Abstract:
A transporting system, for laser processing a workpiece. The system uses a metal belt, formed of a metal material. The belt is formed into a continuously moving conveyor that has plural holes therein that are between 0.005″ in diameter and 0.025 inches in diameter, and are spaced ≦10 mm but ≧5 mm from one another. The holes are beveled in cross-section at an angle between 40 degrees and 60 degrees to form a smaller hole size at the outer surface and a larger hole size at the inner surface. A vacuum source is connected to apply vacuum to the inner surface of the belt, to each of the larger size sections of the plural holes. A vacuum source is connected to apply vacuum to the inner surface of the belt, to each of the plural holes. A laser system, directs its output beam towards a laser processing area in an area of the belt on the outer surface to process the workpiece.

Description:
This application claims priority from provisional application No. 61/930,998, filed Jan. 24, 2014, the entire contents of which are herewith incorporated by reference. 
    
    
     BACKGROUND 
     Laser materials processing uses a laser to cut, score, scribe, mark, weld, and perforate materials such as paper, plastics, and other target materials. 
     Metal belts with vacuum holes have been used in industrial applications to hold and transport target materials to be processed or converted by mechanical methods. Metal belts have not been commonly used in laser processing, however. One reason that metal belts are not commonly used is because the laser and the byproducts of laser processing can damage these metal belts and target materials during laser processing. 
     SUMMARY 
     The present invention describes an optimized solution for supporting, controlling, and transporting a workpiece or target materials during laser materials processing. 
     Embodiments can aid in the technical field of industrial laser materials processing by performing the following functionalities; 
     Holding target material at a constant focal plane during laser processing; 
     Accurately transporting the target material throughout laser processing; 
     Reducing smoke and debris collection on target material; 
     Reducing back reflection of the focused laser beam by the metal belt; 
     Reduction of abrupt reaction and a burning process caused from laser intersection with vacuum holes in the metal belt; 
     Being capable of withstanding high power outputs and energy densities from the laser source. 
     Being capable of accurately controlling small parts formed in the target material from laser processing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a focused laser beam impinging on target material and metal belt with vacuum holes 
         FIG. 2  shows a vacuum hole design on a metal belt 
         FIG. 3  shows the metal belt installed on a transport conveyor. 
         FIG. 4  shows a cross-section of a metal belt installed on a transport conveyor 
     
    
    
     DETAILED DESCRIPTION 
     Metal vacuum belts typically use a pattern of vacuum holes in the belt, through which a vacuum is applied from an external vacuum source to hold the target material onto the belt. The inventors realized metal belts have not been successfully used for laser processing because of the criticality of the vacuum hole diameter to clean and efficient laser processing of the target material. There are two possible failure modes in such a design. If the vacuum hole is too small, the hole will not have enough area to hold the target material down via an applied vacuum. When the target material is being processed by the laser, there is a vapor pressure created from the vaporization of the material. If there is not enough vacuum force holding down the target material, the material can be lifted by this vapor pressure. This can cause smoke and debris to get trapped under the target material and contaminate the material. Lifting of the material causes additional issues, including undesirable interference or defocus of the laser beam. 
     Conversely if the vacuum hole is too large, the hole will have too much area which can cause burning or contamination of the material in the diameter of the hole. Smoke and small particulates produced by laser processing can cause permanent damage to the bottom of the target material. A large vacuum hole also exposes the bottom of the target material to more oxygen that can increase burning of the material in the hole causing additional damage to the material. 
     The inventors also realized the criticality of the vacuum hole geometry. If the walls of the vacuum hole are angled in, when viewing from the laser processing side, the laser beam can be reflected back into the target material causing undesirable damage to the underside of the material. Alternatively if the walls of the vacuum hole are angled out, when viewing from the laser processing side, the laser beam will be reflected away from the bottom of the target material. 
     In summary, the size and geometry of the vacuum hole impacts how target materials are held to the surface of the belt as well as the magnitude of unwanted reflections or burn marks on the target material. 
