Abstract:
A cartridge for an electrohydrodynamic spraying device and a spraying device incorporating the cartridge, where the cartridge includes a locking mechanism. The cartridge is disposable, and can contain therapeutic or other fluid products. The fluid is delivered from the cartridge by a shaft-mounted piston, while the locking mechanism can be selectively engaged with the shaft such that in the engaged position, the locking mechanism prevents the piston from advancing by inhibiting movement of the shaft. When the locking mechanism is disengaged from the shaft, the shaft and piston are free to move, such as in response to a power source in the spraying device. The selective engagement between the locking mechanism and the shaft during periods of inoperability of the spray device prevents the buildup of fluid pressure in the cartridge that otherwise could blurt out upon subsequent operation.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/001,751, filed Dec. 10, 2007, and entitled “LEAD SCREW LOCKING DEVICE,” the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to spraying finely dispersed liquids contained in a cartridge used in a handheld spraying device, and more particularly to a device and method for locking the cartridge during periods of non-use to avoid leakage therefrom. 
         [0003]    Spraying using electrohydrodynamic (EHD) technology (also referred to as electric field effect technology (EFET)) is a process where fluids or other bulk solutions are dispensed through electrically-charged nozzles. In an EHD spray nozzle, the material to be sprayed flows through a region of high electric field strength made possible by the application of a high voltage to the nozzles and associated nozzle geometry. The high voltage causes the fluid material to acquire an electric charge; the electric field present at the nozzle tips applies a pole to the fluid; the poled fluid charge induces a force that acts in opposition to the surface tension of the material. This surface charge causes the formation of at least one ligament of thin jet of material, causing comminution of the fluid into fine droplets. 
         [0004]    In one embodiment, EHD spraying devices are incorporated into hand-held sprayers, where additional flexibility can be built in through the use of disposable cartridges. This is beneficial in situations where prolonged or excessive exposure to the fluid being dispensed is undesirable, such as with pesticides or other materials used to treat horses and other domesticated animals. Disposable cartridges typically define a cylindrical fluid storage compartment and include a complementary-shaped piston threadably mounted onto a lead screw, where the piston is driven along the length of the compartment upon rotation of the lead screw. The extension of the lead screw into the compartment causes it to contact the fluid to be dispensed; such a configuration is known as a wetted lead screw. The compartment defines a fluid path with a discharge orifice (or outlet) so that fluid disposed between the piston and the discharge orifice is pumped through the orifice in response to the increasing pressure caused by piston movement toward the orifice. 
         [0005]    To reduce the amount of fluid that could leak out between uses, a valve, plug or related flow control mechanism can be placed at or near the discharge orifice to allow the user to shut off the fluid flow. Such an approach works well if the user remembers to open the flow control mechanism before each use; however, if the user should forget to open the flow control mechanism before turning on the pump, pressure will build inside the cartridge that, upon opening the flow control mechanism, would cause the fluid to burst out in an uncontrolled manner, known as a “blurt”. 
         [0006]    One method to mitigate blurting would be to use sensors or some other feedback means to prevent the lead screw from being turned when the flow control mechanism is closed. Such remedies are unavailing in cost sensitive cartridge designs. What is desired is a simple, inexpensive way to lock the cartridge. What is further desired is such a way to provide a locking mechanism that can be used on a disposable cartridge. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    These desires are met by the present invention, wherein a device and a method of dispensing a fluid are disclosed. In accordance with a first aspect of the present invention, a fluid dispensing cartridge for use with an electrohydrodynamic spray device is disclosed. The cartridge includes a body with a fluid chamber and discharge aperture formed in the chamber. A rotatable shaft is placed in the fluid chamber, and a piston is threaded onto the shaft so that rotation of the shaft causes the piston to advance, thereby forcing at least a portion of a fluid disposed in the fluid chamber to pass from the chamber and through the discharge aperture. To keep the cartridge from being inadvertently discharged when not in use, as well as to avoid pressure build-ups in the fluid chamber or discharge aperture that could result from the shaft and piston continuing to pump fluid, a locking mechanism is included. The locking mechanism selectively engages the shaft such that in a first position (which may occur, for example, when the spray device is turned off), the locking mechanism engages the shaft to inhibit its rotation, while in a second position (which may occur, for example, when the spray device is being used to dispense the liquid) the locking mechanism disengages from the shaft, thereby permitting shaft rotation. 
