High speed laser processes for marking articles

Abstract

A laser marked article having predetermined features marked on a wall thereof, 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 to a method for marking such an article. [Background technology]

[0002] Short pulse laser decoration utilizes energy from nano-, pico- and femto-short pulse lasers across a range of wavelengths and energies to mark decorative patterns on articles such as products and / or packaging. Any and all other decoration techniques that may be applied to products and / or packaging (i.e., labels, screen printing, digital printing, etc.) may be used in conjunction with laser marking to achieve a variety of decorative and functional effects. The laser technology used for short pulse laser marking is importantly a high throughput technique that uses a stationary laser source where the laser beam is directed by electronically / mechanically controlled mirrors (i.e., "galvo" sets) and lenses (i.e., F-theta and similar lenses) to the product or package to be marked. 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 (e.g., from a computer file such as a PDF file), to the surface of the package or product. This approach has an additional advantage over other decoration techniques in that the use of digital images allows for customization and personalization of the decoration.

[0003] There is great interest in the possibilities offered by laser marking articles, such as by short-pulse laser marking. For example, replacing adhesive labels on polymer containers is not only economically beneficial, but also ecologically beneficial. Removing adhesive labels on polymer containers, for example, reduces the total weight of packaging materials, which reduces the amount of petroleum-derived materials per package and reduces the weight of packaging, thereby requiring less fuel for transportation. Furthermore, the absence of adhesive labels allows polymer containers to be recycled more easily, since adhesive labels often need to be removed before recycling due to potential impurities that may be introduced into the recycling stream.

[0004] Laser marking of small articles (i.e., golf balls, etc.) and / or small areas on articles (i.e., date codes, address labels on finished packages) is known. Although lasers are improving and newer lasers have a variety of energies and wavelengths, these marking processes can still be slow and expensive. Furthermore, they do not have the capability to mark small characters that require 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 with relatively simple lasers, but they use single lines and relatively large font characters with large, imprecise, or unevenly spaced spots (ranging from 250 μm to over 800 μm in diameter). This is equivalent to printing stick figures that, while adequate for some purposes, are difficult for consumers to read and nearly impossible for machines to read. More specifically, a single line of large, imprecise, or unevenly spaced spots cannot currently be used to mark high precision small font text or machine-readable graphics, such as UPC or QR codes, on an article.

[0005] The current state of the art in laser marking processes includes "raster" and "vector" marking processes, which are either fast but have low precision and resolution, or slow but have high precision and resolution. The combination of high speed and high precision does not exist in the prior art. This problem is particularly evident 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 provided on at least one side of the article (many of which are required for regulatory purposes) are provided via laser marking.

[0006] Raster laser marking processes place individual laser marks in a grid, and an image is marked row by row, point by point by a laser. Each of the pulses is "gated" so that a pulse is only fired for dark pixels of the image, and no pulse is fired for light pixels of the image (or vice versa). Each of the pulses is gated individually, and the pulse energy of each pulse can be varied to produce grayscale. State-of-the-art raster marking processes are effectively limited to lasers with repetition rates of about 100 kHz, given the practical limit of an update rate of about 10 us in signaling the laser's on / off function (i.e., "gating"), and can only be made faster by increasing the pulse spacing, which may sacrifice fine detail such as that required for marking small font text and graphics.

[0007] State-of-the-art vector marking processes can run at over 100 kHz because pulses are typically gated open while the laser beam is "steered" (by mirrors) into the shape of the vector line to be marked. Vector marked articles containing text can often be recognized because the marked line is typically one pulse wide (unless filled) and the pulses come close together near corners where the surface speed of the laser beam slows as it turns the corner. However, it has been found that the accuracy of mark placement with vector marking is compromised when the surface speed of the laser beam is very high.

[0008] Currently, moderately high speed laser marking can be achieved with polygon scanners (e.g., the High Throughput Raster Processing Polygon scanner system from Next Scan Technology (Evergem, Belgium)), which can be optimized for high speed and high accuracy. Polygon scanner systems use a rotating polygon mirror for row scanning. These scanners are typically used for full-area processing of regular patterns. Specifically, the field of view is typically square, which is relatively large by printing standards, and the repeating pattern is marked in its entirety many times on subsequent articles. The square field of view configuration of these scanners does not lend itself to precise marking of things such as small letters, alphanumeric characters, logos, pictures, etc.

[0009] Thus, there remains a need for faster, more economical, and more accurate laser marking. Both the hardware and software that control the lasing devices can be improved, and the methods of using these improved lasing devices can also be improved. Additionally, the placement of the laser mark on the article can be improved to provide both precision and speed. Summary of the Invention [Problem to be solved by the invention]

[0010] It is therefore desirable to provide improved laser devices, along with software for operating the laser devices, and processes for marking articles with high speed and precision, including 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 enable the resulting articles to have consumer-readable and machine-readable features that can replace labels and adhesives, among other advantages. [Means for solving the problem]

[0011] The present invention provides a solution to one or more of the shortcomings of the prior art, as well as other advantages. The specification, claims, and drawings describe various features and embodiments of the invention, including an article having a surface marked by a pulsed laser that includes a predetermined checkerboard pattern including alphanumeric characters in the form of text. The checkerboard pattern has a plurality of locations positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of locations of the plurality of locations along any of the two or more rows being separated by an X distance, and each adjacent pair of locations in the two or more rows being separated by a Y distance. The pulsed laser has a beam that moves across the rows as successive marks are formed at a constant surface velocity of greater than about 8 m / s, preferably greater than about 10 m / s, even more preferably greater than about 15 m / s, and 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. Preferably, the Y distance exceeds the X distance with a standard deviation of less than 10% for the Y distance. Similarly, the alphanumeric characters may have an average % deviation of less than about 150%, preferably less than about 120%, preferably less than about 100%, more preferably less than about 70%, and even more preferably less than about 50%. Also, the average % mismarked of the alphanumeric characters may be less than about 20%, preferably less than about 15%, more preferably less than about 10%, and even more preferably less than about 5%. Furthermore, the alphanumeric characters that make up the text have a Y distance standard deviation of less than about 0.040, preferably less than about 0.034, preferably less than about 0.028, more preferably less than about 0.010, and even more preferably less than about 0.005.

[0012] In another embodiment of the invention, the beam of the pulsed laser moves in a bi-directional profile such that the laser beam moves across the face of the article along a first row of the grid in a first direction while marking the article, and moves along a second row of the grid in a second direction. The alternation may continue for the remaining rows. Preferably, the first row and the second row are adjacent rows.

[0013] The text may have a font size in the range of 6pt to 10pt, with the Y distance being at least 1.2 times, preferably 1.5 times, more preferably 1.7 times, and even more preferably 2 times, the X distance. Alternatively, the text may have a font size in the range of 11pt to 16pt, with the Y distance being at least 2 times, preferably 2.5 times, more preferably 3 times, and even more preferably 4 times, the X distance.

[0014] In yet another embodiment of the present invention, the pulsed laser beam is directed by two galvo sets, each comprising a mirror and a galvo, wherein the angular velocity of rotation of at least one of the galvo sets is greater than about 40 rad / sec, the pulsed laser beam has a repetition rate greater than about 100 kHz, the pulsed laser beam has a pulse energy of about 10 μJ to about 1000 μJ, and the pulsed laser beam has a pulse duration of less than about 100 nanoseconds.

[0015] In another embodiment of the invention, the article is a container having a body portion, an opening in fluid communication with an interior space, and a base, the body portion having one or more walls extending from the opening to the base and enclosing the interior space. Further, the body portion comprises a first side and a second side, at least one side being free of ink, adhesive and / or label and comprising a predetermined checkerboard pattern of laser markings.