     Extensive testing and analysis by the inventors was used to define characteristics of and create a vacuum hole shape and size to minimize the effects described above. 
     What was found is that holes larger than 0.635 mm (0.025″) tended to cause burning of the bottom of the target material that was located within the diameter of the hole. Holes greater than 0.635 mm (0.025″) in diameter would occasionally cause burning due to back reflection of the laser energy onto the bottom of the target material being processed. The inventors found that holes smaller than 0.127 mm (0.005″) tended to cause a significant amount of back reflection and also did not hold the target material to the vacuum belt very well. In order to eliminate back reflection of the laser energy a reverse bevel of 40-60 degrees was used. These results are specific to CO 2  laser sources, but similar kinds of hole to wavelength ratios for other laser sources can be used. 
     Another effect studied by the inventors is when cutting target materials with a laser source, vaporization pressure is created as the target material is removed or vaporized by the energy of the laser. Cutting out small parts from the target material can cause these parts to be randomly ejected upwards from the surface of target material due to vaporization pressures. These small parts may fall on other areas of the target material and prevent the laser from correctly processing those covered areas. Extensive testing and analysis was completed by the inventors to determine optimal vacuum hole size and location to minimize ejection of small parts. Testing was completed using a CO2 laser source having a wavelength of 10.6 microns and 400 W maximum laser power, a laser beam focused to a diameter of 300 microns (0.012″) on a target material of 200 micron (0.008″) thick paper or plastic sheets, a laser processing area of 350 mm by 350 mm (13.8″ by 13.8″), a metal vacuum belt measuring 550 mm (21.7″) wide and approximately 4000 mm (157″) in circumference, a transport conveyor with servo motor to accurately move the metal vacuum belt and therefore the target material, and a vacuum blower fan to supply a vacuum source through the transport conveyor to the underside of the metal vacuum belt. The sheets of target material was automatically fed and removed from the metal vacuum belt using well know means for feeding or stacking or the sheets were manually placed on the metal vacuum belt. 
     Embodiments describe a metal vacuum belt optimized for laser materials processing by achieving one or more of these specifications: 
     The belt material is capable of withstanding focused high power laser energy (&gt;100 W). 
     The belt is configured to hold target material at a constant focal plane of the laser beam. 
     Vacuum hole geometry has reverse bevel inner walls of 40-60 degrees to minimize burning and back reflection onto the target material. 
     Vacuum hole diameter is small enough (&lt;0.635 mm or 0.025″) to minimize burning and back reflection of the target material. 
     Vacuum hole diameter is large enough (&gt;0.127 mm or 0.005″) to hold the target material and small parts to the belt while laser processing. 
     Vacuum hole spacing and location is optimized to prevent small part ejection while minimizing the possibility of vacuum hole intersection with the laser beam. Hole spacing is based upon the average smallest part diameter to retain on the belt and prevent the part from ejecting from the belt and potentially interfering with the laser beam. The hole spacing is typically less than the average diameter of the smallest parts that are required to be retained on the belt. Hole spacing is usually less than 10 mm (0.39″) but greater than 5 mm (0.20″). 
     Vacuum holes are to be placed into a belt and negative pressure is applied to the back surface of the belt. Target material placed on the belt is drawn close to the top surface of the belt because of the pressure difference. This keeps the target material flat and controls the movement of the target material to accurately process the target material with a focused laser beam while the belt is moving. The vacuum hole geometry and location require precise configuration to ensure damage and discoloration is not caused to the target material as well as small part ejection. 
       FIG. 1  illustrates an embodiment, showing the laser beam, with a focus  10 , impinging on the belt  12  that holds the target material  11 . The belt  12  includes a number of different vacuum holes  13 . The holes  13  have a beveled side wall design in one embodiment. The belt  12  is oriented to allow the bevel to diverge from the belt surface making contact with the bottom surface of the target material being processed. Because of the beveled design, back reflection onto the material is avoided. Any reflection of the beam energy will be directed away from the material. 
