Abstract:
A system and method is provided for virtually tracking unfinished ceramic structures moved by a conveyor system through a plurality of manufacturing loops which reliably and accurately preserves both identification and manufacturing information during all steps of manufacture, and in particular during mark-obliterating steps such as firing or contouring. The method includes the steps of loading the marked, unfinished ceramic structure at a selected position on the conveyor system; relaying both the information in the identification mark and the selected position of the unfinished ceramic structure on the conveyor system; conveying the unfinished ceramic structure through at least one mark-obliterating manufacturing step, and identifying the ceramic structure after completion of the mark-obliterating step by relaying and processing information relating to its position on the conveyor system. The ceramic structure is then re-marked with a second mark after completing all mark-obliterating steps of manufacturing, such as firing and contouring. The second mark includes all of the identification and other data carried by the first mark. Both the first and second marks include the combination of a machine-readable and human-readable component, such as the combination of a two-dimensional bar code and an alpha-numeric code.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention generally relates to the tracking of unfinished ceramic structures during manufacture, and is specifically concerned with a system and method for marking, virtually tracking, and re-marking a ceramic structure after it undergoes firing so that information relating to the identification and manufacturing conditions of the ceramic structure may be reliably preserved for quality control purposes. 
       BACKGROUND OF THE INVENTION 
       [0002]    Ceramic honeycomb structures are widely used as anti-pollutant devices in the exhaust systems of automotive vehicles, both as catalytic converter substrates in automobiles, and diesel particulate filters in diesel-powered vehicles. In both applications, the ceramic honeycomb structures are formed from a matrix of thin ceramic webs which define a plurality of parallel, gas conducting channels. In honeycomb structures used as ceramic catalytic substrates, the cell density may be as high as about 900 cells per square inch. To reduce the pressure drop that the exhaust gases create when flowing through the honeycomb structure, the web walls are rendered quite thin, i.e. on the order of 2-6 mils. Ceramic honeycomb structures used as diesel particulate filters have a lower cell density of between about 100 and 400 cells per square inch, formed from webs on the order of 12-25 mils thick. In both cases, the matrix of cells is preferably surrounded by an outer skin which is quite thin, i.e. generally two or three times thicker than the web walls. 
         [0003]    Such ceramic honeycomb structures are typically manufactured by way of a procedure in which conveyor units in the form of trams, trays or pallets of a conveyor system continuously move unfinished ceramic bodies through a number of stations, hereinafter referred to as “manufacturing loops”, each of which completes one or more necessary manufacturing steps. In the first steps of the manufacturing process, the ceramic ingredients are pulverized and mixed together with a binder to form a paste-like substance which is extruded into a honeycomb body. The extruded honeycomb body is cut into segments that form green ceramic bodies, which are then loaded into the automatic conveyor system. The conveyor system then slowly moves these green bodies through a kiln, where they are fired at temperatures of typically 1300° C. or higher in order to fuse the batch constituent particles present in the extruded material into a ceramic fired body. The ceramic fired bodies may then be conveyed to a contouring station where all the outer skin of the body is abraded off, and replaced with a new skin that meets precise dimensions. The conveyor system may then move the contoured ceramic bodies through another kiln in which they are fired again at lower temperatures, for example, on the order of 800° C. or more, and from there to a coating station that coats the gas contacting surfaces with a washcoat that may contain catalytic metals. Finally, the automatic conveyor system moves the finished ceramic structures to a packaging station where they are packaged and arranged for shipping. 
         [0004]    Due to the thinness of the outer skin and the inner cell-forming webs, the substantial thermal stresses that the unfinished ceramic structures undergo during the firing processes, and the necessary mechanical handling of the green and fired bodies during the manufacturing process, defects such as internal cracks and voids may occur, as well as separations between the outer skin and the inner matrix of webs. To reduce the occurrence of such defects, it would be desirable to have a quality control procedure which allowed the manufacture to reliably trace any defective ceramic honeycomb structure back to the specific factory, kiln, and batch that it originated from. Such a procedure would allow the manufacturer to review the particular manufacturing parameters used to fabricate the defective unit and to modify its manufacturing operation in order to reduce the occurrence of such defects in future articles. Accordingly, it is a known procedure to mark, after the final firing or heating step, finished ceramic honeycomb structures with marks containing manufacturing information so that remedial manufacturing operations may be implemented. 
