Abstract:
A machine for applying ultraviolet light to curable coatings on floors and other wide area surfaces. A housing encloses rotating arms carrying UV lamps spinning about a central axis. Rotation is caused by reactive momentum from heated air jets coming from fans in barrels blowing air over heated wires, resembling hand held hair dryers, with the barrels supported under rotating arms. The heated wires are ballast for the lamps, providing thermal and electrical stability. The rotating lamps cover an annular pattern which, when advanced forwardly, becomes a linear swath, almost as wide as the housing. A floor, or similar surface, can be cured in a few minutes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from provisional application Ser. No. 61/098,602 filed Sep. 19, 2008 for Rotating UV Source for Wide Area Curing and is a continuation-in-part of application Ser. No. 12/209,080 filed Sep. 11, 2008 , now U.S. Pat. No. 7,731,379, and application Ser. No. 12/112,753 filed Apr. 30, 2008, now U.S. Pat. No. 7,775,690, all by George Wakalopulos. 
    
    
     TECHNICAL FIELD 
     The invention relates to apparatus for applying radiant energy to coating materials, and in particular to applying ultraviolet (UV) energy to coatings on floors. 
     BACKGROUND OF THE INVENTION 
     Beams of high intensity UV light are useful for curing polymers in certain coatings, such as paints, inks adhesives and the like. Such coatings are often used to treat large surface areas, such as floors and so there is a need to cure coatings on such surface areas with UV light. U.S. Pat. No. 6,761,127 describes apparatus for curing floor coatings using two UV lamps at different wavelengths with energy applied in a linear stripe pattern. This apparatus is said to be limited to no more than 75 watts per inch. 
     More power density is useful for faster curing. In prior patent application Ser. No. 12/209,080 filed Sep. 11, 2008, G. Wakalopulos described how a known reliable source of UV light at good power is a mercury vapor street light. Typical power is 175 watts per inch available a few minutes after starting. At start-up a small pool of mercury is vaporized and heated. The lamp is a negative resistance device requiring ballast to prevent increasing current from damaging the lamp. The negative resistance is offset by a positive impedance that tends to limit current. As the lamp heats up during operation, internal gas pressure rises and a higher voltage is required to maintain the discharge. The resistive drop across the ballast supplies the required voltage until the required voltage cannot be supplied to maintain the discharge. At that point, the discharge is extinguished, the lamp cools, the gas pressure is reduced and the ballast is again effective once the lamp is started. An auxiliary high voltage electrode is used to restart the arc discharge. Such power in a UV lamp would be desirable for curing floor coatings if heat and electrical stability problems could be solved with appropriate ballast in a convenient radiant energy delivery system adapted for surfaces such as floors. If heat and electrical stability problems are not solved, the lamp fails. 
     SUMMARY OF THE INVENTION 
     The present invention deploys ultraviolet lamps of the kind found in street lamps on radially extending arms about an axial support shaft. There are two problems. A first problem is to focus the light onto the floor in an efficient high intensity beam. A second problem is to provide thermal and electrical ballast to the lamp to prevent lamp failure. 
     The first problem is solved in an embodiment using a U-shaped channel housing that is a shell supporting shiny spars that form a reflector for an elongated lamp tube placed between the spars at a focal location. The lamp tube axis is parallel to the arm. A gap between the spars allows air flow between spars to cool the lamp. 
     The second problem is more difficult and is solved in an embodiment using a Nichrome wire of the type found in a common hair dryer, providing resistive ballast. Air is blown across the heated wire in a path that takes hot air past the lamp. The reflector is vented so that air can enter a plenum defined by the reflector wherein the lamp is mounted. When the lamp is cold, heated air passing over the resistive wire heats the lamp toward a desired operating temperature. When the lamp temperature exceeds the temperature of the heated wire the air cools the lamp tending to stabilize thermal performance. 
     Circulation of hot air is established by air jets coming from fans in tubes that resemble hair dryer barrels. The barrels are aligned transverse to the arms like jets engines on aircraft wings to provide circumferential reactive momentum to arms on which they are mounted, similar to other arms mounting the lamps, all rotating about the same axis. Thus the barrels provide jet momentum that rotates the arms about the axis as well as air that regulates the lamps also being rotated by the jet momentum. As lamp temperature increases, voltage across the lamp increases, causing increased fan speed increasing jet momentum thereby cooling the lamp, lowering voltage, and lowering jet momentum. In this manner, the lamp achieves ballast while jet momentum alternates between two values. 
     In summary, elongated UV lamps of the type commonly used as street lamps, mounted on freely rotating arms, trace an annular pattern on a floor. As a spindle or shaft, carrying the arms, is advanced, a wide swath of a floor is treated. Hot air from a blower is used for thermal stabilization of the lamps. It may also be used to rotate the arms by reactive momentum transfer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a machine for applying ultraviolet radiant energy to coatings on a floor in accordance with the invention. 
