High-speed laser process for marking articles

Abstract

A process for laser marking an article having predetermined features marked on the wall, the features being user readable, machine readable, or both. Also, a method of making an article marked by laser marking.

Description

Technical Field

[0001] The present invention relates to a process for laser marking an article and a method for marking such an article.

Background Art

[0002] Short pulse laser decoration utilizes energy from nano, pico, and femto short pulse lasers over a variety of wavelengths and energies to mark decorative patterns on articles such as products and / or packages. Any and all other decoration techniques that can be applied to products and / or packages (i.e., labels, screen printing, digital printing, etc.) can be used in conjunction with laser marking to achieve various decorative and functional effects. The laser technology used for short pulse laser marking is, importantly, a high throughput technology that uses a fixed laser source where the laser beam is directed towards the product or package to be marked by electronically / mechanically controlled mirrors (i.e., a “galvo” set) and lenses (i.e., F theta and similar lenses). These mirrors and lenses steer the laser beam across the surface of the article (this steering is also called “scanning”) so that the laser can impart an image such as a digital image (from a computer file such as a PDF file) onto the surface of the package or product. This approach has the further advantage over other decoration techniques in that the use of digital images enables customization and personalization of the decoration.

[0003] There is considerable interest in the possibilities presented by laser-marked items, such as those using short-pulse laser marking. For example, replacing adhesive labels on polymer containers is not only economically beneficial but also ecologically beneficial. Removing adhesive labels from polymer containers reduces the total weight of the packaging material, which in turn reduces the amount of petroleum-derived material per package, thus reducing the weight of the packaging and thus requiring less fuel for transportation. Furthermore, the absence of adhesive labels makes it easier to recycle polymer containers, as adhesive labels often need to be removed before recycling due to potential impurities that may be introduced into the recycling process.

[0004] Laser marking of small items (i.e., golf balls, etc.) and / or small areas on items (i.e., date codes, address labels on finished packages) is known. Lasers are improving, and newer lasers have a variety of energies and wavelengths, but these marking processes can still be slow and expensive. Furthermore, they lack the ability to mark small characters requiring high precision, such as small font text consisting of alphanumeric characters (i.e., instructions for use, ingredient lists). For example, date codes are marked on packages by relatively simple lasers, but these use single lines of large, inaccurate, or unevenly spaced spots (ranging from 250 μm to over 800 μm in diameter) and relatively large font characters. This is equivalent to printing stick figures that are suitable for some purposes but are difficult for consumers to read and almost impossible for machines to read. More specifically, large, inaccurate, or unevenly spaced single lines cannot currently be used to mark high-precision small font text or machine-readable graphics, such as UPC or QR codes, on articles.

[0005] Current state-of-the-art laser marking processes include "raster" and "vector" marking processes, which are either high-speed but low-precision and-resolution, or low-speed but high-precision and-resolution. A combination of high speed and high precision does not exist in prior art. This issue is particularly pronounced when marking large areas on an article, such as when using laser marking as a complete replacement for other decorative techniques, where all text and / or graphics (many of which are required for regulatory purposes) to be provided on at least one face of the article are provided via laser marking.

[0006] The raster laser marking process places individual laser marks in a grid, and the image is marked row by row, dot by dot by the laser. Each pulse is "gate-controlled" so that the pulse is emitted only to dark pixels in the image and not to bright pixels (or vice versa). Each pulse is individually gate-controlled, and the pulse energy of each pulse can be varied to produce a grayscale. State-of-the-art raster marking processes are virtually limited to lasers with a repetition rate of about 100 kHz, considering the practical limit of the update rate of about 10 uS when signaling the on / off function of the laser (i.e., "gating"), and can only be made faster by increasing the pulse interval, which may come at the expense of fine detail such as that required to mark small font text and graphics.

[0007] State-of-the-art vector marking processes can run at speeds exceeding 100 kHz, as pulses are typically gated open while the laser beam is "directed" (by mirrors) to the shape of the vector line to be marked. Vector-marked items, including text, are often recognizable because the marked line is typically one pulse width (unless filled in), and the pulses converge near corners where the surface velocity of the laser beam slows down as it bends the corner. However, it has been found that the precision of mark placement by vector marking is compromised when the surface velocity of the laser beam is very high.

[0008] Currently, relatively high-speed laser marking can be achieved using polygon scanners (for example, the High Throughput Raster Processing Polygon scanner system from Nexgcan Technology (Evergem, Belgium)), which can be optimized for high speed and high precision. Polygon scanner systems use rotating polygon mirrors for column scanning. These scanners are typically used for full-surface processing of regular patterns. Specifically, the field of view is typically square, which is relatively large depending on the printing standard, and repeating patterns are marked repeatedly on subsequent items. The square field of view configuration of these scanners is not suitable for accurate marking of small letters, alphanumeric characters, logos, pictures, etc.

[0009] Therefore, there remains room for the need for faster, more economical, and more accurate laser marking. Both the hardware and software controlling the raising device can be improved, as can the methods for using these improved raising devices. Furthermore, the placement of laser marks on articles can be improved to provide both precision and speed.

[0010] Therefore, it is desirable to provide, along with an improved raising device, software to operate the raising device, and a process for marking articles at high speed and with high precision (such as directly reproducing label information, aesthetic features, and functional features). These improvements should make the process fast, simple, cost-effective, and scalable to mass production, and the resulting articles should have consumer-readable and machine-readable features that can replace labels and adhesives, among other advantages. [Overview of the Initiative] [Means for solving the problem]

[0011] The present invention provides solutions to one or more of the shortcomings of the prior art, as well as other advantages. This specification, claims, and drawings describe various features and embodiments of the present invention, including a method for marking an article with a pulsed laser, the process comprising: providing a pulsed laser configured to produce a laser beam that is pulsed; providing an article including an article surface; and using the laser beam to form a plurality of marks on the article surface in a grid pattern by at least one of foaming, ablation, etching, reduction, oxidation, and carbonization. The process further includes moving a laser beam along a first row at a constant velocity while interacting with the surface of an article, forming a plurality of marks, wherein the constant velocity is greater than about 8 m / s, preferably greater than about 10 m / s, more preferably greater than about 15 m / s, most preferably greater than about 18 m / s, or greater than about 22 m / s, or greater than about 32 m / s, or greater than about 45 m / s, or greater than about 60 m / s, or greater than about 75 m / s, or greater than about 90 m / s.

[0012] The method of this embodiment may further include the step of moving a laser beam in bidirectional motion such that the laser beam moves across a first row in a first direction and across a second row in a second direction, wherein the first direction is opposite to the second direction, and preferably the first and second rows are adjacent. The grid pattern may have a plurality of positions positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of positions in the plurality along any one of the two or more rows being separated by an X distance, and each adjacent pair in the two or more rows being separated by a Y distance, where the Y distance is different from the X distance. Each of the plurality of positions may include either a mark or a void (absence of a mark in the grid position).

[0013] In another embodiment, the laser beam moves across each position in the grid pattern, and the laser beam moves at a constant velocity as consecutive marks are formed at adjacent positions within the same row. The laser beam can be accelerated as it moves across consecutive positions that have voids. Furthermore, the laser beam has a reversal deceleration / acceleration shape as the laser beam moves from a first row to a second row.

[0014] A method is further provided in which the laser beam has a repetition rate greater than about 100 kHz, preferably greater than about 200 kHz, more preferably greater than about 500 kHz, and most preferably greater than about 1000 kHz. Furthermore, the laser beam has a pulse energy of about 10 μJ to about 1000 μJ, preferably about 20 μJ to about 800 μJ, more preferably about 30 μJ to about 600 μJ, and even more preferably about 40 μJ to about 500 μJ. Furthermore, the laser beam has a focal length of about 100 mm to about 1200 mm, preferably about 200 mm to about 380 mm, and the laser beam has a wavelength of about 300 nm to about 1100 nm. The laser beam may also have a pulse duration of less than about 100 nanoseconds, preferably less than about 50 nanoseconds, more preferably less than about 30 nanoseconds, and most preferably less than about 1.5 nanoseconds.

[0015] In another embodiment of the present invention, a method is provided for marking an article with a pulsed laser, the process comprising: providing a pulsed laser configured to produce a laser beam containing pulses; providing an article having an article surface; and using the laser beam to form a plurality of marks on the article surface in a grid pattern by at least one of foaming, ablation, etching, reduction, oxidation, and carbonization. The laser beam is moved across each of the positions in the grid pattern, the laser beam moves at a constant velocity as consecutive marks are formed at adjacent positions in the same row, and the laser beam accelerates as it moves across consecutive positions having at least three voids.

