Patent Application
20180264491
Embodiments of the present disclosure relate to the field of precision metering and dispensing of liquid fluids. More specifically the embodiments provide a liquid dispensing and metering system and method a dispensed liquid volume is measured and/or controlled by measurement of a gas volume and/or flow in and from a liquid container.
Fluid dispensing is a critical process in a broad range of applications, including medical and biomedical applications, but also industrial applications, where precise dispensing of metered amounts of liquid fluids is required.
An industrially widely used dispensing approach is “Time Pressure Dispensing” (TPD). TPD is a method of dispensing liquid materials (surface mount adhesives and gasketing materials) that uses air pressure applied to the top of a syringe to force material through a needle. The amount of time the air pressure is applied is directly related to the amount of adhesive dispensed. Common time pressure dispensing setups are easily implemented. However, TPD allows no feedback of the liquid dispensed during the dispensing cycle. Especially syringe fill-level, viscosity of the medium, syringe to syringe variation and clogging are influencing the amount of liquid dispensed. Measures to account for those disturbance variables are matter of current research activities. (Dixon 2004; Chen et al. 2007).
In biomedical and laboratory applications most often volume defined pumps are used. Syringe pumps allow precise dispensing of small volumes. However, they are expensive and bulky. Alternatively, peristaltic pumps, smaller and lower in cost, can be used which create a pulsating flow, which can be problematic in many applications. Generally all pumping mechanisms can be used and observed with a flowmeter within the liquid path. However, a flowmeter in liquid communication itself often has to be calibrated and gives output correlating with the media physical properties such as viscosity.
To improve upon the previously described limitations of existing dispensing systems such as TPD systems, the embodiments of the present disclosure add, for example, the possibility of dispensed volume feedback.
According to embodiments of the present disclosure there is provided a fluid dispensing or aspirating apparatus as defined in claim 1 for dispensing or aspirating a predetermined volume of liquid fluid in a container comprising a chamber having an internal volume V and at least an opening for granting communication with the chamber.
Examples of the apparatus of the disclosure comprises:
at least one connecting port for connecting the apparatus to the container about the opening in a gas and liquid tight manner;
a dispensing unit for dispensing and/or aspirating a predetermined volume of liquid fluid from the chamber, the dispensing unit comprising a dispensing channel having a first end in fluidic communication with a liquid containing part of the chamber and a second end opposite the first end extending outside the container for dispensing a metered amount of liquid fluid, liquid flow controlling means being arranged on the dispensing channel to open/close the channel respectively or actively pump the liquid; and
a metering unit for metering a compressible gas flow injected or released from the chamber,
the dispensing unit and metering unit being in fluidic communication with the chamber through the at least one connecting port.
In some embodiments, the metering unit comprises a gas feedthrough channel having a first end in fluidic communication with a gas containing part of the chamber and a second end opposite the first end extending outside the chamber. In these and other embodiments, the metering unit further comprising a flow sensing assembly configured to measure a gas flow V{dot over ( )} within the gas feedthrough channel and to introduce or release a determined volume of gas in the chamber after a controlled volume of liquid has been aspirated in or dispensed from the chamber.
Embodiments of the present disclosure further relate to a method for dispensing or aspirating liquid as defined in claim 9.
The method comprises:
providing a container comprising a chamber having an internal volume V and an opening for granting communication with the chamber, the chamber comprising a volume V1 of a liquid fluid and a volume V2 of a compressible gas, such that, when the chamber is closed V=V1+V2;
providing an apparatus, for example, as previously described above;
connecting the apparatus to the opening of the chamber by the connecting port such that a first end of the gas feedthrough channel extends in a gas containing part of the chamber and the second end of the gas feedthrough channel extends outside the chamber, and such that the first end of the dispensing channel extends in the liquid contained in the chamber and the second end of the dispensing channel extends outside the container;
opening the liquid flow controlling means in the dispensing channel and closing it after a predetermined time;
metering the induced flow from the pressure source or ambient pressure into the chamber and observing the form of the gas flow profile; and
calculating container fill level Vgas and dispensed amount of liquid.
