Abstract:
An apparatus for applying permanent markings onto products using a Vacuum Arc Vapor Deposition (VAVD) marker by accelerating atoms or molecules from a vaporization source onto a substrate to form human and/or machine-readable part identification marking that can be detected optically or via a sensing device like x-ray, thermal imagining, ultrasound, magneto-optic, micro-power impulse radar, capacitance, or other similar sensing means. The apparatus includes a housing with a nozzle having a marking end. A chamber having an electrode, a vacuum port and a charge is located within the housing. The charge is activated by the electrode in a vacuum environment and deposited onto a substrate at the marking end of the nozzle. The apparatus may be a hand-held device or be disconnected from the handle and mounted to a robot or fixed station.

Description:
ORIGIN OF THE INVENTION 
     This invention was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or thereof. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to the method of depositing thin films as a means to apply safe permanent human and/or machine-readable identification markings to the surfaces of materials that do not outgas in a vacuum environment, and specifically to apparatus for applying these markings. 
     (2) Description of the Related Art 
     Industry utilizes part identification markings to identify parts and components. The use of machine readable binary codes in the form of matrix representations is described in U.S. Pat. No. 5,380,415. A wide range of marking methods has been developed for his purpose including means to apply machine-readable symbols used for automatic data collection. These methods involve the use of attached identification means such as adhesive backed labels and tapes, bands, tags, identification plates and direct part markings (DPM) which are applied to, or formed by altering a surface of a part. 
     DPM is generally recommended in applications where: 1) traceability is required after the product is separated from its temporary identification, such as marked packaging, 2) the part is too small to be marked with a bar code labels or tags, or 3) the part is subjected to environmental conditions that preclude the use of an attached identification means that will not survive those conditions. 
     DPM can generally be subdivided into two general categories: non-intrusive and intrusive. Intrusive marking, methods alter a surface by abrasion, cutting, burning, vaporizing or other destructive means. Intrusive marking methods include methods such as micro-abrasive blast, dot peening, electrochemical etch, machine engraving, milling, laser etching and engraving or other similar marking methods. 
     Non-intrusive markings, also known as additive markings, can be produced as part of the manufacturing, process, such as cast, forge or mold operations, or by adding, a layer of media to a surface using methods that have no adverse effects on material properties. Examples of additive markings would include ink jet printing, silk screening, stenciling or other similar marking methods. 
     While both non-intrusive and intrusive marking methods are widely used in industry, their applications are limited. Non-intrusive markings are not generally used in applications associated with harsh environments. For instance, ink marking would not be used to mark engine components because the high heat experienced by the part would burn off the marking media. Intrusive markings, which are designed to survive harsh environments, may be considered to be controlled defects in high stress applications and could degrade material properties beyond a point of acceptability. 
     Some intrusive markings, especially those done by lasers, are generally not used in safety critical applications without appropriate metallurgical testing and engineering approval. Safety critical applications include parts whose failure could result in hazardous conditions. Examples of safety critical applications include systems related to aircraft propulsion, vehicle control, equipment handling, high pressure, pyrotechnics, and nuclear, biological and chemical containment applications. An example of an inappropriate use of an intrusive marking would be the laser etching of an engine turbine blade in a critical stress location. Although safe settings could be established through metallurgical testing, there remains a risk of input errors when entering settings. For example, an input error made during a turbine blade marking operation could result in the application of a mark that is applied with too much heat, resulting in micro-cracks that could propagate under stress over time. Unknown defects in engine blades could result in part failures leading to catastrophic engine loss and subsequent loss of aircraft and personnel. 
     The aerospace industry has been seeking new marking methods that are safe and that can withstand harsh environments. The National Aeronautics and Space Administration (NASA) investigated a number of methods to spray and bond particles consisting of atoms and ions of source material onto surfaces. These included plasma-activated chemical vapor deposition, laser chemical deposition, sputtering, cathode-spot arc coating, electron beam evaporation deposition, ion plating, arc evaporation and cathode arc plasma deposition. However, all of the known processes tend to have relatively slow deposition rates compared to non-vapor coating methods. Consequently, NASA developed a Vacuum Arc Vapor Depression (VAVD) apparatus, as described in U.S. Pat. No. 5,380,415, consisting of a vacuum chamber system for producing vapor deposits. It utilizes the arc formed in a gas flowing through a hollow tungsten electrode in a substantially vacuum environment. The VAVD process is capable of high deposition rates and produces no hazardous wastes or by-products. 
