Abstract:
A system and method for encoding objects with a microscopically visible code are provided. A laser beam is passed through a mask to impose a pattern representative of the code on the beam. The power level of the beam is adjusted in accordance with the output of a reflectivity sensor which measures the object, so that the beam intensity is sufficient to produce a microscopically visible pattern, but insufficient to produce a visible pattern.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a system and method for encoding objects. More particularly, this invention relates to a system and method for using a laser to place a microscopically visible code on an object. 
     For various reasons, it may be desirable to place a code on an object, such as an identification code, that can be read only under magnification. Such a code might be useful, for example, in identifying such articles if they are stolen. 
     Another use of such a code is in certain retail industries, such as the limited distribution cosmetic and fragrance industry. In such industries, distribution of products is limited to certain authorized retailers. However, it is known that some authorized dealers &#34;divert&#34; a portion of their stock to unauthorized dealers. Manufacturers therefore code each product package so that if it is diverted, the manufacturer can determine the identity of the authorized dealer who was the intended recipient of the package when it was shipped by the manufacturer. The manufacturer can then stop doing business with that dealer, or take other action against him. Unfortunately, the diverters have learned many of the coding systems and have devised means to defeat or attempt to defeat them. 
     In one system, for example, a pattern of fine pinholes is punched into the cardboard carton containing the product. The placement of the pinholes represents a numerical code identifying the dealer for whom the product was intended. The pinhole pattern is relatively easy to find, particularly because mechanical and aesthetic considerations usually limit its placement to the bottom of the carton. Diverters have learned to defeat the pin coding system by cutting out the coded portion of the package and placing an adhesive label over the damaged area or by adding additional pinholes to the pattern. They can also discard the carton and sell the product without it, or they can substitute a new carton for the coded carton. 
     It therefore would be desirable to be able to encode objects in a way that the code is difficult to detect, to increase the difficulty of finding and altering or obliterating the code. 
     It also would be desirable to to able to place the same code in multiple and random locations on an object to further decrease the possibility that all codes will be detected. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to encode objects in such a way that the code is difficult to detect, to increase the difficulty of finding and altering or obliterating the code. 
     It also is an object of this invention to place the same code in multiple and random locations on an object to further decrease the possibility that all codes will be detected. 
     These objects are accomplished by the system of the invention for placing a microscopically visible pattern of an object. The system includes means for generating a beam of coherent electromagnetic radiation of a desired wavelength, the beam having an intensity and a cross-sectional area. The system also includes means for adjusting the beam intensity, mask means for imposing the desired pattern on the beam, means for transporting the object past the beam generating means, and means for measuring the reflectivity of the object. Additional means, responsive to the reflectivity measurement, cause the adjusting means to adjust the beam intensity such that the beam intensity is insufficient to produce on the object a pattern that is visible to an unaided eye, but is sufficient to produce on the object a pattern that is visible with the aid of an optical magnifying device. 
     A method according the invention for placing the pattern on an object includes the steps of generating a beam of coherent electromagnetic radiation of a desired wavelength, the beam having an intensity and cross-sectional area, imposing the desired pattern on the beam, transporting the object past the generating means, measuring the reflectivity of the object, and adjusting the beam intensity in response to the reflectivity measurement such that the beam intensity is insufficient to produce on the object a pattern visible to an unaided eye, but sufficient to produce on the object a pattern that is visible with the aid of an optical magnifying device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: 
     FIG. 1 shows the coding matrix used in the preferred embodiment of the invention; 
     FIG. 1A shows a sample code in the coding matrix of FIG. 1; 
     FIG. 1B shows the dot pattern of FIG. 1A without the grid lines of the coding matrix; 
     FIG. 2 is a schematic elevational view of the system of the invention; 
     FIG. 3 is a plan view of the system of the invention, taken from line 3--3 of FIG. 2; 
     FIG. 4 is an elevational view of a beam attenuator according to the invention; 
     FIG. 5 is an elevational view of a mask according to the invention; 
     FIG. 6 is a cross-sectional view of the mask of FIG. 5, taken from line 6--6 of FIG. 5; 
     FIGS. 7A-I are a flowchart of a first software program used with the invention; 
     FIGS. 8A-F are a flowchart of a second software program used with the invention; and 
     FIGS. 9A-G are a flowchart of a third software program used with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention uses a beam of coherent electromagnetic radiation, such as the beam from a carbon dioxide laser, to code objects, such as cosmetic and fragrance product packages, with a pattern of dots. The pattern of dots is similar to that applied by a mechanical pin coder. However, because of the ability of the laser beam to be finely focused, the pattern can be made quite small. In addition, the intensity of the laser beam can be controlled so that the code is barely etched onto the surface of the package, making it difficult to detect without special microscopes. Further, by pulsing the laser several times while the package is being moved through its field, several identical codes can be placed on the package, further reducing the likelihood that the coding will be defeated by increasing the number of codes a diverter must find. 
