Abstract:
A blasting system for the removal of coatings or paint from an underlying surface uses an optical device to position the blasting nozzle an appropriate stand-off distance from the surface. The blasting media can use a variety of blasting media including abrasives, water, and various specialty blasting media. The preferred optical system is mounted to or integral with the blasting nozzle, and uses a diode laser, a beam splitter and a reflecting mirror to generate a reference beam and a gauge beam. Alternatively, two diode lasers can be used to generate the reference beam and gauge beam respectively. The reference beam propagates in a fixed forward direction, but the direction of the gauge beam is adjustable. The user adjusts the orientation of the gauge beam so that the image of the beam on the surface aligns with the image of the reference beam on the surface when the blasting nozzle is positioned at the appropriate stand-off distance from the surface. Alternatively, the center of the blasting pattern o the surface can be used as a rough estimate for the reference beam, thereby avoiding the need to generate and align two non-parallel beams.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to the removal of coatings, such as paint, from an underlying surface using blasting media. In particular, it relates to the use of an optical targeting and positioning system in such blasting applications.  
       BACKGROUND OF THE INVENTION  
       [0002]     In order to remove coatings from underlying surfaces, industry is moving away from the use of chemical striping agents and towards the use of blasting techniques. With these blasting techniques, abrasive or non-abrasive media or water are blasted onto the coated surface at high velocity to remove the coating. There is a wide variety of blasting nozzles and blasting media on the market. The most widely used blasting systems use pressurized blasting media. Other systems use a suction feed in which the blasting media is fed into a high velocity air stream via suction. Suction feed systems do not typically have as much power as a pressurized blasting media system. Commonly used blasting media includes sand, plastic, glass or water, but there is also a wide range of specialized blasting media ranging from steel shots, on one hand, to corn starch or soybean media on the other.  
         [0003]     In a typical set up, the user holds the blasting nozzle by hand and blasts the media towards the workpiece. The distance that the blasting nozzle is from the workpiece is commonly referred to in the trade as “stand-off” distance. The stand-off distance is important because it regulates the velocity of the blasting media as it impacts the coated surface. The user aims the high-velocity jet containing the entrained blasting media at the surface until the coating is removed at that spot. The user then moves the jet across the surface in a back and forth motion in order to remove the coating from the surface. When the user starts a job, the user might not know the thickness of the coating and therefore must guess through trial and error or experience as to the appropriate stand-off distance.  
         [0004]     If the nozzle is too close, impact of the blasting media may damage the surface. On the other hand, if the stand-off distance is too great, the blasting media will not have enough velocity to remove the coating. The ideal stand-off distance for a majority of blasting media is about 12 inches. Corn starch or soybean media or water blasting requires a distance of about 6 inches. On the other hand using steel shots as a blasting media may require a stand -off distance of about 18 inches. The appropriate stand-off distance for a given situation also depends on the pressure at the blasting nozzle as well as the thickness of the coating and the characteristics of the underlying substrate. For example, when the underlying substrate is made of a certain types of light weight composite material, holding the blasting nozzle too close to the substrate might not only damage the surface of the substrate, but might actually blow a hole through the substrate.  
         [0005]     Thus, the optimum stand-off distance varies in the field depending on many factors including the type of blasting system being used (e.g. pressurized blasting media, water blasting, suction feed, etc.) and its set up parameters, the type of blasting media being used, the nature of the underlying substrate, the nature of the coating and possibly other factors. While there is some published data on what is believed to be the optimum stand-off distance under various conditions, such information is not often readily available to the user. Moreover, even armed with knowledge of the optimum stand-off distances under various conditions, it is difficult for users to maintain the blasting nozzle at the optimum stand-off distance from the surface as they move the nozzle back and forth the remove the coating. This can be especially difficult for novices.  
         [0006]     The Assignee of this application has developed optical targeting and positioning systems for spray painting apparatus. Representative systems are shown in Klein II et al U.S. Pat. No. 5,598,972 issued Feb. 4, 1007; Klein II et al U.S. Pat. No. 5,857,652 issued Jan. 12, 1999 the disclosures of which are hereby incorporated by reference. Generally, these patents illustrate the concept of mounting a light beam emission arrangement on a spray paint gun or within the housing of the spray paint gun. The light beam emission apparatus directs a pair of light beams in a direction from the gun towards the surface to be sprayed. The light beams are oriented so as to converge towards each other as the beams propagate in a direction away from the gun towards the surface. The light beams form spots on the surface. The spots are aligned on the surface, such as merged together to form a single point of light on the surface, when the spray head of the spray gun is held at a predetermined stand-off distance from the surface. The angle of the light beams can be adjusted to vary the convergence distance, thus allowing the user to customize the desired stand-off distance indicated by the optical positioning system. The user can accommodate different spray painting operating parameters or characteristics, such as air pressure, coating type and the like, when setting up the optical positioning system for the appropriate stand-off distance, thus facilitating optimal application of the spray coating (e.g. paint) to the surface and minimizing overspray and waste. While this type of targeting and positioning system has been proven effective to optimize the application of sprayed coatings, it has not heretofore been used in connection with coating removal systems using blasting media.  
