Abstract:
A system and a method for delivering and metering a fixed volume of liquid, such as a liquid sterilant from a container into a vaporization system. The method for the delivering system includes the steps of sensing a requirement for additional liquid sterilant, determining whether the liquid sterilant to be added is acceptable for use, and delivering the liquid sterilant from a container into an accumulator. The method of metering the liquid sterilant into the vaporization system includes creating a vacuum in a chamber connected to the vaporizer and delivering the liquid sterilant into a vaporizer while continually sensing the flow of the delivery. The metering system maintains a slow, controlled flow in order to achieve efficient vaporization of the liquid sterilant and to provide accurate sensing of the gas/liquid interface.

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 09/499,418, filed Feb. 7, 2000 now U.S. Pat. No. 6,279,622. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system and a method of delivering and metering a liquid, and more particularly to a system and a method of delivering and metering a liquid sterilant from a container into a vaporization system. The vapor or gas produced by the vaporization system is typically used for sterilization and/or decontamination purposes. 
     2. Background of the Invention 
     In order to sterilize certain devices or apparatus, particularly in the medical field, the device or apparatus can be placed in a chamber where liquid sterilant is vaporized. In order to ensure effective and efficient sterilization, the liquid sterilant must be metered in accurately and reproducibly measured amounts into the vaporization chamber. 
     One conventional method of metering liquid sterilant into a vaporization chamber involves extracting predetermined doses of liquid sterilant from a sealed cell. A cassette holds a group of these cells and in order to extract a dosage from each cell, a dispensing apparatus punctures each cell individually and pneumatic pressure drives the liquid sterilant out of the punctured cell. 
     This method presents several problems. First, using cassettes of cells offers little flexibility because the amount of liquid sterilant drawn into the chamber is limited to the individual cell volume, or multiples thereof. Secondly, in multi-phase or flow-through sterilization cycles where large volumes of liquid sterilant may be required, multiple cassettes are needed, making this method not only inflexible, but also uneconomical and impractical. Lastly, liquid sterilant (such as hydrogen peroxide) is susceptible to degrade into gases or vapors. When this degradation occurs, the gases or vapors may rupture the cassette cells unless the cells are vented. However, over time, venting reduces the concentration of the sterilant. 
     In another conventional method, the liquid sterilant is pumped from a reservoir into a vaporization chamber. The key to this method is the proper metering of the liquid sterilant in order to accomplish effective and efficient sterilization. Several control mechanisms exist to meter the proper amount of liquid sterilant, such as controlling the pump volume directly, controlling the revolution rate or dispensing time of a continuous flow, fixed output pump, and monitoring the weight loss of the reservoir as the liquid is pumped from the reservoir. 
     As with the conventional cassette method, these methods also suffer from difficulties associated with the degradation of the liquid sterilant over time. As discussed above, the liquid sterilant can degrade over time to form gases and vapors. Air bubbles created by the degraded gaseous sterilant will disrupt the effectiveness, efficiency, and accuracy of any of these control mechanisms. For example, air bubbles can cause a “vapor lock” in a stroke-type pump if it is allowed to remain idle for an extended period of time. Moreover, in a control mechanism which meters liquid sterilant by controlling the dispensing time period at a fixed pressure or vacuum, the liquid is pushed or sucked into the vaporizer, along with the air bubbles, in a non-uniform matter, causing significant decreases in efficiency and effectiveness. As a final example, the formation of gases and vapors will disrupt the effectiveness of a control mechanism which monitors weight loss from the liquid reservoir. When such a system remains idle for an extended period, the weight loss from the reservoir, as measured by the balance, will not account for the air bubbles formed in the dispensing lines, which are dispensed into the vaporizer at start-up. 
     In addition to the problems created when the liquid sterilant is allowed to degrade into gases and vapors over time, the conventional methods used to control the metering of the liquid sterilant face additional problems if they rely on high injection rates and high pressures. That is, in order to circumvent the problems of degradation described above, conventional control mechanisms apply high injection rates and high pressures in order to dispense the liquid sterilant as quickly as possible. However, these high injection rates and high pressures place an extra strain on the equipment and can often lead to system leaks. Moreover, due, to the substances involved, compatibility problems may arise when attempting to reduce system leaks by constructing the equipment with certain types of material which can sustain such high pressures. 