[0016] The present invention offers many advantages over the prior art because laser marking can be, for example, consumer readable alphanumeric characters, sentences, paragraphs, and other visual communication methods that can be marked on an article without the need for traditional labels. Specifically, the process and article of the present invention can be marked with ingredient lists, instructions, UPC codes, and the like in a fast, cost-effective manner without the use of labels and adhesives. This reduces costs, is environmentally friendly (less wasted stickers on the package), and allows for instantaneous changes in the message communicated to the consumer. For example, if an ingredient is changed in a formula, a new ingredient label can be marked on the article as soon as a change can be made in the computer instructions to the laser device. No new labels are required. [Brief description of the drawings]

[0017] [Figure 1] 1 is an article according to the present invention marked with alphanumeric characters in a checkerboard pattern. [Diagram 2] FIG. 1 is a schematic diagram of a lasing apparatus according to the present disclosure. [Diagram 3] A grid according to the present disclosure, with adjacent parallel row positions stacked. [Figure 4] Grid pattern according to the present disclosure, with offset locations in adjacent parallel rows. [Diagram 5] 1 is an alphanumeric character marked with a checkerboard pattern in accordance with the present invention. [Figure 6A] 1 is a checkerboard pattern of alphanumeric characters marked in accordance with the present invention. [Figure 6B] 1 is a checkerboard pattern of alphanumeric characters marked according to a prior art process. [Figure 7] 1 is an industry standard UPC code printed by the laser and process of the present invention. [Figure 8] 1 shows a standardized rectangular pattern laser printed by a prior art vector laser process compared to the same pattern laser printed in accordance with the present invention. [Figure 9] 1 is an exemplary grid of standardized rectangles in accordance with the present invention. [Figure 10] FIG. 6 is a modified version of FIG. 5 to show the mismarked % calculation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Goods As used herein, an "article" refers to an individual object, such as an object for consumer use, such as a container suitable for containing a material or composition. The article may be a container, non-limiting examples of which include bottles, tubes, films, laminates, bags, wraps, drums, jars, cups, caps, and the like. The composition contained in such a container may be any of a variety of compositions, including, but not limited to, detergents (e.g., laundry detergents, fabric softeners, dishwashing, skin care, and hair care), beverages, powders, paper (e.g., tissues, wipes), diapers, beauty care compositions (e.g., cosmetics, lotions), medicines, oral care (e.g., toothpaste, mouthwash), and the like. The container may be used to store, transport, and / or dispense the material and / or composition contained therein. The article may be made of any of a variety of common materials, including: PET, PETG, HDPE, PP, PVOH, LDPE, LLDPE, steel, glass, aluminum, cellulose, pulp, paper, and the like.

[0019] FIG. 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, an alphanumeric character, a company logo, a drawing, artwork, a UPC or QR code, etc. In this example, the marked location 12 constitutes an alphanumeric character 14, which in this case is the number 2, "2". The unmarked location 11 in the grid 16 is shown for illustrative purposes only and will not appear on the final marked article 10. The article 10 is shown as a container, having an opening 11 and a neck 13 that provides access to an interior space 15.

[0020] An article 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 one another. The two or more materials may comprise layers within the article. When the article has different layers, the material that comprises each of the layers may be the same or different from any other layer. For example, the article may be made of polyethylene terephthalate (PET), polyethylene terephthalate glycol (PETG), polystyrene (PS), polycarbonate (PC), polyvinylchloride (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 a polyolefin, such as low-density polyethylene (LDPE), polyolefin (POF ... The article may include one or more layers of a thermoplastic resin selected from the group consisting of one of linear low-density polyethylene (LDPE), linear low-density polyethylene (LLPDE), high-density polyethylene (HDPE), propylene (PP), and combinations thereof. The article may also include a cellulosic material such as pulp or paper.The cellulosic material may be included with an additional second material, which may be a second cellulosic material or may include a resin, including a thermoplastic material or a water / solvent based coating.

[0021] Recycled thermoplastics and / or cellulosic materials, such as, for example, post-consumer recycled ("PCR") materials, post-industrial recycled ("PIR") materials, and regrind materials, such as, for example, polyethylene terephthalate (PCRPET), high density polyethylene (PCRHDPE), low density polyethylene (PCRLDPE), polyethylene terephthalate (PIRPET), high density polyethylene (PIRHDPE), low density polyethylene (PIRLDPE), may also be used.

[0022] Thermoplastic materials may include monomers derived from renewable resources and / or monomers derived from non-renewable (e.g., petroleum) resources, or a combination thereof. For example, a thermoplastic may include a polymer made entirely from bio-derived monomers, or a polymer made partially from bio-derived monomers and partially from petroleum-derived monomers.

[0023] Pigments, colorants, and laser absorbing additives may be added to the materials of the articles of the present invention. A suitable selection of the laser wavelength in combination with the pigment / colorant / additive may provide suitable marking of the article. If the contrast or speed of marking is not sufficient, these pigments / colorants / additives may facilitate the absorption of the laser energy, thereby functioning as laser absorbing additives. Laser absorbing additives known to those skilled in the art may facilitate the formation of the laser mark, making the laser marking clearer and more easily readable by users and machines, as well as increasing the rate at which the article can be marked. These laser absorbing additives generally absorb the laser energy specific to the laser wavelength, and subsequently initiate a color change to the surrounding matrix (via localized heating that causes 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 opacify containers to protect the contents from the effects of light, and may also function as laser absorbing additives depending on the wavelength of the laser used. Additional examples of laser absorbing 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, graphitic 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. An example of a laser marking laser absorbing additive is commonly sold under the trade name "Iriotec®" by Merck KGaA of Darmstadt, Germany.

[0024] Lasers and Laser Devices Pulsed lasers, such as short-pulse lasers, can be used to mark articles according to the present invention. Lasers for use in the present invention are commercially available and include nanosecond, picosecond, and femtosecond lasers. These short-pulse lasers can emit pulses that are applied at high energy density and high repetition rate, which is important to enable high speed laser marking of articles. Laser marks themselves include marks made on articles, such as products or packages, by oxidizing, reducing, ablation, etching, foaming, and carbonizing.

[0025] Any suitable laser can be used to mark the article 10. FIG. 2 shows an embodiment of a lasing apparatus 200 including a laser 20 useful for marking an article according to the present invention. The lasing 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 a power output in the range of 1 W to 60 W and a laser wavelength of 355 nanometers, or an IR marking laser having a power output in the range of 1 W to 300 W or even 500 W and a laser wavelength of 1064 nanometers. Such lasers are available from a variety of 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 styles and types of lasers are possible and different power ranges and settings may be used. The lasing device can include optics, if desired, that can be used to direct the laser beam and / or modify the laser beam, such as by changing the energy density and / or spot size of the laser beam 28.

[0026] 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 100 kHz repetition rate laser delivers 100,000 pulses / second. Repetition rate can be important to process certain lasing jobs in a short amount of time (i.e., high speed laser marking). More pulses per unit time available correlate approximately linearly (inversely) to the time required to mark a given row for a particular job.

[0027] Pulse energy is the amount of energy a single laser pulse contains, typically measured in μJ or mJ. Typically, pulse energies are in the range of 5 μJ to 2000 μJ (2 mJ), preferably in the range of 7 μJ to 1000 μJ, more preferably in the range of 10 μJ to 300 μJ. The average power of the laser is then given as the pulse energy times the repetition rate. Average power = pulse energy (J) * Repetition rate (Hz or 1 / sec).

[0028] Peak power is equal to pulse energy divided by pulse duration, which may be less than 100 nanoseconds, less than 50 nanoseconds, less than 20 nanoseconds, less than 10 nanoseconds, or less than 1 nanosecond. Thus, pulse energy and pulse duration are linearly related to peak power. The shorter pulse durations achievable with nanosecond, picosecond, and femtosecond lasers allow for very high peak powers that aid in the ability to mark articles.

[0029] In the lasing apparatus 200 depicted in FIG. 2, the laser 20 projects a laser beam 28 onto an X-mirror 22 that is rotated by an X-galvo 21. The X-mirror 22 and the X-galvo 21 collectively form an X-galvo set. The laser beam 28 then projects onto a Y-mirror 24 that is rotated by a Y-galvo 23. The Y-mirror 24 and the Y-galvo 23 collectively form a Y-galvo set. The X-mirror 22 and the Y-mirror 24 each cooperate to direct the laser beam 28 to a location where a desired mark 29 is to be marked on the article 27. The laser beam 28 will typically pass through a lens 26 before reaching the article 27. The distance from the lens 26 to the article 27 is the focal length 25.