         [0005]    Unfortunately, the applicants have observed that such a marking procedure does not reliably result in an accurate recovery of the manufacturing information associated with a particular ceramic honeycomb structure. In particular, the applicants have observed that subsequent to the manufacture of the green bodies of such structures, different batches of fired bodies from different kilns necessarily become mixed together in order to efficiently implement other stages of the fabrication process. Additionally, different unfinished ceramic structures may be removed from one or more manufacturing loops, put into storage, and then reintroduced either onto the conveyor system or directly into another manufacturing loop. Hence a quality control process where manufacturing information is printed on the finished ceramic honeycomb structures may not accurately reflect the actual manufacturing conditions and history of the structures, as structures which end up adjacent to one another in the final conveyor units might have quite different manufacturing histories. 
         [0006]    Some of the aforementioned problems could be avoided by printing a data-carrying mark on the side wall of the green bodies that ultimately form finished completed ceramic honeycomb structures. Such a mark could include a detailed manufacturing history of the structure. However, even the best high-temperature inks known in the prior art fade or run when subjected to the 1100° C. to 1460° C. temperatures necessary to fire the green bodies into the ceramic structures, thereby making it difficult for the mark (whether in the form of a bar code or alpha-numeric code) to maintain the number of characters necessary to accurately preserve a detailed manufacturing history of the ceramic structure. And even if more durable high-temperature inks are ultimately discovered, there are some steps in the manufacture of ceramic honeycomb structures, such as contouring, which require the outer skin of the structure to be removed, thereby unequivocally obliterating any data-carrying mark printed on the outer surface of such structures. 
         [0007]    Accordingly, there is a need for a system and method for reliably and accurately preserving both identification and manufacturing information throughout the manufacture of an unfinished honeycomb ceramic structure, and in particular throughout mark-obliterating manufacturing steps such as firing and contouring. Ideally, such a system and method would be easy and inexpensive to incorporate into presently-used ceramic manufacturing facilities, and would not result in production bottlenecks which would slow the rate of production. Finally, it would be desirable if the amount of manufacturing information preserved for each individual ceramic structure was not confined to the informational limits of a bar code or other type of data-carrying mark that could be rapidly and easily printed on the side of a ceramic structure during manufacture. 
       SUMMARY OF THE INVENTION 
       [0008]    Generally speaking, the invention is a system and method for tracking unfinished ceramic structures moved by a conveyor system during manufacture which reliably and accurately preserves both identification and manufacturing information during all steps of manufacture, and in particular during mark-obliterating steps such as firing or contouring. To this end, the system of the invention includes a conveyor system for conveying an unfinished ceramic structure to and from a mark-obliterating manufacturing step; a marking mechanism that provides an identification mark on the unfinished ceramic structure prior to the conveyance of said unfinished ceramic structure through said mark-obliterating step; a positioning mechanism for placing said unfinished ceramic structure on a selected unique position on said conveyor system, and a digital processor for receiving and processing both the information in the identification mark and the selected unique position of the unfinished ceramic structure on the conveyor system, such that the ceramic structure may be identified by its unique position on the conveyor system when the ceramic structure is conveyed from said mark-obliterating manufacturing step. 
