HANDHELD PULSED LASER DEVICE FOR CLEANING OR TREATING A SURFACE

Abstract

The present invention relates to a handheld pulsed laser device for cleaning or treating a surface, comprising a laser source, a focal distance adjuster and a beam deflector. The laser source is configured to emit a pulsed laser beam and the focal distance adjuster, is configured to change a focal distance of the beam. The beam deflector may comprise at least one movable mirror onto which the beam is deflected, wherein the deflector is configured to deflect the beam to scan the beam along the surface.

The device further comprises at least one sensor, configured to provide a sensor signal that is representative for a parameter that is related to a characteristic of the surface, and a control unit, configured to control the beam deflector to scan the beam along the surface in an, at least, two-dimensional pattern, based on the sensor signal.

The present invention further relates to a method for using the pulsed laser cleaning device during cleaning or treating of a surface.

Claims

1. A handheld pulsed laser device for cleaning or treating a surface, comprising: a laser source, configured to emit a pulsed laser beam; a focal distance adjuster, configured to change a focal distance of the beam, and; a beam deflector, configured to deflect the beam to scan the beam along the surface; at least one sensor, configured to provide a sensor signal, representative for of a parameter that is related to a characteristic of the surface; and a control unit, configured to control the beam deflector to scan the beam along the surface in an, at least, two-dimensional pattern, based on the sensor signal.

2. The pulsed laser device according to claim 1, wherein the pattern of the beam comprises an outer contour and wherein the outer contour is filled-up by the beam with a back-and-forth scanning movement within the outer contour.

3. The pulsed laser device according to claim 2, wherein the back-and-forth scanning movement is superpositioned with a sinusoidal pattern.

4. The pulsed laser device according to claim 2, wherein the back-and-forth scanning movement is superpositioned with a spiral pattern.

5. The pulsed laser device according to claim 1, wherein the beam deflector comprises at least one mirror, which is tiltable around at least one perpendicular axis.

6. The pulsed laser device according to claim 1, wherein the focal distance adjuster comprises a movable lens element and a piezo-element, which is configured move the movable lens element to adjust the focal distance of the beam.

7. The pulsed laser device according to claim 1, wherein the at least one sensor is a spectral analysis sensor, configured to provide a signal that is representative of at least one of intensities and wavelengths of emitted electromagnetic radiation from the surface.

8. The pulsed laser device according to claim 1, wherein the at least one sensor is a distance sensor, configured to transmit a signal that is representative of a measured relative distance between the device and the surface.

9. The pulsed laser device according to claim 1, comprising an accelerometer, which is configured to transmit a signal that is representative of at least one of an orientation and displacement of the device.

10. The pulsed laser device according to claim 1, wherein, during cleaning or treating of the surface, the focal distance adjuster is configured to vary the focal distance of the beam.

11. The pulsed laser device according to claim 10, wherein the focal distance adjuster is configured to sinusoidally vary the focal distance of the beam around the measured relative distance.

12. A method for using the handheld pulsed laser device according to claim 1, during cleaning or treating of a surface, the method comprising the steps of: providing, with a sensor, a sensor signal, representative of a parameter that is related to a characteristic of the surface; focussing, with a focal distance adjuster, a pulsed laser beam on the surface; and scanning, using a beam deflector, the beam along the surface in an, at least, two-dimensional pattern.

13. The method according to claim 12, wherein the step of scanning comprises repeating the steps of: describing an outer contour of the pattern; and describing a filling, back-and-forth scanning movement within the outer contour of the pattern.

14. The method according to claim 12, comprising repeating the steps of: measuring at least one of intensities and wavelengths of emitted electromagnetic radiation from the surface; and controlling, based on the measured at least one of intensities and wavelengths, one or more of: a density of the filling, back-and-forth scanning movement within the outer contour of the pattern; an energy of a laser pulse; at least one of a distance and time between consecutive laser pulses on the surface; and an amount of laser pulses per unit of surface area.

15. The method according to claim 12, comprising repeating the steps of: measuring a relative distance between the device and the surface; and controlling, based on the measured distance, one or more of: a density of the filling back-and-forth scanning movement within the outer contour of the pattern; an energy of a laser pulse; at least one of a distance and time between consecutive laser pulses on the surface; and an amount of laser pulses per unit of surface area.