         [0008]    Optionally, the shaft is a lead screw, and more particularly a wetted lead screw. The cooperation between the locking mechanism and the shaft is preferably through a rotatable gear formed on one of the locking mechanism and the shaft, where individual teeth formed on the radial periphery of the gear selectively engage a complementary-shaped detent that is separately mounted. In this way, in a first position, the detent interferes with the rotation of the gear by having the detent situated between the teeth, while in the second position, the detent is moved away from the teeth so that it does not interfere with the gear to effect the permitted rotation. The locking mechanism may additionally include a hand-grippable knob. In one form, this knob is placed at one end of the cartridge, and can be made to turn (for example, by rotation) to place the detent in one of the first or second positions. In a more particular form, the cartridge defines a substantially cylindrical profile, and has a proximal end where the shaft can engage the spray device and a distal end where the knob can be placed. In a more particular form, the profile is an elongate cylinder such that the elongate axis extends substantially longitudinally. The knob can be made such that the movement of the knob is rotational about the longitudinal axis of the cartridge. In one particular example, the shaft and knob may each be rotated about axes that are parallel to and laterally offset from one another. In this way, movement of the detent is eccentric relative to movement of the gear that is mounted to or formed on the shaft. In a particular arrangement of the locking mechanism, the gear is disposed at the distal end of the shaft, while the detent is part of a rotational member that has at least a portion of its movement decoupled from the shaft. In one form, a non-axisymmetric socket or related recess can be formed in the distal end of the shaft such that the gear with the toothed profile extends axially from the distal shaft end. The teeth of the gear and the detent ensure that when engaged, the shaft and knob are coupled so that shaft rotation is prevented. In one form, the teeth making up the gear define rounded (rather than squared-off) end profiles. 
         [0009]    In one particular form, the detent is made up of at least one finger. The one or more fingers are situated on a rotatable member (for example, a plate, disc or related member that can be oriented such that a longitudinal axis of the shaft is oriented normal to that plate&#39;s major surface. In this way, the finger, which is mounted to and extends radially outward from a periphery of the plate, can be rotated into engagement with the teeth of the shaft. In other words, upon rotation of the plate or related member, the detent or finger travels along an arcuate gear engagement path defined by the radial outer bounds of the plate. Thus, the teeth in the first position prevent rotation of the gear, and in the second position do not fit between adjacent the teeth, thereby allowing rotation of the gear. A stopcock may also be included. It may be sized to fit within a volume defined by the knob, and may further be integrated with parts of the locking mechanism (such as the rotatable member discussed above) so that such components are formed on the stopcock. The stopcock includes a fluid passageway to convey the fluid that is placed on the cartridge between the cartridge and the spray device. In another option, various components can be formed from a plastic material. Specific components, such as the shaft, may be made from particular materials, such as nylon, whether reinforced or not. To decrease wobble, it may be useful to secure the shaft at both its proximal and distal ends. The ends of the shaft, as they come in close proximity to, or even penetrate through the end walls of the cartridge, may be supported by a race, boss, bearing, trough or related device formed into, extending from or otherwise cooperative with the walls. At the distal end of the cartridge, an axial connection (such as those examples just mentioned) between the shaft and the locking mechanism could provide the necessary support. In a particular form, the arcuate gear engagement path that is formed on the rotational member defines a cammed profile that stays in substantial contact with a peripheral dimension formed by the teeth. In such case, the detent extends in a radially outward direction from the cammed profile such that rotational movement between the arcuate gear engagement path and the gear moves the finger into one of the first and second positions. 
