Abstract:
Provided is a hand-held, portable, battery operated, reliable, and inexpensive, ultrasonic, visible vapor generator or fog generator for use in contamination sensitive areas, such as clean rooms. The ultrasonic fog generator is useful for visualizing laminar airflow between rooms, around equipment, around ventilation systems, and the like. The ultrasonic fog generator includes a housing and a battery pack sized to be carried by a user. The fog generator of the present invention, therefore, is capable of being easily moved around a room and does not take up valuable floor space in the clean room.

Description:
This application claims priority from U.S. Provisional Pat. Appln. Ser. No. 60/124,911, filed Mar. 17, 1999, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to equipment for visualizing airflow and, more particularly, to a hand-held ultrasonic fog generator for visualizing laminar airflow in contamination sensitive areas such as clean rooms. 
     2. Description of the Prior Art 
     Integrated circuit chips (ICs) are manufactured in hyper clean environments termed clean rooms. Even the smallest of particulates in a clean room can contaminate the wafer under process by introducing, e.g., short circuits that result in a failed IC and a consequent lower yield. Ventilation or air ducts and other such equipment are notorious particulate carriers. For this reason, it is critical to control the airflow in clean rooms. Fog generators are used in clean rooms to visualize laminar airflow emanating from ventilation and air ducts or other such equipment. 
     There are generally four types of visual vapor or fog generators on the market today. Carbon dioxide (CO 2 ) fog generators generate a visual fog using a solid block of CO 2 —dry ice—dropped into a super heated—140 deg F or higher—bath of deionized (DI) water. CO 2  fog generators require an alternating current (AC) power source to heat the DI bath. Once the DI bath is heated, however, the CO 2  fog generator can be disconnected from its AC power source. One disadvantage of the CO 2  fog generator is that the fog quantity it produces is unregulated. That is, the fog quantity cannot be tuned to the particular application because the fog it produces is largely based on the size of the block of dry ice. As the dry ice melts, the quantity of fog output from the fog generator diminishes. Another disadvantage is that CO 2  fog generators must be reconnected to its AC power source after each use to reheat the DI water bath. Yet another disadvantage is that CO 2  fog generators are large taking up valuable floor space in the clean room. CO 2  fog generators are also unwieldy being difficult to move around the clean room. 
     Helium (He) bubble generators, as the name implies, generate small He filled bubbles of water that float in the air at almost neutral buoyancy. The primary disadvantage with He bubble generators is that they only produce a small quantity of bubbles that do not easily visualize laminar airflow. 
     Ultrasonic fog generators create a fog by vibrating a bath of DI water using ultrasonic sound. Ultrasonic fog generators use an AC power source. One disadvantage of ultrasonic fog generators is that the unit must be kept stationary to operate properly because if the fog generator is tipped from a horizontal position, the transducers are exposed causing them to burnout and fail prematurely. 
     The ultrasonic fog generator disburses the water vapor through a long hose. The long hose causes the DI water vapor fog to condense on the inside and drip out the end of the hose creating a possible safety hazard by dripping on the clean room floor. If the ultrasonic fog generator is used over a chemical bath, the hose drippings may additionally contaminate the bath or wafer being fabricated therein. Much like the CO 2  fog generators, ultrasonic fog generators are large and unwieldy. 
     DI fog generators generate a fog by using steam from boiling DI water. The DI water is heated until boiling produces water bubbles. The bubbles are passed through a bath of liquid nitrogen (N 2 ) creating a super cooled fog that visualizes airflow. An example of a DI fog generator is described in U.S. Pat. Nos. 4,771,608 and 4,875,340 to Liu et al., incorporated herein by reference. As shown in both the above-mentioned Liu patents, DI fog generators are unusually large. DI fog generators are either fixedly installed or wheeled to the site. Another disadvantage of DI fog generators is that they require an AC power source and liquid N 2 . DI fog generators are very expensive to own and operate. DI fog generators are the most hazardous of all the above-listed fog generators because they require both a boiler to heat the DI water and extremely cold liquid N 2  to operate. 
     Accordingly, a need remains for an ultrasonic fog generator that is hand-held, portable, battery operated, reliable, and inexpensive to own and operate. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to overcome the disadvantages associated with prior art fog generators for visualizing airflow in clean rooms. 
