Laser surface treatment device and process
Patent Information
- Application Number
- FR2023001665
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-02-23
- Publication Date
- 2025-02-14
- Estimated Expiration
- 2043-02-23
Smart Images
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Abstract
Description
Title of the invention: Device and method for surface treatment using LASER State of the art
[0001] The present application relates to a device and a method for surface treatment of a part using a LASER. Such devices and methods are used in particular for texturing operations.
[0002] LASER texturing is a process that modifies the surface properties of a material by changing its texture and roughness. The LASER beam creates patterns on the surface of the material with a LASER ablation process that removes layers of material with micron-level accuracy and perfect repeatability. Recurring patterns include grooves, circular cavities, freeform shapes, etc.
[0003] Surface texturing can be used to improve certain properties such as adhesion, wettability and friction. For example, texturing can increase the adhesion of the surface of a material before a coating is applied to its surface such as an adhesive, paint or ceramic. Texturing a surface can be carried out using a LASER.
[0004] Furthermore, gluing is advantageous in that it makes it possible to obtain lighter assemblies than those made using mechanical fasteners.
[0005] To achieve good bonding, it is necessary to prepare the surfaces to be bonded, on the one hand by cleaning these surfaces to ensure their cleanliness and on the other hand by modifying their microscopic structure in order to improve their adhesion. Cleaning surfaces by degreasing, sandblasting, chemical baths, etc. generates pollution and / or consumes a lot of water. Dry cleaning using a LASER is therefore preferred, as are LASER texturing treatments. In addition, these treatments are automatable, reproducible and easy to control.
[0006] Known LASER surface treatment devices, such as those illustrated in Figures 1 to 3, include in particular a tool comprising: a scanner head 1, a LASER source emitting a treatment LASER beam 3, and a lens 2 which makes it possible to focus said beam at a focusing point where the diameter of the beam is minimal and the energy density is maximum, this focusing point being located on the lens image plane. At the output of the focusing lens 2, the treatment beam 3 extends in a direction, called the treatment direction, which is preferably substantially orthogonal to the surface of the part to be treated 100.
[0007] Throughout the description, the term “treatment point” means the intersection between the treatment beam and the surface of the part to be treated. For a LASER treatment, and in particular a texturing treatment, to be precise and effective, the focal point must fall exactly on the surface of the part to be treated, that is to say, the focal point must coincide with the treatment point and the area affected by the LASER beam must therefore have a minimal diameter.
[0008] To this end, the known devices further comprise means for positioning the tool in the treatment direction, such as a linear axis, making it possible to modify the distance between the tool (or more precisely the lens) and the surface of the part, i.e. to move the tool away from or closer to the part to be treated.
[0009] As illustrated in [Fig.l], these positioning means according to the processing direction are associated with a remote LASER rangefinder 4, which is part of the tool and is attached to the scanner head 1, which remote rangefinder 4 makes it possible to measure in real time a distance between a reference point of the rangefinder (fixed relative to the scanner head and the lens) and the surface of the part 100 using a measuring LASER beam 5.
[0010] In certain known devices such as that of [Fig.l], the measuring beam 5 is parallel to the treatment beam 3; it therefore makes it possible to measure the distance between the tool and the part at a point 7 of the latter, called the measuring point, which is offset by several centimeters relative to the treatment point 6 where the treatment beam strikes the part.
[0011] In the case of a part whose surface is flat or of a very simple shape and with small curvatures (for example a cylinder of very large radius) and without singularity, this does not pose a problem. In the case of a 3D part of a more complex shape, with curved, concave or convex portions, with strong curvatures, the distances between the tool and the part respectively at the measuring point 7 and at the processing point 6 are different. The same applies if the part is globally flat and it has a singularity precisely at the measuring point 7 or at the processing point 6.
[0012] In these known devices, the measured distance therefore does not allow the distance between the tool and the treatment point to be deduced exactly. Therefore, the position of said tool cannot be adjusted with precision and certainty so that the focal point is positioned on the surface to be treated.
[0013] In other known devices, the measuring beam 5 is inclined relative to the treatment beam 3 so as to intersect the latter precisely at its focal point, as illustrated in [Fig.2]. The measurement carried out by the remote rangefinder 4 then makes it possible to calculate the residual distance between the focal point and the surface of the part.