         [0010]    According to another aspect of the invention, an EHD spray device is disclosed. The device includes a fluid dispensing cartridge with a fluid chamber that can contain a fluid. The fluid chamber has a proximal end and a distal end substantially opposite one another. A lead screw is placed within the fluid chamber, while a piston is coupled to the lead screw such that upon rotation of the lead screw, the piston advances toward the distal end to force at least a portion of the fluid out of the cartridge. A locking mechanism can be made to selectively couple to the lead screw such that in a first position, the locking mechanism engages the lead screw to inhibit screw rotation, while in a second position, the locking mechanism disengages the lead screw to permit the screw to rotate. A handle can releasably receive the cartridge; in this way, the cartridge may be configured for one-time (i.e., disposable) use. The handle houses numerous components, including a rotational power source (such as a motor and shaft coupling responsive to the motor), a high voltage electrical source, a switch to turn the spray device on and off, a spray manifold and a plurality of nozzles. Fluid communication is established between the spray manifold, nozzles and cartridge. In addition, one or more of the manifold and the nozzles are in electrically coupled with the high voltage electrical source such that upon operation of the spray device, a voltage is applied to force comminution of the fluid being discharged from the nozzles. 
         [0011]    Optionally, the locking mechanism includes a hand-turnable knob and a detent member cooperative with the knob, where the knob moves about a first axis of rotation. In addition, a gear is disposed on the lead screw such that the gear and the lead screw define a second axis of rotation that is substantially parallel to and laterally offset from the first axis of rotation. In this way, upon rotational movement of the knob, the detent member selectively engages or disengages the gear. In another option, the spray device further includes a stopcock fluidly disposed between the fluid chamber and the spray manifold such that it can help convey the fluid from the cartridge to the nozzles. The detent member may be formed on the stopcock such that both are rotationally cooperative with the knob. In addition, the engagement of the detent member with the gear can be made to occur when the spray device is turned off. Contrarily, the disengagement of the detent member from the gear can be made to occur when the spray device is turned on. Thus, when the knob is turned to lock the detent and the gear together, the lead screw and piston are disabled from pumping liquid; this prevents a buildup of pressure within the cartridge that might otherwise cause blurting once operation of the spray device commences. 
         [0012]    According to yet another aspect of the present invention, a method of operating an EHD fluid sprayer is disclosed. The method includes configuring a sprayer to have a handle and a cartridge that is removably attachable to the handle. As discussed in the previous aspect, the handle includes a rotational power source, high voltage electrical source, switch, spray manifold and nozzles in fluid communication with the spray manifold. The method further includes disposing a fluid within a cartridge, and having the handle be in fluid communication with the spray manifold. The cartridge includes a fluid chamber, lead screw, piston and locking mechanism cooperative with the lead screw such that in a first position, the locking mechanism engages the lead screw to inhibit screw rotation, while in a second position, the locking mechanism disengages the lead screw to permit screw rotation. The method further includes connecting the cartridge to the handle and the spray manifold. During a period when the fluid is to be dispensed from the spray device, the method further includes rotationally moving the lead screw to advance the piston while the locking mechanism is disengaged from the lead screw, while during a period when the fluid is to not be dispensed from the spray device, engaging the locking mechanism and the lead screw so that the lead screw does not rotate. 