         [0007]     Horan U.S. Patent Application US2003/0178503A1 entitled “Single Beam Spray Gun Positioning System”, filed on Mar. 20, 2002 and published on Sep. 25, 2003 discloses a targeting and positioning system for a spray paint gun in which a single light beam is used to provide a rough estimate the distance of the spray nozzle from the surface being painted. The system does this by illuminating an optical beam at an angular orientation with respect to the center line of the spray pattern. It then requires the user to align the illuminated spot on the surface with the approximate center of the spray pattern on the surface being painted. As with the two beam systems described above, the desired stand-off distance can be adjusted by adjusting the direction of the light beam.  
       SUMMARY OF THE INVENTION  
       [0008]     The invention involves use of optical beam targeting and positioning systems in a blasting system for removing coatings (e.g. paint) from an underlying surface or substrate. In one aspect, the invention is a method for positioning a blasting nozzle at a selected stand-off distance from the surface from which it is desired to remove a coating. The method includes the steps of emitting a first light beam from the blasting nozzle or an attachment to the blasting nozzle and propagating the beam in a first direction towards the coated surface to illuminate a first spot on the surface. This first light beam is preferable propagated in a fixed forward-direction. This beam is referred to as the reference beam. A second light beam, referred to as the gauge beam, is also emitted from the blasting nozzle or an attachment to the blasting nozzle. The second beam or gauge beam propagates in a second direction towards the surface to illuminate a second spot on the surface. The gauge beam is not parallel to the reference beam. The orientation of the light beams is set to facilitate the locating of the blasting nozzle at the selected stand-off distance from the surface. This is accomplished when the first and second illuminated spots are aligned on the surface, preferably as an illuminated convergence point, when the nozzle is located at the desired stand-off distance from the surface. Preferably, the user can adjust the selected stand-off distance by adjusting the direction of the gauge beam with respect to the direction of the reference beam by a selected amount. Also preferably, the beams should be oriented so that the illuminated convergence point is located roughly in the center of the jet of blasting media as it impinges the surface.  
         [0009]     The invention also contemplates the use of a single light beam method in which the first light beam or reference beam propagating in the forward direction towards the surface is eliminated. Rather, the blasting media expelled from the nozzle in the fixed forward direction acts as a rough proxy for the reference beam. When the hand-held blasting nozzle is located at the selected stand-off distance in this embodiment, the gauge light beam illuminates a spot on the surface in the center of the jet as it impinges the surface.  
         [0010]     In another aspect, the invention relates to coating removal systems implementing the above described methods. In one embodiment, the system comprises the combination of a blasting nozzle to which a light beam targeting and positioning device is mounted. In another embodiment, the light beam targeting and positioning device is integral with the blasting nozzle, and preferably located within the housing of the nozzle. In either set up, the light beam targeting and positioning device preferably emits two light beams: a reference beam and a gauge beam. In a system in which the light beam targeting and positioning device is mounted to the blasting nozzle, it is preferred that a single laser produce a generated beam, and that a beam splitter be employed to split the generated beam into the first (reference) and second (gauge) light beams. In such a system, the targeting and positioning unit further comprises an adjustable reflecting mirror that reflects the second (gauge) beam towards the surface. A control knob is provided so that the user can change the attitude of the reflecting mirror and thereby adjust the orientation between the first (reference) and second (gauge) beams and thus change the selected stand-off distance at which the first and second illuminated points out align or converge with each other on the surface.  
         [0011]     When the coating removal system includes a light beam targeting and positioning device that is integral with or interior to the housing of the blasting nozzle, it may be preferred to use two separate light generating devices with at least one having an adjustable orientation, although it is possible to use a singe light generating device with the beam splitter as described above. When the light beam targeting and positioning device is disposed within the interior of the housing, the light beams must be communicated exteriorly of the housing towards the surface preferably through a pair of light emission locations spaced apart from each other on the housing.  
         [0012]     Of course, systems using a single gauge beam without a reference beam use a single laser without a beam splitter to generate the single beam.  