[0014] In such an inclined measuring beam device, the measuring point 7 and the processing point 6 are much closer than in a device with parallel processing and measuring beams, so that the evaluation of the tool / point distance treatment seems more precise and more reliable. But here again, the measurement can be distorted by a singularity resulting in an offset between treatment point 6 and measurement point 7 as illustrated in [Fig.3]. The measurement error then induces an error in the adjustment of the height of the treatment head relative to the part and a processing defect.
[0015] Furthermore, in addition to the means for adjusting the “height” of the tool, i.e. the distance between the tool (and more precisely the lens) and the part in the processing direction, the known devices usually comprise motorized means for moving the tool relative to the part, making it possible to move the tool (or the part) in at least one direction of movement. For example, the device comprises a robotic arm at the end of which the tool is mounted.
[0016] The accuracy with which the position of the tool can be adjusted in the processing direction and in the direction of movement can be of the order of + / - 0.5 mm. Furthermore, the accuracy with which the part is positioned in the device is also at best equal to + / - 0.5 mm, as is the measurement uncertainty of the rangefinder. Added to these uncertainties is the effect of the flexibility of the part, if applicable. In the end, it is difficult to achieve an actual processing accuracy of less than 2 mm. Statement of the invention
[0017] The invention aims to overcome at least one of the aforementioned drawbacks. In particular, the invention aims to provide a device and a method for LASER surface treatment which make it possible to treat parts of complex shape and / or large dimensions with a robotic arm type system. Another objective is to provide a device and a method for LASER surface treatment whose precision is improved.
[0018] To do this, the invention proposes a device for LASER surface treatment of a part, the device comprising a tool comprising:
[0019] - a first LASER source, emitting pulsed radiation Power LASER, called treatment beam,
[0020] - a lens, configured to focus at a point located on an image plane while radiation entering the lens through a first face of the latter,
[0021] - a scanner head between the first LASER source and the lens, said scanner head being configured to guide the treatment beam downstream of the first LASER source along an optical path, called the treatment optical path, striking the first face of the lens and passing through said lens to be focused at a focusing point located on the image plane of the lens,
[0022] - a second LASER source, emitting a second LASER radiation called a beam incident measurement,
[0023] - a measuring sensor for detecting a reflected measuring beam from the reflection on the part of the incident measuring beam,
[0024] - calculation means configured to calculate a distance, called working distance instantaneous, between the part and the lens, from the reflected measuring beam detected by the sensor.
[0025] The treatment device according to the invention is characterized in that:
[0026] - the scanner head, the first LASER source and the second LASER source are configured so that the incident measurement beam passes through the scanner head along an optical path, called the measurement optical path, striking the first face of the lens and passing through said lens to be focused in the image plane of the lens at a point which is located at a distance from the focusing point of the treatment beam called the offset distance in the image plane,
[0027] - the calculating means are configured to calculate the instantaneous working distance when the incident measuring beam passes through the lens along a central axis of the latter.
[0028] Thus, in the device according to the invention, the measuring beam and the treatment beam follow almost the same optical path in that they both pass through the scanner head and the lens. Therefore, the treatment point, defined as the point where the treatment beam strikes the part to be treated, and the measurement point, defined as the point where the measuring beam strikes said part, are very close.
[0029] Throughout the description, the distance between the measuring and processing beams in the image plane of the lens is called the "offset distance in the image plane", and this distance to the surface of the part is called the "offset distance on the part". The simplified expression "offset distance" refers to both of the preceding distances or only to one of them when the context clearly allows which one to be identified.
[0030] Since the beams follow almost the same optical path, the offset distance on the part is very small (of the order of a few millimeters, at least when the part is substantially in the image plane of the lens) in comparison with the distances (from one to several centimeters) which separate the treatment and measurement points of the known prior devices illustrated in Figures 1 and 2. The measurement is therefore not distorted due to the complex shape of the part or the existence of a singularity at the treatment point or in the vicinity thereof.
