• the method further comprises: digitally processing, with a processing device, the images taken by the optical device to determine characteristics of the holes formed; and providing data resulting from the processing step to user presenting means or a controlling device of a micro-drilling machine comprising the laser head.
• the data can be the characteristics themselves or a determination made based on the characteristics about the micro-drilling process.
• said device may in turn take one or more actions based on the data, for example but without limitation, positioning the laser head relative to the workpiece so that it processes a particular portion of the workpiece, stopping the micro-drilling, digitally flagging the micro- drilled workpiece as erroneously processed, etc.
• the digital processing conducted performs border detection, preferably at subpixel level.
• the digital processing filters the borders based on circularity and/or size criteria, and measures the size of the hole subsequently, for instance the diameter thereof.
• the border filtering provides contrast in two areas limited by a border, especially when an illuminating device illuminates the hole formed from beneath, i.e. towards the camera.
• the light going through the hole causes a great level of contrast with the border of the hole.
• the digital processing is capable of detecting the border of the hole and other phenomena such as blackening or presence of dark oxides or stains in the area that can be disregarded.
• the size of the hole is preferably measured in two ways and the average of the two resulting measurements is then considered as the size of the hole.
• a first way of measuring the hole is Feret’s maximum diameter, which is the modulus of the line segment between two points of the perimeter that are the farthest away between them: where F y2 is the y-coordinate of the second point, F yl is the y-coordinate of the first point, F x2 is the x-coordinate of the second point, and F xl is the x-coordinate of the first point.
• a second possible technique for measuring the size of the hole is the diameter of a discus with the same surface as that of the detected hole, namely, the Waddel diameter: where A is the surface of the hole.
• the averaging of two different measurements of the size or diameter of the hole is preferred because the circular symmetry of the hole can be considered and, at the same time, a degree of freedom for deviations that may exist in the circular symmetry is provided.
• the averaging combines both criteria, hence changes in the symmetry of the holes will result in a greater dispersion of the diameters of the holes and, therefore, in a greater standard deviation.
• the method further comprises: providing measurements of encoders of the laser head to a controlling device of the micro-drilling machine, the measurements being indicative of a movement of the laser head; and commanding the intermittent output of the laser beam, with the controlling device, based on the measurements.
• the micro-drilling is preferably effected while the laser head is moving so as to reduce the processing time per workpiece and, consequently, increase the efficiency of the micro-drilling.
• a plurality of micro-holes may have to be formed in each workpiece, and said plurality can be in the order of e.g. 10 3 holes, 10 5 holes, 10 6 holes, 10 7 holes, etc., and the separation between each pair of micro-holes can be between e.g. 0,1 mm to 1 ,5 mm.
• a laser head moving at a speed between e.g. 10 mm per minute and 50 mm per minute, and a hole formation of between 1 and 500 holes per second, requires a very accurate clock signal to form holes with constant separation between neighboring holes.
• the laser head can be commanded to provide the laser beam towards the workpiece based on the position of the laser head rather than being based or being based only on a clock signal.
• the provision and non-provision of the laser beam can be adjusted by a blocking mechanism that lets the laser beam be outputted or not.
• the laser beam can be outputted with a greater precision in the separation between the different holes.
• the method further comprises: arranging a distance measuring sensor on the nozzle of the laser head; and measuring a distance that the laser head is apart from the workpiece with the distance measuring sensor while moving the laser head.
• the distance measuring sensor comprises one of: a laser distance measurement sensor, an eddy current sensor, and a sensor based on optical coherence tomography.
• the distance measuring sensor is arranged concentric with the nozzle and/or flush with the first end of the nozzle.
• the provision of the distance measuring sensor enhances the reliability of the micro-drilling since the measured distance can be provided to the controlling device, which in turn moves the laser head relative to the workpiece so as to maintain a constant distance.
• the concentrical and/or flush arrangement improves the distance measuring.
• the workpiece comprises or is of titanium.
• a panel or outer panel of an airplane such as, e.g. a leading edge of a vertical stabilizer, a horizontal stabilizer, a wing, etc.
• a second aspect of the invention relates to a micro-drilling machine for micro-drilling of a workpiece, comprising: a laser head comprising a nozzle for outputting a laser beam through a first end of an opening of the nozzle towards the workpiece, the first end being a laser output end -and opposite a second end which is a laser input end through which a laser source provides the laser radiation;- a controlling device for controlling operation of the micro-drilling machine; and a first plurality of optical fibers arranged on the laser head or a support thereof such that an end of each optical fiber of the first plurality is to face the workpiece, the optical fibers of the first plurality being coupled with a single photodiode (also referred to as first photodiode).
• the optical fibers of the first plurality are preferably arranged to have the end face towards a region onto which laser beams are to impinge on the surface of the workpiece.
