US 20050218125 A1
A method for marking a polymeric surface includes directing a first laser beam on the surface to form a lightened area on the surface and directing a second laser beam upon the lightened area to form a mark darker than the lightened area.
25. An article marking system comprising:
a laser; and
a controller configured to generate control signals, wherein the laser is configured to form a lightened area upon a surface of an article and is also configured to form a darker mark over the lightened area in response to the control signals.
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Most of today's products or product parts include identification marks to assist in part or product tracking, inventory management and point of sale pricing and data collection. Common two-dimensional identification marking schemes include stickers attached to the part or product and inkjet marking. Identification stickers must be inventoried, require application to the part or product and are susceptible to being separated from the part or product. Inkjet identification marks require the consumption of ink, printhead replacement and maintenance, and process time for drying of the ink.
As an alternative to stickers and inkjet marking, lasers have been employed to form identification marks on products. Such marks are commonly used to form a dark mark on a lighter colored plastic or a light mark on a dark colored plastic. Unfortunately, such laser produced identification marks frequently lack sufficient contrast for being reliably read by many optical reading devices such as handheld scanners. Moreover, such laser-produced identification marks frequently become damaged or scratched, further impeding a reliable reading of the identification marks.
According to one exemplary embodiment, a method is disclosed for marking a polymeric surface. The method includes directing a first laser beam on the surface to form a lightened area on the surface and directing a second laser beam upon the lightened area to form a mark darker than the lightened area.
Galvanometer 14 comprises an X-Y mirror configured to direct laser beam 22 through lens 16. Lens 16 focuses laser beam 22 onto an object, article or part 24 supported by stage 18. Laser 12, galvanometer 14 and lens 16 are specifically configured to generate and direct a laser beam 22 configured to treat one or more materials along surface 26 of part 24 so as to lighten portions of surface 26 of part 24 or alternatively to darken portions of surface 26 of part 24.
Stage 18 generally comprises a structure configured to support part 24 as laser beam 22 is irradiating surface 26. In one embodiment, stage 18 comprises a stationery structure. In another embodiment, stage 18 is configured to move part 24. For example, stage 18 may be movably supported upon bearings, tracks, slides and the like and may be operably coupled to an actuator such as one or more hydraulic cylinders, pneumatic cylinders, electric solenoids and motor-driven actuators which move stage 18 in response to control signals received from controller 20. Although stage 18 is illustrated as a platform, stage 18 may have various sizes, shapes and configurations depending upon the configuration of part 24. In still other embodiments, stage 18 may be configured to be manually moved. In particular applications, stage 18 may be configured to grip or engage particular portions of part 24 so as to function as a fixture.
Controller 20 generally comprises a processor unit configured to generate control signals based upon a set of instructions 28 for the operation of one or more of laser 12, galvanometer 14 and stage 18. For purposes of the disclosure, the term “processor unit” shall include a conventionally known or future developed processing unit that executes sequences of instructions contained in a memory. Execution of the sequences of instructions causes the processing unit to perform steps such as generating control signals. The instructions may be loaded in a random access memory (RAM) for execution by the processing unit from a read only memory (ROM), a mass storage device, or some other persistent storage. In other embodiments, hard wired circuitry may be used in place of or in combination with software instructions to implement the functions described. Controller 20 is not limited to any specific combination of hardware circuitry and software, nor to any particular source for the instructions executed by the processing unit. In one particular embodiment, controller 20 generates control signals based in part upon instructions from computer or processor readable media 28, such as software provided by digital media, optical media, (e.g., CD, DVD) or magnetic media (floppy disk, tape, etc.). The instructions contained on media 28 cause laser 12, galvanometer 14 and stage 18 to cooperate with one another such that beam 22 is directed on surface 26 of part 24.
Surface 26 of part 24 is generally formed from a polymeric material configured to be lightened upon being irradiated by a laser beam and also configured to be darkened upon being irradiated by a laser beam. The polymeric material forming surface 26 generally includes one or more resins and one or more additives that absorb light in the visible range. To lighten the polymeric material, the surface 26 is irradiated with a selected power density (i.e., watts per second per cm2) by a laser beam at a selected energy density (also known as fluence, i.e., Joules/cm2) with a selected exposure time such that one or more additives are bleached or vaporized. This reduces the ability of those irradiated portions to absorb light, decreasing the darkness of those irradiated portions.
The same polymeric material is darkened by irradiating portions of surface 26 at a selected power density such that the polymeric resin itself is carbonized or burnt. The carbonized polymeric material absorbs visual light at a greater rate as compared to the raw polymeric material, causing such burnt portions to be darker. Examples of polymeric resins include, but are not limited to, noryl (such as, for example, the formulation known as noryl PPX630 produced by GE Plastics), liquid crystal polymer (LCP), polyethersulfone (PES), polyphenalsulfide (PES), polystyrene, polypropylene, polyethylene, polyethylene terephthalate (PET), polyvinylchloride (PVC) and acrylonitrile butadiene styrene (ABS). Examples of such additives include, but are not limited to, carbon black, graphite, calcium silicates, zirconium silicates, zeolite, mica, kaolin, talc and cordierite, which comprise laser energy absorbing additives. Other examples of additives include colorants such as organic pigments, inorganic pigments or polymer-compatible organic dyes.