     Another object of the present invention is to provide a hand-held and portable ultrasonic fog generator. 
     Yet another object of the present invention is to provide an ultrasonic fog generator that is battery operated allowing for ease of movement. 
     Yet another object of the present invention is to provide an ultrasonic fog generator that allows the user to choose between a battery pack and a remote power source. 
     Yet another object of the present invention is to provide an ultrasonic fog generator that includes easily accessible trigger switches for turning the fog vapor on and off. 
     Yet another object of the present invention is to provide an ultrasonic fog generator that delivers fog without dripping condensation from a fog exit or barrel. 
     Yet another object of the present invention is to provide an ultrasonic fog generator that includes sensors to prevent the operation of transducers without a predetermined level of water covering the transducers thereby eliminating transducer burnout and failure. 
     Yet another object of the present invention is to provide an ultrasonic fog generator that includes circuitry to prevent battery over charging and discharging. 
     Yet another object of the present invention is to provide an ultrasonic fog generator that is reliable and inexpensive to own and operate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features, and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment that proceeds with reference to the following drawings. 
     FIG. 1 is a perspective view of the fog generator of the present invention. 
     FIG. 2 is a perspective view of the fog generator shown in FIG. 1 without the barrel or the lid. 
     FIG. 3 is a perspective view of the bottom of fog generator shown in FIG.  1 . 
     FIG. 4 is a perspective view of the internal components of the fog generator shown in FIG.  1 . 
     FIG. 5 is a perspective cutaway view of the lid of the fog generator shown in FIG.  1 . 
     FIG. 6 is a perspective view of the water container of the fog generator shown in FIG.  1 . 
     FIG. 7 is an illustration of a method of using the fog generator shown in FIG.  1 . 
     FIGS. 8A-C are a front, side, and top view of the holster loop included in the battery pack of the fog generator shown in FIG.  7 . 
     FIGS. 9A-B are a side and front view of the clip included in the fog generator shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The hand-held ultrasonic fog generator of the present invention is used to visualize laminar airflow in contamination sensitive areas such as clean rooms. Referring to FIGS. 1-4, the fog generator  10  includes a housing  12  sized to be carried by a user. A handle  20  protrudes from a side of the housing  12  to accommodate the user&#39;s handgrip (not shown) allowing the fog generator to be hand-held and portable. An on/off switch  46  is located at a top end of the handle  20 . The on/off switch  46  is actuated by the user&#39;s finger as the user&#39;s hand grips the handle  20  (FIG.  7 ). The position of the on/off switch  46  allows the user to easily turn the fog generator on and off. The on/off switch  46  is, for example, push button S/ST switch, part number GCE-35-430STD manufactured by C&amp;K Components, Inc. headquartered in Massachusetts. The housing  12  is preferably made of injection-molded plastic or the like. 
     The housing  12  includes a lower cavity  14  separated from an upper cavity  16  by a stiffener member  18 . The lower cavity  14  is positioned at a lower end of the housing  12 . The lower cavity  14  substantially encloses a fan  26  operated by a fan switch  28 . The fan switch  28  is a common switch used to drive the fan  26  in one of two positions. A fan vent or opening  30  is positioned at a bottom end of the lower cavity  14 . The fan vent  30  allows air to be sucked into and pressurize the interior of the housing  12 . A user  74  sets the speed of the fan  26  by sliding the fan switch  28  in one of two positions. The fan is a readily available two-speed direct current (DC) fan, for example, 12 volt DC fan part number 273-243 manufactured by Radio Shack. The fan switch is also readily available two-position slide fan switch, for example, part number DTSP SW 10A manufactured by Radio Shack. 
     The housing  12  can rest on a plurality of feet  24  when not in use. The feet  24  are preferably made of a polymer such as rubber. A power inlet  22  is located on a bottom side of the housing  12  for receiving a removable power cord  64  (FIG. 7) that couples the battery pack  60  (FIG. 7) to the housing  12 . 
