Abstract:
An article treatment system and method utilizing an air-cooled lamp and having reduced cooling requirement. A power supply responds to a sensor sensing the presence of an article at an article treating location by providing power to an air-cooled lamp, causing the lamp to project radiation onto the article at a radiation level sufficient to effectively treat the article. An air blower blows air onto the lamp, and a blower driver is responsive to the level of the power being provided to the lamp to drive the air blower at a speed blowing air onto the lamp with an air pressure having a non-linear relationship with the power level.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 09/989,037, filed Nov. 21, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention pertains to a system for and method of treating articles. Further, the present invention pertains to a lamp system usable in an article treating system and method. More particularly, the present invention pertains to controlling the cooling of an air-cooled lamp, such as an ultraviolet lamp, so as to optimize operation of the lamp.  
         BACKGROUND OF THE INVENTION  
         [0003]    Lamps, and in particular ultraviolet lamps such as electrodeless ultraviolet lamps, are utilized in various manufacturing operations. By way of example, many materials are cured by exposure to ultraviolet radiation from electrodeless ultraviolet curing lamps. Such electrodeless lamps are energized by, for example, a magnetron which receives power from a power supply and generates microwaves that energize the electrodeless ultraviolet lamp. Such an ultraviolet lamp must not be allowed to become overheated, or the life of the lamp will be significantly shortened. In use in commercial operations, such as curing of materials that have been applied on products being manufactured, the lamps might be operated at a high power level. To avoid overheating of the lamps, cooling air is blown onto the lamps from a blower. If the lamps are continuously operated at their intended full-power level, cooling air at a high pressure is required. This results in a high energy requirement for the blower providing the cooling air.  
           [0004]    To avoid this, it is known to operate the lamps at a somewhat lower power level. While this enables adequate cooling to be provided with air at a lower pressure, it also reduces the efficiency of the curing process since the lamps emit less radiation at the lower power level. It is also known to operate the lamps with a duty cycle of, for example, four seconds on and one second off. High efficiency ultraviolet lamps use multiple element emitter type fills, such as mercury and iron halides. In normal operation such lamps might have a temperature in the range of from about 750° C. to about 950° C., and these fills are in a gaseous state. If the ultraviolet lamp is shut off for any significant time, the fills may condense. In addition, if the lamp is turned off, then the ionized plasma extinguishes and the mercury vapor must be allowed to cool for a period of time, generally between fifteen seconds and two minutes, before the lamp can again be powered. This can significantly delay the process in which the lamps being used. Additional problems which can result from such overcooling include unstable and erratic ultraviolet output levels, especially at 60% and lower power levels, delays in ultraviolet output response of three seconds or more when going from lower power to high power, spectral changes, resulting in shifting of the ultraviolet band, which can have a negative impact in some ultraviolet curing applications, bulb fill condensation, resulting in unwanted chemical reactions of some bulb fill additives with the ultraviolet lamp bulb, thereby reducing the bulb life, and excessive noisy and unnecessary cooling at power levels less than 100%. As a consequence, rather than turning such lamps off during their duty cycle, the lamps are usually powered at a low level, for example being provided with 2% to 50% of their intended full power.  
