Patent Application
20080223834
The present invention relates to laser systems and particularly a method and apparatus for laser marking objects at high speed.
It is known that food and medicinal products that are susceptible to spoilage or effectiveness often have a use by or expiration date that is printed on the items themselves or on the packaging of the items so a purchaser or potential user of the goods can make a judgment of whether the product is current or outdated. This is particularly important for some food products, which can become dangerous, with chicken eggs being a prime example because of the threat of salmonella poisoning.
It is for that reason that eggs are commonly packed in cartons that have expiration dates printed on the carton. A problem with this type of dating is that consumers often remove the eggs from a carton and put them in a special holders of their refrigerator and therefore lose the important expiration date information. Although it is not believed to be a widespread practice, there have been instances where establishments have removed eggs from one printed carton and placed in another having a later expiration date which can lead to usage beyond the date by which salmonella bacteria can develop into a dangerous condition. While there have been attempts to print expiration dates on the eggs themselves with ink jet printing or other type of marking, the permanency of such printed information is suspect and can often be removed.
A particularly desirable way in which to mark eggs is to use a laser to etch an expiration date and other information on the shell of the egg which results in a permanent marking that cannot be removed from the egg itself. Such marking is described in a patent application entitled METHOD AND APPARATUS FOR MARKING AN EGG WITH AN ADVERTISEMENT, A FRESHNESS DATE AND A TRACEABILITY CODE, having Ser. No. 11/333,580, filed Jan. 17, 2006, which is specifically incorporated by reference herein.
Because billions of eggs are produced annually in the United States alone, marking even a fraction of such numbers of eggs is a formidable undertaking. A large majority of eggs sold in the United States are produced in only a few hundred locations. At these locations, grader systems clean, candle, grade and pack eggs in large volumes. High volume grader systems generally have from two to six rows of eggs that are conveyed through the various stages of the grading system and can currently process up to 175,000 eggs an hour.
Since marking of eggs must be done during this grading process to be economical, it is necessary to mark the eggs very rapidly without slowing down the speed of operation of the grader system. Thus, the marking operation must necessarily occur within a very small time and physical size window. Because of time and physical size constraints, the amount and complexity of indicia that can be marked on the eggs is limited, and the laser marking apparatus must be sized to fit in the grader in a manner which does not interfere with the normal operation of the grader.
Embodiments of the present invention comprise an apparatus for laser marking individual objects with indicia at a marking station wherein a predetermined window exists during which each object can be marked as the objects are conveyed along at least one path at a predetermined speed, the apparatus comprising, at least first and second lasers positioned adjacent one or more paths configured to direct a laser beam onto the objects to mark the same with indicia as the objects pass through the marking station, with each of the first and second lasers marking alternate following objects as they pass through the marking station.
Various embodiments of the invention also comprise a method of laser marking individual objects while they travel along at least one path through a marking station at a preferably predetermined speed, comprising the steps of activating a first laser to begin marking a first object when it enters the marking station and continuing to mark the object through a first predetermined time window within the station, activating a second laser to begin marking a successive object when it enters the marking station and continuing to mark the successive object through a second predetermined time window within the station, the first and second predetermined time windows overlapping with one another so that both objects are being simultaneously marked for at least a portion of the length of the time windows.
Embodiments of the present invention are directed to apparatus as well as a method for laser marking objects as they pass through a marking station, with the marking being carried out by lasers that are designed and configured to render graphic representations as the objects pass through the marking station. While the objects may comprise many different sizes and forms, and may be made of many different types of materials, the objects that are of particular importance and are the subject of the present invention are eggs produced by chickens.
Parenthetically, it should be understood that terms “marking” or “etching” as used herein is intended to mean that a laser is employed as a radiant energy source. The laser beam is applied to leave most of the area of the eggshell unaffected so as to provide contrast between the unaffected areas and the marking. The laser beam ablates and melts the outer surface material from the egg shell. A significant benefit of the use of laser marking is that brown eggs have etched indicia that is a contrasting white color, while white eggs have etched indicia that is a contrasting dark brown color. The structural integrity of the egg shell is not affected because the etching by the beam only affects the outer approximately 50 to approximately 90 micrometers of the egg shell, which is approximately 5% to approximately 8% of the thickness of the egg shell.
Of the billions of eggs that are produced every year, the vast majority of them are produced in a rural facility, which often have hundreds of thousands of chickens which collectively produce more than a million eggs per day. These eggs are processed through grading systems that wash, grade, candle and pack the eggs at the facility, and which are then shipped to various destinations. The grading operation is carried out by high speed graders, some of which can handle up to 175,000 eggs per hour.