Various preferred features of both the apparatus of the disclosure are defined throughout the disclosure and in the dependent claims.
The foregoing aspects and many of the attendant advantages of the claimed subject matter will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
The detailed description set forth below in connection with the appended drawings, where like numerals reference like elements, is intended as a description of various embodiments of the disclosed subject matter and is not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the claimed subject matter to the precise forms disclosed.
Embodiments of the present disclosure provide a liquid fluid dispensing or aspirating apparatus 1 and a method for dispensing or aspirating metered controlled amounts of a liquid 2 contained in an arbitrary container 4 together with a compressible gas 5 relying on the recovery of the internal pressure of the compressible gas 5 towards the externally applied pressure and the gas flow caused thereby through a flow sensing assembly 72. Embodiments of the present disclosure enable the precise dispensing and aspiration of liquids and are independent of the liquids viscosity.
The liquid 2 fill-level in the container 4 can be metered and the accuracy of the dispensed or aspirated volumes can be metered and adjusted for future dispense cycles (e.g. correction of time for next TPD cycle). In addition, real-time adjustment of a current dispensing cycle can be achieved through detailed analysis of the flow profile measured with the flow sensing assembly. In case of a pressure driven system (
Embodiments of the dispensing or aspiration apparatus 1 comprise at least a connection port 6, a metering unit 7 and a dispensing unit 8. The connection port 6 is adapted to allow an air and liquid tight connection of the apparatus 1 to the chamber 3 through an opening 31 arranged in the container's wall 41.
The container 4 is defined as arbitrary in that it does not need to be known in advance, neither the volume V of the chamber 3 delimited in the container 4. The container 4 can thus be of any container or bottle of unknown internal volume. In some embodiments, the only required feature for the container 4 is that its walls 41, no matter the material they are made of, are stiff enough to prevent deformation under the pressure differences caused by the dispensing method. In other words, deformable plastic bottles or vials of blow-molded polyethylene do not form good enough candidates for carrying out the disclosure. Hard plastic cans or bottles are therefore preferred, as well as glass containers, which present the least contamination risk with the liquid to be contained and dispensed.
The internal chamber 3 of the container 4 is filled with a volume V1 of liquid and a volume V2 of gas, which remains in equilibrium in the chamber such that the volume V of the chamber is such that V=V1+V2. The liquid 2 being denser that the gas 5 it fills up the bottom part of the chamber 3 of the container while the gas fills up the remaining top part of the chamber 3, as shown in the FIGURES.
According to the embodiments of the present disclosure it is not necessary to know any of the volumes V, V1, V2 to carry out metered dispensing of aliquots of liquid 2 from the container 4 through the connection port 6 using the metering unit 7 and dispensing unit 8.
In the embodiments shown, the metering unit 7 comprises a gas feedthrough channel 71 having a first end 71a connected to a gas containing part of the chamber 3 and a second end 71b which is either open to atmosphere or connected to an internal or external pressure supply (positive or negative pressure). The metering unit 7 further comprises a flow sensing assembly 72 configured to measure a gas pressure differential Δp and/or gas flow {dot over (V)} within the gas feedthrough channel 71 while externally applied pressure is recovered within the container 4 during and after a dispensing cycle is performed.
In a first embodiment the flow sensing assembly 72 also comprises at least a restrictor 73 arranged on the compressible gas feedthrough channel 71 in between its two ends 71a, 71b. In addition, the flow sensing assembly 72 comprises at least one differential pressure sensor 74 connected before and after the restrictor 73.
The differential pressure sensor 74 is preferably chosen to be of low-millibar or sub-millibar range, to provide fast dynamic response of the metering unit with extremely low pressure variations upon dispensing or aspirating, e.g., small gas flow over the restrictor 73.