           [0005]    If the ultraviolet lamp is provided with cooling air a constant pressure, then during the high power portions of the duty cycle, the lamp temperature increases, while during the low power portions of the duty cycle, the temperature of the lamp decreases. It is necessary to maintain the lamp temperature within an operating range of about 700° C. to about 1000° C., preferably 750° C. to 950° C., since temperatures lower than that range can result in the lamp fills condensing, causing damage to the lamp, while temperatures in excess of the range can shorten the lamp life. To accommodate this, it is known to adjust the air pressure in proportion to the power provided to the ultraviolet lamp. See, for example, U.S. Pat. No. 4,032,817. However, in fact the cooling requirements are not proportional to the power provided to the ultraviolet lamp. Consequently, such systems can overcool the ultraviolet lamps.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is a system for and method of controlling the cooling in a lamp system, as well as a system for and method of treating articles with a lamp system. In accordance with the present invention, an air-cooled lamp such as an electrodeless ultraviolet lamp, is provided with power, while an air blower blows air onto the air-cooled lamp to cool the lamp, and a blower driver is responsive to the power level of the power being provided to the air-cooled lamp to drive the air blower at a speed blowing air onto the air-cooled lamp with an air pressure having a non-linear relationship with the power level when the power level is expressed as a percentage of the lamps intended full-power level. Preferably, the relationship is substantially exponential or is substantially defined by A p =(P−P o ) 2 , where A p  is the air pressure, P is the power level of the power being provided to the air-cooled lamp as a percentage of the full-power level, and P o  is a power level as a percentage of the full-power level that when provided to the air-cooled lamp requires no air to be blown by the air blower onto the air-cooled lamp. Preferably, also, the cooling level is minimized as much as possible at all power levels, while not overheating the air-cooled lamp. Further, the present invention is a machine-readable medium having stored thereon at least one sequence of instructions that, when executed, cause a machine to cool an air-cooled lamp. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    These and other aspects and advantages of the present invention are more apparent from the following detailed description and claims, particularly when considered in conjunction with the accompanying drawings. In the drawings:  
         [0008]    [0008]FIG. 1 is a block diagram of a first embodiment of an article treatment system in accordance with the present invention;  
         [0009]    [0009]FIG. 2 is a graph illustrating the cooling air pressure requirement for a lamp system as a function of the power provided to the lamp, expressed as a percentage of the lamp&#39;s intended full-power level, in order to provide satisfactory lamp bulb cooling, in accordance with the present invention;  
         [0010]    [0010]FIG. 3 is a graph illustrating an example of a duty cycle of a lamp; and  
         [0011]    [0011]FIG. 4 is a block diagram of a second embodiment of an article treatment system in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0012]    [0012]FIG. 1 illustrates a number of articles  10  approaching, and then being conveyed on an article conveyor  12 . Article conveyor  12  is provided with a number of article conveying stations, illustrated in FIG. 1 as stations  12   a - 12   f . An article  10  is mounted on an article holder  14  at station  12   a . Machine controller  16  provides a start signal to motor  18 , causing the motor to drive article conveyor  12 , for example by means of a drive belt  20 , so that in the representative embodiment of FIG. 1 article conveyor  12  rotates in a clockwise direction, bringing each article  10  in turn from station  12   a  through station  12   b  and to an article treating location at station  12   c . An air-cooled lamp assembly  22  is positioned to project radiation onto an article  10  when that article is at article treating location  12   c . A rotation device  24  rotates counterclockwise in the embodiment of FIG. 1 to cause the article  10  at station  12   c  to rotate clockwise about the axis of article holder  14  so as to sequentially expose the entire side surface of that article  10  to radiation from lamp assembly  22 .  
         [0013]    A power supply  26  provides power to lamp assembly  22 , while a blower  28  provides cooling air to the lamp assembly. Blower  28  is controlled by blower driver  30 , for example a variable frequency motor drive, with the speed of blower  28  being proportional to the frequency of the motor drive output.  
         [0014]    In the illustrative example of FIG. 1, lamp assembly  22  includes a magnetron  32  which receives power from power supply  26  to generate microwaves, an electrodeless ultraviolet bulb  34 , and a reflector  36 . The microwave energy from magnetron  32  energizes bulb  34 , causing the bulb to emit ultraviolet radiation. Reflector  36  concentrates that radiation on the article  10  at article treating station  12   c . High pressure air from air blower  28  flows over magnetron  32 . Reflector  36  is provided with openings for passage of the air to permit the air to cool bulb  34 . Since the end of lamp assembly  22  facing article treating location  12   c  is open, the area surrounding bulb  34  is at substantially atmospheric pressure. An air pressure gage  38  provides an indication of the pressure differential across reflector  36 , and thus the air pressure within lamp assembly  22 .  
         [0015]    Once the article  10  is treated by the radiation at article treating station  12   c , continued rotation of article conveyor  12  brings the treated article  10  to station  12   d  at which the treated article is removed from the article holder  14 , as indicated in FIG. 1. Further rotation of article conveyor  12  then brings that article holder through stations  12   e  and  12   f , and back to station  12   a  for receipt of another article  10 .  
