The present invention relates generally to devices for spraying finely dispersed liquids, and more particularly to the use of a disposable cartridge that is compatible with a handheld electrohydrodynamic (EHD) and electrostatic spray devices.
Spraying using 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.
By contrast, electrostatic spraying results from forcing a jet of fluid out an orifice under pressure and electrically charging the fluid that exits the nozzle under pressure. Once out of the nozzle, the droplets form a charged spray cloud which is attracted to the nearest grounded surface. Numerous electrostatic spray nozzles are known in the art, and have critical orifice sizes designed to produce electrostatically charged particles with defined size distributions.
One advantage of the EHD process is that high fluid forcing pressures are not required, thereby reducing high-velocity fluid movement and concomitant levels of noise associated with fluid dispersal. As the fluid exits the nozzle, the repelling forces of the surface charge balance against the surface tension of the material, causing the formation of a conical spray pattern (often referred to as a Taylor cone). The tip of the cone has the greatest concentration of charge and, at that point, the electrical forces overcome the surface tension, generating the thin jet of material that breaks up into charged droplets of generally uniform size.
In either of the electrostatic or EHD methods, charged droplets or particles are readily attracted to a grounded target, adhering readily to it. As portions of the target become coated with the material, the relative electrostatic potential between coated sections and uncoated sections causes subsequent application of the charged material to be preferentially attracted to an uncoated portion of the target, thereby promoting more uniform coverage. The charged nature of the droplets is further beneficial in that their like charge tends to force them to avoid agglomeration. Soon after being deposited on the target, the material loses its charge, leaving an electrically-neutral end product.
Within the cartridge art are containers in which a generally cylindrical-shaped piston is driven along the length of a complementary-shaped inner wall of the cartridge upon rotation of a lead screw. The lead screw is threaded through the piston and extends into the fluid chamber of the cartridge. Because the screw is immersed in the fluid that is contained within the cartridge, it is sometimes referred to as a “wetted” lead screw. Fluid disposed downstream of the piston is forced through an outlet or an orifice in response to the increasing pressure within the cartridge by piston movement in the downstream direction.
Unfortunately, the above-mentioned cartridge is prone to leakage, especially in regions between the outer periphery of the piston and the inner wall of the cartridge, as well as the threaded space between the screw and the piston. In an application where a cartridge of this type may be used in a device with electronics, the fluid can potentially leak into regions where electronic and other liquid-intolerant components reside. As well, when the cartridge or device is being stored during long periods of time during shipping and storage on shelves or between uses, an unacceptable quantity of fluid may be lost. This problem is particularly acute in situations where the liquid is expensive or hazardous, such as a pesticide, herbicide, flammable materials or the like. This problem is exacerbated when the cartridge is used for applications requiring higher fluid pressures, such as for higher viscosity fluids or in conjunction with the aforementioned electrostatic spraying device.
What is desired is a leak-free cartridge, and more desirably, a leak-free disposable cartridge that can be used with an EHD or electrostatic device that is inexpensive to manufacture and easy to dispose of once the contents are dispensed.
These desires are met by the present invention, wherein a cartridge, a spray device and a method of dispensing a fluid are disclosed. In accordance with a first aspect of the present invention, a cartridge that is configured to cooperate with an electrostatic-based, EHD-based or other pressure-based spray device is disclosed. The cartridge preferably includes a fluid chamber that has a proximal end (nearest the user) and a distal end in opposition to one another. A lead screw is situated within the fluid chamber, and extends substantially between the proximal and distal ends. In addition, the cartridge includes a piston defining a bore therein such that the piston is threadably cooperative with the lead screw. With this arrangement, when the lead screw turns, the piston advances toward one end of the fluid chamber to force at least a portion of a fluid disposed therein out a discharge aperture formed in the cartridge. A self-actuating seal disposed in the bore is threadably cooperative with the lead screw so that fluid leakage between the bore and the lead screw is inhibited. Moreover, the seal extends beyond the axial footprint of the piston so that the outer surface of the seal is exposed to the increased pressure of the fluid that is being pressurized by the movement of the piston. The fluid pressure in turn imparts a force to the surface of the seal, causing it to compress and tighten its fit with the lead screw. In addition, a fluid outlet is coupled to the fluid chamber such that fluid forced out of the fluid chamber by operation of the lead screw and piston will be discharged through the outlet.
Optionally, the seal has an elastomeric sleeve disposed on its outer surface. In one configuration, the seal is integrally formed with the piston.
The outer surface of the seal may be tapered from a first outer diameter at a more proximal end to a second outer diameter at a more distal end. This gives the seal a frustro-conical shape with the second outer diameter being smaller than the first outer diameter. The threadably cooperative portions of the lead screw and the seal may comprise complementary-shaped threads formed in each. The seal and the piston may be integrally formed as a one-piece device, or may be separately formed as multiple pieces that can cooperate together. In this latter configuration, they are rigidly affixed to one another such that neither substantially rotate in response to the rotation of the lead screw.