         [0013]     Various other features, objects and advantages of the invention will be made apparent from the drawings and the following description.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a side elevational view of a hand-held blasting nozzle having an optical light beam targeting and positioning device mounted thereto in accordance with a first embodiment of the invention.  
         [0015]      FIG. 2  is a front elevational view of the hand-held blasting nozzle and light beam targeting and positioning unit shown in  FIG. 1 .  
         [0016]      FIG. 3  is schematic view illustrating adjustments that can be made while mounting the light beam targeting and positioning unit to the hand-held blasting nozzle.  
         [0017]      FIG. 4  is a schematic view illustrating the use of the light beam targeting and positioning unit to locate a hand-held blasting nozzle at a desired stand-off distance from a surface when blasting media is being expelled from the nozzle at the surface.  
         [0018]      FIG. 5  is a sectional view of the optical targeting and positioning device taken along line  5 - 5  in  FIG. 2 .  
         [0019]      FIG. 6  is a sectional view of the light beam targeting and positioning device taken along line  6 - 6  in  FIG. 5 .  
         [0020]      FIGS. 7 and 8  are schematic drawings illustrating the adjustment of the light beam targeting and positioning device to various desired stand-off distances.  
         [0021]      FIG. 9  is a side elevational view of a second embodiment of the invention in which a light beam targeting and positioning device is integral with the housing for the hand-held blasting nozzle.  
         [0022]      FIG. 10  is a front elevational view of the hand-held blasting nozzle shown in  FIG. 9 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]      FIGS. 1 and 4  illustrate a hand-held blasting nozzle  10  having a light beam targeting and positioning system  12  mounted to the nozzle  10  in accordance with a first preferred embodiment of the invention. The blasting nozzle  10  is connected to a pressurized feed line  14  that supplies pressurized air and blasting media to the nozzle  10 . In use, the blasting nozzle  10  is used to blast a high velocity jet  16  of blasting media onto a substrate  20  in order to remove a coating from the surface  18  of the substrate  20 . The blasting nozzle  10  includes a barrel portion  22  and a tip  24  which is coaxially aligned with the nozzle. A levered valve member  26  is mounted to the barrel  22 . The levered valve  26  includes a valve stop  28  that covers the exit orifice of the nozzle tip  24  when the valve is closed. The levered valve member  26  is mounted to the nozzle barrel  22  such that the levered valve member  26  can rotate around a fulcrum  30 . When the handle  32  of the levered valve member  26  is pushed towards the barrel  22  of the nozzle  10 , the valve stop  28  rotates upward and allows a high velocity jet  16  of blasting media to be expelled from the blasting nozzle  10 , as shown in  FIG. 4 . While the blasting nozzle  10  illustrated in  FIGS. 1 and 4  represent the construction of blasting nozzles commonly used throughout industry, it should be recognized that in accordance with the invention, the light beam targeting and positioning system  12  can be mounted to or integral with other types of blasting nozzles. Moreover, while the blasting nozzle  10  depicted in the drawings is hand-held, the invention is useful for automated or remote controlled systems as well. For example, in some systems in the art the user is located in a booth isolated from the blasting environment, and manipulates the blasting nozzle robotically using a remote control rather than holding the blasting nozzle in their hand.  
         [0024]     Still referring to  FIGS. 1 and 4 , the light beam targeting and positioning system  12  emits two non-parallel laser beams: a reference beam  34  and a gauge beam  36 . These beams  34  and  36  are shown schematically on  FIG. 4  by broken lines. While it is preferred that the beams  34  and  36  converge to illuminate a single spot on the surface  18  when the nozzle  10  is located at the selected stand-off distance from the surface  18 , the invention can be implemented without convergence to a single point. For example, the illuminated spots from the beams  34  and  36  on the surface  18  can come in to horizontal or vertical alignment as an indication of the nozzle  10  being located at the appropriate stand-off distance from the surface  18 . Moreover, the invention can be implemented with a light beam targeting and positioning system that emits only a single light beam. In such a system, the center of the spray pattern is used as a rough estimate for the reference beam. The gauge beam  36  propagates at an angular orientation with respect to the center line of the jet  16  of blasting material media. The blasting nozzle  10  would be located at a distance from the surface  18  such that the illuminated spot on the surface is located roughly in the center of the jet of blasting media as it impinges the surface  18 .  