[0031] The impact of the treatment beam on the part generates both a plasma and ejectates, the ejectates being particles of molten material torn from the surface of the part by the treatment beam and ejected in the form of droplets, expelled at very high speed from the surface of the part towards the tool.
[0032] The offset distance has the effect of preventing the measuring sensor from is dazzled or disturbed by the plasma generated by the impact of the treatment beam on the part. It also has the effect of preventing the ejectates, or at least part of them, from crossing the incident measurement beam before it reaches the surface of the part, generating significant measurement noise preventing correct adjustment of the working distance.
[0033] Thus, by carrying out the measurement close to the point of impact of the treatment beam, with a measurement beam which is integrated in the scanner head and which follows the same optical path (with a slight angular deviation at the entrance of the lens) as the treatment beam, the invention makes it possible both to improve the accuracy of the measurement and to avoid errors due to the geometry of the surface of the part. By providing, however, an adequate offset distance between the measurement point and the treatment point, which results from a slight divergence (or angular deviation) at the entrance of the lens between the treatment beam and the measurement beam, the noise on the measurement signal is reduced and the reliability of the measurement is increased.
[0034] The invention further provides for calculating the instantaneous working distance from the detected reflected beam resulting from the reflection of the incident measuring beam which passes through the lens along a central axis thereof. In other words, the measurement is triggered at the moment when the measuring beam is aligned with the axis of the lens. The interest of this characteristic, applied to a device having more means for scanning the processing and measuring beams will be better understood later.
[0035] The maximum possible offset distance is dependent on the maximum permissible divergence between the measurement and processing beams upstream of the lens. This maximum possible divergence is a function of the dimensions of the lens and the architecture and dimensions of the scanner head. An example of determining the maximum offset distance will be provided later in the case of a particular embodiment of the tool comprising a dichroic mirror and at least one deflection mirror upstream of the lens.
[0036] According to a possible characteristic of the invention, the lens is a lens of the F-theta type (focusing in the same plane throughout the working field of the lens). It may be, for example, an F-theta 160 lens, that is to say an F-theta lens having a focal length of 160mm and a theoretical working distance of the order of 182mm, associated with a scanner head marketed under the name SCANcube III 14. In this case, the maximum possible offset distance on the image plane, and therefore also on the part when the latter is at the correct working distance, is of the order of 12mm.
[0037] According to a possible characteristic of the invention, the measuring sensor is a detector based on conoscopic holography and on coaxial technology, which means that it detects radiation which is reflected along the same axis as the incident measuring beam and which follows the same optical path in the opposite direction as the beam. incident measurement, as opposed to the triangulation technologies found in the remote rangefinders of earlier LASER processing devices shown in Figures 1 and 2 (in these remote rangefinders, the sensor detects reflected radiation that does not follow the same path, in the opposite direction, as the incident measurement beam).
[0038] A conoscopic sensor also has the advantage of not being or being only slightly sensitive to the plasma generated by the impact of the treatment beam on the part.
[0039] According to a possible characteristic of the invention, the scanner head comprises motorized scanning means configured to oscillate the treatment beam and the incident measurement beam upstream of the lens in a scanning plane on either side of the central axis of the lens. As defined above, the measurement sensor and the calculation means of the tool are further configured to calculate the instantaneous working distance from the detected reflected beam resulting from the reflection of the measurement beam which passes through the lens along its central axis. In other words, in the case of a measurement beam oscillating on either side of the central axis of the lens, the calculation means are programmed so that the distance measurement is triggered at the moment when the measurement beam is aligned with the axis of the lens.
[0040] In a preferred embodiment of the invention:
[0041] - the tool comprises a dichroic mirror having a first face capable of transmitting the treatment beam and a second face capable of reflecting the incident measurement beam, the first face of the dichroic mirror being struck by the treatment beam and the second face of the dichroic mirror being struck by the incident measurement beam, the dichroic mirror being oriented so that the incident measurement beam and the treatment beam form a non-zero angle between them at the output of said dichroic mirror,
[0042] - the scanner head comprises one or more deflection mirrors arranged in series between the dichroic mirror and the lens, for the orientation of the measurement and treatment beams towards the first face of the lens, each of said deflection mirrors being pivotally mounted around an axis of said mirror (axis specific to each mirror, contained in the plane of said mirror).
