Patent Publication Number: US-6663276-B2

Title: Stirring element and associated metering gun

Description:
This patent application is being filed in the United States Patent and Trademark office as a 37 CFR 1.53(b) application of U.S. provisional application No. 60/239,322 filed Oct. 10, 2000 in the United States Patent and Trademark office. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to the stirring of a substance in a container and the metering of quantities of such substance from the container. More specifically, the present invention relates to the design of the stirring element or agitator used to stir substances in containers. 
     BACKGROUND ART 
     Liquid metering systems are used in a wide variety of applications in the pharmaceutical industry, such as for injecting metered doses of viscous or concentrated suspensions or slurries onto or into substrates and other drug containment media. FIG. 1 illustrates an example of a recently developed liquid metering device in the form of a liquid metering gun generally designated  10 . Metering gun  10  is generally supported by a mounting bracket  12 . Included with this particular system are a solenoid  14 , a syringe-type liquid cylinder  16 , a needle valve assembly generally designated  20 , and a magnetically-driven stirring assembly generally designated  50 . Liquid cylinder  16  is secured and sealed to solenoid  14  with a TEFLON® cap  31 . Cap  31  is attached to solenoid  14  by means of four machine screws  32  (only two of which are shown in FIG.  1 ). An O-ring  33  is fit into a groove of cap  31  located at the end of cap  31  most distal to solenoid  14 . O-ring  33  seals cylinder  16  and maintains the dispensing pressure differential. 
     Needle valve assembly  20  includes an elongate pin or needle  22 , a needle seat  24  and a needle seat holder  26 . An outer gun casing  35  is coaxially disposed around liquid cylinder  16 , and includes a lower cap  37  in which needle seat holder  26  and a nozzle  39  are disposed. A conical element  22 A (also shown in perspective view in FIG. 3) is slid onto needle  22  such that it rests on the top surface of a suspension contained in cylinder  16 . Conical element  22 A prevents upward splashing of the suspension during agitation thereof, and also prevents evaporation of volatile media during agitation. 
     Stirring assembly  50  includes an external magnetic drive member or stirring ring  52  mounted coaxially around gun casing  35 . Magnetic drive member  52  includes two diametrically opposed external magnets  54 A and  54 B, and is operatively connected to a pneumatic stirrer motor  56  through a coupling  58 . Coupling  58  operates to transfer rotational force developed by stirrer motor  56  to rotational motion effected by stirring ring  52 , such that external magnets  54 A and  54 B can rotate about the central longitudinal axis of metering gun  10 . For example, coupling  58  could be a toothed gear which engages teeth on stirring ring  52 . The position of motor  56  is determined by a mounting bracket  59 . Stirring assembly  50  also includes a stirring element in the form of a magnetic stir bar  60 , which has a dominant length along an axis transverse to the central longitudinal axis of metering gun  10 . Magnetic stir bar  60  has a bore drilled therethrough, such that needle  22  extends through the center of magnetic stir bar  60  and the magnet therein. Importantly, magnetic stir bar  60  is by necessity supported by an O-ring  62 . 
     In operation, cylinder  16  is filled with a suspension and secured to solenoid  14 . Magnetic drive assembly  50  is activated such that external magnets  54 A and  54 B rotate around cylinder  16  and induce a magnetic coupling with magnetic stir bar  60 . This in turn causes magnetic stir bar  60  to rotate about needle  22  to thereby agitate the suspension contained in cylinder  16  and prevent the suspension from separating in cylinder  16 , such as by sedimentation or creaming. Needle  22  is used to meter suspension from cylinder  16 . When needle  22  is seated in needle seat  24 , metering gun  10  is closed. At predetermined intervals, however, solenoid  14  of metering gun  10  causes needle  22  to lift upwardly out of needle seat  24  to create a passage from cylinder  16  to nozzle  39 , and a metered dose of the suspension can be dispensed through nozzle  39  under the influence of a pressure differential. 