• the controlling device is configured to determine whether holes formed during operation of the micro-drilling machine meet one or more predetermined criteria based on measurements of the photodiode coupled with the first plurality, and further configured to, when it determines that one or more holes do not meet the one or more predetermined criteria, perform at least one of: stop operation of the micro-drilling machine, provide the measurements or results of the determination made to user presenting means of the micro-drilling machine or communicatively coupled thereto, and flag the processed workpiece with a flag indicative of erroneous processing.
• the micro-drilling machine further comprises a support, and a second plurality of optical fibers arranged on the support such that an end of each optical fiber of the second plurality faces opposite an optical fiber of the first plurality, the optical fibers of the second plurality being coupled with a single photodiode (also referred to as second photodiode).
• the optical fibers of the second plurality are preferably arranged to have the end face towards a region onto which laser beams are to impinge on the surface of the workpiece, but from the opposite side -i.e. on the surface of the workpiece through which the laser beam exit the workpiece-, that is to say, in a direction opposite the direction along which the laser beams are outputted from the laser head.
• each photodiode coupled with a plurality of optical fibers is a photodiode with four quadrants
• each plurality of optical fibers comprises four optical fibers.
• the ends of each optical fiber of each plurality of optical fibers are arranged according to a square arrangement around the laser head, that is, at intervals between 85° and 95°, and preferably at 90° intervals.
• the controlling device determines whether holes formed during operation of the micro-drilling meet one or more predetermined criteria based on a calculation of: intensity of light based on a sum of the measurements of the respective photodiode in its four respective quadrants; and/or angular dispersion of the light based on one or more differences between: o the sum of the measurements of the respective photodiode in two adjacent quadrants of its respective four quadrants and the sum of the measurements of the respective photodiode in its other four adjacent quadrants of its respective four quadrants; and/or o the measurement of the respective photodiode in a quadrant of its respective four quadrants and the measurement of the respective photodiode in other quadrant of its respective four quadrants.
• the micro-drilling machine further comprises an optical device arranged on the laser head such that it is to face the workpiece; and the controlling device being further configured to command the optical device to take images of the workpiece after one or more laser beams have been outputted by the laser head.
• the optical device is preferably arranged to face towards a region onto which laser beams are to impinge on the surface of the workpiece.
• the micro-drilling machine further comprises a processing device configured to digitally process the images taken by the optical device to determine characteristics of the holes formed, and further configured to provide data resulting from the image processing to user presenting means or the controlling device.
• the controlling device is preferably configured to take one or more actions based on the data provided by the processing device.
• the micro-drilling machine further comprises encoders indicative of a movement of the laser head; and the controlling device being further configured to command the laser head to intermittently output the laser beam based on the measurements of the encoders.
• the micro-drilling machine further comprises a distance measuring sensor arranged on the nozzle so as to measure a distance spacing apart the laser head from the workpiece.
• the distance measuring sensor comprises one of: a laser distance measurement sensor, an eddy current sensor, and a sensor based on optical coherence tomography.
• the distance measuring sensor is arranged concentric with the nozzle and/or flush with the first end of the nozzle.
• Figure 1 shows a micro-drilling machine in accordance with embodiments.
• Figures 2A and 2B show graphs of diameters of the beam relative to the position of a lens of a laser head, and measurements of two photodiodes of a micro-drilling machine.
• Figure 3 shows a time difference between light captured on the two sides of a workpiece.
• Figure 4 shows a micro-drilling machine in accordance with embodiments.
• Figure 1 diagrammatically shows a cross-section of a micro-drilling machine 100a in accordance with embodiments.
• the micro-drilling machine 100a comprises a laser head 10 that, in turn, comprises a nozzle 20 suitable for the output of a laser beam by means of an opening 21 thereof.
• the laser beam is outputted through a first end -shown with reference 22 in Figure 4 for the sake of clarity- of both the nozzle 20 and the opening 21, and is coupled from a laser source into the opening 21 through a second end thereof.
• the nozzle 20 preferably has a shape suitable for the laser beam outputting, for example a frustoconical shape.
• the opening 21 has a center axis 25 - shown with a dotted line in Figure 4 for illustrative purposes only.
• the laser head 10 and/or the micro-drilling machine 100a can be moved along the Z axis represented so as to position the laser head 10 at a distance from the workpiece 5, and along one or both of the X and Y axes represented so as to process different parts of the workpiece 5.
• a plurality of holes can be formed in the workpiece 5.
• the micro-drilling machine 100a may include a distance measuring sensor - illustrated with reference 30 in Figure 4 for determining the distance that the workpiece 5 is apart from the opening 21, thereby easing to maintain a constant separation between the two.