         [0009]    The method of the invention comprises the steps of loading the marked, unfinished ceramic structure at a selected position on a conveyor system; processing the information in the identification mark and the selected position of the unfinished ceramic structure on the conveyor system; conveying the unfinished ceramic structure through at least one mark-obliterating manufacturing step, and identifying the ceramic structure after completion of the mark-obliterating step by determining its position on the conveyor system and processing information relating to the determined position along with the information relating to the identification mark and the selected position. The ceramic structure may then be re-marked with a second mark after completing all mark-obliterating steps of manufacturing, such as firing and contouring. The second mark may include all of the identification and other data carried by the first mark. While both marks are preferably a combination of machine-readable and human-readable marks such as a two-dimensional bar code accompanied by an alpha-numeric code, the invention encompasses any type of mark capable of carrying a code or a unique number, whether machine-readable or human-readable or both. 
         [0010]    The selected position may be recorded as a unique combination of three coordinates of the tram or other conveyor unit if the ceramic structures are arranged in a multi-layer stack, or a unique combination of only two coordinates if the ceramic structures are arranged in a single layer as they may on a conveyor-belt type component of the conveyor system. The individual trams, trays or conveyor belt slats may be bar-coded to assist with the step of assigning each unfinished ceramic structure with a unique position in the conveyor system. Optical bar code readers may be provided to read the barcodes, sensors may be provided at various manufacturing stations and loops to generate data concerning ambient manufacturing conditions, and a digital processor connected to the optical bar code readers and sensors may be used to convert the barcodes into position information and to associate it with one of the ceramic structures as well as the particular time and conditions surrounding each manufacturing step. The manufacturing conditions recorded may include, for example, date and time that a firing step was implemented, the ambient temperature, humidity, and atmospheric pressure, the position of the ceramic structure on the conveyer unit that moved the ceramic structure through the kiln, the amount of time that the ceramic structure was in or exposed to the kiln, and variations in the measured temperature in the kiln over the time period that the ceramic structure was fired. 
         [0011]    The system and method of the invention reliably and accurately preserve the manufacturing history of each ceramic structure from green body to finished structure despite the mark-obliterating manufacturing steps that such structures are ordinarily subjected to, and despite batch-mixing at one or more manufacturing loops which typically occurs to maximize production efficiency. The fact that a digital processor is used to store the detailed manufacturing history of the ceramic structure, instead of the marks themselves, allows the use of a mark which carries no more than identification information to retrieve a detailed manufacturing history of the ceramic structure from the digital processor used to implement the method. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic diagram of a preferred system for implementing the first steps of the method, wherein green bodies from a green body extrusion station are marked with an identification code, palletized, stored, retrieved, and then loaded onto a conveyor system that takes them to a kiln; 
           [0013]      FIG. 2  is a side view of green bodies being conveyed into the entrance of a kiln by a train of kiln cars, each car of which is marked with an identification label, illustrating the steps of the method wherein a unique position on the kiln cars is associated with the identification mark on the green body and recorded by a digital processor; 
           [0014]      FIG. 3  is a perspective view of a ceramic honeycomb structure bearing an identification mark formed from a machine-readable two-dimensional bar code in combination with a human readable alpha-numeric code; 
           [0015]      FIG. 4  is a plan view of fired ceramic structures exiting the kiln shown in  FIG. 3 , illustrating the method steps wherein each fired structure exiting the kiln is identified by its unique position on the kiln car and then re-marked with an identification code, and 
