Patent Application
20230049111
The present invention relates to a laser marking system and method for marking a target. The laser marking system comprises a laser configured to produce a laser beam, a marking head configured to project the laser beam onto a target, and a negative curvature hollow core fiber configured to transmit the laser beam from the laser to the marking head. Aspects and implementations of the present disclosure are directed generally to laser marking equipment.
Current laser markers and scanners are limited during automated production operations in packaging as well as in parts marking production lines. Current laser markers and scanners are typically fixed into production systems relative to articles being marked.
It is in object of the present invention to provide a laser marking system that obviates or mitigates one or more problems of the prior art whether identified herein or elsewhere.
Fiber optics has long been the preferred form of beam delivery for fiber lasers, semiconductor lasers, and laser diodes. The fiber technology and materials are well suited for high power and high-quality beam delivery for applications ranging from cutting and welding to high precision marking and coding. The use of fibers has not reached CO2 laser applications. The use of fiber delivery of CO2 laser beams has been limited to low power and low beam-quality applications such as found in medical and low-end material processing.
Use of fibers in other types of laser, such as lasers configured to provide ultraviolet radiation or near infrared radiation, may also be limited to certain applications due to having a limited transmission quality. Solid-state lasers comprising, for example, Nd:YAG (neodymium doped yttrium aluminum garnet, i.e. a YAG laser) or Nd:VO4 (neodymium doped yttrium orthovanadate, i.e. a vanadate laser) crystals may be used to produce near infrared light for marking and/or coding. These solid-state lasers typically emit light having a wavelength of about 1.06 μm.
Ultraviolet light may be produced by applying a non-linear optical process to the near infrared light discussed above. For example, near infrared light produced by a solid-state laser may be passed through a non-linear crystal such as KTP (potassium titanyl phosphate), KTA (potassium titanyl arsenate) or BBO (beta barium borate).
Depending on the design, the near infrared radiation may be converted to green wavelengths (e.g. about 0.532 μm by doubling) or to ultraviolet wavelengths (e.g. about 0.355 μm by tripling or to 0.265 μm by quadrupling). It will be appreciated that other laser technologies may be used to produce laser light at these and/or other wavelengths covering the electromagnetic spectrum (e.g. from deep ultraviolet to the far infrared), and that any of these laser technologies may be used for marking applications.
Known hollow core fibers made of silica glass have been used for years in medical and industrial applications for laser power transmission. The inside diameter of the fiber is typically coated with a reflective coating such as silver or a silver-based compound. The coating quality determines the power transmission loss, bending loss, and reliability. For power transmission the inside diameter of the fiber typically ranges from 500 μm to 1 mm. However, if the application requires good beam quality, the inside diameter must be less than 400 μm and typically less than 300 μm for CO2 laser transmission. The coating process limits the length of small diameter fibers to less than 3 meters. Due to material absorption, the coupling efficiency is critical at CO2 wavelengths and the power transmission losses increases exponentially above wavelengths of about 9.5 μm. A combination of the need of small inner diameter for good beam quality; the need for good coupling efficiency; and an avoidance of high-power loss severely restricts the usefulness of known hollow core fibers for marking applications.
Solid core fibers have also been developed for laser delivery. These fibers typically comprise silver halide and are limited to 30-40 W of radiative power with a typical transmission of about 40% through a 4-meter length fiber. The largest radiative loss through such fibers is due to Fresnel reflection losses at interfaces of the fiber. Silver halide is also photosensitive and requires shielding from visible and UV light to prevent darkening and increased absorption loss. Furthermore, the complexities of cooling and coupling such fibers have prevented the use in laser marking applications.
According to a first aspect of the invention, there is provided a laser marking system comprising a laser configured to produce a laser beam, a marking head configured to project the laser beam onto a target, and a negative curvature hollow core fiber configured to transmit the laser beam from the laser to the marking head.
The laser may comprise a gas laser, e.g. a CO2 laser. The laser may comprise a solid-state laser. The solid-state laser may comprise, for example, a Nd:YAG (neodymium doped yttrium aluminum garnet, i.e. a YAG) laser or a Nd:VO4 (neodymium doped yttrium orthovanadate, i.e. a vanadate) laser. The laser may comprise a non-linear optical element configured to convert a first wavelength of light to a second wavelength light (e.g. converting near infrared light to ultraviolet light). The non-linear optical element may comprise a crystal such as, for example, KTP (potassium titanyl phosphate), KTA (potassium titanyl arsenate) or BBO (beta barium borate).
The laser marking system advantageously allows the transmission of wavelengths of radiation (e.g. infrared) in high-energy pulses that have not previously been possible. The laser marking system advantageously improves the transmission of wavelengths of ultraviolet and/or near infrared radiation in high-energy pulses compared to known laser marking systems. The efficiency of the laser marking system is greater than known laser marking systems. The separation of the laser and the marking head using the negative curvature hollow core fiber advantageously enables greater flexibility of use of the laser marking system in production lines.
Known hollow core fibers cannot be used to transmit ultraviolet radiation because the internal wall coatings cannot withstand the high power of ultraviolet radiation and suffer material degradation. Known solid core fibers may be used to transmit ultraviolet radiation for a limited range of uses. However, the known solid core fibers suffer material degradation when exposed to ultraviolet radiation energy at the power levels required for laser marking applications. Known fibers in general have a low threshold for damage and are therefore difficult to optically couple to other optical components. For example, known solid core fibers have a core diameter that may be about five times smaller than that of negative curvature hollow core fibers, making the known solid core fibers less mechanically robust and more difficult and expensive to optically couple to other optical components (e.g. the marking head) compared to negative curvature hollow core fibers.
The negative curvature hollow core fiber has a lower bending loss compared to known fibers. This advantageously allows the negative curvature hollow core fiber to transmit radiation (e.g. infrared, near infrared and/or ultraviolet radiation) in confined spaces (e.g. compact production lines comprising multiple components) by allowing bending of the negative curvature hollow core fibre around obstacles without causing an unacceptable loss in transmission. The negative curvature hollow core fiber performs better (i.e. experiences lower losses and has a higher damage threshold) than known fibers when transmitting high-power pulses of laser light. The negative curvature hollow core fiber may have a larger core diameter than known fibers. This advantageously increases mechanical robustness of the negative curvature hollow ore fiber and reduces a difficulty and cost of coupling the negative curvature hollow core fiber to other optical components compared to known fibers.
The negative curvature hollow core fiber may be an anti-resonant negative curvature hollow core fiber.
Anti-resonant hollow core fibers are negative curvature fibers having a cladding structure that reduces or inhibits optical coupling between a core of the fiber and a cladding of the fiber, resulting in reduced losses at the desired wavelengths.
The laser beam may comprise infrared electromagnetic radiation.