     A stiffener member  18  separates the lower cavity  14  from the upper cavity  16 . The stiffener member  18  includes a vent or opening  19  that channels air between the lower cavity  14  and the upper cavity  16 . The upper cavity  16  substantially encloses a container or receptacle  42  for containing water as best shown in FIG.  6 . The water in container  42  is not shown. The container  42  preferably contains DI water. The container  42  is substantially cylindrical having a bottom end  43  and sidewalls  44 . 
     A level sensor  40  (FIGS. 1-4) is positioned on a sidewall  44  mounted on a level sensor mount  41 . The level sensor  40  is wired through the on/off switch  46 . When the level sensor  40  detects that the water level has reached a predetermined low level, the level sensor  40  causes the on/off power switch  46  to turn off the fog generator. More particularly, the level sensor  40  will turn off the power to the fog generator  10  when it detects that the water is low enough to expose the transducers  36 . By doing so, the level sensor  40  prevents the transducers  36  from prematurely failing due to burnout. The level sensor  40  eliminates the requirement of having to keep the fog generator  10  level and stationary as is necessary with the prior art fog generators described previously. The level sensor  40  is, for example, part number PSF100A pressure sensor manufactured by World Magnetics, Inc. 
     Transducers  36  are mounted to a bottom end  44  of the container  42  on transducer mounts  38  as best shown in FIG.  6 . In the preferred embodiment, four transducers  36  are mounted on four transducer mounts  38 . The number and placement of the transducers  36 , however, is not critical and can change to accommodate differently sized and shaped housings  12 , among other considerations. The container  42  is preferably made of injection-molded plastic or the like. The transducer mounts  38  and the level sensor mount  41  are preferably molded into the container  42 . 
     The fog generator  10  uses ultrasonic vibrations to generate the fog that is used to visualize laminar airflow in clean rooms. A transducer driver circuit  34  operates each of the transducers  36 . The driver circuits  34  are printed circuit assemblies shown conceptually in block form in FIGS. 1-4. Where four transducers  36  are used—as shown in FIGS.  1 - 4 —four driver circuits  34  are necessary. It is possible, however, to integrate the transducer driver circuits  34  such that a one to one relationship between transducers  36  and transducer driver circuits  34  is not required. The transducer driver circuits  34  generate all of the control signals necessary to drive the transducers  36 . The transducer driver circuits  34  receive power from the battery pack  60  (FIG. 7) through the power inlet  22 . 
     The transducers  36  include a crystal (not shown) that vibrates in response to the power received from the battery pack  60  through the driver circuits  34 . The transducers  36  preferably vibrate at around 40,000 cycles per second. A metal plate (not shown) bonded to the crystal in the transducers  36  is submerged in the water contained in container  42 . The ultra high frequency vibrations produced by the transducer  36  atomize or vaporize the water in container  42  producing a cool fog (not shown) at the surface of the water. The fog is forced out the container  42  by the air sucked into the interior of the fog generator  10  by the fan  26 . 
     Each driver circuit  34  is mounted on a heatsink  32  through its driver circuit heatsink  35  as best shown in FIG.  1 . Where four driver circuits  34  are used, two driver circuits  34  are mounted on a top side of the heatsink  32  while the remaining two driver circuits  34  are mounted on a bottom side of the heatsink  32  through their corresponding driver circuit heatsinks  35 . The heatsink  32  is preferably made of extruded aluminum. The heatsink  32 , in turn, is mounted either to the bottom end of the housing  12  or a bottom end  43  of the container  42 . The air drawn from the vent  30  by the fan  26  cools the heatsink  32  and the driver circuit heatsinks  35 . 
     The transducers  36  are, for example, part number HV0604 manufactured by Stolz of North America, Inc. The transducer driver circuits  34  are, for example, part number HV0610 also manufactured by Stolz of North America, Inc. 
     Referring to FIG. 5, a lid  52  caps the container  42 . A lip  53  surrounds the perimeter of the lid  52 . The lip  53  allows the lid  52  to rest on the top end  45  of the container  42 . The lid includes openings  50  that allow fog generated inside of the container  42  to escape. The lid  52  includes a labyrinth seal  54  that prevents the water contained in container  42  from running out of the barrel  56  (FIGS. 1-3) or back into the container  42  when the fog generator  10  is not held in a horizontal position. 