         [0025]     Referring again to the specific embodiment shown in  FIGS. 1 and 4 , the light beam targeting and positioning unit  12  is mounted to the blasting nozzle  10  such that the reference beam  34  propagates in the same forward direction as defined by the high velocity jet  16  of blasting media. In other words, the reference beam  34  propagates in the same generally forward direction that the gun is aimed. The reference beam  34  illuminates the substrate surface  18  at a first illumination location. The gauge beam  36  emits from the light beam unit  12  at a location that is offset from the location where the reference beam  34  emits from the unit  12 . The gauge beam  36  propagates from the unit  12  and intersects the reference beam  34  at a convergence point which is illustrated in  FIG. 4  to occur at the surface  18 .  
         [0026]     Referring now to  FIGS. 2 and 3 , the laser targeting and positioning unit  12  is preferably mounted to the nozzle barrel  22  using an adjustable mounting bracket  38 . The adjustable mounting bracket  38  has a vertical leg  40  and a horizontal leg  42  which intersect to form a right angle. The vertical leg  40  includes a longitudinal slot  44 . A screw  46  passing through the slot  44  is used to mount the bracket  38  to the barrel  22 . Arrow  48  in  FIG. 3  illustrates that the vertical position of the bracket  38  with respect to the nozzle barrel  22  can be adjusted by moving the screw position within the slot  44 . Arrow  50  indicates that the angular orientation of the bracket  38  with respect to the horizontal axis  52  (axis of the screw  40 ) can be adjusted as well. The horizontal leg  42  of the bracket  38  contains a mounting hole  54  for a threaded stud  56  protruding from the top surface of the laser targeting and positioning unit  12 . The base of threaded stud  56  is vertically fixed to the housing body  58  of the unit  12 . A wing nut  60  is used to attach the threaded stud  56  to the horizontal leg  42  of the mounting bracket  38 , bushing  62  and washer  64  facilitate this attachment and maintain separation between the horizontal leg  42  of the bracket  38  and the housing  58 . Arrow  66  in  FIG. 3  illustrates that the angular orientation with respect to the vertical axis  68  (axis of the stud  56 ) can be adjusted. Prior to use, the user should adjust the mounting bracket  38  vertically in accordance with arrow  48 , and angularly with respect to arrows  50  and  66  so that the reference beam  34  impinges on the surface  18  of the substrate  20  at a location desired by the user when the blasting nozzle  10  is placed at the expected stand-off distance for the user&#39;s application. For example, the user might mount the laser targeting and positioning unit  12  so that the reference beam  34  impinges on the surface  18  roughly in the expected center of the jet  16  as it impinges the surface  18  when the tip  24  of the blasting nozzle  10  is located 12 inches from the surface  18 .  
         [0027]     Reference numeral  12   a  in  FIG. 1  illustrates that it may be desirable to mount the light targeting and positioning unit  12  at different locations along the length of the nozzle barrel  22 . The adjustable mounting bracket  38  described in  FIGS. 2 and 3  is well adapted for such use.  
         [0028]      FIGS. 5 and 6  show the light beam targeting and positioning unit  12  of the first preferred embodiment in more detail. The unit  12  has a diode laser  72  that emits a laser beam  74 . The laser beam  74  propagates towards a beam splitter  76  in a fixed forward direction. The laser diode is preferably a class IIIA type laser with a wave length 630 to 680 nM and a peak power of less than 5 mW. The beam splitter  76  is a 50/50 beam splitter. The reference beam  34  propagates from the beam splitter  76  in the same fixed forward direction as the beam  74  is emitted from the laser  72 . The beam splitter  76  is positioned within the housing at a 45° angle to the beam  74  from the laser  72 , and thus the split beam (which becomes the gauge beam  36 ) propagates from the beam splitter  76  at a 90° angle from the reference beam  34  towards an adjustable reflecting mirror  78 . The adjustable reflecting mirror  78  reflects the gauge beam  36  so that the reflected gauge beam  36  propagates from the adjustable mirror  78  in a plane that includes both the direction in which the reference beam  34  propagates and the splitting direction in which the gauge beam propagates towards the reflecting mirror  78 . As shown best in  FIG. 6 , the reflecting mirror  78  is fixed to a threaded body  80  to which a control knob  70  is affixed or integral. The control know  70  is accessible to the user and adjusts the direction that the gauge beam  36  propagates. In this manner, adjusting the control knob  70  adjusts the stand-off distance at which the illuminated spots from the beams  34 ,  36  will converge or become aligned. The control knob  70  is preferably calibrated so that the user can select the stand-off distance from unit  12  to the surface  18 . The unit preferable includes a set screw  82  through the housing  58  that can be used to fix the position of the control knob  70  and, hence, the reflecting mirror  78  once the user has established the desired stand-off distance and light beam orientation.  