           [0016]      FIG. 5  is a schematic diagram of a preferred system for implementing subsequent steps of the method wherein the identification code of each ceramic structure is associated with a unique slat on the conveyor system and recorded by the digital processor, the skin of the ceramic structure is removed (thereby obliterating the identification code) but the identity retained by its position on a unique slat of the conveyor system. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    With reference to  FIG. 1 , wherein like numerals designate like components throughout all the several figures, the system  1  of the invention includes a green body extrusion station  3  that extrudes and dries unfinished ceramic structures  4  which ultimately become finished ceramic structures after firing and other manufacturing steps. A conveyor system  5  formed from individual conveyor units  6  (which may be trams, cars, or individual slats of a conveyor belt) conveys the structures  4  to a palletizing area  7 . In this application, the term “conveyor unit” refers to any component of the conveyor system that moves a ceramic structure during any step of the manufacturing process, either automatically or manually. Additionally, the term “unfinished” ceramic structure refers to any precursor to a finished ceramic structure that must undergo at least one firing step to become a finished structure, including a dried green body or an unfired or partially fired green body. In route to the palletizing area  7 , an ink jet printer  9  that is controlled by a digital processor  11  prints a unique identification mark  13  onto the side of the unfinished ceramic structure, and an optical reader  15  likewise controlled by the processor  11  reads the printed mark in order to confirm the integrity of the printed mark. As will be discussed in more detail later, the mark  13  is essentially a unique number that acts as a “license plate” for the ceramic structure through every stage of manufacture which ultimately allows a complete and detailed manufacturing history to be recalled for each final, finished ceramic structure. Here, in the initial steps of the method of the invention, the date, time, batch number and specific green body fabricating conditions and any additional information are relayed to the digital processor  11  at the time the printer prints an identification mark  13  onto the side of the unfinished ceramic structure  4 . Additional information may also be sensed and relayed including temperature, humidity, partial pressure, customer identification, downstream manufacturing steps to be performed, shipping date or any other information that an ordinarily skilled artisan may wish to include. In addition, any information related to conditions during manufacturing, both during normal manufacturing processes and during test manufacturing processes or manufacturing processes that may have experienced abnormal conditions such as power fluctuations, variations of temperature, and sudden or unexpected changes in conditions may be recorded and relayed to the digital processor. The digital processor  11  then proceeds to associate and record the corresponding green body manufacturing information with each identification mark  13 , thereby beginning the recordation of a unique and detailed manufacturing history for each of the structures  4 . 
         [0018]    The unfinished ceramic structures  4  are moved off the conveyer system  5  and placed on to a unique position  18  on a pallet  19  having a unique identifying number assigned to it. This may be implemented by a robotic arm  17  that is programmed to relay the position  18  of each unfinished ceramic structure  4  that it stacks on the pallet  19   a  to the digital processor  11 . The digital processor  11  proceeds to associate and record the identification number  13  read by the optical reader  15  with the position  18  on the particular pallet  19   a . These steps are taken as a precaution in the event that the identification mark  13  is marred or obliterated on the pallet  19   a  as the result of an accident or other unforeseen event, and will allow the structures  4  to be identified via pallet number and unique position  18 . While the positioning of the structures  4  is implemented by a robotic arm  17  in this example, such positioning can also be done manually. 
         [0019]    In the alternative, the unfinished ceramic structures  4  can be transported by the conveyor system  5  directly from the extrusion station  3  to further manufacturing stations such as kilns, dryers, contouring stations, laser gauge stations, skinning stations, or any other processing stations. It should be noted that the palletizing and storage steps discussed in this specification do not form, in and of themselves, part of the method of the invention. Such steps are discussed only to illustrate how the method of the invention may be applied to a typical ceramic structure manufacturing process where palletizing and storage occurs between one or more of the manufacturing steps which ultimately convert a green body into a finished ceramic structure. 
         [0020]    Subsequent to the aforementioned palletizing steps, the pallet  19   a  is moved to a storage facility  21  prior to the implementation of firing and other manufacturing steps. While the storage facility  21  is schematically represented as a single facility, it may in fact include facilities at several locations, some of which are off-site to the factory, others of which are on-site. As is schematically indicated in  FIG. 1 , the storage facility includes an ambient condition monitoring device  22  which relays information to the digital processor  11  concerning the storage conditions for each individual unfinished ceramic structure, including date of entry, ambient conditions of storage (i.e. temperature and humidity) and date of departure. The storage facility  21  also has its own optical readers (none of which are shown) for scanning the identification marks  13  of structures entering and exiting the facility and relaying this information to the digital processor  11 . 