         [0013]    Optionally, the method includes moving a detent that is formed as part of the locking mechanism into an interference fit with a gear that is coupled to the lead screw to establish the first (locked) position. Establishing the second (unlocked) position includes moving the detent out of the interference fit with the gear. Such moving the detent comprises rotationally turning a knob that is coupled to the detent. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]    The following detailed description of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
           [0015]      FIG. 1  shows a cartridge according to an aspect of the present invention, and connection of the cartridge to an EHD spray device; 
           [0016]      FIG. 2  shows the cartridge of  FIG. 1  removed from the EHD spray device with a locking mechanism placed adjacent a distal end of a lead screw used to move fluid through the cartridge; 
           [0017]      FIG. 3  shows a perspective cutaway view of the cartridge of  FIG. 1 ; 
           [0018]      FIG. 4  shows a partially proximal-looking-distal cutaway view of the locking mechanism and its cooperation with the wetted lead screw and a distal end wall of the cartridge of  FIG. 2 ; 
           [0019]      FIG. 5  shows a partial cutaway view of the locking mechanism during a locked position; 
           [0020]      FIG. 6  shows an exploded view of a knob used to selectively engage a locking mechanism with the lead screw; 
           [0021]      FIG. 7  shows a partial cutaway view of the locking mechanism during a locked position where some components making up the locking mechanism have been removed for clarity; 
           [0022]      FIG. 8  shows a partial cutaway view of the locking mechanism during an unlocked position where some components making up the locking mechanism have been removed for clarity; 
           [0023]      FIG. 9  shows rotational engagement of the screw and portions of the knob, where the cartridge has been removed for clarity; and 
           [0024]      FIG. 10  shows an end view of the locking mechanism showing the gear engaged in a locked position with the stopcock, where other components have been removed for clarity. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Referring first to  FIG. 1 , a sprayer (also called a spray device)  10  includes a fluid-containing cartridge  20 , handle  26  and a cartridge interface  29 . The cartridge  20  and the cartridge interface  29  are adapted to enable the cartridge  20  to attach and detach quickly, easily, and without spillage of contained liquid. An array of nozzles  22  are situated beneath cartridge  20 , and are in fluid communication therewith to dispense a fluid. The handle  26  is used to house a power supply  12 , a converter (also referred to as an electronics or circuit board)  14 , a motor  16 , a drive mechanism  18  and driver  19 , and a high voltage multiplier  30  (also referred to as a voltage multiplier circuit). In the present context, the term “high voltage” and its variants is used to represent increases in voltage over that provided by the power supply  12  due to the operation of the voltage multiplier  30 , rather than as indicia of a particular voltage level. By way of example, for a voltage measured at the output of the power supply  12  of six volts, a voltage of thousands of volts measured at the output of the voltage multiplier  30  would constitute a high voltage. The power supply  12  may comprise a portable, on-board voltage supply, such as through a set of batteries, for example four AA batteries, which may or may not be rechargeable. Converter  14  includes a processor, transformer and potting material (none of which are shown, and the last of which to encase the multiplier  30  to provide insulation for the high voltage emanating therefrom). The converter  14  acts to step up the voltage from the power supply  12  to a higher level in order that it may (among other things) power the multiplier  30 . The multiplier  30 , in turn, converts the voltage from the converter  14  to a level suitable for comminuting a liquid contained within the cartridge  20  with EHD forces. The multiplier  30  may be configured as a flyback oscillator circuit as understood by those skilled in the art. In an exemplary form, converter  14  (with transformer  17  and multiplier  30 ) can take an input voltage of between four and six DC volts and convert that to between twenty thousand and thirty thousand DC volts. An electrical connection (not shown) between the multiplier  30  and the nozzles  22  enables a necessary charge to be formed on the latter such that when fluid passes therethrough, it is comminuted. In alternative configurations where the cartridge  20  is not detachable from the handle  26 , the handle  26  may include any combination of the power supply, fluid reservoir, pump, controller/processor or related componentry. 
         [0026]    For EHD spraying, the pressure necessary to move the fluid is nominal Enough is needed to continuously provide fluid to replace that which is dispensed at what are referred to as Taylor cones formed at the nozzles  22 . The nozzles  22  are preferably fixed to the cartridge  20 , promoting ease of use as they may be disposed of or reusable together. Alternatively, the nozzles  22  may be separable and reusable from the cartridge  20 . The nozzles  22  are preferably electrically connected to a high voltage source within the sprayer  10 , as can the manifold  90 . In either way, the EHD sprayer  10  can impart the necessary charge to the droplets of liquid that are discharged from the nozzles  22 . The nozzles  22 , manifold  90  (shown in  FIG. 3 ) or both can be made of a conductive plastic material, using as base materials polymers, for example polycarbonate, high density polypropylene, or preferably polypropylene, acrylonitrile-butadiene-styrene (ABS) and high density polyethylene (HDPE), which can be appropriately compounded as known in the art to exhibit conductive properties. Preferably, such materials exhibit surface resistivity from approximately 10 2  to 10 14  ohm/square, and volume resistivity of 10 2  to 10 14  ohm/cm. Alternatively, the nozzles  22  may be made of other electrically conductive (for example, metallic) materials that can be cast or otherwise formed into the appropriate geometry. 