     The coding matrix 10 used in the preferred embodiment of the present invention is shown in FIG. 1. Coding matrix 10 consists of seven rows 11a-g of ten columns 12a-j each. The entire grid, as applied to a package, preferably occupies an area of 0.2 inch by 0.16 inch. The three dots 13a-c are used to determine matrix orientation--i.e., when a package is examined and the code pattern is found, dots 13a-c enable the observer to orient the package properly and read the code. Rows 11a, g are not otherwise used. Five additional dots, one each in rows 11b-f, represent a five digit decimal number, row 11b representing the most significant digit and row 11f representing the least significant digit. Columns 12a-j represent the digits 0-9. 
     For example, the dot pattern shown in FIG. 1A represents the code &#34;62785&#34;. Of course, the grid lines will not appear on the package, but dots 13a-c and 14a-e will, as shown in FIG. 1B. 
     The same grid could be used for other than decimal codes by using more than one dot in each of rows 11b-f. However, in the preferred embodiment, mechanical limitations, to be described below, prevent the use of more than one dot per row. 
     A preferred embodiment of the overall system 20 of the invention is shown in FIGS. 2 and 3. A carbon dioxide laser 21 projects a beam 22 of laser light (coherent electromagnetic radiation) at a wavelength of 10,600 nm. Beam 22 is reflected by mirror 23 so that it is aimed upwards through gap 31 between the two segments 32a, b of split conveyor belt 30. Beam 22 then passes through mask 24, described in more detail below, which is set to the desired pattern. Next, beam 22 passes through beam attenuator 25 which attenuates the beam to the desired intensity as discussed below. Condensing lens 26 is interposed between attenuator 25 and conveyor belt 30 to reduce the cross-sectional area of patterned beam 22, and thus to reduce the size of the pattern produced on the surface of package 27, as well as to increase the energy per unit area (intensity) of beam 22. A hood 28 surrounds the laser head area of the system 20--i.e, the area where beam 22 emerges to impinge on package 27--to prevent eye injuries by preventing operators or other personnel from looking into beam 22. 
     When package 27 is over the laser head area, light source 33, which may be an infrared light-emitting diode having a wavelength of 900 nm, illuminates package 27 with a known light intensity and reflectivity sensor 34 measures the intensity of the reflected light at the point at which beam 22 will strike. Based on that reflectivity measurement, control computer 29, such as an IBM PC or equivalent microcomputer, adjusts beam attenuator 25 to select an intensity for beam 22 which will produce a pattern on package 27 that is not visible to an unaided eye, but is visible under an optical magnifying device such as a 30-power microscope. The necessary intensity is determined by control computer 29 based on two competing factors. First, the lighter the color of the package 27, the lighter the imprinted pattern can be and still be detected by an unaided eye. Second, the lighter the color of the package 27, the more beam energy will be reflected by the package. Therefore, for a lighter package, a certain minimum intensity is necessary to achieve the imprinting of the pattern because of the reflection of beam energy, but there is also a maximum allowable intensity beyond which the imprinted pattern will be dark enough to be visible to the naked eye. On the other hand, a darker package will reflect less of the beam energy, but will require a greater intensity to produce a pattern that is dark enough to be visible even under the microscope. 
     As package 27 approaches the laser head area, it also passes a package-approaching sensor which prepares the laser firing controls for the impending firing of laser 21. The package-approaching sensor consists of a light source 35a, such as a light emitting diode, and a detector 35b. When package 27 interrupts the beam of light between source 35a and detector 35b, the interuption is interpreted by control computer 29 as the approach of a package. Belt speed sensor 201 allows computer 29 to estimate the time of arrival of package 27 and to prepare the laser firing sequence, which includes the charging of an energy storage capacitor, which requires about 60 milliseconds. When the package is in the field of the laser, a package-present sensor, similarly consisting of a light source 36a and a detector 36b, triggers the firing of laser 21. 
     In the preferred embodiment, laser 21 itself is always operated at its maximum energy level. Laser 21 preferably should be rated at three joules per pulse, and in any case should be rated at at least 15 pulses per second (45 watts of power). A minimum beam intensity of 0.58 joules/cm 2  is required prior to lens 26. Beam intensity is controlled by attenuator 25, shown in FIG. 4, which is a rotating disk 40 rotated by a motor 200. Disk 40 has eight transmissive areas 41a-h which can be rotated into the path of beam 22. Each of areas 41a-h contains a material having a different transmittance at the wavelength of beam 22. For example, each of areas 41a-h may have a different thickness of a plastic film having a known transmittance-per-unit thickness at the appropriate wavelength. In the preferred embodiment, Cannings SCB-25, a 25 micron polypopylene film sold by Cannings Parry Packaging of Bristol, England, is used. Area 41a has no film, while areas 41b-h have 1-7 layers of film, respectively. Each layer transmits 92% of incident beam power. Therefore, the percentage of beam power transmitted through each of areas 41a-h is, respectively, 100%, 92%, 85%, 78%, 72%, 66%, 61%, and 56%. 
