Abstract:
A method for preventing either the introduction of air into a liquid aspirated from a container through an aspiration line passing through a container cap, or the over-filling or non-filling of a container by a liquid dispensed through a dispensing line passing through a container cap. Such method comprises the steps of simultaneously detecting that (a) the container cap is properly positioned on and secured to a liquid container from which liquid is to be aspirated, or into which a liquid is to be dispensed, and (b) detecting that the level of liquid in the container is either above or below a predetermined level.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to improvements in automated methods and apparatus for aspirating liquids from containers, and/or for dispensing liquids into containers. More particularly, this invention is directed to improvements in methods and apparatus for minimizing (a) the inadvertent introduction of air into an aspirated liquid, and/or (b) the overfilling or non-filling of a container by a dispensed liquid. 
     2. The Prior Art 
     In automated analytical laboratory instruments, it is common to selectively mix together various reagents and sample materials in a mixing chamber in order to study, for example, the effects of such reagents on the sample material. Typically, in automated, high-throughput, instruments designed to repetitively perform various tests on a multitude of samples presented to it, the reagents (including sample diluents) are contained in relatively large containers or reservoirs that are stowed within, or adjacent to, the instrument housing. Such containers usually carry a cap through which a liquid-aspiration line or conduit passes that serves to gain access to the contained liquid. A syringe pump or the like operates to transfer a predetermined (relatively small) volume of the contained liquid to a desired location (e.g., the inlet of a mixing chamber) within the instrument. To avoid the aspiration of any air from the liquid container during the liquid aspirating process, it is essential, of course, that the free or distal end of the aspiration line be maintained below the level of liquid in the container. Any air introduced into the aspirated liquid will lead to erroneous test results since it compromises the provision of prescribed volumes of liquid required for a given test. Thus, to assure that the end of the aspiration line is safely below the liquid level in the container, it is common for the container cap to support a float switch or some other liquid level-sensor that serves to activate an alarm when the liquid level drops below a preset minimum value within the container, typically when the distal end of the aspiration line is just below a safe level. When an alarm occurs, the instrument operator must replace the nearly empty container with a fresh container of liquid and then attach the aspiration line-supporting and level-sensing cap to the new container. 
     In instruments of the above noted type, it is also common to dispense the liquid waste products from all the tests conducted within the instrument into a relatively large waste container located within or near the instrument housing. Here again, the cap of such container commonly supports a conduit or dispense line through which the waste liquid can enter the container. To assure the container is not overfilled, which could result in contaminating the laboratory area with a bio-hazardous liquid, the waste container cap also supports a float switch or the like that activates an alarm when the liquid waste level exceeds a predetermined safe level. When such an alarm occurs, the instrument operator will remove the nearly full waste container and replace it with an empty container, being certain to attach the dispense line and level-sensing cap. 
     In liquid aspirating and dispensing systems of the type described, there is always a possibility that the instrument operator, in changing reagent or waste containers, will not properly attach, or even forget to attach, the aforementioned aspiration/dispensing cap to the top of the new container. Note, when changing containers, the caps can be set down in an orientation in which the float switches which, upon being removed from the liquid, are free to assume either an OPEN or CLOSED state, will mistakenly indicate to the instrument logic that the liquid level is within a safe limit. When the caps are not properly attached to their intended container, air can enter the aspiration line, or waste liquid can leak from the waste container or even be dispensed outside the container. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing discussion, an object of this invention is to provide a fail-safe method and apparatus for aspirating and dispensing liquids from and to a container, whereby the above-noted air-introduction and leakage problems cannot occur. 
     By virtue of the present invention, the aspiration (and dispensing) of a liquid from (and to) a container can only occur when the container cap through which such aspiration (and dispensing) takes place is securely attached to the mouth of the container, and the level of liquid in the container is at an appropriate level. Thus, according to a first aspect of the invention, there is provided an improved apparatus for preventing either the introduction of air into a liquid aspirated from a container through an aspiration line passing through a container cap, or the over-filling or non-filling of a container by a liquid dispensed through a dispensing line passing through a container cap. Such apparatus comprises a pair of detectors, one operating to detect that such container cap is properly positioned on and secured to a liquid container from which liquid is to be aspirated, or into which a liquid is to be dispensed, and the other detector operating to detect that the level of liquid in the container is either above a predetermined level (in the case of liquid aspiration) or below a preset level (in the case of liquid dispensing). A system controller operates to enable aspiration or dispensing of liquid only in the event both of these detectors sense the presence of proper cap attachment and a safe liquid level within the container. 