The infrared electromagnetic radiation may comprise a wavelength that is greater than or equal to about 8 μm. The infrared electromagnetic radiation may comprise a wavelength that is less than or equal to about 11 μm. The infrared electromagnetic radiation may comprise a wavelength of about 9.3 μm. The infrared electromagnetic radiation may comprise a wavelength of about 9.6 μm. The infrared electromagnetic radiation may comprise a wavelength of about 10.2 μm. The infrared electromagnetic radiation may comprise a wavelength of about 10.6 μm.
The laser beam may comprise near infrared electromagnetic radiation. The near infrared electromagnetic radiation may comprise a wavelength that is greater than or equal to about 0.780 μm. The near infrared electromagnetic radiation may comprise a wavelength that is less than or equal to about 3 μm. The near infrared electromagnetic radiation may comprise a wavelength of about 1.06 μm.
The laser beam may comprise ultraviolet electromagnetic radiation. The ultraviolet electromagnetic radiation may comprise a wavelength that is greater than or equal to about 100 nm. The ultraviolet electromagnetic radiation may comprise a wavelength that is less than or equal to about 400 nm. The ultraviolet electromagnetic radiation may comprise a wavelength of about 265 nm. The ultraviolet electromagnetic radiation may comprise a wavelength of about 355 nm.
The negative curvature hollow core fiber may comprise chalcogenide glass.
The chalcogenide glass may comprise one or more of the following materials: As30Se50Te20; As2S3; As2Se3; Ge15As25Se40Te20; and, As40S30Se30. The chalcogenide glass may comprise other combinations and/or dopants such as rare earth elements.
The negative curvature hollow core fiber may comprise silica for ultraviolet transmission and/or near infrared transmission. The negative curvature hollow core fiber may comprise Hydrogen infused silica for ultraviolet radiation transmission. Hydrogen infused silica may advantageously improve a transmission of ultraviolet radiation and/or improve an operational lifetime of the negative curvature hollow core fiber when used to transmit ultraviolet radiation.
The laser marking system may comprise an umbilical between the laser and the marking head. The negative curvature hollow core fiber may be located within the umbilical.
The umbilical may have a length of about 3 metres or more. The umbilical may have a length of about 10 metres.
An end of the negative curvature hollow core fiber may be tapered.
A tapered fiber advantageously improves a coupling efficiency of the negative curvature hollow core fiber with the laser and/or the marking head, thereby improving an efficiency of the laser marking system.
The negative curvature hollow core fiber may comprise a plurality of capillaries. The capillaries may have generally arched, generally circular, generally oval or generally conical shapes. The capillaries may form one or more ring structures around the core of the negative curvature hollow core fiber. Each ring of capillaries may comprise a different number of capillaries and/or different sized capillaries and/or different shaped capillaries. A ring of generally round or generally circular capillary tubes may be preferable due to their relatively high mechanical strength and a relative ease with which they may be manufactured compared to other shapes. The capillaries may be formed from optical fibers.
Thicknesses of the capillary walls may be selected in accordance with the following equation:
where t is the capillary wall thickness, λ is the wavelength of radiation that the negative curvature hollow core fiber is configured to transmit, n1 is the refractive index of the capillary material, and m is a positive integer. The smaller the value of m, the smaller the thickness of the capillary walls. As such, selection of the value of m may at least partially depend upon fabrication limitations of a material used to from the capillary walls. The thicknesses of the capillary walls may be within the inclusive range of about −5% to about +5% of the calculated value of t.
The thicknesses of the capillary walls may be about 0.3 μm or more for transmitting infrared radiation (e.g. produced by a CO2 laser). The thicknesses of the capillary walls may be about 15 μm or less for transmitting infrared radiation (e.g. produced by a CO2 laser). The thicknesses of the capillary walls may be about 0.3 μm or more for transmitting near infrared radiation. The thicknesses of the capillary walls may be about 3 μm or less for transmitting near infrared radiation. The thicknesses of the capillary walls may be about 100 nm or more for transmitting ultraviolet radiation. The thicknesses of the capillary walls may be about 600 nm or less for transmitting ultraviolet radiation. The thicknesses of the capillary walls may be selected at least partially based on a refractive index of the capillaries and/or a wavelength of radiation that is to be transmitted by the negative curvature hollow core fiber and/or a geometry of the anti-resonant structure (e.g. number of capillaries, diameters of the capillaries, spacing of capillaries, shapes of capillaries).
A ratio of an inner diameter of the capillaries to an outer diameter of the capillaries may be selected in at least partial dependence on properties of the laser beam (e.g. a wavelength and/or a power of the laser beam) that the negative curvature hollow core fiber is configured to transmit. For example, for transmitting infrared light generated by a CO2 laser, a ratio of an inner diameter of the capillaries to an outer diameter of the capillaries may be between about 0.8 and about 0.9. It will be appreciated that this range of ratios of inner and outer capillary diameters is merely an example, and that the range of ratios will vary depending on the planned application of the negative curvature hollow core fiber (e.g. wavelength of light to be transmitted, cross-sectional size and length of the negative curvature hollow core fiber, etc.).
The capillaries may form part of a cladding layer of the negative curvature hollow core fiber. A diameter of the hollow core of the fiber may correspond to the diameter of the largest circle that can be circumscribed within an internal perimeter formed by the capillaries. The core diameter may be selected at least partially based on a refractive index of the capillaries and/or a wavelength of radiation that is to be transmitted by the negative curvature hollow core fiber and/or a geometry of the anti-resonant structure (e.g. number of capillaries, diameter of capillaries, spacing of capillaries, shapes of capillaries). In general, the core diameter may scale with a wavelength of the laser beam that is to be transmitted by the negative curvature hollow core fiber. In general, a quality of a laser beam transmitted by the negative curvature hollow core fiber may be improved by reducing a core diameter of the negative curvature hollow core fiber. The core diameter may be at least partially determined by a geometry of the capillaries and/or a cladding structure of the negative curvature hollow core fiber. For example, in the case of a ring of generally round or generally circular capillaries, the core diameter of the negative curvature hollow core fiber may be selected in at least partial dependence on the following equation:
where Dcore is the core diameter of the negative curvature hollow core fiber, dtube is the diameter of the capillaries, t is the thickness of the capillary walls, g is the gap distance between adjacent capillaries, and N is the number of capillaries. This equation may be used to estimate the core diameter of other capillary structures and geometries such as, for example, generally arched, generally oval, generally conical, etc. shapes. For example, the term representing the diameters of the generally round or generally circular capillaries may be replaced by a term representing a greatest diameter of a shape of the capillaries. The core diameter of the negative curvature hollow core fiber may be within the inclusive range of about −10% and about +10% of the calculated value of Dcore.
The negative curvature hollow core fiber may have a core diameter of about 200 μm or more for transmitting infrared radiation (e.g. produced by a CO2 laser). The negative curvature hollow core fiber may have a core diameter of about 500 μm or less for transmitting infrared radiation (e.g. produced by a CO2 laser). The negative curvature hollow core fiber may have a core diameter of about 10 μm or more for transmitting ultraviolet radiation. The negative curvature hollow core fiber may have a core diameter of about 20 μm or less for transmitting ultraviolet radiation. The negative curvature hollow core fiber may have a core diameter of about 20 μm or more for transmitting near infrared radiation. The negative curvature hollow core fiber may have a core diameter of about 100 μm or less for transmitting near infrared radiation.
