Abstract:
An electrostatic spraying device which is configured and disposed to electrostatically charge and dispense a product from a supply to a point of dispersal. The electrostatic spraying device has a reservoir configured to contain the supply of product and a nozzle to disperse the product. The nozzle being disposed at the point of dispersal. The nozzle has an exit orifice. A channel is disposed between the reservoir and the nozzle, wherein the channel permits the electrostatic charging of the product upon the product moving within the channel. A positive displacement mechanism is used to move the product from the reservoir to the nozzle. A power source supplies an electrical charge. A high voltage power supply, high voltage contact, and high voltage electrode are used. A portion of the high voltage electrode being disposed between the reservoir and the nozzle is used to electrostatically charge the product within the channel at a charging location. A distance between the charging location and the nozzle exit orifice is governed by the following relationship: V O /d&lt;100,000, wherein V O =an output voltage of said high voltage power supply and d=linear distance between the charging location and said nozzle exit orifice. A moveable electrode cover may be used to substantially conceal the high voltage contact when the disposable cartridge is removed from the device. The high voltage electrode may recess when the disposable cartridge is removed from the device or resurface when the disposable cartridge is inserted into the device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation-in-part of our earlier applications, U.S. Ser. No. 09/377,332, filed on Aug. 18, 1999 and U.S. Ser. No. 09/377,333, filed on Aug. 18, 1999. 
     
    
     
       TECHNICAL FIELD OF INVENTION  
         [0002]    This invention relates to a portable electrostatic spray device designed for personal use. More particular, this invention is focused on providing improvements to both the electronic circuit and mechanical designs which lead to the reduction/elimination of shock potentials, thereby improving the safety of the device for the user.  
         BACKGROUND OF THE INVENTION  
         [0003]    In U.S. Pat. No. 4,549,243, Owen describes a spraying apparatus that can be held in the human hand for applications such as graphic work where it is desired that the area to which the spray is applied can be precisely controlled (Col 1, 11 5-9). Owen acknowledges both the benefits and hazards associated with stored capacitance when he describes that the high voltage circuit has sufficient capacitance that, during use, the desired electrical gradient at the nozzle is maintained between pulses but on the other hand should have a low stored energy, preferably less 10 mJ, so that no safety hazard is presented to the user for example by accidental contact of the user with the nozzle or on contact of the nozzle with an earthed surface (Col 5, 11 52-59). Owen further describes the occurrence of spark discharges and offers a solution to reduce such discharges, “ . . . when a nozzle with a high potential applied thereto is brought close to an earthed surface, spark discharges from the nozzle to the earthed surface may occur instead of spraying; it is preferred that the field strength at the nozzle is such that the maximum distance of the nozzle from an earthed surface at which spark discharges occur is less than 5 mm” (Col 6, 11 14-20). Although recognizing the dangers associated with stored capacitance within the device, Owen fails to offer a means of dissipating said capacitance and chooses to try to design around it. The approach of designing around the internal capacitance, limiting to 10 mJ or less, limits the size/quantity of capacitors within the circuitry which in turn limits the ability to hold the output high voltage at a steady value. Further, Owen&#39;s electrical gradient design of limiting the distance at which a spark discharge will occur is not a consumer viable solution as it is very likely that a consumer will come in direct contact with the nozzle area (i.e. less than the 5 mm distance) either while the device is in operation or shortly thereafter before stored charge has been dissipated from the device.  
           [0004]    In U.S. Pat. No. 5,222,664, Noakes provides an electrostatic spraying device with the added benefit of a shock suppression by means of high voltage circuitry having a bi-polar output with a frequency no greater than 10 Hz. The system described by Noakes uses an alternating polarity power supply for generation of a high voltage potential. Noakes recognizes for example, where a direct current electrostatic spraying device which is wholly hand held is used (and hence where no other path to ground exists other than through the operator), and if the operator is or becomes substantially isolated from ground (for instance, as a result of standing on a synthetic fiber carpet or wearing shoes having soles of insulating material), during spraying, charge will accumulate on the operator and, if the operator subsequently touches a grounded conductor, he/she will experience an electrical shock (Col 1, 11 46-56). Owen offers a solution for such problem by thus appropriate selection of the frequency (of the high voltage power supply switching between opposite polarities), it is possible to eliminate the sensation of electrical shock by the operator or at least reduce the sensation to a level at which the risk of an accident as a result of an involuntary reaction by the operator is reduced (Col 2, 11 26-30). However, the solution that Noakes sets forth as a means to reduce the potential for the user to build-up a charge and subsequently discharge this charge in the form of a shock is to provide specifications for the switching frequency of the alternating polarity power supply. While this may represent a viable solution for some cases, this does not find application in electrostatic spraying devices that generate high voltage power using a rectifier which use a single polarity output.  