[0016] In yet another embodiment of the present invention, there exists a process for marking an article with a pulsed laser, the process comprising: providing a laser source configured to emit a pulsed laser beam; providing a first galvanometer ("Garbo") set and a second Garbo set configured to redirect the pulsed laser beam, each Garbo set comprising a mirror and a Garbo; providing an article having an article surface; rotating a first mirror with the first Garbo at a first angular velocity, the first angular velocity being greater than about 40 rad / s, while marking the article surface; and rotating a second mirror with the second Garbo at a second angular velocity, the second angular velocity being greater than about 40 rad / s, preferably greater than about 50 rad / s, more preferably greater than about 70 rad / s, and most preferably greater than about 100 rad / s, while marking the article surface. A first Garbo set can control the motion of the laser beam in the Y direction of the grid, and a second Garbo set can control the motion of the laser beam in the X direction. The ratio of the angular velocity of the second Garbo to the angular velocity of the first Garbo can be 1:1, 1.5:1, or 2:1. There are multiple marks formed by at least one of foaming, ablation, etching, reduction, oxidation, and carbonization of the surface of the article with the laser beam. In this embodiment, the first mirror and the second mirror may each have a mass of less than about 150 g. Furthermore, the first mirror has a first mass and the second mirror has a second mass, with the first mass being smaller than the second mass, and the first mirror controls the movement of the laser beam in the X direction. The ratio of the mass of the first mirror to the mass of the second mirror can be 1:1, 1.5:1, or 2:1.

[0017] The method comprises the steps of a laser beam interacting with the surface of an article to form a plurality of marks in a grid pattern, the grid pattern comprising a plurality of positions positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of positions along any of the two or more rows being separated by an X distance, and each adjacent pair in the two or more rows being separated by a Y distance, where the Y distance is different from the X distance. The laser beam can be moved at a constant velocity across each position in the grid pattern when consecutive marks or voids are formed at adjacent positions in the same row, and the laser beam can be accelerated as it moves across consecutive positions having voids, the constant velocity being greater than about 8 m / s, preferably greater than about 10 m / s, more preferably greater than about 15 m / s, most preferably greater than about 18 m / s, or greater than about 22 m / s, or greater than about 32 m / s, or greater than about 45 m / s, or greater than about 60 m / s, or greater than about 75 m / s, or greater than about 90 m / s.

[0018] The present invention offers numerous advantages over the prior art, including increased marking speed and accuracy. Laser marking can replace the need for conventional labels, for example, by being used to produce consumer-readable alphanumeric characters (including small font characters) forming text, paragraphs, etc., as well as other methods of visual communication on articles (e.g., graphics). Specifically, the process and articles of the present invention can provide laser-marked ingredient lists, usage instructions, machine-readable graphics such as UPC or QR codes, etc., in a fast and cost-effective manner without the use of labels and adhesives. This reduces costs, is environmentally friendly (fewer unnecessary stickers on packaging), and allows for instantaneous changes to the message communicated to consumers. For example, if an ingredient is changed in a formulation, the change can be made via a computer command to the laser device, and a new ingredient label can be marked on the article immediately. A new label is not required. [Brief explanation of the drawing]

[0019] [Figure 1] An article according to the present invention in which alphanumeric characters are marked in a checkerboard pattern. [Figure 2] A schematic diagram of a raising device according to the present disclosure. [Figure 3] A checkerboard according to the present disclosure, in which the positions of adjacent parallel columns are stacked. [Figure 4] A checkerboard according to the present disclosure, in which the positions in adjacent parallel columns are offset. [Figure 5] Alphanumeric characters marked in a checkerboard pattern according to the present invention. [Figure 6A] Alphanumeric characters in a checkerboard pattern marked in accordance with the present invention. [Figure 6B] Alphanumeric characters in a checkerboard pattern marked according to prior art processes. [Figure 7] An industry standard UPC code printed by the laser and process of the present invention. [Figure 8] A standardized rectangular pattern laser printed by a prior art vector laser process is shown compared to the same pattern laser printed in accordance with the present invention. [Figure 9] An exemplary checkerboard of a standardized rectangle according to the present invention.

Mode for Carrying Out the Invention

[0020] Article As used herein, “article” refers to individual objects such as objects for consumer use, including containers suitable for containing materials or compositions. Articles can be containers, and non-limiting examples include bottles, tubes, films, laminates, bags, wraps, drums, jars, cups, caps, etc. Compositions contained in such containers may be any of a variety of compositions, including, but not limited to, detergents (e.g., laundry detergents, fabric softeners, dishwashers, skincare products, and haircare products), beverages, powders, paper (e.g., tissues, wipes), diapers, beauty care compositions (e.g., cosmetics, lotions), pharmaceuticals, oral care products (e.g., toothpaste, mouthwash), etc. Containers may be used to store, transport, and / or dispense the materials and / or compositions contained therein. Articles can be made from any of a variety of common materials, including: PET, PETG, HDPE, PP, PVOH, LDPE, LLDPE, steel, glass, aluminum, cellulose, pulp, paper, etc.

[0021] Figure 1 shows an article 10 having a predetermined feature 17 laser-marked as a grid 16. The predetermined feature 17 can be consumer-readable, machine-readable, or both. The predetermined feature 17 can be, for example, alphanumeric characters, a company logo, a drawing, artwork, a UPC, or a QR code. In this example, the marked position 12 constitutes the alphanumeric character 14, which in this case is the digit 2, "2". The unmarked positions 11 in the grid 16 are shown for illustrative purposes only and do not appear on the final marked article 10. The article 10 is shown as a container and has an opening 11 and a neck 13 that provides access to an internal space 15.

[0022] Articles according to the present invention may be formed from a single thermoplastic material or resin, or, in one or more embodiments, from two or more materials that are different from each other. Two or more materials may constitute layers within the article. If the article has different layers, the materials constituting each layer may be the same as or different from any other layer. For example, articles may be made of polyethylene terephthalate (PET), polyethylene terephthalate glycol (PETG), polystyrene (PS), polycarbonate (PC), polyvinyl chloride (PVC), polyethylene naphthalate (PEN), polycyclohexylenedimethylene terephthalate (PCT), glycol-modified PCT copolymer (PCTG), copolyester of cyclohexanedimethanol and terephthalic acid (PCTA), polybutylene terephthalate (PBCT), acrylonitrile styrene (AS), styrene butadiene copolymer (SBC), or polyolefins, such as low-density polyethylene. The article may include one or more layers of thermoplastic resin selected from the group consisting of polyethylene (LDPE), linear low-density polyethylene (LLPDE), high-density polyethylene (HDPE), propylene (PP), and combinations thereof. The article may also include cellulosic materials such as pulp or paper.Cellulosic materials may be included together with an additional second material, the additional second material may be a second cellulosic material, or it may include a thermoplastic material or a resin containing a water / solvent-based coating.

[0023] For example, recycled thermoplastics and / or cellulosic materials such as polyethylene terephthalate (PCRPET), high-density polyethylene (PCRHDPE), low-density polyethylene (PCRLDPE), polyethylene terephthalate (PIRPET), high-density polyethylene (PIRHDPE), and low-density polyethylene (PIRLDPE), as well as post-consumer recycled (PCR) materials, post-industrial recycled (PIR) materials, and regrinded materials may also be used.

[0024] Thermoplastic materials may include monomers derived from renewable resources and / or monomers derived from non-renewable resources (e.g., petroleum) or combinations thereof. For example, thermoplastic resins may include polymers made entirely from bio-derived monomers, or polymers made partly from bio-derived monomers and partly from petroleum-derived monomers.

[0025] Pigments, colorants, and laser-absorbing additives may be added to the materials of the articles of the present invention. A suitable selection of laser wavelengths in combination with pigments / colorants / additives may provide suitable marking of articles. If the contrast or speed of the marking is insufficient, these pigments / colorants / additives can promote the absorption of laser energy and thereby function as laser-absorbing additives. Laser-absorbing additives known to those skilled in the art can promote the formation of laser marks, making laser markings clearer, easier to read by users and machines, and increasing the rate at which articles can be marked. These laser-absorbing additives generally absorb laser energy specific to the laser wavelength and subsequently initiate a color change into the surrounding matrix (via local heating causing carbonization, foaming, etc.), or the laser-absorbing additive itself undergoes a chemical or physical change. Titanium dioxide and carbon black are pigments commonly used to opaque containers to protect contents from the effects of light and can also function as laser-absorbing additives depending on the wavelength of the laser used. Additional examples of laser absorption additives include titanium dioxide (TiO2), antimony tin oxide (ATO), ATO-coated substrates such as mica, Sb2O3, indium tin oxide, tin oxide, iron oxide, zinc oxide, carbon black, graphite carbon, bismuth oxide, mixed metal oxides, metal nitrides, doped metal nitrides, metal carbides, metal borides, tungsten oxide, doped tungsten oxide, pearlescent pigments, zero-valent metals such as aluminum, and mixtures thereof. Examples of laser marking laser absorption additives are commercially available from Merck KGaA in Darmstadt, Germany, under the trade name "Iriotec®".