         [0016]    A sensor  40  is provided adjacent station  12   f  to detect the presence or absence of an article holder at that station. Because the stations  12   a - 12   f  are equally spaced about the circumference of article conveyor  12 , detection of the presence or absence of an article holder at station  12   f  detects the presence or absence of an article at the article treating location of station  12   c . The output from sensor  40  is applied to machine controller  16  and to power supply  26 . Power supply  26  provides blower driver  30  with a signal indicating the level of the power supplied to lamp assembly  22 .  
         [0017]    In operation, machine controller  16  actuates motor  18  to rotate article conveyor  12 , bringing an article  10  to the article treating location at station  12   c . When sensor  40  senses the article holder  14  at station  12   f , the sensor applies a signal to machine controller  16  and to power supply  26 , deactivating machine controller  16  so as to shut off motor  18 , and bringing power supply  26  to its high power state, so as to cause lamp assembly  22  to emit radiation at a level sufficient to effectively treat the article at station  12   c . Based on the signal from power supply  26  indicating the level of the power being supplied to lamp assembly  22 , blower driver  20  actuates blower  28  at a speed to blow air at an appropriate pressure onto lamp assembly  22  to cool the lamp sufficiently to avoid overheating.  
         [0018]    After a time sufficient to permit complete treatment of the article  10  at article treating location  12   c , machine controller  16  again actuates motor  18  to rotate article conveyor  12 , advancing the treated article to station  12   d  for removal of the treated article from article conveyor  12 , and advancing the next article  10  from station  12   b  to station  12   c  for treatment. Rotating article convey  12  is, of course, only one type of conveyor that might be utilized to convey articles to and then from an article treating station such as station  12   c . By way of example, an endless belt conveyor might be used. Machine controller  16 , for example, might be an electronic switch and a timer to turn off motor  18  in response to a presence-of-article signal from sensor  40  and to turn the motor back on after sufficient time for rotation device  24  to have rotated the article being treated for full treatment.  
         [0019]    Continuous operation of lamp assembly at full power for an extended time can result in overheating of the lamp unless sufficient air cooling is provided, having an air pressure around magnetron  32  significantly greater than that within reflector  36  around bulb  34 . Continued operation of blower  28  at a level providing such a high air pressure is uneconomical. It is common practice, therefore, to provide a lower level of power to lamp assembly  22  when sensor  40  senses the absence of articles at article treating location  12   c  and to slow the blower operation so as to decrease the air pressure proportionally. However, often that causes overcooling of the bulb, resulting in poor performance and damage to the bulb.  
         [0020]    [0020]FIG. 2 is a graph illustrating the cooling air pressure differentials required for satisfactory operation of lamp assembly  22 . The horizontal axis represents percentage of the lamp&#39;s intended full power, while the vertical axis represent the relative air pressure differential across reflector  36  for satisfactory operation of lamp assembly  22 . Curve  50  presents the maximum air pressure differential for satisfactory operation, while curve  52  presents the minimum air pressure differential. For a lamp operating at any given percentage of full power, it is desired that the air pressure differential fall between the maximum and the minimum in order to maintain the temperature of lamp assembly  22  within the acceptable operating range. By way of illustration, if lamp assembly  22  is operating at 81% of full power, then the air pressure differential must fall between point  50   a  on curve  50  and point  52   a  on curve  52 .  
         [0021]    Curves  50  and  52  are approximately, but not exactly, general exponential curves, or curves approximately satisfying the relationship A p =(P−P o ) 2 , where A p  is air pressure, P is the power level of the power being provided to the air-cooled lamp as a percentage of the lamp&#39;s intended full-power level, and P o  is a power level, as a percentage of that full-power level, which when provided to the air-cooled lamp requires no air pressure differential for adequate cooling at the intended full power level of the lamp. FIG. 2 illustrates this as P 0 =25%. The reduced power level might be provided as continuous power at the reduced level, for example 80%. Alternatively, the power might be provided at the reduced level by cycling power supply  26  between a high power level and a low power level, the reduced provided power then being the average power provided over each cycle.  