     Tests conducted using the VAVD apparatus produced high quality thin film coatings including small, high fidelity human and machine-readable part identification symbols in seconds. This activity however, was deemed impractical for use because the size and operation of the vacuum chamber limited both the size and volume of parts being marked and required operation within a vacuum chamber. 
     SUMMARY OF THE INVENTION 
     Consequently, it is a primary object of the present invention to provide a marking apparatus and method that can be used to produce human and/or machine readable identification markings by applying thin films of material onto surfaces using Vacuum Arc Vapor Deposition technology. 
     Another object of the present invention is to provide a means to apply thin film deposition identification marks to a surface using a mask to form a representation of a human or machine-readable part identification symbol, said symbol preferably being a Data Matrix Symbol. 
     A further object of the present invention is to provide a means to apply a thin film identification mark of contrasting color to a surface, the area of which is limited to the size of the desired mark, that is subsequently selectively removed using a separate device that becomes a marker, such as a laser, to form a representation of a part identification marking symbol, the symbol marking being captured and decoded using an optical reader fitted with a light detector like a charged-coupled device (CCD) or complementary metal-oxide semi-conductor (CMOS). 
     A still further object of the invention involves the addition of a removable coating to a surface, the area of which is limited to the size of the desired mark, using ink jet, laser bonding, or similar marking technique to form a mask to block the VAVD coating process, said coating being subsequently removed to expose a representation of a part identification symbol or other desired marking. 
     It is yet another object of present invention to provide a thin film coating applied to a surface, the area of which is limited to the size of the desired mark, that exhibits a difference in density, reflectivity, absorption or other variance to promote the capture and decoding of a part identification marking, using a image sensing reader, said sensing means including but are not limited to, capacitance, magneto-optic, micro-power impulse radar, thermal, IR, x-ray, and ultrasound. 
     Still another object of the present invention provides a symbol which represents a human and/or machine readable identification marking, and which exhibits a difference in density, reflectivity, absorption or other variance which is optionally covered with a coating so as to hide the mark for aesthetic or security reasons and then capturing the symbol with a sensing reader and decoder to yield human-readable information. 
     The present invention relates to a method and apparatus for applying symbols by using VAVD technology. The apparatus may be a hand-held device or mounted to a robot or fixed station. The apparatus is adapted to be used in a manufacturing or other environment. The apparatus preferably contains a housing. The housing contains a chamber housing an electrode, a charge and a vacuum port fixed with a deformable nozzle. A mask is placed between the nozzle and a substrate to be marked. With the nozzle sealed against the mask and/or substrate, a vacuum is drawn in the chamber. Next, the charge is at least partially vaporized by the electrode allowing the vapor to deposit on the portion of the substrate exposed through the mask. The apparatus may be hand-held or may be a fixed component in a manufacturing facility or other location. Some of the materials deposited using the VAVD process include pure metals such as aluminum, chromium, gold, molybdenum, nickel, silver, stainless steel, titanium and tungsten. Commonly used alloys include stainless steel, nickel-chromium, lead, tin and M—Cr—Al—Y. Typical compounds used in the process include Al 2 O 3 , TiC and TiB 2 . 
     The present invention overcomes many of the drawbacks and disadvantages of known marking methods and similar thin film deposition devices. One object of the preferred embodiment is to provide a means to clean and prepare a surface prior to applying a thin film deposition identification marking. The cleaning device preferably utilizes a high frequency generator and a cathode ring in close proximity to the part surface. This cleaning method removes contaminants and oxides from the area that will contain the identification mark. 