     Some problems have been observed in the use of metering systems such as that described hereinabove. The configuration of stirring assembly  50  is such that O-ring  62  is needed to support the vertical position of magnetic stir bar  60  within cylinder  16  and needle  22  is needed to maintain a proper axis of rotation for magnetic stir bar  60 . With repeated use of metering gun  10 , O-ring  62  begins to loosen from its fixed position on needle  22  and slip downwardly towards the bottom of cylinder  16 . This causes magnetic stir bar  60  to jam or seize against the inside surface of cylinder  16 , thereby defeating the function of stirring assembly  50 . On other occasions, either the weight of magnetic stir bar  60  on O-ring  62 , the mass of magnetic stir bar  60 , or the contact made between magnetic stir bar  60  and needle  22  causes downward and/or lateral forces on needle  22 . Consequently, needle  22  is often deflected laterally and hence fails to seat properly onto needle seat  24  at the intended points of time, thereby causing a “constantly open” malfunction. Alternatively, the forces imparted on needle  22  can cause needle  22  to become jammed in needle seat  24  such that the valve becomes clogged. These failure events have been observed to occur both sporadically and completely, and are believed to be due at least in part to the rocking of magnetic stir bar  60  back and forth at an angle to needle  22 . In addition, the rapid vertical oscillation of needle  22  during high-frequency metering operations imparts a hammering effect on magnetic stir bar  60 , causing stir bar  60  to move O-ring  62  downwardly. 
     An additional problem stems from the fact that a bore is drilled through magnetic stir bar  60  to enable needle  22  to pass therethrough. The drilling of the bore can produce residual ferromagnetic particles which, due to magnetic attraction, are difficult to identify and eliminate from the bore prior to installation of magnetic stir bar  60  in cylinder  16 . These particles can contaminate the suspension, and additionally can cause seizing of stir bar  60  on needle  22 . 
     The configuration of magnetic stir bar  60  is also believed to engender a further problem observed wherein portions of the suspension splash upwardly to regions of cylinder  16  from which the suspension cannot easily be extracted, especially when the height of the suspension falls down to or below the level at which stir bar  60  is operating. 
     It is also believed that the configuration of the stirring element could be improved over the current stir bar design in order to improve the ability to stir suspensions having broader concentration, viscosity and thickness ranges. 
     The present invention is provided to solve these and other problems associated with the operations of liquid metering systems. 
     DISCLOSURE OF THE INVENTION 
     According to one embodiment of the present invention, an agitator assembly for agitating a substance in a container comprises a container, a magnetic drive device, and an agitator element. The container has a central longitudinal axis and includes a lateral wall defining an inside wall surface and an outside wall surface. The magnetic drive device is disposed adjacent to the outside wall surface of the lateral wall. The agitator element is disposed in the container and is magnetically coupled with the magnetic drive device for self-supported rotation about the central longitudinal axis. The agitator element includes an agitator body, a first magnet mounted at the agitator body, and a second magnet mounted at the agitator body and circumferentially spaced from the first magnet. The agitator element substantially centered about the central longitudinal axis and supported at a substantially constant axial position within the container by the magnetic drive device. 
     According to another embodiment of the present invention, a fluid metering device comprises a container, an elongate valve member, and an agitator assembly including a drive device and a movable agitator element. The container has a longitudinal axis and includes a lateral wall and an outlet aperture. The elongate valve member extends into the container, and is movable substantially along the longitudinal axis to alternately open and close the outlet aperture. The agitator element includes surfaces adapted to agitate a substance contained in the container. The agitator element is disposed in the container in non-contacting relation with the valve member, and is supported at a substantially constant axial position within the container at a distance from the outlet aperture. 
     The present invention further provides a method for agitating a substance in a container. In the method, a container is filled with a substance such as a viscous or a concentrated suspension. A magnetic drive device is mounted at a position adjacent to a lateral wall of the container. An agitator element is constructed by forming an agitator body, mounting a first magnet to the agitator body, and mounting a second magnet to the agitator body in circumferentially spaced relation to the first magnet. The agitator element is then immersed in the substance. The agitator element is caused to maintain a vertically suspended position along a length of the container by establishing a magnetic couple between the magnetic drive device and the agitator element. The agitator element is caused to rotate about a central longitudinal axis of the container, while remaining substantially centered along the longitudinal axis, by rotating the magnetic drive device around the container. 
     It is therefore an object of the present invention to provide a stirring element which is self-supporting at a relatively constant vertical position within a liquid cylinder or other container without the need to make physical contact with additional support structure within such cylinder. 
     It is another object of the present invention to provide a stirring element which does not jam or seize against the cylinder or against a metering needle or other valve component provided with the cylinder. 