[0030] The combined optics of the lasing apparatus may function to sweep the laser beam across the surface of the article in successive passes. The laser beam may be directed by the X mirror to sweep across the article along a first row in the grid in the X direction while emitting (or omitting) a pulse. The combination of the sweep speed of the laser beam across the surface of the article, also referred to as the surface speed of the laser beam, and the repetition rate of the laser pulses determines the spacing of the marks along the X direction. X Spacing * Repetition rate = surface speed

[0031] The laser may emit one or more pulses while sweeping across the article at a given location, thereby resulting in a marked location(s), or the laser may omit pulses while sweeping across the article at a given location, thereby resulting in an unmarked location (i.e., a void). The laser beam may be swept across the article at a constant surface speed while emitting and / or omitting pulses. The surface speed or sweep speed 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 across the subsequent / adjacent row "right to left".

[0032] 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 may be absorbed by the substrate of the article or by a laser absorbing additive incorporated into the article. The wavelength of the laser may match an absorption band, band gap energy, or surface plasmon / plasma resonance frequency in the UV-vis-NIR-IR spectrum of at least one of the substrate of the article or the laser absorbing additive 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 substrates or laser absorbing additives of the article exist and are contemplated herein.

[0033] Laser marking The articles of the present invention are typically marked by the process of foaming, carbonization, ablation, etching, reduction, oxidation, and / or phase change. The term foaming refers to the process where the laser beam melts and vaporizes a portion of the material, creating bubbles that are trapped in the molten resin and diffusely reflect light when cooled. Foaming generally results in a lighter marking in the laser marked area, and this method is most commonly used for dark materials such as plastics or translucent materials. The term "semi-transparent" as used herein means that the material, layer, article, or part of the article being measured has a total luminous transmittance of greater than 0% and less than or equal to 90%. The term "opaque" as used herein means that the material, layer, article, or part of the article being measured has a total luminous transmittance of about 0%. Total luminous transmittance is measured according to ASTM D1003.

[0034] Carbonization-based marking is a process that produces strong dark contrast on light 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 a combination of oxygen, hydrogen, or decomposition products. Carbonization generally leads to a dark mark with a higher carbon content relative to the original material, making it a good choice for lighter colored articles, but the contrast is rather minimal on darker materials.

[0035] Reduction and oxidation involves the laser energy changing the oxidation state of at least one of the article's components, such as a laser absorbing additive or an opacifying pigment, resulting in a discoloration or color change that is visible as a mark. For example, without being bound by theory, the energy imparted from a UV laser can promote the reduction of TiO2 to form titanium suboxide, where the titanium is reduced to an oxidation state below +4, which reduction results in a color change from white / colorless to blue to dark blue to black.

[0036] There are additional methods of marking articles. For example, annealing is a specific laser process available for metals and other materials. Energy from the laser beam creates an oxidation process below the surface of the material, which results in a color change on the material surface.

[0037] Tinting is another marking process that can be achieved as a result of a chemical reaction created on the material when the energy of the laser beam is applied. The change in hue will depend on the composition of the material being tinted. For example, light-colored plastic materials often discolor during the laser etching process, resulting in dark markings from the resulting soot particles.

[0038] Laser engraving is another process that involves removing material as the workpiece surface is melted and vaporized by a laser beam, which creates an impression on the engraved surface. Removing material is sometimes referred to as etching or ablation. Laser etching is a process in which a laser beam removes a coating previously applied to the top surface of a substrate, or to the substrate of an article. Contrast results from the different colors of the topcoat and substrate, or the different topography and texture of the etched area versus the adjacent areas. Common materials that are laser marked by removing material include anodized aluminum, coated metals, foils and films, or laminates. The term "etching," as used herein as a noun, refers to the cavities that are formed when material is removed from a surface. As verbs, the terms "etch" and "etching" refer to the act of removing material from a surface. Etching can be done mechanically, chemically, and thermally (e.g., with a laser). While there are no particular limitations on the maximum or minimum depth of etching, the etching depth is typically in the range of about 0.01 mm to about 2.0 mm, including any depth within the range, such as, 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.

[0039] Bleaching or photobleaching (sometimes called fading) is a photochemical change in a chromophore (such as in a pigment or dye) or fluorophore molecule such that it permanently loses its inherent color and / or is no longer able to fluoresce. This is caused by scission of covalent bonds or non-specific reactions between the chromophore / fluorophore and surrounding molecules, and may also be affected by laser marking.

[0040] Spot size is an important parameter of the laser marking of the present invention and is related to the focal area where the laser beam contacts the article. "Spot size" is the diameter of a circular spot. Although the spot is circular, it is possible to achieve an elliptical spot by controlling the laser beam optics on the article. The spot size can be modified by focusing or defocusing the laser beam, but the "fluence" (=energy per unit area) in the spot decreases as the spot is enlarged or defocused. Theoretically, the minimum spot size achievable with any laser is the wavelength of the laser itself. As a practical matter, the minimum spot size achievable with a pulsed laser is about 7 to 20 μm. The spot size of the laser marking of the present invention can 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, spot sizes for conventional laser marking such as date codes (e.g., using CO2 lasers) are 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 a paintbrush an artist uses to paint a picture. When very fine detail is desired, a smaller spot size is utilized. A larger area to be covered may favor a larger spot size. However, laser marking mechanisms require a minimum fluence to achieve the desired mark, and therefore a balance between pulse energy, pulse duration, pulse overlap, and spot size is important.

[0041] Additionally, there is an area around the laser contact spot that may be heated during the marking process, but little or no material is marked. This "heat affected zone" can still result in effects such as crystallization that can affect the appearance and / or performance of the target material. Short pulse lasers (e.g., nanosecond lasers) have some heat affected zone, but it is substantially smaller than microsecond pulse lasers or CW type lasers (e.g., CO2, longer pulse IR lasers, etc.). Picosecond and femtosecond lasers are often referred to as "ultrashort pulse" and have little or no heat affected zone. This ability helps control the thermal effects of marking.

[0042] The geometry of the mark spacing is a major contributor to the cycle time and fluence (or energy per unit area) provided to the article. For example, the spacing between marks can be such that the marks do not overlap at all, having 0% overlap. At 0% overlap, each individual laser pulse contributes energy provided to mark the article. If the laser does not have enough pulse energy or peak power to achieve the desired mark, the pulse spacing can be reduced to the point where the spots overlap in either or both the X and Y directions. Overlapping 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 the main lever of cycle time. When a laser has a fixed repetition rate or pulse frequency, it is desired 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.

[0043] Pulse duration is the length of time that a pulse remains continuously above half its maximum value. Shorter pulses can produce higher peak powers for a given average power. This is known as Average Power = Pulse Energy (J). * This is because of the repetition rate (Hz or 1 / sec). Peak power is equal to the pulse energy divided by the pulse duration. Therefore, as the pulse duration becomes significantly smaller, the resulting peak pulse power becomes significantly higher. This peak power allows for improved carbonization, bubbling, oxidation, reduction, etc. on the target being marked. Short pulse lasers take advantage of this phenomenon to mark articles, allowing for marking mechanisms not typically found with longer pulse lasers.

[0044] Varying the power / fluence output of the laser in creating the laser mark can also be manipulated during marking to create grayscales, also known as dithering. Such a process is a known aspect of the raster process of laser marking. Without wishing to be bound by theory, it is believed that such dithering during laser marking also increases 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. A constant power can be maintained while the laser is marking within an entire row, or even while the laser is marking between rows throughout the entire marked pattern.

[0045] Grid As used herein, a "grid" or "bitmap grid" is taken to mean a regular periodic array of locations that may contain a plurality of marks. The periodicity of the array includes periodicity in both the X and Y directions. The plurality of marks in the grid may or may not be present at each of the locations in the grid. That is, a mark may be formed at a location in the grid or may not be present at that location (i.e., a void). As mentioned, the lasing device sweeps a laser beam across an article while either a laser pulse is being emitted from the laser or no pulse is being emitted. A marked location occurs when the laser emits a pulse at a given location and an unmarked location occurs when the laser does not emit a pulse at a given location. The laser beam may be swept across the article at a constant surface speed while the repetition rate of the laser is constant, and thus the periodicity of the positions will be regular (i.e., X distance) in the direction in which the laser beam is swept across the article (i.e., X direction) even if the marked positions are not equally spaced, but taking into account the possibility of unmarked positions, in which case the distance between any marked positions along the same direction (i.e., X direction) may be an integer number (i.e., 2x, 3x or more) of the minimum distance measured between marks in that direction (i.e., X direction).