The laser marking system may comprise one or more coupling lenses for optically coupling the negative curvature hollow core fiber to one or more other optical elements. An optimum ratio of a focal length to a diameter of an entrance pupil (i.e. an optimum F #) of the coupling lens for coupling into the negative curvature hollow core fiber may be selected in at least partial dependence on the following equation:
where Dcore is the core diameter of the negative curvature hollow core fiber, and A is the wavelength of radiation that the negative curvature hollow core fiber is configured to transmit. In practice, if the F # of the coupling lens is less than F #Opt then more optical power may be coupled into higher order modes within the negative curvature hollow core fiber and thereby be attenuated. In practice, if the F # of the coupling lens is less than F #Opt then the optical power may be clipped at an entrance to the negative curvature hollow core fiber, which may in turn result in heating and possible thermal damage caused to the entrance of the negative curvature hollow core fiber. As such, the F # of the coupling lens may preferably be within the inclusive range of −5% and 2% of F #Opt.
The F # of the coupling lens may be selected in at least partial dependence on properties of the laser beam (e.g. a wavelength of the laser beam) that is to be transmitted and/or a geometry of the negative curvature hollow core fiber itself. For example, for transmitting infrared light generated by a CO2 laser, the negative curvature hollow core fiber may have a core diameter of about 300 μm, and the F # of the coupling lens may be between about 15.4 and about 17.0. It will be appreciated that this range of F # is merely an example, and that the range of F # will vary depending on the planned application of the negative curvature hollow core fiber (e.g. wavelength of light to be transmitted, core diameter of the negative curvature hollow core fiber, etc.).
Once the properties of the laser beam (e.g. the wavelength, power, the radiation source type—CO2, solid-state, etc.) and the optimum F # of the coupling lens are known, the coupling lens (or lenses) may be designed using standard optical design techniques. Laser sources typically used in laser marking applications may have laser beam diameters at the output of the laser source in the inclusive range of about 0.2 mm to about 4.0 mm, and full-angle beam divergences in the inclusive range of about 2.0 mrad to about 8.0 mrad. Laser sources typically used in laser marking applications may have a beam parameter product in the inclusive range of about 0.2 mm mrad to about 10.0 mm mrad. The beam parameter product may be defined as the laser beam radius multiplied by the half-angle beam divergence. In practice, as the laser beam passes through the optics of the laser marking system, the laser beam may become distorted due to optical aberrations and/or mode degradation in the negative curvature hollow core fiber. This may result in an increase of the beam parameter product at an output of the laser marking system compared to the input of the negative curvature hollow core fiber. The beam parameter product at the output of the laser marking system may generally be in the inclusive range of about 1.0 mm mrad to about 40.0 mm mrad.
A cross-sectional radius of the laser beam when entering the negative curvature hollow core fiber may be selected in at least partial dependence on properties of the laser beam (e.g. a wavelength and/or power of the laser beam) that is to be transmitted and/or a geometry of the negative curvature hollow core fiber itself. For example, for transmitting infrared light generated by a CO2 laser, the negative curvature hollow core fiber may have a core diameter of about 300 μm, and the laser beam may have a cross-sectional radius of between about 91 μm and about 100 μm when entering the negative curvature hollow core fiber from the laser. A beam parameter product of the laser beam may be about 4.0 or less at the target. The beam parameter product of the laser beam may be about 3.5 or less at the target. A beam parameter product of the laser beam may be about 3.5 or less at an output of the laser. The beam parameter product of the laser beam may be about 3.0 or less at the output of the laser. The laser beam may have a cross-sectional radius of between about 0.7 mm and about 1.3 mm. The laser beam may have a half-angle divergence of between about 2.3 mrad and about 4.3 mrad. It will be appreciated that values merely provide an example, and that the ranges of cross-sectional radii, beam parameter products and half-angle divergences will vary depending on the planned application of the negative curvature hollow core fiber (e.g. wavelength of light to be transmitted, cross-sectional size and length of the negative curvature hollow core fiber, etc.).
The laser marking system may comprise an optical alignment system located between the laser and the negative curvature hollow core fiber configured to change a position and/or angle of the laser beam relative to a core of the negative curvature hollow core fiber.
Gas lasers in general (e.g. CO2 lasers) may be unstable until they reach what may be referred to as thermal equilibrium. When the laser is activated, the laser heats and plasma optical characteristics change non-uniformly along a length of the laser. The optical axis of the laser may change as the housing or extrusion thermally expands and/or deforms, and optical mounts of the laser may flex as they heat and cool non-uniformly. All of these thermal movements can cause the laser beam exiting the laser to move around in the output aperture and/or deviate angularly from the optical axis of the laser marking system. This all contributes to what may be referred to as pointing error, and is a dynamic characteristic that may require dynamic compensation to reduce the negative effects on the performance of the laser marking system. The optical alignment system may compensate for such thermal alignment errors.
The optical alignment system may advantageously improve a coupling efficiency of the negative curvature hollow core fiber and thereby improves an efficiency of the laser marking system.
The optical alignment system may comprise a first adjustable optical element configured to receive the laser beam from the laser. The optical alignment system may comprise a second adjustable optical element configured to receive the laser beam from the first adjustable optical element and direct the laser beam towards an input of the core of the negative curvature hollow core fiber. The optical alignment system may comprise a first detector configured to detect a position of the laser beam relative to the second adjustable optical element. The optical alignment system may comprise a second detector configured to detect a position of the laser beam relative to the input of the core of the negative curvature hollow core fiber.
Two mirrors, typically in a periscope configuration, may be used within the optical alignment system. The mirrors may each be affixed to a mount with tip-tilt adjustment via electronically adjustable screws or linear motors. The first mirror tip-tilt adjustment screws or motors may position the laser beam on the surface of the second mirror. The second mirror tip-tilt adjustment screws or motors may position the laser beam to be co-axial with a desired optical axis through the laser marking system. In this manner, any misalignment error from any source of misalignment can be compensated for.
The first and second detectors may be configured to detect angular and/or translational positions of the laser beam.
The first adjustable optical element may comprise a first rotatable reflector. The second adjustable optical element may comprise a second rotatable reflector.
The first detector may be located behind the second rotatable reflector. The first detector may be configured to detect a portion of the laser beam that transmits through the second detector.
The second reflector may have a reflectivity of between about 97% and about 99.7%.
The second rotatable reflector has a non-zero thickness through which the second portion of the laser beam transmits. The second portion of the laser beam may undergo refraction when passing through the second rotatable reflector and change direction. A centre point of the first position detector may be positioned offset a centre point of the second rotatable reflector to account for the change in direction of the second portion of the laser beam caused by refraction through the second rotatable reflector.