         [0022]    [0022]FIG. 3 illustrates a cycle typical of those that might be provided to lamp assembly  22 . In the illustrative example of FIG. 3, power is provided with a the duty cycle made up of alternating intervals  60  of high power and intervals  62  of low power. FIG. 3 illustrates the high power intervals  60  at 100% of intended full power with a duration in the order of four seconds and the low power intervals  62  at 5% of full power with a duration in the order of one second, thus providing an 81% time-weighted average power level. For relatively short cycle times, for example high power intervals  60  of not more than eight seconds with low power intervals  62  of not more than two seconds, blower  28  can provide air at a continuous pressure between points  50   a  and  52   a  in FIG. 2. For longer cycle times, blower  28  can provide air at a pressure in the range between the 100% points on curves  50  and  52  during high power intervals  60 , while during the low power intervals  62  blower  28  can be stopped or slowed so that it results in an insignificant air pressure differential. In either case, lamp assembly  22  is maintained at at least a standby power level which is insufficient to cause lamp assembly  22  to project radiation at a level effective in treating an article  10 , but sufficient to maintain ionization of the bulb plasma and also to allow the bulb fill to remain in a vaporized state longer.  
         [0023]    During cyclical operation, the high power intervals  60  might provide power at a level substantially equal to the intended full-power level of lamp assembly  22 , for example 2800 watts. Due to the advantageous effects of the cooling in accordance with the present invention, such a lamp assembly might instead be operated in a cycle having an ultra-high power level, in excess of the intended full-power level, for example a power level of 4200 watts. Nevertheless, the cyclical operation results in the average power level being lower, and with a cooling air pressure differential based on the average power level in accordance with the present invention, satisfactory cooling is obtained.  
         [0024]    [0024]FIG. 4 is a block diagram of a second embodiment of an article treatment system in accordance with the present invention. The system of FIG. 4 differs from that of FIG. 1 by omitting machine controller  16  and by having a system controller  42 . The output of sensor  40  is applied to system controller  42 . System controller  42  provides start and stop signals to motor  18  and power supply  26   a  based on the signals from sensor  40  which indicate the presence or absence of an article at article treating location  12   c . Power supply  26   a  provides power to lamp assembly  22  and provides system controller  42  with a signal indicating the level of that power. System controller  42  provides a signal to blower driver  30  which causes blower  28  to provide air with a pressure differential to result in proper cooling of lamp assembly  22 , based on the power level signal applied to the system controller by power supply  26   a.    
         [0025]    Lamp assembly  22  is generally provided with power at a constant voltage of, for example, 4000 volts, with a current that varies from 0.05 amps at its lowest power level to one amp at full power. The power level signal applied by power supply  26  to blower driver  30  or applied by power supply  26   a  to system controller  42  can be, for example, an analog signal varying as the average power supplied to lamp assembly  22  varies from 5% of full power to 100% of full power. By way of example, the signal might be a voltage which varies, say, from 0.5 volts to 10 volts as the lamp power varies from 5% to 100% of full power. Alternatively, it might be a current which varies from, say, 1 ma to 20 ma as the lamp power varies from 5% to 100% of full power. The speed of blower  28  is generally directly proportional to the drive frequency from blower driver  30 . The air pressure resulting from operation of blower  30  has a relationship to the blower speed that is approximately exponential or approximately given by P=(S−S 0 ) 2 , where P is the pressure, S is the blower speed, and S 0  is the blower speed at which P=P 0 .  
         [0026]    Preferably, blower driver  30  is a programmable variable frequency driver, such as an Allen Bradley Series  160  driver, that is programmed with the necessary parameters for the characteristics of lamp assembly  22  and blower  28 , enabling the blower driver to automatically and rapidly provide the necessary drive frequency to blower  28 . Likewise, in the embodiment of FIG. 4, preferably system controller  42  is programmed to provide the necessary signals based on these same factors.  
         [0027]    The present invention thus provides improved cooling of air-cooled lamps and improved treatment of articles. Although the invention has been described with reference to preferred embodiments, various substitutions, alterations, and rearrangements might be made, and still the result would be within the scope of the invention. By way of example, a lamp assembly with an electroded bulb might be used. Likewise, a blower that is responsive to applied voltage, rather than the applied frequency might be utilized, together with a variable voltage motor driver.