[0043] In this preferred embodiment, the maximum possible divergence between the treatment and measurement beams incident upstream of the lens depends on the dimensions and locations of the deflection mirrors, this divergence being in fact limited by the fact that the path of the treatment and measurement beams must not leave the surface of the deflection mirrors.
[0044] In this embodiment, the direction of the treatment beam is not adjustable downstream of the first LASER source (which generates this beam). The treatment beam passes through the dichroic mirror, to then enter the scanner head, while the other side of this mirror reflects the measuring beam. It is the orientation of the dichroic mirror that creates a divergence of the measuring beam relative to the treatment beam. To know the maximum offset distance of the device, it is sufficient to modify the orientation of the dichroic mirror starting from the position in which the two beams are coaxial at the exit of said mirror (they are then also coaxial at the exit of the scanner head and the treatment and measurement points on the part are merged) until the measuring beam leaves the surface of the deflection mirrors of the scanner head (it is then no longer deflected towards the lens and no longer appears at the exit of the scanner head). The maximum offset distance (in the image plane or on the part) corresponds to that obtained at the precise moment when the measuring beam leaves the surface of the deflection mirrors and the measurement point on the part disappears.
[0045] According to a possible characteristic of the invention, at least one of the deflection mirrors is associated with motorized oscillation means configured to oscillate the mirror around its axis. The deflection mirrors which are thus mounted oscillating and the associated oscillation means constitute the aforementioned scanning means.
[0046] The use of such oscillating mirrors arranged immediately upstream of the first face of the lens and which can be small in size (and therefore very easy to handle), makes it possible to have an extremely rapid scanning speed and therefore cost-effective processing on an industrial level.
[0047] According to a possible characteristic of the invention, the processing device comprises relative movement means, for the relative movement of the tool relative to the part in a direction called the relative movement direction. The relative movement means can be configured to be able to move the tool relative to the part in one or more relative movement directions.
[0048] Preferably, the scanning plane may be oriented so as to be substantially orthogonal to the direction of relative movement of the tool.
[0049] In the case of relative movement, the movement means may be configured to move either the workpiece, the tool, or both. The relative movement means comprise, for example:
[0050] - a linear conveyor belt capable of receiving the part, in which case said means of relative displacement are configured to move the part in a single direction of movement,
[0051] - a Cartesian table capable of receiving the part, in which case said means of relative placement are configured to move the part in several directions parallel to the Cartesian table, in particular in two directions orthogonal to each other,
[0052] a positioner, in particular a two-axis positioner.
[0053] Alternatively, the relative movement means may be configured to move the tool in the direction of movement while the part remains fixed. They comprise, for example, a robotic articulated arm having a distal end on which the tool is mounted. The position of the tool relative to the part, or even the orientation of the direction of relative movement or the orientation of the central axis of the lens, may thus be modified by actuating the robotic arm. Such an arm also makes it possible to move the tool not only in at least two directions of movement orthogonal to the processing direction, but also in the processing direction for the purpose of adjusting the tool / part distance.
[0054] As a further variant, the device combines first relative movement means, configured to move the part in at least one direction of relative movement, and second relative movement means, configured to move the tool in at least one (the same or another) direction of relative movement. The device thus comprises, for example, both a two-axis positioner and a robotic arm.
[0055] According to a possible characteristic of the invention:
[0056] - the processing device comprises a storage module of a circuit of processing on the part along which the tool is programmed to move as the processing progresses (of course, the movement of the tool along said processing circuit can be achieved by moving the tool or by moving the part or by combined movement of the tool and the part),
[0057] - the processing circuit being previously determined, depending on the part to be treat in such a way as not to cross a singularity of the said part,
[0058] - the scanning means are programmed to orient the tool so that the axis central part of the lens points at the treatment circuit and to scan the treatment beam on either side of said treatment circuit.