           [0005]    In U.S. Pat. No. 5,337,963, Noakes provides for an electrostatic spray device for the spraying of liquids and is particularly concerned with devices for spraying liquids into the surroundings. One aspect of the device set forth by Noakes is that when the cartridge is in place in the compartment and is connected to the high voltage output of the generator, the fact that the voltage is applied through the liquid column in the narrow bore of the tube will provide a high resistance path (and hence suppression of shock that would otherwise be experienced by touching the tip of the tube) by virtue of the resistivity of the liquid and the cross-section and length dimensions of the tube bore (Col 10, 11 22-30). This design, while offering some means of shock suppression, is not a consumer viable system in that it ignores the scenario where the column of liquid between the charging location and the discharge point is no longer filled with product, and therefore no longer offering a resistive path. This is the likely scenario where a user would receive a shock from such a device.  
         SUMMARY OF THE INVENTION  
         [0006]    An electrostatic spraying device which is configured and disposed to electrostatically charge and dispense a product from a supply to a point of dispersal. The electrostatic spraying device has a reservoir configured to contain the supply of product and a nozzle to disperse the product. The nozzle being disposed at the point of dispersal. The nozzle has an exit orifice. A channel is disposed between the reservoir and the nozzle, wherein the channel permits the electrostatic charging of the product upon the product moving within the channel. A positive displacement mechanism is used to move the product from the reservoir to the nozzle. A power source supplies an electrical charge. A high voltage power supply, high voltage contact, and high voltage electrode are used. A portion of the high voltage electrode being disposed between the reservoir and the nozzle is used to electrostatically charge the product within the channel at a charging location. A distance between the charging location and the nozzle exit orifice is governed by the following relationship: V O /d&lt;100,000, wherein V O =an output voltage of said high voltage power supply and d=linear distance between the charging location and said nozzle exit orifice. A moveable electrode cover may be used to substantially conceal the high voltage contact when the disposable cartridge is removed from the device. The high voltage electrode may recess when the disposable cartridge is removed from the device or resurface when the disposable cartridge is inserted into the device.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    While the specification concludes with claims particularly pointing out and distinctly claiming the present invention it is believed that the same will be better understood from the following description, taken in conjunction with the accompanying drawings, in which:  
         [0008]    [0008]FIG. 1 is an exploded isometric view of a hand-held, self-contained electrostatic spraying device having a disposable cartridge;  
         [0009]    [0009]FIG. 2 is an assembled isometric view of the device within FIG. 1;  
         [0010]    [0010]FIG. 3 is an exploded isometric view of the disposable cartridge within FIG. 1;  
         [0011]    [0011]FIG. 4 is a cross-sectional view of the exiting portion of the device within FIG. 1;  
         [0012]    [0012]FIG. 5 is a schematic view of the electrical circuitry of one embodiment of an electrostatic spray device of the present invention;  
         [0013]    [0013]FIG. 6 is a schematic view of a portion the electrical circuitry of another embodiment of an electrostatic spray device of the present invention;  
         [0014]    [0014]FIG. 7 is a schematic view of a portion the electrical circuitry of another embodiment of an electrostatic spray device of the present invention;  
         [0015]    [0015]FIG. 8 is a schematic view of a portion the electrical circuitry of another embodiment of an electrostatic spray device of the present invention;  
         [0016]    [0016]FIG. 9 is a schematic view of a portion the electrical circuitry of another embodiment of an electrostatic spray device of the present invention;  
