Abstract:
The invention is a microwave powered lamp ( 10 ). The lamp includes a light reflective cavity ( 28 ); an electrodeless bulb ( 16 ) contained in the light reflective cavity ( 26 ) from which light is emitted when the electrodeless bulb is excited by microwaves; a magnetron ( 12 ) for providing the microwaves for exciting the electrodeless bulb; a waveguide ( 14 ) which couples the microwaves emitted by the magnetron to the light reflective cavity for exciting the electrodeless bulb; a housing ( 22 ) which contains the lamp; a detector ( 102, 202 ) disposed within the housing, which detects the microwaves which are not coupled to the bulb during operation of the magnetron and outputs a signal indicative of a level of received microwaves; and a magnetron control ( 300 ), coupled to the detector, which causes the magnetron to be turned off when a level of the signal indicates the level of received microwaves exceeds a threshold.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to microwave powered lamps and more specifically, to microwave powered lamps having reliable detection of bulb failure or degrading of performance.  
         [0003]     2. Description of the Prior Art  
         [0004]      FIG. 1  illustrates a prior art microwave powered lamp  10  of the type sold by the Assignee of the present invention and as described in the Assignee&#39;s U.S. Pat. No. 6,445,138 which is incorporated herein by reference in its entirety. The microwave-powered lamp may be used to produce ultraviolet (UV) or visible light depending on the application such as, but not limited to, curing surface coatings. A magnetron  12  provides microwaves transmitted through a microwave cavity/waveguide  14  to a microwave excited bulb  16  which outputs light, as stated above, in either the UV or visible spectrum depending upon the application. An air source  18  blows air  20  through a housing  22  which contains the magnetron  12 , microwave cavity/waveguide  14 , and microwave excited bulb  16 . As indicated, air  20  flows through the housing around the magnetron  12  to provide cooling thereof and into the microwave cavity/waveguide  14  into and around the bulb  16  to provide cooling of the bulb. The lamp housing  22  is designed to channel air  20  in contact with cooling fins  23  of the magnetron  12  through openings  24  and then through openings (not illustrated) in the reflector  26  past the bulb  16  as described above and out of the housing  22 . The air  20 , which is heated by the magnetron  12  and the bulb  16 , exits through the opening  29  which is covered by a microwave retaining screen (not illustrated) through which the light Is outputted after being reflected by a light reflective cavity  28 .  
         [0005]     The magnetron  12  is subject to damage if the light bulb  16  becomes inoperative. An assembly of a photocell  32  and an associated circuit  33 , which senses variation in the resistance of the photocell that detects light  34  emitted from the bulb  16  passing through an opening in the reflector  28  to contact the photocell, is used to detect an inoperative bulb. The resistivity of the photocell  32  changes, which is sensed by the associated circuit  33 , to produce a control signal which is applied to the magnetron controller (not illustrated). The magnetron controller functions, when the photocell indicates that light is not being received, to disconnect the electrical power from the magnetron  12  to thereby turn it off.  
         [0006]     A typical microwave-powered UV lamp is six or ten inches in length and incorporates one or more magnetrons  12 , as illustrated in  FIGS. 1 and 2 , to provide microwave power to excite a bulb  16 . When the lamp  10  is first turned on, there is a high voltage standing wave ratio (VSWR) seen by the magnetron  12  because the bulb  16  is cool and the impedance of the bulb at the microwave frequency is not well matched. As the bulb  16  warms up, the VSWR gradually decreases to a steady state value as illustrated in  FIG. 8 . High VSWR transients are a normal part of starting ignition of a plasma-filled bulb  16 . During the transient period, it is possible for arcing to occur in the microwave cavity/waveguide  14  which can destroy the magnetron. The magnetron may also experience severe anode dissipation during the transient period.  