16. The method according to claim 12, comprising the step of periodically varying a focal distance of the beam.

17. The method of claim 16, wherein the step of periodically varying the focal distance of the beam comprises sinusoidally varying the focal distance of the beam.

Description

[0126] Further characteristics of the pulsed laser device according to the invention will be explained below, with reference to embodiments thereof, which are displayed in the appended drawings, in which:

[0127] FIG. 1 schematically depicts an embodiment of the handheld pulsed laser device according to the invention,

[0128] FIG. 2 schematically depicts the handheld pulsed laser device at least partially, upon interaction of a laser beam onto the surface,

[0129] FIGS. 3A-3E schematically depict various patterns, which the handheld pulsed laser device is configured to protect onto a surface, and

[0130] FIG. 4 schematically depicts the sinusoidal variation of the focal distance of the beam during scanning across the surface.

[0131] Throughout the figures, the same reference numerals are used to refer to corresponding components or to components, which have a corresponding function.

[0132] FIG. 1 schematically depicts an embodiment of the handheld pulsed laser device, generally denoted by reference numeral 1. The device 1 is in particular configured to remove a contaminant surface layer from a substrate 100, for example to remove an oxide layer or organic deposits from a metal surface.

[0133] It is remarked that the representation of the device 1, throughout the figures, is schematic and that the figures are intended to provide insight into which features may be combined to achieve the technical effect of the invention.

[0134] The pulsed laser device 1 in FIG. 1 comprises a laser source 10, which is configured to emit a laser beam 20, which is projected away from the source 10 in a projection direction (P). In the present embodiment, the source 10 comprises optical elements and control means, such that the emitted beam 20 has an energy density that is sufficient for achieving the desired interaction between the beam 20 and a surface 101 of the substrate 100. The laser source 10 is mounted to a fixed reference frame of the device 1, onto which other components are mounted as well in order to assure a relative position between the components.

[0135] The source 10 is configured to emit both a continuous beam, as well as a pulsed laser beam 20. In particular a pulsed laser beam 20 has been found to give rise to sufficient cleaning properties of the surface 101. When projecting such a pulsed beam 20, the source 10 is configured to alternatingly intermit the projection of the beam 20, in order to achieve the pulsed behaviour. In an embodiment, the laser source 10 may have a power in between 10 and 1000 Watts, whereas a pulse-energy may be in between 1 and 100 mJ.

[0136] After the beam 20 has been emitted by the source 10, it passes through a focal distance adjuster 30 of the device 1. The focal distance adjuster 30 comprises, in the present embodiment, three optical elements, with which it is configured to change certain properties of the beam 20, as well as to adjust a focal distance (D.sub.F), defined between the device 1 and the surface 101 of the substrate 100.

[0137] In the focal distance adjuster 30, the beam 20 first passes through a lens 31, which is fixed with respect to the laser source 10. The fixed lens 31 is a biconvex lens, comprising two convex outer surfaces on opposite ends, seen along the propagation direction (P). The fixed biconvex lens 31 is configured to narrow the laser beam 20, in order to achieve a converging laser bundle. Such a converging bundle is known to have a focal point, in which the laser power, per unit of projected area, is the largest. The focal point lies in front of the lens with which the beam is converged, when seen along the propagation direction.

[0138] It is understood that, in alternative embodiments, other fixed lenses may be provided to further focus the beam and to further narrow the bundle. Alternatively, the focal distance adjuster may comprise one or more biconcave lenses, which comprise two concave outer surfaces and which are configured to diverge the laser bundle.

[0139] The focal distance adjuster 30 further comprises a movable optical element 32, which is movable by means of a piezo-element 33. The movable optical element 32 is, like the fixed lens 31, a biconvex lens 32, which is movable with respect to the laser source 10 in a back-and-forth direction that is parallel to the projection direction (P) of the beam 20 through the lens 32.

[0140] The piezo-element 33 is provided between the movable lens 32 and a reference frame element that is fixedly connected to the source 10. The piezo-element 33 is configured to move the lens 32 with respect to the source 10, in the direction parallel to the projection direction (P) of the beam 20. Upon movement of the movable lens 32, a focal point (f.sub.P) of the beam 20 is shifted accordingly, resulting in a change of the focal distance (D.sub.F). Providing that the device 1 remains stationary with respect to the substrate 100, the position of the focal point (f.sub.P) is thereby changed with respect to the substrate 100.