         [0017]    [0017]FIG. 10 is an exploded isometric view of the insert sleeve and accompanying parts within FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    Referring to FIGS. 1 and 2, a hand-held, self-contained electrostatic spraying device  5  having a disposable cartridge  200  is shown. Disposable cartridge  200  may contain a variety of product, including but not limited to, cosmetics, skin creams, and skin lotions. The product in disposable cartridge  200  may be positively displaced (discussed infra) and powered by gearbox/motor component  10 . Gearbox/motor component  10  may be fixed onto a left or first housing  30 . The gearbox/motor component  10  can be affixed into place mechanically, adhesively, or by any other suitable technique. Gearbox/motor component  10  preferably comprises a precision motor  10   a  connected to a gearbox  10   b.  Power source  20  provides power to the device. An example of a suitable power source  20  includes, but is not limited to, two “AAA” type batteries. The power source  20  provides power to the device through the control circuit  60 , the high voltage power supply  40 , and then the high voltage contact  50 , which contacts the disposable cartridge  200 . High voltage power supply  40  is powered and controlled by control circuit  60  (discussed infra). Power-on switch  80  permits the user to cause an interruption between power source  20  and circuit control  60 . Power-on switch  80  is designed such that voltage is supplied to the remainder of the circuit only when switch  80  is in the “ON” or closed position. Apply switch  70  permits the user to selectively activate motor  10   a,  thereby activating the delivery and spraying of the product. Gearbox/motor component  10  has a driver  90  fastened to a shaft (not shown in FIGS. 1 &amp; 2, see FIG. 3) of gearbox  10   b,  for example, with a set screw (not shown). Driver  90  has a number of protruding fingers, for example, three, which can fit into the matching recesses on the back of actuator  240 .  
         [0019]    Referring now to FIG. 4, a first aspect of this invention is directed at defining a spark gap  300  between the charging location  310  (e.g. a point within the open chamber of disposable cartridge  200  and also near high voltage electrode  210 ) and the nozzle exit orifice  280  (e.g. point at which spray exits device  5 ). In order to minimize the risk of electrical shock in the form of a tactile discharge to the user, it is essential to maximize the distance between charging location  310  and nozzle exit orifice  280 . It is currently believed that the prior art fails to teach this important relationship necessary to minimize the risk of electrical shock.  
         [0020]    The preferred spacing between the charging location  310  and nozzle exit orifice  280  is governed by the following relationship:  
           V   O   /d&lt; 100,000  
         [0021]    Where:  
         [0022]    V O =output voltage of high voltage power supply  40  (v)  
         [0023]    d=spark gap  300  (ie: linear distance between charging location  310  and nozzle exit orifice  280  (in))  
         [0024]    As shown, it is desirable for this quotient (V O /d) to be limited to preferably less than 100,000 V/in, more preferred is to limit this quotient to less than 70,000 V/in and most preferred is limiting this quotient to less than 50,000 V/in. Although not limited to, it is preferred that “V O ” range from 10,000 V to 20,000 and that “d” range from 0.1 in to 0.5 in. One skilled in the art could appreciate “V O ” and “d” values outside of these ranges so long as the above quotient was maintained.  
         [0025]    In a first embodiment of this invention, as exampled in FIGS. 3 and 4, disposable cartridge  200  has a conductive shield  210  which is positioned substantially around the outer perimeter of product reservoir  220 . Conductive shield  210  may be constructed using conductive plastic (e.g. acrylonitrile butadiene styrene (ABS) filled with 10% carbon fibers), metal (e.g. aluminum) or any other suitable material. Conductive shield  210  may be formed as an integral part to cartridge insulator  260 , such as through co-injection or two shot molding or any other manufacturing techniques. Alternatively, conductive shield  210  may be formed separately and then later connected to cartridge insulator  260  by any suitable technique, including but not limited to, force fitting. Actuator  240  is located at the non-discharge end of disposable cartridge  200 . Actuator  240  may have internal threads (not shown) for passage of one end of a threaded shaft  250 , and a snap bead  245  to snap into an open end of product reservoir  220 . The opposite end of threaded shaft  250  can have a piston  230  which moves about. The threaded shaft  250  can thereby connect the piston  230  with actuator  240 , such that piston  230  can slide along an inner surface of product reservoir  220 , toward a nozzle  270 , in response to the turning of actuator  240  by the gearbox/motor component  10 . This movement of piston  230  can thus displace product from the product reservoir  220 .  