         [0007]     If there is no protection provided by the photocell  32  and protection circuit  33 , the VSWR will remain unacceptably high until the magnetron is destroyed. The power supply (not illustrated) of the magnetron  12  applies high voltage to the magnetron. The magnetron controller is responsive to a signal from the protection circuit  33 . If no signal is received indicating ignition within a set period of time, the magnetron controller assumes the bulb has failed to ignite and cuts electrical power to protect the magnetron  12  given the fault condition indication of no ignition.  
         [0008]     The use of a photocell  32  and protection circuit  33  is subject to being unable to distinguish between light  34  from the bulb  16  and stray ambient light which enters the housing  22  from other sources. The presence of ambient light may result in the photocell  32  and protection circuit  33  sensing the ambient light from another source as an indication that the bulb has ignited. If in fact the bulb  16  has not ignited, damage to the magnetron  12  will occur by its continuing to provide output power the bulb  16  which is not absorbed by the plasma therein. Furthermore, the photocell  32  and control circuit  33  may fail requiring repair resulting in costly downtime for any system relying upon the operation of the microwave powered lamp and furthermore, if repair is not made, the probability of the magnetron  12  being permanently damaged by power being applied thereto is high.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention is a microwave powered lamp and method of control of a microwave powered lamp. The present invention replaces the prior art photocell and control circuit with a detector which is disposed within the housing of the microwave powered lamp which detects microwaves which are not coupled to the microwave excited lamp during operation of the magnetron and outputs a signal indicative of a level of received microwaves. A magnetron control is coupled to the detector which causes the magnetron to be turned off when a level of the detected signal indicates that the level of received microwaves exceeds a threshold. Since ignition of the microwave powered bulb represents an electrical load to the magnetron, the resultant level of microwave energy received by the detector, whether inside the microwave cavity/waveguide or inside the microwave housing, drops. The sensed microwave energy during normal bulb operation is below a level associated with non-ignition of the bulb such as that caused by bulb failure. A set period of time is allowed for the level of the detected microwaves to stabilize to avoid turning off of the magnetron power supply during transient voltage swings that occur during the first turning on of the bulb which otherwise might provide a false triggering signal turning off the magnetron power supply. With the invention, the sensing of the ignition condition (either on or off) of the bulb occurs reliably much more rapidly than with the prior art photocell and control circuit.  
         [0010]     Additionally, the reliable detection of a non-ignition condition allows the power to be removed quickly from the magnetron long before any damage occurs from power not being absorbed by the plasma in bulb. This removes high stress and thermal loading of the magnetron as a result of the microwave output not being absorbed by the plasma in the bulb.  
         [0011]     Additionally, the presence of ambient light within the housing of the microwave-powered lamp does not produce false indications of bulb ignition as with the prior art.  
         [0012]     The invention is a microwave powered lamp. A microwave powered lamp in accordance with the invention includes a light reflective cavity; an electrodeless bulb contained in the light reflective cavity from which light is emitted when the electrodeless bulb is excited by microwaves; a magnetron for providing the microwaves for exciting the electrodeless bulb; a waveguide which couples the microwaves emitted by the magnetron to the light reflective cavity for exciting the electrodeless bulb; a housing which contains the lamp; a detector disposed within the housing, which detects the microwaves which are not coupled to the bulb during operation of the magnetron and outputs a signal indicative of a level of received microwaves; and a magnetron control, coupled to the detector, which causes the magnetron to be turned off when a level of the signal indicates the level of received microwaves exceeds a threshold. The detector may comprise an electrical field probe disposed in the waveguide at a location which produces a response to microwaves not coupled to the bulb sufficient to detect when the bulb is not ignited during magnetron operation and the magnetron control may be a control circuit which produces a control signal for turning off the magnetron by removing electrical power from the magnetron when the threshold is exceeded. The electrical field probe may be located at an electrical field maximum in the waveguide. The detector may comprise an antenna located within the housing which receives spurious microwaves leaking from any of at least one of the magnetron, waveguide or light reflective cavity which produces a response to the spurious microwaves sufficient to detect when the electrodeless bulb is not ignited during magnetron operation and the magnetron control may be a control circuit which produces a control signal for turning off the magnetron by removing electrical power from the magnetron when the threshold is exceeded. The magnetron control may comprise a power supply of the magnetron and the electrical power from the power supply to the magnetron may be reduced or turned off when the signal indicates the level of received microwaves exceeds the threshold for a set period of time.  