[0026] Laser and Raising Equipment To mark articles according to the present invention, pulsed lasers, such as short-pulse lasers, may be used. Lasers for use in the present invention are commercially available and include nanosecond, picosecond, and femtosecond lasers. These short-pulse lasers can emit pulses applied at high energy density and high repetition rates, and the high energy and high repetition rate are important to enable laser marking of articles at high speed. The laser mark itself includes marks made on articles such as products or packages by oxidation, reduction, ablation, etching, foaming, and carbonization.

[0027] Any suitable laser can be used to mark article 10. Figure 2 shows an embodiment of a lathing apparatus 200 equipped with a laser 20 useful for marking articles according to the present invention. The lathing apparatus 200 includes a laser 20 which may be any laser capable of generating sufficient energy to mark an article, such as a UV laser having an output in the range of 1W to 60W and a laser wavelength of 355 nanometers, or an IR marking laser having an output in the range of 1W to 300W, and even 500W, and a laser wavelength of 1064 nanometers. Such lasers are available from various suppliers, including the IPG ULPN-355-10-1-3-M marker or YLPN-1-1x350-50-3M MOPA module available from IPG Photonics (Oxford, MA, United States). Other forms and types of lasers are also possible, and different output ranges and settings may be used. The raising device may include an optical system that can be used, if necessary, to direct the laser beam and / or modify the laser beam by changing the energy density and / or spot size of the laser beam 28.

[0028] Frequency, or repetition rate, measured in Hz, is the number of laser pulses a single laser can deliver per second. For example, a 1 MHz laser delivers 1,000,000 pulses / second, and a laser with a repetition rate of 100 kHz delivers 100,000 pulses / second. The repetition rate can be important for processing certain lazing jobs (i.e., high-speed laser marking) in a short amount of time. More pulses available per unit time correlate almost linearly (inversely) to the time required to mark a given column for a particular job.

[0029] Pulse energy is the amount of energy contained in a single laser pulse and is typically measured in μJ or mJ. Typically, pulse energy is in the range of 5 μJ to 2000 μJ (2 mJ), preferably 7 μJ to 1000 μJ, and more preferably 10 μJ to 300 μJ. The average output of the laser is then given as pulse energy × repetition rate. Average power = pulse energy (J) * Repeat rate (Hz or 1 / second).

[0030] The peak power is equal to the pulse energy divided by the pulse duration, which can be less than 100 nanoseconds, less than 50 nanoseconds, less than 20 nanoseconds, less than 10 nanoseconds, or less than 1 nanosecond. Therefore, the pulse energy and pulse duration are linearly related to the peak power. Shorter pulse durations achievable with nanosecond, picosecond, and femtosecond lasers enable very high peak power, which is useful for marking objects.

[0031] In the raising apparatus 200 depicted in Figure 2, the laser 20 projects a laser beam 28 onto an X-mirror 22 rotated by an X-Garbo 21. The X-mirror 22 and X-Garbo 21 collectively form an X-Garbo set. The laser beam 28 is then projected onto a Y-mirror 24 rotated by a Y-Garbo 23. The Y-mirror 24 and Y-Garbo 23 collectively form a Y-Garbo set. The X-mirror 22 and Y-mirror 24 cooperate to direct the laser beam 28 to a position on the article 27 where a desired mark 29 should be marked. The laser beam 28 typically passes through a lens 26 before reaching the article 27. The distance from the lens 26 to the article 27 is the focal length 25.

[0032] The combined optical system of a laising device may function to sweep a laser beam across the surface of an article in a series of passes. The laser beam may sweep across the article along a first row of a grid in the X direction, directed by an X-mirror while emitting (or omitting) pulses. The combination of the sweeping speed of the laser beam across the surface of the article, also called the surface velocity of the laser beam, and the repetition rate of the laser pulses determines the spacing of the marks along the X direction. X interval * Repetition rate = surface velocity

[0033] The laser may emit one or more pulses while sweeping across the article at a given position, thereby resulting in marked positions (or multiple positions), or the laser may omit pulses while sweeping across the article at a given position, thereby resulting in unmarked positions (i.e., voids). The laser beam may sweep across the article at a constant velocity while emitting and / or omitting pulses. The surface velocity or sweep velocity is defined above. The laser beam may then sweep across the article along a second row of the grid (such as a row adjacent to the first row) while emitting (or omitting) pulses. The laser beam may sweep across the first and second rows in the same or opposite directions. For example, the laser beam may sweep across the first row "left to right" and then sweep across the subsequent / adjacent rows "right to left".

[0034] Those skilled in the art will understand that for an article to be marked, the laser energy must be absorbed by the material of the article. The laser energy can be absorbed by the substrate of the article or by laser-absorbing additives incorporated into the article. The wavelength of the laser may coincide with the absorption band, bandgap energy, or surface plasmon / plasma resonance frequency in the UV-vis-NIR-IR spectrum of at least one of the substrates or laser-absorbing additives incorporated into the article. For example, a pulsed laser utilizing 355 nm (UV) may be absorbed by TiO2 added to the article, and 532 nm (green) may be absorbed by precious metal nanoparticles such as gold, silver, and copper. Other laser wavelengths, such as 1030 nm to 1064 nm or 9 to 12 μm (infrared), may be absorbed by PET, which may be the substrate of the article. Other combinations of laser wavelengths and the substrates or laser-absorbing additives of the article exist and are construed herein.

[0035] Laser marking Articles of the present invention are typically marked by processes of foaming, carbonization, ablation, etching, reduction, oxidation, and / or phase change. The term foaming refers to the process by which a laser beam melts and vaporizes a portion of a material, creating bubbles that are trapped within the molten resin and, upon cooling, diffusely reflect light. Foaming generally results in brighter markings in the laser-marked area, and this method is most commonly used for dark-colored materials such as plastics or translucent materials. The term "translucent," as used herein, means that the material, layer, article, or portion of an article being measured has a total luminous transmittance greater than 0% and less than or equal to 90%. The term "opaque," as used herein, means that the material, layer, article, or portion of an article being measured has a total luminous transmittance of about 0%. Total luminous transmittance is measured according to ASTM D1003.

[0036] Carbonization-based marking is a process that produces a strong dark contrast on lighter surfaces and is commonly used on carbon-containing polymers or biopolymers or natural materials such as leather and wood and pulp-based materials. When carbonizing a material, a laser heats the surface of the material (generally to a minimum of 100°C) and emits oxygen, hydrogen, or a combination of decomposition products. Carbonization generally leads to a dark mark with a higher carbon content than the original material, making it a good choice for lighter-colored articles, although the contrast is rather minimal on darker materials.

[0037] Reduction and oxidation involve laser energy altering the oxidation state of at least one component of an article, such as a laser-absorbing additive or opacifying pigment, resulting in discoloration or a change in color that is visible as a mark. For example, though not bound by theory, the energy imparted from a UV laser could accelerate the reduction of TiO2 to form titanium dioxide, where the oxidation state of titanium is reduced to less than +4, thereby resulting in a color change from white / colorless to blue, and from dark blue to black.

[0038] There are additional methods for marking objects. For example, annealing is a unique laser process that can be used on metals and other materials. The energy from the laser beam creates an oxidation process beneath the surface of the material, which results in a change in color on the material's surface.

[0039] Coloring is another marking process achievable as a result of chemical reactions that occur on a material when energy from a laser beam is applied. The change in hue will depend on the composition of the material being colored. For example, light-colored plastic materials often discolor during the laser etching process, resulting in darker markings from the resulting soot particles.