[0046] The laser beam may be swept across the article in subsequent rows. The laser beam may be swept from left to right or right to left, may be swept in the same direction as it moves from row to row (e.g., like a carriage return on a typewriter as in a raster process), or may be swept in alternating directions as it moves from row to row. A major contributor to reducing cycle time includes sweeping the laser beam in alternating directions as it moves from row to row. The rows may be approximately parallel to one another. The distance between adjacent rows is the Y distance. The positions of adjacent rows may be directly above / below one another or may be offset with respect to one another. It is understood that an offset equal to the X distance results in a realignment of the positions between the rows.

[0047] Alphanumeric characters are letters or numbers, for example, in English, letters are A-Z including uppercase and lowercase, and universal numbers are 0-9 and combinations thereof. Alphanumeric characters are not limited to any particular style or font. Chinese, Japanese (e.g., Kanji, Katakana), Russian, Arabic, and other languages ​​have different alphanumeric characters that can be marked with the pulsed laser according to the present invention.

[0048] Those skilled in the art will understand that the size of a printed, or in this case marked, alphanumeric character is measured by its font. The smallest font that is generally accepted as consumer readable on a marked article is about 6pt. Font size can be increased to very large sizes, but when marking the face of a consumer package, fonts of more than, for example, 20 are not practical, since a few characters may fill the entire package. A "face" of a consumer package is typically the front or back of the package, and these faces typically have different markings. For example, the product name and general product description (shampoo, conditioner, soap, etc.) are typically found on the front, while the ingredients list, UPC code, and instructions for use are usually found on the back. For a cylindrical package, an imaginary vertical plane can be drawn down the bottle, with the front side on one side of the imaginary plane and the back side on the other side of the imaginary plane.

[0049] As discussed above, the laser marks may not overlap to reduce the time required to mark a given pattern (i.e., "time to mark"). The time to mark can be further reduced by spacing the marks in either or both of the X and / or Y directions, but this increased spacing may lead to poor legibility of any alphanumeric characters that make up the given pattern. For example, increasing the X distance allows for a faster surface speed 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 predetermined pattern.

[0050] Surprisingly, it has been found that for a particular given pattern, increasing the Y distance (fewer reversals) can have a greater impact on reducing the time to marking than increasing the X distance (faster surface speed). While conventional raster marking processes include equal X and Y spacing, the present invention can include a Y distance that exceeds the X distance. It has further been found that the legibility of alphanumeric characters marked by the constant surface speed (CV) bitmap process of the present invention can depend on the X and Y spacing 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, it is about 0.010 mm to about 0.100 mm, and even more preferably, it is about 0.040 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, it is about 0.050 mm to about 0.150 mm, and even more preferably, it is about 0.060 mm to about 0.075 mm.

[0051] If a given alphanumeric character has a font size in the range of 6pt to 10pt, the Y distance may be at least 1.2 times the X distance, preferably 1.5 times, more preferably 1.7 times, and even more preferably 2 times. If a given alphanumeric character has a font size in the range of 11pt to 16pt, the Y distance is at least 2 times the X distance, preferably 2.5 times, more preferably 3 times, and even more preferably 4 times.

[0052] 3, 4 and 5 all show various depictions of a grid in accordance with the present invention. More specifically, FIG. 3 illustrates a grid 39 in accordance with the present invention with an X-direction 30, a Y-direction 32, an X-distance 31 and a Y-distance 33. Potential marking locations 36 are depicted by empty circles that make up the grid. Furthermore, in FIG. 3, locations 36 between parallel rows 38 are "stacked" when the angle 35 between the location in the adjacent row 34 depicted in the Y-direction between two potential marking locations 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), locations are stacked when the parallelogram's interior angles are approximately 90 degrees. Locations are offset when the parallelogram's interior angles are different from 90 degrees (i.e., 120 degrees and 60 degrees). The X-distance is measured from the center of one location to the center of the adjacent location in the X-direction.

[0053] Those skilled in the art will understand that a checkerboard unit cell has four axes of symmetry: horizontal, vertical, and two diagonals. The laser marking discussed herein can be done along any of these four axes. For simplicity, the vertical and horizontal directions shown in FIG. 5 are described. FIG. 5 can be rotated 45 degrees and the diagonals become vertical and horizontal. Again, as shown in FIG. 5, the laser marking occurs across one row, and then the laser moves up or down the row above or below and marks in the opposite direction.

[0054] 4 is 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 closest position 46 in an adjacent row 48, and the offset 44 exists when the angle 45 is greater than or less than 90 degrees. FIG. 4 further shows an X direction 40, an X distance 41, a Y direction 42, and a Y distance 43.

[0055] FIG. 5 shows an alphanumeric character 52 marked on a grid 50. The alphanumeric character is the number "2" and is marked with a laser marked location 54 as opposed to an unmarked location 56. When multiple alphanumeric characters, e.g., words, sentences, or paragraphs, are printed, characters that share the same column of text will also share the same horizontal column 53 of laser markings. That is, the laser device will go across a column, marking the required locations for each alphanumeric character, and then leave as many unmarked locations between characters as necessary to form a column in which the marking is associated with multiple characters in that column. In this manner, words, sentences, and paragraphs can be marked and are clearly legible to a consumer or machine.

[0056] Horizontal columns 53 and vertical columns 55 define a grid 50. The distance between marked locations 54 or unmarked locations 56 in horizontal columns 53 defines an X-distance 51. Additionally, the distance between marked locations 54 or unmarked locations 56 in vertical columns 55 defines a Y-distance 57. It is important to note that the X-distance 51 and Y-distance 57 are defined relative to the horizontal orientation (53) and vertical orientation (55), respectively, of the marked indicia, in this case the number "2." However, the marked locations 54 can be marked in a horizontal direction 59 or a vertical direction 58. More specifically, when marking in a horizontal direction 59, the laser moves across the horizontal columns 53 either marking each location (54 and 56, respectively) or leaving it unmarked. The laser then moves down or up one Y distance and begins to run across another row above or below the previously marked row. Similarly, when marking in the vertical direction 58, the laser moves up or down vertical row 55, either marking each location (54 and 56, respectively) or leaving it unmarked. The laser then moves across one X distance and begins to run up or down the vertical row adjacent to the previously marked vertical row.

[0057] 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 FIG. 5 is greater than 1 because its height is greater than its width. It can be easily seen that marking the number "2" in the vertical direction 58 requires less inversion than marking in the horizontal direction 59. This can make marking this indicia faster when sweeping the laser beam while marking in the vertical direction 58. Many considerations will be made when deciding 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 will always be defined for the indicia being marked in the horizontal and vertical directions, respectively.

[0058] The periodicity of the positions constituting the grid includes periodicity in the X direction and periodicity in the Y direction. The X direction and the Y direction may be substantially orthogonal to each other. As depicted in Figures 3 and 4, the grids 39 and 49 may each be in the form of evenly spaced positions along successive parallel rows. The direction parallel to the successive parallel rows is the X direction (30, 40), and the direction substantially perpendicular to the X direction is the Y direction (32, 42). The spacing between adjacent positions along any parallel row (e.g., in the X direction) is referred to as the X distance (31, 41), and the distance between adjacent parallel rows is referred to as the Y distance (33, 43).

[0059] The grid 39 may be a stacked grid as depicted in FIG. 3. In a stacked grid, a location along a first row where a mark may be made is directly below the first row and directly above a location along a second row. Stated differently, the angle 35 formed between a row segment connecting a first location along the first row with an adjacent location along the first row and a row segment connecting the first location with its nearest location along the second row is 90 degrees. o In the stacked grid, the spacing between adjacent positions along the X axis is equal to the X distance 31, and the shortest spacing between adjacent positions between adjacent X axes is the Y distance 33.

[0060] The grid may be an offset grid as depicted in FIG. 4. In an offset grid 49, the location where a mark may be placed along the first X-axis is not immediately below the first X-axis and immediately above the location along the second X-axis. Stated another way, the angle 45 formed between a row segment connecting a first location along the first X-axis with an adjacent location along the first X-axis and a row segment connecting the first location with its nearest location along the second X-axis is 90 degrees. o Greater or smaller than.