         [0026]    Electrical shock in the form of a tactile discharge to the user is likely to occur when no product is located within spark gap  300 . Such a condition can exist, for example, when the user is using a disposable cartridge  200  for the first time (ie: before spark gap  300  is filled with product during a first product application). In this condition the above mentioned relationship is optimized (ie: minimize the quotient value) to prevent exceeding the break-down potential of air when a grounded object such as a the operator&#39;s finger is brought within immediate proximity of nozzle exit orifice  280 .  
         [0027]    For conductive fluids, electrical shock in the form of a tactile discharge to the user is also likely to occur when product fills spark gap  300 . Such a condition exists, for example, when the user has already fully dispensed product from disposable cartridge  200  and thus the product pathway is full. In this condition the above mentioned relationship may need to be set at a quotient value less than  100 , 000  to prevent an electrical shock from occur. The actual reduced quotient value will be dependent upon the conductivity of the conductive fluid (ie: higher conductivity value of the fluid will require a lower quotient value).  
         [0028]    It may also be appreciated by one skilled in the art that use of the above mentioned relationship must also be balanced with the need to maintain a certain voltage at nozzle exit orifice  280 . That is, ideally, for electrostatic spraying devices where charging of the fluid occurs at a point remote from the nozzle (e.g. charging location  310 ), the ideal situation is for the charging of the fluid to occur at a maximum distance away from said nozzle exit orifice  280 , thereby providing the highest degree of safety. However, there does exist a distance, that when charging occurs beyond said distance, the voltage drop within the volume of fluid between said charging location  310  and said nozzle exit orifice  280  is sufficiently large enough so as to effect the spray formation. Spray formation is affected because the voltage at nozzle exit orifice  280  is below that needed to form an optimal spray. Therefore, this distance must be optimized so as to not to significantly affect the spray quality.  
         [0029]    In yet another aspect of this invention, as exampled in FIGS. 1 and 10, a moveable electrode cover  400  is added. Electrode cover  400  is designed such that it substantially conceals high voltage contact  50  when disposable cartridge  200  is removed from device  5 . Electrode cover  400  may be connected to insert sleeve  110 . Insert sleeve  110  may house disposable cartridge  200 . Electrode cover  400  is movably connected within slide channel  410 . Bias springs  420  are positioned such that when no disposable cartridge  200  is within insert sleeve  110 , bias springs  420  slide electrode cover  400  in a normally closed position that shields high voltage contact  50 . When disposable cartridge  200  is placed within insert channel  110 , electrode cover  400  is slid back in slide channel  410  to expose high voltage contact  50 , such that it can then contact conductive shield  210  on disposable cartridge  200 . Electrode cover  400  is of sufficient insulative quality so as to prevent electrical discharges from high voltage contact  50  through electrode cover  400  to a user.  
         [0030]    A further embodiment of electrode protection could also be in the form a high voltage electrode in the device positioned such that said high voltage electrode recesses when a cartridge is removed and makes proper contact with the cartridge electrode only when a cartridge is properly installed (not shown).  
         [0031]    [0031]FIG. 5 shows an electrical schematic of one embodiment of an electrostatic spraying device. The power source  510  shown can be a battery or other power source known in the art. For example, the power source can be one or more user replaceable battery such as two standard “AAA” batteries. Alternatively, the power source could be user-rechargeable cells, a non-user serviceable rechargeable power pack, or an external source (i.e. “line” supply). In at least one arrangement of the circuitry, power source  510  can be separated from the rest of the circuit by a power switch  520 . The power switch  520  can extend the active life of a self-contained power source  510  such as a battery. The power switch  520  can also add a margin of safety to a line-voltage power supply by supplying power to the remainder of the circuit only when the power switch  520  is closed. In one embodiment, the power switch  520  can be a toggle switch that is able to maintain its setting until a later actuation. When switch  520  is turned to the “on” position, power is supplied to the DC/DC Converter  530 .  