The first detector may be located between the first rotatable reflector and the second rotatable reflector. The first detector may comprise an alignment aperture that is aligned with an optical axis of the laser marking system. The alignment aperture may have a diameter that is substantially equal to a diameter of the laser beam.
A second implementation would be to use a quadrant detector having a hole at the centre of the detector. The hole diameter may be sized to be the size of the laser beam. The detector should be positioned such that the centre of the hole is aligned with the desired axis of the beam. In this manner, any beam position error from the desired beam axis would be detected by the quadrant detector and provide a signal to the appropriate actuators on the first mirror mount to move the beam to the desired position.
The optical alignment system may comprise a beam sampler located between the first rotatable reflector and the second rotatable reflector. The beam sampler may be configured to direct a portion of the laser beam to the first detector.
The beam sampler may be positioned in the beam path as close to the input side or the exit side of the second mirror. The beam sampler may be a beam splitter such as an optical flat having one side coated to reflect a small percentage of the beam (<1%) to a quadrant detector and the other side anti-reflection coated allowing the remaining percentage of the beam to pass through the device. The effect of the thickness of the device being compensated in the positioning of the second mirror or by placing a second flat of the same thickness at a complimentary angle in the beam path after the beam sampler.
The beam sampler may comprise a beam splitter.
The beam sampler may comprise a reflective element having an alignment aperture that is aligned with an optical axis of the laser marking system. The alignment aperture may have a diameter that is substantially equal to a diameter of the laser beam.
The second detector may be located between the second rotatable reflector and the input of the core of the negative curvature optical fiber. The second detector may comprise an alignment aperture that is aligned with an optical axis of the laser marking system. The alignment aperture of the second detector may have a diameter that is substantially equal to a diameter of the laser beam.
The optical alignment system may comprise a beam sampler located between the second rotatable reflector and the input of the core of the negative curvature hollow core fiber. The beam sampler may be configured to direct a portion of the laser beam to the second detector.
The beam sampler may comprise a beam splitter.
The beam sampler may comprise a reflective element having an alignment aperture that is aligned with an optical axis of the laser marking system. The alignment aperture may have a diameter that is substantially equal to a diameter of the laser beam.
The beam sampler may be a reflector with a hole the size of the beam where the mirror reflects any portion of beam missing the hole to a quadrant detector. In this configuration, the signal from the quadrant detector drives the alignment mirror in such a way as to minimize the beam hitting the quadrant detector thereby keeping the beam aligned.
The detector may be a quadrant detector. The quadrant detector may have a hole at the centre of the detector. The hole diameter may be sized to be the size of the laser beam. The detector may be positioned such that the centre of the hole is aligned with the desired axis of the beam. In this manner, any beam position error from the desired beam axis would be detected by the quadrant detector and provide a signal to the appropriate actuators on the first mirror mount to move the beam to the desired position.
The optical alignment system may comprise a controller configured to receive signals from the first and second detectors and use the signals to control rotational positions of the first and second rotatable reflectors.
The optical alignment system may comprise a fixed reflector that is aligned with a desired optical axis of the laser marking system. The fixed reflector may be configured to receive the laser beam from the laser and direct the laser beam to a rotatable reflector. The rotatable reflector may be configured to correct angular errors and direct the laser beam to the input of the negative curvature hollow core fiber
The first and second rotatable reflectors may be driven by first and second controllers that are capable of changing the rotational positions of the first and second rotatable reflectors by sub-micron amounts.
The first and second controllers may be capable of changing the rotational positions of the first and second rotatable reflectors by sub-micron amounts along two substantially orthogonal rotation axis to allow fine (x, y) control of the position of the laser beam.
The first and second detectors may each comprise a quadrant detector.
A quadrant detector is able to output a signal that will enable the accurate determination of the x and y co-ordinate, (x,y), position of the laser beam on the detector. This data may be used to drive the actuators of the rotatable reflectors in a feedback manner to improve an alignment of the laser beam with the optical axis of the laser marking system. For example, the rotatable reflectors may be adjusted in accordance with the detector signals until (x, y) position coordinates stay below a threshold value or reach an aligned value of (0, 0). The feedback signal may be kept at (0, 0) and the laser beam may remain aligned with the optical axis of the laser marking system.
The laser marking system may comprise a first protective aperture located between the laser and the negative curvature hollow core fiber at an input of the core of the negative curvature hollow core fiber. The first protective aperture may have a diameter that is substantially equal to a core diameter of the negative curvature hollow core fiber.
The laser marking system may comprise a second protective aperture located between the laser marking head and the negative curvature hollow core fiber at an output of the core of the negative curvature hollow core fiber. The second protective aperture may have a diameter that is substantially equal to a core diameter of the negative curvature hollow core fiber.
The first and/or second protective apertures may comprise a pin-hole. To protect the end of the fiber from damage from the focused beam of the laser, a protective pin-hole having the same diameter as the core of the fiber is placed at the input end of the fiber. To protect the end of the fiber from damage from radiation backscattered into the marking head, a protective pin-hole having the same diameter as the core of the fiber is placed at the output end of the fiber. Either pin-hole may be part of the fiber mount or a separate device. Either pin-hole is easily replaced and may be considered to be a sacrificial device to protect the more expensive and difficult to replace fiber.
According to a second aspect of the invention, there is provided a method of marking a target with a laser beam comprising using the laser marking system of the first aspect.
According to a third aspect of the invention, there is provided a method of designing the laser marking system of the first aspect comprising:
(a) selecting a desired laser beam spot size at the target and a desired distance between the marking head and the target;
(b) designing optical components of the marking head in at least partial dependence on step (a) and determining a beam parameter product of the laser beam at the target;
(c) designing first coupling optics between the negative curvature hollow core fiber and the marking head in at least partial dependence on step (b);
(d) selecting a desired beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head and designing the negative curvature hollow core fiber in at least partial dependence on the beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head;
(e) designing second coupling optics between the laser and the negative curvature hollow core fiber in at least partial dependence on step (d); and,
(f) designing the laser in at least partial dependence on the beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head.
Regarding step (a), the desired laser beam spot size may be about 100 μm or more. The desired laser beam spot size may be about 500 μm or less. The desired distance between the marking head and the target may be about 50 mm or more. The desired laser beam spot size may be about 250 μm. The desired distance between the marking head and the target may be about 250 mm or less. The desired distance between the marking head and the target may be about 125 mm.
Regarding step (b), the beam parameter product of the laser beam at the target may be defined as the product of the radius of the laser beam and the divergence of the laser beam at the target.