     According to a second aspect of this invention, an improved method is provided for preventing either the introduction of air into a liquid aspirated from a container through an aspiration line passing through a container cap, or the over-filling or non-filling of a container by a liquid dispensed through a dispensing line passing through a container cap. Such method comprises the steps of simultaneously detecting that (a) the container cap is properly positioned on and secured to a liquid container from which liquid is to be aspirated, or into which a liquid is to be dispensed, and (b) detecting that the level of liquid in the container is either above or below a predetermined level; and enabling liquid aspiration or dispensing only when conditions (a) and (b) are detected. 
     The invention and its various aspects and advantages will be better understood from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings in which like reference characters denote like parts or components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric illustration of apparatus embodying the present invention; 
         FIG. 2  is both a cross-sectional illustration of the apparatus shown in  FIG. 1 , and a schematic illustration of; 
         FIG. 3  is a cross-sectional illustration of the apparatus of  FIG. 1  when attached to a nearly empty container of liquid; 
         FIGS. 4A and 4B  illustrate the apparatus of the invention when used in a liquid aspiration mode; 
         FIGS. 5A and 5B  illustrate the apparatus of the invention when used in a liquid dispensing mode; and 
         FIGS. 6A and 6B  are perspective and cross-sectional illustrations of another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings,  FIG. 1  illustrates a preferred embodiment of the invention that is adaptable to both aspirate a liquid from a container C (shown in  FIG. 3 ), and to dispense a liquid to such container through a port P. To simplify this description, the apparatus will be initially described as it is used to aspirate liquid from a container. Later, the use of such apparatus as a liquid dispenser will be described. 
     The liquid-aspirating apparatus  10  of  FIG. 1  comprises an elongated and hollow aspiration tube  12  having a distal end  12 A and a proximal end  12 B (see  FIG. 2 ). The latter is in fluid communication with port P via a container-attachment assembly  13  which rigidly supports both the proximal end of the aspiration tube  12  and port P. As its name implies, the container-attachment assembly  13  serves to releasably attach the liquid aspiration apparatus to the mouth of a container of liquid. When apparatus  10  is used to aspirate liquid from a container, as shown in  FIG. 3 , the length of the aspiration tube is such that the distal end thereof is positioned at or closely spaced from the container bottom B. The container-attachment assembly comprises a cylindrically-shaped housing  14  that rotatably supports, at its base, a threaded cylindrical collar  16 , the latter being supported for rotation about the central axis A of housing  14 . Such rotational support is provided by the combination of a circular ring  14 A extending outwardly from the base of housing  14 , and an inwardly-extending circular flange  16 A formed at the top of collar  16 . The threaded inside surface  16 B of collar  16  is structured to threadingly engage a complimentary threaded surface surrounding the mouth M of container C as the collar rotates about axis A. In attaching the liquid-aspirating apparatus to the mouth of container C, ring  14 A and flange  16 A are compressed into sliding engagement. 
     In addition to supporting the aspiration tube  12 , housing  14  also rigidly supports an elongated electrical conduit  20  that contains a cable  21  comprising a pair of electrical leads L 1  and L 2 . As indicated in  FIGS. 4A and 4B , leads L 1  and L 2  define a wire loop circuit LC that extends along a substantial portion of the conduit. (See  FIG. 2 ). Connected in series, as shown in this circuit, is a pair of magnetic proximity switches S 1  and S 2 . Preferably, conduit  20  is cylindrical in shape, and it extends parallel to tube  12 , in close proximity therewith. A float member  22  surrounds the tube/conduit combination and is mounted for sliding movement over the outer surfaces of the tube/conduit combination. Such sliding movement is limited by a pair of stops  25 ,  26 , preferably formed on the exterior surface of conduit  20 . As the float member slides from a position in which its bottom surface contacts from stops  25  to a position in which its top surface contacts stop  26 , a magnetic member  28  embedded in the float member causes switch S 2  to change its state (here, from OPEN to CLOSED). Sliding of float member  22  upwardly (from stop  25  to  26 ) results when the float is immersed in liquid and the buoyant force of the liquid on the float exceeds the gravitational force on the float member, and sliding of the float member downwardly results under the converse conditions, i.e., when the gravitational force exceeds the buoyant force of the liquid. 