         [0032]    The DC/DC Converter  530  receives an input voltage supply from power source  510 , for example, a nominal 3.0 volt supply from two conventional “AAA” type batteries, and converts that to a higher voltage signal such as a 5.0 volt supply. The DC/DC Converter  530  can be, for example, a 3 to 5 V DC converter available from Linear Technology Corporation (Part number LT1317BCMS8-TR). The DC/DC Converter  30  can also be used to send a signal to indicator  540 . This signal can be either a portion of the supply signal from power source  10 , or a portion of the output signal, for example 5.0 volts. The indicator  540 , for example, can be an LED that emits light in the orange range of the visible electromagnetic (EM) spectrum. As shown in FIG. 5, the indicator  540  can be arranged to emit visible light only when the power switch  520  is in the “on” position and sufficient voltage is supplied to the indicator  540  from DC/DC Converter  530 . A user controlled apply switch  545  can be depressed or turned to the “on” position, depending on the type of switch employed, to complete the power supply circuit and provide power to the voltage regulator  550 . The voltage regulator  550  can control the input voltage to a motor  560 , if necessary. The nominal voltage output from the voltage regulator can be about 3.3 volts. The voltage regulator  550  can also send an output signal to the high voltage switch  570 . The high voltage switch  570 , for example, can be a transistor or diode element such as a transistor from NEC Corporation part number 2SA812.  
         [0033]    The high voltage switch  570  supplies power to the remaining high voltage generation circuitry in response to a signal from the voltage regulator  550 . The high voltage switch  570  sends a signal to both high voltage control block  580  and a signal generator such as square wave generator  590 . The high voltage control block  580  compares a signal from storage capacitor  610  and current limiter  670  to an internally set reference voltage. Depending upon the value of the feedback signal from storage capacitor  110  and/or a signal from the current limiter  670 , the high voltage control block  580  will send either an “ON” or an “OFF” signal to the DC/DC converter  600 . The high voltage control block  580 , for example, can be an op-amp such as Toshiba Corporation part number TC75W57FU.  
         [0034]    The DC/DC converter  600  converts a lower input voltage to a higher output voltage. For example, the DC/DC converter  600  can convert a nominal input voltage of about 5.0 volts to a higher nominal output voltage of about 25.0 volts. The output from the DC/DC converter  600  charges the storage capacitor  610 . The storage capacitor  610  provides an input voltage to the primary coil of the high voltage transformer  620 . The frequency of the higher voltage output of DC/DC converter  600  is controlled, as described in more detail later, by a feedback loop to ensure that a substantially constant supply, such as about a 25.0 volts supply, is available to the high voltage transformer  620  from the storage capacitor  610 . The DC/DC converter  600  can be, for example, a DC/DC Converter from Toshiba Corporation such as part number TC75W57FU. The high voltage switch  570  can also send an “ON” signal to the square wave generator  590 , which is also connected to the primary coil of the high voltage transformer  620 . This results in about a 25.0 volt peak to peak AC pulses being generated through the primary coil of the high voltage transformer  620 . The square wave generator  590  can be, for example, an op-amp element from Toshiba Corporation such as part number TC75W57FU. The turn ratio of the high voltage transformer  620  can be, for example, about 100:1 such that an input voltage of about 25.0 volt at the primary coil would result in about a 2.5 kV (2500 volt) output voltage from the secondary coil. The output voltage from the high voltage transformer  620  can then be supplied to a voltage multiplier  630 .  
         [0035]    The voltage multiplier  630  rectifies the output signal from the high voltage transformer  620  and multiplies it to provide a higher voltage DC output voltage. If the output voltage of the high voltage transformer  620  is about a 2.5 kV AC signal, for example, the voltage multiplier  630  could rectify this signal and multiply it to provide a higher voltage DC output such as a 14.0 kV DC output voltage. In one embodiment, the voltage multiplier  630  can be a six stage Cockroft-Walton diode charge pump. A stage for a Cockroft-Walton diode charge pump is commonly defined as the combination of one capacitor and one diode within the circuit. One skilled in the art would recognize that the number of stages needed with a voltage multiplier is a function of the magnitude of the input AC voltage source and is dependent upon the required output voltage. In one embodiment, the high voltage transformer  620  and the voltage multiplier  630  can be encapsulated in a sealant such as a silicon sealant such as one available from Shin-Etsu Chemical Company, Ltd. as part number KE1204(A.B)TLV. By encapsulating the high voltage transformer  620  and the voltage multiplier  630  in the sealant, the electrical leakage and corona discharge from these high voltage components can be reduced to increase their efficiency.  