Regarding step (c), the first coupling optics may be configured to convert a divergent laser beam exiting the negative curvature hollow core fiber into a collimated laser beam entering the marking head. The first coupling optics may comprise one or more lenses of a material having a relatively high transmissivity (e.g. coated lenses for a transmissivity of about 99% or more) at the desired wavelength (e.g. infrared, near infrared or ultraviolet wavelengths). Alternatively, the first coupling optics may comprise one or more mirrors having a relatively high reflectivity (e.g. a reflectivity of about 99% or more). For infrared transmission, the lenses used in the first coupling optic may comprise one or more materials such as zinc selenide, zinc sulphide, germanium, gallium arsenide or other materials that are sufficiently transparent at infrared wavelengths (e.g. wavelengths of radiation generated by a CO2 laser). For near infrared transmission, the lenses used in the first coupling optic may comprise one or materials such as fused silica, a crown glass (e.g. borosilicate or BK7) and/or a synthetic fused silica such as SUPRSIL provided by Heraeus, a German company. For ultraviolet transmission, the lenses used in the first coupling optic may comprise, for example, ultraviolet grade fused silica. A geometry of the lenses (e.g. a diameter and curvature of the lens surfaces) may depend on the diameter and divergence of the laser beam exiting the negative curvature hollow core fiber and/or the desired diameter of the laser beam entering the marking head.
Regarding step (d), designing the laser marking system such that the beam parameter product at the target is greater than the beam parameter product between the negative curvature hollow core fiber and the marking head may reduce radiative loses and/or improve a performance and efficiency of the laser marking system.
Regarding step (e), the relevant design parameters for designing the second coupling optics may be the same the relevant design parameters for the output coupling optics as described for step (c) above.
Regarding step (f), the relevant design parameters for coupling the laser to the negative curvature hollow core fiber may comprise the diameter of the laser beam output by the laser and/or the divergence of the laser beam output by the laser. The beam parameter product of the laser (i.e. the product of the laser beam radius and the laser beam divergence) may be less than that of all the following components of the laser marking system. For example, the beam parameter product of the laser may be about 3.5 or less to reduce radiative losses through the laser marking system.
The method may further comprise using forward and/or backward iteration to adjust the laser marking system.
Forward and/or backward iteration may involve considering factors such as the tolerances of the components of the laser marking system, the availability of materials, costs, and performance variances, and determining suitable compromises between these factors. If the design of the laser marking system begins with the marking head and progresses through the negative curvature hollow core fiber back to the laser, then if constraints on the laser design prevent meeting the desired design goal, it may be necessary to reverse the design process with the new constrained laser design. This process may be iterated to achieve an improved performance with the modified design parameters.
According to another aspect of the invention, there is provided a laser marking system designed in accordance with the method of the third aspect of the invention.
According to a fourth aspect of the invention, there is provided a method of manufacturing a laser marking system comprising providing a laser configured to generate a laser beam, providing a marking head configured to project the laser beam onto a target to be marked, and connecting the laser to the marking head using a negative curvature hollow core fiber configured to transmit the laser beam from the laser to the marking head.
According to a fifth aspect of the invention, there is provided an optical alignment system comprising a first adjustable optical element configured to receive a laser beam, a second adjustable optical element configured to receive the laser beam from the first adjustable optical element and direct the laser beam towards a target, a first detector configured to detect a position of the laser beam relative to the second adjustable optical element, and a second detector configured to detect a position of the laser beam relative to the target.
The first adjustable optical element may comprise a first rotatable reflector. The second adjustable optical element may comprise a second rotatable reflector.
The first detector may be located behind the second rotatable reflector and may be configured to detect a portion of the laser beam that transmits through the second detector.
The first detector may be located between the first rotatable reflector and the second rotatable reflector and may comprise an alignment aperture that is aligned with an optical axis of the optical alignment system. The alignment aperture may have a diameter that is substantially equal to a diameter of the laser beam.
The optical alignment system may comprise a beam sampler located between the first rotatable reflector and the second rotatable reflector. The beam sampler may be configured to direct a portion of the laser beam to the first detector.
The beam sampler may comprise a beam splitter.
The beam sampler may comprise a reflective element having an alignment aperture that is aligned with an optical axis of the laser marking system. The alignment aperture may have a diameter that is substantially equal to a diameter of the laser beam.
The detectors may be quadrant detectors.
The optical alignment system may be used in laser marking applications and/or could auto-alignment of articulated arms used in medical and material processing applications of lasers.
Features described above with reference to one aspect of the invention may be used in combination with other aspects of the invention. For example, features of an optical alignment system described above with reference to the first aspect of the invention may be combined with the optical alignment system of the fifth aspect of the invention, and vice versa.
The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labelled in every drawing. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:
Aspects and embodiments disclosed herein are not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Aspects and embodiments disclosed herein are capable of being practiced or of being carried out in various ways.
Aspects and embodiments disclosed herein include a marking head for projecting a radiation beam of a laser scanning or marking system and a laser scanning or marking system including such a system. Laser marking systems may be utilized in production lines for marking various types of articles. Laser marking systems may be utilized to imprint bar codes, unique identifying marks, expiration dates, or other information on items passing through a production line. In some implementations, carbon dioxide (CO2) gas lasers may be used in laser marking systems. Carbon dioxide lasers may produce beams of infrared radiation in four principal wavelength bands centering on 9.3, 9.6, 10.2, and 10.6 micrometers (μm). In other implementations, a laser configured to produce near infrared radiation may be used in laser marking systems. In alternative implementations, a laser configured to produce ultraviolet radiation may be used in laser marking systems. Lasers utilized in laser marking systems are typically operated at laser power levels in the tens of watts.
Laser scanning or marking systems are not limited to using CO2 lasers. In some implementations, fiber lasers or diode lasers may be used in laser marking systems. In some aspects and embodiments, optical scanners or markers may utilize lasers that operate in the ultraviolet, visible, or near infrared wavelengths or any other type of laser or optical illumination source. The use of visible radiation beams in laser scanner systems may be advantageous in that a user can see the laser beam where it illuminates an object being scanned so the user can adjust the position of the laser scanner or object being scanned so that the laser illuminates a desired portion of the object.
Embodiments of laser scanners disclosed herein may include a marking head comprising at least two mirror turning devices such as piezoelectric or magnet drives, direct current drives, stepper motors, servomotors, or galvanometers having mirrors attached. The mirrors used in embodiments of the laser marking system disclosed herein may be silver coated or gold-coated mirrors or any other suitably coated material. Windows and lenses used in embodiments of the laser scanner/marker disclosed herein may be, for example, germanium, zinc selenide, quartz, BK7 borosilicate glass, SUPRSIL provided by Heraeus, a German company, ultraviolet grade fused silica or any other suitable material.
The laser marking system 100 further comprises a marking head 130 configured to project the laser beam onto a target (not shown) to be marked by the laser marking system 100. The marking head 130 may comprise an electromagnetic radiation steering mechanism (not shown) configured to steer the laser beam exiting the marking head 130. The marking head 130 may further comprise a variable optical path length assembly (not shown) configured to adjust a focal plane of the laser marking system 100. The marking head 130 may further comprise focusing optics (not shown) and/or a collimator (not shown).