     In another use of the present invention, a matte finish thin film coating is applied to a surface, the area of which is limited to the size of the desired mark, to reduce the amount of glare radiating from a surface, thereby improving the readability of a machine-readable symbol using optical readers. 
     In still another use of the present invention, a thin film of clear metal can be deposited over an identification mark, the area of which is limited to the size of the desired mark, to provide protection from adverse environmental conditions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The particular features and advantages of the invention as well as other objects will become apparent from the following, description taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a diagrammatic sectional view of the marking apparatus constructed in accordance with the present invention; 
     FIG. 2 provides a diagrammatic sectional view of a portion of the marking apparatus illustrated in FIG. 1 positioned to coat a product in accordance with the principles of the present invention; and 
     FIG. 3 is a hand-held version of a marking apparatus similar to that of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The Vacuum Arc Vapor Deposition marking method and apparatus of the present invention can be used to apply graphical representations, human-readable characters, and a wide range of different machine-readable identification symbols to both metallic and non-metallic surfaces. The preferred symbol is a matrix symbol is described in detail in U.S. Pat. No. 4,939,354. In the matrix code format, black squares (data cells) represent a binary “1” and white data cells represent a binary “0”. When these binary values are used together in specific sequences, they represent alphanumeric characters. Some advantages of using data matrices for identification include: 
     (1) Equal-sized data cells provide for an easier decoding logic decision process than for bar codes; (2) by knowing the size and shape of a symbol and its individual data cells, decoding software can quickly reconstruct damaged portions of the code; (3) matrix symbols can be produced in both square and rectangular format and scaled in size to fit into an available marking area, (4) matrix codes designed to be applied to any of a variety of articles and products, (5) a matrix code can store from one to 2335 alphanumeric characters in any language, (6) an encoding scheme for use with such a symbol has a high degree of redundancy that permits most marking defects to be overcome (i.e., 16-bit cyclic redundancy check and data reconstruction capabilities are included in one version; and Reed-Solomon error correction is included in another), (7) up to 16 symbols can be concatenated, (8) error correction and checking (ECC) code  200  is preferred; and (9) at least some Data Matrix symbols have been placed in the public domain and recommended by the American National Standards Institute (ANSI) for use in direct part marking. 
     FIG. 1 provides a diagrammatic view of the basic components of the marking device  10 . Although all components may not be required in all applications, the preferred embodiment includes: a welding power and water lead  12 , a return water lead  14 , a gas lead  16 , a vacuum line  17 , an anode assembly  18 , a backfill vent line  19 , a vacuum chamber area  20 , a back fill vacuum port  22 , a seal  24 , a cleaning device  26 , a cathode assembly  28 , or welding torch, a quick disconnect removable front end  30  with aperture  32  sized to the desired exposure area, a shutter control device  34  used to isolate the vacuum chamber with shutter  36  during cycle on and off  34 . A housing  40  with a nozzle  38  contains many of the components of the marking device and may be mounted to an apparatus  44  such as a hand-held device or fixed station mounting. The hand-held version is the presently preferred embodiment. 
     The marking device  10  is connected to a controller  50  which may-be connected to a conventional 110 volt outlet with plug  52 . The controller  50  preferably includes a grounded power supply  54 , water recirculation pump  56 , gas supply  58 , vacuum pump  60  and a timer  62  that sequences the operation of the pumps  56 ,  60 , gas supply  58 , and ultrasonic cleaner  26  and electrode assembly  28 , the latter being portions of the device  10 , to be described in greater detail as follows. 
     Referring now to FIG. 2, to operate the system, the marking apparatus  10  is positioned over a substrate  70  covered with a mask  72  containing openings  74  that assist to form a representation of a marking on the substrate  70  such as the codes illustrated and described in U.S. Pat. No. 4,939,354 or other symbols. Masks  72  may include mechanical or laser cut stencils having openings  74  to allow deposition through the opening  74  in the desired shape of a symbol on the substrate  70 . Silk screening impressions may also be utilized as a mask  72  using photographic or thermal printing processes. Other mask types may also be utilized. 