         [0036]    A current limiting resistor  640  can be located between the output of high voltage multiplier  630  and the high voltage electrode  650 . The current limiting resistor  640  can be used to limit the current output from the high voltage multiplier  630  available to the high voltage electrode  650 . In one particular embodiment, the current limiting resistor  640  could be, for example, about 20 megaohms. One skilled in the art would recognize, however, that if a higher output current is desired, then a current limiting resistor with a lower resistance would be desired. Conversely, if a lower output current is desired, then a current limiting resistor with a higher resistance would be desired. The high voltage electrode  650  can be made from a suitable metal or conductive plastic, such as acrylonitrile butadiene styrene (ABS) filled with 10% carbon fibers. A bleeder resistor  660 , which is described in more detail below, can also be connected as shown in FIG. 5. The current limiter  670  is also connected to the output circuitry of the high voltage multiplier  630 .  
         [0037]    A ground contact  680  can also be provided to establish a common ground between the circuitry of the electrostatic spraying device and the user in order to reduce the risk of shocking the user. Further, in personal care applications, the ground contact  680  can also prevent charge from building-up on the skin of the user as the charged particles accumulate on the skin of the user. The ground contact  680  can be integrated into apply switch  545  and/or substantially adjacent to apply switch  545  such that the user cannot energize the motor  560  and the high voltage supply circuitry without simultaneously grounding themselves to the device. For example, the apply switch  545  can be made of metal and/or the ground contact can be a conductive contact or a grounding electrode can be located next to apply switch  545 .  
         [0038]    A further aspect of this invention allows the electrostatic spray device to reduce after-spray. After-spray is defined as when the electrostatic spraying device momentarily continues to spray product after power has been shut down to the high voltage power supply. Electrostatic spray devices with integral high voltage power supplies typically use capacitor-diode ladders to step-up output voltage from a primary high voltage transformer. One suitable capacitor-diode ladder is a Cockroft-Walton type diode charge pump. Capacitors are also used in electrostatic spray circuitry to improve the quality in the high voltage output and to reduce variations or noise. After the user turns off the device, the capacitors function as electrical storage elements and store the high voltage charge until the charge is dissipated such as through corona leakage to the atmosphere or a spark discharge to a point having a lower electrical potential (e.g., a shock to a user). This stored charge can continue to provide power to the high voltage electrode  650  and may create enough of a potential difference between the product and nearby surfaces to allow for the product to spray after the power has been cut off to the high voltage power supply until the charge in the capacitors is sufficiently dissipated.  
         [0039]    An after-spray condition is undesirable because the device continues to spray product after the user has turned off the device and the spray quality is inconsistent because the charge-to-mass ratio significantly varies. The desired charge-to-mass ratio is not maintained because there is not a consistent supply of high voltage current available to completely atomize the product into a spray. The charge stored within the device can partially atomize the product for a period of time while the charge dissipates to create an after-spray. Since the voltage supply to atomize the product is not constant, the charge-to-mass ratio of the resulting spray will vary resulting in the production of a spray that has varying spray quality. Further, the after-spray condition can produce a spray at an unintended time and/or location, such as continuing to spray after the user has placed the device in a purse or storage cabinet. This can create an unexpected and undesirable mess.  
         [0040]    After-spray can be reduced or eliminated by rapidly discharging the capacitive elements after the power has been shut down to the high voltage power supply. In a first embodiment of this invention, a high voltage resistor, such as bleeder resistor  660  shown in FIG. 5, can be connected between the high voltage output electrode  650  and a point at a lower potential within the device. The bleeder resistor  660  can provide a path by which excess stored energy in the device, such as the energy stored in the capacitors within the voltage multiplier  630 , can be dissipated in a relatively short period of time after the user has completed the spraying operation, thereby reducing the occurrence of after-spray. The bleeder resistor  660  should be selected to have a large enough resistance so that the impedance of bleeder resistor  660  will be significantly high when compared to the output current limiting resistor and the spray load so as to not dramatically effect the quality of spray or output of the high voltage generator during normal operation. If the value of bleeder resistor  660  is too low, bleeder resistor  660  will provide a path of lesser resistance than the resistance represented by the spraying operation. In this case bleeder resistor  160  will drain more current then desired during normal spraying operation. When the current passing through bleeder resistor  660  in normal spraying operation is too high, there will be insufficient current available for atomizing and charging the product. The bleeder resistor can further shorten the life of a portable power source such as a battery. The bleeder resistor  660  should, however, have a resistance low enough so as to allow for dissipation of stored energy in a relatively short period of time. The time needed to dissipate the stored energy of the device can be estimated by using the value of said capacitance multiplied by the value of bleeder resistor  660  to determine the value of an RC time constant. This relationship is given by:  
         τ A   =C   D   ×R   B    
         [0041]    Where:  
         [0042]    τ A =Time to drain approximately 63% of the stored capacitance from spraying device (sec)  
         [0043]    C D =Device capacitance (F)  
         [0044]    R B =Value of bleeder resistor (Ω)  
         [0045]    This RC time constant, τ A , represents the approximate time required to dissipate approximately 63% of the charge of the storage device. The term C D  represents a sum of the capacitance from conventional capacitor elements within the high voltage power supply circuit as well as capacitance of the product reservoir and other stray capacitance from within the device. Therefore, while applying this relationship, which has been adopted from conventional circuitry, it will be understood that in practice, τ A  represents a time in which greater than 63% of the stored charge is dissipated.  