[0061] Those skilled in the art will appreciate that the X and Y directions are somewhat arbitrarily selected for a given pattern. For example, Figure 6B depicts an example of a "2" created by laser marking, where the X direction is perpendicular to the marked "2" 61. Those skilled in the art will appreciate that the X direction could just as easily be horizontal to the marked "2" 61.

[0062] One skilled in the art will understand that the grid (e.g., 39 and 49) and the regular spacing between adjacent locations assumes a flat surface of the article. If the article surface is curved, the spacing may vary with the curvature of the surface.

[0063] The X-distance may be the same between all parallel rows that make up the grid. That is, the X-distance does not vary along the X-direction of a given row, nor does it vary between rows of grids that comprise the given pattern. Alternatively, the given pattern may include multiple regions where the X-spacing within each region is the same but varies between regions. For example, one X-distance may be used consistently when marking alphanumeric characters, and a different X-distance may be used when marking machine-readable codes such as UPC codes. Similarly, the Y-distance may not vary within a given pattern, or may vary between regions within a given pattern. The surface speed and / or marking direction (i.e., up / down or left / right) of the laser beam may also vary between regions. For example, it should be noted that articles that are laser marked using a vector marking process (i.e., as opposed to the CV bitmap marking process of the present invention) generally exhibit variable spacing of positions / marks along any of their marked directions as the laser accelerates (making the marks farther apart) and / or decelerates (making the marks closer together) along the course of marking the article. Laser marking of the present invention is typically performed at a constant speed when the laser is marking. The movement of the laser beam stops after finishing one row along the X direction, moves up or down to the next row along the Y direction, and then starts marking a new row, also at a constant speed. This speed can also be the same throughout the marking of a given pattern. Articles marked with a CV bitmap checkerboard marking process can be distinguished from articles marked with a vector marking process by the regular periodicity of the marks and often by the absence of a contour or "border" that defines the marked area (see, for example, border 63 in FIG. 6B).

[0064] Figures 6A and 6B illustrate the difference between laser marking via bitmap checkerboard marking according to the present invention's CV bitmap process 6A and the prior art vector marking process 6B, in which alphanumeric characters 60 and 61 (i.e., the number "2") are laser marked in both cases. Alphanumeric character 60 has clean, crisp edges and is substantially better defined with very few stray markings. Figure 6B is in stark contrast, with mostly undefined edges and a significant number of stray markings 62 outside the boundaries of alphanumeric character 61. Both characters 60 and 61 were marked in roughly the same amount of time.

[0065] Improved laser marking rate As will be discussed, the present invention is capable of laser marking articles at higher speeds and with higher precision than prior processes. Existing raster processes are very slow but relatively accurate, while vector laser marking processes are faster and more accurate at slower speeds, but are very rough at higher speeds, resulting in unclear 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 difference between the modes required to laser each type is in the galvo movement, or laser beam steering, and the parameters used.

[0066] Vector paths are typically slower because, for an image, multiple fixed short start and stop points require the galvo set to spend time accelerating to the user set maximum surface speed (determined by the pulse interval multiplied by the repetition rate) and the length of the vector distance. A long vector distance allows the vector lasing device to reach its maximum surface speed, while a shorter vector distance forces the lasing device to constantly accelerate and decelerate, never reaching the maximum surface speed, resulting in a longer marking cycle time.

[0067] Vector processes are also less accurate than CV bitmap processes at high speeds due to the acceleration / deceleration of the galvos steering the laser beam. Specifically, the location of each laser mark must be communicated from the 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 approximately 10 μs, so a laser outputting pulses with a 100 kHz repetition rate would allow an update in communication for each individual position within the grid. This also applies to raster laser marking processes, which may further include variations in pulse power for each pulse as a means of achieving gray scale (e.g., dithering). As the surface speed of the laser beam across the surface of the article increases, repetition rates in excess of 100 kHz are required to achieve the desired X spacing within the row, and each update from the software must communicate the location of multiple laser markings (or voids / non-marks). Although the calculations can be done nearly instantaneously, in the extremely fast time domain of high speed laser marking, the galvo cannot respond as quickly, and the acceleration / deceleration shape of the vector process is believed to result in a significant number of misplaced marks in a given row for the constant surface velocity profile of the present invention.

[0068] Figure 6B depicts the effect of running a vector-based process too quickly when marking text containing alphanumeric characters, and the misplacement of marks within a column. The figure shows many rows that are offset from one another, and starting the marking either too early or too late can result in jagged edges in the alphanumeric characters, making the overall appearance unclear and unreadable (e.g., being unable to distinguish an "8" from a "0").

[0069] In contrast, the process and resulting patterns of the present invention can be produced by a constant surface velocity (CV) bitmap path. The CV bitmap laser marking process allows for increased speed and increased precision since there is no start and stop point within the row, but rather a user-defined maximum surface velocity (again, the pulse interval multiplied by the repetition rate) that is constant while applying the pulses or marking. Additionally, the lasing device of the present invention can increase speed when not marking over a relatively long distance (relative 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 lasing device can accelerate without losing precision, otherwise moving at a constant surface velocity while pulsing the laser beam. This is yet another reason why the marking system of the present invention is faster and more precise than prior devices.

[0070] A smaller set of galvos (e.g., with mirrors of lower mass) allows for a higher acceleration to reach this user-defined maximum surface velocity. These galvos can be adjusted to higher acceleration values ​​that allow the mirror to reach its desired angular velocity in a shorter time. Interestingly, these values ​​can be adjusted specifically for bitmap processing at higher values ​​versus vector processing. Additionally, in the vector laser software, there is a maximum marking surface velocity limit that is set so that the laser markings are closer to their desired commanded positions. As the maximum surface velocity threshold is increased, the laser pulses will have more error relative to their desired positions in vector processing. Note that in CV bitmap marking mode, since the surface 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 surface velocity threshold can be increased significantly to achieve an overall lower marking cycle time versus vectors and still keep the pulses at their designated positions.

[0071] The angular velocity of the galvo set is important to the job cycle time because it is directly related to the surface speed of the laser beam across the article, which is set by the angular velocity of the galvo / mirror pair and the focal length of the lasing device. Surface speed = galvo angular velocity (rad / sec) * Focal length (mm)

[0072] The surface speed when producing laser marks in a given row is primarily controlled by the X galvo / mirror set. Job cycle time may depend more on the laser surface speed in the X direction than in the Y direction, and the X galvo / mirror set may be more responsive than the Y galvo / mirror set. For example, the mirrors on the X galvo / mirror set may be smaller (i.e. lower mass, smaller mirror size, lower inertia, higher acceleration motor capability).

[0073] The surface speed of the laser beam across the surface of an article in current CV bitmap processes is much faster than is achievable with currently available laser marking processes, such as raster and vector marking processes. Current processes are typically exemplified with surface speeds on the order of 1-2 m / s or less. The CV bitmap process of the present invention provides surface speeds of greater than 8 m / s, and even surface speeds of 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.

[0074] The sweep path of the laser beam across the surface of the article can also contribute to reducing cycle time. Conventional raster laser marking processes sweep the laser beam across the rows in either a right-to-left or left-to-right direction, also known as unidirectional, and "jump" the laser beam back after marking each row to start the subsequent row (like a carriage return on a typewriter). In this way, subsequent rows can be easily aligned (i.e., stacked) and the grid positions can be aligned based on this same starting point. To eliminate the jump distance and reduce the time between each marked row, current CV bitmap processes use a "bidirectional" process in which marking can be alternated bidirectionally (i.e., marking is done from left to right on the first row and right to left on subsequent rows).

[0075] To keep the trains of pulses aligned, the lasering device can be programmed to incorporate a laser on adjust, which is a delay function for every alternating train to keep the pulses aligned. For example, at a marking surface speed of about 22.5 m / sec, a delay of 8 microseconds is used for every alternating train. 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.

[0076] The laser on adjust is an element of the reversal shape of the laser beam sweep path. The reversal shape refers to the path followed by the galvo set directing the laser beam while the laser beam is reversing between rows (i.e., marking a row from left to right, then reversing to mark the next row from right to left). The laser is typically off (i.e., does not emit a pulse) during the reversal. The laser on adjust helps to align the marks in adjacent rows. For example, if the squares are stacked squares, the laser on adjust ensures that the marks in adjacent rows remain stacked. If offset squares are used, the laser on adjust ensures that the squares remain offset, and that the amount of offset remains relatively constant. The laser on adjust can be determined experimentally and generally varies with the angular velocity of the galvo set.

[0077] The flip shape of the laser beam after completing a row can also contribute to reducing cycle time. As discussed above, the laser beam is steered by a galvo set, and the ability of the galvo set to accelerate and decelerate is a known limitation to the speed and accuracy of laser marking in other (e.g., vector) marking processes. The current CV bitmap process overcomes these limitations. For example, the current CV bitmap process does not accelerate or decelerate the laser beam while the laser is emitting a pulse (i.e., creating a laser mark). Instead, the laser beam is only accelerated / decelerated while the laser is not marking the article, for example, when the laser beam is skipping multiple voids (or entire rows) or when the laser beam is flipping at the end of a row before marking the next row. The flip shape can be symmetric or asymmetric. If the speed at which the laser beam sweeps across the surface of the article is high, an asymmetric flip shape may be preferred.

[0078] As mentioned above, the geometry of the mark spacing is a major contributor to cycle time. As discussed, spreading out the locations within the grid (i.e., increasing the X and Y distances) can result in a decrease in cycle time. Within a row, the X distance contributes to the cycle time in that the laser surface speed is determined by the laser repetition rate and the X distance. Increasing the Y distance improves the cycle time by reducing the number of reversals the galvo set must make (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 speeds. For example, the X distance can be decreased and the Y distance increased to obtain a similar looking image at a reduced overall cycle time. Furthermore, it has been found that increasing the Y distance while simultaneously decreasing the X distance provides faster cycle times and improved legibility of the marked features.

[0079] As discussed above, X-distance and Y-distance and their ratios can contribute to laser marking small font text or images that are legible at high speeds (i.e., low cycle times). X-spacing and Y-spacing can also be important when marking images such as graphics, especially when the images contain grayscale. Whereas known processes of raster marking produce grayscale by varying the energy of individual laser pulses, the CV bitmap process instead achieves grayscale by spacing full energy pulses in different patterns that run too fast and do not vary the energy of these pulses individually to make the grayscale appear.

[0080] The selection of the marking direction orientation 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 the feature's height to its width. If the height and width are approximately similar, the aspect ratio is close to 1 and the impact (on job cycle time) of selecting the marking direction relative to the feature's dimensions may be minimal. However, for features with high aspect ratios (e.g., height >> width) or low aspect ratios (e.g., width >> height), the job cycle time can be reduced by selecting the marking direction relative to the feature's dimensions. For example, the marking direction can be selected to be approximately parallel to the feature's longer dimension (i.e., major axis), or the marking direction can be selected to be approximately parallel to the feature's shorter dimension (i.e., minor axis) (see again FIG. 5). While there are many factors that affect job cycle time, it is believed that having the marking direction correspond to the feature's major axis reduces the number of flips required when marking the feature, thereby reducing job cycle time.

[0081] The choice of marking direction orientation can also affect job cycle time at very high surface speeds. At very high surface speeds, flip times can increase to the point where they dominate the job cycle time. By choosing a marking direction approximately parallel to the long dimension of the feature, flips can be minimized and job cycle time can be reduced. As discussed above, the X and Y distances can be different, and this difference can contribute to a reduction in job cycle, and loss of image clarity of features such as alphanumeric characters can be compensated for by decreasing the X distance while increasing the Y distance.

[0082] As discussed above, the smallest font that is generally accepted as consumer readable on a marked article is about 6 pt. Font size can be increased to very large sizes, but when marking the surface of a consumer package, fonts greater than, for example, 20 are not practical since several characters may fill the entire package. If a given alphanumeric character has a font size in the range of 6 pt to 10 pt, the X distance may be at least 1.2 times, preferably 1.5 times, more preferably 1.7 times, and even more preferably 2 times, the Y distance. If a given alphanumeric feature has a font size in the range of 11 pt to 16 pt, 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 X and Y distances are defined relative to the horizontal and vertical directions, respectively, relative to the indicia being marked, regardless of whether the sweep direction of the laser beam is perpendicular or horizontal to the indicia.

[0083] In the laser marking process of the present invention, the laser source is stationary and the laser beam is directed by a lasing device that includes a series of lenses and mirrors controlled by an algorithm. The algorithm can read a digital image of the 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 provided by IPG Photonics, 50 Old Webster Road, Oxford, MA 01540, USA.

[0084] Microscopy A number of articles were marked according to the method of the present invention and comparative articles were marked by existing methods. The results of these comparisons are shown in Tables 1, 2 and 3, and in Figures 7 and 8. To obtain these comparative data, samples are cut from laser-marked HDPE blow-molded bottles containing TiO2 using a utility knife and scissors. If the cut samples are not suitably flat, the samples are flattened on the microscope stage using tape or a frame. A stereo microscope such as a motorized Zeiss SteREO Discovery.V20 (Carl Zeiss Microscopy, LLC, Thornwood, NY) equipped with a color camera such as Axiocam 305 (5 megapixel CMOS, Carl Zeiss Microscopy, LLC, Thornwood, NY) is used to capture the letters, numbers and images of the sample objects using reflected light illumination 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). A typical light intensity of 80-100% of maximum light intensity is used. The individual laser markings that combine to form the target letter, number, or image are resolved using a suitable magnification in combination with a zoom magnification such that the total magnification is 10x-345x using an objective lens such as an Achromat S 1.5x FWD 28mm (Carl Zeiss Microscopy, LLC, Thornwood, NY). As an example, for a letter, number, or image with a font size of 10pt, the total magnification is about 40x. After the target number is within the field of view of the camera, the letter, number, or image is 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).Prior to collecting the image of the letter, number, or image, the imaging settings are optimized by using the auto exposure option from the user interface platform along with the lamp intensity. The image is collected in the highest resolution format possible, such as ZVI, and then exported as a Tiff file with a resolution of approximately 2464 x 2056 pixels. Furthermore, the marked row of letters, numbers, or artwork should be approximately parallel to the horizontal border of the image. If necessary, multiple images taken at higher magnifications can be precisely stitched together to encompass the entire area of ​​the letter, number, or image.

[0085] Image analysis The 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 and several other image processing steps. Analysis functions implemented in MATLAB available from The Mathworks, Inc. (Natick, Mass.) are referenced in the description of this method.

[0086] The microscopy and subsequent image analysis may be traced across one or more predefined patterns, portions of predefined patterns, or individual images within a predefined pattern, such as graphics or alphanumeric characters. If image analysis is performed on a portion of a predefined pattern, the portion (such as an individual graphic or alphanumeric character) must be separated from any surrounding images, characters, or artwork prior to analysis. A mask may be drawn around the character or image of interest in the predefined pattern. The mask separates the character or image from other partial characters, numbers, bar codes, artwork, smudges, or other defects that may occur in the image.

[0087] Image analysis relies on first identifying the laser marks that make up the image. The laser marks can be identified by any reasonable means, for example by iteratively thresholding a grayscale image from a microscope. A start threshold is set to capture only a few pixels that fall into some of the markings. The threshold is then gradually changed to capture ever-increasing areas of the marks. Progressive thresholding continues from the start threshold to a stop threshold. The stop threshold may be determined automatically, such as by using MATLAB's "multithresh" function (i.e., Otsu's method). Progressive thresholding may be advantageous in the 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 example presented, dark marks are identified against a relatively light background.

[0088] Then, once the regions reach a certain size, the connected components can be used to identify individual marks. A connected components algorithm is run with each new threshold to group touching pixels into blobs. Once a blob reaches 50% of the area of ​​a mark, it is identified as a mark. The center coordinates of the mark are found using a centroid method implemented in MATLAB's "regionprops" function. The centers are then used to determine the spacing between adjacent marks within a column (e.g., X distance) and the spacing between adjacent columns of marks (e.g., Y distance) (see below).