[0141] With the focal distance adjuster 30, the focal point (f.sub.P) may be moved such, that it lies on top of the surface 101 that is to be cleaned. The energy of the beam 20, and in particular the energy density, which is the energy per unit of projected area, is concentrated on the surface 101, and the highest possible amount of energy is localized therein.

[0142] The piezo-element 33 comprises a piece of piezo-electric material, which deforms when an electric voltage is applied across it. In the present embodiment, the piezo-element 33 is fixed to the reference frame with one end thereof. The deformation of the material, under the influence of the voltage, will induce a change-in-length of the piezo-element 33. The movable lens 32 is affixed to a second end of the piezo-element 33, opposing the one end, and will be moved together with the second end upon deformation of the piezo-element 33.

[0143] By providing a piezo-element 33, the movable lens 32 may be moved relatively fast and reliably. This mainly lies in the fact that, when a piezo-element 33 is provided, virtually no other elements, such as transmissions etc., need to be provided. Furthermore, piezo-elements 33 suffer less from wear, because they lack moving parts.

[0144] In alternative embodiments, however, other types of linear actuators may be used to induce the linear back-and-forth movement of the movable lens.

[0145] The focal distance adjuster 30 further comprises an array lens 34, which is, seen along the projection direction (P), arranged behind the fixed lens 31 and the movable lens 32. The array lens 34 is configured to transform a Gaussian laser beam, having a Gaussian wavelength distribution spectrum, into a homogenous laser beam, being substantially monochromatic. The beam 20 that is generated in the source 10 does therefore not need to be monochromatic yet, since the array lens 34 may provide for such a transformation.

[0146] When the laser beam 20 has passed the focal distance adjuster 30, it is guided through the beam deflector 40, which is, seen along the projection direction (P), arranged downstream the focal distance adjuster 30.

[0147] The beam deflector 40 comprises, in the present embodiment, a first tiltable mirror 41 and a second tiltable mirror 42. The mirrors 41, 42 each comprise a reflective mirror surface and are substantially flat, so that an angle of incidence between the beam 20 and the mirror surface is the same as an angle of reflection between the beam 20 and the mirror surface. The beam deflector 40 is, by means of the mirrors 41, 42, configured to deflect the beam 20, so that the projection direction (P) of the beam 20 before entering the beam deflector 40 may differ from a projection direction (P) of the beam 20, after it has left the beam deflector 40.

[0148] It is understood that, in an alternative embodiment, the beam deflector may comprise other movable optical elements with which the beam may be deflected. For example, tiltable lenses may be provided with which the beam may be deflected and, simultaneously, be focussed.

[0149] The mirrors 41, 42 are tiltably mounted to the reference frame of the device 1. The first mirror 41 is thereby tiltable around a first axis, with respect to the frame. The second mirror 42 is tiltable around a second axis, wherein the second axis is aligned perpendicular to the first axis.

[0150] In a neutral position of both mirrors 41, 42, displayed in FIG. 1, the mirror surfaces of both mirrors 41, 42 are aligned anti-parallel. The angle between the mirror surface of the first mirror 41 and its angle of incidence with the beam 20 is 45. As a result, the projection direction (P) of the beam 20, behind the beam deflector 40, is aligned parallel to the projection direction (P) in front of the beam deflector 40.

[0151] When, for example, the first mirror 41 is tilted from its neutral position, the angle of incidence between the beam 20 and the mirror surface of the first mirror 41 is changed. As a result, the angle of reflection of the beam 20 on the first mirror 41 becomes changed as well. Accordingly, the position at which the beam 20 is projected on the second mirror 42 is changed, just as the angles of incidence and reflection on the mirror surface thereof. As such, the projection direction (P) of the beam 20, behind the beam deflector 40, is changed, which ultimately results in a shift of the beam 20 along the surface 10.

[0152] In the present embodiment, the mirrors 41, 42 are each mounted to the reference frame by means of an axle that is tiltably supported in the frame. The beam deflector 40 may comprise a first actuator and a second actuator, which are, respectively, configured to induce a tilting movement to the first mirror 41 and to the second mirror 42.