In some embodiments, the restrictor 73 is adapted to the differential pressure sensor 74 sensitivity, e.g., creating a pressure drop that gives a targeted resolution of the flow, but does not limit the pressure recovery within the container significantly.
Alternatively, the flow sensing assembly 72 may comprise a gas flow sensor in lieu of the restrictor 73 and differential pressure sensor 74. In such case, any kind of gas flow sensor could be used.
In operative electrical connection with the differential pressure sensor 74, or the flow sensor, the flow sensing assembly 72 also comprises electronic control means configured to receive electrical signals from the previously mentioned sensors and computing therefrom volumes of liquids to be dispensed or aspirated as well as the fill level of the container. The electronic control means may comprise a battery and an integrated circuit, or ASIC embedded with a computer program designed to run all necessary computation from signal received from the sensors of the metering unit and further trigger dispensing or aspiration of liquid from or in the chamber respectively in connection with the dispensing unit. Other electronic control means and their equivalents may be practiced with embodiments of the present disclosure, including but not limited to analog circuitry, digital circuitry, or combination of analog and digital circuitry, programmed FPGAs, digital signal processors, microprocessors, computers, or other devices, etc., and any associated electronic components (e.g., buffers, relays, memory, I/O circuitry, signal conditioners, etc.). These and other structure of the electronic control means can also be referred to as “control engines,” “computing engines” and the like.
The dispensing unit 8 is composed of at least dispensing channel 81 having a first end 81a in communication or extending in the liquid 2 in the chamber 3 and a second end 81b open to atmosphere or connected to a secondary containment, either for receiving aliquots of liquid 2 dispensed in the containment or forming a liquid reservoir from which liquid is aspirated to the chamber. In addition, the dispensing unit 8 also comprises one of a dispensing valve 82 (
The compressible gas 5 volume and thereby the fill level of the container may be unknown when the apparatus 1 is activated. The apparatus 1 however allows for dispensing controlled volumes of liquids through the dispensing channel 81 only relying on the metering the gas flow V over the restrictor 73.
Indeed, measurements of the gas flow {dot over (V)} (or pressure difference Δpmax) over the restrictor 73, e.g., by the differential pressure sensor 74 signal, upon dispensing of identical liquid volumes at various filling levels for a same container 4 and plotting of the corresponding curves over time results shows that the curves are analogous, with only the intensity of the peak corresponding to the bottle fill level and the area under the curves corresponding to the dispensed liquid volume.
Accordingly, after proper calibration process of the apparatus and plotting a number of curves for various filling levels of a container it is then possible to meter the compressible gas volume in the container 4 for any given filling level in routine measurements.
Through this gas volume measurement principle, it is possible for a user to be warned if the liquid volume is used up because absence of liquid will automatically be detected in the gas flow signal.
In addition, the gas volume measured in the container can also be used as an indicator of the accuracy of the dispensed or aspirated volumes. Indeed, the more constant the gas flow {dot over (V)} signal from the differential pressure sensor 74 is over time, the more precise and repetitive the dispensing of accurate aliquots of liquid from the container is carried out. The inventors have however determined that the gas volume in the container 4 should not be bigger than 40,000 times the dispensed or aspirated volumes of liquid for the dispensing process to be sufficiently accurate.
The dispensing or aspirating of aliquots of liquid using the apparatus of the disclosure requires opening of the dispensing channel 81 through actuation of the valve 82 or pump 83 to allow liquid to flow from the chamber 3 in the channel by gravity and/or gas pressure effect on the liquid inside the chamber, where necessary through external pressurization.
To calculate the volume of liquid dispensed or aspirated V1 the time integral of the gas flow {dot over (V)} is taken, as follows:
V
1
=∫{dot over (V)}(dp)dt (1)
The gas flow {dot over (V)}, which can be defined as (2) V{dot over ( )}˜dp(t), is proportional to the differential pressure dp(t) over the restrictor 73.