     It is a yet another object of the present invention to provide a stirring element which rotates around a central longitudinal axis of the cylinder in a substantially constant radial position with respect to such longitudinal axis, and which does not rely on the presence of a metering needle to maintain such position. 
     It is a further object of the present invention to provide a stirring element which does not impair and affect the oscillatory and seating operations of a metering needle or other valve component provided with the cylinder. 
     It is a still further object of the present invention to provide a stirring element which permits a higher stirring rate without shearing the magnetic couple produced between the stirring element and an external magnetic drive device driving the stirring element. 
     Some of the objects of the invention having been stated hereinabove, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view of a liquid metering device known to applicants; 
     FIG. 2 is a vertical cross-sectional view of a liquid metering device provided in accordance with the present invention; 
     FIG. 2A is a vertical cross-sectional view of an alternative liquid metering device provided in accordance with the present invention; 
     FIG. 3 is an exploded view of the liquid metering device of FIG. 2; 
     FIG. 4A is a perspective view of a stirring element according to the present invention; 
     FIG. 4B is a partially cutaway side elevation view of the stirring element of FIG. 4A; and 
     FIG. 4C is a top plan view of the stirring element of FIG.  4 A. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 2 and 3, an improved liquid metering device generally designated  100  is provided in accordance with the present invention. In comparing improved metering device  100  to previously-described metering gun  10  of FIG. 1, it is seen that many of the components remain essentially unchanged or unmodified. These components are thus designated with the same reference numerals. The primary difference relates to an improved drum-shaped stirring or agitator element generally designated  160 . Stirring element  160  is adapted to operate in conjunction with needle valve assembly  20  and stirring assembly  50 , as shown in FIGS. 1 and 3. 
     The details of stirring element  160  are best shown in FIGS. 4A,  4 B and  4 C. Stirring element  160  can be fabricated by modifying, in accordance with the present invention, a stir drum available from VWR International, Plainfield, N.J., and designated as Part No. 58949-004. Stirring element  160  includes an agitator body  162  preferably constructed from a light-weight polymeric material. Agitator body  162  includes a centrally disposed disk-shaped portion  164 , such that the cross-section of stirring element  160  is circular rather than rectilinear as in the case of above-described magnetic stir bar  60 . In order to improve the agitating capability of stirring element  160 , vanes or fins  166  are formed above and below central portion  164  of agitator body  162 . An enlarged axial through-bore  162 A is drilled through the center of agitator body  162  to enable needle  22  to pass through agitator body  162  while maintaining an annular gap between needle  22  and agitator body  162 . 
     Agitator body  162  also includes a radial through-bore  162 B drilled through central portion  164 . While radial through-bore  162 B could receive a solid cylindrical magnet as in the case of magnetic stir bar  60 , it was discovered to be much more advantageous to mount two separate, diametrically opposed internal magnets  168 A and  168 B at the outer ends of radial through-bore  162 B. In this manner, there is no need to drill a bore through the magnetic portion of stirring element  160  and hence there are no residual magnetic particles which could contaminate the suspension. In addition, the portion of radial through-bore  162 B between internal magnets  168 A and  168 B cooperates with axial through-bore  162 A to define an interior  171  of agitator body  162  that is open to cylinder  16  through the ends of axial through-bore  162 A. Preferably, internal magnets  168 A and  168 B are constructed from a rare earth material. 
     Metering device  100  is assembled as shown in FIGS. 2 and 3. A magnetic drive member is again provided in the form of stirring ring  52  on which external magnets  54 A and  54 B are mounted, and a shim  173  coaxially disposed around outer gun casing  35  can be used to elevate the position of stirring ring  52  relative to the height of cylinder  16 . 
     In the operation of metering device  100 , it was found to be an unexpected and surprising result that stirring element  160  designed according to the present invention spun along the central longitudinal axis of metering device  100  in a completely self-supporting or self-suspending manner. That is, stirring element  160  is structurally isolated from needle  22  and does not require O-ring  62  shown in FIG.  1 . The magnetic coupling produced between external magnets  54 A and  54 B of stirring ring  52  and internal magnets  168 A and  168 B of stirring element  160  is sufficient to maintain the vertical position of stirring element  160  with respect to cylinder  16 . The improved magnetic force is due at least in part to the use of two internal magnets  168 A and  168 B instead of a single magnet. Even when stirring element  160  is immersed in a highly viscous or concentrated suspension, stirring element  160  rotates about the central longitudinal axis with little or no rocking or wobbling. Stirring ring  52  thus operates to both rotate stirring element  160  and maintain its vertical position within cylinder  16 . It is also believed that, upon immersion in the suspension, interior  171  of agitator body  162  fills with suspension material and that the stirring motion of stirring element  160  imparts a flushing action in agitator body interior  171  to prevent the suspension material from causing seizing of stirring element  160  on needle  22 . 