[0040] Laser engraving is another process that involves removing material from the surface of a workpiece as it is melted and evaporated by a laser beam, which creates an indentation on the engraved surface. Removing material is sometimes referred to as etching or ablation. Laser etching is the process in which a laser beam removes the top layer of a substrate or a coating previously applied to the substrate of an article. Contrast results from the different colors of the topcoat and substrate, or from the different topography and texture of the etched area versus the adjacent area. Common materials that are laser-marked by removing material include anodized aluminum, coated metals, foils and films, or laminates. The term "etching," when used as a noun herein, refers to the cavity formed when material is removed from a surface. As a verb, the terms "etch" and "to etch" refer to the action of removing material from a surface. Etching can be done mechanically, chemically, and thermally (e.g., with a laser). There are no specific limits on the maximum or minimum etching depth, but the etching depth is typically in the range of approximately 0.01 mm to approximately 2.0 mm, including any depth within the range of, for example, 0.010 mm, 0.075 mm, 0.100 mm, 0.200 mm, 0.300 mm, 0.400 mm, 0.500 mm, 1.0 mm, 1.5 mm, etc.

[0041] Bleaching or photobleaching (sometimes called color fading) is a photochemical change in which a chromophore (such as in a pigment or dye) or fluorophore molecule permanently loses its intrinsic color and / or can no longer fluoresce. This is caused by the breaking of covalent bonds or nonspecific reactions between the chromophore / fluorophore and surrounding molecules, and laser marking may also be involved.

[0042] Spot size is a key parameter of the laser marking of the present invention and relates to the focused region in contact with the article. "Spot size" is the diameter of a circular spot. While the spot is circular, it is possible to achieve an elliptical spot by controlling the laser beam optics relative to the article. Spot size can be modified by focusing or defocusing the laser beam, but the "fluence" (energy per unit area) within the spot decreases as the spot is enlarged or defocused. Theoretically, the smallest spot size achievable with any laser is the wavelength of the laser itself. In practice, the smallest spot size achievable with a pulsed laser is about 7 to 20 μm. The spot size of the laser marking of the present invention may be in the range of about 10 μm to about 150 μm, preferably about 20 μm to about 100 μm, more preferably about 30 μm to about 80 μm, and even more preferably about 40 μm to about 60 μm. As discussed in the background technology, the spot size for conventional laser marking (e.g., using a CO2 laser), such as date codes, is a minimum of 250 μm and can exceed 800 μm. Another way to think about spot size in the context of marking is the size of the paintbrush a painter uses to paint. Smaller spot sizes are used when very fine detail is desired. Larger areas to be covered may prefer larger spot sizes. However, laser marking mechanisms require a minimum fluence to achieve the desired mark, and therefore, the balance between pulse energy, pulse duration, pulse overlap, and spot size is crucial.

[0043] Furthermore, there is an area around the laser contact spot that can be heated during the marking process, but the material is little to no marking. This "thermal-affected zone" can still result in effects such as crystallization, which can affect the appearance and / or performance of the target material. Short-pulse lasers (e.g., nanosecond lasers) have some thermal-affected zone, but it is substantially smaller than that of microsecond-pulse lasers or CW-type lasers (e.g., CO2, longer-pulse IR lasers). Picosecond and femtosecond lasers are often called "ultrashort pulses" and have little to no thermal-affected zone. This ability helps control the thermal effects of marking.

[0044] The geometric shape of the mark spacing is a major contributing factor to the cycle time and fluence (or energy per unit area) provided to the article. For example, the spacing between marks may be such that the marks do not overlap at all, or have 0% overlap. With 0% overlap, each individual laser pulse contributes to the energy provided to mark the article. If the laser does not have sufficient pulse energy or peak output to achieve the desired marks, the pulse spacing can be reduced to a point where the spots overlap in either the X and Y directions, or both. Overlapping the spots involves providing two or more laser pulses to the area of ​​the article where the spots overlap, which provides a higher fluence or energy per unit area to that part of the article. In addition, pulse spacing is a major lever for cycle time. If the laser has a fixed repetition rate or pulse frequency, it is desirable to spread the pulses as much as possible while still achieving the desired mark type and mark contrast in order to achieve the lowest process time (also called cycle time). In one embodiment of the present invention, the pulses do not overlap.

[0045] Pulse duration is the length of time a pulse continuously remains above half its maximum value. Shorter pulses can produce higher peak power at a typical average power output. This is because average power = pulse energy (J). * This is because the repetition rate is (Hz or 1 / second). The peak power is equal to the pulse energy divided by the pulse duration. Therefore, if the pulse duration becomes significantly shorter, the resulting peak pulse power becomes significantly higher. This peak power enables improved carbonization, foaming, oxidation, reduction, etc., on the target being marked. Short-pulse lasers utilize this phenomenon to mark articles, enabling marking mechanisms that are typically not found with longer-pulse lasers.

[0046] Changing the laser power / fluence output when creating laser marks can also be manipulated during marking to produce a grayscale, also known as dithering. Such a process is a known aspect of the raster process in laser marking. While not bound by theory, such dithering during laser marking is also thought to increase process time, in that each laser pulse must be signaled to emit a different power / fluence. In one embodiment of the present invention, the laser pulse is of constant power. Constant power can be maintained while the laser is marking within an entire row, or even while the laser is marking between rows across the entire marked pattern.

[0047] Go board pattern As used herein, “grid” or “bitmap grid” is interpreted to mean a regular, periodic array of positions that may contain multiple marks. The periodicity of the array includes periodicity in both the X and Y directions. Multiple marks in the grid may or may not be present at each position in the grid. That is, marks may or may not be formed at a position in the grid (i.e., voids). As mentioned, the lazing device sweeps a laser beam across an article while either laser pulses are being emitted from the laser or no pulses are being emitted. Marked positions occur when the laser pulses at a given position, and unmarked positions occur when the laser does not pulse at a given position. A laser beam can be swept across an object at a constant velocity while the laser repetition rate is constant. Therefore, the periodicity of the position will be regular (i.e., X-distance) in the direction the laser beam is swept across the object (i.e., the X-direction), even if the marked positions are not spaced equally, considering the possibility of unmarked positions. For unmarked positions, the distance between any marked positions along the same direction (i.e., the X-direction) can be an integer (i.e., 2x, 3x or greater) of the smallest distance measured between marks in that direction (i.e., the X-direction).

[0048] A laser beam can be swept across articles in subsequent rows. The laser beam can be swept from left to right or right to left, and as it moves from row to row, it can be swept in the same direction (e.g., like a carriage return on a typewriter in a raster process), or it can be swept in alternating directions as it moves from row to row. A major contributing factor to reducing cycle time involves sweeping the laser beam in alternating directions as it moves from row to row. Rows can be approximately parallel to each other. The distance between adjacent rows is the Y distance. The positions of adjacent rows can be directly above / below each other, or offset relative to each other. An offset equal to the X distance is understood to result in a realignment of the positions between rows.

[0049] Those skilled in the art will understand that the size of printed, or in this case, marked, alphanumeric characters is measured by their font. The smallest font generally accepted as consumer-readable on marked articles is about 6pt. While font sizes can be increased to very large sizes, fonts larger than 20, for example, are impractical when marking the surface of consumer packaging, as a few characters may fill the entire package.

[0050] As discussed earlier, laser marks may not overlap to reduce the time required to mark a given pattern (i.e., "time to mark"). Time to mark can be further reduced by spacing the marks in either or both the X and / or Y directions, although increasing this spacing may lead to poor legibility of any alphanumeric characters that make up a given pattern. For example, increasing the X distance allows for a faster surface velocity of the laser beam across the surface of the article when marking a given row (at a constant repetition rate). Increasing the Y distance allows for fewer reversals in the process of marking a given pattern.

[0051] Surprisingly, it has been found that for certain predetermined patterns, increasing the Y distance (fewer inversions) can have a greater impact on reducing the time to marking than increasing the X distance (faster surface velocity). Conventional raster marking processes include equal X and Y spacings, but the present invention may include a Y distance greater than the X distance. It has been further found that the legibility of alphanumeric characters marked by the constant velocity (CV) bitmap process of the present invention may depend on the X and Y spacings as a function of the font size of the characters. The X distance is preferably in the range of about 0.005 mm to about 0.500 mm; more preferably about 0.010 mm to about 0.100 mm, and even more preferably about 0.040 mm to about 0.075 mm. The Y distance is preferably in the range of about 0.010 mm to about 2.0 mm; more preferably about 0.050 mm to about 0.150 mm, and even more preferably about 0.060 mm to about 0.075 mm.