[0059] It is recalled that, according to the invention, the measurement sensor is configured to detect a reflected measurement ray corresponding to the moment when the incident measurement beam is aligned with the central axis of the lens. The measurement is therefore taken when the incident measurement beam points at the processing circuit. By choosing the processing circuit so that it does not cross a singularity of the part to be treated such as a fixing hole for example, any risk of measurement error is avoided. The actual working distance can therefore be adjusted precisely and reliably so as to correspond to the theoretical working distance of the lens, that is to say the distance at which the image plane of the lens is located.
[0060] The invention extends to a LASER surface treatment method using a device as previously defined, i.e. using a device comprising notably :
[0061] - a tool comprising a first power LASER source, a lens and a scanner head,
[0062] - a second LASER source, a sensor and calculation means,
[0063] This method comprises the following steps or operations:
[0064] - the first LASER source of the scanner head generates a pulsed power LASER radiation called treatment beam, which treatment beam is guided by the scanner head along an optical treatment path which strikes an entry zone of the lens located on a first face thereof,
[0065] - said lens focuses the treatment beam at a focusing point located on the image plane of the lens,
[0066] - the second LASER source emits LASER radiation called a measuring beam incident,
[0067] - the sensor detects a reflected measuring beam resulting from the reflection on the part of the incident measuring beam, and the calculation means calculate a distance between the part and the tool, called the instantaneous working distance, from the reflected measuring beam detected by the measuring sensor.
[0068] The method according to the invention is characterized in that:
[0069] - the incident measuring beam passes through the scanner head along an optical path, said optical measuring path, striking the first face of the lens and passing through said lens to be focused on the image plane of the lens at a point which is located at a distance from the focusing point of the treatment beam called the offset distance in the image plane,
[0070] - the calculation means calculate the instantaneous working distance when the beam incident measurement light passes through the lens along a central axis of the latter.
[0071] According to a possible characteristic of the invention, the method further comprises:
[0072] - the relative movement of the tool with respect to the part along a circuit of predetermined treatment, in a direction called the direction of relative movement, the tool being oriented so that the central axis of the lens points at all times on said treatment circuit, the treatment circuit being predetermined so as not to cross a point singularity of the part to be treated,
[0073] - scanning the measurement and processing beams in a scanning plane of on either side of the central axis of the lens. The treatment point, which is the intersection between the surface of the part and the treatment beam, therefore oscillates on either side of the treatment circuit at the same time as it advances in the direction of relative movement along this circuit. Scanning the treatment beam on either side of the treatment circuit thus makes it possible to treat a surface band centered on said circuit.
[0074] As previously defined, the method also comprises the detection of the reflected measuring beam resulting from the reflection on the part of the incident measuring beam when said incident measuring beam (which oscillates in the scanning plane) is aligned with the central axis of the lens and the calculation of the instantaneous working distance from this detection. In other words, the method comprises a step of measuring the distance separating the part from the lens at the moment when the measuring point is located on the processing circuit.
[0075] The processing circuit may be determined during a prior step of locating the part to be processed, in which the part is scanned to determine its shapes and contours. Alternatively, it is determined on the basis of a plan or a digital twin of the part to be processed, for example provided by a manufacturer or designer of said part.
[0076] The processing circuit is chosen so as not to cross any singularities of the part, such as fixing holes, bosses, shoulders or others. Thus the measurements carried out on the processing circuit as the tool advances do not fall within these singularities and are therefore accurately representative of the distance between the tool and the part over the entire scanning surface, so that they make it possible to position the focusing point on the surface of the part in real time, with greatly improved precision, in this case of the order of 0.25 mm. The processing circuit is also preferably determined so that the scanning processing band which follows the processing circuit completely covers the surface to be treated on the part. Brief description of the drawings
[0077] The invention, according to an exemplary embodiment, will be well understood and its advantages will appear better on reading the detailed description which follows, given for information purposes and in no way limiting, with reference to the appended drawings in which:
[0078] [Fig.l] [Fig.l] schematically represents, in front view, a surface treatment device of the prior art, comprising a remote telemeter 4 emitting a measurement beam 5 parallel to the treatment beam 3, so that the measurement point 7 is spaced from the treatment point 6 as explained in the introduction.
[0079] [Fig.2] [Fig.2] schematically represents, in front view, a device for surface treatment of the prior art, comprising a remote rangefinder 4 emitting a measuring beam 5 inclined relative to the treatment direction so as to cut the treatment beam at the focusing point.