         [0029]      FIGS. 7 and 8  illustrate that the adjustment of the control knob  70  and the orientation of the reflecting mirror  78  changes the distance at which the beams  34 ,  36  converge or come into alignment. Note that the reflecting mirror  78  is roughly set at a 45° angle with respect to the beam being propagated from the beam splitter  76  in both cases. Arrow  84  in  FIG. 8  shows that rotating the control knob  70  and reflecting mirror  78  slightly will shorten the convergence or alignment distance from unit  12  significantly.  
         [0030]     Referring again to  FIGS. 5 and 6 , the housing  58  for the laser targeting and positioning unit  12  is preferably made of a single piece of machined acetal resin, such as sold under the trade name Delrin®. The housing body  58  is machined to provide access for assembling the components of the unit  12  within the housing  58 , namely, laser diode  72 , battery holder  88 , beam splitter  76 , control knob  70 , reflecting mirror  78 , and window  102  The laser diode  72  receives power from a battery  86 , preferably a lithium battery (3.6 volts) which is housed within a battery holder  88 . The battery holder  88  includes a switch  90  that is accessible to the user from the rear of the unit  12 . D.C. power is provided from the terminal  92  of the battery holder  88  through wire  94  when the switch  90  is turned on. During assembly, the battery holder  88  is press fit into a machined opening in the rear of the housing  58 . The laser diode  72  is inserted through a rearward looking access hole in a similar manner. The laser diode access hole is likewise plugged after assembly. An access hole  98  is preferably provided in the housing so that the wire  94  from the battery terminal  92  and a wire  96  leading to the laser diode  72  can be soldered together. After soldering, the access hole  98  is plugged. The housing  58  includes a machine slot  100  in which the beam splitter  76  is inserted in a fixed 45° position with respect to the laser diode emission. The window  102  is inserted in the housing  58  as well. If necessary, set screws can be used when necessary to maintain the fixed alignment of the laser diode  72 . The housing  58  is threaded to receive the generally cylindrical body  80  to which the reflecting mirror  78  is attached (threads not shown in  FIG. 6 ). The cylindrical body  80  is preferably machined plastic.  
         [0031]      FIGS. 9 and 10  show another embodiment of the invention in which the laser targeting and positioning system  112  is integral with the hand-held blasting nozzle  110  and contained within a housing  158  for the hand-held blasting nozzle  110 . In other respects, the blasting nozzle  110  shown in  FIGS. 9 and 10  is similar to the blasting nozzle  10  illustrated in  FIGS. 1-4 . The embodiment shown in  FIGS. 9 and 10  uses two separate light generating devices or laser diodes  172 ,  173  to produce the reference beam  134  and gauge beam  136  respectively. The laser diode  172  for the reference beam  134  is mounted within the housing at a fixed orientation, preferably in alignment with the longitudinal axis of the blasting nozzle  110  in the expected direction of the jet of expelled blasting media. On the other hand, the laser diode  173  that emits the gauge beam  136  is mounted such that its orientation can be changed by rotating control knob  170  as shown by arrow  184  in  FIG. 9 . Preferably, the control knob  170  is integral with or attached to a generally cylindrical threaded body (shown in phantom) to which the laser diode is affixed. A set screw (not shown in  FIGS. 9 and 10 ) is preferably used to maintain the position of the control knob  170  and laser diode once the user has established the desired stand-off distance and light beam orientation. In this embodiment, it is preferred that the light beams  134 ,  136  be communicated from the interior of the housing  158  through a pair of light emission openings  190  and  192  in the housing  158  to the exterior of the housing. The light emission openings  190 ,  192  should be spaced apart from one another in appropriate distance. Although not shown in  FIGS. 9 and 10 , it is likely desirable that the diode lasers  172  and  173  be powered by battery power in a similar manner as described above with respect to  FIG. 5 .  
         [0032]     It should be appreciated that modifications may be-possible that do not substantially depart from the spirit of the invention and that such modifications should be considered as part of the invention. For example, in accordance with the invention, the integral unit described with respect to  FIGS. 9 and 10  may use a single light generator or diode laser to create a single light beam, or with the combination of a beam splitter and reflecting mirror may create two light beams as described above with respect to  FIGS. 1-8 . Likewise, a system in which the laser targeting and positioning system  12  is mounted to an existing blasting nozzle  10 , as in  FIGS. 1-8 , can use two light generating devices or diode lasers to generate the reference and gauge beams respectively, or as mentioned previously, can use a single light generating device or diode laser to generate a single beam while using the center of the jet pattern on the surface as a rough estimate for a reference beam.