[0052] If the predetermined alphanumeric characters have a font size in the range of 6pt to 10pt, the Y distance may be at least 1.2 times, preferably 1.5 times, more preferably 1.7 times, and even more preferably 2 times, the X distance. If the predetermined alphanumeric feature part has a font size in the range of 11pt to 16pt, the Y distance is at least 2 times, preferably 2.5 times, more preferably 3 times, and even more preferably 4 times, the X distance.

[0053] Figures 3, 4, and 5 all illustrate various depictions of a grid according to the present invention. More specifically, Figure 3 is a grid 39 according to the present invention, illustrating the X direction 30, Y direction 32, X distance 31, and Y distance 33. Potential marking positions 36 are depicted by empty circles that make up the grid. Furthermore, in Figure 3, positions 36 between parallel columns 38 are "stacked" when the angle 35 between the position in the adjacent column 34 drawn in the Y direction between two potential marking positions and the X direction 30 is approximately 90 degrees. In other words, when using vectors to connect adjacent marks from an array to form a parallelogram (i.e., a unit cell), positions are stacked when the interior angles of the parallelogram are approximately 90 degrees. If the interior angles of the parallelogram are different from 90 degrees (i.e., 120 degrees and 60 degrees), the positions are offset. The X distance is measured from the center of one position to the center of an adjacent position in the X direction.

[0054] Those skilled in the art will understand that a grid unit cell has four axes of symmetry: horizontal, vertical, and two diagonals. The laser marking considered herein can be performed along any of these four axes. For simplicity, the vertical and horizontal directions shown in Figure 5 will be described. Figure 5 can be rotated 45 degrees so that the diagonals are vertical and horizontal. Again, as shown in Figure 5, the laser marking occurs across one row, and then the laser moves up or down to the row above or below, marking in the opposite direction.

[0055] Figure 4 shows another grid 49 according to the present invention, showing an offset 44 with an offset distance 47 between adjacent parallel rows 48. The offset 44 is defined by an angle 45 between a position 46 in one row 48 and the nearest position 46 in the adjacent row 48, and the offset 44 exists when the angle 45 is greater than or less than 90 degrees. Figure 4 further shows the X direction 40, the X distance 41, the Y direction 42, and the Y distance 43.

[0056] Figure 5 shows alphanumeric characters 52 marked on a grid 50. The alphanumeric character is the number "2," and is marked by the laser-marked position 54, in contrast to the unmarked position 56. When multiple alphanumeric characters, such as words, sentences, or paragraphs, are printed, characters that share the same column of text will also share the same horizontal column 53 of laser marking. That is, the laser device moves across a column, marking the necessary positions for each alphanumeric character, and then forms a column where the markings are associated with multiple characters within that column, leaving the necessary number of unmarked positions between the characters. In this way, words, sentences, and paragraphs can be marked and are clearly legible to consumers or machines.

[0057] Horizontal columns 53 and vertical columns 55 define the grid 50. The distance between a marked position 54 and an unmarked position 56 in the horizontal column 53 defines the X distance 51. Furthermore, the distance between a marked position 54 and an unmarked position 56 in the vertical column 55 defines the Y distance 57. It is important to note that the X distance 51 and the Y distance 57 are defined with respect to the horizontal orientation (53) and vertical orientation (55), respectively, of the marked indicia, in this case the number "2". However, the marked position 54 can be marked in the horizontal direction 59 or the vertical direction 58. More specifically, when marking in the horizontal direction 59, the laser moves across the horizontal column 53, either marking each position (54 and 56, respectively) or leaving them unmarked. Next, the laser moves down or up by one Y distance and begins to travel across another column above or below the previously marked column. Similarly, when marking in the vertical direction 58, the laser moves up or down the vertical column 55, either marking or leaving each position (54 and 56, respectively) unmarked. The laser then moves across one X distance and begins to travel up or down the vertical column adjacent to the previously marked vertical column.

[0058] The aspect ratio of a number or letter is the ratio of its height to its width. The aspect ratio of the number "2" shown in Figure 5 is greater than 1 because its height is greater than its width. It is easy to see that marking the number "2" vertically at 58 requires fewer inversions than marking it horizontally at 59. This means that marking this indicia can be faster when sweeping the laser beam while marking vertically at 58. Many considerations are made when deciding whether to mark horizontally or vertically. However, when considering the relative spacing and font size of alphanumeric characters, the X distance 51 and Y distance 57 are always defined horizontally and vertically, respectively, with respect to the indicia being marked.

[0059] The periodicity of the positions constituting the grid includes periodicity in the X direction and periodicity in the Y direction. The X and Y directions can be approximately orthogonal to each other. As depicted in Figures 3 and 4, the grid 39 and 49 can take the form of being evenly spaced along consecutive parallel rows, respectively. The direction parallel to consecutive parallel rows is the X direction (30, 40), and the direction approximately perpendicular to the X direction is the Y direction (32, 42). The distance between adjacent positions along any parallel row (e.g., in the X direction) is considered the X distance (31, 41), and the distance between adjacent parallel rows is considered the Y distance (33, 43).

[0060] The grid 39 can be a stacked grid as depicted in Figure 3. In a stacked grid, the positions where marks can be placed along the first X-axis are directly above the positions along the second X-axis that are directly below the first X-axis. In other words, the angle 35 formed between the column segment connecting the first position along the first X-axis to an adjacent position along the first X-axis and the column segment connecting the first position to its nearest position along the second X-axis is 90°. In a stacked grid, the distance between adjacent positions along the X-axis is equal to the X-distance 31, and the shortest distance between adjacent positions along adjacent X-axis is the Y-distance 33.

[0061] The grid can be an offset grid as depicted in Figure 4. In an offset grid 49, the positions where marks can be placed along the first X-axis are not directly above the positions along the second X-axis that are directly below the first X-axis. In other words, the angle 45 formed between the column segment connecting the first position along the first X-axis to an adjacent position along the first X-axis and the column segment connecting the first position to its nearest position along the second X-axis is greater than or less than 90°.

[0062] Those skilled in the art will understand that the X and Y directions can be selected to some extent arbitrarily for a given pattern. For example, Figure 6B depicts an embodiment of "2" produced by laser marking, where the X direction is perpendicular to the marked "2" 61. Those skilled in the art will understand that the X direction can easily be horizontal to the marked "2" 61.

[0063] Those skilled in the art will understand that the grid pattern (e.g., 39 and 49) and the regular spacing between adjacent positions assume a flat surface of the article. If the surface of the article is curved, the spacing may change with the curvature of the surface.

[0064] The X distance can be the same across all parallel rows that make up the grid. That is, the X distance does not change along the X direction of a given row, nor does it change between rows of a grid containing a given pattern. Alternatively, a given pattern may include multiple regions where the X spacing within each region is the same but differs between regions. For example, one X distance may be used consistently when marking alphanumeric characters, while different X distances may be used when marking machine-readable codes such as UPC codes. Similarly, the Y distance may not change within a given pattern, or it may change between regions within a given pattern. The surface velocity of the laser beam and / or the marking direction (i.e., up / down or left / right) may also differ between regions. For example, it should be noted that articles laser-marked using a vector marking process (i.e., for the CV bitmap marking process of the present invention) will generally exhibit variable position / mark spacing along one of their marked directions as the laser accelerates (moving marks further apart) and / or decelerates (moving marks closer together) along the process of marking the article. The laser marking of the present invention is typically performed at a constant speed while the laser is marking. The movement of the laser beam stops after the completion of one row along the X direction, moves up or down to the next row along the Y direction, and then starts marking the new row at a constant speed. This speed can also be the same throughout the entire marking of a given pattern. Articles marked with the CV bitmap grid marking process can be distinguished from articles marked with the vector marking process by the regular periodicity of the marks and, in many cases, by the absence of contours or "boundaries" that define the marked areas (see, for example, boundary 63 in Figure 6B).

[0065] Figures 6A and 6B illustrate the difference between laser marking via bitmap grid marking using the CV bitmap process 6A of the present invention and the prior vector marking process 6B, in which the alphanumeric characters 60 and 61 (i.e., the digit "2") are laser marked. The alphanumeric character 60 has clean, sharp edges and is substantially better defined with very little stray marking. Figure 6B is very contrasting, with mostly undefined edges and a considerable number of stray markings 62 outside the boundary of the alphanumeric character 61. Both characters 60 and 61 were marked in approximately the same amount of time.

[0066] Improvement of laser marking rate As can be considered, the present invention enables laser marking of articles at a faster and more precise rate than prior processes. Existing raster processes are very slow but relatively accurate, while vector laser marking processes are faster and more accurate at low speeds but very coarse at high speeds, resulting in illegible markings that are difficult for consumers or machines to read. Raster and vector are different graphic file types that require different modes of laser processing. The main differences between the modes required to laser process each type lie in the movement of the garbo, or laser beam steering, and the parameters used.