         [0046]    In some cases, the charge dissipated within τ A  is sufficient to reduce the charge within the device to a point where after-spray is reduced or eliminated. However, in some cases, the time τ A  may not be sufficient time to drain enough charge to reduce or completely eliminate after-spray. In these cases, the designer may desire to drain the entire stored charge from the within the device. In this case, it will be understood that the following relationship approximates a time, τ B , that will ensure complete dissipation of any stored charge. This relationship is given by:  
         τ B =5×τ A =5× C   D   ×R   B    
         [0047]    Where:  
         [0048]    τ B =Time to drain 100% of the stored charge from the spraying device (sec)  
         [0049]    C D =Device capacitance (F)  
         [0050]    R B =Value of bleeder resistor (Ω)  
         [0051]    One suitable range for a typical bleeder resistor is between about 1 MΩ and about 100 GΩ, another suitable range is between about 500 MΩ and about 50 GΩ, and yet another suitable range is between about 1 GΩ and about 20 GΩ. In one embodiment, for example, it may be desirable to completely drain the stored charge of the power supply in less than about 60 seconds, preferably in less than about 30 seconds, and most preferably in less than about 5 seconds. Using an example to illustrate, if it is desirable to dissipate at least about 63% of the stored charge of an electrostatic spraying device having a capacitance of about 500 pF (the device capacitance can be estimated by the sum of the capacitance in the high voltage power supply, the capacitance within the product reservoir and an estimate of the stray device capacitance) in about 5 seconds or less would require a bleeder resistor having a resistance of no more than about a 10 GΩ resistor.  
           R   B =5.0  sec/ 500  pF= 10  GΩ   
         [0052]    Depending upon the distribution of the capacitance (within voltage multiplier  630 , the product reservoir capacitance and other stray capacitance) the 10 GΩ resistor, although dissipating at least 63% of the stored capacitance, may not in practice always eliminate the after-spray condition. Therefore, to ensure that 100% of the device capacitance is drained in the same 5 second interval the resistance of the bleeder resistor  660  would need to be no more than about 2 GΩ.  
           R   B =(5.0  sec/ 500  pF )/5=2  GΩ   
         [0053]    In at least one embodiment, for example, bleeder resistor  660  could be a high voltage resistor having a resistance of about 10 GΩ such as the high voltage resistor available from Nihon Hydrajinn Company available under the part number LM20S-M 10G.  
         [0054]    In another embodiment of this invention shown in FIG. 6, a mechanical switch  690  can be provided to reduce the effects of after-spray. The high voltage mechanical switch  690  performs a similar function as bleeder resistor  660  with the exception that the high voltage mechanical switch  690  is not an active circuit element during normal spraying operation. Rather, the mechanical switch is arranged so that during normal spraying operation the switch is in the open position and is not drawing any current. However, when the user intends to cease the spraying operation and de-energizes the device, the high voltage mechanical switch  690  is shifted from the open position to the closed position so that a conductive path exists between the output electrode directly to the grounded side of the device circuit, thereby providing a nearly instantaneous release for any stored charge within the device. One advantage of the high voltage mechanical switch  690  design is that the conductive path to ground does not need to include a resistor and allows for a faster discharge rate. Further, the conductive path is only available when the device is de-energized, i.e., in the off position, and does not interfere with normal spraying operation by draining energy from the high voltage electrode  650  and will not require the high voltage generating circuitry to generate excess power to compensate for power losses associated with the bleeder resistor  660 .  
