Air-cooled lamp, and article treatment system and method utilizing an air-cooled lamp

[0002] This application is a continuation-in-part of U.S. patent application Ser. No. 09/989,037, filed Nov. 21, 2001.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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_pis 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_ois 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.

[0008] 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:

[0009] FIG. 1 is a block diagram of a first embodiment of an article treatment system in accordance with the present invention;

[0010] 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's intended full-power level, in order to provide satisfactory lamp bulb cooling, in accordance with the present invention;

[0011] FIG. 3 is a graph illustrating an example of a duty cycle of a lamp; and

[0012] FIG. 4 is a block diagram of a second embodiment of an article treatment system in accordance with the present invention.

[0013] 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 12a-12f. An article 10 is mounted on an article holder 14 at station 12a. 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 12athrough station 12band to an article treating location at station 12c. An air-cooled lamp assembly 22 is positioned to project radiation onto an article 10 when that article is at article treating location 12c. A rotation device 24 rotates counterclockwise in the embodiment of FIG. 1 to cause the article 10 at station 12cto 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.

[0014] 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.

[0015] 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 12c. 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 12cis 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.

[0016] Once the article 10 is treated by the radiation at article treating station 12c, continued rotation of article conveyor 12 brings the treated article 10 to station 12dat 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 12eand 12f, and back to station 12afor receipt of another article 10.

[0017] A sensor 40 is provided adjacent station 12fto detect the presence or absence of an article holder at that station. Because the stations 12a-12fare equally spaced about the circumference of article conveyor 12, detection of the presence or absence of an article holder at station 12fdetects the presence or absence of an article at the article treating location of station 12c. 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.

[0018] In operation, machine controller 16 actuates motor 18 to rotate article conveyor 12, bringing an article 10 to the article treating location at station 12c. When sensor 40 senses the article holder 14 at station 12f, 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 12c. 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.

[0019] After a time sufficient to permit complete treatment of the article 10 at article treating location 12c, machine controller 16 again actuates motor 18 to rotate article conveyor 12, advancing the treated article to station 12dfor removal of the treated article from article conveyor 12, and advancing the next article 10 from station 12bto station 12cfor 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 12c. 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.

[0020] 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 12cand 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.

[0021] 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'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 50aon curve 50 and point 52aon curve 52.

[0022] 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_pis air pressure, P is the power level of the power being provided to the air-cooled lamp as a percentage of the lamp's intended full-power level, and P_ois 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 P₀=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.

[0023] 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 50aand 52ain 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.

[0024] 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.

[0025] 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 26abased on the signals from sensor 40 which indicate the presence or absence of an article at article treating location 12c. Power supply 26aprovides 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 26a.

[0026] 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 26ato 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−S₀)², where P is the pressure, S is the blower speed, and S₀is the blower speed at which P=P₀.

[0027] 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.

[0028] 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.