The marking head 130 may be substantially cylindrical. The marking head 130 may have a first dimension in a first direction of less than around 400 mm and a second dimension in a second direction perpendicular to the first direction of less than around 60 mm. The marking head 130 may have a third dimension in a third direction perpendicular to the first direction and the second direction of less than around 60 mm.
The marking head 130 may comprise a cooling system (not shown) for providing cooling to a component (e.g. actuators of the electromagnetic radiation steering mechanism and/or the variable optical path length assembly). The marking head 130 may further comprise a detector (not shown) configured to detect a presence of the target to be marked. The detector may comprise a camera. The laser marking system 100 may further comprise an encoder (not shown) for converting marking instructions to control signals for the marking head 130.
The laser marking system 100 may further comprise a user interface (not shown), e.g. a graphical user interface. The user interface may form part of a controller of the laser marking system (not shown). The user interface may comprise a screen for providing visual signals to a user and/or a speaker for providing audio signals to a user. The laser marking system 100 may comprise a transceiver for remote control of the laser marking system 100. The laser marking system 100 may comprise a connection (e.g. an Internet connection of an Ethernet connection) for integration with other devices (e.g. on a production line of which the laser marking system forms a part) via the Internet of Things.
The laser marking system 100 further comprises a negative curvature hollow core fiber 120 configured to transmit the laser beam from the laser 110 to the marking head 130. The negative curvature hollow core fiber 120 is described and shown in more detail with respect to
The laser marking system 100 of
A laser marking process using the laser marking system may include providing radiation to the negative curvature hollow core fiber 120 by coupling the laser 110 to the umbilical 140. The negative curvature hollow core fiber 120 may direct the laser beam to a collimator of the marking head 130. The collimator may condition the laser beam in a desired manner before directing the laser beam to other components of the marking head 130 such as the variable optical path length assembly (which may alter a focal plane of the laser marking system 100 in a desired manner) and/or the electromagnetic radiation steering mechanism (which may steer the laser beam exiting the marking head 130 in a desired manner).
Thicknesses of the capillary walls may be selected in accordance with the following equation:
where t is the capillary wall thickness, λ is the wavelength of radiation that the negative curvature hollow core fiber is configured to transmit, n1 is the refractive index of the capillary material, and m is a positive integer. Capillary walls having thickness that satisfy the equation may provide anti-resonant effects that reduce the optical coupling of the laser beam between the core 215 and the cladding 210, thereby reducing radiative losses within the negative curvature hollow core fiber 120. Multiple capillary wall thicknesses are possible for each wavelength of light as determined by the value of the positive integer m. The thicknesses of the capillary walls may be within the inclusive range of about −5% to about +5% of the calculated value of t.
The thicknesses of the capillary walls may be selected at least partially based on a refractive index of the capillaries and/or a wavelength of radiation that is to be transmitted by the negative curvature hollow core fiber and/or a geometry of the anti-resonant structure (e.g. number of capillaries, diameters of the capillaries, spacing of capillaries, shapes of capillaries). The thicknesses of the capillary walls may be about 0.3 μm or more for transmitting infrared radiation (e.g. produced by a CO2 laser). The thicknesses of the capillary walls may be about 15 μm or less for transmitting infrared radiation (e.g. produced by a CO2 laser). The thicknesses of the capillary walls may be about 0.3 μm or more for transmitting near infrared radiation. The thicknesses of the capillary walls may be about 3 μm or less for transmitting near infrared radiation. The thicknesses of the capillary walls may be about 100 nm or more for transmitting ultraviolet radiation. The thicknesses of the capillary walls may be about 600 nm or less for transmitting ultraviolet radiation.
The negative curvature hollow core fiber 120 may be an anti-resonant negative curvature hollow core fiber. That is, the cladding 210 of the negative curvature hollow core fiber 120 may comprise features (e.g. the capillaries 220) configured to reduce or inhibit optical coupling between a core of the negative curvature hollow core fiber 120 and the cladding 210, resulting in reduced radiative losses at desired wavelengths (e.g. infrared, near infrared and/or ultraviolet wavelengths).
The core diameter 230 of the negative curvature hollow core fiber 120 may at least partially depend on a wavelength of radiation that is to be transmitted by the negative curvature hollow core fiber 120. For example, the negative curvature hollow core fiber 120 may have a core diameter 230 of between about 150 μm and about 300 μm for infrared laser marking applications (e.g. wavelengths having a range of between about 8 μm and about 11 μm). As another example, the negative curvature hollow core fiber 120 may have a core diameter 230 of between about 20 μm and about 100 μm for near infrared laser marking applications (e.g. wavelengths having a range of between about 0.78 μm and about 3 μm). As a further example, the negative curvature hollow core fiber 120 may have a core diameter 230 of between about 10 μm and about 20 μm for ultraviolet laser marking applications (e.g. wavelengths having a range of between about 100 nm and about 400 nm).
The core diameter 230 may be selected at least partially based on a refractive index of the capillaries 220 and/or a wavelength of radiation that is to be transmitted by the negative curvature hollow core fiber 120 and/or a geometry of the anti-resonant structure (e.g. number of capillaries, diameter of capillaries, spacing of capillaries, shapes of capillaries). For example, in the case of a ring of generally round or generally circular capillaries, the core diameter 230 of the negative curvature hollow core fiber 120 may be selected in at least partial dependence on the following equation:
where Dcore is the core diameter of the negative curvature hollow core fiber, dtube is the diameter of the capillaries, t is the capillary wall thicknesses, g is the gap distance between adjacent capillaries, and N is the number of capillaries. This equation may be used to estimate the core diameter 230 of other capillary structures and geometries such as, for example, the generally arched capillaries of
Aspects of the laser marking system 100 may be designed and/or operated in at least partial dependence on the core diameter 230 of the negative curvature hollow core fiber 120 such that acceptable coupling occurs between the negative curvature hollow core fiber 120 and the laser 110 and/or marking head 130. In general, selecting a cross-sectional radius of the laser beam for improved coupling into the negative curvature hollow core fiber 120 may at least partially depend on the wavelengths of radiation within the laser beam and/or the core diameter 230.
In an example embodiment involving transmitting infrared radiation produced by a CO2 laser, the negative curvature hollow core fiber 120 may have a core diameter 230 of about 300 μm or less. In this example, the laser beam may be controlled by optics in the laser 110 to have a cross-sectional radius of about 91 μm or more when entering the negative curvature hollow core fiber 120 from the laser 130. The laser beam may have a cross-sectional radius of about 100 μm or less when entering the negative curvature hollow core fiber 120 from the laser.