         FIG. 2  is a top perspective view of an embodiment of a machine similar to the apparatus of  FIG. 1 . 
         FIG. 3  is a top perspective view of the machine of  FIG. 2  with top cover removed. 
         FIG. 4  is a top view of the machine of  FIG. 2  with top cover removed. 
         FIG. 5  is a bottom view of the machine of  FIG. 2  with top cover removed. 
         FIG. 6  is an end view of a beam forming reflector structure for use in the machine shown in  FIG. 1 . 
         FIG. 7  is a perspective view of a beam forming reflector structure for use in the machine shown in  FIG. 1 . 
         FIG. 8  is an electrical plan for the machine shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , a machine  11  cures a coating on floor, F, using UV light sources in housing  13 . The machine sweeps a swath, S, that is almost as wide as housing  13 . Because lamps within the housing rotate, edge effects are minimal. The machine has small rollers that allow the housing  13  to easily move over the floor when pushed by handle  15 . 
     In  FIG. 2 , a hand movable version of the machine of  FIG. 1  is shown with a housing  23 , a handle  21 , a central axial shaft  25  and a plurality of vent ports  27  allowing the escape of hot air from blowers described below. Housing  23  also moves on wheels or rollers as described above. 
     With reference to  FIG. 3 , housing  23  is seen to have arms  16 ,  17 ,  18 , and  19  connected to collar  27  that freely rotates about a supporting axial shaft  25 . The arms  16 - 19  extend radially outwardly from the shaft and rotate about it. Arm  16  supports an elongated UV lamp within reflector  31 . The lamp and reflector are axially parallel to arm  16  although this is not required. The lamp has a length that is coextensive with most of the length of the supporting arm. This permits most of the diameter of housing  23  to be effective in creating a curing footprint for the apparatus similar to the swath, S, shown in  FIG. 1 . Of course, to create the swath another UV lamp with reflector  33  is used in tandem, with UV lamps opposite each other. Reflector  33  is carried by arm  18  diametrically opposed to arm  16 . The reflectors, lamps, and arms are mirror images of each other about shaft  25 . In rotation, the lamps sweep an annular pattern. However, as the annular pattern of illumination is advanced, a swath or stripe pattern is illuminated. A housing would typically have a diameter of 28 inches with a swath 24 inches wide. This allows 24 inch stripes of a coating on a floor to be cured by UV light by slowly advancing the housing over a floor coated with a UV light curable coating. There should be some overlap between adjacent stripes to avoid any edge effects and to avoid untreated gaps. 
     Perpendicular, or at least transverse, to arms  16  and  18  are arms  17  and  19 . Arm  17  carries a pair of blowers  35  and  36 . Similarly, arm  19  carries a pair of blowers  37  and  38 . The blowers are similar in size, appearance, and performance to the barrels of hand held hair dryers. Each blower has a Nichrome heating wire inside of the barrel across which air is blown by a motor driven fan or cage. Hot air emerges from the barrel. Other electronics associated with the Nichrome wire are also in the barrel. When the UV lamps are at relatively low temperature compared to their ideal operating temperature, air heated by being blown across the Nichrome wire heats the lamps by convection associated with rotation of the arms. When the temperature of the lamps exceeds the ideal operating temperature, air blown across the wire, at the same temperature as described above, now cools the lamps because the lamps are hotter than the hot air. In this manner the lamp operating temperature is stabilized. It is seen that the preferred operating temperature for air heated by the Nichrome wire is equal to the ideal operating temperature of the lamps. Since the Nichrome wire operates by resistive heating, similar to a toaster, the amount of resistance of the wire is adjusted to achieve the desired air heating. This can either be established at the time of manufacture by calibration or an electronic feedback system having a temperature sensor and variable resistance controller can be used. Without temperature stabilization, many lamps would fail. 
     Each of the blowers has a exit port for heated air. The exit ports  45 ,  46  are associated with respective blowers  35 ,  36 . The air exit ports for blowers  37 ,  38  cannot be seen because they face in an opposite direction but have the effect of complementing the reactive momentum of the other blowers. The blowers are mounted below respective support arms, like jet engines mounted below an aircraft wing. Just like jet engines, the blowers establish reactive momentum that propels the arms causing the collar  27  to rotate about axial shaft  25 . In  FIG. 3 , the direction of rotation would be clockwise rotation. Some of the heated air is blown toward deflector  41  and  42  that direct heated air out of the housing  23  allowing less resistance to the reactive momentum of the blowers. The deflectors are bent pieces of sheet metal mounted to each arm that carries blowers. 