[0089] The observed X and Y distances and the standard deviation are determined. An exemplary means for determining the X and Y distances and their standard deviations may also be performed using image analysis, although one skilled in the art will appreciate that any means of determining these distances and standard deviations may be used. One means of determining these values ​​by image analysis involves the use of "Delaunay triangulation." For Delaunay triangulation, the center coordinates of the marks are passed to MATLAB's "Delaunay triangulation" function, which creates a triangulation based on the center points. The edges of a Delaunay triangulation never cross, and center points are connected at nearest neighbors.

[0090] The X-distance is taken as the distance between adjacent marked positions along a given column in the grid. Adjacent marked positions along a given column result in horizontal edges in the Delaunay triangulation data structure. These horizontal edges can be separated from other edges in the triangulation by calculating the angle of the edge. Horizontal edges in a column of the grid are within + / - 10 degrees of a horizontal edge of the image. Since the grid consists of periodic spacing of positions along columns, the X-spacing should be relatively consistent (e.g., have a low standard deviation). In this analysis, horizontal edges having a length greater than twice the programmed distance can be removed from consideration as indicative of non-adjacent positions. The observed X-distance, determined when analyzing an image such as an alphanumeric character, is taken as the average length of the horizontal edge between adjacent marks for all marks / columns in a given image or character. The X-distances for multiple characters in a macroscopic image can then be further averaged to provide an average X-distance for a given marking condition and a given image or pattern. Table 1 shows the observed X-distances for the letters / digits associated with the indicated UPC codes for a range of marking conditions.

[0091] The Y distance can be determined as the vertical distance between adjacent columns. In a Delaunay triangulation, a horizontal edge can be part of two adjacent triangles. Each base edge contributes two vertices to each triangle, and the third vertex is the nearest mark in the adjacent column either above or below the base edge.

[0092] For each base edge, the vertical distance to the nearest mark above and below the base edge is determined. Only the minimum (i.e., closest) of these two distances is recorded. Using only the minimum distance helps ensure that the columns are adjacent and helps prevent double counting of columns. The average and standard deviation of these vertical distances across a given image are then taken as the average Y-distance and standard deviation of the image. The top and bottom columns of letters / numbers are not used as the base of the measured triangle since they only have one adjacent column. The Y-distances of multiple images in a given pattern or portion thereof can then be further averaged to provide the average Y-distance and standard deviation of a given pattern or portion thereof (such as a given alphanumeric character). Table 1 shows the average Y-distances and standard deviations observed for letters / numbers associated with the indicated UPC codes (FIG. 7) for a range of marking conditions.

[0093] As shown in FIG. 6B, vector laser marking processes at high speeds can result in substantial displacement or overhang of marks or voids in a row, resulting in blurred images (such as alphanumeric characters) with jagged contours. The laser marking process of the present invention and articles marked thereby do not result in such substantial displacement and blurring. Any of a number of means can be used to indicate displacement in a row, including simple visual inspection. For example, such means can include simply observing a character (or other element of a given pattern) and assessing whether it is legible given prior knowledge of the intended marked pattern (e.g., alphanumeric characters). Displacement can also be quantified. Importantly, human and machine readable patterns generally include "smooth" contours (versus the jagged contours shown in FIG. 6B). Stated another way, for user-readable and machine-readable patterns, the left-most and right-most marked locations in a given row or marked portion of a row are generally not substantially displaced (in the X direction) from the left-most and right-most marked locations (respectively) in adjacent rows (above and below) over an X distance. This displacement of marked locations results in smeared and unclear patterns, produces larger patterns / characters than intended, and reduces both user and machine readability.

[0094] In quantifying the displacement, the start point of each marked portion in a column of a given character or pattern element is considered the leftmost mark, and the end point of each marked portion in a column is considered the rightmost mark. The start and end points for each marked portion in a column are determined relative to the corresponding start and end points (respectively) of the adjacent columns above and below it. The column under consideration is determined to be "displaced" to the left of the character / pattern element if the start points of both the column above and the column below are to the left of the measured start point of the column, and the column under consideration is determined to be "displaced" to the right if the end points of both the column above and the column below are to the right of the measured end point of the column. The horizontal distance from the start point (and end point) of the column to the start points (and end points, respectively) of the columns above and below is determined, and the displacement is taken as the lesser of these two distances. The left displacement is the displacement determined by the start point, and the right displacement is the displacement determined by the end point. A marked portion in a column may include no displacement, include a left or right displacement, or include both a left and a right displacement. The top and bottom columns containing the image being analyzed (i.e., alphanumeric characters) are omitted from the analysis because they do not have two adjacent columns. One means of identifying the start and end points of each column uses the Delaunay triangulation analysis described above to determine the X and Y distances and standard deviations.

[0095] The "% displacement" for a given image, such as an alphanumeric character, is the sum of the displacements for the columns that contain the character divided by the number of columns that make up the character. %Displacement = (total displacement in character) / (number of columns in character) * 100

[0096] The "A%D" or average % deviation for a given pattern containing multiple alphanumeric characters as text is simply the sum of the % deviations for each character in the sample set divided by the number of characters in the sample, "n."

[0097] Yet another way to quantify the accuracy of the high speed laser marking of the present invention is the percentage of mismarked locations, or "% Mismarked." Referring now to FIG. 10, which is a modified version of FIG. 5 for illustrative purposes. FIG. 5 shows the alphanumeric character "2" marked in a checkerboard pattern in accordance with the present invention. There are approximately 130 marked locations 54. In FIG. 10, there are eight voids 101 that should be marked locations. In addition, there are four marked locations 100 that should be voids. As is apparent, both the voids that should be marked locations and the marked locations that should be voids are mismarked misses, and therefore, they are added together and compared to the number of marked locations. In the example of FIG. 10, there are 12 (8+4) misses out of a total of 130 desired marked locations. % Mismarked = Number of misses divided by number of desired marked locations multiplied by 100, ((12 / 130) * 100)=9.23%. FIG. 6B shows a severely mismarked alphanumeric character ("2") with a % mismarked of over 20%.

[0098] The "average % mismarked" for a given pattern containing multiple alphanumeric characters as text is simply the sum of the % mismarked for each alphanumeric character divided by the number of alphanumeric characters. To achieve the desired readability of text composed of alphanumeric characters, the average % mismarked for the alphanumeric characters is less than about 20%, preferably less than about 15%, more preferably less than about 10%, and even more preferably less than about 5%. The following criteria are used to calculate the average, both for calculating the % accuracy and for providing the standard deviation: Character fonts must be 6pt or larger, and there must be at least 10 marked columns per character.

[0099] Samples and Data Table 1 displays data obtained by laser marking four different articles with the same pattern and then analyzing them using the method described above. The marking in this case was the industry standard UPC code. Those skilled in the art will understand that the UPC, which must appear on all goods purchased by a consumer, must have clearly defined black bars and alphanumeric characters against a lighter, preferably white, background in order for a UPC scanner to quickly and accurately read the code. In other words, the UPC code must be printed or marked with a precision such that it can be accurately read by a scanner or a person. As an example, FIG. 7 shows a UPC code 70 that has been laser marked according to the process of the present invention. The UPC code 70 is a mixture of bars 72 of various widths and alphanumeric characters 74.

[0100] Prior to the present 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 decreases substantially. More specifically, vector marking was tested at maximum galvo angular velocities of 15.6, 350, and 1000 rad / sec and compared to the CV bitmap marking of the present invention at the maximum surface speed of 1000 rad / sec. The target Y distance is provided in the first column and the actual Y distance for each of the n samples was measured (in mm) and then averaged. More importantly, sigma, σ, the standard deviation, was calculated for the n samples using a standard mathematical formula. Standard deviation is a measure of how far the individual samples deviated from the target Y distance. For example, if only two samples were run with 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 may be compromised. The standard deviation in this example is a large number indicating a lack of precision for these two hypothetical samples whose averages appear to be on target.

[0101] Comparing vector marking at a galvo angular velocity of 15.6 rad / s (first entry in Table 1) with CV bitmap marking at 1000 rad / s (last entry in Table 1), the average X and Y distances and corresponding standard deviations are similar across the four target X and Y distances tested. When the galvo angular velocity of the vector marking is increased to 1000 rad / s, the average X distance and corresponding standard deviation remain reasonable, but the Y distance standard deviation becomes unacceptable, and the UPC code is ultimately unreadable for both machines reading the barcode 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 galvo angular velocity of 1000 rad / s. The CV bitmap laser marking of the present invention thereby provides clear advantages of speed and precision over prior vector marking systems.