The laser marking system may comprise one or more coupling lenses for optically coupling the negative curvature hollow core fiber to one or more other optical elements. An optimum ratio of a focal length to a diameter of an entrance pupil (i.e. an optimum F #) of the coupling lens for coupling into the negative curvature hollow core fiber may be selected in at least partial dependence on the following equation:
where Dcore is the core diameter of the negative curvature hollow core fiber, and A is the wavelength of radiation that the negative curvature hollow core fiber is configured to transmit. In practice, if the F # of the coupling lens is less than F #Opt then more optical power may be coupled into higher order modes within the negative curvature hollow core fiber and thereby be attenuated. In practice, if the F # of the coupling lens is less than F #Opt then the optical power may be clipped at an entrance to the negative curvature hollow core fiber, which may in turn result in heating and possible thermal damage caused to the entrance of the negative curvature hollow core fiber. As such, the F # of the coupling lens may preferably be within the inclusive range of −5% and 2% of F #Opt.
The F # of the coupling lens may be selected in at least partial dependence on properties of the laser beam (e.g. a wavelength of the laser beam) that is to be transmitted and/or a geometry of the negative curvature hollow core fiber itself. A ratio of a focal length of a coupling lens located between the laser 110 and the negative curvature hollow core fiber 120 to a diameter of an entrance pupil of the negative curvature hollow core fiber 120 may at least partially depend on the core diameter 230.
For example, when transmitting an infrared laser beam produced by a CO2 laser, the ratio of a focal length of the coupling lens located between the laser 110 and the negative curvature hollow core fiber 120 to a diameter of an entrance pupil of the negative curvature hollow core fiber 120 may be about 15.4 or more. The ratio of a focal length of the coupling lens located between the laser 110 and the negative curvature hollow core fiber 120 to a diameter of an entrance pupil of the negative curvature hollow core fiber 120 may be about 17.0 or less.
A cross-sectional radius of the laser beam when entering the negative curvature hollow core fiber may be selected in at least partial dependence on properties of the laser beam (e.g. a wavelength and/or power of the laser beam) that is to be transmitted and/or a geometry of the negative curvature hollow core fiber itself. For example, for transmitting infrared light generated by a CO2 laser, and referring again to
The negative curvature hollow core fiber 120 may comprise silica, e.g. fused silica. Silica advantageously transmits ultraviolet radiation with relatively low radiative losses. The negative curvature hollow core fiber 120 may comprise chalcogenide glass. Chalcogenide glass may be used to transmit infrared radiation and/or near infrared radiation. The chalcogenide glass may comprise one or more of the following materials: As30Se50Te20 (not suitable for near infrared transmission); As2S3; As2Se3; Ge15As25Se40Te20 (not suitable for near infrared transmission); and, As40S30Se30. The chalcogenide glass may comprise other combinations and/or dopants such as rare earth elements such as, for example, La, Tb, Tl, Ge, Sb, As, Ga. Chalcogenide glass advantageously transmits infrared radiation with relatively low radiative losses. A thickness and spacing between the capillaries may be selected to reduce radiative losses at desired wavelengths of radiation. The desired wavelengths of radiation may comprise infrared radiation produced by a CO2 laser, near infrared radiation produced by a solid-state laser, e.g. comprising a Nd:YAG (neodymium doped yttrium aluminum garnet—a YAG laser) crystal or a Nd:VO4 (neodymium doped yttrium orthovanadate—a vanadate laser) crystal, and/or ultraviolet radiation produced by a solid-state laser comprising a non-linear optical element, e.g. a non-linear crystal such as KTP (potassium titanyl phosphate), KTA (potassium titanyl arsenate) or BBO (beta barium borate).
An end (not shown) of the negative curvature hollow core fiber 120 may be tapered to improve a coupling efficiency of the negative curvature hollow core fiber 120 with the laser 110 and/or the marking head 130, thereby improving an efficiency of the laser marking system 100.
In the example of
In the example of
The optical alignment system further comprises a second beam sampler 460 located between the second rotatable reflector 420 and the input of the core of the negative curvature hollow core fiber. The second beam sampler 460 is configured to direct a portion of the laser beam to the second detector 440. The second beam sampler 460 may comprise a beam splitter, such as an optical flat having one side coated to reflect a small percentage (e.g. <1%) of the laser beam to the second detector 440. The other side of the optical flat may comprise an anti-reflection coating that allows the remaining percentage of the laser beam to transmit through the second beam sampler 460 towards the input of the core of the negative curvature hollow core fiber. The refraction of the laser beam caused by transmitting through the beam splitter may be compensated for by positioning the input of the core of the negative curvature hollow core fiber accordingly and/or by placing a second optical flat of substantially the same thickness at a complimentary angle in the laser beam path after the second beam sampler 460.
The optical alignment system further comprises a controller 910 configured to receive signals from the first and second detectors 430, 440 and use the signals to control rotational positions of the first and second rotatable reflectors 415, 425.
The portion of the laser beam 900 that does not transmit through the second rotatable reflector 425 is reflected by the second rotatable reflector 425 towards a coupling lens 500. The coupling lens 500 focuses the laser beam 900 towards a beam sampler 700. In the example of
The portion of the laser beam 900 that transmits through the beam sampler 700 is incident on a first protective cap 915 comprising a first protective aperture 920. The first protective cap 915 is located proximate an input of the core of the negative curvature hollow core fiber (not shown). The laser marking system may comprise a second protective cap (not shown) comprising a second protective aperture (not shown). The second protective cap may be located proximate an output of the core of the negative curvature hollow core fiber. The first and second protective apertures 920 have a diameter that is substantially equal to a core diameter of the negative curvature hollow core fiber. The first and second protective apertures 920 are configured to protect the cladding of the negative curvature hollow core fiber from damage caused by the focused laser beam 900 and/or backscattered laser radiation that may otherwise re-enter the laser marking system. That is, radiation that is not aligned with the core of the negative curvature hollow core fiber is prevented from damaging the cladding and/or capillaries of the fiber by being blocked by the first protective cap 915. The first and/or second protective apertures 920 may each comprise a protective pin-hole having the same diameter as the core of the negative curvature hollow core fiber and may be placed at the input and output ends of the negative curvature hollow core fiber. The pin-holes may be part of the negative curvature hollow core fiber mount or a separate device. The first and/or second protective caps 915 may be replaceable and may be considered to be sacrificial devices to protect the more expensive negative curvature hollow core fiber.
A second step S2 of the method includes designing optical components of the marking head in at least partial dependence on the first step S1 and determining a beam parameter product of the laser beam at the target. The beam parameter product of the laser beam at the target may be defined as the product of the radius of the laser beam and the divergence of the laser beam at the target. The radius of the laser beam and the divergence of the laser beam at the target may be determined using the following equations:
where ωo is the radius of the laser beam, f is the focal length, D is the diameter of the laser beam at a focusing lens, and θ is the half-angle divergence of the beam in mrad. The focal length of the focusing lens may be approximately the same as the distance between the marking head and the target.