During operation of laser marking system 10, controller 20 generates control signals based in part upon instructions from media 28 which cause laser 12, galvanometer 14 and stage 18 to cooperate with one another to irradiate surface 26 with a first laser beam 22 to form a lightened area and to irradiate the lightened area with a second laser beam 22′ (shown in
Depending upon characteristics of the polymeric material forming surface 26, the energy density applied to the lightened area by laser beam 22′ may be configured to either (1) vaporize, cut away or remove particular portions of surface 26 that have been lightened or (2) carbonize or burn the polymeric material, such as its resins or additives. By vaporizing, cutting away or removing portions of surface 26, the first method exposes the underlying raw or untreated polymeric material previously below the lightened layer along surface 26. The exposed polymeric material including the additives absorbs a greater amount of light as compared to the remaining surrounding lightened area on surface 26. As a result, the exposed raw or untreated polymeric material with additives forms dark marks within the lightened area.
By carbonizing or burning portions of the previously formed lightened area, the second method forms marks that have higher contrast with the lightened area. In particular, the energy density applied by the second laser beam is generally insufficient to burn or cut through the lightened area but it is sufficient to burn or char portions of the lightened area. These charred or burnt portions of the lightened area form marks that are darker than the surrounding lightened area that do not receive energy from the second laser beam.
With particular polymeric materials, to remove or burn selected portions of the previously lightened area of surface 26 requires the application of a greater power density by the second laser beam 22′ (shown in
In one example embodiment, the polymeric material forming surface 26 comprises polymeric resin, stabilizers and carbon black. The ratio of carbon black is approximately one percent. Laser marking system 10 comprises a Nd:YAG laser having a wave length of 1064 nanometers. Laser 12 includes a Q-switch to vary the frequency of the laser beam generated by laser 12. Galvanometer 14 comprises an X-Y mirror while lens 16 comprises a telecentric F-Theta lens. Controller 20 generates control signals such that laser beam 22 has a power of 4.38 watts and a frequency of 60 kHz. Controller 20 further generates control signals such that laser beam 22 and/or stage 18 move relative to one another such that laser beam 22 traverses surface 26 at a speed of about 1500 millimeters per second in a raster to form a lightened area. To form the dark marks upon the lightened area, controller 20 generates control signals such that at least one of laser beam 22′ (shown in
In other embodiments, other lasers may be employed having different wave lengths. For example, lasers having wave lengths of between about 1000 nanometers and 1500 nanometers may be employed or carbon dioxide lasers may be employed having wave lengths of between 9.2 micrometers and 10.6 micrometers. In other embodiments, laser 12 may have a power of between about 1 watt and 50 watts. The resulting laser beam 22 or 22′ may traverse surface 26 of part 24 during the formation of the lightened area or formation of the mark at a scanned speed of between about 100 millimeters per second and 4000 millimeters per second. In other embodiments, power, scan speed and frequency may be adjusted beyond such ranges, depending upon the polymeric material being marked and relative scan speeds, laser powers and laser frequencies.
The overall marking scheme or arrangement consisting of the lightened area and the overlying darkened mark or marks has improved contrast and angular viewability as compared to laser-formed marks formed upon an original surface 26 of part 24. In particular, the lightened area produced by the first laser beam 22 has consistent or uniform surface reflection qualities. Plastic mold surfaces change over time imparting changes in surface reflection characteristics. The lightened area of surface 26 bleached by the first laser beam 22 normalizes variations in surface reflections, glints and glares to provide consistent defuse contrast that are unencumbered by spurious environmental reflections.
In addition, because surface 26 is bleached or lightened as compared to the remainder of surface 26 which are not lightened, the lightened area of surface 26 has a greater contrast with the darkened marks formed thereon as compared to the surrounding unbleached portions of surface 26. This improved contrast enables the one or more darker marks formed upon the lightened area to be more easily and reliably read by optical scanning devices such as handheld optical scanners. This improved contrast also enables a plurality of spaced darker marks, such as those commonly used for part identification purposes, to be smaller and more closely spaced to reduce the overall size of the marking arrangement while maintaining the readability of the marking arrangement by an optical scanning device.
Moreover, because the darker marks are formed directly upon or through the lightened area, rather than being formed upon untreated polymeric material simply alongside the lightened area, adjacent edges of the lightened area and darker marks are always maintained in an abutting relationship. In other words, where the mark ends, the lightened area begins. The possibility of forming a mark 232 at a location slightly spaced from lightened area 230 and leaving an untreated portion of surface 126 between the lightened area and the mark (which may impair reading of the marking scheme) is eliminated. This further enhances the ability of system 10 to produce more closely spaced marks and a more compact marking scheme.
Marking arrangement 112 is formed upon surface 126 and includes a lightened area 130 and a plurality of darkened marks 132. Lightened area 130 comprises an area of surface 126 which has been treated by a first laser beam 22 (shown in
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In those applications where marks 232 are alternatively formed by burning or charring portions of lightened area 230, rather than cutting through lightened area 230, floor 262 of scratch 246 shall expose the underlying polymeric material. While the underlying polymeric material is generally lighter than those unscratched portions of marks 232 which have been burnt, the underlying polymeric material is still darker than adjacent portions of lightened area 130, enabling detector 252 to still distinguish between the floor 262 of scratch 246 across mark 232 and adjacent lightened area 130.
Although the present invention has been described with reference to example embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Those skilled in the art will appreciate that certain of these advantages can be obtained separately through reconfiguring the foregoing structure without departing from the spirit and scope of the present invention. Because the technology of the present invention is relatively complex, not all changes in the technology are foreseeable. The present invention described with reference to the example embodiments and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements.