WO2019173513A1

WO2019173513A1 - Infrared laser marking using digital mirror systems and devices

Info

Publication number: WO2019173513A1
Application number: PCT/US2019/021011
Authority: WO
Inventors: Ashoke Kumar BANERJEE; Patrick Victor JOYCE
Original assignee: Markem-Imaje Corporation
Priority date: 2018-03-06
Filing date: 2019-03-06
Publication date: 2019-09-12

Abstract

Systems and devices for laser-based marking, such as for industrial product marking systems, include: a laser source configured to produce an infrared laser beam to modify a surface of a material to be marked; a digital mirror device including an array of mirrors, electrically actuated electro-mechanical hinge components coupled with respective mirrors in the array of mirrors, and a semiconductor substrate including electrical circuits coupled with the electrically actuated electro-mechanical hinge components, wherein each of the mirrors in the array of mirrors has a reflective surface portion including gold; and beam shaping and projection optics positioned in an optical path of the infrared laser beam before the digital mirror device, the beam shaping and projection optics being configurable to shape the infrared laser beam into a rectangle of uniform infrared laser light and project the rectangle of infrared laser light with respect to the array of mirrors.

Description

INFRARED LASER MARKING USING

DIGITAL MIRROR SYSTEMS AND DEVICES

BACKGROUND

[0001] This specification relates to laser-based marking systems, such as product marking apparatus that employ a C02 laser to ablate a surface of a material of products being marked.

[0002] Industrial product marking systems, such as laser-based marking systems, are widely employed in product manufacturing, packaging and distribution facilities. Such product marking systems are used to add product codes, such as bar codes, serials numbers, sell-by dates, etc., to products, their packaging, or collections of products (e.g., a pallet with multiple products on it). Laser-based marking systems typically use galvanometers (e.g., X and Y galvos) to steer a laser beam to mark an image on an object. Such marking systems scan the laser beam across the object to be marked (using vector-based or dot-matrix-based patterns) to form the desired image on the object. While the galvos in such systems can be very fast, there is still a speed limitation, which becomes apparent with complex images to be marked, such as when printing two dimensional (2D) bar codes. To address the speed issue, a polygon scanner can be used, but such an approach often suffers from ramp up time delays, due to the mass of the polygon scanner, and increased potential for mechanical failure.

[0003] In addition, others have proposed using spatial light modulators in laser-based marking systems. U.S. Patent No. 6,836,284 describes reducing the flux density of a laser beam and adding a radiation sensitive material to an object to be marked in order to use a digital mirror device (DMD) to mark the object. U.S. Patent Pub. No. 2010/0054287 describes adding an optical amplifier to receive and amplify a laser beam from a spatial light modulator (SLM) that receives the laser beam from a laser source and that can generate a data code matrix across the beam cross-section. Finally, U.S. Patent No. 9,570,874 describes using an optical amplifier on light from an SLM and also turning the profile of the laser beam directed at the SLM into a non-Gaussian flat-top profile. SUMMARY

[0004] This specification describes technologies relating to laser-based marking systems, such as product marking apparatus that employ a C02 laser to ablate (or otherwise modify an optical characteristic of) a surface of a material of products being marked.

[0005] In general, one or more aspects of the subject matter described in this specification can be embodied in one or more laser marking systems that include: a laser source configured to produce an infrared laser beam to modify a surface of a material to be marked; a digital mirror device including an array of mirrors, electrically actuated electro-mechanical hinge components coupled with respective mirrors in the array of mirrors, and a

semiconductor substrate including electrical circuits coupled with the electrically actuated electro-mechanical hinge components, wherein each of the mirrors in the array of mirrors has a reflective surface portion including gold; and beam shaping and projection optics positioned in an optical path of the infrared laser beam before the digital mirror device, the beam shaping and projection optics being configurable to shape the infrared laser beam into a rectangle of uniform infrared laser light and project the rectangle of infrared laser light with respect to the array of mirrors. These and other embodiments can optionally include one or more of the following features.

[0006] A laser marking system can include focusing optics positioned in an optical path of the infrared light between the digital mirror device and the surface of the material to be marked, wherein the focusing optics and the beam shaping and projection optics include one or more Zinc Selenide (ZnSe) optical components, including at least one ZnSe lens. The laser source can include a pulsed, C02 infrared laser. The reflective surface portion of each mirror of the mirrors in the array of mirrors can include gold plating over a base material of the mirror. The gold can be gold plating applied over both (i) a base material of each of the mirrors in the array of mirrors and (ii) at least a portion of the electrically actuated electro- mechanical hinge components. The digital mirror device can include a ZnSe glass faceplate covering the array of mirrors. Each mirror of the mirrors in the array of mirrors can include an adhesive layer between the gold plating and the base material of the mirror, the base material of the mirror including, e.g., aluminum. Further, the base material of the mirror can include copper. [0007] A laser marking system can include a controller configured to operate the system to ensure that the rectangle of infrared laser light does not impinge on any portion of the digital mirror device outside of a boundary of the array of mirrors, and to set a size of the rectangle of infrared laser light in accordance with a size of an image to be formed on the surface of the material to be marked. The controller can be configured to adjust a power of the infrared laser beam produced by the laser source in accordance with the size of the rectangle of infrared laser light set by the controller. The laser marking system can include a translation stage coupled with at least the digital mirror device, wherein the controller is configured to operate the translation stage to adjust a relative distance between the digital mirror device and the beam shaping and projection optics to set the size of the rectangle. The translation stage can be designed to operate in X and Y dimensions, in addition to a Z dimension, and the controller can be configured to operate the translation stage to select different, non-overlapping proper subsets of the mirrors in the array for respective marking operations. Moreover, the laser source, the digital mirror device, and the beam shaping and projection optics can be built into a single housing of an industrial laser printer device.

[0008] One or more aspects of the subject matter described in this specification can also be embodied in one or more methods that include setting an initial power level of a laser source based on an amount of energy that needs to be absorbed by a surface of a material, in a defined period of time, to mark the surface of the material with an image, wherein the laser source is an infrared laser source having a light wavelength between and 2.6 and 11 micron; setting a size of a rectangle of uniform laser light to be produced by beam shaping and projection optics positioned between the laser source and a digital mirror device, the size of the rectangle being set based on a size of the image to be marked on the surface of the material; adjusting the power level of the laser source in accordance with the size of the rectangle of uniform laser light; causing the laser source to output laser light, at the adjusted power level, into the beam shaping and projection optics to illuminate the digital mirror device; and causing the illuminated digital mirror device to redirect selected portions of the incident laser light to mark the image on the surface of the material. These and other embodiments can optionally include one or more of the following features.

[0009] Setting the initial power level of the laser source can include setting the power level to cause ablation of the surface of the material. Setting the size of the rectangle of uniform laser light can include moving a translation stage coupled with the digital mirror device. The translation stage can include an X, Y and Z translation stage, and the method can include: moving the translation stage to select different, non-overlapping proper subsets of mirrors in the digital mirror device for respective marking operations, thereby distributing heat from the incident laser light across the mirrors of the digital mirror device; and redirecting the selected portions of light from the digital mirror device, using focusing optics positioned in an optical path of the selected portions of light, in accordance with the different, non-overlapping proper subsets, different target marking locations, or both.

Moreover, causing the illuminated digital mirror device to redirect selected portions of the incident laser light can include loading the digital mirror device with a bitmap image defining the image including a two dimensional (2D) barcode.

[0010] Various embodiments of the subject matter described in this specification can be implemented to realize one or more of the following advantages. An infrared laser-based marking system can rapidly mark objects, such as products or product packaging/labelling on a product line, with complex images, such as 2D bar codes. The use of gold coatings on mirrors in a digital mirror device (DMD) allows infrared laser energy to be applied directly to the DMD mirror array. Note that the typical wavelength of infrared C02 lasers (e.g., 10.6 micron) has substantial reflectivity (e.g., more than 99.7%) for gold coated mirrors, as described herein, and these gold coated mirrors can readily withstand C02 laser powers of up to several kilowatts. Cover glass material made of Zinc Selenide (ZnSe) (e.g., a ZnSe faceplate for the DMD with anti -reflection coatings appropriate for the infrared laser light) can also be employed to facilitate use of the infrared laser light up to 11 micron (e.g., existing cover glass faceplates made to pass light of wavelengths between 350 and 2500 nm can be replaced with cover glass faceplates made of ZnSe). Further, the beam print area can be adjusted to the size of the image to be printed, which can prevent undue heating of the mirror array in areas where there is no image data. By keeping the laser beam area equal to the information code area on the DMD, useless areas of the DMD mirrors (those not helping to print the mark) are not hit with laser light, thus reducing heat generation at the DMD.

Further, the flux density of the laser light impinging on the DMD can be adjusted based on the beam print area and/or the specific application. For example, higher laser flux density can be readily used in applications that require higher power. [0011] The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the invention will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1A shows an example of a digital mirror device.

[0013] FIGs. 1B and 1C show examples of a mirror for a digital mirror device.

[0014] FIGs. 1D-1F show an example of a process of reengineering a digital mirror device.

[0015] FIGs. 2A-2D show examples of a laser-based marking system employing a digital mirror device.

[0016] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0017] FIG. 1A shows an example of a digital mirror device (DMD) 100. The DMD 100 includes only two mirrors 105 A, 105B for ease of presentation, but as will be appreciated, the DMD 100 will include a rectangular (e.g., square) array of many such mirrors (e.g., thousands of individually-addressable, tiltable mirrors). In some implementations, the DMD 100 is a digital micro-mirror device, in which each respective mirror 105 A, 105B is very small (e.g., 2 to 32 micron square, and typically between 4 and 16 micron on each side) and the individual mirrors 105 A, 105B are separated from each other by an even smaller distance (e.g., 0.5 to 1.5 micron, and typically about 1 micron).

[0018] In addition to the array of mirrors 105 A, 105B, the DMD 100 includes a semiconductor substrate 120 and electro-mechanical hinge components 110 thereon. The electro-mechanical hinge components 110 can include various micromechanical structures that are electrically actuated when electricity is applied through the semiconductor substrate 120. The electro-mechanical hinge components 110 control each respective mirror 105A, 105B to either tilt the mirror into an on position, where the mirror redirects the light to impinge on a target object, or tilt the mirror into an off position, where the mirror redirects the light to impinge on an optical absorber (or beam dump area). [0019] For example, the electro-mechanical hinge components 110 include electro- mechanical hinge components 115 for mirror 105 A. As shown, the electro-mechanical hinge components 115 are tilting the mirror 105 A at an angle different from that of mirror 105B. The difference in angles can be +/- 10 to 20 degrees. In some implementations, the electro- mechanical hinge components 110 include (for each mirror) a torsional hinge, a yoke, a mirror address electrode, a yoke address electrode, a bias-reset bus, and a via to contact circuitry in the underling semiconductor substrate 120. Other implementations of the electro- mechanical hinge components 110 are also possible. For example, the array of mirrors 105 and the electro-mechanical hinge components 110 can be implemented as an array of microelectromechanical system (MEMS) mirror devices. In any case, each mirror 105 can be individually actuated between two angle positions (on or off).

[0020] The semiconductor substrate 120 can be a CMOS (Complementary Metal Oxide Semiconductor) device defining the circuitry used to control the electro-mechanical hinge components 110 and thus the array of mirrors 105. But regardless of the type of substrate, the circuitry 120 connects with the electro-mechanical hinge components 110 to provide individual addressability of each mirror 105 A, 105B in the array 105, such that each mirror forms a pixel of an image to be formed. In this fashion, the DMD can rapidly modulate incoming light into a complex spatial pattern corresponding to an electrical input for an image to be printed.

[0021] As described in further detail below, the incoming light can be infrared (IR) laser light, e.g., from a C02 laser or CO laser. Traditionally, DMDs are used to reflect light in the visible spectrum, and typical DMDs use aluminum to make the individual mirrors in the DMD. However, such DMDs are not rated for use with higher power IR lasers. Thus, traditional DMDs will absorb too much heat from an IR laser, which can lead to device failures. For example, for laser light at a 10.6 micron wavelength, bare uncoated aluminum in the DMD will absorb a significant percentage of incident C02 laser light, creating thermal issues of burning and/or damage, as well as potentially deforming the pixel mirrors of the DMD due to the intense C02 laser power being used, e.g., to ablate a surface material to mark codes on objects.

[0022] FIG. 1B shows an example of a mirror 150 for a digital mirror device. The mirror

150 can be replicated for each of the image forming mirrors of the DMD 100. In order to work with infrared laser light (e.g., of high power), each such mirror 150 includes gold in at least a reflective surface portion of the mirror 150 to improve the efficiency of laser light reflection. For example, gold plating 160 can be added onto a base material 155 (e.g., aluminum) that forms the face of the mirror 150. Gold is known to be a good reflector for C02 IR light at the 10.6 micron wavelength. In some implementations, the gold plating 160 is added to the base material 155 of the mirror 150 using vacuum vapor deposition or other suitable optical component coating techniques. The base material 155 can be aluminum, e.g., the gold plating 160 can be added to a previously manufactured DMD mirror made with aluminum. Since gold does not stick well to aluminum, an adhesive layer can be used to bond gold coats on the aluminum mirror surface.

[0023] FIG. 1C shows an example of a mirror 170 for a digital mirror device. As for the mirror 150, the mirror 170 can be replicated for each of the image forming mirrors of the mirror array of the DMD 100. Further, an adhesive 175 is included between the base material 155 and the gold 160 to facilitate bonding the gold coat(s) on at least the face of the mirror 170. The adhesive layer 175 can be formed using chromium, titanium, nickel-chromium, etc.

The finished surface after gold coating will thus be a gold mirror finish on the original aluminum mirror surface. Note that the adhesive layer 175 can have a thickness of between 100 and 500 angstroms, and the gold plating 160 can likewise have a thickness of between 100 and 500 angstroms. Since the mirror 170 (or the mirror 150) will typically have a thickness of between 1 and 2 micron, the thickness of the pixel mirror 170 (or the pixel mirror 150) remains essentially unchanged after adding the adhesive layer 175 and the gold plating 160 (or just the gold plating 160). Note that surface irregularities introduced by the added coating(s) will not need to be addressed in many implementations, e.g., due to the long wavelength of a C02 laser at 10.6 micron.

[0024] In some implementations, a base material 155 other than aluminum is used. For example, the base material 155 of each mirror can be made of copper, e.g., oxygen free, high conductivity copper. Examples of thermal conductivity for various materials are shown in Table 1 below:

Table 1 - Thermal Conductivities of Mirror Base Materials

As shown above, copper provides higher thermal conductivity than aluminum. A copper base 155 with a gold coating 160 is a good reflector of C02 laser light, and copper is an excellent thermal conductor, which can assist in heat removal from the mirror and likewise from the DMD. Note that heat that is absorbed and not removed from the DMD and its mirrors can cause thermal expansion, which can change the shapes of the mirrors and thus cause defocusing of the reflected light. Using appropriate materials for the mirror, such as copper and gold, can assist in reducing or eliminating heat buildup.

[0025] In some implementations, the copper mirror surfaces for the DMD are vacuum coated with pure gold, and for good adhesion, an intermediate adhesive layer can be vacuum deposited as well. In addition, Zinc Selenide (ZnSe) glass can replace traditional visible light glass and be used to cover and protect the mirrors of the DMD. Further, the coating(s) can be done by the DMD manufacturer at the time the DMD is first built, or by another company that purchases DMDs that have been manufactured for use with visible light and then reengineers them for use with IR laser light.

[0026] FIG. 1D shows a cross sectional view of a DMD 180 (e.g., that has a mirror array 105 with aluminum used as the mirror surfaces). In addition to the mirror array 105, the electro-mechanical hinge components 110, and the semiconductor substrate 120 (contained in a DMD package/housing) the DMD 180 includes a glass faceplate 185. The glass faceplate 185 can be removed, and then vacuum vapor deposition 190 can be used to apply a gold layer

(e.g., after applying an adhesive layer) as shown in FIG. 1E. Then, a ZnSe faceplate 195 with anti -reflection coatings appropriate for the IR laser light to be used (e.g., appropriate for C02 laser light at a 10.6 micron wavelength) is installed in the DMD 180 to cover and protect the mirror array 105 (and other components within the DMD package/housing), as shown in FIG. 1F. The use of ZnSe glass helps to ensure that IR light can pass through the protective cover 195 with minimal loss.

[0027] FIG. 2A shows an example of a laser-based marking system 200 employing a digital mirror device (DMD) 220. The DMD 220 can be constructed with mirrors 230, in accordance with any of the examples detailed above in connection with FIGs. 1 A-1F, and the DMD 220 is illuminated using an infrared laser source 210. The infrared laser source 210 can be a continuous wave (CW) or pulsed laser light source, a fundamental mode or multi -mode laser light source, a C02 or a CO laser light source, or combination thereof. For example, the infrared laser source 210 can employ a C02 laser with a wavelength in the range of 9 to 11 micron. Commercially available C02 lasers that can be used have wavelengths of 10.6, 9.6, and 9.4 micron, respectively. As another example, the infrared laser source 210 can employ a CO laser with a wavelength in the range of 2.6 to 4 micron or 4.8 to 8.3 micron. In general, the infrared laser source 210 has a flux density high enough to damage a traditional DMD, absent the systems and techniques described herein.

[0028] The infrared laser source 210 generates an infrared laser beam 215, which is directed to beam shaping and projection optics 240. The optics 240 are positioned in an optical path of the infrared laser beam 215 and can shape the beam 215 to have a uniform intensity (flux density) before projecting the shaped infrared laser light 245 onto the array of mirrors 230. Further, the optics 240 can include rectangular shaping optics configurable to shape the infrared laser beam 215 into a rectangle of uniform intensity (flux density) infrared laser light 245.

[0029] The beam shaping and projection optics 240 can include various optical components, such as diffractive optical elements and a collimator (as described in further detail below) that are usable to shape the incoming laser beam 215 to match a corresponding light incident area designated for the mirrors 230 within the DMD 220. The optical components (e.g., diffractive optical elements and a collimator) can be made of appropriate material(s) (e.g., ZnSe material) to facilitate use with infrared laser light. Further, in some implementations, the beam shaping and projection optics 240 include a waveguide (e.g., a hollow core waveguide) having a round input diameter (e.g., of 0.75 mm) where the waveguide is tapered gently from the round end to the other end, into a rectangular shape, such that the output beam is rectangular. This rectangular output beam 245 can then fall directly on the DMD’s active mirror surface area.

[0030] Based on the tilt angle settings of the mirrors 230, selected portions (pixels) of the infrared laser light 245 (e.g., to form a 2D bar/matrix code, one or more authentication codes, manufacturer information/logo, expiration date, etc.) are redirected to a target object 270 (e.g., a product or packaging/labelling for a product) and additional selected portions (pixels) of the infrared laser light 245 are redirected to an optical absorber 260. The optical absorber 260 is a black body absorber, which can be designed for the specific wavelength being used in a given application, e.g., by application of one or more black coating layers of appropriate materials. In some implementations, depending on the amount of heat to be dissipated, the optical absorber 260 also has one or more associated cooling devices/structures, such as fans, Peltier coolers, heat sinks (e.g., metal or liquid), and phase change (heat pipe) devices.

[0031] The infrared laser light that is directed to the target object 270 has sufficient power to mark a surface of a material of the target object 270. In some implementations, the infrared laser light that is directed to the target object 270 has a flux density high enough to ablate the surface of the target object 270. For example, the IR laser light can burn away a surface portion of product packaging/labelling to make the mark. In some implementations, the infrared laser light that is directed to the target object 270 has a flux density high enough to modify the appearance of the target object 270 (e.g., a portion of the target object 270 undergoes a phase change). For example, a product (or packaging/labelling therefor) is coated with an imaging material that changes color when thermal energy comes into contact with the imaging material.

[0032] In addition, in some implementations, focusing optics 275 are positioned between the DMD 220 and the target object 270 to provide appropriate magnification of the infrared laser light. The focusing optics 275 can include suitable optical components (e.g., one or more lenses) to facilitate the immediate transfer (marking) of an entire code (or two or more codes when different portions of the DMD mirrors 230 are used for different respective codes) in one shot, which can provide significant advantages over sequential marking methods (e.g., dot matrix laser ablation). Further, as with the beam shaping and projection optics 240, the optical components of the focusing optics 275 can be made of appropriate material (e.g., a distortion fee ZnSe lens) to facilitate use with infrared laser light. Note that the specific materials used for the optics 240, 275 can vary with the wavelength being used by the system 200, and in general, the material(s) used are selected to minimize light/energy loss in the optics 240, 275. Thus, in the near infrared range (e.g., 2.6 to 3 or 4 micron) a silicon lens can be used instead of a ZnSe lens.

[0033] The laser-based marking system 200 also includes at least one controller 250. The controller 250 is shown as separate from, but connected with the infrared laser source 210, the beam shaping and projection optics 240, and the DMD 220. However, as will be appreciated, the controller 250 can include one or more controllers that are integrated with respective components, as appropriate. For example, in some implementations, the infrared laser source 210 and the DMD 220 include local controllers 250A, 250B (also referred to as drivers) that are integrated into these respective devices, and the controller 250

communicates with these local controllers 250A, 250B, as well as potentially with the beam shaping and projection optics 240, to control overall operation of the laser-based marking system 200. For example, the controller 250 can set the mirror tilt states for the DMD 220 by communicating image information through a software code interface or by feeding an image into the DMD 220 through the local controller 250B.

[0034] In various implementations, one or more controllers 250, 250A, 250B can be implemented using one or more programmable hardware processors executing one or more computer programs (e.g., operating system code embedded in firmware and/or application code stored in a non-transitory computer-readable medium), special purpose logic circuitry (e.g., using FPGA (field programmable gate array) or ASIC (application-specific integrated circuit) circuity), or a combination thereof. For example, the controller 250 can be a computer programmed to map an image (e.g., a bitmap image) to the array of mirror elements of the DMD 220, using the local controller 250B, to direct the infrared laser light to the target object 270, where each on-pixel represents a single mirror steering the IR light to the target object 270, and each off-pixel represents a single mirror steering the IR light to the optical absorber 260. In addition, various subsets (or all) of the components described in connection with FIG. 2A can be built into a single housing 280, thus forming an industrial laser printer device from the system 200. [0035] The cross-sectional area of the laser light 245 can be limited to a size that ensures none of the laser light 245 impinges on any portion of the DMD 220 outside of the array of mirrors 230. In some implementations, the controller 250 can adjust the cross-sectional area of the laser light 245 impinging on the DMD 220, such as adjusting the area in accordance with the size of the image to be marked on the target 270. This limits the number of mirrors 230 being hit by the laser light 245 to only the mirrors needed to make the mark on the target object 270, which can reduce the amount of heating of the mirror array 230 and thus the DMD 220. Further, as noted above, the optics 240 can shape the beam 215 to have a uniform intensity (flux density) for the projected infrared laser light 245.

[0036] The traditional Gaussian beam cross section, which has a peak power in the center and less power at the beam’s edges, can be replaced with a flatter beam profile that has substantially less gradient across the beam’s cross section. The components used for the optics 240 to achieve a flat top beam profile for the laser light 245 can include a Gaussian-to- flat-top beam distribution converter (e.g., refractive beam shapers) and/or other optical components, such as diffractive optical elements, one or more lenses with aspheric surfaces, etc. In addition to shaping the laser beam 215 to be a uniform intensity beam 245, the optics 240 can include components to shape the laser beam 215 to be a divergent, rectangular beam 245. Various commercially available optical components can be used to perform this shaping, and various component configurations can be employed, including putting both the rectangular shaping optics and the uniform intensity optics in the optics 240, as described herein, or integrating the uniform intensity optics into the infrared laser source 210 (e.g., the infrared laser source 210 is a multimode laser source (or a laser with higher-order modes) that is configured to provide a laser beam 215 with a flat-top profile), the beam shaping and projection optics 240, both and/or neither (e.g., the uniform intensity optics components can be placed in the optical path between the infrared laser source 210 and the beam shaping and projection optics 240).

[0037] FIG. 2B shows further details of an example of a configuration for the laser-based marking system 200 of FIG. 2A. In this example, the beam shaping and projection optics 240 include a beam collimator 242 and rectangle & profile shaping optics 244. The beam collimator 242 includes one or more lens that are positioned at a distance (from the exit port of the laser source 210) that is equal to its focal length so the laser beam 243 is collimated. The laser beam 243 is then made rectangular and of uniform intensity (i.e., change the irradiance distribution of the laser beam from a Gaussian to a flat-top beam distribution) using the rectangle & profile shaping optics 244.

[0038] For further details regarding systems and devices used to generate non-Gaussian irradiance distribution for a laser beam, see U.S. Patent No. 9,570,874, which is hereby incorporated by reference. In some cases, combinations of aspheric lenses can be used, or some diffractive optics can be used to generate a flat-top intensity distribution from a Gaussian laser beam. In some implementations, the laser beam is sent through a rectangular core fiber as is done with Ceram Optec GmbH’s NCC fiber. In some implementations, the laser beam is truncated by an appropriately shaped aperture at the expense of some energy loss.

[0039] In some implementations, refractive optics are used, such as conversion of Gaussian intensity distribution of fundamental laser mode (TEM (0,0) beam to flat top (uniform distribution) using refractive beam shapers like pishaper, manufactured by

AdlOptica GmbH of Berlin, Germany, which provides a collimated output beam of low divergence and uniform intensity distribution. In some cases, certain combinations of aspheric lenses can be used to generate flat top intensity distribution of a Gaussian laser beam like Coherent’s beam shaping products, e.g., a set of Powell lens. A Powell lens is a type of aspheric cylindrical lens, which has power in one plane. Two different Powell lenses in orthogonal orientation can be arranged such that the output is a square or rectangle having virtually any aspect ratio and uniform illumination.

[0040] In some implementations, a diffractive beam shaper is used. As the Gaussian beam transmits through the optical diffractive element, the Gaussian intensity of the laser beam is redistributed for uniformity, and the laser beam is then brought down to a focus near which the desired output (which can have any desirable aspect ratio) can be realized. Such diffractive beam shapers are commercially available from Holo/Or Ltd., of Rehovot, Israel.

In general, the optical components used to redistribute flux density, reshape, and project the laser beam 215 can use reflective or transmissive optics, and such optical components can employ appropriate materials (e.g., ZnSe) and/or be appropriately coated (e.g., gold plating) for the laser light being used (e.g., for C02 or CO laser beam transmission and/or reflection). [0041] In any case, the controller 250 can be configured to adjust the area/size of the uniform intensity, rectangular laser light 245 that falls on the mirrors of the DMD 220. In the example shown in FIG. 2B, the controller 250 moves the DMD 220 on translation stage 222 to bring the DMD 220 closer or farther away from the divergent, uniform intensity, rectangular laser light 245, thereby adjusting the number of mirrors illuminated by the laser light 245. Thus, the DMD 220 can be moved back and forth between a first position 224, where all of the mirrors of the DMD 220 are illuminated, and a second position 226, where only a proper subset of the mirrors are illuminated. Note that many different positions can be used in order to illuminate different sets of mirrors in the mirror array of the DMD 220. Further, these positions can be set to correspond to different print image sizes and/or resolutions on the target object 270, i.e., the controller 250 can vary the distance between the optics 240 and the DMD 220 based on the image size/resolution being marked on the target 270.

[0042] However, as will be appreciated, various options are available for adjusting this area/size of the laser light 245 falling on the mirrors of the DMD 220, including moving the optics 240, the optics 244, portions thereof, or both these optics and the DMD 220. In general, description of movement of any of these components to adjust the area/size of the laser light 245 falling on the mirrors of the DMD 220 indicates some movement of one or more suitable components of the system 200, relative one or more other or remaining suitable components of the system 200, to modify the area/size of the laser light 245 falling on the mirrors of the DMD 220. In addition, a translation stage 222 is not required. Rather than using (or in addition to using) the translation stage 222, the image size/resolution being marked on the target object 270 can be modified by swapping one set of optics 240 with an alternative set of optics 240 (e.g., designed for a different and/or specific application).

[0043] FIG. 2C is another view of the beam shaping and projection optics 240 and the

DMD 220. As shown, the optics 240 reshape the laser beam into a projected rectangle 245 A of infrared light that stays within a boundary 225 of the array of mirrors 230. By shaping the laser beam into a rectangle that stays within the boundary 225, the laser-based marking system 200 ensures that the projected infrared light 245 impinges on an area of the DMD 220 where only the mirror array 230 is (or a proper subset of the mirror area pixels are) found, and not on the surrounding structure of the DMD 220 (e.g., package/housing, circuitry, and/or other devices on the DMD 220 outside of the mirror array 230) which could be over heated if exposed to the infrared light 245. Thus, the laser beam 215 can be expanded and shaped into a rectangle such that the infrared light 245 incident on the DMD 220 will fill only the active rectangular pixel area 230 with uniform intensity laser light 245.

[0044] In addition, in some implementations, only the area of the DMD mirror array 230 that is needed for the next marking operation will be illuminated by the rectangular area of the incident laser light. As noted above, the relative position of the DMD 220 can be moved to adjust the size and/or resolution of the print image on the target object 270. In addition, as described further below, the flux density of the infrared light 245 falling on the DMD mirror array 230 can be adjusted by the controller 250 based on the size/resolution adjustment and/or the specific application (i.e., some applications will need different power levels independent of any needed image size/resolution adjustments).

[0045] To adjust the size of the rectangle of uniform density infrared light 245 on the DMD mirror array 230, the approach shown in FIG. 2B need only employ a translation stage 222 that operates in just the Z dimension (e.g., using a stepper motor and a threaded shaft, or other such mechanical movement structures, coupled with the DMD 220). The rectangular laser beam 245 is a divergent beam, where the rectangular shape gets bigger the further the divergent beam 245 travels before it reaches the DMD 220, and so the projected rectangle 245A gets smaller the closer the relative position of the DMD 220 is to the optics 240. Thus, movement of the translation stage 222 allows different sized images to be marked/printed on the target object 270 and changed as needed (e.g., on the fly, in real time).

[0046] In some implementations, the projected rectangle 245 A is always centered on the DMD mirror array 230, as the projected rectangle 245A is shrunk and grown by relative movement of the DMD 220. In such implementations, the mark/print can be constantly directed to the same location on the target 270 (e.g., a fixed marking location for products passing by on a conveyor in a product manufacturing and/or packaging facility) without using additional components in the optics 275 to reposition the printing location. However, in some implementations, such repositioning optics 275 can be used, either with a single Z dimension translation stage 222, or with a translation stage 222 that moves in the Z and X dimensions, in the Z and Y dimensions, in the X, Y and Z dimensions, or in only the X and Y dimensions. Note one or more such translation stages 222 can be coupled with the DMD 220 (as shown in FIG. 2B) with the optics 240 (as shown in FIG. 2C) or both.

[0047] In some implementations, the repositioning optics 275 redirect the printing beam to compensate for different incoming portions of the light from the DMD 220. For example, in FIG. 2C, the translation stage 222 can be and X and Y translation stage, and different, non overlapping proper subsets of the mirrors 230 can be used (e.g., separate quadrants) for respective prints; the repositioning optics 275 redirect the incoming light from the DMD 220, based on the mirror subset being used, to hit the same target location for each print using different mirror sets, thus decreasing heating of and/or enabling better heat dissipation from the DMD 220. Further, in these or other implementations, the printing beam can be redirected from one target location to one or more other target locations, on the same product and/or on different product(s). For example, when other heat reduction/elimination systems and techniques are sufficient, the DMD mirrors 230 can be used to rapidly print at different target locations, on the same product and/or on different product(s).

[0048] FIG. 2D shows the same view of FIG. 2C of the beam shaping and projection optics 240 and the DMD 220, but the translation stage 222 is now an XYZ translation stage attached to the DMD 220 and/or the optics 240 (e.g., a stepper motor to cause movement in the X and Y dimensions in addition to the Z dimension) allowing full flexibility in which set of mirrors 230 are illuminated by the projected rectangle of light. In the example shown in FIG. 2D, the beam shaping and projection optics 240 have been reconfigured and/or repositioned relative to the DMD 220 (e.g., by the controller 250) to reduce the size of (and reposition) the rectangle illuminating the DMD mirrors 230. Thus, a projected rectangle 245B of infrared light stays not only within the boundary 225, but also only covers a proper subset of the mirrors 230. In the example shown, the proper subset is fifteen mirrors out of a total of fifty mirrors, but as will be appreciated, the total number of mirrors 230 can be much larger, and the various possible subsets of the mirrors 230 that can be illuminated by adjusting the cross-sectional, rectangular dimensions of the projected laser light 245 are substantial.

[0049] Moving the printing image laser light around the available mirrors 230 in the DMD 220 can extend the life of the DMD 220. Depending on the number of mirrors 230 in the DMD 220 and the size of the image printing area on the target 270, the printing image laser light can be moved such that the same area of the mirror array 230 is only used every other print, or every third print, every fourth print, every sixth print, etc. Note that many variations are possible here depending the DMD array being used and the nature of the marking/printing application. For example, when printing two dimensional bar codes that are 144x144 pixels in dimensions, a DMD with a mirror array of 768x1024 pixels can have thirty five separate areas of the DMD mirror array available for printing, and thus the same mirror area need only be used every thirty sixth print.

[0050] In general, by allowing only the area of the DMD mirror array 230 that will be used for printing to receive the rectangular beam area of the laser light 245, the amount of heating of the DMD 220 can be reduced, which can increase the useable life of the DMD

220. Further, by distributing the laser energy over the entire array for images that are smaller than the total array area (as described above) the time between prints by a particular subset of mirrors is increased, thereby allowing more time for heat dissipation. In some

implementations, heat dissipation from the mirror array is facilitated using one or more cooling devices/structures, such as fans, Peltier coolers, heat sinks (e.g., metal or liquid), and phase change (heat pipe) devices (which may or may not also be used with the optical absorber 260). In any case, controlling the X and Y positioning of the projected rectangle 245 in addition to controlling the size of the projected rectangle 245 (and likewise the resolutions of the mark/print in accordance with the number of mirrors in the mirror subset) allows the controller 250 to optimize use of the array 230 for each mark/print.

[0051] In addition, the laser power can be adjusted (e.g., by the controller 250) to compensate for the size of the mirror array 230 area being used, the required power level of the light incident on the target 270, or both. For example, to compensate for the power intensity across the image area to be printed, as the image area is changed, the power output to the laser source 210 is adjusted to compensate by adjusting the pulse width modulation (PWM) signal that is applied to the laser tube source used to fire the laser energy (such as described in further detail the following paragraph). Alternatively or additionally, Liquid Crystal on Silicon (LCoS) technology can be used to design a filter used between the beam shaping optics 240 and the DMD 220, where the LCoS filter is electronically controlled by the controller 250. [0052] Referring again to FIG. 2A as an example, power output from a C02 laser 210 is adjusted by controller 250 using a PWM digital signal provided by the controller 250 to the laser source driver 250A. The PWM signal is a pulse stream, and the ratio of the high to low durations is adjusted to increase or decrease the power. When the signal is always ON or HIGH, the PWM is described as 100% commanding full power from the laser. Similarly, when the signal is always OFF or LOW the PWM is described as 0% commanding zero power from the laser. When the ratio of the ON or HIGH state of the signal equals the LOW or OFF state the PWM is then commanding 50% power. While the frequency of the PWM signal is dependent on the laser source 210, it can typically be between 5 and 20kHz.

[0053] In any case, due to this adjustability of the laser power, the flux density of the laser beam 215 (and thus the flux density of the laser light 245) can be adjusted (e.g., by controller 250) based on the application at hand, e.g., based on how much power is needed to ablate a portion of a target object 270. For example, depending on the material to be marked, the C02 laser power can be varied from ten watts to several hundreds of watts (or even kilowatts) for both CW and pulsed C02 lasers. Other applications will use different power levels, such as when using phase changing material for marking. In general, the power level should be set based on the amount of heat that needs to be absorbed by the target over a given period of time to make the mark, and the power level of the incident light 245 can then be adjusted downward and/or upward based on the size of the projected rectangle on the DMD mirror array 230 to keep the appropriate power level at the target.

[0054] Further, with or without the use of different areas of the mirror array 230, the DMD 220 can be designed to reduce its absorption of heat, as described above. The additional material(s) added to the DMD 220 (e.g., gold coatings) increase reflection of the incident light and reduce absorption of the light, thereby reducing heat generation at the DMD 220. In some implementations, these additional material(s) are designed to reduce heating of (and resist damage to) the DMD mirror array 230 when the mirror array 230 is exposed to laser light in the infrared range of 2.5 to 11 micron (e.g., 2.6 to 4 micron range, or 4.8 to 8.3 micron range, or 9 to 11 micron range).

[0055] In some implementations, the use of a pulsed C02 laser provides additional advantages over using a CW C02 laser. Pulsed C02 lasers can give a high peak power (which is good for buming/ablation) over a very short duration pulse. For example, an externally Q switched pulsed C02 laser can have a pulse width of a few nanoseconds to tens of microseconds, with single pulse energy from a tenth of a milliJoule (mJ) to a few mJ, and repeat rates of several kilohertz (kHz). This leads to average powers of a few Watts while the peak power within each pulse can be millions of Watts. Note that near IR laser pulse widths can go from femtoseconds to CW.

[0056] Thus, using a short duration laser pulse, the pulsed C02 laser generates lower average power than a similar CW C02 laser, which lessens the heat delivered to the DMD, reducing the risk of induced heat damage or deformation of the pixel mirrors in the DMD. In some implementations, successful marking is determined by the pulse rate of the C02 laser, the pulse width duration (e.g., from micro to pico-seconds), the peak energy, and the on time of the pixel mirrors. For example, a commercially available DLP device (e.g., DLP 7000 available from Texas Instruments) can have a refresh rate maximum of 32.5 kHz, and the rate can be lowered to 1900 Hz for 8 bit grey scale.

[0057] In addition, further steps can be taken to reduce heat buildup in the DMD and/or to conduct heat generated at the DMD away from the DMD. As noted above, the DMD will have 0.5 to 1.5 micron (e.g., 1 micron) of space between each mirror. Thus, as shown in FIGs. 2C and 2D, the mirrors 230 of the DMD 220 have a pixel mirror separation 235 between each pair of mirrors 230. This separation means that some of the laser light 245 will fall through these gaps 235 and onto the structures underlying the mirrors 230, e.g., the electro-mechanical hinge components 110 and the semiconductor substrate 120 of the DMD 100 in FIG. 1 A. As this can cause undesirable heating of these underlying structures, in some implementations, the additional materials described above for use with the mirrors (e.g., gold coatings) can also be used for these underlying structures. For example, the gold coating can be applied using vapor deposition to both the mirrors 230 and to the underlying structures (e.g., through the gaps 235 between the mirrors 230 in the DMD 220). This can help with reducing laser energy absorption within the underlying areas of the pixel gaps 235. In some implementations, heat dissipation from the structures underlying the mirrors 230 is facilitated using one or more cooling devices/structures, as described above. Moreover, as with the mirrors, copper (e.g., oxygen free, high conductivity copper) can also be used with the underlying structures to both reduce laser energy absorption and to assist in conducting heat energy out of the DMD 220. [0058] In some implementations, further features can be added to facilitate operation of the laser-based marking system. For example, the laser-based marking system can include a laser diode to generate a visible light (e.g., red) laser beam that is used to project a perimeter around the images (e.g., texts, codes, logos, etc.) to be marked on an object, such that the projected perimeter of a visible light laser beam is displayed on the target object to provide a visual aid to the user. This allows the intended area of the target for marking to be readily ascertained by the user of the laser-based marking system. Note that the visible light laser beam generated by the laser diode should have just enough power to make the projected perimeter visible to the user, but should not have enough power to cause any ablation or phase change of a surface material (i.e., no marking by the visible laser light perimeter). In some implementations, the visible light generated by the laser diode is itself expanded and shaped to illuminate the entire active mirror area of the DMD so that the image to be marked is visually displayed on the target material (without ablation) as a visual aid to show how the image (e.g., text, code, logo, etc.) appears on the target before actually marking the target with the C02 laser light.

[0059] As noted above, various implementations can use one or more programmable hardware processors that execute one or more computer programs. Hardware processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, such as a mobile telephone, a personal digital assistant (PDA), a mobile audio or video player, a controller for a laser printer/marking device, to name just a few. Devices suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM (Erasable

Programmable Read-Only Memory), EEPROM (Electrically Erasable Programmable Read- Only Memory), and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0060] To provide for interaction with a user, embodiments of the subject matter described in this specification can be implemented on a computer having a display device, e.g., an LCD (liquid crystal display) display device, an OLED (organic light emitting diode) display device, or another monitor, for displaying information to the user, and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0061] While this specification contains many implementation details, these should not be construed as limitations on the scope of the invention or of what may be claimed, but rather as descriptions of features specific to particular embodiments of the invention. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. Thus, unless explicitly stated otherwise, or unless the knowledge of one of ordinary skill in the art clearly indicates otherwise, any of the features of the embodiment described above can be combined with any of the other features of the embodiment described above.

[0062] Thus, particular embodiments of the invention have been described. Other embodiments are within the scope of the following claims. For example, rather than using a DMD with a 2D array, a 1D array DMD can be employed and used in a thermal transfer printhead, which can be used with reel-to-reel ribbon printing or continuous band printing; note that a single row of mirrors in such a printhead can change on the fly, in real time, as the target ribbon or band moves past the 1D array, which thus prints the image one column at a time. As another example, the distribution of laser light across different regions of a DMD to reduce heating and increase opportunity for heat dissipation, can be employed in laser marking systems using light wavelengths outside of the IR range (e.g., as low as 0.78 micron).

Claims

CLAIMS What is claimed is:

1. A laser marking system comprising:

a laser source configured to produce an infrared laser beam to modify a surface of a material to be marked;

a digital mirror device comprising an array of mirrors, electrically actuated electro- mechanical hinge components coupled with respective mirrors in the array of mirrors, and a semiconductor substrate including electrical circuits coupled with the electrically actuated electro-mechanical hinge components, wherein each of the mirrors in the array of mirrors has a reflective surface portion comprising gold; and

beam shaping and projection optics positioned in an optical path of the infrared laser beam before the digital mirror device, the beam shaping and projection optics being configurable to shape the infrared laser beam into a rectangle of uniform infrared laser light and project the rectangle of infrared laser light with respect to the array of mirrors.

2. The laser marking system of claim 1, comprising focusing optics positioned in an optical path of the infrared light between the digital mirror device and the surface of the material to be marked, wherein the focusing optics and the beam shaping and projection optics comprise one or more Zinc Selenide (ZnSe) optical components, comprising at least one ZnSe lens.

3. The laser marking system of claim 2, wherein the laser source comprises a pulsed,

C02 infrared laser.

4. The laser marking system of any of claims 1-3, wherein the gold is gold plating applied over both (i) a base material of each of the mirrors in the array of mirrors and (ii) at least a portion of the electrically actuated electro-mechanical hinge components.

5. The laser marking system of claim 4, wherein the digital mirror device comprises a

ZnSe glass faceplate covering the array of mirrors.

6. The laser marking system of claim 4, wherein each mirror of the mirrors in the array of mirrors comprises an adhesive layer between the gold plating and the base material of the mirror, the base material of the mirror comprising aluminum.

7. The laser marking system of claim 4, wherein the base material of the mirror comprises copper.

8. The laser marking system of any of claims 1-3, comprising a controller configured to operate the system to ensure that the rectangle of infrared laser light does not impinge on any portion of the digital mirror device outside of a boundary of the array of mirrors, and to set a size of the rectangle of infrared laser light in accordance with a size of an image to be formed on the surface of the material to be marked.

9. The laser marking system of claim 8, wherein the controller is configured to adjust a power of the infrared laser beam produced by the laser source in accordance with the size of the rectangle of infrared laser light set by the controller.

10. The laser marking system of claim 9, comprising a translation stage coupled with at least the digital mirror device, wherein the controller is configured to operate the translation stage to adjust a relative distance between the digital mirror device and the beam shaping and projection optics to set the size of the rectangle.

11. The laser marking system of claim 10, wherein the translation stage operates in X and Y dimensions, in addition to a Z dimension, and the controller is configured to operate the translation stage to select different, non-overlapping proper subsets of the mirrors in the array for respective marking operations.

12. The laser marking system of any of claims 1-3, wherein the reflective surface portion of each mirror of the mirrors in the array of mirrors comprises the gold being gold plating over a base material of the mirror, and wherein the digital mirror device comprises a ZnSe glass faceplate covering the array of mirrors.

13. The laser marking system of claim 12, wherein each mirror of the mirrors in the array of mirrors comprises an adhesive layer between the gold plating and the base material of the mirror, the base material of the mirror comprising aluminum.

14. The laser marking system of claim 12, wherein the base material of the mirror comprises copper.

15. The laser marking system of any of claims 1-3, wherein the laser source, the digital mirror device, and the beam shaping and projection optics are built into a single housing of an industrial laser printer device.

16. A method comprising:

setting an initial power level of a laser source based on an amount of energy that needs to be absorbed by a surface of a material, in a defined period of time, to mark the surface of the material with an image, wherein the laser source is an infrared laser source having a light wavelength between and 2.6 and 11 micron;

setting a size of a rectangle of uniform laser light to be produced by beam shaping and projection optics positioned between the laser source and a digital mirror device, the size of the rectangle being set based on a size of the image to be marked on the surface of the material;

adjusting the power level of the laser source in accordance with the size of the rectangle of uniform laser light;

causing the laser source to output laser light, at the adjusted power level, into the beam shaping and projection optics to illuminate the digital mirror device; and

causing the illuminated digital mirror device to redirect selected portions of the incident laser light to mark the image on the surface of the material.

17. The method of claim 16, wherein setting the initial power level of the laser source comprises setting the power level to cause ablation of the surface of the material.

18. The method of claim 16 or claim 17, wherein setting the size of the rectangle of uniform laser light comprises moving a translation stage coupled with the digital mirror device.

19. The method of claim 18, wherein the translation stage comprises an X, Y and Z translation stage, and the method comprises:

moving the translation stage to select different, non-overlapping proper subsets of mirrors in the digital mirror device for respective marking operations, thereby distributing heat from the incident laser light across the mirrors of the digital mirror device; and

redirecting the selected portions of light from the digital mirror device, using focusing optics positioned in an optical path of the selected portions of light, in accordance with the different, non-overlapping proper subsets, different target marking locations, or both.

20. The method of claim 16 or claim 17, wherein causing the illuminated digital mirror device to redirect selected portions of the incident laser light comprises loading the digital mirror device with a bitmap image defining the image comprising a two dimensional (2D) barcode.