         [0027]    In another form, the nozzles  22  themselves do not have to be electrically conductive. For instance, they could be nonconductive with a conductive coating on the outside or inside to help establish the proper electric fields. Where the formulation of the fluid is sufficiently conductive, it would be enough that the high voltage contact the fluid somewhere upstream of the nozzles  22 . Optionally, the handle  26  includes a grip made from a metal, an electrically conductive material including electrically conductive plastic, electrically conductive polymer, electrically conductive rubber, or combinations thereof. In another option, the remainder of the handle  26  could be made from the same materials as the grip. 
         [0028]    There are various ways to establish fluid connection between the fluid chamber of cartridge  20  and the nozzles  22  in such a way as to reduce the likelihood of leakage. In one form, the cartridge  20  includes a septum (not shown) disposed at the distal end  20 B. A cap (not shown) may also be disposed at the distal end  20 B; the cap cooperative with the septum such that upon engagement of the two, the cap forms the aperture in the distal end and forms the sealing force. In another form, the aforementioned stopcock  101  is disposed at the distal end  20 B to allow for repeated opening and closing of the cartridge. In either form, such act as a closure device configured to keep a liquid disposed within the cartridge  20  from exiting through the distal end  20 B. As also stated above, the stopcock  101  may also define a continuously open path between the cartridge  20  and the nozzles  22  such that, when the detent  101 B and the teeth of gear  41  are engaged, no fluid pressure is applied from piston  50  or shaft  40 , so that the sprayer  10  is for all intents and purposes leakage-free. 
         [0029]    Referring next to  FIGS. 2 and 3 , a cartridge  20  is shown. In a preferable embodiment, cartridge  20  is disposable and not reusable, such that it is designed for a one-time use. Cartridge  20  includes generally opposing ends: a proximal end  20 A that is adjacent to and cooperative with the cartridge interface  29  and driver  19 , and a distal end  20 B through which the fluid to be dispensed flows, for example, through discharge aperture  80 . The interior  20 C of cartridge  20  is shown with particularity in  FIG. 3 , and defines a fluid chamber between the proximal and distal ends  20 A,  20 B. A perspective cutaway view of the cartridge  20  removed from the sprayer  10  shows that the body of cartridge  20  defines a generally elongate cylindrical shape. In the present context, a cartridge is considered to be generally cylindrical when it includes cylindrical fluid reservoir; it does not require a precisely cylindrical cross-sectional profile. For example, if the cartridge exhibits a slightly prolate, oblate or egg-shaped cross-section, it would still be considered to exhibit generally cylindrical properties as long as it has a substantially cylindrical fluid chamber. Stated another way, the cartridge body may be tubular in shape. In the present context, the term “tubular” refers to a hollow shape which has in cross-section a geometrical or irregular form. The tubular body may be either axially elongate or axially squat, where the former refers to the extension of such form substantially along an axis a distance sufficient to define a fluid chamber, and the latter refers to an axial dimension of the fluid chamber that is relatively small when compared to the radial dimension. 
         [0030]    A hand-rotatable knob  100  is placed at the distal end  20 B of cartridge  20 , and can be used to actuate a locking mechanism  150  that is discussed in more detail below. A discharge aperture  80  can formed in knob  100  and used to route fluid that exits the cartridge  20 . In one form, a conduit formed to establish fluid communication between the discharge aperture  80  and cartridge  20  may be permanently opened, such that no valve or related flow shut off componentry is needed. 