[0153] In an alternative embodiment, the beam deflector may comprise a single tiltable mirror. For achieving the same, at least, two-dimensional pattern on the surface, the single mirror is, by means of two actuators, tiltable around two perpendicular axes. In a further alternative embodiment, the single mirror comprises six actuators, with which a change in the orientation of the mirror may be provided along six degrees of freedom.

[0154] Behind the beam deflector 40, the laser beam 20 emerges from the device 1, in order to be projected onto the surface 101 of the substrate 100.

[0155] The device 1 comprises two sensors 50, of which a first one is a distance sensor 51, the distance sensor 51 is directed towards the substrate 100 and is configured to transmit a signal that representative for a distance between the device 1 and the substrate 100. The distance sensor 51 is mounted to the reference frame as well, so that a relative position of the distance sensor 51 with respect to other components in the device 1 is fixed.

[0156] The distance sensor 51 is configured to measure the distance between the substrate 100 and the sensor 51 itself, which is, due to the fixed position of the sensor 51 within the device 1, a measure of the distance between the device 1 and the substrate 100.

[0157] The device 1 further comprises a control unit 60, which is electronically connected to the laser source 10, to the focal distance adjuster 30 and to the beam deflector 40. The control unit 60 is configured to control those during operational use of the device 1. The control unit 60 may further comprise a user interface, with which an operator may set parameters in the control unit 60, on the basis of which the laser source 10, the focal distance adjuster 30 and the beam deflector 40 may be controlled.

[0158] The control unit 60 is configured to set parameters for the laser source 10, such that the laser beam 20, which is emitted by the source 10, may have optimal properties for cleaning the surface 101 of the substrate 100 in a certain situation. The control unit 60 may, 20 for example, set appropriate values for the pulse frequency or the energy density of the laser beam 20.

[0159] Additionally, the control unit 60 is configured to control the focal distance adjuster 30, such that the focal point (f.sub.P) of the beam 20 is projected on the surface 101 of the substrate 100.

[0160] Furthermore, the focal distance adjuster 40 is configured to apply, upon control by the control unit 60, an oscillatory variation on the movable lens 32. The oscillatory variation is a variation of the position of the movable lens 32 along the projection direction (P). Similar as to during the setting of the focal distance, the oscillatory variation is induced by actuation of the piezo-element 33, upon deformation thereof.

[0161] The control unit 60 is further configured to control the beam deflector 40, in order to project the pattern on the surface 101. Based on parameter values, which may be set in the control unit 60 by an operator, the control unit 60 may select appropriate values for the shape of the projected pattern, for the scanning frequency or for a distance between adjacent laser pulses on the surface 101.

[0162] Additionally, the control unit 60 is electronically connected to the distance sensor 51. The distance sensor 51 is thereby configured to transmit the signal, representative for the distance between the device 1 and the surface 101, towards the control unit 60.

[0163] Based on the signal from the distance sensor 51, the control unit 60 may, for example further control the focal distance adjuster 30 in case a set value for the focal distance in the focal distance adjuster 30 does not correspond to the measured focal distance (D.sub.F). The control unit is thereby configured to calculate a difference between the set and the measured focal distance and may control the focal distance adjuster 30 to minimize this difference.

[0164] Further reference is made to FIG. 2, in which the embodiment of the device 1 is displayed as well, comprising the distance sensor 51 and a spectral analysis sensor 52. The distance sensor 51 and the spectral analysis sensor 52 are both directed towards the surface 101 of the substrate 100 and are both electrically connected to the control unit 60, which is arranged within the device 1.

[0165] During cleaning of the surface 101 with the device 1, the laser beam 20 is projected onto the surface 101 in order to vaporize and/or to oxidize a top layer 102 on the surface 101. The device 1, and in particular the control unit 60 of the device 1, is thereby configured to control laser parameters such, that a sub-surface layer 103 of the substrate 100 is kept intact.

[0166] When the laser beam 20 is scanned along the surface 101, radiation is emitted back from the surface 101. With the spectral analysis sensor 52, the emitted radiation may be measured and a wavelength distribution of the emitted radiation may be constructed by the control unit 60.in the distribution, the measured intensity of radiation is displayed, for certain wavelength ranges.