• the workpiece 5 can also be moved in one or both of the X and Y axes so that the relative displacement between the workpiece 5 and the laser head 10 can be used for forming the holes over part or the entirety of the workpiece 5; further, in some cases, the workpiece 5 can also be moved along the Z axis.
• the surface on which the workpiece 5 is resting can be a conveyor belt or a moving platform capable of moving in these manners.
• the micro-drilling machine 100a further includes a first photodiode 50a coupled with optical fibers 51a.
• Respective ends 52a of the fibers 51a are arranged on a support 53a -that, for example, but not necessarily, can be made by means of rapid prototyping- such that they are oriented towards a first surface 6 of the workpiece 5, preferably towards a position thereof where a laser beam of the laser head 10 is to impinge on.
• four optical fibers 51a are arranged on the support 53a such that an end thereof is facing towards the first surface 6 and, more preferably, to the aforesaid position thereon; the ends 52a of the four fibers 51a are equidistantly distributed around the nozzle 20.
• the optical fibers 51a capture the backscattered light produced during the emission of the laser beams and provide it to the first photodiode 50a for establishing whether the micro-drilling process is correct or not according to predetermined parameters, which can be established based on testing.
• the measurements of the first photodiode 50a can be provided to a controlling device 60 of the micro-drilling machine 100a so as to turn off the laser head 10 or the emission of the laser beams when it is digitally established that the micro-drilling process it not being carried out according to the predetermined parameters.
• the controlling device 60 likewise can provide, to user presenting means 70, the measurements or a determination made by the controlling device 60 about the micro-drilling process.
• the micro-drilling machine 100a further includes a second photodiode 50b coupled with respective optical fibers 51b.
• Respective ends 52b of the fibers 51b are arranged on a support 53b of the micro-drilling machine 100a that is beneath -according to the Z axis represented- the workpiece 5; the ends 52b are oriented towards a second surface 7 of the workpiece 5 that is opposite the first surface 6, preferably towards a position thereof where the laser beam of the laser head 10 is to exit once a through hole is formed.
• the arrangement of the second plurality of optical fibers 51b is preferred when through holes are being formed so that the micro-drilling process can be monitored also in respect of the light produced by the laser beam on the second surface 7 of the workpiece 5.
• four optical fibers 51b are arranged on the support 53b such that and thereof is facing towards the second surface 7 and, more preferably, to the aforesaid position thereon; the ends 52b of the four fibers 51b are equidistantly distributed on the support 53b.
• the first and second photodiodes 50a, 50b can be e.g. silicon -Si- detectors with sensibility in the range from 350 to 1100 nm, and have respective transimpedance amplifiers.
• filters are arranged before the photodiodes 50a, 50b so that only light of certain wavelength(s) can go through them, for example light at 1070 nm. That way, the filters can be arranged between the fibers 51a, 51b and the respective photodiode 50a, 50b. Further, the filters preferably have a narrow spectral width -e.g.
• spectral width 10 nm or less, more preferably of 5 nm or less- so that only light at said wavelength(s) and nearby wavelengths is provided to the photodiode or photodiodes.
• neutral density filters are provided in order to avoid saturation, thereby having a clear capture of the voltage signal acquired by adjusting the filters to the intensity levels expected from the light captured on the respective surface 6, 7 of the workpiece 5.
• Figure 2A shows a graph with diameters of the beam relative to the position of a lens of a laser head.
• the configuration of the laser optics is important for adjusting the size of the diameters of the holes to be formed.
• the diameter of the beam at the impinging side -e.g. the first side 6 in the example of Figure 1 ; shown with black circles- and the diameter of the beam upon exit through the other side -e.g. the second side 7 in the example of Figure 1 ; shown with white circles- can be set.
• a 0 mm position of the lens means that the beam waist is placed on the surface of the workpiece.
• Figure 2B shows a graph with measurements of the first and second photodiodes of a micro-drilling machine, e.g. the micro-drilling machine 100a of Figure 1.
• One signal represented in the graph is the integrated signal of the backscattered light captured on the first surface 6 -shown with white circles- during the formation of e.g. 10 holes, versus the position of the lens.
• the other signal represented shows the same type of integrated signal but of the backscattered light captured on the second surface 7 -shown with black circles- during the formation of the same holes.
• the integrated signal is for light at a wavelength of 1070 nm owing to the filters arranged in the light path towards the respective photodiode.
• FIG. 3 shows a time difference between light captured on the two sides of a workpiece.
• the solid line corresponds to measurements of photodetectors capturing the light produced on the laser beam impinging side
• the dashed line with star markers corresponds to measurements of photodetectors capturing the light produced on the laser beam exiting side.