[0067] The vector path, typically in the case of images, becomes slower to require the Garbo set to spend time accelerating to a user-defined maximum speed (determined by multiplying the pulse interval by the repetition rate) and the length of the vector distance. A longer vector distance allows the vector raising device to reach its maximum speed, while a shorter vector distance causes the raising device to constantly accelerate and decelerate, never reaching its maximum speed, resulting in a longer marking cycle time.

[0068] The vector process is also less accurate than the CV bitmap process at high speeds due to the acceleration / deceleration of the Garbo that steers the laser beam. Specifically, the position of each laser mark must be communicated from computer-driven software to the laser marking device, and such communication must be updated during the marking of a given pattern, for example, as the laser beam traverses a given row. A typical update frequency for this communication is about 10 μs, and therefore a laser that outputs pulses with a repetition rate of 100 kHz allows for updates in the communication for each individual position in the grid. This also applies to raster laser marking processes, which may further include variations in pulse output for each pulse as a means of achieving grayscale (e.g., dithering). As the speed of the laser beam traversing the surface of the article increases, repetition rates exceeding 100 kHz are required to achieve the desired X spacing in the row, and each update from the software must communicate the positions of multiple laser marks (or voids / unmarked areas). While the calculations can be performed almost instantaneously, in the extremely fast time domain of high-speed laser marking, Garbo cannot respond so quickly, and the acceleration / deceleration shape of the vector process is thought to result in a considerable number of misplaced marks within a given row compared to the constant velocity shape of the present invention.

[0069] Figure 6B illustrates the benefits of using a fast vector-based process when marking text containing alphanumeric characters, as well as the misplacement of marks within columns. This figure shows many rows that are misaligned, and if the marking starts either too early or too late, the outlines of the alphanumeric characters may become jagged, the overall appearance blurred, and potentially illegible (for example, it may be impossible to distinguish an "8" from a "0").

[0070] In contrast, the process and resulting patterns of the present invention can be produced by a constant velocity (CV) bitmap path. The CV bitmap laser marking process allows for increased speed and precision because there are no start and stop points within the row, but rather a user-defined maximum velocity (again, the pulse interval multiplied by the repetition rate) that is constant while pulses are applied or marking is being performed. Furthermore, the lathing device of the present invention can increase speed when marking is not being performed over a relatively long distance (with respect to the X distance). For example, if there is a distance of 2-3 mm (or more) between markings in a row of marks, the lathing device can accelerate without losing precision, or otherwise move the laser beam at a constant velocity while pulsing it. This is yet another reason why the marking system of the present invention is faster and more accurate than prior devices.

[0071] Smaller Garbo sets (e.g., including lower-mass mirrors) allow higher acceleration to reach this user-defined maximum velocity. These Garbos can be adjusted to higher acceleration values ​​that allow the mirrors to reach their desired angular velocity in a shorter time. Interestingly, these values ​​can be specifically adjusted for bitmap processing at higher values ​​than for vector processing. In addition, the vector laser software has a maximum marking velocity limit set so that the laser marks are close to their desired commanded positions. As the maximum velocity threshold increases, the laser pulses have more error with respect to their desired positions in vector processing. Note that in CV bitmap marking mode, since the velocity (e.g., both the angular velocity of the mirror and the surface velocity of the laser beam) is constant during the marking process, the maximum velocity threshold can be increased significantly to achieve lower marking cycle times overall compared to vectors, while still keeping the pulses in place.

[0072] The angular velocity of the Garbo set is important for the job cycle time because it directly relates to the surface velocity of the laser beam across the object. The surface velocity of the laser beam is set by the angular velocity of the Garbo / Miller pair and the focal length of the raising device. Surface velocity = Garbo angular velocity (rad / sec) * Focal length (mm)

[0073] The surface velocity when creating laser marks within a given row is primarily controlled by the X-Garbo / mirror set. Job cycle time may depend more on the laser surface velocity in the X direction than in the Y direction, and the X-Garbo / mirror set may be more responsive than the Y-Garbo / mirror set. For example, the mirrors on the X-Garbo / mirror set can be smaller (i.e., lower mass, smaller mirror size, lower inertia, higher acceleration motor capability).

[0074] The surface velocity of the laser beam across the surface of an article in current CV bitmap processes is far faster than that achievable in currently available laser marking processes such as raster marking and vector marking processes. Current processes are typically good examples of surface velocities on the order of 1-2 m / s or less. The CV bitmap process of the present invention provides surface velocities exceeding 8 m / s, and even 10 m / s, 15 m / s, 18 m / s, 22.5 m / s, 32.5 m / s, 45 m / s, 60 m / s or more, and even 90 m / s or more.

[0075] The sweep path of the laser beam across the surface of an object can also contribute to reducing cycle time. Conventional raster laser marking processes sweep the laser beam across a column in either a right-to-left or left-to-right direction, also known as unidirectional, and then "jump" the laser beam back (like a typewriter's carriage return) after marking each column to start the subsequent column. In this way, subsequent columns can be easily aligned (i.e., stacked) and the grid positions can be aligned based on this identical starting point. To eliminate the jump distance and reduce the time between each marked column, current CV bitmap processes use a "bidirectional" process in which marking can be performed alternately in both directions (i.e., marking is done from left to right in the first column and from right to left in the subsequent columns).

[0076] To keep the pulses aligned, the lathing device can be programmed to incorporate a laser-on-adjust, which is a delay function for each alternating row to keep the pulses aligned. For example, at a marking speed of approximately 22.5 m / s (i.e., surface speed), an 8-microsecond delay is used for alternating rows. A typical bitmap laser software setup allows for the selection of a single pulse interval or pitch that is common in both the X and Y directions. By producing different X and Y distances, similar contrast can be produced for both human-readable (e.g., text) and machine-readable (e.g., UPC, QR code) objects.

[0077] Laser-on-adjust is an element of the inversion shape of the laser beam sweep path. The inversion shape refers to the path traced by the Garbo set directing the laser beam while the laser beam is reversing between rows (i.e., reversing to mark a row from left to right, then reversing to mark the next row from right to left). The laser is typically off (i.e., not emitting pulses) during the reversal. Laser-on-adjust helps align marks in adjacent rows. For example, if the grid is a stacked grid, laser-on-adjust ensures that the marks in adjacent rows remain stacked. If an offset grid is used, laser-on-adjust ensures that the grid remains offset, and that the amount of offset remains relatively constant. Laser-on-adjust can be determined experimentally and generally varies with the angular velocity of the Garbo set.

[0078] The inversion of the laser beam's shape after completing a row can also contribute to reducing cycle time. As discussed earlier, the laser beam is steered by a Garbo set, and the Garbo set's ability to accelerate and decelerate is a known limitation on the speed and accuracy of laser marking in other (e.g., vector) marking processes. Current CV bitmap processes overcome these limitations. For example, current CV bitmap processes do not accelerate or decelerate the laser beam while the laser is emitting pulses (i.e., creating laser marks). Instead, the laser beam is accelerated / decelerated only when the laser is not marking an article, for example, when the laser beam is skipping multiple voids (or an entire row), or when the laser beam is inverted at the end of a row before marking the next row. The inversion shape can be symmetrical or asymmetrical. An asymmetrical inversion shape may be preferable when the speed at which the laser beam sweeps across the surface of the article is high.

[0079] As mentioned earlier, the geometric shape of the mark spacing is a major contributor to the cycle time. As considered, widening the positions within the grid (i.e., increasing the X and Y distances) can lead to a reduction in cycle time. Within a row, the X distance contributes to the cycle time in that the laser surface velocity is determined by the laser repetition rate and the X distance. Increasing the Y distance improves the cycle time by reducing the number of inversions that the Garbo set must perform (i.e., the number of rows with a given feature), which can account for up to 30-70% of the total cycle time at high speed. For example, to obtain similar-looking images within the reduced overall cycle time, the X distance can be made smaller and the Y distance larger. Furthermore, it has been found that increasing the Y distance while simultaneously decreasing the X distance provides faster cycle times and improved readability of the marked feature.

[0080] As discussed earlier, the X and Y distances, and their ratio, can contribute to laser marking small font text or images that are legible at high speed (i.e., low cycle time). The X and Y spacings can also be important when marking images such as graphics, especially when the image contains grayscale. While known raster marking processes produce grayscale by varying the energy of individual laser pulses, the CV bitmap process, instead, achieves grayscale by running too fast and not individually varying these pulse energies, but by spacing out full-energy pulses in different patterns to produce grayscale.