         [0055]    In yet another embodiment shown in FIG. 7, the device comprises a high voltage electrical switch  700 , such as a transistor, in place of bleeder resistor  660  shown in FIG. 5. During normal spraying operation, the switch is in the open position and the conductive path to a point of lower potential of the circuitry is not active. However, upon the operator de-energizing the device, the switch is closed and the conductive path to a point of the circuit having a lower potential is then available to drain the stored charge in the device. Again, the high voltage electrical switch  700  can provide a lower resistance than the bleeder resistor  660  and, thus, allows for a quicker discharge of the stored charge in the device. The high voltage electrical switch  700  further provides a conductive path that is only available when the device is de-energized, i.e., in the off position, and does not interfere with normal spraying operation by draining energy from the high voltage electrode  650  and will not require the high voltage generating circuitry to generate excess power to compensate for power losses associated with the bleeder resistor  660 .  
         [0056]    One skilled in the art may appreciate that either of the arrangements shown in FIG. 6 or FIG. 7 may also include a bleeder resistor  660  such as shown in FIG. 8. In some cases it may be desirable to control the rate at which the stored capacitance is discharged. In such a case, the bleeder resistor  660  can be connected to either the high voltage mechanical switch  690  or the high voltage electrical switch  700  as shown in FIG. 8. Further, one skilled in the art will also recognize that a bleeder resistor and/or mechanical or electrical switches may be arranged in other configurations. For example, FIG. 9 shows one alternative configuration in which the bleeder resistor  660  is connected between the voltage multiplier  630  and the current limiting resistor  670  and a point at a lower potential.  
         [0057]    Yet another aspect of this invention, as exampled in FIG. 5, is providing current limiting control circuitry to control the output current from the high voltage supply means. Current limiter  570  monitors the output current at the first stage of voltage multiplier  530 . Current limiter can be an op-amp element of the type, for example, from Toshiba Corporation, part number TC75W57FU. Current limiter, as shown, tracks the current in ground return loop of voltage multiplier  630 . When the output current exceeds a predetermined value, said predetermined value set using a reference voltage to the op-amp, current limiter  670  sends an override signal to high voltage control block  580 . The override signal sent to high voltage control block  580  overrides the signal from ground return loop  630  and changes the output from to DC/DC converter  600  from “ON” to “OFF”, thereby preventing a further increase in current through voltage multiplier  630 . When the current in feedback loop  710  drops below the predetermined setpoint, the signal from current limiter  670  to high voltage control block  680  changes, thereby allowing high voltage control block  580  to resume monitoring feedback loop  710  and sending an “ON” signal to DC/DC converter  600 . The need for current limiter  670  is very important, for example, when using a circuit with an adjustable output power supply. As described, high voltage control block  580  is designed to monitor the voltage output of the device, and when needed (e.g. in high humidity conditions) increases the current output of voltage multiplier  630  to maintain the desired voltage at high voltage electrode  650 . Without current limiter  670 ,the current output of voltage multiplier  630 , in cases of an extremely loaded condition (e.g. high humidity) would increase to levels which are unsafe and thereby increasing the shock potential of a tactile discharge to a user.  
         [0058]    Having shown and described the preferred embodiments of the present invention, further adaptions of the present invention as described herein can be accomplished by appropriate modifications by one of ordinary skill in the art without departing from the scope of the present invention. Several of these potential modifications and alternatives have been mentioned, and others will be apparent to those skilled in the art. For example, while exemplary embodiments of the present invention have been discussed for illustrative purposes, it should be understood that the elements described will be constantly updated and improved by technological advances. Accordingly, the scope of the present invention should be considered in terms of the following claims and is understood not to be limited to the details of structure, operation or process steps as shown and described in the specification and drawings.  
         [0059]    Incorporation by Reference:  
         [0060]    Relevant electrostatic spray devices and cartridges are described in the following commonly-assigned, concurrently-filed U.S. Patent Applications, and hereby incorporated by reference:  
         [0061]    “Electrostatic Spray Device”, which is assigned Attorney Docket No. 8394.  
         [0062]    “Electrostatic Spray Device”, which is assigned Attorney Docket No. 8395.  
         [0063]    “Disposable Cartridge For Electrostatic Spray Device”, which is assigned Attorney Docket No. 8397.