[0080] [Fig.3] [Fig.3] schematically represents a zoom of [Fig.2] on the surface of the part to be treated, in the case where the part has a singularity at the measurement point inducing a height shift between the measurement point 7 and the treatment point 6.
[0081] [Fig.4] [Fig.4] is a very schematic top view of a treatment device surface according to the invention.
[0082] [Fig.5] [Fig.5] is a schematic side view of the surface treatment device of [Fig.4].
[0083] [Fig.6] [Fig.6] is a schematic perspective view of a part (the head scanner) of the surface treatment device of figures 4 and 5.
[0084] [Fig.7] [Fig.7] represents, in top view, a pattern formed by the beam of treatment on the surface of a part to be treated.
[0085] [Fig.8] [Fig.8] is a graphic representation reproducing three images, made with a fast camera, of the impact of the treatment beam and the measurement beam on the part, at three successive moments in the scanning plane. Detailed description
[0086] Identical elements shown in the above-mentioned figures are identified by identical numerical references.
[0087] Figures 1 to 3, which relate to devices of the prior art, have been described above.
[0088] Figures 4 to 6 show an embodiment of a surface treatment device according to the invention, respectively seen from above, seen from the side and in perspective. This surface treatment device comprises a tool 30 comprising:
[0089] - a first LASER source 12 emitting pulsed LASER radiation of power forming a treatment beam 14,
[0090] - a scanner head 10, crossed by the treatment beam,
[0091] - a lens 11, visible only in [Fig.5], arranged at the outlet of the head scanner 10 and crossed by the treatment beam 14 exiting the scanner head.
[0092] Said scanner head 10 is configured to guide and orient the treatment beam 14 towards an entry zone of the lens and to oscillate said treatment beam in a scanning plane within the limits of said entry zone, in order to scan the treatment beam on the surface of a part to be treated 100.
[0093] [Fig. 7] shows an example of a path, referred to as a brush pattern, that the treatment beam can follow on the part. In this example, the beam is scanned from left to right and vice versa in a scanning plane P as the tool 30 is moved in the direction of movement ô. The tool thus follows a treatment circuit represented by the line 22 which materializes the movement of the central axis of the lens on the part. The movement of the tool along the treatment circuit 22 and the scanning of the treatment beam in the plane P, which is substantially orthogonal to the direction of movement ô, makes it possible to treat the part on a strip centered on the treatment circuit 22. The width of this strip depends in particular the optical characteristics of the lens (in particular its focal length) and the characteristics of the scanner head used.
[0094] To enable the scanning of the treatment beam, the scanner head comprises two small deflection mirrors 101, 102, arranged in series immediately upstream of the output of the scanner head opposite which the lens 11 is arranged. The mirror 101 is mounted oscillating about an axis 1011, while the mirror 102 is mounted oscillating about an axis 1021; in the example illustrated, the axes 1011 and 1021 are orthogonal. Only the mirror 101 has been shown in [Fig.4], while only the mirror 102 is shown in [Fig.5]. The arrangement of the two mirrors appears more clearly in [Fig.6], in perspective.
[0095] It should be noted that the invention makes it possible to use a conventional commercially available scanner head, which makes it possible to offer a surface processing device at a lower cost.
[0096] The surface treatment device further comprises relative movement means making it possible to move the tool 30 relative to the part to be treated 100, in particular in the direction of movement δ. For example, the treatment device comprises a robotic articulated arm (not shown) having a distal end on which the tool 30 is mounted.
[0097] For the surface treatment to be precise and effective, the distance separating the optical center of the lens 11 from the surface of the part 100 must be equal to the focal length of the lens (i.e. the distance between the optical center of the lens and its image plane), or the actual instantaneous working distance separating the exit face of the lens 11 from the surface of the part 100 must be equal to the theoretical working distance of the lens (the two aforementioned conditions being equivalent), so that the focal point of the treatment beam 14 at the exit of the lens falls precisely on the surface of the part 100.