[0167] The emitted radiation comprises a first portion, which is radiation that is reflected back from the surface as infrared radiation 21. The infrared radiation 21 directly originates from the laser beam 20, since no interaction has taken place between the surface 101 and the beam 20, other than reflection. A wavelength of the infrared radiation 21 therefor corresponds to a wavelength of the laser beam 20.

[0168] A second portion of the emitted radiation comprises heat-induced radiation 22, which is radiation that is emitted from the surface 101 due to heating thereof.

[0169] A third portion of the emitted radiation comprises plasma light 23, of which a wavelength and intensity are representative for the type of metal that is being oxidized during the cleaning. If for example the top layer 102, an organic contaminant, is being oxidized, the wavelength profile will differ from when, for example, an iron sub-surface layer 103 is being oxidized.

[0170] A fourth portion of the emitted radiation comprises visible light 24, of which the intensity and wavelength profile are representative for the type of oxidized elements as well.

[0171] The control unit 60 is configured to further control the laser source 10, focal distance adjuster 30 and the beam deflector 40 on the basis of the intensities and wavelength profiles, which are being measured by the spectral analysis sensor 52. For example, when the intensity of the heat-induced radiation 22 becomes too high, the control unit 60 may determine to decrease the energy density of the laser beam 20, in order to prevent substantial heating of the sub-surface layer 103.

[0172] In FIGS. 3A-3E, a projected pattern of the laser beam from the pulsed laser device 1 onto the surface is displayed, with a viewing direction from above, normal the surface. The pattern is repeatedly projected on the surface, until an operator may decide to stop operation of the device 1.

[0173] Besides the scanning movement of the beam to form the pattern, the laser device 1 may be moved in its entirety as well, for example by an operator. In particular with this handheld device, the operator may guide the projected pattern along the surface by inducing a relative movement between the device 1 and the surface. For the projected patterns in FIGS. 3A-3E, a relative movement between the device 1 and the surface is in a direction of propagation (D.sub.p).

[0174] In FIG. 3A, a first projected pattern 200 is displayed. During the scanning of the pattern 200, first, an ellipsoid outer contour 201 is described on the surface. Thereafter, the outer contour 201 is filled with a back-and-forth scanning movement. During the back-and-forth scanning movement, the beam is configured to describe a plurality of linear passes 202 across the surface. The linear passes 202 are aligned perpendicular to the direction of propagation (D.sub.p) and extend in between lines of the outer contour 201, across substantially the entire width of the outer contour 201.

[0175] After describing the outer contour 201, the laser beam is deflected towards a top portion 201 of the outer contour 201, in order to start filling thereof with linear passes 202. When a first linear pass 202 has been described by the laser in a transverse direction (T), the beam is moved along the surface, parallel to the direction of propagation (D.sub.p). Then, the beam is deflected to describe a second linear pass 202, in a direction opposing the transverse direction (T). This shifting between consecutive linear passes 202 is repeated until a bottom portion 201 of the outer contour 201 has been reached. Then, another outer contour is described and the scanning is repeated.

[0176] In FIG. 3B, a second projected pattern 300 is displayed, for which, first, an outer contour 301 is projected onto the surface with the laser beam. After the outer contour 301 has been projected, it is filled with linear passes 302 by means of a back-and-forth scanning movement of the laser beam as well.

[0177] However, the linear passes 302 are superpositioned with a sinusoidal pattern 303, which is projected by means of an oscillatory movement of the beam in an amplitude direction (A), parallel to the direction of propagation (D.sub.p). By superpositioning the linear passes 302 with the sinusoidal pattern 303, ripple stresses may be induced in the contaminate layer that is to be removed from the surface. These ripple stresses are induced by temperature gradients within the contaminant layer, which may give rise to local thermal expansion and thermal contraction and will induce buckling of the surface layer. As such, the sinusoidal pattern 303 may give rise to improved cleaning properties.

[0178] It is understood that, instead of a sinusoidal pattern, other wave-like patterns may be superpositioned with the linear passes as well in order to obtain the improved cleaning effect.

[0179] In FIG. 3C, a third projected pattern 400 is displayed. Similar to the second projected pattern 300, an outer contour 401 is described by the laser beam, which is filled with a back-and-forth scanning movement of the beam to describe linear passes 402. Opposed to the second projected pattern 300, in the third projected pattern 400, the linear passes 402 are superpositioned with a spiral pattern 403. The spiral pattern 403 is projected by an oscillatory movement of the beam in two amplitude directions (A, A).