         [0013]     The invention is also a method of control of a microwave powered lamp. A method of control of a microwave powered lamp includes a light reflective cavity, an electrodeless bulb contained in the light reflective cavity from which light is emitted when the electrodeless bulb is excited by microwaves, a magnetron for providing the microwaves for exciting the electrodeless bulb, a waveguide which couples microwaves emitted by the magnetron to the light reflective cavity for exciting the electrodeless bulb, a housing which contains the lamp, a detector disposed within the housing which detects microwaves which are not coupled to the bulb during operation of the magnetron and a magnetron control coupled to the detector for controlling activation of the magnetron comprises providing a signal from the detector indicative of a level of detected microwaves; and the magnetron control reduces power to the magnetron when a level of the signal indicates the level of the detected microwaves exceeds a threshold. The detector may comprise an electrical field probe disposed in the waveguide at a location which produces a response to microwaves not coupled to the bulb sufficient to detect when the bulb is not ignited during magnetron operation and the magnetron control may be a control circuit which produces a control signal for turning off the magnetron by removing electrical power from the magnetron when the threshold is exceeded. The electrical field probe may be located at an electrical field maximum in the waveguide. The detector may comprise an antenna located within the housing which receives spurious microwaves leaking from any of at least one of the magnetron, waveguide or light reflective cavity which produces a response to the spurious microwaves sufficient to detect when the electrodeless bulb is not ignited during magnetron operation and the magnetron control may be a control circuit which produces a control signal for turning off the magnetron by removing electrical power from the magnetron when the threshold is exceeded. The magnetron control may comprise a power supply of the magnetron and the electrical power from the power supply to the magnetron may be reduced or turned off when the signal indicates the level of received microwaves exceeds the threshold for a set period of time. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIGS. 1 and 2  respectively illustrate a side and front elevational view of a prior art microwave powered lamp of the type manufactured by the Assignee of the present invention.  
         [0015]      FIG. 3  illustrates a side elevational view of a first embodiment of the present invention.  
         [0016]      FIG. 4  illustrates a front elevational view of the first embodiment of the present invention.  
         [0017]      FIG. 5  illustrates a side elevational view of a second embodiment of the present invention.  
         [0018]      FIG. 6  illustrates a front elevational view of the second embodiment of the present invention.  
         [0019]      FIG. 7  illustrates a VSWR detection circuit used for generating a signal indicative of the operational state of the ignition of an electrodeless bulb in accordance with the present invention.  
         [0020]      FIG. 8  illustrates operational data obtained from operation and failure of a 9 mm H+ bulb of the Assignee utilizing the circuit of  FIG. 7 . 
     
    
       [0021]     Like reference numerals identify like parts throughout the drawings.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     The present invention may be practiced in numerous microwave powered lamp designs with one acceptable design being the prior art microwave powered lamp design illustrated in  FIGS. 1 and 2  as discussed in conjunction with first and second embodiments  100  and  200  respectively illustrated in  FIGS. 3 and 4  and  5  and  6 . With the invention, the photocell  32  and control circuit  33  of the prior art is replaced with a microwave detector which is located within the microwave cavity/waveguide  14  or within the housing  22  of a microwave powered lamp  100  or  200  as respectively illustrated in  FIGS. 3 and 4  and  5  and  6 . The detector location in the housing may be with the detector extending into the microwave cavity/waveguide  14  where the VSWR is sensed, as illustrated in the embodiment  100  in  FIGS. 3 and 4 , or external to the microwave cavity/waveguide  14  but within the housing  22 , as illustrated in  FIGS. 5 and 6 . In the first embodiment  100 , as illustrated in  FIGS. 3 and 4 , a microwave probe  102  extends into the microwave cavity/waveguide  14  and in the second embodiment, illustrated in  FIGS. 5 and 6 , a loop antenna  202  receives spurious microwaves leaking from any of the at least one of the magnetron  12 , microwave cavity/waveguide  14  or light reflection cavity  204  of the second embodiment  200  of  FIGS. 5 and 6 .  