For this type of production to be maintained, an egg marking apparatus and method must be highly efficient to mark such numbers of eggs as they are processed through the grader. This is particularly true if a significant amount of indicia, such as graphic representations, is desired to be etched onto every egg. It may also be necessary to use multiple lasers if several lines of graphical representations are placed on each egg, and particularly if there are several rows of eggs. Not only that, if a complex graphical representation is marked on an egg, such as an intricate or extensive logo or design, for example, it is necessary to process the graphical representations in a manner whereby the graphic representation can be rendered on the egg with visual fidelity to the representation within the constraints of the physical and time window that exists for each egg that passes through a marking station.
More particularly, and referring to
Two different laser marking apparatus, indicated generally at 30 and 32, are shown in connection with a system that includes a grader 34 in
Since the movement of the eggs from the grader 34 is to the left, obviously the left marking apparatus 32 would not mark eggs that are diverted at packing stations 38, 40 and 42. Each of the apparatus 30, 32 has the capability of handling two rows of eggs A and B as shown in
Each of the marking apparatus 30, 32 are shown in
At that speed, there is a time window of about 69 milliseconds for each laser marking unit to mark each successive egg that passes through the marking station, which means that 14 eggs are marked per second. In this regard, a marking station is defined as the distance along the conveying lines A and B wherein one or more of the laser marking units 50 and 52 can mark eggs, it being understood that the laser beam that is emitted from the units can be moved within an arc 58 having a range of about 30 to about 35 degrees as is generally indicated in
Turning now to the laser marking units 50, 52, and referring to
The laser generator 64 is preferably a CO2 laser having approximately a maximum of about 70 watts of power, but which can be adjusted downwardly if desired. The galvanometer scanning head is preferably a SCANcube® 7 scan head having a digital standard interface controlled by a RTC® PC interface board or a PC independent RTC® SCANalone board as sold by the SCANLAB America, Inc. of Naperville, Ill. The scan head has a 7 millimeter aperture, a beam displacement of 9.98 mm, a dynamic performance tracking error of 0.14 msec, an optical performance skew of less than 6 mrad, a step response time at 1% of full scale of 0.25 ms, a typical marking speed of 2.5 m/sec, a typical positioning speed of 12.0 m/s and a typical good writing quality speed for single stroke characters of 1 millimeter height of 900 cps.
As shown in
The retracting capability enables the laser control units to be separated from the grader conveyor line 36 and serviced, without stopping the grader if necessary. Because of clearances, before it is retracted, it may be necessary to lower the galvanometer scanning heads 80 and this is accomplished by having pivot connections 90 on each side of the rear corner of the enclosure 62, and a tilt frame actuator assembly 92 on the front that can tilt the entire enclosure 62 which lowers the galvanometer scanning heads 80 so that the cabinet can be moved away from the conveyor 36.
Another enclosure 94 is mounted on the frame structure 84 which includes control and operating equipment, including program logic controllers, computers that also include RTC® PC interface boards for controlling the galvanometer scanning heads 80, modems for communicating with lap top computers as well as off site networking equipment that upload and download data relating to the operation of the equipment. The data files that define the graphic representations including those that provide vector coordinate information are generally downloaded from off-site networking, and the production information is uploaded for billing and other purposes. The computers are also interconnected with the computer system associated with the grader 34 that provides washer environmental information such as wash water temperature, rinse water temperature and wash water pH values. There are sensors that sense operating temperatures of the laser generators and of the galvanometer scanning heads 80, as well as current sensors for power supplies. Position sensors are also provided so that the operating status of all important moving components are monitored. The temperature and humidity within each of the enclosures is monitored.
An operator keyboard 96 and LCD display 98 are provided to enable on-site trouble shooting or maintenance work. However, during normal operation, and because of the extent of the monitoring and reporting that is done, the need for an on-site attendant is minimized for many types of maintenance work. If a problem arises, there are typically employees at the production facility that oversee the grader 34 operation among other activities that can use the keyboard 96 and display 98 while communicating with off-site personnel knowledgeable about the marking apparatus and rectify most problems. A laser marking unit power switch 100 is provided, as is an emergency stop switch 102. Because of the heat that is generated by the equipment, coupled with relatively high ambient temperature and humidity in such production facilities, air conditioning units 104 are provided for each enclosure. A main power disconnect panel 106 is located on the end of the apparatus.