         [0021]    Subsequent to storage, a pallet  19   b  of green body-type unfinished ceramic structures  4  is transported to a de-palletizing area  20 . A robotic arm  23  removes the structures, moves them past another optical reader  25  that reads the individual identification numbers  13  and relays them to the digital processor  11 , and positions the structures  4  onto unique positions  26  on kiln cars  27  forming part of the conveyor system  5 . The robotic arm is programmed to relay to the digital processor  11  the unique position  26  on the kiln car  27  where it places a particular structure  4 . With reference now to both  FIGS. 1 and 2 , the kiln cars  27  slowly transport the structures  4  through the entrance  30  of a kiln  31  in order to fire them. Each kiln car  27  includes an identifying plate  29  with a number on it, and a pair of optical scanners  32   a ,  32   b  is provided on either side of the kiln so that the processor  11  knows exactly which structure  4  stands on each unique position  26  in each unique kiln car  27 . As is evident in  FIG. 2 , the unfinished ceramic structures  4  may be arranged in a “stacked” configuration when entering the kiln  31 , in which case the unique position  26  will be recorded in terms of three dimensions, i.e., as x-y-z coordinates. 
         [0022]      FIG. 3  illustrates one example of the type of individual identification mark  13  that the previously-referred to printer  9  shown in  FIG. 1  might print on the side of the structure  4 . Mark  13  is a combination of a machine-readable component  35 , and a human-readable alpha-numeric code  37 , both of which preferably contain a same identification number. The machine readable component  35  may be a two-dimensional bar code formed from a digital pattern of inked and uninked areas. Such a two-dimensional bar code  35  has the advantage that it can preserve all of its data (which in this case is a unique identification number) even if up to 30% of its area is obliterated or rendered illegible. The parallel provision of the same identification number  37  in human readable form facilitates rapid identification of the structure in instances where the use of an optical reader is either difficult or impossible. Other types of identification symbols and schemes are within the scope of the invention, so long as the information contained within them is sufficient to uniquely identify the unfinished ceramic structure  4  that they are printed on or otherwise attached to. 
         [0023]      FIG. 4  illustrates how the system  1  implements the method of the invention after the unfinished ceramic structures  4  have been subjected to a mark-obliterating manufacturing step, which in this case is the firing step. During firing, the green body-type unfinished ceramic structures  4  are typically subjected to temperatures on the order of 1100° C. to 1350° C. for time periods which may exceed 16 hours. The precise firing conditions (i.e., time and temperature and other parameters measured by sensors in the kiln  31  which are not shown) are relayed to the digital processor  11 , which proceeds to associate such data with each individual structure  4  and to record it. Under such harsh conditions, all known high-temperature inks that are printable on the surfaces of ceramic green bodies either fade or run to the extent that relatively complex markings of the type needed to contain a unique identification number are either seriously degraded or obliterated to the point of illegibility. Hence printed marks are unreliable identification tools for ceramic structures experiencing these extreme conditions. To solve this problem, as the fired ceramic structures  4  leave the exit  39  of the kiln  31 , optical readers  41   a ,  41   b  read the identity plates  29  on the kiln cars  27 , and relay this information to the digital processor  11 . The digital processor  11  then associates each of the unique positions  26  on the kiln cars  27  with a particular ceramic structure, and proceeds to operate a pair of vertically movable ink jet print heads  43   a ,  43   b  to re-print an identifying mark  44  on each of the structures  4 . The newly-printed mark  44  may be the same mark  13 , or a different mark that the digital processor  11  associates with the original mark  13 . Either way, the identity and manufacturing history of each ceramic structure  4  is maintained with the memory of the digital processor  11 . A pair of optical readers  45   a ,  45   b  located downstream of the print heads  43   a ,  43   b  confirm the integrity of the newly-printed marks  44 . The ceramic structures  4  may then be palletized for storage or move directly into further manufacturing stations. 
         [0024]      FIG. 5  illustrates how the method of the invention may be implemented with respect to optional manufacturing steps which may occur after the initial firing of the ceramic structures  4 . For the purposes of simplification, the palletizing, de-palletizing and storage steps that are often associated with these steps have been largely eliminated from this description, it being understood that such steps may or may not be included between the optional manufacturing steps described hereinafter. 