[0102]

number

[0103] When determining the average % displacement or average % mismarked across a series of alphanumeric characters such as text, the sample size must include at least six different alphanumeric characters selected from the group consisting of S, s, R, r, T, t, N, n, A, a, E, e, O, o, U, u, 1, 2, 3, 4, 5, 6, 7, 8, and 9, and the sample size should be no more than 10 alphanumeric characters. Additionally, the alphanumeric characters should be in the range of 6pt to 16pt font sizes (approximately 2.1mm to 5.64mm in height).

[0104] [Table 1] *This row represents the maximum galvo speed available for the equipment used, not the actual speed. See also Table 3 where the maximum galvo speed is given in the third column. ** Surface speed = 22.5 m / s, X(target) = 0.045 mmX(target) = 0.050 mm Surface speed = 25 m / s

[0105] Table 2 is another set of comparative data where the UPC code was laser marked with legible accuracy; that is, the time required to produce a machine-readable UPC at each speed and each target Y and X distance was measured. As can be clearly seen, with each successive increase in Velocity Max, the time required to laser mark the UPC code in an accurate / readable manner actually took longer for the vector marking process.

[0106] [Table 2]

[0107] Table 3 contains data obtained from the laser marked samples shown in Figure 8. The top row 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 (the alphanumeric characters "Abg123"), and a series of 1 mm by 5 mm rectangles 86 spaced 1 mm apart. The repetition rate was 700,000 rad / sec. 2500 khz using a normal acceleration of 100 Hz. The second row of Table 3 shows how each sample was marked, the third row is the maximum galvo angular velocity for laser marking, and the fourth and fifth rows are qualitative descriptions of the results. Actual data for marking a 5 mm square 88, text 87, and a 1 mm x 5 mm standardized rectangle 86 are shown in the remaining rows of Table 3. Again, it is clear that the speed and precision of laser marking with the CV bitmap of the present invention is far superior to conventional vector marking systems. An f-theta lens with a focal length of 250 mm was used.

[0108] [Table 3]

[0109] Standardized rectangle method The standardized rectangle method is a standardized test for measuring both the speed and accuracy of any laser printer. In simple terms, any laser printer that can be programmed to print 20 identical rectangles (similar to a simplified UPC code) can be tested. The details of the test are provided below, but one skilled in the art will understand that the time it takes to print the standardized rectangle is important to demonstrating the advantages of the present invention. The last two rows of Table 3 show examples of the time required to print a standardized rectangle using four laser printers / processes available today and one laser printer / process according to the present invention. Prior laser printers / processes required 1.5-1.0 seconds to print a standardized rectangle. The laser printer / process according to the present invention required only 0.185 seconds, 500%-800% faster than the prior device.

[0110] As shown in FIG. 8, the standardized rectangle 86 is a series of 20 identical rectangles 91 in FIG. 9, with a width 95 of about 1 mm, a height 93 of about 5 mm, and spaced apart by about 1 mm. 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 includes 80 to 84 parallel rows 97. Each row spans an X direction 92, i.e., a width 98 of 1 mm. Thereby, the Y distance 96, which is the distance between the rows, ranges from 0.24 mm to 0.26 mm. There are 20 to 24 marks 99 in each row 97. It is clear that for the sake of clarity, not all marks 99 are shown.

[0111] Unless otherwise specified, all percentages are weight percent based on the weight of the composition. Unless otherwise stated, all ratios are weight ratios. All numerical ranges are inclusive of narrower ranges. Upper and lower range limits delimited are interchangeable to create further ranges not expressly delimited. Significant digits do not limit the indicated amounts or the precision of the measurements. All measurements are understood to be made at about 25°C and ambient conditions, where "ambient conditions" means conditions at about 1 atmosphere and about 50% relative humidity.

[0112] Dimensions and values ​​disclosed herein should not be understood as being strictly limited to the exact numerical values ​​recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm."

[0113] All documents cited herein, including any cross-referenced or related patents or patent applications, and any patent applications or patents to which this application claims priority or benefit, are incorporated herein by reference in their entirety, unless expressly stated to the contrary. The citation of any document shall not be deemed to be prior art to any invention disclosed or claimed herein, or to teach, suggest, or disclose any such invention, either alone or in combination with any other reference or references. Furthermore, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition given to that term in this document shall govern.

[0114] While particular embodiments of the present invention have been illustrated and described, it would be obvious 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. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

1. 1. An article having a surface marked by a pulsed laser, the surface including a predetermined pattern of locations each including a mark or a void within a checkerboard pattern; the predetermined pattern includes alphanumeric characters in the form of text; the checkerboard pattern includes a plurality of locations positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of locations of the plurality of locations along any of the two or more rows being separated by an X distance, and each adjacent pair of locations of the two or more rows being separated by a Y distance; 1. An article, wherein the pulsed laser has a beam that moves across the row at a constant surface velocity of greater than about 8 m / s, preferably 14 m / s, more preferably 18 m / s, and even more preferably 22 m / s, as successive marks are formed.

2. 10. The article of claim 1, wherein the beam of the pulsed laser moves in a bi-directional profile such that the laser beam moves along a first row in a first direction and a second row in a second direction.

3. The article of claim 2 , wherein the first row and the second row are adjacent rows.

4. 2. The article of claim 1, wherein the text has a font size in the range of 6 pt to 10 pt, and the Y distance is at least 1.2 times, preferably 1.5 times, more preferably 1.7 times, and even more preferably 2 times the X distance.

5. 2. The article of claim 1, wherein the text has a font size in the range of 11 pt to 16 pt, and 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.

6. 10. The article of claim 1, wherein the pulsed laser beam is directed by two galvo sets, each comprising a mirror and a galvometer, and the angular velocity of rotation of at least one galvo set is greater than about 40 rad / sec.

7. 10. The article of claim 1, wherein the beam of the pulsed laser has a repetition rate greater than about 100 kHz.

8. 1. An article having a surface marked by a pulsed laser, the surface including a predetermined pattern of locations each including a mark or a void within a checkerboard pattern; the predetermined pattern includes alphanumeric characters in the form of text; the checkerboard pattern includes a plurality of locations positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of locations of the plurality of locations along any of the two or more rows being separated by an X distance, and each adjacent pair of locations of the two or more rows being separated by a Y distance; wherein the beam of the pulsed laser moves across the row at a constant surface velocity of greater than about 8 m / s, preferably greater than 14 m / s, more preferably greater than 18 m / s, even more preferably greater than 22 m / s as successive marks are formed; An article, wherein the average percentage of alphanumeric characters mismarked is less than about 20%, preferably less than about 15%, more preferably less than about 10%, and even more preferably less than about 5%.

9. 9. The article of claim 8, wherein the text has a font size in the range of 6 pt to 10 pt, and the Y distance is at least 1.2 times, preferably 1.5 times, more preferably 1.7 times, and even more preferably 2 times the X distance.

10. 9. The article of claim 8, wherein the text has a font size in the range of 11 pt to 16 pt, and 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.

11. 1. An article having a surface marked by a pulsed laser, the surface including a first predetermined pattern of locations each including a mark or a void within a checkerboard pattern, and a second predetermined pattern of locations each including a mark or a void within the checkerboard pattern; the first predetermined pattern includes alphanumeric characters in the form of text; the first checkerboard pattern and the second checkerboard pattern include a plurality of locations positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of locations of the plurality of locations along any of the two or more rows being separated by an X distance, and each adjacent pair of locations of the two or more rows being separated by a Y distance; the first checkerboard pattern and the second checkerboard pattern differ in at least one of the X distance and the Y distance; the average percentage of mismarked alphanumeric characters within the first predetermined pattern is less than about 20%, preferably less than about 15%, more preferably less than about 10%, and even more preferably less than about 5%; and 1. An article, wherein the pulsed laser has a beam that moves across the row at a constant surface velocity of greater than about 8 m / s, preferably 14 m / s, more preferably 18 m / s, and even more preferably 22 m / s, as successive marks are formed.

12. The article of claim 11 , wherein the second predetermined pattern comprises a non-alphanumeric image, preferably wherein the non-alphanumeric image comprises a machine-readable image such as a UPC code or a QR code.

Images