[0081] The choice of marking direction can affect job cycle time, especially when marking features with high (or low) aspect ratios. The aspect ratio of a feature is generally considered to be the ratio of its height to its width. When the height and width are nearly equal, the aspect ratio is close to 1, and the impact of choosing the marking direction relative to the feature dimensions (on job cycle time) may be minimal. However, for features with high aspect ratios (e.g., height >> width) or low aspect ratios (e.g., width >> height), job cycle time can be reduced by choosing the marking direction relative to the feature dimensions. For example, the marking direction may be chosen to be approximately parallel to the longer dimension of the feature (i.e., the major axis), or it may be chosen to be approximately parallel to the shorter dimension of the feature (i.e., the minor axis) (see Figure 5 again). While many factors affect job cycle time, aligning the marking direction with the major axis of the feature is thought to reduce the number of inversions required when marking the feature, thereby reducing job cycle time.

[0082] The choice of marking direction can also affect job cycle time at very high surface velocities. At very high surface velocities, reversal time can increase to a point where it dominates job cycle time. By selecting the marking direction to be approximately parallel to the longer dimension of the feature, reversal can be minimized, thereby reducing job cycle time. As discussed earlier, the X and Y distances can differ, and this difference can contribute to reducing the job cycle. Loss of image clarity in feature areas such as alphanumeric characters can be compensated for by decreasing the X distance while increasing the Y distance.

[0083] As discussed earlier, the smallest font size generally accepted as consumer-readable on marked articles is approximately 6pt. While font sizes can be increased to very large sizes, fonts larger than 20, for example, are impractical when marking the surface of consumer packaging, as a few characters may fill the entire package. When a given alphanumeric character has a font size in the range of 6pt to 10pt, the X distance can be at least 1.2 times, preferably 1.5 times, more preferably 1.7 times, and even more preferably 2 times, the Y distance. When a given alphanumeric feature has a font size in the range of 11pt to 16pt, the X distance is at least 2 times, preferably 2.5 times, more preferably 3 times, and even more preferably 4 times, the Y distance. As discussed, these ratios of the X and Y distances are defined horizontally and vertically, respectively, with respect to the marked indicia, regardless of whether the sweep direction of the laser beam is perpendicular or horizontal to the indicia.

[0084] In the laser marking process of the present invention, the laser source is stationary, and the laser beam is guided by a lathing device including a series of lenses and mirrors controlled by an algorithm. The algorithm can read a digital image of a desired mark pattern (e.g., from a PDF file of the desired image) and replace that image with the mark pattern on the target. The lens / mirror system and algorithm are supplied by IPG Photonics (50 Old Webster Road, Oxford, MA 01540, USA).

[0085] Microscopy Numerous articles were marked according to the method of the present invention, and comparison articles were marked using existing methods. The results of these comparisons are shown in Tables 1, 2, and 3, and in Figures 7 and 8. To obtain these comparison data, samples were cut from laser-marked blow-molded bottles using a utility knife and scissors. If the cut samples were not suitably flat, the samples were flattened on a microscope stage using tape or a frame. Stereoscopic microscopes such as a motorized Zeiss SteREO Discovery V20 (Carl Zeiss Microscopy, LLC, Thornwood, NY) equipped with a color camera such as an Axiocam 305 (5-megapixel CMOS, Carl Zeiss Microscopy, LLC, Thornwood, NY) were used to image the target letters, numbers, and images of the samples using reflected light illumination, such as achieved with an LED ring light and light source such as a cold-light source CL 6000 LED lamp (Carl Zeiss Microscopy, LLC, Thornwood, NY). Typical light intensities of 80-100% of the maximum light intensity were used. Individual laser markings, combined to form the target letters, numbers, or images, are resolved using a suitable magnification, combined with a zoom magnification such as 10x to 345x, using an objective lens such as an Achromat S 1.5x FWD 28mm (Carl Zeiss Microscopy, LLC, Thornwood, NY). For example, for letters, numbers, or images with a font size of 10pt, the total magnification is approximately 40x. After the target numbers enter the camera's field of view, the letters, numbers, or images are focused using manual skill or, preferably, using an autofocus module via a user interface platform (such as Zen V2.6 Blue Edition or higher with Zen Autofocus module, Carl Zeiss Microscopy, LLC, Thornwood, NY).Before collecting images of letters, numbers, or pictures, the imaging settings are optimized by using the automatic exposure option from the user interface platform along with the lamp intensity. Images are collected in the highest possible resolution format, such as ZVI, and then exported as TIFF files with a resolution of approximately 2464 x 2056 pixels. Furthermore, the marked columns of letters, numbers, or artwork should be approximately parallel to the horizontal boundaries of the image. If necessary, multiple images taken at higher magnifications can be precisely stitched together to encompass the entire area of ​​the letters, numbers, or images.

[0086] Image analysis Images from the microscope appear gray, but are captured in color. The images are converted to grayscale using the NTSC protocol. Suitable image analysis software is required to perform this step and several other image processing steps. Analysis functions implemented in MATLAB, available from The Mathworks, Inc. (Natick, MA), are referenced in this description of the method.

[0087] Microscopy and subsequent image analysis may be performed on one or more predetermined patterns, parts of predetermined patterns, or individual images within a predetermined pattern, such as graphics or alphanumeric characters. If image analysis is performed on a part of a predetermined pattern, that part (such as individual graphics or alphanumeric characters) must be isolated from any surrounding images, characters, or artwork before analysis. A mask may be drawn around the character or image in the predetermined pattern. The mask isolates the character or image from other partial characters, numbers, barcodes, artwork, smudges, or other defects that may occur in the image.

[0088] Image analysis first relies on identifying the laser marks that make up the image. Laser marks can be identified by any reasonable means, for example, by repeatedly thresholding a grayscale image from a microscope. The starting threshold is set to capture only a few pixels that fall within some of the markings. The threshold then gradually changes to capture the continuously increasing area of ​​the markings. Progressive thresholding continues from the starting threshold to the stopping threshold. The stopping threshold can be determined automatically, for example, by using MATLAB's "multithresh" function (i.e., Otsu's method). Progressive thresholding can be advantageous in analysis because areas of markings may overlap and / or merge, and the background may not be perfectly uniform. The direction of threshold progression (i.e., light to dark, or dark to light) can be used to identify dark markings against a relatively light background, or light markings against a relatively dark background. In the presented embodiment, dark marks against a relatively light background are identified.

[0089] Next, when the region reaches a certain size, connected components can be used to identify individual marks. The connected component algorithm is executed with each new threshold to group contact pixels into blobs. When a blob reaches 50% of the mark's area, it is identified as a mark. The center coordinates of a mark are found using the centroid method, which is implemented in MATLAB's "regionprops" function. Its center is then used to determine the spacing between adjacent marks in a column (e.g., X distance) and the spacing between adjacent columns of a mark (e.g., Y distance) (see below).

[0090] Samples and data Table 1 shows data obtained by laser marking the same pattern onto four different articles and then analyzing them using the method described above. In this case, the marking was the industry standard UPC code. Those skilled in the art will understand that, in order for a UPC scanner to read the code quickly and accurately, the UPC, which must be displayed on all goods purchased by a consumer, must have black bars and alphanumeric characters that are clearly defined against a brighter, preferably white, background. In other words, the UPC code must be printed or marked with precision so that it can be accurately read by a scanner or a person. As an example, Figure 7 shows a UPC code 70 laser-marked according to the process of the present invention. The UPC code 70 is a mixture of bars 72 of varying widths and alphanumeric characters 74.

[0091] Prior to this invention, vector laser marking was the fastest laser marking system available, but Table 1 clearly shows that as the speed of vector marking increases, the precision of the marking substantially decreases. More specifically, vector marking was tested at maximum gavlo angular velocities of 15.6, 350, and 1000 radians / second and compared with the CV bitmap marking of this invention at a maximum speed of 1000 radians / second. The target Y distance is provided in the first column, where the actual Y distance for each of the n samples was measured (in mm) and then averaged. More importantly, the sigma σ standard deviation was calculated for the n samples using the standard formula. The standard deviation is a measure of how far each individual sample deviated from the target Y distance. For example, if only two samples were performed at a target Y distance of 0.150, and one sample was 0.200 and the other was 0.100, their average would be exactly 0.150, the target value. However, precision is unavoidable. The standard deviation in this example is a large number indicating a lack of precision for these two hypothetical samples, whose mean appears to be as intended.