     In  FIG. 4 , the deflectors  41  and  42  are seen from the top with the cover of the housing  23  removed. Deflected air is directed upwardly through ports in the cover of the housing while some of the heated air rushes past lamps within reflectors  31 ,  33  carried by arms  16  and  18  respectively. Note that housing  23  has handles  30 ,  40  to move the housing by hand over a surface. 
     In  FIG. 5 , housing  23  has a protective grill  51  with parallel ribs  53  that support rollers  55 . The rollers may be roller bearings or wheels. Grill  51  is sufficiently open to a support surface, such as a floor, so that radiation from lamps  61  and  63  within respective reflectors  31  and  33 , can reach the support surface. The distance from the lamps to the support surface is only a few inches. The lamps spin at a variable rate as the reactive momentum from blowers  35 - 38  drives the arms of the device about the center collar and axial shaft. The blowers include a barrel having a fan driven by a motor and a resistively heated wire in front of the fan to heat air blown out of the barrel. 
     In  FIG. 6  a reflection  31  for a UV lamp  61  is seen to have a rib  71  which is one of a number of parallel, spaced apart identical ribs. The ribs support lengthwise shiny metal spars  73 ,  75  that are thin, elongated metal strips that flex and can be bent to assume the shape of the ribs. The ribs have an internal parabolic shape. Flexing of a spar is indicated by arrows, D, such that spar  73  assumes the shape of the spar  75 . A further reflective element can be a shiny metal slot  77  placed in a slot  79  in a position between proximate ends of spars  73  and  75  near the internal vertex of the parabolic reflector. If UV lamp  61  has an axis aligned with the focal line of the elongated parabolic reflector formed by the ribs, spars, and slots, then UV light will emerge from the reflector as a beam. 
     In  FIG. 7 , reflector  31  is seen to be an elongated structure that carries a UV lamp  61  that is a mercury vapor street lamp. The lamp  61  is axially mounted at or near the focus of a parabolic reflector  31  formed by the shiny metal spars and the shiny metal slot  77  in slat  79 . The spars are held in place by a series of parallel ribs including a first rib  71 . Positions of other ribs are identified by fasteners  81  holding the ribs in place. Arm  16  is seen supporting the reflector  31 . 
       FIG. 8  shows electrical relationships of the blower and lamp members shown in  FIGS. 3-5 . Blower  35  has an electrical connection to an AC plug  83  that has a pair of wires  85  connected to AC motor  87  which drives fan  89 . Wires  85  are also connected to the UV lamp  61  within reflector  31  by means of electrodes A, B, and C. Separating the contacts between electrodes A and B is a ballast resistor  91  which is a Nichrome wire of the type found in hair dryers and toasters and described above. Fan  89  directs air, indicated by arrows, through the Nichrome wires and towards the lamp  61  within the housing. Electrodes A and B of the lamp are connected to a voltage multiplier circuit  93  which serves as a starter for the lamp. Diodes  95  and  96  are oppositely biased at opposite plates of a first capacitor  97  while a second capacitor  98  forms a quasi-bridge circuit for voltage multiplication. The circuit draws little current but high voltage from the circuit allows ignition of a material such as molten mercury within the lamp which will form an ionic plasma in lamp tube  61 . The ballast resistor  91  is used to counteract the negative resistance of the mercury vapor ultraviolet lamp  61 . The ballast resistor  91  prevents the lamp from drawing excessive current and provides electrical stability as the lamp warms. However, the temperature of the lamp will exceed the temperature of the hot air being blown across it from heating of the ballast resistor. As the lamp continues to heat up during operation, internal gas pressure within the lamp tube causes a higher voltage to be required to maintain the arc discharge. The higher voltage is not available through the ballast circuit. Since the voltage necessary to maintain the arc exceeds the voltage provided by the electrical ballast, the arc fails. The lamp momentarily goes out and begins to cool down. As gas pressure in the tube goes down, liquid mercury will form and the high voltage multiplier circuit  93  can be used to ignite the arc and send current into ballast resistor  91 , plus generate heat from the Nichrome wire resistor  91  blown by the fan toward the lamp. This heats the lamp causing the lamp to glow and produce infrared light once again. This on-off cycle is inherent in the performance of the lamp and allows relatively high intermittent power to be obtained from a simple circuit. The fan also generates reactive momentum causing rotation of the arms carrying the lamps. As the lamps rotate, they trace an annular pattern where intense UV light energy has been delivered. As the housing is advanced along a line, the annular pattern becomes a stripe pattern. This allows a coating on a floor to be cured by a succession of parallel stripes where intense UV light has been delivered. The invention is not limited to use on floors but could be used on any area. For example, in graffiti removal from walls such as on box cars, curable coatings are often used. The hand held version of the present invention, shown in  FIG. 2 , could be used to cure coatings.