In a particular form of the cartridge, the seal that is situated between the screw and the piston is preferably made up of material having the substantially the same or higher durometer as the material of either the lead screw or the piston, and may be molded with the piston as a single component. Seal materials may include, for example, silicone, rubber, urethane, and like flexible polymers that are compatible for use with a fluid to be dispensed from the cartridge and have the necessary properties to seal against the wetted lead screw in accordance with the present invention. In particular, the seal includes a sleeve which extends into the fluid chamber and which is designed to be self-actuating to provide additional sealing pressure to prevent leakage at the wetted lead screw as pressure in the fluid chamber increases.
The cartridge may further comprise a frame configured to provide axial and radial support to the lead screw. More particularly, the frame is connected to the fluid chamber such that the frame inhibits movement of the lead screw toward one end (for example, the proximal end) of the cartridge. Another function of the frame is to support and center the screw as the piston advances. In one configuration, the frame is made up of a central hub from which numerous radially-extending spokes contact the inner wall of the fluid chamber.
According to another aspect of the invention, a spray device is disclosed which includes a fluid dispensing cartridge. The cartridge includes a fluid chamber with proximal and distal ends substantially opposite one another, a lead screw disposed within the fluid chamber, a piston cooperative with the lead screw so that when the lead screw rotates, the piston advances toward the distal end to pressurize a fluid contained in the cartridge, and a self-actuating seal disposed between a bore formed in the piston and the lead screw. The self-actuating nature of the seal is such that it is responsive to environmental changes (specifically, changes in pressure in the fluid chamber) to inhibit fluid leakage that would otherwise be prevalent under such environmental changes. In particular, the seal achieves at least some of its self-actuating capability by its distal extension into the fluid chamber. Pressure applied to an outer surface of the distal extension from the pressurized fluid causes the seal to compress, thereby increasing tightness of fit between the seal and the screw. The device additionally includes one or more discharge nozzles in fluid communication with the fluid chamber, as well as a handle configured to attachably receive the cartridge. The handle includes a power source that, through cooperation with the lead screw, pressurizes the fluid disposed in the fluid chamber so that at least a portion of the fluid is discharged. The handle also includes a high voltage electrical source configured to impart an electric charge to one or both of the fluid and the discharge nozzle(s), and a switch to selectively turn the spray device on and off. In configurations where multiple nozzles are used, the manifold is preferably designed to maintain substantially equal flow to each nozzle; however, the cartridge of the present invention does not depend on such flow being substantially equal, and may be used with other nozzle configurations. The handle preferably includes the power supply (preferably batteries, disposable or rechargeable), motor, drive mechanism for the lead screw, high voltage converter, and controller components. In alternative configurations where the cartridge is not detachable from the handle, the handle may include any combination of the power supply, fluid reservoir, pump, or controller/processor.
The cartridge can be equipped with one of various forms of discharge closure means, examples of which include a septum or a stop-cock valve (the latter formed in an end cap) and operable to either establish fluid flow or seal the cartridge, either of which are placed at the distal end of the fluid chamber to prevent leakage or spillage of the liquid when the device is not in use. In a particular form, the spray device is an EHD spray device. As previously mentioned, a spray manifold and numerous nozzles in fluid communication with the spray manifold can be used, where one or both of the manifold and the nozzles are electrically coupled with the high voltage electrical source so that the fluid being discharged from the nozzles is comminuted. The spray device may also be configured an electrostatic spray device, where higher pressure fluid environments may involve the use of handle or cartridge components that are compatible with such higher pressures. Regardless of whether the spray device is an EHD or electrostatic device, it may also include a closure valve fluidly disposed between the fluid chamber and the one or more discharge nozzles.
In a preferred (although not necessary) embodiment, the cartridge is filled only once and is non-reusable or disposable. Although the nature of what is disposable in a pedestrian sense is almost limitless, it will be appreciated that in the present context, non-reuseable fluid containing and dispensing components such as the cartridge are distinguished over their reuseable counterparts when it is more practical (for example, from a cost, contamination, cleanliness or hygenic perspective) to dispose of the fluid container once the fluid has been expended rather than refilling and resealing the container. Evidence of non-reuseability of the cartridge includes having the fluid hermetically sealed inside the cartridge such that prior to the cartridge being coupled to the handle, the fluid inside is substantially isolated from the ambient environment. Upon receipt of the cartridge into the handle, a permanent aperture is formed in the cartridge (such as by a needle on the handle puncturing a septum in the end of the cartridge). In a non-reuseable cartridge, replacement of coverage of the aperture is impractical or otherwise not-cost effective relative to the cost of providing a new cartridge. The present disposable features can be extended to other parts such that an assembly of such parts is disposable. For example, the cartridge of the spray device can be rigidly affixed to at least one of the spray manifold and the nozzles such that once the fluid contained in the fluid chamber is dispensed, the cartridge, the spray manifold and the nozzles form a disposable assembly.