     There is a need for a system and method of metering and delivering containers of liquid sterilant into a system which meters the liquid sterilant from a reservoir into a vaporization system. This process needs to be accomplished in accurately and reproducibly measured amounts. There is also a need for a metering system and method which can deliver a fixed and measured volume of the liquid sterilant into the vaporizer chamber at reduced flow rates to avoid system leaks and material compatibility problems. A flow sensor needs to be incorporated with such a system in order to achieve this objective. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a system and a method is provided for delivering and metering a liquid, such as a liquid sterilant, from a container into a vaporization system. 
     In one embodiment of the invention, the delivering system comprises an accumulator for receiving a liquid from a container. The delivery system includes a sensor to determine a pre-defined specification of the accumulator, such as the level of liquid in the accumulator. The delivery system also includes a second sensor to determine a pre-defined specification of the container, such as whether or not the liquid in the container is acceptable for use. A delivery mechanism can be employed for loading the container into a carrier which can be opened by an operator after being released by a release mechanism. A second delivery mechanism can be employed for delivering the liquid in the container into the accumulator and a locking mechanism secures the container in this second delivery mechanism during the delivery of the liquid into the accumulator. 
     The method for this delivering system can include the steps of determining whether the liquid in the accumulator satisfies a pre-defined specification and then generating a signal prompting the loading of the container into the container delivery system. The delivering system can then determine whether the liquid in the container satisfies a second pre-defined specification and if so then release the container delivery system to accept the loading of the container into the container delivery system. Once the container is loaded into the container delivery system, the container is locked in order to secure the container in the container delivery system. When the container is locked in place, then the liquid is delivered from the container into the accumulator. 
     In one embodiment of the metering system, the invention can comprise an accumulator for delivering the liquid to a metering tube which delivers a metered volume of the liquid to the vaporizer. The metering system employs a plurality of valves which control the direction and flow of the fluid in the system. Moreover, the metering system includes a delivery mechanism for delivering the liquid from the accumulator to the metering tube at a first flow rate. A second delivery mechanism delivers the liquid from the metering tube to the vaporizer at a second flow rate, wherein the second flow rate is slower than the first flow rate. 
     The method for this metering system can include the steps of evacuating the vaporizer and the metering tube and then delivering the liquid from the accumulator into the metering tube at a first flow rate. Then the metering system can deliver the liquid from the metering tube into the vaporizer at a second flow rate, wherein the second flow rate is slower than the first flow rate. The metering system maintains a slow, controlled flow in order to achieve efficient vaporization of the liquid sterilant and to provide accurate sensing of the air/liquid interface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a container delivering system in the closed position. 
     FIG. 2 is a perspective view of a container delivering system in the open position. 
     FIG. 3 is a perspective view of a container holding liquid sterilant. 
     FIG. 4 is a detailed side view of a container delivering system in the open position ready for delivery of a container. 
     FIG. 5 is an exterior side view of a releasing mechanism for the container delivering system. 
     FIG. 6 is a detailed side view of the releasing mechanism in operation. 
     FIG. 7 is a detailed side view of a container delivering system in the open position with a container loaded. 
     FIG. 8 is a detailed perspective view of a spike assembly. 
     FIG. 9 is a schematic view of a metering system. 
     FIG. 10 is a detailed side view of a metering system. 
     FIG. 11 is a table illustrating one embodiment of a method of a metering system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, FIGS. 1 and 2 depict a container delivering system. FIG. 3 depicts a container which can be loaded into the system of FIGS. 1 and 2. 
     FIG. 1 generally depicts a container delivering system in a closed position. In the embodiment illustrated, the system includes both the container delivering system and a metering system enclosed in one structure. The metering system, discussed in further detail below, is encased behind the delivery panel  1 . A vaporization chamber can be enclosed in the front panel  2 , located above the container delivering system. Maintenance, repair, or other service can be accomplished via access through a service panel  3  or a side panel  4 . The external components of the container delivering system comprise a lid  5 , a latch  6 , a pocket handle  7 , and a fascia  8 . 