In other words, embodiments of the apparatus 1 allow for precisely metering and dispensing (or aspirating) of aliquots of liquids having a volume V1 without having any active element, in particular sensor or any other metering device or arrangement in the dispensing unit, in particular in the dispensing channel 81. Volume V1 is essentially controlled through the integration of the gas flow measured in the gas feedthrough channel 71 during each dispensing cycle, which gives an image of the volume of liquid dispensed. It must be noted that in the case of high viscosity liquids it may be preferable to mount a pump 83 or a valve 82 not in the dispensing channel 81 but rather in the gas feedthrough channel 71 to pressurize the chamber 3 with the compressible gas 5 in order to push liquid through the dispensing channel 81 rather than letting it flow as with less viscous liquids.
Further, the embodiments of the apparatus 1 also allows for building a manifold dispenser/aspirator. In such case, either the metering unit 7 is used commonly for all compartments of the manifold or each supply line towards the compartments has its own differential pressure sensors (higher cost but also higher dispensing accuracy) but a common, shared, electronic control means.
In order to pump a wide variety of liquids, the tubes forming the dispensing channel 81 are made out of, e.g., polytetrafluoroethylene (PTFE), and the pump 83 parts in contact with the liquid are, e.g., very chemically resistant PVDF polymer and FFPM elastomer.
The differential pressure sensor sensitivity plays an important role versus the dimensions of the restrictor. Indeed, the more sensitive the differential pressure sensor the less resistant, e.g., narrow, the restrictor can be chosen, and therefore the faster the system's response time.
In the example of
While the peak signal is higher at higher filling level, the integrated signal is approximately the same, and is directly linear to the liquid amount dispensed, as can be seen in
In general, the measurement accuracy of the dispensing method of the disclosure increases with the amount of liquid dispensed and the liquid level in the vial 4. In any case, very small relative liquid amounts (<0.004% of total chamber 3 volume) can be detected using the disclosed apparatus 1 and corresponding dispensing method as shown in
These apparatus and method are also applicable for liquids with a high vapor pressure as well as high viscosity liquids, e.g., liquids having a μ of more than 0.01 Pa·s or more than 10 centipoise. Furthermore, most dispensing procedures happen in a relatively short period of time, where the amount of vapor leaving the container 4 can be neglected, even if any vapor generated was not compensated for.
Embodiments of the apparatus 1 and method of the disclosure provide the following advantages over existing TPD systems:
reduced size of dispensing apparatus with additional control compared to “TPD” processes;
combination of volume measurement and dispensing with only one differential pressure sensor 74 (or gas flow sensor);
online dispensing feedback in “TPD” applications by measuring the gas flow into the tank;
filling level feedback by analysing the pressure levels of the gas flow into the tank;
metered dispensing of aggressive media possible;
active sensing element is being positioned in the less critical gas path and not in the liquid dispensing channel;
dispensing is independent from liquid viscosity and partial clogging;
the gas flow compensating the dispensed liquid in the container 4 is measured and therefore gives a direct feedback of the dispensed liquid;
reduced costs and space requirements especially in manifold setups; and
high system pressures possible.
Any existing TPD systems (system with liquid tank, liquid valve, pressurized gas to move liquid) can be equipped with a metering unit 7 as taught by the present disclosure in the gas supply line. The induced flow profile gives feedback about the gas volume in the liquid container (fill level) and the amount of compressible gas flown into the liquid container is equal to the dispensed liquid volume.
Using the feedback of the dispensed liquid volume, the apparatus' accuracy is independent of partial clogging, viscosity or temperature changes of the liquid being dispensed (or aspired) as well as that of the compressible gas in the container.
The principles, representative embodiments, and modes of operation of the present disclosure have been described in the foregoing description. However, aspects of the present disclosure which are intended to be protected are not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. It will be appreciated that variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present disclosure. Accordingly, it is expressly intended that all such variations, changes, and equivalents fall within the spirit and scope of the present disclosure, as claimed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17160725.2 | Mar 2017 | EP | regional |