     The marking process may begin with the loading of the anode assembly  18  of the marking device  10 . Loading drawer  76 , illustrated in the housing  40  is placed in the open position. Inside the drawer  76  is a holder  78  designed to hold a small amount of sacrificial material  80 . The holder is preferably ceramic with conductive element. The material  80  is commonly called a charge and can be in the form of chunks, wire, slugs, and so on. After the charge is inserted, the drawer  76  is pushed to the closed position. The holder  78  is placed proximate to the anode assembly  18  and cathode  28  is used to create the metallic vapor used in the coating process. The material used in the marking device  10  may be similar to that described in U.S. Pat. No. 5,380,415. 
     As illustrated in FIG. 2, after loading, the marker nozzle  38  is pressed down upon a substrate or a mask at its marking end  90  to create a seal between the nozzle seal  24  and the substrate  70  to form a substantially airtight compartment  20 . While depressing, the nozzle  38  to the surface, the controller  60  is activated to begin the marking process. The nozzle  38  may be deformable as illustrated. 
     The marking process preferably begins with the activation of the cleaner  26  and the vacuum pump  56 . The cleaning device  26  preferably consists of a ring attached to the inside of the nozzle  38  that is connected to a high-frequency generation transducer  84  that generates an ultrasonic wave to loosen impurities from the substrate. The vacuum pump  56  draws impurities from the surface along with a substantial portion of ambient air out through vacuum port  17  from the chamber  20  leaving a clear path of flow for the thin film vapor generated by the marking device  10 . Pressure within the vacuum chamber  20  is preferably 25 microns or less after drawing the vacuum. 
     A small amount of inert gas, such as argon, is injected into the chamber  20  to serve as the ionization medium that allows an arc to be sustained in the vacuum environment. The argon may be provided through cathode assembly  28  or otherwise. After the flow of gas is released, a high-current, low voltage arc is produced between the slightly separated charge (anode)  80  and the electrode  82  of cathode assembly  28  to create a blast of ionized metal vapor plasma at minute hot  3 spots on the charge  80 . The resulting, plasma is typically accelerated onto the item to be marked at directed energies of 25-150 eV. The typical plasma temperature is approximately 3 eV. The plasma striking the object to be marked forms an amorphous film that can range in thickness from angstroms to several thousandths of an inch, depending upon the length of the firing time and current used. 
     If used as a fixed station marking device, robot mechanism  45  may be used to position the marking device  10  relative to the substrate  70 . Fixed station uses maybe efficient in high volume part marking applications. Otherwise the marking device  10  may be portable as a hand held device or any other desired configuration. 
     Film coatings may include a matte finish coating to reduce the amount of glare radiating from the substrate after deposition of the desired mark. The matte finish may prove the readability of a machine-readable symbol using optical readers. Film coatings may exhibit different density, reflectivity, absorption or other variance to assist in the capture and decoding of a part identification marking, using capacitance, magneto-optic, micro-power impulse radar, thermal (IR), x-ray, ultrasound or other similar sensing apparatus. Additionally, a thin film of clear metal maybe applied to a substrate to provide protection from adverse environmental conditions. 
     A second, and presently more preferred, embodiment of the marking device is illustrated as a hand-held unit  110  in FIG.  3 . This embodiment includes: a welding power and water lead  112 , a return water lead  114 , a gas lead  116 , a vacuum line  117 , and a back fill vent line  119 . These lines connect with the welding power and water lead  12 , return water lead  14 , gas lead  16 , vacuum line  17  and back fill vent line  19  of FIG. 1 when used as a hand-held embodiment. The hand-held unit  110  also includes a trigger  131  which may be utilized to begin the marking process and/or to activate the cathode assembly  128 . This embodiment also preferably includes back fill vacuum port  122 , vacuum chamber area  120 , anode assembly  118 , cleaning device  124 , seal  126 , cathode assembly  128 , removable front end  130 , aperture  132 , shutter control device  134 , housing  140  and nozzle  138 . 
     Numerous alternations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to the preferred embodiment of the invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.