Compressed symbology is a product-identification method that was pioneered by NASA for tracking space-shuttle parts and is now being used to mark everything from groceries to automobile parts. Based on a system of two-dimensional marks applied to parts, compressed symbology was developed at NASA's Marshall Space Flight Center in response to the inherent need in the aerospace industry to track parts for configuration management.
The focus at Marshall is on ensuring the quality and safety of products. To be certain of the integrity of a product, each part must be tracked every step of the way — where it was made, who touched it along the way, and when and where it is installed. For NASA, that means tracking millions of parts — even tiny electrical parts no larger than a dime. Since bar codes were implemented in the mid-1980s, they have been used extensively and have saved NASA millions of dollars annually through automatic entry of data from manufacturing work orders and other paper media. However, bar-code labels have not worked well on some parts, especially small ones. Even in cases in which adhesive bar-code labels have been small enough, labels have come off, contaminating processes with glue and paper, and thereby giving rise to additional cleaning processes specifically designed to remove contaminants like glue from space-shuttle parts. In addition, spaceflight is also hostile to bar-code labels.
Another problem that has been encountered is that of compiling information about parts. At the beginning of the space-shuttle program, parts were tracked manually. As the flight rate increased, the amount of data collected was roughly equivalent to the amount of data collected in several large grocery stores each day. This situation created a backlog of paperwork that took as long as three months to catch up with the finished product.
Around this time, a Department of Defense study found that people made errors on one out of every 200 characters entered. For NASA, that meant, theoretically, that one out of every 10 part numbers entered into a data base was affected by a data-entry error. The direction was clear: To ensure the timely flight-worthiness of the space shuttle, it was becoming necessary to develop new techniques for marking parts without damaging them, and to develop an identification system, based on marks, as efficient as that of bar codes.
Because of the inherent limitations of bar codes for direct marking of parts in the aerospace industry, NASA sought a more suitable method of automated identification tracking. In September 1991, Marshall Space Flight Center established the Compressed Symbology Laboratory to investigate marks, roughly equivalent to bar codes, that could be applied directly to parts by use of permanent marking methods. The chosen general form for such marks was that of a two-dimensional matrix symbol that stores up to 100 times as much information as does a one-dimensional, linear bar code in the same area. The matrix symbol is a small square that resembles a checkerboard. The symbol is read by use of a charge-coupled-device (CCD) video camera.
Thirty marking methods were evaluated on more than 60 materials. Included were methods of computer-controlled direct marking by laser irradiation, dot peening, micro-sandblasting, and machine engraving; these methods worked well on metals. For marking such other materials as ceramics, mica, and graphite it was found necessary to apply permanent inks, precious metals, and ceramic-based coatings, sometimes in conjunction with engraving to penetrate coated surfaces.
Marking of textile products (including clothing, parachutes, tent materials, and other items) was upgraded by use of an automated-embroidery marking method. Gold was marked by depositing a thin liquid film of platinum. To facilitate the non-automated marking, new techniques of stenciling were tried. Some of these techniques were derived from a photographic transfer process, and others from computer-driven cutter/plotters. Finally, a process that closely resembles today's direct hot ink transfer was used in some applications to transfer patterns from film sheets to surfaces of parts.
By 1996, Marshall Space Flight Center researchers felt that many aspects of compressed symbology were ready for introduction into the commercial sector, even though the marking techniques developed to that point had not proven suitable for highly stressed NASA parts or could not provide the resolution needed for small parts. In August 1997, Marshall Technology Transfer formed an alliance with CiMatrix and its parent company, Robotic Vision Systems, Inc., (RVSI) to develop commercial applications for NASA's marking processes for the Data Matrix™, which is the CiMatrix patented version of the matrix symbol. The alliance also enabled development of new marking methods that would satisfy NASA's requirements on stress-critical hardware.
The applications for the Data Matrix™ seem unlimited. Readable symbols have been applied on more than 80 different materials, including metals, plastics, glass, paper, fabric, ceramics, and others. Application processes have been tailored to materials, and some materials can be marked by use of multiple techniques.
Matrix symbols can be applied to aluminum by dot-peening, electrochemical etching, laser marking, or laser bonding; or by ink-jet, silk-screen, stencil, or film deposition. The symbols can be embroidered on cloth or stenciled onto rubber. There is a technique for marking almost any substance or item. Regardless of the technique used, the mark is permanent, is smaller than a bar code, and can be easily read by use of a CCD video camera.
Before compressed symbology was available, manufacturers of computer chips had no way of marking their products, and counterfeit chips flooded the market. The same is true of other small electronic parts. Automobile manufacturers can use compressed symbology to track each piece of an automobile, thereby narrowing the scope of, and simplifying, the recall process. The symbols have already begun appearing on items used every day. Because of their versatility, data-matrix symbols are being used to mark a wide variety of products, including such household items as jars of mustard, deodorant sticks, vitamin jars, and packages of photographic film. Data Matrix™ has now become the symbol of choice for direct marking of parts in the automotive, electronics, and aircraft industries.
But it does not stop there because NASA has part-identification needs that go beyond visible marks. Identification marks might be covered by paint, cork, foam, or a number of other coatings designed to protect parts. Six techniques for reading identification symbols under coatings, through containers, and within an assembly are in the patent process. NASA has engaged partners to develop portable devices to implement these techniques.
Compressed symbology will have untold implications for industry as well as for NASA. New marking techniques within the ambit of compressed symbology, possibly ready this year, should open the door to marking stress-critical hardware.
The 15-year effort to develop these identification technologies has resulted in a NASA preferred standard and handbook. NASA Technical Standard 6002, "Applying Data Matrix Identification Symbols to Aerospace Parts" and NASA Technical Handbook, "Application of Data Matrix Identification Symbols to Aerospace Parts using Direct Part Marking Methods/Technologies" can be found at website http://standards.nasa.gov.
This work was performed by Fred Schramm of Marshall Space Flight Center; Donald L. Roxby of the CiMatrix Symbology Research Center (formerly of Rockwell); Willis L. Pavolini, Terry L. Higdon, and James D. Teed of Rockwell/Boeing; and Ward F. Davis and Robert Sant'anselmo of Veritec.
Refer to MFS-28960/61/28776/867/ 974/959/31015 volume and number of this NASA Tech Briefs issue; and the page number.