[0098] To do this, it is necessary to adjust in real time the “height” of the tool relative to the part (the term “height” here designating the distance between the tool and the part to be treated), and therefore to measure in real time the instantaneous working distance between the exit face of the lens (or possibly the optical center of the lens, or any other reference point) and the surface of the part.
[0099] To this end, the tool 30 further comprises:
[0100] - a second LASER source 16 emitting LASER radiation forming a incident measuring beam 18,
[0101] - a sensor 17, capable of detecting reflected measurement radiation which follows the same path, in the opposite direction, than the incident measuring radiation 18,
[0102] - a dichroic mirror 20 (or semi-reflecting mirror) arranged between the first LASER source 12 and lens 11, more precisely between the first LASER source 12 and the scanner head 10.
[0103] The first LASER source 12 and the second LASER source 16 are arranged so that the treatment beam 14 and the measurement beam 18 are substantially coplanar and orthogonal (see [Fig.5]). The dichroic mirror 20 is positioned on the optical path of the treatment beam 14 and on the optical path of the measurement beam 18, at the “meeting” point of said beams, so as to be struck on its first face by the treatment beam 14, and on its second face by the measurement beam 18. The dichroic mirror 20 is configured so that its first face transmits the treatment beam while its second face reflects the measurement beam.
[0104] The orientation of the dichroic mirror 20 is adjusted so that the treatment beam 14 and the measurement beam 18 at the output of said mirror are not exactly coaxial but have a slight angular offset.
[0105] If we consider that the treatment beam 14 passes through the dichroic mirror 20 without being deflected and that the incident treatment and measurement beams are orthogonal upstream of the dichroic mirror (as in the example illustrated), this means that the dichroic mirror is oriented so that, for example, the treatment beam strikes the first face of the mirror with an angle of 45° and the measurement beam 18 strikes the second face of the mirror with an angle close to 45° but not equal to 45°.
[0106] The angle between the two beams 14 and 18 at the output of the dichroic mirror 20 must not be too large so that each of the two beams strikes the deflection mirrors 101, 102 and then the lens. However, it must be large enough so that the treatment point 6 and the measurement point 7 on the part to be treated 100 are separated by an offset distance “d” (the part sufficient so that the measurement is not distorted or rendered unusable by the presence of the ejectates generated by the impact of the treatment beam on the part, which ejectates can generate significant measurement noise by crossing the incident measurement beam 18. By thus distancing the measurement point 7 from the ejectates, the measurement noise is reduced and the measurement is made more reliable.
[0107] Note that in the attached drawings, it is considered that the part 100 is located in the image plane of the lens, so that “d” designates both the offset distance on the part and the offset distance in the image plane (which is a parameter inherent to the architecture of the tool according to the invention, independent of the position of the part).
[0108] The offset distance “d” on the part required to sufficiently limit the measurement noise depends on various parameters, including the power of the treatment LASER, the focal length of the lens, the speed at which the treatment point 6 is moved over the surface to be treated and other parameters of use or construction of the scanner head (size of the deflection mirrors for example). The man of the trade is able, using simple tests and without demonstrating inventive activity, to determine this offset distance depending on the material used.
[0109] As an example, for a device comprising a first 100W LASER 12 source, and an F-theta 160 lens having a focal length of 160mm and a theoretical working distance of the order of 182mm, an offset distance of 12mm is perfectly suitable. The device obtained then has a precision in maintaining the lens / surface to be treated distance of the order of 0.25mm.
[0110] [Fig. 8] is a graphic reproduction of three successive images, taken by a high-speed camera. These reproductions illustrate the impact of the treatment and measurement beams on the part, during a scan of said beams from left to right in the plane P (the arrow F indicating the scanning direction), on either side of the central axis 24 of the lens. These reproductions make it possible to observe the ejecta 26 generated at the treatment point 6 by the impact of the treatment beam 14 on the part. Also shown are the measurement beam 18 and its intersection with the part 3 (“measuring point 7”).
[0111] According to the invention, the measurement is triggered when the measuring beam 18 is aligned with the central axis 24 of the lens, which corresponds to the central image of [Fig.8]. This means that the measurement is triggered when the measuring point 7 is located on the processing circuit 22 ([Fig.7]). However, the processing circuit is previously determined as a function of the geometry of the part to be processed (as well as the processing to be carried out). By choosing a processing circuit outside the point or linear singularities of the part, situations similar to that illustrated in [Fig.3] are avoided, which lead to a misinterpretation of the measurement and to a poor adjustment of the height of the scanner head and therefore to processing defects.