Because the galvanometer scanning heads 80 are located below the eggs 20, there is a likelihood that some eggs will be cracked and leaking or will otherwise be wet so that material will drop toward the galvanometer scanning heads 80 and impair their operation. To guard against such occurrences, a protective plate structure 110 shown in
An alternative embodiment is shown in
With regard to laser marking eggs, a more powerful laser does not necessarily enable the speed to be increased. It takes time to transfer energy to get the right effect. For example, baking a potato generally takes about 45 minutes, and using a more powerful oven may explode the potato. There is also a power transfer function to an egg shell that produces the right effect on the egg. The laser generator is sometimes adjusted downwardly, so the maximum of 70 watts is not used. Wet eggs and soft eggs may require power nearer the upper value. Experience has shown that time is more valuable than power in marking eggs. It is for that reason that it is preferred to maximize the writing time of the particular graphic being written to the full 138 millisecond window (or 69 milliseconds for some of the lasers). The preferred optics produced by the lens 72 is 100 millimeters which produces width of the beam or spot size of about 0.3 millimeters. These optical characteristics also provide good depth of focus effect, which means that the eggs need not be the same size. Stated in other words, a 10 millimeter change caused by different size eggs does not matter because the focal point of the beam accommodates for such differences.
During operation, there are four laser marking units 50 or 52 marking eggs in each row, and the four units mark the upper, middle and bottom lines as shown in the egg 20 in
When an involved graphic representation is to be marked on an egg, it is accomplished by mapping a plurality of vectors on a physical grid that has a maximum size of about 20 millimeters by 40 millimeters. Referring to the graphic representation shown in
The start and stop coordinates for every vector have to be programmed. This is generally done with an automatic conversion tool from web images that are used in various steps to produce a vector representation of the image. CorelDRAW® can be used, for example, which will produce a vector graphic representation from a bit graphic representation. However, the effectiveness of such tools may be sufficiently lacking that it is necessary to manually render certain types of graphics to obtain the right style of the graphic. The graphics can be provided in a PostScipt format, i.e., “pps” or “ps”. Also there is a vector based plot file format called a “.plt” that can be used.
Generally, as the graphic representation moves through the time and spatial window, all of the lines on the left third are preferably completed as the middle third is being rendered, and similarly the middle third is rendered before the right third is rendered. This generally requires very long vectors to be segmented. The graphic is generally drawn from left to right, but the rendering is not strictly required. However, it is not be possible to render a vector beginning at the left edge of the graphic if most rendering is being performed at the right third of it. To achieve the above, the order of every vector must be programmed and becomes part of the electronic file of a graphic representation. The programming is done so that all of the vectors are specified consistent with these requirements.
Based on the fact that the eggs are moving at a predetermined speed and galvanometer parameters are known and/or set, such as turning on and turning off delay times, repositioning times, positioning speed, and the fact that only 70 milliseconds are available, the marking or writing speed is determined to render the image of the graphic based on those calculations and determine whether the representation can be effectively rendered. Since all of the vectors are known, together with the above parameters, it can be calculated at what speed the galvanometer scanning head 80 must write to complete the representation. Through experience, it has been found that approximately 200 vectors can be rendered in the 138 millisecond time window with acceptable quality. Because the physical size of the window on the egg is 20 millimeters by 40 millimeters, vectors can be removed without significantly detrimentally affecting the visual fidelity of the representation that is being rendered. The marking speed is preferably within the range of 400-800 bits per millisecond with an acceptable result being achieved at 800, a good result at 600 and a great result at 400. These units represent the coordinate space of 16 by 16 (0-65535 bits) that cover the 20 by 40 millimeter physical size of the window. the galvanometer scanning heads 80 can scan the entire field of 65535 bits in 65 milliseconds at a marking speed of 1000. Based on the optics described above, a marking speed of 1000 also translates to a distance of approximately 100 millimeters per millisecond. The quality of the mark can be affected by the quality of egg, so that a mark rendered on good eggs by the system at a particular set of parameters may be good, while those on poor eggs may not be.
Returning to
Vector thinning involves a process for simplifying the representation by reducing the number of vectors using an algorithm that is based on the Douglas Ramer Peucker algorithm for line simplification and generalization, which is used in digital cartography. The method for removing intermediate points, i.e., vectors, consists of joining the two ends of the line with a straight line, called the base line. The perpendicular distances of all intermediate points from this base line are then calculated. If all these distances are less than some predefined tolerance, representing half the width of the graphic line at source scale, these points may be discarded and the original line can be represented by the base line. If any of the intermediate points fall outside the tolerance band, the line is split into two parts at the furthest point and the process is repeatedly applied to the two resulting parts.