[0180] Preferably, the two amplitude directions (A, A) are aligned perpendicular to each other. In the projected pattern 400 in FIG. 3C, a first amplitude direction (A) is aligned parallel to the direction of propagation (D.sub.p), whereas a second amplitude direction (A) is aligned parallel to the transverse direction (T), perpendicular to the first amplitude direction (A) and perpendicular to the direction of propagation (D.sub.p).

[0181] In FIG. 3D, a fourth projected pattern 500 is displayed. The fourth projected pattern 500 is similar to the first projected pattern 100 that is displayed in FIG. 3A, but comprises an outer contour 501 with a rectangular shape. Two of the four projected lines, that form the rectangular outer contour 501, are thereby aligned parallel to the direction of propagation (D.sub.p), whereas two other lines of the rectangular outer contour 501 are aligned parallel to the transverse direction (T).

[0182] By projecting a rectangular outer contour 501, filled with linear passes 502, the advantage is provided that the beam needs to be deflected along only one direction, of the direction of propagation (D.sub.p) and the transverse direction (T), at the same time. With, for example, an ellipsoid outer contour, simultaneous deflection of the beam along both the direction of propagation (D.sub.p) and the transverse direction (T) is needed, which may require more advanced actuators of the beam deflector or more complex controlling software in the control unit.

[0183] In FIG. 3E, a projected pattern of the laser beam on the surface is displayed. The laser beam is guided by the beam deflector to describe a back and forth scanning movement over a scanning width (SW). The scanning movement comprises a first sinusoidal pass (A), which propagates in a first direction, and a second sinusoidal pass (B), which propagates in a second direction that opposes the first direction.

[0184] The first sinusoidal (A) and the second sinusoidal (B) have a half wavelength (Wf) and the scanning width (SW) is set to be not equal to an exact plurality of the half wavelength (Wf). It is therefore achieved that the first sinusoid (A) is out of phase with the second sinusoid (B). A spiral-like waveform may thereby be created which propagates in the first and/or second direction. This can be seen in FIG. 3E, in which it is displayed that the first sinusoidal pass (A) intersects the propagation axis (x) at a first intersection point (a), whereas the second sinusoidal pass (B) intersects the propagation axis (x) at a second intersection point (b), wherein the second intersection point (b) does not fall together with the first intersection point (a).

[0185] As such, it is achieved that knot points of the pattern, in which subsequent first and second scanning passes (A, B) intersect, are not present at a fixed location on the surface, but that these knot points move along the surface, which is indicated by the arrow in FIG. 3E. By moving the knot points, with their relatively high energy density, along the surface, the energy input into the surface is spread better, which allows the cleaning effect to be more even and better spread over the surface.

[0186] In FIG. 4, a further embodiment of the laser cleaning device according to the invention is displayed. The device 601 is displayed in an operative condition, projecting a laser beam 620 on a surface 101 of a substrate 100 to-be-cleaned, in order to remove a contaminant top layer 102 from a sub-surface layer 103.

[0187] The focal distance (D.sub.f) of the beam 620 is, by a focal distance adjuster in the device 601, adjusted such that a focal point (f.sub.p) of the beam 620 lies on the surface 101. The device 601 is, by means of a distance sensor 651, configured to measure a relative distance between the device 601 and the surface 101, and configured to adjust the focal distance (D.sub.f), based on the measured relative distance.

[0188] During scanning of the beam 620 across the surface 101, the device 601 is configured to sinusoidally vary the focal distance (D.sub.f) of the beam 620, as is displayed in FIG. 4 by a sinusoidally variable focal point (f.sub.p). The focal distance adjuster is thereby configured to periodically vary the focal distance (D.sub.f), wherein an amplitude of this variation, parallel to a projection direction (P) of the beam 620, is relatively small compared to the focal distance (D.sub.f).

[0189] By periodically varying the focal distance (D.sub.f), an effective focal length of the device 601 may be increased. This may result therein that disturbances in the position of the device 601, relative to the surface 101, do not substantially influence the working of the laser. A certain amount of movement of the device 601, in hands of the operator, becomes allowable, while the cleaning of the surface 101 by the device 601 remains sufficient.