         [0031]    The inside (fluid-containing) portion of cartridge  20  is bounded at its proximal and distal ends  20 A,  20 B by a piston  50  and an end wall  24 , and radially by the inner wall  20 C such that a fluid chamber is defined. End wall  24  forms a closure barrier at the distal end  20 B of cartridge  20 , and can be penetrated by a rotatable shaft (more particularly and alternately referred to as a wetted lead screw or lead screw, familiar to those skilled in the art)  40  formed as part of cartridge  20  such penetration may include a seal (not shown) to inhibit leakage. Shaft  40  extends along the longitudinal dimension of cartridge  20  from the proximal end  20 A to the distal end  20 B, and while the shaft  40  can be made from any suitable structural material, in a preferred embodiment it is made of plastic. Piston  50  is mounted onto shaft  40 , where threads on both cooperate with each other such that upon rotation of shaft  40 , piston  50  progresses from the proximal end  20 A to the distal end  20 B. While the direction of travel of the piston  50  towards the distal end  20 B as described above is preferred, it is not intended to limit the scope of the invention described herein. As such, it will be appreciated by those skilled in the art that the cartridge  20  may be designed so that the shaft  40  drives the piston  50  from the distal end  20 B towards the proximal end  20 A of the fluid chamber. 
         [0032]    A relatively snug fit between the outer periphery of the piston  50  and the inner wall  20 C prevents the piston  50  from sympathetically turning with the shaft  40 . It will be understood by those skilled in the art that other anti-rotation features may be employed, such as an axial key and slot arrangement formed in the piston and cartridge inner wall, or by forming the inner wall and piston with complementary oval or other non-axisymmetric shape. While such shapes could cause the cartridge  20  to depart from a truly cylindrical profile, it will be understood that all such configurations are within the scope of the present invention. While it is preferable that the piston not rotate in relation to the inner wall  20 C, in some cylindrical applications the piston may rotate slightly in relation to the bore wall, but at a rate slower than the shaft  40 . The construction of piston  50  is such that it acts like a plunger in that it pushes fluid situated on its downstream portion out of the fluid chamber of the cartridge  20 . Retaining ring  55  may be disposed substantially about the periphery of piston  50  to promote rigidity and shape retention. Cartridge  20  may optionally include a window, or be made of a transparent or translucent material (none of which are shown) to provide a visual dose cue to indicate the volume of fluid or number of doses remaining. Other indicia, such as an auditory application cue (not shown) through timed sounds linked to volume dispensing rate could also be used. 
         [0033]    In one form, a bayonet-type attachment  110  may be employed, as well as a keyed slot  120  to ensure proper alignment between the cartridge  20  and the handle  26  of sprayer  10 . Such an attachment ensures quick connection and removal. The bayonet-type attachment  110  may be disposed on both sides of cartridge  20 , so long as both can be engaged or disengaged simultaneously by relative rotation in one direction or the other between the cartridge  20  and handle  26 . Alternatively, a twist-type attachment (not shown) with a positive or friction lock, a spring mounted pin and hole arrangement (not shown), or other means for positively connecting the cartridge to the handle would be suitable. The cartridge  20  and handle  26  are preferably detachable, so that cartridge  20  may, as previously stated, be disposable (or refillable), or so that one cartridge may be exchanged for another having a different fluid. The handle interface  29  thus includes both mechanical and electrical interfaces. Use of the cartridge  20  with the handle  26  of a hand-held EHD spray device, is preferred, but the cartridge  20  may be used with non-hand-held EHD spray devices. 
         [0034]    A seal  70  is situated between an axial bore  52  formed in the piston  50  and the threads of shaft  40 . As with the piston  50 , seal  70  may include threads on its inner bore so that the seal  70  can cooperate with the rotational movement of shaft  40 . In order to maximize its sealing feature, seal  70  is preferably made from a softer material than that of the shaft  40  or piston  50 . This results in a more compliant form that can better maintain small gaps between the seal  70  and the threads of the shaft  40 , thereby reducing the possibility of backwards leakage along the shaft  40 . Examples of seal material can be a silicone-based or plastic-based structure. In one form, the seal  70  can be integrally manufactured into piston  50  to ensure a leak-free connection. 