Raster scanning involves rasterizing all of the vectors onto a fixed grid that enables the determination of the existence of coincident points, which is a process for removing redundant coordinates. When points of two vectors are coincident with one another, one is preferably eliminated. The grid is defined and vectors are drawn on the grid from longest to smallest. If a new vector is drawn without changing any of the grid, that means it is on top of another, and the point or points of coincidence are removed by turning off the laser at those points. This is done by digital differential analysis. This raster thinning eliminates vector elements that provide no additional graphics artifacts. It is not technically a graphics grid, but is an internal memory grid. When vectors are rasterized from longest to smallest and when get to small vectors, if not shading new grid squares, then nothing is being added to the final rendering and they are eliminated.
The process uses a digital differential analysis process that is similar to that described in a publication entitled Digital Differential Analyzer for Lines by Jon Kirwan, published at http://users.easystreet.com/jkirwan/dda.html, copyright November, 1999, where there are a series of coordinates that make up a string of lines. This publication is specifically incorporated by reference herein. If redundant grid locations are already filled in, that portion of the vector is eliminated. The grid is preferably comprised of a 16×16 bit matrix that is mapped to a 15×15 bit physical grid that lays out on a 20×40 millimeter space on an egg. The physical grid therefore contains about 65536 blocks. The grid shown in the upper right-hand corner of
Very short vectors and point or near-point artifacts can be also removed because they are not visible when rendered. Such a process together with other processes was used to reduce the number of vectors shown in
The processes are illustrated in
An example of the vector thinning simplification is shown by comparing connected vectors 142, 144, 146, 148, 150, 152 and 154 in
An example of the raster scanning is represented by the enlargement of box 140 from
Given that a laser etched line has a discrete width, another technique that can be used is that if two lines that are crossing or are very close together, there can be over-burn because of the width aspect of the line. Therefore, vector boundaries can be compared with other vector boundaries and thinning appropriately done. Given that it takes time to turn the laser on and off, there is a point of diminishing returns with the complexity of a vector thinning process.
The galvanometer scanning heads 80 are controlled by the RTC® PC interface boards which are programmed using a 16-bit coordinate system. To compensate for marking a moving product, that graphics are staged to the far right, i.e., when the left end of the representation of
This cannot be done with the 16-bit coordinate system, so it is mapped into a 15 bit physical window, which essentially halves the size of the coordinate space. A correction matrix ignores coordinates that are outside of the 15 bit space. So the graphic is positioned in virtual space so that when the egg comes into the frame, the galvanometer scanning heads 80 is moved over to the edge and starts rendering the image immediately.
This technique is necessary because the entire graphic must be sent to the galvanometer system in a coordinate system. Without the virtual mapping, it would be necessary for the entire graphic to be within the physical window before rendered could begin, which would dramatically reduce the time in which rendering could occur. This technique enables the system to render the graphic during the entire window, i.e., the entire time in which rendering can be done.
If this were completely in the real or principal coordinate system, the system cannot start rendering until the whole graphic is within the spatial window. The graphic is staged as far to the right as possible with respect to the coordinate system. So when the galvanometer scanning head 80 is to start rendering, it will move to the right and move with the egg so that when the egg comes into the real coordinate system, the galvanometer scanning head 80 can be controlled to go to a physical coordinate, i.e. an edge in the physical space so that it can start rendering the graphic when it appears in the 15 bit coordinate space.
It may be highly desirable for embodiments of the present invention to mark multiple objects with different graphical representations. In the event that eggs are being marked, it may be desired to have a carton of a dozen eggs marked with 12 different graphical representations, i.e., advertisements for 12 different products or messages. In such event, the complexity of the graphical representations may vary significantly. For a complex representation, the marking speed may have to be increased to a relative maximum to complete the entire representation. The faster marking speed will reduce the print contrast, and conversely a slower marking speed will increase the print contrast. It is desirable to have the greatest possible print contrast and therefore it is desirable to mark each graphical representation using the entire 69 or 138 millisecond time window. Since each graphical representation is contained in a separate file, the optimum marking speed for each representation is made to be part of the file, and the operating parameters of the apparatus are thereby tuned or configured for utilizing the entire time window during marking. In the example of having 12 different representations for a dozen eggs in a carton, the apparatus would likely have its operating characteristics change during the marking of each successive egg having a different representation. Such configuration flexibility optimizes the effectiveness and quality of the marking operation.
While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.
Various features of the invention are set forth in the appended claims.