     The specified vacuum holes can be produced with desired geometry, size, and location using a chemical etch, laser cutting, or other processes. The vacuum holes have a required diameter and side wall configuration to optimize laser processing as described earlier. The metal vacuum belt is now ready for installation in a conveyor designed to accurately transport the target material through the laser processing area. 
       FIG. 1  shows the target material  11  held flat and at a constant focal plane on the top surface of the belt  12  during laser processing. The focused laser beam  10  will not reflect energy off of the side walls of the vacuum holes and incident energy on the belt will reduce laser bending of the belt material and damage to the target material. 
     The shape and size of vacuum holes  13  in the belt  12  results in diverging side wall geometry with smooth surfaces and holes less than the diameter causing undesirable burn marks on the target material. 
       FIG. 2  is a drawing of a belt intended for laser processing applications. The drawing highlights dimensions of the belt including a vacuum hole pattern that defines the vacuum hole geometry, size, quantity, and location. 
     The belt has a width  200 , and a length or circumference  205 . These are both set according to the transport conveyor specification required in the final laser processing system. The entirety of the belt is formed with a pattern of vacuum holes of the type described above. Detail  210  shows the pattern of vacuum holes over the entirety of the belt. The holes can be spaced from one another by a distance in the conveyor transport or X-direction  222  and in the cross-conveyor or Y-direction  223 . The vacuum holes are shown as  225 . The vacuum holes formed in the belt are shown in detail  230  as having a top diameter  217  (in contact with the bottom surface of the target material) and a bottom diameter  218 . An angle  219  defines the angle of the sidewall of the hole and in turn the shape of the hole. As described above, the angle is preferably between 40 and 60 degrees. Based on the predetermined laser source and focused laser beam size, dimensions shown in detail  230  are specified to ensure that laser beam back reflection and unwanted burning of the target material is minimized. The diameter of the hole  217  and the hole spacing  222 ,  223  are defined to minimize the probability of the focused laser beam and vacuum hole intersecting, ensure proper holding force of a target material, and minimizing ejection of small parts formed in the target material. 
     The tabs  216  called out in  FIG. 2  can be used for laser welding the ends of the metal belt by the previously described belt manufacturing process. The beginning and end of a laser weld will have undesirable properties that are different than remainder of the weld so these tabs  216  are removed after welding. 
       FIG. 3  shows a complete transport conveyor system with the metal vacuum belt  300  installed. 
       FIG. 4  shows a cross-section of a transport conveyor system showing how vacuum is delivered to the underside of the metal vacuum belt  300  from an external vacuum source  400  the vacuum source  400  creates a vacuum in a number of vacuum chambers shown generally as  410   412 . Each vacuum chamber is maintained under a specified level of vacuum by the vacuum pump  400 . The vacuum is correspondingly formed through the holes  420  in the metal belt  300 . 
     Although only a few embodiments have been disclosed in detail above, other embodiments are possible and the inventors intend these to be encompassed within this specification. The specification describes certain technological solutions to solve the technical problems that are described expressly and inherently in this application. This disclosure describes embodiments, and the claims are intended to cover any modification or alternative or generalization of these embodiments which might be predictable to a person having ordinary skill in the art. 
     For example, the inventors have created alternative embodiments, described herein is an alternative belt design, such as a belt with no holes. This belt design requires alternative methods to hold the target material to the belt. One such alternative method is to use electrostatic forces to hold the target material to the belt. Several difficulties can arise in using electrostatic forces including static generation prior to laser processing and static discharge after laser processing. Also, some belt materials may not be susceptible to holding a charge. The belt material in this embodiment must have an attractive surface charge to hold the target material but does not discharge into the target material. Accumulating electrostatic charge on these materials can also be dangerous to both operators and equipment. The inventors discovered that coatings or different materials may be applied to the belt to achieve the desired result. Another alternative method for holding the target material to the belt is to use a removable adhesive.