         [0023]     In each embodiment, the detected microwaves, whether detected from within the microwave cavity/waveguide  14  or within the housing  22 , are processed by a VSWR detection circuit  300 , which may be in accordance with the design of  FIG. 7 , that performs microwave detection and provides a variable current, such as, but not limited to between 4 to 20 milliamps range which drives a threshold control circuit  302  to produce an INTERLOCK CONTROL SIGNAL  304  which is applied to the magnetron power supply  306 . The INTERLOCK CONTROL SIGNAL turns off the magnetron  12  when the microwave signal detected by the microwave probe  102  or loop antenna  202  or other detector design rises above a threshold as described in detail below with respect to  FIG. 8  for longer than a set time interval. The set interval may be less than one second during which the effect of transient VSWR variation subsides to a condition reflecting normal ignition of the electrodeless bulb  16 .  
         [0024]     In the embodiment of  FIGS. 3 and 4 , the microwave probe  102  is associated with the VSWR detection circuit  300  of  FIG. 7 . The flange  104  is attached to the sidewall  106  of the waveguide/microwave cavity  14  by suitable connectors  108 . The microwave probe functions as a E (electrical) field detector and is preferably located at an electrical field maximum in the microwave cavity/waveguide  14 . The location of the microwave probe  102  may be disposed at other locations than at an electrical field maximum within the microwave cavity/waveguide  14  but location at a E field maximum enhances the detected voltage.  
         [0025]     The second embodiment  200  of the invention in  FIGS. 5 and 6  functions in the same manner as the first embodiment with the difference being that the VSWR detection circuit  300  is mounted on one of the internal sidewalls  206  of housing  22  at a location where sufficient spurious microwave energy, which leaks from the microwave cavity/waveguide  14 , light reflective cavity  204  or magnetron  12 , is detected if the bulb  16  is ignited. When proper bulb operation occurs, the loading of the output from the magnetron  12  keeps the signal level produced by the VSWR detection circuit  300  below a threshold as discussed below in conjunction with  FIG. 8 . The signal level produced by the VSWR detection circuit  300  below the threshold results in the INTERLOCK CONTROL SIGNAL  304  being applied from the threshold control circuit  302  to the magnetron power supply  306  not turning off the magnetron power supply  304 .  