• a graph has also been represented in an inner part of the Figure so as to show a zoomed-in part of the graph as can be seen from the elapsed time represented in each of the two graphs.
• This time difference is also indicative of whether the micro-drilling process under way is being performed within certain predetermined parameters.
• the reason for this is that the time difference that exists between the time when the light captured at the impinging side and the time when the light captured at the exit side is correlated with the hole formation. Therefore, when the time elapsed between the two moments exceeds a predetermined maximum value or is below a predetermined minimum value, it can be determined that the micro-drilling process is not within the predetermined parameters.
• Figure 4 diagrammatically shows a cross-section of a micro-drilling machine 100b in accordance with embodiments, and a workpiece 5 illustrated in perspective only for the sake of clarity.
• the micro-drilling machine 100b includes a laser head 10, for example the laser head 10 of Figure 1 , and further includes an optical device 80 arranged on the laser head 10.
• the optical device 80 includes a camera 81 aimed like the opening 21 of the nozzle 20, i.e. towards a surface of the workpiece 5 to be processed, a lens 82 in front of the camera 81 , and a first lighting device 83 producing first light 84 towards a first surface 6 of the workpiece 5 where the laser beams impinge on.
• the first lighting device 83 is aimed like the camera 81 so that the first light 84 goes towards the position that the camera 81 will take pictures of.
• the first lighting device 83 can be a ring LED illuminator.
• the optical device 80 further includes a second lighting device 85 arranged such that it aims towards a second surface 7 of the workpiece 5 through which laser beams exit when through holes are formed.
• the second lighting device 85 produces second light 86 towards the same position at which the first light 84 is aimed.
• the second lighting device 85 can be a backlight device such as a high power backlight. Thanks to the first and second lights 84, 86, the camera 81 takes pictures of the through hole 8 formed previously by a single pulse laser emitted through the nozzle 20. While the first light 84 illuminates the area of the workpiece, the second light 86 provides light in the through hole 8 formed, and said light can be captured by the camera 81 for establishing the characteristics of the through hole 8 with greater contrast and definition.
• the photos of the camera 81 can show a first diameter d1 of the hole 8 on the impinging surface 6 of the workpiece, and a second diameter d2 of the hole 8 on the exit surface 7 of the workpiece, which is smaller than the first diameter d1.
• a processing device 65 of the micro-drilling machine 100b processes the photos.
• the result of the processing can be provided to a user by means of user presenting means 70 -e.g. a human machine interface-, and/or to a controlling device 60 for operating the micro-drilling machine 100b.
• the optical device 80 is arranged on the laser head 10 such that it is aiming at the holes 8 formed by the laser head 10 after moving the laser head 10 and/or micro-drilling machine 100b for forming new holes 8.
• the advancement of the laser head 10 and/or micro-drilling machine 100b for processing the workpiece 5 is, at least during some parts of the micro-drilling process, along the positive side of the X axis illustrated.
• the optical device 80 is arranged on the negative side of the X axis illustrated, once a drill 8 is formed and the laser head 10 and/or micro-drilling machine 100b keeps advancing, the optical device 80 will be positioned aiming at the drill 8 formed so that a photo thereof can be taken.
• the laser head 10 and/or micro-drilling machine 100b may also move towards the negative side of the X axis illustrated at some point, or move relative to the Y axis illustrated, but preferably the optical device 80 is arranged in the aforesaid manner taking into account the main movement of the laser head 10 and/or micro-drilling machine 100b for drilling the workpiece 5.
• the optical device 80 is a camera matrix that takes images of the holes and arranges them in matrix form.
• the image-taking and the processing of the images taken can be reduced and, hence, simplified. Accordingly, this can avoid taking images each time a new hole is formed.
• the micro-drilling machine 100b further comprises a first photodiode coupled with respective optical fibers like the first plurality described with reference to Figure 1 , and preferably also comprises a second photodiode coupled with respective optical fibers like the second plurality described with reference to Figure 1.
• aspects of the invention relate to a method and a micro-drilling machine as described with reference to the first and second aspects of the invention, but in which the most general embodiments include the optical device 80 as the main means for monitoring the micro-drilling process, and in some embodiments thereof the first plurality of optical fibers and, optionally, the second plurality of optical fibers -as described, for instance, with reference to Figure 1- are present as additional means for the monitoring.
• first, second, third, etc. have been used herein to describe several devices, elements or parameters, it will be understood that the devices, elements or parameters should not be limited by these terms since the terms are only used to distinguish one device, element or parameter from another.
• first plurality could as well be named second plurality
• second plurality could be named first plurality without departing from the scope of this disclosure.
• the invention is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art -for example, as regards the choice of materials, dimensions, components, configuration, etc.,- within the general scope of the invention as defined in the claims.

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