     FIG. 2 illustrates this same embodiment in the open position. A container  9  (as shown in FIG. 3) containing a liquid, such as a liquid sterilant, liquid disinfectant, or any liquid germicide, can be loaded into the open container carrier  10  once an operator has pulled the fascia  8  out and away from the system structure by pulling on the pocket handle  7 . A container carrier assembly  11  comprising the lid  5 , the container carrier  10 , the guard  12 , the latch  6 , the pocket handle  7 , and the fascia  8 , pivots at an angle when the system is opened so that the lid  5  can be opened and a container  9  can be placed inside for delivering. 
     However, in the preferred embodiment, the operator will not be able to open the delivering system if the liquid in the container  9  to be loaded into the system is determined to be unacceptable. The determination of whether the liquid in the container  9  is acceptable for use can be accomplished, for example, by scanning a bar code  13  affixed to the container  9 . As shown in FIG. 3, the bar code  13  can contain digitized information detailing the relevant data of the liquid sterilant stored in a particular container. Every container  9  has a unique bar code  13  to prevent the misuse of a container. As an example, the operator could use a movable bar code reader, mounted on or near the container delivering system, to scan the bar code  13  on the container  9  to be loaded. 
     Referring now to FIG. 4, an interlock mechanism comprising a ratchet  14  and controlled by a solenoid  15  prevents opening of the delivering system if the liquid in the container  9  is determined to be unacceptable. If the container and the liquid contained therein are determined to be acceptable, then a solenoid  15  is activated to release the ratchet  14 . 
     The side view of this interlock mechanism is depicted in FIGS. 2 and 5. A bearing  16  that is fixedly connected to the guard  12  and the container carrier  10  lies in a horizontal track  17 . As shown in FIG. 6, the ratchet  14  is shaped with a tip  18  to prevent the lateral movement of the bearing  16  and thus the container carrier  10 . Therefore, once the ratchet  14  is released to move by the solenoid  15 , the bearing  16  remains prevented from movement by the tip  18  of the ratchet. To overcome this, the operator must push the container carrier  10  by the pocket handle  7  in, towards the structure. This movement created by the operator creates a gap  19  which allows the tip  18  of the ratchet  14  to clear the bearing  16 . Once a gap  19  is created by the movement of the bearing  16  by the operator, the ratchet  14  pivots upward to release the bearing  16  to move laterally out within the track  17 . 
     Referring again to FIGS. 4 and 5, with the bearing  16  free to move laterally out within the track, the container carrier assembly  11  comprising the container carrier  10 , the fascia  8 , the accumulator  20 , the blade  21  and a spike assembly  22 , the pocket handle  7 , the lid  5 , and the latch  6  pivot about pivot  23 . At the same time, the entire container carrier assembly  11  moves laterally as guided by the horizontal movement of the bearing  16  within the track  17 . The end of the track  17  stops the lateral movement of the bearing  16  and hence blocks the further lateral and pivoting movement of the container carrier assembly  11 . As shown in FIG. 7, as the bearing  16  comes to stop on the track  17 , a pin  24  on a linkage  25  rotates about point  40  and rests on the ledge  26  to lock the container carrier assembly in place. Preferably, the linkage  25  keeps the container carrier  10  in the open position while delivering or undelivering the container  9  or while lifting the lid  5 . In another embodiment, the container carrier  10  can also work without being locked in the open position by the linkage  25 . 