     In practice, it has been found that instead of rotating the desired one of areas 41a-h into the beam path when firing laser 21, it is more efficient to allow disk 40 to rotate at a constant speed of, e.g., 1,500 r.p.m., allowing control computer 29 to keep track of the angular position of the disk and to fire laser 21 when the correct one of areas 41a-h is in position in the beam path. A maximum firing delay of 40 milliseconds, the time required for one full revolution of disk 40 at 1,500 r.p.m., will be encountered as control computer 29 waits for the correct one of areas 41a-h to be present in the beam path. 
     Beam intensity could also be controlled by directly varying the power of laser 21 itself. However, that would require varying the voltage on the energy storage capacitor, which could cause unpredictable transient effects if the variations must be accomplished at high speeds. 
     Before passing through attenuator 25, beam 22, which preferably has a cross-sectional area of approximately one square inch, impinges on pattern generating mask 24. Mask 24 is shown in FIGS. 5 and 6 and includes a mask plate 50 which has a cross-sectional area greater than that of beam 22 and which has three holes 51a-c which result in the formation of dots 13a-c in pattern 10, and five rows 52a-e of ten holes each for forming the five-digit decimal number. Five slides 53a-e overlie rows 52a-e. Each of slides 53a-e has one hole 54a-e respectively. Slides 53a-e slide in blocks 55. Stepping motors 56a-e are connected to respective ones of slides 53a-e via rotary-to-linear motion converters 57a-e and plastic arms 58a-e. Stepping motors 56a-e are reliably and easily controlled by computer 29 to accurately line up holes 54a-e over the desired ones of the holes in rows 52a-e to produce the desired pattern. Mask plate 50 and slides 53a-c are preferably made of a material which is both wear-resistant and laser-reflective, such as beryllium-copper alloy, while blocks 55 are preferably made from a heat-resistant material such as aluminum alloy. 
     The size of the matrix of holes in rows 52a-e preferably is 1.0 inch by 0.8 inch. Using a 5-to-1 condensing lens 26, a pattern size of 0.2 inch by 0.16 inch can be produced. Each of slides 53a-e is provided with chemically etched markings (not shown), and a respective sensor (not shown) can read the markings and confirm to control computer 29 that each slide is being properly positioned for generation of the pattern. 
     When system 20 is in operation, computer 29 is programmed to set mask 24 to the desired pattern. An operator simply lays packages 27 on belt 30 so that they lie across gap 31. The particular orientation is unimportant and, in fact, the more randomly they are placed, the more random the pattern placement will be. If desired, a group of packages can be run through the system several times to place several patterns on each package, and the patterns can be the same or different for each repetition. In addition, laser 21 can be pulsed to place a row of patterns on each package 27 as it passes through the field of laser 21. The number of patterns that can be imprinted by pulsing laser 21 is limited by the maximum pulse rate of laser 21, the package size and shape, and the belt speed. The rotation speed of disk 40 is also a limiting factor because even if laser 21 is ready to pulse, it cannot be fired until the correct one of areas 41a-h is in the beam path, as discussed above. 
     Control computer 29 sets the laser power levels and controls the pattern matrix 24 and the firing of laser 21. The main program for use on computer 29, a BASIC listing of which is provided as Appendix A, allows the operator to allow computer 29 to control the beam intensity as determined by reflectivity sensor 34 or to override that intensity selection manually. For example, it may be learned through experience that a particular type of packaging always needs a certain intensity and that because of its color or texture the sensor-controlled intensity is incorrect. The program further allows the operator to instruct the computer to set all intensities for all packages 27 a set number of increments higher (or lower) than the intensities determined by sensor 34. A flowchart of this program, the blocks of which are keyed to the lines of the program listing, as shown in FIGS. 7A-I. Program listings of two major subroutines of this program are provided as Appendices B and C, and flowcharts keyed to the lines of the subroutine listings are shown in FIGS. 8A-F and 9A-G, respectively. 
     Other programs for use on computer 29 are provided. These other programs allow the operator to create and update account files, to select a code, thereby setting the mask generator, to test various system components, to start up the laser and the conveyor belt, and other similar utility functions. Program listings of these other programs are provided in Appendix D. 
     The present invention places few limitations on the type of packaging that can be used. One limitation is that if a package is to be wrapped in cellophane or other plastic film--as many packages are, particularly when a group of two or more packages are to be sold as a unit, the film used must be transparent or nearly transparent at the wavelength of beam 22. It is known that certain plastic films are nearly opaque at the desired wavelength while others are nearly transparent. 
     Thus, a system and method are provided for printing on an object a pattern which is only microscopically visible. One skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which are presented for purposes of illustration and not of limitation, and the present invention is limited only by the claims which follow. ##SPC1##