     Referring to FIGS. 1-3, the barrel  56  is positioned on the top end of the fog generator  10 . The barrel  56  includes a condensate trap  58  to keep water condensed inside from dripping out the barrel  56 . The condensate trap  58  is shaped as a lip on the end of the barrel  56 . The condensate trap  58  eliminates safety hazards when the fog generator  10  is used over chemical baths or water sensitive equipment by preventing condensed water from dripping out of the barrel  56 . The barrel  56  shown in FIGS. 1 and 3 has a substantially square cross section and is about 6 inches long. The barrel  56 , however, can have a variety of shapes and sizes depending on the application. 
     Referring again to FIGS. 1-6, the container  42  includes an air vent or opening  48  in communication with a top end of the handle  20  and a lid opening  49  (FIG.  5 ). Air is initially sucked into the interior of the housing  12  by the fan  26  through the fan vent  30  as explained above. The air is then channeled from the lower cavity  14  to the upper cavity  16  and the handle  20  through the opening  19  on the stiffener member  18 . The air pressurizes the interior of the housing  12  and escapes through the container opening  48  and the lid opening  49 . The air then travels through the labyrinth seal  54  of the lid  52  down into the container  42  and mixes with the fog generated by the transducers  36  inside of the container  42 . The fog/air combination then travels into the openings  48  and  49  down the barrel  56 . Once the power switch is depressed to an on position, fog is generated out of the barrel  56  almost instantaneously. 
     Referring to FIG. 7, the fog generator includes a battery pack  60  connected to the fog generator  10  using a removable power cord  64 . The removable power cord  64  is plugged into the power inlet  22 . The battery pack  60  preferably includes four 12V sealed lead-acid batteries (not shown) that provide 48 volts DC power to the fog generator  10 . The number and voltage of the batteries can vary depending on the application. The batteries are, for example, part number BP2.3-12V batteries from Northwest Battery Supply. The battery pack  60  also includes a charging/discharging circuit (not shown) that controls the charging, discharging, charge level indication, and fusing of the batteries in the battery pack  60 . The charging/discharging circuit is, for example, circuit part number 845-4800 fuse holder panel mount manufactured by Little Fuse, Inc. available through Allied Electronics, Inc. The battery pack  60  allows the user  74  to transport the unit without requiring long extension cords or power outlets. 
     The battery pack  60  includes a wide strap  66  that allows the battery pack  60  to be carried by a user  74  over his or her shoulder. The battery pack  60  is made of injection-molded plastic or the like. The battery pack  60  includes a holster loop  76 . The fog generator  10  includes a clip  78  that mounts on the holster loop  76  allowing the fog generator  10  to clip on the battery pack  60  for hands free transportation from one location to another. The holster loop  76  is shown in FIGS. 8A-C. The clip  78  is shown in FIGS. 9A-B. When fully charged, the batter pack  60  will give up to 1.5 hours of continuous power to the fog generator  10 . The combined weight of the fog generator  10  and the battery pack  60  is around 20 pounds. 
     The fog generator  10  includes a common battery charger (not shown) for charging and discharging the battery pack  60 . The battery charger is a common off the shelf unit that recharges the battery pack  60  in about 4 hours using a common AC power source. The battery charger is connected to the battery pack  60  through the same outlet as is used to connect to the fog generator  10  to the battery pack  60 . The battery charger is connected to the AC power source using a 25-foot removable cord (not shown) that can be used in place of the battery pack  60  to power the fog generator  10 . The battery charger includes a printed circuit assembly that automatically changes from a charge mode (for charging the battery pack  60 ) to a power mode (for directly powering the fog generator  10 ). An example of the battery charger is model number PSC-241000A (24V/1A) manufactured by Power Sonics, Corporation headquartered in San Diego, Calif. 
     Although the fog generator of the present invention has been described with respect to its use in clean rooms, a person skilled in the art would recognize other applications of the fog generator herein described where a visual vapor or fog is desired. 
     Having illustrated and described the principles of my invention in a preferred embodiment thereof, it should be readily apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. I claim all modifications coming within the spirit and scope of the accompanying claims.