         [0026]      FIG. 7  illustrates an embodiment of a VSWR detection circuit  300  which may be used with the practice of the present invention. The E field probe  102  and loop antenna  202  are illustrated, but it should be understood that the present invention is not limited to any type of a microwave detector. The E field probe  102  or loop antenna  202  produces a very small voltage signal representative of the level of detected microwaves either within the microwave cavity/waveguide  14  or within the housing  22 . The small voltage signal produced by the E field probe  102  or loop antenna  202  is coupled by coupling capacitor C 4  and resistor R 4  to an integrated circuit  310  which amplifies the small voltage signal input into an output signal  312  which may have a voltage range between 300 and 1,000 millivolts. The output signal  312  is applied to operational amplifier  314  which produces a further output voltage gain. Signal  316  has sufficient gain to drive a voltage to constant current converting integrated circuit  318 . The output signal  320  produced by the voltage to current converting integrated circuit  318  produces a constant current output which is not effected by line drop which may be resultant from the coupling of the output signal to a remote magnetron power supply  306  which contains a threshold control circuit  302 . The output signal  320  is coupled to the threshold control circuit  302 , which as discussed above, detects if the voltage sensed by the E field probe  102  or loop antenna  202  is above a threshold which is indicative of a signal level representing failure of the electrodeless bulb  16 . Failure causes the VSWR signal, after transients have subsided as the result of the initial turning on of the magnetron  12 , to reach a steady state level indicative of an unacceptably high VSWR ratio being present either within the microwave cavity/waveguide  14  or spurious microwave leakage of sufficient magnitude being within the housing  22 . The threshold control circuit  302  senses if the output signal  320  is above a set threshold level, as illustrated in  FIG. 8 , for a time period chosen to be representative of when steady state operation occurs during normal operation of the microwave powered lamp which period may be, as illustrated in  FIG. 8 , a fraction of a second or longer. The threshold control circuit  302  produces an INTERLOCK CONTROL SIGNAL  304  which has one of two levels which respectively close and open a switch  307  which is indicated schematically and in practice may be any type of switching device that controls connection of the high voltage potential  309  to the magnetron  12 . The first level is indicative of the electrodeless bulb  16  representing a proper electrical load to the magnetron  12  which causes switch  309  to be in a closed state (not illustrated) and the second level which causes the switch to be in an open state as illustrated is indicative of failure of the electrodeless bulb  16  which causes the VSWR ratio within the microwave cavity/waveguide  14  or housing  22  to be unacceptably high. The second level signal causes the magnetron power supply  306  to be turned off as an interlock function of the magnetron power supply.  
         [0027]      FIG. 8  illustrates the operation of the present invention with a 9 mm H+ bulb of the Assignee in a microwave powered lamp such as that illustrated in  FIGS. 3 and 4 . As is seen, at approximately 3 seconds, the power supply  306  is turned on which causes the magnetron  12  to produce microwaves which excite the electrodeless bulb  16  and produce standing waves within the microwave cavity/waveguide  14  which rapidly ramp up in level. As indicated in the key in the bottom right-hand corner of  FIG. 8 , the threshold control circuit  302  senses when the output signal  320  reaches the threshold level of approximately 3.4 volts. As indicated with proper operation of the 9 mm. H+ bulb, as identified by the curve composed of small circles, when the bulb is warming up the signal level fluctuates and actually exceeds the threshold for a small period of time. Thereafter the voltage stabilizes below the threshold value which causes the INTERLOCK CONTROL SIGNAL  304  to be at the first level which permits the magnetron power supply  306  to continue to apply power to the magnetron  12 . However, in the situation where the 9 mm H+ bulb is blown, as indicated by the curve composed of small diamonds, the output voltage of the signal  320  rises in a steady state above the threshold.  
         [0028]     While a time lapse of almost 8 seconds is shown in  FIG. 8 , which is representative of the time lapse which is built into the prior art, photocell  32  and circuit detector  33  in order to indicate the failure of a bulb, in fact a reliable indication of bulb failure may be obtained much earlier. This time lapse may be from a half to one second since from the period of reaching the initial level above the threshold in view of a steady state output voltage of the signal  320  being reached in that time frame. At that point (while a much longer time period of approximately 8 seconds was allowed to elapse) the second level of the INTERLOCK CONTROL SIGNAL  304  may be used to turn off the magnetron power supply  306 . The time lag and the threshold level are design parameters of the particular circuits and E field probe  102  or loop antenna  202  or other detectors which may be used for sensing the VSWR.  
         [0029]     The present invention provides a reliable mechanism for detecting failure of an electrodeless bulb  16  which is indicated by a sensed unacceptably high detected VSWR ratio within the cavity  22  or within the microwave cavity/waveguide  14  and is not subject to false indications resulting from light from other light sources since the detection of a failed electrodeless bulb is not dependent upon light detection.  
         [0030]     While the invention has been described in terms of its preferred embodiments, it should be understood that numerous modifications may be made thereto without departing from the spirit and scope of the present invention. It is intended that all such modifications fall within the scope of the appended claims.