[0092] Comparing vector marking at a Garbo angular velocity of 15.6 radians / second (first entry in Table 1) with CV bitmap marking at 1000 radians / second (last entry in Table 1), the average X-distance, average Y-distance, and corresponding standard deviations are similar across the four target X-distances and Y-distances tested. As the Garbo angular velocity of vector marking increases to 1000 radians / second, the average X-distance and corresponding standard deviation remain reasonable, but the Y-distance standard deviation becomes unacceptable, and the UPC code becomes ultimately unreadable for both barcode readers and humans reading the underlying digits. For UPC codes marked by the process of the present invention, both the average X-distance and standard deviation, and the average Y-distance and standard deviation are very good, even at the maximum Garbo angular velocity of 1000 radians / second. Thus, the CV bitmap laser marking of the present invention offers a clear advantage in speed and precision over prior vector marking systems.

[0093]

number

[0094] [Table 1] * When X (target) = 0.045 mm, the laser beam velocity is 22.5 m / s; when X (target) = 0.050 mm, the laser beam velocity is 25 m / s.

[0095] Table 2 shows another set of comparative data where UPC codes were laser-marked with legible precision. Specifically, the time required to produce a machine-readable UPC was measured for each velocity and each target Y and X distance. As is clearly shown, for every successive increase in Velocity Max, the time required to laser-mark the UPC code accurately / legibly actually increased with the vector marking process.

[0096] [Table 2]

[0097] Table 3 contains data obtained from the laser-marked samples shown in Figure 8. The top column of Table 3 indicates which of the five samples shown in Figure 8 (81-85) the data corresponds to, how each sample was laser-marked, and how it compares to the other samples. Figure 8 shows a 5 mm square 88, sample text 87 (alphanumeric "Abg123"), and a series of 1 mm × 5 mm rectangles 86 spaced 1 mm apart. The repetition rate is 700,000 rad / sec 2 The normal acceleration was used at 500 kHz. The second row of Table 3 shows how each sample was marked, the third row is the maximum Garbo angular velocity of the laser marking, and the fourth and fifth rows are qualitative descriptions of the results. Actual data for marking 5 mm squares 88, text 87, and 1 mm × 5 mm standardized rectangles 86 are shown in the remaining rows of Table 3. In this case as well, it is clear that the speed and precision of laser marking with CV bitmaps of the present invention are far superior to conventional vector marking systems. An f-theta lens with a focal length of 250 mm was used.

[0098] [Table 3]

[0099] Standardized rectangle method The standardized rectangle method is a standardized test for measuring both the speed and accuracy of any raising device. Simply put, it can test any raising device that can be programmed to print 20 identical rectangles (similar to a simplified UPC code). While the test details are provided below, those skilled in the art will understand that the time required to print the standardized rectangles is crucial to demonstrating the advantages of the present invention. The last two rows of Table 3 show examples of the time required to print standardized rectangles using four raising devices / processes available today and one raising device / process according to the present invention. Prior raising devices / processes required 1.5–1.0 seconds to print standardized rectangles. The raising device / process according to the present invention required only 0.185 seconds, which was 500–800% faster than the prior devices.

[0100] As shown in Figure 8, the standardized rectangle 86 is a series of 20 identical rectangles 91 in Figure 9, with a width 95 of approximately 1 mm, a height 93 of approximately 5 mm, and spaced about 1 mm apart. The width 95 of the rectangles must be in the range of 0.94 mm to 1.22 mm. The height 93 of the rectangles must be in the range of 4.8 mm to 5.00 mm. Each rectangle contains 80 to 84 parallel columns 97. Each column extends in the X direction 92, i.e., with a width 98 of 1 mm. Thus, the Y distance 96, which is the distance between columns, is in the range of 0.24 mm to 0.26 mm. Each column 97 has 20 to 24 marks 99. For clarity, it is obvious that not all marks 99 are shown.

[0101] Unless otherwise specified, all percentages are weight percentages based on the weight of the composition. Unless otherwise specifically stated, all ratios are weight ratios. All numerical ranges include narrower ranges. Divided upper and lower range limits are interchangeable in creating further ranges that are not explicitly defined. Significant digits do not limit the indicated quantity or the precision of the measurement. All measurements are understood to be taken at approximately 25°C and under ambient conditions, where “ambient conditions” means conditions at approximately 1 atmosphere and approximately 50% relative humidity.

[0102] The dimensions and values ​​disclosed herein should not be understood as being strictly limited to the exact numerical values ​​listed. Instead, unless otherwise specified, each such dimension is intended to mean both the listed value and the functionally equivalent range encompassing that value. For example, a dimension disclosed as "40 mm" is intended to mean "approximately 40 mm."

[0103] All documents referenced herein, including any patents or patent applications that are cross-referenced or related, and any patent applications or patents on which this application claims priority or benefit thereof, are incorporated herein by reference in their entirety unless explicitly stated to be excluded or otherwise limited. No reference to any document shall be deemed prior art to any invention disclosed or claimed herein, nor shall it be deemed to teach, suggest or disclose any such invention, either alone or in combination with any other reference. Furthermore, if any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in any document incorporated by reference, the meaning or definition given to the term in this document shall apply.

[0104] While specific embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, it is intended that all such changes and modifications within the scope of the invention be covered in the appended claims.

Claims

1. A method for marking an object with a pulsed laser, the process being: The steps include providing a pulsed laser configured to produce a laser beam containing pulses, A step of providing an article including the surface of the article, A step of using the laser beam to form a plurality of marks in a grid pattern on the surface of the article by foaming, ablation, etching, reduction, oxidation, and carbonization, The steps include: moving the laser beam along a first row at a constant velocity while interacting with the surface of the article, the constant velocity being greater than 8 m / s; The aforementioned multiple marks are formed when the laser beam moves in the column direction. The grid pattern comprises a plurality of positions positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of positions along any one of the two or more rows being separated by a distance X, and each adjacent pair in the two or more rows being separated by a distance Y, where the Y distance is greater than the X distance.

2. The method according to claim 1, wherein the laser beam moves in bidirectional motion such that the laser beam moves across the first row in a first direction and across the second row in a second direction, the first direction being opposite to the second direction, and preferably the first row and the second row being adjacent.

3. The method according to claim 1, wherein each of the plurality of positions includes a mark or a void.

4. The method according to claim 3, comprising moving the laser beam across each of the positions of the grid pattern, wherein the laser beam moves at a constant velocity when consecutive marks are formed at adjacent positions in the same row, and the laser beam accelerates when the laser beam moves across consecutive positions having voids.

5. The method according to claim 2, wherein the laser beam has a reversal acceleration shape when the laser beam moves from the first row to the second row.

6. The method according to claim 1, wherein the laser beam has a repetition rate greater than 100 kHz.

7. The method according to claim 1, wherein the laser beam has a pulse energy of 10 μJ to 1000 μJ.

8. The method according to claim 1, wherein the laser beam has a focal length of 100 mm to 1200 mm.

9. The method according to claim 1, wherein the laser beam has a wavelength of 300 nm to 1100 nm.

10. The method according to claim 1, wherein the laser beam has a pulse duration of less than 100 nanoseconds.

11. A process for marking an article with a pulsed laser, wherein the process is: The steps include providing a laser source configured to emit a pulsed laser beam, A step of providing a first Garbo set and a second Garbo set configured to change the direction of the pulsed laser beam, wherein each Garbo set comprises a mirror and a Garbo, The steps include providing an article having an article surface, A step of rotating the first mirror at a first angular velocity using the first Garbo to move the pulsed laser beam between rows while marking the surface of the article, wherein the first angular velocity is greater than 40 rad / second, A step of rotating the second mirror at a second angular velocity using the second Garbo to move the pulsed laser beam in the column direction while marking the surface of the article, wherein the second angular velocity is greater than 40 rad / second, The process includes the step of forming a plurality of marks in a grid pattern on the surface of the article by foaming, ablating, etching, reducing, oxidizing, and carbonizing the surface of the article with the laser beam, The aforementioned multiple marks are formed when the pulsed laser beam moves in the column direction, The second angular velocity is greater than the first angular velocity. The grid pattern includes a plurality of positions positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of positions along any one of the two or more rows being separated by a distance X, and each adjacent pair in the two or more rows being separated by a distance Y, where the Y distance is greater than the X distance. process.

12. The process according to claim 11, wherein each of the first mirror and the second mirror has a mass of less than 150 g each.

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