     Similar to the manner in which the tube/conduit combination slidable supports float member  22 , it also slidably supports a piston member  30  that comprises a magnetic proximity switch S 1 . Piston member  30 , which contains a magnetic switch-actuating member  34 , is movable between a first position in which the bottom surface  30 A of piston member  30  abuts a stop  32  formed on the outer surface of conduit  20 , and a second position in which its top surface  30 B contacts the bottom surface  14 C of housing  14 . In moving from its first to seconded position, the piston member operates to change the state of the magnetic switch S 1  from OPEN to CLOSED. A coil spring  33  (or the like) surrounding the tube/conduit combination and positioned between surfaces  14 C and  30 B, serves to spring bias the piston member downward, into engagement with stop  32 , thereby rendering the state of switch S 1  NORMALLY OPEN. Sliding movement of piston  30  against the bias force of spring  33  is achieved when the aspiration tube is inserted through the mouth of container C, as explained below. 
     Referring to  FIG. 3 , piston member  30  is shown as comprising a lower cylindrical portion  30 C having a diameter that enables such portion to pass through the circular rim  50  of the container mouth, and a concentric upper circular flange  30 D of greater diameter which prevents it from passing through the container rim. Thus, as the aspiration tube is inserted into the container and downward pressure is manually applied, piston  30  is driven upwardly by the engagement between the container rim  50  and flange  30 D. Continued movement of the apparatus into the container enables the threaded collar  16  to engage the threaded surface surrounding the container mouth, and rotation of the collar draws the piston member  30  further upwardly until the collar is secured to the container mouth. At this time, the magnetic member  34  embedded in the piston member will be positioned to change the conductive state of magnetic switch S 1  (i.e., changing from OPEN, as shown in  FIG. 2 , to CLOSED, as shown in  FIG. 3 ). Thus, the state of switch S 1  will always indicate whether or not the apparatus is properly attached to a container, and the state of switch S 2  will indicate whether or not the liquid level LL in the container is at a safe level for aspiration. 
     Referring to  FIG. 4A , the liquid level LL in container C is shown to be ample to raise the float member  22  into engagement with stop  26 , at which time switch S 2  is caused to operate in a CLOSED state, as shown in the circuit diagram. Meanwhile, switch S 1  is CLOSED by virtue of the apparatus being properly attached to the container mouth. Only in the event that both switches are CLOSED will the instrument&#39;s microprocessor  40  enable pump  42  to aspirate liquid from the container. Under all other conditions, the aspiration pump  42  remains disabled. 
     In  FIG. 4B , the liquid level LL is shown to have dropped to a lower level in which the float member is no longer buoyed up by the liquid and the bottom of the float member  22  is now dropped into contact with stop  25 . At this time, the magnetic member  28  within the float no longer functions to close switch S 2 , and the latter operates in its OPEN state. This condition, i.e., S 1  CLOSED and S 2  OPEN, is transmitted to the instruments microprocessor  40 , which then disables pump  42  and thereby prevents aspiration. Whenever the container C requires replacement, e.g., to provide a fresh supply liquid, the operator will unscrew the cap assembly  13  and withdraw the aspiration tube from the container. During this time period, spring  33  will urge piston  30  back into engagement with stop  32 , thereby removing the magnetic member  34  from the vicinity of the previously CLOSED switch S 1 , thereby allowing switch S 1  to return to its normally OPEN state. Note, unlike the float switch S 2  in which the moving element is allowed to move freely along the aspiration tube/conduit combination, the moving element of the proximity switch S 1  (piston  30 ) must be biased towards a direction in which the switch state will be OPEN whenever the cap is removed from the container. Otherwise, both switches could be inadvertently moved to a CLOSED state, enabling the pump to draw air into the aspiration line. The consequences are much more sever in the case the apparatus of the invention is used in a dispense mode, as described below. 