         [0035]    A proximal end of shaft  40  fans out to define a hub  42 , while at its distal end, shaft  40  preferably has a geared end (also called gear)  41  supported in a race  24 A, trough or similar socket (collectively referred to as a race  24 A) in end wall  24 . In one form, the teeth making up the geared end  41  could be bigger than the diameter of the shaft  40  to have more mass and strength, especially if made as a separate part. In such circumstance, the race  24 A would have to be bigger than shown to accommodate the larger diameter teeth. Alternatively, the shaft  40  may be cantilevered, supported at the one end and by the piston  50  and frame  60 . To keep shaft  40  radially centered in the fluid chamber and aligned with the driver  19 , hub  42  is mounted to a frame  60 . Preferably, the frame  60  is made from a relatively rigid material, such as metal. In yet another alternate embodiment, an additional shaft may be used, such that a screw-based auger approach could be employed. 
         [0036]    Referring next to  FIGS. 4 through 6 , two cutaway assembled views ( FIGS. 4 and 5 ) and one exploded view ( FIG. 6 ) show the connectivity of the shaft  40  and knob  100  as components making up the locking mechanism  150 . The locking mechanism  150  additionally includes a stopcock  101  that is affixed to knob  100  through a mounting surface  102  the latter of which could form a structural member or other reinforcement to knob  100 . Stopcock  101  acts as a rotatable conduit to ensure fluid communication between the fluid chamber of cartridge  20 , the discharge aperture  80  (which may be situated in the wall at the distal end  20 B of cartridge  20 , or at the end of a conduit or related tube that extends from cartridge  20 ) and the nozzles  22 . Unlike a traditional stopcock, stopcock  101  need not employ a valve to selectively close off flow, as it uses the geared locking mechanism  150  (which is described in more detail below) to achieve the same flow limitation without the danger of a pressure buildup and concomitant startup blurt. Stopcock  101  is axially offset from shaft  40  such that the two do not turn about the same axis of rotation. For example, as shown with particularity in  FIG. 5 , shaft  40  rotates about an axis of rotation R s , while the knob  100  rotates about an axis of rotation R k  that centers on stopcock  101 . Discharge tube  80  can be passed through knob  100  in order to be fluidly coupled to the fluid chamber of cartridge  20  through a passageway  101 A in stopcock  101 . 
         [0037]    Referring next to  FIGS. 7 and 8 , the locking mechanism (which may be considered to include the gear  41 ) includes a mating detent  101 B that extends radially outward from stopcock  101  to interfere with the teeth on the gear  41 , not allowing it or screw  40  to rotate. As shown, stopcock  101  may form part of the locking mechanism  150 , while in other embodiments, may merely provide the necessary fluid passage between the cartridge  20  and nozzles  22 . In such case, a plate-like, generally planar rotating member (also called fluid lever), which mimics the functions of a surface of stopcock  101  in a manner generally shown in  FIGS. 7 and 8 , is used to provide the selectively engageable detent  101 B. Specifically,  FIG. 7  shows how the teeth of the gear  41  get locked by the detent  101 B in the fluid lever.  FIG. 8  shows the position just before locking. By having the end profile of the teeth be rounded, the likelihood of detent  101 B directly hitting the peak of a tooth is reduced. It will be appreciated that many of the components making up knob  100  and locking mechanism  150  are removed from  FIGS. 7 and 8  in order to enhance the clarity of the cooperation between the gear  41  and detent  101 B. 