     Referring back to FIG. 4, as the container carrier  10  is fully opened, the operator uses one hand to unlatch latch  6  and lift the lid  5  up, insert the container  9  with the cap  27  down into the container carrier  10 , and close the lid  5  with a latch  6 . This configuration is illustrated in FIG. 7 where the container  9  has been inserted into the container carrier  10 . At this point, the container  9  is not punctured and the seal  28  on the cap  27  is ready to be punctured. In order to puncture the seal  28 , the operator must close the container carrier  10  by pressing down the linkage  25  to unlock the container carrier  10  and then push the container carrier assembly  11  inward. This locking movement will force the container to move vertically down onto the spike assembly  22 . A blade on the spike assembly will puncture the seal  28  of the container  9 . The seal  28  of the container  9  will only be punctured after the ratchet  14  locks onto the bearing  16 . The container carrier assembly  11  is locked in the closed position so that container  9  cannot be retrieved during or after the seal  28  is punctured by the spike assembly  22 . 
     When the seal  28  is punctured by the blade  21 , the contents of the container  9  are gravity-drained into the accumulator  20 . In the preferred embodiment, the volume of the accumulator  20  is greater than the volume of the container  9 . A significant advantage of this system is the reliance on gravity to manually load the container. Moreover, the system uses the closing mechanism of the door to puncture the seal on the container. These two features allow the design to be much more reliable than using pneumatics or solenoids to drive the container up and down to open the seal. 
     Once the container carrier  10  is closed, two sensors detect the container  9  and the liquid in the container  9 . A container sensor  29  as shown in FIG. 4 detects the liquid flow out of the container  9  to ensure that the blade  21  breaks the seal  28 . The level sensor  30  detects the liquid flowing into the accumulator  20  and detects the liquid when it is at a low level. If the accumulator is at a low-level mark, the level sensor  30  indicates to an operator by display that the system needs a new container loaded. 
     In the preferred embodiment, the spike assembly  22  comprises an opening mechanism as illustrated in FIG.  8 . The opening mechanism  31  is fixedly attached on top of the spike assembly  22 . The opening mechanism  31  comprises two members positioned vertically with a separating mechanism  32  connected between the two members. One member is a blade  21  which serves as a first puncturing device and may be positioned at an angle to the vertical axis of the spike assembly. The second member is a second puncturing device  33  for the opening mechanism. When the container is lowered down onto the spike assembly as the container carrier assembly  11  is closed, the seal  28  of the container  9  is punctured by both the blade  21  and the second puncturing device  33  of the spike assembly. The blade  21  creates a first opening in the seal  28  and the second puncturing device  33  creates a second opening. As the container  9  is forced to move further downward, the separating mechanism  32  slices a slit between the first opening in the seal  28  and the second opening. As the container  9  is forced to move further downward into position, the separating mechanism  32  widens the slit. This process allows the opening mechanism of the spike assembly  22  to create a sufficient opening in the seal  28  of the container  9  such that any liquid contained therein can more easily gravity drain into the accumulator  20 . 
     The container delivering system is designed to reliably determine if the liquid sterilant in the container  9  and the accumulator  20  is acceptable to use and to inform the user of the determination. If the liquid sterilant in the accumulator  20  is determined to be unacceptable, the user can purge the liquid sterilant to the drain container  36  as shown in FIG.  9  and described below. 
     Once a container  9  is loaded into the container delivering system and the liquid sterilant is directed into an accumulator, a metering system then dispenses the liquid sterilant to the vaporizer when needed. FIG. 9 illustrates a schematic view of a metering system and FIG. 10 depicts a side view of the metering system. The metering system is designed so that it will reliably transfer pre-determined quantities of liquid sterilant such as hydrogen peroxide to a vaporizer for sterilization of medical devices and apparatus. 
     In one embodiment, the metering system will be controlled by software to deliver an amount of liquid sterilant, such as liquid hydrogen peroxide, when an injection is required. The software will turn on or off four valves together with vacuum available inside the chamber to drive pre-determined quantities of liquid hydrogen peroxide from the metering tube to the vaporizer. These valves are depicted in FIG. 9 as valve # 1   71 , valve # 2   72 , valve # 3   73 , and valve # 4   74 . 