[0112] Furthermore, since the distance measurement is carried out at the center of the treatment strip, in the axis of the lens, the treatment device is able to treat with precision and without error non-planar parts having relatively significant curvatures.
Claims
Claims
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3. LASER processing device for LASER surface treatment of a workpiece (100), the device comprising a tool (30) comprising - a first LASER source (12), emitting pulsed power LASER radiation, called the treatment beam, - a lens (11), configured to focus at a point located on an image plane any radiation entering the lens through a first face thereof, - a scanner head (10) between the first LASER source (12) and the lens (11), said scanner head being configured to guide the treatment beam downstream of the first LASER source along an optical path, called the treatment optical path, striking the first face of the lens and passing through said lens to be focused at a focusing point located on the image plane of the lens, - a second LASER source (16), emitting a second LASER radiation called the incident measuring beam (18), - a measuring sensor (17) for detecting a reflected measuring beam resulting from the reflection on the part of the incident measuring beam, and calculation means configured to calculate a distance, called instantaneous working distance, between the part (100) and the lens (11), from the reflected measuring beam detected by the sensor, characterized in that: - the scanner head (10), the first LASER source (12) and the second LASER source (16) are configured so that the incident measurement beam (18) passes through the scanner head along an optical path, called the measurement optical path, striking the first face of the lens (11) and passing through said lens to be focused in the image plane of the lens at a point which is located at a distance from the focusing point of the treatment beam called the offset distance in the image plane (d), - the calculation means are configured to calculate the instantaneous working distance when the incident measuring beam (18) passes through the lens along a central axis (24) thereof. LASER treatment device according to claim 1, characterized in that the lens (11) is a lens of the F-theta type. LASER treatment device according to one of claims 1 to 2, ca- characterized in that the measuring sensor (17) is a detector based on conoscopic holography and coaxial technology.
4. LASER treatment device according to one of claims 1 to 3, characterized in that the scanner head (10) comprises motorized scanning means (101, 102) configured to oscillate the treatment beam (14) and the incident measurement beam (18) upstream of the lens (11) in a scanning plane (P) on either side of the central axis (24) of the lens.
5. LASER processing device according to one of claims 1 to 4, characterized in that: - the tool (30) comprises a dichroic mirror (20) having a first face capable of transmitting the processing beam (14) and a second face capable of reflecting the incident measurement beam (18), the first face of the dichroic mirror being struck by the processing beam and the second face of the semi-reflecting mirror being struck by the incident measurement beam, the dichroic mirror (20) being oriented so that the incident measurement beam and the processing beam form a non-zero angle between them at the output of said dichroic mirror, - the scanner head comprises one or more deflection mirrors (101, 102) arranged in series between the dichroic mirror (20) and the lens (11), for orienting the measurement (18) and processing (14) beams towards the first face of the lens,each of said deflection mirrors being pivotally mounted around an axis of said mirror.,
6. LASER treatment device according to claim 5, characterized in that at least one of the deflection mirrors (101, 102) is associated with motorized oscillation means configured to oscillate said mirror around its axis.
7. LASER processing device according to one of claims 1 to 6, characterized in that the processing device comprises relative displacement means for the relative displacement of the tool (30) relative to the part (100) in a direction (ô) called the direction of relative displacement.
8. LASER treatment device according to claim 7, characterized in that the relative displacement means comprise a robotic articulated arm having a distal end on which the tool (30) is mounted.
9. LASER treatment device according to one of claims 7 to 8, characterized in that: - the treatment device comprises a module for storing a processing circuit (22) on the part along which the tool (30) is programmed to move as the processing progresses, - the processing circuit (22) being previously determined as a function of the part so as not to cross a singularity of said part - the relative movement means and the scanning means are programmed to orient the tool so that the central axis (24) of the lens points on the processing circuit (22) and to scan the processing beam (14) on either side of said processing circuit.