         [0038]    Referring next to  FIGS. 4 and 5  in conjunction with  FIGS. 7 and 8 , the particular configuration of the stopcock  101  is shown. In particular, a series of non-axisymmetric features are included so that upon rotation of the knob  100  and stopcock  101 , the teeth of geared end  41  of the shaft  40  selectively engage a detent  101 B that is situated on the periphery of the stopcock  101 .  FIG. 7  depicts a locked relationship between the teeth and detent  101 B, thereby preventing discharge of fluid from the cartridge  20 , whereas  FIG. 8  depicts an unlocked relationship between them such that upon activation of the shaft  40  and piston  50 , the fluid can be discharged. As can be seen, the detent  101 B is parallel to the tangent of the rotating stopcock when positioned near the stopcock. An aperture (not shown) formed in end wall  24  can be positioned in such a way so that it always maintains fluid communication between the passageway  101 A and the fluid chamber of cartridge  20 . In one configuration, the aperture can be oversized relative to the passageway  101 A and define a generally banana-shaped profile in end wall  24  so that regardless of where passageway is situated along an arc defined by rotation of knob  100 , it is in communication with the aperture in the end wall  24 . In another configuration, the axis of rotation R k  can be centered on passageway  101 A rather than on the center of stopcock  101 . In this way, the aperture (which now may be of a conventional circular or related shape) formed in end wall  24  is placed in a location so that it always maintain fluid communication between the passageway  101 A and the fluid chamber. 
         [0039]    In yet another configuration, rotation of the knob  100  relative to the cartridge  20  may selectively establish and cut off fluid access between the passageway  101 A and aperture. In such event, the rotational movement acts like a valve, although without the possibility of such valve allowing a pressure build-up in the cartridge  20  and subsequent blurt as discussed in conjunction with the prior art. Such problem is avoided by the rigid mechanical coupling between the knob  100 , stopcock  101 , shaft  40  and piston  50 , as the cooperation among them ensures that the only time the piston  50  can be pumping fluid is during periods where fluid access through discharge aperture  80  through passageway  101 A is established. Contrarily, in situations where a sprayer is not being used, stopcock  101  can be engaged to make certain that shaft  40  can&#39;t turn (through the engagement of the stopcock  101  with the teeth of the geared end  41  of shaft  40 . Referring next to  FIGS. 7 and 8 , such conditions are shown in the preferred embodiment. 
         [0040]    For best operation, the sprayer  10  should be referenced between the user and the target during EHD spraying. The handle  26  preferably comprises a conductive material suitable for making electrical contact between the sprayer  10  and the user. The material may be, for example, a metal, conductive rubber, plastic, or other polymer. The material for the handle  26  may also comprise a soft-touch material to provide tactile contact between the user and the sprayer  10 . As shown in the embodiment illustrated in  FIG. 1 , the power supply  12  may comprise a power supply pack positioned in the front of the handle  26 . In an alternate embodiment (not shown), the power supply and associated electronics may be positioned in the rear of handle  26 . As discussed above, balance and ergonomic weight distribution is an important consideration for the sprayer  10 . In addition to ergonomic considerations, the sprayer  10  may also be designed so that such balance that favors causing the sprayer to strike the ground at the rear (i.e., butt) end of the handle  26  to minimize the potential for damage to the nozzles  22 . 
         [0041]    Fluid that is forced out of cartridge  20  passes through discharge tube or aperture  80  and into manifold  90 , where a series of channels (shown and described in more detail below) distribute the fluid to the nozzles  22 . To promote EHD operation, high voltage from handle  26  is imparted to at least one of the manifold  90  and nozzles  22  so that an adjacent charge field to act upon the fluid. An electrical connection  99  is used to establish electrical continuity between the power source  12  and associated voltage multiplying components situated on converter  14 . 
         [0042]    Referring next to  FIG. 9  in conjunction with  FIG. 1 , internal views with various components removed for clarity are shown. In the partially distal-looking-proximal view of  FIG. 1 , the lead screw and piston (both described below as being used to force a fluid from the fluid chamber) are omitted, while in  FIG. 9 , a partially proximal-looking-distal view shows a geared end  41  of the shaft  40  engaging a complementary surface of stopcock  101  that is presently shown as connected to knob  100 , while the cartridge  20  has been removed. Discharge tube  80 A, which forms a conduit for discharge aperture  80  maintains fluid coupling between the cartridge and the manifold  90 . The manifold  90  is preferably designed to maintain substantially equal flow to each nozzle  22 , however, the cartridge  20  of the present invention does not depend on such flow being substantially equal, and may be used with other nozzle configurations to achieve EHD spraying with various characteristics. 
         [0043]    While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention, which is defined in the appended claims.