     Referring to FIGS. 9 and 10, one embodiment of the metering system includes a metering tube  90  into which liquid sterilant from an accumulator  20  can be dispensed. As described above, the level sensor  30  of the accumulator  20  can provide indication of the level of liquid sterilant in the accumulator  20 . A dispensing tube  85  of small diameter (for example ¼ inches) leads from the bottom of the accumulator  20  to a valve # 1   71 . In the preferred embodiment, a screen  87  is located between the accumulator  20  and the dispensing tube  85  (or in the accumulator  20 ) prevents any solid particulates from being passed to the metering tube  90 . Valve # 1   71  is connected to the metering tube  90 . A second valve, valve # 3   73 , which is connected to an air source, is also connected to the metering tube  90 . The volume of the metering tube  90  is fixed. The metering tube is connected to two more valves, valve # 2   72  and valve # 4   74 . A purging tube  100  extends from valve # 4   74  to allow for purging of unacceptable liquid sterilant. An injection tube  105  extends from valve # 2   72  into a vaporizer  110  to allow for injection of the liquid sterilant into the vaporizer  110 . The vaporizer is fluidly connected to a sterilization chamber  115  which can be placed under a vacuum. 
     As shown in FIG. 9, the container delivering system provides a secondary container  34  to house the container  9 , an accumulator  20 , and the metering system. If the container delivering system experiences a leakage or an overflow, the secondary container  34  will keep the spilled liquid inside the closed system. 
     FIG. 11 depicts a table listing the various states of the metering method employed by one embodiment of the metering system. In state  1 , the system is idle, and all four valves (that is, valve # 1   71 , valve # 2   72 , valve # 3   73 , and valve # 4   74 ) are closed. At state  2 , the metering tube  90  is evacuated when valve # 2   72  opens. The metering tube  90  is filled with liquid sterilant from the accumulator  20  by closing valve # 2   72  and opening valve # 1   71  in state  3 . Next, in state  4 , the liquid sterilant is injected into the vaporizer  110  by first closing valve # 1   71 , opening valve # 2   72 , and then, after a short delay, opening valve # 3   73 . Following the injection of the metered liquid sterilant into the vaporizer  110 , a flow sensor  120  senses air in the injection tube following valve # 2   72  and will prompt the closing of valve # 3   73  in state  5 . At this point, the metering process is complete. The valve # 2   72  is then closed and ready for the next injection. State  6  represents the configuration when liquid sterilant in the accumulator  20  is determined to be unacceptable for use and can be purged from the system by opening valve # 1   71  and valve # 4   74 . The unacceptable liquid sterilant is gravity drained from the accumulator  20  through the purging tube  100  into a drain container  36 . 
     In the embodiment described above, the size and diameter of the injection tube  105  is smaller than the size and diameter of valve # 1   71  and dispensing tube  85 . For example, valve # 1   71  and dispensing tube  85  can have ¼ inch diameter to allow for the liquid sterilant to fill the metering tube  90  more quickly. In this same example, valve # 2   72  and the injection tube  105  could have {fraction (1/16)} inch diameter. The smaller diameter will allow for slower flow. Slower flow into the vaporizer maximizes the efficiency of vaporization by allowing the vaporizer to remain hot during the vaporization state. Slower flow also improves the accurate sensing of the air/liquid interface in the injection tube  105 . 
     Throughout these states, a vacuum can be placed on the sterilization chamber  115 . In states  2  and  3 , a vacuum can be placed on the sterilization chamber while the metering and injection tubes are evacuated and the metering tube is filled. During injection of the liquid sterilant in states  4  and  5 , the vacuum on the sterilization chamber  115  can be turned off. During purge in state  6 , the vacuum on the sterilization chamber  115  can be either on or off. A vacuum can always be off in state  1  when the metering system is idle. By using the vacuum available in the sterilization chamber to drive liquid sterilant into the vaporizer, there is no need to use any pumps to deliver liquid into the vaporizer. 
     While the above detailed description has shown, described and pointed out fundamental novel features of the invention as applied to various embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated may be made by those skilled in the art, without departing from the spirit of the invention. For example, while the present invention has been described with respect to use in a sterilization system, it should, of course, be understood that a system and method of delivering and metering can be applied to other systems in which it is desirable to improve the efficiency and effectiveness of dispensing fixed volumes of liquid into a container.