     In a dispense mode, as illustrated in  FIGS. 5A and 5B , the length of the tube  12 /conduit  20  combination is considerably shorter than that of the combination in the aspiration mode, the object being, of course, to substantially fill the container C with liquid rather than to substantially empty it. In the dispense mode, the magnetic member  28  of the float switch is positioned within the float member to CLOSE the float switch S 2  when the float is resting on stop  25 , as it will be when the liquid level is below a safe level. Thus, as liquid is dispensed into the container through the distal end of tube  12 , the liquid level will rise from the bottom of the container until the buoyant force of the liquid urges the top of float member  22  into contact with the upper stop  26 . At this time, the magnetic member  28  within float  22  moves away from its switch-closing position to enable switch S 2  to OPEN, as shown in  FIG. 5B . At this time, the instrument microprocessor  40  will disable the (dispense) pump  42 . As the container cap is unscrewed from the container and the dispense tube  12  is withdrawn, e.g., for the purpose of changing containers, the float member  22  will, under the force of gravity, immediately slide back to its switch-closing position in which the bottom of float member  22  again contacts stop  25  (as shown in  FIG. 5A ); however, as the container cap is removed, piston  30  is, under the influence of spring  33 , immediately returned to its switch-opening position in which the bottom surface  30 A of the piston member will abut stop  32 . Thus, any liquid dispensing will be prevented until both switches are again closed, as occurs when the liquid-dispensing cap is properly screwed onto to an empty (or partially empty) container, thereby overcoming the bias force of spring  33  (tending toward opening the proximity switch S 2 ), and the float member is resting on stop  25 , indicating a liquid-accepting condition. 
     Technical advantages resulting from the aforedescribed apparatus include: (a) a liquid-aspirating/dispensing instrument cannot operate when either the liquid level in the container is unsafe, or the aspirating/dispensing assembly is not properly secured to a container; (b) by integrating two switches into a single sensing circuit, only one sensing resource is needed on the microprocessor board; and (c) if the electrical connection with the microprocessor is lost, the instrument will stop aspirating/dispensing liquid. 
     In many applications, the dispensing of waste liquid results in the formation of a liquid foam that occupies a significant space inside the container. As waste liquid is continually added to the container and the foam begins to accumulate, the foam may eventually escape from the container through a vent hole V formed in housing  14  of the liquid-dispensing assembly to prevent any pressure build-up in the container. To avoid this potential biohazard condition, it is preferred that the liquid dispensing apparatus described above be modified as follows: Referring to  FIGS. 6A and 6B , housing  14  is shown as supporting a liquid-dispensing tube  60  through which liquid L, entering port P is dispensed, and within which a rigid electrical conduit  62  containing the afore-described magnetic switching circuit is contained. Like tube  60 , conduit  62  is cylindrical in shape and concentrically arranged on the longitudinal axis of the tube. A space S is provided between the inside of tube  60  and the outside of conduit  62 , such space providing annular passage for liquid L to enter the container from the dispensing tube. Axially spaced from the distal end  60 A of tube  60  (e.g., by about 14 mm.) is a deflector plate  66 , e.g. a disk, carried by conduit  62 . Plate  66  is positioned to deflect the incoming dispensed liquid so as to form a fountain of liquid that spreads laterally outwardly and then downwardly towards the container bottom. This fountain-like flow has the effect of suppressing the formation (and breaking up) of any foam that might otherwise form atop the dispensed liquid. Thus, this altered apparatus has the effect of substantially reducing any tendency for the dispensed liquid to create a liquid-foam atop the liquid surface within the container that can escape the container through the vent hole V. This apparatus operates precisely as described above to avoid overfilling (or non-filling) of the container when assembly  13  is not properly attached to the container mouth, or when an excess amount of liquid is dispensed into the container. 
     The invention has been described with reference to certain preferred embodiments. Clearly, variations can be made without departing from the spirit of the invention, and such variations are intended to fall within the scope of the appended claims.