A third step S3 of the method includes designing first coupling optics between the negative curvature hollow core fiber and the marking head in at least partial dependence on the second step S2. The first coupling optics may be configured to convert a divergent laser beam exiting the negative curvature hollow core fiber into a collimated laser beam entering the marking head. The first coupling optics may comprise one or more lenses of a material having a relatively high transmissivity (e.g. coated lenses for a transmissivity of about 99% or more) at the desired wavelength (e.g. infrared, near infrared or ultraviolet wavelengths). Alternatively, the first coupling optics may comprise one or more mirrors having a relatively high reflectivity (e.g. a reflectivity of about 99% or more). The lenses used in the first coupling optics may comprise one or more materials such as zinc selenide, zinc sulphide, germanium, gallium arsenide or other materials that are sufficiently transparent at infrared wavelengths (e.g. wavelengths of radiation generated by a CO2 laser). For near infrared transmission, the lenses used in the first coupling optic may comprise one or materials such as fused silica, a crown glass (e.g. borosilicate or BK7) and/or a synthetic fused silica such as SUPRSIL provided by Heraeus, a German company. For ultraviolet transmission, the lenses used in the first coupling optic may comprise, for example, ultraviolet grade fused silica. A geometry of the lenses (e.g. a diameter and curvature of the lens surfaces) used in the first coupling optics may at least partially depend on the diameter and/or divergence of the laser beam at the target and/or the optical components of the marking head with which the laser beam interacts before reaching the target.
A fourth step S4 of the method includes selecting a desired beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head and designing the negative curvature hollow core fiber in at least partial dependence on the beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head. Designing the laser marking system such that the beam parameter product at the target is greater than the beam parameter product between the negative curvature hollow core fiber and the marking head may reduce radiative loses and/or improve a performance and efficiency of the laser marking system.
The relevant design parameters for designing the negative curvature hollow core fiber may comprise the following:
A fifth step S5 of the method includes designing second coupling optics between the laser and the negative curvature hollow core fiber in at least partial dependence on the fourth step S4. The relevant design parameters for designing the second coupling optics may be the same the relevant design parameters for the output coupling optics as described for the third step S3. An additional constraint may be that the minimal coupling loss occurs when the laser beam spot size between the laser and the negative curvature hollow core fiber conforms to the following equation:
where ωo is the radius of the laser beam between the laser and the negative curvature hollow core fiber and d is the diameter of the core of the negative curvature hollow core fiber.
A sixth step S6 of the method includes designing the laser in at least partial dependence on the beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head. The relevant design parameters for coupling the laser to the negative curvature hollow core fiber may comprise the diameter of the laser beam output by the laser and/or the divergence of the laser beam output by the laser. The beam parameter product of the laser (i.e. the product of the laser beam radius and the laser beam divergence) may be less than that of all the following components of the laser marking system. For example, the beam parameter product of the laser may be about 3.5 or less to reduce radiative losses through the laser marking system.
The method may further comprise a seventh step (not shown) including using forward and/or backward iteration to adjust the laser marking system. Forward and/or backward iteration may involve considering factors such as the tolerances of the components of the laser marking system, the availability of materials, costs, and performance variances, and determining suitable compromises between these factors. If the design of the laser marking system begins with the marking head and progresses through the negative curvature hollow core fiber back to the laser, then if constraints on the laser design prevent meeting the desired design goal, it may be necessary to reverse the design process with the new constrained laser design. This process may be iterated to achieve an improved performance with the modified design parameters.
The optical components of the laser marking system (e.g. first and second coupling optics and/or the optical components of the marking head), like any fabricated part, are manufactured within design tolerances. In general, the tighter the tolerance, the costlier the component. A typical optical component may be made to standard manufacturing tolerances on design parameters such as centration, diameter, surface quality, flatness, parallelism, etc. In most laser marking applications, the standard tolerances are sufficient and no further compensation is required. The same is true for the mechanical components holding the optical components in the system. Parts can be machined to very tight tolerance at a cost. However, in the case of trying to couple a laser beam having a 200 μm spot size into a 300 μm diameter core of a negative curvature hollow core fiber, the stack-up of tolerance errors may become a problem. These are errors that may negatively affect coupling efficiency and may not be directly related to the laser marking process except with regards to a reduction in radiative power delivered to the target. The impact of such errors may be reduced by “hard” and “soft” alignment techniques.
Hard alignment techniques comprise processes and tools used during the manufacturing process to ensure satisfaction of system specifications. For example, a laser in a typical marking system is mounted on a base plate that has position adjusting screws. The laser and the base plate are put on a specially designed tooling to permit adjustment of the screws to position the laser beam from the output of the laser to a particular point on a reference target. In this way, when the laser is put in a laser marking system and attached to a marking head, the laser beam is automatically aligned to the optics in the marking head and no further adjustment is required. Likewise, a lens may be positioned in its mount using set-screws and tooling to compensate for centration errors. These are all means of compensation that are done during the manufacturing process and are fixed in place when completed.
Soft alignment comprises techniques that may be implemented “off-line” by service personnel, customers, or controlled dynamically. This may include using the optical alignment system (e.g. the first and second rotatable reflectors) to adjust a position and/or angle of the laser beam. The first rotatable reflector may keep the laser beam positioned on a desired point (the point where the design optical axis intersects a surface of the second rotatable reflector) on the second rotatable reflector. The second rotatable reflector may adjust a position and/or angle of the laser beam to keep the laser beam aligned with the optical axis of the laser marking system. In this way, the two rotatable reflectors compensate for tolerance errors of all optical components of the laser marking system upstream of the first and second rotatable reflectors.
For example, thermal movement due to expansion and contraction of materials and vibration due to internal cooling devices and external sources such as other equipment may cause unwanted movement of the optical components that have not been compensated for by the hard and soft alignment techniques. Hard alignment techniques may be used to compensate, such as mounting optical components using vibration isolation materials, expansion coefficients of materials used may be matched with one another, etc. Soft alignment techniques may be used to compensate, such as controlling the optical alignment system (e.g. the first and second rotatable reflectors) using motor driven adjustment screws on the rotatable reflectors and feedback from the first and/or second detectors.
Having thus described several aspects of at least one implementation, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the disclosure. The acts of methods disclosed herein may be performed in alternate orders than illustrated, and one or more acts may be omitted, substituted, or added. One or more features of any one example disclosed herein may be combined with or substituted for one or more features of any other example disclosed. Accordingly, the foregoing description and drawings are by way of example only.
The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, the term “plurality” refers to two or more items or components. As used herein, dimensions which are described as being “substantially” similar may be considered to be within about 25% of one another. The terms “comprising,” “including,” “carrying,” “having,” “containing,” and “involving,” whether in the written description or the claims and the like, are open-ended terms, i.e., to mean “including but not limited to.” Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. Only the transitional phrases “consisting of” and “consisting essentially of,” are closed or semi-closed transitional phrases, respectively, with respect to the claims. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.
The laser marking system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and/or other types of optical components, or any combination thereof, for directing, shaping, and/or controlling electromagnetic radiation.
While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/052435 | 2/2/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62969273 | Feb 2020 | US |