According to still another aspect of the invention, a method of spraying a fluid is disclosed. The method includes disposing a fluid within a cartridge, providing power to the cartridge through a handle so that a lead screw advances a piston to pressurize the fluid and force it out of the cartridge, and inhibiting fluid leakage between a self-actuating seal and the piston by having the seal distally extend into the fluid chamber from the piston such that the pressurized fluid applies pressure to an outer surface of the seal. In this way, the application of pressure from the fluid compresses the seal an amount necessary to increase the tightness of a fit between the seal and the screw.
Optionally, the seal and the piston are integrally formed as a unitary (i.e., one-piece) structure. In another option, the seal is made up of a material that is at least as hard as a material making up the piston. The seal may additionally have an elastomeric sleeve placed on it. The spray device may be an electrostatic or EHD spray device; in the case of the latter, the handle further comprises: a rotational power source and a high voltage electrical power source, a power switch, a spray manifold and numerous nozzles in fluid communication with the spray manifold. At least one of the manifold and the nozzles are electrically coupled with the high voltage electrical power source such that upon application of a voltage, at least a portion of the fluid being discharged from the plurality of nozzles is comminuted during the method.
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:
Referring first to
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. 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. As shown with particularity in
As mentioned above, the cartridge 20 may also be made compatible with spraying devices that require higher fluid pressures, such as electrostatic spraying devices. In such circumstances, the spraying device 10 described herein for use in EHD spraying could, with appropriate modifications, be used as an electrostatic or related high pressure spraying device. Although a number of components of the sprayer may be similar, the operating requirements for production of a Taylor cone necessary for EHD spraying versus a jet necessary for electrospraying may dictate changes in certain componentry. In particular, an electrostatic spraying device would include a larger motor 16 to generate higher pressures, corresponding strength in the fluid chamber and piston 50, as well as the need for smaller apertures 25, and fluid channels, manifolds and nozzles having orifices properly sized for the kind of operation that leads to electrostatic spraying. While use of the cartridge 20 is especially beneficial in EHD spraying and that at least one preferred embodiment of the present invention be configured for EHD spraying, the present inventors believe that its use in electrostatic and other high pressure-based spraying is warranted. Thus, even though the particle size and control over the particle size that is achievable with EHD spraying is sacrificed in higher pressure electrospraying applications, where a charged jet rather than a Taylor cone is produced at the nozzles, other desired characteristics of spraying charged particles are still preserved using the cartridge of the present invention, particularly in such higher pressure electrospraying configurations. The present inventors have also recognized that the presently-shown EHD spraying device 10 may require similar increases in motor or piston robustness in circumstances where the fluid being dispensed has a high viscosity. Referring to
In an alternative configuration shown in
Referring again to
Piston 50 is mounted onto a wetted lead screw 40. Threads on both cooperate with each other such that upon rotation of screw 40, piston 50 progresses from the proximal end 20A to the distal end 20B. While the direction of travel of the piston 50 towards the distal end 20B 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 wetted lead screw 40 drives the piston 50 from the distal end 20B towards the proximal end 20A of the fluid chamber. A relatively snug fit between the outer periphery of the piston 50 and the inner wall 20C prevents the piston 50 from sympathetically turning with the lead screw 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 alternatively, an oval piston. While it is preferable that the piston not rotate in relation to the inner wall 20C, in some applications the piston may rotate slightly in relation to the bore wall, but at a rate slower than the lead screw. 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 (not shown) or be made of a transparent or translucent material 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.
Referring next to
In order to maximize its sealing feature, seal 70 is preferably made from a material a durometer the same as or greater than that of the screw 40 or piston 50, and is more preferably formed as a one-piece element with the piston 50. This latter one-piece configuration is particularly well-suited to a self-actuating structure, as the application of pressure from the fluid in the fluid chamber puts added pressure on the outer surfaces of the sleeve 71 of seal 70, increasing the sealing pressure between the seal 70 and the threads of the screw 40. Such is advantageous in that it reduces the possibility of backwards leakage along the screw 40. As shown with particularity in
Referring with particularity to
For best sealing properties, the seal 70 is manufactured or molded to match the thread design of the wetted lead screw 40. As shown illustratively in
The seal 70 of the present invention may include an additional sleeve 71 to help the seal 70 compresses more tightly against the lead screw 40 to increase sealing pressure against leakage. Seal 70, by virtue of being made from a material that is the same or softer than that of lead screw 40, assumes a shape that closely conforms to the screw's threads. Such conformal fit promotes a sealing action at the thread interface. The inclusion of sleeve 71 introduces additional compression forces such that the seal 70 would experience an increased force at the interface of the threads to enhance the sealing action. The sealing pressure of the sleeve 71 is preferably enhanced by producing the sleeve with a slight inward taper, provided the taper is not sufficient to block the travel of the wetted lead screw 40. As seen best in
The seal designs of
Referring again to
Various rotational couplings between the driver 19 and wetted lead screw 40 are shown. Drive mechanism 18 (shown in
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. An example of such connection can be seen in
Referring next to
Additional ergonomic features of the handle are shown in
Referring next to
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.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2007/014799 | 6/26/2007 | WO | 00 | 12/23/2008 |
Number | Date | Country | |
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60816549 | Jun 2006 | US |