         [0025]    In a case where the fired and re-marked ceramic structures  4  are subjected to a contouring operation, the fired, unfinished ceramic structures  4  are moved to a de-palletizing area  50  where a robotic arm  52  controlled by the digital processor  11  unloads them onto a portion of the conveyor system  5  formed from a belt of conveyor slats  54 , each of which has its own identification plate  56 . The conveyor slats  54  carry the fired and re-marked ceramic structures to an optical reader  57  placed in front of a contouring station or loop  60 . The optical reader  57  reads the new identification mark  44  of the structure  4  just before it enters the station  60 . The outer skin and the new mark  44  are completely removed at the contouring station  60  via conventional abrasive manufacturing procedures. After the skin of the structure is removed, the skinless and markless ceramic structure  61  is placed back onto one of the slats  54 . At that time, optical readers  62   a ,  62   b  read the identification plate  56  of the particular slat  54  that the structure  61  is placed on and the digital processor  11  associates the slat identification number with the mark  44  that was obliterated as a result of the contouring step. Movement to and from the contouring station  60  is preferably implemented by robotic arms, not shown. Conditions accompanying the contouring step of manufacture are relayed from a sensor  63  to the digital processor  11 , which records this information and associates it with the identification number of the ceramic structure  61 . 
         [0026]    After contouring has been completed, and the ceramic structure  61  has been subjected to a series of laser-implemented measurements at a measuring station (not shown) to determine its outside dimensions, it then proceeds to a skinning station  66  where a new skin is molded over its exterior, the thickness of the skin being selected so as to achieve a desired product size. Identification is accomplished by optical readers  64   a ,  64   b  which read the identification-plate  56  of the slat  54  that the ceramic structure  61  is positioned and relay the plate number to the digital processor  11 , which in turn associates the plate number with the identification number of the ceramic structure  61 . After the skinning step has been completed, the specific conditions surrounding the skinning operation are sensed by sensor  67  and relayed to the digital processor  11 , which associates this information with the identification number contained in the mark  44  and records it. The skinned ceramic structure  69  is then removed from the skinning station  66  and positioned on a different slat  54 . At this time, a pair of optical readers  68   a ,  68   b  read the identification plate  56  of the new slat that the ceramic structure  69  is placed on and again relay this information to the digital processor  11 , which again associates this plate number with the identification number that was present in the mark  44 . 
         [0027]    This same procedure for maintaining the identification of the ceramic structure  69  is followed via optical readers  70   a ,  70   b  and  74   a ,  74   b  as the structure  69  enters and leaves optional processing station  72 , which may be a plugging station, a polishing station, a subsequent firing station, etc. Again, the specific conditions of the optional processing station  71  are relayed to the digital processor  11  via condition sensor  72 , which again associates this information with the identification number that was embedded in the mark  44 , and records it. Finally, this same procedure is followed as the further processed ceramic structure  73  enters a manufacturing station  75  that implements a final mark obliterating the manufacturing step. Specifically, an optical reader  77  reads the identification tag  56  on the slat  54  that the structure  73  rests on, and relays this number to the digital processor  11 , which in turn looks up the identity of the ceramic structure  73 . The digital processor  11  then associates all of the conditions of the station  75  relayed to it by the sensor  76  with the identified ceramic structure  73 , and records it, thereby substantially completing its manufacturing history. A printer  78  controlled by the digital processor  11  then re-prints, for the final time, an identifying mark  79  on the ceramic structure  73  which may be the same as the original mark  13  printed on the green body  4  that became the fired, contoured, skinned and further processed ceramic structure  73 . A final optical reader  80  connected to the digital processor  11  confirms the legibility of the mark  79  printed on the ceramic structure  73 . 
         [0028]    Different modifications, additions, and variations of this invention may become evident to the persons in the art. All such variations, additions, and modifications are encompassed within the scope of this invention, which is limited only by the appended claims and the equivalents thereto.