     In addition to the elimination of seizing problems, the performance of needle  22  is greatly improved. The physical isolation of stirring element  160  from needle  22  prevents any contact that might interfere with the proper seating of needle  22  during its operation. This isolation also removes the weight of stirring element  160  from needle  22 , thereby permitting the acceleration/deceleration profiles that control solenoid  14  to operate as originally intended. This is an improvement over the use of magnetic stir bar  60  in FIG. 1, whose contact with needle  22  is believed to cause dragging forces which alter the acceleration/deceleration profiles by decreasing both acceleration and deceleration. 
     Not only is the magnetic coupling between stirring ring  52  and stirring element  160  of sufficient magnitude to magnetically suspend stirring element  160  during the entire dispensing process, but the magnetic force produced is also strong enough to allow much higher stirring rates than heretofore possible without causing a shearing or breaking down of the magnetic coupling. In addition, a broader range of suspensions, whether concentrated, unconcentrated, viscous or diluted, can now be stirred at a higher rate. 
     Furthermore, the large cross-sectional profile presented by central portion  164  of agitator body  162 , and the vertical orientation of fins  166 , may assist in preventing upward splashing of the suspension and evaporation of volatile media during agitation. Consequently, conical element  22 A shown in FIGS. 1 and 3 may not be needed in the present invention. 
     Referring to FIG. 2A, an alternative embodiment is provided wherein a paddle-type stirring element generally designated  180  is installed in cylinder  16  of metering device  100  in a case where a positively driven agitator element might be found to be more suitable than magnetically driven stirring element  160 . Paddle-type stirring element  180  is an assembly which includes a shaft  182  extending into cylinder  16  from the upper portion of metering device  100  containing solenoid  14 . A stirring element in the form of a paddle  184 , such as a blade-type paddle, is attached to the end of shaft  182 . Shaft  182  is coupled to a conventional rotational drive device such as a motor and gear assembly (not shown) located in the upper portion of metering device  100 . Although paddle-type stirring element  180  could be disposed in an offset relation to the central longitudinal axis of cylinder  16 , it is more preferable that shaft  182  and paddle  184  both be provided as hollow components, such that shaft  182  and paddle  184  are centralized within cylinder  16  and needle  22  extends through shaft  182  and beyond the tip of paddle  184 . An annular gap  186  is thus defined between paddle-type stirring element  180  and needle  22 . In this manner, paddle-type stirring element  180  performs agitation operations within cylinder  16  without interfering with the operation of needle  22  and does not require structural support from needle  22 . 
     In a case where cylinder  16  is of significant length for holding a larger quantity of media, a plurality of agitator bodies  162  or paddles  184  can be vertically spaced along the length of cylinder  16 . Where magnetically driven stirring element  160  is employed, this alternative also requires the use of a plurality of corresponding stirring rings  52  to drive each stirring element  160 . 
     In other cases, it may also be desirable that metering device  100  have the capability of varying the vertical position of agitator body  162  or paddle  184  as the level of media within cylinder  16  changes. Thus, a suitable motor and gear drive or structure requiring manual adjustment (not shown) could be provided to adjust the height of stirring assembly  50  or shaft  182 . 
     It therefore can be seen that the present invention provides a magnetically driven or paddle-type stirring element which is self-supporting at a relatively constant vertical position within a liquid cylinder or other container without the need to make physical contact with additional support structure within such cylinder, such as an O-ring or metering needle. It can also be seen that the stirring element does not jam or seize against the cylinder or against the metering needle, and rotates around the central longitudinal axis of the cylinder in a substantially constant radial position with respect to such longitudinal axis. Because the stirring element does not depend on the needle for structural support, it does not impair the successful operation of the needle within the cylinder. In addition, the configuration of the stirring element results in an improved agitation effect and permits increased stirring rates. 
     It will be understood that magnetic stirring element  160  provided by the present invention is not limited to use in connection with any specific metering or stirring device. 
     It will be further understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.